JP5742153B2 - Multi-layer carbon material for non-aqueous secondary battery, negative electrode material using the same, and non-aqueous secondary battery - Google Patents

Description

  The present invention relates to a multilayer carbon material used for a non-aqueous secondary battery, a negative electrode formed using the material, and a non-aqueous secondary battery having the negative electrode.

In recent years, demand for high-capacity secondary batteries has increased with the downsizing of electronic devices. In particular, non-aqueous secondary batteries having higher energy density and excellent large current charge / discharge characteristics have attracted attention as compared to nickel / cadmium batteries and nickel / hydrogen batteries.
As a negative electrode material for a non-aqueous secondary battery, a graphite material or amorphous carbon is often used in terms of cost and durability. However, the amorphous carbon material has a small reversible capacity within the range of materials that can be put to practical use, and the graphite material breaks down when the active material layer containing the negative electrode material is densified to increase the capacity. As a result, the irreversible charge / discharge capacity at the initial cycle increases, and as a result, there is a problem that the capacity cannot be increased.

In order to solve the above problems, for example, as a carbon material, Patent Document 1 discloses that a mesophase microsphere is 40 ° C./hour as a carbon material for an electrode of a lithium battery having a large discharge capacity and charge / discharge efficiency and a manufacturing method thereof. Firing while heating at the following heating rate, carbonizing mesophase microspheres having a quinoline insoluble content of 89.5 wt% or more and / or toluene insoluble content of 93.6 wt% or more, and crushing mesophase microspheres By doing so, the particle size d50 is 1.3 to 1
After making the powder particles 5 μm, carbonize at a temperature of 600-1500 ° C. or carbonize mesophase spherules at a temperature of 600-1500 ° C. and then pulverize to obtain an average particle size d50 of 1.8- It is disclosed that it is made into a granular material of 15 μm. Further, Patent Document 2 discloses spheroidized graphite and carbonaceous particles obtained by processing a graphite material which has a high capacity but is difficult to obtain a filling property in order to obtain rapid charge / discharge characteristics and a high capacity. And a multi-layer structure carbon material obtained by carbonizing the organic compound after mixing with the obtained spheroidized graphite and the organic compound.

  Patent Document 3 discloses that an amount of carbon remaining on the surface of the graphitic carbonaceous material is 12 parts by weight or less and 0.1 parts by weight or more with respect to 100 parts by weight of the graphitic carbonaceous material. By using an electrode material to which a small amount (thin) organic carbide is attached, the electric capacity is high and the retention is kept low compared to graphite alone or a conventional clear multi-phase multi-layer carbon material. It is disclosed that a non-aqueous solvent secondary battery having extremely good electrical performance and high safety against an electrolytic solution can be obtained.

Japanese Patent No. 3634408 Japanese Patent No. 3916012 Japanese Patent No. 3712288

However, according to the study by the present inventors, the technique described in Patent Document 1 has a problem that if mesophase spherules are used, there is a limit to the electrode density and it is difficult to achieve both high capacity and high efficiency.
In the technique described in Patent Document 2, a graphite having a spheroidizing treatment is used as nuclear graphite, and after mixing with an organic compound, a multi-layer structure carbon material obtained by carbonizing the organic compound is used. There was a problem that the weight ratio was high and the reaction resistance was high.

In Patent Document 3, it is possible to suppress a decrease in specific surface area by coating a graphitic carbonaceous material with a thin organic carbide, but since the particle size is large, the negative electrode resistance is effectively reduced, There was a problem that it was difficult to reduce the storage characteristics (negative electrode double layer capacity).
On the other hand, graphite with a small particle size usually has a broad particle size distribution, does not have a high tap density, and further, when applied to the electrode, fine powder aggregates, making it difficult to make an electrode. .

  Therefore, the present invention has been made in view of the background art, and the problem is a non-aqueous secondary battery that has good coating properties to the electrode and has a good balance between negative electrode resistance reduction and storage characteristics. It is to provide a negative electrode material for manufacturing, and as a result, to provide a high capacity non-aqueous secondary battery.

As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have obtained a multilayer structure carbon produced by coating amorphous carbon on the surface of a graphite particle having a small average particle diameter thinner than before. By using the material for the negative electrode material, it was found that a non-aqueous secondary battery excellent in balance between negative electrode resistance reduction and storage characteristics can be obtained, and the present invention has been achieved.
That is, the gist of the present invention is a multi-layer structure carbon material in which the surface of graphite particles is coated with amorphous carbon, which satisfies the following conditions (1) to (4): Multi-layer carbon material for secondary batteries.
(1) The average particle diameter d50 of the multi-layer structure carbon material is 1 μm or more and 18 μm or less. (2) The weight ratio of graphite particles / amorphous carbon is 96/4 or more and 99.99 / 0.01 or less. (3) The tap density of the multi-layer structure carbon material is 0.95 g / cm ³ or more and 1.3 g / cm ³ (4) The specific surface area (SA) measured using the BET method is 6.5 m ² / g or more and 10 m ² / g or less.

  The non-aqueous electrolyte secondary battery using the carbon material for a non-aqueous electrolyte secondary battery negative electrode obtained by the present invention as an electrode effectively reduces the negative electrode resistance and has storage characteristics (negative electrode double layer capacity). The characteristic which reduces a fall is shown.

Equivalent circuit diagram

Hereinafter, the contents of the present invention will be described in detail. The description of the invention constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these forms unless it exceeds the gist.
<Multi-layer carbon material for non-aqueous secondary batteries>
The multi-layer structure carbon material for non-aqueous secondary batteries in the present invention (also referred to as multi-layer structure carbon material in the present invention) is a multi-layer structure carbon material in which the surface of graphite particles is coated with amorphous carbon. And if it is the multilayer structure carbon material for non-aqueous secondary batteries characterized by satisfy | filling all the following conditions (1) and (3), there will be no restriction | limiting in particular.
(1) The average particle diameter d50 of the multi-layer structure carbon material is 1 μm or more and 18 μm or less. (2) The weight ratio of graphite particles / amorphous carbon is 96/4 or more and 99.99 / 0.01 or less. (3) The tap density of the multi-layer structure carbon material is 0.85 g / cm ³ or more and 1.3 g / cm ³ or less.

・ Main physical properties of multi-layer carbon material (1) Volume-based average particle diameter (average particle diameter d50)
The volume-based average particle diameter (also referred to as an average particle diameter d50 in the present specification) of the multilayer structure carbon material is usually 18 μm or less, preferably 12 μm or less, more preferably 10 μm or less, and further preferably 8 μm or less. Moreover, it is 1 micrometer or more normally, Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more, More preferably, it is 6 micrometers or more. If the volume-based average particle size is too large, the balance between the negative electrode resistance reduction and the storage characteristics tends to be lost.If the volume-based average particle size is too small, the cohesiveness of the particles themselves is increased. It tends to cause problems such as pulling.

  The volume-based average particle diameter in the present invention is 0.01 g of a carbon material in 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (for example, Tween 20 (registered trademark)) which is a surfactant. Was suspended in a commercially available laser diffraction / scattering particle size distribution measuring device “LA-920 manufactured by HORIBA”, irradiated with 28 kHz ultrasonic waves at an output of 60 W for 1 minute, and then used as a volume-based median diameter in the measuring device. The measured value is defined as d50 in the present invention.

(2) Weight ratio of graphite particles / amorphous carbon The weight ratio of graphite particles (parts by weight) / amorphous carbon (parts by weight) in the multi-layered carbon material is the ratio of amorphous carbon to graphite particles. The amount of coating is usually 96/4 or more, preferably 97/3 or more, more preferably 98/2 or more, and still more preferably 99/1 or more. Moreover, it is 99.99 / 0.01 or less normally, More preferably, it is 99.9 / 0.1 or less. If the weight ratio of graphitic particles / amorphous carbon is too small, the balance between negative electrode resistance reduction and storage characteristics tends to be lost, and if the weight ratio of graphite particles / amorphous carbon is too large, multiple layers It tends to be difficult to obtain the effect. That is, if the amorphous material is thin but present uniformly throughout the surface, the effect of the present invention can be obtained. However, if the amorphous material becomes too small and the graphite particles themselves appear on the outermost surface, the effect is difficult to obtain. Tend to be.

Further, the weight ratio of graphitic particles / amorphous carbon in the present invention can be calculated from the firing yield before and after firing the material. At this time, the calculation is made assuming that there is no change in weight of the graphite particles before and after firing.
When w1 is the weight of graphite carbon particles before firing (kg), w2 is the raw material weight of amorphous carbon (kg), and a is the firing yield (%),
Graphite particles / amorphous carbon = w1 / {(w1 + w2) × a / 100−w1}
It is calculated by the measurement method.

(3) Tap density The tap density of the multilayer structure carbon material of the present invention is usually 0.85 g / cm ³ or more, preferably 0.90 g / cm ³ or more, more preferably 0.95 g / cm ³ . Moreover, it is 1.3 g / cm < ³ > or less normally, Preferably it is 1.2 g / cm < ³ > or less, More preferably, it is 1.1 g / cm < ³ > or less. If the tap density is too low, streaking is likely to occur when forming the electrode plate, which tends to cause a problem in the process. When the tap density is too high, the intra-particle carbon density increases, the rollability is lacking, and it tends to be difficult to form a high-density negative electrode sheet.

The tap density of the multi-layered carbon material is filled with a powder density measuring device by dropping the carbon material through a sieve having a diameter of 1.6 cm and a volume capacity of 20 cm ³ through a sieve having a mesh opening of 300 μm. Then, a tap having a stroke length of 10 mm is performed 1000 times, and the density obtained from the volume at that time and the weight of the sample is defined as the tap density.
-Other physical properties The multi-layer structure carbon material for lithium ion secondary batteries of the present invention, as long as the above requirements are satisfied, can exhibit the above-described effects of the present invention and exhibit sufficient performance. Furthermore, it is preferable that one or more of the following (4) to (15) are simultaneously satisfied.

(4) X-ray parameters In the multi-layer structure carbon material, the d value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method is usually 0.337 nm or less. If the d002 value is too large, it indicates that the crystallinity is low, and the initial irreversible capacity may increase. On the other hand, the theoretical value of the interplanar spacing of the 002 plane of graphite is 0.335 nm and is usually 0.335 nm or more. Further, the crystallite size (Lc) of the carbon material determined by X-ray diffraction by the Gakushin method is usually 1.5 nm or more, preferably 3.0 nm or more. Beyond this range, particles with low crystallinity are produced, and the reversible capacity may be reduced. The lower limit is the theoretical value of graphite.

(5) Ash content The ash content in the multilayer carbon material is 1% by mass or less, particularly 0.5% by mass or less, especially 0.1% by mass or less, as a lower limit, based on the total mass of the multilayer carbon material. Is preferably 1 ppm or more. When the above range is exceeded, deterioration of the battery performance due to the reaction with the electrolyte during charging / discharging may not be negligible. Below this range, the manufacturing process requires a lot of time, energy and equipment for preventing contamination, which may increase costs.

(6) BET specific surface area The specific surface area (SA) measured using the BET method of the multi-layer structure carbon material is usually 0.1 m ² / g.
As mentioned above, Preferably it is 0.7 m < ² > / g or more, More preferably, it is 1 m < ² > / g or more, More preferably, it is 2.0 m < ² > / g or more. Further, it is usually 100 m ² / g or less, preferably 25 m ² / g or less,
More preferably, it is 15 m < ² > / g or less, More preferably, it is 10 m < ² > / g or less. When the value of the specific surface area is too low, the reaction area when used as a negative electrode material is particularly reduced, and a long time until full charge is required, and a preferable battery tends to be hardly obtained. On the other hand, if the value of the specific surface area is too high, the reactivity with the electrolyte increases when used as a negative electrode material, gas generation tends to increase, and a preferable battery tends to be difficult to obtain.

The BET specific surface area was measured by using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken), preliminarily drying the sample for 15 minutes at 350 ° C. under a nitrogen flow, and then measuring the relative pressure of nitrogen with respect to atmospheric pressure. This is defined by a value measured by a nitrogen adsorption BET one-point method using a gas flow method, using a nitrogen-helium mixed gas that is accurately adjusted to have a value of 0.3.
(7) Pore distribution As the multi-layer structure carbon material, voids in the particle corresponding to a diameter of 0.01 μm or more and 1 μm or less, and the amount of irregularities due to the step of the particle surface, which are determined by mercury porosimetry (mercury intrusion method) However, it is usually 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more. Moreover, it is 0.6 mL / g or less normally, Preferably it is 0.4 mL / g or less, More preferably, it is 0.3 mL / g or less. If the amount of unevenness is too large, a large amount of binder may be required when forming a plate. When the amount of the unevenness is too small, the high current density charge / discharge characteristics are deteriorated, and the effect of relaxing the expansion / contraction of the electrode during charge / discharge tends to be not obtained.

  The total pore volume is usually 0.1 mL / g, preferably 0.2 mL / g or more, more preferably 0.25 mL / g or more. Moreover, it is 10 mL / g or less normally, Preferably it is 5 mL / g or less, More preferably, it is 2 mL / g or less. If the total pore volume is too large, a large amount of binder tends to be required when forming an electrode plate. If the total pore volume is too small, there is a tendency that the effect of dispersing the thickener or the binder cannot be obtained when forming an electrode plate.

  The average pore diameter is usually 0.03 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more, and further preferably 0.5 μm or more. Moreover, it is usually 80 μm or less, preferably 50 μm or less, more preferably 20 μm or less. If the average pore diameter is too large, a large amount of binder tends to be required, and if the average pore diameter is too small, the high current density charge / discharge characteristics tend to deteriorate.

  As an apparatus for mercury porosimetry, a mercury porosimeter (Autopore 9520: manufactured by Micromeritex Corporation) was used. A sample (negative electrode material) was weighed so as to have a value of about 0.2 g, sealed in a powder cell, and pretreated by degassing at room temperature under vacuum (50 μmHg or less) for 10 minutes. Subsequently, the pressure was reduced to 4 psia (about 28 kPa), mercury was introduced, the pressure was increased stepwise from 4 psia (about 28 kPa) to 40000 psia (about 280 MPa), and then the pressure was reduced to 25 psia (about 170 kPa). The number of steps at the time of pressure increase was 80 points or more, and the mercury intrusion amount was measured after an equilibration time of 10 seconds in each step. The pore distribution was calculated from the mercury intrusion curve thus obtained using the Washburn equation. The mercury surface tension (γ) was calculated as 485 dyne / cm, and the contact angle (ψ) was calculated as 140 °. As the average pore diameter, the pore diameter when the cumulative pore volume was 50% was used.

(8) Circularity The circularity of the multilayer carbon material is usually 0.85 or more, more preferably 0.87 or more, and still more preferably 0.88 or more. Further, it is usually 1 or less, preferably 0.98 or less, more preferably 0.97 or less. If the circularity is too small, the high current density charge / discharge characteristics tend to decrease. The circularity is defined by the following formula, and when the circularity is 1, a theoretical sphere is obtained.
Circularity = (perimeter of equivalent circle having the same area as the particle projection shape) / (actual circumference of particle projection shape)
As the value of the circularity, for example, a flow type particle image analyzer (for example, FPIA manufactured by Sysmex Industrial Co., Ltd.) is used, and about 0.2 g of a sample is mixed with polyoxyethylene (20) sorbitan monolaurate as a surfactant. After being dispersed in a 0.2 mass% aqueous solution (about 50 mL) and irradiating 28 kHz ultrasonic waves at an output of 60 W for 1 minute, the detection range is specified as 0.6 to 400 μm, and the particle size is in the range of 1.5 to 40 μm. The values measured for the particles are used.

  The method for improving the degree of circularity is not particularly limited, but a spheroidized sphere is preferable because the shape of the interparticle void when the electrode body is formed is preferable. Examples of spheroidizing treatment include a method of mechanically approaching a sphere by applying a shearing force and a compressive force, a mechanical / physical processing method of granulating a plurality of fine particles by the binder or the adhesive force of the particles themselves, etc. Is mentioned.

(9) True density The true density of the multi-layer structure carbon material is usually 1.9 g / cm ³ or more, preferably 2 g / cm ³ or more, more preferably 2.1 g / cm ³ or more, and even more preferably 2.2 g / cm ^3. cm ³ and the upper limit is 2.26 g / cm ³ or less. The upper limit is the theoretical value of graphite. Below this range, the crystallinity of the carbon is too low and the initial irreversible capacity may increase.

(10) Aspect ratio The aspect ratio of the multilayer carbon material in the powder state is theoretically 1 or more, preferably 1.1 or more, more preferably 1.2 or more. Moreover, it is 10 or less normally, Preferably it is 8 or less, More preferably, it is 5 or less. When the aspect ratio is too large, streaking or a uniform coated surface cannot be obtained when forming an electrode plate, and the high current density charge / discharge characteristics tend to deteriorate.

The aspect ratio is expressed as A / B, where the longest diameter A of the carbon material particles when observed three-dimensionally and the shortest diameter B orthogonal to the carbon material particles. The carbon particles are observed with a scanning electron microscope capable of magnifying observation. Arbitrary 50 graphite particles fixed on the end face of a metal having a thickness of 50 microns or less are selected, and the stage on which the sample is fixed is rotated and tilted, and A and B are measured. Find the average value of.

(11) Maximum particle size dmax
The maximum particle size dmax of the multilayer structure carbon material is usually 77 μm or less, preferably 45 μm or less, and more preferably 39 μm or less. If it is too large, it tends to cause streaking.
Further, the maximum particle size in the present invention is defined as the largest value at which particles are measured in the particle size distribution obtained in the measurement term of average particle size.

(12) The Raman R value of the Raman R value graphite particles of graphite particles was measured and the intensity _{I A} of the peak _{P A} in the vicinity of 1580 cm ^-1, and an intensity _{I B} of a peak _{P B} in the vicinity of 1360 cm ^-1, The intensity ratio R (R = I _B / I _A ) is calculated and defined. The value is usually 0.15 or more, preferably 0.2 or more. Moreover, it is 0.6 or less normally, Preferably it is 0.55 or less, More preferably, it is 0.5 or less. If the Raman R value is too small, the crystallinity of the particle surface becomes too high, and when the density is increased, the crystals tend to be oriented in the direction parallel to the electrode plate, and the load characteristics tend to decrease. On the other hand, if the Raman R value is too large, the crystal on the particle surface is disturbed, the reactivity with the electrolytic solution increases, and the charge / discharge efficiency tends to decrease and the gas generation tends to increase.

The Raman spectrum can be measured with a Raman spectrometer. Specifically, the sample particles are naturally dropped into the measurement cell to fill the sample, and the measurement cell is rotated in a plane perpendicular to the laser beam while irradiating the measurement cell with an argon ion laser beam. Measure.
Argon ion laser light wavelength: 514.5 nm
Laser power on sample: 25 mW
Resolution: 4cm ^-1
Measurement range: 1100 cm ^{−1 to} 1730 cm ⁻¹
Peak intensity measurement, peak half width measurement: background processing, smoothing processing (convolution 5 points by simple average) (10) DBP oil absorption

(13) DBP oil absorption The DBP (dibutyl phthalate) oil absorption is usually 65 ml / 100 g or less, preferably 62 ml / 100 g or less, more preferably 60 ml / 100 g or less, and still more preferably 57 ml / 100 g or less. Moreover, it is 30 ml / 100g or more normally, Preferably it is 40 ml / 100g or more. If the DBP oil absorption is too large, the progress of spheroidization is not sufficient, and it tends to cause streaking during coating, and if it is too small, there may be almost no pore structure in the particles. Yes, the reaction surface tends to become dull.

  In addition, the DBP oil absorption amount in the present invention is defined by measured values when 40 g of a measurement material is added, the dropping speed is 4 ml / min, the rotation speed is 125 rpm, and the set torque is 500 N · m in accordance with JIS K6217. . For measurement, an Absorbometer E type manufactured by Brabender was used.

(14) Average particle diameter d10
The particle size (d10) corresponding to a cumulative 10% from the small particle side on the volume basis of the multilayer carbon material is usually 10 μm or less, preferably 8 μm or less, more preferably 6 μm or less. Moreover, it is 1 micrometer or more normally, Preferably it is 3 micrometers or more, More preferably, it is 4 micrometers or more. When d10 is too large, the size of the particles becomes large, and the effect of the present invention tends to be difficult to obtain. In general, small-diameter graphite has a small d10, a tendency to aggregate particles, and tends to cause streaking during coating. In the present invention, this d10 may be a graphite that does not become as small as possible. This is important for more manifesting the effects of the present invention. In the present invention, d10 is defined as a value obtained by integrating 10% from a particle size having a small particle frequency% in the particle size distribution obtained in the measurement term of the average particle size.

(15) Average particle diameter d90
Graphite particles obtained by laser diffraction / scattering method have a d90 (particle size that is 90% cumulative from small particles on a volume basis) of usually 8 μm or more, preferably 9 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. It is. Moreover, it is 50 micrometers or less normally, Preferably it is 30 micrometers or less, More preferably, it is 25 micrometers or less, More preferably, it is 20 micrometers or less. If d90 is too small, the irreversible capacity increases and the initial battery capacity tends to be lost. If d90 is too large, the effect of the present invention tends to be difficult to obtain. In the present invention, d90 is defined as a value obtained by integrating 90% from a particle size having a small particle frequency% in the particle size distribution obtained in the measurement term of the average particle size.

<Graphite particles>
It is preferable that the graphite particles that are the core graphite of the multilayer structure carbon material satisfy one or more of the following physical properties.
(1) X-ray parameters As for graphite particles, the d002 value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method is usually 0.335 nm or more. Moreover, although it is usually less than 0.340 nm, Preferably it is 0.337 nm or less. If the d002 value is too large, the crystallinity is lowered and the initial irreversible capacity tends to increase.

The crystallite size (Lc) of the carbon material determined by X-ray diffraction by the Gakushin method is usually in the range of 30 nm or more, preferably 50 nm or more, more preferably 100 nm or more. Below this range, crystallinity decreases and the initial irreversible capacity tends to increase.
(2) Ash content The ash content in the graphite particles is usually 1% by mass or less, preferably 0.5% by mass or less, more preferably 0.1% by mass or less, based on the total mass of the graphite particles. . Moreover, it is preferable that it is 0.0001 mass% or more normally. When there is too much ash content, there exists a tendency for the battery performance to deteriorate by reaction with the electrolyte solution at the time of charging / discharging. Moreover, when there is too little ash content, manufacturing requires a lot of time, energy, and the equipment for pollution prevention, and there exists a tendency for cost to also rise to the range which is unpreferable as an industrial product.

(3) Volume-based average particle diameter The volume-based average particle diameter (d50) of the graphite particles is usually 1 μm or more, preferably 3 μm or more, based on the volume-based average particle diameter (d50) determined by the laser diffraction / scattering method. More preferably, it is 5 micrometers or more, More preferably, it is 6 micrometers or more. Moreover, an upper limit is 18 micrometers or less normally, Preferably it is 12 micrometers or less, More preferably, it is 10 micrometers or less, More preferably, it is 8 micrometers or less. If the average particle size is too small, the irreversible capacity tends to increase, leading to a loss of initial battery capacity. If the average particle size is too large, the effect of the present invention tends to be difficult to obtain. In particular, in the present invention, it is preferable to use graphite particles having a volume-based average particle diameter (d50) in the above-described range as a raw material for the multilayer structure carbon material.

(4) Raman R value and Raman half-value width The Raman R value of graphite particles measured using an argon ion laser Raman spectrum method is usually 0.01 or more, preferably 0.03 or more, more preferably 0.10 or more. The upper limit is 0.60 or less, preferably 0.50 or less, more preferably 0.40 or less. If the Raman R value is too small, the crystallinity of the particle surface becomes too high, and there is a tendency that the number of sites where Li enters between the layers increases with charge / discharge. That is, there is a tendency that charge acceptance is lowered. On the other hand, if the Raman R value is too large, the crystallinity of the particle surface is lowered, the reactivity with the electrolytic solution is increased, and there is a tendency that efficiency is lowered and gas generation is increased.

Further, the Raman half-width in the vicinity of 1360 cm ^{−1 of the} graphite particles is not particularly limited, but is usually 10 cm ⁻¹ or more, preferably 15 cm ⁻¹ or more. Usually, it is 90 cm ⁻¹ or less, preferably 70 cm ⁻¹ or less, more preferably 60 cm ⁻¹ or less. If the Raman half-value width is too small, the crystallinity of the particle surface becomes too high, and there is a tendency that the number of sites where Li enters between the layers increases with charge / discharge. That is, there is a tendency that charge acceptance is lowered. On the other hand, if the Raman half-value width is too large, the crystallinity of the particle surface decreases, the reactivity with the electrolytic solution increases, and the efficiency tends to decrease and the gas generation increases.
The method for measuring the Raman R value and the Raman half-value width is as described above.

(5) BET specific surface area The specific surface area of the graphite particles measured by the BET method is usually 0.1 m ² / g or more, preferably 0.7 m ² / g or more, more preferably 1 m ² / g or more, and more Preferably it is 2 m ² / g or more. The upper limit is usually 100 m ² / g or less, preferably 25 m ² / g or less, more preferably 20 m ² / g or less. When the value of the specific surface area is too small, lithium acceptability tends to be deteriorated during charging when used as a negative electrode material. On the other hand, if the value of the specific surface area is too large, the reactivity between the portion exposed to the electrolytic solution and the electrolytic solution when used as a negative electrode material is increased, gas generation tends to increase, and a preferable battery tends to be difficult to obtain. . Further, if the proportion of amorphous carbon is increased in order to reduce the BET specific surface area of the multi-layer structure carbon material, excess amorphous material is increased and high output characteristics tend to be difficult to obtain.

(6) Pore distribution The amount of voids in the particle corresponding to a diameter of 0.01 μm or more and 1 μm or less, and the amount of irregularities due to the step on the particle surface, which is obtained by mercury porosimetry (mercury intrusion method) of the graphite particles, is usually 0. 0.01 mL / g or more, preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more. Moreover, it is 0.6 mL / g or less normally, Preferably it is 0.4 mL / g or less, More preferably, it is the range of 0.3 mL / g or less. If it exceeds this range, a large amount of binder may be required when forming an electrode plate. When the amount of the unevenness is too small, the high current density charge / discharge characteristics are deteriorated, and the effect of relaxing the expansion / contraction of the electrode during charge / discharge tends to be not obtained.

  Further, the total pore volume is usually 0.1 or more, preferably 0.2 mL / g or more, more preferably 0.25 mL / g or more. Moreover, it is 10 mL / g or less normally, Preferably it is 5 mL / g or less, More preferably, it is the range of 2 mL / g or less. If the total pore volume is too large, a large amount of binder tends to be required when forming an electrode plate. If the total pore volume is too small, there is a tendency that the effect of dispersing the thickener and the binder cannot be obtained when forming an electrode plate.

  The average pore diameter is usually 0.05 μm or more, preferably 0.75 μm or more, more preferably 0.1 μm or more, and further preferably 0.5 μm or more. Further, it is usually 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. If the average pore diameter is too large, a large amount of binder tends to be required. On the other hand, if the average pore diameter is too small, high current density charge / discharge characteristics tend to decrease.

(7) Circularity The circularity of the graphite particles is usually 0.1 or more, preferably 0.2 or more, particularly preferably 0.5 or more, more preferably 0.8 or more, and further preferably 0.85 or more. is there. Also, it is usually 1 or less, preferably 0.99 or less, more preferably 0.98 or less. If the circularity is too small, the high current density charge / discharge characteristics tend to decrease. Although the method for improving the circularity is not particularly limited, as described above, a method of performing spheroidization is preferable, and examples thereof include a method of mechanically approaching a sphere by applying a shearing force and a compressive force, and a plurality of fine particles And a mechanical / physical treatment method in which the particles are granulated by the adhesive force of the binder or the particles themselves.

(8) True density The true density of the graphite particles is usually 2 g / cm ³ or more, preferably 2.1 g / cm ³ or more, more preferably 2.2 g / cm ³ or more, and further preferably 2.22 g / cm ^3. The upper limit is 2.26 g / cm ³ or less. The upper limit is the theoretical value of graphite. If the true density is too low, the crystallinity of the carbon is too low and the initial irreversible capacity tends to increase. The true density in the present invention is defined by a value measured by a liquid phase substitution method (pycnometer method) using butanol.

(9) Tap Density Tap density graphite particles is usually 0.67 g / cm ³ or higher, preferably 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, particularly preferably 0.88 g / It is desired to be cm ³ or more. And usually 1.5 g / cm ^3, preferably 1.4 g / cm ³ or less, more preferably 1.2 g / cm ³ or less, particularly preferably 1.1 g / cm ³ or less. If the tap density is too small, the packing density is difficult to increase when used as a negative electrode, and it tends to be difficult to obtain a high-capacity battery. Therefore, it is difficult to ensure the conductivity of the battery, and it is difficult to obtain preferable battery characteristics. In particular, in the present invention, it is preferable to use graphite particles having a tap density in the above-described range as a raw material for the multilayer structure carbon material.

(10) Orientation ratio The orientation ratio of the graphite particles in the powder state is usually 0.01 or more, preferably 0.02 or more, more preferably 0.04 or more, and the upper limit is 0.67 or less. When the orientation ratio is too small, the high-density charge / discharge characteristics tend to decrease.
(11) Aspect ratio The aspect ratio of the graphite particles in a powder state is usually 1 or more, usually 10 or less, preferably 8 or less, and more preferably 5 or less. When the aspect ratio is too large, streaking or a uniform coated surface cannot be obtained when forming an electrode plate, and the high current density charge / discharge characteristics tend to deteriorate.

(12) Average particle diameter d10
The particle size (d10) corresponding to a cumulative 10% from the small particle side on the volume basis of the graphite particles is usually 10 μm or less, preferably 8 μm or less, more preferably 6 μm or less. Moreover, it is 1 micrometer or more normally, Preferably it is 3 micrometers or more, More preferably, it is 4 micrometers or more. When d10 is too large, the size of the particles becomes large, and the effect of the present invention tends to be difficult to obtain. In general, small-diameter graphite has a small d10, a tendency to aggregate particles, and tends to cause streaking during coating. In the present invention, this d10 may be a graphite that does not become as small as possible. This is important for more manifesting the effects of the present invention. In the present invention, d10 is defined as a value obtained by integrating 10% from a particle size having a small particle frequency% in the particle size distribution obtained in the measurement term of the average particle size.

(13) Average particle diameter d90
Graphite particles obtained by laser diffraction / scattering method have a d90 (particle size that is 90% cumulative from small particles on a volume basis) of usually 8 μm or more, preferably 9 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. It is. Moreover, it is 50 micrometers or less normally, Preferably it is 30 micrometers or less, More preferably, it is 25 micrometers or less, More preferably, it is 20 micrometers or less. d9
If 0 is too small, the irreversible capacity increases and the initial battery capacity tends to be lost. If d90 is too large, the effect of the present invention tends to be difficult to obtain. In the present invention, d90 is defined as a value obtained by integrating 90% from a particle size having a small particle frequency% in the particle size distribution obtained in the measurement term of the average particle size.

(14) Maximum particle size dmax
The maximum particle diameter dmax of the graphite particles is usually 300 μm or less, preferably 250 μm or less, more preferably 100 μm or less. If it is too large, it tends to cause streaking.
Further, the maximum particle size in the present invention is defined as the largest value at which particles are measured in the particle size distribution obtained in the measurement term of average particle size.

・ Method for producing graphite particles
The graphite particles of the present invention include, as a raw material, graphite particles containing natural graphite and / or artificial graphite, or coal-based coke, petroleum-based coke, furnace black, acetylene black, and a slightly lower crystallinity than these. Those containing a fired product and / or graphitized material selected from the group consisting of pitch-based carbon fibers are preferred, and graphitic particles containing natural graphite and / or artificial graphite are more preferred. Among these, spheroidized natural graphite obtained by spheronizing natural graphite is particularly preferable.

  As an apparatus used for the spheroidization treatment, for example, an apparatus that repeatedly gives mechanical action such as compression, friction, shearing force, etc. including the interaction of particles mainly with impact force to the particles can be used. Specifically, it has a rotor with a large number of blades installed inside the casing, and when the rotor rotates at high speed, mechanical action such as impact compression, friction, shearing force, etc. is applied to the carbon material introduced inside. An apparatus that provides a surface treatment is preferable. Moreover, it is preferable to have a mechanism that repeatedly gives mechanical action by circulating the carbon material. Preferable apparatuses include, for example, a hybridization system (manufactured by Nara Machinery Co., Ltd.), kryptron (manufactured by Earth Technica Co., Ltd.), CF mill (manufactured by Ube Industries, Ltd.), mechanofusion system (manufactured by Hosokawa Micron Corporation), Etc.). Among these, a hybridization system manufactured by Nara Machinery Co., Ltd. is preferable. The graphite particles of the present invention are mainly produced by pulverization into base particles that are made spherical by spheroidizing the flaky natural graphite or by pulverizing the peripheral edge portion. Produced by performing spheronization treatment under the condition that the fine particles of 5 μm or less adhere and the surface functional group amount O / C value of the graphite particles after spheronization treatment is 1% or more and 4% or less. Is preferred.

  In this case, it is preferable to carry out in an active atmosphere so that the oxidation reaction of the graphite surface is advanced by the energy of mechanical treatment, and acidic functional groups can be introduced into the graphite surface. For example, when processing using the above-mentioned apparatus, the peripheral speed of the rotating rotor is preferably 30 to 100 m / sec, more preferably 40 to 100 m / sec, and 50 to 100 m / sec. Is more preferable.

  The mechanical treatment can be performed simply by passing the graphite particles, but it is preferable to circulate or stay in the apparatus for 30 seconds or longer, and to circulate or stay in the apparatus for 1 minute or longer. Is more preferable. By applying such a strong spheronization treatment, it is possible to greatly remove fine powder, and as a result, it is possible to obtain graphitic particles having characteristics of high tap density and / or smaller average particle diameter.

In producing the multilayer structure carbon material of the present invention, it is more preferable to use the graphite particles subjected to such treatment as a raw material of nuclear graphite.
Specific examples of artificial graphite include coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride. , Organic substances such as polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin, usually in a range of 2500 ° C. or more and usually 3200 ° C. or less. Examples thereof include those calcined at a temperature and graphitized.

  Further, as the graphite particles having a low graphitization degree, those obtained by firing an organic substance at a temperature of usually 2500 ° C. or less are used. Specific examples of organic substances include coal-based heavy oils such as coal tar pitch and dry-distilled liquefied oil; straight-run heavy oils such as atmospheric residual oil and vacuum residual oil; by-product during thermal decomposition of crude oil, naphtha, etc. Petroleum heavy oils such as cracked heavy oils such as ethylene tar; Aromatic hydrocarbons such as acenaphthylene, decacyclene and anthracene; Nitrogen-containing cyclic compounds such as phenazine and acridine; Sulfur-containing cyclic compounds such as thiophene; Aliphatic cyclic compounds; polyphenylenes such as biphenyl and terphenyl; polyvinyl esters such as polyvinyl chloride, polyvinyl acetate and polyvinyl butyral; and thermoplastic polymers such as polyvinyl alcohol.

  Further, when obtaining graphitic particles having a low degree of graphitization, the firing temperature of the organic substance is usually 600 ° C. or higher, preferably 900 ° C. or higher, more preferably 950 ° C. or higher. The upper limit varies depending on the desired degree of graphitization imparted to the carbon material and the like, but is usually 2500 ° C. or lower, preferably 2000 ° C. or lower, more preferably 1400 ° C. or lower. At the time of baking, acids such as phosphoric acid, boric acid and hydrochloric acid, and alkalis such as sodium hydroxide may be mixed with the organic matter.

  The graphite particles may be used by appropriately mixing graphite particles with metal particles, metal oxide particles, and the like in any combination. Further, a plurality of materials may be mixed in each particle. For example, carbonaceous particles having a structure in which the surface of graphite is coated with a carbon material having a low graphitization degree, or particles obtained by aggregating graphite particles with an appropriate organic substance and regraphitizing may be used. Furthermore, the composite particles may contain a metal that can be alloyed with Li, such as Sn, Si, Al, Bi.

<Amorphous carbon>
Amorphous carbon refers to a carbonaceous material with low crystallinity.
Specifically, the carbon material described in the following (a) or (b) is preferable as a carbon precursor for obtaining amorphous carbon.
(A) Coal heavy oil, DC heavy oil, cracked heavy oil, aromatic hydrocarbon, N ring compound, S ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin and Examples thereof include carbonizable organic substances selected from the group consisting of thermosetting resins.

(B) Carbonized organic substance dissolved in low molecular weight organic solvent As coal-based heavy oil, coal tar pitch from dry pitch to hard pitch, dry distillation liquefied oil, etc. are preferable, and DC heavy oil as Normal pressure residue, reduced pressure residue, etc., and cracked petroleum heavy oil is preferably ethylene tar produced as a by-product during thermal decomposition of crude oil, naphtha, etc., and aromatic hydrocarbons are acenaphthylene, decacyclene, Anthracene, phenanthrene, and the like are preferable. As the N ring compound, phenazine, acridine, and the like are preferable. As the S ring compound, thiophene, bithiophene, and the like are preferable. As the polyphenylene, biphenyl, terphenyl, and the like are preferable. Polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, and the like Preferred are natural products, polyacrylonitrile, polypyrrole, polythiophene, polystyrene, etc., natural polymers are preferably polysaccharides such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, saccharose, etc., and thermoplastic resins are polyphenylene Sulfide, polyphenylene oxide and the like are preferable, and as the thermosetting resin, a furfuryl alcohol resin, a phenol-formaldehyde resin, an imide resin and the like are preferable.
Moreover, it is also preferable that it is carbide | carbonized_materials, such as a solution dissolved in low molecular organic solvents, such as benzene, toluene, xylene, quinoline, and n-hexane.

-Physical property of amorphous carbon As a physical property of amorphous carbon, it is desirable to satisfy any one or plural of the following (1) to (4). One kind of amorphous carbon exhibiting such physical properties may be used alone, or two or more kinds may be used in combination in any combination.
(1) X-ray parameters For the amorphous carbon portion, the d002 value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction by the Gakushin method is usually 0.340 nm or more, but is not less than 0.30 nm. It is preferably 340 nm or more, and particularly preferably 0.341 nm or more. Moreover, 0.380 nm or less is preferable normally, More preferably, it is 0.355 nm or less, More preferably, it is 0.350 nm or less. If the d002 value is too large, the surface is remarkably low in crystallinity, and the irreversible capacity tends to increase. On the other hand, if the value is too small, the effect of improving the charge acceptability obtained by disposing the low crystalline carbonaceous material on the surface. It is small and the effect of the present invention tends to be small. The crystallite size (Lc) of the carbon material determined by X-ray diffraction by the Gakushin method is usually in the range of 1 nm or more, preferably 1.5 nm or more. Below this range, the crystallinity may decrease and the increase in initial irreversible capacity may increase.

(2) Ash content The ash content contained in the amorphous carbon portion is usually 1% by mass or less, preferably 0.5% by mass or less, more preferably 0.1% by mass with respect to the total mass of the multilayer carbon material. It is as follows. Usually 0.001% by mass or more. Moreover, when there is too little ash content, manufacturing requires a lot of time, energy, and the equipment for pollution prevention, and there exists a tendency for cost to also rise to the range which is unpreferable as an industrial product.

(3) Raman R value and Raman half-value width The Raman R value of the amorphous carbon portion measured using an argon ion laser Raman spectrum method is usually 0.5 or more, preferably 0.7 or more, more preferably 0.8. 9 or more. Moreover, it is 1.5 or less normally, Preferably it is 1.4 or less. If the Raman R value is too small, the crystallinity of the particle surface becomes too high, and there is a tendency that the number of sites where Li enters between the layers increases with charge / discharge. That is, there is a tendency that charge acceptance is lowered. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals tend to be oriented in the direction parallel to the electrode plate, and the load characteristics tend to decrease. On the other hand, if the Raman R value is too large, the crystallinity of the particle surface is lowered, the reactivity with the electrolytic solution is increased, and there is a tendency that efficiency is lowered and gas generation is increased.

Further, the Raman half-width in the vicinity of 1580 cm ^{−1 of the} amorphous carbon portion is not particularly limited, but is usually 60 cm ⁻¹ or more, preferably 80 cm ⁻¹ or more, and usually 150 cm ⁻¹ or less, preferably 140 cm ⁻¹ or less. . If the Raman half-value width is too small, the crystallinity of the particle surface becomes too high, and there is a tendency that the number of sites where Li enters between the layers increases with charge / discharge. That is, there is a tendency that charge acceptance is lowered. In addition, when the negative electrode is densified by applying it to the current collector and then pressing it, the crystals tend to be oriented in a direction parallel to the electrode plate, and the load characteristics tend to be reduced. On the other hand, if the Raman half-value width is too large, the crystallinity of the particle surface decreases, the reactivity with the electrolytic solution increases, and the efficiency tends to decrease and the gas generation increases.
In addition, the measuring method of a Raman R value and a Raman half value width is as above-mentioned.

(4) True density The true density of the amorphous carbon portion is usually 1.4 g / cm ³ or more, preferably 1.5 g / cm ³ or more, more preferably 1.6 g / cm ³ or more, and still more preferably 1. It is 7 g / cm ³ or more, usually 2.1 g / cm ³ or less, preferably 2 g / cm ³ or less. If the true density is too large, charge acceptance tends to be impaired.
If the true density is too low, the crystallinity of the carbon is too low and the initial irreversible capacity tends to increase.

<Production method of multi-layer carbon material>
The method for producing a multilayer structure carbon material of the present invention is such that the surface of the graphite particles is coated with amorphous carbon, and the resulting multilayer structure carbon material has an average particle diameter d50 of the multilayer structure carbon material of 1 μm or more. 18 μm or less, the weight ratio of graphite particles / amorphous carbon is 96/4 or more and 99.99 / 0.01 or less, and the tap density of the multi-layer structure carbon material is 0.85 g / cm ³ or more and 1 If it is manufactured to be ³ g / cm ³ or less, it is not particularly limited. A more specific method for producing a multi-layer carbon material is to use the above graphite particles as nuclear graphite, a carbon precursor for obtaining amorphous carbon as a coating raw material, and mix and fire these. The multilayer carbon material of the present invention can be produced by combining these raw materials and controlling the specific graphite particle / amorphous carbon weight ratio.

  The method of coating amorphous carbon on graphite particles is to use a carbon precursor for obtaining amorphous carbon as it is, and heat-treat the mixture of the carbon precursor and the graphite particle powder to form a composite powder. A method in which an amorphous carbon powder obtained by partially carbonizing the carbon precursor described above is prepared in advance, mixed with a graphite particle powder, and heat-treated to form a composite. A method of preparing a carbonaceous powder in advance, mixing a graphite particle powder, an amorphous carbon powder, and a carbon precursor, and performing a heat treatment to form a composite can be employed. In the latter two methods of preparing amorphous carbon powder in advance, it is preferable to use amorphous carbon having an average particle diameter of 1/10 or less of the average particle diameter of the graphite particles. In addition, by applying mechanical energy such as pulverization to amorphous carbon and graphite particles prepared in advance, it is possible to adopt a method in which the other is involved in one or a structure that is electrostatically attached. is there.

Obtain a mixture of graphite particles and a carbon precursor, or heat a mixture of graphite particles and amorphous carbon and a carbon precursor to obtain an intermediate substance, and then carbonize and fire, It is preferable to obtain a multi-layer structure carbon material in which amorphous carbon is finally combined with graphite particles by pulverization.
A more specific manufacturing process for obtaining a multi-layer structure carbon material in the present invention is divided into the following four processes.

First step: Graphite particles, a carbon precursor of amorphous carbon, and, if necessary, a solvent are mixed using various commercially available mixers and kneaders to obtain a mixture.
Second step: The mixture is heated to obtain an intermediate material from which volatile components generated from the solvent and the carbon precursor are removed. At this time, if necessary, the mixture may be stirred. Further, even if the volatile matter remains, it is not a problem because it is removed in a later third step.

Third step: The mixture or intermediate substance is heated to 400 ° C. or higher and 3200 ° C. or lower in a gas atmosphere such as nitrogen gas, carbon dioxide gas, argon gas, or a gas atmosphere generated from the mixture or intermediate, and has a multilayer structure. Obtain carbon material.
Fourth step: The multi-layered carbon material is subjected to powder processing such as pulverization, pulverization, and classification as required.

Among these steps, the second step and the fourth step may be omitted depending on circumstances, and the fourth step may be performed before the third step. However, when the fourth step is performed before the third step, powder processing such as pulverization, pulverization, and classification treatment is performed again as necessary to obtain a multilayered carbon material.
Although there is no restriction | limiting in particular as an apparatus used for the heat processing of the raw material of a 3rd process, For example, reaction furnaces, such as a shuttle furnace, a tunnel furnace, a lead hammer furnace, a rotary kiln, an autoclave, a coker (heat processing tank of coke manufacture), a Tamman furnace, As the Atchison furnace and heating method, a high-frequency induction heating furnace, direct resistance heating, indirect resistance heating, direct combustion heating, radiant heat heating, or the like can be used. During the treatment, stirring may be performed as necessary.

  In addition, the heat history temperature condition is important as the heat treatment condition. The lower limit of temperature is usually 700 ° C. or higher, preferably 800 ° C. or higher, more preferably 900 ° C. or higher, although it varies slightly depending on the type of carbon precursor and its thermal history. On the other hand, the upper limit temperature can be raised to a temperature that basically has no structural order exceeding the crystal structure of the graphite particle nucleus. Therefore, the upper limit temperature of the heat treatment is 3200 ° C. or less, preferably 2000 ° C. or less, more preferably 1500 ° C. or less, and further preferably 1200 ° C. or less. In such a heat treatment condition, the heat history temperature condition, the heating rate, the cooling rate, the heat treatment time, and the like are appropriately set so that the weight ratio of the graphite particles / amorphous carbon falls within the above range.

Further, after heat treatment in a relatively low temperature region, the temperature can be raised to a predetermined temperature. In addition, the reactor used for this process may be a batch type or a continuous type, and may be one or more.
The furnace that can be used in the third step is not particularly limited as long as it satisfies the above requirements, but the following apparatus is preferable.
The apparatus used for the pulverization in the fourth step is not particularly limited. For example, examples of the coarse pulverizer include a shearing mill, a jaw crusher, an impact crusher, and a cone crusher. Examples of the intermediate pulverizer include a roll crusher and a hammer mill. Examples of the pulverizer include a ball mill, a vibration mill, a pin mill, a stirring mill, and a jet mill.

  There is no particular limitation on the apparatus used for classification, but for example, in the case of dry sieving, a rotary sieving, a swaying sieving, a rotating sieving, a vibrating sieving, etc. can be used. In this case, gravity classifiers, inertial force classifiers, centrifugal classifiers (classifiers, cyclones, etc.) can be used. A centrifugal wet classifier or the like can be used.

<Sub-material>
In addition to the multilayer carbon material, the multilayer carbon material in the lithium ion secondary battery of the present invention contains one or more carbonaceous materials (carbonaceous materials) having different carbonaceous physical properties from the carbon material. Furthermore, it is possible to improve battery performance. The “carbonaceous physical properties” mentioned here are X-ray diffraction parameters, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, circularity, ash content. Exhibit one or more characteristics. Further, as a preferred embodiment, when the volume-based particle size distribution is not symmetrical with respect to the median diameter, it contains two or more carbon materials having different Raman R values, and the X-ray parameters are different. And so on. As an example of the effect, electrical resistance is reduced by containing carbon materials such as graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon such as needle coke as secondary materials. For example. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When added as a secondary material, it is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and usually 80% by mass or less, preferably 50% by mass or less. More preferably, it is 40 mass% or less, More preferably, it is 30 mass% or less. If it is less than this range, the effect of improving conductivity tends to be difficult to obtain. If it exceeds the upper limit, the initial irreversible capacity is increased, which is not preferable.

<Electrode production>
The negative electrode may be manufactured by a conventional method. For example, it is formed by adding a binder, a solvent, and if necessary, a thickener, a conductive material, a filler, etc. to a multi-layer structure carbon material to form a slurry, which is applied to a current collector, dried and then pressed. can do. The thickness of the multi-layer structure carbon material layer per side in the stage immediately before the electrolyte solution injection step of the battery is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is 150 μm or less, preferably 120 μm. Hereinafter, it is more preferably 100 μm. If it exceeds this range, the electrolyte solution hardly penetrates to the vicinity of the current collector interface, which is not preferable in that the high current density charge / discharge characteristics are deteriorated. On the other hand, if it falls below this range, the volume ratio of the current collector to the multilayer structure carbon material increases, and the battery capacity decreases, which is not preferable. Further, the multilayer structure carbon material may be roll-formed to form a sheet electrode, or may be compressed to a pellet electrode.

<Negative electrode>
As the current collector for holding the multi-layer structure carbon material, a known one can be arbitrarily used. Examples of the current collector for the negative electrode include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Of these, copper is particularly preferable from the viewpoint of ease of processing and cost. When the current collector is a metal material, examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Among them, a metal thin film is preferable, a copper foil is more preferable, and a rolled copper foil by a rolling method and an electrolytic copper foil by an electrolytic method are more preferable, and both can be used as a current collector. When the thickness of the copper foil is less than 25 μm, a copper alloy (phosphor bronze, titanium copper, Corson alloy, Cu—Cr—Zr alloy, etc.) having higher strength than pure copper can be used.

  A current collector made of a copper foil produced by a rolling method is suitable for use in a small cylindrical battery because the copper crystals are arranged in the rolling direction so that the negative electrode is hard to crack even if it is rounded sharply or rounded at an acute angle. be able to. For example, an electrolytic copper foil is prepared by immersing a metal drum in an electrolytic solution in which copper ions are dissolved, and flowing current while rotating the copper drum, thereby depositing copper on the surface of the drum and peeling it off. It is obtained. Copper may be deposited on the surface of the rolled copper foil by an electrolytic method. One side or both sides of the copper foil may be subjected to a roughening treatment or a surface treatment (for example, a chromate treatment having a thickness of about several nm to 1 μm, a base treatment such as Ti).

Further, the following physical properties are desired for the current collector substrate.
(1) Average surface roughness (Ra)
The average surface roughness (Ra) of the active material thin film forming surface of the current collector substrate defined by the method described in JIS B0601-1994 is not particularly limited, but is usually 0.01 μm or more, preferably 0.03 μm or more, usually It is 1.5 μm or less, preferably 1.3 μm or less, particularly preferably 1.0 μm or less. By setting the average surface roughness (Ra) of the current collector substrate within the range between the lower limit and the upper limit described above, good charge / discharge cycle characteristics can be expected. By setting it to the above lower limit or more, the area of the interface with the active material thin film is increased, and the adhesion with the active material thin film is improved. The upper limit of the average surface roughness (Ra) is not particularly limited, but those having an average surface roughness (Ra) exceeding 1.5 μm are generally difficult to obtain as foils having a practical thickness as a battery. 1.5 μm or less is preferable.

(2) Tensile strength The tensile strength of the current collector substrate is not particularly limited, but is usually 50 N / mm ² or more, preferably 100 N / mm ² or more, and more preferably 150 N / mm ² or more. The tensile strength is obtained by dividing the maximum tensile force required until the test piece breaks by the cross-sectional area of the test piece. The tensile strength in the present invention is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high tensile strength, cracking of the current collector substrate due to expansion / contraction of the active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained.

(3) 0.2% proof stress of 0.2% proof stress current collector substrate is not particularly limited, normally 30 N / mm ² or more, preferably 100 N / mm ² or more, particularly preferably 150 N / mm ² or more . The 0.2% proof stress is the magnitude of the load necessary to give a plastic (permanent) strain of 0.2%. It means that The 0.2% proof stress in the present invention is measured by the same apparatus and method as the elongation rate. If the current collector substrate has a high 0.2% proof stress, plastic deformation of the current collector substrate due to expansion / contraction of the active material thin film accompanying charging / discharging can be suppressed, and good cycle characteristics can be obtained. it can. Although the thickness of a metal thin film is arbitrary, it is 1 micrometer or more normally, Preferably it is 3 micrometers or more, More preferably, it is 5 micrometers or more. Moreover, an upper limit is 1 mm or less normally, Preferably it is 100 micrometers or less, More preferably, it is 30 micrometers or less. If the thickness is less than 1 μm, the strength is lowered, so that coating becomes difficult, which is not preferable in the process. If it is thicker than 100 μm, it is difficult to change the shape of the electrode such as winding because of difficulty in the process. The metal thin film may be mesh.

(4) Ratio of current collector and active material layer thickness The ratio of current collector and active material layer thickness is not particularly limited, but (thickness of active material layer on one side immediately before electrolyte injection) / (Thickness of current collector) is 150 or less, preferably 20 or less, more preferably 10 or less, and the lower limit is 0.1 or more, preferably 0.4 or more, more preferably 1 or more. is there. Above this range, the current collector generates heat due to Joule heat during high current density charge / discharge, which is not preferable. Below this range, the volume ratio of the current collector to the multilayer structure carbon material increases, and the battery capacity decreases, which is not preferable.

(5) Electrode density The electrode structure of the multi-layered carbon material is not particularly limited, but the density of the active material present on the current collector is preferably 1 g / cm ³ or more, more preferably Is 1.1 g / cm ³ , more preferably 1.2 g / cm ³ or more, and the upper limit is 2 g / cm ³ or less, preferably 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less. More preferably, it is in a range of 1.7 g / cm ³ or less. Exceeding this range is preferable because the active material particles are destroyed, the initial irreversible capacity increases, the permeability of the electrolyte solution near the current collector / active material interface decreases, and the high current density charge / discharge characteristics decrease. Absent. On the other hand, if it is lower, the conductivity between the active materials is lowered, the battery resistance is increased, and the capacity per unit volume is lowered.

(6) Electrode orientation ratio The electrode orientation is 0.01 or more, preferably 0.05 or more, more preferably 0.10 or more, and the upper limit is 0.67 or less, which is a theoretical value. Below this range, the high-density charge / discharge characteristics deteriorate, which is not preferable.
The measurement of the electrode plate orientation ratio is as follows. About the negative electrode after pressing to the target density, the active material orientation ratio of the electrode is measured by X-ray diffraction. The specific method is not particularly limited, but as a standard method, peak separation is performed by fitting the peaks of (110) and (004) diffraction of carbon by X-ray diffraction using asymmetric Pearson VII as a profile function. The integrated intensities of the peaks of (110) diffraction and (004) diffraction are calculated. From the obtained integrated intensity, a ratio represented by (110) diffraction integrated intensity / (004) diffraction integrated intensity is calculated and defined as the active material orientation ratio of the electrode.

The X-ray diffraction measurement conditions here are as follows. “2θ” indicates a diffraction angle.
-Target: Cu (Kα ray) graphite monochromator-Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree-Measurement range and step angle / measurement time:
(110) plane: 76.5 degrees ≦ 2θ ≦ 78.5 degrees 0.01 degrees / 3 seconds (004) plane: 53.5 degrees ≦ 2θ ≦ 56.0 degrees 0.01 degrees / 3 seconds Sample preparation: glass (7) Impedance The resistance of the negative electrode when charged from the discharged state to 60% of the nominal capacity is preferably 100Ω or less, particularly preferably 50Ω or less, more preferably 20Ω. or less and / or double-layer capacity is preferably not less than 1 × 10 ^-6 F, particularly preferably 1 × 10 ^-5 F or more, more preferably 1 × 10 ^-
4 F or more. Within this range, the output characteristics are good and preferable.

The resistance and double layer capacity of the negative electrode are measured by the following procedure. The lithium-ion secondary battery to be measured is charged at a current value that can be charged for 5 hours in a nominal capacity, then maintained in a state where it is not charged / discharged for 20 minutes, and then discharged at a current value that can be discharged in 1 hour for a nominal capacity. The capacity when the capacity is 80% or more of the nominal capacity is used. About the lithium ion secondary battery of the above-mentioned discharge state, it charges to 60% of a nominal capacity with the electric current value which can charge a nominal capacity in 5 hours, Immediately transfers a lithium ion secondary battery in the glove box under argon gas atmosphere. Here, the lithium ion secondary battery is quickly disassembled and taken out in a state where the negative electrode does not discharge or short-circuit, and if it is a double-sided coated electrode, the electrode active material on one side is peeled off without damaging the electrode active material on the other side, Two electrodes are punched to 12.5 mmφ, and are opposed to each other so that the active material surface does not shift through a separator. 60 μL of the electrolytic solution used in the battery is dropped and adhered between the separator and both negative electrodes, and kept in a state where it is not in contact with the outside air, the current collectors of both negative electrodes are made conductive, and the AC impedance method is performed. The measurement was performed at a temperature of 25 ° C. and a complex impedance measurement was performed in a frequency band of 10 ⁻² to 10 ⁵ Hz, and the surface resistance (R) was obtained by approximating the arc of the negative resistance component of the obtained Cole-Cole plot with a semicircle. And double layer capacity | capacitance (Cdl) is calculated | required.

(8) Electrode Area When using the non-aqueous electrolyte solution of the present invention, the area of the positive electrode active material layer may be larger than the outer surface area of the battery outer case from the viewpoint of enhancing the stability at high output and high temperature. preferable. Specifically, the total electrode area of the positive electrode with respect to the surface area of the exterior of the secondary battery is preferably 20 times or more, and more preferably 40 times or more. The outer surface area of the outer case is the total area obtained by calculation from the vertical, horizontal, and thickness dimensions of the case part filled with the power generation element excluding the protruding part of the terminal in the case of a bottomed square shape. . In the case of a bottomed cylindrical shape, the geometric surface area approximates the case portion filled with the power generation element excluding the protruding portion of the terminal as a cylinder. The sum of the electrode areas of the positive electrode is the geometric surface area of the positive electrode mixture layer facing the composite layer containing the multi-layer structure carbon material, and is formed by forming the positive electrode mixture layer on both sides with a current collector foil. In the structure, it means the sum of areas where each surface is calculated separately.

<Binder>
The binder for binding the active material is not particularly limited as long as it is a material that is stable with respect to the electrolyte and the solvent used when manufacturing the electrode. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene / butadiene rubber), isoprene rubber, butadiene rubber, fluorine rubber, NBR ( Acrylonitrile-butadiene rubber), rubbery polymers such as ethylene / propylene rubber; styrene / butadiene / styrene block copolymers and hydrogenated products thereof; EPDM (ethylene-propylene-diene terpolymer), styrene / ethylene / Thermoplastic elastomeric polymers such as butadiene / styrene copolymer, styrene / isoprene / styrene block copolymer and hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinegar Soft resinous polymers such as vinyl copolymers and propylene / α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene / ethylene copolymers Molecule: a polymer composition having ion conductivity of alkali metal ions (particularly lithium ions), and the like. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

The solvent for forming the slurry is not particularly limited as long as it is a solvent capable of dissolving or dispersing the active material, binder, thickener and conductive agent used as necessary. Either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, alcohol and the like, and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N -N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexameryl phosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. . In particular, when an aqueous solvent is used, a dispersant or the like is added in addition to the above-described thickener, and a slurry is formed using a latex such as SBR. In addition, these may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio.

  The ratio of the binder to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 20% by mass or less, preferably 15% by mass or less. More preferably, it is 10 mass% or less, More preferably, it is the range of 8 mass% or less. If it exceeds this range, the binder ratio in which the amount of the binder does not contribute to the battery capacity increases, and the battery capacity may decrease. On the other hand, if it is lower, the strength of the negative electrode is lowered, which may be undesirable in the battery production process. In particular, when a rubbery polymer typified by SBR is contained as a main component, the ratio of the binder to the active material is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.00%. The upper limit is 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. Further, when the main component contains a fluorine-based polymer typified by polyvinylidene fluoride, the ratio to the active material is 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more. As an upper limit, it is 15 mass% or less, Preferably it is 10 mass% or less, More preferably, it is the range of 8 mass% or less.

  A thickener is usually used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used individually by 1 type, or may use 2 or more types together by arbitrary combinations and a ratio. When a thickener is further added, the ratio of the thickener to the active material is 0.1% by mass or more, preferably 0.5% or more, more preferably 0.6% or more. It is 5 mass% or less, Preferably it is 3 mass% or less, More preferably, it is the range of 2 mass% or less. Below this range, applicability may be significantly reduced. If it exceeds, the ratio of the active material in the multi-layer structure carbon material layer may decrease, and there may occur a problem that the capacity of the battery decreases and a problem that the resistance between the multi-layer structure carbon material increases.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present invention is described in detail below.
Battery shape The battery shape is not particularly limited, and examples thereof include a bottomed cylindrical shape, a bottomed square shape, a thin shape, a sheet shape, and a paper shape. When incorporating into a system or device, in order to increase the volumetric efficiency and increase the storage capacity, it may be of a different shape such as a horseshoe shape, a comb shape, etc. considering the fit to the peripheral system arranged around the battery . From the viewpoint of efficiently releasing the heat inside the battery to the outside, a rectangular shape having at least one surface that is relatively flat and has a large area is preferable.

In a battery having a bottomed cylindrical shape, since the outer surface area with respect to the power generating element to be filled becomes small, it is preferable to design so that Joule heat generated by the internal resistance at the time of charging and discharging efficiently escapes to the outside. Moreover, it is preferable to design so that the filling ratio of the substance having high thermal conductivity is increased and the temperature distribution inside is reduced.
In the bottomed square shape, the ratio of the area S of the largest surface (the product of the width and height of the outer dimensions excluding the terminal part, unit m ² ) to the thickness T (unit m) of the battery outer shape The 2S / T value is preferably 100 or more, and more preferably 200 or more. By increasing the maximum surface, it is possible to improve characteristics such as cycle performance and high-temperature storage even for high-power and large-capacity batteries, and increase the heat dissipation efficiency during abnormal heat generation. Can be prevented from becoming a dangerous state.

Battery configuration The lithium ion secondary battery of the present invention includes a positive electrode and a negative electrode capable of occluding and releasing lithium ions, a non-aqueous electrolyte, a separator disposed between the positive electrode and the negative electrode, a current collecting terminal, and an outer case. At least composed. If necessary, a protective element may be mounted inside the battery and / or outside the battery.

<Positive electrode>
The positive electrode according to the present invention comprises a positive electrode active material and an active material layer containing an organic substance (binder) having a binding and thickening effect on a current collector substrate. A process of thinly applying and drying a slurry in which an organic substance having a binding and thickening effect is dispersed in water or an organic solvent on a current collector substrate, followed by pressing to a predetermined thickness and density It is formed by a process.

The positive electrode active material is not particularly limited as long as it has a function capable of inserting and extracting lithium. For example, lithium transition metal composite oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide Materials: transition metal oxide materials such as manganese dioxide; carbonaceous materials such as fluorinated graphite can be used. Specifically, LiFeO ₂ , Li
CoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ and their non-stoichiometric compounds, MnO ₂ , TiS ₂ , FeS ₂ , Nb ₃ S ₄ , Mo ₃ S ₄ , CoS ₂ , V ₂ O ₅ , P ₂ O ₅ , CrO ₃ , V ₃ O ₃ , TeO ₂ , GeO _2, LiNi _0.33 Mn _0.33 Co _0.33 O ₂ or the like can be used.

  A positive electrode conductive agent can be used for the positive electrode active material layer. The positive electrode conductive agent may be any electron conductive material that does not cause a chemical change at the charge / discharge potential of the positive electrode active material used. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, metal fiber, etc. Conductive fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as polyphenylene derivatives It can be included alone or as a mixture thereof. Among these conductive agents, artificial graphite and acetylene black are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1-50 weight% is preferable with respect to positive electrode active material material, and 1-30 weight% is especially preferable. In the case of carbon or graphite, 2 to 15% by weight is particularly preferable.

There is no restriction | limiting in particular as an organic substance which has a binding and thickening effect used for formation of a positive electrode active material layer, Any of a thermoplastic resin and a thermosetting resin may be sufficient. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrif Oroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or (Na ⁺ ) ion crosslinked product, ethylene-methacrylic acid copolymer or (Na ⁺ ) ion crosslinked product of the material, ethylene-methyl acrylate copolymer, or (Na ⁺ ) ion crosslinked product of the material, ethylene-methacrylic acid Examples thereof include an acid methyl copolymer or a (Na ⁺ ) ion-crosslinked product of the above materials, and these materials can be used alone or as a mixture. Among these materials, more preferable materials are polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

  In addition to the conductive agent described above, the positive electrode active material layer may further contain a filler, a dispersant, an ionic conductor, a pressure enhancer, and other various additives. Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0-30 weight% is preferable as content in an active material layer.

In preparing the positive electrode active material slurry, an aqueous solvent or an organic solvent is used as a dispersion medium. As the aqueous solvent, water is usually used, and additives such as alcohols such as ethanol and cyclic amides such as N-methylpyrrolidone may be added to water up to about 30% by weight or less. it can.
As the organic solvent, usually, cyclic amides such as N-methylpyrrolidone, linear amides such as N, N-dimethylformamide and N, N-dimethylacetamide, and aromatic carbonization such as anisole, toluene and xylene Examples thereof include alcohols such as hydrogens, butanol and cyclohexanol, among which cyclic amides such as N-methylpyrrolidone, linear amides such as N, N-dimethylformamide and N, N-dimethylacetamide are preferable. .

A positive electrode active material, a binder as a binder, an organic substance having a thickening effect, a positive electrode conductive agent blended as necessary, and other fillers are mixed in these solvents to prepare a positive electrode active material slurry, The positive electrode active material layer is formed by applying this to the positive electrode current collector substrate so as to have a predetermined thickness.
The upper limit of the concentration of the positive electrode active material in the positive electrode active material slurry is usually 70% by weight or less, preferably 55% by weight or less, and the lower limit is usually 30% by weight or more, preferably 40% by weight or more. If the concentration of the positive electrode active material exceeds this upper limit, the positive electrode active material in the positive electrode active material slurry tends to aggregate, and if it falls below the lower limit, the positive electrode active material tends to settle during storage of the positive electrode active material slurry.

Further, the upper limit of the concentration of the binder in the positive electrode active material slurry is usually 30% by weight or less, preferably 10% by weight or less, and the lower limit is usually 0.1% by weight or more, preferably 0.5% or more. . When the concentration of the binder exceeds the upper limit, the internal resistance of the positive electrode obtained is increased, and when the concentration is lower than the lower limit, the binding property of the positive electrode active material layer is deteriorated.
For the positive electrode current collector substrate, it is preferable to use, for example, a valve metal or an alloy thereof that forms a passive film on the surface by anodic oxidation in an electrolytic solution. Examples of the valve metal include metals belonging to Groups 4, 5, and 13 of the periodic table and alloys thereof. Specifically, Al, Ti, Zr, Hf, Nb, Ta and alloys containing these metals can be exemplified, and Al, Ti, Ta and alloys containing these metals can be preferably used. . In particular, Al and its alloys are desirable because of their light weight and high energy density. The thickness of the positive electrode current collector substrate is not particularly limited, but is usually about 1 to 50 μm.

<Electrolyte>
Any electrolyte such as an electrolytic solution or a solid electrolyte can be used as the electrolyte. Here, the electrolyte refers to all ionic conductors, and both the electrolytic solution and the solid electrolyte are included in the electrolyte.
As the electrolytic solution according to the present invention, for example, a solution obtained by dissolving a solute in a non-aqueous solvent can be used. As the solute, an alkali metal salt, a quaternary ammonium salt, or the like can be used. Specifically, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (C
F ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) _{3 and the} like are preferably used. One kind of these solutes may be selected and used, or two or more kinds may be mixed and used.

The content of these solutes in the electrolytic solution is preferably 0.2 mol / L or more, particularly 0.5 mol / L or more, and 2 mol / L or less, particularly 1.5 mol / L or less.
Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; cyclic ester compounds such as γ-butyrolactone; chain ethers such as 1,2-dimethoxyethane; crown ethers, 2- Cyclic ethers such as methyltetrahydrofuran, 1,2-dimethyltetrahydrofuran, 1,3-dioxolane, and tetrahydrofuran; chain carbonates such as diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate can be used. Among these, a nonaqueous solvent containing a cyclic carbonate and a chain carbonate is preferable.

One type of these solvents may be selected and used, or two or more types may be mixed and used.
The nonaqueous electrolytic solution according to the present invention may contain various auxiliary agents such as a cyclic carbonate having an unsaturated bond in the molecule, a conventionally known overcharge inhibitor, a deoxidizer, and a dehydrator.
Examples of the cyclic carbonate having an unsaturated bond in the molecule include vinylene carbonate compounds, vinyl ethylene carbonate compounds, methylene ethylene carbonate compounds, and the like.

Examples of the vinylene carbonate compounds include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, fluoro vinylene carbonate, trifluoromethyl vinylene carbonate, and the like.
Examples of the vinyl ethylene carbonate compound include vinyl ethylene carbonate, 4-methyl-4-vinyl ethylene carbonate, 4-ethyl-4-vinyl ethylene carbonate, 4-n-propyl-4-vinyl ethylene carbonate, 5-methyl- Examples include 4-vinylethylene carbonate, 4,4-divinylethylene carbonate, 4,5-divinylethylene carbonate, and the like.

Examples of the methylene ethylene carbonate compound include methylene ethylene carbonate, 4,4-dimethyl-5-methylene ethylene carbonate, 4,4-diethyl-5-methylene ethylene carbonate, and the like.
Of these, vinylene carbonate and vinyl ethylene carbonate are preferable, and vinylene carbonate is particularly preferable.
A suitable example is a difluorophosphate such as lithium difluorophosphate.

These may be used individually by 1 type, or may use 2 or more types together.
When the non-aqueous electrolyte contains a cyclic carbonate compound having an unsaturated bond in the molecule,
The proportion in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably 0.3% by weight or more, and most preferably 0.5% by weight or more. It is 8% by weight or less, preferably 4% by weight or less, particularly preferably 3% by weight or less.

  By including in the electrolyte a cyclic carbonate having an unsaturated bond in the molecule, the cycle characteristics of the battery can be improved. Although the reason is not clear, it is presumed that a stable protective film can be formed on the surface of the negative electrode. However, when the content is small, this property is not sufficiently improved. However, if the content is too large, the gas generation amount tends to increase during high-temperature storage, so the content in the electrolyte is preferably in the above range.

Examples of the overcharge inhibitor include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; 2-fluoro Partially fluorinated products of the above aromatic compounds such as biphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; fluorine-containing compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole and 2,6-difluoroanisole Anisole compounds and the like can be mentioned.
These may be used alone or in combination of two or more.
The ratio of the overcharge inhibitor in the non-aqueous electrolyte is usually 0.1 to 5% by weight. By containing an overcharge preventing agent, rupture / ignition of the battery can be suppressed during overcharge or the like.

  Examples of other auxiliaries include carbonate compounds such as fluoroethylene carbonate, trifluoropropylene carbonate, phenylethylene carbonate, erythritan carbonate, spiro-bis-dimethylene carbonate, methoxyethyl-methyl carbonate; succinic anhydride, anhydrous glutar Carboxylic acid anhydrides such as acid, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride; Ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone and tetramethylthiuram monos Sulfur-containing compounds such as fido, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1 , 3-dimethyl-2-imidazolidinone and nitrogen-containing compounds such as N-methylsuccinimide; hydrocarbon compounds such as heptane, octane and cycloheptane; fluorobenzene, difluorobenzene, hexafluorobenzene, benzotrifluoride, etc. And fluorine-containing aromatic compounds.

These may be used alone or in combination of two or more.
The ratio of these auxiliaries in the nonaqueous electrolytic solution is usually 0.1 to 5% by weight. By containing these auxiliaries, capacity maintenance characteristics and cycle characteristics after high-temperature storage can be improved.
Further, the non-aqueous electrolyte solution may contain an organic polymer compound in the electrolyte solution, and may be a gel, rubber, or solid sheet solid electrolyte. In this case, specific examples of organic polymer compounds include polyether polymer compounds such as polyethylene oxide and polypropylene oxide; crosslinked polymers of polyether polymer compounds; vinyl alcohol polymers such as polyvinyl alcohol and polyvinyl butyral. Compound; insolubilized product of vinyl alcohol polymer; polyepichlorohydrin; polyphosphazene; polysiloxane; vinyl polymer such as polyvinyl pyrrolidone, polyvinylidene carbonate, polyacrylonitrile; poly (ω-methoxyoligooxyethylene methacrylate), Examples thereof include polymer copolymers such as poly (ω-methoxyoligooxyethylene methacrylate-co-methyl methacrylate).

<Separator>
The separator used in the present invention has a predetermined mechanical strength that electrically insulates both electrodes, has a high ion permeability, and has resistance to oxidation on the side in contact with the positive electrode and reduction on the negative electrode side. There is no particular limitation as long as it has both. As a material for the separator having such required characteristics, a resin, an inorganic material, glass fiber, or the like is used. As the resin, olefin polymer, fluorine polymer, cellulose polymer, polyimide, nylon and the like are used. Specifically, it is preferable to select from materials that are stable with respect to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene.

  As the inorganic substance, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used, and those having a particle shape or fiber shape are used. As the form, a thin film shape such as a non-woven fabric, a woven fabric, or a microporous film is used. In the thin film shape, those having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. In addition to the independent thin film shape, a separator formed by forming a composite porous layer containing the inorganic particles on the surface layer of the positive electrode and / or the negative electrode using a resin binder can be used. For example, a porous layer may be formed on both surfaces of the positive electrode using alumina particles having a 90% particle size of less than 1 μm as a binder.

  The non-aqueous electrolyte of the present invention is effective in reducing reaction resistance related to lithium insertion / extraction with respect to the electrode active material, which is considered to be a factor that can realize good low-temperature discharge characteristics. However, it has been found that a battery having a large direct current resistance is inhibited by the direct current resistance and the effect of reducing the reaction resistance cannot be reflected 100% on the low temperature discharge characteristics. This can be improved by using a battery having a small DC resistance component, and the effect of the non-aqueous electrolyte solution of the present invention can be sufficiently exhibited.

<Exterior case>
The material of the outer case is not particularly limited as long as it is a substance that is stable with respect to the nonaqueous electrolyte used. Specifically, a nickel-plated steel plate, stainless steel, aluminum, an aluminum alloy, a metal such as a magnesium alloy, or a laminated film (laminate film) of a resin and an aluminum foil is used. From the viewpoint of weight reduction, an aluminum or aluminum alloy metal or a laminate film is preferably used.

In the exterior case using the above metals, a laser-sealed, resistance-welded, ultrasonic welding is used to weld the metals together to form a sealed sealed structure, or a caulking structure using the above-mentioned metals via a resin gasket To do.
Examples of the outer case using the laminate film include those having a sealed and sealed structure by heat-sealing resin layers. In order to improve the sealing performance, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when a resin layer is heat-sealed through a current collecting terminal to form a sealed structure, a metal and a resin are joined, so that a resin having a polar group or a modified group having a polar group introduced as an intervening resin is used. Resins are preferably used.

<Protective element>
As the above-mentioned protective element, PTC (Positive Temperature Coefficient), thermal fuse, thermistor, whose resistance increases when abnormal heat generation or excessive current flows, current that flows in the circuit due to sudden rise in battery internal pressure or internal temperature during abnormal heat generation For example, a valve (current cutoff valve) that shuts off the current is mentioned. It is preferable to select a protective element that does not operate under normal use at a high current. From the viewpoint of high output, it is more preferable that the protective element is designed so as not to cause abnormal heat generation or thermal runaway without a protective element.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded.
Table 1 shows the physical properties of the graphite particles used in the present invention. In addition, about the measuring method of the physical property as described in an Example, it shall follow the measuring method mentioned above.

(Example 1)
Spherical natural graphite (A) is used as the graphite particles, petroleum heavy oil obtained at the time of naphtha pyrolysis is mixed as the amorphous carbon precursor, heat treatment at 1000 ° C. is performed in an inert gas, and thereafter By pulverizing and classifying the fired product, a multi-layered carbon material (G), which is a multi-layered carbon structure in which carbonaceous materials having different crystallinity were deposited on the surface of spherical natural graphite (A) particles, was obtained. . From the firing yield, it was confirmed that the obtained multilayer structure carbon material powder was coated with 2.5 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Example 2)
Spherical natural graphite (B) was used as the graphite particles, and petroleum heavy oil obtained during naphtha pyrolysis was mixed as the amorphous carbon precursor. At this time, since the ratio of the amorphous carbon precursor is small, the mixing was made uniform by using a chopper attached to the apparatus in order to make the mixing uniform. The obtained mixture was heat-treated at 1000 ° C. in an inert gas, and then the fired product was pulverized and classified to deposit carbonaceous materials having different crystallinity on the surface of the spherical natural graphite (B) particles. A multilayer carbon material (H) that is a multilayer carbon structure was obtained. From the firing yield, it was confirmed that the obtained multilayer carbon material powder was coated with 0.6 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Example 3)
Spherical natural graphite (B) was used as the graphite particles, and petroleum heavy oil obtained during naphtha pyrolysis was mixed as the amorphous carbon precursor. At this time, since the ratio of the amorphous carbon precursor is small, the mixing was made uniform by using a chopper attached to the apparatus in order to make the mixing uniform. The obtained mixture was heat-treated at 1000 ° C. in an inert gas, and then the fired product was pulverized and classified to deposit carbonaceous materials having different crystallinity on the surface of the spherical natural graphite (B) particles. A multilayer carbon material (I) that is a multilayer carbon structure was obtained. From the firing yield, it was confirmed that the obtained multilayer structure carbon material powder was coated with 1.4 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

( Comparative Example 9 )
Spherical natural graphite (B) is used as the graphite particles, petroleum heavy oil obtained at the time of naphtha pyrolysis is mixed as the amorphous carbon precursor, heat treatment is performed at 1000 ° C. in an inert gas, and thereafter By pulverizing and classifying the fired product, a multi-layered carbon material (J), which is a multi-layered carbon structure in which carbonaceous materials having different crystallinity were deposited on the surface of spherical natural graphite (B) particles, was obtained. . From the firing yield, it was confirmed that the obtained multilayer carbon material powder was coated with 3.3 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Example 5)
Spherical natural graphite (B) was used as the graphite particles, and petroleum heavy oil obtained during naphtha pyrolysis was mixed as the amorphous carbon precursor. At this time, since the ratio of the amorphous carbon precursor is small, the mixing was made uniform by using a chopper attached to the apparatus in order to make the mixing uniform. The obtained mixture was heat-treated at 1100 ° C. in an inert gas, and then the fired product was pulverized and classified to deposit carbonaceous materials having different crystallinity on the spherical natural graphite (B) particle surfaces. A multilayer carbon material (K) that is a multilayer carbon structure was obtained. From the firing yield, it was confirmed that the obtained multilayer structure carbon material powder was coated with 0.9 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

( Comparative Example 10 )
Spherical natural graphite (B) was used as the graphite particles, and petroleum heavy oil obtained during naphtha pyrolysis was mixed as the amorphous carbon precursor. At this time, since the ratio of the amorphous carbon precursor is small, the mixing was made uniform by using a chopper attached to the apparatus in order to make the mixing uniform. The obtained mixture was heat-treated at 1100 ° C. in an inert gas, and then the fired product was pulverized and classified so that carbonaceous materials having different crystallinity were deposited on the spherical natural graphite (B) particle surfaces. A multilayer carbon material (L) that is a multilayer carbon structure was obtained. From the firing yield, it was confirmed that the obtained multi-layer structure carbon material powder was coated with 1.5 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

( Comparative Example 11 )
Spherical natural graphite (B) was used as the graphite particles, and petroleum heavy oil obtained during naphtha pyrolysis was mixed as the amorphous carbon precursor. At this time, since the ratio of the amorphous carbon precursor was small, the mixing was made uniform by using a chopper attached to the apparatus in order to make the mixing uniform. The obtained mixture was heat-treated at 1100 ° C. in an inert gas, and then the fired product was pulverized and classified so that carbonaceous materials having different crystallinity were deposited on the spherical natural graphite (B) particle surfaces. A multilayer carbon material (M) having a multilayer carbon structure was obtained. From the firing yield, it was confirmed that the obtained multilayer carbon material powder was coated with 2.2 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

( Comparative Example 12 )
Spherical natural graphite (D) was used as the graphite particles, and petroleum heavy oil obtained at the time of naphtha pyrolysis was mixed as the amorphous carbon precursor. At this time, since the ratio of the amorphous carbon precursor is small, the mixing was made uniform by using a chopper attached to the apparatus in order to make the mixing uniform. The obtained mixture is subjected to heat treatment at 1000 ° C. in an inert gas, and then the calcined product is pulverized and classified to adhere carbonaceous materials having different crystallinity to the spherical natural graphite (D) particle surface. A multilayer carbon material (N) that was a multilayer carbon structure was obtained. From the firing yield, it was confirmed that the obtained multi-layer structure carbon material powder was coated with 0.5 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Comparative Example 1)
Spherical natural graphite (A) is used as graphite particles, petroleum heavy oil obtained at the time of naphtha pyrolysis is mixed as amorphous carbon precursor, heat treatment at 1000 ° C. is performed in an inert gas, and thereafter The fired product was pulverized and classified to obtain a multi-layered carbon material (O) having a multi-layered carbon structure in which carbonaceous materials having different crystallinity were deposited on the spherical natural graphite (A) particle surfaces. From the firing yield, it was confirmed that the obtained multilayer structure carbon material powder was coated with 7.6 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Comparative Example 2)
Spherical natural graphite (D) is used as the graphite particles, petroleum heavy oil obtained at the time of naphtha pyrolysis is mixed as the amorphous carbon precursor, and heat treatment at 1000 ° C. is performed in an inert gas. The fired product was pulverized and classified to obtain a multi-layered carbon material (P) having a layered carbon structure in which carbonaceous materials having different crystallinity were deposited on the surface of spherical natural graphite (D) particles. From the firing yield, it was confirmed that the obtained multi-layer structure carbon material powder was coated with 2.8 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Comparative Example 3)
Spherical natural graphite (E) was used as the graphite particles, and petroleum heavy oil obtained at the time of naphtha pyrolysis was mixed as the amorphous carbon precursor. At this time, since the ratio of the amorphous carbon precursor is small, the mixing was made uniform by using a chopper attached to the apparatus in order to make the mixing uniform. The obtained mixture was heat-treated at 1000 ° C. in an inert gas, and then the fired product was pulverized and classified to deposit carbonaceous materials having different crystallinity on the surface of the spherical natural graphite (E) particles. A multilayer carbon material (Q) having a multilayer carbon structure was obtained. From the firing yield, it was confirmed that the obtained multi-layer structure carbon material powder was coated with 0.5 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Comparative Example 4)
Spherical natural graphite (C) is used as the graphite particles, petroleum heavy oil obtained at the time of naphtha pyrolysis is mixed as the amorphous carbon precursor, heat treatment is performed at 1000 ° C. in an inert gas, and thereafter The fired product was pulverized and classified to obtain a multi-layered carbon material (R) having a multi-layered carbon structure in which carbonaceous materials having different crystallinity were deposited on the spherical natural graphite (C) particle surfaces. From the firing yield, it was confirmed that the obtained multi-layer structure carbon material powder was coated with 5.0 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Comparative Example 5)
Spherical natural graphite (F) was used as the graphite particles, and petroleum heavy oil obtained at the time of naphtha pyrolysis was mixed as the amorphous carbon precursor. At this time, since the ratio of the amorphous carbon precursor is small, the mixing was made uniform by using a chopper attached to the apparatus in order to make the mixing uniform. The obtained mixture was heat-treated at 1000 ° C. in an inert gas, and then the fired product was pulverized and classified to deposit carbonaceous materials having different crystallinity on the spherical natural graphite (F) particle surfaces. A multilayer carbon material (P) having a multilayer carbon structure was obtained. From the firing yield, it was confirmed that the obtained multilayer structure carbon material powder was coated with 0.7 parts by weight of amorphous carbon with respect to parts by weight of the graphite particles.

(Comparative Example 6)
Spherical graphite (C) was used as it was.
(Comparative Example 7)
Spherical graphite (E) was used as it was.
(Comparative Example 8)
Scaly graphite (T) was used as it was.
Tables 1 and 2 show the physical properties, production conditions, and evaluation results of the carbon materials described in Examples 1 to 3 , 5 and Comparative Examples 1 to 12 .

・ Production of battery (Production of negative electrode)
As a multi-layer structure carbon material, 97.7 parts by weight of the multi-layer structure carbon material (F), and 130 wt. Of an aqueous dispersion of sodium carboxymethyl cellulose (concentration of 1% by mass of carboxymethyl cellulose sodium) as a thickener and binder, respectively. And 2.5 parts by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber 40% by mass) were added and mixed with a rotation / revolution mixer to form a slurry. The obtained slurry was applied to both sides of a 10 μm rolled copper foil, dried, and rolled to 75 μm with a press machine. The active material layer size was 30 mm in width, 40 mm in length, and was not used as a current collector tab weld. It cut out in the shape which has a coating part, and was set as the negative electrode. At this time, the density of the active material of the negative electrode was 1.35 g / cm ³ .

(Preparation of positive electrode)
The positive electrode active material is a lithium transition metal composite oxide synthesized by the method shown below, and is represented by the composition formula LiMn _0.33 Ni _0.33 Co _0.33 O ₂ . Mn ₃ O ₄ as a manganese raw material, NiO as a nickel raw material, and Co (OH) ₂ as a cobalt raw material are weighed so as to have a molar ratio of Mn: Ni: Co = 1: 1: 1, and pure water is added thereto. In addition, it was made into a slurry, and while being stirred, the solid content in the slurry was wet pulverized so as to have a median diameter of 0.2 μm using a circulating medium stirring type wet bead mill.

The slurry was spray-dried with a spray dryer to obtain substantially spherical granulated particles having a particle size of about 5 μm, which consisted only of manganese raw material, nickel raw material and cobalt raw material. Add LiOH powder with a median diameter of 3 μm to the resulting granulated particles so that the ratio of the number of moles of Li to the total number of moles of Mn, Ni, and Co is 1.05, and mix with a high-speed mixer. Thus, a mixed powder of granulated particles of nickel raw material, cobalt raw material, manganese raw material and lithium raw material was obtained. This mixed powder was fired at 950 ° C. for 12 hours under air flow (climbing temperature rate 5 ° C./min), then crushed and passed through a sieve having an opening of 45 μm to obtain a positive electrode active material. The positive electrode active material has a BET specific surface area of 1.2 m ² / g, an average primary particle diameter of 0.8 μm, a median diameter d ₅₀ of 4.4 μm,
The tap density was 1.6 g / cm ³ .

90% by mass of the positive electrode active material described above, 5% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in an N-methylpyrrolidone solvent, Slurried. The obtained slurry was applied to a 15 μm aluminum foil, dried, and rolled to a thickness of 81 μm with a press machine. The positive electrode active material layer had a width of 30 mm, a length of 40 mm, and an uncoated part for current collection. It was cut out into a shape having a positive electrode. The density of the positive electrode active material layer is 2.35 g / cm ³ , (the thickness of the positive electrode active material layer on one side) / (the thickness of the current collector) is 2.2, and L / (2 × S ₂ ) Was 0.2.

(Preparation of electrolyte)
Hexafluoroline sufficiently dried at a concentration of 1 mol / L in a mixture (volume ratio 3: 3: 4) of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) under an inert atmosphere It was used by dissolving lithium acid (LiPF _6).

(Production of battery)
One positive electrode and one negative electrode were arranged so that the active material surfaces face each other, and a porous polyethylene sheet separator (25 μm) was sandwiched between the electrodes. At this time, the positive electrode active material surface was faced so as not to be detached from the multilayer structure carbon material surface. A current collector tab is welded to the uncoated portion of each of the positive electrode and the negative electrode to form an electrode body, and a laminate sheet (total thickness) in which a polypropylene film, an aluminum foil having a thickness of 0.04 mm, and a nylon film are laminated in this order. 0.1 mm) was sandwiched with a laminate sheet so that the polypropylene film was on the inner surface side, and the area without electrodes was heat-sealed except for one piece for injecting the electrolyte solution. Thereafter, 200 μL of a non-aqueous electrolyte was injected into the active material layer, sufficiently infiltrated into the electrode, and sealed to produce a laminate cell. The rated capacity of this battery is 20 mAh.

・ Battery evaluation (capacity measurement)
For a battery that has not undergone a charge / discharge cycle, a voltage range of 4.1 V to 3.0 V and a current value of 0.2 C at 25 ° C. In the same manner, the following initial charge / discharge was performed for 5 cycles. The discharge capacity at the 5th cycle at this time was defined as the initial capacity. Next, the following output measurement was performed.

(Reaction resistance / double layer capacitance measurement)
After charging at a constant current of 0.2 C and a capacity of 50% of the initial capacity in a 25 ° C. environment, and then storing in a -10 ° C. constant temperature bath for 3 hours or more, Solartron 1280C (manufactured by Solartron) The impedance measurement was performed at a voltage amplitude of 10 mV and 0.1 Hz to 20000 Hz. The obtained data was fitted using the equivalent circuit of FIG. 1, and a resistance derived from a resistance component in the vicinity of 10 Hz was defined as a reaction resistance, and Cdl corresponding to the resistance component was defined as an electrochemical double layer capacity.
It was performed battery production and battery also similarly evaluated Examples 2 to 3, 5 and Comparative Examples 1 to multilayer structure carbonaceous material, spherical graphite, flaky graphite produced in 12. The results are shown in Table 2.

  From the results of Table 2, the multilayer carbon material thinly coated with amorphous carbon with smaller particle size graphite particles surprisingly does not have a large increase in electrochemical double layer capacity, only the reaction resistance. I found a reduction effect. That is, by applying the multi-layer structure carbon material of the present invention to the negative electrode material, the reaction resistance is very small and the electrochemical double layer capacity is suppressed, thereby suppressing unnecessary reactions and higher input / output. It became possible to express the characteristics.

In general, a carbon material having a small particle size causes streaking during electrode formation due to the influence of the fine particle side of the particle size distribution, but the multi-layered carbon material of the present invention can reduce the oil absorption. An improvement was seen.

The multi-layer structure carbon material of the present invention provides a practical negative electrode material for non-aqueous secondary batteries that effectively reduces negative electrode resistance and does not decrease storage characteristics (electrochemical double layer capacity derived from the negative electrode). be able to. Moreover, according to the manufacturing method of the said material, since there are few processes, it can manufacture stably and efficiently and cheaply.

Rs. DC resistance R1. Reaction resistance R2. Reaction resistance R3. Reaction resistance CPE1. Double layer capacity (Cdl)
CPE2. Double layer capacity (Cdl)
CPE3. Double layer capacity (Cdl)

Claims (4)

A multilayer carbon material for a non-aqueous secondary battery, characterized in that it is a multilayer carbon material obtained by coating the surface of graphite particles with amorphous carbon, and satisfies the following conditions (1) to (4): Material.
(1) The average particle diameter d50 of the multilayer carbon material is 1 μm or more and 18 μm or less. (2) The weight ratio of graphite particles / amorphous carbon is 96/4 or more and 99.99 / 0.01 or less ( 3) The tap density of the multi-layer structure carbon material is 0.95 g / cm ³ or more and 1.3 g / cm ³ or less. (4) The specific surface area (SA) measured using the BET method is 6.5 m ² / g or more. 10 m ² / g or less Multilayer structure carbonaceous material is, spacing of 002 surface by X-ray wide angle diffraction method (d002) is 0.337nm or less, and the peak intensity ratio in the vicinity of 1360 cm ^-1 to the peak intensity near 1580 cm ^-1 in the argon ion laser Raman spectrum The multilayer structure carbon material for non-aqueous secondary batteries according to claim 1, wherein the Raman R value is 0.15 to 0.6.   It comprises a current collector and a multilayer structure carbon material layer formed on the current collector, and the multilayer structure carbon material layer contains the carbon material according to claim 1 or 2. And a negative electrode for a non-aqueous secondary battery.   A nonaqueous secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and an electrolyte, wherein the negative electrode is the negative electrode for a nonaqueous secondary battery according to claim 3.

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