JP2008171809A - Lithium secondary cell and anode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary cell having enough active material intensity and adhesiveness in an anode by making exist a spherical substance in an anode active material layer with the use of a scale-like carbon substance, even if housed in a case having shape changeability. <P>SOLUTION: In the lithium secondary cell made by housing lithium secondary cell elements consisting of a cathode, an anode and electrolyte in a case having shape changeability, the anode contains a scale-like carbon substance with an aspect ratio of 1.1 to 2.9, and a spherical substance with an aspect ratio of 1.0 to 1.5, and the scale-like carbon substance is a graphite carbonaceous object at least with a part of the surface coated with amorphous coke, with the spherical graphite of meso-carbon micro beads. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery.

Various devices such as camera-integrated VTR devices, audio devices, portable computers, and cellular phones are becoming smaller and lighter, and there is an increasing demand for higher performance of batteries as power sources for these devices. In particular, lithium secondary batteries capable of realizing high voltage and high energy density are actively developed.
As an active material used for the negative electrode of a lithium secondary battery, it is known to use a scaly carbonaceous material such as scaly graphite. The flaky carbonaceous material is an excellent negative electrode active material that suppresses the formation of lithium dendrite compared to the case where lithium metal is used for the negative electrode, and can ensure high capacity and high safety. When a scaly carbonaceous material is used, lithium is intercalated between layers of a carbon layered structure. In general, such an electrode is formed by forming an active material layer containing an active material on a current collector.

  On the other hand, in recent years, a lithium secondary battery element having a positive electrode, a negative electrode, and an electrolyte (hereinafter, this may be simply referred to as “lithium secondary battery element” or “battery element” in the present specification) has been conventionally used. In place of the metal can, it has been proposed to be housed in a laminated film case having a shape changeability formed by laminating a metal layer and a resin layer. Such a laminate film is not only easier to process than conventional metal cans, but also thinner and lighter, so that the volume energy density and weight energy density of the entire battery can be further improved.

  However, according to the study by the present inventors, it has been found that when the above scaly carbonaceous material is used for an electrode, the strength of the active material layer is weak and the adhesiveness is poor. In other words, the scale-like carbonaceous material expands and contracts during charge and discharge, and when charging and discharging are repeated, the active material layer is eventually peeled off from the current collector, so that the characteristics of the lithium secondary battery are large. It will deteriorate.

  The characteristic deterioration of the lithium secondary battery due to insufficient strength and poor adhesion of the active material layer becomes a problem particularly when a case having shape variability is used as a case for housing a lithium secondary battery element. That is, when the battery element is stored in the metal can, the strength of the active material layer and the adhesiveness against the external force are not so serious problems because the strength of the metal can itself is large, and the entire battery element is pressed against the metal can. Therefore, even if the active material of the electrode expands and contracts with charge / discharge, the effect on the active material layer is small. On the other hand, when a case with shape changeability is used, the active material layer is not only easily destroyed by external force, but also the force to hold down the entire battery element by the case is weak, so that the active material layer is repeatedly expanded and contracted. The effect on the adhesiveness between the active material layer itself and the active material layer and the current collector is large.

Therefore, the above-mentioned problems due to the use of the scaly carbonaceous material for the electrode adversely affect the cycle characteristics of the lithium secondary battery, for example. Especially when the battery element is housed in a case having shape changeability, The problem is particularly apparent.
An object of the present invention is to obtain a lithium secondary battery having a negative electrode having sufficient active material strength and adhesiveness, and in particular, sufficient active material strength even when housed in a case having a variable shape. The object is to obtain a lithium secondary battery having a negative electrode having adhesiveness.

  According to the present invention, it is possible to effectively solve the problem of insufficient strength and adhesive strength of the negative electrode active material layer, which is a particular problem when a lithium secondary battery element having a negative electrode having a scaly carbonaceous material is housed in a case. A lithium secondary battery having excellent performance such as cycle characteristics, rate characteristics, capacity, and safety, and a negative electrode for a lithium secondary battery capable of realizing such a lithium secondary battery can be obtained.

  As a result of intensive studies to solve the problem, the present inventor has found that the lack of strength and adhesion of the active material layer using the scaly carbonaceous material can be solved by the presence of a spherical material in the active material layer. In particular, in a lithium secondary battery in which a lithium secondary battery element is housed in a case having shape changeability, it is found that the effect of the presence of a spherical material in the active material layer is remarkably exhibited. completed.

That is, the gist of the present invention resides in the following (1) to (17).
(1) A lithium secondary battery in which a lithium secondary battery element having a positive electrode, a negative electrode, and an electrolyte is housed in a case, wherein the negative electrode is a flaky carbonaceous material having an aspect ratio of 1.1 to 2.9. A lithium secondary battery comprising a spherical substance.
(2) In a lithium secondary battery in which a lithium secondary battery element having a positive electrode, a negative electrode, and an electrolyte is housed in a case having shape changeability, the negative electrode contains a scaly carbonaceous material and a spherical material. A lithium secondary battery characterized by that.
(3) The lithium secondary battery according to (2), wherein the scaly carbonaceous material has an aspect ratio of 1.1 to 6.0 and the spherical material has an aspect ratio of 1.0 to 1.5.
(4) The lithium secondary battery according to (2) or (3), wherein the scale-like carbonaceous material has an aspect ratio of 1.1 to 2.9.
(5) The lithium secondary battery according to any one of (1) to (4), wherein an average particle diameter of the spherical substance is 2/3 or less of an average particle diameter of the scaly carbonaceous substance.
(6) The lithium secondary battery according to any one of (1) to (5), wherein the spherical substance is a spherical carbonaceous substance.
(7) The lithium secondary battery according to any one of (1) to (6), wherein the scaly carbonaceous material is a graphite-based carbonaceous material in which at least a part of the surface is coated with amorphous coke.
(8) The lithium secondary battery according to any one of (1) to (7), wherein the weight ratio of the spherical substance to the scaly carbonaceous substance is 10 to 70%.
(9) The lithium secondary battery according to any one of (1) to (8), wherein the scaly carbonaceous material is scaly graphite and the spherical material is spherical graphite.
(10) The lithium secondary battery according to (9), wherein the spherical graphite is mesocarbon microbeads.
(11) The lithium secondary battery according to (9) or (10), wherein amorphous coke is coated on at least part of the surface of the scaly graphite.
(12) The lithium secondary battery according to any one of (1) to (11), which has a non-fluidic electrolyte between the positive electrode and the negative electrode.
(13) The lithium secondary battery according to any one of (2) to (12), wherein the case having shape variability is made of a laminate film in which a resin layer is provided on both surfaces of the gas barrier layer.
(14) The lithium secondary battery according to any one of (2) to (13), wherein the lithium secondary battery element is enclosed in a case under reduced pressure.
(15) Any of (1) to (14), wherein the electrolyte includes an electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent, and 60% by volume or more of the non-aqueous solvent is a high boiling point solvent having a boiling point of 150 ° C. or higher. The lithium secondary battery as described in any one.
(16) The lithium secondary battery according to (15), wherein the high boiling point solvent includes at least one selected from the group consisting of propylene carbonate, ethylene carbonate, and γ-butyrolactone.
(17) A negative electrode for a lithium secondary battery, comprising a flaky carbonaceous material having an aspect ratio of 1.1 to 2.9 and a spherical material.

The lithium secondary battery of the present invention has a positive electrode, a negative electrode, and an electrolyte.
One of the characteristics of the present invention is that a scaly carbonaceous material and a spherical material coexist in the negative electrode.

As described later, since the shape of the scaly carbonaceous material is usually a flat plate, it is easily oriented in the negative electrode active material layer in the direction perpendicular to the negative electrode film thickness direction. Therefore, the negative electrode containing scaly carbonaceous material has a problem that it tends to peel off in the negative electrode thickness direction. Therefore, if a spherical substance is further contained in the negative electrode, the orientation is suppressed, and the strength and adhesiveness of the negative electrode active material layer are increased.
The scaly carbonaceous material has a high capacity and is a useful material as a negative electrode material for a lithium secondary battery. The scaly carbonaceous material has shape anisotropy, and its shape is usually a flat plate shape. The aspect ratio (the ratio between the longest diameter and the shortest diameter) is larger than 1. Here, the longest diameter and the shortest diameter can be measured by SEM (Scanning Electron Microscope).

  The scaly carbonaceous material used in the present invention preferably has an aspect ratio in a predetermined range. Here, the upper limit of the aspect ratio is usually 6.0 or less, preferably 3.0 or less, more preferably 2.9 or less, and particularly preferably 2.8 or less. When the aspect ratio is large, the scaly carbonaceous material is oriented in the negative electrode, and the basal surface of the scaly carbonaceous material tends to be in the negative electrode film thickness direction and the edge surface is in the direction perpendicular to the negative electrode film thickness direction. However, by setting the aspect ratio to be equal to or less than the above numerical value, the scaly carbonaceous material can be oriented so that the edge surface faces the film thickness direction of the negative electrode. Since the scaly carbonaceous material occludes and releases lithium ions at its edge surface, it becomes possible to efficiently occlude and release lithium ions when the edge surface is oriented in the film thickness direction. In addition, since the bend degree of the negative electrode can be lowered by setting the aspect ratio to be equal to or less than the above value, lithium can be more efficiently inserted and released while maintaining the high capacity that is an advantage of the scaly carbonaceous material. Will be able to. On the other hand, the lower limit of the aspect ratio is usually 1.1 or more, preferably 1.2 or more, more preferably 1.5 or more. Since it is industrially difficult to set the aspect ratio of the scaly carbonaceous material to 1.0, it is preferable to set the aspect ratio or more in consideration of production efficiency.

As a method for controlling the aspect ratio, for example, a method of performing spheroidization processing can be cited. Details of the spheroidization process will be described later.
The average particle size of the scaly carbonaceous material is usually 1 μm or more, preferably 5 μm or more, and is usually 45 μm or less, preferably 35 μm or less, more preferably 25 μm or less. If the average particle size is too small, the irreversible capacity may increase and the battery capacity may decrease. On the other hand, if the average particle size is too large, the film thickness of the active material layer is limited and a uniform active material layer can be formed on the substrate. It becomes difficult.

Examples of such a scaly carbonaceous material include various carbonaceous materials such as coke and graphite-based carbonaceous materials, but graphite-based carbonaceous materials are preferable because of their large capacity.
Graphite-based carbonaceous materials (hereinafter sometimes abbreviated as graphite materials) include graphitized products of conductive carbon black such as acetylene black and ketjen black, graphite powder such as artificial graphite and natural graphite, and purified products thereof. And carbon fibers such as vapor-grown carbon fibers. Any graphite material may be used, but scale-like graphite made of natural graphite or the like is preferable. Further, a graphite material having a predetermined relationship between the particle size and specific surface area as shown in the following (I) to (IV), a Raman R value in a specific numerical range, a full width at half maximum, and the like is more preferable.
(I) When the specific surface area value measured by the BET method (nitrogen gas adsorption) is Y (m ² / g) and the particle size value of the powder is X (μm), 1 ≦ X ≦ 45, 0 .. 1 ≦ Y ≦ 25 and Y ≦ ax ^b (where a = 52, b = −0.6) is preferred. For the measurement of the particle size, a laser diffraction method, an electric resistance method, a direct particle size evaluation method by processing a photographic image of a CCD high-sensitivity camera, or the like can be used. For the measurement of the specific surface area, a BET method based on gas molecule adsorption, an organic molecule adsorption method, or an organic solvent adsorption method can be used.
(II) A graphite material having an R value (= IB / IA) in a Raman spectrum analysis of 0.001 or more and 0.2 or less, particularly 0.15 or less, and further 0.07 or less is preferable.
(III) in the Raman spectrum analysis, it is the half width of peaks present in 1570~1620cm ^-1 △ v magnitude of value, preferably graphite material is 14~22cm ^-1.
(IV) plane spacing d ₀₀₂ of the X-ray diffraction (002) plane is 3.38Å or less, and particularly preferably between 3.36Å or less. In addition, a graphite material having a crystallite size (Lc) in the c-axis direction of 1000 mm or less is preferable.

Specific examples of the graphite material that can be used in the present invention include the following. These high purity purified products may also be used.
(1) High crystalline natural graphite or artificial graphite.
(2) Natural graphite, artificial graphite, or expanded graphite reheated product.
(3) A graphite having the same performance as the above (1) and (2) produced by graphitizing from a graphitizable organic raw material as in the following (a) and (b).

  (A) Coal tar pitch, coal heavy oil, atmospheric residue, petroleum heavy oil, aromatic hydrocarbon, nitrogen-containing cyclic compound, sulfur-containing cyclic compound, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile , Polyvinyl butyral, natural polymer, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, one or more organic substances selected from phenolic imide resins, graphitized at a firing temperature of, for example, 2500 ° C. to 3200 ° C. .

(B) The graphitizable organic substance of the above (a) is lithium, beryllium, boron, magnesium, aluminum, silicon, potassium, calcium, titanium, vanadium, chromium, manganese, copper, zinc, nickel, platinum, palladium, cobalt, In the presence of at least one powder selected from ruthenium, tin, lead, iron, germanium, zirconium, molybdenum, silver, barium, tantalum, tungsten, rhenium, or a catalyst such as a thin film, 400 ° C to 2500 ° C, More preferably graphitized by firing at 1000 ° C. or more and 2000 ° C. or less.
(4) The graphite material particle size measurement and Raman spectroscopic analysis result in a graphite material that does not have a numerical value within a desired certain range that can be expected to have a high negative electrode capacity and a high rate charge / discharge resistance characteristic. Graphite that can keep the numerical value obtained from the particle size measurement and Raman spectroscopic analysis of the fired material within a desired constant range by re-firing the material at a temperature of 2000 ° C. or higher and 3200 ° C. or lower.
(5) The specific surface area measurement by the BET method (nitrogen gas adsorption) of the graphite material and the result of the Raman spectroscopic analysis are numerical values within a desired fixed range in which high negative electrode capacity and high rate resistance against charge / discharge can be expected. Although it is a graphite material that does not have, by re-firing these materials at a temperature of 2000 ° C. or more and 3200 ° C. or less, the numerical values obtained from the specific surface area measurement and Raman spectroscopic analysis of the fired material are set to a desired constant value. Graphite that can fit in the range.

In the present invention, as described above, the orientation of the scaly carbonaceous material in the negative electrode is controlled so that the edge surface of the scaly carbonaceous material faces the negative electrode film thickness direction, and the bending degree of the negative electrode is increased. In order to improve, it is preferable that the aspect ratio of the scaly carbonaceous material is within a predetermined range.
A scaly carbonaceous material having such an aspect ratio can be obtained, for example, by spheroidizing a scaly carbonaceous material having a large aspect ratio. The spheronization treatment is performed by scraping off the corners of the scaly carbonaceous material before the treatment. If the corners are cut away, the shape of the scaly carbonaceous substance will approach that of a rugby ball, and the aspect ratio will decrease. If the above process is further advanced, the shape of the scaly carbonaceous substance approaches a sphere and the aspect ratio can be further reduced.

The spheronization treatment is usually performed by pulverizing the scaly carbonaceous material before the treatment.
Crushing is classified according to the type of force applied to the substance and the form of treatment. The types of force include crushing force (impact force), crushing force (compression force), crushing force (grinding force), and scraping force (shearing). The processing mode is roughly divided into two types: volume pulverization in which cracks are generated and propagated inside the particles, and surface pulverization in which the particle surface is scraped off. Volume pulverization proceeds by impact force, compression force, and shear force, and surface pulverization proceeds by grinding force and shear force. The pulverization is a process in which the types of forces applied to these objects to be crushed and the processing forms are combined at various ratios. The spheronization treatment of the present invention is preferably performed mainly on surface grinding using grinding force and shearing force.

  In order to remove the corners of the scaly carbonaceous material and introduce roundness into the particle shape, it is important that surface grinding is performed. For this purpose, the selection of the type of equipment to be treated and the equipment has It is important to determine the grinding ability. The former is to select the type of apparatus according to the type of crushing force applied to the object to be crushed, and the latter is to use the limit (crushing limit) of the crushing force existing for each apparatus model. The pulverization limit refers to the particle size region, and the particle size at which volume pulverization proceeds is the lowest limit region. That is, the particle diameter is reduced, the collision probability is lowered, and the weight of the particles is also reduced, so that a large stress is not generated even when the collision occurs and the volume pulverization does not proceed. In this region, surface grinding is performed instead of volume grinding.

  As a type of apparatus capable of performing surface pulverization, it has been clarified by the inventors that an apparatus in which pulverization proceeds by a shearing force is effective. Examples of such an apparatus include an apparatus that uses pulverized media such as a ball mill, a vibration mill, and a medium stirring mill. In models that can use these crushing media, it is considered that crushing is centered on the crushing force and the truncation force, and crushing that takes corners can be performed. Wet pulverization is preferred as well as dry pulverization. As an example, the name of the device is a vibration mill and ball mill manufactured by Chuo Kako Co., Ltd., a mechano mill manufactured by Okada Seiko Co., Ltd., and both dry and wet manufactured by Kurimoto Iron Works Co., Ltd. And a medium stirring mill. In addition, for example, when the processed material passes between the rotating container and the taper attached to the inside of the container, the compressive force and the shearing force due to the speed difference between the rotating container and the taper are applied to the processed material. The apparatus which is is also preferable as an apparatus which advances surface grinding | pulverization. These devices are originally devices for compounding two or more kinds of powders and performing surface modification of the powders. However, since these devices are strongly applied with shearing force, It is thought that the improvement, that is, the particles can be rounded. As specific examples of device names, theta composer manufactured by Tokuju Kogakusho Co., Ltd., mechano-fusion system manufactured by Hosokawa Micron Co., Ltd., and the like.

When a graphite-based carbonaceous material such as flaky graphite is used as the flaky carbonaceous material, it is preferable to coat at least a part of its surface with amorphous carbonaceous material (especially coke) (hereinafter, such a surface). A graphite-based carbonaceous material in which at least a part of the carbonaceous material is coated with amorphous coke may be abbreviated as a carbon-coated graphite-based carbonaceous material). A lithium secondary battery using a carbon-coated graphite-based carbonaceous material as a negative electrode has an advantage of excellent rate characteristics and cycle characteristics as compared with a lithium secondary battery using a graphite-based carbonaceous material without coating as a negative electrode. This carbon-coated graphite-based carbonaceous material can be produced by coating a graphite-based carbonaceous material with an organic material that can be carbonized, carbonizing the coated body by firing, and grinding the carbonized material as necessary. Yes, it has the property of occluding and releasing lithium ions.

This carbon-coated graphite-based carbonaceous material is usually a carbonaceous particle having the following characteristics (a) to (c).
(A) The value of the (002) plane distance d ₀₀₂ obtained from X-ray diffraction is 3.35 mm or more and 3
. Have a value of 39mm or less.
(B) R value calculated | required from a Raman spectrum analysis is 0.15-1.0, More preferably, it is 0.2-0.5, especially said R value is R of graphite-type carbonaceous material before coating | cover. Be greater than or equal to the value.
(The peak and R value, which is present in the Raman spectrum analysis using an argon ion laser beam having a wavelength of 5145 Å, the intensity of a peak existing in the range of 1570~1620cm ^-1 IA, in the range of 1350 ^-1 When the strength of IB is IB, the ratio IB / IA is expressed.Hereinafter, the R value means the same unless otherwise specified.)
(C) The specific surface area measured using the BET method by nitrogen gas adsorption is 13 m ² / g or less, more preferably 10 m ² / g or less, further preferably 5 m ² / g or less, and 0.1 m ²
/ G or more.

  Examples of the organic substance used for forming a carbon-coated graphite-based carbonaceous material film include organic substances that progress in carbonization in the liquid phase and various organic substances that progress in carbonization in the solid phase. Organic substances that undergo carbonization in the liquid phase include coal-based heavy oils such as coal tar pitch and dry distillation liquefied oil including soft pitch to hard pitch, and direct-current heavy oil such as atmospheric residual oil and vacuum residual oil. Petroleum heavy oils such as cracked heavy oils such as ethylene tar, which are by-produced during thermal cracking of crude oil, crude oil, naphtha and the like. In addition, aromatic hydrocarbons such as acenaphthylene, decacyclene and anthracene, nitrogen-containing cyclic compounds such as phenazine and acridine, sulfur-containing cyclic compounds such as thiophene, alicyclic hydrocarbons such as adamantane, polyphenyls such as biphenyl and terphenyl, etc. Can be mentioned. In addition, organic substances that undergo carbonization in the solid phase include natural polymers such as cellulose and saccharides, thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, furfuryl alcohol resin (furan resin), phenol-formaldehyde resin, and imide resin. And thermosetting resins. Of course, a plurality of these organic substances can be used in combination.

In order to obtain a carbon-coated graphite-based carbonaceous material, it is advantageous to use an organic material that is carbonized in a liquid phase.
Note that the coating is coke, for example, by (a) a TEM photograph, or (b) subtracting the X-ray diffraction peak of the graphite-based carbon material before coating from the X-ray diffraction peak after coating, or (C) It is easily confirmed by measuring the film remaining after dissolving the graphite-based carbon material with a Simon reagent (silver chromate-sulfuric acid) by a known method (TEM, X-ray diffraction, Raman spectroscopic analysis, etc.). be able to.

  Carbon-coated graphite-based carbonaceous material is a mixture of the above organic substance and graphite material, usually 700 ° C. or higher, preferably 900 ° C. or higher, more preferably 1000 ° C. or higher, particularly preferably 1100 ° C. or higher, while usually 2800 ° C. or lower. Preferably it can obtain by baking at 1500 degrees C or less. The temperature range may be appropriately selected according to the performance desired for the carbon-coated graphite-based carbonaceous material, but if the firing temperature is too low, the organic material is not sufficiently fired and the conductivity of the carbon-coated graphite-based carbonaceous material is low. It may be insufficient. On the other hand, if the firing temperature is too high, the surface treatment effect of the carbon-coated graphite-based carbonaceous material may be insufficient.

The carbon-coated graphite-based carbonaceous material may sometimes obtain particles having an average particle diameter of usually 1 to 100 μm, and further 5 to 50 μm. These particles are further subjected to a pulverization treatment as necessary, whereby a carbon-coated graphite-based carbonaceous material having a desired particle size can be obtained.
The composition of the carbon-coated graphite-based carbonaceous material is such that when the total of the graphite-based carbonaceous material and the organic material is 100% by weight, the ratio of the organic material is usually 50% by weight or less, preferably 25% by weight or less, more preferably It is 10% by weight or less, particularly preferably 8% by weight or less, on the other hand, usually 1% by weight or more, preferably 2% by weight or more, more preferably 5% by weight or more. When there are too many organic baked material compositions, there exists a tendency for potential reduction and rapid charge / discharge characteristics to be less improved. Moreover, when there are too many composition of baking products of organic substance, in order to improve a performance further, the effect of the process by an acid or an alkali preferable to implement after baking may not be so remarkable. On the other hand, if the composition of the organic baked product is too small, the desired effect may not be obtained. The above range is not the raw material charge ratio but the composition of the final product. Therefore, at the time of preparation, it is necessary to determine the blending amount of the raw material in consideration of the composition ratio in the final stage. The lithium ion secondary battery using the carbon-coated graphite-based carbonaceous material thus prepared for the negative electrode exhibits excellent rate characteristics and cycle characteristics as compared with the case of using the graphite negative electrode without coating.

  The spherical substance contained in the negative electrode together with the flaky carbonaceous substance has little shape anisotropy, and its aspect ratio (ratio of longest diameter to shortest diameter) is usually 1.5 or less, Preferably it is 1.45 or less, More preferably, it is 1.4 or less, On the other hand, it is 1.0 or more normally, Preferably it is 1.1 or more, More preferably, it is 1.2 or more. Note that the aspect ratio does not become smaller than 1. Further, the longest diameter and the shortest diameter of the spherical particles can be measured by SEM. When a spherical substance having an aspect ratio within the above range is used together with a scaly carbonaceous substance, the degree of bending of the negative electrode can be reduced, so that lithium ions are efficiently absorbed and released in the negative electrode. Examples of the material constituting such a spherical substance include carbonaceous substances, alumina, titanium oxide, acrylic resins, and the like, preferably carbonaceous substances, particularly graphite. That is, as the spherical substance, a spherical carbonaceous substance is preferably used, and spherical graphite is particularly preferably used. The carbonaceous material itself functions as an active material because lithium is intercalated, and as a result, the battery capacity can be further improved. Here, specific examples of the spherical graphite include mesocarbon microbeads and glassy carbon, and the mesocarbon microbeads are preferable.

Mesocarbon microbeads (MCMB) are spherical particles that can be obtained by heat-treating mesophase spherules produced during pitch carbonization at high temperatures and graphitizing them. ). Further, the degree of graphitization of MCMB is an important factor. When expressed in terms of carbon physical property parameters, the plane spacing (d ₀₀₂ ) of the 002 plane is 3.
It is preferably 35 to 3.42 mm, particularly 3.36 to 3.40 mm. Moreover, the specific surface area by the BET method has a preferable thing of 0.7-5 m < ² > / g. Mesocarbon microbeads, for example, heat-treat heavy coal oil such as coal tar and coal tar pitch at a low temperature of about 300 to 500 ° C. to obtain mesophase microspheres, which are further heated to a high temperature of about 2000 to 3000 ° C. Can be obtained by heat treatment.

The average particle diameter of the spherical material is usually 0.5 μm or more, preferably 3 μm or more, and usually 30 μm or less, preferably 10 μm or less. If the average particle size is too small, the effect of improving the coating film strength is small, and if too large, it is difficult not only to form a coating film with a uniform film thickness, but also in this case, the effect of improving the coating film strength tends to be small. is there.
The ratio of the average particle diameter of the spherical substance to the average particle diameter of the scaly carbonaceous substance is usually less than 1, but among them, it is preferably 2/3 or less, more preferably 2/5 or less, and preferably It is 1/5 or more, more preferably 1/4 or more. If this ratio is too small, the effect of improving the coating strength and adhesiveness tends to be small, and if it is too large, the battery capacity tends to decrease.

  The weight ratio of the spherical substance to the scaly carbonaceous substance is usually 100% or less, preferably 70% or less, more preferably 50% or less, most preferably 40% or less, usually 1% or more, preferably 5% or more. More preferably, it is 10% or more, and most preferably 15% or more. If this weight ratio is too small, the effect of improving the coating strength and adhesiveness tends to be small, and if it is too large, the battery capacity tends to decrease.

  The negative electrode is usually formed by forming an active material layer containing the scaly carbonaceous material and the spherical material on a current collector. The active material layer usually contains a scaly carbonaceous material, a spherical material, and a binder, and further, the scaly carbonaceous material and the spherical material are dispersed in each other. Such a negative electrode can be produced by converting a scaly carbonaceous substance and a spherical substance into a dispersion paint using a solvent capable of dissolving the binder together with a binder, and applying and drying the paint on a current collector. it can.

The ratio of the flaky carbonaceous material in the negative electrode is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, and usually 89.9% by weight or less, preferably 80% by weight or less. is there. If the amount is too large, the mechanical strength of the electrode tends to be inferior. If the amount is too small, the battery performance such as capacity tends to be inferior.
The binder used for the negative electrode active material layer needs to be stable with respect to an electrolytic solution and the like, and various materials are used from the viewpoint of weather resistance, chemical resistance, heat resistance, flame retardancy, and the like. Specifically, inorganic compounds such as silicate and glass, alkane polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene, polymethylstyrene, Examples thereof include polymers having a ring structure in a polymer chain such as polyvinyl pyridine and poly-N-vinyl pyrrolidone.

  Other specific examples include acrylic derivative polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide; Fluorine resins such as vinyl chloride, polyvinylidene fluoride and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; Polyvinyl alcohol polymers such as polyvinyl acetate and polyvinyl alcohol; Halogen-containing polymers such as vinylidene; conductive polymers such as polyaniline can be used.

  Further, a mixture such as the above-mentioned polymer, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, and the like can be used. The weight average molecular weight of these resins is usually about 10,000 to 3,000,000, preferably about 100,000 to 1,000,000. If it is too low, the strength of the coating film tends to decrease. On the other hand, if it is too high, the viscosity increases and it may be difficult to form an electrode. Preferable binder resins include fluorine resins and CN group-containing polymers, and more preferably polyvinylidene fluoride.

The usage-amount of a binder is 0.1 weight part or more normally with respect to 100 weight part of scaly carbonaceous materials, Preferably it is 1 weight part or more, and is 30 weight part or less normally, Preferably it is 20 weight part or less. If the amount of the binder is too small, the strength of the active material layer tends to decrease, and if the amount of the binder is too large, the battery capacity tends to decrease.
If necessary, the active material layer may contain additives, powders, fillers, and the like that exhibit various functions such as a conductive material and a reinforcing material.

  Examples of the solvent used when forming the active material layer include N-methylpyrrolidone and dimethylformamide, and N-methylpyrrolidone is preferable. The solvent concentration in the coating is at least 10% by weight, but is usually 20% by weight or more, preferably 30% by weight or more, and more preferably 35% by weight or more. Moreover, as an upper limit, it is 90 weight% or less normally, Preferably it is 80 weight% or less. If the solvent concentration is too low, coating may be difficult. If the solvent concentration is too high, it may be difficult to increase the coating thickness and the stability of the coating may be deteriorated.

For dispersion coating, a commonly used disperser can be used, and a planetary mixer, a ball mill, a sand mill, a biaxial kneader, or the like can be used.
There are no particular restrictions on the coating device for applying the paint on the current collector, such as slide coating, extrusion type die coating, reverse roll, gravure coater, knife coater, kiss coater, micro gravure coater, rod coater, blade coater, etc. Although die coating is preferable, an extrusion type die coating is most preferable in consideration of paint viscosity, coating film thickness, and the like.

After the coating material is applied on the current collector, the active material layer is formed by drying the coating film at a temperature of about 120 ° C. for about 10 minutes, for example.
The thickness of the active material layer is usually 10 μm or more, preferably 20 μm or more, and is usually 200 μm or less, preferably 150 μm or less. If it is too thin, the battery capacity may be too small. On the other hand, if it is too thick, the rate characteristics may be deteriorated too much.

  As the current collector used for the negative electrode, various materials that can function as a battery current collector can be used without causing problems such as electrochemical elution, and usually metals such as copper, nickel, stainless steel, etc. An alloy is used. Preferably, copper is used. The thickness of the current collector is usually 0.1 μm or more, preferably 1 μm or more, and is usually 100 μm or less, preferably 30 μm or less, more preferably 20 μm or less. If it is too thin, the mechanical strength tends to be weak, which causes a problem in production. If it is too thick, the capacity of the battery as a whole decreases. In order to reduce the weight of the secondary battery, that is, to improve the weight energy density, a perforated type base material such as expanded metal or punching metal can be used. In this case, the weight can be freely changed by changing the aperture ratio. In addition, when contact layers are formed on both sides of such a perforated type substrate, the rivet effect of the coating film through this hole tends to make the coating film more difficult to peel off, but the aperture ratio is too high. In such a case, the contact area between the coating film and the base material becomes small, so that the adhesive strength may be lowered. Moreover, in order to improve adhesiveness with an active material layer, the surface of a collector can be previously roughened. Current roughening methods include a method of rolling with a blasting process or a rough roll, a polishing cloth with a fixed abrasive particle, a grinding wheel, emery buff, a wire brush with a steel wire, etc. Examples thereof include a mechanical polishing method for polishing the surface, an electrolytic polishing method, and a chemical polishing method.

  An undercoat primer layer may be formed between the current collector and the active material layer. By providing the primer layer, the adhesion of the negative electrode to the current collector can be improved. As a result, battery internal resistance can be reduced, and rapid capacity reduction due to coating film detachment from the current collector in the charge / discharge cycle test process can be prevented. The undercoat primer layer can be formed, for example, by applying an undercoat primer material paint containing a conductive material, a binder, and a solvent on a current collector, and then drying it. Examples of the conductive material used for the undercoat primer layer include carbon materials such as carbon black and graphite, metal powders, and conductive organic conjugated resins. As the binder and solvent used for the undercoat primer layer, the same binders and solvents used for the coating material of the electrode material can be used. The thickness of the undercoat primer layer is usually 0.05 μm or more, preferably 0.1 μm or more, and usually 10 μm or less, preferably 1 μm or less. If it is too thin, it will be difficult to ensure uniformity, and if it is too thick, the volume capacity of the battery may be too low.

The lithium secondary battery element has a positive electrode, a negative electrode, and an electrolyte.
An electrolyte used for a lithium secondary battery usually has an electrolytic solution obtained by dissolving a lithium salt, which is a supporting electrolyte, in a non-aqueous solvent.
The non-aqueous solvent is not particularly limited, but a relatively high dielectric constant solvent is preferably used. Specifically, cyclic carbonates such as ethylene carbonate and propylene carbonate, acyclic carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, glymes such as tetrahydrofuran, 2-methyltetrahydrofuran and dimethoxyethane, γ-butyllactone, etc. Lactones, sulfur compounds such as sulfolane, nitriles such as acetonitrile, and the like. Among them, it is preferable to use a high boiling point solvent having a boiling point of 150 ° C. or higher, particularly 200 ° C. or higher. Examples of such a high boiling point solvent include propylene carbonate, ethylene carbonate, butylene carbonate, and γ-butyrolactone. Among them, it is preferable to use propylene carbonate, ethylene carbonate, or γ-butyrolactone as a high boiling point solvent.

  The above non-aqueous solvent can use multiple types together. When the high boiling point solvent is used, the ratio of the high boiling point solvent to the non-aqueous solvent used is preferably 60% by volume or more, more preferably 70% by volume or more, more preferably 80% by volume or more, and most preferably 90%. Volume% or more. Moreover, it is preferable that the boiling point as the whole non-aqueous solvent when using several solvent together shall be 200 degreeC or more. By using the high boiling point solvent, even when the lithium secondary battery element is housed in the shape-variable case, the shape change (deformation) of the battery at a high temperature or the like can be suppressed. “Boiling point X ° C. or higher” means that the vapor pressure does not exceed 1 atm even when heated from room temperature to X ° C. under a pressure of 1 atm. That is, when heated from room temperature to 200 ° C. under a pressure of 1 atm, it means that the vapor pressure is always 1 atm or less.

The non-aqueous solvent preferably has a viscosity of 1 mPa · s or more.
The lithium salt is a supporting electrolyte used in the _{electrolyte, LiPF 6, LiAsF 6, LiSbF} 6, LiBF 4, LiClO 4, LiI, LiBr, LiCl, LiAlCl, L
Examples include iHF ₂ , LiSCN, LiSO ₃ CF _{2 and the} like. Of these, LiPF ₆ and LiClO ₄ are particularly preferred. The content of these supporting electrolytes in the electrolytic solution is usually 0.5 to 2.5 mol / l.

  The electrolyte exists as an electrolyte layer between the positive electrode and the negative electrode, and the electrolyte of the electrolyte layer preferably has non-fluidity. As a result, even when the battery element is housed in a case having shape variability, the leakage of the electrolyte can be effectively prevented. Specific examples of such a non-flowable electrolyte include a so-called polymer electrolyte in which the electrolyte solution is held by a polymer in addition to a completely solid electrolyte. The polymer electrolyte usually exhibits a gel state by holding the non-aqueous electrolyte with a polymer. The concentration of the polymer with respect to the electrolytic solution is usually 0.1 to 30% by weight, although it depends on the molecular weight of the polymer used. If the concentration is too low, it is difficult to form a gel, and the retention of the electrolytic solution is lowered, which may cause problems of flow and liquid leakage. On the other hand, when the concentration is too high, the viscosity becomes too high, resulting in difficulty in the process, and the ratio of the electrolytic solution is lowered, the ionic conductivity is lowered, and the battery characteristics such as the rate characteristics tend to be lowered. Examples of the polymer that holds the electrolyte include various polymers having the above functions, such as an alkylene oxide polymer having an alkylene oxide unit, and a fluorine polymer such as polyvinylidene fluoride and a vinylidene fluoride-hexafluoropropylene copolymer. Can be mentioned.

As a method of forming a non-fluidic electrolyte, a method of using it as an electrolyte coating in which a polymer is previously dissolved in an electrolytic solution, or a crosslinking reaction of an electrolytic coating containing a polymerizable monomer in the electrolytic solution to obtain a non-fluidic electrolyte. The electrolyte layer can be formed by adopting materials and manufacturing methods as required, such as methods.
In the case of forming the non-fluidic electrolyte in the present invention by a method in which a coating containing a polymerizable monomer in the electrolytic solution is subjected to a cross-linking reaction to obtain a non-fluidized electrolyte, a polymerization treatment such as ultraviolet curing or thermosetting is performed. A paint is prepared by adding a monomer that forms a polymer as a polymerizable monomer to the electrolyte.

  Examples of the polymerizable monomer include those having an unsaturated double bond such as an acryloyl group, a methacryloyl group, a vinyl group, and an allyl group. Specifically, for example, acrylic acid, methyl acrylate, ethyl acrylate, ethoxyethyl acrylate, methoxyethyl acrylate, ethoxyethoxyethyl acrylate, polyethylene glycol monoacrylate, ethoxyethyl methacrylate, methoxyethyl methacrylate, ethoxyethoxyethyl methacrylate, polyethylene Examples include glycol monomethacrylate, N, N-diethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, glycidyl acrylate, and allyl acrylate.

  Other usable examples include acrylonitrile, N-vinylpyrrolidone, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene. Examples include glycol dimethacrylate, polyethylene glycol dimethacrylate, polyalkylene glycol diacrylate, and polyalkylene glycol dimethacrylate. Trifunctional monomers such as trimethylolpropane alkoxylate triacrylate and pentaerythritol alkoxylate triacrylate, pentaerythritol alkoxylate Tetraacrylate Ditrimethylolpropane alkoxylate monomers having four or more functional such tetraacrylate or the like can be also used. Of these, those preferable from the viewpoint of reactivity, polarity, safety, etc. may be used alone or in combination. Of these, diacrylates and triacrylates containing a plurality of ethylenoxide groups are particularly preferred. By polymerizing these monomers with heat, ultraviolet rays, electron beams or the like, the electrolyte can be made into a non-flowable electrolyte. The content of the polymerizable monomer in the electrolytic solution is not particularly limited, but is preferably 1% by weight or more in the paint. When the content is low, the formation efficiency of the polymer is lowered, and it is difficult to make the electrolyte non-fluid. On the other hand, if it is too much, residual unreacted monomer and operability as an electrolyte coating are deteriorated.

  In a method for producing a non-fluid electrolyte using an electrolyte coating containing a polymer in advance, it is preferable to use a polymer that dissolves in an electrolyte at a high temperature and forms a gel electrolyte at room temperature. Any polymer can be used as long as it has such characteristics and is stable as a battery material. For example, polymers having a ring such as polyvinyl pyridine and poly-N-vinyl pyrrolidone; polymethyl methacrylate, poly Acrylic derivative polymers such as ethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide; fluorinated resins such as polyvinyl fluoride and polyvinylidene fluoride; CN group-containing polymers such as acrylonitrile and polyvinylidene cyanide; polyvinyl alcohol polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride. Among these, polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, or modified products thereof are preferable.

  Moreover, it can be used even if it is a mixture, such as said polymer, a modified body, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, etc. As will be described later, since the electrolyte and electrolyte used in the lithium battery have polarity, it is preferable that the polymer (polymer) has a certain degree of polarity. Furthermore, the weight average molecular weight of these polymers is preferably in the range of 10,000 to 5,000,000. If the molecular weight is low, it is difficult to form a gel. On the other hand, if the molecular weight is too high, the viscosity becomes too high and handling becomes difficult.

  In the method of forming a non-fluidized electrolyte using a polymer that dissolves in an electrolytic solution at a high temperature and forms a gel electrolyte at a normal temperature, the polymer is heated and dissolved in the electrolytic solution. As heating temperature, it is 50-200 degreeC, Preferably, it is 100-160 degreeC. If it seems to dissolve at too low a temperature, the stability of the non-fluidized electrolyte is reduced. If the melting temperature is too high, decomposition of the electrolyte component, polymer, etc. may be caused. As the non-fluidization condition, it is preferable to cool the polymer-dissolved electrolyte at room temperature, but it may be forcedly cooled.

Various additives can be added to the electrolyte as needed to improve battery performance.
The electrolyte layer is preferably used in combination with a support such as a porous film. As the porous film, a film made of a polymer resin or a thin film made of a powder and a binder can be preferably used, and more preferably a porous film made of polyethylene, polypropylene or the like.

Examples of the active material used for the positive electrode of the lithium secondary battery include a composite oxide of lithium and a transition metal. Specifically, lithium nickel composite oxides such as LiNiO ₂ and LiNiCoO ₂ , LiCoO _{2 and the} like Examples thereof include lithium cobalt composite oxides and lithium manganese composite oxides such as LiMn ₂ O ₄ . Some of the transition metal sites of these composite oxides may be substituted with other elements. By substituting a part of the transition metal with another element, the stability of the crystal structure can be improved. As other elements for substituting a part of the transition metal site at this time (hereinafter referred to as substitution elements), Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg , Ga, Zr, etc., preferably Al, Cr, Fe, Co, Li, Ni, Mg, Ga, and more preferably Al. The transition metal site may be substituted with two or more other elements. The substitution ratio by the substitution element is usually 2.5 mol% or more of the base transition metal element, preferably 5 mol% or more of the base transition metal element, and usually 30 mol% or less of the base transition metal element, Preferably it is 20 mol% or less of the transition metal element used as a base. If the substitution ratio is too small, the crystal structure may not be sufficiently stabilized. If the substitution ratio is too large, the capacity of the battery may be reduced. Of the lithium transition metal composite oxides, lithium cobalt composite oxides and lithium nickel composite oxides are more preferable, and LiCoO ₂ is particularly preferable. The particle size of the positive electrode active material is usually about 1 to 30 μm, preferably about 1 to 10 μm, in terms of excellent battery characteristics such as rate characteristics and cycle characteristics. The positive electrode is usually formed by forming an active material layer having a positive electrode active material and a binder on a current collector. The kind of binder used for the positive electrode and the method for forming the active material layer are the same as those for the negative electrode.

  A lithium secondary battery element having a positive electrode, a negative electrode, and an electrolyte is housed in a case. Examples of the lithium secondary battery element include a form in which a laminate in which a positive electrode and a negative electrode are laminated via an electrolyte layer is wound, a form in which a positive electrode, a negative electrode, and an electrolyte layer are laminated in a flat plate shape, or the flat plate shape A plurality of lithium secondary battery elements stacked on each other may be prepared and further stacked.

  Examples of the case for storing the battery element include a metal can and a case having shape variability. The effects of the present invention are basically exhibited without depending on the case to be stored, but the effects of the present invention are particularly remarkable when the shape-variable case is used. That is, the active material layer using the scaly carbonaceous material has low mechanical strength. Therefore, when the shape-variable case having low strength is used, the problem that the active material layer is easily broken by an external force becomes remarkable, and the effect of the present invention in which the negative electrode contains a spherical material becomes remarkable. Moreover, the active material layer using a scaly carbonaceous material has poor adhesion to the current collector. Therefore, when the shape-variable case having a weak force for pressing the battery element is used, the problem that the active material layer is peeled off from the current collector becomes remarkable, and the effect of the present invention in which a spherical material is contained in the negative electrode becomes remarkable. The battery element is preferably housed in close contact with a case having shape variability. More preferably, sealing is performed under reduced pressure, and the battery element is pressed by atmospheric pressure.

  Examples of case members constituting the case having shape variability include flexible plastics, polymer films, metal films, rubber, thin metal plates, and laminated films in which resin layers are provided on both sides of a gas barrier layer. Preferably, it is a laminate film in which resin layers are provided on both sides of the gas barrier layer. A metal layer is preferably used as the barrier layer of the laminate film. As the laminate film, usually, a film made of a laminate material of a metal layer and a polymer film can be suitably used.

  As the material of the metal layer when using a laminate film, a single metal such as aluminum, iron, copper, nickel, titanium, molybdenum and gold, an alloy such as stainless steel and hastelloy, and a metal oxide such as silicon oxide and aluminum oxide are used. Can be used. Preferably, aluminum is lightweight and excellent in workability. As the resin used for the resin layer, various synthetic resins such as thermoplastics, thermoplastic elastomers, thermosetting resins, plastic alloys, and the like can be used. These resins include those in which fillers such as fillers are mixed. Specifically, polyethylene, polypropylene, modified polyolefin, ionomer, amorphous polyolefin, polyethylene terephthalate, polyamide, ethylene-vinyl acetate copolymer, ABS resin, polycarbonate resin, etc. are excellent in chemical resistance and mechanical strength. Resin is desirable. The resin layer is preferably formed on both surfaces of the metal layer.

  The member thickness of the case having shape variability is usually 0.01 μm or more, preferably 0.02 μm or more, more preferably 0.05 μm or more, and usually 5 mm or less, preferably 1 mm or less, more preferably 0.5 mm. Hereinafter, it is most preferably set to 0.3 mm or less. The thinner the battery, the smaller and lighter the battery can be and the greater the effect of the present invention. However, if the battery is too thin, sufficient rigidity may not be imparted or the sealing performance may be reduced.

  The method of housing the lithium secondary battery element when using a case having shape changeability is arbitrary, but it is preferable to enclose the lithium secondary battery element in a case under reduced pressure. Examples of such a storage method include a method in which both ends of a film-like case member are bonded to form a cylinder, and after the lithium secondary battery element is stored inside, the upper and lower sides of the cylinder are further bonded under reduced pressure. can do. Moreover, after accommodating a lithium secondary battery element between two pieces of film-like case members, the method of bonding a peripheral part under reduced pressure is also employable.

  The case with shape changeability does not have the same weight and rigidity as metal cans, and has flexibility, flexibility, flexibility, etc., so it can be bent after storing the battery and can be reduced in weight. Has the advantage. Of course, for the convenience of mounting the battery on the device, etc., it is possible to enclose the battery in a case and then store a plurality of cases in a rigid outer case if necessary.

Examples The present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
Example 1 [Production of scale-like carbonaceous material]
Natural graphite powder spheroidized by mechano-fusion system manufactured by Hosokawa Micron Co., Ltd. in a stainless steel tank with an internal volume of 20 liters (average particle size 22-23 μm, specific surface area measured by BET method 4.7 m ² / g ) 3.0 kg was mixed with 1.0 kg of ethylene heavy end tar (EHE; manufactured by Mitsubishi Chemical Corporation) obtained during naphtha decomposition. The obtained slurry-like mixture was devolatilized by heat treatment for 1 hour while keeping it at 700 ° C. in an inert atmosphere in a batch heating furnace. Next, the temperature was raised to 1300 ° C., held for 2 hours, and fired. The fired product was pulverized and adjusted to a particle size of 20 to 25 μm using a vibrating sieve to obtain a scale-like carbon-coated graphite-based carbonaceous material.

The specific surface area of the obtained carbon-coated graphite-based carbonaceous material measured by the BET method was 3.1 m ² / g. Further, when the obtained carbon-coated graphite-based carbonaceous material and the graphite-based carbon material before coating were subjected to Raman spectrum analysis using an argon ion laser beam having a wavelength of 5145 mm, the R value was obtained. Was 0.21, and the graphite-based carbon material before coating was 0.11.

For the Raman spectrum measurement, JASCO NR-1800 was used, and an argon ion laser beam having a wavelength of 5145 mm was used at an intensity of 30 mW.
[Confirmation of shape anisotropy]
An SEM image of the powder was taken at 1000 times, 100 particles were randomly extracted, the longest diameter and the shortest diameter of the particles were measured with calipers, and the average of the longest diameter / shortest diameter value was measured as shape anisotropy. As a result, the longest diameter / shortest diameter ratio of the carbon-coated graphite-based carbonaceous material was 1.6.
[Measurement of average particle size]
The average particle size was measured using a Horiba microtrack in which the particles were dispersed in an aqueous solvent. As a result, the average particle diameter D50 of the carbon-coated graphite-based carbonaceous material was 20.0 μm.
[Manufacture of negative electrode]
Mesocarbon microbeads (MCMB6-28, manufactured by Osaka Gas Chemical Co., Ltd .; longest diameter / shortest diameter = 1.1, average particle diameter D50 = 6.1 μm) as a spherical substance with respect to 100 parts by weight of the carbon-coated graphite-based carbonaceous material. ) 20 parts by weight, 10 parts by weight of polyvinylidene fluoride (binder) and 100 parts by weight of N-methyl-2-pyrrolidone (solvent) were prepared and kneaded for 2 hours with a kneader to obtain a dispersion paint for negative electrode. The obtained dispersion paint for negative electrode was applied to a 20 μm thick copper current collector substrate by an extrusion type die coating so that the film thickness after drying was 50 μm, dried at 120 ° C. for 10 minutes, A film was created in which the material was bound onto the current collector by a binder.

Next, a negative electrode was obtained by consolidation using a roll press (calendar) under a linear pressure of 100 kgf / cm.
[Production of positive electrode]
A dispersion paint for positive electrode obtained by kneading 90 parts by weight of lithium cobaltate, 5 parts by weight of acetylene black, 5 parts by weight of polyvinylidene fluoride and 80 parts by weight of N-methyl-2-pyrrolidone with a kneader for 2 hours is obtained with a thickness of 20 μm. The aluminum current collector was applied and dried by extrusion-type die coating so that the film thickness after drying was 60 μm, and a film in which the active material was bound on the current collector by a binder was created. Next, a positive electrode was obtained by consolidation using a roll press (calendar) under a linear pressure of 100 kgf / cm.
[Manufacture of lithium secondary batteries]
14 parts by weight of tetraethylene glycol diacrylate, 7 parts by weight of polyethylene oxide triacrylate, 21 parts by weight of LiPF ₆ , 1 part by weight of a polymerization initiator, 1 additive (acid anhydride)
4 parts by weight, 120 parts by weight of propylene carbonate and 120 parts by weight of ethylene carbonate were mixed and dissolved by stirring to obtain an electrolyte coating.

Apply the above electrolyte paint to the above positive electrode and negative electrode, laminate a polyethylene porous film having a slightly larger area than the electrode soaked in the electrolyte paint, and heat it at 90 ° C. for 10 minutes. The electrolyte was defluidized to obtain a flat lithium secondary battery element having a positive electrode, a negative electrode, and a non-fluidic electrolyte. A tab for taking out current was connected to the obtained battery element. Two thin laminate films having shape variability formed by forming a synthetic resin layer on both surfaces of the aluminum layer are prepared, and the peripheral portion of the case member is vacuum-sealed with the battery element disposed therebetween. A flat lithium secondary battery was obtained.
Comparative Example 1
A lithium secondary battery was obtained in the same manner as in Example 1 except that the amount of the scaly carbon-coated graphite-based carbonaceous material was increased by that amount without adding the spherical substance.
Test Example The negative electrode and lithium secondary battery obtained in Example 1 and Comparative Example 1 were evaluated by the following methods.

First, as an adhesive strength test, a peel test using an adhesive tape was performed on the obtained negative electrode. The area where the negative electrode active material layer remained without being peeled off from the current collector was measured.
Next, a cycle test was performed on the obtained lithium secondary battery. The capacity | capacitance after charging / discharging 100 cycles was measured with respect to the obtained battery, and it represented with the ratio with respect to the capacity | capacitance of the 1st cycle. In this case, at the time of charging, constant current charging was performed up to 4.2 V at 1 C, and then low voltage charging was performed until C / 25. At the time of discharge, constant current discharge was performed to 3.0V at 1C.

  Furthermore, the battery after 100 cycles was disassembled, and the adhesion between the active material layer and the current collector in the negative electrode was visually observed. The results are shown in Table-1.

  From Table 1, in the lithium secondary battery in which the battery element is housed in a case having shape variability, the adhesive force between the negative electrode active material layer and the current collector is weak, and the characteristics deteriorate due to repeated charge and discharge, The phenomenon that the active material layer actually peels off from the current collector tends to occur, but it can be seen that these problems can be greatly improved by adding a spherical material.

Claims (17)

  A lithium secondary battery in which a lithium secondary battery element having a positive electrode, a negative electrode, and an electrolyte is housed in a case, wherein the negative electrode includes a flaky carbonaceous material and a spherical material having an aspect ratio of 1.1 to 2.9. A lithium secondary battery comprising:   In a lithium secondary battery in which a lithium secondary battery element having a positive electrode, a negative electrode, and an electrolyte is housed in a case having shape changeability, the negative electrode contains a scaly carbonaceous substance and a spherical substance. Lithium secondary battery.   The lithium secondary battery according to claim 2, wherein the scale-like carbonaceous material has an aspect ratio of 1.1 to 6.0, and the spherical material has an aspect ratio of 1.0 to 1.5.   The lithium secondary battery according to claim 2 or 3, wherein the scale-like carbonaceous material has an aspect ratio of 1.1 to 2.9.   The lithium secondary battery according to any one of claims 1 to 4, wherein an average particle diameter of the spherical substance is 2/3 or less of an average particle diameter of the scaly carbonaceous substance.   The lithium secondary battery according to any one of claims 1 to 5, wherein the spherical substance is a spherical carbonaceous substance.   The lithium secondary battery according to any one of claims 1 to 6, wherein the scaly carbonaceous material is a graphite-based carbonaceous material in which at least a part of the surface is coated with amorphous coke.   The lithium secondary battery according to any one of claims 1 to 7, wherein a weight ratio of the spherical substance to the scaly carbonaceous substance is 10 to 70%.   The lithium secondary battery according to any one of claims 1 to 8, wherein the scaly carbonaceous material is scaly graphite and the spherical material is spherical graphite.   The lithium secondary battery according to claim 9, wherein the spherical graphite is mesocarbon microbeads.   The lithium secondary battery according to claim 9 or 10, wherein amorphous coke is coated on at least part of the surface of the scaly graphite.   The lithium secondary battery according to claim 1, further comprising a non-fluidic electrolyte between the positive electrode and the negative electrode.   The lithium secondary battery according to any one of claims 2 to 12, wherein the case having shape variability is made of a laminate film in which resin layers are provided on both surfaces of the gas barrier layer.   The lithium secondary battery according to any one of claims 2 to 13, wherein the lithium secondary battery element is sealed in a case under reduced pressure.   15. The electrolyte according to claim 1, wherein the electrolyte includes an electrolytic solution obtained by dissolving a lithium salt in a non-aqueous solvent, and 60% by volume or more of the non-aqueous solvent is a high-boiling solvent having a boiling point of 150 ° C. or higher. Lithium secondary battery.   The lithium secondary battery according to claim 15, wherein the high boiling point solvent contains at least one selected from the group consisting of propylene carbonate, ethylene carbonate, and γ-butyrolactone.   A negative electrode for a lithium secondary battery, comprising a flaky carbonaceous material having an aspect ratio of 1.1 to 2.9 and a spherical material.