JP2017174664A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery superior in high-rate charge and discharge characteristics.SOLUTION: A secondary battery 100 is provided according to the present invention, which comprises: a positive electrode 50 having a positive electrode active material layer 54 including at least a positive electrode active material; a negative electrode 60 having a negative electrode active material layer 64 including at least a negative electrode active material; and a separator 70 serving to electrically isolate the positive and negative electrodes from each other. In the secondary battery 100 as described above, the negative electrode active material layer 64 includes a subsidiary material higher, in compression modulus, than the negative electrode active material at 3-20 mass% to a total solid content of the negative electrode active material layer 64, namely 100 mass%. The porosity of the negative electrode active material layer 64 is 45-55%. The compression modulus of the negative electrode 60 in a thickness direction is 1.2 to 3.3 times the compression modulus of the separator 70 in a thickness direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a secondary battery.

  Secondary batteries such as lithium secondary batteries (lithium ion secondary batteries) and sodium ion secondary batteries have been used in recent years as so-called portable power sources such as personal computers and portable terminals and power sources for driving vehicles. In particular, a lithium secondary battery that is lightweight and has a high energy density is preferably used as a high-output power source for driving vehicles such as electric vehicles (EV), hybrid vehicles (HV), and plug-in hybrid vehicles (PHV). .

  A secondary battery typically includes an electrode body in which a positive electrode including a positive electrode active material layer, a negative electrode including a negative electrode active material layer are stacked via a separator, and an electrolytic solution. Such a secondary battery is typically a battery that performs charge and discharge by charge carriers (for example, lithium ions) in the electrolyte solution passing between the electrodes. When charging the secondary battery, charge carriers (typically lithium ions) are released (desorbed) from the positive electrode active material constituting the positive electrode active material layer, and the negative electrode active material layer constituting the negative electrode active material layer Charge carriers are occluded (inserted) in Conversely, during discharge, charge carriers (typically lithium ions) are released (desorbed) from the negative electrode active material, and the charge carriers are occluded (inserted) into the positive electrode active material. Thus, when charge carriers (typically lithium ions) are occluded and released in the active material as the secondary battery is charged and discharged, the positive and negative electrode active materials (that is, the positive and negative electrode active material layers having the active materials) ) Expands and contracts.

JP 2000-285966 A

When the secondary battery having the above-described configuration is used for a purpose of repeating high-rate charge / discharge (for example, in-vehicle use), the electrode body (for example, by the expansion and contraction of the positive / negative electrode active material (positive / negative electrode active material layer) accompanying charge / discharge) There was a risk that the electrolyte held in the negative electrode) would be pushed out of the electrode body. For this reason, the liquid volume of the electrolyte solution held in the electrode body is uneven, and there are cases where a portion where the electrolyte solution exists in the electrode body and a portion where the electrolyte solution volume is small (insufficient) are generated.
In a portion of the electrode body where the electrolytic solution is small (typically a portion where the liquid withered), the amount of the electrolytic solution present in the portion is less than the required amount, and the charge / discharge performance of the battery as a whole tends to deteriorate. . In addition, since the battery reaction concentrates on a portion of the electrode body where the electrolytic solution is relatively large, deterioration of the portion tends to be promoted. All of these events are undesirable because they cause performance degradation (such as increased battery resistance and capacity degradation). In particular, for secondary batteries used for the purpose of requiring high-rate charge / discharge characteristics, it is important to suppress the performance deterioration due to the uneven amount of the electrolyte in the electrode body.

  Patent Document 1 discloses that the negative electrode active material layer has a compression elastic modulus lower than that of the negative electrode active material layer by increasing the compression elastic modulus of the negative electrode higher than that of the positive electrode or the separator, It describes a technique for reducing the outflow (extrusion) of the electrolytic solution from the negative electrode active material layer during charge and discharge by absorption by the separator. In Patent Document 1, as a method for adjusting the compression modulus of the negative electrode, it is described that the press pressure on the negative electrode active material layer at the time of forming the negative electrode active material layer is adjusted. However, according to such a method, it is necessary to press the negative electrode active material layer at a high pressure in order to increase the compression elastic modulus of the negative electrode, and the porosity of the negative electrode active material layer tends to be reduced. The negative electrode active material layer having a small porosity reduces the amount of electrolyte solution that can be retained, and thus high-rate charge / discharge characteristics may not be sufficiently exhibited.

  The present invention has been created to solve the above-described conventional problems, and an object of the present invention is to provide a secondary battery excellent in high rate charge / discharge characteristics.

  According to the present invention, there are provided a positive electrode having a positive electrode active material layer containing at least a positive electrode active material, a negative electrode having a negative electrode active material layer containing at least a negative electrode active material, and a separator for electrically isolating the positive and negative electrodes. A secondary battery is provided. In such a secondary battery, the negative electrode active material layer includes a secondary material having a compressive modulus higher than that of the negative electrode active material. It is included in the content ratio. And the porosity of the said negative electrode active material layer is 45% or more and 55% or less, and the compression elastic modulus of the thickness direction of the said negative electrode is 1.2 times or more of the compression elastic modulus of the thickness direction of the said separator 3.3. It is characterized by being less than double.

The secondary battery having such a configuration can increase the compression elastic modulus of the negative electrode active material layer by including the secondary material having a high compression elastic modulus in the negative electrode active material layer in the above ratio. Thereby, the liquid volume nonuniformity of the electrolyte solution in the negative electrode active material layer accompanying charging / discharging can be reduced. In addition, since the negative electrode of the secondary battery having the above structure includes a negative electrode active material layer having a large porosity, a large amount of electrolytic solution can be held in the negative electrode active material layer.
That is, according to the present invention, a battery excellent in high rate charge / discharge characteristics can be provided.

It is a perspective view which shows typically the external shape of the secondary battery which concerns on one Embodiment of this invention. It is a longitudinal cross-sectional view which shows typically the cross-sectional structure which follows the II-II line | wire in FIG.

Hereinafter, a suitable embodiment of the present invention will be described taking a lithium secondary battery (lithium ion secondary battery) as an example, with appropriate reference to the drawings. It should be noted that matters other than matters specifically mentioned in the present invention and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field. In addition, in the following drawings, the same code | symbol is attached | subjected and demonstrated to the member and site | part which show | plays the same effect | action, and the overlapping description may be abbreviate | omitted or simplified. Further, the dimensional relationship (length, width, thickness, etc.) in each drawing does not necessarily reflect the actual dimensional relationship.
Note that the lithium secondary battery is an example, and the technical idea of the present invention is not limited to this. For example, various secondary batteries that can be repeatedly charged and discharged by the movement of charges accompanying the movement of charge carriers between the positive and negative electrodes can be applied. Specifically, in addition to lithium secondary batteries that use lithium ions as charge carriers, other secondary batteries (eg, magnesium secondary batteries, sodium ion secondary batteries) that include other charge carriers (eg, magnesium ions, sodium ions, etc.). The technical idea of the present invention is also applied to secondary batteries and the like.

  One embodiment of the secondary battery disclosed herein will be described using the lithium secondary battery 100 shown in FIGS.

  A lithium secondary battery 100 disclosed herein is a battery in which an electrode body 20 and an electrolytic solution (not shown) are accommodated in a battery case (that is, an exterior container) 30 as shown in FIGS. The battery case 30 has a box-shaped (that is, bottomed rectangular parallelepiped) case body 32 having an opening at one end (corresponding to the upper end in a normal use state of the battery), and the opening of the case body 32 is sealed. The lid body 34 is configured. Further, as shown in the figure, the lid 34 is provided with a positive terminal 42 and a negative terminal 44 for external connection. The lid 34 is provided with a safety valve 36 for discharging the gas generated inside the battery case 30 to the outside of the battery case and an inlet (not shown) for injecting the electrolyte into the battery case. ing. As the material of the battery case 30, a metal material (for example, aluminum) that is lightweight and has good thermal conductivity can be preferably used.

  As shown in FIG. 2, the wound electrode body 20 is formed by laminating (superimposing) a long positive electrode 50 and a long negative electrode 60 via two long separators 70. It is wound in the longitudinal direction. The flat wound electrode body 20 is formed by, for example, laminating the positive electrode 50, the negative electrode 60, and the separator 70 and winding the wound body in one direction orthogonal to the winding axis (typically Can be shaped by crushing (pressing) and kidnapping (from the side).

  The negative electrode 60 includes a negative electrode active material layer 64 formed along the longitudinal direction on one or both surfaces (here, both surfaces) of a long negative electrode current collector 62. The negative electrode active material layer 64 includes a negative electrode active material and a secondary material having a compressive elastic modulus larger than that of the negative electrode active material.

The negative electrode 60 has a compressive modulus in the thickness direction that is greater than the compressive modulus in the thickness direction of the separator 70. Preferably, the compression elastic modulus in the thickness direction of the negative electrode 60 is 1.2 times or more the compression elastic modulus in the thickness direction of the separator 70. The upper limit of the compressive elastic modulus in the thickness direction of the negative electrode 60 is not particularly limited, but may be, for example, 3.3 times or less the compressive elastic modulus in the thickness direction of the separator 70.
The compressive elastic modulus is calculated from the amount of deformation in the thickness direction of the negative electrode (or separator) when a predetermined load is applied to the negative electrode (or separator) in the thickness direction. That is, it is calculated from the following equation: compression modulus (kN / mm) = load (kN) / deformation amount (mm) of negative electrode (or separator).

  As the negative electrode active material contained in the negative electrode active material layer 64, those used in conventional secondary batteries can be used without any particular limitation. For example, a carbon material having a graphite structure (layered structure) at least partially, lithium transition metal nitride, and the like can be given. Carbon materials such as so-called graphitic materials (graphite), non-graphitizable carbon materials (hard carbon), graphitizable carbon materials (soft carbon), and materials having a combination of these are preferably used. obtain. Further, the surface of the carbon material (the carbon material serving as the core) may be covered with an amorphous carbon film.

The secondary material included in the negative electrode active material layer 64 is not particularly limited as long as it has a compressive modulus higher than that of the negative electrode active material, and is, for example, three times that of the negative electrode active material (typically the carbon material). It has a compression elastic modulus of the above (preferably 10 times or more). From the viewpoint of reducing the side reaction between the secondary material and the electrolytic solution (typically the solvent of the nonaqueous electrolytic solution), a material that does not react with the charge carrier is preferable.
Here, the compression elastic modulus of the secondary material and the negative electrode active material is calculated from the amount of deformation of the secondary material (or the negative electrode active material) when a predetermined load is applied to the secondary material or the negative electrode active material. That is, the compression elastic modulus is calculated from the following formula: compression elastic modulus (kN / mm) = load (kN) / deformation amount (mm) of secondary material (or negative electrode active material). The compression modulus of the secondary material (negative electrode active material) can be measured using a compression tester (such as a micro compression tester) corresponding to the powder material.

  Preferable examples of the material of the secondary material include ceramic materials such as alumina, boehmite, zirconia, and magnesia, aluminum hydroxide, and the like. From the viewpoint of availability at a relatively low cost, at least one selected from the group consisting of alumina, boehmite, and aluminum hydroxide is preferable. Here, in general, the compression elastic modulus of the alumina is about 2300 MPa or more, the compression elastic modulus of zirconia is about 1200 MPa or more, which is sufficiently higher than the compression elastic modulus of 100 MPa of graphite generally used as a negative electrode active material. It has a compression modulus.

If the particle size of the secondary material is too large, the electronic conductivity between the negative electrode active materials tends to be lowered. For this reason, although it does not specifically limit, the secondary material whose particle diameter (average particle diameter) is smaller than the average particle diameter of a negative electrode active material is preferable. For example, the average particle size of the negative electrode active material is more preferably 1/2 or less (for example, approximately 1/5). By setting the average particle diameter of the secondary material in such a range, the compressive elastic modulus of the negative electrode 60 can be increased while maintaining the electronic conductivity between the negative electrode active materials.
In addition, the average particle diameter of a negative electrode active material is not specifically limited, What is necessary is just to be comparable as the conventional secondary battery. For example, the average particle diameter of the negative electrode active material can be, for example, 50 μm or less (typically 20 μm or less, for example, 1 μm to 20 μm, preferably 5 μm to 15 μm).
In this specification, “average particle size” means, unless otherwise specified, a particle size (50% volume) at an integrated value of 50% in a particle size distribution measured by a particle size distribution measuring apparatus based on a laser scattering / diffraction method. average particle diameter; hereinafter shall mean also) be abbreviated as D _50..

The negative electrode active material layer 64 has a certain percentage of holes that can be impregnated with the electrolyte. That is, the negative electrode active material layer 64 has a porosity of 45% or more and 55% or less. By setting the porosity of the negative electrode active material layer 64 in the above range, an appropriate amount of electrolytic solution can be held in the negative electrode active material layer 64.
Here, the porosity of the negative electrode active material layer 64 indicates a volume-based ratio of pores in the negative electrode active material layer 64. That is, it can be represented by the ratio of the volume of pores formed inside the negative electrode active material layer 64 to the apparent volume of the negative electrode active material layer 64.
The volume of the holes formed in the negative electrode active material layer 64 can be determined by a mercury intrusion method, and can be measured using a conventionally known mercury porosimeter. Further, the apparent volume of the negative electrode active material layer 64 is determined by the product of the area of the negative electrode active material layer 64 in plan view and the thickness. That is, in this specification, “porosity” means a value obtained by dividing the total pore volume obtained by measurement using a mercury porosimeter by the apparent volume of the negative electrode active material layer 64 and multiplying by 100 ( Porosity (%) = (Volume volume / negative electrode active material layer volume) × 100).
The average thickness of the negative electrode active material layer 64 is not particularly limited, and may be, for example, 40 μm or more (typically 50 μm or more) per side and 110 μm or less (typically 100 μm or less). .

In a preferred embodiment, the negative electrode active material layer 64 may include a conductive material. Thereby, the electronic conductivity between negative electrode active materials can be improved, and the high-rate charge / discharge characteristic of a battery can be improved. From the viewpoint of improving the electronic conductivity between the negative electrode active materials, the conductive material is disposed on the surface of the secondary material (typically, the surface of the secondary material is covered with the conductive material). It is preferably present in the negative electrode active material layer 64, and more preferably, the secondary material and the conductive material are in a form in which the conductive material is fixed to the surface of the secondary material by a physical method (typically mechano-fusion). It exists in the negative electrode active material layer 64.
In addition, the said electrically conductive material can use the thing similar to what is used for the conventional secondary battery without a restriction | limiting in particular. For example, carbon materials such as carbon powder and carbon fiber are exemplified as suitable ones. As the carbon powder, carbon powders such as various carbon blacks (for example, acetylene black, carbon black, ketjen black) and graphite powder can be used. One kind selected from such conductive materials may be used alone, or two or more kinds may be used in combination.

The content ratio of the secondary material in the entire negative electrode active material layer 64 is 3% by mass or more with respect to 100% by mass of the total solid content in the negative electrode active material layer 64. By exhibiting the content ratio of the secondary material contained in the negative electrode active material layer 64 within the above range, the effect of increasing the compression elastic modulus of the negative electrode due to the inclusion of the secondary material in the negative electrode active material layer 64 is exhibited at a high level. Can do. On the other hand, if the proportion of the secondary material present in the negative electrode active material layer 64 is too large, the electron conductivity between the negative electrode active materials may be reduced. For this reason, the upper limit of the content ratio of the secondary material in the entire negative electrode active material layer 64 can be 20% by mass or less with respect to 100% by mass of the total solid content in the negative electrode active material layer 64.
In addition, when using the said electrically conductive material, when there is too much content rate of this electrically conductive material in the said whole negative electrode active material layer 64, there exists a possibility that battery capacity may fall. For this reason, the content ratio of the conductive material present in the negative electrode active material layer 64 is not particularly limited. For example, it is 2% by mass or less (preferably with respect to 100% by mass of the total solid content in the negative electrode active material layer 64). 1 mass% or more and 2 mass% or less).

  As the negative electrode current collector 62 constituting the negative electrode 60, for example, a copper foil or the like can be suitably used. Moreover, the negative electrode active material layer 64 can contain components other than the active material and the conductive material, such as a binder and a thickener. As the binder, styrene butadiene rubber (SBR) or the like can be used. As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

The positive electrode 50 includes a positive electrode active material layer 54 including at least a positive electrode active material formed along the longitudinal direction on one or both surfaces (here, both surfaces) of a long positive electrode current collector 52.
Examples of the positive electrode current collector 52 include an aluminum foil. Examples of the positive electrode active material include lithium composite metal oxides such as a layered structure and a spinel structure (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn). ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiFePO _4, etc.). The positive electrode active material layer 54 can include components other than the active material, such as a conductive material and a binder. As the conductive material, carbon black such as acetylene black (AB) and other (such as graphite) carbon materials can be suitably used. PVDF or the like can be used as the binder.

  Examples of the separator 70 include a porous sheet (film) mainly composed of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such a separator may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer).

  Although not particularly limited, in the present embodiment, the positive electrode 50 has the positive electrode current collector 52 exposed without forming the positive electrode active material layer 54 along the edge on one side in the width direction of the positive electrode current collector 52. The positive electrode active material layer non-formed portion 53 is set. Similarly, in the negative electrode 60, the negative electrode active material layer non-formed portion 63 in which the negative electrode current collector 62 is exposed without forming the negative electrode active material layer 64 along the edge on one side in the width direction of the negative electrode current collector 62. Is set. As shown in FIG. 2, the wound electrode body 20 has the positive electrode active material layer non-formed part 53 and the negative electrode active material layer non-formed part 63 protruding outward from both ends in the wound axis direction. It may have been rolled over and rolled up. Then, as shown in FIG. 2, the positive electrode active material layer non-forming portion 53 and the positive electrode terminal 42 (for example, made of aluminum) are electrically connected via the positive electrode current collector plate 42a, and the negative electrode active material layer non-forming portion 63 The negative electrode terminal 44 (for example, made of nickel) can be electrically connected through the negative electrode current collector plate 44a. The positive and negative electrode current collector plates 42a and 44a and the positive and negative electrode active material layer non-forming portions 53 and 63 (typically the positive and negative electrode current collectors 52 and 62) are respectively formed by, for example, ultrasonic welding, resistance welding, or the like. Can be joined.

The property of the electrolytic solution is not particularly limited, but can typically be a nonaqueous electrolytic solution containing a supporting salt in an organic solvent (nonaqueous solvent).
As the non-aqueous solvent, for example, one kind of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. may be used alone or in two kinds. The above can be combined as appropriate (for example, a mixed solvent containing EC, EMC, and DMC at a volume ratio of 3: 4: 3). As the supporting salt, for example, a lithium salt (preferably LiPF ₆ ) such as LiPF ₆ , LiBF ₄ , or LiClO ₄ can be used. The concentration of the supporting salt is, for example, 0.7 mol / L or more and 1.3 mol / L or less (preferably about 1.0 mol / L).

  Although the secondary battery disclosed here can be used for various applications, it is characterized by being a battery excellent in high-rate charge / discharge. Therefore, taking advantage of such characteristics, it can be suitably used as a secondary battery used for a driving power source mounted on a vehicle, for example. The type of vehicle is not particularly limited, and examples thereof include plug-in hybrid vehicles (PHV), hybrid vehicles (HV), electric vehicles (EV), electric trucks, motorbikes, electric assist bicycles, electric wheelchairs, electric railways, and the like. .

  EXAMPLES Examples (test examples) relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples (test examples).

  A lithium secondary battery according to Examples 1 to 21 was constructed by the following materials and processes. In addition, about the battery which concerns on each example, the battery used for the below-mentioned high-rate charge / discharge test and the battery used for a limit current confirmation test were prepared separately.

[Construction of lithium secondary battery]
<Example 1>
A positive electrode was produced with the following materials and processes. First, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (LNCM) having an average particle size (D ₅₀ of 5 μm) was prepared as a positive electrode active material. Next, the LNCM and acetylene black ( AB) and polyvinylidene fluoride (PVdF) as a binder are mixed with N-methylpyrrolidone (NMP) at a mass ratio of LNCM: AB: PVdF = 92: 5: 3 to obtain a paste-like (slurry) positive electrode A composition for forming an active material layer was prepared, and this composition was applied to both sides of a long aluminum foil (positive electrode current collector) having an average thickness of 15 μm, with one end in the width direction of the positive electrode current collector. The positive electrode active material layer non-formation portion is left in a band shape along the surface, and the application surface of the composition for forming the positive electrode active material layer is uniform so as to be a band shape having a length of 100 mm in the width direction facing the longitudinal direction. Apply to The positive electrode current collector provided with the composition for forming a positive electrode active material layer as described above was dried and pressed to produce a positive electrode having a positive electrode active material layer on the positive electrode current collector. The press conditions were adjusted so that the average thickness of the positive electrode active material layer was 80 μm.

Next, a negative electrode was produced by the following materials and processes. First, graphite (C) as a negative electrode active material and alumina as a secondary material were prepared. Here, graphite having an average particle diameter (D ₅₀ ) of 10 μm was used, and alumina (Al ₂ O ₃ ) having an average particle diameter (D ₅₀ ) of 2 μm was used. Next, graphite (C), alumina (Al ₂ O ₃ ), styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, C: Al ₂ O ₃ : SBR: A paste-like (slurry) negative electrode active material layer forming composition was prepared by dispersing in water at a mass ratio of CMC = 96: 3: 0.5: 0.5. This composition was applied in a strip shape on both sides of a long copper foil (negative electrode current collector) having an average thickness of 10 μm. At this time, the application surface of the negative electrode active material layer forming composition is in the width direction opposite to the longitudinal direction while leaving the negative electrode active material layer non-formed portion in a strip shape along one end in the width direction of the negative electrode current collector. It was uniformly applied so as to form a belt having a length of 105 mm. And the negative electrode collector which provided the composition for negative electrode active material layer formation as mentioned above was dried and pressed, and the negative electrode which has a negative electrode active material layer on a negative electrode collector was produced. At this time, the pressing conditions were adjusted so that the porosity of the negative electrode active material layer was 45% and the average thickness of the negative electrode active material layer was 74 μm.

  The positive electrode and the negative electrode manufactured by the above-described method were overlapped in the longitudinal direction via two separators, wound in the longitudinal direction, and then crushed and ablated to produce a flat wound electrode body. Here, as the separator, a three-layer structure having an average thickness of 24 μm and a porous polypropylene layer formed on both sides of the porous polyethylene layer was used.

Next, the wound electrode body and the nonaqueous electrolytic solution were accommodated in a rectangular battery case (made of aluminum), and a lithium secondary battery according to Example 1 was constructed. As the non-aqueous electrolyte, a mixed solvent containing EC, DMC, and EMC at a volume ratio of EC: DMC: EMC = 3: 3: 4, and LiPF ₆ as a supporting salt at a concentration of 1.0 mol / L. The non-aqueous electrolyte dissolved in (1) was used.

<Examples 2 to 11 and Examples 14 to 21>
The materials and average particle diameters shown in Table 1 were used as the secondary material (Examples 14 to 17 do not use the secondary material), and the content ratio of the secondary material contained in the negative electrode active material layer (that is, formation of the negative electrode active material layer) Except that the press conditions were appropriately changed so that the porosity and average thickness of the negative electrode active material layer were the thicknesses shown in Table 1. Lithium secondary batteries according to Examples 2 to 11 and Examples 14 to 21 were produced using the same materials and processes as in Example 1. Here, the content (mass%) of the secondary material in Table 1 indicates the content ratio of the secondary material relative to the total 100 mass% of the solid content contained in the negative electrode active material layer. At this time, the ratio (X) of the secondary material mixed in the negative electrode active material layer forming composition is such that the negative electrode active material (here, graphite (C)) and secondary material (here, alumina (Al ₂ O ₃ )) _{There, C: Al 2 O 3 =} (99-X): was changed so that the X mass ratio.

<Examples 12 and 13>
The negative electrode active material layer (that is, the composition for forming the negative electrode active material layer) contains acetylene black (AB) as a conductive material in the ratio shown in Table 1, and the content ratio of the secondary material included in the negative electrode active material layer (that is, The ratio of the secondary material mixed in the negative electrode active material layer forming composition) is changed to the ratio shown in Table 1, and the press conditions are appropriately set so that the porosity and average thickness of the negative electrode active material layer are the thicknesses shown in Table 1. Except for the changes, lithium secondary batteries according to Examples 12 and 13 were produced by the same materials and processes as in Example 8. Here, content (mass%) of the electrically conductive material in Table 1 shows the content rate of the electrically conductive material with respect to 100 mass% of the total amount of solid content contained in a negative electrode active material layer. At this time, the proportion of the secondary material (X) and the proportion of the conductive material (Y) mixed in the negative electrode active material layer forming composition are as follows: negative electrode active material (here, graphite (C)) and secondary material (here, alumina) (Al ₂ O ₃ )) and the conductive material (here acetylene black (AB)) are changed to have a mass ratio of C: Al ₂ O ₃ : AB = (99−X−Y): X: Y. did.
In Examples 12 and 13, alumina (Al ₂ O ₃ ) and acetylene black (AB) are mixed at a predetermined mass ratio (Example 12 is Al ₂ O ₃ : AB = 10: 1, Example 13 is Al ₂ O ₃ : AB = 10: 2), and the surface of alumina was coated with acetylene black by mechanofusion under the conditions of a rotational speed of 2000 rpm and a treatment time of 40 minutes.

[Measurement of compression modulus]
The compression modulus of the negative electrode used for the construction of the battery according to each of the above examples was measured by the following method. That is, 50 measurement samples of 5 cm × 5 cm square were cut out from the negative electrode according to each example (part where the negative electrode active material layer was formed) and laminated. These laminated measurement samples were sandwiched between SUS plates, and the amount of change in the thickness of the laminated sample was measured when a predetermined load was applied in the thickness direction of the negative electrode with an autograph precision universal testing machine. Then, the compression modulus (N1) of the negative electrode was calculated by the following formula: compression modulus (kN / mm) = load (kN) / thickness change (mm). Moreover, the compression elastic modulus (N2) of the separator was also measured by the same method as that for the negative electrode. Moreover, the ratio (N1 / N2) of the compression elastic modulus (N1) of the negative electrode and the compression elastic modulus (N2) of the separator was calculated. The results are shown in the corresponding column of Table 1.

[Measurement of initial resistance (IV resistance)]
The initial resistance of the battery according to each example constructed as described above was measured under the following conditions. The battery adjusted to the SOC 60% charge state was subjected to constant current discharge (CC discharge) for 10 seconds at a rate of 20 C under a temperature condition of 25 ° C., and the voltage drop (V) was calculated. Then, the value (V) of the voltage drop amount was divided by the corresponding current value (I) to calculate the IV resistance (mΩ), and the average value was used as the initial battery resistance.
“1C” means a current value at which the battery capacity (Ah) predicted from the theoretical capacity can be charged in one hour. For example, when the battery capacity is 1 Ah, 1C = 1A.

[High rate charge / discharge test]
Next, for the batteries according to the respective examples in which the initial battery resistance was measured as described above, a charge / discharge cycle test was repeated for 2000 cycles under a temperature condition of 25 ° C., and the battery resistance increase rate after the cycle test was measured. did.
The charge / discharge cycle test is carried out with a constant current charge (CC charge) for 10 seconds at a charge rate of 30 C, then paused for 10 seconds, and then with a constant current discharge (CC discharge) for 300 seconds at a discharge rate of 1 C, Thereafter, charging / discharging for 10 seconds was defined as one cycle.
And the battery resistance (IV resistance) of the battery which concerns on each example after the said charging / discharging cycle test was measured by the method similar to the measurement of the said initial resistance, and the increase rate (%) of IV resistance was computed. And the relative value when IV resistance increase rate of Example 14 was set to 100 was calculated, and it was set as IV resistance increase rate (relative value) of each example. The results are shown in the corresponding column of Table 1.

[Limit current check test]
In addition, for the batteries according to each example constructed as described above, the current value (hereinafter referred to as the battery capacity) that cannot be maintained high (95% or more of the initial battery capacity) after the pulse charge / discharge cycle test at a predetermined charge / discharge rate. The current value is referred to as the limiting current value).
First, the initial battery capacity (initial battery capacity) of the battery according to each example was measured. CCCV charge (4.1V, rate 0.2C) was performed on the battery of each example under a temperature condition of −10 ° C., and then CCCV discharge (3.0V, rate 0.2C) was performed. The discharge capacity at this time was measured and used as the initial battery period capacity (initial battery capacity) (Ah). The initial battery capacity of the batteries according to each example was 5 Ah.
Next, under a temperature condition of −10 ° C., a set of pulse charging / discharging cycles in which charging / discharging at a predetermined charging / discharging rate (C _X ) is repeated 200 cycles is set as one set, and a plurality of sets of pulse charging / discharging are changed. Discharge was performed. Discharge pattern of such pulses charge and discharge cycles, a constant current charging for 10 seconds at a predetermined charge rate (C _X) (CC charging), and a pause of 10 seconds, then at a predetermined discharge rate (C _X) 10 Charging / discharging which performed constant current discharge (CC discharge) for 1 second, and stopped for 10 seconds after that was made into 1 cycle. At this time, the charge / discharge rate (C _X ) started from 10C, and the charge / discharge rate was increased by 2C for each set. Then, for each set of pulse charge / discharge, the battery capacity is measured by the same method as the measurement of the initial battery capacity, and the maximum pulse current value that can maintain the battery capacity corresponding to 95% of the initial battery capacity is defined as the limit current value. . And the relative value when the limiting current value of Example 14 was set to 100 was calculated, and it was set as the limiting current value (relative value) of each example. The results are shown in the corresponding column of Table 1.

As shown in Table 1, the batteries according to Examples 1 to 9 achieved both a low IV resistance increase rate and a high limit current value as compared with Examples 14 to 19. That is, it was confirmed that the secondary battery disclosed here is a battery that can realize excellent high-rate charge / discharge characteristics.
In addition, Examples 3, 6, and 8 in which the porosity of the negative electrode active material layer is 45% or more have an IV resistance increase rate after high-rate charge / discharge compared to Example 19 in which the porosity of the negative electrode active material layer is 40%. It was small and the limit current value was high. In the batteries according to Examples 3, 6, and 8, the increase in the IV resistance after high-rate charge / discharge was small and the limit current value tended to be higher as the porosity of the negative electrode active material layer was larger. On the other hand, Example 21 in which the porosity of the negative electrode active material layer is 57% has a larger increase rate of IV resistance after high-rate charge / discharge than Example 8 in which the porosity of the negative electrode active material layer is 55%. The limit current value was low. That is, it was confirmed that the preferable range of the porosity of the negative electrode active material layer was 45% or more and 55% or less.
From the results of Examples 8, 9, and 20, it was confirmed that an increase in IV resistance after a high rate cycle can be reduced by using a secondary material having a particle size of 2 μm or more and 5 μm or less. That is, the preferable range of the particle size of the secondary material was 2 μm or more and 5 μm or less.
Further, from the results of Examples 10 and 11, it was confirmed that boehmite and aluminum hydroxide can be suitably used as a secondary material in the same manner as alumina.
Further, from the results of Examples 12 and 13, by including a conductive material in the negative electrode active material layer (here, a secondary material coated with a conductive material is used), the high rate charge / discharge characteristics are realized at a higher level. Confirmed to get.

  As mentioned above, although the specific example of this invention was demonstrated in detail, the said embodiment and Example are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

20 Winding electrode body 30 Battery case 32 Battery case main body 34 Cover body 36 Safety valve 42 Positive electrode terminal 42a Positive electrode current collector plate 44 Negative electrode terminal 44a Negative electrode current collector plate 50 Positive electrode 52 Positive electrode current collector 53 Positive electrode active material layer non-formation part 54 Positive electrode Active material layer 60 Negative electrode 62 Negative electrode current collector 63 Negative electrode active material layer non-formed portion 64 Negative electrode active material layer 70 Separator 100 Secondary battery (nonaqueous electrolyte secondary battery)

Claims (1)

A secondary battery comprising: a positive electrode having a positive electrode active material layer containing at least a positive electrode active material; a negative electrode having a negative electrode active material layer containing at least a negative electrode active material; and a separator for electrically isolating the positive and negative electrodes. And
The negative electrode active material layer contains a secondary material having a higher compression modulus than that of the negative electrode active material in a content ratio of 3% by mass to 20% by mass with respect to 100% by mass of the total solid content of the negative electrode active material layer. And
The porosity of the negative electrode active material layer is 45% or more and 55% or less,
A secondary battery in which a compression elastic modulus in a thickness direction of the negative electrode is 1.2 times or more and 3.3 times or less of a compression elastic modulus in a thickness direction of the separator.

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