JP2019145308A - Lithium ion secondary battery - Google Patents

Abstract

To suppress fever during a nail penetration test.SOLUTION: A lithium ion secondary battery includes at least a positive electrode 10, a negative electrode, and an electrolyte. The positive electrode 10 includes at least a positive electrode mixture layer 12. The positive electrode mixture layer 12 includes at least a positive electrode active material 1 and a boron particle group 2. The positive electrode mixture layer 12 includes the boron particle group 2 in an amount of 1 part by mass or more and 20 parts by mass or less with respect to the positive electrode active material 1 of 100 parts by mass. The boron particle group 2 has a d50 of 0.1 μm or more and 5 μm or less.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to a lithium ion secondary battery.

  Japanese Patent Laying-Open No. 2017-037776 (Patent Document 1) discloses lithium nickel cobalt manganate as a positive electrode active material of a lithium ion secondary battery.

JP 2017-037776 A

  Lithium-containing metal oxides are known as positive electrode active materials for lithium ion secondary batteries. The positive electrode active material contains oxygen in the crystal structure. It is considered that oxygen is released from the positive electrode active material when the temperature of the positive electrode active material rises during the nail penetration test. It is considered that oxygen released from the positive electrode active material is active and rich in reactivity. It is considered that various exothermic reactions occur due to oxygen released from the positive electrode active material.

  An object of the present disclosure is to suppress heat generation during a nail penetration test.

  The technical configuration and operational effects of the present disclosure will be described below. However, the mechanism of action of the present disclosure includes estimation. The scope of the claims should not be limited by the correctness of the action mechanism.

  The lithium ion secondary battery of the present disclosure includes at least a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes at least a positive electrode mixture layer. The positive electrode mixture layer includes at least a positive electrode active material and a boron particle group. In the positive electrode mixture layer, the boron particle group is contained in an amount of 1 part by mass to 20 parts by mass with respect to 100 parts by mass of the positive electrode active material. The boron particle group has a d50 of 0.1 μm or more and 5 μm or less.

  In the lithium ion secondary battery of the present disclosure, a group of boron particles is included in the positive electrode mixture layer. The boron particle group is substantially composed of simple boron. From the thermodynamic point of view, boron is considered to be easier to combine with oxygen than the positive electrode active material (metal oxide). Since the boron particle group is included in the positive electrode mixture layer, it is expected that oxygen released from the positive electrode active material quickly combines with boron during the nail penetration test. This is expected to suppress heat generation during the nail penetration test.

  However, the content of the boron particle group is 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. If the boron particle group content is less than 1 part by mass, the heat generation suppressing effect may be small. Boron particles have high electrical resistance. When the content of the boron particle group exceeds 20 parts by mass, the resistance may increase to a degree that cannot be ignored.

  Further, the boron particle group has a d50 of 0.1 μm or more and 5 μm or less. “D50” indicates a particle size at which the cumulative particle volume from the fine particle side is 50% of the total particle volume in the volume-based particle size distribution. The volume-based particle size distribution is measured by a laser diffraction particle size distribution measuring apparatus. When d50 of the boron particle group is less than 0.1 μm, particle aggregation is likely to occur. Due to the particle aggregation, the distribution of the boron particle groups in the positive electrode mixture layer varies, and heat generation may be promoted in a region where the existing ratio of the boron particle groups is low. If the d50 of the boron particle group exceeds 5 μm, the specific surface area of the boron particle group is considered to be small because the particle size of each boron particle is large. As a result, the reaction between boron and oxygen may become inactive.

FIG. 1 is a first schematic diagram showing an example of the configuration of the lithium ion secondary battery of the present embodiment. FIG. 2 is a second schematic diagram showing an example of the configuration of the lithium ion secondary battery of the present embodiment. FIG. 3 is a conceptual cross-sectional view showing the configuration of the positive electrode of the present embodiment.

  Hereinafter, an embodiment of the present disclosure (referred to as “the present embodiment” in the present specification) will be described. However, the following description does not limit the scope of the claims. Hereinafter, a lithium ion secondary battery may be abbreviated as “battery”.

<Lithium ion secondary battery>
FIG. 1 is a first schematic diagram showing an example of the configuration of the lithium ion secondary battery of the present embodiment.
The battery 100 is a lithium ion secondary battery. Battery 100 includes a case 90. Case 90 is a pouch made of an aluminum laminate film. That is, the battery 100 is a laminated battery. However, the case 90 may be made of metal. The battery 100 may be a square battery, a cylindrical battery, or the like. Case 90 is sealed. The positive electrode tab 81 and the negative electrode tab 82 communicate with the inside and outside of the case 90.

FIG. 2 is a second schematic diagram showing an example of the configuration of the lithium ion secondary battery of the present embodiment.
The case 90 houses the electrode group 50 and an electrolyte (not shown). The electrode group 50 is a stacked type. The electrode group 50 is formed by alternately laminating one or more positive electrodes 10 and negative electrodes 20. That is, battery 100 includes at least positive electrode 10, negative electrode 20, and electrolyte. A separator 30 is disposed between each of the positive electrode 10 and the negative electrode 20. Each of the positive electrodes 10 is electrically connected to the positive electrode tab 81. Each of the negative electrodes 20 is electrically connected to the negative electrode tab 82.

  The electrode group 50 may be a wound type. That is, the electrode group 50 may be formed by laminating the positive electrode 10, the separator 30, and the negative electrode 20 in this order, and further winding them in a spiral shape.

《Positive electrode》
FIG. 3 is a conceptual cross-sectional view showing the configuration of the positive electrode of the present embodiment.
The positive electrode 10 has a sheet shape. The positive electrode 10 includes at least a positive electrode mixture layer 12. The positive electrode mixture layer 12 may be formed on the surface of the positive electrode current collector 11. That is, the positive electrode 10 may further include the positive electrode current collector 11. The positive electrode current collector 11 may be, for example, an aluminum (Al) foil. The positive electrode current collector 11 may have a thickness of, for example, 5 μm or more and 50 μm or less. The positive electrode mixture layer 12 may be formed on both the front and back surfaces of the positive electrode current collector 11.

  The positive electrode mixture layer 12 includes at least the positive electrode active material 1 and the boron particle group 2. The positive electrode mixture layer 12 containing the boron particle group 2 is expected to suppress heat generation during the nail penetration test. This is probably because oxygen released from the positive electrode active material 1 quickly combines with boron.

(Boron particle group)
The boron particle group 2 is an aggregate (powder) of boron particles. Each boron particle is substantially composed of simple boron. However, as long as the effect of suppressing heat generation is obtained during the nail penetration test, each boron particle may contain a trace amount of elements other than boron. The content of the boron particle group 2 is 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material 1. If the content of the boron particle group 2 is less than 1 part by mass, the heat generation suppressing effect may be small. The boron particle group 2 has high electrical resistance. When the content of the boron particle group 2 exceeds 20 parts by mass, the resistance may increase to a degree that cannot be ignored.

  The content of the boron particle group 2 may be, for example, 5 parts by mass or more with respect to 100 parts by mass of the positive electrode active material 1. The content of the boron particle group 2 may be, for example, 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material 1. In these content ranges, the balance between the heat generation suppressing effect and the resistance may be improved.

  The boron particle group 2 has a d50 of 0.1 μm or more and 5 μm or less. When d50 of the boron particle group 2 is less than 0.1 μm, particle aggregation is likely to occur. Due to the particle agglomeration, the distribution of the boron particle group 2 in the positive electrode mixture layer 12 may vary, and heat generation may be promoted in a region where the boron particle group 2 is present in a low ratio. If the d50 of the boron particle group 2 exceeds 5 μm, the specific surface area of the boron particle group 2 is considered to be small because the particle size of each boron particle is large. As a result, the reaction between boron and oxygen may become inactive. The d50 of the boron particle group 2 may be smaller than the d50 of the positive electrode active material. This may increase the heat generation suppression effect.

(Positive electrode active material)
The positive electrode active material 1 is typically a particle group. The positive electrode active material 1 may have a d50 of 1 μm or more and 30 μm or less, for example. The positive electrode active material 1 occludes and releases lithium ions. The positive electrode active material 1 is a lithium-containing metal oxide. The positive electrode active material 1 is, for example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (eg LiMnO ₂ , LiMn ₂ O ₄ etc.), nickel cobalt lithium manganate (eg LiNi _1/3 Co _{1). / 3} Mn _1/3 O ₂ etc.), nickel cobalt lithium aluminate (eg LiNi _0.82 Co _0.15 Al _0.03 O ₂ etc.), etc. One type of positive electrode active material 1 may be included in the positive electrode mixture layer 12 alone. Two or more positive electrode active materials 1 may be included in the positive electrode mixture layer 12.

(Conductive material)
The positive electrode mixture layer 12 may further include a conductive material (not shown). The conductive material is electronically conductive. The conductive material forms an electron conduction path in the positive electrode mixture layer 12. The conductive material may be, for example, carbon black (for example, acetylene black), graphite, graphene flake, carbon short fiber, or the like. One type of conductive material may be included in the positive electrode mixture layer 12 alone. Two or more kinds of conductive materials may be included in the positive electrode mixture layer 12. The content of the conductive material may be, for example, 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material 1.

(Binder)
The positive electrode mixture layer 12 may further include a binder (not shown). The binder binds the constituent elements of the positive electrode mixture layer 12. The binder binds the positive electrode mixture layer 12 and the positive electrode current collector 11. The binder should not be particularly limited. The binder may be, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), carboxymethylcellulose (CMC), or the like. One kind of binder may be included in the positive electrode mixture layer 12 alone. The positive electrode mixture layer 12 may contain two or more binders. The content of the binder may be, for example, 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material 1.

<Negative electrode>
The negative electrode 20 has a sheet shape. The negative electrode 20 includes at least a negative electrode mixture layer. The negative electrode mixture layer may be formed on the surface of the negative electrode current collector. That is, the negative electrode 20 may further include a negative electrode current collector. The negative electrode mixture layer may be formed on both the front and back surfaces of the negative electrode current collector. The negative electrode current collector may be, for example, a copper (Cu) foil. The negative electrode current collector may have a thickness of, for example, 5 μm or more and 50 μm or less.

  The negative electrode mixture layer may have a thickness of 10 μm to 200 μm, for example. The negative electrode mixture layer includes at least a negative electrode active material. The negative electrode active material is typically a group of particles. The negative electrode active material may have a d50 of 1 μm or more and 30 μm or less, for example. The negative electrode active material occludes and releases lithium ions. The negative electrode active material should not be particularly limited. The negative electrode active material may be, for example, graphite, graphitizable carbon, non-graphitizable carbon, silicon, silicon oxide, silicon-based alloy, tin, tin oxide, tin-based alloy, lithium titanate, and the like. One type of negative electrode active material may be contained alone in the negative electrode mixture layer. Two or more negative electrode active materials may be included in the negative electrode mixture layer.

  The negative electrode mixture layer may further contain a binder. The binder binds the constituent elements of the negative electrode mixture layer. The binder binds the negative electrode active material and the negative electrode current collector. The binder should not be particularly limited. The binder may be, for example, CMC and styrene butadiene rubber (SBR). The content of the binder may be, for example, 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the negative electrode active material.

<< Separator >>
The separator 30 is electrically insulating. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20. The positive electrode 10 and the negative electrode 20 are separated from each other by a separator 30. The separator 30 is a porous film. The separator 30 may have a thickness of 10 μm or more and 30 μm or less, for example. The separator 30 may be a porous film made of polyolefin, for example.

  Separator 30 may have a single layer structure. The separator 30 may be formed only from a porous film made of polyethylene (PE), for example. The separator 30 may have a multilayer structure (for example, a three-layer structure). The separator 30 may be formed, for example, by laminating a porous film made of polypropylene (PP), a porous film made of PE, and a porous film made of PP in this order. The separator 30 may include a heat resistant film on its surface. The heat resistant film includes a heat resistant material. The heat resistant material may be boehmite, for example.

"Electrolytes"
The electrolyte is a lithium ion conductor. The electrolyte may be a liquid electrolyte, for example. The electrolyte may be a gel electrolyte, for example. The electrolyte may be a solid electrolyte, for example. The liquid electrolyte may be, for example, an electrolytic solution or an ionic liquid. In the present specification, an electrolytic solution is described as an example.

The electrolytic solution includes at least a supporting salt and a solvent. The electrolytic solution may contain, for example, a supporting salt of 0.5 mol / L or more and 2 mol / L or less (0.5 M or more and 2 M or less). The supporting salt is dissolved in the solvent. The supporting salt may be, for example, LiPF ₆ , LiBF ₄ , Li [N (FSO ₂ ) ₂ ], Li [N (CF ₃ SO ₂ ) ₂ ] and the like. One kind of supporting salt may be contained alone in the electrolytic solution. Two or more kinds of supporting salts may be contained in the electrolytic solution.

  The solvent is aprotic. The solvent may be, for example, a mixture of cyclic carbonate and chain carbonate. The mixing ratio may be, for example, “cyclic carbonate: chain carbonate = 1: 9 to 5: 5 (volume ratio)”.

  The cyclic carbonate may be, for example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), or the like. One kind of cyclic carbonate may be contained alone in the solvent. Two or more cyclic carbonates may be contained in the solvent.

  The chain carbonate may be, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), or the like. One kind of chain carbonate may be contained alone in the solvent. Two or more chain carbonates may be contained in the solvent.

  The solvent may contain, for example, lactone, cyclic ether, chain ether, carboxylic acid ester and the like. The lactone may be, for example, γ-butyrolactone (GBL), δ-valerolactone, and the like. The cyclic ether may be, for example, tetrahydrofuran (THF), 1,3-dioxolane, 1,4-dioxane and the like. The chain ether may be, for example, 1,2-dimethoxyethane (DME). The carboxylic acid ester may be, for example, methyl formate (MF), methyl acetate (MA), methyl propionate (MP) or the like.

The electrolytic solution may further contain various additives in addition to the supporting salt and the solvent. The electrolytic solution may contain, for example, an additive of 0.005 mol / L or more and 0.5 mol / L or less. Examples of the additive include a gas generating agent (also referred to as an overcharge additive), a SEI (Solid Electrolyte Interface) film forming agent, a flame retardant, and the like. The gas generating agent may be, for example, cyclohexylbenzene (CHB), biphenyl (BP), or the like. Examples of the SEI film forming agent include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), Li [B (C ₂ O ₄ ) ₂ ], LiPO ₂ F ₂ , propane sultone (PS), and ethylene sulfite (ES). Etc. The flame retardant may be, for example, phosphate ester, phosphazene or the like.

  Examples of the present disclosure are described below. However, the following description does not limit the scope of the claims.

<Manufacture of lithium ion secondary batteries>
Example 1
1. Production of positive electrode The following materials were prepared.
Positive electrode active material 1: Powder of nickel cobalt lithium manganate Boron particle group 2: Powder of boron simple substance (d50 = 1 μm)
Conductive material: Acetylene black Binder: PVdF
Solvent: N-methyl-2-pyrrolidone Cathode current collector 11: Al foil

  The positive electrode slurry was prepared by mixing the positive electrode active material 1, the conductive material, the binder, the boron particle group 2, and the solvent. The mixing ratio of the positive electrode active material 1, the conductive material and the binder is “positive electrode active material: conductive material: binder = 93: 4: 3 (mass ratio)”. The content of the boron particle group 2 is 1 part by mass with respect to 100 parts by mass of the positive electrode active material 1.

  The positive electrode slurry was applied to the surface (both front and back surfaces) of the positive electrode current collector 11 and dried to form the positive electrode mixture layer 12. Thereby, the positive electrode raw material was manufactured. The positive electrode raw material was rolled so as to have a predetermined thickness. The positive electrode original fabric was cut so as to have a predetermined outer dimension. Thus, the positive electrode 10 was manufactured.

2. Production of negative electrode The following materials were prepared.
Negative electrode active material: Graphite and silicon oxide Binder: CMC and SBR
Solvent: Water Negative electrode current collector: Cu foil

  A negative electrode slurry was prepared by mixing the negative electrode active material, the binder, and the solvent. The mixing ratio of the negative electrode active material and the binder is “negative electrode active material: binder = 99: 1 (mass ratio)”. The mixing ratio of the negative electrode active material is “graphite: silicon oxide = 95: 5 (mass ratio)”. The mixing ratio of the binder is “CMC: SBR = 1: 1 (mass ratio)”.

  The negative electrode slurry was applied to the surface (both front and back surfaces) of the negative electrode current collector and dried to form a negative electrode mixture layer. Thereby, a negative electrode original fabric was manufactured. The negative electrode raw material was rolled so as to have a predetermined thickness. The negative electrode original fabric was cut so as to have a predetermined outer dimension. Thus, negative electrode 20 was manufactured.

3. Assembly Separator 30 was prepared. Separator 30 has a three-layer structure. The separator 30 is formed by laminating a porous film made of PP, a porous film made of PE, and a porous film made of PP in this order.

  The electrode group 50 was formed by alternately laminating the eight positive electrodes 10 and the nine negative electrodes 20. Separators 30 were respectively disposed between the positive electrode 10 and the negative electrode 20. A positive electrode tab 81 and a negative electrode tab 82 were attached to the electrode group 50. Case 90 was prepared. Case 90 is a pouch made of an aluminum laminate film. The electrode group 50 was accommodated in the case 90.

An electrolyte was prepared. The electrolytic solution includes the following components.
Supporting salt: LiPF ₆ (1 mol / L)
Solvent: [EC: DMC: EMC = 3: 4: 3 (volume ratio)]

  An electrolytic solution was injected into the case 90. Case 90 was sealed. Thus, the battery 100 (lithium ion secondary battery) was manufactured. The design capacity of the battery 100 is 600 mAh. The initial charge / discharge of the battery 100 was performed in the range of 2.5 to 4.2 V with a current of 1 / 3C. Thereby, the battery 100 was made into the initial state. Note that at a current of “1C”, the design capacity of the battery 100 is discharged in one hour.

<< Comparative Example 1 >>
A battery 100 was manufactured in the same manner as in Example 1 except that the boron particle group 2 was not mixed with the positive electrode slurry.

<< Examples 2 and 3, Comparative Examples 2 and 3 >>
As shown in Table 1 below, batteries 100 were produced in the same manner as in Example 1 except that the content of the boron particle group 2 in the positive electrode mixture layer 12 was changed.

<< Comparative Example 5 >>
A battery 100 was manufactured in the same manner as in Example 1 except that a boric acid particle group was used instead of the boron particle group 2.

<Evaluation>
1. Measurement of DC Resistance In a temperature environment of 25 ° C., the SOC (state of charge) of the battery 100 was adjusted to 50%. In a temperature environment of 0 ° C., the battery 100 was charged for 10 seconds by the current I ₁ . I ₁ is 0.3C. The voltage 10 seconds after the start of charging was measured. The voltage is V ₁ .

Similarly, in a temperature environment of 0 ° C., the battery 100 was charged for 10 seconds by the current I ₂ . I ₂ is 0.5C. The voltage 10 seconds after the start of charging was measured. The voltage is set to V _2. Following formula:
DC resistance = (V ₂ −V ₁ ) / (I ₂ −I ₁ )
The DC resistance was calculated by The DC resistance is also called IV resistance. The DC resistance is shown in Table 1 below.

2. Nail penetration test The SOC of the battery 100 was adjusted to 100% in a temperature environment of 25 ° C. A nail was prepared. The nail has a body diameter of 3 mm. The nail was pushed into the battery 100 to such an extent that the case 90 (aluminum laminate film) was not broken. The indentation speed is 1 mm / second. The nail was stopped when a voltage drop was detected. After the nail stops, the magnitude of the fever was evaluated. The evaluation results are shown in Table 1 below.

<Result>
Comparative Example 1 generates a large amount of heat during the nail penetration test. It is considered that various exothermic reactions occur due to oxygen released from the positive electrode active material 1.

  In Examples 1 to 4, heat generation during the nail penetration test is small. In Examples 1 to 4, the positive electrode mixture layer 12 includes the boron particle group 2. Since the oxygen released from the positive electrode active material 1 quickly combines with the boron particle group 2, it is considered that heat generation is suppressed. In Examples 1 to 4, the content of the boron particle group 2 is 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material. In Examples 1 to 4, d50 of the boron particle group 2 is 0.1 μm or more and 5 μm or less.

  Comparative Example 2 was significantly below the design capacity (600 mAh). In Comparative Example 2, the content of the boron particle group 2 exceeds 20 parts by mass. It is considered that the battery capacity is reduced due to an increase in resistance that cannot be ignored. In Comparative Example 2, since the battery capacity cannot be lowered, the direct current resistance measurement and the nail penetration test are not performed.

  Comparative Example 3 generates a large amount of heat during the nail penetration test. In Comparative Example 3, the content of the boron particle group 2 is less than 1 part by mass. Since the content of the boron particle group 2 is excessively small, it is considered that the heat generation suppressing effect is small.

  Comparative Example 4 generates a large amount of heat during the nail penetration test. In Comparative Example 4, d50 of the boron particle group 2 exceeds 5 μm. It is considered that the specific surface area of the boron particle group 2 is small because the particle size of each boron particle is large. Therefore, it is considered that the reaction between boron and oxygen is inactive.

  Comparative Example 5 generates a large amount of heat during the nail penetration test. In Comparative Example 5, boric acid (a type of boron compound) is used instead of boron (simple substance). It is considered that boric acid becomes boron oxide through decomposition and dehydration due to the temperature rise during the nail penetration test. It is thought that boron oxide is less likely to react with oxygen than boron (simple substance). Therefore, it is considered that the same heat generation suppressing effect as that of boron (simple substance) cannot be obtained depending on boric acid.

  The embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The technical scope determined by the description of the scope of claims includes meanings equivalent to the scope of claims and all modifications within the scope.

  DESCRIPTION OF SYMBOLS 1 Positive electrode active material, 2 Boron particle group, 10 Positive electrode, 11 Positive electrode collector, 12 Positive electrode compound material layer, 20 Negative electrode, 30 Separator, 50 Electrode group, 81 Positive electrode tab, 82 Negative electrode tab, 90 Case, 100 Battery (lithium) Ion secondary battery).

Claims (1)

Including at least a positive electrode, a negative electrode, and an electrolyte;
The positive electrode includes at least a positive electrode mixture layer,
The positive electrode mixture layer includes at least a positive electrode active material and a boron particle group,
The boron particle group is included in the positive electrode mixture layer in an amount of 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material, and the boron particle group has a d50 of 0.1 μm or more and 5 μm or less.
Lithium ion secondary battery.

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