JP6813008B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present disclosure relates to a non-aqueous electrolyte secondary battery.

Japanese Unexamined Patent Publication No. 2007-080651 (Patent Document 1) discloses that a phosphazene compound is added to an electrolytic solution.

JP-A-2007-080651

Generally, the separator and the electrolytic solution of a non-aqueous electrolytic solution secondary battery (hereinafter, may be abbreviated as "battery") are combustibles. For example, when an internal short circuit occurs, it is considered that the heat generated by the battery increases due to the combustion of the separator and the electrolytic solution.

It has been proposed to add a phosphazene compound to the electrolytic solution in order to suppress the combustion reaction. However, the addition of the phosphazene compound tends to increase the battery resistance.

An object of the present disclosure is to suppress heat generation at the time of a short circuit while suppressing an increase in battery resistance.

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

（式中、Ｘはハロゲン原子を示し、Ｙはアルコキシ基を示す。） The non-aqueous electrolyte secondary battery includes at least a positive electrode active material layer, an intermediate layer, a separator, a negative electrode active material layer and an electrolytic solution. The intermediate layer is arranged between the positive electrode active material layer and the separator. The intermediate layer contains a binder of 30% by mass or more and 95% by mass or less, and the remaining inorganic filler. The phosphazene compound is added to the electrolytic solution in an amount of 0.1% by mass or more and 3% by mass or less. The phosphazene compound is at least one selected from the group consisting of compounds represented by the following formulas (1) or (2).

(In the formula, X represents a halogen atom and Y represents an alkoxy group.)

For example, when the positive electrode and the negative electrode are short-circuited through a conductive foreign substance, the positive electrode active material layer generates heat. That is, a heat source is generated. It is considered that combustibles (separator and electrolytic solution) are heated by the heat source and a combustion reaction occurs.

It is expected that the addition of the phosphazene compound to the electrolytic solution suppresses the combustion reaction of the separator and the electrolytic solution at the time of a short circuit. However, the phosphazene compound added to the electrolytic solution is also distributed to the positive electrode active material layer. It is considered that this increases the reaction resistance of the positive electrode active material layer and increases the battery resistance.

In the present disclosure, an intermediate layer is arranged between the positive electrode active material layer and the separator. The middle layer contains the binder. Further, in the present disclosure, a phosphazene compound represented by the above formula (1) or (2) is used. Hereinafter, in the present specification, the phosphazene compound represented by the above formula (1) or (2) is also referred to as "specific phosphazene compound".

It is considered that the specific phosphazene compound is easily adsorbed on the intermediate layer due to the interaction with the binder contained in the intermediate layer (for example, hydrogen bond). Therefore, it is considered that the specific phosphazene compound tends to collect in the intermediate layer. It is considered that the specific phosphazene compound distributed to the positive electrode active material layer is relatively reduced by collecting the specific phosphazene compound in the intermediate layer. This is expected to suppress the increase in battery resistance.

Further, the intermediate layer is closer to the separator than the positive electrode active material layer. The separator and electrolyte are flammable. The separator is a porous membrane. The pores of the separator are impregnated with a large amount of electrolytic solution. It is expected that the combustion reaction of the separator and the electrolytic solution is efficiently suppressed by adsorbing the specific phosphazene compound on the intermediate layer.

Based on the above, according to the present disclosure, it is considered that heat generation at the time of short circuit is suppressed while suppressing an increase in battery resistance.

As a similar compound of the specific phosphazene compound, a phosphazene compound represented by the following formula (3) can be considered.

However, the phosphazene compound represented by the above formula (3) is considered to have a small effect of suppressing heat generation. The specific phosphazene compound [the above formula (1) or (2)] has one or two alkoxy groups (Y). The phosphazene compound represented by the above formula (3) has three alkoxy groups (Y). If the number of alkoxy groups (Y) exceeds 2, it is considered that the steric hindrance becomes large and the interaction becomes weak.

The amount of the specific phosphazene compound added is 0.1% by mass or more and 3% by mass or less. If the amount added is less than 0.1% by mass, the heat generation suppressing effect may be insufficient. If the amount added exceeds 3% by mass, the increase in battery resistance may not be suppressed.

The binder content of the intermediate layer is 30% by mass or more and 95% by mass or less. If the binder content is less than 30% by mass, the interaction with the specific phosphazene compound is weak, and the heat generation suppressing effect may be insufficient. If the binder content exceeds 95% by mass, the increase in battery resistance may not be suppressed. This is probably because the movement of lithium ions is inhibited.

FIG. 1 is a schematic view showing an example of the configuration of the non-aqueous electrolyte secondary battery of the present embodiment. FIG. 2 is a schematic view showing an example of the configuration of the electrode group of the present embodiment. FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the electrode group of the present embodiment. FIG. 4 is a graph showing the relationship between the temperature reached during the nail piercing test and the binder content of the intermediate layer, and the relationship between the battery resistance and the binder content of the intermediate layer.

Hereinafter, embodiments 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 claims.

<Non-aqueous electrolyte secondary battery>
FIG. 1 is a schematic view showing an example of the configuration of the non-aqueous electrolyte secondary battery of the present embodiment.
The battery 100 is a non-aqueous electrolyte secondary battery. The battery 100 includes a case 101. The case 101 may be made of, for example, an aluminum (Al) alloy. The case 101 is hermetically sealed. The case 101 is square (flat rectangular parallelepiped). However, the case 101 may be cylindrical, for example. The case 101 may be, for example, a pouch made of an aluminum laminated film or the like. That is, the battery 100 may be a laminated battery.

The case 101 includes a container 102 and a lid 103. The lid 103 is joined to the container 102 by, for example, laser welding. The lid 103 is provided with a positive electrode terminal 91 and a negative electrode terminal 92. The lid 103 may be further provided with a liquid injection port, a gas discharge valve, a CID (curent interrupt device), and the like. The case 101 houses the electrode group 50 and the electrolytic solution (not shown).

FIG. 2 is a schematic view showing an example of the configuration of the electrode group of the present embodiment.
The electrode group 50 is a winding type. The electrode group 50 is formed by laminating a positive electrode 10, a separator 30, a negative electrode 20, and a separator 30 in this order, and further winding them in a spiral shape.

The electrode group 50 may be of a stacked type. That is, the electrode group 50 may be formed by alternately stacking one or more positive electrodes 10 and 20. A separator 30 is arranged between each of the positive electrode 10 and the negative electrode 20.

FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the electrode group of the present embodiment.
The electrode group 50 includes a positive electrode 10, an intermediate layer 40, a separator 30, and a negative electrode 20. The electrode group 50 is impregnated with an electrolytic solution (not shown). The positive electrode 10 includes a positive electrode active material layer 12. The negative electrode 20 includes a negative electrode active material layer 22. That is, the battery 100 includes at least a positive electrode active material layer 12, an intermediate layer 40, a separator 30, a negative electrode active material layer 22, and an electrolytic solution.

The positive electrode active material layer 12 and the negative electrode active material layer 22 face each other. The separator 30 is arranged between the positive electrode active material layer 12 and the negative electrode active material layer 22. The intermediate layer 40 is arranged between the positive electrode active material layer 12 and the separator 30. A specific phosphazene compound is added to the electrolytic solution. In the present embodiment, it is considered that the specific phosphazene compound is easily adsorbed on the intermediate layer 40 by the interaction between the specific phosphazene compound and the binder of the intermediate layer 40. As a result, it is considered that heat generation at the time of short circuit is suppressed while suppressing an increase in battery resistance.

《Middle layer》
The intermediate layer 40 is arranged between the positive electrode active material layer 12 and the separator 30. The intermediate layer 40 may be formed on the surface of, for example, the positive electrode active material layer 12. The intermediate layer 40 may be formed on the surface of the separator 30, for example.

(composition)
The intermediate layer 40 contains a binder of 30% by mass or more and 95% by mass or less, and the remaining inorganic filler. The binder is a polymer compound. It is desirable that the binder contains abundant hydrogen atoms in the molecular chain. This is because a hydrogen bond can be formed between the nitrogen atom (N) or the halogen atom (F, Cl, etc.) of the specific phosphazene compound and the hydrogen atom (H) of the binder. It is considered that the specific phosphazene compound stays in the intermediate layer 40 due to the hydrogen bond.

The binder may be a homopolymer. The binder may be a copolymer. The binder may be, for example, an acrylic binder, polyethylene (PE), polypropylene (PP), polyacrylic acid (PAA), polyvinylidene fluoride (PVdF), and a modified product thereof. The acrylic binder represents a polymer compound formed by polymerizing at least one monomer selected from the group consisting of acrylic acid ester, methacrylic acid ester and acrylonitrile. One kind of binder may be contained alone in the intermediate layer 40. The intermediate layer 40 may contain two or more kinds of binders. For example, the binder may be at least one selected from the group consisting of acrylic binders, PAA and PVdF.

The binder content in the intermediate layer 40 is 30% by mass or more and 95% by mass or less. If the binder content is less than 30% by mass, the interaction with the specific phosphazene compound is weak, and the heat generation suppressing effect may be insufficient. If the binder content exceeds 95% by mass, the increase in battery resistance may not be suppressed. The binder content may be, for example, 50% by mass or more and 80% by mass or less.

In the intermediate layer 40, the balance excluding the binder contains an inorganic filler. The balance may consist substantially only of the inorganic filler. For example, a conductive material (carbon black, graphite, etc.) may be contained in the balance. The balance may contain, for example, a substance that may be involved in the charge / discharge reaction.

Inorganic fillers should not be particularly limited. The inorganic filler may be, for example, alumina, silica, boehmite, titania, magnesia, zirconia or the like. The intermediate layer 40 may contain one kind of inorganic filler alone. The intermediate layer 40 may contain two or more kinds of inorganic fillers. The inorganic filler may have, for example, a D50 of 0.5 μm or more and 2 μm or less. D50 indicates a particle size in which the integrated particle volume from the fine particle side is 50% of the total particle volume in the volume-based particle size distribution. D50 can be measured by, for example, a laser diffraction type particle size distribution measuring device or the like.

(Porosity)
The intermediate layer 40 is porous. The porosity of the intermediate layer 40 can be adjusted by, for example, the binder content, the particle size of the inorganic filler, and the like. The higher the porosity of the intermediate layer 40, the more electrolytic solution can be impregnated in the intermediate layer 40. That is, more specific phosphazene compounds can be distributed to the intermediate layer 40. This is expected to increase the effect of suppressing heat generation at the time of short circuit. If the porosity becomes excessively high, it is considered difficult to maintain the structure of the intermediate layer 40. The intermediate layer 40 may have a porosity of, for example, 20% or more and 80% or less. The intermediate layer 40 may have a porosity of, for example, 50% or more and 80% or less.

《Electrolytic solution》
(Li salt)
The electrolytic solution contains at least a lithium (Li) salt and a solvent. The Li salt is dissolved in the solvent. The concentration of the Li salt may be, for example, 0.5 mol / L or more and 2 mol / L or less (0.5 M or more and 2 M or less). The Li salt may be, for example, LiPF ₆ , LiBF ₄ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) _2, or the like. The electrolytic solution may contain one kind of Li salt alone. The electrolytic solution may contain two or more kinds of Li salts.

(solvent)
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. The solvent may contain one type of cyclic carbonate alone. The solvent may contain two or more cyclic carbonates.

The chain carbonate may be, for example, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) or the like. The solvent may contain one kind of chain carbonate alone. The solvent may contain two or more chain carbonates.

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 or the like. The chain ether may be, for example, 1,2-dimethoxyethane (DME) or the like. The carboxylic acid ester may be, for example, methylformate (MF), methylacetate (MA), methylpropionate (MP) or the like.

(Specific phosphazene compound)
In the present embodiment, 0.1% by mass or more and 3% by mass or less of the specific phosphazene is added to the electrolytic solution. If the amount of the specific phosphazene compound added is less than 0.1% by mass, the heat generation suppressing effect may be insufficient. If the amount added exceeds 3% by mass, the increase in battery resistance may not be suppressed. The amount of the specific phosphazene compound added may be, for example, 0.5% by mass or more and 1% by mass or less.

The specific phosphazene compound is represented by the above formula (1) or (2).
In the above formula (1) or (2), the halogen atom (X) may be at least one selected from the group consisting of, for example, a fluorine atom (F) and a chlorine atom (Cl).
In the above formula (1), the alkoxy group (Y) may be a phenoxy group (OPh) or an ethoxy group (OEt).
In the above formula (2), the alkoxy group (Y) may be at least one selected from the group consisting of, for example, a phenoxy group (OPh) and an ethoxy group (OEt).

(Other additives)
As long as the specific phosphazene compound is added to the electrolytic solution, other additives may be contained in the electrolytic solution. As other additives, for example, a gas generating agent (also referred to as "overcharge additive"), a SEI (solid electrolyte interface) film forming agent, and the like can be considered. 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), LiB (C ₂ O ₄ ) ₂ , LiPO ₂ F ₂ , propane sulton (PS), ethylene sulfite (ES), and the like. You may. The amount of other additives added may be, for example, 0.1% by mass or more and 5% by mass or less.

《Positive electrode》
The positive electrode 10 is a sheet. The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 is formed on the surface of the positive electrode current collector 11. The positive electrode active material layer 12 may be formed on only one side of the positive electrode current collector 11. The positive electrode active material layer 12 may be formed on both the front and back surfaces of the positive electrode current collector 11.

The positive electrode current collector 11 may be, for example, an Al foil or the like. 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 active material layer 12 may have a thickness of, for example, 10 μm or more and 200 μm or less. The positive electrode active material layer 12 contains at least the positive electrode active material. The positive electrode active material layer 12 may further contain, for example, a conductive material and a binder.

The positive electrode active material is typically a group of particles. The positive electrode active material may have, for example, a D50 of 1 μm or more and 30 μm or less. The positive electrode active material should not be particularly limited. The positive electrode active material is, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (for example, LiMnO ₂ , LiMn ₂ O ₄ ), lithium nickel cobalt manganate (for example, LiNi _1/3 Co _{1 /). 3} Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ etc.), nickel cobalt cobalt oxide (for example, LiNi _0.82 Co _0.15 Al _0.03 O ₂ etc.), lithium iron phosphate (LiFePO ₄ ), etc. Good. The positive electrode active material layer 12 may contain one kind of positive electrode active material alone. The positive electrode active material layer 12 may contain two or more kinds of positive electrode active materials.

The positive electrode active material layer 12 may further contain a conductive material. The conductive material should not be particularly limited. The conductive material may be, for example, carbon black (for example, acetylene black, furnace black, thermal black, etc.), carbon short fibers, or the like. The positive electrode active material layer 12 may contain one kind of conductive material alone. Two or more kinds of conductive materials may be contained in the positive electrode active material layer 12. The content of the conductive material may be, for example, 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

The positive electrode active material layer 12 may further contain a binder. Binders should not be particularly limited. The binder may be, for example, PVdF or the like. The positive electrode active material layer 12 may contain one kind of binder alone. The positive electrode active material layer 12 may contain two or more kinds of binders. The content of the binder may be, for example, 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

<< Separator >>
The separator 30 is arranged 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 the separator 30. The separator 30 is a porous membrane. The separator 30 is electrically insulating. The separator 30 may have a thickness of, for example, 5 μm or more and 50 μm or less. The separator 30 may be made of, for example, polyolefin.

The separator 30 may be made of, for example, polyethylene (PE). The separator 30 may be made of polypropylene (PP), for example. The separator 30 may have, for example, a single-layer structure. The separator 30 may be made of, for example, only a porous membrane made of PE. The separator 30 may have, for example, a multilayer structure. The separator 30 may be formed, for example, by laminating a porous film made of PP, a porous film made of PE, and a porous film made of PP in this order.

《Negative electrode》
The negative electrode 20 is a sheet. The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The negative electrode active material layer 22 is formed on the surface of the negative electrode current collector 21. The negative electrode active material layer 22 may be formed on only one side of the negative electrode current collector 21. The negative electrode active material layer 22 may be formed on both the front and back surfaces of the negative electrode current collector 21.

The negative electrode current collector 21 may be, for example, a copper (Cu) foil or the like. The negative electrode current collector 21 may have a thickness of, for example, 5 μm or more and 50 μm or less.

The negative electrode active material layer 22 may have a thickness of, for example, 10 μm or more and 200 μm or less. The negative electrode active material layer 22 contains at least the negative electrode active material. The negative electrode active material layer 22 may further contain, for example, a binder.

The negative electrode active material is typically a group of particles. The negative electrode active material may have, for example, a D50 of 1 μm or more and 30 μm or less. The negative electrode active material should not be particularly limited. The negative electrode active material is, for example, graphite, graphitizable carbon, graphitizable carbon, silicon, silicon oxide, silicon-based alloy, tin, tin oxide, tin-based alloy, lithium (single unit), lithium alloy (for example, Li-Al alloy). Etc.) etc. The negative electrode active material layer 22 may contain one kind of negative electrode active material alone. The negative electrode active material layer 22 may contain two or more kinds of negative electrode active materials.

Binders should not be particularly limited either. The binder may be, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), or the like. The content of the binder may be, for example, 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the negative electrode active material.

Hereinafter, examples of the present disclosure will be described. However, the following description does not limit the scope of claims.

<Manufacturing of non-aqueous electrolyte secondary batteries>
<< Example 1 >>
1. 1. Manufacture of positive electrode The following materials were prepared.
Positive electrode active material: Lithium nickel cobalt manganate (having a layered rock salt type crystal structure)
Conductive material: Acetylene black (powdered product)
Binder: PVdF
Solvent: N-methyl-2-pyrrolidone Positive current collector: Al foil

A slurry was prepared by mixing the positive electrode active material, the conductive material, the binder and the solvent. The 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 active material layer 12. As a result, the positive electrode 10 was manufactured. The positive electrode 10 is a strip-shaped sheet. The positive electrode 10 was compressed by the rolling roller.

The positive electrode active material layer 12 has a composition of “positive electrode active material: conductive material: binder = 98: 1: 1 (mass ratio)”. The basis weight (mass per unit area) of the positive electrode active material layer 12 is 40 mg / cm ² . The width dimension (dimension in the x-axis direction of FIG. 2) of the positive electrode active material layer 12 is 110 mm.

2. 2. Manufacture of negative electrode The following materials were prepared.
Negative electrode active material: Natural graphite binder: CMC and SBR
Solvent: Ion-exchanged water Negative electrode current collector: Cu foil (thickness 10 μm)

A slurry was prepared by mixing the negative electrode active material, the binder and the solvent. The slurry was applied to the surface (both front and back surfaces) of the negative electrode current collector 21 and dried to form the negative electrode active material layer 22. The basis weight of the negative electrode active material layer 22 is 30 mg / cm ² . The width dimension (dimension in the x-axis direction of FIG. 2) of the negative electrode active material layer 22 is 112 mm. From the above, the negative electrode 20 was manufactured. The negative electrode 20 is a strip-shaped sheet.

3. 3. Preparation of Separator A PE porous membrane (width dimension 120 mm, thickness 15 μm) was prepared as the separator 30. The separator 30 has a multi-layer structure.

4. Formation of intermediate layer The following materials were prepared.
Inorganic filler: Alumina (D50 2 μm)
Binder: Acrylic binder

A slurry was prepared by mixing an inorganic filler, a binder and a solvent. The slurry was applied to the surface (one side) of the separator 30 and dried to form the intermediate layer 40. The intermediate layer 40 has a thickness of 10 μm. The intermediate layer 40 has a porosity of 50%. The intermediate layer is composed of a 50% by mass binder and a 50% by mass (remaining) inorganic filler.

5. Preparation of electrolytic solution The electrolytic solution was prepared. The electrolytic solution consists of the following components.
Li salt: LiPF ₆ (concentration 1 mol / L)
Solvent: [EC: EMC: DEC = 3: 4: 3 (volume ratio)]
Phosphazene compound: Pentafluoro (phenoxy) cyclotriphosphazene Addition amount of phosphazene compound: 3% by mass

Pentafluoro (phenoxy) cyclotriphosphazene represents a compound in which X is F and Y is OPh in the above formula (1).

6. Assembly The positive electrode 10, the separator 30, the negative electrode 20, and the separator 30 were laminated in this order, and further wound in a spiral shape. As a result, the electrode group 50 was formed. The intermediate layer 40 was arranged between the positive electrode active material layer 12 and the separator 30.

Case 101 was prepared. The case 101 is square. The case 101 has an external dimension of height dimension (75 mm) × width dimension (120 mm) × depth dimension (15 mm). The height dimension is the dimension in the z-axis direction of FIG. The width dimension is the dimension in the x-axis direction of FIG. The depth dimension is the dimension in the y-axis direction of FIG. The case 101 has a wall thickness of 1 mm.

A positive electrode terminal 91 and a negative electrode terminal 92 were connected to the electrode group 50. The electrode group 50 was housed in the case 101. The electrolytic solution was injected into the case 101. The case 101 was sealed. From the above, the battery 100 (non-aqueous electrolyte secondary battery) was manufactured. The battery 100 is designed to have a rated capacity of 5 Ah in the range of 3.0 to 4.1 V.

7. Finish Charging / Discharging The battery 100 was charged to 4.2 V at a current rate of 1 C in a temperature environment of 25 ° C. At a current rate of "1C", the rated capacity is charged in 1 hour. After a 5-minute pause, the battery 100 was discharged to 3.0 V at a current rate of 1C.

Furthermore, the initial capacity of the battery 100 was confirmed by the following constant current-constant voltage (CC-CV) method charging and CC-CV method discharging.

CC-CV method charge: CC = 1C, CV = 4.1V, 0.01C cut CC-CV method discharge: CC = 1C, CV = 3.0V, 0.01C cut

<< Examples 2 to 13, Comparative Examples 1 to 7 >>
The battery 100 was manufactured in the same manner as in Example 1 except that the configuration of each part was changed as shown in Table 1 below.

<Evaluation>
《Nail piercing test》
The SOC (state of charge) of the battery 100 was adjusted to 100%. The nails were prepared. The nail has a body diameter of 3 mm and a tip R of 1 mm. A nail was inserted into the battery 100 at a speed of 1 mm / sec. The ultimate temperature of the battery 100 was measured. The reached temperature indicates the surface temperature of the battery 100 1 second after the nail is inserted. The reached temperatures are shown in Table 1 below. It is considered that the lower the temperature reached during the nail piercing test, the more the heat generated during a short circuit is suppressed.

《Battery resistance》
The SOC of battery 100 was adjusted to 50%. The battery 100 was discharged for 10 seconds at a current rate of 10C. The amount of voltage drop 10 seconds after the start of discharge was measured. The battery resistance was calculated from the relationship between the voltage drop and the current rate. Battery resistance is shown in Table 1 below. It is considered that the smaller the battery resistance is, the more the increase in battery resistance due to the addition of the phosphazene compound is suppressed.

<< Distribution of phosphazene compounds >>
Battery 100 was discharged to 2.5V. Immediately after the end of discharge, the battery 100 was disassembled. The positive electrode 10, the intermediate layer 40 (separator 30), and the negative electrode 20 were recovered. Each member was dissolved in aqua regia. As a result, ICP measurement samples were prepared respectively. Nitrogen (N) content was measured by ICP measurement. The N content was converted to the phosphazene compound content. The results are shown in Table 1 below.

<Result>
<< Examples 1 to 5, Comparative Examples 1 to 3 >>
In Examples 1 to 5, the battery resistance is low, and the temperature reached during the nail piercing test is low. That is, in Examples 1 to 5, heat generation at the time of short circuit is suppressed while the increase in battery resistance is suppressed. In Examples 1 to 5, the binder content of the intermediate layer 40 is 30% by mass or more and 95% by mass or less.

In Comparative Example 1, heat generation at the time of short circuit is large. In Comparative Example 1, the binder content of the intermediate layer 40 is less than 30% by mass. Therefore, it is considered that the amount of the phosphazene compound distributed to the intermediate layer 40 is small.

Comparative Example 2 has a high battery resistance. In Comparative Example 2, the binder content of the intermediate layer 40 exceeds 95% by mass. Therefore, the porosity of the intermediate layer 40 is low. It is considered that the battery resistance is increased due to the inhibition of the movement of lithium ions.

From the results of Examples 1 to 5 and Comparative Examples 1 to 3, it is considered that the porosity of the intermediate layer 40 can be adjusted by the binder content of the intermediate layer 40 and the particle size (D50) of the inorganic filler.

FIG. 4 is a graph showing the relationship between the temperature reached during the nail piercing test and the binder content of the intermediate layer, and the relationship between the battery resistance and the binder content of the intermediate layer.
In the range of the binder content of 50% by mass or more and 80% by mass or less, the balance between the battery resistance and the heat generation suppressing effect tends to be improved.

<< Examples 6 and 7 >>
As the type of binder changes, the temperature reached during the nail piercing test also changes. It is considered that the morphology of the interaction (for example, hydrogen bond) changes due to the change in the type of binder (for example, the amount of hydrogen atoms changes), and the adsorption amount of the phosphazene compound in the intermediate layer 40 changes. Be done.

<< Examples 1, 8 to 10, Comparative Examples 4, 5 >>
If the amount of the phosphazene compound added is less than 0.1% by mass, the heat generation suppressing effect is not sufficient (Comparative Example 4). If the amount of the phosphazene compound added exceeds 3% by mass, the increase in battery resistance cannot be suppressed (Comparative Example 5). In the examples, the amount of the phosphazene compound added is 0.1% by mass or more and 3% by mass or less (Examples 1, 8 to 10).

<< Examples 1, 11 to 13, Comparative Examples 6 and 7 >>
When the number of alkoxy groups (Y) in the phosphazene compound is increased from one to two, the heat generation suppressing effect is increased (Examples 1 and 11). However, when the number of alkoxy groups (Y) is three, the heat generation suppressing effect is reduced (Comparative Example 6). This is thought to be due to steric hindrance.

The heat generation suppressing effect is changed by changing the types of the halogen atom (X) and the alkoxy group (Y) (Examples 1, 12, and 13). It is considered that the morphology of radicals generated from the phosphazene compound changes depending on the type of substituent.

The embodiments and examples disclosed this time are exemplary in all respects and are not restrictive. The technical scope defined by the description of the scope of claims includes all changes within the meaning and scope equivalent to the description of the scope of claims.

10 Positive electrode, 11 Positive electrode current collector, 12 Positive electrode active material layer, 20 Negative electrode, 21 Negative electrode current collector, 22 Negative electrode active material layer, 30 Separator, 40 Intermediate layer, 50 Electrode group, 91 Positive electrode terminal, 92 Negative electrode terminal, 100 Battery (non-aqueous electrolyte secondary battery), 101 case, 102 container, 103 lid.

Claims (1)

Containing at least a positive electrode active material layer, an intermediate layer, a separator, a negative electrode active material layer and an electrolytic solution,
The intermediate layer is arranged between the positive electrode active material layer and the separator.
The intermediate layer contains a binder of 30% by mass or more and 95% by mass or less, and the remaining inorganic filler.
The binder is at least one selected from the group consisting of an acrylic binder, polyacrylic acid and polyvinylidene fluoride.
The phosphazene compound is added to the electrolytic solution in an amount of 0.1% by mass or more and 3% by mass or less.
The phosphazene compound is at least one selected from the group consisting of compounds represented by the following formulas (1) or (2).

(Wherein, X represents a C androgenic atom, Y represents an alkoxy group.)
Non-aqueous electrolyte secondary battery.

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