JP6702231B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

  Japanese Patent Laying-Open No. 2013-149434 (Patent Document 1) discloses a separator for a non-aqueous electrolyte secondary battery, and a heat resistant porous layer containing an insulating inorganic filler is formed on the surface of the separator. The insulating inorganic filler is a first insulating inorganic filler (heat absorbing material) made of a metal hydroxide or a hydrate of a metal oxide, and a second insulating material having a thermal conductivity of 10 W/m·K or more. Including a mixture with an inorganic filler.

JP, 2013-149434, A

  In Patent Document 1, even when a local abnormal heat generation occurs in a non-aqueous electrolyte secondary battery (hereinafter, may be abbreviated as “battery”) due to the separator having the heat resistant porous layer, It is described that the temperature rise of the entire battery can be effectively suppressed. However, there is room for further improvement from the viewpoint of suppressing the temperature rise when heat is generated in the electrodes inside the battery.

  Therefore, an object of the present disclosure is to effectively suppress a temperature rise when heat is generated in an electrode or the like in a non-aqueous electrolyte secondary battery including a separator having a porous heat-resistant layer on the surface.

The non-aqueous electrolyte secondary battery of the present disclosure includes a positive electrode, a negative electrode and a separator.
The separator has a porous heat-resistant layer on the surface.
The heat resistant layer contains heat resistant particles.
The heat-resistant particles include core particles made of a high specific heat metal, and a coating layer made of an insulating high thermal conductive material that covers at least a part of the surface of the core particles.
The high specific heat metal has a volume specific heat of 3.2 J/(cm ³ ·K) or more, and the core particles have an average particle diameter of 25 μm or less.
The insulating high thermal conductive material has a thermal conductivity of 50 W/(m·K) or more, and the coating layer has a thickness of 0.05 μm or more and 10 μm or less.
The heat resistant layer has a thickness of 0.5 μm or more.

  Heat generation mainly occurs at the electrodes. In the non-aqueous electrolyte secondary battery of the present disclosure, the porous heat-resistant layer on the surface of the separator is composed of a core particle made of a high specific heat metal, and an insulating high thermal conductive material coating at least a part of the surface of the core particle. Since it is composed of heat-resistant particles containing a coating layer, it is expected that the electrode and the high thermal conductive material of the heat-resistant layer (heat-resistant particles) will come into contact efficiently. Further, the high thermal conductive material and the high specific heat metal are also in contact with each other. Therefore, the heat generated in the electrodes due to overcharging or the like is quickly diffused to a wide range and quickly transferred to the high specific heat metal through the high thermal conductive material existing on the surface of the heat resistant particles. Thereby, the generated heat is diffused and used to efficiently heat the high specific heat metal, and the temperature rise of the entire battery is suppressed.

However, when the specific heat of the high specific heat metal is small, the generated heat cannot be sufficiently absorbed, and the effect of suppressing the temperature rise of the battery may not be sufficiently obtained.
Further, if the average particle size of the core particles (high specific heat metal) is large, it becomes difficult for heat to be transferred to the inside (center part) of the core particles, so the effect of suppressing the temperature rise of the battery may not be sufficiently obtained. ..
When the thermal conductivity of the high thermal conductive material is low, the generated heat cannot be efficiently transferred and diffused, and the effect of suppressing the temperature rise of the battery may not be sufficiently obtained.
If the thickness of the coating layer (insulating high thermal conductive material) is too thin, the heat resistance of the heat resistant layer (heat resistant particles) may be insufficient. In addition, the effect of suppressing the temperature rise of the battery may not be sufficiently obtained due to the difficulty of heat transfer. In addition, OCV (open circuit voltage) defect of the battery may occur. On the other hand, when the thickness of the coating layer is too thick, the distance between the electrode and the high specific heat metal becomes large, so that the heat transfer becomes inefficient and the effect of suppressing the temperature rise of the battery may not be sufficiently obtained.
In addition, when the heat-resistant layer is thin, the amount of heat-resistant particles is small, so that the effect of suppressing the temperature rise of the battery may not be sufficiently obtained. An internal short circuit is also likely to occur.

Therefore, in the non-aqueous electrolyte secondary battery of the present disclosure, the high specific heat metal has a volume specific heat of 3.2 J/(cm ³ ·K) or more, and the core particles have an average particle size of 25 μm or less. Further, the insulating high thermal conductive material has a thermal conductivity of 50 W/(m·K) or more, and the coating layer has a thickness of 0.05 μm or more and 10 μm or less. The heat-resistant layer has a thickness of 0.5 μm or more. The inventors of the present invention have found that, when the heat-resistant layer satisfies these conditions, the above effect of suppressing the temperature rise is easily exhibited sufficiently.

  From the above, according to the present disclosure, in a non-aqueous electrolyte secondary battery provided with a separator having a porous heat-resistant layer on the surface, it is possible to effectively suppress the temperature rise when heat is generated in the electrodes and the like. it can.

It is a cross-sectional schematic diagram which shows the structure of the separator which concerns on embodiment of this indication. It is a cross-sectional schematic diagram which shows the heat resistant particle which concerns on embodiment of this indication.

  Hereinafter, embodiments of the present disclosure will be described. However, the present disclosure is not limited to these.

<Non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a separator.

《Separator》
The separator 1 is an insulating porous film. Referring to FIG. 1, the separator 1 according to the present embodiment has a porous heat resistant layer 12 on the surface. In FIG. 1, the heat resistant layer 12 is provided on one surface of the base material 11, but the heat resistant layer 12 may be provided on both surfaces of the base material 11. In many cases, depending on the design of the battery, heat is likely to occur mainly in either the positive electrode or the negative electrode. Therefore, when the heat resistant layer 12 is provided on one surface of the base material 11, the separator 1 and the electrode are laminated so that the heat resistant layer 12 is in contact with the electrode (positive electrode or negative electrode) where heat is easily generated. To be done.

  As the base material 11, various materials (for example, resin such as polyethylene) used as a base material of a separator for a battery can be used. The thickness of the base material 11 is about 0 to 50 μm. The separator 1 only needs to have the porous heat-resistant layer 12 on the surface, and the separator 1 may include only the heat-resistant layer 12 without including the base material 11.

  The heat resistant layer 12 includes heat resistant particles 13. With reference to FIG. 2, heat-resistant particles 13 include core particles 131 made of a metal having a high specific heat, and a coating layer 132 made of an insulating high thermal conductive material that covers at least a part of the surface of core particles 131. In addition, in FIG. 2, the entire surface of the core particle 131 is depicted as being covered with the coating layer 132, but it is not necessary that the entire surface of the core particle 131 is coated in this manner. As long as the disclosed effect is exhibited, at least a part of the surface of the core particle 131 may be coated. For example, a plurality of particles of an insulating high thermal conductive material may adhere to the surface of the core particles to form coated particles.

The high specific heat metal has a volume specific heat of 3.2 J/(cm ³ ·K) or more. The volume specific heat can be obtained by performing a qualitative analysis by an X-ray diffraction (XRD) method or the like and adopting a literature value based on the analysis result, or can be measured by a hydrothermal measurement method. Examples of the high specific heat metal include copper, iron, nickel, cobalt, nickel chrome alloy, and manganin.

  The core particles 131 have an average particle diameter of 25 μm or less. The lower limit of the average particle diameter of the core particles 131 is not particularly limited, but is, for example, about 1 μm. In the present specification, the term "average particle size" is also referred to as a particle size ("D50", "median size") at an integrated value of 50% in a volume-based particle size distribution measured by a laser diffraction/scattering method. Means).

  The shape of the core particles 131 is not particularly limited, but a spherical shape is preferable. This is because in the case of a spherical shape, heat is evenly transmitted from all directions, and the effect is likely to be exhibited. However, the effects of the present disclosure can be exhibited even in a flat shape, a polyhedron, or the like.

  The insulating high thermal conductive material has a thermal conductivity of 50 W/(m·K) or more. The thermal conductivity can be determined by performing a qualitative analysis by an X-ray diffraction (XRD) method or the like and adopting a literature value based on the analysis result. Examples of the insulating high thermal conductive material include boron nitride, aluminum nitride, silicon nitride, silicon carbide and the like.

  The coating layer 132 has a thickness of 0.05 μm or more and 10 μm or less. The thickness of the coating layer 132 can be measured, for example, by elemental analysis of the cross section of the heat resistant particles 13. Specifically, elemental analysis of the cross section of the heat-resistant particles 13 may be performed to measure the thickness at any 5 points in the cross section, and the average value thereof may be used as the thickness of the coating layer 132. The heat-resistant particles of the present embodiment, the high specific heat metal is covered with an insulator (insulating high thermal conductive material), even if adhered to the electrode or other parts, such as internal short circuit occurs hard.

  The heat resistant layer 12 has a thickness of 0.5 μm or more. The upper limit of the thickness of the heat resistant layer 12 is not particularly limited, but is, for example, about 20 μm. Regarding the thickness of the heat-resistant layer 12, the thickness of the coating layer 132 may be determined by measuring the thickness at any 5 points in the cross-section in the SEM image of the cross-section in the thickness direction of the heat-resistant layer 12.

The heat resistant layer 12 is insulative. Here, that the heat-resistant layer 12 is insulative means that, for example, the volume resistance in the surface direction of the heat-resistant layer 12 is 1.0×10 ⁶ Ω·cm or more. It is possible to actually disassemble the battery, take out the heat resistant layer 12, and measure the resistance of the heat resistant layer 12 by the direct current 4-terminal method. As the measuring device, for example, Loresta GP or Hiresta UP (both manufactured by Mitsubishi Chemical Analytech Co., Ltd.) can be used.

  If the non-aqueous electrolyte secondary battery of the present disclosure is disassembled, the structure, composition, etc. of the high specific heat metal and the insulating high thermal conductive material can be easily specified by, for example, structural analysis by XRD, elemental analysis by XRF, or the like. It is possible to

《Positive electrode》
The positive electrode includes a positive electrode current collector and a positive electrode mixture layer provided on one surface or both surfaces of the positive electrode current collector.

  The positive electrode current collector may be, for example, Al foil or the like. The positive electrode current collector may have a thickness of, for example, about 10 to 30 μm. The positive electrode mixture layer is formed on the surface of the positive electrode current collector.

  The positive electrode mixture layer may have a thickness of, for example, about 10 to 150 μm. The positive electrode mixture layer contains a positive electrode active material, a conductive material, a binder and the like. The positive electrode mixture layer contains, for example, 80 to 98% by mass of the positive electrode active material, 1 to 15% by mass of the conductive material, and 1 to 5% by mass of the binder.

The positive electrode active material, the conductive material, and the binder are not particularly limited. The positive electrode active material may be, for example, LiCoO ₂ , LiNiO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO _4, or the like. The conductive material may be, for example, acetylene black (AB), furnace black, vapor grown carbon fiber (VGCF), graphite or the like. The binder may be, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), or the like.

《Negative electrode》
The negative electrode includes a negative electrode current collector and a negative electrode mixture layer provided on one surface or both surfaces of the negative electrode current collector.

  The negative electrode current collector may be, for example, a copper (Cu) foil or the like. The negative electrode current collector may have a thickness of, for example, about 5 to 20 μm.

  The negative electrode mixture layer may have a thickness of, for example, about 10 to 150 μm. The negative electrode mixture layer contains a negative electrode active material, a binder material and the like. The negative electrode mixture layer contains, for example, 95 to 99% by mass of the negative electrode active material and 1 to 5% by mass of the binder.

  The negative electrode active material and the binder are not particularly limited. The negative electrode active material may be, for example, graphite, graphitizable carbon, non-graphitizable carbon, silicon, silicon oxide, tin, tin oxide or the like. The binder may be, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), or the like.

<Manufacture of non-aqueous electrolyte secondary battery>
An example of manufacturing the non-aqueous electrolyte secondary battery of the present embodiment will be described below.

First, the positive electrode and the negative electrode are manufactured as follows.
For example, a coating material containing the material for the positive electrode mixture layer and a solvent is prepared. The positive electrode mixture layer is formed by applying the coating material to the surface of the positive electrode current collector and drying it. Thereby, the positive electrode is manufactured. However, the present invention is not limited to this, and the positive electrode may be produced by roll molding, roll transfer, or the like. The positive electrode is processed into a predetermined size according to the specifications of the secondary battery. Similarly, a negative electrode is produced using the coating material containing the material of the negative electrode mixture layer and the solvent, and the negative electrode current collector.

Next, the separator is manufactured as follows.
First, a powder of high specific heat metal is prepared as a material of the core particles, and a powder of an insulating conductive material is prepared as a material of the coating layer. The powder of the high specific heat metal and the powder of the insulating high thermal conductive material are mixed, and the particles of the high specific heat metal (core particles) and the particles of the insulating high thermal conductive material are mechanically collided with each other in a ball mill, whereby core particles are obtained. A coating layer made of an insulating high thermal conductive material is formed on the surface of the. Thereby, heat resistant particles are prepared. However, the method for preparing the heat resistant particles should not be particularly limited to such a method.

  The heat resistant particles and a binder (for example, an acrylic binder) are mixed, a solvent such as water is added to the mixture, and the mixture is further mixed to prepare a raw material paste for the heat resistant layer. The non-volatile fraction of the raw material paste (the proportion of non-volatile components other than the solvent) is, for example, about 20 to 60 mass %. The content ratio of the binder in the non-volatile component is, for example, about 1 to 10 mass %. Next, this raw material paste is applied to one side or both sides of the base material so as to have a predetermined thickness and dried. In this way, a separator having a porous heat-resistant layer on its surface is produced.

  Next, a non-aqueous electrolyte secondary battery is manufactured from the above positive electrode, negative electrode, separator and the like as follows.

  An electrode group is produced from the separator and the positive electrode and the negative electrode. For example, an electrode group (wound electrode group) is produced by winding a laminated body in which a belt-shaped positive electrode and a belt-shaped negative electrode are laminated with a belt-shaped separator interposed therebetween. The electrode group (laminated electrode group) may be produced by alternately stacking a plurality of sheet-shaped positive electrodes and a plurality of sheet-shaped negative electrodes via sheet-shaped separators.

The electrode group is housed in a predetermined exterior body together with the electrolyte. The positive electrode of the electrode group is electrically connected to the positive electrode terminal, and the negative electrode is electrically connected to the negative electrode terminal. The electrolyte is, for example, a liquid electrolyte (non-aqueous electrolyte) in which a Li salt (LiPF ₆ or the like) is dissolved in an aprotic solvent (ethylene carbonate, dimethyl carbonate or the like). The exterior body is, for example, a metal housing made of Al alloy, stainless steel, or the like. The battery is manufactured by sealing the outer casing.

  The non-aqueous electrolyte secondary battery of the present disclosure can be used as a power source for, for example, a hybrid vehicle (HV), an electric vehicle (EV), a plug-in hybrid vehicle (PHV), and the like. However, the non-aqueous electrolyte secondary battery of the present disclosure is not limited to such applications and can be applied to all applications.

  Examples will be described below. However, the following examples do not limit the scope of the present disclosure.

<<Comparative Example 1>>
[Preparation of positive electrode]
First, the following materials were prepared.
・Positive electrode active material: LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (average particle size: 5 μm)
・Conductive material: acetylene black (AB)
・Binder: polyvinylidene fluoride (PVdF)
-Solvent: N-methyl-2-pyrrolidone-Positive electrode current collector: Al foil (thickness 15 μm)

  The positive electrode active material, the conductive material, the binder and the solvent were put into a mixing container of the planetary mixer and kneaded to obtain a positive electrode mixture paste. The mass ratio of the non-volatile components (components other than the solvent) was positive electrode active material:conductive material:binder=92:5:3.

  The positive electrode mixture paste was applied to both surfaces of the positive electrode current collector using a die coater and dried. As a result, a strip-shaped positive electrode was obtained in which the positive electrode mixture layers (width: 100 mm) were formed on both surfaces of the positive electrode current collector. The dried positive electrode mixture layer was compressed to a predetermined thickness. Further, the positive electrode was cut into a predetermined length.

[Preparation of negative electrode]
First, the following materials were prepared.
・Negative electrode active material: graphite (average particle size: 10 μm)
・Binder: SBR
・Thickening agent: CMC
・Solvent: Water/Negative electrode current collector: Copper foil (thickness 10 μm)

  The negative electrode active material, the binder, and the thickener were put into the mixing tank of the mixing device and mixed. A solvent (water) was further charged into the mixing tank of the mixing device and mixed to prepare a negative electrode mixture paste. The mass ratio of the non-volatile components was negative electrode active material:binder:thickener=98:1:1.

  The negative electrode mixture paste was applied to both surfaces of the negative electrode current collector using a die coater and dried. As a result, a strip-shaped negative electrode was obtained in which the negative electrode mixture layers (width: 105 mm) were formed on both surfaces of the negative electrode current collector. The dried negative electrode mixture layer was compressed to a predetermined thickness. Further, the negative electrode was cut into a predetermined length.

[Preparation of separator]
To 95 parts by mass of alumina powder and 5 parts by mass of acrylic resin (binder) powder, water was added so that the nonvolatile content was 40% by mass, and an ultra-high speed stirring system (TK Robomix: The mixture was stirred and mixed using PRIMIX Corporation to prepare a raw material paste for the heat-resistant layer. Next, the raw material paste was applied to both surfaces of the base material (polyethylene film, thickness 25 μm, porosity 50%) to a predetermined thickness (thickness after drying: 5 μm) and dried. As a result, a strip-shaped separator having heat resistant layers on both sides was produced.

(Preparation of non-aqueous electrolyte)
EC, DMC, and DEC were mixed in a volume ratio of EC:DMC:DEC=1:1:1 to obtain an aprotic solvent. Next, 1.0 M (1.0 mol/L) LiPF ₆ was dissolved as a solute in the aprotic solvent to prepare a non-aqueous electrolyte.

(Preparation of non-aqueous electrolyte secondary battery)
Next, a battery was manufactured using the materials manufactured as described above.

  A laminate obtained by laminating a positive electrode and a negative electrode via a separator was wound into an elliptic cylinder, and then pressed by a flat plate to produce a flat wound electrode group (tableless electrode group).

  Next, the electrode group is housed in a rectangular outer case, and each of the negative electrode current collector and the positive electrode current collector is electrically connected to the negative electrode terminal and the positive electrode terminal provided in the sealing body (lid) on the upper part of the outer case. did.

  Next, the non-aqueous electrolyte was injected into the outer case through the injection hole provided in the sealing body, and then the injection hole was sealed with a screw for sealing. As described above, the battery of Comparative Example 1 (non-aqueous electrolyte secondary battery, prismatic lithium ion secondary battery) was produced. The side surface of the battery was restrained by a SUS plate with a load of 500 kgf.

<<Comparative Examples 2-5>>
Instead of alumina, each material shown in Table 1 was used as the material of the core particles. Other than that, the batteries of Comparative Examples 2 to 5 were manufactured by the same method as in Comparative Example 1 basically. The “mixing ratio” column in Table 1 is the mixing ratio when two types of materials are used in combination (Comparative Examples 3 and 5), and when one type of material is used, it is written as 100 (mass %). is doing.

<<Example 1>>
A coating layer made of boron nitride is formed on the surface of copper particles (core particles) by mixing copper (high specific heat metal) powder and boron nitride (insulating high thermal conductive material) powder and mechanically colliding them with a ball mill. Then, heat resistant particles were obtained. The heat resistant particles were used instead of the alumina powder. A battery of Example 1 was manufactured in the same manner as in Comparative Example 1 except for the points described above.

<<Examples 2 and 3, Comparative Examples 6 and 7>>
The coating amount of boron nitride (thickness of coating layer) on the surface of the copper powder was changed as shown in Table 1. Except for this, the batteries of Examples 2 and 3 and Comparative Examples 6 and 7 were manufactured in basically the same manner as in Example 1. The coating amount was controlled by changing the treatment time by the ball mill. It should be noted that when the treatment time is lengthened, the thickness of the coating layer is increased, and when the treatment time is shortened, the thickness of the coating layer is decreased. Specifically, the treatment times in Example 1, Examples 2 and 3 and Comparative Examples 6 and 7 are 3 hours, 10 minutes, 20 hours, 5 minutes and 30 hours, respectively.

<<Examples 4 and 5, Comparative Example 8>>
The thickness of the heat-resistant layer (the coating amount of the raw material paste of the heat-resistant layer) was changed as shown in Table 1. Except for this, the batteries of Examples 4 and 5 and Comparative Example 8 were manufactured by basically the same method as that of Example 1.

<<Example 6>>
A heat-resistant layer (separator consisting of only the heat-resistant layer) was formed on the surface (both sides) of the negative electrode in the same manner as in Example 1 without using the substrate (polyethylene film), to produce a negative electrode with a separator. A wound type electrode group was produced by winding a laminated body formed by laminating the negative electrode and the positive electrode. A battery of Example 6 was manufactured in the same manner as in Example 1 except for the points described above.

<<Example 7, Comparative Example 9>>
The particle size of the core particles was changed as shown in Table 1. Except for this, the batteries of Example 7 and Comparative Example 9 were manufactured in the basically same manner as in Example 1.

<<Examples 8 to 12, Comparative Examples 10 and 11>>
The material type of the core particles was changed as shown in Table 1. Except for this, the batteries of Examples 8 to 12 and Comparative Examples 10 and 11 were manufactured in basically the same manner as in Example 1.

<<Examples 13 to 15 and Comparative Examples 12 and 13>>
The material type of the coating layer was changed as shown in Table 1. Except for this, the batteries of Examples 13 to 15 and Comparative Examples 12 and 13 were manufactured in the basically same manner as in Example 1.

<Evaluation>
The following evaluations were performed on the batteries of the above Examples and Comparative Examples.

<<Volume resistivity of heat resistant layer>>
Before being laminated with the positive electrode and the negative electrode, the volume resistivity of the heat-resistant layer of the separator was measured by a DC 4-terminal method. Loresta GP (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) was used as a measuring instrument. The measurement results are shown in the column of "Volume resistivity of heat resistant layer" in Table 1.

《Overcharge test》
The overcharge test was performed as follows. The battery was charged in an environment of 25° C. until the voltage of the battery reached 4.2V. After that, the charging was further continued at a current of 10 C, and the charging was continued until the liquid injection valve was opened by the internal pressure. Whether or not smoke was generated when the liquid injection valve of the battery was opened was visually confirmed. The results are shown in the column "Presence or absence of smoke" in "Overcharge test" of Table 1. It is considered that, if smoke is generated, the temperature rise inside the battery due to overcharge is large, and if there is no smoke, the temperature rise inside the battery due to overcharge is small.
During the overcharge test, the temperature of the side surface of the battery was measured while the thermocouple was attached to the side surface of the battery, and the maximum temperature reached was measured. The measurement results are shown in the "maximum temperature reached" column of the "overcharge test" in Table 1.

<<Defective rate (OCV defective rate)>>
For each of the above-mentioned Examples and Comparative Examples, 10 batteries were produced, and the number of defects that had occurred until the battery was completed (including initial charging) was counted. It should be noted that the presence/absence of defects was counted including the presence/absence of defects other than OCV defects, but the defects that occurred this time were all OCV defects). Note that the OCV defect is a defect in which the OCV (open circuit voltage) decreases even after charging (during initial charging). The result of the defective rate (ratio of the number of defectives out of 10) is shown in the column of "OCV defective rate" in Table 1.

In addition, in the "core particle" column of the "heat resistant layer" of Table 1, "volume specific heat" is the volume ratio (volume ratio) of the material shown in the "material" column, and is a literature value. Further, "D50" is a particle size at an integrated value of 50% in a volume-based particle size distribution measured by a laser diffraction/scattering method.
In the column of "coating layer" of "heat resistant layer" in Table 1, "thermal conductivity" is the thermal conductivity of the material shown in the "material" column, and is a literature value. The numerical value in the "thickness" column is the thickness of the coating layer measured by elemental analysis of the cross section of the heat resistant particles. Specifically, it is an average value of the measurement values obtained by measuring the thickness at any 5 points in the cross section by elemental analysis of the cross section of the heat resistant particles.
The numerical value in the “thickness” column of the “heat resistant layer” is the average value of the measured values obtained by measuring the thickness at any 5 points in the cross section in the SEM image of the cross section in the thickness direction of the heat resistant layer. ..

<Results>
The results shown in Table 1 are described below.

As a material for the core particles of the heat-resistant particles, a material having a volume specific heat of less than 3.2 J/(cm ³ ·K) (alumina, boron nitride, or a mixture of aluminum hydroxide and boron nitride) is used. In the batteries of Comparative Examples 1 to 3 which were not covered with the coating layer, smoke was generated during overcharge, and the maximum temperature reached was high. Regarding Comparative Example 2, although boron nitride has a relatively high thermal conductivity, the battery capacity was large and the current value was also large. Therefore, it is considered that the movement of heat did not catch up with the heat generation and the temperature of the battery increased. .. Further, in Comparative Example 3, even when aluminum hydroxide, which is an endothermic material that causes an endothermic reaction, was used, the endothermic action did not catch up with the heat generation, so the battery temperature increased.

In Comparative Examples 4 and 5, by using a high specific heat metal material having a volume specific heat of 3.2 J/(cm ³ ·K) or more as the core particles, the maximum temperature reached at the time of overcharging was slightly lowered, but smoke was emitted. Yes, it is considered that the effect of suppressing the temperature rise was not sufficient. It is considered that this is because the core particles were not covered with the insulating high thermal conductive material, so that the generated heat was not sufficiently diffused and conducted to the high specific heat metal.
Also, OCV defects frequently occurred. Since the conductive metal (copper) powder is used as the material of the uncoated core particles, the insulating property of the heat-resistant layer is low (volume resistivity is low), and the conductive metal is used during battery fabrication. Since it may adhere to the positive electrode, the negative electrode, other parts, etc., it is considered that an internal short circuit occurred.

On the other hand, in Example 1, by using a high specific heat metal having a volume specific heat of 3.2 J/(cm ³ ·K) or more for the core particles and coating the surface thereof with an insulating high thermal conductivity material, There was no smoke during charging and the temperature rise during overcharging was sufficiently suppressed. This is because the heat generated in the electrode or the like in the overcharged state is quickly transferred to the high specific heat metal (core particle) through the high thermal conductive material (coating layer) existing on the surface of the heat resistant particle forming the heat resistant layer. It is considered that this is because the generated heat was efficiently transferred to the high specific heat metal.
Further, no OCV failure occurred. This is because the conductive high specific heat metal (core particle) is covered with the insulator (insulating high thermal conductive material), so that the heat-resistant layer has high insulation (high volume resistivity), and if the electrode or It is considered that even if it adheres to parts or the like, it is unlikely that a defect such as an internal short circuit will occur.

From the results of Examples 2 and 3 and Comparative Examples 6 and 7, it is understood that when the thickness of the coating layer made of the high thermal conductive material is thin (less than 0.05 μm), the temperature rise during overcharge cannot be sufficiently suppressed. It is considered that this is because the heat transfer to the high specific heat metal is slow and the temperature rise during overcharge becomes large. In addition, it is considered that since the heat-resistant layer has low insulation (low volume resistivity), insulation cannot be ensured and OCV failure of the battery occurs.
On the other hand, it can be seen that even when the thickness of the coating layer made of the high thermal conductive material is large (greater than 10 μm), the temperature rise during overcharge cannot be sufficiently suppressed. It is considered that this is because the distance between the electrode and the high specific heat metal is large, so that the heat transfer efficiency is reduced and the battery temperature is increased.

  From the results of Examples 4 and 5 and Comparative Example 8, it can be seen that when the thickness of the heat resistant layer is less than 0.5 μm, the temperature rise during overcharge cannot be sufficiently suppressed. It is considered that this is because the heat-resistant layer was too thin, so that the apparent specific heat became small and the temperature increased. Further, in this case, although the heat resistance layer has a high volume resistance value, sufficient insulation is not performed because the heat resistance layer is too thin, an internal short circuit is likely to occur, and an OCV defect is considered to have occurred.

  From the results of Example 6, it was confirmed that the effect of suppressing the temperature rise was sufficiently obtained even when there was no resin base material such as polyethylene. Further, the heat-resistant layer had an insulating property (high volume resistivity), and no OCV failure occurred.

From the results of Example 7 and Comparative Example 9, it can be seen that when the average particle diameter (D50) of the core particles is more than 25 μm, the effect of suppressing the temperature rise cannot be sufficiently obtained. It is considered that this is because when the particle size of the core particles is large, the heat is not transferred to the inside of the core particles (high specific heat metal), and the efficiency of absorbing the heat generated in the electrodes and the like is low. In addition, there is a difference of about 50000 μm ³ in volume per core particle between the case where the average particle size is 25 μm and the case where the average particle size is 30 μm. The easiness of transmitting heat to the inside drops sharply.

From the results of Examples 8 to 12 and Comparative Examples 10 and 11, when the volume specific heat of the constituent material of the core particles is less than 3.2 J/(cm ³ ·K), the temperature rise during overcharge cannot be sufficiently suppressed. I understand.

  From the results of Examples 13 to 15 and Comparative Example 12, it can be seen that when the thermal conductivity of the constituent material of the coating layer is less than 50 W/(m·K), the temperature rise during overcharge cannot be sufficiently suppressed. .. It is considered that this is because the heat generated in the electrodes and the like could not be efficiently transferred, which led to an increase in battery temperature.

  In Comparative Example 13, since the thermal conductivity of the constituent material (graphite) of the coating layer was large, the temperature increase during overcharge was suppressed, but graphite had a high electric conductivity (not insulating), and thus OCV failure. The rate has increased.

  The embodiments and examples disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present disclosure is shown not by the above description but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

  1 separator, 11 base material, 12 heat resistant layer, 13 heat resistant particles, 131 core particles, 132 coating layer.

Claims (1)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a separator,
The separator has a porous heat-resistant layer on the surface,
The heat-resistant layer contains heat-resistant particles,
The heat-resistant particles include a core particle made of a high specific heat metal, and a coating layer made of an insulating high thermal conductive material that covers at least a part of the surface of the core particle,
The high specific heat metal has a volume specific heat of 3.2 J/(cm ³ ·K) or more, and the core particles have an average particle size of 25 μm or less,
The insulating high thermal conductive material has a thermal conductivity of 50 W/(m·K) or more, and the coating layer has a thickness of 0.05 μm or more and 10 μm or less,
The non-aqueous electrolyte secondary battery, wherein the heat-resistant layer has a thickness of 0.5 μm or more.

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