JP6729642B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

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

Japanese Patent Laying-Open No. 2014-075335 (Patent Document 1) discloses disposing a layer having a larger electric resistance than the positive electrode current collector between the positive electrode current collector and the positive electrode active material layer.

JP, 2014-075335, A

As one of the abnormal modes of the non-aqueous electrolyte secondary battery (hereinafter, may be abbreviated as “battery”), a short circuit due to an external input is considered. For example, a short circuit may occur due to a conductive foreign object penetrating the battery case. A short circuit due to external input is simulated by, for example, a nail penetration test.

Generally, the positive electrode current collector has a small electric resistance. The positive electrode current collector is covered with the positive electrode active material layer. However, the positive electrode active material layer may fall off due to the impact of external input, and the positive electrode current collector may be exposed. It is considered that when the exposed positive electrode current collector and the counter electrode (negative electrode) come into contact with each other, a large short circuit current is generated. It is considered that the large heat generation of the battery is caused by the generation of the large short-circuit current.

It is possible to arrange an intermediate layer between the positive electrode current collector and the positive electrode active material layer in order to suppress the exposure of the positive electrode current collector during external input. The intermediate layer has a larger electric resistance than the positive electrode current collector. Therefore, the intermediate layer contains an insulating material such as an inorganic filler.

However, during normal use, it is necessary to exchange electric current between the positive electrode current collector and the positive electrode active material layer through the intermediate layer. If the exchange of current through the intermediate layer is not smooth, for example, the resistance increase during normal use may increase. Therefore, the intermediate layer contains a conductive material such as carbon black.

Since the intermediate layer contains a conductive material, a short circuit may continue through the conductive material of the intermediate layer during external input. As a result, the heat generation of the battery may increase.

An object of the present disclosure is to suppress heat generation during external input while suppressing an increase in resistance during normal use.

Hereinafter, technical configurations and operational effects of the present disclosure will be described. However, the mechanism of action of the present disclosure includes inference. The claims should not be limited by the correctness of the mechanism of action.

The non-aqueous electrolyte secondary battery of the present disclosure includes at least a positive electrode. The positive electrode includes a positive electrode current collector, an intermediate layer and a positive electrode active material layer. The intermediate layer is arranged between the positive electrode current collector and the positive electrode active material layer. The intermediate layer contains a conductive material, a binder and an inorganic filler. The conductive material is contained in the intermediate layer in an amount of 0.3% by mass or more and 7% by mass or less. The residual mass ratio of the conductive material after heating is 0.2% by mass or more and 30% by mass or less. The mass residual ratio after heating indicates the ratio of the mass of the conductive material after heating to the mass of the conductive material before heating when the conductive material is heated in air at 450° C. for 1 hour.

Generally, the conductive material is a carbon material. A part or all of the conductive material may be burned off by reacting with oxygen in the process of heat generation of the battery. It is considered that the conductive paths are lost due to the burning of the conductive material.

The “mass residual ratio after heating” is considered to indicate the easiness of burning of the conductive material during external input. It is considered that when the residual mass ratio after heating is 30% by mass or less, the conductive paths remaining during external input are reduced. This makes it difficult for the short-circuited state to continue and is expected to reduce the heat generation of the battery. If the mass residual rate after heating is less than 0.2 mass %, the resistance increase during normal use may increase.

However, the content of the conductive material in the intermediate layer is 0.3% by mass or more and 7% by mass or less. When the content of the conductive material exceeds 7% by mass, the short-circuit state may continue during external input even if the residual mass ratio after heating is 30% by mass or less. When the content of the conductive material is less than 0.3% by mass, the resistance increase during normal use may be large even if the residual mass ratio after heating is 0.2% by mass or more.

FIG. 1 is a schematic diagram showing an example of the configuration of the non-aqueous electrolyte secondary battery of this embodiment. FIG. 2 is a schematic diagram showing an example of the configuration of the electrode group of this embodiment. FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the positive electrode of this embodiment.

Hereinafter, an embodiment of the present disclosure (herein referred to as “this embodiment”) will be described. However, the following description does not limit the scope of the claims.

<Non-aqueous electrolyte secondary battery>
FIG. 1 is a schematic diagram showing an example of the configuration of the non-aqueous electrolyte secondary battery of this embodiment.
The battery 100 includes a case 80. The case 80 is sealed. The case 80 may be made of, for example, an aluminum (Al) alloy. The case 80 is rectangular (flat rectangular parallelepiped). However, the shape of the case 80 should not be limited. The case 80 may have a cylindrical shape. The case 80 may be, for example, a pouch made of Al laminated film. That is, the battery 100 may be, for example, a laminated battery.

The case 80 includes terminals 81. The case 80 may be provided with, for example, a CID (current interrupt device), a gas discharge valve, a liquid injection hole, and the like. The case 80 houses the electrode group 50 and an electrolyte (not shown). The electrode group 50 is electrically connected to the terminal 81.

FIG. 2 is a schematic diagram showing an example of the configuration of the electrode group of this embodiment.
The electrode group 50 is a wound type. The electrode group 50 is formed by laminating the positive electrode 10, the separator 30, the negative electrode 20, and the separator 30 in this order, and further winding them in a spiral shape. That is, the battery 100 includes at least the positive electrode 10. The electrode group 50 may be formed in a flat shape.

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

《Positive electrode》
FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the positive electrode of this embodiment.
The positive electrode 10 is a sheet. The positive electrode 10 includes a positive electrode current collector 11, an intermediate layer 13, and a positive electrode active material layer 12. The intermediate layer 13 and the positive electrode active material layer 12 may be arranged on only one surface of the positive electrode current collector 11. The intermediate layer 13 and the positive electrode active material layer 12 may be arranged on both front and back surfaces of the positive electrode current collector 11.

(Positive electrode current collector)
The positive electrode current collector 11 may be, for example, an Al foil. The Al foil may have a thickness of 5 μm or more and 17 μm or less, for example. The positive electrode current collector 11 may be, for example, a titanium (Ti) foil. The Ti foil may have a thickness of 1 μm or more and 15 μm or less, for example.

(Middle layer)
The intermediate layer 13 is arranged between the positive electrode current collector 11 and the positive electrode active material layer 12. The intermediate layer 13 may have a thickness of 0.5 μm or more and 10 μm or less (for example, 2 μm). The intermediate layer 13 includes a conductive material, a binder and an inorganic filler. For example, the intermediate layer 13 may be composed of 0.3% by mass or more and 7% by mass or less of the conductive material, 0.1% by mass or more and 10% by mass or less of the binder, and the balance of the inorganic filler.

(Conductive material)
The conductive material is a conductive carbon material. The conductive material may include at least one selected from the group consisting of furnace black (FB), channel black (CB), acetylene black (AB), and graphite. The graphite may be natural graphite. The graphite may be artificial graphite. Ketjen Black® is considered to be included in FB. Materials other than these may be used as the conductive material.

The content of the conductive material is 0.3% by mass or more and 7% by mass or less. If the content of the conductive material is less than 0.3% by mass, the resistance increase during normal use may be large. If the content of the conductive material exceeds 7% by mass, heat generation during external input may increase. The content of the conductive material may be, for example, 0.5% by mass or more. The content of the conductive material may be, for example, 1.5% by mass or more. The content of the conductive material may be, for example, 5% by mass or less. The content of the conductive material may be 3% by mass or less.

From the viewpoint of increasing the resistance during normal use, it is desirable that the conductive material contains at least one selected from the group consisting of AB and graphite. For example, each of AB and graphite may be contained in the conductive material in an amount of 0.2% by mass or more.

(Mass residual rate after heating)
When the positive electrode current collector 11 is an Al foil or the like, when the temperature of the short-circuited portion reaches 660° C. during external input, it is considered that the positive electrode current collector 11 melts and the short-circuit current does not flow. It is considered that the heat generation of the battery 100 is reduced by cutting the conductive path by the conductive material before the positive electrode current collector 11 melts (that is, near 450° C.).

The “mass residual ratio after heating” indicates the ratio of the mass of the conductive material after heating to the mass of the conductive material before heating when the conductive material is heated in air at 450° C. for 1 hour. The mass residual ratio after heating is considered to indicate the easiness of burning of the conductive material during external input.

In the present embodiment, the mass residual rate of the conductive material after heating is 0.2% by mass or more and 30% by mass or less. When the mass residual ratio after heating is 30 mass% or less, it is expected that heat generation during external input will be reduced. If the mass residual ratio after heating is less than 0.2 mass %, the resistance increase during normal use may increase. The mass residual rate after heating may be 10% by mass or less. The residual mass after heating may be 5% by mass or less. The mass residual rate after heating may be 1% by mass or more.

The mass residual rate after heating can be adjusted by, for example, the composition of the conductive material. That is, FB, CB, AB and graphite may be combined so that the mass residual rate after heating is 0.2% by mass or more and 30% by mass or less. The ignition temperature of each material is as follows.

FB: About 350 to 385°C CB: About 290°C AB: About 600°C Graphite: About 700 to 800°C

For example, it is considered that when the ratio of AB and graphite increases, the mass residual rate after heating increases. This is because the ignition temperatures of AB and graphite are higher than 450°C. For example, it is considered that when the ratio of FB and CB increases, the mass residual ratio after heating decreases. This is because the ignition temperatures of FB and CB are less than 450°C.

(Measurement method of mass residual ratio after heating)
The mass residual rate after heating is measured by the following procedure.
A heat resistant container is prepared. The heat-resistant container is made of Al, for example. A predetermined amount (for example, about 1 to 5 g) of a conductive material is put in a heat resistant container in the atmosphere. A heating furnace is prepared. The heating furnace may be, for example, a muffle furnace or the like. A heat resistant container is placed in the heating furnace. The temperature of the heat-resistant container can be measured by, for example, a thermocouple. For example, the thermocouple may be fixed with a polyimide tape or the like.

The heat-resistant container is heated from room temperature (about 25° C.) to 450° C. at a rate of 5° C./min. After the temperature of the heat-resistant container reaches 450° C., the temperature of the heat-resistant container is maintained at 450° C. for 1 hour. Then, the temperature of the heat-resistant container is lowered to room temperature at a rate of 7.5° C./min. The mass of the conductive material after heating is measured.

The mass of the conductive material after heating is divided by the mass of the conductive material before heating. The percentage of the division result is the residual mass ratio after heating. The mass residual rate after heating is effective up to the first decimal place. The second decimal place and below are rounded off. After heating, the mass residual rate is measured at least three times. An arithmetic average of at least 3 is adopted.

The conductive material can be recovered from the inside of the battery 100 by, for example, the following procedure.
The battery 100 is disassembled and the positive electrode 10 is collected. The intermediate layer 13 and the positive electrode active material layer 12 are separated from the positive electrode current collector 11. The intermediate layer 13 is washed with a solvent (for example, dimethyl carbonate or the like). As a result, the electrolytic solution attached to the intermediate layer 13 is washed away. After washing, the intermediate layer 13 is vacuum dried at 110°C. This gives a powder. The powder is weighed. The weighed powder is put in aqua regia. By heating the aqua regia, part of the powder is dissolved in the aqua regia. After the dissolution treatment, insoluble components are filtered off. Insoluble components are washed with acid and warm water. After washing, the insoluble components are dried at 110°C. The ratio of the insoluble component contained in the mid layer 13 is obtained. The insoluble component is considered to be a mixture of binder and conductive material. The binder is removed with a solvent (for example, N-methyl-2-pyrrolidone or the like). As a result, the conductive material is recovered. The recovered conductive material is used for measurement of the mass residual rate after heating.

It is also possible to obtain a TG curve by a thermogravimetric analysis method. The weight derived from the binder is removed from the TG curve. It is also conceivable to determine the mass residual rate of the conductive material at 450° C. from the remaining TG curve.

When the binder is polyvinylidene fluoride (PVdF), the concentration of fluorine (F) in the insoluble component may be measured by the combustion ion chromatography method. The F concentration is converted into the PVdF content. Thereby, the content of the binder in the insoluble component is obtained.

(Binder)
The content of the binder may be, for example, 0.1% by mass or more and 10% by mass or less. The binder should not be particularly limited. The binder may be, for example, PVdF, vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), acrylic resin, polytetrafluoroethylene (PTFE), or the like. The intermediate layer 13 may contain one kind of binder alone. The intermediate layer 13 may contain two or more kinds of binders.

(Inorganic filler)
The content of the inorganic filler may be, for example, 85% by mass or more and 99.4% by mass or less. The inorganic filler should not be particularly limited. The inorganic filler may be, for example, at least one selected from the group consisting of boehmite, α-alumina, titania, and magnesium hydroxide. The titania may be rutile type. Titania may be of the anatase type. The inorganic filler may have a D50 of, for example, 0.1 μm or more and 3 μm or less.

(Method of forming the intermediate layer)
The intermediate layer 13 can be formed by the following method, for example.
A conductive carbon material (FB, CB, AB, graphite, etc.) is dry-mixed in a predetermined composition. Thereby, the conductive material is prepared. The first dispersion liquid is prepared by mixing the conductive material, the binder and the solvent. The solid content concentration (NV) of the first dispersion may be 55% by mass or more and 70% by mass or less (for example, 60% by mass). A solvent is added to the first dispersion and the first dispersion is further mixed. The NV of the first dispersion liquid after the addition of the solvent may be 35% by mass or more and 45% by mass or less (for example, 40% by mass).

The second dispersion liquid is prepared by mixing the inorganic filler, the binder, and the solvent. The NV of the second dispersion may be 35% by mass or more and 45% by mass or less (for example, 40% by mass).

The 1st dispersion liquid and the 2nd dispersion liquid are mixed so that it may become a target solid content composition. Thus, the intermediate layer paste is prepared. The intermediate layer paste is applied to the surface of the positive electrode current collector 11. The thickness of the intermediate layer 13 is adjusted by the coating amount. A general coating machine can be used for the coating operation. For example, a gravure coater, a knife coater, a multi coater, a die coater, a doctor blade, an ink jet coater or the like can be used. The intermediate layer 13 is formed by drying the intermediate layer paste. The drying temperature may be 60° C. or higher and 110° C. or lower (for example, 80° C.). The drying time may be, for example, about 10 minutes.

In addition, a suitable solvent should be used according to the type of binder. For example, when the binder is PVdF, PVdF-HFP or the like, N-methyl-2-pyrrolidone (NMP) or the like can be used as the solvent. For example, when the binder is an aqueous acrylic resin, water or the like can be used as the solvent. For example, when the binder is an oily acrylic resin, NMP or the like can be used as a solvent. For example, when the binder is PTFE, water or the like can be used as the solvent.

(Cathode active material layer)
The positive electrode active material layer 12 is formed on the surface of the intermediate layer 13. The positive electrode active material layer 12 can be formed, for example, by applying a paste containing a positive electrode active material on the surface of the intermediate layer 13 and drying it. The positive electrode active material layer 12 may have a thickness of 50 μm or more and 100 μm or less (for example, 75 μm). The positive electrode active material layer 12 contains at least a positive electrode active material. For example, the positive electrode active material layer 12 may include 0.1% by mass or more and 10% by mass or less of a conductive material, 0.1% by mass or more and 10% by mass or less of a binder, and the balance of the positive electrode active material.

The positive electrode active material is not particularly limited. The positive electrode active material may be, for example, a lithium (Li)-containing metal oxide. The positive electrode active material may include, for example, lithium nickel cobalt aluminate (NCA) or the like. NCA is, for example, the following formula (1):
LiNi _x1 Co _y1 Al _z1 O ₂ (1)
[Where x1, y1 and z1 satisfy 0.82≦x1≦0.95, 0.01≦y1≦0.15, 0.01≦z1≦0.15 and x1+y1+z1=1. ]
Can be represented by x1 may be, for example, 0.88.

The positive electrode active material may include, for example, lithium nickel cobalt manganate (NCM) or the like. NCM is, for example, the following formula (2):
LiNi _x2 Co _y2 Mn _z2 O ₂ (2)
[Where x2, y2 and z2 satisfy 0.35≦x2≦0.95, 0.01≦y2≦0.60, 0.01≦z2≦0.60 and x2+y2+z2=1. ]
Can be represented by

The positive electrode active material may include both NCA and NCM. The positive electrode active material may contain, for example, lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium iron phosphate, etc., in addition to NCA and NCM. Each Li-containing metal oxide may contain an additive such as an alkaline earth metal, a transition metal, a base metal or a semimetal. The additive may replace, for example, a part of the base material element. The additive may be attached to the surface of the base material particles. The total content of additives is about 5 mol% or less.

The conductive material should not be particularly limited. The conductive material may be, for example, AB, FB, CB, graphite, carbon nanotube (CNT), graphene, amorphous carbon, low crystalline carbon, or the like. The positive electrode active material layer 12 may include one kind of conductive material alone. The positive electrode active material layer 12 may contain two or more kinds of conductive materials.

The binder should not be particularly limited. The binder may be, for example, PVdF, PVdF-HFP, acrylic resin, PTFE or the like. The positive electrode active material layer 12 may include one kind of binder alone. The positive electrode active material layer 12 may include two or more binders.

《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 intermediate layer 13 described above may be disposed between the negative electrode current collector 21 and the negative electrode active material layer 22. Since the negative electrode 20 also includes the intermediate layer 13, it is expected that heat generation during external input will be further reduced.

The negative electrode current collector 21 may be, for example, a copper (Cu) foil. The Cu foil may have a thickness of 5 μm or more and 12 μm or less (for example, 10 μm). The Cu foil may have a thickness of 5 μm or more and 8 μm or less. The negative electrode current collector 21 may be, for example, a Ti foil. The Ti foil may have a thickness of 1 μm or more and 15 μm or less, for example.

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 surface of the negative electrode current collector 21. The negative electrode active material layer 22 may be formed on both front and back surfaces of the negative electrode current collector 21. The negative electrode active material layer 22 may have a thickness of 40 μm or more and 125 μm or less (for example, 80 μm). The negative electrode active material layer 22 contains at least a negative electrode active material. For example, the negative electrode active material layer 22 may include 0.1% by mass or more and 10% by mass or less of a conductive material, 0.1% by mass or more and 10% by mass or less of a binder, and the balance of the negative electrode active material.

The negative electrode active material is not particularly limited. The negative electrode active material may include, for example, graphite, low crystalline carbon (eg hard carbon, soft carbon, etc.), amorphous carbon, silicon oxide, etc. For example, the negative electrode active material may contain 4% by mass or more and 70% by mass or less of silicon oxide. The silicon oxide may be previously doped with Li. The silicon ratio of silicon oxide may be, for example, 10 mol% or more and 80 mol% or less.

The conductive material should not be particularly limited. The conductive material may be FB, CB, thermal black, AB, CNT, graphene or the like. The negative electrode active material layer 22 may include one kind of conductive material alone. The negative electrode active material layer 22 may contain two or more kinds of conductive materials. The binder should not be particularly limited. The binder may be, for example, carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

《Separator》
The separator 30 is a porous film. The separator 30 is electrically insulating. The separator 30 may have a single layer structure. The separator 30 may be composed of only a porous film made of polyethylene (PE), for example. The single-layer structure separator 30 may have a thickness of 5 μm or more and 30 μm or less (for example, 16 μm). The separator 30 may have a multi-layer structure. The separator 30 may be formed, for example, by stacking a polypropylene (PP) porous film, a PE porous film, and a PP porous film in this order. The separator 30 having a multilayer structure may have a thickness of, for example, 10 μm or more and 30 μm or less. In the separator 30 having a multilayer structure, each of the PP porous film and the PE porous film may have a thickness of, for example, 3 μm or more and 10 μm or less.

A heat resistant film may be formed on the surface of the separator 30. The heat resistant film may have a thickness of 1 μm or more and 12 μm or less (for example, 5 μm). The heat resistant film includes a heat resistant material. For example, the heat resistant film may be composed of 1% by mass or more and 30% by mass (for example, 4% by mass) of a binder and the balance of the inorganic filler. The binder should not be particularly limited. The binder may be, for example, acrylic resin, PVdF, PVdF-HFP, aramid, SBR, PTFE or the like. The heat resistant film may contain one kind of binder alone. The heat resistant film may contain two or more kinds of binders. The inorganic filler should not be particularly limited either. The inorganic filler may be, for example, boehmite, α-alumina, titania, zirconia, magnesia, aluminum hydroxide, magnesium hydroxide, zinc hydroxide or the like. The heat resistant film may contain one kind of inorganic filler alone. The heat resistant film may contain two or more kinds of inorganic fillers.

"Electrolytes"
The electrolyte is a lithium ion conductor. The electrolyte may be a liquid electrolyte, a gel electrolyte, or a solid electrolyte. The liquid electrolyte may be, for example, an electrolytic solution or an ionic liquid. An electrolyte is described herein as an example of an electrolyte.

The electrolytic solution contains a solvent and a supporting salt. The supporting salt is dissolved in the solvent. The concentration of the supporting 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 supporting salt may be, for example, LiPF ₆ , LiBF ₄ , LiN(FSO ₂ ) ₂ or LiN(CF ₃ SO ₂ ) ₂ . The electrolytic solution may contain one type of supporting salt alone. The electrolytic solution may contain two or more types of supporting salts.

The solvent is aprotic. The solvent may include, for example, cyclic carbonate and chain carbonate. The mixing ratio of the cyclic carbonate and the chain carbonate 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 cyclic carbonate alone. The solvent may contain two or more cyclic carbonates.

The chain carbonate may be, for example, dimethyl carbonate (DMC), ethylmethyl 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 kinds of chain carbonates.

The solvent may contain, for example, lactone, cyclic ether, chain ether, carboxylic acid ester, or the like. The lactone may be, for example, γ-butyrolactone (GBL), δ-valerolactone or 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 1,2-dimethoxyethane (DME) or the like. 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 solvent and the supporting salt. The concentration of the additive may be, for example, 0.005 mol/L or more and 0.5 mol/L or less. Examples of the additive include a gas generating agent (so-called “overcharge additive”), a SEI (solid electrolyte interface) film forming agent, 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), vinylethylene carbonate (VEC), LiB(C ₂ O ₄ ) ₂ , LiBF ₂ (C ₂ O ₄ ), LiPF ₂ (C ₂ O ₄ ) ₂ , LiPO ₂ It may be F ₂ , propane sultone (PS), ethylene sulphite (ES) or the like. The electrolyte may contain one kind of additive alone. The electrolytic solution may contain two or more kinds of additives.

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

<Examples 1 to 20, Comparative Examples 1 to 8>
The positive electrodes 10 according to Examples 1 to 20 and Comparative Examples 1 to 8 were manufactured. Each positive electrode 10 includes an intermediate layer 13 shown in Tables 1 and 2 below. The "heated mass residual rate" in Tables 1 and 2 below is measured by the method described above. Further, a battery 100 including the positive electrode 10 was manufactured. The structure of each part of the battery 100 is as follows.

Positive electrode 10
Positive electrode current collector 11: Al foil (thickness 15 μm)
Positive electrode active material layer 12: One side thickness 75 μm

Negative electrode 20
Negative electrode current collector 21: Cu foil (thickness 10 μm)
Negative electrode active material layer 22: thickness on one side 80 μm

Electrolyte (electrolyte)
Solvent: [EC:EMC:DMC=3:3:4 (volume ratio)]
Supporting salt: LiPF ₆ (1.1 mol/L)

Electrode group 50
Width dimension (dimension in the x-axis direction in FIG. 1): 130 mm
Height dimension (dimension in the z-axis direction in FIG. 1): 50 mm
Winding tension: 0.35 N / mm ² or more 4.3 N / mm ² or less Note "winding tension" indicates the tension applied to the separator 30 at the time of winding is divided by the cross-sectional area of the separator 30 values.

<Evaluation>
《High load charge/discharge test》
The high load charge/discharge test evaluated the increase in resistance during normal use. The high load charge/discharge test corresponds to an accelerated test for promoting the increase in resistance.

1000 cycles of charging and discharging were performed. One cycle indicates one cycle of the following "charging", "first rest", "discharging" and "second rest". The cell resistance was measured after 1 cycle and 1000 cycles, respectively. The resistance increase rate was calculated by dividing the battery resistance after 1000 cycles by the battery resistance after 1 cycle. The rate of resistance increase is shown in Tables 1 and 2 below. It is considered that the lower the resistance increase rate, the more the resistance increase during normal use is suppressed.

Charge: Current rate=2.5C, Time=240 seconds First rest: 120 seconds Discharge: Current rate=30C, Time=20 seconds Second rest: 120 seconds

At the current rate of "1C", the rated capacity of the battery 100 is discharged in 1 hour. 2.5C is 2.5 times the current rate of 1C. 30C is a current rate 30 times that of 1C.

<< nail penetration test >>
The nail penetration test evaluated heat generation during external input.
The nails are prepared. The nail has a body diameter of 3 mm. The battery 100 has been charged. The battery 100 after charging was heated to 60°C. A nail was stuck into the battery 100 which was in a charged state and a heated state. The surface temperature of the case 80 was measured at a position 1 cm away from the position where the nail was inserted. The maximum surface temperature is the reached temperature after the nail is pierced. The temperatures reached are shown in Tables 1 and 2 below. It is considered that the lower the ultimate temperature is, the more the heat generation during external input is suppressed.

<Results>
<<(Table 1) Examples 1-10, Comparative Examples 1-6>>
In Comparative Examples 1, 3 and 4, the temperature reached by the nail penetration test is high. It is considered that the residual mass ratio of the conductive material after heating exceeds 30% by mass.

Comparative Examples 2, 5 and 6 have a high resistance increase rate in the high load charge/discharge test. It is considered that the residual mass ratio of the conductive material after heating is less than 0.2% by mass.

In Examples 1 to 10, the resistance increase rate in the high load charge/discharge test is low and the ultimate temperature in the nail penetration test is low. In Examples 1 to 10, the residual mass of the conductive material after heating is 0.2% by mass or more and 30% by mass or less.

<<(Table 2) Examples 11 to 20 and Comparative Examples 7 to 8>>
Comparative Example 7 has a high resistance increase rate in the high load charge/discharge test even though the mass residual rate after heating is 0.2% by mass or more and 30% by mass or less. It is considered that in Comparative Example 7, the content of the conductive material is less than 0.3% by mass.

In Comparative Example 8, the reached temperature during the nail penetration test is high even though the residual mass ratio after heating is 0.2% by mass or more and 30% by mass or less. It is considered that in Comparative Example 8, the content of the conductive material exceeds 7 mass %.

In Examples 11 to 20, the resistance increase rate in the high load charge/discharge test is low, and the ultimate temperature in the nail penetration test is low. In Examples 11 to 20, the content of the conductive material is 0.3% by mass or more and 7% by mass or less.

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

10 positive electrode, 11 positive electrode current collector, 12 positive electrode active material layer, 13 intermediate layer, 20 negative electrode, 21 negative electrode current collector, 22 negative electrode active material layer, 30 separator, 50 electrode group, 80 case, 81 terminal, 100 battery ( Non-aqueous electrolyte secondary battery).

Claims (1)

At least a positive electrode,
The positive electrode includes a positive electrode current collector, an intermediate layer and a positive electrode active material layer,
The intermediate layer is disposed between the positive electrode current collector and the positive electrode active material layer,
The intermediate layer contains a conductive material, a binder and an inorganic filler,
The conductive material is contained in the intermediate layer in an amount of 0.3% by mass or more and 7% by mass or less,
The mass residual rate of the conductive material after heating is 0.2% by mass or more and 30% by mass or less,
The post-heating mass residual rate indicates a ratio of the mass of the conductive material after heating to the mass of the conductive material before heating when the conductive material is heated in air at 450° C. for 1 hour,
Non-aqueous electrolyte secondary battery.

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