Non-aqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte secondary battery according to one embodiment of the present invention is provided with: a positive electrode which comprises a positive electrode core body and a positive electrode mixture layer that is provided on the positive electrode core body; and a negative electrode which comprises a negative electrode core body and a negative electrode mixture layer that is provided on the negative electrode core body. The 0.2 percent proof stress of the positive electrode core body is larger than the 0.2 percent proof stress of the negative electrode core body. It is preferable that the 0.2 percent proof stress of the positive electrode core body is not less than 1.05 times the 0.2 percent proof stress of the negative electrode core body.

Description

[Technical Field]

[0001] This disclosure relates to a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In non-aqueous electrolyte secondary batteries such as lithium-ion batteries, the positive and negative electrodes are positioned opposite each other so that the negative electrode's composite layer is always positioned opposite the positive electrode's composite layer via a separator, preventing the deposition of metallic lithium at the negative electrode. However, repeated charging and discharging of the battery can increase the internal pressure of the battery, for example, due to the expansion of the negative electrode's composite layer, leading to increased pressure load on the electrode plates and causing them to stretch. Conventional non-aqueous electrolyte secondary batteries are designed so that the negative electrode is slightly larger than the positive electrode in order to maintain the opposing state of the positive and negative electrode's composite layers even when the positive electrode stretches due to charging and discharging.

[0003] Conventionally, various studies have been conducted on the core material of the electrode plates in order to improve battery performance (see, for example, Patent Documents 1 to 4). Patent Document 1 discloses an aluminum alloy foil for positive electrode core material with a tensile strength of 180 MPa or more and a 0.2% yield strength of 160 MPa or more. Patent Document 2 also discloses an aluminum alloy foil for positive electrode core material with a tensile strength of 220 MPa or more and a 0.2% yield strength of 180 MPa or more. However, Patent Documents 1 and 2 do not contain any description regarding the physical properties of the negative electrode core material.

[0004] Patent Document 3 states that the 0.2% proof stress is 18-25 kgf / mm². 2 Furthermore, electrolytic copper foil for negative electrode cores with an elongation rate of 10% or more is disclosed. In addition, Patent Document 4 discloses a 0.2% proof stress of 250 N / mm². 2 The above discloses electrolytic copper foil for negative electrode cores with an elongation of 2.5% or more. Note that Patent Documents 3 and 4 do not contain any descriptions regarding the physical properties of positive electrode cores. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2013 / 018161 [Patent Document 2] International Publication No. 2013 / 018162 [Patent Document 3] International Publication No. 2008 / 132987 [Patent Document 4] Japanese Patent Publication No. 2012-151106 [Overview of the project] [Problems that the invention aims to solve]

[0006] As mentioned above, conventional non-aqueous electrolyte secondary batteries are designed so that the negative electrode is slightly larger than the positive electrode, preventing the formation of a non-opposing region of the positive electrode mixture layer even when the positive electrode expands during charging and discharging. However, designing the negative electrode to have a margin of error relative to the positive electrode is undesirable when considering increasing the battery capacity. Conventionally, no consideration was given to the amount of expansion of the negative and positive electrodes during charging and discharging, making it difficult to increase the capacity of non-aqueous electrolyte secondary batteries by reducing the size difference between the positive and negative electrodes.

[0007] The purpose of this disclosure is to provide a non-aqueous electrolyte secondary battery that can more reliably suppress the occurrence of a non-opposing region of the negative electrode in the positive electrode mixture layer, even when the difference in size between the positive electrode and the negative electrode is reduced. [Means for solving the problem]

[0008] The non-aqueous electrolyte secondary battery according to this disclosure is a non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode core and a positive electrode mixture layer provided on the positive electrode core, and a negative electrode having a negative electrode core and a negative electrode mixture layer provided on the negative electrode core, characterized in that the 0.2% proof strength of the positive electrode core is greater than the 0.2% proof strength of the negative electrode core. [Effects of the Invention]

[0009] According to the non-aqueous electrolyte secondary battery of this disclosure, even when the electrode plates elongate due to charging and discharging, the occurrence of a non-opposing region of the negative electrode in the positive electrode mixture layer can be suppressed more reliably. Therefore, for example, the size difference between the positive electrode and the negative electrode can be reduced, that is, the positive electrode can be made larger, and the battery capacity can be increased. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. [Modes for carrying out the invention]

[0011] The inventors of this invention conducted diligent studies to solve the above problems and found that the core strength of the electrode plate, particularly the yield stress of the core, greatly affects the elongation of the electrode plate during charging and discharging of the battery. When tensile stress is applied to the electrode plate core, in the region where the strain is small, the stress and strain are proportional, and when the load is removed, the core returns to its original size. This region, where the core returns to its original size when the load is removed, is called the elastic region. When stress is applied to the core, beyond a certain point, the core no longer returns to its original size even when the load is removed. This region is called the plastic region, and in the plastic region, the proportional relationship between stress and strain does not hold. The point at which the elastic region changes to the plastic region is called the yield point, and the stress at the yield point is called the yield stress. In conventional batteries, the elastic region of the positive electrode core is smaller than the elastic region of the negative electrode core.

[0012] Repeated charging and discharging of a battery increases the expansion rate of the negative electrode mixture layer. As a result, the pressure load on the electrode plate gradually increases, and the deformation of the electrode plate eventually exceeds the elastic region and reaches the plastic region. In that case, even when the pressure load is released by discharge, the electrode plate will not return to its original length. That is, as charging and discharging occur, the amount of plastic deformation of the positive electrode becomes larger than that of the negative electrode, and the amount of elongation of the positive electrode becomes larger than that of the negative electrode. As a result, there is a possibility that a region of the positive electrode mixture layer that does not face the negative electrode will occur. This disclosure is based on the inventors' findings as described above.

[0013] According to the non-aqueous electrolyte secondary battery of the present disclosure, by making the 0.2% proof stress of the positive electrode core greater than the 0.2% proof stress of the negative electrode core, even when charge and discharge are repeated, generation of the non-negative electrode facing region of the positive electrode mixture layer at the end of the positive electrode can be more reliably suppressed. In this case, the difference in the amount of plastic deformation accumulated in the positive electrode and the negative electrode can be reduced, or the amount of plastic deformation of the positive electrode can be made smaller than that of the negative electrode, and the generation of the non-negative electrode facing region is highly suppressed. Note that since the yield point may not clearly appear depending on the material, the 0.2% proof stress is used instead of the yield point in the present disclosure.

[0014] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. Note that selectively combining a plurality of embodiments and modification examples described below is included in the present disclosure.

[0015] Hereinafter, a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer can 16 will be exemplified, but the outer package of the battery is not limited to a cylindrical outer can. For example, it may be a rectangular outer can (rectangular battery), a coin-shaped outer can (coin-shaped battery), or an outer package (laminated battery) composed of a laminated sheet including a metal layer and a resin layer. Further, the electrode body may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated via a separator.

[0016] FIG. 1 is a diagram schematically showing a cross section of a non-aqueous electrolyte secondary battery 10 which is an example of an embodiment. As shown in FIG. 1, the non-aqueous electrolyte secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an outer can 16 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The outer can 16 is a metal container having a bottomed cylindrical shape with one side in the axial direction open, and the opening of the outer can 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the side of the battery sealing body 17 is taken as the upper side, and the bottom side of the outer can 16 is taken as the lower side.

[0017] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and mixed solvents of two or more of these are used. The non-aqueous solvent may contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen element such as fluorine. As an example of the non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and mixed solvents thereof are mentioned. As the electrolyte salt, for example, lithium salts such as LiPF6 are used. Note that the non-aqueous electrolyte is not limited to a liquid electrolyte and may be a solid electrolyte.

[0018] The positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode body 14 are all strip-shaped elongated bodies, and are alternately laminated in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed with dimensions slightly larger than those of the positive electrode 11 in order to prevent the precipitation of lithium. That is, the negative electrode 12 is formed longer in both the longitudinal direction and the width direction (short side direction) than the positive electrode 11. The separator 13 is formed with dimensions at least slightly larger than those of the positive electrode 11, and two sheets are arranged so as to sandwich the positive electrode 11. The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0019] Although it will be described in detail later, in the non-aqueous electrolyte secondary battery 10, by making the 0.2% proof stress of the positive electrode core 30 larger than the 0.2% proof stress of the negative electrode core 40, the amount of plastic deformation of the positive electrode 11 accompanying charge and discharge can be made smaller than the amount of plastic deformation of the negative electrode 12. For this reason, although it is preferable that the negative electrode 12 is larger than the positive electrode 11, compared with conventional batteries, the difference in size between the positive electrode 11 and the negative electrode 12 can be reduced, and a higher capacity of the non-aqueous electrolyte secondary battery 10 can be achieved using a larger positive electrode 11.

[0020] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends outside the insulating plate 19 towards the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative electrode terminal.

[0021] As described above, the outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction. A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery and insulation between the outer casing 16 and the sealing body 17. The outer casing 16 has a grooved portion 22 formed on its side, which protrudes inward to support the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the grooved portion 22 and the open end of the outer casing 16 which is crimped to the sealing body 17.

[0022] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheries. When a malfunction occurs in the battery and the internal pressure rises, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0023] The following describes in detail the positive electrode 11, negative electrode 12, and separator 13 that constitute the non-aqueous electrolyte secondary battery 10, with particular attention paid to the cores that make up the positive electrode 11 and the negative electrode 12.

[0024] [Positive electrode] The positive electrode 11 comprises a positive electrode core 30 and a positive electrode mixture layer 31 provided on the surface of the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable within the potential range of the positive electrode 11, a film with the metal arranged on its surface, or the like. The thickness of the positive electrode core 30 is, for example, 5 μm to 35 μm, or 10 μm to 20 μm. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both sides of the positive electrode core 30, excluding the core exposed portion where the positive electrode lead is connected. The thickness of the positive electrode mixture layer 31 on one side of the positive electrode core 30 is, for example, 50 μm to 150 μm. The positive electrode 11 can be manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder to the surface of the positive electrode core 30, drying the coating, and then compressing it to form a positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0025] Lithium transition metal composite oxides are used as the positive electrode active material. Elements other than Li that may be included in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, Si, and P. A suitable example of a lithium transition metal composite oxide is one containing at least one element selected from Ni, Co, and Mn. Specific examples include lithium transition metal composite oxides containing Ni, Co, and Mn, and lithium transition metal composite oxides containing Ni, Co, and Al.

[0026] Examples of conductive agents included in the positive electrode mixture layer 31 include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of binders included in the positive electrode mixture layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. The positive electrode mixture layer 31 may further contain cellulose derivatives such as carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0027] From the viewpoint of current collection performance, processability, and material cost, it is preferable to use aluminum alloy foil for the positive electrode core 30. The aluminum alloy foil applied to the positive electrode core 30 mainly consists of aluminum and contains at least one metal selected from, for example, iron, manganese, copper, magnesium, zinc, zirconium, silicon, chromium, titanium, and nickel. An example of the aluminum content is 90-99.9% by mass or 95-99.5% by mass. The aluminum alloy foil preferably contains at least iron, for example, 1-3% by mass of iron. The physical properties of the positive electrode core 30, such as the 0.2% proof stress, can be controlled by adjusting the composition of the aluminum alloy, specifically the type and amount of additive elements such as iron. Generally, the more iron and other elements added, the higher the 0.2% proof stress of the alloy foil.

[0028] The 0.2% yield strength of the positive electrode core 30 must be greater than that of the negative electrode core 40. In this case, the amount of plastic deformation of the positive electrode 11 and the negative electrode 12 during charging and discharging can be kept at roughly the same level, or the amount of plastic deformation of the positive electrode 11 can be made smaller than that of the negative electrode 12, thereby more reliably suppressing the occurrence of a negative electrode non-facing region in the positive electrode composite layer 31 that does not face the composite layer of the negative electrode 12. The 0.2% yield strength of the core is determined from the stress-strain curve (SS curve) obtained by a tensile test of the core. Specifically, using the 0.2% strain point of the SS curve as a reference, when a straight line parallel to the slope of the rising edge of the SS curve is drawn from that reference point, the intersection of that straight line and the SS curve becomes the 0.2% yield strength point. The SS curve of the core is measured in accordance with JIS C5016-1994.

[0029] The 0.2% proof stress (hereinafter referred to as "0.2% proof stress P") of the positive electrode core 30 should be greater than the 0.2% proof stress of the negative electrode core 40, but preferably it is 1.05 times or more the 0.2% proof stress of the negative electrode core 40 (hereinafter referred to as "0.2% proof stress N"). In this case, it becomes even easier to suppress the occurrence of a negative electrode non-facing region in the positive electrode mixture layer 31. The upper limit of the ratio of 0.2% proof stress P to 0.2% proof stress N is not particularly limited, but if the strength of the positive electrode core 30 is increased too much, problems such as core fracture may occur, so it is preferably 1.3 times or 1.2 times. An example of a suitable ratio range is 1.05 to 1.20 or 1.05 to 1.10.

[0030] The 0.2% yield strength P is, for example, 120-250 N / mm². 2 , or 150~200 N / mm 2 Therefore, if the 0.2% proof stress P is within this range, it becomes easier to suppress the occurrence of a non-opposing region of the negative electrode in the positive electrode mixture layer 31 while preventing defects such as core fracture. However, in suppressing the occurrence of a non-opposing region of the negative electrode, the relationship between the 0.2% proof stress P and the 0.2% proof stress N is important, and if the relationship 0.2% proof stress P > 0.2% proof stress N is satisfied, then the 0.2% proof stress P is 120 N / mm 2 The following may also apply. The elongation at break of the positive electrode core 30 is, for example, 1-5% or 2-4%.

[0031] The 0.2% yield strength P can be adjusted by the composition of the metal foil constituting the positive electrode core 30, as described above. Furthermore, the 0.2% yield strength P can also be adjusted by changing the conditions of the heat treatment, rolling, and alloying treatments of the positive electrode core 30. For example, in a positive electrode core 30 made of aluminum alloy foil, the lower the heat treatment temperature, the higher the 0.2% yield strength P tends to be. The heat treatment can be performed, for example, using a roll press at a temperature of 200°C or lower. The heat treatment of the positive electrode core 30 may be performed before the positive electrode mixture layer 31 is formed, or it may be performed in the state of the positive electrode 11 with the positive electrode mixture layer 31 formed.

[0032] [Negative electrode] The negative electrode 12 comprises a negative electrode core 40 and a negative electrode mixture layer 41 provided on the surface of the negative electrode core 40. The negative electrode core 40 can be made of a metal foil that is stable within the potential range of the negative electrode 12, a film with the metal arranged on its surface, or the like. The thickness of the negative electrode core 40 is, for example, 3 μm to 20 μm, or 5 μm to 15 μm. The negative electrode mixture layer 41 contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core 40, excluding the core exposed portion where the negative electrode lead is connected. The thickness of the negative electrode mixture layer 41 on one side of the negative electrode core 40 is, for example, 50 μm to 150 μm. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core 40, drying the coating, and then compressing it to form a negative electrode mixture layer 41 on both sides of the negative electrode core 40.

[0033] The negative electrode active material is a material that reversibly intercepts and releases lithium ions, such as a carbon-based active material. Suitable carbon-based active materials include natural graphite such as flake graphite, lumpy graphite, and clay graphite, as well as artificial graphite such as lumpy artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). The negative electrode active material may also contain at least one of an element that alloys with Li, such as Si or Sn, and a compound containing such an element, and carbon-based active materials and such active materials may be used in combination. For example, carbon-based active materials and Si-based active materials are used in combination as negative electrode active materials. An example of a suitable Si-based active material is a compound in which Si fine particles are dispersed in a silicon oxide phase or a silicate phase such as lithium silicate.

[0034] The binder in the negative electrode mixture layer 41 may be fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., as in the case of the positive electrode 11, but styrene-butadiene rubber (SBR) is preferred. The negative electrode mixture layer 41 may further contain CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. Among these, the combination of SBR and CMC or its salt is preferred. A conductive agent may also be added to the negative electrode mixture layer 41.

[0035] From the viewpoint of strength, current collection performance, processability, and material cost, it is preferable to use copper foil for the negative electrode core 40. The copper foil applied to the negative electrode core 40 may be either rolled copper foil produced by hot rolling of a high-purity ingot, or electrolytic copper foil produced by electroplating. Electrolytic copper foil is manufactured by controlling the grain size by adjusting the type, concentration, and deposition rate of additives. Generally, the larger the grain size of the copper foil, the lower the strength of the copper foil, and the smaller the grain size, the higher the strength of the copper foil. The grain size of the copper foil can be confirmed by scanning electron microscope (SEM).

[0036] The 0.2% proof stress N of the negative electrode core 40 must be smaller than the 0.2% proof stress P of the positive electrode core 30. As described above, by setting 0.2% proof stress N < 0.2% proof stress P, it becomes possible to suppress the occurrence of a non-opposing region of the negative electrode in the positive electrode mixture layer 31, even when the size difference between the positive electrode 11 and the negative electrode 12 is small. The 0.2% proof stress N is, for example, 150 N / mm 2 However, if the condition 0.2% yield strength N < 0.2% yield strength P is met, then 150 N / mm 2 It can be larger.

[0037] The 0.2% proof stress N can be adjusted by appropriately changing the composition, heat treatment, rolling treatment, alloying treatment, and other conditions of the metal foil constituting the negative electrode core 40. For example, in a negative electrode core 40 made of copper foil, the 0.2% proof stress N can be increased by adjusting the grain size to an appropriate range through heat treatment. Furthermore, the 0.2% proof stress N can be increased by adding iron, nickel, chromium, phosphorus, etc., to the negative electrode core 40.

[0038] [Separator] For the separator 13, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, a non-woven fabric, etc. As the material of the separator 13, polyolefins such as polyethylene, polypropylene, and copolymers of ethylene and α-olefin, cellulose, etc. are suitable. The separator 13 may have either a single-layer structure or a laminated structure. On the surface of the separator 13, a heat-resistant layer containing inorganic particles, a heat-resistant layer composed of a resin with high heat resistance such as an aramid resin, a polyimide, or a polyamide-imide may be formed.

Example

[0039] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0040] <Example 1> [Fabrication of the positive electrode] As the positive electrode core, an aluminum alloy foil with a thickness of 15 μm was used. The composition of the aluminum alloy was determined so as to have a predetermined 0.2% proof stress and elongation rate, and the alloy foil was heat-treated. A test piece of 12.5 mm × 63 mm was cut out from the positive electrode core and subjected to a tensile test using a precision universal testing machine AG-I / 50N-10kN manufactured by Shimadzu Corporation. The test conditions conformed to JIS C5016-1994. When the 0.2% proof stress and the elongation at break of the positive electrode core were specified from the obtained SS curve, they were 152 N / mm 2 , 3%, respectively.

[0041] As the positive electrode active material, LiNi 0.88 Co 0.09 Al 0.03A composite oxide represented by O2 was used. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 100:1:0.9, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode slurry. This positive electrode slurry was applied to both sides of the positive electrode core, and after the coating film was dried, it was compressed using a roller to produce a positive electrode in which a positive electrode slurry layer was formed on both sides of the positive electrode core. A core exposure area without slurry coating was formed in the longitudinal center of the positive electrode, and an aluminum positive electrode lead was ultrasonically welded to this exposed area.

[0042] [Fabrication of the negative electrode] As a negative electrode core, the 0.2% yield strength is 141 N / mm². 2 A copper foil with a thickness of 8 μm and an elongation at break of 4% was used. The 0.2% yield strength and elongation at break of the negative electrode core were determined by the same tensile test as for the positive electrode core.

[0043] Graphite was used as the negative electrode active material. The negative electrode active material, styrene-butadiene rubber (SBR) dispersion, and carboxymethylcellulose (CMC) were mixed in a solid content mass ratio of 100:1:1, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both sides of the negative electrode core, and after the coating film was dried, it was compressed using a roller to produce a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core. A core exposure area without slurry coating was formed at one end in the longitudinal direction of the negative electrode, and a nickel negative electrode lead was ultrasonically welded to this exposed area.

[0044] [Preparation of non-aqueous electrolyte solution] A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:3:4 (at 25°C).

[0045] [Fabrication of non-aqueous electrolyte secondary batteries] The fabricated positive and negative electrodes were wound in a spiral pattern via a separator, and a winding stopper tape was applied to create a wound electrode body. At this time, the negative electrode was wound so that the negative electrode lead was located on the outer circumference of the electrode body. For the separator, a heat-resistant layer containing polyamide and alumina fillers was formed on one side of a polyethylene microporous membrane. The electrode body was housed in a bottomed cylindrical outer container with an outer diameter of 21 mm and a height of 70 mm, and after injecting the prepared non-aqueous electrolyte, the opening of the outer container was sealed with a gasket and a sealing body to create a non-aqueous electrolyte secondary battery.

[0046] <Comparative Example 1> A 15 μm thick aluminum alloy foil was used as the positive electrode core. The heat treatment of the alloy foil was performed at a higher temperature than in Example 1, resulting in a 0.2% yield strength of 41 N / mm². 2 Except for the change made, the positive electrode core was prepared in the same manner as in Example 1, and the positive electrode and non-aqueous electrolyte secondary battery were fabricated.

[0047] For each battery in the examples and comparative examples, charging and discharging were repeated under the following conditions, and the elongation rate of the electrode plates was determined after 200 cycles and 500 cycles. The evaluation results, along with the 0.2% yield strength of the electrode core, are shown in Table 1.

[0048] [Cycle Test] Each battery was charged with a constant current of 0.5C until the battery voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the charging current was reduced to 0.05C. Next, the batteries were discharged with a constant current of 0.5C until the battery voltage reached 3.0V. This charge-discharge cycle was considered one cycle, and 500 charge-discharge cycles were performed.

[0049] [Measurement of growth rate] X-ray CT scans of each battery were performed using a Shimadzu inspeXio SMX-255CT FPD HR at the 1st, 200th, and 500th cycles of the above charge-discharge process. Using Media Cybernetics' Image-Pro Analyser software, the elongation rate of the electrode plates after 200 and 500 cycles was measured from the X-ray CT images of each battery, using the electrode plate length at the 1st cycle as a reference.

[0050] [Table 1]

[0051] As shown in Table 1, in the example battery, the elongation rates of the positive and negative electrodes were approximately the same. In contrast, in the comparative example battery, the elongation rate of the positive electrode was greater than that of the negative electrode, and the difference in elongation rates became more pronounced as the number of cycles increased. In other words, by making the 0.2% proof strength of the positive electrode core greater than that of the negative electrode core, it is possible to maintain a similar difference in elongation rates between the positive and negative electrodes even after repeated charging and discharging. Alternatively, it is also possible to make the elongation rate of the positive electrode smaller than that of the negative electrode.

[0052] In the battery of the example, since the elongation rates of the positive electrode and the negative electrode are similar, even if the difference in size between the positive electrode and the negative electrode is smaller than that of a conventional battery like the comparative example, the occurrence of a non-opposing region of the negative electrode in the positive electrode mixture layer at the edge of the positive electrode can be more reliably suppressed. In other words, the battery of the example can use a larger positive electrode than the battery of the comparative example, making it possible to increase capacity. [Explanation of Symbols]

[0053] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 18,19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating material, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core body, 31 Positive electrode mixture layer, 40 Negative electrode core body, 41 Negative electrode mixture layer

Claims

1. A positive electrode having a positive electrode core and a positive electrode mixture layer provided on the positive electrode core, A negative electrode having a negative electrode core and a negative electrode mixture layer provided on the negative electrode core, A non-aqueous electrolyte secondary battery comprising, The 0.2% proof stress of the positive electrode core is greater than the 0.2% proof stress of the negative electrode core. The 0.2% proof stress of the positive electrode core is 1.05 to 1.3 times that of the negative electrode core. A non-aqueous electrolyte secondary battery in which the elongation at break of the positive electrode core is 1% to 5%.

2. The 0.2% yield strength of the positive electrode core is 150 to 200 M / mm ２ The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode core has a yield strength of 1.1 times or less than that of the negative electrode core.

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