Positive electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Abstract

This positive electrode for a nonaqueous electrolyte secondary battery has: a positive electrode current collector; and a positive electrode mixture layer disposed on the surface of the positive electrode current collector. The positive electrode current collector is a metal foil containing Al. A positive electrode lead is connected to the positive electrode current collector in a positive electrode current collector exposed section where the positive electrode current collector is exposed. The surface of the positive electrode current collector has a first region, in which the positive electrode lead is connected to the positive electrode current collector, and a second region, in which the positive electrode mixture layer is disposed. In an X-ray diffraction measurement of the positive electrode current collector, a half-value width W1 of a peak near a diffraction angle of 45° by Al obtained from the first region and a half-value width W2 of a peak near a diffraction angle of 45° by Al obtained from the second region satisfy the relationship 0.3 ≤ W2 / W1 ≤ 5. An average aspect ratio A1 of the metal particles in the first region and an average aspect ratio A2 of the metal particles in the second region satisfy the relationship A2 / A1 > 1.0.

Description

Positive electrode for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a positive electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery, and more particularly to a positive electrode for a nonaqueous electrolyte secondary battery in which a current collector is a metal foil containing Al, and a nonaqueous electrolyte secondary battery including this positive electrode.

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been widely used for various applications such as vehicle applications and power storage applications, and many studies have been conducted on non-aqueous electrolyte secondary batteries. Patent Document 1 discloses a technology for suppressing wrinkling and breakage of an electrode caused by rolling, in which the tensile strength of a portion of a current collector exposed portion formed at an end of an electrode to which a lead is not connected is set to be smaller than the tensile strength of a portion to which a lead is connected, within a predetermined range.

[0003] Japanese Patent Application Laid-Open No. 2022-75609

[0004] In recent years, non-aqueous electrolyte secondary batteries have become increasingly high-capacity, and the packing density inside the battery has also increased. As a result of extensive research, the inventors have discovered that the expansion of the negative electrode during charging exerts a large pressure on the positive electrode lead, which may cause the positive electrode current collector to break at the outer periphery of the positive electrode lead. In particular, after repeated charge / discharge cycles, the electrode expands, further increasing the pressure on the positive electrode lead. Furthermore, expansion of the positive electrode may cause the size of the positive electrode to exceed that of the negative electrode, potentially rendering the battery unusable. Existing technologies such as those described in Patent Document 1 do not address the adverse effects of breaking the positive electrode current collector at the outer periphery of the positive electrode lead or the expansion of the positive electrode, and therefore there is still room for improvement.

[0005] An object of the present disclosure is to provide a positive electrode for a non-aqueous electrolyte secondary battery that suppresses breakage of the current collector at the outer periphery of the lead while reducing the risk of elongation.

[0006] a positive electrode for a non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure, the positive electrode current collector having a positive electrode current collector exposed portion where the positive electrode current collector is exposed and no positive electrode current collector mixture layer is disposed; the positive electrode current collector being a metal foil containing Al; a positive electrode lead being connected to the positive electrode current collector exposed portion; the positive electrode current collector having a surface including a first region to which the positive electrode lead is connected and a second region in which the positive electrode mixture layer is disposed; and X-ray diffraction measurement of the positive electrode current collector showing that a half width W1 of a peak at a diffraction angle of approximately 45° due to Al obtained from the first region and a half width W2 of a peak at a diffraction angle of approximately 45° due to Al obtained from the second region satisfy a relationship of 0.3≦W2 / W1≦5; and an average aspect ratio A1 of metal particles in the first region and an average aspect ratio A2 of metal particles in the second region satisfy a relationship of A2 / A1>1.0.

[0007] A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure includes the positive electrode for the non-aqueous electrolyte secondary battery described above, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on a surface of the negative electrode current collector, and the negative electrode mixture layer contains graphite and a Si-containing material.

[0008] The positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure can reduce the risk of elongation while suppressing breakage of the current collector at the outer periphery of the lead.

[0009] 1 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, taken along line AA in FIG.

[0010] Due to the recent trend toward higher capacity, the packing density inside nonaqueous electrolyte secondary batteries has increased, and the pressure applied to the components inside the battery has also increased. Furthermore, after repeated charge / discharge cycles, the electrodes expand, further increasing the pressure applied to the positive electrode lead. The inventors have discovered that the application of large pressure to the positive electrode lead may cause the positive electrode current collector to break at the outer periphery of the positive electrode lead. Furthermore, if the positive electrode expands beyond its initial dimensions as a result of repeated charge / discharge cycles, the size of the positive electrode may exceed the size of the negative electrode, potentially rendering the battery unusable.

[0011] After further investigation, the inventors discovered that a positive electrode current collector made of a metal containing Al can be divided into a first region connected to a positive electrode lead and a second region in which a positive electrode mixture layer is disposed, with the first region made of a material that is resistant to breakage due to pressure and the second region made of a material that is resistant to stretching. By appropriately controlling the size and shape of the metal particles in the first region relative to the size and shape of the metal particles in the second region so that the half-width W1 of the peak at a diffraction angle of approximately 45° due to Al obtained from the first region and the half-width W2 of the peak at a diffraction angle of approximately 45° due to Al obtained from the second region satisfy the relationship 0.3≦W2 / W1≦5, it is possible to suppress fracture of the current collector at the outer periphery of the positive electrode lead while reducing the risk of stretching of the positive electrode.

[0012] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining the respective components of the multiple embodiments and variations described below are included within the scope of the present disclosure.

[0013] In the following, a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical outer can 15 with a bottom is exemplified as a nonaqueous electrolyte secondary battery, but the outer can of the battery is not limited to a cylindrical outer can. The nonaqueous electrolyte secondary battery according to the present disclosure may be, for example, a prismatic battery having a prismatic outer can, a coin battery having a coin-shaped outer can, or a pouch-type battery having an outer can made of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode assembly is not limited to a wound type, and may be a stacked type electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked with separators interposed therebetween.

[0014] FIG. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte, and an outer can 15 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 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 spirally wound with the separator 13 interposed therebetween. The outer can 15 is a cylindrical metal container with a bottom and an open end in the axial direction, and the opening of the outer can 15 is closed by a sealing member 16. Hereinafter, for convenience of explanation, the sealing member 16 side of the battery is referred to as the top, and the bottom side of the outer can 15 is referred to as the bottom.

[0015] The non-aqueous electrolyte has, for example, lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0016] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0017] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0018] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methyl phenyl ether. and chain ethers such as ethyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0019] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiClO ４ , LiBF ４ , LiPF ６ , LiAlCl ４ , LiSbF ６ , LiSCN, LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiB １０ Cl １０ , lower aliphatic lithium carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO ２ F ２Examples of the borate salt include lithium bis(oxalato)borate (LiBOB) and lithium difluoro(oxalato)borate (LiDFFOB). Examples of the imide salt include lithium bisfluorosulfonylimide (LiN(FSO ２ ) ２ ), lithium bistrifluoromethanesulfonyl imide (LiN(CF ３ SO ２ ) ２ ), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), lithium bispentafluoroethanesulfonyl imide (LiN(C ２ F ５ SO ２ ) ２ Among these, LiPF is preferred from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ The concentration of the lithium salt may be, for example, 4 mol or less, or 3 mol or less, preferably 1.8 mol or less, and more preferably 0.8 mol or more and 1.8 mol or less, per 1 L of the non-aqueous solvent.

[0020] The non-aqueous electrolyte may contain an additive such as an unsaturated carbonate ester, an acid anhydride, a phenol compound, a benzene compound, a nitrile compound, an isocyanate compound, a sultone compound, a sulfate compound, a borate ester compound, a phosphate ester compound, or a phosphite ester compound.

[0021] Examples of unsaturated cyclic carbonates include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. One type of unsaturated cyclic carbonate may be used alone, or two or more types may be used in combination. Some of the hydrogen atoms in the unsaturated cyclic carbonate may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by intermolecular condensation of multiple carboxylic acid molecules, but is preferably an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0022] Examples of phenolic compounds include phenol, hydroxytoluene, etc. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, cyclohexylbenzene (CHB), etc.

[0023] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanatomethylcyclohexane (BIMCH). Examples of sultone compounds include propane sultone and propene sultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethyl borate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethyl phosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethyl phosphite and tris(trimethylsilyl)phosphite.

[0024] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0025] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode assembly 14 are all strip-shaped, elongated bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in both the length and width directions than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and, for example, two sheets are arranged to sandwich the positive electrode 11. The separator 13 is, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, nonwoven fabrics, etc. Suitable separator materials include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may also be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Alternatively, the separator may be a multilayer separator including a polyethylene layer and a polypropylene layer, or one in which a material such as aramid resin or ceramic is applied to the surface of the separator 13. The electrode body 14 has a positive electrode lead 19 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 20 connected to the negative electrode 12 by welding or the like.

[0026] Insulating plates 17 and 18 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 19 passes through a through-hole in the insulating plate 17 and extends toward the sealing body 16, and the negative electrode lead 20 passes outside the insulating plate 18 and extends toward the bottom side of the outer can 15. The positive electrode lead 19 is connected to the underside of a filter 22 in the sealing body 16 by welding or the like, and a cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. The negative electrode lead 20 is connected to the inner bottom surface of the outer can 15 by welding or the like, and the outer can 15 serves as the negative electrode terminal.

[0027] A gasket 27 is provided between the exterior can 15 and the sealing body 16 to ensure airtightness inside the battery. The exterior can 15 has a grooved portion 21 formed on its side surface that protrudes inward and supports the sealing body 16. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior can 15, and supports the sealing body 16 on its top surface. The sealing body 16 is fixed to the top of the exterior can 15 by the grooved portion 21 and the open end of the exterior can 15 that is crimped to the sealing body 16.

[0028] The sealing body 16 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 23 deforms and breaks, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. When the internal pressure further increases, the upper valve body 25 breaks, and gas is discharged from the opening of the cap 26.

[0029] 2 and 3, the positive electrode 11 and the negative electrode 12 that constitute the nonaqueous electrolyte secondary battery 10 will be described in detail, particularly the positive electrode 11. Fig. 2 is a front view showing the positive electrode and the negative electrode that constitute the electrode assembly according to one example of the embodiment in a developed state. Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2.

[0030] [Positive Electrode] The positive electrode 11 has a positive electrode current collector 30 and a positive electrode mixture layer 32 disposed on the surface of the positive electrode current collector 30. The positive electrode mixture layer 32 is preferably disposed on both sides of the positive electrode current collector 30. The positive electrode current collector 30 is a metal foil containing Al, such as Al or an Al alloy. The positive electrode current collector 30 is composed of a plurality of grain boundaries, and each region partitioned by the grain boundaries is defined as a metal particle. The thickness of the positive electrode current collector 30 is, for example, 10 μm or more and 30 μm or less.

[0031] The positive electrode mixture layer 32 includes, for example, a positive electrode active material, a conductive agent, and a binder. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm to 150 μm on one side of the positive electrode current collector 30. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry including a positive electrode active material, a conductive agent, a binder, etc. to the surface of the positive electrode current collector 30, drying the coating, and then rolling the coating to form the positive electrode mixture layer 32 on both sides of the positive electrode current collector 30.

[0032] The positive electrode active material is composed, for example, of a lithium transition metal composite oxide as a main component. Elements other than Li contained 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. An example of a suitable lithium transition metal composite oxide is a composite oxide containing at least one of Ni, Co, and Mn. Specific examples include a lithium transition metal composite oxide containing Ni, Co, and Mn, and a lithium transition metal composite oxide containing Ni, Co, and Al.

[0033] The lithium transition metal composite oxide contains, for example, secondary particles formed by aggregation of primary particles. The particle size of the primary particles is, for example, 0.02 μm or more and 2 μm or less. The particle size of the primary particles is measured as the diameter of the circumscribed circle in a particle image observed with a scanning electron microscope (SEM). The average particle size of the secondary particles is, for example, 2 μm or more and 30 μm or less. Here, the average particle size refers to the volume-based median diameter (D50). D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the secondary particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0034] The particle fracture strength of the positive electrode active material is, for example, 100 MPa or more. In this case, when pressure is applied to the positive electrode, the positive electrode active material particles absorb the pressure, reducing the load on the positive electrode current collector 30. This makes the effect of the present disclosure of suppressing breakage of the current collector at the outer periphery of the lead while reducing the risk of elongation more pronounced. The particle fracture strength can be calculated using a microcompression tester (e.g., MCT-211 manufactured by Shimadzu Corporation). A load is applied to one positive electrode active material particle using a flat upper pressure indenter with a tip of φ50 μm at a loading rate of 2.7 mN / sec, and the fracture load at which the positive electrode active material fractures is measured. The fracture load is measured for 10 lithium transition metal composite oxide particles in the same manner, and the average value is taken as the particle fracture strength.

[0035] Examples of conductive agents contained in the positive electrode mixture layer 32 include carbon black (CB) such as acetylene black (AB) and ketjen black, carbon nanotubes (CNT), graphene, graphite, and other carbon-based particles. These may be used alone or in combination of two or more. Examples of binders contained in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide-based resins, acrylic resins, polyolefin-based resins, and polyacrylonitrile (PAN). These may be used alone or in combination of two or more.

[0036] A positive electrode current collector exposed portion 34, which is an exposed portion of the positive electrode current collector 30, is disposed on the surface of the positive electrode 11, and a positive electrode lead 19 is connected to the positive electrode current collector exposed portion 34. The positive electrode current collector exposed portion 34 is a portion of the surface of the positive electrode current collector 30 that is not covered with the positive electrode mixture layer 32. For example, the positive electrode current collector exposed portion 34 is provided by intermittent application of a positive electrode mixture slurry to a portion of the positive electrode current collector 30. The positive electrode current collector exposed portion 34 is preferably provided on both sides of the positive electrode 11 so as to overlap in the thickness direction of the positive electrode 11. The positive electrode lead 19 is joined to the positive electrode current collector exposed portion 34 by, for example, ultrasonic welding. In this specification, the outer periphery of the positive electrode lead 19 refers to the end portion of the positive electrode lead 19 located on the positive electrode current collector 30. In the example shown in FIG. 2 , this refers to ends 19a and 19b along the short direction of the positive electrode 11 and end 19c along the long direction of the positive electrode 11.

[0037] In the example shown in Fig. 2, a positive electrode current collector exposed portion 34 is provided at approximately the center in the longitudinal direction of the positive electrode 11, over the entire length in the lateral direction. Although the position of the positive electrode current collector exposed portion 34 is not limited to this example, from the viewpoint of current collection performance, the positive electrode current collector exposed portion 34 is preferably provided at a position approximately equidistant from the winding start end and the winding end end of the positive electrode. Note that the form of the positive electrode current collector exposed portion 34 is not limited to the example shown in Fig. 2. For example, the positive electrode current collector exposed portion 34 may be arranged so as to contact only one end in the lateral direction of the positive electrode 11, or a plurality of positive electrode current collector exposed portions 34 may be arranged on the surface of the positive electrode 11, and a positive electrode lead 19 may be connected to each of the plurality of positive electrode current collector exposed portions 34.

[0038] As shown in FIG. 3 , the surface of the positive electrode current collector 30 includes a first region 50 to which the positive electrode lead 19 is connected and a second region 52 in which the positive electrode mixture layer 32 is disposed. In X-ray diffraction measurement of the positive electrode current collector 30, the half-width W1 of the peak at a diffraction angle of approximately 45° due to Al obtained from the first region 50 and the half-width W2 of the peak at a diffraction angle of approximately 45° due to Al obtained from the second region 52 satisfy the relationship 0.3≦W2 / W1≦5. In the X-ray diffraction measurement, a diffraction line of the (200) plane of Al appears near a diffraction angle of 45°. When W2 and W1 satisfy the above relationship in this diffraction line, fracture of the current collector at the outer periphery of the positive electrode lead 19 can be suppressed while reducing the risk of elongation of the positive electrode. It is preferable that W1 and W2 satisfy the relationship 1.7≦W2 / W1≦3.1.

[0039] 3 , a third region 54 is present between the first region 50 and the second region 52. The half-width W3 of the peak at a diffraction angle of about 45° due to Al obtained from the third region 54 may be substantially the same as the half-width W1 in the first region 50 or may be substantially the same as the half-width W2 in the second region 52. Furthermore, the half-width W3 may be different from the half-width W1 and the half-width W2.

[0040] X-ray diffraction measurement of the first region 50 is performed, for example, near the portion where the positive electrode lead 19 is connected. X-ray diffraction measurement of the second region 52 is performed, for example, near the center of the portion where the positive electrode mixture layer 32 is present. In the example shown in FIG. 3 , the positive electrode mixture layer 32 is present on both the winding start end side and the winding end side adjacent to the positive electrode current collector exposed portion 34, so the half-width is measured for each of these two regions, and the average value of these measurements is defined as the half-width W2 in the second region 52. The average aspect ratio and tensile strength, which will be described later, are also measured in the same manner.

[0041] X-ray diffraction measurement can be performed using, for example, an X-ray diffractometer (manufactured by Rigaku Corporation, trade name "RINT-TTR", radiation source Cu-Kα) under the following measurement conditions: Measurement range: 15-90°, Scan rate: 7° / min, Analysis range: 15-90°

[0042] The method for producing the first region and the second region that satisfy the above relationship is not particularly limited. For example, the first region and the second region may be produced by using a positive electrode current collector with small metal particles and heating the area near the connection of the positive electrode lead 19 to make the metal particles larger. Alternatively, the first region and the second region may be produced by using a positive electrode current collector with large metal particles and applying pressure to the area where the positive electrode mixture layer is formed to make the metal particles smaller.

[0043] The average aspect ratio A1 of the metal particles in the first region 50 and the average aspect ratio A2 of the metal particles in the second region 52 may, for example, satisfy the relationship A2 / A1 > 1.0, or may satisfy the relationship 1.0 < A2 / A1 ≦ 3.0. The aspect ratio of the metal particles can be calculated from images of the metal particles obtained using a scanning electron microscope (SEM). Observation using the SEM is performed, for example, under conditions of an acceleration voltage of 3 kV and a magnification of 3000x, by obtaining backscattered electron images. Using the SEM image, the aspect ratio of each of 10 metal particles is obtained by dividing the length of the major axis by the length of the minor axis in the direction perpendicular to the major axis, and these are averaged to calculate the average aspect ratio of the metal particles. Note that metal particles are defined as particles with a minor axis of 1 μm or more in images obtained by SEM.

[0044] The tensile strength of the positive electrode current collector 30 in the first region 50 is, for example, 5.0 kgf or more and 14.5 kgf or less, and may be 5.0 kgf or more and 12.0 kgf or less. The tensile strength is measured, for example, using a universal testing machine (SDMK-1000-D), by cutting a test piece of a predetermined size from the first region 50 and testing it at 20 mm / min. The tensile strength is calculated using the following formula: Tensile strength = Maximum point test force / (Test piece thickness × Test piece width)

[0045] [Negative Electrode] The negative electrode 12 has, for example, a negative electrode current collector 40 and a negative electrode mixture layer 42 disposed on the surface of the negative electrode current collector 40. The negative electrode mixture layer 42 is preferably disposed on both sides of the negative electrode current collector 40. For example, a foil of a metal such as copper, or a film having such a metal disposed on its surface layer, is used for the negative electrode current collector 40. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less.

[0046] The anode mixture layer 42 includes, for example, a anode active material and a binder. The thickness of the anode mixture layer 42 is, for example, 10 μm to 150 μm on one side of the anode current collector 40. The anode 12 can be produced, for example, by applying an anode mixture slurry including the anode active material, the binder, and the like to the surface of the anode current collector 40, drying the coating, and then rolling the coating to form the anode mixture layer 42 on both sides of the anode current collector 40.

[0047] The negative electrode active material includes, for example, graphite and a Si-containing material. The graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. The Si-containing material can occlude more lithium ions per unit mass than carbon materials such as graphite. Therefore, using a Si-containing material as the negative electrode active material can achieve a high battery capacity. The content of the Si-containing material in the negative electrode mixture layer 42 may be 6% by mass or more relative to the total mass of the graphite and the Si-containing material. The upper limit of the content of the Si-containing material in the negative electrode mixture layer 42 is, for example, 30% by mass.

[0048] The Si-containing material contained in the negative electrode mixture layer may be any material containing Si, and examples thereof include Si alloys, Si compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The volume-based median diameter (D50) of the composite material is generally smaller than the volume-based median diameter (D50) of the carbon material. The volume-based median diameter (D50) of the composite material is, for example, 1 μm or more and 15 μm or less. Note that one type of Si-containing material may be used alone, or two or more types may be used in combination.

[0049] A suitable Si-containing material is a composite particle containing an ion-conducting phase and a silicon phase dispersed in the ion-conducting phase. The silicon phase is formed by dispersing Si in the form of fine particles. The composite particle may also have a conductive layer covering a portion of the surface of the ion-conducting phase. The conductive layer is made of a material with higher conductivity than the ion-conducting phase and forms a good conductive path in the negative electrode mixture layer. The conductive layer contains, for example, conductive carbon and covers 30% to 70% of the surface area of ​​the ion-conducting phase. The coverage of the conductive layer can be calculated, for example, using X-ray photoelectron spectroscopy (XPS).

[0050] The ion-conducting phase is a continuous phase composed of an aggregate of particles finer than the silicon phase. The ion-conducting phase is, for example, at least one selected from the group consisting of a silicate phase, a carbon phase, a silicide phase, and a silicon oxide phase. The silicide phase is a phase of a compound consisting of Si and an element more electropositive than Si, such as NiSi, Mg ２ Si, TiSi ２ Examples include:

[0051] The silicate phase preferably contains at least one element selected from lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, and radium, for example, from the viewpoint of high lithium ion conductivity, etc. Among these, a silicate phase containing lithium (hereinafter sometimes referred to as a lithium silicate phase) is preferred, for example, from the viewpoint of high lithium ion conductivity, etc.

[0052] The lithium silicate phase can be, for example, a compound of the formula: Li ２ｚ SiO ２＋ｚ (0<z<2). From the viewpoints of stability, ease of preparation, lithium ion conductivity, and the like, z preferably satisfies the relationship 0<z<1, and more preferably z=1 / 2.

[0053] Another example of a suitable Si-containing material is a material having a sea-island structure in which fine silicon phases are uniformly dispersed in an amorphous silicon oxide phase, and which is generally represented by the general formula SiO ｘ(0<x≦2). The main component of the silicon oxide may be silicon dioxide. The content ratio (x) of O to Si is, for example, 0.5≦x<2.0, preferably 0.8≦x≦1.5.

[0054] Another example of a suitable Si-containing material is composite particles having a sea-island structure in which fine silicon phases are substantially uniformly dispersed in a carbon phase. The carbon phase is preferably an amorphous carbon phase. The carbon phase may contain a crystalline phase component, but preferably contains a larger amount of amorphous phase components. The amorphous carbon phase is, for example, composed of a carbon material having an average interplanar spacing of (002) planes of more than 0.34 nm as measured by X-ray diffraction. The amorphous carbon phase is, for example, composed of amorphous carbon particles. Note that when the Si-containing material is a composite particle having a sea-island structure in which fine silicon phases are substantially uniformly dispersed in a carbon phase, the total mass of Si contained in the Si-containing material may be equal to the mass of the silicon phase.

[0055] The mass ratio of the silicon phase to the total mass of the Si-containing material is preferably 30% by mass or more. In this case, the discharge capacity is increased, and the battery is likely to have high output. Furthermore, the mass ratio of the silicon phase to the total mass of the Si-containing material is preferably 60% by mass or less. In this case, the volume change of the negative electrode mixture layer during charge and discharge can be reduced, the expansion and contraction of the electrode body 14 during charge and discharge can be suppressed, and the battery is likely to have excellent durability. Therefore, the mass ratio of the silicon phase to the total mass of the Si-containing material is preferably 30% by mass or more and 60% by mass or less.

[0056] Examples of the binder contained in the negative electrode mixture layer 42 include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH ４ and the like, which may be a partially neutralized salt), polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, and the like, which may be a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0057] In the example shown in FIG. 2 , a negative electrode current collector exposed portion 44, where the negative electrode current collector 40 is exposed, is disposed near the winding end of the surface of the negative electrode 12. The negative electrode current collector exposed portion 44 is a portion of the surface of the negative electrode current collector 40 that is not covered with the negative electrode mixture layer 42, and is provided, for example, by intermittent application of the negative electrode mixture slurry to a portion of the negative electrode current collector 40. A negative electrode lead 20 is connected to the negative electrode current collector exposed portion 44. The negative electrode current collector exposed portions 44 are preferably provided on both sides of the negative electrode 12 so as to overlap in the thickness direction of the negative electrode 12. The negative electrode lead 20 is joined to the negative electrode current collector exposed portion 44 by, for example, ultrasonic welding.

[0058] Hereinafter, the present disclosure will be further described with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0059] Example 1 [Fabrication of Positive Electrode] A positive electrode active material having a particle breaking strength of 180 MPa and a composition formula of LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ A lithium transition metal composite oxide represented by the formula (I) was used. The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were mixed in a solids mass ratio of 95:3:2, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. This positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of 15 μm thick Al foil, and after drying the coating, the coating was rolled using a roller and cut to a predetermined electrode size, resulting in a positive electrode with a positive electrode mixture layer formed on both sides of the positive electrode current collector. An exposed portion where the current collector surface was exposed was located in the longitudinal center of the positive electrode. This exposed portion was locally heated, and then a positive electrode lead was welded to this exposed portion. The W2 / W1 value was 1.7, the A2 / A1 value was 1.6, and the tensile strength of the positive electrode current collector in the first region was 8.3 kgf.

[0060] [Preparation of Negative Electrode] A mixture of graphite and SiC in a mass ratio of 94:6 was used as the negative electrode active material. The negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a solid mass ratio of 100:1:1, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, and the coating was dried. The coating was then rolled using a roller and cut to a predetermined electrode size to obtain a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode current collector. An exposed portion where the current collector surface was exposed was arranged at the longitudinal end of the negative electrode, and a negative electrode lead was welded to this exposed portion.

[0061] [Preparation of non-aqueous electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 20:5:75. Lithium hexafluorophosphate (LiPF ６ ) was dissolved in the solution to a concentration of 1.3 mol / L to prepare a non-aqueous electrolyte (non-aqueous electrolytic solution).

[0062] [Preparation of Test Cell (Non-Aqueous Electrolyte Secondary Battery)] A wound electrode assembly was prepared by spirally winding a positive electrode and a negative electrode with a polyolefin separator interposed therebetween. Insulating plates were placed on the top and bottom of the electrode assembly, and the electrode assembly was housed in an outer can. The negative electrode lead was welded to the bottom of the cylindrical outer can with a bottom, and the positive electrode lead was welded to a sealing member. An electrolyte was poured into the outer can, and the opening of the outer can was sealed with a sealing member via a gasket to prepare a non-aqueous electrolyte secondary battery as a test cell.

[0063] Example 2 In the preparation of the positive electrode, a LiNi alloy having a particle breaking strength of 250 MPa was used as the positive electrode active material. ０．９ Co ０．０５ Mn ０．０５ O ２ A test cell was prepared in the same manner as in Example 1, except that the temperature was changed to 100°C, and the timing of heating the exposed portion was changed so that the exposed portion was heated after the coating film dried and before the coating film was rolled with the rollers.

[0064] <Example 3> In the production of the positive electrode, the positive electrode active material was LiNi０．９ Co ０．０５ Mn ０．０５ O ２ A test cell was fabricated in the same manner as in Example 1, except that the temperature was changed to 100°C and the heating temperature of the exposed portion was increased by 7°C.

[0065] Example 4 In the preparation of the positive electrode, a LiNi alloy having a particle breaking strength of 95 MPa was used as the positive electrode active material. ０．９ Co ０．０５ Mn ０．０５ O ２ A test cell was fabricated in the same manner as in Example 1, except that the temperature was changed to 100°C and the heating temperature of the exposed portion was increased by 3°C.

[0066] <Comparative Example 1> In the production of a positive electrode, a positive electrode active material was used, which was LiNi with a particle breaking strength of 95 MPa. ０．９ Co ０．０５ Mn ０．０５ O ２ A test cell was produced in the same manner as in Example 1, except that the temperature was changed to the temperature at which the exposed portion was heated in Example 1, and that the exposed portion was not heated, but the portion on which the positive electrode mixture layer was formed was heated at the temperature at which the exposed portion was heated in Example 1.

[0067] <Comparative Example 2> In the preparation of the positive electrode, the positive electrode active material was LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ A test cell was fabricated in the same manner as in Example 1, except that the temperature was changed to 10°C and the heating temperature was increased by 10°C.

[0068] Comparative Example 3 A test cell was produced in the same manner as in Example 1, except that in producing the positive electrode, the portion on which the positive electrode mixture layer was formed was heated at the same temperature as in Example 1 to which the exposed portion was heated.

[0069] Comparative Example 4 In the preparation of the positive electrode, the positive electrode active material was LiNi ０．９ Co ０．０５ Mn ０．０５ O ２ A test cell was prepared in the same manner as in Example 1, except that the pressure applied to the coating film during rolling by the roller was increased and the exposed portion was not heated.

[0070] Comparative Example 5 In the preparation of the positive electrode, the positive electrode active material was LiNi having a particle breaking strength of 95 MPa. ０．９ Co ０．０５ Mn ０．０５ O ２ A test cell was produced in the same manner as in Example 1, except that the temperature was changed to the temperature at which the exposed portion was heated in Example 1, and that the portion on which the positive electrode mixture layer was formed was heated at a temperature 5° C. higher than the temperature at which the exposed portion was heated in Example 1 without heating the exposed portion.

[0071] [Cycle Test] The test cells of the examples and comparative examples were charged at a constant current of 0.2 C in a temperature environment of 25° C. until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.02 C. Thereafter, the test cells were discharged at a constant current of 0.2 C until the battery voltage reached 2.5 V. This charge / discharge cycle was counted as one cycle, and 200 cycles were performed.

[0072] [Evaluation of Elongation and Fracture] After the cycle test, the test cell was disassembled and the positive electrode was removed. Regarding elongation, the length of the short side of the positive electrode (the side parallel to the axial direction of the electrode body) was measured, and the amount of elongation was calculated from the length of the short side of the positive electrode before being incorporated into the test cell. An elongation of 1% or less was evaluated as ⊚, 1% or more and 2.5% or less was evaluated as ◯, 2.5% or more and 3.5% or less was evaluated as △, and more than 3.5% was evaluated as ×. Fracture in the outer periphery of the positive electrode lead was visually confirmed. A ◎ was evaluated when there was no fracture, and if there was fracture, a ◯ was evaluated when the length of the fractured portion relative to the total length of the outer periphery was 20% or less, a △ was evaluated when it was more than 20% and 40% or less, and an × was evaluated when it was more than 40%.

[0073] The evaluation results of the test cells of the examples and comparative examples are shown in Table 1. Table 1 also shows the values ​​of W2 / W1, A2 / A1, and the tensile strength of the positive electrode current collector in the first region.

[0074]

[0075] As shown in Table 1, the positive electrodes of the examples had small elongation amounts after charge-discharge cycles and a small percentage of breakages at the outer periphery of the positive electrode lead. On the other hand, the positive electrodes of the comparative examples had large elongation amounts and a large percentage of breakages at the outer periphery of the positive electrode lead. Therefore, by satisfying the relationship of 0.3≦W2 / W1≦5 and by satisfying the relationship A2 / A1>1.0 between the average aspect ratio A1 of the metal particles in the first region and the average aspect ratio A2 of the metal particles in the second region, it is possible to suppress breakage of the current collector at the outer periphery of the positive electrode lead while reducing the risk of elongation of the positive electrode.

[0076] The present disclosure will be further described by the following embodiments. Configuration 1: A positive electrode for a non-aqueous electrolyte secondary battery, comprising a positive electrode current collector and a positive electrode mixture layer disposed on a surface of the positive electrode current collector, wherein the surface of the positive electrode current collector has a positive electrode current collector exposed portion where the positive electrode mixture layer is not disposed and the positive electrode current collector is exposed, the positive electrode current collector is a metal foil containing Al, and a positive electrode lead is connected to the positive electrode current collector exposed portion, and the surface of the positive electrode current collector has a first region to which the positive electrode lead is connected and a second region in which the positive electrode mixture layer is disposed, A positive electrode for a non-aqueous electrolyte secondary battery, wherein, in an X-ray diffraction measurement of the positive electrode current collector, a half-width W1 of a peak at a diffraction angle of about 45° due to Al obtained from the first region and a half-width W2 of a peak at a diffraction angle of about 45° due to Al obtained from the second region satisfy a relationship of 0.3≦W2 / W1≦5, and an average aspect ratio A1 of metal particles in the first region and an average aspect ratio A2 of metal particles in the second region satisfy a relationship of A2 / A1>1.0. Configuration 2: A positive electrode for a non-aqueous electrolyte secondary battery according to Configuration 1, wherein W1 and W2 satisfy a relationship of 1.7≦W2 / W1≦3.1. Configuration 3: A positive electrode for a non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein A1 and A2 satisfy a relationship of 1.0<A2 / A1≦3.0. Configuration 4: The positive electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the positive electrode mixture layer contains a positive electrode active material, and the particle fracture strength of the positive electrode active material is 100 MPa or more. Configuration 5: The positive electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the tensile strength of the positive electrode current collector in the first region is 5.0 kgf or more and 14.5 kgf or less. Configuration 6: The positive electrode for a non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the tensile strength of the positive electrode current collector in the first region is 5.0 kgf or more and 12.0 kgf or less. Configuration 7: A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, a negative electrode, and a nonaqueous electrolyte, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on a surface of the negative electrode current collector, and the negative electrode mixture layer contains graphite and a Si-containing material.Configuration 8: The nonaqueous electrolyte secondary battery according to Configuration 7, wherein the content of the Si-containing material in the negative electrode mixture layer is 6 mass % or more with respect to the total mass of the graphite and the Si-containing material.

[0077] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 grooved portion 21, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 27 gasket, 30 positive electrode current collector, 32 positive electrode mixture layer, 34 exposed portion of positive electrode current collector, 40 negative electrode current collector, 42 negative electrode mixture layer, 44 exposed portion of negative electrode current collector, 50 first region, 52 second region, 54 third region

Claims

1. A positive electrode for a non-aqueous electrolyte secondary battery having a positive electrode current collector and a positive electrode mixture layer disposed on a surface of the positive electrode current collector, wherein the surface of the positive electrode current collector has a positive electrode current collector exposed portion where the positive electrode mixture layer is not disposed and the positive electrode current collector is exposed, the positive electrode current collector is a metal foil containing Al, and a positive electrode lead is connected to the positive electrode current collector exposed portion, and the surface of the positive electrode current collector has a first region to which the positive electrode lead is connected and a second region in which the positive electrode mixture layer is disposed, a positive electrode for a nonaqueous electrolyte secondary battery, wherein, in an X-ray diffraction measurement of the positive electrode current collector, a half width W1 of a peak at a diffraction angle of about 45° due to Al obtained from the first region and a half width W2 of a peak at a diffraction angle of about 45° due to Al obtained from the second region satisfy a relationship of 0.3≦W2 / W1≦5, and an average aspect ratio A1 of metal particles in the first region and an average aspect ratio A2 of metal particles in the second region satisfy a relationship of A2 / A1>1.

0.

2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein W1 and W2 satisfy the relationship 1.7≦W2 / W1≦3.

1.

3. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein A1 and A2 satisfy the relationship 1.0<A2 / A1≦3.

0.

4. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode mixture layer contains a positive electrode active material, and the particle crushing strength of the positive electrode active material is 100 MPa or more.

5. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the tensile strength of the positive electrode current collector in the first region is 5.0 kgf or more and 14.5 kgf or less.

6. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the tensile strength of the positive electrode current collector in the first region is 5.0 kgf or more and 12.0 kgf or less.

7. A non-aqueous electrolyte secondary battery comprising the positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on the surface of the negative electrode current collector, and the negative electrode mixture layer contains graphite and a Si-containing material.

8. The nonaqueous electrolyte secondary battery according to claim 7, wherein the content of the Si-containing material in the negative electrode mixture layer is 6 mass % or more with respect to the total mass of the graphite and the Si-containing material.

Images