Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises an electrode body that includes a positive electrode, a negative electrode, and a separator (13), the non-aqueous electrolyte secondary battery being characterized in that the separator (13) has a base material layer (30), and a polymer material (32) that is supported on the surface of the base material layer (30) and has a chelate group.

Description

Nonaqueous electrolyte secondary battery

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

[0002] In recent years, non-aqueous electrolyte secondary batteries have been widely used as high-power, high-energy-density secondary batteries. These batteries comprise an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and an outer casing that houses these components. The separator has the function of holding the non-aqueous electrolyte while separating the positive electrode and the negative electrode. Patent Document 1 discloses a separator in which resin particles made of a polymer material are arranged on the surface of a substrate layer.

[0003] International Publication No. 2021 / 161842

[0004] In non-aqueous electrolyte secondary batteries, metal ions originating from the positive electrode active material may precipitate on the negative electrode surface after repeated charging and discharging. From the perspective of improving the reliability of non-aqueous electrolyte secondary batteries, it is important to suppress the precipitation of such metal ions while ensuring battery performance.

[0005] One embodiment of the present disclosure is a non-aqueous electrolyte secondary battery comprising an electrode body including a positive electrode, a negative electrode, and a separator, wherein the separator comprises a substrate layer and a polymer material having chelating groups supported on the surface of the substrate layer.

[0006] According to a non-aqueous electrolyte secondary battery, which is one aspect of this disclosure, it is possible to suppress the deposition of metal ions on the negative electrode surface while ensuring battery performance.

[0007] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is one example of an embodiment. This is a schematic diagram showing a cross-section of a separator constituting a non-aqueous electrolyte secondary battery, which is one example of an embodiment. This is an axial cross-sectional view of an electrode body constituting a non-aqueous electrolyte secondary battery, which is one example of an embodiment, illustrating the movement of lithium ions during charging. This is a schematic diagram showing a cross-section of a separator constituting a non-aqueous electrolyte secondary battery, which is another example of an embodiment. This is an axial cross-sectional view of an electrode body constituting a non-aqueous electrolyte secondary battery, which is another example of an embodiment, illustrating the movement of lithium ions during charging.

[0008] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail while referring to the drawings. Note that configurations formed by selectively combining the components of the plurality of embodiments and modification examples described below are included in the scope of the present disclosure.

[0009] Hereinafter, as a non-aqueous electrolyte secondary battery, a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical exterior body 16 will be exemplified, but the exterior body of the battery is not limited to a cylindrical exterior body. The non-aqueous electrolyte secondary battery according to the present disclosure may be, for example, a square battery provided with a square exterior body, a coin-type battery provided with a coin-type exterior body, or a pouch-type battery provided with an exterior body composed of a laminate sheet including a metal layer and a resin layer. Further, the electrode body is not limited to a wound type, and may be a stacked electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked via a separator. Further, the design of the non-aqueous electrolyte secondary battery according to the present disclosure is not limited to the design of the exemplified non-aqueous electrolyte secondary battery, and a known non-aqueous electrolyte secondary battery design may be applied.

[0010] FIG. 1 is an axial cross-sectional view of a cylindrical 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 exterior body 16 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 includes 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 exterior body 16 is a bottomed cylindrical metal container having an open end on one side in the axial direction, and the opening of the exterior body 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the battery is referred to as the upper side, and the bottom side of the exterior body 16 is referred to as the lower side.

[0011] The positive electrode 11, negative electrode 12, and separator 13 that constitute the electrode body 14 are all rectangular elongated bodies, and are wound in a spiral shape in the longitudinal direction so as to be alternately laminated in the radial direction of the electrode body 14. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. Two separators 13 are arranged, for example, so as to sandwich the positive electrode 11. The electrode body 14 includes 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. In the electrode body 14, the longitudinal directions of the positive electrode 11 and the negative electrode 12 are the winding directions, and the short-side directions of the positive electrode 11 and the negative electrode 12 are the axial directions. That is, the end faces in the short-side direction of the positive electrode 11 and the negative electrode 12 form the end faces in the axial direction of the electrode body 14.

[0012] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14. In the example shown in FIG. 1, the positive electrode lead 20 extends toward the sealing body 17 through the through-hole of the insulating plate 18, and the negative electrode lead 21 extends toward the bottom side of the exterior body 16 through the outside of the insulating plate 19. The positive electrode lead 20 is connected by welding or the like to the lower surface of the internal terminal plate 23 of the sealing body 17, and the cap 27, which is the top plate of the sealing body 17 electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected by welding or the like to the inner surface of the bottom of the exterior body 16, and the exterior body 16 serves as the negative electrode terminal.

[0013] A gasket 28 is provided between the exterior body 16 and the sealing body 17 to ensure the sealing performance inside the battery. The exterior body 16 is formed with a groove portion 22 that supports the sealing body 17, with a part of the side surface portion projecting inward. The groove portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior body 16, and supports the sealing body 17 on its upper surface. The sealing body 17 is fixed to the upper part of the exterior body 16 by the groove portion 22 and the open end portion of the exterior body 16 caulked to the sealing body 17.

[0014] 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 laminated in this order from the side of the electrode body 14. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each member except the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating member 25 is interposed between the peripheral portions of each. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 is deformed and broken so as to push up the upper valve body 26 toward the cap 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further rises, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0015] Hereinafter, the positive electrode 11, negative electrode 12, separator 13, and non-aqueous electrolyte constituting the non-aqueous electrolyte secondary battery 10 will be described in detail, particularly the separator 13.

[0016] [Positive Electrode] The positive electrode 11 is composed of, for example, a positive electrode core such as a metal foil and a positive electrode mixture layer disposed on the positive electrode core. For the positive electrode core, a foil of a metal stable within the potential range of the positive electrode 11 such as aluminum, a film having the metal disposed on its surface layer, etc. can be used. The positive electrode mixture layer contains, for example, a positive electrode active material, a binder, a conductive agent, etc. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, etc. onto the positive electrode core, drying to form a positive electrode mixture layer, and then rolling this positive electrode mixture layer.

[0017] Examples of the positive electrode active material include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium transition metal oxide is, for example, Li ｘ CoO ２ , Li ｘ NiO ２ , Li ｘ MnO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Co ｙ M １－ｙ O ｚ , Li ｘ Ni １－ｙ Mｙ O ｚ Li ｘ Mn ２ O ４ Li ｘ Mn ２－ｙ M ｙ O ４ LiMPO ４ Li ２ MPO ４ F(M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used individually or in combination of two or more types.

[0018] In terms of enabling higher capacity of non-aqueous electrolyte secondary batteries, the positive electrode active material is Li ｘ NiO ２ Li ｘ Co ｙ Ni １－ｙ O ２ Li ｘ Ni １－ｙ M ｙ O ｚ Preferably, the material contains lithium nickel composite oxides such as (where M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, with 0 < x ≤ 1.2, 0 < y ≤ 0.9, and 2.0 ≤ z ≤ 2.3).

[0019] Examples of conductive agents included in the positive electrode mixture layer include carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), graphene, and other carbon-based particles such as graphite. These may be used individually or in combination of two or more types.

[0020] Examples of binders included in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These may be used individually or in combination of two or more types.

[0021] [Negative Electrode] The negative electrode 12 may, for example, have a negative electrode core and a negative electrode mixture layer formed on the surface of the negative electrode core, or a metallic Li foil may be used as the negative electrode 12. Alternatively, the negative electrode 12 may have a negative electrode core, and lithium metal may be deposited on the surface of the negative electrode core by charging. When the negative electrode 12 has a negative electrode mixture layer, it is preferable that the negative electrode mixture layer is formed on both sides of the negative electrode core. For the negative electrode core, a foil of a metal that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on the surface layer, can be used. The thickness of the negative electrode core is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The thickness of the negative electrode mixture layer is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode core. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc., to the surface of the negative electrode core, drying the coating, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0022] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly intercept and release lithium ions, and generally carbon materials such as graphite are used. The graphite may be any of the following: natural graphite such as flake graphite, lump graphite, or clay graphite; lump artificial graphite; or artificial graphite such as graphitized mesophase carbon microbeads. In addition, metals that alloy with Li such as Si and Sn, metal compounds containing Si and Sn, or lithium titanium composite oxides may be used as the negative electrode active material. Furthermore, materials with a carbonaceous coating may also be used. For example, SiO ｘ Si-containing compounds represented by (0.5 ≤ x ≤ 1.6), or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine Si particles are dispersed in a lithium silicate phase represented by (0 < y < 2) may be used in combination with graphite.

[0023] Examples of binders included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0024] [Separator] Next, the separator 13 will be described in detail with reference to Figures 2 and 3. Figure 2 is a schematic diagram showing a cross-section of the separator 13. Figure 3 is an axial cross-sectional view of the electrode body 14, which schematically shows the movement of lithium ions during charging.

[0025] As shown in Figure 2, the separator 13 has a base layer 30 and a polymer material 32 supported on the surface of the base layer 30. In this embodiment, the polymer material 32 has a particle shape and is dispersed throughout the surface of the base layer 30. As will be described in detail later, the polymer material 32 has chelate groups.

[0026] As the base layer 30, for example, a porous sheet having ion permeability and insulating properties can be used. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the base layer 30 is not particularly limited, but examples include polyethylene, polypropylene, polyolefins such as copolymers of polyethylene and α-olefin, acrylic resin, polystyrene, polyester, cellulose, polyimide, polyphenylene sulfide, polyetheretherketone, and fluororesin. The base layer 30 may have a single-layer structure or a multi-layer structure.

[0027] The thickness of the base layer 30 is preferably 3 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less.

[0028] The porosity of the base layer 30 is preferably, for example, 30% or more and 70% or less, in order to ensure ionic conductivity during battery charging and discharging. The porosity of the base layer 30 is measured by the following method: (1) Ten circular pieces with a diameter of 2 cm are punched out of the base layer 30, and the thickness h and mass w of the center of each punched-out piece of base layer 30 are measured. (2) From the thickness h and mass w, the volume V and mass W of the ten pieces are determined, and the porosity ε is calculated from the following formula: Porosity ε (%) = ((ρV - W) / (ρV)) × 100 ρ: density of the material constituting the base

[0029] The polymer material 32 is a material having chelate groups. As a result, when metal ions such as Ni and Mn contained in the positive electrode active material are eluted due to charging and discharging, these metal ions are captured by the polymer material 32. Therefore, even if metal ions such as Ni and Mn are eluted from the positive electrode active material, the deposition of these metal ions on the surface of the negative electrode 12 can be suppressed. As a result, for example, the cycle characteristics can be improved.

[0030] In the example shown in Figure 2, the polymer material 32 is provided on one side of the base layer 30. The side on which the polymer material 32 is provided is, for example, positioned to face the positive electrode 11. Alternatively, the side on which the polymer material 32 is provided may be positioned to face the negative electrode 12. Furthermore, the polymer material 32 may be provided on both sides of the base layer 30.

[0031] As described above, in this embodiment, the polymer material 32 has a particle shape and is dispersed throughout the surface of the substrate layer 30. As a result, gaps are formed between the polymer material 32 particles, as shown in Figure 3. Therefore, Li ions can move through these gaps during charging and discharging. Consequently, the deposition of metal ions on the surface of the negative electrode 12 can be suppressed while suppressing the increase in electrical resistance. In other words, if a non-porous layer is formed on the surface of the substrate layer 30, the movement of Li ions is inhibited, and electrical resistance tends to increase.

[0032] If the polymer material 32 has a particle shape, the average particle size (D50) of the polymer material 32 is preferably 0.1 μm or more and 5.0 μm or less. In this case, gaps are more easily formed on the surface of the substrate layer 30, which further suppresses the increase in electrical resistance and suppresses the deposition of metal ions on the surface of the negative electrode 12. The average particle size (D50) of the polymer material 32 refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution, and is also called the median diameter. The particle size distribution of the polymer material 32 can be measured using a laser diffraction particle size distribution analyzer (for example, Microtrac-Bell MT3000II) with water as the dispersion medium.

[0033] The materials constituting the polymer material 32 are not particularly limited as long as they are polymers into which chelating groups can be introduced. Examples of materials constituting the polymer material 32 include cellulose, polyvinyl alcohol, ethylene-vinyl alcohol, polyolefin, polyamide, and polystyrene. These may be used individually or in combination of two or more. Among these, it is preferable to include cellulose from the viewpoint of exhibiting a significant chelating effect and suppressing the deposition of metal ions on the surface of the negative electrode 12.

[0034] Cellulose can be, for example, natural cellulose fibers such as coniferous tree pulp, hardwood pulp, esparto pulp, Manila hemp pulp, sisal hemp pulp, or cotton pulp, or regenerated cellulose fibers such as lyocell, which are produced by organic solvent spinning of these natural celluloses. These may be used individually or in combination of two or more types.

[0035] The fiber length of the cellulose is, for example, 0.1 mm or more and 5.0 m or less. By setting the fiber diameter of the cellulose to 0.1 mm or more and 5.0 m or less, compared to cases where the above range is not met, denser pores are formed in the separator, for example, making it easier to exert a chelating effect. Alternatively, two or more types of cellulose with different fiber diameters may be used.

[0036] The fiber diameter of the cellulose is, for example, between 50 μm and 200 μm. By setting the fiber diameter of the cellulose to between 50 μm and 200 μm, compared to cases where the above range is not met, for example, dense pores are formed in the separator, making it easier to exert a chelating effect. Alternatively, two or more types of cellulose fibers with different fiber diameters may be used.

[0037] Examples of chelating groups include iminodiacetic acid group, nitrilotriacetic acid group, hydroxyethylglycine group, hydroxyethyliminodiacetic acid group, aminomethylphosphonic acid group, and methylphosphonic acid group. Among these, the iminodiacetic acid group is preferred as the chelating group from the viewpoint of efficiently capturing metal ions eluted from the positive electrode active material.

[0038] The amount of chelating groups in the polymer material 32 is, for example, 0.1 mmol / g or more and 5 mmol / g or less, preferably 0.5 mmol / g or more and 3 mmol / g or less, relative to the mass of the polymer material. When the amount of chelating groups in the polymer material 32 satisfies the above range, the deposition of metal ions on the surface of the negative electrode 12 can be further suppressed.

[0039] The content of the polymer material 32 is, for example, 0.01% by mass or more and 10% by mass or less, or 0.05% by mass or more and 5% by mass or less, relative to the mass of the base layer 30. Even in very small amounts, the polymer material 32 exhibits the effect of suppressing the deposition of metal ions on the negative electrode 12.

[0040] If the polymer material 32 on the surface of the separator 13 is in the form of particles, this can be confirmed, for example, by scanning electron microscopy. When the surface of the separator 13 is observed with a scanning electron microscope, the number of polymer material 32 detected in a 100 μm × 100 μm area is, for example, between 10 and 1000. In this case, it is possible to suppress the increase in electrical resistance and suppress the deposition of metal ions on the surface of the negative electrode 12 at a high level.

[0041] The Gurley value of the separator 13 is preferably 50 s or more and 5000 s or less, and more preferably 100 s or more and 2000 s or less. When the Gurley value of the separator 13 is 50 s or more and 5000 s or less, an appropriate gap is formed on the surface of the separator 13, allowing for the smooth movement of Li ions. In other words, if a non-porous layer is formed on the surface of the substrate layer 30, the Gurley value will exceed 5000, which may inhibit the movement of Li ions. As a result, the electrical resistance tends to increase. The Gurley value can be evaluated by the method based on JIS P 8117:2009.

[0042] The separator 13 of this embodiment can be manufactured, for example, by applying a dispersion containing a polymer material 32 to the surface of a substrate layer 30 and drying it. When cellulose is used for the polymer material 32, water or an organic solvent such as ethanol can be used as the dispersion medium for the dispersion containing the polymer material 32. The content of the polymer material 32 in the dispersion is, for example, 1 g / L or more and 100 g / L or less. Methods for applying the dispersion to the surface of the substrate layer 30 include spraying, gravure coating, die coating, roll coating, reverse roll coating, screen printing, and inkjet, with spraying being preferred. The drying method is not particularly limited and may be performed by natural drying, aeration drying with hot air, heating drying, reduced pressure / vacuum drying, or a combination thereof. The drying temperature is generally 10°C or more and 150°C or less, and may be 25°C or more and 125°C or less.

[0043] Next, a modified example of the separator 13 will be described with reference to Figures 4 and 5. Figure 4 is a schematic diagram showing a cross-section of the separator 13 in the modified example. Figure 5 is an axial cross-sectional view of the electrode body 14, which schematically shows the movement of lithium ions during charging.

[0044] As shown in Figure 4, the separator 13 of this embodiment has a base layer 30 and a layered polymer material 32 formed on the surface of the base layer 30. In other words, the polymer material 32 of this embodiment does not have a granular shape and is formed in layers. The polymer material 32 is a porous layer having voids inside. The surface on which the polymer material 32 is provided is arranged to face the positive electrode 11, for example, as in the case of Figure 2. Alternatively, the surface on which the polymer material 32 is provided may be arranged to face the negative electrode 12. Furthermore, the polymer material 32 may be provided on both sides of the base layer 30.

[0045] In the layered polymer material 32 shown in Figure 4, metal ions such as Ni and Mn eluted from the positive electrode active material are captured by the chelating action of the polymer material 32. This suppresses the deposition of metal ions on the surface of the negative electrode 12. Furthermore, as shown in Figure 5, Li ions can move through the voids in the polymer material 32, ensuring smooth movement of Li ions. As a result, an increase in electrical resistance can be suppressed.

[0046] The thickness of the polymer material 32 is less than the thickness of the substrate layer 30. For example, the thickness of the polymer material 32 is between 0.5 μm and 5.0 μm.

[0047] [Non-aqueous electrolytes] Non-aqueous electrolytes are ionic conductive (for example, lithium ion conductive). Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0048] A liquid electrolyte (electrolyte solution) includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixtures of two or more of these. The non-aqueous solvent may contain halogen-substituted solvents in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of halogen-substituted solvents include fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0049] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate esters 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 linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0050] Examples of the above 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 methylphenyl ether. Examples include chain ethers such as ethylphenyl ether, butylphenyl ether, pentylphenyl 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.

[0051] The electrolyte salt is preferably a lithium salt. A suitable lithium salt is 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 Examples include lithium lower aliphatic carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO4). ２ F ２ Examples include lithium difluorobis(oxalato)phosphate (LiDFOBP), lithium tetrafluoro(oxalato)phosphate, etc. Examples of borates include lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), etc. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO)). ２ ) ２ ), bistrifluoromethanesulfonate lithium (LiN(CF ３ SO ２ ) ２ ), trifluoromethanesulfonic acid nonafluorobutanesulfonic acid lithium (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), bispentafluoroethanesulfonate lithium (LiN(C) ２ F ５ SO ２ ) ２ ) etc. are used. Of these, LiPF is used from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ It is preferable to use the following. The concentration of the lithium salt may be, for example, 4 moles or less per liter of non-aqueous solvent, or 3 moles or less, preferably 1.8 moles or less, and more preferably 0.8 moles or more and 1.8 moles or less.

[0052] Non-aqueous electrolytes may contain additives. Examples of additives include unsaturated carbonate esters, acid anhydrides, phenol compounds, benzene compounds, nitrile compounds, isocyanate compounds, sultone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0053] Examples of unsaturated cyclic carbonate esters 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. Unsaturated cyclic carbonate esters may be used individually or in combination of two or more. Some hydrogen atoms in the unsaturated cyclic carbonate esters may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by the intermolecular condensation of multiple carboxylic acid molecules, but it is preferable that it be an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0054] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0055] 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 bisisocyanate methylcyclohexane (BIMCH). Examples of sultone compounds include propanesultone and propensultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethylborate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethylphosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethylphosphite and tris(trimethylsilyl)phosphite.

[0056] 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, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, 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 a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0057] The present disclosure will be further illustrated below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0058] <Example 1> [Preparation of Positive Electrode] A positive electrode slurry was prepared by mixing 100 parts by mass of positive electrode active material, 1.1 parts by mass of acetylene black as a conductive agent, and 0.9 parts by mass of polyvinylidene fluoride as a binder, and then mixing this with N-methyl-2-pyrrolidone (NMP). Next, the positive electrode slurry was applied to one side of a positive electrode core made of 15 μm thick aluminum foil. After the coating film was dried, the coating film was rolled using a rolling roller and cut to a predetermined electrode size to produce a positive electrode for evaluation. The positive electrode was provided with a 20 mm × 20 mm region to function as a positive electrode and a 5 mm × 5 mm region for connecting to the lead. Subsequently, the positive electrode slurry layer formed on the connection region was scraped off to expose the positive electrode core. Then, the exposed portion of the positive electrode core was connected to the positive electrode lead, and a predetermined region on the outer circumference of the positive electrode lead was covered with an insulating film.

[0059] [Fabrication of the negative electrode] The negative electrode was fabricated by fusing a Ni mesh to a Ni lead using a resistance welding machine, and then pressing a lithium metal foil (300 μm thick) onto the Ni mesh. The lithium metal foil was 25 mm x 25 mm in size.

[0060] [Preparation of Separator (First Separator)] As the cellulose containing chelating groups, we used Kirest Fiber IRY-LW manufactured by Kirest Co., Ltd. The cellulose was pulverized using a ball mill manufactured by Lechner (model name: MM400) while being cooled with liquid nitrogen to obtain a polymer material. When the particle size of the prepared polymer material was observed with a scanning electron microscope, it was found to be approximately 1 μm or more and 5 μm or less.

[0061] 0.2 g of the prepared polymer material was placed in 20 mL of ethanol and stirred to prepare a dispersion. The prepared dispersion was then applied to one side of a 10 μm thick substrate layer consisting of three layers of polyethylene / polypropylene / polyethylene. The material was then vacuum-dried at 60°C for 12 hours to prepare a separator with the polymer material on one side of the substrate layer. The Gurley value of the prepared separator was measured to be 100 s.

[0062] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4. Lithium hexafluoride phosphate (LiPF) was added to this mixed solvent. ６ A non-aqueous electrolyte was prepared by dissolving the substance to a concentration of 1.2 mol / liter.

[0063] [Preparation of Test Cells] Test cells for evaluation were prepared using evaluation positive and negative electrodes. First, the positive and negative electrodes were placed opposite each other with a separator in between so that the positive electrode mixture layer and the negative electrode mixture layer overlapped to obtain an electrode plate group. Here, a first separator having the above-mentioned polymer material and a second separator consisting only of a base material layer were stacked, with the first separator on the positive electrode side and the second separator on the negative electrode side. Furthermore, the first separator was positioned so that the side with the polymer material facing the positive electrode.

[0064] Next, a 60 x 90 mm rectangle of Al laminate film (100 μm thick) was folded in half, and the 60 mm long end was heat-sealed at 230°C to form a 60 x 45 mm tube. Then, the prepared electrode group was placed inside the tube, and the end face of the Al laminate film was aligned with the position of the insulating film of each lead, and heat-sealed at 230°C. Next, a 0.3 cm non-aqueous electrolyte solution was poured into the unheat-sealed short side of the Al laminate film. ３ The solution was injected, and after injection, the mixture was left to stand for 5 minutes under reduced pressure of 0.06 MPa to impregnate each mixture layer with the electrolyte. Finally, the end face of the Al laminate film on the injected side was heat-sealed at 230°C to prepare the test cell. The test cell was prepared in a dry environment with a dew point of -50°C or lower.

[0065] [Evaluation of Trickle Charge Capacity] Under an ambient temperature of 45°C, the fabricated test cells were charged with a constant current of 0.2C up to 4.5V, and then further charged with a constant voltage of 4.5V for 72 hours. The trickle charge capacity was then measured.

[0066] [Evaluation of Metal Deposition Amount] Under an ambient temperature of 45°C, the fabricated test cell was charged with a constant current of 0.2C to 4.5V, then further charged with a constant voltage of 4.5V for 72 hours, and subsequently discharged to 2.5V at a constant current of 0.2C under an ambient temperature of 25°C. The test cell, which underwent this charge-discharge cycle twice, was charged to 4.5V at a constant current of 0.2C under a temperature environment of 25°C, and then charged to 0.02C at a constant voltage of 4.5V. Subsequently, it was discharged to 2.5V at a constant current of 0.2C. The test cell that underwent the above tests was disassembled, and the negative electrode (lithium metal foil) and the second separator were removed. The negative electrode and the second separator were then dissolved in ultrapure water and acid, and the resulting solution was filtered. The amounts of Ni and Mn (ppm) in the filtrate were calculated using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0067] <Example 2> In preparing the separator, a test cell was prepared and evaluated in the same manner as in Example 1, except that Kirest Fiber IRY-HW manufactured by Kirest Co., Ltd. was used as the cellulose having a chelating group. The Gurley value of the prepared separator was measured to be 100 s.

[0068] <Comparative Example 1> In the preparation of the separator, the test cell was prepared and evaluated in the same manner as in Example 1, except that the polymer material was not applied to the surface of the substrate layer. In other words, the separator of Comparative Example 1 does not have a polymer material.

[0069] Table 1 shows the evaluation results for the trickle charge capacity and metal deposition amount of the test cells of Examples 1 and 2 and Comparative Example 1. The metal deposition amounts in Table 1 are values ​​normalized by the weight of the positive electrode active material in each test cell. Furthermore, the metal deposition amounts in Table 1 are relative values ​​with the metal deposition amount of the test cell of Comparative Example 1 set to 100. A smaller metal deposition value indicates suppressed metal ion deposition on the negative electrode surface. The trickle charge capacity in Table 1 is also a relative value with the trickle charge capacity of the test cell of Comparative Example 1 set to 100.

[0070]

[0071] As shown in Table 1, the amount of metal deposited in the test cells of Examples 1 and 2 was significantly reduced compared to the amount of metal deposited in Comparative Example 1. Furthermore, the trickle charge capacity of the test cells of Examples 1 and 2 was reduced compared to the trickle charge capacity of Comparative Example 1. This suggests that the presence of polymer material improved the durability of the separator, and the reduction in the amount of deposited metal reduced side reactions originating from that metal.

[0072] This disclosure is further illustrated by the following embodiments: Configuration 1: A non-aqueous electrolyte secondary battery comprising an electrode body including a positive electrode, a negative electrode, and a separator, wherein the separator comprises a substrate layer and a polymer material having chelating groups supported on the surface of the substrate layer. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the polymer material comprises cellulose. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the polymer material has a particle shape. Configuration 4: The non-aqueous electrolyte secondary battery according to Configuration 3, wherein the average particle size of the polymer material is 0.1 μm or more and 5.0 μm or less. Configuration 5: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the polymer material is a porous layer having voids inside. Configuration 6: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the chelating groups are iminodiacetic acid groups. Configuration 7: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the Gurley value of the separator is 50 s or more and 5000 s or less. Configuration 8: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the Gurley value of the separator is 100 s or more and 2000 s or less.

[0073] 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 member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Base layer, 32 Polymer material.

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode body including a positive electrode, a negative electrode, and a separator, wherein the separator comprises a base layer and a polymer material having chelating groups supported on the surface of the base layer.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer material includes cellulose.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer material has a particle shape.

4. The non-aqueous electrolyte secondary battery according to claim 3, wherein the average particle size of the polymer material is 0.1 μm or more and 5.0 μm or less.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer material is a porous layer having voids inside.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the chelating group is an iminodiacetic acid group.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the Gurley value of the separator is 50 s or more and 5000 s or less.

8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the Gurley value of the separator is 100 s or more and 2000 s or less.

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