Secondary battery

Abstract

The present invention improves charge / discharge characteristics. This secondary battery comprises a positive electrode, a negative electrode, and an electrolyte solution. The positive electrode is provided with a positive electrode current collector containing aluminum. The electrolyte solution contains an electrolyte and a solvent. The electrolyte contains a bis(fluorosulfonyl) imide salt. The solvent contains at least one compound selected from a first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and γ-butyrolactone. The intrinsic molar ratio of the solvent to lithium ions, calculated from the vibrational spectrum of the electrolyte, is greater than 0 and not greater than 1.76.

Description

secondary battery

[0001] The present invention relates to a secondary battery.

[0002] Patent Document 1 discloses a secondary battery in which the positive electrode has a positive electrode current collector made of aluminum or an aluminum alloy, and the electrolyte contains lithium bis(fluorosulfonyl)imide.

[0003] Japanese Patent Application Laid-Open No. 2015-133315

[0004] However, in the secondary battery disclosed in Patent Document 1, there is a possibility that the charge / discharge characteristics may be deteriorated due to the electrolyte.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to improve charge / discharge characteristics.

[0006] A secondary battery according to one embodiment of the present invention is a secondary battery including a positive electrode, a negative electrode, and an electrolyte solution, wherein the positive electrode includes a positive electrode current collector containing aluminum, the electrolyte includes an electrolyte and a solvent, the electrolyte includes a bis(fluorosulfonyl)imide salt, and the solvent includes at least one selected from a first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma butyrolactone, and the molar ratio of the solvent to lithium ions calculated from a vibrational spectroscopy spectrum of the electrolyte solution is greater than 0 and equal to or less than 1.76.

[0007] A secondary battery according to another aspect of the present invention is a secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode current collector containing aluminum, the electrolyte includes an electrolyte and a solvent, the electrolyte includes a bis(fluorosulfonyl)imide salt, and the solvent includes at least one selected from a first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma butyrolactone, and the molar ratio of the solvent to lithium ions calculated from a vibrational spectroscopy spectrum of the electrolyte is greater than 0 and less than or equal to 1.72.

[0008] According to the present invention, the charge / discharge characteristics can be improved.

[0009] FIG. 1 is a perspective view showing the configuration of a secondary battery according to one embodiment. FIG. 2 is an enlarged cross-sectional view showing the configuration of the battery element shown in FIG. 1. FIG. 3 is a schematic cross-sectional view showing a negative electrode active material particle according to a fourth embodiment. FIG. 4 is a schematic cross-sectional view showing a portion of an electrode assembly according to a sixth embodiment. FIG. 5 is a schematic cross-sectional view showing a portion of an electrode assembly according to the sixth embodiment. FIG. 6 is a schematic cross-sectional view showing a negative electrode active material particle according to an eighth embodiment. FIG. 7 is a schematic cross-sectional view showing a negative electrode active material particle according to a ninth embodiment. FIG. 8 is a diagram showing the cross-sectional configuration of a secondary battery according to a tenth embodiment. FIG. 9 is a developed view of a battery element according to a tenth embodiment. FIG. 10A is a developed view of a positive electrode according to a tenth embodiment. FIG. 10B is a view showing a cross section taken along line IIIB-IIIB in FIG. 10A , as viewed in the direction of the arrows. FIG. 11A is a developed view of a negative electrode according to a tenth embodiment. FIG. 11B is a view showing a cross section taken along line IVB-IVB in FIG. 11A , as viewed in the direction of the arrows. Fig. 12A is a schematic diagram showing an example of the configuration of a positive electrode current collector plate according to the tenth embodiment. Fig. 12B is a schematic diagram showing an example of the configuration of a negative electrode current collector plate according to the tenth embodiment. Fig. 13 is a process chart illustrating a method for manufacturing a secondary battery according to the tenth embodiment. Fig. 14A is a developed view schematically showing the configuration of a positive electrode of a secondary battery having a multi-tab structure. Fig. 14B is a developed view schematically showing the configuration of a positive electrode of a secondary battery having a multi-tab structure.

[0010] Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to this embodiment.

[0011] (First embodiment) (Secondary battery) A description will be given of a secondary battery according to the first embodiment. The secondary battery according to the first embodiment is a secondary battery that obtains battery capacity by utilizing the occlusion and release of an electrode reactant, and includes a positive electrode, a negative electrode, and an electrolyte.

[0012] The type of electrode reactant is not particularly limited, and specifically includes light metals such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, and potassium. Specific examples of alkaline earth metals include beryllium, magnesium, and calcium. The electrode reactant may also be other light metals such as aluminum.

[0013] In the following description, an example will be given in which the electrode reactant is lithium. A secondary battery that obtains battery capacity by utilizing the absorption and desorption of lithium is, for example, a lithium ion secondary battery. In a lithium ion secondary battery, lithium is absorbed and desorbed in the ionic state.

[0014] Fig. 1 is a perspective view showing the configuration of a secondary battery according to one embodiment. Fig. 2 is an enlarged cross-sectional view showing the configuration of the battery element shown in Fig. 1. Fig. 1 shows a state in which an exterior film 10 and a battery element 20 are separated from each other, and the cross section of the battery element 20 is shown by a dashed line. Fig. 2 shows the cross section of only a portion of the battery element 20.

[0015] As shown in FIGS. 1 and 2, the secondary battery 1 includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 33 and .

[0016] As described above, the secondary battery 1 in Fig. 1 uses the exterior film 10 as an exterior member for housing the battery element 20. Therefore, the secondary battery 1 shown in Fig. 1 is a so-called laminate film type secondary battery.

[0017] 1, the exterior film 10 is an exterior member that houses the battery element 20, and has a sealed bag-like structure when the battery element 20 is housed therein. As a result, the exterior film 10 houses a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte solution (not shown), which will be described later.

[0018] In the example of Fig. 1, the exterior film 10 is a single film-like member that is folded in a folding direction F. The exterior film 10 has a recessed portion 10U for accommodating the battery element 20. The recessed portion 10U is a so-called deep-drawn portion.

[0019] Specifically, the exterior film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside. When the exterior film 10 is folded, the outer peripheral edges of the opposing fusion layers are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon. The configuration (number of layers) of the exterior film 10 is not particularly limited and may be one layer, two layers, or four or more layers.

[0020] 1 and 2 , the positive electrode lead 31 is a positive electrode wiring connected to the positive electrode current collector 21A of the positive electrode 21, and is drawn out to the exterior of the exterior film 10. The positive electrode lead 31 includes at least one type of conductive material such as a metal material, and a specific example of the conductive material is aluminum. The shape of the positive electrode lead 31 is not particularly limited, and may be, for example, a thin plate shape or a mesh shape.

[0021] (Negative Electrode Lead) As shown in FIGS. 1 and 2 , the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode current collector 22A of the negative electrode 22, and is drawn out to the exterior of the exterior film 10. The negative electrode lead 32 includes at least one type of conductive material such as a metal material. A specific example of the conductive material is copper. The shape of the negative electrode lead 32 is not particularly limited, and may be, for example, a thin plate or a mesh shape.

[0022] (Sealing Film) As shown in Fig. 1, the sealing film 33 is inserted between the exterior film 10 and the positive electrode lead 31. Furthermore, as shown in Fig. 1, the sealing film 34 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 33 and 34 may be omitted.

[0023] The sealing film 33 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. The sealing film 33 contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31. A specific example of the polymer compound is polypropylene.

[0024] The sealing film 34 is a sealing member that prevents outside air and the like from entering the inside of the exterior film 10. The sealing film 33 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32. A specific example of the polymer compound is polypropylene.

[0025] (Battery Element) The battery element 20 is housed in the space of the recess 10U of the exterior film 10. The battery element 20 is a so-called power generating element. As shown in Figures 1 and 2, the battery element 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte solution (not shown).

[0026] 1 , battery element 20 is a so-called wound electrode body. Therefore, positive electrode 21 and negative electrode 22 are wound around winding axis P while facing each other via separator 23. In the following description, the direction along winding axis P may be referred to as the Y direction, the longitudinal direction of battery element 20 perpendicular to winding axis P as the X direction, and the lateral direction of battery element 20 perpendicular to winding axis P as the Z direction.

[0027] In the example of FIG. 1 , the battery element 20 has a flat, three-dimensional shape. That is, the shape of a cross section (cross section along the XZ plane) of the battery element 20 intersecting the winding axis P of the battery element 20 is a flat shape defined by a major axis J1 and a minor axis J2. The major axis J1 is an imaginary axis extending in the X-axis direction and has a length greater than the length of the minor axis J2. The minor axis J2 is an imaginary axis extending in the Z-axis direction and has a length smaller than the length of the major axis J1. As a result, the cross-sectional shape of the battery element 20 is a flat, approximately elliptical shape. Note that the three-dimensional shape of the battery element 20 is merely an example and is not limited to the above.

[0028] The positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B. In the positive electrode 21, the positive electrode current collector 21A is laminated between the positive electrode active material layers 21B. However, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A, that is, on the side where the positive electrode 21 faces the negative electrode 22.

[0029] The positive electrode current collector 21A contains aluminum and may be, for example, aluminum foil. The surface state of the positive electrode current collector 21A will be described later.

[0030] The positive electrode active material layer 21B is a layer containing a positive electrode active material capable of absorbing and releasing lithium. The positive electrode active material layer 21B contains a positive electrode active material. The positive electrode active material layer 21B is not limited to the materials listed above, and may further contain, for example, a binder, a conductive agent, and a dispersant.

[0031] The positive electrode active material is preferably a lithium-containing compound such as a lithium-containing composite oxide or a lithium-containing phosphate compound. The lithium-containing composite oxide is an oxide containing lithium and one or more elements other than lithium as constituent elements. The lithium-containing composite oxide has, for example, a layered rock salt type or a spinel type crystal structure. The lithium-containing phosphate compound is a phosphate compound containing lithium and one or more elements other than lithium as constituent elements. The lithium-containing phosphate compound has, for example, an olivine type crystal structure. A specific example of the lithium-containing composite oxide is LiNiO ２ , LiCoO ２ , LiCo ０．９８ Al ０．０１ Mg ０．０１ O ２ , LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiNi ０．３３ Co ０．３３ Mn ０．３３ O ２ , Li １．２ Mn ０．５２ Co ０．１７５ Ni ０．１ O ２ , Li １．１５ (Mn ０．６５ Ni ０．２２ Co ０．１３ ) O ２ , LiMn ２ O ４ Specific examples of lithium-containing phosphate compounds include LiFePO ４ , LiMnPO ４ , LiFe ０．５ Mn ０．５ P.O. ４, LiFe ０．３ Mn ０．７ P.O. ４ And so on.

[0032] The binder (positive electrode binder) contained in the positive electrode active material layer 21B may be any material, and may include, for example, one or more of synthetic rubber and polymer compounds. Examples of synthetic rubber include styrene-butadiene rubber, fluorine-based rubber, and ethylene-propylene-diene. Examples of polymer compounds include polyvinylidene fluoride (PVdF) and polyimide.

[0033] The conductive agent (positive electrode conductive agent) contained in the positive electrode active material layer 21B may be any material, including, for example, carbon. Examples of carbon include graphite, carbon black, acetylene black, and ketjen black. However, the conductive agent contained in the positive electrode active material layer 21B is not limited to these materials as long as it is a conductive material, and may also be a metal material, a conductive polymer, or the like.

[0034] The negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B. In the negative electrode 22, the negative electrode current collector 22A is stacked between the negative electrode active material layers 22B. However, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A that faces the positive electrode 21.

[0035] The negative electrode current collector 22A is a conductor, and for example, copper foil or the like can be used.

[0036] The negative electrode active material layer 22B is a layer containing a negative electrode active material capable of absorbing and releasing lithium. The negative electrode active material layer 22B is not limited to being composed only of a negative electrode active material, and may contain, for example, a conductive agent and a binder.

[0037] The negative electrode active material preferably contains at least one of a carbon material and a metal-based material. This allows for a high energy density to be obtained. Specific examples of carbon materials used as the negative electrode active material include graphitizable carbon, non-graphitizable carbon, natural graphite, and artificial graphite. The metal-based material used as the negative electrode active material is a material containing, as a constituent element, one or more of metal elements and metalloid elements that can form an alloy with lithium. Specific examples of metal elements and metalloid elements used as the negative electrode active material include silicon and tin. The metal-based material used as the negative electrode active material may be a simple substance, an alloy, a compound, a mixture of two or more types, or a material containing two or more types of phases. Specific examples of metal-based materials used as the negative electrode active material include TiSi ２ , SiO ｘ (0<x≦2), etc.

[0038] The negative electrode active material layer 22B is not limited to containing only the negative electrode active material.

[0039] For example, the negative electrode active material layer 22B may further contain a negative electrode binder. The negative electrode binder includes at least one of synthetic rubber, polymer compound, etc. Specific examples of synthetic rubber used as the negative electrode binder include styrene-butadiene rubber, fluorine-containing rubber, and ethylene propylene diene. Specific examples of polymer compounds used as the negative electrode binder include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0040] For example, the negative electrode active material layer 22B may further contain a negative electrode conductive agent. The negative electrode conductive agent includes at least one of a carbon material, a metal material, and a conductive polymer compound. Specific examples of carbon materials used as the negative electrode conductive agent include particulate carbon materials such as carbon black, acetylene black, and ketjen black, and fibrous carbon materials such as carbon nanotubes. Examples of carbon nanotubes include single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs). Whether a CNT is a SWCNT can be determined by Raman measurement, specifically, by measuring the length of a CNT measured at 100 cm. －１ More than 300cm －１ If a peak is observed in the following range, it can be said that the negative electrode active material layer contains SWCNT. The number of MWCNT layers can be determined by sampling the negative electrode active material layer with a focused ion beam and observing the sample with a transmission electron microscope (TEM). This can improve the electronic conductivity of the particle surfaces of the first negative electrode active material. The mass ratio of the negative electrode conductive agent to the negative electrode active material layer 22B is preferably 5% or less, more preferably 2% or less. This can improve the coating properties of the negative electrode slurry.

[0041] The separator 23 is a film that insulates the positive electrode 21 from the negative electrode 22. The separator 23 is provided between the main surface of the positive electrode 21 and the main surface of the negative electrode 22 so that the positive electrode 21 and the negative electrode 22 do not come into direct contact with each other.

[0042] The separator 23 is preferably made of a material that is electrically stable, chemically stable against the positive electrode active material, the negative electrode active material, and the electrolyte, and is insulating. The separator 23 may be made of, for example, a polymer nonwoven fabric, a porous film, or a layer of glass or ceramic fibers. The separator 23 is more preferably made of a porous polyolefin film. This improves the safety of the battery by preventing short circuits and providing a shutdown effect.

[0043] The electrolyte solution is impregnated into each of the positive electrode 21, the negative electrode 22, and the separator 23. In the example of Fig. 1, the electrolyte solution fills the space inside the exterior member 30. The electrolyte solution is a non-aqueous electrolyte solution containing an electrolyte salt and a solvent that dissolves the electrolyte salt.

[0044] The electrolyte salt is lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO ２ F ２ ) ２ The electrolyte salt may contain other electrolyte salts used as electrolyte salts for lithium ion batteries. The other electrolyte salts may be light metal salts such as lithium salts. Specific examples of lithium salts include lithium hexafluorophosphate (LiPF ６ ), lithium monofluorophosphate (Li ２ PFO ３ ), lithium difluorophosphate (LiPF ２ O ２ ) and lithium tetrafluoroborate (LiBF ４ ), lithium bis(oxalato)borate (LiB(C ２ O ４ ) ２ It is preferable that the electrolyte salt is a lithium salt containing boron (B), such as lithium trifluoromethanesulfonate (LiCF), etc. This allows P and B to be contained in the surface of the positive electrode current collector 21A. The other electrolyte salt is not limited to the above, and may be lithium trifluoromethanesulfonate (LiCF), etc. ３ SO ３ ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF ３ SO ２ ) ２ ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF ３ SO ２ ) ３ ) etc.

[0045] The solvent comprises at least one member of a first group consisting of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and gamma butyrolactone (GBL).

[0046] The solvent preferably further contains at least one of a carbonate ester and a chain carboxylic acid ester excluding the compounds included in Group 1. This can further improve charge-discharge characteristics. Examples of carbonate esters excluding the compounds included in Group 1 include diethyl carbonate (DEC) and ethyl methyl carbonate (EMC). Examples of chain carboxylic acid esters include propyl propionate (PrPr), ethyl propionate (PrEt), methyl propionate, propyl acetate (AcPr), ethyl acetate (AcEt), and methyl acetate (AcMe). Of the chain carboxylic acid esters and carbonate esters excluding the compounds included in Group 1, the solvent preferably contains at least one of DEC, EMC, PrPr, PrEt, AcPr, AcEt, and AcMe, and more preferably contains at least one of EMC, PrPr, PrEt, AcPr, AcEt, and AcMt. This can further improve charge-discharge characteristics.

[0047] The solvent may further include other nonaqueous solvents used as nonaqueous solvents in lithium-ion batteries. Examples of such nonaqueous solvents include ethers such as 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane. The ethers may be compounds in which some or all of the hydrogen atoms have been substituted with fluorine atoms, such as 1,1,2-tetrafluoroethyl 2,2,2,3,3-tetrafluoropropyl ether.

[0048] The electrolytic solution may contain substances other than the electrolyte salt and the solvent, such as additives.

[0049] The electrolyte may contain additives such as unsaturated cyclic carbonates such as vinylene carbonate, methylene ethylene carbonate, and vinyl ethylene carbonate; halogenated cyclic carbonates such as monofluoroethylene carbonate and difluoroethylene carbonate; hydrofluoroethers; sulfonates; phosphates; acid anhydrides; and isocyanates. Specific examples of sulfonates include propane sultone and propene sultone. Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate. Specific examples of acid anhydrides include succinic anhydride, 1,2-ethanedisulfonic anhydride, and 2-sulfobenzoic anhydride. Specific examples of isocyanates include hexamethylene diisocyanate.

[0050] The molar ratio of the original solvent to lithium ions calculated from the vibrational spectroscopy spectrum of the electrolyte solution is greater than 0 and not greater than 1.76. The molar ratio of the original solvent to lithium ions is preferably greater than 0 and not greater than 1.72. The molar ratio of the original solvent to lithium ions is preferably 0.10 or greater. This can improve charge / discharge characteristics. In the present disclosure, the original solvent refers to solvent molecules contained in the electrolyte solution that are not solvated with lithium ions. The original molar ratio of the solvent to lithium ions according to the present disclosure is calculated by multiplying the original amount of substance M of the solvent calculated by the following formula (1): ０ Here, when the electrolyte solution contains multiple types of solvents, the original substance amount M of each solvent can be calculated by the following formula (1): ０ The weighted average weighted by the molar ratio of the plurality of solvents is calculated, and the weighted average is divided by the amount of substance of lithium ions contained in the electrolyte solution, thereby calculating the amount of substance of the original solvent used in calculating the molar ratio of the original solvent to lithium ions. ０ =M ａｌｌ -M Ｎ =M ａｌｌ -c ｔ / {1+Γ(I o / I ｓ )} (1) Here, in formula (1), M ａｌｌ is the total amount of solvent contained in the solution, M Ｎis the amount of solvent molecules solvated by lithium ions, c ｔ is the solvent concentration, Γ is the vibrational spectrum intensity ratio per unit concentration, I ｏ is the peak intensity of the solvent itself, I ｓ Here, the vibrational spectrum intensity ratio Γ per unit concentration is ｏ is the concentration of the solvent that is not solvated with lithium ions, c ｓ When the concentration of the solvent solvating the lithium ion is ｓ / c ｏ is the horizontal axis and I ｓ / I ｏ This can be determined by plotting the vertical axis as the slope of the graph.

[0051] Here, "peak of the solvent itself" means a peak observed at the peak position (wave number) when a solvent not solvated with lithium ions is subjected to vibrational spectroscopy, i.e., when only the solvent is subjected to vibrational spectroscopy. Also, "peak of the solvent of the solvate" refers to a peak position when a solvent solvated with lithium ions is subjected to vibrational spectroscopy. Here, the peak of the solvent of the solvate can be distinguished from the peak of the solvent itself because the vibrational spectroscopy spectrum is shifted relative to the peak of the solvent itself. Therefore, the height from the baseline to the peak top of each of the peak of the solvent itself and the peak of the solvent of the solvate is called the peak intensity I. ｏ , I ｓ In addition, when there are multiple peaks of the solvent itself and multiple peaks of the solvate solvent in the vibrational spectroscopy spectrum of the electrolyte solution, the peak intensity I ｏ , I ｓ The ratio of peaks is easy to determine based on the peak intensity I ｏ , I ｓ In addition, when the shift of the peak of the solvent of the solvate relative to the peak of the original solvent is small and the peak of the original solvent and the peak of the solvent of the solvate overlap to form a gentle peak, the peak intensity I can be calculated by performing peak separation using a known means. ｏ , I ｓ The ratio may be calculated.

[0052] Table 1 shows examples of the wave numbers of the peaks of the solvent itself and the solvate solvent in the vibrational spectroscopy spectrum of the electrolyte solution of the present invention. The wave numbers of the peaks of the solvent itself and the solvate solvent shown in Table 1 are respectively I ｏ and I ｓ can be used to measure. Here, as shown in Table 1, the FEC peak is near the EC peak and the DMC peak, and therefore may overlap with each other. Since it can be assumed that FEC has the same vibrational spectroscopy spectrum intensity ratio Γ per unit concentration as EC and DMC, when a solvent contains at least one of EC and DMC and FEC, the original amount of substance of the solvent may be calculated using a composition in which FEC is replaced with the same amount of EC. Note that the values ​​shown in Table 1 are merely examples, and the wavenumber of the observed peak may differ from the wavenumber shown in Table 1 depending on the vibrational spectroscopy spectrum measurement device, measurement environment, and measurement conditions.

[0053]

[0054] In the present disclosure, the vibrational spectroscopy of an electrolyte solution is measured by Raman spectroscopy or Fourier transform infrared spectroscopy using an electrolyte solution extracted from a secondary battery to be measured using a centrifuge. Here, the measurement of the vibrational spectroscopy of an electrolyte solution is preferably performed in an environment where the influence of atmospheric moisture can be reduced or ignored. The measurement of the vibrational spectroscopy of an electrolyte solution can be performed under low-humidity or humidity-free conditions, such as a dry room or a glove box, or by using an electrolyte solution sealed in a transparent, sealed container as a sample. The electrolyte solution extracted from the secondary battery to be measured can be quantitatively analyzed using ICP (Inductively Coupled Plasma), NMR (Nuclear Magnetic Resonance), or GC-MS (Gas Chromatography Mass Spectrometry). Based on the obtained composition of the electrolyte solution, an electrolyte solution having the same composition as the electrolyte solution in the secondary battery to be measured can be prepared, and the prepared electrolyte solution can be used as the sample for measuring the vibrational spectroscopy spectrum.

[0055] As described above, the secondary battery 1 according to the first embodiment is a secondary battery including a positive electrode 21, a negative electrode 22, and an electrolyte. The positive electrode 21 includes a positive electrode current collector 21A containing aluminum. The electrolyte includes an electrolyte and a solvent. The electrolyte includes a bis(fluorosulfonyl)imide salt. The solvent includes at least one solvent selected from a first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma butyrolactone. The molar ratio of the solvent to lithium ions calculated from the vibrational spectroscopy spectrum of the electrolyte is greater than 0 and less than or equal to 1.76. This improves charge / discharge characteristics.

[0056] In a preferred embodiment, the solvent further contains at least one of a carbonate ester and a chain carboxylic acid ester excluding the compounds included in Group 1. This can further improve the charge-discharge characteristics.

[0057] In a more preferred embodiment, the solvent further contains at least one of diethyl carbonate, ethyl methyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, and methyl acetate, which can further improve the charge-discharge characteristics.

[0058] In a more preferable embodiment, the solvent further contains at least one of ethyl methyl carbonate, propyl propionate, ethyl propionate, propyl acetate, ethyl acetate, and methyl acetate, which can further improve the charge-discharge characteristics.

[0059] The secondary battery 1 according to the first embodiment includes a positive electrode 21, a negative electrode 22, and an electrolyte. The positive electrode 21 includes a positive electrode current collector 21A containing aluminum. The electrolyte includes an electrolyte and a solvent. The electrolyte includes a bis(fluorosulfonyl)imide salt. The solvent includes at least one solvent selected from a first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma butyrolactone. The molar ratio of the solvent to lithium ions calculated from the vibrational spectroscopy spectrum of the electrolyte is greater than 0 and less than or equal to 1.72. This improves charge / discharge characteristics.

[0060] (Method for manufacturing secondary battery) Here, an example of a method for manufacturing the secondary battery 1 according to the first embodiment will be described. The method for manufacturing the secondary battery 1 according to the first embodiment includes a step of fabricating the positive electrode 21, a step of fabricating the negative electrode 22, a step of preparing an electrolyte solution, a step of assembling the secondary battery 1, and a charge / discharge step.

[0061] In the process of fabricating the positive electrode 21, the positive electrode 21 is fabricated by the following method. A positive electrode active material, a positive electrode binder, and a positive electrode conductive agent are mixed to prepare a positive electrode mixture. The prepared positive electrode 21 mixture is then dispersed in a dispersion liquid such as N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry, and the prepared positive electrode mixture slurry is then uniformly applied to both surfaces of the positive electrode current collector 21A. The resulting coating is dried with hot air or the like, and then compression-molded using a roll press or the like to fabricate the positive electrode 21. A positive electrode 21 lead is attached to the fabricated positive electrode 21 at a portion where the positive electrode current collector 21A is exposed.

[0062] In the process of fabricating the negative electrode 22, the negative electrode 22 is fabricated by the following method. A negative electrode active material and a negative electrode binder are mixed to prepare a negative electrode mixture. The prepared negative electrode mixture is dispersed in a dispersion liquid such as NMP to prepare a negative electrode mixture slurry, and the negative electrode mixture is then uniformly applied to both sides of a negative electrode current collector. The resulting coating is dried using hot air or the like, and then compression-molded using a roll press or the like to fabricate the negative electrode 22. A negative electrode 22 lead is attached to the fabricated negative electrode 22 at the exposed portion of the negative electrode current collector 22A.

[0063] In the step of preparing the electrolyte solution, an electrolyte salt is dissolved in a solvent to prepare the electrolyte solution.

[0064] In the process of assembling the secondary battery 1, the secondary battery 1 is assembled by the following method. The positive electrode 21, separator 23, and negative electrode 22 are stacked in this order and wound longitudinally to produce an electrode assembly. The produced electrode assembly is loaded into an exterior member, and three sides of the exterior member are heat-sealed, leaving one side unheat-sealed to form an opening. Thereafter, an electrolyte is poured into the opening of the exterior member, and the remaining side of the exterior member is heat-sealed in a reduced-pressure environment to seal the exterior member and form a laminate cell.

[0065] In the charge / discharge process, one charge / discharge cycle is performed on the fabricated laminate cell. Here, one charge / discharge cycle can be performed under charge / discharge condition A, for example. Charge / discharge condition A refers to a condition in which a first charge, a first standing time, a second charge, a second standing time, and a discharge are performed in the following order at a temperature of 33°C. This allows a good coating to be formed on the positive electrode current collector 21A, and the secondary battery 1 can be made electrochemically stable. First charge method: CCCV First charge rate: 0.2C First charge control voltage: 3.0V First cut-off time: 1 hour First standing time: 12 hours Second charge method: CCCV Second charge rate: 0.2C Second charge control voltage: 4.2V Second cut-off time: 8 hours Second standing time: 12 hours Discharge method: CC Discharge rate: 0.2C End-of-discharge voltage: 2.5V

[0066] Through the above steps, the secondary battery 1 according to the first embodiment can be fabricated. Note that the above-described method for manufacturing a secondary battery is an example, and the method is not limited to this.

[0067] (Examples of the First Embodiment) Examples of the first embodiment will be described below. Note that the present invention is not limited to these examples.

[0068] Table 2 shows Comparative Examples 1-1 to 1-6 and Examples 1-1 to 1-48.

[0069]

[0070] Comparative Example 1-1 A positive electrode according to Comparative Example 1-1 was prepared by the following method. ０．８２ Co ０．１４ Al ０．４ O ２ ), polyvinylidene fluoride (PVdF) as a positive electrode binder, and carbon black as a positive electrode conductive agent were mixed in a mass ratio of 91:3:6 to prepare a positive electrode mixture. The prepared positive electrode mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry, and then a strip-shaped aluminum foil with a thickness of 12 μm was prepared as a positive electrode current collector, and the prepared positive electrode mixture slurry was uniformly applied to both sides of the aluminum foil. The obtained coating was dried with hot air and then compression-molded using a roll press to prepare a positive electrode. A positive electrode lead was attached to the exposed portion of the positive electrode current collector of the prepared positive electrode.

[0071] The negative electrode according to Comparative Example 1-1 was prepared by the following method. The negative electrode mixture was prepared by mixing artificial graphite as the negative electrode active material and PVdF as the negative electrode binder in a mass ratio of 93:7. The prepared negative electrode mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a negative electrode mixture slurry, and then a copper foil with a thickness of 15 μm was prepared as a negative electrode current collector, and the negative electrode mixture was uniformly applied to both sides of the copper foil. The obtained coating was dried with hot air and then compression-molded using a roll press to prepare a negative electrode. A negative electrode lead was attached to the exposed portion of the negative electrode current collector of the prepared negative electrode.

[0072] The separator according to Comparative Example 1-1 was a microporous polyethylene film having a thickness of 15 μm.

[0073] The electrolyte solution according to Comparative Example 1-1 was prepared by dissolving LiFSI as an electrolyte salt in a solvent prepared by mixing the components shown in Table 2 in the mass ratio shown in Table 2, so that the concentration of the electrolyte salt was the concentration shown in Table 2.

[0074] The secondary battery according to Comparative Example 1-1 was fabricated by the following method. The above-described positive electrode and negative electrode were stacked with the above-described separator interposed therebetween, tightly adhered, and wound longitudinally to fabricate an electrode assembly. The fabricated electrode assembly was loaded into an exterior member, and three sides of the exterior member were heat-sealed, with one side left unheat-sealed to form an opening. The exterior member was a laminate film formed by laminating a 25 μm-thick nylon film as the outermost layer, a 40 μm-thick aluminum foil as the metal layer, and a 30 μm-thick polypropylene film as the insulating layer. The above-prepared electrolyte solution was then injected through the opening in the exterior member, and the remaining side of the exterior member was heat-sealed in a reduced-pressure environment to seal the exterior member and form a laminate cell.

[0075] In Comparative Example 1-1, the prepared laminate cell was subjected to one charge / discharge cycle in an environment of 23°C under the following conditions: first charge, first standing, second charge, second standing, and discharge in that order. This resulted in the preparation of a battery according to Comparative Example 1-1. First charge method: CCCV First charge rate: 0.2C First charge control voltage: 3.0V First cut-off time: 1 hour First standing time: 12 hours Second charge method: CCCV Second charge rate: 0.2C Second charge control voltage: 4.2V Second cut-off time: 8 hours Second standing time: 12 hours Discharge method: CC Discharge rate: 0.2C End-of-discharge voltage: 2.5V

[0076] <Vibrational Spectroscopy Measurement> In Comparative Example 1-1, vibrational spectroscopy of the electrolyte solution was performed by the following method. In the vibrational spectroscopy measurement, the prepared electrolyte solution was sealed in a sealed glass container to prepare a sample. The sample was then introduced into a Raman spectrometer (manufactured by Nanophoton Inc.), and measurement was performed with the excitation laser wavelength set to 758 nm. As a result, the peak intensity I ｏ and the peak intensity I of the solvent of the solvate ｓ Based on this, the original amount of substance M of the solvent can be calculated by the above-mentioned formula (1). ０ The original molar ratio of the solvent to lithium ions was calculated by calculating the original molar ratio M of the solvent for each type of solvent.０ The amount of the solvent was calculated by calculating the weighted average weighted by the molar ratio of the multiple solvents. As a result, the molar ratio of the solvent to the lithium ions was calculated as shown in Table 2.

[0077] <Cycle characteristic test> In Comparative Example 1-1, a cycle characteristic test was carried out in the following manner.

[0078] The secondary battery prepared above was charged and discharged 100 times in an environment of 60°C under the following conditions, and the discharge capacity at the first cycle and the discharge capacity at the 100th cycle were measured. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was calculated as the cycle retention rate. That is, the cycle retention rate was calculated based on the following formula: Cycle retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the 1st cycle) x 100. Charging method: CCCV, Charging rate: 0.1 C, Charging control voltage: 4.2 V, Charging cut-off current: 0.05 C, Discharging method: CC, Discharging rate: 0.1 C, Discharging cut-off voltage: 2.5 V

[0079] <Storage characteristic test> In Comparative Example 1-1, a storage characteristic test was carried out by the following method.

[0080] The secondary battery prepared above was subjected to a first charge / discharge cycle at 23°C under the following conditions, and the discharge capacity before storage was measured: Charging method: CCCV, Charging rate: 0.1C, Charging control voltage: 4.2V, Charging cut-off current: 0.05C, Discharging method: CC, Discharging rate: 0.1C, Discharging cut-off voltage: 2.5V.

[0081] The battery was then placed in a thermostatic chamber and stored in an 80°C environment for 10 days, and then discharged under the following conditions to measure the discharge capacity after storage. Charge and discharge were performed in an environment of 23°C. The ratio of the discharge capacity before storage to the discharge capacity after storage was calculated as the storage retention rate. That is, the storage retention rate was calculated based on the formula: storage retention rate (%) = (discharge capacity after storage / discharge capacity before storage) x 100. Discharge method: CC Discharge rate: 0.1C End-of-discharge voltage: 2.5V

[0082] <Low Temperature Load Characteristic Test> In Comparative Example 1-1, a low temperature load characteristic test was carried out in the following manner.

[0083] The secondary battery fabricated above was subjected to the first charge-discharge cycle in an environment of 23°C under the following conditions. Thereafter, the second to 100th charge-discharge cycles were performed in an environment of -10°C under the same conditions as the first charge-discharge cycle, under the following conditions. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was calculated as the low-temperature load retention rate. That is, the low-temperature load retention rate was calculated based on the following formula: low-temperature load retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) x 100. Charging method: CCCV, charging rate: 0.1 C, charge control voltage: 4.2 V, charge cut-off current: 0.05 C, discharging method: CC, discharge rate: 0.1 C, discharge cut-off voltage: 2.5 V

[0084] (Comparative Example 1-2 to Example 1-6 and Example 1-1 to Example 1-36) In Comparative Example 1-2 to Example 1-6 and Example 1-1 to Example 1-36, secondary batteries were fabricated in the same manner as the battery of Comparative Example 1-1, and measurements and tests were performed. The batteries were fabricated using an electrolyte solution prepared by dissolving LiFSI as an electrolyte salt in a solvent prepared by mixing the components shown in Table 2 in the mass ratios shown in Table 2.

[0085] (Examples 1-37 to 1-48) In Examples 1-37 to 1-48, the components shown in Table 2 were mixed in the mass ratio shown in Table 2 as the solvent, and LiFSI and LiPF were added as electrolyte salts. ６ Each of the above components was dissolved to have the concentration shown in Table 2 to prepare an electrolyte solution, and a battery was fabricated using the electrolyte solution. A secondary battery was fabricated in the same manner as the battery according to Comparative Example 1-1, and measurements and tests were performed.

[0086] As shown in Table 2, Examples 1-1 to 1-48, in which the molar ratio of the original solvent to lithium ions was greater than 0 and 1.76 or less, showed improved cycle retention rates and storage retention rates compared to Comparative Examples 1-1 to 1-6, in which the molar ratio of the original solvent to lithium ions was greater than 0 or 1.76. Therefore, it can be seen that the charge-discharge characteristics can be improved by having the molar ratio of the original solvent to lithium ions be greater than 0 and 1.76 or less.

[0087] As shown in Table 2, in Examples 1-3 to 1-48, in which the molar ratio of the original solvent to lithium ions was greater than 0 and 1.72 or less, the cycle retention rate and storage retention rate were improved compared to Comparative Examples 1-1 to 1-6, in which the molar ratio of the original solvent to lithium ions was greater than 0 or 1.72. Therefore, it can be seen that the charge-discharge characteristics can be improved by having the molar ratio of the original solvent to lithium ions be greater than 0 and 1.72 or less.

[0088] As shown in Table 2, Examples 1-1 to 1-48, in which the molar ratio of the original solvent to lithium ions was 0.10 or more, had improved charge-discharge characteristics compared to Comparative Example 1-5 and Example 1-6, in which the molar ratio of the original solvent to lithium ions was less than 0.10. Therefore, it can be seen that the charge-discharge characteristics can be improved by setting the molar ratio of the original solvent to lithium ions to 0 or more and 1.76 or less.

[0089] As shown in Table 2, in Examples 1-2 and 1-4 to 1-48, the solvent further contains at least one of carbonate esters (DEC, EMC) and chain carboxylic acid esters (PrPr, PrEt, AcPr, AcEt, AcMe) excluding EC, FEC, and DMC contained in Group 1. The charge-discharge characteristics were further improved compared to Examples 1-1 and 1-3, in which the solvent consists of EC and DMC contained in Group 1. Therefore, it can be seen that the charge-discharge characteristics can be further improved by further containing at least one of carbonate esters and chain carboxylic acid esters excluding the compounds contained in Group 1.

[0090] As shown in Table 2, in Examples 1-2 and 1-4 to 1-48, in which the solvent further contains at least one of DEC, EMC, PrPr, PrEt, AcPr, AcEt, and AcMe, the charge-discharge characteristics were improved compared to Examples 1-1 and 1-3, in which the solvent does not contain DEC, EMC, PrPr, PrEt, AcPr, AcEt, or AcMe. Therefore, it can be seen that the charge-discharge characteristics can be further improved by further containing at least one of DEC, EMC, PrPr, PrEt, AcPr, AcEt, and AcMe.

[0091] As shown in Table 2, in Examples 1-2 and 1-5 to 1-48, in which the solvent further contained at least one of EMC, PrPr, PrEt, AcPr, AcEt, and AcMe, the low-temperature load characteristics were further improved compared to Examples 1-1, 1-3, and 1-4, in which the solvent did not contain PrPr, PrEt, AcPr, AcEt, or AcMe. Therefore, it can be seen that the charge-discharge characteristics can be further improved by further including at least one of EMC, PrPr, PrEt, AcPr, AcEt, and AcMe in the solvent.

[0092] Other embodiments will be described below.

[0093] In the following explanation, in the "Charge / Discharge Conditions" column of the table, "A" indicates that the laminated cell was charged and discharged under the above-mentioned charge / discharge conditions A in the charge / discharge process, and "B" indicates that the laminated cell was charged and discharged under the charge / discharge conditions B in the charge / discharge process.

[0094] Here, charge / discharge condition B refers to a condition in which charging, standing, and discharging are carried out in the following order at a temperature of 25°C. That is, unlike charge / discharge condition A in which charging is divided into two steps, charge / discharge condition B involves charging in one step. Charging method: CCCV, Charge rate: 0.2C, Charge control voltage: 4.2V, Cut-off time: 8 hours, Standing time: 5 minutes, Discharge method: CC, Discharge rate: 0.2C, Discharge end voltage: 2.5V

[0095] In the following description, analytical measurement methods and analytical measurement devices may be referred to by their abbreviations. The abbreviations indicate the following: EDX: Energy Dispersive X-ray Spectroscopy XRD: X-ray Diffraction XPS: X-ray Photoelectron Spectroscopy SEM: Scanning Electron Microscope NMR: Nuclear Magnetic Resonance

[0096] In addition, in this disclosure, unless otherwise specified, ５０ D refers to the particle size corresponding to a cumulative frequency of 50% in the particle size distribution, which is the so-called median size. ５０ D can be obtained by measuring the major axis (μm) of a plurality of particles to be observed using an observation image of the cross section of the electrode of the measurement object (for example, the positive electrode 21 or the negative electrode 22) using an SEM or the like, and then calculating the average value of the major axis of each particle of 50 measured particles. ５０ Alternatively, for example, may be calculated from the average value of the volume-based particle size distribution obtained by a laser diffraction particle size distribution device.

[0097] Second Embodiment In a secondary battery according to a second embodiment, the negative electrode active material layer contains a carbon material. The thickness of the negative electrode active material layer is 30 μm or more and 100 μm or less, and the volume density of the negative electrode active material layer is 1.4 g / cm ３ 2.0g / cm or more ３ The following is the result.

[0098] (Example of Second Embodiment) An example of the second embodiment will be described below. Note that the present invention is not limited to this example.

[0099] Tables 3 to 8 show Examples 2-1 to 2-87 and Comparative Examples 2-1 to 2-7.

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106] (Examples 2-1 to 2-87, Comparative Examples 2-1 to 2-7) In Examples 2-1 to 2-87 and Comparative Examples 2-1 to 2-7, as shown in Tables 3 to 8, the type of negative electrode active material in the negative electrode active material layer and the interplanar spacing between (002) planes of graphite (interplanar spacing d ００２), the thickness and volume density of the negative electrode active material layer, and the electrolyte solution were prepared as shown in Tables 3 to 8. Except for this, secondary batteries were prepared in the same manner as the battery of Comparative Example 1-1, and measurements and tests were carried out. Here, in Examples 2-68 to 2-73, secondary batteries were prepared by replacing part of the artificial graphite in the negative electrode active material with a silicon compound. The type of silicon compound and the ratio of the artificial graphite to the silicon compound are as shown in Table 7.

[0107] As shown in Tables 3 to 8, the thickness of the negative electrode active material layer is 30 μm or more and 100 μm or less, and the volume density is 1.4 g / cm ３ 2.0g / cm or more ３ In the following Examples 2-1 to 2-54, 2-57 to 2-60, 2-63 to 2-66, and 2-68 to 2-73, the thickness of the negative electrode active material layer was less than 30 μm or more than 100 μm, or the volume density was 1.4 g / cm ３ Less than or 2.0 g / cm ３ Therefore, the thickness of the negative electrode active material layer was 30 μm or more and 100 μm or less, and the volume density was 1.4 g / cm or less. ３ 2.0g / cm or more ３ It can be seen that the battery characteristics can be improved by satisfying the following.

[0108] Third Embodiment In a secondary battery according to a third embodiment, the negative electrode active material layer contains graphite and styrene-butadiene rubber (SBR).

[0109] The spacing between the (002) planes of the graphite in the negative electrode active material layer (graphite plane spacing d ００２ ) is preferably 0.3372 nm or less. This increases the capacity of the secondary battery. ００２ More specifically, the negative electrode active material layer is crushed and subjected to powder XRD, and the lattice constant can be calculated based on the lattice constant determined in accordance with JIS R7651:2007.

[0110] The negative electrode active material layer preferably further contains carboxymethyl cellulose (CMC), which improves the cycle retention rate, high-temperature storage characteristics, and low-temperature load.

[0111] The negative electrode active material layer preferably contains at least one of polyacrylic acid (PAA) and polyacrylamide (PAM), which improves the cycle retention rate.

[0112] The negative electrode active material preferably contains at least one of silicon carbide (SiC) and silicon oxide (SiO), which improves low-temperature load.

[0113] (Example of the Third Embodiment) An example of the third embodiment will be described below. Note that the present invention is not limited to this example.

[0114] Tables 9 to 14 show Examples 3-1 to 3-82 and Comparative Examples 3-1 to 3-7.

[0115]

[0116]

[0117]

[0118]

[0119]

[0120]

[0121] (Examples 3-1 to 3-82, Comparative Examples 3-1 to 3-7) In Examples 3-1 to 3-82 and Comparative Examples 3-1 to 3-7, as shown in Tables 9 to 14, the type of negative electrode active material in the negative electrode active material layer and the graphite plane spacing d ００２, anode active material layer binder, and an electrolyte solution as shown in Tables 9 to 14 were used to prepare batteries. Except for this, secondary batteries were prepared in the same manner as the battery according to Comparative Example 1-1, and measurements and tests were performed. Here, in Examples using SBR and CMC as the anode binder, 100 parts by weight of natural graphite, 3 parts by weight of SBR, 1 part by weight of CMC-Na, and 100 parts by weight of water were mixed to prepare anode mixture slurry. Also, in Examples using SBR and CMC as the anode binder, PAA or PAM was mixed with 100 parts by weight of natural graphite, 1.5 parts by weight of SBR, 1 part by weight of CMC-Na, 1.5 parts by mass of PAA or PAM, and 100 parts by weight of water to prepare anode mixture slurry. Also, in Examples 3-61 to 3-68, secondary batteries were prepared by replacing a portion of the artificial graphite of the anode active material with a silicon compound. The types of silicon compounds and the ratio of artificial graphite are as shown in Table 13.

[0122] As shown in Tables 9 to 14, Examples 3-1 to 3-54 and Examples 3-56 to 3-82 in which the negative electrode active material layer contained SBR exhibited better charge-discharge characteristics than Example 3-55 in which the negative electrode active material layer did not contain SBR. This shows that the battery characteristics can be improved by including SBR in the negative electrode active material layer.

[0123] As shown in Tables 9 to 14, the graphite plane spacing d ００２ In Examples 3-56 to 3-58, in which the graphite interplanar spacing d ００２ It can be seen that the battery characteristics can be improved by making the thickness 0.3372 nm or less.

[0124] As shown in Tables 9 to 14, in Examples 3-54 and 3-56 to 3-82 in which the negative electrode active material layer contained CMC, good charge-discharge characteristics were exhibited. Therefore, it can be seen that the battery characteristics can be improved by including CMC in the negative electrode active material layer.

[0125] As shown in Tables 9 to 14, Examples 3-59 to 3-60 and Examples 3-67 to 3-82, in which the negative electrode active material layer contained at least one of PAA and PAM, exhibited better charge-discharge characteristics than Example 3-B, in which the negative electrode active material layer did not contain PAA or PAM. Therefore, it can be seen that the battery characteristics can be improved by including at least one of PAA and PAM in the negative electrode active material layer.

[0126] (Fourth embodiment) Fig. 3 is a schematic cross-sectional view showing a negative electrode active material particle according to a fourth embodiment. In a secondary battery according to the fourth embodiment, the negative electrode active material layer includes composite particles P1 shown in Fig. 3 as negative electrode active material particles. The composite particles P1 include a porous conductive matrix P10 having pores P11 and silicon-containing particles P20 located in the pores P11. In the example of Fig. 3, the composite particles P1 include the conductive matrix P10, the silicon-containing particles P20, and a surface coating layer P12 that coats the surface of the conductive matrix P10. This increases the capacity of the secondary battery.

[0127] The conductive matrix P10 preferably contains a carbon material, and more preferably contains an amorphous carbon material such as amorphous graphite. The crystallinity of the carbon material of the conductive matrix P10 can be determined using XRD. Specifically, the diffraction pattern of the negative electrode active material particles is measured. If a narrow, strong peak with a small full width at half maximum (FWHM) is observed at a diffraction angle corresponding to the (002) plane specific to graphite crystals (2θ≒26° in the case of Cu-Kα radiation), the negative electrode active material can be determined to contain crystalline graphite. On the other hand, if a broad, weak peak with a large FWHM is observed at that diffraction angle, the negative electrode active material can be determined to contain an amorphous carbon material.

[0128] The silicon-containing particles P20 are particles composed of at least one of silicon and a silicon compound. A specific example of the silicon compound contained in the silicon-containing particles P20 is silicon oxide (SiOx). The silicon-containing particles P20 are preferably composed of silicon. This can improve the cycle retention rate, storage retention rate, and load characteristics. The presence or absence of the silicon-containing particles P20 can be determined by observing a cross section along the thickness direction of the negative electrode active material layer with a TEM and examining the element distribution with EDX. Specifically, if particles are present inside the pores P11 of the conductive matrix P10 and silicon elements are detected in the pores P11 with EDX, it can be confirmed that the silicon-containing particles P20 are present in the pores of the conductive matrix.

[0129] The surface coating layer P12 is a layer containing carbon. The surface coating layer P12 covers at least a portion of the surface of the conductive matrix P10. The surface coating layer P12 is provided on the surface of the composite particle P1 so that the inner walls of the pores P11 and at least a portion of the silicon-containing particles P20 are exposed. By providing the surface coating layer P12, the amount of silicon-containing particles P20 exposed on the surface of the composite particle P1 can be adjusted. Furthermore, by providing the surface coating layer P12, the silicon-containing particles P20 can be prevented from coming into contact with the electrolyte. This can prevent side reactions between the silicon-containing particles P20 and the electrolyte.

[0130] The specific capacity of the composite particles is 800 mAh / g or more. This improves the cycle retention rate, storage retention rate, and low-temperature load. The specific capacity of the composite particles can be changed by adjusting the amount of silicon-containing particles P20 loaded into the conductive matrix P10 by changing the manufacturing conditions of the composite particles described below. The specific capacity of the composite particles can be measured by a charge-discharge test.

[0131] The composite particles have first pores with a pore diameter of 5 nm or more but less than 10 nm and second pores with a pore diameter of 10 nm or more but less than 50 nm. The ratio of the total volume of the second pores to the total volume of the first pores (hereinafter referred to as the pore volume ratio) is preferably less than 10.9%. This improves cycle retention and storage retention. The pore volume can be measured by nitrogen gas adsorption at the nitrogen boiling point (approximately 77 K) under atmospheric pressure. The nitrogen gas adsorption method involves adjusting the pressure to condense gas within the pores of a solid to examine the porosity and pore size distribution of a material. As the pressure increases, the gas condenses within the pores, and the pressure is continued to increase until the saturation point, where all pores are filled with liquid, is reached. The nitrogen gas pressure is then gradually reduced to evaporate the liquid. The pore volume and pore size distribution can be determined by analyzing the resulting adsorption and desorption isotherms and the hysteresis that occurs between them. Then, the pore volume ratio can be calculated based on the pore volume and pore diameter distribution.

[0132] The silicon content (surface Si content) of the elements on the surface of the composite particle is preferably 30 atomic % or less. This improves the cycle retention rate and storage retention rate. The surface Si content can be determined by performing XPS on the negative electrode active material layer as a sample to measure the binding energy of Si2p (near 100 eV) and the binding energy of C1s (near 285 eV). Based on the Si2p peak and C1s peak that appear in the obtained energy distribution, the ratio of the molar amount of Si to the molar amount of C can be calculated as the surface Si content.

[0133] D of composite particle P1 ５０ It is preferable that the diameter of the composite particle P1 is 0.5 μm or more and less than 40 μm. This improves the cycle retention rate and storage retention rate. ５０ can be obtained by, for example, measuring the maximum lengths of a plurality of (e.g., 50) composite particles using an observation image of the cross section of the negative electrode active material layer by SEM or the like, and then calculating the arithmetic mean value of the maximum lengths. ５０ may be calculated from the average value of the volume-based particle size distribution obtained by a laser diffraction particle size distribution analyzer, for example.

[0134] The composite particles P1 can be produced, for example, by depositing silicon-containing particles P20 inside the pores P11 of the conductive matrix P10 by chemical vapor deposition (CVD) under an inert gas. Specifically, first, the particle size of the conductive matrix P10 is adjusted by airflow pulverization, classification, or the like. Next, silicon is deposited inside the pores P11 of the conductive matrix P10 by chemical vapor deposition under an inert gas, such as nitrogen gas. At this time, CVD is performed by mixing the inert gas with a silicon-containing gas, such as silane. Next, CVD is performed using a hydrocarbon gas, such as acetylene gas, on the conductive matrix P10 in which the silicon-containing particles P20 are disposed. This results in composite particles P1 whose surfaces are coated with a carbonaceous surface coating layer P12.

[0135] (Example of the Fourth Embodiment) An example of the fourth embodiment will be described below. Note that the present invention is not limited to this example.

[0136] Tables 15 to 18 show Examples 4-1 to 4-54 and Comparative Examples 4-1 to 4-7.

[0137]

[0138]

[0139]

[0140]

[0141] (Examples 4-1 to 4-54, Comparative Examples 4-1 to 4-7) In Examples 4-1 to 4-54 and Comparative Examples 4-1 to 4-7, as shown in Tables 15 to 18, negative electrodes were prepared by the method described below using the negative electrode active material particles shown in Tables 15 to 18, and batteries were prepared using the electrolyte solutions shown in Tables 15 to 18. Except for this, secondary batteries were prepared in the same manner as the battery according to Comparative Example 1-1, and measurements and tests were performed.

[0142] In Examples 4-1 to 4-54 and Comparative Examples 4-1 to 4-7, the negative electrode was prepared by applying a negative electrode mixture slurry containing composite particles P1 to a negative electrode current collector (Cu foil). The composite particles P1 were prepared by depositing silicon-containing particles P20 inside the pores P11 of a conductive matrix P10 by chemical vapor deposition (CVD) under an inert gas. Specifically, silicon was first deposited inside the pores P11 of the conductive matrix P10 by chemical vapor deposition under nitrogen gas as the inert gas. At this time, CVD was performed by mixing silane as a silicon-containing gas with the inert gas. Next, CVD was performed using acetylene gas as the hydrocarbon gas on the conductive matrix P10 on which the silicon-containing particles P20 were disposed. This resulted in composite particles P1 whose surfaces were coated with a carbonaceous surface coating layer P12. The negative electrode mixture slurry was prepared using a total of 100 parts by mass of graphite and composite particles as the negative electrode active material, 3 parts by mass of styrene butadiene rubber (SBR) as a negative electrode binder, 1 part by mass of carboxymethyl cellulose (CMC-Na) as a negative electrode thickener, 1 part by mass of carbon black, and 0.1 parts by mass of carbon nanotubes, with water as a solvent. The distribution of graphite and composite particles was as shown in the "Composite Particle Content" column of Tables 15 to 18, with the remainder being graphite. The negative electrode mixture slurry was applied to the main surface of the negative electrode current collector, dried, and then roll-pressed to form a negative electrode blank. The negative electrode blank was then cut into a pancake-shaped negative electrode, and the pancake-shaped negative electrode was then heat-treated to carbonize the CMC. Specifically, the pancake-shaped negative electrode was placed in a vacuum oven, the pressure in the vacuum oven was reduced to 13.3 Pa or less, the temperature was raised from room temperature to 120°C, and the oven was maintained at this temperature for 15 hours, after which the negative electrode was cooled to 80°C or less in vacuum and taken out into the air, thereby producing a negative electrode. In Example 4-24, a negative electrode was produced in the same manner as in Example 4-1, except that silicon particles were used instead of the composite particles.

[0143] As shown in Tables 15 to 18, Examples 4-1 to 4-23 and Examples 4-25 to 4-54, in which the negative electrode active material layer contained composite particles containing a conductive matrix and silicon-containing particles, exhibited better charge-discharge characteristics than Example 4-24, which did not contain such composite particles. This shows that the battery characteristics can be improved by including composite particles containing a conductive matrix and silicon-containing particles in the negative electrode active material layer.

[0144] As shown in Tables 15 to 18, Examples 4-1 to 4-23 and Examples 4-26 to 4-54, in which the conductive matrix was made of amorphous carbon, exhibited better charge-discharge characteristics than Example 4-25, in which the conductive matrix was made of crystalline carbon. Therefore, it can be seen that the battery characteristics can be further improved by using amorphous carbon as the conductive matrix.

[0145] As shown in Tables 15 to 18, Examples 4-1 to 4-23 and Examples 4-27 to 4-54, in which the silicon-containing particles were made of silicon, showed better charge-discharge characteristics than Example 4-26, in which the silicon-containing particles were made of silicon oxide. Therefore, it can be seen that the battery characteristics can be further improved by using silicon-containing particles.

[0146] As shown in Tables 15 to 18, Examples 4-1 to 4-23 and Examples 4-28 to 4-54, in which the specific capacity of the composite particles was 800 mAh / g or more, showed better charge / discharge characteristics than Example 4-27, in which the specific capacity of the composite particles was less than 800 mAh / g. Therefore, it can be seen that the battery characteristics can be further improved by having the specific capacity of the composite particles be 800 mAh / g or more.

[0147] As shown in Tables 15 to 18, in Examples 4-1 to 4-23, Examples 4-29 to 4-42, and Examples 4-46 to 4-53, in which the pore volume ratio was less than 10.9%, better charge / discharge characteristics were exhibited than in Examples 4-28, 4-43 to 4-45, and 4-54, in which the pore volume ratio was 10.9% or more. Therefore, it can be seen that the battery characteristics can be further improved by having a pore volume ratio of less than 10.9%.

[0148] As shown in Tables 15 to 18, Examples 4-1 to 4-23 and Examples 4-28 to 4-53, in which the surface Si amount was 30 atomic % or less, showed better charge-discharge characteristics than Example 4-54, in which the surface Si amount was more than 30 atomic %. Therefore, it can be seen that the battery characteristics can be further improved by having the surface Si amount be 30 atomic % or less.

[0149] As shown in Tables 15 to 18, the D ５０ In Examples 4-32 to 4-38, the D of the composite particles is 0.5 μm or more and less than 40 μm. ５０ The composite particles exhibited better charge-discharge characteristics than those of Examples 4-31 and 4-39, in which the D of the composite particles was less than 0.5 μm or 40 μm or more. ５０ It can be seen that the battery characteristics can be further improved by setting the thickness to 0.5 μm or more and less than 40 μm.

[0150] Fifth Embodiment In a secondary battery according to the fifth embodiment, the porosity of the negative electrode active material layer is 15% or more and 45% or less. A porosity of the negative electrode active material layer of 15% or more can improve high-temperature characteristics and low-temperature load characteristics. The porosity of the negative electrode active material layer can be calculated by measuring the volume of voids present inside the negative electrode active material layer to be measured using, for example, a mercury porosimeter, and then calculating the ratio of the volume of the voids to the total volume, including the voids, of the negative electrode active material layer to be measured. That is, the porosity of the negative electrode active material layer can be calculated using the formula: porosity of the negative electrode active material layer (%) = (volume of voids in the negative electrode active material layer / volume of the negative electrode active material layer) × 100.

[0151] The negative electrode active material layer contains a silicon-carbon composite material. The silicon-carbon composite material includes porous carbon having pores and silicon-containing particles within the pores. The silicon-containing particles include at least one of elemental silicon, a silicon alloy, and silicon oxide. The proportion of the silicon-carbon composite material in the negative electrode active material layer is preferably 1% by mass or more and 70% by mass or less. This increases the capacity of the secondary battery and improves its low-temperature load characteristics.

[0152] The negative electrode active material layer contains graphite particles. ５０It is preferable that the thickness is 30 μm or less. This can improve the tortuosity of carrier ions and improve the low-temperature load characteristics.

[0153] The specific surface area of ​​the negative electrode active material layer is 1 m ２ / g or more 30m ２ / g or less. ２ / g or less, side reactions in the charge / discharge reaction can be suppressed, and high-temperature characteristics can be improved. The specific surface area of ​​the negative electrode active material layer can be calculated as the surface area per mass of the negative electrode active material layer measured by the nitrogen BET method. That is, the specific surface area of ​​the negative electrode active material layer can be calculated using the formula: specific surface area of ​​the negative electrode active material layer = (surface area of ​​the negative electrode active material layer / mass of the negative electrode active material layer).

[0154] The negative electrode active material layer preferably contains a fibrous conductive material. More preferably, the negative electrode active material layer contains carbon nanotubes with 10 or fewer layers as the fibrous conductive material. This can prevent negative electrode active material particles from being electrically isolated from other negative electrode active material particles, thereby improving high-temperature cycle characteristics.

[0155] (Example of Fifth Embodiment) An example of the fifth embodiment will be described below. Note that the present invention is not limited to this example.

[0156] Tables 19 to 22 show Examples 5-1 to 5-59 and Comparative Examples 5-1 to 5-7.

[0157]

[0158]

[0159]

[0160]

[0161] (Examples 5-1 to 5-59, Comparative Examples 5-1 to 5-7) In Examples 5-1 to 5-59 and Comparative Examples 5-1 to 5-7, as shown in Tables 19 to 22, batteries were produced using the components of the negative electrode active material layer and the electrolyte solution as shown in Tables 19 to 22. Except for this, secondary batteries were produced in the same manner as the battery according to Comparative Example 1-1, and measurements and tests were performed. Here, in Examples 5-1 to 5-54 and Comparative Examples 5-1 to 5-7, in which graphite and Si-C composite material were used as the negative electrode active material, a negative electrode mixture slurry was produced by mixing 100 parts by mass of graphite and Si-C composite material in total, 3 parts by mass of SBR, 1 part by mass of CMC-Na, 1 part by mass of carbon black (CB), and 100 parts by mass of water. Further, in Examples 5-55 to 5-58 in which carbon nanotubes (CNT) were used as the negative electrode conductive agent, a negative electrode mixture slurry was prepared by mixing 100 parts by mass of graphite and Si-C composite material, 3 parts by mass of SBR, 1 part by mass of CMC-Na, 0.05 parts by mass of carbon nanotubes, and 100 parts by mass of water. Further, in Example 5-59 in which carbon nanotubes and carbon black were used as the negative electrode conductive agent, a negative electrode mixture slurry was prepared by mixing 100 parts by mass of graphite and Si-C composite material, 3 parts by mass of SBR, 1 part by mass of CMC-Na, 1 part by mass of carbon black, 0.05 parts by mass of carbon nanotubes, and 100 parts by mass of water. Note that here, the mixing ratio of graphite and Si-C composite material is the ratio shown in the "Si-C composite material added amount" column of the table, with the remainder being graphite.

[0162] As shown in Tables 19 to 22, Examples 5-30 to 5-35, in which the porosity of the negative electrode active material layer was 15% or more and 45% or less, exhibited better high-temperature storage characteristics and low-temperature load than Examples 5-29 and 5-36, in which the porosity of the negative electrode active material layer was less than 15% or more than 45%. Therefore, it can be seen that the battery characteristics can be improved by setting the porosity of the negative electrode active material layer to 15% or more and 45% or less.

[0163] As shown in Tables 19 to 22, Example 5-32 and Examples 5-38 to 5-42, in which the content of the Si-C composite material in the negative electrode active material layer was 1% by mass or more and 70% by mass or less, exhibited better battery capacity and low-temperature load characteristics than Example 5-37 and Example 5-43, in which the content of the Si-C composite material in the negative electrode active material layer was less than 1% by mass or more than 70% by mass. Therefore, it can be seen that the battery characteristics can be improved by setting the content of the Si-C composite material in the negative electrode active material layer to 1% by mass or more and 70% by mass or less.

[0164] As shown in Tables 19 to 22, the D of the graphite particles in the negative electrode active material layer ５０ In Examples 5-32 and 5-44 to 5-48, in which the D of the graphite particles in the negative electrode active material layer is 30 μm or less, ５０ The graphite particles in the negative electrode active material layer exhibited good low-temperature load characteristics compared to Example 5-49, in which the diameter of the graphite particles was more than 30 μm. ５０ It can be seen that the battery characteristics can be improved by making the thickness 30 μm or less.

[0165] As shown in Tables 19 to 22, when the specific surface area of ​​the negative electrode active material layer was 1 m ２ / g or more 30m ２ In Examples 5-32, 5-50, 5-52, and 5-54, the specific surface area of ​​the negative electrode active material layer was 30 m / g or less. ２ / g. ２ / g or more 30m ２ It can be seen that the battery characteristics can be improved by keeping the capacitance at 0.15g / g or less.

[0166] As shown in Tables 19 to 22, Examples 5-55 to 5-59 in which the negative electrode active material layer contained a fibrous conductive material (CNT) exhibited better cycle characteristics than Example 5-42 in which the negative electrode active material layer did not contain a fibrous conductive material (CNT). This shows that the battery characteristics can be improved by including a fibrous conductive material in the negative electrode active material layer.

[0167] As shown in Tables 19 to 22, Examples 5-56 to 5-59, in which the negative electrode active material layer contained CNTs with 10 or fewer layers, exhibited better cycle characteristics than Example 5-55, in which the negative electrode active material layer did not contain CNTs with 10 or fewer layers. This shows that the battery characteristics can be improved by including CNTs with 10 or fewer layers in the negative electrode active material layer.

[0168] Sixth Embodiment FIGS. 4 and 5 are schematic cross-sectional views showing a portion of an electrode assembly according to a sixth embodiment. In a secondary battery according to the sixth embodiment, as shown in FIG. 1, the separator 23 includes a substrate 23A containing a polyethylene microporous membrane and coating layers 23B and 23C formed on the main surfaces of the substrate 23A. Here, the coating layer may be provided on only one main surface of the substrate 23A as shown in FIG. 4, or on both main surfaces of the substrate 23A as shown in FIG. 5. The coating layer includes at least one of ceramics, nanofibers, and heat-resistant resin. Furthermore, the coating layer is not limited to being provided on the positive electrode 21 side of the substrate 23A, but may also be provided only on the negative electrode 22 side.

[0169] A separator using ceramics as a coating layer is known as a ceramic coated separator (CCS). Examples of ceramics used as a coating layer include oxides, nitrides, and silicon compounds, specifically aluminum oxide and titanium oxide.

[0170] The nanofibers (NF) used as the coating layer refer to fibrous materials having an average diameter of 200 nm or less, and specific examples thereof include cellulose nanofibers (CNF).

[0171] Examples of the heat-resistant resin used for the coating layer include thermosetting resins, and specific examples thereof include polyimide (PI).

[0172] The thickness of the separator is preferably 15 μm or less, which can improve the battery capacity density.

[0173] The separator preferably has an air resistance of 200 s or less, thereby improving cycle characteristics at high currents. In the present disclosure, air resistance refers to the time required for 100 mL of air to permeate per unit area and unit pressure difference, and can be measured by the Gurley method described in JIS P 8117:2009.

[0174] (Example of Sixth Embodiment) An example of the sixth embodiment will be described below. Note that the present invention is not limited to this example.

[0175] Tables 23 to 25 show Examples 6-1 to 6-30 and Comparative Example 6-1.

[0176]

[0177]

[0178]

[0179] (Examples 6-1 to 6-30, Comparative Example 6-1) In Examples 6-1 to 6-30 and Comparative Example 6-1, as shown in Tables 23 to 25, separators were prepared by the method described below, the components of the electrolyte were set as shown in Tables 23 to 25, and cylindrical cells with a cell size of 21700 and a battery capacity of 5 Ah were prepared, and secondary batteries were prepared in the same manner as the battery according to Comparative Example 1-1, and measurements were performed.

[0180] In Examples 6-2 to 6-3, Examples 6-8 to 6-10, Examples 6-12 to 6-13, Examples 6-18 to 6-20, Examples 6-22 to 6-23, and Examples 6-28 to 6-30, separators were prepared by applying a dispersion of alumina particles to a substrate of polyethylene microporous membrane (manufactured by Seigen Co., Ltd., thickness 10 μm) to form a coating layer. The dispersion was prepared by uniformly dispersing 90 parts by weight of alumina particles (average particle size 0.7 μm) and 10 parts by weight of polyvinyl alcohol (average degree of polymerization 1700, saponification degree 99% or higher) in 150 parts by weight of water and adjusting the viscosity. The coating layer was formed by applying the dispersion to the substrate using a gravure coater and then drying it through a hot air drying oven at 60 °C.

[0181] In Examples 6-6 to 6-7, Examples 6-16 to 6-17, and Examples 6-26 to 6-27, separators were produced by forming a coating layer by applying a nanofiber dispersion solution to a substrate of polyethylene microporous membrane (manufactured by Seigen Co., Ltd., thickness 10 μm). The dispersion solution was prepared by adding 10 parts by weight of unsubstituted CNF (average diameter approximately 50 nm, average length approximately 150 nm, manufactured by Nippon Paper Crecia Co., Ltd.) as nanofibers to 100 parts by weight of deionized water, dispersing the nanofibers by treating with an ultrasonic treatment device for 30 minutes, and adjusting the viscosity. This resulted in a uniform dispersion with appropriate viscosity. The coating layer was formed by applying the dispersion solution to the substrate using a gravure coater under environmental conditions of 25 ° C and 50% humidity, and then drying through a hot air drying oven at 60 ° C.

[0182] In Examples 6-4 to 6-5, 6-14 to 6-15, and 6-24 to 6-25, separators were prepared by forming a coating layer by applying a heat-resistant resin dispersion solution to a polyethylene microporous membrane (manufactured by Seigen Co., Ltd., thickness 10 μm) substrate. The dispersion solution was prepared by adding 10 parts by weight of Matrimid (registered trademark) 5218 (manufactured by Ciba-Geigy), a soluble polyimide resin as the heat-resistant resin, to 80 parts by weight of N-methyl-2-pyrrolidone (NMP), stirring and dissolving the mixture, and then adding 10 parts by weight of Aerosil (registered trademark) 200 (manufactured by Evonik), silica particles with an average particle size of 0.5 μm, to uniformly disperse the mixture, and adjusting the viscosity. The coating layer was formed by applying the dispersion solution to the substrate using a gravure coater, immersing the substrate in pure water at 80°C for 2 hours to remove the silica particles, and then drying the substrate in a hot air drying oven at 60°C.

[0183] In Examples 6-1 to 6-30 and Comparative Example 6-1, a high current cycle characteristic test, a heat ignition test, and a 30-day storage characteristic test were carried out by the following methods.

[0184] <High-Current Cycle Characteristics Test> In the high-current cycle characteristics test, the secondary battery prepared above was repeatedly charged and discharged in a room temperature environment under the following conditions, and the number of cycles at which the discharge capacity could be maintained up to 60% of the discharge capacity at the first cycle was measured as the number of high-current cycles: Charging method: CCCV, Charging rate: 6 A, Charging control voltage: 4.2 V, Charging cut-off current: 1 A, Discharging method: CC, Discharging rate: 50 A, Discharging cut-off voltage: 2.5 V

[0185] <Heat Ignition Test> In the heat ignition test, the secondary battery prepared above was fully charged to 4.2 V at room temperature at 1 A for 2.5 hours, and then heated so that the battery temperature increased at a rate of 1°C / min, and the temperature at which ignition occurred was measured as the heat ignition temperature.

[0186] <30-Day Storage Characteristic Test> In the 30-day storage characteristic test, the secondary battery prepared above was subjected to a first charge-discharge cycle in an environment of 23°C under the following conditions, and the discharge capacity before storage was measured: Charging method: CC, Charging current: 1 A, Charging time: 2.5 hours, End-of-charge voltage: 4.2 V, Discharging method: CC, Discharging current: 1 A, End-of-discharge voltage: 2.5 V.

[0187] The battery was then placed in a thermostatic chamber and stored at 60°C for 30 days, after which it was discharged under the following conditions to measure the discharge capacity after storage. Charge and discharge were performed at 23°C. The ratio of the discharge capacity before storage to the discharge capacity after storage was calculated as the 30-day storage retention rate. That is, the storage retention rate was calculated based on the formula: Storage retention rate (%) = (discharge capacity after storage / discharge capacity before storage) x 100. Discharge method: CC Discharge current: 1 A End-of-discharge voltage: 2.5 V

[0188] Here, a 30-day storage characteristic test was carried out on Comparative Example 6-1, and it was found that a short circuit occurred 98 hours after the start of storage in an environment of 60° C., making it impossible to charge and discharge.

[0189] As shown in Tables 23 to 25, Examples 6-2 to 6-10, 6-12 to 6-20, and 6-22 to 6-30, in which the separator had the coating layer according to the sixth embodiment, exhibited better high-current (50 A) cycle characteristics, high-temperature resistance characteristics, and storage characteristics than Examples 6-1, 6-11, and 6-21, in which the separator did not have the coating layer according to the sixth embodiment. Therefore, it can be seen that the battery characteristics can be improved by providing the separator with the coating layer according to the sixth embodiment.

[0190] As shown in Tables 23 to 25, in Examples 6-2 to 6-8, 6-12 to 6-18, and 6-22 to 6-28, in which the separator air resistance was 200 s or less, the separator air resistance was greater than 200 s. Examples 6-9 to 6-10, 6-19 to 6-20, and 6-29 to 6-30 showed better high current (50 A) cycle characteristics. Therefore, it can be seen that the battery characteristics can be improved by having the separator air resistance of 200 s or less.

[0191] As shown in Tables 23 to 25, Examples 6-2 to 6-9, 6-12 to 6-19, and 6-22 to 6-29, in which the separator thickness was 15 μm or less, showed better battery capacity density than Examples 6-10, 6-20, and 6-30, in which the separator thickness was more than 15 μm. Therefore, it can be seen that the battery characteristics can be improved by making the separator thickness 15 μm or less.

[0192] Seventh Embodiment In a secondary battery according to the seventh embodiment, the negative electrode active material layer contains carbon nanotubes (CNTs). The CNT content in the negative electrode active material layer is 0.01% by mass or more and 1% by mass or less. When the CNT content in the negative electrode active material layer is 0.01% by mass or more, the cycle characteristics and output characteristics are improved. When the CNT content in the negative electrode active material layer is 1% by mass or less, the dispersibility of the negative electrode mixture slurry is improved, and the output characteristics after cycling are improved.

[0193] The negative electrode active material layer preferably contains CNTs with a layer count of 1 to 10. This prevents deterioration of the dispersibility of the negative electrode mixture slurry and improves the output characteristics after cycling. Here, the number of CNT layers refers to the number of graphene sheets forming the wall surfaces of the CNTs, and can be measured from a TEM image of the negative electrode active material layer.

[0194] (Example of Seventh Embodiment) An example of the seventh embodiment will be described below. Note that the present invention is not limited to this example.

[0195] Tables 26 and 27 show Examples 7-1 to 7-23 and Comparative Examples 7-1 and 7-2.

[0196]

[0197]

[0198] (Examples 7-1 to 7-23, Comparative Examples 7-1 to 7-2) In Examples 7-1 to 7-23 and Comparative Examples 7-1 to 7-2, secondary batteries were fabricated and measured in the same manner as the battery according to Comparative Example 1-1, except that batteries were fabricated with the CNT content and number of CNT layers contained in the negative electrode mixture as shown in Tables 26 to 27, as shown in Tables 26 to 27. Here, the negative electrode mixture was prepared by mixing 7% by mass of PVdF as the negative electrode binder, the negative electrode conductive agent at the content shown in Tables 26 to 27, and graphite as the negative electrode active material as the remainder.

[0199] <Slurry Sedimentation Stability Test> Here, a slurry sedimentation stability test was performed on the negative electrode mixture slurries used in the production of the secondary batteries according to Examples 7-1 to 7-23 and Comparative Examples 7-1 and 7-2. In the slurry sedimentation stability test, the negative electrode mixture slurry was uniformly stirred in a dispersion, and a certain amount of the slurry was placed in a cuvette as a sample. The turbidity of the supernatant of the dispersion 60 minutes after the slurry was placed in the cuvette was measured using a spectrophotometer at a measurement light wavelength of 600 nm.

[0200] In Examples 7-1 to 7-23 and Comparative Examples 7-1 and 7-2, a cycle characteristic test was carried out in the same manner as in Comparative Example 1-1, and a 5C output characteristic test was carried out in the following manner.

[0201] <5C Output Characteristics Test> In the 5C output characteristics test, the secondary battery prepared above was subjected to one cycle of charge and discharge in an environment of 23°C under the following first charge and discharge conditions, and the discharge capacity at the first cycle was measured: Charging method: CC, Charging rate: 0.2C, End-of-charge voltage: 4.2V, Discharging method: CC, Discharging rate: 0.2C, End-of-discharge voltage: 2.5V.

[0202] Thereafter, the battery was charged and discharged up to the 100th cycle under the second charge-discharge condition described below, and the discharge capacities at the second and 100th cycles were measured. Charge and discharge were performed in an environment of 23°C. The ratio of the discharge capacity at the second cycle to the discharge capacity at the first cycle was calculated as the 5C discharge retention rate. That is, the 5C discharge retention rate was calculated based on the following formula: 5C discharge retention rate (%) = (discharge capacity at the second cycle / discharge capacity at the first cycle) × 100. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was calculated as the post-cycling 5C discharge retention rate. That is, the post-cycling 5C discharge retention rate was calculated based on the following formula: 5C discharge retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100. Charging method: CC, Charge rate: 0.2C, End-of-charge voltage: 4.2V, Discharging method: CC, Discharge rate: 5C, End-of-discharge voltage: 2.5V

[0203] As shown in Tables 26 and 27, Examples 7-1 to 7-9 and Examples 7-11 to 7-23, in which the CNT content in the negative electrode active material layer was 0.01% by mass or more and 1% by mass or less, exhibited better charge-discharge characteristics than Example 7-10, in which the CNT content in the negative electrode active material layer was less than 0.01% by mass or more than 1% by mass. Therefore, it can be seen that the battery characteristics can be improved by having the CNT content in the negative electrode active material layer be 0.01% by mass or more and 1% by mass or less.

[0204] As shown in Tables 26 and 27, Examples 7-1 to 7-9 and Examples 7-11 to 7-23, in which the number of CNT layers contained in the negative electrode active material layer was 1 to 10, exhibited good charge-discharge characteristics. Therefore, it can be seen that the battery characteristics can be improved by having the number of CNT layers contained in the negative electrode active material layer be 1 to 10.

[0205] Eighth Embodiment Fig. 6 is a schematic cross-sectional view showing a negative electrode active material particle according to an eighth embodiment. In the secondary battery according to the eighth embodiment, the positive electrode active material layer contains at least one of NiOOH, lithium carbonate, and lithium hydroxide, and more preferably contains NiOOH. As shown in Fig. 6, the NiOOH contained in the positive electrode active material layer is preferably contained in a coating P40 of the positive electrode active material particle P30. This protects the surface of the positive electrode active material particle P30 and improves high-temperature storage characteristics while suppressing deterioration of the low-temperature cycle and low-temperature load due to the properties of the electrolyte.

[0206] Whether the positive electrode active material layer contains at least one of NiOOH, lithium carbonate, and lithium hydroxide can be measured using a thermogravimetry mass spectrometer (TG-MS). More specifically, if a weight loss is observed in a temperature range of 200°C or higher and 300°C or lower using TG-MS with a sample of the positive electrode active material layer removed from the secondary battery, it can be determined that the positive electrode active material layer contains at least one of NiOOH, lithium carbonate, and lithium hydroxide. Furthermore, if Ni and O are detected by XPS on the surface of the positive electrode active material particles, it can be determined that the positive electrode active material layer contains NiOOH.

[0207] (Example of Eighth Embodiment) An example of the eighth embodiment will be described below. Note that the present invention is not limited to this example.

[0208] Tables 28 and 29 show Examples 8-1 to 8-20 and Comparative Examples 8-1 and 8-2.

[0209]

[0210]

[0211] (Examples 8-1 to 8-20, Comparative Examples 8-1 to 8-2) In Examples 8-1 to 8-20 and Comparative Examples 8-1 to 8-2, the components of the positive electrode active material layer were LiNi as the positive electrode active material. ０．９２ Co ０．０６ Mn ０．０２ O ２ A secondary battery was produced in the same manner as the battery according to Comparative Example 1-1, except that a battery was produced by mixing polyvinylidene fluoride (PVdF) as a positive electrode binder, carbon black as a positive electrode conductive agent, and NiOOH in a mass ratio of 91:3:(6-x):x (x is the value listed in the "NiOOH content" column in Tables 28 and 29). Charging method: CCCV, charging rate: 0.1C, charging control voltage: 4.2V, charging cut-off current: 0.05C, discharging method: CC, discharging rate: 0.1C, discharging cut-off voltage: 2.5V.

[0212] As shown in Tables 28 and 29, Examples 8-1 to 8-4 and 8-6 to 8-20 in which the positive electrode active material layer contained NiOOH exhibited better charge-discharge characteristics than Example 8-5 in which the positive electrode active material layer did not contain NiOOH. Therefore, it is clear that the battery characteristics can be improved by including NiOOH in the positive electrode active material layer.

[0213] Ninth Embodiment Fig. 7 is a schematic cross-sectional view showing a negative electrode active material particle according to a ninth embodiment. In a secondary battery according to the ninth embodiment, the positive electrode active material layer contains a metal-organic framework. As shown in Fig. 7, the positive electrode active material layer is preferably a composite particle including positive electrode active material particles P50 and a coating layer P60 containing a metal-organic framework. This protects the surface of the positive electrode active material particles P30 and improves high-temperature storage characteristics while suppressing deterioration of cycle characteristics and low-temperature load characteristics due to the characteristics of the electrolyte.

[0214] A metal-organic framework (MOF) is a structure in which a central metal atom and organic ligands (e.g., a multidentate ligand having two or more coordinating functional groups) are continuously bonded. The MOF may be an MOF having multiple metal, metal oxide, metal cluster, or metal oxide cluster structural units. Here, the presence or absence and type of metal-organic framework in the positive electrode active material layer can be identified by XRD.

[0215] Examples of the central metal atom of MOF include zinc, cobalt, niobium, zirconium, cadmium, copper, nickel, chromium, vanadium, titanium, molybdenum, magnesium, iron, aluminum, and zirconium. ４＋ , Zn ２＋ , Cu ２＋ , Ni ２＋ , Co ２＋ and metal-containing secondary building units (SBUs).

[0216] The coordinating functional group of the organic ligand of the MOF may be any functional group capable of coordinating to a metal atom, such as a carboxyl group, imidazole group, hydroxyl group, sulfonic acid group, pyridine group, tertiary amine group, amide group, or thioamide group. Among these, a carboxyl group is preferred. The two or more coordinating functional groups possessed by the organic bridging ligand may be the same or different.

[0217] As the organic ligand of MOF, typically, two or more coordinating functional groups are substituted on a skeleton having a rigid structure (e.g., an aromatic ring, an unsaturated bond, etc.). Specific examples of organic bridging ligands include 1,3,5-tris(4-carboxyphenyl)benzene (BTB), 1,4-benzenedicarboxylic acid (BDC), 2,5-dihydroxy-1,4-benzenedicarboxylic acid (DOBDC), cyclobutyl-1,4-benzenedicarboxylic acid (CB BDC), and 2-amino-1,4-benzenedicarboxylic acid (H2N BDC), tetrahydropyrene-2,7-dicarboxylic acid (HPDC), terphenyl dicarboxylic acid (TPDC), 2,6-naphthalenedicarboxylic acid (2,6-NDC), pyrene-2,7-dicarboxylic acid (PDC), biphenyl dicarboxylic acid (BPDC), any dicarboxylic acid having a phenyl compound, 3,3',5,5'-biphenyltetracarboxylic acid, imidazole, 2-methylimidazole, benzimidazole, 2-nitroimidazole, cyclobenzimidazole, imidazole-2-carboxaldehyde, 4-cyanoimidazole, 6-methylbenzimidazole, 6-bromobenzimidazole, and the like.

[0218] Examples of MOFs include, but are not limited to, the following substances: MOF-177: Zn ４ O(1,3,5-benzenetribenzoate) ２ ・MOF-5 (IRMOF-I): Zn ４ O(1,4-benzenedicarboxylate) ３ ・MOF-74 (Mg): Mg ２ (2,5-dihydroxy-1,4-benzenedicarboxylate) MOF-74(Zn): Zn ２ (2,5-dihydroxy-1,4-benzenedicarboxylate) MOF-505: Cu ２ (3,3',5,5'-biphenyltetracarboxylate) IRMOF-6: Zn ４ O(cyclobutyl-1,4-benzenedicarboxylate) IRMOF-3:Zn ４ O(2-amino-1,4-benzenedicarboxylate) ３・IRMOF-11:Zn ４ O (terphenyl dicarboxylate) ３ or Zn ４ O(tetrahydropyrene-2,7-dicarboxylate) ３ ・IRMOF-8:Zn ４ O(tetrahydropyrene-2,7-dicarboxylate) ３ ZIF-8: Zn(2-methylimidazolate) ２ ZIF-68: Zn(benzimidazolate) (2-nitroimidazolate) ZIF-69: Zn(cyclobenzimidazolate) (2-nitroimidazolate) ZIF-7: Zn(benzimidazolate) ２ ZIF-9: Co(benzimidazolate) ２ ・ZIF-11: Zn ２ (benzimidazolate) ZIF-90: Zn(imidazolate-2-carboxaldehyde) ２ ZIF-82: Zn(4-cyanoimidazolate) (2-nitroimidazolate) ZIF-70: Zn(imidazolate) (2-nitroimidazolate) ZIF-79: Zn(6-methylbenzimidazolate) (2-nitroimidazolate) ZIF-81: Zn(6-bromobenzimidazolate) (2-nitroimidazolate) NU-1000: Zr ６ (OH) ８ (4,4',4'',4''''-(pyrene-1,3,6,8-tetrayl)tetratetrabenzaldehyde) ２ ・UiO-66:Zr ６ (OH) ４ O ４ (Benzene-1,4-dicarboxylate) ６

[0219] Preferred MOFs are zinc-based MOFs such as ZIF-8, and zirconia-based MOFs such as NU-1000 and UiO-66. ZIFs are materials with zeolite-like topology that contain zinc or cobalt as the central metal atom and imidazole-based organic bridging ligands (imidazole, benzimidazole, 2-nitroimidazole, 2-methylimidazole, cyclobenzimidazole, imidazole-2-carboxaldehyde, 4-cyanoimidazole, 6-methylbenzimidazole, 6-bromobenzimidazole, etc.) as organic ligands.

[0220] The MOF may be commercially available or may be produced by a known production method. For example, methods described in International Publication No. 2019 / 039509 and the like can be used as a production method for MOFs. Specifically, a MOF is produced by applying a stimulus to a composition containing a substance (A) containing a central metal atom, an organic substance (B) that coordinates to the central metal atom to form a crystalline body, and a coordination promoter (C). Here, the substance (A) containing a central metal atom is a substance other than a MOF that contains the central metal atom that constitutes the MOF. The organic substance (B) has two or more metal coordination moieties to the central metal atom. The coordination promoter (C) promotes the coordination of the organic substance (B) to the metal atom of the substance (A) by reaction or phase transition. Furthermore, the pore distribution of the produced MOF can be adjusted by changing the type and equivalent of the coordination promoter (C). For example, the pore size of the MOF can be changed by changing the type of base used as the coordination promoter (C) (e.g., amine-borane complex, dicyandiamide, hydrazide, imine, oxazolidine, pyridine, tertiary amine, ketoprofen amine salt, secondary amine, primary amine, or a mixture thereof).

[0221] (Example of the ninth embodiment) An example of the ninth embodiment will be described below. Note that the present invention is not limited to this example.

[0222] Tables 30 and 31 show Examples 9-1 to 9-18.

[0223]

[0224]

[0225] (Examples 9-1 to 9-18) In Examples 9-1 to 9-18, as shown in Tables 30 to 31, the components of the positive electrode active material layer were a positive electrode mixture, a positive electrode active material, polyvinylidene fluoride (PVdF) as a positive electrode binder, carbon black as a positive electrode conductive agent, and MOF as a metal organic framework, mixed in a mass ratio of 91:3:(6-x):x (x is the value listed in the "MOF content" column in Tables 30 to 31). A secondary battery was produced in the same manner as the battery according to Comparative Example 1-1, and measurements were performed. As the positive electrode active material, in Examples 9-1 to 9-6 and Example 9-9, an NCA-based active material (LNCA:LiNi ０．８２ Co ０．１４ Al ０．４ O ２ In Example 9-7, LFP (LiFePO ４ In Example 9-8, LCO (LiCoO ２ As the MOF material, UiO-66 (manufactured by Aldrich) was used in Examples 9-2 to 9-5 and Examples 9-7 to 9-8, and ZIF-8 (manufactured by Aldrich) was used in Example 9-O.

[0226] In Examples 9-1 to 9-18, the above-mentioned cycle characteristic test, storage characteristic test, and low-temperature load characteristic test were carried out.

[0227] As shown in Tables 30 and 31, in Examples 9-2 to 9-8, 9-13 to 9-14, and 9-17 to 9-18, in which the positive electrode active material layer contains MOF as the metal organic framework, the positive electrode active material layer does not contain MOF as the metal organic framework. Compared with Examples 9-1, 9-9 to 9-12, and 9-15 to 9-16, the charge and discharge characteristics were better. Therefore, it can be seen that the battery characteristics can be improved by including MOF as the metal organic framework in the positive electrode active material layer.

[0228] Tenth Embodiment Fig. 8 shows a cross-sectional configuration of a secondary battery according to a tenth embodiment. As shown in Fig. 8, the secondary battery according to the tenth embodiment is a so-called wound cylindrical battery in which an electrode winding body is housed in a cylindrical outer can 11 as a battery element 20. The electrode winding body is stacked with a separator sandwiched between a positive electrode and a negative electrode, and is wound around a central axis extending in a first direction.

[0229] Specifically, the secondary battery 1A includes, for example, a pair of insulating plates 12, 13 and a battery element 20 inside an outer can 11. The battery element 20 is a structure in which, for example, a positive electrode 21 and a negative electrode 22 are stacked and wound with a separator 23 interposed therebetween. The battery element 20 is impregnated with an electrolytic solution, which is a liquid electrolyte. The secondary battery 1A may further include, inside the outer can 11, one or more of a thermosensitive resistor element such as a PTC (Positive Temperature Coefficient) thermistor and a reinforcing member.

[0230] (External Can 11) The external can 11 has, for example, a hollow cylindrical structure with a closed lower end and an open upper end in the Y-axis direction (height direction). Therefore, the upper end of the external can 11 is an open end 11N. The external can 11 is made of a material containing, for example, a metal material such as iron. However, the surface of the external can 11 may be plated with a metal material such as nickel. The insulating plates 12 and 13 are disposed opposite each other in the Y-axis direction, for example, with the battery element 20 sandwiched between them. Note that in the tenth embodiment, the open end 11N and its vicinity in the Y-axis direction may be referred to as the upper portion of the secondary battery 1A, and the closed portion of the external can 11 and its vicinity may be referred to as the lower portion of the secondary battery 1A.

[0231] (Insulating Plates 12, 13) Each of the insulating plates 12, 13 is, for example, a dish-shaped plate having a surface perpendicular to the winding axis of the battery element 20, i.e., a surface perpendicular to the Y-axis in Fig. 8. The insulating plates 12, 13 are arranged to sandwich the battery element 20 therebetween.

[0232] (Crimped structure 11R) The open end 11N of the exterior can 11 has a structure in which the battery lid 14 and the safety valve mechanism 16 are crimped via a gasket 15, i.e., a crimped structure 11R. The battery lid 14 seals the exterior can 11 with the battery element 20 and other components housed inside. The crimped structure 11R is a so-called crimped structure and has a folded portion 11P as a so-called crimp portion.

[0233] (Battery lid 14) The battery lid 14 is a closing member that mainly closes the open end 11N when the battery element 20 and other components are housed inside the exterior can 11. The battery lid 14 contains, for example, the same material as the material from which the exterior can 11 is formed. The central region of the battery lid 14 protrudes upward (in the +Z direction), for example. As a result, the peripheral region of the battery lid 14 other than the central region is in contact with, for example, the safety valve mechanism 16.

[0234] (Gasket 15) The gasket 15 is primarily a sealing member interposed between the folded portion 11P of the outer can 11 and the battery lid 14. The gasket 15 seals the gap between the folded portion 11P and the battery lid 14. However, the surface of the gasket 15 may be coated with, for example, asphalt. The gasket 15 contains, for example, one or more insulating materials. The type of insulating material is not particularly limited, but examples include polymeric materials such as polybutylene terephthalate (PBT) and polypropylene (PP). Among these, polybutylene terephthalate is preferred as the insulating material. This is because the gap between the folded portion 11P and the battery lid 14 is sufficiently sealed while electrically isolating the outer can 11 and the battery lid 14 from each other.

[0235] (Safety valve mechanism 16) The safety valve mechanism 16 is mainly configured to release the internal pressure of the outer can 11 by releasing the sealed state of the outer can 11 as necessary when the pressure inside the outer can 11 (internal pressure) increases. The internal pressure of the outer can 11 may increase, for example, due to gas generated by a decomposition reaction of the electrolyte during charging and discharging. The internal pressure of the outer can 11 may also increase due to external heating.

[0236] (Battery element 20) The battery element 20 is a power generation element that causes charge / discharge reactions to proceed, and is housed inside the outer can 11. The battery element 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution that is a liquid electrolyte.

[0237] FIG. 9 is a development view of a battery element according to a tenth embodiment, schematically illustrating a portion of a laminate structure S20 including a positive electrode 21, a negative electrode 22, and a separator 23. In the battery element 20, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 interposed therebetween. That is, the battery element 20 has a four-layer laminate structure S20 in which the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 are stacked. The positive electrode 21, the negative electrode 22, and the separator 23 are all substantially strip-shaped members with the W-axis direction as their short side and the L-axis direction as their long side. In the battery element 20, the laminate structure S20 is wound around a central axis CL (see FIG. 8 ) extending in the Y-axis direction so as to form a spiral shape in a horizontal cross section perpendicular to the Y-axis direction. At this time, the laminate structure S20 is wound in an orientation in which the W-axis direction is approximately aligned with the Y-axis direction. The battery element 20 has a generally cylindrical appearance overall. The positive electrode 21 and the negative electrode 22 are wound while facing each other with a separator 23 interposed therebetween. A through-hole 26 is formed at the center of the battery element 20 as an internal space. The through-hole 26 is a hole for inserting a winding core for assembling the battery element 20 and an electrode rod for welding.

[0238] The positive electrode 21, the negative electrode 22, and the separator 23 are wound such that the separator 23 is disposed at both the outermost and innermost peripheries of the battery element 20. At the outermost periphery of the battery element 20, the negative electrode 22 is disposed outside the positive electrode 21, and at the innermost periphery of the battery element 20, the negative electrode 22 is disposed inside the positive electrode 21. The number of windings of each of the positive electrode 21, the negative electrode 22, and the separator 23 is not particularly limited and can be set as desired.

[0239] FIG. 10A is a development view of a positive electrode according to the tenth embodiment. It is a schematic representation of the state before winding. FIG. 10B shows a cross-sectional configuration of a positive electrode 21. Note that FIG. 10B shows a cross section taken along line IIIB-IIIB in FIG. 10A as viewed from the arrow direction. The positive electrode 21 includes, for example, a positive electrode current collector 21A and a positive electrode active material layer 21B provided on the positive electrode current collector 21A. The positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A, or on both sides of the positive electrode current collector 21A. FIG. 10B shows a case in which the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A.

[0240] The positive electrode 21 has a positive electrode covering portion 211 in which a positive electrode current collector 21A is covered with a positive electrode active material layer 21B, and a positive electrode exposed portion 212 in which the positive electrode current collector 21A is exposed without being covered with the positive electrode active material layer 21B. As shown in FIG. 10A , the positive electrode covering portion 211 and the positive electrode exposed portion 212 each extend from the innermost peripheral end to the outermost peripheral end of the battery element 20 along the L-axis direction, which is the longitudinal direction. The positive electrode covering portion 211 and the positive electrode exposed portion 212 are adjacent to each other in the W-axis direction, which is the lateral direction. Note that the positive electrode exposed portion 212 is connected to the positive electrode current collector plate 24 as shown in FIG. 8 . An insulating layer 101 may be provided near the positive electrode covering portion 211 and the positive electrode exposed portion 212. The insulating layer 101 may also extend from the innermost peripheral edge to the outermost peripheral edge of the battery element 20, similar to the positive electrode covering portion 211 and the positive electrode exposed portion 212. The detailed configuration of the positive electrode 21 will be described later.

[0241] FIG. 11A is a developed view of the negative electrode of the tenth embodiment, schematically illustrating the state before winding. FIG. 11B illustrates a cross-sectional configuration of the negative electrode 22. Note that FIG. 11B illustrates a cross section taken along line IVB-IVB in FIG. 11A as viewed from the arrow direction. The negative electrode 22 includes, for example, a negative electrode current collector 22A and a negative electrode active material layer 22B provided on the negative electrode current collector 22A. The negative electrode active material layer 22B may be provided on only one side of the negative electrode current collector 22A, or on both sides of the negative electrode current collector 22A. FIG. 11B illustrates a case where the negative electrode active material layer 22B is provided on both sides of the negative electrode current collector 22A.

[0242] The negative electrode 22 has a negative electrode covering portion 221 in which a negative electrode active material layer 22B is covering a negative electrode current collector 22A, and a negative electrode exposed portion 222 in which the negative electrode current collector 22A is exposed without being covered by the negative electrode active material layer 22B. As shown in FIG. 11A , the negative electrode covering portion 221 and the negative electrode exposed portion 222 each extend along the L-axis direction, which is the longitudinal direction. The negative electrode exposed portion 222 extends from the innermost peripheral end to the outermost peripheral end of the battery element 20. In contrast, the negative electrode covering portion 221 is not provided at the innermost peripheral end or the outermost peripheral end of the battery element 20. As shown in FIG. 11A , parts of the negative electrode exposed portion 222 are formed to sandwich the negative electrode covering portion 221 in the L-axis direction, which is the longitudinal direction. Specifically, the negative electrode exposed portion 222 includes a first portion 222A, a second portion 222B, and a third portion 222C. The first portion 222A is adjacent to the negative electrode cover portion 221 in the W-axis direction and extends in the L-axis direction from the innermost peripheral end to the outermost peripheral end of the battery element 20. The second portion 222B and the third portion 222C are arranged to sandwich the negative electrode cover portion 221 in the L-axis direction. The second portion 222B is located near the innermost peripheral end of the battery element 20, for example, and the third portion 222C is located near the outermost peripheral end of the battery element 20. As shown in FIG. 8 , the first portion 222A of the negative electrode exposed portion 222 is connected to the negative electrode current collector plate 25. The detailed configuration of the negative electrode 22 will be described later.

[0243] In the secondary battery 1A, the stacked structure S20 of the battery element 20 is formed by stacking the positive electrode 21 and the negative electrode 22 via the separator 23 so that the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 face opposite each other along the W-axis direction, which is the width direction. The battery element 20 has the end of the separator 23 fixed by attaching a fixing tape 46 to the side surface portion 45 thereof, preventing loosening of the winding.

[0244] In the secondary battery 1A, as shown in FIG. 9 , when the width of the positive electrode exposed portion 212 is WA and the width of the first portion 222A of the negative electrode exposed portion 222 is WB, it is preferable that WA > WB. For example, when the width WA = 7 (mm), the width WB = 4 (mm). Furthermore, when the width of the portion of the positive electrode exposed portion 212 that protrudes from the outer edge of the separator 23 in the width direction is WC and the length of the first portion 222A of the negative electrode exposed portion 222 that protrudes from the outer edge of the separator 23 on the opposite side in the width direction is WD, it is preferable that WC > WD. For example, when the width WC = 4.5 (mm), the width WD = 3 (mm).

[0245] As shown in Fig. 8 , in the upper part of the secondary battery 1A, of the positive electrode exposed portion 212 wound around the central axis CL, a plurality of first edges 212E adjacent in the radial direction (R direction) of the battery element 20 are bent toward the central axis CL so as to overlap with each other. Similarly, in the lower part of the secondary battery 1A, of the negative electrode exposed portion 222 wound around the central axis CL, a plurality of second edges 222E adjacent in the radial direction (R direction) of the battery element 20 are bent toward the central axis CL so as to overlap with each other. Therefore, the plurality of first edges 212E of the positive electrode exposed portion 212 are gathered at an end face 41 of the upper part of the battery element 20, and the plurality of second edges 222E of the negative electrode exposed portion 222 are gathered at an end face 42 of the lower part of the battery element 20. In order to improve contact between the positive electrode current collector plate 24 for extracting current and the first edges 212E, To achieve this, the plurality of first edges 212E bent toward the central axis CL have flat surfaces. Similarly, to improve contact between the negative electrode current collector plate 25 and the second edge portion 222E for extracting current, the plurality of second edges 222E bent toward the central axis CL have flat surfaces. Note that the flat surface referred to here does not only include a completely flat surface, but also includes a surface having some unevenness or surface roughness to the extent that the positive electrode exposed portion 212 and the negative electrode exposed portion 222 can be joined to the positive electrode current collector plate 24 and the negative electrode current collector plate 25, respectively.

[0246] As described above, the positive electrode current collector 21A is made of, for example, aluminum foil. On the other hand, the negative electrode current collector 22A is made of, for example, copper foil, as described above. In this case, the positive electrode current collector 21A is softer than the negative electrode current collector 22A. That is, the Young's modulus of the positive electrode exposed portion 212 is lower than that of the negative electrode exposed portion 222. Therefore, in one embodiment, WA > WB and WC > WD are more preferable. In this case, when the positive electrode exposed portion 212 and the negative electrode exposed portion 222 are folded simultaneously from both electrode sides with the same pressure, the heights of the folded portions measured from the tip of the separator 23 may be approximately the same for the positive electrode 21 and the negative electrode 22. At this time, the multiple first edge portions 212E ( FIG. 8 ) of the positive electrode exposed portion 212 are folded and overlap each other to a moderate degree. This facilitates joining of the positive electrode exposed portion 212 and the positive electrode current collector 24. Similarly, the plurality of second edge portions 222E ( FIG. 8 ) of the negative electrode exposed portion 222 are folded and overlap each other to an appropriate degree, which facilitates joining of the negative electrode exposed portion 222 and the negative electrode current collector plate 25. The joining here means joining by, for example, laser welding, but the joining method is not limited to laser welding.

[0247] As shown in FIG. 9 , the portion of the positive electrode exposed portion 212 of the positive electrode 21 that faces the negative electrode 22 across the separator 23 is covered with an insulating layer 101. The insulating layer 101 has a width of, for example, 3 mm in the W-axis direction. The insulating layer 101 covers the entire area of ​​the positive electrode exposed portion 212 of the positive electrode 21 that faces the negative electrode covering portion 221 of the negative electrode 22 via the separator 23. The insulating layer 101 can effectively prevent an internal short circuit in the secondary battery 1A, for example, when a foreign object enters between the negative electrode covering portion 221 and the positive electrode exposed portion 212. Furthermore, when an impact is applied to the secondary battery 1A, the insulating layer 101 absorbs the impact and can effectively prevent bending of the positive electrode exposed portion 212 and short circuiting between the positive electrode exposed portion 212 and the negative electrode 22.

[0248] (Insulating Tapes 53, 54) The secondary battery 1A may further include insulating tapes 53, 54 in the gap between the outer can 11 and the battery element 20. The positive electrode exposed portion 212 and the negative electrode exposed portion 222, which are gathered on the end faces 41, 42, are conductors such as bare metal foil. Therefore, if the positive electrode exposed portion 212 and the negative electrode exposed portion 222 are in close proximity to the outer can 11, a short circuit may occur between the positive electrode 21 and the negative electrode 22 through the outer can 11. Furthermore, if the positive electrode current collector 24 on the end face 41 comes close to the outer can 11, a short circuit may also occur. For this reason, it is preferable to provide insulating tapes 53, 54 as insulating members. The insulating tapes 53, 54 are, for example, adhesive tapes whose base layer is made of polypropylene, polyethylene terephthalate, or polyimide and whose adhesive layer is formed on one surface of the base layer. In order to prevent the installation of the insulating tapes 53 and 54 from reducing the volume of the battery element 20, the insulating tapes 53 and 54 are positioned so as not to overlap with the fixing tape 46 attached to the side portion 45, and the thickness of the insulating tapes 53 and 54 is set to be equal to or less than the thickness of the fixing tape 46.

[0249] (Positive current collector 24 and negative current collector 25) In a typical lithium-ion secondary battery, for example, a lead for current extraction is welded to each of the positive and negative electrodes. However, this increases the internal resistance of the lithium-ion secondary battery and causes the lithium-ion secondary battery to heat up and reach high temperatures during discharge, making it unsuitable for high-rate discharge. Therefore, in the secondary battery 1A according to the tenth embodiment, the positive current collector 24 is disposed on end face 41 and the negative current collector 25 is disposed on end face 42. The positive electrode exposed portion 212 on end face 41 is welded to the positive electrode collector 24 at multiple points, and the negative electrode exposed portion 222 on end face 42 is welded to the negative electrode collector 25 at multiple points. This reduces the internal resistance of the secondary battery 1A. The flat surfaces of the end faces 41 and 42, as described above, also contribute to the low resistance. The positive current collector 24 is electrically connected to the battery cover 14, for example, via a safety valve mechanism 16. The negative electrode current collector plate 25 is electrically connected to the outer can 11, for example.

[0250] FIG. 12A is a schematic diagram illustrating an example of the configuration of a positive current collector plate according to the tenth embodiment. As shown in FIG. 12A , the positive current collector plate 24 has a shape in which a substantially rectangular band-shaped portion 242 is connected to a substantially fan-shaped sector portion 241. A through-hole 243 is formed near the center of the sector portion 241. In the secondary battery 1A, the positive current collector plate 24 is provided such that the through-hole 243 overlaps with the through-hole 26 in the Y-axis direction. The hatched portion in FIG. 12A is an insulating portion 242A of the band-shaped portion 242. The insulating portion 242A is a portion of the band-shaped portion 242 to which insulating tape is attached or an insulating material is applied. The portion of the band-shaped portion 242 below the insulating portion 242A is a connection portion 242B to the sealing plate, which also serves as an external terminal. 8 , when the secondary battery 1A has a battery structure in which the through-hole 26 does not have a metal center pin, the strip portion 242 is less likely to come into contact with the portion at the negative electrode potential. Therefore, the positive electrode current collector 24 does not need to have the insulating portion 242A. When the positive electrode current collector 24 does not have the insulating portion 242A, the charge / discharge capacity can be increased by increasing the width between the positive electrode 21 and the negative electrode 22 by an amount corresponding to the thickness of the insulating portion 242A.

[0251] FIG. 12B is a schematic diagram illustrating a configuration example of a negative current collector plate according to the tenth embodiment. The shape of the negative current collector plate 25 shown in FIG. 12B is almost identical to the shape of the positive current collector plate 24 shown in FIG. 12A . However, the strip portion 252 of the negative current collector plate 25 is different from the strip portion 242 of the positive current collector plate 24. The strip portion 252 of the negative current collector plate 25 is shorter than the strip portion 242 of the positive current collector plate 24 and does not have a portion corresponding to the insulating portion 242A of the positive current collector plate 24. The strip portion 252 has a round protrusion 254, indicated by multiple circles. During resistance welding, current concentrates on the protrusion 254, melting the protrusion 254 and welding the strip portion 252 to the bottom of the outer can 11. Like the positive current collector plate 24, the negative current collector plate 25 has a through-hole 253 formed near the center of the sector portion 251. In the secondary battery 1A, the negative electrode current collector plate 25 is provided so that the through-hole 253 overlaps with the through-hole 26 in the Y-axis direction.

[0252] Due to its planar shape, the sectorial portion 241 of the positive current collector plate 24 covers only a portion of the end surface 41. Similarly, due to its planar shape, the sectorial portion 251 of the negative current collector plate 25 covers only a portion of the end surface 42. The sectorial portions 241 and 251 do not cover the entire end surface 41 and the end surface 42, for example, for the following two reasons. First, this is to allow the electrolyte to smoothly penetrate into the battery element 20 when assembling the secondary battery 1A, for example. Second, this is to facilitate the release of gas generated when the lithium-ion secondary battery is in an abnormally high temperature state or an overcharged state.

[0253] (Positive electrode active material layer 21B) The area density of the positive electrode active material layer 21B is 21.5 mg / cm ２ 23.5mg / cm or more ２ 10B , the ratio T2 / T1 of the thickness T2 of the positive electrode covering portion 211 to the thickness T1 of the positive electrode current collector 21A, i.e., the total thickness T2 of the positive electrode current collector 21A and the positive electrode active material layer 21B, is preferably 5.0 or more and 6.5 or less. This is because a temperature rise of the secondary battery 1A during high-load rate charging can be suppressed. Furthermore, as shown in FIG. 10B , the ratio T2 / T1 of the thickness T2 of the positive electrode covering portion 211 to the thickness T1 of the positive electrode current collector 21A, i.e., the total thickness T2 of the positive electrode current collector 21A and the positive electrode active material layer 21B, is preferably 5.0 or more and 6.5 or less.

[0254] As described above, in the secondary battery according to the tenth embodiment, the positive electrode has a positive electrode covering portion in which a positive electrode active material layer is covering a positive electrode current collector, and a positive electrode exposed portion in which the positive electrode current collector is not covered by the positive electrode active material layer and is joined to a positive electrode current collector. The negative electrode also has a negative electrode covering portion in which a negative electrode active material layer is covering a negative electrode current collector, and a negative electrode exposed portion in which the negative electrode current collector is not covered by the negative electrode active material layer and is joined to a negative electrode current collector. This improves the output characteristics and large-current discharge cycle characteristics, and extends the battery life.

[0255] (Secondary Battery Manufacturing Method) Fig. 13 is a process chart illustrating a method for manufacturing a secondary battery according to embodiment 10. The method for manufacturing the secondary battery 1A will be described with reference to Fig. 13 in addition to Figs. 8 to 12B.

[0256] First, a positive electrode current collector 21A is prepared, and a positive electrode active material layer 21B is selectively formed on the surface of the positive electrode current collector 21A to form a positive electrode 21 having a positive electrode covering portion 211 and a positive electrode exposed portion 212. Next, a negative electrode current collector 22A is prepared, and a negative electrode active material layer 22B is selectively formed on the surface of the negative electrode current collector 22A to form a negative electrode 22 having a negative electrode covering portion 221 and a negative electrode exposed portion 222. Thereafter, notches are formed in a portion of the positive electrode exposed portion 212 and a portion of the negative electrode exposed portion 222 that correspond to the start of winding. A drying process may be performed on the positive electrode 21 and the negative electrode 22. Next, a stacked structure S20 is formed by stacking the positive electrode 21 and the negative electrode 22 with the separator 23 interposed between them so that the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 are opposite each other in the W-axis direction. Thereafter, the laminated structure S20 is spirally wound so that the through-holes 26 are formed and the notches are positioned near the central axis CL. Furthermore, a fixing tape 46 is attached to the outermost periphery of the spirally wound laminated structure S20. In this way, the battery element 20 is obtained as shown in step S1 of FIG. 13 .

[0257] Next, as shown in step S2 of Fig. 13 , the edge of a flat plate having a thickness of, for example, 0.5 mm is pressed perpendicularly against the end faces 41, 42 of the battery element 20, i.e., in the Y-axis direction, to locally bend the end faces 41, 42. As a result, grooves 43 are formed extending radially from the through-holes 26 in the radial direction (R direction). Note that the number and arrangement of the grooves 43 shown in step S2 of Fig. 13 are merely examples and the present disclosure is not limited thereto.

[0258] 13 , substantially the same pressure is applied from above and below the battery element 20 substantially simultaneously and in a direction approximately perpendicular to the end surface 41 and the end surface 42. This bends the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222, respectively, so that the end surface 41 and the end surface 42 become flat. At this time, the first edge 212E of the positive electrode exposed portion 212 and the second edge 222E of the negative electrode exposed portion 222 on the end surface 41 and the end surface 42 are bent while overlapping toward the through hole 26. After that, the sector-shaped portion 241 of the positive electrode current collector 24 is joined to the end surface 41 by laser welding or the like, and the sector-shaped portion 251 of the negative electrode current collector 25 is joined to the end surface 42 by laser welding or the like.

[0259] Next, insulating tapes 53 and 54 are attached to predetermined positions of the battery element 20. Thereafter, as shown in step S4 of Fig. 13 , the strip portion 242 of the positive current collector plate 24 is bent and inserted into the hole 12H of the insulating plate 12. Also, the strip portion 252 of the negative current collector plate 25 is bent and inserted into the hole 13H of the insulating plate 13.

[0260] Next, the battery element 20 assembled as described above is inserted into the outer can 11 shown in step S5 of Figure 13, and then the bottom of the outer can 11 is welded to the negative electrode current collector 25. After that, a constricted portion 11S is formed near the open end 11N of the outer can 11. Furthermore, after the electrolyte is poured into the outer can 11, the strip portion 242 of the positive electrode current collector 24 is welded to the safety valve mechanism 16.

[0261] Next, as shown in step S6 of FIG. 13, the gasket 15, the safety valve mechanism 16, and the battery lid 14 are used to seal the narrowed portion 11S.

[0262] In this way, the secondary battery 1 according to the tenth embodiment is completed.

[0263] (Example of Tenth Embodiment) An example of the tenth embodiment will be described below. Note that the present invention is not limited to this example.

[0264] Tables 32 to 34 show Examples 10-1 to 10-32 and Comparative Examples 10-1 to 10-5.

[0265]

[0266]

[0267]

[0268] (Examples 10-1 to 10-32, Comparative Examples 10-1 to 10-5) As shown in Tables 32 to 34, in Examples 10-4 to 10-32, a battery having a so-called tabless structure in which a positive electrode current collector plate and a negative electrode current collector plate were used without using a positive electrode tab and a negative electrode tab was used, except that secondary batteries were produced in the same manner as the battery according to Comparative Example 1-1, and measurements and tests were performed. As shown in Tables 32 to 34, in Examples 10-1 to 10-4 and Comparative Examples 10-1 to 10-5, a battery having a multi-tab structure in which a positive electrode tab and a negative electrode tab were used without using a positive electrode current collector plate and a negative electrode current collector plate was used, except that secondary batteries were produced in the same manner as the battery according to Comparative Example 1-1, and measurements were performed.

[0269] In Examples 10-4 to 10-32, secondary batteries having a tabless structure were fabricated by the following method: Here, lithium ion secondary batteries having dimensions of 21 mm in diameter and 70 mm in length were fabricated.

[0270] First, as in the battery according to Comparative Example 1-1, a cathode active material layer 21B was formed on a cathode current collector 21A. A coating material containing polyvinylidene fluoride (PVDF) was applied to the surface of the cathode exposed portion 212 adjacent to the cathode covering portion 211, and the coating material was dried to form an insulating layer 101 having a width of 3 mm. The cathode active material layer 21B was then compression-molded using a roll press. This resulted in a cathode 21 having a cathode covering portion 211 and a cathode exposed portion 212. The width of the cathode covering portion 211 in the W-axis direction was 60 mm, and the width of the cathode exposed portion 212 in the W-axis direction was 7 mm. The length of the cathode 21 in the L-axis direction was 1700 mm. In the obtained cathode 21, the area density of the cathode active material layer 21B was 22.0 mg / cm. ２The volume density of the positive electrode active material layer 21B is 3.55 mg / cm ３ The thickness T1 of the positive electrode covering portion 211 was 62.0 μm. Therefore, the ratio T2 / T1 of the thickness T2 of the positive electrode current collector 21A to the thickness T1 of the positive electrode covering portion 211 was 5.17.

[0271] Similarly to the battery according to Comparative Example 1-1, an anode active material layer 22B was formed on an anode current collector 22A, and then the anode active material layer 22B was compression-molded using a roll press. This resulted in an anode 22 having an anode covering portion 221 and an anode exposed portion 222. Here, the width of the anode covering portion 221 in the W-axis direction was 62 mm, and the width of the first portion 222A of the anode exposed portion 222 in the W-axis direction was 4 mm. The length of the anode 22 in the L-axis direction was 1760 mm.

[0272] Next, the positive electrode 21 and the negative electrode 22 were stacked with the separator 23 interposed therebetween so that the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222 were on opposite sides of each other in the W-axis direction, thereby producing a laminate structure S20. The laminate structure S20 was produced so that the positive electrode active material layer 21B did not protrude from the negative electrode active material layer 22B in the W-axis direction. A polyethylene sheet having a width of 65 mm and a thickness of 14 μm was used as the separator 23. The laminate structure S20 was then spirally wound so that the through-holes 26 were formed and the notch was positioned near the central axis CL, and a fixing tape 46 was attached to the outermost periphery of the wound laminate structure S20. This produced a battery element 20.

[0273] Next, the edges of a 0.5 mm thick flat plate were pressed against the end faces 41 and 42 of the battery element 20 in the Z-axis direction, thereby locally bending the end faces 41 and 42 and creating grooves 43 extending radially from the through hole 26 in the radial direction (R direction).

[0274] Next, substantially the same pressure was applied to the end faces 41 and 42 from above and below the battery element 20 substantially simultaneously and in a direction approximately perpendicular to the end faces 41 and 42, thereby bending the positive electrode exposed portion 212 and the first portion 222A of the negative electrode exposed portion 222, respectively, to make the end faces 41 and 42 flat. At this time, the first edge portion 212E of the positive electrode exposed portion 212 and the second edge portion 222E of the negative electrode exposed portion 222 on the end faces 41 and 42 were bent while overlapping toward the through holes 26. Thereafter, the sector-shaped portion 241 of the positive electrode current collector 24 was joined to the end face 41 by laser welding, and the sector-shaped portion 251 of the negative electrode current collector 25 was joined to the end face 42 by laser welding.

[0275] Next, insulating tapes 53 and 54 are attached to predetermined positions of the battery element 20, and then the strip portion 242 of the positive electrode current collector 24 is bent to insert the strip portion 242 into the hole 12H of the insulating plate 12, and the strip portion 252 of the negative electrode current collector 25 is bent to insert the strip portion 252 into the hole 13H of the insulating plate 13.

[0276] Next, the battery element 20 assembled as described above was inserted into the outer can 11, and the bottom of the outer can 11 was welded to the negative electrode current collector 25. Then, a constricted portion 11S was formed near the open end 11N of the outer can 11. Furthermore, 6.5 g of electrolyte was poured into the outer can 11, and the strip portion 242 of the positive electrode current collector 24 was welded to the safety valve mechanism 16. Finally, the gasket 15, the safety valve mechanism 16, and the battery lid 14 were used to seal the battery lid 14 using the constricted portion 11S. As a result, the lithium ion secondary batteries of Examples 10-4 to 10-32 were obtained.

[0277] FIGS. 14A and 14B are developments that schematically illustrate the configuration of a positive electrode of a secondary battery having a multi-tab structure. In contrast, the lithium-ion secondary batteries of Examples 10-1 to 10-4 and Comparative Examples 10-1 to 10-5 employed a multi-tab structure in which positive and negative electrode tabs were used instead of positive and negative current collectors. Specifically, the positive electrode 121 and negative electrode 122 shown in FIGS. 14A and 14B were employed. Specifically, the positive electrode 121 shown in FIGS. 14A and 14B has a positive electrode exposed portion 121C in the middle of the longitudinal L-axis direction, where the positive electrode active material layer 121B is not formed and the positive electrode current collector 121A is exposed. A positive electrode tab 121T is attached to the positive electrode exposed portion 121C. The positive electrode tab 121T is electrically connected to the battery lid 14 via a safety valve mechanism 16 instead of the positive electrode current collector 24. 14A and 14B , the negative electrode 122 has negative electrode exposed portions 122C at both ends in the L-axis direction, where the negative electrode active material layer 122B is not formed and the negative electrode current collector 122A is exposed, and negative electrode tabs 122T are attached to each negative electrode exposed portion 122C. The negative electrode tabs 122T are electrically connected to the outer can 11 instead of the negative electrode current collector plate 25.

[0278] In Examples 10-1 to 10-32 and Comparative Examples 10-1 to 10-5, a 50 A discharge characteristic test was conducted in addition to the storage characteristic test described above.

[0279] <50 A Discharge Characteristics Test> In the 50 A discharge characteristics test, the secondary battery prepared above was charged and discharged 100 times in an environment of 23°C under the following conditions, and the discharge capacities at the first cycle, the second cycle, and the 100th cycle were measured. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was calculated as the 50 A cycle retention rate. That is, the 50 A cycle retention rate was calculated based on the following formula: 50 A cycle retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100. The ratio of the discharge capacity at the second cycle to the discharge capacity at the first cycle was calculated as the 50 A discharge characteristics. That is, the 50 A discharge characteristics were calculated based on the following formula: 50 A discharge characteristics (%) = (discharge capacity at the second cycle / discharge capacity at the first cycle) × 100. Charging method: CCCV, Charging rate: 0.1C, Charging control voltage: 4.2V, Charging cut-off current: 0.05C, Discharging method: CC, Discharging rate: 50C, Discharge cut-off voltage: 2.5V

[0280] As shown in Tables 32 to 34, Examples 10-4 to 10-32 having a tabless structure exhibited better charge-discharge characteristics than Examples 10-1 to 10-3 having a multi-tab structure. Therefore, it can be seen that the batteries have improved characteristics by having a tabless structure.

[0281] Eleventh Embodiment In a secondary battery according to an eleventh embodiment, the solvent includes a first solvent that is at least one of methyl acetate and ethyl acetate, and a second solvent that is at least one of methyl propionate and ethyl propionate. The first solvent improves output characteristics and enhances large-current discharge characteristics. The second solvent also suppresses deterioration of cycle characteristics due to the first solvent. Here, it is preferable that the mass content of the second solvent in the solvent is greater than the mass content of the first solvent in the solvent. This improves output characteristics and enhances large-current discharge characteristics, while suppressing deterioration of cycle characteristics.

[0282] (Example of Eleventh Embodiment) An example of the eleventh embodiment will be described below. Note that the present invention is not limited to this example.

[0283] Tables 35 to 37 show Examples 11-1 to 11-29 and Comparative Example 11-1.

[0284]

[0285]

[0286]

[0287] (Examples 11-1 to 11-29, Comparative Example 11-1) In Examples 11-1 to 11-29 and Comparative Example 11-1, secondary batteries were fabricated in the same manner as the battery according to Comparative Example 1-1, except that batteries were fabricated using the electrolyte solution components shown in Tables 35 to 37, as shown in Tables 35 to 37, and measurements and tests were performed.

[0288] As shown in Tables 35 to 37, in Examples 11-6 to 11-23 and Examples 11-26 to 11-29 in which the electrolytic solution contained both the first solvent and the second solvent, the electrolytic solution did not contain both the first solvent and the second solvent. Compared to Examples 11-1 to 11-5 and Examples 11-24 to 11-25, which showed better charge / discharge characteristics. Therefore, it can be seen that the battery characteristics can be improved by including both the first solvent and the second solvent in the electrolytic solution.

[0289] As shown in Tables 35 to 37, the mass content of the first solvent in the solvent is greater than the mass content of the second solvent in the solvent, Examples 11-8 to 11-10, Examples 11-13 to 11-15, Examples 11-18 to 11-23 and Examples 11-27 to 11-29, the mass content of the second solvent in the solvent is less than the mass content of the first solvent in the solvent, Examples 11-6 to 11-7, Examples 11-11 to 11-12 and Examples 11-16 to 11-17, compared to Example 11-26 showed good charge and discharge characteristics. Therefore, it can be seen that the mass content of the second solvent in the solvent is greater than the mass content of the first solvent in the solvent, thereby improving the battery characteristics.

[0290] Twelfth Embodiment In a secondary battery according to a twelfth embodiment, the electrolyte contains alkali metal cations and halogen anions. The alkali metal cations contained in the electrolyte are preferably at least one of lithium ions and sodium ions. The halogen anions contained in the electrolyte are preferably at least one of fluoride ions and chloride ions.

[0291] The electrolyte preferably contains LiX (where X is F or Cl) at a concentration of 0.1 ppm by mass to 100 ppm by mass. Here, X in LiX is F or Cl. That is, LiX is lithium fluoride (LiF) or lithium chloride (LiCl). The LiX concentration in the electrolyte can be measured by separating the ions contained in the solution using ion chromatography. Specifically, the electrolyte sample extracted from the secondary battery by centrifugation is passed through an ion exchange resin to separate the anions, and the LiX can be quantified by separating the chloride ions, fluoride ions, and FSI ions based on the differences in retention time of the detected chromatogram. The concentrations can be calculated from the detection peaks of the following ion chromatography detection retention times: fluoride ions: 2 min-4 min, chloride ions: 3 min-5 min, and FSI anions: 20 min-25 min. This allows the concentration of LiX to be quantified from the total amount of detected fluoride ions and chloride ions. The concentration of LiX in the electrolyte may also be measured by NMR.

[0292] The electrolyte preferably contains hydrogen fluoride (HF) in an amount of 1 ppm by mass to 500 ppm by mass, and the HF concentration in the electrolyte can be calculated based on the hydrogen ion concentration measured by neutralization titration of the electrolyte removed from the secondary battery by the above-described method with a strong alkaline aqueous solution (e.g., NaOH).

[0293] (Example of the twelfth embodiment) An example of the twelfth embodiment will be described below. Note that the present invention is not limited to this example.

[0294] Tables 38 to 41 show Examples 12-1 to 12-33 and Comparative Examples 12-1 to 12-11.

[0295]

[0296]

[0297]

[0298]

[0299] (Examples 12-1 to 12-33, Comparative Examples 12-1 to 12-11) In Examples 12-1 to 12-33 and Comparative Examples 12-1 to 12-11, secondary batteries were fabricated in the same manner as the battery according to Comparative Example 1-1, except that batteries were fabricated using the electrolyte solutions with the compositions shown in Tables 38 to 41, as shown in Tables 38 to 41. Here, secondary batteries were fabricated without adding alkali metal halide salts (LiF, LiCl) or hydrogen fluoride to the electrolyte solutions according to Examples 12-1 to 12-3, Examples 12-32 to 12-33, and Comparative Examples 12-1 to 12-5. In Examples 12-32 to 12-33, lithium compounds shown in Tables 38 to 41 were added instead of alkali metal halide salts (LiF, LiCl).

[0300] As shown in Tables 38 to 41, Examples 12-4 to 12-31, in which the electrolyte contained alkali metal halide salts (LiF, LiCl), showed better charge-discharge characteristics than Examples 12-1 to 12-3 and Examples 12-32 to 12-33, in which the electrolyte did not contain alkali metal halide salts (LiF, LiCl). Therefore, it can be seen that the battery characteristics can be improved by including an alkali metal halide salt in the electrolyte.

[0301] As shown in Tables 38 to 41, in Examples 12-28 to 12-29 in which the LiX (X = F, Cl) content of the electrolyte solution was 100 ppm by mass or less, the charge / discharge characteristics were better than those of Example 12-30 in which the LiX (X = F, Cl) content of the electrolyte solution was more than 100 ppm by mass. Therefore, it can be seen that the battery characteristics can be improved by having the LiX (X = F, Cl) content of the electrolyte solution be 100 ppm by mass or less.

[0302] As shown in Tables 38 to 41, Examples 12-25 to 12-26, in which the HF content of the electrolyte solution was 500 ppm by mass or less, showed better charge / discharge characteristics than Example 12-27, in which the HF content of the electrolyte solution was more than 500 ppm by mass. Therefore, it can be seen that the battery characteristics can be improved by setting the HF content of the electrolyte solution to 500 ppm by mass or less.

[0303] Thirteenth Embodiment In a secondary battery according to the thirteenth embodiment, the peel strength of the positive electrode active material layer in a charged state is 0.2 N / mm or more and 0.38 N / mm or less. The peel strength of the positive electrode active material layer in a charged state can be measured using a Surface and Interfacial Cutting Analysis System (SAICAS (registered trademark)). Specifically, a secondary battery charged to a predetermined full charge voltage is disassembled, and the removed positive electrode is cut obliquely from the positive electrode surface with a SAICAS blade. The normal force applied to the positive electrode during cutting can be measured as the peel strength of the positive electrode active material layer in a charged state.

[0304] The weight average molecular weight (Mw) of the positive electrode binder is 25×10 ４ 65 x 10 or more ４ Preferably, the weight average molecular weight of the positive electrode binder in the positive electrode active material layer is 0.6% by mass or more and 5% by mass or less. The weight average molecular weight of the positive electrode binder can be measured by high performance liquid chromatography (HPLC) using a sample solution containing the positive electrode binder obtained by adding a salt-containing polar solvent to the positive electrode active material layer. As the high performance liquid chromatograph, a device manufactured by Waters Corporation can be used, and the measurement can be performed in a mode using a size exclusion chromatography (SEC) column (SEC mode).

[0305] The positive electrode binder preferably contains hexafluoropropylene-modified polyvinylidene fluoride (HFP-modified PVdF). HFP-modified PVdF refers to PVdF in which a portion of the PVdF monomer (vinylidene fluoride, VdF) is substituted with hexafluoropropylene (HFP). In other words, HFP-modified PVdF is a copolymer of vinylidene fluoride and hexafluoropropylene. The HFP-modified PVdF molecule preferably contains 2.5% to 7.5% by mass of HFP monomer. In the following description, the proportion of HFP monomer contained in the HFP-modified PVdF molecule may be referred to as the HPF ratio. By setting the HFP ratio to 2.5% by mass or more, the positive electrode becomes flexible, while by setting the HFP ratio to 7.5% by mass or less, deterioration of battery characteristics due to swelling by the electrolyte can be suppressed. The HPF ratio can be measured by NMR. More specifically, the positive electrode binder was dissolved in DMSO-d6 (dimethyl sulfoxide-d6) as a measurement solvent, and LiFSI was used as a reference substance. １９ F-NMR analysis and tetramethylsilane (TMS) as a standard substance １ By carrying out H-NMR analysis, a quantitative analysis of the VdF monomer and the HFP monomer can be carried out, and the mass proportion of the HFP monomer in the entire molecule can be measured as the HFP ratio.

[0306] In the positive electrode active material layer, the D of the positive electrode active material particles ５０ In addition, among the positive electrode active material particles, D ５０ The proportion of particles having a diameter of 4.0 μm or more and 7.3 μm or less is preferably 10% by mass or more and 100% by mass or less. This improves low-temperature load characteristics and suppresses ignition during an internal short circuit. In the following description, among the positive electrode active material particles, D ５０ The proportion of particles having a particle size of 4.0 μm or more and 7.3 μm or less may be referred to as the small particle positive electrode active material proportion.

[0307] (Example of the 13th embodiment) An example of the 13th embodiment will be described below. Note that the present invention is not limited to this example.

[0308] Tables 42 to 43 show Examples 13-1 to 13-23.

[0309]

[0310]

[0311] (Example 13-1 to Example 13-23) In Examples 13-1 to 13-23, as shown in Tables 42 to 43, the particle size of the positive electrode active material particles and the positive electrode binder were as shown in Tables 42 to 43, and the positive electrode active material similar to that of Comparative Example 1-1, polyvinylidene fluoride (PVdF) as a positive electrode binder, and carbon black as a positive electrode conductive agent were mixed in a mass ratio of 97-x: x: 3 (x is a value described in the column of the content of the positive electrode binder in Tables 42 to 43, and is 0.4 or more and 5.5 or less). Except for this, a secondary battery was produced in the same manner as the battery according to Comparative Example 1-1, and measurements and tests were performed.

[0312] In Examples 13-1 to 13-23, the positive electrode binder was dissolved in DMSO-d6 (deuterated dimethyl sulfoxide-d6), and the HFP ratio was measured using an Advance NEO 500 NMR spectrometer (manufactured by Bruker Corporation). The detailed measurement conditions were as follows: Probe head: 5 mmφ iProbeTBO (PI HR-TBO500-S1-BBF / H / F / D-5.0-Z FP) Temperature control device: SmartCooler BCU II Measurement magnetic field strength: 11.74736 T Measurement temperature: 25°C １９ F-NMR conditions: Observation frequency: 470.5453180 MHz; Observation pulse: 25.0 μs; Acquisition time: 3.59424 s; Pulse waiting time: 20 s; Number of accumulations: 256; Reference material: LiFSI １ H-NMR conditions: Observation frequency: 500.1330883 MHz; Observation pulse: 5.0 μs; Acquisition time: 3.2767999 s; Pulse waiting time: 20 s; Number of accumulations: 256; Reference substance: TMS

[0313] In Examples 13-1 to 13-23, a forced internal short circuit test was conducted in addition to the cycle characteristic test, storage characteristic test, and low-temperature load characteristic test described above.

[0314] <Forced Internal Short Circuit Test> In the forced internal short circuit test, the secondary battery prepared above was charged at 23°C under the following conditions. The outermost winding of the secondary battery was then unwound, and a nickel piece was placed between the positive electrode and the separator, followed by rewinding. The battery was then secured to a pressure device, and the voltage of the electrode assembly was constantly measured. A nitrile rubber pressure jig was lowered at a speed of 0.1 mm / s toward the location of the nickel piece on the battery. When a voltage drop due to an internal short circuit (a drop of 50 mV or more from the initial voltage) was detected, the lowering of the pressure jig was stopped, and the pressure was released after 30 seconds. The pressure at the time of the voltage drop due to the internal short circuit was recorded as the short circuit pressure. The shape and arrangement of the nickel piece used in the forced internal short circuit test, as well as details of the pressure device, refer to the procedure for forced internal short circuit testing for cylindrical batteries described in JIS C 62133-2:2020. Charging method: CCCV Charging rate: 0.1C Charging control voltage: 4.2V Charging end current: 0.05C

[0315] As shown in Tables 42 and 43, Examples 13-11 to 13-23, in which the peel strength of the positive electrode active material layer was 0.2 N / mm or more and 0.38 N / mm or less, showed better charge / discharge characteristics and a short circuit pressure of 800 N or more than Examples 13-1 to 13-10, in which the peel strength of the positive electrode active material layer was less than 0.2 N / mm or more and more than 0.38 N / mm. Therefore, it can be seen that the battery characteristics can be improved by setting the peel strength of the positive electrode active material layer to 0.2 N / mm or more and 0.38 N / mm or less.

[0316] As shown in Tables 42 and 43, the weight average molecular weight of the positive electrode binder is 25 × 10 ４ 65 x 10 or more ４ In the following Examples 13-15 and 13-16, the weight average molecular weight of the positive electrode binder was 25 × 10 ４ Less than or 65 x 10 ４Examples 13-2 and 13-3, in which the weight average molecular weight of the positive electrode binder is greater than 25×10, exhibited better charge-discharge characteristics than Examples 13-2 and 13-3, and the short-circuit pressure was 800 N or more. ４ 65 x 10 or more ４ It can be seen that the battery characteristics can be improved by satisfying the following.

[0317] As shown in Tables 42 and 43, in Examples 13-11 to 13-14 in which the content of the positive electrode binder was 0.6% by mass or more and 5% by mass or less, better charge / discharge characteristics were exhibited than in Examples 13-4 to 13-5 in which the content of the positive electrode binder was less than 0.6% by mass or more than 5% by mass, and the short circuit pressure was 800 N or more. Therefore, it can be seen that the battery characteristics can be improved by setting the content of the positive electrode binder to 0.6% by mass or more and 5% by mass or less.

[0318] As shown in Tables 42 and 43, Examples 13-17 and 13-18, in which the HFP ratio was 2.5% by mass or more and 7.5% by mass or less, showed better charge-discharge characteristics and a short-circuit pressure of 800 N or more than Examples 13-1 and 13-6 to 13-7, in which the HFP ratio was less than 2.5% by mass or more than 7.5% by mass. ５０ It can be seen that the battery characteristics can be improved by setting the thickness of the electrode to 4.0 μm or more and 7.3 μm or less.

[0319] As shown in Tables 42 and 43, the D of the positive electrode active material particles ５０ In Examples 13-19 and 13-20 in which the D of the positive electrode active material particles is 4.0 μm or more and 7.3 μm or less, ５０ Compared with Examples 13-8 to 13-9 in which the diameter was less than 4.0 μm or more than 7.3 μm, the positive electrode active material particles exhibited better charge / discharge characteristics and a short circuit pressure of 800 N or more. ５０ It can be seen that the battery characteristics can be improved by setting the thickness of the electrode to 4.0 μm or more and 7.3 μm or less.

[0320] As shown in Tables 42 and 43, Examples 13-21 to 13-23, in which the small particle positive electrode active material ratio was 10% or more and 100% or less, showed better charge / discharge characteristics and a short circuit pressure of 800 N or more than Example 13-10, in which the small particle positive electrode active material ratio was less than 10%. Therefore, it can be seen that the battery characteristics can be improved by having the small particle positive electrode active material ratio be 10% or more and 100% or less.

[0321] Fourteenth Embodiment In a secondary battery according to a fourteenth embodiment, the negative electrode active material layer contains graphite particles. The graphite particles used as the negative electrode active material may be natural graphite or artificial graphite. ５０ The diameter of the graphite particles is 15 μm or less. This improves the adhesion between the graphite particles, thereby improving the charge / discharge characteristics. ５０ is preferably 5 μm or more and 15 μm or less, and more preferably 10 μm or more and 15 μm or less. This reduces the specific surface area of ​​the graphite particles, improving the charge / discharge characteristics, and also makes it easier for the negative electrode active material particles to deform during the production of the negative electrode active material layer 22B, thereby improving the density of the negative electrode active material layer 22B, thereby improving the manufacturability of the secondary battery 1. Furthermore, in the secondary battery according to the fourteenth embodiment, a stable coating is formed on the negative electrode surface by controlling the solvation ratio, thereby suppressing side reactions on the graphite particle surface. Therefore, by using graphite with a small particle size and a large surface area, it is possible to improve the large-current discharge characteristics while suppressing an increase in resistance during cycling.

[0322] D of graphite particles in the negative electrode active material layer ５０ can be similarly measured by SEM and EDX (Energy Dispersive X-ray Spectroscopy) of the surface of the negative electrode active material layer. More specifically, the battery element 20 is disassembled to expose the surface of the negative electrode active material layer 22B, and an SEM observation image of the surface of the negative electrode active material layer 22B is obtained at a magnification of 500 times. Here, 50 graphite particles are identified from the SEM observation image by EDX C (carbon) mapping or the contrast of particles that appear in the SEM observation image, and the area S occupied by each graphite particle is calculated. ｉ Then, based on the measured particle area, the particle diameter Dｉ The 50% integrated value of the particle size distribution obtained is the D of the graphite particles. ５０ It can be calculated as particle size.

[0323] (Example of the Fourteenth Embodiment) An example of the fourteenth embodiment will be described below. Note that the present invention is not limited to this example.

[0324] Tables 44 to 46 show Examples 14-1 to 14-19 and Comparative Examples 14-1 to 14-11.

[0325]

[0326]

[0327]

[0328] (Examples 14-1 to 14-19, Comparative Examples 14-1 to 14-11) In Examples 14-1 to 14-19 and Comparative Examples 14-1 to 14-11, as shown in Tables 44 to 46, the D of the graphite particles in the negative electrode active material ５０ A secondary battery was fabricated in the same manner as the battery of Comparative Example 1-1, except that the batteries were fabricated using the electrolytes shown in Tables 44 to 46, and measurements were carried out.

[0329] In Examples 14-1 to 14-19 and Comparative Examples 14-1 to 14-11, in addition to the cycle characteristic test, storage characteristic test, and low temperature load characteristic test as in Comparative Example 1-1, a 5C output characteristic test was performed by the following method.

[0330] <5C Output Characteristics Test> In the 5C output characteristics test, the secondary battery prepared above was subjected to one cycle of charge and discharge in an environment of 23°C under the following first charge and discharge conditions, and the discharge capacity at the first cycle was measured: Charging method: CC, Charging rate: 0.2C, End-of-charge voltage: 4.2V, Discharging method: CC, Discharging rate: 0.2C, End-of-discharge voltage: 2.5V.

[0331] Thereafter, the battery was charged and discharged up to the 100th cycle under the second charge-discharge condition described below, and the discharge capacities at the second and 100th cycles were measured. Charge and discharge were performed in an environment of 23°C. The ratio of the discharge capacity at the second cycle to the discharge capacity at the first cycle was calculated as the 5C discharge retention rate. That is, the 5C discharge retention rate was calculated based on the following formula: 5C discharge retention rate (%) = (discharge capacity at the second cycle / discharge capacity at the first cycle) × 100. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the first cycle was calculated as the post-cycling 5C discharge retention rate. That is, the post-cycling 5C discharge retention rate was calculated based on the following formula: 5C discharge retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100. Charging method: CC, Charge rate: 0.2C, End-of-charge voltage: 4.2V, Discharging method: CC, Discharge rate: 5C, End-of-discharge voltage: 2.5V

[0332] As shown in Tables 44 to 46, the D of the graphite particles in the negative electrode active material ５０ In Examples 14-1 and 14-4 to 14-19, where the diameter of the graphite particles in the negative electrode active material is 15 μm or less, ５０ The negative electrode active material exhibited better charge-discharge characteristics than Examples 14-2 and 14-3, in which the diameter of the graphite particles was more than 15 μm. ５０ It can be seen that the battery characteristics can be improved by making the thickness 15 μm or less.

[0333] Fifteenth Embodiment In a secondary battery according to the fifteenth embodiment, the positive electrode conductive agent contains carbon black and carbon nanotubes. The content of the positive electrode conductive agent relative to the total of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 1.0 mass% or more and 2.5 mass% or less. The content of the carbon black relative to the total of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 0.3 mass% or more and 1.5 mass% or less. In the following description, the contents of the positive electrode conductive agent and the carbon black relative to the total of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder may be simply referred to as the positive electrode conductive agent content and the CB content, respectively. This allows the positive electrode active material particles to be connected to each other by the positive electrode conductive agent, thereby suppressing the internal resistance of the positive electrode active material layer and improving charge / discharge characteristics.

[0334] The content of the positive electrode binder relative to the total of the positive electrode active material, positive electrode conductive agent, and positive electrode binder is preferably 0.3 mass% or more and 2.0 mass% or less. In the following description, the content of the positive electrode binder relative to the total of the positive electrode active material, positive electrode conductive agent, and positive electrode binder may be simply referred to as the content of the positive electrode binder. By setting the content of the positive electrode conductive agent to 2.5 mass% or less, it is possible to prevent the surfaces of the positive electrode active material particles from being coated with the positive electrode conductive agent, thereby improving charge / discharge characteristics.

[0335] The CNT content relative to the total of the positive electrode active material, positive electrode conductor, and positive electrode binder is preferably 0.05% by mass or more and 1.5% by mass or less. By setting the positive electrode conductor content to 2.5% by mass or less, it is possible to prevent the surfaces of the positive electrode active material particles from being coated with the positive electrode conductor, thereby improving charge / discharge characteristics. In the following description, the CNT content relative to the total of the positive electrode active material, positive electrode conductor, and positive electrode binder may be simply referred to as the CNT content. As a result, the positive electrode active material particles are connected to each other by the CNTs, thereby suppressing the internal resistance of the positive electrode active material layer and improving charge / discharge characteristics.

[0336] (Example of the 15th embodiment) An example of the 15th embodiment will be described below. Note that the present invention is not limited to this example.

[0337] Tables 47 to 49 show Examples 15-1 to 15-29 and Comparative Examples 15-1 to 15-3.

[0338]

[0339]

[0340]

[0341] (Examples 15-1 to 15-29, Comparative Examples 15-1 to 15-3) In Examples 15-1 to 15-29 and Comparative Examples 15-1 to 15-3, as shown in Tables 47 to 49, secondary batteries were fabricated in the same manner as the battery according to Comparative Example 1-1, except that the components of the positive electrode active material layer and the electrolyte solution were as shown in Tables 47 to 49, and measurements and tests were performed.

[0342] As shown in Tables 47 to 49, in Examples 15-1 and 15-6 to 15-29 in which the content of the positive electrode conductive agent (CB and CNT) was 1.0% by mass or more and 2.5% by mass or less, better charge / discharge characteristics were exhibited than in Examples 15-2 to 15-3 in which the content of the positive electrode conductive agent was more than 2.5% by mass. Therefore, it can be seen that the battery characteristics can be improved by setting the content of the positive electrode conductive agent to 1.0% by mass or more and 2.5% by mass or less.

[0343] As shown in Tables 47 to 49, in Examples 15-1 and 15-6 to 15-29 in which the content of the positive electrode binder was 0.3% by mass or more and 2.0% by mass or less, the charge / discharge characteristics were better than those of Examples 15-4 and 15-5 in which the content of the positive electrode binder was less than 0.3% by mass or more than 2.0% by mass. Therefore, it can be seen that the battery characteristics can be improved by setting the content of the positive electrode binder to 0.3% by mass or more and 2.0% by mass or less.

[0344] As shown in Tables 47 to 49, Examples 15-7 to 15-9, in which the CB content was 0.3% by mass or more and 1.5% by mass or less, showed better charge-discharge characteristics than Examples 15-1 to 15-2, in which the CB content was less than 0.3% by mass or more than 1.5% by mass. Therefore, it can be seen that the battery characteristics can be improved by setting the CB content to 0.3% by mass or more and 1.5% by mass or less.

[0345] As shown in Tables 47 to 49, Examples 15-12 to 15-15, in which the CNT content was 0.05% by mass or more and 1.5% by mass or less, showed better charge-discharge characteristics than Example 15-3, in which the CNT content was more than 1.5% by mass. Therefore, it can be seen that the battery characteristics can be improved by setting the CNT content to 0.05% by mass or more and 1.5% by mass or less.

[0346] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present invention.

[0347] REFERENCE SIGNS LIST 1 secondary battery 10 exterior film 20 battery element 21 positive electrode 21A positive electrode current collector 21B positive electrode active material layer 22 negative electrode 22A negative electrode current collector 22B negative electrode active material layer 23 separator

Claims

1. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode current collector containing aluminum, the electrolyte contains an electrolyte and a solvent, the electrolyte contains a bis(fluorosulfonyl)imide salt, and the solvent contains at least one selected from a first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma butyrolactone, and the molar ratio of the solvent to lithium ions calculated from a vibrational spectroscopy spectrum of the electrolyte is greater than 0 and less than or equal to 1.

78.

2. The secondary battery according to claim 1, wherein the molar ratio of the solvent to lithium ions calculated from the vibrational spectroscopy spectrum of the electrolyte solution is greater than 0 and not greater than 1.

76.

3. The secondary battery according to claim 1 or 2, wherein the solvent further contains at least one of carbonate esters and chain carboxylic acid esters excluding the compounds included in the first group.

4. The secondary battery according to claim 3, wherein the solvent further includes at least one of diethyl carbonate, ethyl methyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, and methyl acetate.

5. The secondary battery according to claim 4, wherein the solvent further contains at least one of ethyl methyl carbonate, propyl propionate, ethyl propionate, propyl acetate, ethyl acetate, and methyl acetate.

6. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode current collector containing aluminum, the electrolyte contains an electrolyte and a solvent, the electrolyte contains a bis(fluorosulfonyl)imide salt, and the solvent contains at least one selected from a first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma butyrolactone, and the molar ratio of the solvent to lithium ions calculated from a vibrational spectroscopy spectrum of the electrolyte is greater than 0 and less than or equal to 1.

72.

7. The secondary battery according to any one of claims 1 to 6, wherein the negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes at least one of elemental silicon, silicon oxide, and silicon carbide.

8. The negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes a carbon material, the negative electrode active material layer has a thickness of 30 μm or more and 100 μm or less, and the volume density of the negative electrode active material layer is 1.4 g / cm ３ 2.0g / cm or more ３ The secondary battery according to any one of claims 1 to 7, wherein:

9. The secondary battery according to any one of claims 1 to 7, wherein the negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes graphite and styrene-butadiene rubber.

10. The secondary battery according to claim 9, wherein the spacing between the (002) planes of the graphite in the negative electrode active material layer is 0.3372 nm or less.

11. The secondary battery according to claim 9 or 10, wherein the negative electrode active material layer further contains carboxymethyl cellulose.

12. The secondary battery according to any one of claims 9 to 11, wherein the negative electrode active material layer contains at least one of polyacrylic acid and polyacrylamide.

13. The secondary battery according to any one of claims 1 to 7, wherein the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes composite particles, the composite particles include a porous conductive matrix having pores and silicon-containing particles located in the pores, and the specific capacity of the composite particles is 800 mAh / g or more.

14. The secondary battery described in claim 13, wherein the composite particles have first pores having a pore diameter of 5 nm or more and less than 10 nm and second pores having a pore diameter of 10 nm or more and less than 50 nm, and the ratio of the total volume of the second pores to the total volume of the first pores is less than 10.9%.

15. A secondary battery according to claim 13 or 14, wherein the content of silicon among the elements on the surface of said composite particles is 30 atomic % or less.

16. The secondary battery according to any one of claims 13 to 15, wherein the conductive matrix material includes a carbon material.

17. The secondary battery according to claim 16, wherein the conductive matrix material comprises an amorphous carbon material.

18. D of the composite particles ５０ The secondary battery according to claim 13 , wherein the thickness is 0.5 μm or more and less than 40 μm.

19. A secondary battery according to any one of claims 1 to 7, wherein the negative electrode includes a negative electrode active material layer, and the porosity of the negative electrode active material layer is 15% or more and 45% or less.

20. The secondary battery of claim 19, wherein the negative electrode active material layer comprises a silicon-carbon composite material, the silicon-carbon composite material comprising porous carbon having pores and silicon-containing particles located in the pores, the silicon-containing particles comprising at least one of elemental silicon, a silicon alloy, and silicon oxide, and the proportion of the silicon-carbon composite material in the negative electrode active material layer is 1% by mass or more and 70% by mass or less.

21. The negative electrode active material layer contains graphite particles, and D of the graphite particles in the negative electrode active material layer ５０ The secondary battery according to claim 19 or 20, wherein the thickness of the first electrode is 30 μm or less.

22. The specific surface area of ​​the negative electrode active material layer is 1 m ２ / g or more 30m ２ The secondary battery according to any one of claims 19 to 21, wherein the SiO2 content is 1 / g or less.

23. A secondary battery according to any one of claims 19 to 22, wherein the negative electrode active material layer contains a fibrous conductive material.

24. A secondary battery according to any one of claims 19 to 23, wherein the negative electrode active material layer contains carbon nanotubes having 10 or fewer walls.

25. The secondary battery according to any one of claims 1 to 7, further comprising a separator laminated between the positive electrode and the negative electrode, the separator comprising a substrate including a polyethylene microporous film and a coating layer formed on a main surface of the substrate, the coating layer comprising at least one of ceramics, nanofibers and heat-resistant resins.

26. The secondary battery according to claim 25, wherein the thickness of the separator is 15 μm or less.

27. The secondary battery according to claim 25 or 26, wherein the separator has an air resistance of 200 s or less.

28. A secondary battery according to any one of claims 1 to 7, wherein the negative electrode has a negative electrode active material layer, the negative electrode active material layer contains carbon nanotubes, and the content of the carbon nanotubes in the negative electrode active material layer is 0.01 mass % or more and 1 mass % or less.

29. The secondary battery according to claim 28, wherein the negative electrode active material layer contains carbon nanotubes having one to ten layers.

30. A secondary battery according to any one of claims 1 to 7, wherein the positive electrode further has a positive electrode active material layer laminated on the positive electrode current collector, and the positive electrode active material layer contains at least one of NiOOH, lithium carbonate, and lithium hydroxide.

31. The secondary battery according to claim 30, wherein the positive electrode active material layer contains NiOOH.

32. The secondary battery according to any one of claims 1 to 7, wherein the positive electrode further has a positive electrode active material layer laminated on the positive electrode current collector, and the positive electrode active material layer includes a metal organic framework.

33. The secondary battery of claim 32, wherein the metal-organic framework has a central metal atom and an organic ligand coordinated to the central metal atom, the central metal atom being at least one of Zn, Co, and Ni, and the organic ligand being at least one of terephthalic acid, 4,4'-bipyridine, and an imidazole derivative.

34. An electrode winding body formed by stacking the positive electrode and the negative electrode with a separator sandwiched between them and wound around a central axis extending in a first direction; a positive electrode current collector arranged to face a first end face of the electrode winding body in the first direction; and a negative electrode current collector arranged to face a second end face of the electrode winding body opposite the first end face in the first direction, wherein the positive electrode further has a positive electrode active material layer stacked on the positive electrode current collector, the negative electrode has a negative electrode current collector and a negative electrode active material layer stacked on the negative electrode current collector, the positive electrode current collector is arranged to face a first end face of the electrode winding body in the first direction, and the negative electrode current collector is arranged to face a second end face of the electrode winding body opposite the first end face in the first direction, 8. The secondary battery according to claim 1, wherein the positive electrode has a positive electrode covering portion in which the positive electrode current collector is covered with the positive electrode active material layer, and a positive electrode exposed portion in which the positive electrode current collector is not covered with the positive electrode active material layer and is joined to the positive electrode current collector plate; and the negative electrode has a negative electrode covering portion in which the negative electrode current collector is covered with the negative electrode active material layer, and a negative electrode exposed portion in which the negative electrode current collector is not covered with the negative electrode active material layer and is joined to the negative electrode current collector plate.

35. A secondary battery according to any one of claims 1 to 7, wherein the solvent includes a first solvent which is at least one of methyl acetate and ethyl acetate, and a second solvent which is at least one of methyl propionate and ethyl propionate.

36. The secondary battery according to claim 35, wherein the mass content of the second solvent in the solvent is greater than the mass content of the first solvent in the solvent.

37. A secondary battery according to any one of claims 1 to 7, wherein the electrolyte contains an alkali metal cation and a halogen anion.

38. The secondary battery according to claim 37, wherein the electrolyte solution contains LiX (X is F or Cl) in an amount of 0.1 ppm by mass or more and 100 ppm by mass or less.

39. The secondary battery according to claim 37, wherein the electrolyte solution contains HF in an amount of 1 ppm by mass or more and 500 ppm by mass or less.

40. A secondary battery according to any one of claims 1 to 7, wherein the positive electrode includes a positive electrode active material layer laminated on the positive electrode current collector, and the peel strength of the positive electrode active material layer in a charged state is 0.2 N / mm or more and 0.38 N / mm or less.

41. The positive electrode active material layer contains a positive electrode binder, and the weight average molecular weight of the positive electrode binder is 25×10 ４ 65 x 10 or more ４ 41. The secondary battery according to claim 40, wherein:

42. A secondary battery according to claim 40 or claim 41, wherein the positive electrode active material layer contains a positive electrode binder, and the content of the positive electrode binder in the positive electrode active material layer is 0.6 mass % or more and 5 mass % or less.

43. The secondary battery according to any one of claims 40 to 42, wherein the positive electrode active material layer contains a positive electrode binder, the positive electrode binder contains HFP-modified polyvinylidene fluoride, and molecules of the HFP-modified polyvinylidene fluoride contain 2.5 mass % or more and 7.5 mass % or less of HFP monomer.

44. The positive electrode active material layer contains positive electrode active material particles made of a positive electrode active material, and among the positive electrode active material particles, D ５０ 44. The secondary battery according to claim 40, wherein a ratio of particles having a size of 4.0 μm or more and 7.3 μm or less is 10 mass % or more and 100 mass % or less.

45. The negative electrode has a negative electrode active material layer, the negative electrode active material layer contains graphite particles, and D of the graphite particles ５０ The secondary battery according to claim 1 , wherein the thickness of the first electrode is 15 μm or less.

46. ​​The secondary battery according to any one of claims 1 to 7, wherein the positive electrode further has a positive electrode active material layer laminated on the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder, the positive electrode conductive agent including carbon black and carbon nanotubes, the content of the positive electrode conductive agent relative to the total of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 1.0 mass% or more and 2.5 mass% or less, and the content of the carbon black relative to the total of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 0.3 mass% or more and 1.5 mass% or less.

47. The secondary battery according to claim 46, wherein the content of the positive electrode binder relative to the total of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 0.3 mass % or more and 2.0 mass % or less.

48. A secondary battery as described in claim 46 or claim 47, wherein the content of the carbon nanotubes relative to the total of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 0.05 mass % or more and 1.5 mass % or less.

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