Secondary battery

Abstract

The present invention improves charge / discharge characteristics. This secondary battery comprises a positive electrode, a negative electrode, and an electrolytic solution. The positive electrode comprises: a positive electrode current collector containing aluminum; and a positive electrode active material layer provided to the positive electrode current collector. The positive electrode active material layer contains a lithium-containing compound. The negative electrode includes a negative electrode active material layer containing graphite particles. The electrolytic solution contains an electrolyte and a solvent. The electrolyte contains a bis(fluorosulfonyl)imide salt. The surface of the positive electrode current collector contains sulfur. The photoelectron spectrum obtained by performing X-ray photoelectron spectroscopy on the surface of the positive electrode current collector has a first signal having a peak within the range of 164.1-164.5 eV and a second signal having a peak within the range of 168.9-169.3 eV. The ratio of the sum of the signal intensity of the first signal and the signal intensity of the second signal to the sum of the signal intensities of the S2p spectrum is 0.97 or lower. The D50 particle size of the graphite particles is 15 μm or less.

Description

secondary battery

[0001] This invention relates to a secondary battery.

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

[0003] Japanese Patent Publication No. 2015-133315

[0004] However, in the secondary battery shown in Patent Document 1, there was a possibility that the charge and discharge characteristics would deteriorate depending on the electrolyte.

[0005] This invention has been made in view of the above problems, and aims to improve charge and discharge characteristics.

[0006] A secondary battery according to one aspect of the present disclosure comprises a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode current collector containing aluminum and a positive electrode active material layer provided on the positive electrode current collector, the positive electrode active material layer contains a lithium-containing compound, the negative electrode comprises a negative electrode active material layer containing graphite particles, the electrolyte comprises an electrolyte and a solvent, the electrolyte contains a bis(fluorosulfonyl)imide salt, the surface of the positive electrode current collector contains sulfur, the photoelectron spectrum obtained by X-ray photoelectron spectroscopy of the surface of the positive electrode current collector has a first signal with a peak in the range of 164.1 eV to 164.5 eV and a second signal with a peak in the range of 168.9 eV to 169.3 eV, the ratio of the sum of the signal intensities of the first signal and the second signal to the sum of the signal intensities of the S2p spectrum is 0.97 or less, and the D of the graphite particles ５０ The particle size is 15 μm or less.

[0007] According to the present invention, charge and discharge characteristics can be improved.

[0008] Figure 1 is a perspective view showing the configuration of a secondary battery according to one embodiment. Figure 2 is an enlarged cross-sectional view showing the configuration of the battery element shown in Figure 1. Figure 3 is a diagram showing the S2p spectrum of XPS against the surface of the positive electrode current collector according to the embodiment. Figure 4 is a diagram showing the F1s spectrum of XPS against the surface of the positive electrode current collector according to the embodiment. Figure 5 is a diagram showing the Al2p spectrum of XPS against the surface of the positive electrode current collector according to the embodiment.

[0009] Embodiments of the present invention are described below. However, the present invention is not limited by these embodiments.

[0010] (Secondary Battery) The secondary battery according to this embodiment will now be described. The secondary battery according to this embodiment is a secondary battery that obtains battery capacity by utilizing the intercalation and deintercalation of electrode reaction materials, and comprises a positive electrode, a negative electrode, and an electrolyte.

[0011] The type of electrode reactant is not particularly limited, but specifically refers to 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.

[0012] The following explanation uses lithium as the electrode reactant as an example. A secondary battery that obtains battery capacity by utilizing the intercalation and deintercalation of lithium is, for example, a lithium-ion secondary battery. In a lithium-ion secondary battery, lithium is intercalated and deintercalated in an ionic state.

[0013] Figure 1 is a perspective view showing the configuration of a secondary battery according to one embodiment. Figure 2 is a cross-sectional view showing an enlarged view of the configuration of the battery element shown in Figure 1. In Figure 1, the outer film 10 and the battery element 20 are shown separated from each other, and the cross-section of the battery element 20 is shown by a dashed line. In Figure 2, only a part of the cross-section of the battery element 20 is shown.

[0014] As shown in Figures 1 and 2, the secondary battery 1 comprises an outer film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42.

[0015] As described above, the secondary battery 1 shown in Figure 1 uses an outer film 10 as an outer material for housing the battery element 20. Therefore, the secondary battery 1 shown in Figure 1 is a so-called laminate film type secondary battery.

[0016] (Outer film) As shown in Figure 1, the outer film 10 is an outer component that houses the battery element 20, and has a sealed bag-like structure when the battery element 20 is housed inside. Thus, the outer film 10 houses the positive electrode 210, negative electrode 220, separator 230, and electrolyte (not shown), which will be described later.

[0017] In the example shown in Figure 1, the outer film 10 is a single film-like component that is folded in the folding direction F. The outer film 10 is provided with a recessed portion 10U for housing the battery element 20. The recessed portion 10U is a so-called deep-drawn portion.

[0018] Specifically, the outer 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 outer film 10 is folded, the outer 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 metallic material such as aluminum. The surface protection layer contains a polymer compound such as nylon. The composition (number of layers) of the outer film 10 is not particularly limited and may consist of one or two layers, or four or more layers.

[0019] (Positive lead) As shown in Figures 1 and 2, the positive lead 31 is a positive electrode wire connected to the positive electrode current collector 211 of the positive electrode 210 and is brought out to the outside of the outer film 10. The positive lead 31 contains at least one type of conductive material such as a metal material, and a specific example of a conductive material is aluminum. The shape of the positive lead 31 is not particularly limited and can be, for example, a thin plate shape or a mesh shape.

[0020] (Negative electrode lead) As shown in Figures 1 and 2, the negative electrode lead 32 is a negative electrode wiring connected to the negative electrode current collector 221 of the negative electrode 220 and is brought out to the outside of the outer film 10. The negative electrode lead 32 contains at least one type of conductive material, such as a metal material. A specific example of a conductive material is copper. The shape of the negative electrode lead 32 is not particularly limited and can be, for example, a thin plate shape or a mesh shape.

[0021] (Sealing Film) As shown in Figure 1, sealing film 41 is inserted between the outer film 10 and the positive lead 31. Also, as shown in Figure 1, sealing film 42 is inserted between the outer film 10 and the negative lead 32. However, one or both of sealing films 41 and 42 may be omitted.

[0022] The sealing film 41 is a sealing member that prevents outside air and other elements from entering the interior of the outer film 10. The sealing film 41 contains a polymer compound such as polyolefin that has good adhesion to the positive electrode lead 31. A specific example of the polymer compound is polypropylene.

[0023] The sealing film 42 is a sealing member that prevents outside air and other elements from entering the interior of the outer film 10. The sealing film 41 contains a polymer compound such as polyolefin that adheres to the negative electrode lead 32. A specific example of the polymer compound is polypropylene.

[0024] (Battery element) The battery element 20 is housed in the space of the recess 10U of the outer film 10. The battery element 20 is a so-called power generation element. As shown in Figures 1 and 2, the battery element 20 includes a positive electrode 210, a negative electrode 220, a separator 230, and an electrolyte (not shown).

[0025] In the example shown in Figure 1, the battery element 20 is a so-called wound electrode body. Therefore, the positive electrode 210 and the negative electrode 220 are wound around the winding axis P, facing each other via a separator 230. In the following description, the direction along the winding axis P may be referred to as the Y direction, the longitudinal direction of the battery element 20 perpendicular to the winding axis P may be referred to as the X direction, and the short direction of the battery element 20 perpendicular to the winding axis P may be referred to as the Z direction.

[0026] In the example shown in Figure 1, the battery element 20 has a flattened three-dimensional shape. That is, the shape of the cross-section of the battery element 20 intersecting the winding axis P (cross-section along the XZ plane) is a flattened shape defined by the major axis J1 and the minor axis J2. The major axis J1 is a virtual 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 a virtual axis extending in the Z-axis direction and has a length less than the length of the major axis J1. As a result, the cross-sectional shape of the battery element 20 is a flattened, approximately elliptical shape. Note that the three-dimensional shape of the battery element 20 is just an example and is not limited to the above.

[0027] The positive electrode 210 comprises a positive electrode current collector 211 and a positive electrode active material layer 212. In the positive electrode 210, the positive electrode current collector 211 is laminated between the positive electrode active material layers 212. However, the positive electrode active material layer 212 may be provided only on one side of the positive electrode current collector 211 on the side of the positive electrode 210 that faces the negative electrode 220.

[0028] The positive electrode current collector 211 contains aluminum, and for example, aluminum foil can be used. The surface condition of the positive electrode current collector 211 will be described later.

[0029] The positive electrode active material layer 212 is a layer containing a positive electrode active material capable of intercalating and deintercalating lithium. The positive electrode active material layer 212 contains a positive electrode active material. The positive electrode active material layer 212 is not limited to the materials listed above, and may further contain, for example, a binder, a conductive agent, and a dispersant.

[0030] The positive electrode active material is preferably a lithium-containing compound, such as a lithium-containing composite oxide or a lithium-containing phosphate compound. A lithium-containing composite oxide is an oxide containing lithium and one or more elements other than lithium as constituent elements. A lithium-containing composite oxide has, for example, a layered rock salt type or spinel type crystal structure. A lithium-containing phosphate compound is a phosphate compound containing lithium and one or more elements other than lithium as constituent elements. A lithium-containing phosphate compound has, for example, an olivine type crystal structure. A specific example of a lithium-containing composite oxide is LiNiO ２ LiCoO ２ LiCo０．９８ 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 and the like. Specific examples of the lithium-containing phosphate compound are LiFePO ４ , LiMnPO ４ , LiFe ０．５ Mn ０．５ PO ４ , LiFe ０．３ Mn ０．７ PO ４ and the like. Here, the presence of the lithium-containing composite oxide and the lithium-containing phosphate compound can be determined by analysis using various elemental analysis methods. This elemental analysis method is, for example, any one or two or more of analysis methods such as X-ray diffraction (XRD: X-ray Diffraction) method, high-frequency inductively coupled plasma (ICP: Inductively Coupled Plasma) emission spectroscopy method, and energy dispersive X-ray spectroscopy (EDX: Energy Dispersive X-ray Spectroscopy).

[0031] It is more preferable that the positive electrode active material is at least one of the first lithium composite oxide and the second lithium composite oxide. The first lithium composite oxide is a lithium-containing compound represented by the formula (1). Li ｘ Ni １－ｙ M1 ｙ O２－ａ X1 ｂ ... (1) (M1 is at least one of Co, Mn, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta and rare earth elements. X1 is at least one of F, Cl, Cr, I, P, S and Si. x, y, a and b satisfy 0.9 ≤ x ≤ 1.1, 0.005 ≤ y ≤ 0.5, -0.1 ≤ a ≤ 0.2 and 0 ≤ b ≤ 0.1.) The second lithium composite oxide is a lithium-containing compound represented by formula (2). Li ｘ Mn １－ｘ－ｙ－ｚ Ni ｙ M2 ｚ O ２－ａ X2 ｂ ... (2) (M2 is at least one of Co, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta and rare earth elements. X2 is at least one of F, Cl, Cr, I, P, S and Si. x, y, a and b satisfy 0 < x ≤ 0.3, 0.3 ≤ y ≤ 0.9, 0 ≤ z ≤ 0.5, -0.1 ≤ a ≤ 0.2 and 0 ≤ b ≤ 0.1.) Herein, in this disclosure, rare earth elements refer to Sc, Y and lanthanides.

[0032] In this embodiment, the positive electrode active material layer 212 contains particles of the positive electrode active material. The particle size of the positive electrode active material is not particularly limited, however, the D of the particles of the positive electrode active material is ５０ From the viewpoint of ionic conductivity, the particle size is preferably 6 μm or more and 23 μm or less. ５０The particle size can be calculated, for example, by the procedure described below. It can be measured using SEM (Scanning Electron Microscope) and EDX (Energy Dispersive X-ray Spectroscopy). More specifically, the electrode body 200 is disassembled to expose the surface of the positive electrode active material layer 212, and an SEM observation image of the surface of the positive electrode active material layer 212 is obtained at 500x magnification. Here, 50 positive electrode active material particles are identified from the SEM observation image by mapping the elements of the positive electrode active material (e.g., Ni) in the EDX image or by the contrast of the particles that appear in the SEM observation image, and the area S occupied by each positive electrode active material particle is calculated. ｉ The particle area is measured, and the particle diameter D is calculated using the following formula (3) based on the measured particle area. ｉ The 50% integrated value of the resulting particle size distribution is calculated to determine the D of the positive electrode active material particles. ５０ It can be calculated as particle size. Here, in equation (3), D ｉ is particle diameter, S ｉ π represents the particle area, and π represents the ratio of a circle's circumference to its diameter (pi).

[0033] The binder contained in the positive electrode active material layer 212 (positive electrode binder) may be any material, for example, containing 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.

[0034] The conductive agent (positive electrode conductive agent) contained in the positive electrode active material layer 212 can be any material, for example, carbon. Examples of carbon include graphite, carbon black, acetylene black, and Ketjenblack. However, the conductive agent contained in the positive electrode active material layer 212 is not limited to these materials, as long as it is a conductive material, it may also be a metallic material, a conductive polymer, etc.

[0035] The negative electrode 220 comprises a negative electrode current collector 221 and a negative electrode active material layer 222. In the negative electrode 220, the negative electrode current collector 221 is laminated between the negative electrode active material layers 222. However, the negative electrode active material layer 222 may be provided only on one side of the negative electrode current collector 221 on the side of the negative electrode 220 that faces the positive electrode 210.

[0036] The negative electrode current collector 221 is a conductor, and can be made of, for example, copper foil.

[0037] The negative electrode active material layer 222 is a layer containing a negative electrode active material capable of intercalating and deintercalating lithium. The negative electrode active material layer 222 is not limited to consisting solely of the negative electrode active material, but may also contain, for example, a conductive agent and a binder.

[0038] The negative electrode active material contains graphite particles. The graphite particles used as the negative electrode active material may be natural graphite or artificial graphite. ５０ The particle size is 15 μm or less. This improves the adhesion between graphite particles, thereby improving charge and discharge characteristics. ５０ The particle size is preferably 5 μm to 15 μm, and more preferably 10 μm to 15 μm. This reduces the specific surface area of ​​the graphite particles, improving the charge-discharge characteristics. Furthermore, it makes the negative electrode active material particles more easily deformable during the fabrication of the negative electrode active material layer 222, thereby improving the density of the negative electrode active material layer 222 and thus improving the manufacturability of the secondary battery 1.

[0039] Here, the D of the graphite particles contained in the negative electrode active material ５０ The particle size of the positive electrode active material was measured using SEM and EDX (Energy Dispersive X-ray Spectroscopy). ５０ It can be measured in the same way as particle size. More specifically, the electrode body 200 is disassembled to expose the surface of the negative electrode active material layer 222, and an SEM observation image of the surface of the negative electrode active material layer 222 is obtained at 500x magnification. Here, 50 graphite particles are identified from the SEM observation image based on the contrast of particles that appear in the EDX C (carbon) mapping or the SEM observation image, and the area S occupied by each graphite particle is determined. ｉ The particle area is measured, and the particle diameter D is calculated using the above formula (3) based on the measured particle area.ｉ The D of graphite particles is calculated and the 50% integrated value of the resulting particle size distribution is obtained. ５０ It can be calculated as particle size.

[0040] The negative electrode active material may further contain materials other than graphite, such as carbon materials or metallic materials. Specific examples of carbon materials used as negative electrode active materials include easily graphitizable carbon and poorly graphitizable carbon. Metallic materials used as negative electrode active materials are materials containing one or more metallic elements and metalloid elements capable of forming alloys with lithium as constituent elements. Specific examples of metallic elements and metalloid elements used as negative electrode active materials include silicon and tin. Metallic materials used as negative electrode active materials may be elements, alloys, compounds, mixtures of two or more elements, or materials containing two or more phases. Specific examples of metallic materials used as negative electrode active materials include TiSi ２ SiO ｘ (e.g., 0 < x ≤ 2).

[0041] Furthermore, the negative electrode active material layer 222 is not limited to containing only the negative electrode active material.

[0042] For example, the negative electrode active material layer 222 may further contain a negative electrode binder. The negative electrode binder includes at least one of synthetic rubber, polymer compounds, etc. Specific examples of synthetic rubber used as a negative electrode binder include styrene-butadiene rubber, fluorine-based rubber, and ethylene-propylenediene. Specific examples of polymer compounds used as a negative electrode binder include polyvinylidene fluoride, polyimide, and carboxymethylcellulose.

[0043] For example, the negative electrode active material layer 222 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 negative electrode conductive agents include particulate carbon materials such as carbon black, acetylene black, and Ketjenblack, and fibrous carbon materials such as carbon nanotubes. Carbon nanotubes are, for example, single-wall carbon nanotubes (SWCNTs). This improves the electronic conductivity of the particle surface of the negative electrode active material. The mass ratio of the negative electrode conductive agent to the negative electrode active material layer 222 is preferably 5% or less, more preferably 2% or less. This improves the paintability of the negative electrode slurry.

[0044] The separator 230 is a film that insulates the positive electrode 210 and the negative electrode 220. The separator 230 is provided between the main surface of the positive electrode 210 and the main surface of the negative electrode 220 so that the positive electrode 210 and the negative electrode 220 do not come into direct contact with each other.

[0045] The material of the separator 230 is preferably electrically stable, chemically stable with respect to the positive electrode active material, negative electrode active material, and electrolyte, and also insulating. The separator 230 can be, for example, a polymer nonwoven fabric, a porous film, or a layer made of glass or ceramic fibers. The material of the separator 230 is more preferably a porous polyolefin film. This improves the safety of the battery by providing short-circuit prevention and shutdown effects.

[0046] The electrolyte is impregnated into the positive electrode 210, the negative electrode 220, and the separator 230, respectively. In the example shown in Figure 1, the electrolyte is filled into the space within the outer casing member 30. The electrolyte is a non-aqueous electrolyte containing an electrolyte salt and a solvent that dissolves the electrolyte salt.

[0047] The electrolyte salts are lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO)). ２ F ２ ) ２It contains bis(fluorosulfonyl)imide salts such as ). This improves charge and discharge characteristics. The electrolyte salt may also contain other electrolyte salts used as electrolyte salts in lithium-ion batteries. Such other electrolyte salts are, for example, light metal salts such as lithium salts. A specific example of a lithium salt is lithium hexafluoride phosphate (LiPF). ６ ), Lithium monofluorophosphate (Li ２ PFO ３ ), lithium difluorophosphate (LiPF ２ O ２ Lithium salts containing phosphorus (P), such as ) and lithium tetrafluoroborate (LiBF) ４ ), bis(oxalato)borate lithium (LiB(C) ２ O ４ ) ２ It is preferable that the lithium salt contains boron (B), such as ). This allows the surface of the positive electrode current collector 211 to contain P and B. The other electrolyte salt is not limited to the above, but may also be lithium trifluoromethanesulfonate (LiCF ３ SO ３ ), bis(trifluoromethanesulfonyl)imide lithium (LiN(CF ３ SO ２ ) ２ ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF ３ SO ２ ) ３ ) etc. are also acceptable.

[0048] The lithium bis(fluorosulfonyl)imide content in the electrolyte is preferably 1.0 mol / kg or more and 3.0 mol / kg or less. This helps to suppress a decrease in charge-discharge characteristics.

[0049] The solvent preferably contains at least one of the first group consisting of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and gamma butyrolactone (GBL), and more preferably contains DMC. This improves the charge-discharge characteristics.

[0050] The solvent preferably further comprises at least one of the carbonate esters and linear carboxylic acid esters, excluding the compounds included in the first group described above. Examples of carbonate esters, excluding the compounds included in the first group described above, include diethyl carbonate (DEC) and ethyl methyl carbonate (EMC). Examples of linear carboxylic acid esters include propyl propionate (PrPr), ethyl propionate (PrEt), methyl propionate, propyl acetate (AcPr), ethyl acetate (AcEt), and methyl acetate (AcMe). Among these, it is more preferable that the solvent comprises at least one of PrEt, AcPr, AcMe, and AcEt. This improves the charge-discharge characteristics.

[0051] The solvent may further contain other non-aqueous solvents used as non-aqueous solvents for lithium-ion batteries. Other non-aqueous 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 are substituted with fluorine, such as 1,1,2-tetrafluoroethyl 2,2,2,3,3-tetrafluoropropyl ether.

[0052] The electrolyte may contain substances other than the electrolyte salt and solvent, such as additives.

[0053] The electrolyte may contain additives such as unsaturated cyclic carbonate esters like vinylene carbonate, methylene carbonate, and vinylethylene carbonate; halogenated cyclic carbonate esters like monofluoroethylene and difluoroethylene carbonate; hydrofluoroethers; sulfonic acid esters; phosphate esters; acid anhydrides; and isocyanates. Specific examples of sulfonic acid esters include propanesultone and propensultone. 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.

[0054] Hereinafter, the surface state of the positive electrode current collector 211 will be described in detail. In the following description, X-ray photoelectron spectroscopy will be described as XPS (X-ray Photoelectron Spectroscopy). Further, in the following description, the wide scan and various narrow scans on the surface of the positive electrode current collector 211 refer to XPS under the conditions shown in Table 1, which is performed on the surface of the positive electrode current collector 211 taken out by disassembling the secondary battery 1. In the wide scan and various narrow scans on the surface of the positive electrode current collector 211, it is preferable to perform multiple measurements with the number of measurements shown in Table 1 and obtain an averaged spectrum.

[0055]

[0056] FIG. 3 is a diagram showing the S2p spectrum of XPS for the surface of the positive electrode current collector according to the present embodiment. The surface of the positive electrode current collector 211 contains sulfur. Here, whether the surface of the positive electrode current collector 211 contains sulfur or not can be determined by a wide scan or an S2p narrow scan on the surface of the positive electrode current collector 211. As shown in FIG. 3, if a peak is detected in the S2p spectrum, it can be said that the surface of the positive electrode current collector 211 contains sulfur. In the present disclosure, the S2p spectrum refers to a spectrum range of 160 eV or more and 180 eV or less.

[0057] As shown in FIG. 3, the photoelectron spectrum obtained by XPS of the surface of the positive electrode current collector 211 has a first signal S1 having a peak in the range of 164.1 eV or more and 164.5 eV or less, and a second signal S2 having a peak in the range of 168.9 eV or more and 169.3 eV or less. The presence or absence of the first signal S1 and the second signal S2 can be determined by performing peak separation on the S2p spectrum obtained by the S2p narrow scan on the surface of the positive electrode current collector 211 using a Gaussian / Lorentz mixed function.

[0058] The signal intensity I of the first signal S1 Ｓ１ and the signal intensity I of the second signal Ｓ２ The ratio of the sum of the signal intensities of the S2p spectrum to the total signal intensity I of the S2p spectrum Ｓｔ (I Ｓ１ + I Ｓ２ ) / I Ｓｔis 0.97 or less. Thereby, charge and discharge can be performed well. The signal intensity I of the first signal S1 Ｓ１ and the signal intensity I of the second signal Ｓ２ refer to the difference between the peak top and the baseline of each of the first signal S1 and the second signal. Also, the total signal intensity I of the S2p spectrum Ｓｔ refers to the difference between the peak top and the baseline of the composite signal St obtained by combining each signal S1 to S3 obtained by peak separation of the S2p spectrum.

[0059] FIG. 4 is a diagram showing the F1s spectrum of XPS for the surface of the positive electrode current collector according to the present embodiment. The surface of the positive electrode current collector 211 preferably further contains fluorine. Here, whether or not the surface of the positive electrode current collector 211 contains fluorine can be determined by a wide scan or an F1s narrow scan on the surface of the positive electrode current collector 211. As shown in FIG. 4, if a peak is detected in the F1s spectrum, it can be said that the surface of the positive electrode current collector 211 contains fluorine. In the present disclosure, the F1s spectrum refers to the range of 679 eV or more and 697 eV or less.

[0060] As shown in FIG. 4, the photoelectron spectrum obtained by XPS on the surface of the positive electrode current collector 211 has a third signal F1 having a peak at 685.7 eV or more and 686.1 eV or less, and a fourth signal F2 having a peak at 687.4 eV or more and 687.8 eV or less. The presence or absence of the third signal F1 and the fourth signal F2 can be determined by performing peak separation on the F1s spectrum obtained by an F1s narrow scan on the surface of the positive electrode current collector 211 using a Gaussian / Lorentz mixed function.

[0061] The ratio of the sum of the signal intensity I of the third signal F1 Ｆ１ and the signal intensity I of the fourth signal F2 Ｆ２ to the total signal intensity I of the F1s spectrum Ｆｔ (I Ｆ１ +I Ｆ２ ) / I Ｆｔ is 0.80 or more. The signal intensity I of the third signal F1 Ｆ１ and the signal intensity I of the fourth signal F2 Ｆ２This refers to the difference between the peak top and baseline of the third signal F1 and the fourth signal F2, respectively. Also, the sum of the signal intensities of the F1s spectrum is I. Ｆｔ This refers to the difference between the peak top and baseline of the synthesized signal Ft, which is obtained by combining the individual signals F1 to F4 obtained by peak separation of the F1s spectrum.

[0062] Figure 5 shows the Al2p spectrum of the XPS for the surface of the positive electrode current collector according to this embodiment. It is more preferable that the surface of the positive electrode current collector 211 further contains aluminum. Here, if a peak is detected in the Al2p spectrum by a wide scan or Al2p narrow scan of the surface of the positive electrode current collector 211, as shown in Figure 5, then it can be said that the surface of the positive electrode current collector 211 contains aluminum. In this disclosure, the Al2p spectrum refers to the range of 61 eV to 84 eV.

[0063] As shown in Figure 5, the photoelectron spectrum obtained by XPS of the surface of the positive electrode current collector 211 has a fifth signal Al1 with a peak between 75.4 eV and 75.8 eV, and a sixth signal Al2 with a peak between 76.4 eV and 76.8 eV. The presence or absence of the fifth signal Al1 and the sixth signal Al2 can be determined by performing peak separation using a Gauss / Lorentz mixing function on the Al2p spectrum obtained by an Al2p narrow scan of the surface of the positive electrode current collector 211.

[0064] Signal intensity I of the fifth signal Al1 Ａｌ１ and the signal intensity I of the sixth signal Al2 Ａｌ２ The sum of the signal intensities of the Al2p spectra, I Ａｌｔ Ratio to (I Ａｌ１ +I Ａｌ２ ) / I Ａｌｔ It is 0.30 or higher. This improves the charge-discharge characteristics. Signal intensity I of the fifth signal Al1 Ａｌ１ and the signal intensity I of the sixth signal Al2 Ａｌ２ This refers to the difference between the peak top and baseline of the fifth signal Al1 and the sixth signal Al2, respectively. It also refers to the sum of the signal intensities of the Al2p spectrum. ＡｌｔThis refers to the difference between the peak top and baseline of the synthesized signal Alt, which is obtained by synthesizing the signals Al1 to Al5 obtained by peak separation of the Al2p spectrum.

[0065] As described above, the secondary battery 1 according to the first embodiment is a secondary battery comprising a positive electrode 210, a negative electrode 220, and an electrolyte. The positive electrode 210 comprises a positive electrode current collector 211 containing aluminum and a positive electrode active material layer 212 provided on the positive electrode current collector 211. The positive electrode active material layer contains a lithium-containing compound. The negative electrode comprises a negative electrode active material layer containing graphite particles. The electrolyte comprises an electrolyte and a solvent. The electrolyte contains a bis(fluorosulfonyl)imide salt. The surface of the positive electrode current collector 211 contains sulfur. The photoelectron spectrum obtained by X-ray photoelectron spectroscopy analysis of the surface of the positive electrode current collector 211 has a first signal S1 with a peak in the range of 164.1 eV to 164.5 eV and a second signal S2 with a peak in the range of 168.9 eV to 169.3 eV. Signal intensity of the first signal S1 Ｓ１ and the signal intensity I of the second signal S2 Ｓ２ The sum of the signal intensities of the S2p spectrum, I Ｓｔ Ratio to (I Ｓ１ +I Ｓ２ ) / I Ｓｔ It is 0.97 or less. D of graphite particles ５０ The particle size is 15 μm or less. This improves the charge and discharge characteristics.

[0066] In a preferred embodiment, the surface of the positive electrode current collector 211 contains fluorine. The photoelectron spectrum obtained by X-ray photoelectron spectroscopy of the surface of the positive electrode current collector 211 has a third signal F1 with a peak between 685.7 eV and 686.1 eV, and a fourth signal F2 with a peak between 687.4 eV and 687.8 eV. The signal intensity of the third signal F1 is Ｆ１ and the signal intensity I of the fourth signal F2 Ｆ２ The sum of the signal intensities of the F1s spectrum, I Ｆｔ Ratio to (I Ｆ１ +I Ｆ２ ) / I Ｆｔ This value is 0.80 or higher. This allows for further improvement of charge and discharge characteristics.

[0067] In a preferred embodiment, the surface of the positive electrode current collector 211 contains aluminum. The photoelectron spectrum obtained by X-ray photoelectron spectroscopy of the surface of the positive electrode current collector 211 has a fifth signal Al1 with a peak between 75.4 eV and 75.8 eV, and a sixth signal Al2 with a peak between 76.4 eV and 76.8 eV. The signal intensity of the fifth signal Al1 is I Ａｌ１ and the signal intensity I of the sixth signal Al2 Ａｌ２ The sum of the signal intensities of the Al2p spectra, I Ａｌｔ Ratio to (I Ａｌ１ +I Ａｌ２ ) / I Ａｌｔ This value is 0.30 or higher. This allows for further improvement of charge and discharge characteristics.

[0068] In a preferred embodiment, the solvent includes dimethyl carbonate (DMC). This improves the chemical state of the surface of the positive electrode current collector 211 and enhances the charge-discharge characteristics.

[0069] In a preferred embodiment, the solvent includes at least one of ethyl propionate, propyl acetate, ethyl acetate, and methyl acetate. This improves the chemical state of the surface of the positive electrode current collector 211 and enhances the charge-discharge characteristics.

[0070] In a more desirable embodiment, the lithium-containing compound includes at least one of a first lithium composite oxide represented by formula (1) and a second lithium composite oxide represented by formula (2). This improves the voltage of the secondary battery 1, thereby further improving the charge-discharge characteristics. Li ｘ Ni １－ｙ M1 ｙ O ２－ａ X1 ｂ ... (1) (M1 is at least one of Co, Mn, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta and rare earth elements. X1 is at least one of F, Cl, Cr, I, P, S and Si. x, y, a and b satisfy 0.9 ≤ x ≤ 1.1, 0.005 ≤ y ≤ 0.5, -0.1 ≤ a ≤ 0.2 and 0 ≤ b ≤ 0.1.) Li ｘ Mn１－ｘ－ｙ－ｚ Ni ｙ M2 ｚ O ２－ａ X2 ｂ ... (2) (M2 is at least one of Co, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X2 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0 < x ≤ 0.3, 0.3 ≤ y ≤ 0.9, 0 ≤ z ≤ 0.5, -0.1 ≤ a ≤ 0.2, and 0 ≤ b ≤ 0.1.)

[0071] In a preferred embodiment, the electrolyte contains light metal ions as cations. Even in this case, the charge-discharge characteristics can be improved. This allows the voltage of the secondary battery 1 to be increased, thereby improving the charge-discharge characteristics.

[0072] In a preferred embodiment, the light metal ions include lithium ions. This allows for a further improvement in the voltage of the secondary battery 1, thereby improving the charge and discharge characteristics.

[0073] In a preferred embodiment, the content of bis(fluorosulfonyl)imide lithium in the electrolyte is preferably 1.0 mol / kg or more and 3.0 mol / kg or less. This improves the ionic conductivity of the electrolyte and further enhances the charge-discharge characteristics.

[0074] In a preferred embodiment, the secondary battery according to this embodiment is a lithium-ion secondary battery. This allows for stable acquisition of sufficient battery capacity by utilizing lithium intercalation and deintercalation, thereby further improving charge and discharge characteristics.

[0075] (Method for manufacturing a secondary battery) Here, an example of a method for manufacturing a secondary battery 1 according to the first embodiment will be described. The method for manufacturing a secondary battery 1 according to the first embodiment includes the steps of manufacturing a positive electrode 210, manufacturing a negative electrode 220, preparing an electrolyte, assembling a laminate cell, and charging and discharging.

[0076] In the process of manufacturing the positive electrode 210, a positive electrode slurry containing dispersed positive electrode material is applied to the positive electrode current collector 211, followed by drying and compression molding to produce the positive electrode 210. The positive electrode mixture is prepared by mixing the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent. The prepared positive electrode mixture is then dispersed in a dispersion such as N-methyl-2-pyrrolidone (NMP) to produce a positive electrode slurry, and the prepared positive electrode slurry is uniformly applied to both sides of the positive electrode current collector 211. After drying the resulting coating with hot air, the positive electrode 210 is manufactured by compression molding using a roll press or the like. A positive electrode lead 31 is attached to the portion of the positive electrode current collector 211 that is exposed on the manufactured positive electrode 210.

[0077] In the process of manufacturing the negative electrode 220, a negative electrode slurry containing dispersed negative electrode mixture is applied to the negative electrode current collector 221, followed by drying and compression forming to manufacture the negative electrode 220. The negative electrode mixture is prepared by mixing the negative electrode active material and the negative electrode binder. The prepared negative electrode mixture is dispersed in a dispersion liquid such as NMP to produce a negative electrode mixture slurry, and then the negative electrode mixture is uniformly applied to both sides of the negative electrode current collector. After drying the resulting coating with hot air, the negative electrode 220 is manufactured by compression forming using a roll press or the like. A negative electrode lead 32 is attached to the portion of the manufactured negative electrode 220 where the negative electrode current collector 221 is exposed.

[0078] In the process of preparing the electrolyte, the electrolyte is prepared by dissolving the electrolyte salt in a solvent.

[0079] In the process of assembling a laminate cell, the electrode body is fabricated, loaded into an outer casing, and the electrolyte is injected to seal the outer casing. The electrode body is fabricated by stacking the positive electrode 210, separator 230, and negative electrode 220 in that order and winding them in the longitudinal direction. The fabricated electrode body is loaded into the outer casing, and three sides of the outer casing are heat-sealed, leaving one side unsealed and with an opening. Then, the electrolyte is injected through the opening in the outer casing, and the remaining side of the outer casing is heat-sealed in a reduced-pressure environment to seal the outer casing and form a laminate cell.

[0080] In the charge-discharge process, one charge-discharge cycle is performed on the fabricated laminate cell. Here, one charge-discharge cycle can be performed, for example, under charge-discharge conditions A, B, or C. Charge-discharge condition A is a condition in which the first charge, first resting period, second charge, second resting period, and discharge are performed sequentially under the following conditions at a temperature of 33°C: First charge method: CCCV First charge rate: 0.2C First charge control voltage: 3.0V First cutoff time: 1 hour First resting time: 12 hours Second charge method: CCCV Second charge rate: 0.2C Second charge control voltage: 4.2V Second cutoff time: 8 hours Second resting time: 12 hours Discharge method: CC Discharge rate: 0.2C Discharge termination voltage: 2.5V

[0081] Charge / discharge condition B is a condition in which the second standing time of charge / discharge condition A is changed to 5 minutes, and the temperature at which charge / discharge is performed is changed to 25°C.

[0082] Charge / discharge condition C is a condition in which the second standing time of charge / discharge condition A is changed to 72 hours, and the temperature at which charging and discharging is performed is changed to 25°C.

[0083] By performing charging and discharging under the above-described charging and discharging conditions A, B, or C, a good coating can be formed on the positive electrode current collector 211, and the secondary battery 1 can be made electrochemically stable.

[0084] The secondary battery 1 according to the first embodiment can be manufactured by the process described above. However, the manufacturing method of the secondary battery described above is just one example and is not limited thereto.

[0085] (Examples) Examples are described below. However, the present invention is not limited by these examples.

[0086] Table 2 shows Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-4.

[0087]

[0088] In the "Charge / Discharge Conditions" column of the tables shown in Table 2 and later, "A," "B," and "C" respectively refer to the charging and discharging of the laminate cell under the respective charge / discharge conditions A, B, and C described above during the charge / discharge process. In the "Charge / Discharge Conditions" column of Table 2 and later, "D" refers to the charging and discharging of the laminate cell under each of the charge / discharge conditions D during the charge / discharge process.

[0089] Here, charge / discharge condition D is a condition in which charging, standing, and discharging are performed in order under the following conditions at a temperature of 25°C. That is, unlike charge / discharge conditions A, B, and C, where charging is divided into two stages, charge / discharge condition D performs charging in a single stage. Charging method: CCCV Charging rate: 0.2C Charging control voltage: 4.2V Cutoff time: 8 hours Standing time: 5 minutes Discharge method: CC Discharge rate: 0.2C Discharge termination voltage: 2.5V

[0090] (Comparative Example 1-1) The positive electrode according to Comparative Example 1-1 was prepared by applying a slurry of positive electrode mixtures in which the positive electrode mixture was dispersed to the positive electrode current collector 211, followed by drying and compression forming. The positive electrode active material was a first lithium composite oxide (LiNi ０．８２ Co ０．１４ Al ０．４ O ２ A positive electrode mixture was prepared by mixing LNCA powder, polyvinylidene fluoride (PVdF) as a positive electrode binder, and carbon black as a positive electrode conductive agent in a mass ratio of 91:3:6. Here, the particle size of the positive electrode active material is as shown in Table 2. ５０ The mixture was given a particle size. The particle-sized positive electrode mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry. Then, a strip of aluminum foil with a thickness of 12 μm was prepared as the positive electrode current collector, and the prepared positive electrode mixture slurry was uniformly applied to both sides of the aluminum foil. After drying the resulting coating with hot air, the positive electrode was manufactured by compression molding with a roll press. The resulting positive electrode was washed to obtain lithium carbonate (Li ２ CO ３ The concentrations of ) and lithium hydroxide (LiOH) were as shown in Table 2. A positive electrode lead was attached to the portion of the positive electrode current collector that was exposed.

[0091] The negative electrode according to Comparative Example 1-1 was prepared by applying a negative electrode mixture slurry, in which the negative electrode mixture was dispersed, to the negative electrode current collector 221, followed by drying and compression forming. The negative electrode active material is shown in Table 2, D. ５０ A negative electrode mixture was prepared by mixing granular artificial graphite and PVdF as a negative electrode binder in a mass ratio of 93:7. The prepared negative electrode mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to make a negative electrode mixture slurry. A 15 μm thick copper foil was prepared as the negative electrode current collector, and the negative electrode mixture was uniformly applied to both sides of the copper foil. After drying the resulting coating with hot air, the negative electrode was fabricated by compression molding using a roll press. Negative electrode leads were attached to the portion of the fabricated negative electrode where the negative electrode current collector was exposed.

[0092] The separator in Comparative Example 1-1 used a microporous polyethylene film with a thickness of 15 μm.

[0093] The electrolyte for Comparative Example 1-1 was prepared using the solvent and electrolyte salt components and proportions shown in Table 2.

[0094] The laminate cell according to Comparative Example 1-1 was assembled by fabricating an electrode body, loading it into an outer casing, injecting an electrolyte, and sealing the outer casing. The electrode body was fabricated by laminating the positive and negative electrodes fabricated above via the separator, tightly sealing them together, and winding them in the longitudinal direction. The fabricated electrode body was loaded into an outer casing, and three sides of the outer casing were heat-sealed, leaving one side unsealed and with an opening. The outer casing used a laminate film consisting of 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. Subsequently, the electrolyte fabricated above was injected through the opening in the outer casing, and the remaining side of the outer casing was sealed by heat-sealing in a reduced-pressure environment to form a laminate cell.

[0095] In Comparative Example 1-1, the fabricated laminate cell was charged and discharged under charge / discharge condition A. This resulted in the production of a battery according to Comparative Example 1-1.

[0096] ≪XPS Measurement≫ In Comparative Example 1-1, XPS measurements were performed on the surface of the positive electrode current collector. For the XPS measurement, the battery was disassembled in a glove box under an argon atmosphere, the positive electrode current collector was removed, and washed with dimethyl carbonate to prepare the sample. Then, without exposing the sample to the atmosphere, it was introduced into an X-ray photoelectron spectrometer (PHI5000 VersaProve, manufactured by ULVAC-PHI, Inc.), and the X-ray beam used for measurement was set to a monochromatized Al-Kα line (1486.6 eV) with a diameter of approximately 100 μm, and wide scans and various narrow scans were performed under the conditions shown in Table 1 above. For the XPS measurement, charge neutralization was performed using an electron beam and an ion beam. Peak separation was performed on the obtained S2p, F1s, and Al2p spectra from the S2p narrow scan, F1s narrow scan, Al2p narrow scan, and wide scan, respectively, using a Gauss / Lorentz mixing function, and the ratio of signal intensity (I) was calculated. Ｓ１ +I Ｓ２ ) / I Ｓｔ , (I Ｆ１ +I Ｆ２ ) / I Ｆｔ , (I Ａｌ１ +I Ａｌ２ ) / I Ａｌｔ The presence or absence of the P2p spectrum was measured, respectively. As a result, (I Ｓ１ +I Ｓ２ ) / I Ｓｔ , (I Ｆ１ +I Ｆ２ ) / I Ｆｔ , (I Ａｌ１ +I Ａｌ２ ) / I Ａｌｔ The respective values ​​and the presence or absence of P2p spectra are shown in Table 2.

[0097] ≪5C Discharge Test≫ In Comparative Example 1-1, a 5C discharge test was performed. In the 5C discharge test, the secondary battery prepared above was charged and discharged in a 23°C environment under the following first charge / discharge conditions for one cycle, and the discharge capacity of the first cycle was measured. Charging method: CCCV Charging rate: 0.1C Charging control voltage: 4.2V Charging termination current: 0.05C Discharging method: CC Discharge rate: 0.1C Discharge termination voltage: 2.5V

[0098] Subsequently, a second charge-discharge cycle was performed under the second charge-discharge conditions described below, and the discharge capacity of the second cycle was measured. The charge-discharge was performed in an environment of 23°C. Here, the ratio of the discharge capacity of the second cycle to the discharge capacity of the first cycle was calculated as the 5C discharge maintenance rate. That is, the 5C discharge maintenance rate was calculated based on the formula: 5C discharge maintenance rate (%) = (discharge capacity of the second cycle / discharge capacity of the first cycle) × 100. Charging method: CCCV Charging rate: 0.1C Charging control voltage: 4.2V Charging termination current: 0.05C Discharging method: CC Discharge rate: 5C Discharge termination voltage: 2.5V

[0099] Furthermore, the charge-discharge cycles from the 3rd to the 99th cycle were performed under the following conditions: the charge-discharge cycle of the 100th cycle was performed under the second charge-discharge conditions described above, and the charge-discharge cycle of the 101st cycle was performed under the first charge-discharge conditions described above. All charge-discharge operations were performed in an environment of 23°C. Here, the ratio of the discharge capacity at the 101st cycle to the discharge capacity at the 1st cycle was calculated as the 5C discharge maintenance rate after 100 cycles. That is, the 5C discharge maintenance rate after 100 cycles was calculated based on the formula: 5C discharge maintenance rate after 100 cycles (%) = (discharge capacity at the 101st cycle / discharge capacity at the 1st cycle) × 100. Charging method: CCCV Charging rate: 1C Charging control voltage: 4.2V Charging termination current: 0.05C Discharging method: CC Discharge rate: 1C Discharge termination voltage: 2.5V

[0100] ≪Cycle Performance Test≫ In Comparative Example 1-1, a cycle performance test was conducted. In the cycle performance test, the secondary battery prepared above was charged and discharged 100 times in a 60°C environment under the following conditions, and the discharge capacity of the first cycle and the discharge capacity of the 100th cycle were measured. The ratio of the discharge capacity of the 100th cycle to the discharge capacity of the first cycle was calculated as the cycle maintenance rate. That is, the cycle maintenance rate was calculated based on the formula: Cycle maintenance rate (%) = (Discharge capacity of the 100th cycle / Discharge capacity of the 1st cycle) × 100. Charging method: CCCV Charging rate: 0.1C Charging control voltage: 4.2V Charging termination current: 0.05C Discharging method: CC Discharge rate: 0.1C Discharge termination voltage: 2.5V

[0101] <<Storage Characteristics Test>> A storage characteristics test was conducted in Comparative Example 1-1. In the storage characteristics test, the secondary battery prepared above underwent its first charge-discharge cycle in a 23°C environment 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 termination current: 0.05C Discharging method: CC Discharge rate: 0.1C Discharge termination voltage: 2.5V

[0102] Subsequently, the batteries were placed in a constant temperature chamber and stored at 80°C for 10 days. After that, they were discharged under the following conditions, and the discharge capacity after storage was measured. Charging and discharging were performed at 23°C. The ratio of the discharge capacity before storage to the discharge capacity after storage was calculated as the retention rate. That is, the retention rate was calculated based on the formula: Retention Rate (%) = (Discharge Capacity After Storage / Discharge Capacity Before Storage) × 100. Discharge Method: CC Discharge Rate: 0.1C Discharge Termination Voltage: 2.5V

[0103] (Comparative Example 1-2, Example 1-1, Example 1-2) As shown in Table 2, in Comparative Example 1-2, Example 1-1 and Example 1-2, the D of the graphite negative electrode active material ５０ Aside from changing the particle size to that shown in Table 2, a secondary battery was manufactured in the same manner as the battery in Comparative Example 1-1, and measurements and tests were performed.

[0104] (Comparative Examples 1-3) As shown in Table 2, in Comparative Examples 1-3, a secondary battery was prepared in the same manner as the battery in Comparative Example 1-1, except that the electrolyte solvent was changed to the one shown in Table 2, and measurements and tests were performed.

[0105] (Comparative Examples 1-4, Examples 1-3, Examples 1-4) As shown in Table 2, in Comparative Examples 1-4, Examples 1-3, and Examples 1-4, the D of the graphite negative electrode active material ５０ Aside from changing the particle size to that shown in Table 2, secondary batteries were manufactured in the same manner as those described in Comparative Examples 1-3, and measurements and tests were performed.

[0106] As shown in Table 2, the D of the graphite particles of the negative electrode active material ５０ In Examples 1-1 to 1-4, where the particle size is 15 μm or less, the D of the graphite particles of the negative electrode active material ５０Compared to Comparative Examples 1-1 to 1-4, where the particle size was greater than 15 μm, the 5C discharge maintenance rate was improved. The cycle maintenance rate was also improved. Therefore, the D of the graphite particles of the negative electrode active material ５０ It can be seen that the charge-discharge characteristics can be improved by having a particle size of 15 μm or less.

[0107] Table 3 shows Examples 2-1 to 2-4 and Comparative Example 2-1.

[0108]

[0109] (Example 2-1) As shown in Table 3, in Example 2-1, a secondary battery was manufactured in the same manner as the battery in Example 1-2, and measurements and tests were performed.

[0110] (Comparative Example 2-1) As shown in Table 3, in Comparative Example 2-1, a secondary battery was manufactured in the same manner as the battery in Example 2-1, except that the conditions for charging and discharging the fabricated laminate cell were changed to charge / discharge condition D. Measurement and testing were then performed.

[0111] (Example 2-2) As shown in Table 3, in Example 2-2, a secondary battery was manufactured in the same manner as the battery in Example 2-1, except that the conditions for charging and discharging the fabricated laminate cell were changed to charge / discharge condition B. Measurement and testing were then performed.

[0112] (Example 2-3) As shown in Table 3, in Example 2-3, a secondary battery was manufactured in the same manner as the battery in Example 2-1, except that the conditions for charging and discharging the fabricated laminate cell were changed to charge / discharge condition C. Measurement and testing were then performed.

[0113] (Example 2-4) As shown in Table 3, in Example 2-4, a secondary battery was prepared in the same manner as the battery in Example 2-1, except that the solvent of the electrolyte was changed, and measurements and tests were performed.

[0114] As shown in Table 3, (I Ｓ１ +I Ｓ２ ) / I Ｓｔ In Examples 2-1 to 2-4, where the value was ≤0.97, charging and discharging were possible, whereas (I Ｓ１ +I Ｓ２ ) / I ＳｔIn Comparative Example 2-1, where the ratio was >0.97, it was not possible to perform 100 charge-discharge cycles. Therefore, (I Ｓ１ +I Ｓ２ ) / I Ｓｔ The fact that it is ≤0.97 indicates that multiple charge-discharge cycles are possible.

[0115] As shown in Table 3, (I Ｆ１ +I Ｆ２ ) / I Ｆｔ In Examples 2-3 and 2-4, where ≥ 0.80, (I Ｆ１ +I Ｆ２ ) / I Ｆｔ Compared to Example 2-2, where the value is <0.80, the charge-discharge characteristics were improved. Therefore, (I Ｆ１ +I Ｆ２ ) / I Ｆｔ It can be seen that a value of ≥0.80 can improve charge and discharge characteristics.

[0116] As shown in Table 3, (I Ａｌ１ +I Ａｌ２ ) / I Ａｌｔ In Examples 2-1 and 2-4, where ≥ 0.30, (I Ａｌ１ +I Ａｌ２ ) / I Ａｌｔ Compared to Example 2-2, where the value was <0.30, the charge-discharge characteristics were improved. Therefore, (I Ａｌ１ +I Ａｌ２ ) / I Ａｌｔ It can be seen that a value of ≥0.30 can improve the charge and discharge characteristics.

[0117] Table 4 shows Examples 3-1 to 3-9.

[0118]

[0119] (Example 3-1) As shown in Table 4, in Example 3-1, a secondary battery was manufactured in the same manner as the battery in Example 2-1, and measurements and tests were performed.

[0120] (Examples 3-2 to 3-9) As shown in Table 4, in Examples 3-2 to 3-9, secondary batteries were prepared in the same manner as the battery in Example 3-1, except that the electrolyte was as shown in Table 4, and measurements and tests were performed.

[0121] As shown in Table 4, in Examples 3-3 to 3-9, where the electrolyte contained at least one of PrEt, AcPr, AcMe, and AcEt, the 5C discharge retention rate after 100 cycles was improved compared to Examples 3-1 and 3-2, where the electrolyte did not contain PrEt, AcPr, or AcMe. Therefore, it can be seen that the charge-discharge characteristics can be improved by including at least one of PrEt, AcPr, AcMe, and AcEt in the electrolyte.

[0122] As shown in Table 4, in Examples 3-7 to 3-9, where the electrolyte contained DMC, the 5C discharge retention rate and the 5C discharge retention rate after 100 cycles were improved compared to Examples 3-1 to 3-6, where the electrolyte did not contain DMC. Therefore, it can be seen that the inclusion of DMC in the electrolyte can improve the charge-discharge characteristics.

[0123] The embodiments described above are for the purpose of facilitating understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included.

[0124] 1 Secondary battery 10 Outer film 20 Battery element 31 Positive electrode lead 32 Negative electrode lead 41, 42 Sealing film 30 Outer material 210 Positive electrode 211 Positive electrode current collector 212 Positive electrode active material layer 220 Negative electrode 221 Negative electrode current collector 222 Negative electrode active material layer 230 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 and a positive electrode active material layer provided on the positive electrode current collector, the positive electrode active material layer contains a lithium-containing compound, the negative electrode comprises a negative electrode active material layer containing graphite particles, the electrolyte comprises an electrolyte and a solvent, the electrolyte contains a bis(fluorosulfonyl)imide salt, the surface of the positive electrode current collector contains sulfur, the photoelectron spectrum obtained by X-ray photoelectron spectroscopy of the surface of the positive electrode current collector has a first signal with a peak in the range of 164.1 eV to 164.5 eV and a second signal with a peak in the range of 168.9 eV to 169.3 eV, the ratio of the sum of the signal intensity of the first signal and the signal intensity of the second signal to the sum of the signal intensities of the S2p spectrum is 0.97 or less, and the D of the graphite particles ５０ A secondary battery with a particle size of 15 μm or less.

2. The secondary battery according to claim 1, wherein the surface of the positive electrode current collector contains fluorine, and the photoelectron spectrum obtained by X-ray photoelectron spectroscopy of the surface of the positive electrode current collector has a third signal with a peak between 685.7 eV and 686.1 eV, and a fourth signal with a peak between 687.4 eV and 687.8 eV, and the ratio of the sum of the signal intensities of the third signal and the fourth signal to the sum of the signal intensities of the F1s spectrum is 0.80 or more.

3. The secondary battery according to claim 1 or 2, wherein the surface of the positive electrode current collector contains aluminum, and the photoelectron spectrum obtained by X-ray photoelectron spectroscopy of the surface of the positive electrode current collector has a fifth signal having a peak between 75.4 eV and 75.8 eV, and a sixth signal having a peak between 76.4 eV and 76.8 eV, and the ratio of the sum of the signal intensities of the fifth signal and the sixth signal to the sum of the signal intensities of the Al2p spectrum is 0.30 or more.

4. The secondary battery according to any one of claims 1 to 3, wherein the solvent comprises dimethyl carbonate.

5. The secondary battery according to any one of claims 1 to 4, wherein the solvent comprises at least one of ethyl propionate, propyl acetate, ethyl acetate, and methyl acetate.

6. The secondary battery according to any one of claims 1 to 5, wherein the lithium-containing compound contains at least one of a first lithium composite oxide represented by formula (1) and a second lithium composite oxide represented by formula (2). Li ｘ Ni １－ｙ M1 ｙ O ２－ａ X1 ｂ ... (1) (M1 is at least one of Co, Mn, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X1 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0.9 ≤ x ≤ 1.1, 0.005 ≤ y ≤ 0.5, -0.1 ≤ a ≤ 0.2, and 0 ≤ b ≤ 0.1.) Li ｘ Mn １－ｘ－ｙ－ｚ Ni ｙ M2 ｚ O ２－ａ X2 ｂ ... (2) (M2 is at least one of Co, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X2 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0 < x ≤ 0.3, 0.3 ≤ y ≤ 0.9, 0 ≤ z ≤ 0.5, -0.1 ≤ a ≤ 0.2, and 0 ≤ b ≤ 0.1.) 7. The secondary battery according to any one of claims 1 to 6, wherein the electrolyte contains light metal ions as cations.

8. The secondary battery according to claim 7, wherein the light metal ions include lithium ions.

9. The secondary battery according to claim 8, wherein the content of bis(fluorosulfonyl)imide lithium in the electrolyte is 1.0 mol / kg or more and 3.0 mol / kg or less.

10. A secondary battery according to any one of claims 1 to 9, which is a lithium-ion secondary battery.

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