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 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, lithium carbonate, and lithium hydroxide. The electrolyte solution includes 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 solution, is greater than 0 and not greater than 1.76.

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 positive electrode 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 invention 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, lithium carbonate, and lithium hydroxide. The electrolyte comprises an electrolyte and a solvent, wherein the electrolyte contains a bis(fluorosulfonyl)imide salt, and the solvent contains at least one from the first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma butyrolactone, and the intrinsic molar ratio of the solvent to lithium ions, calculated from the vibrational spectral spectrum of the electrolyte, is greater than 0 and 1.76 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.

[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 includes 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 where the positive electrode 210 faces the negative electrode 220.

[0028] The positive electrode current collector 211 contains aluminum, and for example, an aluminum foil can be used. The surface state 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 occluding and releasing lithium. The positive electrode active material layer 212 contains a positive electrode active material, lithium carbonate (Li ２ CO ３ ), and lithium hydroxide (LiOH). The positive electrode active material layer 212 is not limited to the materials listed above, and for example, it may further contain 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. 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 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. Specific examples of the lithium-containing composite oxide are 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 １．２Mn 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 Examples include LiFePO4. ４ LiMnPO ４ LiFe ０．５ Mn ０．５ PO ４ LiFe ０．３ Mn ０．７ PO ４ These are some examples. The presence of lithium-containing complex oxides and lithium-containing phosphate compounds can be determined by analyzing them using various elemental analysis methods. These elemental analysis methods include, for example, one or more of the following: X-ray diffraction (XRD), inductively coupled plasma (ICP) emission spectroscopy, and energy dispersive X-ray spectroscopy (EDX).

[0031] The positive electrode active material is more preferably at least one of a first lithium composite oxide and a second lithium composite oxide. The first lithium composite oxide is a lithium-containing compound represented by formula (1). 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.) The second lithium composite oxide is a lithium-containing compound represented by formula (2). Liｘ 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.) 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 of the positive electrode active material is preferably 6 μm or more and 23 μm or less. ５０ This is calculated, for example, by the procedure described below. First, a cross-section of the positive electrode active material layer 212 is observed using a scanning electron microscope (SEM). The observation range and magnification of the cross-section of the positive electrode active material layer 212 can be set arbitrarily. Next, the longest diameter of the positive electrode active material particles is measured based on the observation results (microscope image) of the cross-section of the positive electrode active material layer 212. Finally, the longest diameter of the positive electrode active material particles that make up 50% of the cumulative total is used to determine the D of the positive electrode active material particles. ５０ This is assumed. Furthermore, the D of the particles of the positive electrode active material. ５０ The analysis can be performed automatically using image processing software or similar methods.

[0033] Lithium carbonate and lithium hydroxide are components that remain in the positive electrode active material layer 212 due to being unintentionally formed during the manufacturing process of the lithium-containing compounds described above. In the following explanation, lithium carbonate and lithium hydroxide will be collectively referred to simply as "residual lithium components." A large amount of residual lithium components may degrade the battery characteristics of the secondary battery.

[0034] In this embodiment, with respect to ensuring the battery characteristics of the secondary battery, the amount of residual lithium component in the positive electrode active material layer 212 is set to a range in which the amount of residual lithium component is sufficient. Specifically, the lithium carbonate content in the positive electrode active material layer 212 is preferably greater than 0.05% by mass, and more preferably 0.1% by mass or more. Furthermore, the lithium hydroxide content in the positive electrode active material layer 212 is preferably greater than 0.05% by mass, and more preferably 0.1% by mass or more. This stabilizes the interface between the positive electrode current collector 211 and the positive electrode active material layer 212, and in particular, high charge-discharge characteristics can be obtained even when the secondary battery is used (charged / discharged) or stored in harsh environments such as high-temperature or low-temperature environments.

[0035] In this embodiment, with regard to ensuring the battery characteristics of the secondary battery, the content (remaining amount) of residual lithium component is set to a range where the amount of residual lithium component is not excessive. The lithium carbonate content in the positive electrode active material layer 212 is preferably less than 1.0 mass%, and more preferably 0.7 mass% or less. Furthermore, the lithium hydroxide content in the positive electrode active material layer 212 is preferably less than 1.0 mass%, and more preferably 0.7 mass% or less. This allows for optimization of the surface state of the positive electrode active material, i.e., the elemental distribution on the surface of the lithium-containing compound. Specifically, the content of the constituent elements of the lithium-containing compound on the surface of the lithium-containing compound particles can be made sufficiently larger than the content of the constituent elements of the residual lithium component. This suppresses the generation of gas caused by the presence of residual lithium component, while promoting the insertion and removal of lithium ions into and from the lithium-containing compound, thereby making it less likely for the electrolyte to decompose on the surface of the lithium-containing compound particles. As a result, the above-mentioned advantages can be stably obtained, especially when the secondary battery is used (charged / discharged) or stored in harsh environments such as high-temperature or low-temperature environments.

[0036] The residual lithium content can be measured using the Warder method by following the procedure described below. First, a predetermined amount m (g) of positive electrode active material is weighed, and then the positive electrode active material is placed in a sample bottle. The predetermined amount m (g) is, for example, 10 g. Next, 50 mL (= 50 cm) of ultrapure water is added to the sample bottle along with a stirring bar. ３ After adding the solution, stir the ultrapure water with a stirrer for 1 hour. Then, let the stirred ultrapure water stand for 1 hour, collect the supernatant of the ultrapure aqueous solution using a syringe with a filter, and filter the supernatant. Then, using a volumetric pipette, collect 10 mL (= 10 cm) of the filtered supernatant. ３ After collection, the supernatant liquid is placed in a stoppered flask after filtration. Next, one drop of phenolphthalein solution is added to the supernatant liquid in the flask, and the supernatant liquid is stirred using a stirrer while titrating with hydrochloric acid (HCl) of concentration c as the titration solution. Concentration c is, for example, 0.02 mol / L (= 0.02 mol / dm³). ３ ) can be expressed as follows. Here, assuming that the endpoint of the first titration is reached when the red color of the liquid disappears, the amount of hydrochloric acid added is V ａ (mL) (=V) ａ (cm ３ Read the value. Next, add two drops of bromophenol blue solution to the supernatant, and then, while stirring the supernatant with a stirrer, perform the titration again using the titration solution described above. Here, assuming that the endpoint of the second titration has been reached when the blue color of the solution disappears and it changes to yellowish-green, the amount of hydrochloric acid added is V. ｂ (mL) (=V) ｂ (cm ３ Read the values. Note that the titration apparatus can be the COM-1600 automatic titrator manufactured by Hiranuma Sangyo Co., Ltd. Finally, calculate the lithium carbonate content (mass%) using the following formula (3), and calculate the lithium hydroxide content (mass%) using the following formula (4). (Lithium carbonate content (mass%)) = [(c × 2V ｂ × (f / 1000) × 0.5 × 73.892 × 5) / m] × 100 ... (3) (Lithium hydroxide content (mass%)) = [(c × (V ａ -V ｂ) × (f / 1000) × 23.941 × 5) / m] × 100 ... (4) (In equations (3) and (4), m is the mass (g) of the positive electrode active material, V ａ This is the volume of drops (mL = cm) added to the endpoint of the first titration using phenolphthalein solution. ３ )) and V ｂ This is the volume of titration (mL = cm) from the endpoint of the first titration using phenolphthalein solution to the endpoint of the second titration using bromophenol blue solution. ３ )) where f is a factor that depends on the concentration of the titration solution, and c is the concentration of the titration solution (mol / L (= mol / dm³) 3 )) That is. )

[0037] 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.

[0038] 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.

[0039] 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.

[0040] The negative electrode current collector 221 is a conductor, and can be made of, for example, copper foil.

[0041] 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.

[0042] The negative electrode active material preferably contains at least one of a carbon material and a metallic material. This allows for a high energy density. Specific examples of carbon materials used as negative electrode active materials include easily graphitizable carbon, poorly graphitizable carbon, natural graphite, and artificial graphite. The metallic material used as a negative electrode active material is a material 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. The metallic material used as a negative electrode active material may be an element, an alloy, a compound, a mixture of two or more elements, or a material containing two or more phases. A specific example of a metallic material used as a negative electrode active material is TiSi ２ SiO ｘ (e.g., 0 < x ≤ 2).

[0043] Furthermore, the negative electrode active material layer 222 is not limited to containing only the negative electrode active material.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The electrolyte salts are lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO)). ２ F ２ ) ２It contains salts of bis(fluorosulfonyl)imide such as ( ). As a result, the charge-discharge characteristics can be improved. The electrolyte salt may contain other electrolyte salts used as the electrolyte salt of a lithium-ion battery. The other electrolyte salts are, for example, light metal salts such as lithium salts. Specific examples of the lithium salt are lithium hexafluorophosphate (LiPF ６ ), lithium monofluorophosphate (Li ２ PFO ３ ), lithium difluorophosphate (LiPF ２ O ２ ), etc., lithium salts containing phosphorus (P), or lithium salts containing boron (B) such as lithium tetrafluoroborate (LiBF ４ ), lithium bis(oxalato)borate (LiB(C ２ O ４ )) ２ ). It is preferable that it is a lithium salt containing boron (B). As a result, P and B can be contained on the surface of the positive electrode current collector 211. The other electrolyte salts are not limited to the above, and include lithium trifluoromethanesulfonate (LiCF ３ SO ３ ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF ３ SO ２ )) ２ ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF ３ SO ２ )) ３ ), etc. may also be used.

[0050] The content of lithium bis(fluorosulfonyl)imide in the electrolyte is preferably 1.0 mol / kg or more and 3.0 mol / kg or less. As a result, it is possible to suppress the deterioration of the charge-discharge characteristics.

[0051] The solvent contains at least one selected from the first group consisting of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and gamma-butyrolactone (GBL).

[0052] The solvent preferably further contains at least one of the carbonate esters and linear carboxylic acid esters, excluding the compounds included in the first group described above. This further improves the charge-discharge characteristics. 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). The solvent preferably contains at least one of the linear carboxylic acid esters and carbonate esters, excluding the compounds included in the first group described above, from DEC, EMC, PrPr, PrEt, AcPr, AcEt, and AcMe, and more preferably contains at least one of EMC, PrPr, PrEt, AcPr, AcEt, and AcMe. This further improves the charge-discharge characteristics.

[0053] 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.

[0054] The electrolyte may contain substances other than the electrolyte salt and solvent, such as additives.

[0055] The electrolytic solution may further contain at least one of an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, a dicarboxylic anhydride, a disulfonic anhydride, a sulfate ester, a nitrile compound, and an isocyanate compound as an additive. Specific examples of the unsaturated cyclic carbonate include vinylene carbonate (VC), methylene ethylene carbonate (MEC), vinyl ethylene carbonate (VEC), and the like. Specific examples of the fluorinated cyclic carbonate include fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and the like. Specific examples of the sulfonic acid ester include propane sultone (PS), propene sultone (PRS), and the like. Specific examples of the dicarboxylic anhydride include succinic anhydride (SA), 1,2-ethanedisulfonic anhydride, and the like. Specific examples of the disulfonic anhydride include cyclodison (CD), 2-sulfobenzoic anhydride, and the like. Specific examples of the sulfate ester include ethylene sulfate (DTD), propanedisulfonic anhydride (PSAH), and the like. Specific examples of the nitrile compound include succinonitrile (SN), and the like. Specific examples of the isocyanate compound include hexamethylene diisocyanate (HMI), and the like.

[0056] In addition, the electrolytic solution may further contain at least one of lithium hexafluorophosphate (LiPF ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium bis(oxalato)borate (LiBOB), and lithium difluorophosphate (LiPF ２ O ２ ) as an additive.

[0057] The molar ratio of the solvent originally present to lithium ions, calculated from the vibrational spectrum of the electrolytic solution, is greater than 0 and 1.76 or less. The molar ratio of the solvent originally present to lithium ions is preferably greater than 0 and 1.72 or less. The molar ratio of the solvent originally present to lithium ions is preferably 0.10 or more. Thereby, the charge-discharge characteristics can be improved. In the present disclosure, the solvent originally present refers to the solvent molecules in the electrolytic solution that are not solvated to lithium ions among the solvent molecules contained in the electrolytic solution. The molar ratio of the solvent originally present to lithium ions according to the present disclosure is the amount of substance M of the solvent originally present obtained by the following formula (1) ０This can be calculated by dividing it by the amount of lithium ions contained in the electrolyte. If the electrolyte contains multiple types of solvents, the amount of M of each solvent can be calculated using the following formula (1). ０ By calculating the weighted average of the molar ratios of multiple solvents and dividing by the amount of lithium ions contained in the electrolyte, the original amount of solvent used to calculate the original molar ratio of the solvent to lithium ions can be determined. ０ = M ａｌｌ -M Ｎ = M ａｌｌ -c ｔ / {1+Γ(I o / I ｓ )} ... (1) In the above equation (1), M ａｌｌ M is the total amount of solvent contained in the solution. Ｎ c is the amount of substance of the solvent molecules solvated in lithium ions. ｔ θ is the concentration of the solvent, Γ is the ratio of vibrational spectral intensity per unit concentration, and I ｏ This represents the intrinsic peak intensity of the solvent, I ｓ The peak intensities of the solvent in the solvate are shown, respectively. Here, the vibrational spectral intensity ratio Γ per unit concentration is given by c ｏ The concentration of the solvent that is not solvated with lithium ions, c ｓ If we consider c as the concentration of the solvent solvating the lithium ions, ｓ / c ｏ Using I as the horizontal axis ｓ / I ｏ It can be determined by the slope of a graph plotted with the vertical axis.

[0058] In this disclosure, "solvent peak" refers to the peak observed at the peak position (wavenumber) when a solvent not solvated with lithium ions is measured using vibrational spectroscopy, i.e., when only the solvent is measured using vibrational spectroscopy. Furthermore, "solvent peak of the solvate" refers to the peak position when a solvent solvated with lithium ions is measured using vibrational spectroscopy. Note that the solvent peak of the solvate can be distinguished from the solvent peak because its vibrational spectroscopy spectrum shifts relative to the solvent peak. Therefore, the height from the baseline to the peak top of both the solvent peak and the solvent peak of the solvate is defined as the peak intensity I.ｏ , I ｓ This can be done. Furthermore, if multiple peaks exist in the vibrational spectroscopy spectrum of the electrolyte, both intrinsic and solvate solvent peaks, the peak intensity I ｏ , I ｓ Based on the peaks that make it easier to determine the ratio, the peak intensity I ｏ , I ｓ The ratio of these can be calculated. Furthermore, if the shift of the solvent peak of the solvate relative to the intrinsic solvent peak is small, and the intrinsic solvent peak and the solvent peak of the solvate overlap to form a smooth peak, then the peak intensity I can be determined by performing peak separation using known methods. ｏ , I ｓ You may calculate the ratio.

[0059] Table 1 shows examples of the wavenumber of the intrinsic peak of the solvent and the wavenumber of the solvent peak of the solvate in the vibrational spectroscopy spectrum of the electrolyte of the present invention. The wavenumber of the intrinsic peak of the solvent and the wavenumber of the solvent peak of the solvate shown in Table 1 are, respectively, I ｏ and I ｓ It can be used for the measurement of [the following]. As shown in Table 1, the FEC peak may overlap with the EC peak and the DMC peak because they are in the vicinity of each other. Since it can be assumed that FEC has the same vibrational spectral intensity ratio Γ per unit concentration as EC and DMC, if the solvent contains at least one of EC and DMC and FEC, the original amount of substance of the solvent can 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 spectral measurement device, measurement environment, and measurement conditions.

[0060]

[0061] In this disclosure, the vibrational spectral spectrum of the electrolyte is measured by Raman spectroscopy or Fourier transform infrared spectroscopy using an electrolyte sample extracted from a secondary battery to be measured using a centrifuge, after making an incision in the battery. It is preferable to measure the vibrational spectral spectrum of the electrolyte in an environment in which the influence of atmospheric moisture can be reduced or ignored. Examples of measuring the vibrational spectral spectrum of the electrolyte include performing the measurement under low humidity or no humidity conditions such as a dry room or glove box, or measuring the electrolyte sealed in a transparent sealed container as a sample. Alternatively, the electrolyte extracted from the secondary battery to be measured may be quantitatively analyzed by ICP (Inductively Coupled Plasma), NMR (Nuclear Magnetic Resonance), or GC-MS (Gas Chromatography Mass Spectrometry), and an electrolyte with the same composition as the electrolyte of the secondary battery to be measured may be prepared based on the composition of the extracted electrolyte, and this prepared electrolyte may be used as the sample for measuring the vibrational spectral spectrum.

[0062] 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 212 contains a lithium-containing compound, lithium carbonate, and lithium hydroxide. The electrolyte comprises an electrolyte and a solvent. The electrolyte contains a bis(fluorosulfonyl)imide salt. The solvent contains at least one from the first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma butyrolactone. The intrinsic molar ratio of the solvent to lithium ions, calculated from the vibrational spectral distribution of the electrolyte, is greater than 0 and 1.76 or less. This improves the charge-discharge characteristics.

[0063] In a preferred embodiment, the solvent further comprises at least one of the carbonate esters and linear carboxylic acid esters, excluding the compounds included in the first group. This further improves the charge-discharge characteristics.

[0064] In a more desirable embodiment, the solvent further comprises at least one of diethyl carbonate, ethyl methyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, and methyl acetate. This further improves the charge-discharge characteristics.

[0065] In a more desirable embodiment, the solvent further comprises at least one of ethyl methyl carbonate, propyl propionate, ethyl propionate, propyl acetate, ethyl acetate, and methyl acetate. This further improves the charge-discharge characteristics.

[0066] In a desirable configuration, the intrinsic molar ratio of the solvent to lithium ions, calculated from the vibrational spectroscopy spectrum of the electrolyte, is greater than 0 and 1.72 or less. This allows for further improvement of charge and discharge characteristics.

[0067] In a more desirable embodiment, the lithium carbonate content in the positive electrode active material layer 212 is greater than 0.05 mass% and less than 1.0 mass%. This stabilizes the interface between the positive electrode active material layer and the positive electrode current collector layer, while making it less likely for the electrolyte to decompose on the surface of the lithium-containing compound particles, thereby improving charge and discharge characteristics, especially in harsh environments such as high-temperature or low-temperature environments.

[0068] In a more desirable embodiment, the lithium hydroxide content in the positive electrode active material layer 212 is greater than 0.05% by mass and less than 1.0% by mass. This stabilizes the interface between the positive electrode active material layer and the positive electrode current collector layer, while making it less likely for the electrolyte to decompose on the surface of the lithium-containing compound particles, thereby improving charge and discharge characteristics, especially in harsh environments such as high-temperature or low-temperature environments.

[0069] 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 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.)

[0070] 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.

[0071] 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.

[0072] 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.

[0073] In a preferred embodiment, the electrolyte more preferably further contains at least one of the following: unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, sulfonic acid esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfate esters, nitrile compounds, and isocyanate compounds. This suppresses the decomposition reaction of the electrolyte, thereby further improving the charge-discharge characteristics.

[0074] In a preferred embodiment, the electrolyte further comprises at least one of lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorophosphate. This further improves the lithium ion transfer rate, thereby improving the charge-discharge characteristics.

[0075] 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.

[0076] (Method for manufacturing a secondary battery) An example of a method for manufacturing a secondary battery 1 according to the first embodiment will be described below. 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.

[0077] 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.

[0078] 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.

[0079] In the process of preparing the electrolyte, the electrolyte is prepared by dissolving the electrolyte salt in a solvent.

[0080] 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.

[0081] In the charge-discharge process, one charge-discharge cycle is performed on the fabricated laminate cell. One charge-discharge cycle can be performed, for example, under charge-discharge condition A. Charge-discharge condition A is a condition in which the first charge, first resting period, second charge, second resting period, and discharge are performed in order under the following conditions at a temperature of 33°C. This allows a good film to be formed on the positive electrode current collector 211, making the secondary battery 1 electrochemically stable. 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

[0082] By following the above steps, a secondary battery 1 according to the first embodiment can be manufactured. Note that the method for manufacturing a secondary battery described above is merely an example and is not limited thereto.

[0083] (Examples) Examples are described below. However, the present invention is not limited by these examples.

[0084] Table 2 shows Comparative Examples 1-1 to 1-7 and Examples 1-1 to 1-69.

[0085]

[0086] In the "Charge / Discharge Conditions" column of the tables shown in Table 2 and subsequent tables, "A" and "B" respectively refer to the charge / discharge process being performed on the laminate cell under the charge / discharge conditions A and charge / discharge conditions B described above.

[0087] Here, charge / discharge condition B refers to the conditions under which charging, standing, and discharging are performed sequentially at a temperature of 30°C under the following conditions. That is, unlike charge / discharge condition A, where charging is divided into two stages, charge / discharge condition B involves 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

[0088] (Comparative Example 1) The positive electrode according to Comparative Example 1 was prepared by applying a positive electrode mixture slurry, 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. ５０The prepared positive electrode mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry. 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 compressed and molded using a roll press to produce the positive electrode. By washing the resulting positive electrode, 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 layer that was exposed.

[0089] The negative electrode according to Comparative Example 1-1 was prepared by applying a negative electrode slurry containing a dispersed negative electrode mixture to a negative electrode current collector 221, followed by drying and compression molding. 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. After preparing a negative electrode slurry by dispersing the prepared negative electrode mixture in N-methyl-2-pyrrolidone (NMP), a copper foil with a thickness of 15 μm 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 manufactured by compression molding with a roll press. A negative electrode lead was attached to the portion of the negative electrode current collector that was exposed.

[0090] The separator in Comparative Example 1-1 used a microporous polyethylene film with a thickness of 15 μm.

[0091] The electrolyte for Comparative Example 1-1 was prepared using the solvent and electrolyte salt components and proportions shown in Table 2.

[0092] 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.

[0093] In Comparative Example 1-1, the fabricated laminate cell was subjected to one charge-discharge cycle under the charge-discharge condition B described above. This resulted in the production of the battery according to Comparative Example 1-1.

[0094] <<Vibrational Spectroscopic Spectrum Measurement>> In Comparative Example 1-1, the vibrational spectral spectrum of the electrolyte was measured using the following method. For vibrational spectral spectrum measurement, the electrolyte extracted from the secondary battery to be measured using a centrifuge was sealed in a glass container to prepare the sample. The sample was then introduced into a Raman spectrometer (manufactured by Nanophoton Inc.), and the excitation laser wavelength used for measurement was set to 758 nm. The resulting intrinsic peak intensity I of the solvent was obtained. ｏ and the peak intensity I of the solvent in the solvate ｓ Based on the above equation (1), the original amount of substance M of the solvent is obtained. ０ The intrinsic molar ratio of the solvent to lithium ions was calculated. Since the electrolyte in Comparative Example 1-1 contains multiple types of solvents, the intrinsic amount M of each solvent was calculated using the above formula (1). ０ The intrinsic amount of the solvent was calculated by performing the calculation and then calculating a weighted average based on the molar ratios of multiple solvents. As a result, the intrinsic molar ratio of the solvent to lithium ions is shown in Table 2.

[0095] ≪Cycle Characteristics Test≫ A cycle characteristics test was conducted in Comparative Example 1-1.

[0096] In the cycle performance test, the secondary battery prepared above was subjected to 100 charge-discharge cycles in a 60°C environment under the following conditions, and the discharge capacity at the 1st cycle and the discharge capacity at the 100th cycle were measured. The cycle maintenance rate was calculated as the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle. That is, the cycle maintenance rate was calculated based on the formula: Cycle maintenance rate (%) = (Discharge capacity at the 100th cycle / Discharge capacity at 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

[0097] <Storage Characteristics Test> A storage characteristics test was conducted in Comparative Example 1-1.

[0098] In the storage characteristics test, the secondary batteries prepared as described above underwent their first charge-discharge cycle in a 23°C environment under the following conditions, and their 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

[0099] 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

[0100] <<Low-Temperature Load Characteristics Test>> In Comparative Example 1-1, a low-temperature load characteristics test was conducted.

[0101] In the low-temperature load characteristic test, the secondary battery prepared above underwent its first charge-discharge cycle at 23°C under the following conditions. Subsequently, the second to 100th charge-discharge cycles were performed at -10°C under the same conditions as the first charge-discharge cycle, as described below. The ratio of the discharge capacity at cycle 100 to the discharge capacity at cycle 1 was calculated as the low-temperature load retention rate. That is, the low-temperature load retention rate was calculated based on the formula: Low-temperature load retention rate (%) = (Discharge capacity at cycle 100 / Discharge capacity at cycle 1) × 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

[0102] (Comparative Examples 1-2 to 1-7, Examples 1-1 to 1-37, Examples 1-50 to 1-69) In Comparative Examples 1-2 to 1-7, Examples 1-1 to 1-37, and Examples 1-50 to 1-69, an electrolyte solution was prepared by mixing the components shown in Table 2 as a solvent in the mass ratio shown in Table 2, and dissolving LiFSI as an electrolyte salt to the concentration shown in Table 2. The battery was then prepared in the same manner as the battery in Comparative Example 1-1, except that the charge and discharge conditions were changed to charge and discharge condition A as described above. Measurements and tests were then performed.

[0103] (Examples 1-38 to 1-49) In Examples 1-38 to 1-49, the particle size of the positive electrode active material (D ５０ The size of the ) is as shown in Table 2, and the components shown in Table 2 are mixed as a solvent in the mass ratio shown in Table 2, and LiFSI and LiPF are used as the electrolyte salts. ６ Each of the components was dissolved to prepare an electrolyte solution to the concentrations shown in Table 2. The battery was then prepared in the same manner as the battery in Comparative Example 1-1, except that the charge and discharge conditions were changed to charge and discharge condition A as described above. Measurements and tests were then performed.

[0104] As shown in Table 2, Examples 1-1 to 1-69, in which the intrinsic molar ratio of the solvent to lithium ions was greater than 0 and 1.76 or less, showed improved cycle retention and storage retention compared to Comparative Examples 1-1 to 1-7, in which the intrinsic molar ratio of the solvent to lithium ions was 0 or greater than 1.76. Therefore, it can be seen that the charge-discharge characteristics can be improved by having an intrinsic molar ratio of the solvent to lithium ions that is greater than 0 and 1.76 or less.

[0105] As shown in Table 2, a comparison of Comparative Example 1-1 and Example 1-1 revealed that even with the same electrolyte composition, the inherent molar ratio of the solvent to lithium ions differed due to different charge-discharge conditions. This indicates that the state of the electrolyte changes depending on the charge-discharge conditions because the charge-discharge process causes changes in the chemical state of some of the components of the electrolyte (solvent and electrolyte).

[0106] As shown in Table 2, in Examples 1-3 to 1-69, where the intrinsic molar ratio of the solvent to lithium ions was 1.72 or less, the cycle retention rate and storage retention rate were improved compared to Examples 1-1 and 1-2, where the intrinsic molar ratio of the solvent to lithium ions was greater than 1.72. Therefore, it can be seen that the charge-discharge characteristics can be further improved by having an intrinsic molar ratio of the solvent to lithium ions of 1.72 or less.

[0107] As shown in Table 2, in Examples 1-2 and 1-3 to 1-69, where the solvent further includes at least one of the carbonate esters (DEC, EMC) and linear carboxylic acid esters (PrPr, PrEt, AcPr, AcEt, AcMe) excluding EC, FEC, and DMC included in Group 1, the charge-discharge characteristics were further improved compared to Example 1-1, where the solvent consisted of EC and DMC included in Group 1. Therefore, it can be seen that the charge-discharge characteristics can be further improved by further including at least one of the carbonate esters and linear carboxylic acid esters excluding the compounds included in Group 1 in the solvent.

[0108] As shown in Table 2, in Examples 1-2 and 1-3 to 1-69, where the solvent further includes at least one of DEC, EMC, PrPr, PrEt, AcPr, AcEt, and AcMe, the charge-discharge characteristics were further improved compared to Example 1-1, where the solvent does not include DEC, EMC, 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 DEC, EMC, PrPr, PrEt, AcPr, AcEt, and AcMe in the solvent.

[0109] As shown in Table 2, in Examples 1-2 and 1-4 to 1-69, where the solvent further includes at least one of EMC, PrPr, PrEt, AcPr, AcEt, and AcMe, the low-temperature load characteristics were further improved compared to Examples 1-1 and 1-3, where the solvent did not include 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.

[0110] As shown in Table 2, in Examples 1-54 to 1-57, Examples 1-59 to 1-61, and Examples 1-63 and 1-64, where the lithium carbonate content in the positive electrode active material layer was less than 1.0% by mass, the cycle retention rate and storage retention rate were improved compared to Example 1-62, where the lithium carbonate content in the positive electrode active material layer was 1.0% by mass or more. Therefore, it can be seen that the charge-discharge characteristics can be improved by having a lithium carbonate content in the positive electrode active material layer less than 1.0% by mass.

[0111] As shown in Table 2, in Examples 1-54 to 1-57, Examples 1-59 to 1-61, and Examples 1-63 and 1-64, where the lithium hydroxide content in the positive electrode active material layer was less than 1.0% by mass, the cycle retention rate and storage retention rate were improved compared to Example 1-58, where the lithium hydroxide content in the positive electrode active material layer was 1.0% by mass or more. Therefore, it can be seen that the charge-discharge characteristics can be improved by having a lithium hydroxide content in the positive electrode active material layer less than 1.0% by mass.

[0112] Table 3 shows Comparative Examples 2-1 to 2-6 and Examples 2-1 to 2-29.

[0113]

[0114] (Comparative Examples 2-2 to 2-6, Examples 2-1 to 2-29) In Comparative Examples 2-2 to 2-6 and Examples 2-1 to 2-29, the positive electrode active material was given a particle size (D) as shown in Table 3. ５０ ) Lithium-2 composite oxide (LiMn ０．４ Ni ０．８２ Co ０．１４ O ２ The battery was prepared by changing the composition to LMNC, mixing the components shown in Table 3 as a solvent in the mass ratio shown in Table 3, and dissolving LiFSI as an electrolyte salt in the solvent to the concentration shown in Table 3. The battery was then prepared by changing the charge and discharge conditions to charge and discharge conditions A as described above. Otherwise, a secondary battery was prepared in the same manner as the battery in Comparative Example 1-1, and measurements and tests were performed.

[0115] As shown in Table 3, Examples 2-1 to 2-29, in which the intrinsic molar ratio of the solvent to lithium ions was greater than 0 and 1.76 or less, showed improved cycle retention and storage retention compared to Comparative Examples 2-1 to 2-6, in which the intrinsic molar ratio of the solvent to lithium ions was 0 or greater than 1.76. Therefore, it can be seen that the charge-discharge characteristics can be improved by having an intrinsic molar ratio of the solvent to lithium ions that is greater than 0 and 1.76 or less.

[0116] As shown in Table 3, in Examples 2-3 to 2-29, where the intrinsic molar ratio of the solvent to lithium ions was 1.72 or less, the cycle retention rate and storage retention rate were improved compared to Examples 2-1 and 2-2, where the intrinsic molar ratio of the solvent to lithium ions was greater than 1.72. Therefore, it can be seen that the charge-discharge characteristics can be further improved by having an intrinsic molar ratio of the solvent to lithium ions of 1.72 or less.

[0117] As shown in Table 3, in Examples 2-2 and 2-3 to 2-29, where the solvent further includes at least one of the carbonate esters (DEC, EMC) and linear carboxylic acid esters (PrPr, PrEt, AcPr, AcEt, AcMe) excluding EC, FEC, and DMC included in Group 1, the charge-discharge characteristics were further improved compared to Examples 2-1 and 2-3, where the solvent consisted of EC and DMC included in Group 1. Therefore, it can be seen that the charge-discharge characteristics can be further improved by further including at least one of the carbonate esters and linear carboxylic acid esters excluding the compounds included in Group 1 in the solvent.

[0118] As shown in Table 3, in Examples 2-2 to 2-29, where the solvent further includes at least one of DEC, EMC, PrPr, PrEt, AcPr, AcEt, and AcMe, the charge-discharge characteristics were further improved compared to Example 2-1, where the solvent did not include DEC, EMC, 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 DEC, EMC, PrPr, PrEt, AcPr, AcEt, and AcMe.

[0119] As shown in Table 3, in Examples 2-2 to 2-29, where the solvent further includes at least one of EMC, PrPr, PrEt, AcPr, AcEt, and AcMe, the low-temperature load characteristics were further improved compared to Example 2-1, where the solvent did not include 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.

[0120] As shown in Table 3, in Examples 2-14 to 2-17, Examples 2-19 to 2-21, and Examples 2-23 and 2-24, where the lithium carbonate content in the positive electrode active material layer was less than 1.0% by mass, the cycle retention rate and storage retention rate were improved compared to Example 2-22, where the lithium carbonate content in the positive electrode active material layer was 1.0% by mass or more. Therefore, it can be seen that the charge-discharge characteristics can be improved by having a lithium carbonate content in the positive electrode active material layer less than 1.0% by mass.

[0121] As shown in Table 3, in Examples 2-14 to 2-17, Examples 2-19 to 2-21, and Examples 2-23 and 2-24, where the lithium hydroxide content in the positive electrode active material layer was less than 1.0% by mass, the cycle retention rate and storage retention rate were improved compared to Example 2-18, where the lithium hydroxide content in the positive electrode active material layer was 1.0% by mass or more. Therefore, it can be seen that the charge-discharge characteristics can be improved by having a lithium hydroxide content in the positive electrode active material layer less than 1.0% by mass.

[0122] Table 4 shows Examples 3-1 to 3-13.

[0123]

[0124] (Examples 3-1 to 3-13) As shown in Table 4, in Examples 3-1 to 3-13, secondary batteries were prepared in the same manner as the battery in Example 1-55, except that additives were added to the electrolyte at the concentrations shown in Table 4, and measurements and tests were performed.

[0125] As shown in Table 4, in Examples 3-1 to 3-13, where the electrolyte contained an additive which was at least one of the following: unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, sulfonic acid esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfate esters, nitrile compounds, and isocyanate compounds, the cycle retention rate and storage retention rate were improved compared to Example 1-55, which did not contain any additives. Therefore, it can be seen that the charge-discharge characteristics can be improved by including the above-mentioned additives in the electrolyte.

[0126] Table 5 shows Examples 4-1 to 4-4.

[0127]

[0128] (Examples 4-1 to 4-4) As shown in Table 5, in Examples 4-1 to 4-4, secondary batteries were prepared in the same manner as the battery in Example 1-55, except that additives were added to the electrolyte at the concentrations shown in Table 5 to prepare the secondary battery. Measurements and tests were then performed.

[0129] As shown in Table 5, in Examples 4-1 to 4-4, where the electrolyte contained an additive which was at least one of lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorophosphate, the cycle retention rate and storage retention rate were improved compared to Example 1-55, which did not contain the additive. Therefore, it can be seen that the charge-discharge characteristics can be improved by including the above-mentioned additive in the electrolyte.

[0130] 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.

[0131] 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 comprises a lithium-containing compound, lithium carbonate, and lithium hydroxide, the electrolyte comprises an electrolyte and a solvent, the electrolyte comprises a bis(fluorosulfonyl)imide salt, the solvent comprises at least one from a first group consisting of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, and gamma-butyrolactone, and the intrinsic molar ratio of the solvent to lithium ions, calculated from the vibrational spectral spectrum of the electrolyte, is greater than 0 and 1.76 or less.

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

3. The secondary battery according to claim 2, wherein the solvent further comprises at least one of diethyl carbonate, ethyl methyl carbonate, propyl propionate, ethyl propionate, methyl propionate, propyl acetate, ethyl acetate, and methyl acetate.

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

5. The secondary battery according to any one of claims 1 to 4, wherein the intrinsic molar ratio of the solvent to lithium ions, calculated from the vibrational spectral distribution of the electrolyte, is greater than 0 and 1.72 or less.

6. The secondary battery according to any one of claims 1 to 5, wherein the lithium carbonate content in the positive electrode active material layer is greater than 0.05% by mass and less than 1.0% by mass.

7. The secondary battery according to any one of claims 1 to 6, wherein the lithium hydroxide content in the positive electrode active material layer is greater than 0.05% by mass and less than 1.0% by mass.

8. 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), and the secondary battery according to any one of claims 1 to 7. 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.) 9. The secondary battery according to any one of claims 1 to 8, wherein the electrolyte contains light metal ions as cations.

10. The secondary battery according to claim 9, wherein the light metal ions include lithium ions.

11. The secondary battery according to claim 10, 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.

12. The secondary battery according to any one of claims 1 to 11, wherein the electrolyte further comprises at least one of an unsaturated cyclic carbonate ester, a fluorinated cyclic carbonate ester, a sulfonic acid ester, a dicarboxylic acid anhydride, a disulfonic acid anhydride, a sulfate ester, a nitrile compound, and an isocyanate compound.

13. The secondary battery according to any one of claims 1 to 12, wherein the electrolyte further comprises at least one of lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorophosphate.

14. A lithium-ion secondary battery according to any one of claims 1 to 13.

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