Secondary batteries

Abstract

To improve charge and discharge characteristics. [Solution] The secondary battery comprises a positive electrode, a negative electrode, and an electrolyte. 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. 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 analysis 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.

Description

[Technical Field]

[0001] This invention relates to a secondary battery. [Background technology]

[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. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2015-133315 [Overview of the project] [Problems that the invention aims to solve]

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

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

[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, lithium carbonate, and lithium hydroxide, 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, and 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. [Effects of the Invention]

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

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

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

[0010] (Secondary battery) A secondary battery according to this embodiment will 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 battery element configuration 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] (Exterior 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 recess 10U for housing the battery element 20. The recess 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 electrode 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 electrode 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 electrode lead 31 is not particularly limited and can be, for example, a thin plate shape or a mesh shape.

[0020] (Negative 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, the sealing film 41 is inserted between the outer film 10 and the positive lead 31. Similarly, as shown in Figure 1, the sealing film 42 is inserted between the outer film 10 and the negative lead 32. However, one or both of the 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 adheres 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 one 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, lithium carbonate (Li2CO3), and lithium hydroxide (LiOH). 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. 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, a crystal structure such as an olivine type. Specific examples of the lithium-containing composite oxide are LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2, LiMn2O4, etc. Specific examples of the lithium-containing phosphate compound are LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn 0.7 PO4, etc. 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) method, high frequency inductively coupled plasma (ICP) emission spectroscopy method, and energy dispersive X-ray spectroscopy (EDX) method.

[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 the 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 the 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.) Here, in the present disclosure, the rare earth elements refer to Sc, Y, and lanthanoids.

[0032] In this embodiment, the positive electrode active material layer 212 contains particles of the positive electrode active material. The particle size of the particles of the positive electrode active material is not particularly limited, but it is preferable that D 50 of the particles of the positive electrode active material is 6 μm or more and 23 μm or less from the viewpoint of ionic conductivity. D 50This is calculated, for example, by the procedure described below. First, the 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 This can be calculated 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 their unintentional formation 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 mass%, and more preferably 0.1 mass% or more. Furthermore, the lithium hydroxide content in the positive electrode active material layer 212 is preferably greater than 0.05 mass%, and more preferably 0.1 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 is set to a range where the amount of residual lithium 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 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 this positive electrode active material is placed in a sample bottle. Here, m = 10 (g). Next, 50 mL (= 50 cm³) of ultrapure water is added to the sample bottle along with a stirring bar. 3 After adding the ingredients, 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 collecting the sample, 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. Here, the endpoint of the first titration is considered to be reached when the red color of the liquid disappears, and the amount of hydrochloric acid added is V. a(mL)(=V a (cm 3 Read the value. Here, the concentration c is, for example, 0.02 mol / L (= 0.02 mol / dm³). 3 This can be done. Next, two drops of bromophenol blue solution are added to the supernatant, and the titration is further performed using the titration solution described above while stirring the supernatant with a stirrer. 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. Here, the titration apparatus can be an automatic titrator COM-1600 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 (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 Ketjen black. 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 a single element, an alloy, a compound, a mixture of two or more elements, or a material containing two or more phases. Specific examples of metallic materials used as negative electrode active materials include TiSi2 and SiO2. x (0 <x≦2)などである。

[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, fluororubber, 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, or 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. It is more preferable that the material of the separator 230 includes a porous polyolefin film. This improves the safety of the battery through 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 salt includes bis(fluorosulfonyl)imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI, LiN(SO2F2)2). This improves the charge-discharge characteristics. The electrolyte salt may also include other electrolyte salts used as electrolyte salts in lithium-ion batteries. These other electrolyte salts are, for example, light metal salts such as lithium salts. Specific examples of lithium salts are preferably lithium salts containing phosphorus (P), such as lithium hexafluoride phosphate (LiPF6), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2), or lithium salts containing boron (B), such as lithium tetrafluoroborate (LiBF4) and lithium bis(oxalato)borate (LiB(C2O4)2). This allows P and B to be incorporated into the surface of the positive electrode current collector 211. The other electrolyte salts are not limited to those listed above, and may include lithium trifluoromethanesulfonate (LiCF3SO3), bis(trifluoromethanesulfonyl)imide lithium (LiN(CF3SO2)2), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF3SO2)3), and others.

[0050] 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.

[0051] The solvent includes 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).

[0052] The solvent may further contain 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).

[0053] The solvent may further include 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 also 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 electrolyte may further contain at least one of the following as an additive: unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfate esters, nitrile compounds, and isocyanate compounds. Specific examples of unsaturated cyclic carbonate esters include vinylene carbonate (VC), methylene carbonate (MEC), and vinyl ethylene carbonate (VEC). Specific examples of fluorinated cyclic carbonate esters include monofluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC). Specific examples of sulfonic acid esters include propanesultone (PS) and propensultone (PRS). Specific examples of dicarboxylic acid anhydrides include succinic acid anhydride (SA) and 1,2-ethanedisulfonic acid anhydride. Specific examples of disulfonic acid anhydrides include cyclodisone (CD) and 2-sulfobenzoic acid anhydride. Specific examples of sulfate esters include ethylene sulfarate (DTD) and propanedisulfonic acid anhydride (PSAH). Specific examples of nitrile compounds include succinonitrile (SN). Specific examples of isocyanate compounds include hexamethylene diisocyanate (HMI).

[0056] Furthermore, the electrolyte may also contain at least one of the following as an additive: lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), and lithium difluorophosphate (LiPF2O2).

[0057] The surface condition of the positive electrode current collector 211 will be described in detail below. In the following description, X-ray photoelectron spectroscopy will be referred to as XPS (X-ray Photoelectron Spectroscopy). Furthermore, in the following description, wide scans and various narrow scans on the surface of the positive electrode current collector 211 refer to XPS performed on the surface of the positive electrode current collector 211, which was removed by disassembling the secondary battery 1, under the conditions shown in Table 1. For wide scans 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 to obtain an averaged spectrum.

[0058] [Table 1]

[0059] Figure 3 shows the S2p spectrum of XPS for the surface of the positive electrode current collector according to this embodiment. The surface of the positive electrode current collector 211 contains sulfur. Here, whether or not the surface of the positive electrode current collector 211 contains sulfur can be determined by a wide scan or S2p narrow scan of the surface of the positive electrode current collector 211. If a peak is detected in the S2p spectrum, as shown in Figure 3, then the surface of the positive electrode current collector 211 contains sulfur. In this disclosure, the S2p spectrum refers to the spectral range of 160 eV to 180 eV.

[0060] As shown in Figure 3, the photoelectron spectrum obtained by XPS 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. The presence or absence of the first signal S1 and the second signal S2 can be determined by separating the peaks of the S2p spectrum obtained by an S2p narrow scan of the surface of the positive electrode current collector 211 using a Gauss / Lorentz mixing function.

[0061] Signal intensity I of the first signal S1 S1 and the signal intensity of the second signal I S2 The sum of the signal intensities of the S2p spectra, I St Ratio to (I S1 +I S2 ) / I St It is 0.97 or less. This allows for good charging and discharging. Signal intensity I of the first signal S1 S1 and the signal intensity of the second signal I S2 This refers to the difference between the peak top and baseline of the first signal S1 and the second signal, respectively. It also refers to the sum of the signal intensities of the S2p spectrum. St This refers to the difference between the peak top and baseline of the synthesized signal St, which is obtained by synthesizing the individual signals S1 to S3 obtained by peak separation of the S2p spectrum.

[0062] Figure 4 shows the F1s spectrum of the XPS for the surface of the positive electrode current collector according to this embodiment. Preferably, the surface of the positive electrode current collector 211 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 F1s narrow scan of the surface of the positive electrode current collector 211. If a peak is detected in the F1s spectrum as shown in Figure 4, then the surface of the positive electrode current collector 211 contains fluorine. In this disclosure, the F1s spectrum refers to the range of 679 eV to 697 eV.

[0063] As shown in Figure 4, the photoelectron spectrum obtained by XPS 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 presence or absence of the third signal F1 and the fourth signal F2 can be determined by separating the peaks of the F1s spectrum obtained by an F1s narrow scan of the surface of the positive electrode current collector 211 using a Gauss / Lorentz mixture function.

[0064] Signal intensity I of the third signal F1 F1 and the signal intensity I of the fourth signal F2 F2 The sum of the signal intensities of the F1s spectra, I Ft Ratio to (I F1 +I F2 ) / I Ft The signal intensity of the third signal F1 is 0.80 or higher. F1 and the signal intensity I of the fourth signal F2 F2 This refers to the difference between the peak top and baseline of the third signal F1 and the fourth signal F2, respectively. It also refers to the sum of the signal intensities of the F1s spectrum. 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.

[0065] Figure 5 shows the Al2p spectrum of XPS for the surface of the positive electrode current collector according to this embodiment. The surface of the positive electrode current collector 211 more preferably 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 the surface of the positive electrode current collector 211 can be said to contain aluminum. In this disclosure, the Al2p spectrum refers to the range of 61 eV to 84 eV.

[0066] 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 separating the peaks of the Al2p spectrum obtained by an Al2p narrow scan of the surface of the positive electrode current collector 211 using a Gauss / Lorentz mixing function.

[0067] Signal intensity I of the 5th signal Al1 Al1 and the signal intensity I of the 6th signal Al2 Al2 The sum of the signal intensities of the Al2p spectra, I Alt Ratio to (I Al1 +I Al2 ) / I Alt The value 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 6th 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. Alt This refers to the difference between the peak top and baseline of the synthesized signal Alt, which is obtained by synthesizing each signal Al1 to Al5 obtained by peak separation of the Al2p spectrum.

[0068] The surface of the positive electrode current collector 211 more preferably further contains at least one of boron and phosphorus. Thereby, the charge-discharge characteristics can be further improved. Here, if a peak is detected in the B1s spectrum by a wide scan or B1s narrow scan on the surface of the positive electrode current collector 211, it can be said that the surface of the positive electrode current collector 211 contains boron. In the present disclosure, the B1s spectrum refers to the range of 183 eV or more and 203 eV or less. Further, if a peak is detected in the P2p spectrum by a wide scan or P2p narrow scan on the surface of the positive electrode current collector 211, it can be said that the surface of the positive electrode current collector 211 contains phosphorus. In the present disclosure, the P2p spectrum refers to the range of 127 eV or more and 147 eV or less.

[0069] As described above, the secondary battery 1 according to the first embodiment is a secondary battery including a positive electrode 210, a negative electrode 220, and an electrolytic solution. The positive electrode 210 includes 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, lithium carbonate, and lithium hydroxide. The electrolytic solution includes 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 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 signal intensity I S1 of the first signal S1 and the signal intensity I S2 of the second signal S2, the ratio (I St +I S1 +I S2 ) / I St of the sum to the total signal intensity of the S2p spectrum is 0.97 or less. Thereby, the charge-discharge characteristics can be improved.

[0070] Desirably, 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 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 signal intensity I F1 of the third signal F1 and the signal intensity I F2 of the fourth signal F2, with respect to the total signal intensity I Ft of the F1s spectrum, the ratio (I F1 +I F2 ) / I Ft is 0.80 or more. Thereby, the charge-discharge characteristics can be further improved.

[0071] Desirably, 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 having a peak at 75.4 eV or more and 75.8 eV or less, and a sixth signal Al2 having a peak at 76.4 eV or more and 76.8 eV or less. The signal intensity I Al1 of the fifth signal Al1 and the signal intensity I Al2 of the sixth signal Al2, with respect to the total signal intensity I Alt of the Al2p spectrum, the ratio (I Al1 +I Al2 ) / I Alt is 0.30 or more. Thereby, the charge-discharge characteristics can be further improved.

[0072] More desirably, the surface of the positive electrode current collector 211 contains at least one of boron and phosphorus. Thereby, the charge-discharge characteristics can be further improved.

[0073] More desirably, the content of lithium carbonate in the positive electrode active material layer 212 is greater than 0.05% by mass and less than 1.0% by mass. Thereby, while stabilizing the interface state between the positive electrode active material layer and the positive electrode current collector layer, it becomes difficult for the electrolytic solution to decompose on the surface of the lithium-containing compound particles, and in particular, the charge-discharge characteristics in a severe environment such as a high-temperature environment or a low-temperature environment can be improved.

[0074]

[0075] 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)

[0076] (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.)

[0077] 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 for an increase in the voltage of the secondary battery 1, thereby improving the charge-discharge characteristics.

[0077] In a desirable embodiment, the light metal ions include lithium ions. This allows for a further improvement in the voltage of the secondary battery 1, thereby improving its charge-discharge characteristics.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] (Manufacturing method for secondary batteries) Here, an example of a method for manufacturing the secondary battery 1 according to the first embodiment will be described. The method for manufacturing the secondary battery 1 according to the first embodiment includes the steps of manufacturing a positive electrode 210, manufacturing a negative electrode 220, preparing an electrolyte, assembling a laminate cell, and charging and discharging.

[0083] 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.

[0084] In the process of manufacturing the negative electrode 220, a negative electrode mixture slurry, in which the negative electrode mixture is dispersed, is applied to the negative electrode current collector 221, and then the negative electrode 220 is manufactured by drying and compression molding. 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 prepare 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 molding with 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.

[0085] In the process of preparing the electrolyte, the electrolyte is prepared by dissolving the electrolyte salt in a solvent.

[0086] 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.

[0087] In the charge-discharge process, the fabricated laminate cell undergoes one charge-discharge cycle. This 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 charging method: CCCV First charge rate: 0.2C First charge control voltage: 3.0V First cutoff time: 1 hour First standing period: 12 hours Second charging method: CCCV Second charging rate: 0.2C Second charge control voltage: 4.2V Second cutoff time: 8 hours Second standing period: 12 hours Discharge method: CC Discharge rate: 0.2C Discharge termination voltage: 2.5V

[0088] Charge / discharge condition B is the same as charge / discharge condition A, but with the second resting time changed to 5 minutes and the charging / discharging temperature changed to 25°C.

[0089] Charge / discharge condition C is a condition in which the second resting 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.

[0090] 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.

[0091] 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.

[0092] (Examples) Examples are described below. However, the present invention is not limited by these examples.

[0093] Table 2 shows Examples 1-1 to 1-39 and Comparative Examples 1-1 to 1-3.

[0094] [Table 2]

[0095] In the "Charge / Discharge Conditions" column of the tables shown in Table 2 and later, "A," "B," and "C" respectively refer to the charge / discharge process being performed on the laminate cell under the charge / discharge conditions A, B, and C described above. In the "Charge / Discharge Conditions" column of Table 2 and later, "D" and "E" refer to the charge / discharge process being performed on the laminate cell under the charge / discharge conditions D and E, respectively.

[0096] 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. In other words, unlike charge / discharge conditions A, B, and C, where charging is divided into two stages, charge / discharge condition D 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

[0097] Here, charge / discharge condition E 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 E involves charging in a single stage. Charging method: CCCV Charging rate: 0.1C Charging control voltage: 4.2V Cutoff current: 0.05C Standing time: 5 minutes Discharge method: CC Discharge rate: 0.1C Discharge termination voltage: 2.5V

[0098] (Example 1-1) The positive electrode according to 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 A positive electrode mixture was prepared by mixing O2, 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 cathode mixture was prepared by dispersing the particle-adjusted cathode mixture in N-methyl-2-pyrrolidone (NMP) to create a cathode mixture slurry. A strip of 12 μm thick aluminum foil was prepared as the cathode current collector, and the prepared cathode mixture slurry was uniformly applied to both sides of the aluminum foil. After drying the resulting coating with hot air, the cathode was compressed and molded using a roll press to produce the cathode. After washing the obtained cathode, the concentrations of lithium carbonate (Li2CO3) and lithium hydroxide (LiOH) were as shown in Table 2. A cathode lead was attached to the portion of the cathode current collector that was exposed.

[0099] The negative electrode according to 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.

[0100] The separator used in Example 1-1 was a microporous polyethylene film with a thickness of 15 μm.

[0101] The electrolyte solution for Example 1-1 was prepared using the solvent and electrolyte salt in the components and proportions shown in Table 2.

[0102] The laminate cell according to 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 was made of 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 it in a reduced-pressure environment to form a laminate cell.

[0103] In Example 1-1, the fabricated laminate cell was charged and discharged under charge / discharge condition A. This resulted in the production of the battery described in Example 1-1.

[0104] <<XPS Measurement>> In 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 air, 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 a monochromatized Al-Kα line (1486.6 eV) with a diameter of approximately 100 μm. 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, Al2p, P2p, and B1s 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 P2p spectra 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. Here, in the "Presence or Absence of P2p or B1s" column from Table 2 onward, "Y" indicates that a peak was detected in at least one of the P2p spectrum and the B1s spectrum during the wide scan, and "N" indicates that no peaks were detected in either the P2p spectrum or the B1s spectrum during the wide scan.

[0105] ≪Cycle Characteristics Test≫ In Example 1-1, a cycle performance test was conducted. In the cycle performance test, the secondary battery prepared above underwent 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 end current: 0.05C Discharge method: CC Discharge rate: 0.1C Discharge termination voltage: 2.5V

[0106] <<Storage Characteristics Test>> In Example 1-1, a storage characteristics test was conducted. 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 end current: 0.05C Discharge method: CC Discharge rate: 0.1C Discharge termination voltage: 2.5V

[0107] 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

[0108] ≪Low-Temperature Load Characteristics Test≫ In Example 1-1, a low-temperature load characteristic test was conducted. In the low-temperature load characteristic test, the secondary battery prepared above underwent the first charge-discharge cycle in a 23°C environment under the following conditions. Subsequently, the second to 100th charge-discharge cycles were performed in a -10°C environment 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 end current: 0.05C Discharge method: CC Discharge rate: 0.1C Discharge termination voltage: 2.5V

[0109] (Comparative Example 1-1) As shown in Table 2, in Comparative Example 1-1, a secondary battery was fabricated in the same manner as the battery in Example 1-1, 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.

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

[0111] (Examples 1-3) As shown in Table 2, in Examples 1-3, secondary batteries were fabricated in the same manner as the battery in Example 1-1, except that the conditions for charging and discharging the fabricated laminate cells were changed to charge / discharge condition C. Measurements and tests were then performed.

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

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

[0114] (Examples 1-4 to 1-39) In Examples 1-4 to 1-39, secondary batteries were prepared in the same manner as in Example 1-1, except that the electrolyte was prepared by changing at least one of the following: the particle size of the positive electrode active material particles, the lithium carbonate (Li2CO3) content of the positive electrode active material layer, the lithium hydroxide (LiOH) content of the positive electrode active material layer, the type and concentration of the electrolyte salt, the type of solvent component of the electrolyte, and the ratio of solvent components of the electrolyte. Measurements and tests were then performed.

[0115] As shown in Table 2, (I S1 +I S2 ) / I St In Examples 1-1 to 1-39, where the value was ≤0.97, charging and discharging were possible, whereas (I S1 +I S2 ) / I St In Comparative Examples 1-1 to 1-3, where the ratio was >0.97, charging and discharging was not possible. Therefore, (I S1 +I S2 ) / I St The fact that it is ≤0.97 indicates that charging and discharging are possible.

[0116] As shown in Table 2, (I F1 +I F2 ) / I Ft In Examples 1-3 to 1-39, where ≥0.80, (I F1 +I F2 ) / I Ft Compared to Examples 1-1 and 1-2, where the cycle retention rate was <0.80, the cycle retention rate was improved. Therefore, (IF1 +I F2 ) / I Ft It can be seen that a value of ≥0.80 can improve charge and discharge characteristics.

[0117] As shown in Table 2, (I Al1 +I Al2 ) / I Alt In Examples 1-1 and 1-4 to 1-39, where ≥0.30, (I Al1 +I Al2 ) / I Alt Compared to Examples 1-2 and 1-3, where the storage retention rate and low-temperature load retention rate were <0.30, the storage retention rate and low-temperature load retention rate were improved. Therefore, (I Al1 +I Al2 ) / I Alt It can be seen that a value of ≥0.30 can improve charge and discharge characteristics.

[0118] As shown in Table 2, in Examples 1-17 to 1-22, where at least one of the P2p spectrum and B1s spectrum was detected in XPS measurement, the storage retention rate was improved compared to Example 1-23, where the P2p spectrum was not detected. Therefore, it can be seen that the presence of at least one of phosphorus (P) and boron (B) on the surface of the positive electrode current collector can improve the charge-discharge characteristics.

[0119] As shown in Table 2, in Examples 1-17 to 1-22, where the electrolyte contained at least one of the following substances: lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorophosphate, the storage retention rate was improved compared to Example 1-23, which did not contain these substances. Therefore, it can be seen that the charge-discharge characteristics can be improved by including the above-mentioned substances in the electrolyte.

[0120] As shown in Table 2, in Examples 1-4 to 1-26, Examples 1-28 to 1-30, and Examples 1-32 to 1-39, 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 1-31, 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 2, in Examples 1-4 to 1-26, 1-28 to 1-30, and 1-32 to 1-39, 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 1-27, 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] As shown in Table 2, in Examples 1-4 to 1-14 and Examples 1-16 to 1-39, where the lithium carbonate content in the positive electrode active material layer was greater than 0.05% by mass, the low-temperature load retention rate was improved compared to Example 1-15, where the lithium carbonate content in the positive electrode active material layer was 0.05% by mass or less. 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 greater than 0.05% by mass.

[0123] As shown in Table 2, in Examples 1-4 to 1-14 and Examples 1-16 to 1-39, where the lithium hydroxide content in the positive electrode active material layer was greater than 0.05% by mass, the low-temperature load retention rate was improved compared to Example 1-15, where the lithium hydroxide content in the positive electrode active material layer was 0.05% by mass or less. 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 greater than 0.05% by mass.

[0124] Table 3 shows Examples 2-1 to 2-37 and Comparative Example 2-1.

[0125] [Table 3]

[0126] (Example 2-1) As shown in Table 3, in Example 2-1, the positive electrode active material is a second lithium composite oxide (LiMn 0.4 Ni 0.82 Co 0.14 Aside from changing the powder to O2 (LMNC) to produce a secondary battery, a secondary battery was prepared in the same manner as the battery described in Example 1-1, and measurements and tests were performed.

[0127] (Comparative Example 2-1) As shown in Table 3, in Comparative Example 2-1, a secondary battery was fabricated 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.

[0128] (Example 2-2) As shown in Table 3, in Example 2-2, a secondary battery was fabricated 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.

[0129] (Examples 2-3) As shown in Table 3, in Example 2-3, a secondary battery was fabricated 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.

[0130] (Examples 2-4 to 2-37) In Examples 2-4 to 2-37, secondary batteries were prepared in the same manner as in Example 2-1, except that the electrolyte was prepared by changing at least one of the following: the particle size of the positive electrode active material particles, the lithium carbonate (Li2CO3) content in the positive electrode active material layer, the lithium hydroxide (LiOH) content in the positive electrode active material layer, the type of solvent component in the electrolyte, and the ratio of the solvent component in the electrolyte. Measurements and tests were then performed.

[0131] As shown in Table 3, (I S1 +I S2 ) / I St In Examples 2-1 to 2-37, where the value was ≤0.97, charging and discharging were possible, whereas (I S1 +I S2 ) / I St In Comparative Example 2-1, where the ratio was >0.97, charging and discharging was not possible. Therefore, (I S1 +I S2 ) / I St The fact that it is ≤0.97 indicates that charging and discharging are possible.

[0132] As shown in Table 3, (I F1 +I F2 ) / I Ft In Examples 2-3 to 2-37, where ≥0.80, (I F1 +I F2 ) / I Ft The cycle retention rate was improved compared to Examples 2-1 and 2-2, which had a rate of <0.80. Therefore, (I F1 +I F2 ) / I Ft It can be seen that a value of ≥0.80 can improve charge and discharge characteristics.

[0133] As shown in Table 3, (I Al1 +I Al2 ) / I Alt In Examples 2-1 and 2-4 to 2-37, where ≥0.30, (I Al1 +I Al2 ) / I Alt Compared to Examples 2-2 and 2-3, where the storage retention rate and low-temperature load retention rate were <0.30, the storage retention rate and low-temperature load retention rate were improved. Therefore, (IAl1 +I Al2 ) / I Alt It can be seen that a value of ≥0.30 can improve charge and discharge characteristics.

[0134] As shown in Table 3, in Examples 2-15 to 2-20, where at least one of the P2p spectrum and B1s spectrum was detected in XPS measurement, the storage retention rate was improved compared to Example 2-21, where the P2p spectrum was not detected. Therefore, it can be seen that the presence of at least one of phosphorus (P) and boron (B) on the surface of the positive electrode current collector can improve the charge-discharge characteristics.

[0135] As shown in Table 3, in Examples 2-15 to 2-20, where the electrolyte contained at least one of lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorophosphate, the storage retention rate was improved compared to Example 2-21, which did not contain these substances. Therefore, it can be seen that the charge-discharge characteristics can be improved by including the above-mentioned substances in the electrolyte.

[0136] As shown in Table 3, in Examples 2-4 to 2-28, Examples 2-26 to 2-28, and Examples 2-30 to 2-37, 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 2-29, 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.

[0137] As shown in Table 3, in Examples 2-4 to 2-24, Examples 2-26 to 2-28, and Examples 2-30 to 2-37, 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 2-25, 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.

[0138] Table 4 shows Examples 3-1 to 3-13.

[0139] [Table 4]

[0140] (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 1-23, except that additives were added to the electrolyte at the concentrations shown in Table 4, and measurements and tests were performed.

[0141] 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 1-23, 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.

[0142] Table 5 shows Examples 4-1 to 4-3.

[0143] [Table 5]

[0144] (Examples 4-1 to 4-3) As shown in Table 5, in Examples 4-1 to 4-3, secondary batteries were prepared in the same manner as the battery in Example 1-23, except that additives were added to the electrolyte at the concentrations shown in Table 5. Measurements and tests were then performed.

[0145] As shown in Table 5, in Examples 4-1 to 4-3, where at least one of the P2p spectrum and B1s spectrum was detected in XPS measurement, the storage retention rate was improved compared to Example 1-23, where the P2p spectrum was not detected. Therefore, it can be seen that the presence of at least one of phosphorus (P) and boron (B) on the surface of the positive electrode current collector can improve the charge-discharge characteristics.

[0146] As shown in Table 5, in Examples 4-1 to 4-13, 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 storage retention rate was improved compared to Example 1-23, 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.

[0147] The embodiments described above are for the purpose of facilitating understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included. [Explanation of Symbols]

[0148] 1 Secondary battery 10 Exterior film 20 Battery element 31 Positive lead 32 Negative lead 41, 42 Sealing film 30 Exterior components 210 Positive electrode 211 Positive electrode current collector 212 Cathode 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, The positive electrode is, A positive electrode current collector containing aluminum, The positive electrode active material layer provided on the positive electrode current collector and Equipped with, The positive electrode active material layer comprises a lithium-containing compound, lithium carbonate, and lithium hydroxide. The aforementioned electrolyte solution comprises an electrolyte and a solvent. The electrolyte comprises a bis(fluorosulfonyl)imide salt, The surface of the positive electrode current collector contains sulfur, The photoelectron spectrum obtained by X-ray photoelectron spectroscopy analysis 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. A secondary battery in which 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.

2. The surface of the positive electrode current collector contains fluorine, The photoelectron spectrum obtained by X-ray photoelectron spectroscopy analysis 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. The secondary battery according to claim 1, wherein the ratio of the sum of the signal intensity of the third signal and the signal intensity of the fourth signal to the sum of the signal intensities of the F1s spectrum is 0.80 or more.

3. The surface of the positive electrode current collector contains aluminum, The photoelectron spectrum obtained by X-ray photoelectron spectroscopy analysis of the surface of the positive electrode current collector has a fifth signal with a peak between 75.4 eV and 75.8 eV, and a sixth signal with a peak between 76.4 eV and 76.8 eV. The secondary battery according to claim 1 or 2, wherein the ratio of the sum of the signal intensity of the fifth signal and the signal intensity of 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 surface of the positive electrode current collector contains at least one of boron and phosphorus.

5. The secondary battery according to any one of claims 1 to 4, 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.

6. The secondary battery according to any one of claims 1 to 5, 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.

7. The lithium-containing compound comprises at least one of a first lithium composite oxide represented by formula (1) and a second lithium composite oxide represented by formula (2). A secondary battery according to any one of claims 1 to 6. From ｘ Yes １－ｙ M1 ｙ Oh 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.)

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

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

10. The secondary battery according to claim 9, 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.

11. The secondary battery according to any one of claims 1 to 10, 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.

12. The secondary battery according to any one of claims 1 to 11, wherein the electrolyte further comprises at least one of lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, and lithium difluorophosphate.

13. A lithium-ion secondary battery according to any one of claims 1 to 12.

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