Secondary battery

Abstract

A secondary battery includes: a positive electrode including a lithium nickel complex oxide; a negative electrode; and an electrolyte. In surface analysis of the positive electrode using an X-ray photoelectron spectroscopy, a first O1s spectrum having a peak in a range of 528 eV or more and 531 eV or less, a second O1s spectrum having a peak in a range of more than 531 eV and 535 eV or less, a B1s spectrum, a S2p spectrum, a F1s spectrum, and a Ni3p spectrum are detected. A ratio of an intensity of the first O1s spectrum to an intensity of the second O1s spectrum is 0.5 or more and 0.8 or less, a ratio of an intensity of the B1s spectrum to an intensity of the Ni3p spectrum is 0.9 or more and 1.8 or less, a ratio of an intensity of the S2p spectrum to an intensity of the Ni3p spectrum is 0.4 or more and 1.2 or less, and a ratio of an intensity of the F1s spectrum to an intensity of the Ni3p spectrum is 8 or more and 13 or less.

Description

Technical Field

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

[0002] With the widespread use of mobile phones and other electronic devices, secondary batteries are being developed as small, lightweight power sources capable of achieving high energy density. These secondary batteries contain a positive electrode, a negative electrode, and an electrolyte, and various studies have been conducted on their structure.

[0003] Specifically, various additives are added to the electrolyte to improve various performance characteristics (see, for example, Patent Documents 1-7). These additives include boric acid compounds (tetraboric acid, etc.), compounds containing S=O groups (sulfonates, etc.), and lithium salts (LiPF6, etc.). In this case, lithium nickelate and lithium-nickel composite oxides are used as the positive electrode active material.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 5645144 Specification

[0007] Patent Document 2: US Patent No. 7,235,334

[0008] Patent Document 3: Japanese Patent Application Publication No. 2017-157327

[0009] Patent Document 4: Japanese Patent Application Publication No. 2008-098053

[0010] Patent Document 5: Japanese Patent Application Publication No. 2010-225522

[0011] Patent Document 6: Japanese Patent Application Publication No. 2015-090857

[0012] Patent Document 7: International Publication No. 2016-167316

[0013] Various studies have been conducted on improving the performance of secondary batteries, but the expansion characteristics are still insufficient, so there is room for further improvement.

[0014] This technology was proposed in view of the above-mentioned problems, and its purpose is to provide a secondary battery that can achieve excellent expansion characteristics. Summary of the Invention

[0015] One embodiment of the secondary battery of this technology includes: a positive electrode comprising a lithium-nickel composite oxide; a negative electrode; and an electrolyte. Surface analysis of the positive electrode using X-ray photoelectron spectroscopy revealed: a first O1s spectrum with a peak value in the range of bond energy ≥ 528 eV and ≤ 531 eV; a second O1s spectrum with a peak value in the range of bond energy > 531 eV and ≤ 535 eV; a B1s spectrum; an S2p spectrum; an F1s spectrum; and a Ni3p spectrum. The ratio of the intensity of the first O1s spectrum to the intensity of the second O1s spectrum is ≥ 0.5 and ≤ 0.8, the ratio of the intensity of the B1s spectrum to the intensity of the Ni3p spectrum is ≥ 0.9 and ≤ 1.8, the ratio of the intensity of the S2p spectrum to the intensity of the Ni3p spectrum is ≥ 0.4 and ≤ 1.2, and the ratio of the intensity of the F1s spectrum to the intensity of the Ni3p spectrum is ≥ 8 and ≤ 13.

[0016] The aforementioned "lithium-nickel composite oxides" is a general term for oxides containing both lithium and nickel as constituent elements. It should be noted that detailed information about lithium-nickel composite oxides will be described later.

[0017] According to one embodiment of the present technology, the positive electrode of the secondary battery comprises a lithium-nickel composite oxide. Furthermore, in the surface analysis of the positive electrode using X-ray photoelectron spectroscopy, the aforementioned series of XPS spectra were detected, and a series of ratios defined based on the intensity of these XPS spectra satisfy the aforementioned conditions. Therefore, excellent expansion characteristics can be obtained.

[0018] It should be noted that the effects of this technology are not necessarily limited to those described herein, but can be any of the series of effects related to this technology described later. Attached Figure Description

[0019] Figure 1 This is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0020] Figure 2 It means Figure 1 The diagram shows a cross-sectional view of the structure of the battery element.

[0021] Figure 3 This is a block diagram illustrating the structure of a secondary battery application example. Detailed Implementation

[0022] Hereinafter, one embodiment of the present technology will be described in detail with reference to the accompanying drawings. It should be noted that the description is presented in the following order.

[0023] 1. Secondary battery

[0024] 1-1. Structure

[0025] 1-2. Physical properties

[0026] 1-3. Actions

[0027] 1-4. Manufacturing Method

[0028] 1-5. Functions and Effects

[0029] 2. Variations

[0030] 3. Uses of secondary batteries

[0031] <1. Secondary Battery>

[0032] First, a secondary battery according to one embodiment of this technology will be described.

[0033] The secondary battery described herein is a secondary battery in which battery capacity is obtained by the intercalation and deintercalation of electrode reactants. It includes a positive electrode, a negative electrode, and an electrolyte in liquid form. In this secondary battery, to prevent the electrode reactants from depositing on the surface of the negative electrode during charging, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of ​​the negative electrode is set to be greater than the electrochemical capacity per unit area of ​​the positive electrode.

[0034] There are no particular restrictions on the types of substances used in the electrode reactions. Specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

[0035] The following example uses lithium as the electrode reactant. A secondary battery that utilizes the insertion and extraction of lithium to obtain battery capacity is called a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is inserted and extracted in an ionic state.

[0036] <1-1. Structure>

[0037] Figure 1 The three-dimensional structure of a secondary battery is shown. Figure 2 It shows Figure 1 The cross-sectional structure of the battery element 10 is shown. Additionally, Figure 1 The battery element 10 and the outer membrane 20 are shown in a state where they are separated from each other. Figure 2 Only a portion of battery element 10 is shown.

[0038] like Figure 1 As shown, the secondary battery includes a battery element 10, an outer film 20, a positive electrode lead 31, and a negative electrode lead 32. The secondary battery described here is a laminated film type secondary battery that uses a flexible (or soft) outer component (outer film 20) as the outer component for housing the battery element 10.

[0039] [Exterior film]

[0040] like Figure 1 As shown, the outer casing 20 is a thin film component that can be folded in the direction of arrow R (dotted line). As described above, since the outer casing 20 houses the battery element 10, it also houses the positive electrode 11, the negative electrode 12, and the electrolyte, which will be described later. It should be noted that the outer casing 20 has a recessed portion 20U (so-called deep drawing portion) for accommodating the battery element 10.

[0041] Specifically, the outer casing 20 is a laminated film consisting of three layers: a welding layer, a metal layer, and a surface protective layer, layered sequentially from the inside. When the outer casing 20 is folded, the outer peripheries of the opposing welding layers are bonded together (fused). Thus, the outer casing 20 is a pouch-like structure capable of sealing the battery element 10 inside. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metallic material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

[0042] In addition, there is no particular limitation on the structure (number of layers) of the outer film 20; it can be 1 layer, 2 layers, or more than 4 layers.

[0043] A sealing membrane 21 is inserted between the outer membrane 20 and the positive electrode lead 31, and a sealing membrane 22 is inserted between the outer membrane 20 and the negative electrode lead 32. Sealing membranes 21 and 22 are components used to prevent accidental intrusion of external air or other contaminants into the interior of the outer membrane 20, and each contains one or more polymeric compounds such as polyolefins, which have a sealing property relative to each of the positive electrode lead 31 and the negative electrode lead 32. The polyolefin is polyethylene, polypropylene, modified polyethylene, or modified polypropylene, etc. Alternatively, one or both of the sealing membranes 21 and 22 may be omitted.

[0044] [Battery Components]

[0045] like Figure 1 as well as Figure 2 As shown, the battery element 10 is housed inside the outer membrane 20 and includes a positive electrode 11, a negative electrode 12, a separator 13, and an electrolyte (not shown). The electrolyte is immersed in the positive electrode 11, the negative electrode 12, and the separator 13, respectively.

[0046] The battery element 10 consists of a positive electrode 11 and a negative electrode 12 stacked on top of each other with a separator 13 in between, and the positive electrode 11, negative electrode 12, and separator 13 are wound around a winding axis (wound electrode body). Therefore, the positive electrode 11 and negative electrode 12 are positioned opposite each other with the separator 13 in between. It should be noted that the aforementioned winding axis is an imaginary axis extending along the Y-axis direction.

[0047] Here, the three-dimensional shape of the battery element 10 is a flat shape. That is, the shape of the cross-section (the cross-section along the XZ plane) of the battery element 10 intersecting the winding axis is a flat shape defined by the major axis and the minor axis, more specifically, a flat, approximately elliptical shape. The major axis is an imaginary axis that extends in the X-axis direction and has a relatively large length, and the minor axis is an imaginary axis that extends in the Z-axis direction that intersects the X-axis direction and has a relatively small length.

[0048] (positive electrode)

[0049] like Figure 2 As shown, the positive electrode 11 includes a positive current collector 11A with opposite sides, two positive active material layers 11B disposed on both sides of the positive current collector 11A, and two coatings 11C, the coatings 11C covering the surface of the positive active material layers 11B. Alternatively, the positive active material layers 11B may be disposed only on one side of the positive current collector 11A on the side opposite the negative electrode 12.

[0050] The positive current collector 11A comprises one or more conductive materials, such as metals, aluminum, nickel, and stainless steel. The positive active material layer 11B comprises one or more positive active materials capable of lithium insertion and extraction, and may also include a positive binder and a positive conductive agent.

[0051] The positive electrode active material contains lithium-containing compounds, and more specifically, any one or more of lithium-nickel composite oxides. As mentioned above, "lithium-nickel composite oxide" is a general term for oxides containing lithium and nickel as constituent elements, and has a layered rock salt-type crystal structure. The positive electrode active material includes lithium-nickel composite oxides because it allows for the achievement of high energy density.

[0052] The type (structure) of lithium-nickel composite oxides is not particularly limited as long as they contain oxides with lithium and nickel as constituent elements. Preferably, the lithium-nickel composite oxide contains a compound represented by the following formula (1). This is because a sufficiently high energy density can be obtained.

[0053] Li w Ni (1-x-y-z) Co x M1 y M2 z O2…(1)

[0054] (M1 is at least one of Al and Mn. M2 is at least one element belonging to Groups 2 to 15 of the long-period periodic table (excluding Ni, Co, Al, and Mn). w, x, y, and z satisfy 0.8 ≤ w ≤ 1.2, 0 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.1, and 0 ≤ z ≤ 0.1. Furthermore, the composition of lithium varies depending on the charge / discharge state; w is the value for the fully discharged state.)

[0055] The compound (lithium-nickel composite oxide) shown in formula (1) is an oxide containing lithium and nickel, and, if necessary, also containing cobalt and other elements (M1 and M2) as constituent elements.

[0056] In detail, from the range of possible values ​​of w (0.8≤w≤1.2), it can be seen that lithium-nickel composite oxide contains lithium as a constituent element.

[0057] From the range of possible values ​​for x (0≤x≤0.3), it can be seen that lithium-nickel composite oxides may or may not contain cobalt as a constituent element.

[0058] From the range of possible values ​​of y (0≤y≤0.1), it can be seen that lithium nickel composite oxide can contain other elements (M1) as constituent elements, or it can not contain other elements (M1) as constituent elements.

[0059] Especially when the lithium nickel composite oxide contains other elements (M1) as constituent elements, the lithium nickel composite oxide may contain only aluminum as a constituent element, or only manganese as a constituent element, or both aluminum and manganese as constituent elements.

[0060] From the range of possible values ​​of z (0≤z≤0.1), it can be seen that lithium-nickel composite oxides can contain other elements (M2) as constituent elements, or they can not contain other elements (M2) as constituent elements.

[0061] In particular, when lithium-nickel composite oxides contain other elements (M2) as constituent elements, the other elements (M2) can be only one type or two or more types.

[0062] From the range of possible values ​​for x, y, and z, we know that (1-xyz)≥0.5, therefore, the lithium-nickel composite oxide contains nickel as a constituent element.

[0063] Specific examples of lithium-nickel composite oxides are LiNiO2 and LiNi. 0.70 Co 0.30 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.50 Co0.20 Mn 0.30 O2 and LiNi 0.80 Co 0.10 Al 0.05 Mn 0.05 O2, etc.

[0064] It should be noted that the positive electrode active material only needs to contain the above-mentioned lithium-nickel composite oxide, and may also contain any one or more other lithium-containing compounds.

[0065] Other lithium-containing compounds are not specifically limited in type; specifically, they include lithium transition metal compounds. "Lithium transition metal compounds" is a general term for compounds containing lithium and one or more transition metal elements as constituent elements, and may also contain one or more other elements. The other elements are any elements other than transition metal elements; there are no special limitations. Specifically, they are elements belonging to groups 2 to 15 of the long-period periodic table. Furthermore, the lithium transition metal compounds described here do not include the aforementioned lithium-nickel composite oxides.

[0066] The types of lithium transition metal compounds are not particularly limited, but specifically include oxides, phosphoric acid compounds, silicate compounds, and borate compounds. Specific examples of oxides are LiCoO2 and 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 and LiMn2O4, etc. Specific examples of phosphoric acid compounds are LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0067] The positive electrode binder includes any one or more of synthetic rubbers and polymeric compounds. Synthetic rubbers include styrene-butadiene rubber, fluorinated rubbers, and ethylene propylene diene monomer (EPDM) rubber. Polymeric compounds include polyvinylidene fluoride (PVDF), polyimide, and carboxymethyl cellulose.

[0068] The positive electrode conductive agent includes any one or more conductive materials such as carbon materials, including graphite, carbon black, acetylene black, and Ketjen black. Alternatively, the conductive material can also be a metal or a polymer compound.

[0069] There is no particular limitation on the method for forming the positive electrode active material layer 11B. Specifically, it can be any one or more of the following methods: coating method, etc.

[0070] The coating 11C is a film formed on the surface of the positive electrode active material layer 11B by the charging and discharging of the secondary battery. More specifically, it is a deposition film deposited on the surface of the positive electrode active material layer 11B due to the decomposition reaction of the electrolyte during charging and discharging.

[0071] The coating 11C is mainly formed on the surface of the positive electrode active material layer 11B during the stabilization treatment of the secondary battery, i.e., the initial charge and discharge after the secondary battery is packaged. In addition, the coating 11C can also be additionally formed on the surface of the positive electrode active material layer 11B during the charge and discharge after the stabilization treatment of the secondary battery, i.e., the charge and discharge after the secondary battery is completed.

[0072] It should be noted that the coating 11C can cover the entire surface of the positive electrode active material layer 11B, or it can only cover a portion of the surface of the positive electrode active material layer 11B. Of course, in the latter case, multiple coatings 11C can cover the surface of the positive electrode active material layer 11B at multiple locations that are separated from each other.

[0073] Here, a coating 11C is provided to cover the surface of each of the two positive electrode active material layers 11B, so the positive electrode 11 includes two coatings 11C. Alternatively, the coating 11C may be configured to cover only the surface of one of the two positive electrode active material layers 11B, so the positive electrode 11 includes one coating 11C.

[0074] In particular, in the coated 11C, as described later, the specified XPS spectra (B1s spectrum, S2p spectrum, and F1s spectrum) can be obtained in the surface analysis of the cathode 11 (coated 11C) using X-ray photoelectron spectroscopy (XPS). Therefore, the coated 11C contains boron, sulfur, and fluorine as constituent elements.

[0075] More specifically, as described later, when the electrolyte contains boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds, a coating 11C is formed due to the decomposition reaction of the electrolyte. Therefore, as described above, the coating 11C contains boron, sulfur, and fluorine as constituent elements.

[0076] In this coating 11C, in order to suppress the gas generated by the decomposition reaction of the electrolyte on the surface of the positive electrode 11 by suppressing the decomposition reaction of the electrolyte, the physical properties specified by the analysis results of the positive electrode 11 (coating 11C) using XPS were optimized. Details of the physical properties of the positive electrode 11 (coating 11C) described herein will be described later.

[0077] (negative electrode)

[0078] like Figure 2 As shown, the negative electrode 12 includes a negative electrode current collector 12A having one opposite side and two negative electrode active material layers 12B disposed on both sides of the negative electrode current collector 12A. Alternatively, the negative electrode active material layer 12B may be disposed only on one side of the negative electrode current collector 12A on the side of the negative electrode 12 opposite to the positive electrode 11.

[0079] The negative electrode current collector 12A comprises any one or more conductive materials, such as copper, aluminum, nickel, and stainless steel. The negative electrode active material layer 12B comprises any one or more negative electrode active materials capable of lithium insertion / extraction, and may also include a negative electrode binder and a negative electrode conductive agent. Details regarding the negative electrode binder are the same as those regarding the positive electrode binder, and details regarding the negative electrode conductive agent are the same as those regarding the positive electrode conductive agent.

[0080] The type of negative electrode active material is not particularly limited, but specifically includes carbon materials and metallic materials. Carbon materials include easily graphitized carbon, difficult-to-graphitize carbon, and graphite, which can be natural or artificial graphite. Metallic materials are materials containing one or more metallic elements and half-metallic elements capable of forming alloys with lithium. The types of metallic and half-metallic elements are not particularly limited, but specifically include silicon and tin. Furthermore, metallic materials can be monomers, alloys, compounds, mixtures of two or more of these, or materials containing two or more of these phases.

[0081] Specific examples of metallic materials include SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, and SiO. v (0<v≤2), LiSiO, SnO w (0<w≤2), SnSiO3, LiSnO, and Mg2Sn, etc. Additionally, SiO v The value of v can also satisfy 0.2 < v < 1.4.

[0082] There is no particular limitation on the method of forming the negative electrode active material layer 12B. Specifically, it can be any one or more of the following methods: coating, gas phase, liquid phase, spraying, and firing (sintering).

[0083] (Diaphragm)

[0084] like Figure 2 As shown, the separator 13 is an insulating porous membrane located between the positive electrode 11 and the negative electrode 12, preventing contact between the positive electrode 11 and the negative electrode 12 while allowing lithium ions to pass through. The separator 13 contains any one or more of the following polymer compounds: polytetrafluoroethylene, polypropylene, and polyethylene.

[0085] (electrolyte)

[0086] The electrolyte contains a solvent and an electrolyte salt.

[0087] The solvent includes any one or more non-aqueous solvents (organic solvents), and the electrolyte containing such non-aqueous solvents is called a non-aqueous electrolyte. These non-aqueous solvents are esters and ethers, and more specifically, carbonate compounds, carboxylic acid ester compounds, and lactone compounds. This is because it can improve the dissociation of the electrolyte salt and result in high ion mobility.

[0088] Specifically, carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates are ethylene carbonate and propylene carbonate, while specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0089] Carboxylic acid ester compounds are carboxylic acid esters, etc. Specific examples of carboxylic acid esters include ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate, etc.

[0090] Lactone compounds are lactones, etc. Specific examples of lactones are γ-butyrolactone and γ-pentanolactone, etc. It should be noted that ethers, in addition to the lactone compounds mentioned above, can also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane, etc.

[0091] In addition, non-aqueous solvents can also be unsaturated cyclic carbonates, halocarbonates, sulfonates, phosphates, acid anhydrides, nitrile compounds, and isocyanate compounds, etc. This is because they can improve the chemical stability of the electrolyte.

[0092] Specifically, unsaturated cyclic carbonates include vinylene carbonate (1,3-dioxacyclopenten-2-one), vinylene carbonate (4-vinyl-1,3-dioxacyclopenten-2-one), and methyleneene carbonate (4-methylene-1,3-dioxacyclopenten-2-one). Halogenated carbonates include fluoroethylene carbonate (4-fluoro-1,3-dioxacyclopenten-2-one) and difluoroethylene carbonate (4,5-difluoro-1,3-dioxacyclopenten-2-one). Sulfonates include 1,3-propanesulfonolactone and 1,3-propenesulfonolactone. Phosphate esters include trimethyl phosphate and triethyl phosphate.

[0093] Acid anhydrides include cyclic dicarboxylic acid anhydrides, cyclic disulfonic acid anhydrides, and cyclic carboxylic acid sulfonic anhydrides. Cyclic dicarboxylic acid anhydrides include succinic anhydride, glutaric anhydride, and maleic anhydride. Cyclic disulfonic acid anhydrides include 1,2-ethanedisulfonic anhydride and 1,3-propanedisulfonic anhydride. Cyclic carboxylic acid sulfonic anhydrides include sulfobenzoic anhydride, sulfopropionic anhydride, and sulfobutyric anhydride.

[0094] Nitrile compounds include acetonitrile, succinic anionyl nitrile, and adiponitrile, among others. Isocyanate compounds include hexamethylene diisocyanate, among others.

[0095] The electrolyte salt is any one or more of light metal salts such as lithium salts. The lithium salt includes lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium tri(trifluoromethanesulfonyl)methylide (LiC(CF3SO2)3), lithium difluorooxalateborate (LiBF2(C2O4)), and lithium bis(oxalate)borate (LiB(C2O4)2), etc.

[0096] There is no particular limitation on the content of the electrolyte salt, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent. This is because high ionic conductivity can be obtained.

[0097] It should be noted that, in order to obtain the above physical properties using the surface analysis results of XPS's positive electrode 11 (coated 11C), the electrolyte may contain boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds. Details regarding the boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds described herein will be presented later.

[0098] [Positive and negative leads]

[0099] The positive lead 31 is the positive terminal connected to the positive electrode 11 (positive current collector 11A) and contains one or more conductive materials such as aluminum. The negative lead 32 is the negative terminal connected to the negative electrode 12 (negative current collector 12A) and contains one or more conductive materials such as copper, nickel, and stainless steel. The shapes of the positive lead 31 and the negative lead 32 are not particularly limited; specifically, they can be one or more of the following: a thin plate shape and a mesh shape.

[0100] Here, as Figure 1 As shown, the positive electrode lead 31 and the negative electrode lead 32 are led out from the inside of the outer membrane 20 in the same direction. Alternatively, the positive electrode lead 31 and the negative electrode lead 32 can be led out in different directions.

[0101] Furthermore, the number of positive leads 31 is 1. However, the number of positive leads 31 is not particularly limited, and can be 2 or more. In particular, when the number of positive leads 31 is 2 or more, the resistance of the secondary battery decreases. The explanation regarding the number of positive leads 31 also applies to the number of negative leads 32; therefore, the number of negative leads 32 is not limited to 1, and can also be 2 or more.

[0102] <1-2. Physical Properties>

[0103] In this secondary battery, as described above, the physical properties specified by the surface analysis results of the positive electrode 11 (coating 11C) using XPS were optimized.

[0104] Specifically, the following six XPS spectra were detected in the surface analysis of the positive electrode 11 (coated 11C) using XPS.

[0105] The first XPS spectrum is an O1s spectrum caused by oxygen; more specifically, it is a first O1s spectrum with a peak value in the range of bond energy above 528 eV and below 531 eV. It can be assumed that this first O1s spectrum is primarily detected due to the composition of the positive electrode active material layer 11B (a lithium-nickel composite oxide serving as the positive electrode active material), the bonding state of oxygen atoms in the crystal structure of this positive electrode active material, and the composition of the coating 11C.

[0106] The second XPS spectrum is an additional O1s spectrum caused by oxygen; more specifically, it is a second O1s spectrum with a peak value in the range of bond energy greater than 531 eV and below 535 eV. This second O1s spectrum can be considered the same as the first O1s spectrum described above, and is primarily detected due to the composition of the positive electrode active material layer 11B (positive electrode active material), the bonding state of oxygen atoms in the crystal structure of the positive electrode active material, and the composition of the coating 11C.

[0107] The third XPS spectrum is a B1s spectrum caused by boron. It can be assumed that this B1s spectrum is mainly detected due to the composition of the 11C coating.

[0108] The fourth XPS spectrum is the S2p spectrum caused by sulfur. It can be assumed that this S1s spectrum is mainly detected due to the composition of the coated 11C.

[0109] The fifth XPS spectrum is an F1s spectrum caused by fluorine. It can be assumed that this F1s spectrum is mainly detected due to the composition of the 11C coating, and that the composition of the 11C coating is LiF, etc.

[0110] The sixth XPS spectrum is the Ni3p spectrum caused by nickel. It can be assumed that this Ni3p spectrum is mainly detected due to the composition of the positive electrode active material layer 11B (positive electrode active material) and the bonding state of nickel atoms in the crystal structure of the positive electrode active material.

[0111] In this case, the four ratios (intensity ratios) based on the intensity of the above six XPS spectra satisfy the following conditions.

[0112] First, the intensity ratio IO (=IO1 / IO2), which is the ratio of the intensity IO1 of the first O1s spectrum to the intensity IO2 of the second O1s spectrum, is 0.5 to 0.8.

[0113] Second, the intensity ratio IBN (=IB / IN), which is the ratio of the intensity IB of the B1s spectrum to the intensity IN of the Ni3p spectrum, is 0.9~1.8.

[0114] Third, the intensity ratio ISN (=IS / IN), which is the ratio of the intensity IS of the S2p spectrum to the intensity IN of the Ni3p spectrum, is 0.4~1.2.

[0115] Fourth, the intensity ratio IFN (=IF / IN), which is the ratio of the intensity IF of the F1s spectrum to the intensity IN of the Ni3p spectrum, is 8~13.

[0116] The reason why the strength ratios IO, IBN, ISN, and IFN meet the above conditions is that in the positive electrode 11 containing the positive electrode active material (lithium-nickel composite oxide), the bonding state (oxidation state) of the constituent atoms such as oxygen atoms and nickel atoms in the crystal structure of the positive electrode active material is optimized, thus stabilizing the crystal structure of the positive electrode active material. Furthermore, the surface state of the positive electrode 11 is electrochemically stabilized by the coating 11C. As a result, during charging and discharging, the decomposition reaction of the electrolyte on the surface of the positive electrode 11 can be suppressed, thereby suppressing the gas generated by the decomposition reaction of the electrolyte. Therefore, even though the positive electrode 11 contains lithium-nickel composite oxide, the expansion of the secondary battery can be suppressed during charging and discharging.

[0117] In order to detect the aforementioned B1s, S2p, and F1s spectra in the surface analysis of the positive electrode 11 using XPS, the electrolyte may contain boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds.

[0118] Boron-containing compounds are a general term for compounds that contain boron as a constituent element. There are no specific limitations on the types of boron-containing compounds; specifically, they include any one or more boron-containing lithium salts, etc.

[0119] Specific examples of boron-containing lithium salts include lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(oxalate)borate, which have been described as candidates for electrolyte salts.

[0120] Sulfur-containing compounds are a general term for compounds that contain sulfur as a constituent element. There is no particular limitation on the types of sulfur-containing compounds; specifically, they are any one or more of cyclic disulfonic anhydrides and sulfonic acid alkynyl esters. That is, a sulfur-containing compound can be only a cyclic disulfonic anhydride, only a sulfonic acid alkynyl ester, or both.

[0121] Cyclic disulfonic anhydrides are cyclic compounds obtained by dehydrating disulfonic anhydrides. Specific examples of cyclic disulfonic anhydrides include 1,2-ethanedisulfonic anhydride and 1,3-propanedisulfonic anhydride, which have been described as candidates for non-aqueous solvents. Additionally, cyclic disulfonic anhydrides can also be 1,2-benzenedisulfonic anhydride, etc.

[0122] Sulfonate alkynyl esters are sulfonic acids containing a carbon-carbon triple bond. Specific examples of sulfonate alkynyl esters include propargyl benzenesulfonate and propargyl methanesulfonate.

[0123] Fluorine-containing compounds are a general term for compounds that contain fluorine as a constituent element. There are no specific limitations on the types of fluorine-containing compounds; specifically, they include any one or more of the following: lithium fluoride salts, etc.

[0124] Specific examples of fluorinated lithium salts include lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tri(trifluoromethanesulfonyl)methylide, which have been described as candidates for electrolyte salts. Additionally, lithium hexafluoroarsenate (LiAsF6) can also be a fluorinated lithium salt.

[0125] Furthermore, compounds containing both boron and fluorine as constituent elements are not fluorine-containing compounds, but rather boron-containing compounds. Therefore, as mentioned above, lithium salts containing both boron and fluorine as constituent elements (lithium tetrafluoroborate) are not fluorine-containing compounds (fluorine-containing lithium salts), but rather boron-containing compounds (boron-containing lithium salts).

[0126] There are no specific limitations on the content of boron-containing compounds in the electrolyte; it can be set arbitrarily. The same applies to the content of sulfur-containing compounds and fluorine-containing compounds in the electrolyte.

[0127] It should be noted, and for clarity, that if six XPS spectra are detected in the surface analysis of the positive electrode 11 using XPS, and the intensity ratios of four of them meet the above conditions, the electrolyte may not necessarily contain boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds. In this case, the electrolyte may not contain all boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds, but only any one or two of these compounds.

[0128] Specifically, even if the electrolyte initially contains all boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds, if all boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds are consumed during the charge and discharge process to form the coating 11C during the stabilization treatment of the secondary battery, the electrolyte in the completed secondary battery may not contain boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds.

[0129] Furthermore, even if the electrolyte initially contains all boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds, if any one or two of the boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds are consumed during the charge and discharge process to form the coating 11C during the stabilization treatment of the secondary battery, the electrolyte in the completed secondary battery may contain only the remaining one or two of the boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds.

[0130] <1-3. Actions>

[0131] During the charging of the secondary battery, lithium is deintercalated from the positive electrode 11 and intercalated into the negative electrode 12 via the electrolyte. Conversely, during the discharging of the secondary battery, lithium is deintercalated from the negative electrode 12 and intercalated into the positive electrode 11 via the electrolyte. During these charging and discharging processes, lithium is intercalated and deintercalated in an ionic state.

[0132] <1-4. Manufacturing Method>

[0133] In the case of manufacturing a secondary battery, a positive electrode 11 and a negative electrode 12 are made by following the steps described below, and an electrolyte is prepared. Then, the positive electrode 11, the negative electrode 12, and the electrolyte are used to manufacture a secondary battery.

[0134] [The production of the positive electrode]

[0135] Here, we take the case where the lithium nickel composite oxide, which is used as the positive electrode active material, contains cobalt and other elements (M1, M2) as constituent elements as an example.

[0136] First, as raw materials, prepare a supply source of lithium (lithium compound), a supply source of nickel (nickel compound), a supply source of cobalt (cobalt compound), a supply source of other elements (M1) (first other element compound), and a supply source of other elements (M2) (second other element compound).

[0137] Lithium compounds can be inorganic or organic, and can be of one or more types. Specific examples of inorganic lithium compounds include lithium hydroxide, lithium carbonate, lithium nitrate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium chlorate, lithium perchlorate, lithium bromate, lithium iodate, lithium oxide, lithium peroxide, lithium sulfide, lithium hydrogen sulfide, lithium sulfate, lithium bisulfate, lithium nitride, lithium azide, lithium nitrite, lithium phosphate, lithium dihydrogen phosphate, and lithium bicarbonate. Specific examples of organic lithium compounds include methyllithium, vinyllithium, isopropyllithium, butyllithium, phenyllithium, lithium oxalate, and lithium acetate.

[0138] Here, the description of lithium compounds also applies to each of nickel compounds, cobalt compounds, compounds of the first other element, and compounds of the second other element. That is, nickel compounds, etc., can be any type of inorganic or organic compound, and there can be one or more types of nickel compounds, etc. Furthermore, specific examples of nickel compounds, etc., are compounds in which lithium is replaced by nickel, etc., in the specific examples of lithium compounds described above.

[0139] Next, a precursor is obtained by mixing a lithium compound, a nickel compound, a cobalt compound, a first other element compound, and a second other element compound. The mixing ratio of the lithium compound, nickel compound, cobalt compound, first other element compound, and second other element compound is determined based on the composition of the final lithium-nickel composite oxide.

[0140] Next, the precursor is sintered. The sintering temperature and other conditions can be set arbitrarily. Thus, a compound (lithium-nickel composite oxide) containing lithium, nickel, cobalt and other elements (M1, M2) as constituent elements is synthesized, thereby obtaining the positive electrode active material (lithium-nickel composite oxide).

[0141] In this case, by changing the aforementioned firing temperature and other conditions, the intensity IO1 of the first O1s spectrum and the intensity IO2 of the second O1s spectrum change respectively, thus allowing adjustment of the intensity ratio IO. Furthermore, by changing the firing temperature and firing time, the intensity IN of the Ni3p spectrum also changes.

[0142] It should be noted that when synthesizing the positive electrode active material (lithium-nickel composite oxide), the intensity IN of the Ni3p spectrum changes by changing the composition (nickel content) of the lithium-nickel composite oxide, thus allowing the intensity ratios IBN, ISN, and IFN to be adjusted separately.

[0143] Next, a positive electrode active material (lithium-nickel composite oxide) is mixed with a positive electrode binder and a positive electrode conductive agent to prepare a positive electrode mixture. Next, the positive electrode mixture is added to a solvent such as an organic solvent to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated onto both sides of the positive electrode current collector 11A to form a positive electrode active material layer 11B. Thereafter, the positive electrode active material layer 11B can be compressed using a roller press or the like. In this case, the positive electrode active material layer 11B can be heated, or the compression molding can be repeated multiple times. Finally, by performing the secondary battery stabilization treatment described later, a coating 11C is formed on the surface of the positive electrode active material layer 11B. Thus, a positive electrode 11 is formed on both sides of the positive electrode current collector 11A, along with a positive electrode active material layer 11B and a coating 11C.

[0144] [Making the negative electrode]

[0145] A negative electrode active material layer 12B is formed on both sides of the negative electrode current collector 12A through steps largely the same as those used in the fabrication of the positive electrode 11. Specifically, a negative electrode active material is mixed with a negative electrode binder and a negative electrode conductive agent to prepare a negative electrode mixture. This mixture is then added to a solvent such as an organic solvent to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 12A to form the negative electrode active material layer 12B. The negative electrode active material layer 12B can then be compressed and molded. Thus, the negative electrode active material layer 12B is formed on both sides of the negative electrode current collector 12A, thereby fabricating the negative electrode 12.

[0146] [Preparation of Electrolyte]

[0147] After the electrolyte salt is added to the solvent, boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds are added to the solvent. Thus, the electrolyte salt, boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds are dispersed or dissolved in the solvent, thereby preparing the electrolyte.

[0148] It should be noted that when using boron-containing lithium salts as boron-containing compounds, these lithium salts can also function as electrolyte salts. Similarly, when using fluorine-containing lithium salts as fluorine-containing compounds, these lithium salts can also function as electrolyte salts.

[0149] In this case, by changing the content of the boron-containing compound, the intensity IB of the B1s spectrum changes, thus allowing adjustment of the intensity ratio IBN. Furthermore, by changing the content of the sulfur-containing compound, the intensity IS of the S2p spectrum changes, thus allowing adjustment of the intensity ratio ISN. Additionally, by changing the content of the fluorine-containing compound, the intensity IF of the F1s spectrum changes, thus allowing adjustment of the intensity ratio IFN.

[0150] It should be noted that, as mentioned above, the intensity IN changes depending on factors such as the calcination temperature during the synthesis of the positive electrode active material. Therefore, the intensity ratios IBN, ISN, and IFN can be adjusted separately by varying the intensity IN.

[0151] [Assembly of a secondary battery]

[0152] First, the positive lead 31 is connected to the positive electrode 11 (positive current collector 11A) using a soldering method or the like, and the negative lead 32 is connected to the negative electrode 12 (negative current collector 12A) using a soldering method or the like.

[0153] Next, the positive electrode 11 and the negative electrode 12 are stacked on top of each other with the separator 13 in between, and then the positive electrode 11, the negative electrode 12, and the separator 13 are wound together to form a wound body. This wound body has the same structure as the battery element 10, except that the positive electrode 11, the negative electrode 12, and the separator 13 are not impregnated with electrolyte. Next, the wound body is pressed into a flat shape using a press or the like.

[0154] Next, after housing the wound body inside the recess 20U, the outer film 20 (welding layer / metal layer / surface protective layer) is folded so that the outer films 20 are facing each other. Next, the outer periphery portions of the two sides of the opposing outer films 20 (welding layers) are bonded together using a heat fusion method or the like, thereby housing the wound body inside the bag-shaped outer film 20.

[0155] Finally, after injecting the electrolyte into the pouch-shaped outer film 20, the outer periphery of the remaining side of the outer film 20 (welded layer) is bonded together using a heat-sealing method or the like. In this case, the sealing film 21 is inserted between the outer film 20 and the positive electrode lead 31, and the sealing film 22 is inserted between the outer film 20 and the negative electrode lead 32. Thus, the electrolyte is impregnated into the wound body, thereby forming a battery element 10 as a wound electrode body. Therefore, the battery element 10 is sealed inside the pouch-shaped outer film 20 and assembled into a secondary battery.

[0156] [Stabilization Process]

[0157] The assembled secondary battery is stabilized by charging and discharging it. Various conditions, such as ambient temperature, number of charge / discharge cycles, and charging / discharging conditions, can be arbitrarily set. Therefore, as described above, a coating 11C is formed on the surface of the positive electrode active material layer 11B to form the positive electrode 11. In this case, a coating is also formed on the surface of the negative electrode 12. Thus, to achieve electrochemical stabilization of the secondary battery, a secondary battery using an outer coating 20, i.e., a laminated film type secondary battery, is completed.

[0158] <1-5. Functions and Effects>

[0159] According to this secondary battery, the positive electrode 11 contains a positive electrode active material (lithium-nickel composite oxide). In addition, in the surface analysis of the positive electrode 11 using XPS, six XPS spectra (first O1s spectrum, second O1s spectrum, B1s spectrum, S2p spectrum, F1s spectrum, and Ni3p spectrum) were detected, and four intensity ratios (intensity ratio IO, IBN, ISN, and IFN) met the above conditions.

[0160] In this case, as described above, in the positive electrode 11 containing the positive electrode active material (lithium-nickel composite oxide), the bonding state (oxidation state) of the constituent atoms such as oxygen atoms and nickel atoms in the crystal structure of the positive electrode active material is optimized, thus stabilizing the crystal structure of the positive electrode active material and electrochemically stabilizing the surface state of the positive electrode 11. Therefore, during charging and discharging, the decomposition reaction of the electrolyte on the surface of the positive electrode 11 can be suppressed, thereby suppressing the gas generated by the decomposition reaction of the electrolyte. Therefore, even though the positive electrode 11 contains lithium-nickel composite oxide, the expansion of the secondary battery can be suppressed during charging and discharging, thus achieving excellent expansion characteristics.

[0161] In particular, if the positive electrode 11 includes a positive electrode active material layer 11B (containing lithium nickel composite oxide) and a coating 11C (containing boron, sulfur, and fluorine as constituent elements), the surface analysis of the coating 11C using XPS shows that the coating 11C facilitates the electrochemical stabilization of the surface state of the positive electrode 11, thus achieving higher performance.

[0162] In addition, if the lithium-nickel composite oxide contains the compound shown in formula (1), a sufficiently high energy density can be obtained, thus achieving a higher performance.

[0163] In addition, if the electrolyte contains boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds, it is easy to detect six XPS spectra, and the intensity ratios of four of them are easy to meet the above conditions, thus achieving higher results.

[0164] In this case, if the boron-containing compound contains boron-containing lithium salt, the sulfur-containing compound contains one or both of cyclic disulfonic anhydride and sulfonic acid alkynyl ester, and the fluorine-containing compound contains fluorine-containing lithium salt, then six XPS spectra can be detected stably and easily, and four intensity ratios are more likely to meet the above conditions, thus achieving higher results.

[0165] Furthermore, if the secondary battery has an outer membrane 20 and the battery elements 10 (positive electrode 11, negative electrode 12, and electrolyte) are housed inside the outer membrane 20, the secondary battery will not expand effectively even if the outer membrane 20, which is prone to expansion, is used, thus achieving a higher efficiency.

[0166] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the insertion and extraction of lithium, thus achieving higher performance.

[0167] <2. Variations>

[0168] Next, variations of the aforementioned secondary battery will be described. As explained below, the structure of the secondary battery can be appropriately modified. Furthermore, any two or more of the variations described below can be combined with each other.

[0169] [Variation Example 1]

[0170] The aforementioned secondary battery uses a membrane 13 as a porous membrane. However, although not specifically illustrated here, a laminated membrane comprising layers of polymer compounds can be used instead of the porous membrane 13.

[0171] Specifically, the laminated separator comprises a porous membrane with one and two faces and a polymer compound layer disposed on one or both faces of the porous membrane. This is because, due to the improved adhesion of the separator to each of the positive electrode 11 and the negative electrode 12, the positional displacement of the battery element 10 is less likely to occur. Therefore, even if electrolyte decomposition reactions occur, the secondary battery is less prone to expansion. The polymer compound layer comprises a polymer compound such as polyvinylidene fluoride (PVDF). This is because PVDF and similar compounds possess excellent physical strength and electrochemical stability.

[0172] It should be noted that one or both of the porous membrane and the polymer compound layer may contain any one or more types of insulating particles. This is because multiple insulating particles dissipate heat when the secondary battery heats up, thus improving the safety (heat resistance) of the secondary battery. Insulating particles include inorganic particles and resin particles. Specific examples of inorganic particles include particles of alumina, aluminum nitride, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, and zirconium oxide. Specific examples of resin particles include particles of acrylic resin and styrene resin.

[0173] In the case of fabricating a layered membrane, a precursor solution containing a polymeric compound and an organic solvent is prepared, and then the precursor solution is coated onto one or both sides of a porous membrane. Alternatively, the porous membrane can be impregnated in the precursor solution. In this case, multiple insulating particles can also be added to the precursor solution as needed.

[0174] With the use of this layered separator, lithium ions can also move between the positive electrode 11 and the negative electrode 12, thus achieving the same effect.

[0175] [Variation Example 2]

[0176] The aforementioned secondary battery uses an electrolyte as a liquid electrolyte. However, although not specifically illustrated here, an electrolyte layer as a gel electrolyte can also be used instead of the liquid electrolyte.

[0177] In the battery element 10 using an electrolyte layer, the positive electrode 11 and the negative electrode 12 are stacked on top of each other with the separator 13 and the electrolyte layer in between, and then the positive electrode 11, the negative electrode 12, the separator 13 and the electrolyte layer are wound together. The electrolyte layer is located between the positive electrode 11 and the separator 13, and between the negative electrode 12 and the separator 13.

[0178] Specifically, the electrolyte layer comprises an electrolyte and a polymer compound, and the electrolyte is held in place by the polymer compound within the electrolyte layer. This is to prevent leakage of the electrolyte. The structure of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. In the case of forming the electrolyte layer, after preparing a precursor solution comprising the electrolyte, the polymer compound, and an organic solvent, the precursor solution is coated on one or both sides of each of the positive electrode 11 and the negative electrode 12.

[0179] Even when this electrolyte layer is used, lithium ions can move between the positive electrode 11 and the negative electrode 12 via the electrolyte layer, thus achieving the same effect.

[0180] <3. Uses of Secondary Batteries>

[0181] Next, the uses (application examples) of the above-mentioned secondary batteries will be explained.

[0182] The application of a secondary battery is any machinery, equipment, appliance, device, or system (a collection of multiple devices, etc.) that can primarily use it as a power source for driving or as a power storage source for energy accumulation; there are no particular limitations. A secondary battery used as a power source can be either a main power source or an auxiliary power source. The main power source is the preferred power source, regardless of the availability of other power sources. An auxiliary power source can be used to replace the main power source or can be switched from the main power source as needed. When using a secondary battery as an auxiliary power source, the type of main power source is not limited to a secondary battery.

[0183] Specific examples of the uses of secondary batteries are as follows: Electronic devices (including portable electronic devices) such as camcorders, digital still cameras, mobile phones, laptops, cordless phones, stereo headphones, portable radios, portable televisions, and portable information terminals. Portable household appliances such as electric shavers. Storage devices such as backup power supplies and memory cards. Power tools such as electric drills and chainsaws. Battery packs that serve as detachable power sources for laptops, etc. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid vehicles). Power storage systems such as home battery systems that pre-store power in preparation for emergencies. It should be noted that the battery structure of a secondary battery can be the laminated film type and cylindrical type mentioned above, or other battery structures. In addition, multiple secondary batteries can be used as battery packs and battery modules, etc.

[0184] Battery packs and battery modules are effective in applications such as electric vehicles, energy storage systems, and larger equipment like power tools. As described later, battery packs can use single cells or battery arrays. Electric vehicles are vehicles that operate (drive) using a secondary battery as a power source; as mentioned above, they can also be automobiles (hybrid vehicles, etc.) that have a power source other than a secondary battery. Energy storage systems are systems that use secondary batteries as a source of energy storage. In household energy storage systems, since electricity is stored in the secondary battery that serves as the energy storage source, this electricity can be used to operate household electrical products, etc.

[0185] Here, a specific example of the application of secondary batteries is explained. The structure of the application example described below is only one example and can therefore be modified appropriately.

[0186] Figure 3 The frame structure of the battery pack is shown. The battery pack described here is a simplified type (so-called pouch) that uses a single rechargeable battery and is used in electronic devices such as smartphones.

[0187] like Figure 3 As shown, the battery pack includes a power supply 41 and a circuit board 42. The circuit board 42 is connected to the power supply 41 and includes a positive terminal 43, a negative terminal 44, and a temperature sensing terminal 45. The temperature sensing terminal 45 is a so-called T-terminal.

[0188] The power supply 41 includes a secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 43, and the negative lead is connected to the negative terminal 44. Since the power supply 41 can be connected to an external source through the positive terminal 43 and the negative terminal 44, it can be charged and discharged through these terminals. The circuit board 42 includes a control unit 46, a switch 47, a thermistor (Positive Temperature Coefficient (PTC)) element 48, and a temperature detection unit 49. Alternatively, the PTC element 48 may be omitted.

[0189] The control unit 46 includes a central processing unit (CPU) and memory, and controls the overall operation of the battery pack. The control unit 46 detects and controls the operating status of the power supply 41 as needed.

[0190] It should be noted that when the battery voltage of power supply 41 (secondary battery) reaches the overcharge detection voltage or over-discharge detection voltage, control unit 46 cuts off switch 47, thereby preventing charging current from flowing through the current path of power supply 41. Additionally, when a large current flows during charging or discharging, control unit 46 cuts off switch 47 to block the charging current. The overcharge detection voltage and over-discharge detection voltage are not particularly limited. For example, the overcharge detection voltage is 4.2V ± 0.05V, and the over-discharge detection voltage is 2.4V ± 0.1V.

[0191] Switch 47 includes a charging control switch, a discharging control switch, a charging diode, and a discharging diode, etc., and switches the connection between power supply 41 and external devices according to the instructions of control unit 46. Switch 47 includes a metal-oxide-semiconductor field-effect transistor (MOSFET), etc., and detects the charging and discharging current based on the on-resistance of switch 47.

[0192] The temperature detection unit 49 includes a temperature detection element such as a thermistor, measures the temperature of the power supply 41 using the temperature detection terminal 45, and outputs the temperature measurement result to the control unit 46. The temperature measurement result measured by the temperature detection unit 49 is used for charging and discharging control by the control unit 46 when abnormal heating occurs, and for correction processing by the control unit 46 when calculating the remaining capacity.

[0193] Example

[0194] Embodiments of this technology will be described.

[0195] (Experimental Examples 1-70)

[0196] As explained below, it was made Figure 1 as well as Figure 2 The laminated film type secondary battery (lithium-ion secondary battery) is shown, and its performance is then evaluated.

[0197] [Making a Secondary Battery]

[0198] The secondary battery was made using the following steps.

[0199] (The production of the positive electrode)

[0200] First, lithium compound (lithium sulfate), nickel compound (nickel sulfate), cobalt compound (cobalt sulfate), and a first other element compound (aluminum sulfate) were prepared as raw materials. Next, a precursor was obtained by mixing the lithium compound, nickel compound, cobalt compound, the first other element compound, and the second other element compound. In this case, the mixing ratio was adjusted to ultimately synthesize the lithium-nickel composite oxide (LiNi) described later. 0.80 Co 0.15 Al 0.05 O2). Finally, lithium-nickel composite oxide (LiNi) was synthesized by sintering the precursor. 0.80 Co 0.15 Al 0.05 O2). Thus, the positive electrode active material (lithium-nickel composite oxide) is obtained.

[0201] In this case, the strength ratio IO is varied by changing the firing temperature within the range of 650℃ to 800℃, as shown in Tables 1 to 5.

[0202] Next, 91 parts by mass of the above-mentioned positive electrode active material, 3 parts by mass of the positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of the positive electrode conductive agent (graphite) are mixed to prepare a positive electrode mixture. Next, the positive electrode mixture is added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated onto both sides of the positive electrode current collector 11A (a strip of aluminum foil with a thickness of 12 μm) using a coating apparatus, and then dried to form a positive electrode active material layer 11B. Next, the positive electrode active material layer 11B is compressed and molded using a roller press. Finally, a coating 11C is formed in the secondary battery stabilization treatment described later, thereby forming the positive electrode active material layer 11B and the coating 11C on both sides of the positive electrode current collector 11A to form the positive electrode 11.

[0203] (Making the negative electrode)

[0204] First, 93 parts by mass of the negative electrode active material (artificial graphite as a carbon material) and 7 parts by mass of the negative electrode binder (polyvinylidene fluoride) are mixed to prepare a negative electrode mixture. Next, the negative electrode mixture is added to an organic solvent (N-methyl-2-pyrrolidone) and stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 12A (a strip of copper foil with a thickness of 15 μm) using a coating device, and then dried to form a negative electrode active material layer 12B. Finally, the negative electrode active material layer 12B is compressed and molded using a roller press. Thus, a negative electrode active material layer 12B is formed on both sides of the negative electrode current collector 12A, forming the negative electrode 12.

[0205] (Preparation of electrolyte)

[0206] A boron-containing compound, a sulfur-containing compound, and a fluorine-containing compound are added to a solvent (ethylene carbonate as a cyclic carbonate and diethyl carbonate as a chain carbonate), and the solvent is then stirred. The mixing ratio (by weight) of the solvent is ethylene carbonate : diethyl carbonate = 50 : 50.

[0207] As boron-containing compounds, boron-containing lithium salts, which act as electrolyte salts, were used. The types and contents (wt%) of the boron-containing lithium salts are shown in Tables 1 to 5. Lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiFOB), and lithium bis(oxalate)borate (LiBOB) were used as boron-containing lithium salts. The "content (wt%)" mentioned above refers to the content (wt%) when the solvent is set to 100 wt%, and the same applies thereafter.

[0208] Cyclic disulfonic anhydrides and sulfonate alkynyl esters were used as sulfur-containing compounds. The types and contents (wt%) of the cyclic disulfonic anhydrides and sulfonate alkynyl esters are shown in Tables 1 to 5. 1,3-propanedisulfonic anhydride (PSAH) and 1,2-ethanedisulfonic anhydride (ESAH) were used as cyclic disulfonic anhydrides. Propylbenzenesulfonate (PBS) was used as a sulfonate alkynyl ester.

[0209] Fluorinated lithium salts, which act as electrolyte salts, were used as fluorinated compounds. The types and contents (wt%) of the fluorinated lithium salts are shown in Tables 1 to 5. Lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium tri(trifluoromethanesulfonyl)methylide (LiFSC) were used as fluorinated lithium salts.

[0210] Thus, boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds are dispersed or dissolved in solvents to prepare electrolytes.

[0211] In this case, by changing the contents of boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds, as shown in Tables 1 to 5, the strength ratios IBN, ISN, and IFN were altered respectively. It should be noted that during the synthesis of the above-mentioned positive electrode active material, since the strength IN changes according to the firing temperature, the strength ratios IBN, ISN, and IFN were also changed according to this change in strength IN.

[0212] It should be noted that, for the purpose of comparison, the electrolyte was prepared using the same steps, except that boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds were not used.

[0213] (Assembly of a secondary battery)

[0214] First, the positive lead 31, made of aluminum, is soldered to the positive electrode 11 (positive current collector 11A), and the negative lead 32, made of copper, is soldered to the negative electrode 12 (negative current collector 12A).

[0215] Next, the positive electrode 11 and the negative electrode 12 are stacked on top of each other with a separator 13 (a microporous polyethylene membrane with a thickness of 15 μm) in between, and then the positive electrode 11, the negative electrode 12 and the separator 13 are wound together to form a wound body. Next, the wound body is stamped using a press to form a flat wound body.

[0216] Next, the wound body is housed inside the recess 20U provided in the outer film 20. The outer film 20 uses an aluminum laminate film, which consists of a weld layer (a 30 μm thick polypropylene film), a metal layer (a 40 μm thick aluminum foil), and a surface protective layer (a 25 μm thick nylon film) stacked sequentially. Next, the outer film 20 is folded so that the wound body is sandwiched between the outer film 20 and the weld layer is located inside the outer film 20. Then, the outer periphery portions of two sides of the outer film 20 (weld layer) are heat-fused together, thereby housing the wound body inside the bag-shaped outer film 20.

[0217] Finally, after injecting the electrolyte into the pouch-shaped outer membrane 20, the outer periphery of the remaining edge of the outer membrane 20 (welded layer) is thermally fused together under reduced pressure. In this case, a sealing film 21 (a polypropylene film with a thickness of 5 μm) is inserted between the outer membrane 20 and the positive electrode lead 31, and a sealing film 22 (a polypropylene film with a thickness of 5 μm) is inserted between the outer membrane 20 and the negative electrode lead 32. Thus, the electrolyte is impregnated into the winding body, thereby forming the battery element 10. Therefore, the battery element is sealed inside the outer membrane 20 and assembled into a secondary battery.

[0218] (Stabilization treatment)

[0219] The secondary battery was subjected to one charge-discharge cycle at room temperature (temperature = 23℃). During charging, a constant current of 0.1C was used until the voltage reached 4.2V, followed by constant voltage charging at that 4.2V until the current reached 0.05C. During discharging, a constant current of 0.1C was used until the voltage reached 3.0V. 0.1C refers to the current value required to fully discharge the battery (theoretical capacity) in 10 hours, and 0.05C refers to the current value required to fully discharge the battery (theoretical capacity) in 20 hours.

[0220] Thus, by forming a coating 11C on the surface of the positive electrode active material layer 11B, and forming the positive electrode active material layer 11B and the coating 11C on both sides of the positive electrode current collector 11A, the positive electrode 11 is fabricated. Therefore, the state of the secondary battery is stabilized, and the laminated film type secondary battery is completed.

[0221] [Performance Evaluation]

[0222] The performance (expansion characteristics) of the secondary battery was evaluated, and the results are shown in Tables 1 to 5.

[0223] After completing the secondary battery and before checking its expansion characteristics, the secondary battery was disassembled to recover the positive electrode 11, and then the surface of the positive electrode 11 was analyzed using XPS. Based on the surface analysis results of the positive electrode 11, the intensities of six XPS spectra (first O1s spectrum, second O1s spectrum, B1s spectrum, S2p spectrum, F1s spectrum, and Ni3p spectrum) were measured, and then four intensity ratios (intensity ratio IO, IBN, ISN, and IFN) were calculated based on these measurement results. The calculation results of intensity ratios IO, IBN, ISN, and IFN are shown in Tables 1 to 5.

[0224] To examine the expansion characteristics, the secondary battery was first charged at room temperature, and its thickness (before storage) was measured. Next, the charged secondary battery was stored in a high-temperature environment (temperature = 60°C) for 24 hours, and its thickness (after storage) was measured again. Finally, the expansion rate (%) was calculated as (thickness after storage / thickness before storage) × 100 - 100. It should be noted that the charging conditions were the same as those used during the stabilization treatment of the secondary battery described above.

[0225] [Table 1]

[0226]

[0227] [Table 2]

[0228]

[0229] [Table 3]

[0230]

[0231] [Table 4]

[0232]

[0233] [Table 5]

[0234]

[0235] [Inspection]

[0236] As shown in Tables 1 to 5, the expansion rate of the secondary battery containing lithium nickel composite oxide as the positive electrode active material in the positive electrode 11 varies significantly depending on the physical properties of the positive electrode 11 (intensity ratio IO, IBN, ISN, IFN).

[0237] Specifically, in secondary batteries where the electrolyte does not contain boron-containing compounds, sulfur-containing compounds, or fluorine-containing compounds, when the secondary battery was stabilized (Examples 66-70), not all six XPS spectra were detected, and therefore all four intensity ratios could not be calculated.

[0238] In contrast, in secondary batteries containing boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds in the electrolyte, when the secondary battery was stabilized (Examples 1-65), all six XPS spectra were detected, and therefore all four intensity ratios could be calculated.

[0239] Therefore, when the electrolyte does not contain boron-containing compounds, sulfur-containing compounds, or fluorine-containing compounds (Experimental Examples 66-70), the expansion rate increases significantly.

[0240] In contrast, when the electrolyte contains boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds (Experimental Examples 1-65), the expansion rate decreases. In this case, when all four conditions are met simultaneously (Experimental Examples 2-4, etc.), the expansion rate further decreases compared to cases where these four conditions are not met simultaneously (Experimental Examples 1, 5, etc.), thus the expansion rate is significantly reduced.

[0241] (Experimental Examples 71 and 72)

[0242] For comparison, as shown in Table 6, a secondary battery was fabricated using the same steps, except that lithium cobalt oxide (LiCoO2), which is not a lithium-nickel composite oxide, was used as the positive electrode active material, and the expansion characteristics of the secondary battery were evaluated.

[0243] [Table 6]

[0244]

[0245] As shown in Table 6, in secondary batteries that do not use lithium nickel composite oxide as the positive electrode active material (Experimental Examples 71 and 72), the expansion rate is reduced when the electrolyte contains boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds (Experimental Example 72) compared to when the electrolyte does not contain boron-containing compounds, sulfur-containing compounds, and fluorine-containing compounds (Experimental Example 71).

[0246] However, the expansion rate when lithium nickel composite oxide was not used as the positive electrode active material (Experimental Example 72) was more than three times that when lithium nickel composite oxide was used as the positive electrode active material (Experimental Example 48). Therefore, the expansion rate of the former was not sufficiently reduced compared to the expansion rate of the latter.

[0247] The reason for this can be attributed to the difference in the types of positive electrode active materials. Specifically, when four conditions are met simultaneously (intensity ratio IO = 0.5–0.8, intensity ratio IBN = 0.9–1.8, intensity ratio ISN = 0.4–1.2, and intensity ratio IFN = 8–13), the expansion rate is significantly reduced. This favorable tendency cannot be obtained without using lithium nickel composite oxide as the positive electrode active material; it is a specific tendency that can only be obtained when lithium nickel composite oxide is used as the positive electrode active material.

[0248] [Summarize]

[0249] Based on the results shown in Tables 1 to 6, in the secondary battery with lithium-nickel composite oxide cathode 11, when six XPS spectra (first O1s spectrum, second O1s spectrum, B1s spectrum, S2p spectrum, F1s spectrum, and Ni3p spectrum) were detected in the surface analysis of the cathode 11 using XPS, and when four intensity ratios (intensity ratios IO, IBN, ISN, and IFN) met the above conditions, the expansion rate was significantly reduced. Therefore, excellent expansion characteristics were obtained in the secondary battery.

[0250] The above description, while illustrating the present technology with an example of one implementation method and embodiment, does not limit the structure of the present technology to the structure described in one implementation method and embodiment, and various modifications are possible.

[0251] Specifically, although the case of a laminated film type battery structure for secondary batteries has been described, the battery structure is not particularly limited and can be other battery structures such as cylindrical, square, coin-shaped, and button-shaped.

[0252] Furthermore, although the case of a wound battery element structure has been described, the battery element structure is not particularly limited, so other element structures can be used, such as a stacked type where the electrodes (positive and negative electrodes) are stacked, or a repeatedly folded type where the electrodes (positive and negative electrodes) are folded into a Z-shape.

[0253] Furthermore, while the case where lithium is used as the electrode reactant has been described, this electrode reactant is not particularly limited. Specifically, as mentioned above, the electrode reactant can be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Additionally, the electrode reactant can also be other light metals such as aluminum.

[0254] The effects described in this specification are merely illustrative, and therefore the effects of this technology are not limited to those described in this specification. Thus, this technology can also achieve other effects.

Claims

1. A secondary battery, comprising: The positive electrode contains a lithium-nickel composite oxide; Negative electrode; and Electrolyte In the surface analysis of the cathode using X-ray photoelectron spectroscopy, the following were detected: The first O1s spectrum has a peak value in the range of bond energy above 528 eV and below 531 eV; The second O1s spectrum has a peak in the range of bond energy greater than 531 eV and less than 535 eV; B1s spectrum; S2p spectrum; F1s spectrum; and Ni3p spectrum The ratio of the intensity of the first O1s spectrum to the intensity of the second O1s spectrum is greater than 0.5 and less than 0.

8. The ratio of the intensity of the B1s spectrum to the intensity of the Ni3p spectrum is greater than 0.9 and less than 1.

8. The ratio of the intensity of the S2p spectrum to the intensity of the Ni3p spectrum is greater than 0.4 and less than 1.

2. The ratio of the intensity of the F1s spectrum to the intensity of the Ni3p spectrum is greater than 8 and less than 13.

2. The secondary battery according to claim 1, wherein, The positive electrode includes: The positive electrode active material layer includes the lithium-nickel composite oxide; and The coating, formed on the surface of the positive electrode active material layer, contains boron, sulfur, and fluorine as constituent elements. The coating was analyzed by surface analysis of the positive electrode using the X-ray photoelectron spectroscopy method.

3. The secondary battery according to claim 1 or 2, wherein, The lithium-nickel composite oxide comprises a compound represented by the following formula (1), The w Nor （1-x-y-z） Co x M1 y M2 z O2…(1) In the formula, M1 is at least one of Al and Mn, M2 is at least one of the elements belonging to groups 2 to 15 of the long-period periodic table, excluding Ni, Co, Al and Mn, w, x, y and z satisfy 0.8≤w≤1.2, 0≤x≤0.3, 0≤y≤0.1 and 0≤z≤0.

1. In addition, the composition of lithium varies depending on the charge and discharge state, and w is the value of the fully discharged state.

4. The secondary battery according to claim 1 or 2, wherein, The electrolyte comprises: Boron-containing compounds; Sulfur-containing compounds; and Fluorine-containing compounds.

5. The secondary battery according to claim 4, wherein, The boron-containing compound includes a boron-containing lithium salt. The sulfur-containing compound comprises at least one of cyclic disulfonic anhydrides and sulfonic acid alkynyl esters. The fluorine-containing compound includes a fluorine-containing lithium salt.

6. The secondary battery according to claim 1 or 2, wherein, It also has a flexible external component for housing the positive electrode, the negative electrode, and the electrolyte.

7. The secondary battery according to claim 1 or 2, The secondary battery is a lithium-ion secondary battery.

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