Secondary batteries

Abstract

A secondary battery according to the present invention comprises: a positive electrode; a negative electrode that contains a negative electrode active material; and an electrolyte that contains a thiazole compound. The negative electrode active material includes a core part that occludes and releases an electrode reactant, and a covering part that covers the surface of the core part. The covering part contains at least one of nickel, iron, and copper as a constituent element. The thiazole compound includes a compound represented by formula (1), a compound represented by formula (2), a compound represented by formula (3), and / or a compound represented by formula (4).

Description

[Technical Field]

[0001] This technology relates to secondary batteries. [Background technology]

[0002] With the widespread use of various electronic devices such as mobile phones, development of rechargeable batteries is progressing as a power source that is small, lightweight, and provides high energy density. These rechargeable batteries contain an electrolyte along with a positive electrode and a negative electrode, and various studies are being conducted on the configuration of these batteries.

[0003] Specifically, a benzotriazole derivative having a particular structure is contained in the electrolyte (see, for example, Patent Documents 1 and 2). Alternatively, a benzothiazole derivative having a particular structure is contained in the electrolyte (see, for example, Patent Documents 3 and 4). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2001-273927 [Patent Document 2] Special Publication No. 2013-513923 [Patent Document 3] Patent No. 6056721 Specification [Patent Document 4] International Publication No. 2019 / 181278 Brochure [Overview of the project]

[0005] Although various studies have been conducted on the configuration of secondary batteries, their battery characteristics are still not satisfactory, and there is room for improvement.

[0006] There is a need for a secondary battery that can achieve excellent battery characteristics.

[0007] A secondary battery according to one embodiment of this technology comprises a positive electrode, a negative electrode containing a negative electrode active material, and an electrolyte containing a thiazole-type compound. The negative electrode active material includes a central part that intercepts and releases electrode reactants, and a coating portion that covers the surface of the central part, the coating portion containing at least one of nickel, iron, and copper as constituent elements. The thiazole-type compound includes at least one of the compounds represented by formula (1), formula (2), formula (3), and formula (4).

[0008] [ka] (Each of R1 to R28 is one of the following: hydrogen, fluorine, alkyl group, alkenyl group, alkynyl group, cycloalkyl group, aryl group, alkoxy group, fluorinated alkyl group, fluorinated alkenyl group, fluorinated alkynyl group, fluorinated cycloalkyl group, fluorinated aryl group, fluorinated alkoxy group, amino group, carboxylic acid ester group, or a monovalent bond group formed by the bonding of two or more of these groups.)

[0009] Further details regarding "carboxylic acid ester group" and "monovalent bonding group" will be provided later.

[0010] According to one embodiment of this technology, a secondary battery has a negative electrode active material that includes a core and a coating, the coating containing at least one of nickel, iron, and copper as a constituent element, and the electrolyte contains a thiazole-type compound, thus providing excellent battery characteristics.

[0011] Furthermore, the effects of this technology are not necessarily limited to those described herein, but may include any of the series of effects related to this technology described later. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view showing the configuration of a secondary battery in one embodiment of this technology. [Figure 2] It is a cross-sectional view showing the configuration of the battery element shown in FIG. 1. [Figure 3] It is a cross-sectional view schematically showing the enlarged configuration of the negative electrode active material. [Figure 4] It is a block diagram showing the configuration of an application example of the secondary battery.

Mode for Carrying Out the Invention

[0013] Hereinafter, with respect to an embodiment of the present technology, it will be described in detail while referring to the drawings. The order of description is as follows. 1. Secondary battery 1-1. Overall configuration 1-2. Detailed configuration of the electrolyte 1-3. Operation 1-4. Manufacturing method 1-5. Action and effect 2. Modification example 3. Applications of the secondary battery

[0014] <1. Secondary battery> First, the secondary battery according to an embodiment of the present technology will be described.

[0015] The secondary battery described here is a secondary battery in which the battery capacity is obtained by utilizing the absorption and release of electrode reactants, and includes an electrolyte together with a positive electrode and a negative electrode.

[0016] In this secondary battery, the charging capacity of the negative electrode is larger than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of the negative electrode is set to be larger than the electrochemical capacity per unit area of the positive electrode. This is to prevent the electrode reactant from depositing on the surface of the negative electrode during charging.

[0017] The types of electrode reactants are not particularly limited, but 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.

[0018] In the following example, we will consider the case where lithium is the electrode reactant. A secondary battery that obtains battery capacity by utilizing the intercalation and deintercalation of lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is intercalated and deintercalated in an ionic state.

[0019] <1-1. Overall Structure> Figure 1 shows the cross-sectional configuration of a secondary battery, and Figure 2 shows the cross-sectional configuration of the battery element 20 shown in Figure 1. Figure 3 shows a magnified and schematic representation of the cross-sectional configuration of the negative electrode active material 220, which is the main part of the negative electrode 22.

[0020] As shown in Figures 1 and 2, this secondary battery mainly comprises a battery casing 11, a pair of insulating plates 12 and 13, a battery element 20, a positive electrode lead 25, and a negative electrode lead 26. The secondary battery described here is a cylindrical secondary battery in which the battery element 20 is housed inside a cylindrical battery casing 11.

[0021] [Battery can] As shown in Figure 1, the battery casing 11 is a housing member that contains the battery elements 20 and the like. The battery casing 11 has an open end and a closed end, thus having a hollow structure. Furthermore, the battery casing 11 contains one or more types of metal materials, such as iron, aluminum, iron alloys, and aluminum alloys. The surface of the battery casing 11 may be plated with a metal material such as nickel.

[0022] At the open end of the battery case 11, a battery cover 14, a safety valve mechanism 15, and a thermal resistance element (PTC element) 16 are crimped via a gasket 17. This seals the battery case 11 with the battery cover 14. Here, the battery cover 14 contains the same material as the forming material of the battery case 11. The safety valve mechanism 15 and the PTC element 16 are located inside the battery cover 14, and the safety valve mechanism 15 is electrically connected to the battery cover 14 via the PTC element 16. The gasket 17 contains an insulating material, and its surface may be coated with asphalt or the like.

[0023] In this safety valve mechanism 15, if the internal pressure of the battery can 11 reaches a certain level due to an internal short circuit or external overheating, the disk plate 15A inverts, thereby disconnecting the electrical connection between the battery cover 14 and the battery element 20. To prevent abnormal heat generation caused by high current, the electrical resistance of the PTC element 16 increases in proportion to the rise in temperature.

[0024] [insulating board] As shown in Figure 1, the insulating plates 12 and 13 are arranged to face each other via the battery element 20. As a result, the battery element 20 is sandwiched between the insulating plates 12 and 13.

[0025] [Battery element] As shown in Figures 1 and 2, the battery element 20 is a power generation element that includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0026] This battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23 and are wound facing each other via the separator 23. A center pin 24 is inserted into the winding center space 20S provided at the winding center of the battery element 20. However, the center pin 24 may be omitted.

[0027] (positive electrode) As shown in Figure 2, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0028] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. This positive electrode current collector 21A contains a conductive material such as a metal material, a specific example of which is aluminum.

[0029] The positive electrode active material layer 21B contains one or more types of positive electrode active materials that intercalate and deintercalate lithium. However, the positive electrode active material layer 21B may further contain one or more types of other materials such as positive electrode binders and positive electrode conductive agents. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically includes methods such as coating.

[0030] Here, since the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A, the positive electrode 21 includes two positive electrode active material layers 21B. However, since the positive electrode active material layer 21B is provided on only one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22, the positive electrode 21 may include only one positive electrode active material layer 21B.

[0031] The type of positive electrode active material is not particularly limited, but specifically, it is a lithium-containing compound. This lithium-containing compound is a compound that contains lithium along with one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of other element is not particularly limited as long as it is an element other than lithium and the transition metal elements, but specifically, it is an element belonging to groups 2 to 15 of the long-period periodic table. The type of lithium-containing compound is not particularly limited, but specifically, it is an oxide, a phosphoric acid compound, a silicate compound, and a borate compound.

[0032] Specific examples of oxides include LiNiO2, LiCoO2, and LiCo 0.98 Al 0.01 Mg 0.01 O2, LiLiLi0.5 Co 0.2 Mn 0.3 Examples include O2 and LiMn2O4. Specific examples of phosphorylated compounds include LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 Examples include PO4.

[0033] The positive electrode binder contains one or more materials, such as synthetic rubber and polymer compounds. Specific examples of synthetic rubber include styrene-butadiene rubber, fluorine-based rubber, and ethylene propylene diene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide, and carboxymethylcellulose.

[0034] The positive electrode conductive agent contains one or more types of conductive materials, such as carbon materials. Specific examples of carbon materials include graphite, carbon black, acetylene black, and Ketjenblack. However, the conductive material may also be a metallic material or a polymer compound.

[0035] As described later, the coating portion 222 of the negative electrode active material 220 contains a coating element as a constituent element, and this coating element contains one or more of nickel, iron, and copper. When the source of this coating element is the positive electrode 21, the positive electrode active material layer 21B further contains coating metal powder, and this coating metal powder may contain one or more of nickel powder, iron powder, and copper powder. This coating metal powder is a powdered metal material containing the coating element as a constituent element. The content of coating metal powder in the positive electrode active material layer 21B is not particularly limited and can be set arbitrarily.

[0036] (Negative electrode) As shown in Figure 2, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0037] The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. This negative electrode current collector 22A contains a conductive material such as a metallic material, a specific example of which is copper.

[0038] The negative electrode active material layer 22B contains one or more types of negative electrode active materials that intercalate and deintercalate lithium. However, the negative electrode active material layer 22B may further contain one or more types of other materials such as negative electrode binders and negative electrode conductive agents. The method for forming the negative electrode active material layer 22B is not particularly limited, but specifically, it is one or more types of coating, gas phase, liquid phase, thermal spraying, and firing (sintering) methods.

[0039] Here, since the negative electrode active material layer 22B is provided on both sides of the negative electrode current collector 22A, the negative electrode 22 contains two negative electrode active material layers 22B. However, since the negative electrode active material layer 22B is provided only on one side of the negative electrode current collector 22A on the side where the negative electrode 22 faces the positive electrode 21, the negative electrode 22 may contain only one negative electrode active material layer 22B.

[0040] More specifically, the negative electrode active material layer 22B, as shown in Figure 3, contains multiple particulate negative electrode active materials (negative electrode active material 220), each of which includes a central part 221 and a coating portion 222. However, Figure 3 shows only one negative electrode active material 220.

[0041] The central part 221 contains one or more materials capable of intercalating and deintercalating lithium, such as carbon materials and metallic materials, because a high energy density can be obtained. As a result, the negative electrode material may contain only carbon materials, only metallic materials, or both carbon materials and metallic materials.

[0042] Specific examples of carbon materials include readily graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite).

[0043] The metal-based material is a material containing, as constituent elements, any one or two or more of metal elements and metalloid elements capable of forming an alloy with lithium. Specific examples of the metal elements and metalloid elements include silicon and tin. This metal-based material may be a single substance, an alloy, a compound, a mixture of two or more of them, or a material containing two or more phases of them. Specific examples of the metal-based material include TiSi2 and SiO x (0 < x ≤ 2, or 0.2 < x < 1.4), etc.

[0044] Among them, the negative electrode material preferably contains a metal-based material, and the metal-based material preferably contains silicon as a constituent element. This is because a sufficiently high energy density can be obtained.

[0045] Note that the details regarding the negative electrode binder are the same as those regarding the positive electrode binder, and the details regarding the negative electrode conductive agent are the same as those regarding the positive electrode conductive agent.

[0046] The coating portion 222 covers the surface of the central portion 221. However, the coating portion 222 may cover the entire surface of the central portion 221, or may cover only a part of the surface of the central portion 221. In the latter case, a plurality of coating portions 222 may cover the surface of the central portion 221 at a plurality of locations spaced apart from each other.

[0047] As will be described later, this coating portion 222 is formed by performing a stabilization treatment on the assembled secondary battery in the manufacturing process of the secondary battery. This stabilization treatment is a so-called initial charge-discharge treatment, and is performed to electrochemically stabilize the state of the assembled secondary battery. The conditions of the stabilization treatment can be arbitrarily set as will be described later. That is, the number of charge-discharge cycles in the stabilization treatment is not limited to one, and may be two or more times.

[0048] In this stabilization process, a coating portion 222 is formed to cover the surface of the reactive central portion 221, thereby reducing the reactivity of the central portion 221's surface. As a result, the reactivity of the negative electrode active material 220's surface is reduced, and the decomposition reaction of the electrolyte on the surface of the negative electrode active material 220 is suppressed. Therefore, the decomposition reaction of the electrolyte is suppressed even during subsequent charging and discharging, and the state of the secondary battery is electrochemically stabilized.

[0049] Furthermore, during the stabilization process, not only is a coating 222 formed on the surface of the central part 221, but a coating may also be formed on the surface of the positive electrode active material. This is because the decomposition reaction of the electrolyte on the surface of the positive electrode active material is also suppressed.

[0050] In particular, as described above, the coating portion 222 contains coating elements as constituent elements, and these coating elements include one or more of nickel, iron, and copper. The state of the coating elements in the coating portion 222 is not particularly limited, and may be in elemental form, compound form, alloy form, or two or more of these forms. However, since elemental elements may contain any amount of impurities, the purity of the elemental element is not necessarily limited to 100%.

[0051] The reason the coating portion 222 contains coating elements as constituent elements is that it improves the physical strength of the coating portion 222, making it easier to maintain the coating portion 222 even after repeated charging and discharging. As a result, even after repeated charging and discharging, the decomposition reaction of the electrolyte is suppressed, and the decrease in discharge capacity is suppressed.

[0052] Furthermore, the method of incorporating the coating element as a constituent element in the coating portion 222, or in other words, the source of the coating element, is not particularly limited. Details regarding the source of the coating element will be described later.

[0053] (Separator) As shown in Figure 2, the separator 23 is an insulating porous membrane interposed between the positive electrode 21 and the negative electrode 22, allowing lithium ions to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. This separator 23 contains a polymer compound such as polyethylene.

[0054] (electrolyte) The electrolyte is a liquid electrolyte. This electrolyte is impregnated into the positive electrode 21, the negative electrode 22, and the separator 23, and contains a thiazole compound. The detailed composition of the electrolyte will be described later.

[0055] [Positive lead and negative lead] The positive lead 25 is connected to the positive current collector 21A of the positive electrode 21, as shown in Figures 1 and 2, and contains a conductive material such as aluminum. This positive lead 25 is electrically connected to the battery cover 14 via a safety valve mechanism 15.

[0056] The negative electrode lead 26 is connected to the negative electrode current collector 22A of the negative electrode 22, as shown in Figures 1 and 2, and contains a conductive material such as nickel. This negative electrode lead 26 is electrically connected to the battery can 11.

[0057] <1-2. Detailed composition of the electrolyte> Details regarding the composition of the electrolyte are as follows.

[0058] [Thiazole-type compounds] As described above, this electrolyte contains one or more of the thiazole-type compounds. These thiazole-type compounds are compounds having a thiazole-type structure and are so-called thiazole derivatives.

[0059] Specifically, the thiazole-type compound contains one or more of the compounds represented by formula (1), formula (2), formula (3), and formula (4).

[0060] In the following, the compound shown in formula (1) will be referred to as the "first thiazole compound," the compound shown in formula (2) as the "second thiazole compound," the compound shown in formula (3) as the "third thiazole compound," and the compound shown in formula (4) as the "fourth thiazole compound."

[0061] [ka] (Each of R1 to R28 is one of the following: hydrogen, fluorine, alkyl group, alkenyl group, alkynyl group, cycloalkyl group, aryl group, alkoxy group, fluorinated alkyl group, fluorinated alkenyl group, fluorinated alkynyl group, fluorinated cycloalkyl group, fluorinated aryl group, fluorinated alkoxy group, amino group, carboxylic acid ester group, or a monovalent bond group formed by the bonding of two or more of these groups.)

[0062] The first thiazole compound is a compound containing one benzene ring, as shown in formula (1). The second thiazole compound is a compound containing two benzene rings, as shown in formula (2). The third thiazole compound is a compound in which two first thiazole compounds are indirectly linked to each other via a dithio bond (-SS-), as shown in formula (3). The fourth thiazole compound is a compound in which two first thiazole compounds are directly linked to each other, as shown in formula (4), and the carbon-carbon double bond in each of the two thiazole rings has disappeared.

[0063] The electrolyte contains thiazole compounds because the synergistic effect between the coating elements contained in the coating portion 222 and the thiazole compounds significantly improves the physical strength of the coating portion 222, making it easier to maintain the coating portion 222 even after repeated charging and discharging. As a result, the decomposition reaction of the electrolyte is suppressed even after repeated charging and discharging, thus suppressing the decrease in discharge capacity.

[0064] (composition) Each of R1 to R28 is not particularly limited as long as it is any of the following, as described above: hydrogen (-H), fluorine (-F), alkyl group, alkenyl group, alkynyl group, cycloalkyl group, aryl group, alkosy group, fluorinated alkyl group, fluorinated alkenyl group, fluorinated alkynyl group, fluorinated cycloalkyl group, fluorinated aryl group, fluorinated alkoxy group, amino group (-NH2), carboxylic acid ester group, and monovalent bonding group.

[0065] The number of carbon atoms in an alkyl group is not particularly limited; specific examples of alkyl groups include methyl, ethyl, and propyl groups. However, alkyl groups may be linear or branched.

[0066] The number of carbon atoms in an alkenyl group is not particularly limited; specific examples of such alkenyl groups include vinyl and allyl groups. However, the alkenyl group may be linear or branched.

[0067] The number of carbon atoms in an alkynyl group is not particularly limited; specific examples of such alkynyl groups include ethynyl and propargyl groups. However, the alkenyl group may be linear or branched.

[0068] The number of carbon atoms in a cycloalkyl group is not particularly limited; specific examples of cycloalkyl groups include cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups.

[0069] The number of carbon atoms in an aryl group is not particularly limited; specific examples of aryl groups include phenylene groups and naphthylene groups.

[0070] The number of carbon atoms in an alkoxy group is not particularly limited; specific examples of such alkoxy groups include methoxy, ethoxy, and propoxy groups. However, the alkoxy group may be in a linear or branched form.

[0071] A fluorinated alkyl group is a group in which one or more hydrogen atoms in an alkyl group are substituted with fluorine. A fluorinated alkenyl group is a group in which one or more hydrogen atoms in an alkenyl group are substituted with fluorine. A fluorinated alkynyl group is a group in which one or more hydrogen atoms in an alkynyl group are substituted with fluorine. A fluorinated cycloalkyl group is a group in which one or more hydrogen atoms in a cycloalkyl group are substituted with fluorine. A fluorinated aryl group is a group in which one or more hydrogen atoms in an aryl group are substituted with fluorine. A fluorinated alkoxy group is a group in which one or more hydrogen atoms in an alkoxy group are substituted with fluorine.

[0072] A carboxylic acid ester group is a group represented as -C(=O)-O-R30 (where R30 is an alkyl group), and the details regarding the alkyl group are as described above. Specific examples of carboxylic acid ester groups include the methyl carboxylate group (-C(=O)-O-CH3) and the ethyl carboxylate group (-C(=O)-O-C2H5).

[0073] The type of monovalent bond is not particularly limited. Specific examples of monovalent bond groups include groups in which an alkyl group and a carboxylic acid ester group are bonded to each other (groups in which an alkylene group and a carboxylic acid ester group are bonded to each other), and more specifically, -CH2-C(=O)-O-CH3, etc.

[0074] (Specific example) Specific examples of thiazole-type compounds are as follows.

[0075] Specific examples of first-type thiazole compounds include those represented by formulas (1-1) to (1-27), respectively.

[0076] [ka]

[0077] [ka]

[0078] Specific examples of second-type thiazole compounds include the compounds represented by formulas (2-1) to (2-31), respectively.

[0079] [ka]

[0080] [ka]

[0081] [ka]

[0082] Specific examples of third-type thiazole compounds include those represented by formulas (3-1) to (3-24), respectively.

[0083] [ka]

[0084] [ka]

[0085] [ka]

[0086] [ka]

[0087] [ka]

[0088] Specific examples of thiazole-type compounds include those represented by formulas (4-1) to (4-9), respectively.

[0089] [ka]

[0090] [ka]

[0091] (Content) The content of the thiazole-type compound in the electrolyte is not particularly limited, but is preferably 0.001% to 5% by weight. This is because the physical strength of the coating portion 222 is sufficiently improved, thereby sufficiently suppressing the decomposition reaction of the electrolyte.

[0092] Furthermore, when the electrolyte contains both the first thiazole-type compound and the second thiazole-type compound, the content of the thiazole-type compound in the electrolyte is the sum of the content of the first thiazole-type compound and the content of the second thiazole-type compound in the electrolyte.

[0093] When measuring the content of thiazole-type compounds, the electrolyte is recovered by disassembling the secondary battery, and the content of the thiazole-type compounds is calculated by analyzing the electrolyte. The analytical method for the electrolyte is not particularly limited, but specifically, it may be one or more of the following: inductively coupled plasma (ICP) emission spectroscopy, nuclear magnetic resonance spectroscopy (NMR), and gas chromatography-mass spectroscopy (GC-MS).

[0094] [solvent] Furthermore, the electrolyte may also contain a solvent. This solvent may contain one or more non-aqueous solvents (organic solvents), and an electrolyte containing such a non-aqueous solvent is a so-called non-aqueous electrolyte.

[0095] Non-aqueous solvents include esters and ethers, and more specifically, carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds.

[0096] Carbonate ester compounds include cyclic carbonate esters and linear carbonate esters. Specific examples of cyclic carbonate esters include ethylene carbonate and propylene carbonate. Specific examples of linear carbonate esters include dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.

[0097] Carboxylic acid ester compounds include linear carboxylic acid esters. Specific examples of linear carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl trimethylacetate, methyl butyrate, and ethyl butyrate.

[0098] Lactone compounds include lactones, among others. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0099] The ethers may also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

[0100] (Electrolyte salts) Furthermore, the electrolyte may also contain an electrolyte salt. This electrolyte salt is a light metal salt, such as a lithium salt.

[0101] Specific examples of lithium salts include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF3SO2)3), lithium bis(oxalato)borate (LiB(C2O4)2), lithium difluorooxalatoborate (LiBF2(C2O4)), lithium difluorodi(oxalato)borate (LiPF2(C2O4)2), lithium tetrafluorooxalatophosphate (LiPF4(C2O4)), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2).

[0102] The electrolyte salt content is not particularly limited, but specifically, it is between 0.3 mol / kg and 3.0 mol / kg relative to the solvent. This is because it allows for high ionic conductivity.

[0103] (Additives) Furthermore, the electrolyte may also contain one or more of the additives.

[0104] (Unsaturated cyclic carbonates, fluorinated cyclic carbonates, and cyanated cyclic carbonates) Specifically, the additives are one or more of the following: unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, and cyanated cyclic carbonate esters. This is because it improves the electrochemical stability of the electrolyte. As a result, the decomposition reaction of the electrolyte is further suppressed during the charging and discharging of the secondary battery, and the decrease in discharge capacity is further suppressed even after repeated charging and discharging.

[0105] Unsaturated cyclic carbonate esters are cyclic carbonate esters that contain unsaturated carbon bonds (carbon-carbon double bonds). The number of unsaturated carbon bonds is not particularly limited; there may be one or two or more.

[0106] This unsaturated cyclic carbonate ester contains one or more of the following compounds: vinylene carbonate compounds, vinyl ethylene carbonate compounds, and methylene ethylene carbonate compounds.

[0107] Vinylen carbonate compounds are unsaturated cyclic carbonate esters having a vinylene-type structure. Specific examples of vinylene carbonate compounds include vinylene carbonate (1,3-dioxol-2-one), methylvinylene carbonate (4-methyl-1,3-dioxol-2-one), ethylvinylene carbonate (4-ethyl-1,3-dioxol-2-one), 4,5-dimethyl-1,3-dioxol-2-one, 4,5-diethyl-1,3-dioxol-2-one, 4-fluoro-1,3-dioxol-2-one, and 4-trifluoromethyl-1,3-dioxol-2-one.

[0108] Vinyl ethylene carbonate compounds are unsaturated cyclic carbonate esters having a vinyl ethylene carbonate-type structure. Specific examples of vinyl ethylene carbonate compounds include vinyl ethylene carbonate (4-vinyl-1,3-dioxolan-2-one), 4-methyl-4-vinyl-1,3-dioxolan-2-one, 4-ethyl-4-vinyl-1,3-dioxolan-2-one, 4-n-propyl-4-vinyl-1,3-dioxolan-2-one, 5-methyl-4-vinyl-1,3-dioxolan-2-one, 4,4-divinyl-1,3-dioxolan-2-one, and 4,5-divinyl-1,3-dioxolan-2-one.

[0109] Methylene carbonate compounds are unsaturated cyclic carbonate esters having a methylene carbonate-type structure. Specific examples of methylene carbonate compounds include methylene carbonate (4-methylene-1,3-dioxolan-2-one), 4,4-dimethyl-5-methylene-1,3-dioxolan-2-one, and 4,4-diethyl-5-methylene-1,3-dioxolan-2-one. Here, only compounds having one methylene group are given as examples of methylene carbonate compounds, but these methylene carbonate compounds may have two or more methylene groups.

[0110] Furthermore, cyclic carbonate esters containing unsaturated carbon bonds are classified as unsaturated cyclic carbonate esters, and do not fall under either fluorinated cyclic carbonate esters or cyanated cyclic carbonate esters.

[0111] Fluorinated cyclic carbonates are cyclic carbonates that contain fluorine as a constituent element. The number of fluorine atoms is not particularly limited; there may be one or two or more. In other words, fluorinated cyclic carbonates are compounds in which one or more hydrogen atoms in a cyclic carbonate are substituted with fluorine.

[0112] Specific examples of fluorinated cyclic carbonate esters include fluoroethylene (4-fluoro-1,3-dioxolan-2-one) and difluoroethylene (4,5-difluoro-1,3-dioxolan-2-one).

[0113] Furthermore, cyclic carbonate esters containing fluorine as a constituent element are classified as fluorinated cyclic carbonate esters, and not as unsaturated cyclic carbonate esters or cyanated cyclic carbonate esters.

[0114] A cyanated cyclic carbonate ester is a cyclic carbonate ester containing a cyano group. The number of cyano groups is not particularly limited; there may be one or two or more. In other words, a cyanated cyclic carbonate ester is a compound in which one or more hydrogen atoms of a cyclic carbonate ester are substituted with cyano groups.

[0115] Specific examples of cyanated cyclic carbonate esters include ethylene cyanocarbonate (4-cyano-1,3-dioxolan-2-one) and ethylene dicyanocarbonate (4,5-dicyano-1,3-dioxolan-2-one).

[0116] Furthermore, cyclic carbonate esters containing a cyano group are classified as cyanated cyclic carbonate esters, and not as unsaturated cyclic carbonate esters or fluorinated cyclic carbonate esters.

[0117] (Sulfonic acid esters, sulfuric acid esters, sulfite esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfonic acid carboxylic acid anhydrides, and sulfobenzoic acid imides) Furthermore, the additives are one or more of the following: sulfonic acid esters, sulfuric acid esters, sulfite esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfonic acid carboxylic acid anhydrides, and sulfobenzoic acid imides. This is because it improves the electrochemical stability of the electrolyte. As a result, the decomposition reaction of the electrolyte is further suppressed during the charging and discharging of the secondary battery, and the decrease in discharge capacity is further suppressed even after repeated charging and discharging.

[0118] Specific examples of sulfonic acid esters include 1,3-propanesultone, 1-propene-1,3-sultone, 1,4-butanesultone, 2,4-butanesultone, and propargyl methanesulfonate.

[0119] Specific examples of sulfate esters include 1,3,2-dioxathiolane 2,2-dioxide, 1,3,2-dioxatiane 2,2-dioxide, and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane.

[0120] Specific examples of sulfite esters include 1,3-propanesultone, 1-propene-1,3-sultone, 1,4-butanesultone, 2,4-butanesultone, and propargyl methanesulfonic acid. Specific examples of sulfite esters include 1,3,2-dioxathiolane 2-oxide and 4-methyl-1,3,2-dioxathiolane 2-oxide.

[0121] Specific examples of dicarboxylic acid anhydrides include 1,4-dioxan-2,6-dione, succinic anhydride, and glutaric anhydride.

[0122] Specific examples of disulfonic anhydrides include 1,2-ethanedisulfonic anhydride, 1,3-propanedisulfonic anhydride, and hexafluoro1,3-propanedisulfonic anhydride.

[0123] Specific examples of sulfonic acid carboxylic acid anhydrides include 2-sulfobenzoic acid anhydride and 2,2-dioxoxathiolan-5-one.

[0124] Specific examples of sulfobenzoic acid imides include o-sulfobenzimide and N-methylsaccharin.

[0125] As described above, the coating portion 222 of the negative electrode active material 220 contains a coating element as a constituent element. When the source of this coating element is an electrolyte, the electrolyte may further contain one or more of the coating compounds. This coating compound is a compound that contains one or more of nickel, iron, and copper as constituent elements. The content of the coating compound in the electrolyte is not particularly limited and can be set arbitrarily.

[0126] The types of coating compounds containing nickel as a constituent element are not particularly limited, but specifically include nickel acetate, nickel(II) diethyldithiocarbamate, and bis(cyclopentadienyl)nickel.

[0127] The types of coating compounds containing iron as a constituent element are not particularly limited, but specifically include iron acetate, iron(III) dimethyldithiocarbamate, bis(cyclopentadienyl) iron, tris(1,3-diphenyl-1,3-propanedionato) iron, and tris(hexafluoroacetylacetonato) iron(III).

[0128] The types of coating compounds containing copper as a constituent element are not particularly limited, but specifically include copper acetate, tetrakis(acetonitrile)copper(I)tetrafluoroborate, tetrakis(acetonitrile)copper(I)hexafluorophosphorate, copper(II) dimethyldithiocarbamate, copper(II) tetrafluoroborate, and copper(I) thiocyanate.

[0129] (Nitrile compounds) Furthermore, the additive contains nitrile compounds. This is because it improves the electrochemical stability of the electrolyte. As a result, the decomposition reaction of the electrolyte is further suppressed during charging and discharging, so the decrease in discharge capacity is further suppressed even after repeated charging and discharging, and the generation of gases caused by the decomposition reaction of the electrolyte is also suppressed.

[0130] These nitrile compounds are compounds containing one or more cyano groups (-CN). Specific examples of nitrile compounds include octanenitrile, benzonitrile, phthalonitrile, succinonitrile, glutalonitrile, adiponitrile, sebaconitrile, 1,3,6-hexanetricarbonite, 3,3'-oxydipropionitrile, 3-butoxypropionitrile, ethylene glycol bispropionitrile ether, 1,2,2,3-tetracyanopropane, tetracyanopropane, fumaronitrile, 7,7,8,8-tetracyanoquinodimethane, cyclopentanecarbonite, 1,3,5-cyclohexanetricarbonite, and 1,3-bis(dicyanomethylidene)indan.

[0131] However, the cyanated cyclic carbonate esters mentioned above are excluded from the nitrile compounds described here.

[0132] <1-3. Operation> The secondary battery operates as follows:

[0133] During charging, lithium is released from the positive electrode 21 of the battery element 20, and this lithium is absorbed into the negative electrode 22 via the electrolyte. Conversely, during discharging, lithium is released from the negative electrode 22 of the battery element 20, and this lithium is absorbed into the positive electrode 21 via the electrolyte. During both charging and discharging, lithium is absorbed and released in an ionic state.

[0134] <1-4. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and negative electrode 22 are prepared according to the example procedure described below, and the electrolyte is prepared. The secondary battery is then assembled using the positive electrode 21 and negative electrode 22 together with the electrolyte, and the assembled secondary battery is subjected to stabilization treatment.

[0135] [Fabrication of the positive electrode] First, a positive electrode mixture is prepared by mixing the positive electrode active material, positive electrode binder, and positive electrode conductive agent together. Subsequently, a paste-like positive electrode mixture slurry is prepared by adding the positive electrode mixture to a solvent. This solvent may be an aqueous solvent or an organic solvent. Next, the positive electrode mixture slurry is applied to both sides of the positive electrode current collector 21A to form the positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B may be compressed and molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, the positive electrode 21 is manufactured by forming the positive electrode active material layer 21B on both sides of the positive electrode current collector 21A.

[0136] Furthermore, when using the positive electrode 21 as the source of the coating element, the positive electrode 21 is prepared by the same procedure, except that coating metal powder is added to the positive electrode mixture.

[0137] [Fabrication of the negative electrode] First, the central component 221, the negative electrode binder, and the negative electrode conductive agent are mixed together to form a positive electrode mixture. Subsequently, the negative electrode mixture is added to a solvent to prepare a paste-like negative electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. Next, the negative electrode mixture slurry is applied to both sides of the negative electrode current collector 22A to form the negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B may be compressed and molded using a roll press or the like. In this case, the negative electrode active material layer 22B may be heated, or the compression molding may be repeated multiple times.

[0138] Finally, as will be described later, after assembling the secondary battery, a stabilization treatment is performed on the assembled secondary battery. As a result, a coating portion 222 containing the coating element as a constituent element is formed on the surface of the central portion 221, and the negative electrode active material 220 including the central portion 221 and the coating portion 222 is formed.

[0139] Therefore, a negative electrode active material layer 22B containing the negative electrode active material 220 is formed on both sides of the negative electrode current collector 22A, thereby producing the negative electrode 22.

[0140] [Preparation of electrolyte solution] When preparing an electrolyte, an electrolyte salt is added to the solvent, and then a thiazole compound is added to the solvent. This causes the electrolyte salt and the thiazole compound to dissolve or disperse in the solvent, thus preparing the electrolyte.

[0141] When using an electrolyte as a source of coating elements, the electrolyte is prepared using the same procedure, except that the coating compound is further added to the solvent.

[0142] [Assembly of rechargeable batteries] First, the positive electrode lead 25 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding, and the negative electrode lead 26 is connected to the negative electrode current collector 22A of the negative electrode 22 using a joining method such as welding. Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23, and then the positive electrode 21, the negative electrode 22 and the separator 23 are wound together to create a wound body (not shown) having a winding center space 20S. This wound body has the same configuration as the battery element 20, except that the positive electrode 21, the negative electrode 22 and the separator 23 are not impregnated with electrolyte. Next, a center pin 24 is inserted into the winding center space 20S of the wound body.

[0143] Next, with the winding body sandwiched between the insulating plates 12 and 13, the winding body and insulating plates 12 and 13 are housed inside the battery can 11. In this case, the positive electrode lead 25 is connected to the safety valve mechanism 15 using a joining method such as welding, and the negative electrode lead 26 is connected to the battery can 11 using a joining method such as welding. Subsequently, the electrolyte is injected into the battery can 11, thereby impregnating the winding body with the electrolyte. As a result, the positive electrode 21, the negative electrode 22, and the separator 23 are each impregnated with the electrolyte, and the battery element 20 is fabricated.

[0144] Finally, the battery cover 14, safety valve mechanism 15, and PTC element 16 are placed inside the battery case 11, and then the battery case 11 is crimped via the gasket 17. This fixes the battery cover 14, safety valve mechanism 15, and PTC element 16 to the battery case 11, and also seals the battery element 20 inside the battery case 11, thus assembling the secondary battery.

[0145] [Stabilization of secondary batteries] The assembled secondary battery is charged and discharged. Various conditions such as ambient temperature, number of charge / discharge cycles, and charge / discharge conditions can be set arbitrarily.

[0146] In this stabilization process for the secondary battery, as described above, a coating portion 222 containing the coating element as a constituent element is formed on the surface of the central portion 221, thereby forming a negative electrode active material 220 including the central portion 221 and the coating portion 222. In this case, a coating may also be formed on the surface of the positive electrode active material.

[0147] Therefore, the state of the secondary battery becomes electrochemically stable, and the secondary battery is completed.

[0148] <1-5. Mechanism and Effects> In this secondary battery, the negative electrode active material 220 of the negative electrode 22 includes a central part 221 and a coating part 222, the coating part 222 contains one or more of nickel, iron, and copper as coating elements, and the electrolyte contains a thiazole compound.

[0149] In this case, as described above, the physical strength of the coating portion 222 is improved by the synergistic effect between the coating element and the thiazole-type compound. As a result, even with repeated charging and discharging, the decomposition reaction of the electrolyte is suppressed, and the decrease in discharge capacity is suppressed. Therefore, excellent battery characteristics can be obtained.

[0150] In particular, if the central part 221 contains a metallic material, and that metallic material contains silicon as a constituent element, a sufficiently high energy density can be obtained, thus enabling a higher effect.

[0151] Furthermore, if the content of thiazole-type compounds in the electrolyte is between 0.001% and 5% by weight, the physical strength of the coating portion 222 is sufficiently improved. Therefore, the decomposition reaction of the electrolyte is sufficiently suppressed, and a higher effect can be obtained.

[0152] Furthermore, if the electrolyte contains one or more of the following: unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, and cyanated cyclic carbonate esters, the decomposition reaction of the electrolyte is further suppressed, resulting in a higher effectiveness.

[0153] Furthermore, if the electrolyte contains one or more of the following: sulfonic acid esters, sulfuric acid esters, sulfite esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfonic acid carboxylic acid anhydrides, and sulfobenzoic acid imides, the decomposition reaction of the electrolyte is further suppressed, thus achieving a higher effect.

[0154] Furthermore, if the secondary battery is a lithium-ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the intercalation and deintercalation of lithium, thus achieving a higher level of efficiency.

[0155] <2. Variant> The configuration of the secondary battery described above can be modified as appropriate, as explained below. However, any two or more of the variations described below may be combined with each other.

[0156] [Example 1] The explanation described the case where the battery structure of a secondary battery is cylindrical. However, although not specifically illustrated here, the type of battery structure is not particularly limited, and may include laminate film type, rectangular type, coin type, button type, etc.

[0157] [Differentiation 2] A porous membrane separator 23 was used. However, although not specifically shown in the diagram, a laminated separator containing a polymer compound layer may also be used.

[0158] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both sides of the porous membrane. This improves the adhesion of the separator to the positive electrode 21 and the negative electrode 22, thereby suppressing misalignment (winding misalignment) of the battery element 20. As a result, swelling of the secondary battery is suppressed even if decomposition reactions of the electrolyte occur. The polymer compound layer contains polymer compounds such as polyvinylidene fluoride. Polyvinylidene fluoride and similar compounds are chosen because they have excellent physical strength and are electrochemically stable.

[0159] Furthermore, one or both of the porous membrane and the polymer compound layer may contain one or more types of insulating particles. This is because the multiple insulating particles promote heat dissipation when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The insulating particles include one or both of inorganic materials and resin materials. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials include acrylic resin and styrene resin.

[0160] When fabricating a laminated separator, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is applied to one or both sides of a porous membrane. In this case, if necessary, multiple insulating particles may be added to the precursor solution.

[0161] Even when using this stacked separator, lithium ions can move between the positive electrode 21 and the negative electrode 22, thus achieving a similar effect. In this case, as mentioned above, the safety of the secondary battery is improved, resulting in an even greater effect.

[0162] [Difference 3] A liquid electrolyte solution was used. However, although not specifically illustrated here, a gel-like electrolyte layer may also be used.

[0163] In the battery element 20 using an electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23 and the electrolyte layer, and the positive electrode 21, negative electrode 22, separator 23, and electrolyte layer are wound together. This electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

[0164] Specifically, the electrolyte layer contains a polymer compound along with the electrolyte, and the electrolyte is held in place by the polymer compound. This prevents leakage of the electrolyte. The composition of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolyte, polymer compound, and solvent is prepared, and then the precursor solution is applied to one or both sides of the positive electrode 21 and the negative electrode 22, respectively.

[0165] Even when this electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, thus achieving a similar effect. In this case, in particular, as mentioned above, leakage of the electrolyte is prevented, resulting in an even greater effect.

[0166] <3. Applications of rechargeable batteries> The uses (application examples) of secondary batteries are not particularly limited. Secondary batteries used as power sources may be the primary power source or the auxiliary power source in electronic devices and electric vehicles, etc. A primary power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source may be a power source used in place of the primary power source, or a power source that can be switched from the primary power source.

[0167] Specific examples of secondary battery applications are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals; backup power supplies and storage devices such as memory cards; power tools such as electric drills and electric saws; battery packs installed in electronic devices; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles); and power storage systems such as household or industrial battery systems that store power in preparation for emergencies. In these applications, one secondary battery may be used, or multiple secondary batteries may be used.

[0168] The battery pack may use individual cells or a battery pack. An electric vehicle is a vehicle that operates (drives) using a secondary battery as a power source, and may also be a hybrid vehicle equipped with other power sources in addition to the secondary battery. In a household power storage system, the electricity stored in the secondary battery, which is the power storage source, can be used to power household electrical appliances, etc.

[0169] Here, we will specifically explain one example of a secondary battery application. The configuration of the application example described below is merely an example and can be modified as needed.

[0170] Figure 4 shows the block configuration of the battery pack. The battery pack described here is a single rechargeable battery pack (a so-called soft pack) and is installed in electronic devices such as smartphones.

[0171] As shown in Figure 4, this battery pack comprises a power supply 51 and a circuit board 52. The circuit board 52 is connected to the power supply 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0172] The power supply 51 includes one secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. Since the power supply 51 can be connected to the outside via the positive terminal 53 and the negative terminal 54, it can be charged and discharged. The circuit board 52 includes a control unit 56, a switch 57, a PTC element 58, and a temperature detection unit 59. However, the PTC element 58 may be omitted.

[0173] The control unit 56 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. This control unit 56 detects and controls the usage status of the power supply 51 as needed.

[0174] Furthermore, when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or over-discharge detection voltage, the control unit 56 disconnects the switch 57 to prevent charging current from flowing through the current path of the power supply 51. The overcharge detection voltage is not particularly limited, but specifically it is 4.20V ± 0.05V, and the over-discharge detection voltage is not particularly limited, but specifically it is 2.40V ± 0.1V.

[0175] Switch 57 includes a charge control switch, a discharge control switch, a charging diode, and a discharging diode, and switches the connection between the power supply 51 and external equipment according to the instructions of the control unit 56. This switch 57 includes a field-effect transistor (MOSFET) using a metal oxide semiconductor, and the charge / discharge current is detected based on the ON resistance of switch 57.

[0176] The temperature detection unit 59 includes a temperature detection element such as a thermistor. This temperature detection unit 59 measures the temperature of the power supply 51 using the temperature detection terminal 55 and outputs the temperature measurement result to the control unit 56. The temperature measurement result measured by the temperature detection unit 59 is used when the control unit 56 performs charge / discharge control in the event of abnormal heat generation and when the control unit 56 performs correction processing when calculating the remaining capacity. [Examples]

[0177] An example of this technology will be described below.

[0178] <Examples 1-48 and Comparative Examples 1-24> As explained below, after manufacturing the rechargeable batteries, their battery characteristics were evaluated.

[0179] [Manufacturing of secondary batteries] The cylindrical lithium-ion secondary batteries shown in Figures 1 and 2 were manufactured using the procedure described below.

[0180] (Fabrication of the positive electrode) First, 94 parts by mass of positive electrode active material (lithium cobaltate (LiCoO2)), a lithium-containing compound (oxide), 3 parts by mass of positive electrode binder (polyvinylidene fluoride), and 3 parts by mass of positive electrode conductive agent (acetylene black) were mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to both sides of the positive electrode current collector 21A (a strip of aluminum foil with a thickness of 12 μm) using a coating apparatus, and the positive electrode mixture slurry was dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B was compressed and molded using a roll press. This completed the production of the positive electrode 21.

[0181] When using the positive electrode 21 as a source of coating elements (nickel (Ni), iron (Fe), and copper (Cu)), the positive electrode 21 was prepared using the same procedure as above, except that coating metal powder (nickel powder, iron powder, and copper powder, median diameter D50 = 0.2 μm) was added to the positive electrode mixture. In this case, a portion of the positive electrode conductive agent was replaced with coating metal powder, and the content of coating metal powder in the positive electrode mixture was set to 0.0005 parts by mass. When using two or more types of coating metal powder, the content of each of those two or more types of coating metal powder was set to the same amount.

[0182] (Fabrication of the negative electrode) First, a negative electrode mixture was prepared by mixing 93 parts by mass of negative electrode active material (center 221) and 7 parts by mass of negative electrode binder (polyvinylidene fluoride). For the center 221, a mixture of 63 parts by mass of artificial graphite, a carbon material, and 30 parts by mass of silicon oxide (SiO), a metallic material, was used.

[0183] Next, the negative electrode mixture was added to a solvent (the organic solvent N-methyl-2-pyrrolidone), and the solvent was stirred to prepare a paste-like negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (a strip of copper foil with a thickness of 15 μm) using a coating apparatus, and the negative electrode mixture slurry was dried to form the negative electrode active material layer 22B. Subsequently, the negative electrode active material layer 22B was compression molded using a roll press machine.

[0184] Finally, as will be described later, after assembling the secondary battery, a stabilization treatment was performed on the assembled secondary battery. As a result, a coating portion 222 containing the coating element as a constituent element was formed on the surface of the central portion 221, and thus the negative electrode active material 220 including the central portion 221 and the coating portion 222 was formed. Thus, the negative electrode 22 was fabricated.

[0185] Furthermore, the negative electrode 22 was fabricated using the same procedure, except that only carbon material was used for the central part 221 instead of metallic material.

[0186] Here, for comparison, the negative electrode 22 was fabricated using the same procedure, except that a coating element was not used, thereby forming a coating portion 222 that did not contain the coating element as a constituent element.

[0187] (Preparation of electrolyte solution) Solvents (ethylene carbonate, a cyclic carbonate ester, and dimethyl carbonate, a chain carbonate ester) were prepared. The mixing ratio (by weight) of the solvents was ethylene carbonate:dimethyl carbonate = 20:80. Next, an electrolyte salt (LiPF6, a lithium salt) was added to the solvent, and the solvent was stirred. The electrolyte salt content was 1.2 mol / kg relative to the solvent. Finally, a thiazole compound was added to the solvent containing the electrolyte salt, and the solvent was stirred. The classification, type, and content (by weight %) of the thiazole compound are shown in Tables 1 to 5. This completed the preparation of the electrolyte solution.

[0188] When using an electrolyte as a source of coating elements, the electrolyte was prepared using the same procedure as above, except that the coating compound was added to a solvent containing a thiazole-type compound. In this case, bis(cyclopentadienyl)nickel was used as the coating compound containing nickel, bis(cyclopentadienyl)iron was used as the coating compound containing iron, and tetrakis(acetonitrile)copper(I)hexafluorophosphorate was used as the coating compound containing copper. The content of the coating compound in the electrolyte was set to 0.05% by weight. When using two or more types of coating compounds, the content of each of those two or more coating compounds was set to be equal.

[0189] Here, the electrolyte was prepared using the same procedure, except that a thiazole compound was not used for comparison.

[0190] The meaning of the "classifications" shown in Tables 1 to 5 is as follows: "1st" represents the first thiazole type compound, "2nd" represents the second thiazole type compound, "3rd" represents the third thiazole type compound, and "4th" represents the fourth thiazole type compound.

[0191] (Assembly of secondary batteries) First, the positive electrode lead 25 (aluminum foil) was welded to the positive electrode current collector 21A of the positive electrode 21, and the negative electrode lead 26 (copper foil) was welded to the negative electrode current collector 22A of the negative electrode 22.

[0192] Next, the positive electrode 21 and the negative electrode 22 were stacked on top of each other via a separator 23 (a microporous polyethylene film with a thickness of 15 μm), and then the positive electrode 21, the negative electrode 22, and the separator 23 were wound together to create a wound body having a winding center space 20S. Subsequently, a center pin 24 was inserted into the winding center space 20S of the wound body.

[0193] Next, insulating plates 12 and 13 were placed inside the battery can 11 along with the wound material. In this case, the positive electrode lead 25 was welded to the safety valve mechanism 15, and the negative electrode lead 26 was welded to the battery can 11. Subsequently, electrolyte was injected into the battery can 11. As a result, the wound material was impregnated with electrolyte, and the battery element 20 was fabricated.

[0194] Finally, the battery cover 14, safety valve mechanism 15, and PTC element 16 were placed inside the battery case 11, and then the battery case 11 was crimped via the gasket 17. This sealed the battery case 11, and the secondary battery was assembled.

[0195] (Stabilization of secondary batteries) A secondary battery was subjected to one charge-discharge cycle in a normal temperature environment (temperature = 23°C). During charging, constant current charging was performed at a current of 0.1C until the voltage reached 4.2V, and then constant voltage charging was performed at that voltage of 4.2V until the current reached 0.05C. During discharging, constant current discharge was performed at a current of 0.1C until the voltage reached 3.0V. 0.1C is the current value required to completely discharge the battery capacity (theoretical capacity) in 10 hours, and 0.05C is the current value required to completely discharge the battery capacity in 20 hours.

[0196] As a result, as described above, a coating portion 222 containing the coating element as a constituent element was formed on the surface of the central portion 221, thus forming the negative electrode active material 220. Therefore, the state of the secondary battery was electrochemically stabilized, and the secondary battery was completed.

[0197] Furthermore, after the secondary battery was completed, the negative electrode active material 220 was recovered by disassembling the battery. The results of the analysis of the negative electrode active material 220 using a scanning electron microscope (Scanning electron microscope SU3800 / SU3900 manufactured by Hi-Tech Corporation), an energy-dispersive X-ray spectrometer (EDS), and an X-ray photoelectron spectroscopy (EDX) are shown in Tables 1 to 5.

[0198] Furthermore, after the completion of the secondary battery, the content (weight %) of thiazole-type compounds in the electrolyte was measured using ICP emission spectrometry, and the results are shown in Tables 1 to 5.

[0199] [Evaluation of battery characteristics] The battery's cycle characteristics were evaluated using the procedure described below, and the results shown in Tables 1 to 5 were obtained.

[0200] First, the secondary battery was charged in a high-temperature environment (temperature = 50°C), and then the charged secondary battery was left undisturbed in the same environment (undisturbed time = 3 hours). During charging, constant current charging was performed at a current of 1C until the voltage reached 4.2V, and then constant voltage charging was performed at that voltage of 4.2V until the current reached 0.05C. 1C is the current value required to completely discharge the battery capacity in one hour.

[0201] Next, the discharge capacity (discharge capacity in the first cycle) was measured by discharging the secondary battery in the same environment. During discharge, a constant current discharge was performed at a current of 3C until the voltage reached 3.0V. 3C is the current value required to completely discharge the battery capacity in 1 / 3 of an hour.

[0202] Next, the secondary battery was repeatedly charged and discharged in the same environment until it reached 100 cycles, and the discharge capacity (discharge capacity at 100 cycles) was measured. The charge and discharge conditions for the second and subsequent cycles were the same as those for the first cycle.

[0203] Finally, the capacity retention rate (%) was calculated based on the formula: Capacity retention rate (%) = (Discharge capacity at 100 cycles / Discharge capacity at 1 cycle) × 100, which is an indicator for evaluating cycle characteristics.

[0204] [Table 1]

[0205] [Table 2]

[0206] [Table 3]

[0207] [Table 4]

[0208] [Table 5]

[0209] [Consideration] As shown in Tables 1 to 5, the capacity retention rate varied depending on the configuration of the secondary battery.

[0210] Specifically, when both carbon materials and metallic materials were used as the negative electrode active material (Examples 1-45 and Comparative Examples 1-12), the results described below were obtained.

[0211] Here, the volume retention rate in the case where the coating portion 222 does not contain coating elements as constituent elements and the electrolyte does not contain thiazole-type compounds (Comparative Example 1) is used as the comparison standard.

[0212] When the coating portion 222 contained the coating element as a constituent element, and the electrolyte did not contain a thiazole-type compound (Comparative Examples 2-11), the volume retention rate decreased.

[0213] Furthermore, when the coating portion 222 did not contain the coating element as a constituent element, and the electrolyte contained a thiazole-type compound (Comparative Example 12), the volume retention rate increased slightly.

[0214] Considering these results (Comparative Examples 1-12), it is expected that if the coating portion 222 contains the coating element as a constituent element and the electrolyte contains a thiazole-type compound, the volume retention rate will be maintained at approximately the same level.

[0215] However, in reality, results different from those predicted above were obtained. Specifically, when the coating portion 222 contained the coating element as a constituent element and the electrolyte contained a thiazole-type compound (Examples 1 to 45), the volume retention rate increased significantly.

[0216] The reason for the significant increase in capacity retention is thought to be that, as described above, a coating with excellent electrochemical durability was formed on the surface of the negative electrode 22 due to the synergistic effect between the coating element and the thiazole-type compound.

[0217] In particular, when the coating portion 222 contains the coating element as a constituent element and the electrolyte contains a thiazole-type compound (Examples 1 to 45), the tendencies described below were observed.

[0218] Firstly, a high volume retention rate was obtained regardless of whether the first, second, third, or fourth thiazole-type compound was used. Secondly, the volume retention rate increased further when the content of the thiazole-type compound in the electrolyte was between 0.001% and 5% by weight. Thirdly, a high volume retention rate was obtained regardless of the type of source of the coating element.

[0219] It should be noted that the results described here are not limited to cases where both carbon materials and metallic materials are used as the negative electrode active material (Examples 1-45 and Comparative Examples 1-12), but were similarly obtained when only carbon materials were used as the negative electrode active material (Examples 46-48 and Comparative Examples 13-24).

[0220] <Examples 49-54> As shown in Table 6, secondary batteries were prepared using the same procedure as in Example 4, except that the electrolyte contained an additive (unsaturated cyclic carbonate ester, fluorinated cyclic carbonate ester, or cyanated cyclic carbonate ester), and then the battery characteristics were evaluated. The classification, type, and content (weight %) of the additives are as shown in Table 6.

[0221] Specifically, vinylene carbonate (VC) was used as the unsaturated cyclic carbonate ester. Ethylene fluorocarbonate (FEC) was used as the fluorinated cyclic carbonate ester. Ethylene cyanocarbonate (CEC) was used as the cyanated cyclic carbonate ester.

[0222] [Table 6]

[0223] As shown in Table 6, when the electrolyte contained an additive (unsaturated cyclic carbonate ester, fluorinated cyclic carbonate ester, or cyanated cyclic carbonate ester) (Examples 49-54), the volume retention rate was greater compared to when the electrolyte did not contain an additive (Example 4).

[0224] <Examples 55-74> As shown in Tables 7 and 8, secondary batteries were prepared using the same procedure as in Example 4, except that the electrolyte contained additives (sulfonic acid esters, sulfuric acid esters, sulfite esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfonic acid carboxylic acid anhydrides, or sulfobenzoic acid imides), and then the battery characteristics were evaluated. The classification, type, and content (weight %) of the additives are as shown in Tables 7 and 8.

[0225] Specifically, the sulfonic acid esters used were 1,3-propanesultone (PS), 1-propene-1,3-sultone (PRS), 1,4-butanesultone (BS1), 2,4-butanesultone (BS2), and propargyl methanesulfonic acid ester (MSP).

[0226] As sulfate esters, 1,3,2-dioxathione 2,2-dioxide (OTO), 1,3,2-dioxatian 2,2-dioxide (OTA), and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathione (SOTO) were used.

[0227] As sulfite esters, 1,3,2-dioxathiolane 2-oxide (DTO) and 4-methyl-1,3,2-dioxathiolane 2-oxide (MDTO) were used.

[0228] As dicarboxylic acid anhydrides, 1,4-dioxan-2,6-dione (DOD), succinic anhydride (SA), and glutaric anhydride (GA) were used.

[0229] As disulfonic anhydrides, 1,2-ethanedisulfonic anhydride (ESA), 1,3-propanedisulfonic anhydride (PSA), and hexafluoro-1,3-propanedisulfonic anhydride (FPSA) were used.

[0230] As sulfonic acid carboxylic acid anhydrides, 2-sulfobenzoic acid anhydride (SBA) and 2,2-dioxoxathiolan-5-one (DOTO) were used.

[0231] As sulfobenzoimides, o-sulfobenzimide (SBI) and N-methylsaccharin (NMS) were used.

[0232] [Table 7]

[0233] [Table 8]

[0234] As shown in Tables 7 and 8, when the electrolyte contained additives (sulfonic acid esters, sulfuric acid esters, sulfite esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfonic acid carboxylic acid anhydrides, or sulfobenzoic acid imides) (Examples 55-74), the volume retention rate was greater compared to when the electrolyte did not contain additives (Example 4).

[0235] [summary] The results shown in Tables 1 to 8 indicate that when the negative electrode active material 220 of the negative electrode 22 includes a central part 221 and a coating portion 222, and the coating portion 222 contains coating elements as constituent elements, and the electrolyte contains a thiazole-type compound, a high capacity retention rate was obtained, resulting in improved cycle characteristics. Therefore, excellent battery characteristics were obtained in a secondary battery using an electrolyte.

[0236] Although the present technology has been described above with reference to one embodiment and one example, the configuration of the present technology is not limited to the configuration described in the one embodiment and one example, and can be modified in various ways.

[0237] Specifically, the case where the element structure of the battery element is a wound type has been described. However, since the element structure of the battery element is not particularly limited, other element structures such as a laminated type and a ninety-nine-fold type may also be used. In the laminated type, the positive electrode and the negative electrode are alternately laminated via a separator, and in the ninety-nine-fold type, the positive electrode and the negative electrode are folded in a zigzag manner while facing each other via a separator.

[0238] In addition, although the case where the electrode reactant is lithium has been described, the electrode reactant is not particularly limited. Specifically, the electrode reactant may be another alkali metal such as sodium and potassium, or an alkaline earth metal such as beryllium, magnesium, and calcium as described above. In addition, the electrode reactant may be another light metal such as aluminum.

[0239] The effects described in this specification are merely examples, and the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

[0240] Incidentally, the present technology can also adopt the following configuration. <1> A positive electrode, [[ID=ID=18]] A negative electrode containing a negative electrode active material, An electrolytic solution containing a thiazole-type compound And comprising, The negative electrode active material is A central portion that occludes and releases an electrode reactant, A coating portion that covers the surface of the central portion [[ID=ID=31]]And including, The coating portion contains at least one of nickel, iron, and copper as a constituent element, The thiazole-type compound includes at least one of a compound represented by formula (1), a compound represented by formula (2), a compound represented by formula (3), and a compound represented by formula (4), A secondary battery.

Chemical formula

Claims

1. Positive electrode and, A negative electrode containing a negative electrode active material, Electrolyte containing thiazole-type compounds and Equipped with, The aforementioned negative electrode active material is The central part that absorbs and releases electrode reactants, A covering portion that covers the surface of the central part and Includes, The coating portion contains at least one of nickel, iron, and copper as a constituent element. The thiazole-type compound comprises at least one of the compounds represented by formula (1), formula (2), formula (3), and formula (4). Secondary battery. 【Chemistry 1】 (Each of R1 to R28 is one of the following: hydrogen, fluorine, alkyl group, alkenyl group, alkynyl group, cycloalkyl group, aryl group, alkoxy group, fluorinated alkyl group, fluorinated alkenyl group, fluorinated alkynyl group, fluorinated cycloalkyl group, fluorinated aryl group, fluorinated alkoxy group, amino group, carboxylic acid ester group, or a monovalent bond group formed by the bonding of two or more of these groups.)

2. The aforementioned central part includes a metallic material, The aforementioned metallic material contains silicon as a constituent element. The secondary battery according to claim 1.

3. The content of the thiazole-type compound in the electrolyte is 0.001% by weight or more and 5% by weight or less. The secondary battery according to claim 1.

4. The electrolyte further comprises at least one of unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, and cyanated cyclic carbonate esters. A secondary battery according to any one of claims 1 to 3.

5. The electrolyte further comprises at least one of the following: sulfonic acid ester, sulfuric acid ester, sulfite ester, dicarboxylic acid anhydride, disulfonic acid anhydride, sulfonic acid carboxylic acid anhydride, and sulfobenzoic acid imide. A secondary battery according to any one of claims 1 to 3.

6. Lithium-ion rechargeable batteries, A secondary battery according to any one of claims 1 to 3.

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