Secondary battery

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

secondary battery

[0001] The present technology relates to a secondary battery.

[0002] Due to the widespread use of various electronic devices such as mobile phones, secondary batteries have been developed as small, lightweight power sources that can provide high energy density. These secondary batteries contain a positive electrode, a negative electrode, and an electrolyte solution, and various studies have been conducted on the configuration of these secondary batteries.

[0003] Specifically, a benzotriazole derivative having a specific structure is contained in the electrolyte solution (see, for example, Patent Documents 1 and 2). Also, a benzothiazole derivative having a specific structure is contained in the electrolyte solution (see, for example, Patent Documents 3 and 4).

[0004] Japanese Patent Publication No. 2001-273927, Japanese Patent Publication No. 2013-513923, Japanese Patent No. 6056721, International Publication No. 2019 / 181278, Pamphlet

[0005] Although various studies have been conducted on the configuration of secondary batteries, the battery characteristics of the secondary batteries are still insufficient and there is room for improvement.

[0006] There is a demand for a secondary battery that can provide excellent battery characteristics.

[0007] According to one embodiment of the present disclosure, there is provided a secondary battery including a positive electrode, a negative electrode including a negative electrode active material, and an electrolyte including a thiazole-type compound. The negative electrode active material includes a core portion that occludes and releases an electrode reactant and a coating portion that coats the surface of the core portion. The coating portion includes 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).

[0008] (Each of R1 to R28 is any one of hydrogen, fluorine, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, an alkoxy group, a fluorinated alkyl group, a fluorinated alkenyl group, a fluorinated alkynyl group, a fluorinated cycloalkyl group, a fluorinated aryl group, a fluorinated alkoxy group, an amino group, a carboxylic acid ester group, and a monovalent bonding group in which two or more of these groups are bonded to each other.)

[0009] The details of the "carboxylic acid ester group" and the "monovalent bonding group" will be described later.

[0010] According to a secondary battery of one embodiment of the present technology, the negative electrode active material includes a core and a coating portion, the coating portion includes at least one of nickel, iron, and copper as a constituent element, and the electrolyte solution includes a thiazole-type compound, so that excellent battery characteristics can be obtained.

[0011] Note that the effects of the present technology are not necessarily limited to the effects described here, but may be any of a series of effects related to the present technology described below.

[0012] Fig. 2 is a cross-sectional view showing the configuration of a secondary battery according to an embodiment of the present technology. Fig. 3 is a cross-sectional view showing the configuration of the battery element shown in Fig. 1. Fig. 4 is a cross-sectional view showing an enlarged schematic view of the configuration of a negative electrode active material. Fig. 5 is a block diagram showing the configuration of an application example of a secondary battery.

[0013] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The description will be made in the following order: 1. Secondary battery 1-1. Overall configuration 1-2. Detailed configuration of electrolyte solution 1-3. Operation 1-4. Manufacturing method 1-5. Actions and effects 2. Modifications 3. Uses of secondary battery

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

[0015] The secondary battery described here is a secondary battery that obtains battery capacity by utilizing the absorption and desorption of electrode reactants, and is equipped with a positive electrode, a negative electrode, and an electrolyte.

[0016] In this secondary battery, the charge capacity of the negative electrode is larger than the discharge 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 deposition of electrode reactants on the surface of the negative electrode during charging.

[0017] The type of electrode reactant is not particularly limited, but specifically includes light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, and alkaline earth metals include beryllium, magnesium, and calcium.

[0018] In the following, we will take the case where the electrode reactant is lithium as an example. A secondary battery that obtains battery capacity by utilizing the absorption and desorption of lithium is called a lithium ion secondary battery. In this lithium ion secondary battery, lithium is absorbed and desorbed in the ionic state.

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

[0020] 1 and 2, this secondary battery mainly includes a battery can 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 the cylindrical battery can 11.

[0021] [Battery Can] As shown in FIG. 1 , the battery can 11 is a housing member that houses the battery element 20 and other components. The battery can 11 has an open end and a closed end, and thus has a hollow structure. The battery can 11 contains one or more metal materials such as iron, aluminum, iron alloys, and aluminum alloys. The surface of the battery can 11 may be plated with a metal material such as nickel.

[0022] A battery lid 14, a safety valve mechanism 15, and a thermosensitive resistor (PTC element) 16 are crimped to one open end of the battery can 11 via a gasket 17. This seals the battery can 11 with the battery lid 14. Here, the battery lid 14 contains the same material as the material from which the battery can 11 is formed. The safety valve mechanism 15 and the PTC element 16 are each provided inside the battery lid 14, and the safety valve mechanism 15 is electrically connected to the battery lid 14 via the PTC element 16. The gasket 17 contains an insulating material, and the surface of the gasket 17 may be coated with asphalt or the like.

[0023] In this safety valve mechanism 15, when the internal pressure of the battery can 11 reaches a certain level due to an internal short circuit, external heating, or the like, the disk plate 15A reverses, thereby cutting off the electrical connection between the battery lid 14 and the battery element 20. To prevent abnormal heat generation due to a large current, the electrical resistance of the PTC element 16 increases with increasing temperature.

[0024] 1, the insulating plates 12 and 13 are arranged to face each other with the battery element 20 interposed therebetween.

[0025] [Battery Element] As shown in FIGS. 1 and 2, the battery element 20 is a power generating element including 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 with a separator 23 interposed therebetween, and are wound while facing each other with the separator 23 interposed therebetween. A center pin 24 is inserted into a 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 FIG. 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. The positive electrode current collector 21A contains a conductive material such as a metal material, and a specific example of the conductive material is aluminum.

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

[0030] Here, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A, and therefore 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 includes a lithium-containing compound. This lithium-containing compound is a compound containing lithium and one or more transition metal elements as constituent elements, and may further include 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 transition metal elements, but specifically includes elements belonging to Groups 2 to 15 of the long period periodic table. The type of lithium-containing compound is not particularly limited, but specifically includes oxides, phosphate compounds, silicate compounds, borate compounds, and the like.

[0032] A specific example of the oxide is LiNiO 2 , LiCoO 2 , LiCo 0.98 Al 0.01 Mg 0.01 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 and LiMn 2 O 4 Specific examples of phosphate compounds include LiFePO 4 , LiMnPO 4 and LiFe 0.5 Mn 0.5 P.O. 4 And so on.

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

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

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

[0036] (Negative Electrode) As shown in FIG. 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. The negative electrode current collector 22A contains a conductive material such as a metal material, and a specific example of the conductive material is copper.

[0038] The negative electrode active material layer 22B includes one or more types of negative electrode active materials that absorb and release lithium. However, the negative electrode active material layer 22B may further include one or more types of other materials, such as a negative electrode binder and a negative electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited, and specifically includes one or more types of a coating method, a vapor phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method).

[0039] Here, the anode active material layer 22B is provided on both sides of the anode current collector 22A, and therefore the anode 22 includes two anode active material layers 22B. However, since the anode active material layer 22B is provided on only one side of the anode current collector 22A on the side where the anode 22 faces the cathode 21, the anode 22 may include only one anode active material layer 22B.

[0040] More specifically, as shown in Fig. 3 , the anode active material layer 22B includes a plurality of particles of anode active material (anode active material 220), and the anode active material 220 includes a center portion 221 and a coating portion 222. However, Fig. 3 shows only one anode active material 220.

[0041] The core 221 contains one or more materials capable of absorbing and releasing lithium, such as a carbon material and a metal-based material, because a high energy density can be obtained from these materials. As a result, the negative electrode material may contain only a carbon material, only a metal-based material, or both a carbon material and a metal-based material.

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

[0043] The metallic material is a material containing, as a constituent element, one or more of metallic elements and semi-metallic elements that can form an alloy with lithium, and specific examples of the metallic element and semi-metallic element include silicon and tin. The metallic material may be a simple substance, an alloy, a compound, a mixture of two or more of these, or a material containing two or more of these phases. Specific examples of metallic materials include TiSi 2 and SiO x (0<x≦2, or 0.2<x<1.4), etc.

[0044] In particular, the negative electrode material preferably contains a metal-based material, and the metal-based material preferably contains silicon as a constituent element, because this allows for a sufficiently high energy density to be obtained.

[0045] 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 covering portion 222 covers the surface of the central portion 221. However, the covering portion 222 may cover the entire surface of the central portion 221, or may cover only a portion of the surface of the central portion 221. In the latter case, a plurality of covering portions 222 may cover the surface of the central portion 221 at a plurality of locations that are spaced apart from one another.

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

[0048] In this stabilization treatment, the covering portion 222 is formed so as to cover the surface of the reactive central portion 221, and the covering portion 222 is used to reduce the reactivity of the surface of the central portion 221. This reduces the reactivity of the surface of the negative electrode active material 220, thereby suppressing the decomposition reaction of the electrolyte on the surface of the negative electrode active material 220. Therefore, the decomposition reaction of the electrolyte is suppressed even during subsequent charge and discharge, and the state of the secondary battery is electrochemically stabilized.

[0049] In the stabilization treatment, not only is the coating portion 222 formed on the surface of the center portion 221, but a coating may also be formed on the surface of the positive electrode active material, 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 a coating element as a constituent element, and the coating element includes one or more of nickel, iron, and copper. The state of the coating element in the coating portion 222 is not particularly limited, and may be a simple substance, a compound, an alloy, or two or more of these. However, since the simple substance may contain any amount of impurities, the purity of the simple substance is not necessarily limited to 100%.

[0051] The reason why the coating element is included in the coating portion 222 as a constituent element is that the physical strength of the coating portion 222 is improved, and the coating portion 222 is more likely to be maintained even after repeated charge and discharge. As a result, even after repeated charge and discharge, the decomposition reaction of the electrolyte is suppressed, and therefore the decrease in discharge capacity is suppressed.

[0052] The method for including the coating element as a constituent element in the coating portion 222, in other words, the source of the coating element, is not particularly limited. The details of the source of the coating element will be described later.

[0053] 2, the separator 23 is an insulating porous film interposed between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

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

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

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

[0057] <1-2. Detailed Configuration of Electrolyte Solution> Details regarding the configuration of the electrolyte solution are as described below.

[0058] [Thiazole-Type Compound] As described above, the electrolyte solution contains one or more thiazole-type compounds. The thiazole-type compounds are compounds having a thiazole-type structure, and are so-called thiazole derivatives.

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

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

[0061] (Each of R1 to R28 is any one of hydrogen, fluorine, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, an alkoxy group, a fluorinated alkyl group, a fluorinated alkenyl group, a fluorinated alkynyl group, a fluorinated cycloalkyl group, a fluorinated aryl group, a fluorinated alkoxy group, an amino group, a carboxylic acid ester group, and a monovalent bonding group in which two or more of these groups are bonded to each other.)

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

[0063] The electrolyte solution contains a thiazole-type compound because the synergistic effect of the thiazole-type compound and the coating elements contained as constituent elements in coating portion 222 significantly improves the physical strength of coating portion 222, making it easier to maintain coating portion 222 even after repeated charge and discharge. This suppresses the decomposition reaction of the electrolyte solution even after repeated charge and discharge, thereby suppressing a decrease in discharge capacity.

[0064] (Configuration) As described above, each of R1 to R28 is hydrogen (-H), fluorine (-F), an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, an alkoxy group, a fluorinated alkyl group, a fluorinated alkenyl group, a fluorinated alkynyl group, a fluorinated cycloalkyl group, a fluorinated aryl group, a fluorinated alkoxy group, an amino group (-NH 2 ), a carboxylic acid ester group, or a monovalent linking group, but is not particularly limited thereto.

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

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

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

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

[0069] The number of carbon atoms in the aryl group is not particularly limited, and specific examples of the aryl group include a phenylene group and a naphthylene group.

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

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

[0072] The carboxylic acid ester group is a group represented by -C(=O)-O-R30 (R30 is an alkyl group), and details regarding the alkyl group are as described above. Specific examples of the carboxylic acid ester group include a methyl carboxylate group (-C(=O)-O-CH 3 ) and a carboxylic acid ethyl group (—C(═O)—O—C 2 H 5 ) etc.

[0073] The type of the monovalent linking group is not particularly limited. Specific examples of the monovalent linking group include a group in which an alkyl group and a carboxylic acid ester group are bonded to each other (a group in which an alkylene group and a carboxylic acid ester group are bonded to each other), and more specifically, —CH 2 -C(=O)-O-CH 3 And so on.

[0074] (Specific Examples) Specific examples of the thiazole-type compound are as follows.

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

[0076]

[0077]

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

[0079]

[0080]

[0081]

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

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] Specific examples of the quaternary thiazole type compound include compounds represented by formulas (4-1) to (4-9).

[0089]

[0090]

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

[0092] In addition, when the electrolyte solution contains both the first thiazole type compound and the second thiazole type compound, the content of the thiazole type compound in the above-mentioned electrolyte solution is the sum of the content of the first thiazole type compound in the electrolyte solution and the content of the second thiazole type compound in the electrolyte solution.

[0093] In addition, when measuring the content of thiazole-type compounds, the secondary battery is disassembled to recover the electrolyte, and the electrolyte is then analyzed to calculate the content of the thiazole-type compounds. The method for analyzing the electrolyte is not particularly limited, but specifically, any one or more of inductively coupled plasma (ICP) atomic emission spectroscopy, nuclear magnetic resonance spectroscopy (NMR), and gas chromatography mass spectrometry (GC-MS) can be used.

[0094] [Solvent] The electrolytic solution may further contain a solvent. This solvent contains one or more types of non-aqueous solvents (organic solvents), and the electrolytic solution containing the non-aqueous solvent is a so-called non-aqueous electrolytic solution.

[0095] The non-aqueous solvent is an ester, an ether, or the like, and more specifically, a carbonate ester compound, a carboxylic acid ester compound, a lactone compound, or the like.

[0096] Carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates include ethylene carbonate and propylene carbonate. Specific examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0097] The carboxylic acid ester compound is a chain carboxylic acid ester, etc. Specific examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl trimethylacetate, methyl butyrate, and ethyl butyrate.

[0098] The lactone compound is lactone, etc. Specific examples of lactone include γ-butyrolactone and γ-valerolactone.

[0099] The ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, or the like.

[0100] (Electrolyte Salt) The electrolytic solution may further contain an electrolyte salt, which is a light metal salt such as a lithium salt.

[0101] A specific example of the lithium salt is lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(fluorosulfonyl)imide (LiN(FSO 2 ) 2 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ) 2 ), lithium tris(trifluoromethanesulfonyl)methide (LiC(CF 3 SO 2 ) 3 ), lithium bis(oxalato)borate (LiB(C 2 O 4 ) 2 ), lithium difluorooxalatoborate (LiBF2 (C 2 O 4 )), lithium difluorodi(oxalato)borate (LiPF 2 (C 2 O 4 ) 2 ), lithium tetrafluorooxalatophosphate (LiPF 4 (C 2 O 4 )), lithium monofluorophosphate (Li 2 PFO 3 ) and lithium difluorophosphate (LiPF 2 O 2 ) etc.

[0102] The content of the electrolyte salt is not particularly limited, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent, because high ionic conductivity can be obtained.

[0103] (Additives) The electrolytic solution may further contain one or more of the additives.

[0104] (Unsaturated cyclic carbonate, fluorinated cyclic carbonate, and cyanized cyclic carbonate) Specifically, the additive is one or more of unsaturated cyclic carbonate, fluorinated cyclic carbonate, and cyanized cyclic carbonate. This is because the electrochemical stability of the electrolyte is improved. This further suppresses the decomposition reaction of the electrolyte during charge and discharge of the secondary battery, thereby further suppressing the decrease in discharge capacity even when charge and discharge are repeated.

[0105] The unsaturated cyclic carbonate is a cyclic carbonate containing an unsaturated carbon bond (carbon-carbon double bond). The number of unsaturated carbon bonds is not particularly limited, and may be one or two or more.

[0106] The unsaturated cyclic carbonate contains one or more of a vinylene carbonate compound, a vinylethylene carbonate compound, and a methyleneethylene carbonate compound.

[0107] Vinylene carbonate compounds are unsaturated cyclic carbonates having a vinylene carbonate structure. Specific examples of vinylene carbonate compounds include vinylene carbonate (1,3-dioxol-2-one), methyl vinylene carbonate (4-methyl-1,3-dioxol-2-one), ethyl vinylene 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] The vinylethylene carbonate compound is an unsaturated cyclic carbonate ester having a vinylethylene carbonate type structure. Specific examples of the vinylethylene carbonate compound include vinylethylene 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 ethylene carbonate compounds are unsaturated cyclic carbonates having a methylene ethylene carbonate structure. Specific examples of methylene ethylene carbonate compounds include methylene ethylene 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. While compounds having only one methylene group have been exemplified as methylene ethylene carbonate compounds here, the methylene ethylene carbonate compounds may have two or more methylene groups.

[0110] It should be noted that a cyclic carbonate containing an unsaturated carbon bond does not fall under either a fluorinated cyclic carbonate or a cyanated cyclic carbonate, but falls under an unsaturated cyclic carbonate.

[0111] A fluorinated cyclic ester carbonate is a cyclic ester carbonate containing fluorine as a constituent element. The number of fluorine atoms is not particularly limited, and may be one or two or more. That is, a fluorinated cyclic ester carbonate is a compound in which one or two or more hydrogen atoms in a cyclic ester carbonate are substituted with fluorine atoms.

[0112] Specific examples of fluorinated cyclic carbonates include ethylene fluorocarbonate (4-fluoro-1,3-dioxolan-2-one) and ethylene difluorocarbonate (4,5-difluoro-1,3-dioxolan-2-one).

[0113] It should be noted that a cyclic carbonate containing fluorine as a constituent element does not fall into either the category of an unsaturated cyclic carbonate or a cyanated cyclic carbonate, but falls into the category of a fluorinated cyclic carbonate.

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

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

[0116] It should be noted that a cyclic carbonate containing a cyano group does not fall into either the category of an unsaturated cyclic carbonate or a fluorinated cyclic carbonate, but falls into the category of a cyanated cyclic carbonate.

[0117] (Sulfonate esters, sulfate esters, sulfite esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfonic acid carboxylic acid anhydrides, and sulfobenzoimide) The additive is one or more of sulfonate esters, sulfate esters, sulfite esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfonic acid carboxylic acid anhydrides, and sulfobenzoimide. This is because the electrochemical stability of the electrolyte is improved. This further suppresses the decomposition reaction of the electrolyte during charge and discharge of the secondary battery, thereby further suppressing the decrease in discharge capacity even when charge and discharge are repeated.

[0118] Specific examples of sulfonic acid esters include 1,3-propane sultone, 1-propene-1,3-sultone, 1,4-butane sultone, 2,4-butane sultone, and methanesulfonic acid propargyl ester.

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

[0120] Specific examples of sulfites include 1,3-propane sultone, 1-propene-1,3-sultone, 1,4-butane sultone, 2,4-butane sultone, and methanesulfonic acid propargyl ester. Specific examples of sulfites 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-dioxane-2,6-dione, succinic anhydride, and glutaric anhydride.

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

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

[0124] Specific examples of sulfobenzoimides 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 solution, the electrolyte solution may further contain one or more of the coating compounds. The coating compound is a compound containing one or more of nickel, iron, and copper as a constituent element. The content of the coating compound in the electrolyte solution is not particularly limited and can be set as desired.

[0126] The type of coating compound containing nickel as a constituent element is not particularly limited, but specific examples include nickel acetate, nickel (II) diethyldithiocarbamate, and bis(cyclopentadienyl)nickel.

[0127] The type of coating compound containing iron as a constituent element is not particularly limited, but specific examples include iron acetate, iron(III) dimethyldithiocarbamate, bis(cyclopentadienyl)iron, tris(1,3-diphenyl-1,3-propanedionato)iron, and tris(hexafluoroacetylacetonato)iron(III).

[0128] The type of coating compound containing copper as a constituent element is not particularly limited, but specific examples include copper acetate, tetrakis(acetonitrile)copper(I) tetrafluoroborate, tetrakis(acetonitrile)copper(I) hexafluorophosphate, copper(II) dimethyldithiocarbamate, copper(II) tetrafluoroborate, and copper(I) thiocyanate.

[0129] (Nitrile Compound) The additive also contains a nitrile compound. This is because the electrochemical stability of the electrolyte solution is improved. This further suppresses the decomposition reaction of the electrolyte solution during charge and discharge, thereby further suppressing the decrease in discharge capacity even when charge and discharge are repeated, and also suppressing the generation of gas due to the decomposition reaction of the electrolyte solution.

[0130] The nitrile compound is a compound containing one or more cyano groups (—CN). Specific examples of the nitrile compound include octanenitrile, benzonitrile, phthalonitrile, succinonitrile, glutaronitrile, adiponitrile, sebaconitrile, 1,3,6-hexanetricarbonitrile, 3,3′-oxydipropionitrile, 3-butoxypropionitrile, ethylene glycol bispropionitrile ether, 1,2,2,3-tetracyanopropane, tetracyanopropane, fumaronitrile, 7,7,8,8-tetracyanoquinodimethane, cyclopentanecarbonitrile, 1,3,5-cyclohexanetricarbonitrile, and 1,3-bis(dicyanomethylidene)indane.

[0131] However, the above-mentioned cyanated cyclic carbonate is 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 is absorbed into the negative electrode 22 via the electrolyte. During discharging, lithium is released from the negative electrode 22 of the battery element 20 and is absorbed into the positive electrode 21 via the electrolyte. During 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 the negative electrode 22 are fabricated and an electrolytic solution is prepared according to the procedure described below as an example. Thereafter, the positive electrode 21, the negative electrode 22, and the electrolytic solution are used to assemble a secondary battery, and a stabilization process is performed on the assembled secondary battery.

[0135] [Fabrication of Positive Electrode] First, a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent are mixed together to form a positive electrode mixture. The positive electrode mixture is then poured into a solvent to prepare a paste-like positive electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. The positive electrode mixture slurry is then applied to both surfaces 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 compression-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. This results in the positive electrode active material layer 21B being formed on both surfaces of the positive electrode current collector 21A, thereby fabricating the positive electrode 21.

[0136] When the positive electrode 21 is used as a supply source of the coating element, the positive electrode 21 is produced by the same procedure except that the coating metal powder is further added to the positive electrode mixture.

[0137] [Fabrication of Negative Electrode] First, the center portion 221, the negative electrode binder, and the negative electrode conductive agent are mixed together to form a positive electrode mixture. The negative electrode mixture is then poured into a solvent to prepare a paste-like negative electrode mixture slurry. This solvent may be an aqueous solvent or an organic solvent. The negative electrode mixture slurry is then applied to both surfaces 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 compression-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 described later, after assembling the secondary battery, the assembled secondary battery is subjected to a stabilization treatment, whereby coating portion 222 containing the coating element as a constituent element is formed on the surface of center portion 221, thereby forming negative electrode active material 220 including center portion 221 and coating portion 222.

[0139] Thus, the anode active material layers 22B containing the anode active material 220 are formed on both sides of the anode current collector 22A, and the anode 22 is fabricated.

[0140] [Preparation of Electrolyte Solution] When preparing an electrolyte solution, an electrolyte salt is added to a solvent, and then a thiazole-type compound is added to the solvent, whereby the electrolyte salt and the thiazole-type compound are dissolved or dispersed in the solvent, thereby preparing the electrolyte solution.

[0141] When an electrolyte solution is used as a supply source of the coating element, the electrolyte solution is prepared in the same manner except that the coating compound is further added to the solvent.

[0142] [Assembly of Secondary Battery] First, a 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 a 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 together with the separator 23 interposed therebetween, and the positive electrode 21, the negative electrode 22, and the separator 23 are then wound to produce a wound body (not shown) having a winding central space 20S. This wound body has a configuration similar to that of the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with an electrolyte. Next, a center pin 24 is inserted into the winding central space 20S of the wound body.

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

[0144] Finally, the battery lid 14, the safety valve mechanism 15, and the PTC element 16 are housed inside the battery can 11, and then the battery can 11 is crimped via the gasket 17. As a result, the battery lid 14, the safety valve mechanism 15, and the PTC element 16 are fixed to the battery can 11, and the battery element 20 is sealed inside the battery can 11, thereby assembling a secondary battery.

[0145] [Stabilization of Secondary Battery] The secondary battery is charged and discharged after assembly, and various conditions such as the ambient temperature, the number of charge / discharge cycles (number of cycles), and the charge / discharge conditions can be set arbitrarily.

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

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

[0148] <1-5. Actions and Effects> According to this secondary battery, the negative electrode active material 220 of the negative electrode 22 includes the core 221 and the coating portion 222, the coating portion 222 includes, as a coating element, one or more of nickel, iron, and copper as a constituent element, and the electrolyte solution includes a thiazole-type compound.

[0149] In this case, as described above, the synergistic effect of the coating element and the thiazole-type compound improves the physical strength of the coating portion 222. This suppresses the decomposition reaction of the electrolyte even with repeated charge and discharge, thereby suppressing the decrease in discharge capacity. As a result, excellent battery characteristics can be obtained.

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

[0151] Furthermore, if the content of the thiazole-type compound in the electrolyte is 0.001% by weight to 5% by weight, the physical strength of the coating portion 222 is sufficiently improved, and the decomposition reaction of the electrolyte is sufficiently suppressed, thereby achieving a greater effect.

[0152] Furthermore, if the electrolyte solution contains one or more of unsaturated cyclic carbonates, fluorinated cyclic carbonates, and cyanated cyclic carbonates, the decomposition reaction of the electrolyte solution is further suppressed, thereby achieving a greater effect.

[0153] Furthermore, if the electrolyte solution contains one or more of sulfonic acid esters, sulfate esters, sulfite esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfonic acid carboxylic acid anhydrides, and sulfobenzoic acid imides, the decomposition reaction of the electrolyte solution is further suppressed, thereby achieving a greater effect.

[0154] Furthermore, if the secondary battery is a lithium ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, and therefore a greater effect can be obtained.

[0155] 2. Modifications The configuration of the secondary battery described above can be modified as appropriate, as described below. However, any two or more of the series of modifications described below may be combined with each other.

[0156] [Variation 1] The secondary battery has been described as having a cylindrical battery structure. However, although not specifically illustrated here, the type of battery structure is not particularly limited, and may be a laminate film type, a square type, a coin type, a button type, or the like.

[0157] [Modification 2] A porous film separator 23 is used. However, although not specifically shown here, a laminated separator including 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 surfaces of the porous membrane. This is because the separator improves adhesion to each of the positive electrode 21 and the negative electrode 22, thereby suppressing misalignment (winding misalignment) of the battery element 20. This suppresses swelling of the secondary battery even if a decomposition reaction of the electrolyte solution occurs. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride and other polymers have excellent physical strength and are electrochemically stable.

[0159] One or both of the porous film and the polymer compound layer may contain one or more types of insulating particles. This is because the insulating particles promote heat dissipation when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The insulating particles contain one or both of an inorganic material and a resin material. 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 a laminated separator is produced, 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 film. In this case, multiple insulating particles may be added to the precursor solution as needed.

[0161] Even when this laminated separator is used, the same effect can be obtained because lithium ions are able to move between the positive electrode 21 and the negative electrode 22. In this case, as described above, the safety of the secondary battery is particularly improved, and therefore, even greater effects can be obtained.

[0162] [Modification 3] An electrolytic solution that is a liquid electrolyte is used. However, although not specifically shown here, an electrolyte layer that is a gel electrolyte may also be used.

[0163] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 and the electrolyte layer interposed therebetween, and the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte layer are wound together. The 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 together with an electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. The polymer compound contains polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolytic solution, the polymer compound, a solvent, etc. is prepared, and then the precursor solution is applied to one or both surfaces of each of the positive electrode 21 and the negative electrode 22.

[0165] Even when this electrolyte layer is used, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer. In this case, particularly, as described above, leakage of the electrolyte solution is prevented, so that a greater effect can be obtained.

[0166] 3. Uses of Secondary Batteries There are no particular limitations on the uses (application examples) of secondary batteries. Secondary batteries used as power sources may be the main power source or auxiliary power source in electronic devices, electric vehicles, and the like. The main power source is a power source that is used preferentially regardless of the presence or absence of other power sources. The auxiliary power source may be a power source used in place of the main power source or a power source that can be switched from the main power source.

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

[0168] The battery pack may use a single cell or a battery pack. The electric vehicle is a vehicle that operates (travels) using a secondary battery as a driving power source, and may be a hybrid vehicle that also has a driving source other than the secondary battery. In a home power storage system, power stored in a secondary battery, which is a power storage source, can be used to power home electrical appliances, etc.

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

[0170] Figure 4 shows the block diagram of a battery pack. The battery pack described here is a battery pack (a so-called soft pack) that uses one secondary battery, and is installed in electronic devices such as smartphones.

[0171] 4, the battery pack includes 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 source 51 includes one secondary battery. The positive electrode lead of this secondary battery is connected to a positive electrode terminal 53, and the negative electrode lead is connected to a negative electrode terminal 54. The power source 51 can be connected to the outside via the positive electrode terminal 53 and the negative electrode terminal 54, and is therefore capable of charging and discharging. 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. The control unit 56 detects and controls the usage state of the power source 51 as necessary.

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

[0175] Switch 57 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, etc., and switches between the connection and disconnection of power supply 51 and an external device in response to instructions from control unit 56. Switch 57 includes a metal oxide semiconductor field effect transistor (MOSFET), etc., and the charge / discharge current is detected based on the ON resistance of switch 57.

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

[0177] An embodiment of the present technology will be described.

[0178] Examples 1 to 48 and Comparative Examples 1 to 24 As will be described below, secondary batteries were manufactured, and then the battery characteristics of the secondary batteries were evaluated.

[0179] [Manufacturing of Secondary Battery] A cylindrical lithium ion secondary battery shown in FIGS. 1 and 2 was manufactured according to the procedure described below.

[0180] (Fabrication of Positive Electrode) First, a positive electrode active material (lithium-containing compound (oxide) lithium cobalt oxide (LiCoO 2 )), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 3 parts by mass of a positive electrode conductive agent (acetylene black) were mixed together to prepare a positive electrode mixture. Subsequently, 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 a positive electrode current collector 21A (a strip-shaped aluminum foil having a thickness of 12 μm) using a coating device, and the positive electrode mixture slurry was then dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B was compression-molded using a roll press. Thus, the positive electrode 21 was produced.

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

[0182] (Fabrication of Negative Electrode) First, 93 parts by mass of a negative electrode active material (central portion 221) and 7 parts by mass of a negative electrode binder (polyvinylidene fluoride) were mixed together to prepare a negative electrode mixture. The central portion 221 was a mixture of 63 parts by mass of artificial graphite, which is a carbon material, and 30 parts by mass of silicon oxide (SiO), which is a metallic material.

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

[0184] Finally, as described below, the secondary battery was assembled, and then the assembled secondary battery was subjected to a stabilization treatment. 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 a negative electrode active material 220 including the central portion 221 and the coating portion 222 was formed. Thus, the negative electrode 22 was produced.

[0185] The negative electrode 22 was fabricated in the same manner except that the central portion 221 was made of only a carbon material without using a metal-based material.

[0186] For comparison, a negative electrode 22 was fabricated using the same procedure, except that a coating portion 222 was formed that did not contain the coating element as a constituent element by not using a source of the coating element.

[0187] (Preparation of Electrolyte Solution) A solvent (ethylene carbonate, which is a cyclic carbonate ester, and dimethyl carbonate, which is a chain carbonate ester) was prepared. The mixing ratio (weight ratio) of the solvent was ethylene carbonate:dimethyl carbonate = 20:80. Next, an electrolyte salt (LiPF , which is a lithium salt) was added to the solvent. 6 ) was added to the solvent, and the solvent was stirred. The content of the electrolyte salt was 1.2 mol / kg relative to the solvent. Finally, a thiazole-type compound was added to the solvent to which the electrolyte salt had been added, and the solvent was stirred. The classification, type, and content (wt%) of the thiazole-type compound are shown in Tables 1 to 5. In this way, an electrolytic solution was prepared.

[0188] When an electrolyte solution was used as a source of coating elements, the electrolyte solution was prepared using the same procedure, 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 as a constituent element, bis(cyclopentadienyl)iron was used as the coating compound containing iron as a constituent element, and tetrakis(acetonitrile)copper(I) hexafluorophosphate was used as the coating compound containing copper as a constituent element. The content of the coating compound in the electrolyte solution was 0.05 wt %. When two or more types of coating compounds were used, the respective contents of the two or more types of coating compounds were the same.

[0189] For comparison, an electrolyte solution was prepared in the same manner except that no thiazole-type compound was used.

[0190] The meaning of the "classification" shown in Tables 1 to 5 is as follows: "First" represents the first thiazole-type compound, "Second" represents the second thiazole-type compound, "Third" represents the third thiazole-type compound, and "Fourth" represents the fourth thiazole-type compound.

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

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

[0193] Next, the insulating plates 12 and 13 were housed together with the wound body inside the battery can 11. 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. Next, the electrolyte was injected into the battery can 11. As a result, the wound body was impregnated with the electrolyte, and the battery element 20 was produced.

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

[0195] (Stabilization of Secondary Battery) The secondary battery was subjected to one cycle of charge and discharge in a room temperature environment (temperature = 23°C). During charging, the battery was charged at a constant current of 0.1 C until the voltage reached 4.2 V, and then charged at a constant voltage of 0.05 C at the same voltage of 4.2 V. During discharging, the battery was discharged at a constant current of 0.1 C until the voltage reached 3.0 V. 0.1 C is the current value at which the battery capacity (theoretical capacity) is fully discharged in 10 hours, and 0.05 C is the current value at which the battery capacity is fully discharged in 20 hours.

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

[0197] After the secondary battery was completed, the secondary battery was disassembled to recover the negative electrode active material 220. The negative electrode active material 220 was then analyzed using a scanning electron microscope (a scanning electron microscope SU3800 / SU3900 manufactured by Hi-Tech Corporation), an energy dispersive X-ray analyzer (EDS), and an X-ray photoelectron spectrometer (EDX). The results are shown in Tables 1 to 5.

[0198] After the secondary battery was completed, the content (wt %) of the thiazole-type compound in the electrolyte was measured using ICP atomic emission spectroscopy, and the results are shown in Tables 1 to 5.

[0199] [Evaluation of Battery Characteristics] The cycle characteristics were evaluated as the battery characteristics according to 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 to stand in the same environment (standing time = 3 hours). During charging, the battery was charged at a constant current of 1 C until the voltage reached 4.2 V, and then at the same voltage of 4.2 V, the battery was charged at a constant voltage of 0.05 C. 1 C is the current value at which the battery capacity is fully discharged in 1 hour.

[0201] Subsequently, the secondary battery was discharged in the same environment to measure the discharge capacity (discharge capacity at the first cycle). During discharge, the secondary battery was discharged at a constant current of 3 C until the voltage reached 3.0 V. 3 C is the current value at which the battery capacity is fully discharged in 1 / 3 of an hour.

[0202] Subsequently, the discharge capacity (discharge capacity at the 100th cycle) of the secondary battery was measured by repeatedly charging and discharging the battery in the same environment until the number of cycles reached 100. 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, which is an index for evaluating cycle characteristics, was calculated based on the formula: capacity retention rate (%)=(discharge capacity at 100th cycle / discharge capacity at 1st cycle)×100.

[0204]

[0205]

[0206]

[0207]

[0208]

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

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

[0211] Here, the capacity retention rate when the coating portion 222 does not contain the coating element as a constituent element and the electrolyte does not contain a thiazole-type compound (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 to 11), the capacity retention rate decreased.

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

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

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

[0216] The reason for the significant increase in capacity retention rate is believed 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 action of the coating element and the thiazole-type compound.

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

[0218] First, high capacity retention was achieved regardless of whether the first, second, third, or fourth thiazole-type compound was used. Second, the capacity retention was further increased when the content of the thiazole-type compound in the electrolyte was 0.001 wt % to 5 wt %. Third, high capacity retention was achieved regardless of the type of coating element source.

[0219] The results described here are not limited to the cases where both a carbon material and a metal-based material were used as the negative electrode active material (Examples 1 to 45 and Comparative Examples 1 to 12), but were also obtained in the cases where only a carbon material was used as the negative electrode active material (Examples 46 to 48 and Comparative Examples 13 to 24).

[0220] Examples 49 to 54 Secondary batteries were fabricated and their battery characteristics were evaluated in the same manner as in Example 4, except that an additive (unsaturated cyclic ester carbonate, fluorinated cyclic ester carbonate, or cyanated cyclic ester carbonate) was added to the electrolyte solution as shown in Table 6. The classification, type, and content (wt %) of the additive are as shown in Table 6.

[0221] Specifically, vinylene carbonate (VC) was used as the unsaturated cyclic carbonate, fluoroethylene carbonate (FEC) was used as the fluorinated cyclic carbonate, and cyanoethylene carbonate (CEC) was used as the cyanated cyclic carbonate.

[0222]

[0223] As shown in Table 6, when the electrolyte solution contained an additive (unsaturated cyclic carbonate, fluorinated cyclic carbonate, or cyanated cyclic carbonate) (Examples 49 to 54), the capacity retention rate was increased more than when the electrolyte solution did not contain an additive (Example 4).

[0224] Examples 55 to 74 Secondary batteries were fabricated in the same manner as in Example 4, except that additives (sulfonic acid ester, sulfate ester, sulfite ester, dicarboxylic acid anhydride, disulfonic acid anhydride, sulfonic acid carboxylic acid anhydride, or sulfobenzoic acid imide) were added to the electrolyte solution as shown in Tables 7 and 8. The classification, type, and content (wt %) of the additives are as shown in Tables 7 and 8.

[0225] Specifically, 1,3-propane sultone (PS), 1-propene-1,3-sultone (PRS), 1,4-butane sultone (BS1), 2,4-butane sultone (BS2), and methanesulfonic acid propargyl ester (MSP) were used as sulfonate esters.

[0226] As sulfates, 1,3,2-dioxathiolane 2,2-dioxide (OTO), 1,3,2-dioxathiane 2,2-dioxide (OTA), and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane (SOTO) were used.

[0227] As sulfites, 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-dioxane-2,6-dione (DOD), succinic anhydride (SA) and glutaric anhydride (GA) were used.

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

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

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

[0232]

[0233]

[0234] As shown in Tables 7 and 8, when the electrolyte solution contained an additive (sulfonic acid ester, sulfate ester, sulfite ester, dicarboxylic acid anhydride, disulfonic acid anhydride, sulfonic acid carboxylic acid anhydride, or sulfobenzoic acid imide) (Examples 55 to 74), the capacity retention rate was increased more than when the electrolyte solution did not contain an additive (Example 4).

[0235] [Summary] From the results shown in Tables 1 to 8, when the negative electrode active material 220 of the negative electrode 22 includes the core portion 221 and the coating portion 222, the coating portion 222 includes the coating element as a constituent element, and the electrolyte solution includes a thiazole-type compound, a high capacity retention rate was obtained, and therefore, the cycle characteristics were improved. Therefore, excellent battery characteristics were obtained in a secondary battery using the electrolyte solution.

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

[0237] Specifically, the battery element has been described as having a wound structure. However, the structure of the battery element is not particularly limited, and other structures such as a stacked structure and a zigzag structure may also be used. In the stacked structure, positive and negative electrodes are alternately stacked with a separator interposed therebetween, while in the zigzag structure, the positive and negative electrodes are folded in a zigzag pattern while facing each other with the separator interposed therebetween.

[0238] Although the electrode reactant is lithium in the above description, the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Alternatively, the electrode reactant may be other light metals 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] The present technology can also be configured as follows: <1> A secondary battery comprising: a positive electrode; a negative electrode containing a negative electrode active material; and an electrolyte solution containing a thiazole-type compound, wherein the negative electrode active material includes a core that occludes and releases an electrode reactant, and a coating portion that coats the surface of the core, wherein the coating portion includes at least one of nickel, iron, and copper as a constituent element, and 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). (Each of R1 to R28 is any one of hydrogen, fluorine, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, an alkoxy group, a fluorinated alkyl group, a fluorinated alkenyl group, a fluorinated alkynyl group, a fluorinated cycloalkyl group, a fluorinated aryl group, a fluorinated alkoxy group, an amino group, a carboxylic acid ester group, and a monovalent bonding group in which two or more of the above are bonded to each other.) <2> The secondary battery according to <1>, wherein the core includes a metal-based material, and the metal-based material includes silicon as a constituent element. <3> The secondary battery according to <1> or <2>, wherein the content of the thiazole-type compound in the electrolyte solution is 0.001% by weight or more and 5% by weight or less. <4> The secondary battery according to any one of <1> to <3>, wherein the electrolyte solution further includes at least one of an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, and a cyanated cyclic carbonate. <5> The secondary battery according to any one of <1> to <4>, wherein the electrolyte solution further contains at least one of a sulfonic acid ester, a sulfate ester, a sulfite ester, a dicarboxylic acid anhydride, a disulfonic acid anhydride, a sulfonic acid carboxylic acid anhydride, and a sulfobenzoic acid imide. <6> The secondary battery according to any one of <1> to <5>, wherein the secondary battery is a lithium ion secondary battery.

Claims

1. A positive electrode and a negative electrode including a negative electrode active material; An electrolyte solution containing a thiazole type compound; Equipped with The negative electrode active material is A central portion that absorbs and releases an electrode reactant; a covering portion that covers a surface of the central portion; 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). Secondary battery. 【Chemistry 1】 (Each of R1 to R28 is any one of hydrogen, fluorine, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, an alkoxy group, a fluorinated alkyl group, a fluorinated alkenyl group, a fluorinated alkynyl group, a fluorinated cycloalkyl group, a fluorinated aryl group, a fluorinated alkoxy group, an amino group, a carboxylate group, and a monovalent bonding group in which two or more of these groups are bonded to each other.)

2. the core portion includes a metal-based material; The metal-based material contains silicon as a constituent element. The secondary battery according to claim 1 .

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

4. The electrolyte solution further contains at least one of an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, and a cyanated cyclic carbonate. The secondary battery according to claim 1 .

5. The electrolytic solution further contains at least one of a sulfonic acid ester, a sulfate ester, a sulfite ester, a dicarboxylic acid anhydride, a disulfonic acid anhydride, a sulfonic acid carboxylic acid anhydride, and a sulfobenzoic acid imide. The secondary battery according to claim 1 .

6. It is a lithium-ion secondary battery. The secondary battery according to claim 1 .

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