Electrolyte for secondary battery and secondary battery

Abstract

This secondary battery comprises a positive electrode, a negative electrode, and a secondary battery electrolyte. The secondary battery electrolyte includes a lithium salt and a sulfonyl compound. The sulfonyl compound includes two or more compounds from among cyclic compounds represented by formula (1) and chain-like compounds represented by formula (2). The ratio of the number of moles of the sulfonyl compound to the number of moles of the lithium salt is 2-4.

Description

Technical Field

[0001] The present technology relates to an electrolyte for a secondary battery and a secondary battery.

Background Art

[0002] Due to the widespread use of various electronic devices such as mobile phones, the development of secondary batteries is underway as a power source that is small and lightweight and can obtain a high energy density. This secondary battery includes an electrolyte (electrolyte for a secondary battery) together with a positive electrode and a negative electrode, and various studies have been made on the configuration of the secondary battery.

[0003] Specifically, the electrolyte contains a solvent for dissolving an electrolyte salt and an electrolyte salt, and the solvent for dissolving the electrolyte salt contains a predetermined amount of a sulfolane compound (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Although various studies have been made to improve the battery characteristics of secondary batteries, the battery characteristics are not yet sufficient, so there is room for improvement.

[0006] There is a demand for an electrolyte for a secondary battery and a secondary battery that can obtain excellent battery characteristics.

[0007] The electrolyte for a secondary battery according to one embodiment of the present technology contains a lithium salt and a sulfonyl compound. The sulfonyl compound contains two or more of a cyclic compound represented by the formula (1) and a chain compound represented by the formula (2), and the ratio of the number of moles of the sulfonyl compound to the number of moles of the lithium salt is 2 or more and 4 or less.

[0008] [Chemistry] (R1 is an alkylene group.)

[0009] [Chemistry] (Each of R2 and R3 is an alkyl group.)

[0010] Further, a secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolytic solution for a secondary battery, and the electrolytic solution for a secondary battery has the same configuration as the configuration of the electrolytic solution for a secondary battery according to an embodiment of the present technology described above.\

[0011] According to the electrolytic solution for a secondary battery or the secondary battery according to an embodiment of the present technology, the electrolytic solution for a secondary battery contains a lithium salt and a sulfonyl compound, the sulfonyl compound contains two or more of a cyclic compound and a chain compound, and the ratio of the number of moles of the sulfonyl compound to the number of moles of the lithium salt is 2 or more and 4 or less, so excellent battery characteristics can be obtained.\

[0012] Note that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described later.\ [Brief Description of Drawings]

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

[0014] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The order of description is as follows. 1. Electrolyte for secondary battery 1-1. Configuration 1-2. Manufacturing method 1-3. Action and effect 2. Secondary battery 2-1. Configuration 2-2. Operation 2-3. Manufacturing method 2-4. Action and effect 3. Modification example 4. Applications of secondary batteries

[0015] <1. Electrolyte for secondary battery> First, an electrolyte for a secondary battery (hereinafter simply referred to as "electrolyte") according to an embodiment of the present technology will be described.

[0016] The electrolyte described here is a liquid electrolyte used in a secondary battery, which is an electrochemical device. However, the electrolyte may be used in other electrochemical devices. Specific examples of other electrochemical devices include capacitors.

[0017] <1-1. Configuration> The electrolyte contains a lithium salt and a sulfonyl compound. That is, the sulfonyl compound is a solvent for dissolving or dispersing the lithium salt, and the lithium salt is an electrolyte salt that ionizes in the solvent.

[0018] As described above, this electrolyte contains a sulfonyl compound as a solvent for dissolving or dispersing the lithium salt, which is an electrolyte salt, and thus does not contain a general solvent.

[0019] A general solvent is a solvent generally used in the electrolyte of a secondary battery, specifically, esters and ethers described later, and more specifically, carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds.

[0020] Carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates are ethylene carbonate and propylene carbonate. Specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0021] Carboxylic acid ester compounds are chain carboxylic acid esters, etc. Specific examples of the chain carboxylic acid esters are ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethylacetate.

[0022] Lactone compounds are lactones, etc. Specific examples of the lactones are γ-butyrolactone and γ-valerolactone.

[0023] [Lithium salt] Lithium salts are a general term for salts containing lithium ions as cations. However, the type of lithium salt may be only one type or two or more types.

[0024] The type of lithium salt is not particularly limited. Specific examples of lithium salts are lithium hexafluorophosphate (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 difluorooxalato borate (LiBF2(C2O4)), lithium difluoro bis(oxalato)borate (LiPF2(C2O4)2), lithium tetrafluorooxalatophosphate (LiPF4(C2O4)), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2).

[0025] [Sulfonyl compound] Sulfonyl compounds are a general term for compounds containing a sulfonyl group (-S(=O)2-). However, the types of sulfonyl compounds may be only one type or two or more types.

[0026] Specifically, the sulfonyl compound contains two or more types among the cyclic compound represented by formula (1) and the chain compound represented by formula (2).

[0027] That is, since the sulfonyl compound contains two or more types of cyclic compounds, it may not contain a chain compound. Or, since the sulfonyl compound contains two or more types of chain compounds, it may not contain a cyclic compound. Or, the sulfonyl compound may contain one or more cyclic compounds and one or more chain compounds together.

[0028]

Chemical formula

[0029]

Chemical formula

[0030] The reason why the sulfonyl compound contains two or more types among the cyclic compound and the chain compound is that, compared with the case where the sulfonyl compound contains only one of the cyclic compound and the chain compound, its lithium salt is more easily and stably dissolved by the sulfonyl compound. As a result, the mixture of the lithium salt and the sulfonyl compound becomes a liquid instead of a solid, so that the mixture can be used as an electrolyte.

[0031] (Cyclic compound) As is clear from formula (1), the cyclic compound is a cyclic compound containing a sulfonyl group.

[0032] The number of carbon atoms in the alkylene group is not particularly limited. The alkylene group may be linear or branched with one or more side chains.

[0033] Specific examples of the alkylene group include an ethylene group, a propylene group, a butylene group, and a pentylene group. However, by way of example, the pentylene group may be an n-pentylene group, an isopentylene group, a sec-pentylene group, a 3-pentylene group, a tert-pentylene group, or a neopentylene group.

[0034] Among them, the number of carbon atoms in the alkylene group is preferably 5 or less. This is because the lithium salt is more easily dissolved sufficiently by the sulfonyl compound since the number of carbon atoms in the alkylene group does not become too large.

[0035] Specific examples of the cyclic compound include sulfolane (R1 is an n-butylene group (so-called tetramethylene group)), 3-methylsulfolane (R1 is an isopentylene group), and trimethylene sulfone (R1 is an n-propylene group (so-called trimethylene group)).

[0036] (Chain compound) As is clear from formula (2), the chain compound is a chain compound containing a sulfonyl group. The type of R2 and the type of R3 may be the same as each other or different from each other.

[0037] The number of carbon atoms in the alkyl group is not particularly limited. The alkyl group may be linear or branched with one or more side chains.

[0038] Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group. However, by way of example, the butyl group may be an n-butyl group, an isobutyl group, a sec-butyl group, or a tert-butyl group.

[0039] Among them, the number of carbon atoms of the alkyl group is preferably 2 or less. This is because when the number of carbon atoms of the alkyl group does not become too large, the lithium salt is more easily dissolved by the sulfonyl compound.

[0040] Specific examples of the chain compound include dimethyl sulfone (R2 is a methyl group, R3 is a methyl group), diethyl sulfone (R2 is an ethyl group, R3 is an ethyl group), ethyl methyl sulfone (R2 is an ethyl group, R3 is a methyl group), and ethyl isopropyl sulfone (R2 is an ethyl group, R3 is an isopropyl group).

[0041] (molar ratio) The relationship between the content of the lithium salt in the electrolyte and the content of the sulfonyl compound in the electrolyte is optimized.

[0042] Specifically, the molar ratio M, which is the ratio of the number of moles M2 of the sulfonyl compound to the number of moles M1 of the lithium salt, is 2 to 4. When the lithium salt and the sulfonyl compound are used in combination, the relationship between the content of the lithium salt and the content of the sulfonyl compound is optimized, so that the lithium salt is more easily and stably dissolved by the sulfonyl compound. As a result, as described above, the mixture of the lithium salt and the sulfonyl compound becomes a liquid instead of a solid, and thus the mixture can be used as an electrolyte. This molar ratio M is calculated based on the calculation formula M = M2 / M1.

[0043] The procedure for calculating the molar ratio M is as described below. First, prepare an electrolyte. When using a secondary battery equipped with the electrolyte, the electrolyte is recovered by disassembling the secondary battery. Subsequently, the electrolyte is analyzed using high-frequency inductively coupled plasma (ICP) optical emission spectrometry to identify the content (number of moles M1) of the lithium salt and the content (number of moles M2) of the sulfonyl compound. Finally, based on the number of moles M1 and M2, the molar ratio M is calculated using the above-described calculation formula.

[0044] (Preferred configuration 1) Among them, the sulfonyl compound preferably contains two types of cyclic compounds. This is because the lithium salt is more easily dissolved by the sulfonyl compound.

[0045] Specifically, the sulfonyl compound preferably contains sulfolane. That is, the sulfonyl compound preferably contains sulfolane as the first type of cyclic compound among the two types of cyclic compounds. This is because the lithium salt is more easily and stably dissolved by the sulfonyl compound.

[0046] In this case, the sulfonyl compound preferably further contains a derivative of sulfolane. That is, the sulfonyl compound preferably contains a derivative of sulfolane as the second type of cyclic compound among the two types of cyclic compounds. This is because the lithium salt is more easily and stably dissolved by the sulfonyl compound.

[0047] The derivative of sulfolane is a compound having a skeleton similar to that of sulfolane, and specific examples of the sulfolane derivative include 3-methylsulfolane and the like.

[0048] When the sulfonyl compound contains two types of cyclic compounds, the molar ratio M is 2 to 4 as described above.

[0049] (Preferred Configuration 2) Alternatively, the sulfonyl compound preferably contains one type of cyclic compound and one type of chain compound. This is because the lithium salt is more easily dissolved by the sulfonyl compound.

[0050] Specifically, the sulfonyl compound preferably contains sulfolane. That is, the sulfonyl compound preferably contains sulfolane as the cyclic compound. This is because the lithium salt is more easily and stably dissolved by the sulfonyl compound.

[0051] In this case, since the type of the chain compound is not particularly limited, it can be arbitrarily selected. If the sulfonyl compound contains sulfolane as a cyclic compound, the lithium salt is more likely to be stably dissolved by the sulfonyl compound regardless of the type of the chain compound.

[0052] Among them, the sulfonyl compound preferably contains one or both of dimethyl sulfone and ethyl methyl sulfone as the chain compound. This is because the lithium salt is more likely to be stably dissolved by the sulfonyl compound.

[0053] When the sulfonyl compound contains one type of cyclic compound and one type of chain compound, the molar ratio M is 2 to 4 as described above.

[0054] [Additive] In addition, the electrolytic solution may further contain any one or two or more of the additives. Since the type of the additive is not particularly limited, it can be arbitrarily selected.

[0055] (Fluorinated ether compound) Specifically, the additive is a fluorinated ether compound represented by the formula (3). This is because the viscosity of the electrolytic solution decreases. However, the type of the fluorinated ether compound may be only one type or two or more types.

[0056] R4-O-R5 ···(3) (Each of R4 and R5 is a fluorinated alkyl group.)

[0057] As is clear from the formula (3), the fluorinated ether compound is a compound in which two fluorinated alkyl groups (R4 and R5) are bonded to each other via an ether bond (-O-). The type of R4 and the type of R5 may be the same as each other or different from each other.

[0058] A fluorinated alkyl group is a group in which one or more of the plurality of hydrogens contained in an alkyl group are substituted with fluorine. As a result, the fluorinated alkyl group may be a group in which only a part of the plurality of hydrogens is substituted with fluorine (a partially substituted fluorinated alkyl group), or a group in which all of the plurality of hydrogens are substituted with fluorine (a fully substituted fluorinated alkyl group). This fully substituted fluorinated alkyl group is a so-called perfluoroalkyl group. The details regarding the alkyl group are as described above.

[0059] The carbon number of the fluorinated alkyl group is not particularly limited. Further, the fluorinated alkyl group may be linear or branched having one or more side chains.

[0060] Specific examples of the fluorinated alkyl group include a partially substituted methyl group, a fully substituted methyl group, a partially substituted ethyl group, a fully substituted ethyl group, a partially substituted propyl group and a fully substituted propyl group, a partially substituted butyl group and a fully substituted butyl group, and the like.

[0061] Among them, the carbon number of the fluorinated alkyl group is preferably 3 or less, and more preferably 2 or less. This is because the compatibility of the fluorinated ether compound is improved since the carbon number of the fluorinated alkyl group does not become too large.

[0062] Specific examples of the fluorinated ether compound include hydrofluoroethers having a structure represented by CHF2-CF2-O-CH2-CF2-CHF2 (where R4 is -CF2-CHF2 and R5 is -CH2-CF2-CHF2).

[0063] Note that the content of the fluorinated ether compound in the electrolytic solution is not particularly limited and can be arbitrarily set.

[0064] (Fluorinated cyclic carbonate) Further, the additive is a fluorinated cyclic carbonate. During charge and discharge of a secondary battery equipped with the electrolytic solution, a film derived from the fluorinated cyclic carbonate is formed on the surface of the negative electrode, thereby suppressing the decomposition reaction of the electrolytic solution. However, the type of the fluorinated cyclic carbonate may be only one type or two or more types.

[0065] The fluorinated cyclic carbonate is a cyclic carbonate containing fluorine as a constituent element. The number of fluorine atoms is not particularly limited, so it may be only one or two or more. That is, the fluorinated cyclic carbonate is a compound in which one or two or more hydrogens in the cyclic carbonate are substituted by fluorine.

[0066] Specific examples of the fluorinated cyclic carbonate include fluoroethylene carbonate and the like. Note that the content of the fluorinated cyclic carbonate in the electrolytic solution is not particularly limited and can be arbitrarily set.

[0067] (Unsaturated cyclic carbonate) Further, the additive is an unsaturated cyclic carbonate. During charge and discharge of a secondary battery equipped with the electrolytic solution, a film derived from the unsaturated cyclic carbonate is formed on the surface of the negative electrode, thereby suppressing the decomposition reaction of the electrolytic solution. In particular, when the fluorinated cyclic carbonate and the unsaturated cyclic carbonate are used in combination, a good film is formed, so the decomposition reaction of the electrolytic solution is more suppressed. However, the type of the unsaturated cyclic carbonate may be only one type or two or more types.

[0068] 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, so it may be only one or two or more.

[0069] Specific examples of the unsaturated cyclic carbonate include vinylene carbonate and the like. Note that the content of the unsaturated cyclic carbonate in the electrolytic solution is not particularly limited and can be arbitrarily set.

[0070] (Others) In addition, the additive may be any one or more of materials such as butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N,N-dimethylimidazolidinone, nitromethane, nitroethane, dimethyl sulfoxide, and trimethyl phosphate. This is because when the secondary battery equipped with the electrolyte is charged and discharged, a film is formed on the surface of the negative electrode, thereby suppressing the decomposition reaction of the electrolyte.

[0071] Since the additive described here is an optional component after all, the electrolyte may or may not contain the additive. Thereby, as described above, if the electrolyte contains a sulfonyl compound that is a solvent for dissolving or dispersing the lithium salt, it may not contain a general solvent.

[0072] <1-2. Manufacturing Method> When manufacturing the electrolyte, a lithium salt is added to the sulfonyl compound. In this case, additives such as one or both of a fluorinated ether compound and a fluorinated cyclic carbonate may be further added to the sulfonyl compound. Thereby, since the lithium salt is dissolved or dispersed in the sulfonyl compound, the electrolyte is prepared.

[0073] <1-3. Action and Effect> According to this electrolyte, the electrolyte contains a lithium salt and a sulfonyl compound, the sulfonyl compound contains two or more of a cyclic compound and a chain compound, and the molar ratio M is 2 to 4.

[0074] In this case, since the sulfonyl compound contains two or more of a cyclic compound and a chain compound, as described above, the lithium salt is easily and stably dissolved by the sulfonyl compound. As a result, the mixture of the lithium salt and the sulfonyl compound becomes a liquid instead of a solid.

[0075] Moreover, since the molar ratio M is optimized, as described above, the lithium salt is more easily and stably dissolved by the sulfonyl compound. As a result, the mixture of the lithium salt and the sulfonyl compound becomes a liquid more stably.

[0076] From these facts, since the mixture of the lithium salt and the sulfonyl compound can be used as an electrolyte, a secondary battery using the electrolyte can be realized. In this case, since the state (liquid) of the electrolyte is easily maintained, a secondary battery having excellent battery characteristics can be realized using the electrolyte.

[0077] In particular, if the sulfonyl compound contains two kinds of cyclic compounds, the lithium salt is sufficiently easily dissolved by the sulfonyl compound, so that a higher effect can be obtained.

[0078] In this case, if the sulfonyl compound contains sulfolane, the lithium salt is more stably and easily dissolved by the sulfonyl compound, so that an even higher effect can be obtained. Further, if the sulfonyl compound further contains 3-methylsulfolane, the lithium salt is more stably and easily dissolved by the sulfonyl compound, so that a remarkably high effect can be obtained.

[0079] Also, if the sulfonyl compound contains one kind of cyclic compound and one kind of chain compound, the lithium salt is sufficiently easily dissolved by the sulfonyl compound, so that a higher effect can be obtained.

[0080] In this case, if the sulfonyl compound contains sulfolane, the lithium salt is more likely to be stably dissolved by the sulfonyl compound, so that a higher effect can be obtained. Further, if the sulfonyl compound further contains one or both of dimethyl sulfolane and diethyl sulfolane, the lithium salt is more likely to be stably dissolved by the sulfonyl compound, so that a remarkably high effect can be obtained.

[0081] In addition, if the electrolytic solution further contains a fluorinated ether compound, the viscosity of the electrolytic solution decreases, so that a higher effect can be obtained.

[0082] In addition, if the electrolytic solution further contains a fluorinated cyclic carbonate, the decomposition reaction of the electrolytic solution is suppressed during charge and discharge of the secondary battery provided with the electrolytic solution, so that a higher effect can be obtained.

[0083] <2. Secondary battery> Next, a secondary battery using the above-described electrolytic solution will be described.

[0084] The secondary battery described here is a secondary battery in which a battery capacity is obtained by utilizing the occlusion and release of an electrode reactant, and includes an electrolytic solution together with a positive electrode and a negative electrode.

[0085] 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.

[0086] The type of the electrode reactant is not particularly limited. Specifically, the electrode material is a light metal such as an alkali metal and an alkaline earth metal. Specific examples of the alkali metal include lithium, sodium, and potassium, and specific examples of the alkaline earth metal include beryllium, magnesium, and calcium. However, the type of the electrode reactant may be other light metals such as aluminum.

[0087] Hereinafter, the case where the electrode reactant is lithium will be taken as an example. 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.

[0088] <2-1. Configuration> FIG. 1 shows a perspective configuration of a secondary battery, and FIG. 2 shows a cross-sectional configuration of the battery element 20 shown in FIG. 1. However, in FIG. 1, a state where the exterior film 10 and the battery element 20 are separated from each other is shown, and a cross-section of the battery element 20 along the XZ plane is shown by a dashed line. In FIG. 2, only a part of the battery element 20 is shown.

[0089] As shown in FIGS. 1 and 2, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminate film type secondary battery using a flexible or pliable exterior film 10.

[0090] [Exterior Film] As shown in FIG. 1, the exterior film 10 is an exterior member that houses the battery element 20, and has a bag-like structure that is sealed in a state where the battery element 20 is housed inside. Thereby, the exterior film 10 houses the electrolyte together with the positive electrode 21 and the negative electrode 22 described later.

[0091] Here, the exterior film 10 is a single film-like member and is folded in the folding direction F. A recessed portion 10U (so-called deep drawing portion) for housing the battery element 20 is provided in the exterior film 10.

[0092] Specifically, the exterior film 10 is a three-layer laminated film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside. In the state where the exterior film 10 is folded, the outer peripheral edge portions of the fusion layers facing each other are fused to each other. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0093] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, so it may be one layer or two layers, or four layers or more.

[0094] [Battery element] As shown in FIGS. 1 and 2, the battery element 20 is a power generation element including a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution (not shown), and is housed inside the exterior film 10.

[0095] This battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are laminated on each other with the separator 23 interposed therebetween, and are wound around a winding axis P while facing each other with the separator 23 interposed therebetween. This winding axis P is a virtual axis extending in the Y-axis direction.

[0096] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the three-dimensional shape of the battery element 20 is flat, the cross-section of the battery element 20 intersecting the winding axis P (the cross-section along the XZ plane) has a flat shape defined by a major axis J1 and a minor axis J2. This major axis J1 is a virtual axis extending in the X-axis direction and having a length larger than the minor axis J2, and the minor axis J2 is a virtual axis extending in the Z-axis direction intersecting the X-axis direction and having a length smaller than the major axis J1. Here, since the three-dimensional shape of the battery element 20 is a flat cylindrical shape, the shape of the cross-section of the battery element 20 is a flat substantially elliptical shape.

[0097] [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.

[0098] 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, and specific examples of the conductive material are aluminum and the like.

[0099] The positive electrode active material layer 21B contains any one or two or more of positive electrode active materials capable of occluding and releasing lithium. However, the positive electrode active material layer 21B may further contain any one or two or more of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0100] Here, the positive electrode active material layer 21B is provided on both surfaces of the positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically, it is a coating method or the like.

[0101] The type of the positive electrode active material is not particularly limited, but specifically, it is a lithium-containing compound or the like. This lithium-containing compound is a compound containing one or two or more transition metal elements as constituent elements together with lithium, and may further contain one or two or more other elements as constituent elements. The type of the other element is not particularly limited as long as it is an element other than each of lithium and the transition metal element, but specific examples of the other element are elements belonging to Groups 2 to 15 in the long-period type periodic table. The type of the lithium-containing compound is not particularly limited, but specifically, the lithium-containing compound is an oxide, a phosphate compound, a silicate compound, a borate compound, or the like.

[0102] Specific examples of the oxide are LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2 and LiMn2O4 etc. Specific examples of the phosphate compound are LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4 etc.

[0103] The positive electrode binder contains any one or two or more of materials such as synthetic rubber and polymer compounds. Specific examples of the synthetic rubber are styrene-butadiene rubber, fluorine rubber and ethylene propylene diene etc. Specific examples of the polymer compound are polyvinylidene fluoride, polyimide and carboxymethyl cellulose etc.

[0104] The positive electrode conductive agent contains any one or two or more of conductive materials such as carbon materials, and specific examples of the carbon materials are graphite, carbon black, acetylene black and ketjen black etc. However, the conductive material may also be a metal material, a polymer compound or the like.

[0105] (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.

[0106] 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 metal material, and specific examples of the conductive material are copper etc.

[0107] The negative electrode active material layer 22B contains any one or two or more of negative electrode active materials capable of occluding and releasing lithium. However, the negative electrode active material layer 22B may further contain any one or two or more of other materials such as a negative electrode binder and a negative electrode conductive agent.

[0108] Here, the negative electrode active material layer 22B is provided on both sides of the negative electrode current collector 22A. However, the negative electrode active material layer 22B may be 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 method for forming the negative electrode active material layer 22B is not particularly limited, but specifically, it is any one or two or more of a coating method, a vapor phase method, a liquid phase method, a spraying method, and a firing method (sintering method).

[0109] The type of the negative electrode active material is not particularly limited, but specifically, it is a carbon material, a metal-based material, etc. This is because a high energy density can be obtained. Specific examples of the carbon material are graphitizable carbon, non-graphitizable carbon, and graphite (natural graphite and artificial graphite). The metal-based material is a material containing any one or two or more of metal elements and metalloid elements capable of forming an alloy with lithium as constituent elements, and specific examples of the metal elements and metalloid elements are silicon, tin, etc. 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 are TiSi2 and SiO x (0 < x ≤ 2, or 0.2 < x < 1.4), etc.

[0110] Details regarding each of the negative electrode binder and the negative electrode conductive agent are the same as those regarding each of the positive electrode binder and the positive electrode conductive agent.

[0111] (Separator) As shown in FIG. 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. This separator 23 contains a polymer compound such as polyethylene.

[0112] (Electrolyte solution) The electrolyte solution is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23, and has the above-described configuration. That is, the electrolyte solution contains a lithium salt and a sulfonyl compound.

[0113] [Positive electrode lead and negative electrode lead] As shown in FIGS. 1 and 2, the positive electrode lead 31 is a positive electrode terminal connected to the positive electrode current collector 21A of the positive electrode 21, and is led out from the inside to the outside of the exterior film 10. This positive electrode lead 31 contains a conductive material such as a metal material, and specific examples of the conductive material are aluminum and the like. The shape of the positive electrode lead 31 is not particularly limited, but specifically, the positive electrode lead 31 is either in a thin plate shape or a mesh shape.

[0114] As shown in FIGS. 1 and 2, the negative electrode lead 32 is a negative electrode terminal connected to the negative electrode current collector 22A of the negative electrode 22, and is led out from the inside to the outside of the exterior film 10. This negative electrode lead 32 contains a conductive material such as a metal material, and specific examples of the conductive material are copper and the like. Here, the leading direction of the negative electrode lead 32 is the same as the leading direction of the positive electrode lead 31. Note that the details regarding the shape of the negative electrode lead 32 are the same as the details regarding the shape of the positive electrode lead 31.

[0115] [Sealing film] The sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0116] This sealing film 41 is a sealing member that prevents the intrusion of outside air or the like into the exterior film 10. Further, the sealing film 41 contains a polymer compound such as polyolefin having adhesiveness to the positive electrode lead 31, and the polyolefin is polypropylene or the like.

[0117] The configuration of the sealing film 42 is the same as that of the sealing film 41 except that it is a sealing member having adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin having adhesiveness to the negative electrode lead 32.

[0118] <2-2. Operation> During charging of the secondary battery, in the battery element 20, lithium is released from the positive electrode 21 and the lithium is occluded in the negative electrode 22 through the electrolytic solution. On the other hand, during discharging of the secondary battery, in the battery element 20, lithium is released from the negative electrode 22 and the lithium is occluded in the positive electrode 21 through the electrolytic solution. During these charging and discharging processes, lithium is occluded and released in an ionic state.

[0119] <2-3. Manufacturing method> When manufacturing a secondary battery, each of the positive electrode 21 and the negative electrode 22 is produced by the procedure of an example described below, and after assembling the secondary battery using the electrolytic solution together with the positive electrode 21 and the negative electrode 22, the stabilization treatment of the secondary battery is performed. The procedure for preparing the electrolytic solution is as described above.

[0120] [Production of positive electrode] First, a paste-like positive electrode mixture slurry is prepared by introducing a mixture (positive electrode mixture) in which a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent are mixed with each other into a solvent. This solvent may be an aqueous solvent or an organic solvent. Subsequently, a positive electrode active material layer 21B is formed by applying the positive electrode mixture slurry to both surfaces of the positive electrode current collector 21A. Finally, the positive electrode active material layer 21B is compression-molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or compression molding may be repeated a plurality of times. As a result, since the positive electrode active material layers 21B are formed on both surfaces of the positive electrode current collector 21A, the positive electrode 21 is produced.

[0121] [Fabrication of negative electrode] A negative electrode 22 is formed by the same procedure as the fabrication procedure of the positive electrode 21 described above. Specifically, first, a paste-like negative electrode mixture slurry is prepared by introducing a mixture (negative electrode mixture) in which a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent are mixed with each other into a solvent. Details regarding the solvent are as described above. Subsequently, a negative electrode active material layer 22B is formed by applying the negative electrode mixture slurry to both surfaces of the negative electrode current collector 22A. Finally, the negative electrode active material layer 22B is compression-molded. As a result, since the negative electrode active material layers 22B are formed on both surfaces of the negative electrode current collector 22A, the negative electrode 22 is produced.

[0122] [Assembly of secondary battery] First, a positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as a welding method, and a negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22 using a joining method such as a welding method.

[0123] Subsequently, after laminating the positive electrode 21 and the negative electrode 22 with each other via a separator 23, a wound body (not shown) is produced by winding the positive electrode 21, the negative electrode 22, and the separator 23. This wound body has the same configuration as the configuration of the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with the electrolytic solution. Subsequently, the wound body is pressed using a press or the like to mold the wound body into a flat shape.

[0124] Subsequently, after accommodating the wound body inside the recessed portion 10U, the exterior film 10 (fusion layer / metal layer / surface protection layer) is folded so that the exterior films 10 face each other. Subsequently, by using an adhesion method such as a thermal fusion method, the outer peripheral edge portions of two sides among the fusion layers facing each other are adhered to each other, thereby accommodating the wound body inside the bag-shaped exterior film 10.

[0125] Finally, after injecting the electrolytic solution inside the bag-shaped exterior film 10, the outer peripheral edge portions of the remaining one side among the fusion layers facing each other are adhered to each other by using an adhesion method such as a thermal fusion method. In this case, a sealing film 41 is inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the exterior film 10 and the negative electrode lead 32.

[0126] As a result, since the wound body is impregnated with the electrolytic solution, the battery element 20, which is a wound electrode body, is manufactured. Therefore, since the battery element 20 is enclosed inside the bag-shaped exterior film 10, a secondary battery is assembled.

[0127] [Stabilization of the secondary battery] The assembled secondary battery is charged and discharged. Various conditions such as the environmental temperature, the number of charge and discharge cycles (cycle number), and the charge and discharge conditions can be arbitrarily set. As a result, a film is formed on the surfaces of the positive electrode 21 and the negative electrode 22, respectively, so that the state of the secondary battery is electrochemically stabilized. Therefore, the secondary battery is completed.

[0128] <2-4. Action and effect> According to this secondary battery, the secondary battery includes an electrolytic solution, and the electrolytic solution has the above-described configuration. Therefore, for the reasons described above, a secondary battery having excellent battery characteristics can be realized by using the electrolytic solution. These battery characteristics are capacity characteristics, cycle characteristics, and the like.

[0129] In particular, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the intercalation and deintercalation of lithium, so that higher effects can be obtained.

[0130] Other actions and effects of this secondary battery are the same as those of the above-described other actions and effects of the electrolytic solution.

[0131] <3. Modification Examples> The configuration of the secondary battery described above can be appropriately changed as described below. However, a series of modification examples described below may be combined with each other.

[0132] [Modification Example 1] The separator 23 which is a porous membrane was used. However, although not specifically illustrated here, a laminated separator including a polymer compound layer may be used.

[0133] 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 adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, and thus the displacement (winding displacement) of the battery element 20 is suppressed. As a result, even if a side reaction such as a decomposition reaction of the electrolytic solution occurs, the swelling of the secondary battery is suppressed. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because excellent physical strength and excellent electrochemical stability can be obtained.

[0134] Note that one or both of the porous membrane and the polymer compound layer may contain any one or two or more of a plurality of insulating particles. This is because when the secondary battery generates heat, the plurality of insulating particles promote heat dissipation, and thus the safety (heat resistance) of the secondary battery is improved. The insulating particles contain one or both of an inorganic material and a resin material. Specific examples of the inorganic material are aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of the resin material are acrylic resin and styrene resin.

[0135] When producing a laminated separator, after preparing a precursor solution containing a polymer compound, a solvent, etc., the precursor solution is applied to one or both sides of a porous membrane. In this case, if necessary, a plurality of insulating particles may be added to the precursor solution.

[0136] Even when using this laminated separator, since lithium ions can move between the positive electrode 21 and the negative electrode 22, the same effects can be obtained. In this case, in particular, as described above, since the safety of the secondary battery is improved, higher effects can be obtained.

[0137] [Modification Example 2] An electrolytic solution that is a liquid electrolyte was used. However, although not specifically illustrated here, an electrolyte layer that is a gel electrolyte may be used.

[0138] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are laminated on each other via the separator 23 and the electrolyte layer, and the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte layer are wound. This electrolyte layer is interposed between the positive electrode 21 and the separator 23 and is also interposed between the negative electrode 22 and the separator 23.

[0139] Specifically, the electrolyte layer contains a polymer compound together with the electrolytic solution, and the electrolytic solution is retained by the polymer compound. This is because leakage of the electrolytic solution is prevented. The configuration of the electrolytic solution is as described above. The polymer compound includes polyvinylidene fluoride, etc. When forming the electrolyte layer, after preparing a precursor solution containing the electrolytic solution, the polymer compound, a solvent, etc., the precursor solution is applied to one or both sides of each of the positive electrode 21 and the negative electrode 22.

[0140] Even when using this electrolyte layer, lithium ions can move between the positive electrode 21 and the negative electrode 22 through the electrolyte layer, so the same effect can be obtained. In this case, in particular, as described above, since leakage of the electrolyte is prevented, a higher effect can be obtained.

[0141] <4. Applications of Secondary Batteries> The applications (application examples) of secondary batteries are not particularly limited. A secondary battery used as a power source may be a main power source or an auxiliary power source in electronic devices and electric vehicles, etc. The main power source is a power source that is preferentially used regardless of the presence or absence of other power sources. The auxiliary power source may be a power source used instead of the main power source or a power source that can be switched from the main power source.

[0142] Specific examples of the applications of secondary batteries are as follows. Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power sources and memory cards. Electric tools such as electric drills and electric saws. Battery packs mounted on electronic devices, etc. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric automobiles (including hybrid automobiles). Power storage systems such as household or industrial battery systems that store power in case of emergencies, etc. In these applications, one secondary battery may be used, or a plurality of secondary batteries may be used.

[0143] The battery pack may use a single cell or a battery module. An electric vehicle is a vehicle that operates (runs) using a secondary battery as a driving power source, and may be a hybrid automobile that also includes other driving sources in addition to the secondary battery. In a household power storage system, household electrical appliances, etc. can be used by utilizing the power stored in the secondary battery that is the power storage source.

[0144] Here, a specific example of an application example of a secondary battery will be described. Since the configuration of the application example described below is merely an example, it can be changed as appropriate.

[0145] Figure 3 shows the block configuration of a battery pack. The battery pack described here is a battery pack (so-called soft pack) using one secondary battery, and is mounted on an electronic device typified by a smartphone.

[0146] As shown in Figure 3, this battery pack includes a power source 51 and a circuit board 52. This circuit board 52 is connected to the power source 51 and includes a positive electrode terminal 53, a negative electrode terminal 54, and a temperature detection terminal 55.

[0147] The power source 51 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to the positive electrode terminal 53, and the negative electrode lead is connected to the negative electrode terminal 54. Since this power source 51 can be connected to the outside via the positive electrode terminal 53 and the negative electrode 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.

[0148] The control unit 56 includes a central processing unit (CPU) and a memory, etc., and controls the operation of the entire battery pack. This control unit 56 detects and controls the usage state of the power source 51 as necessary.

[0149] In addition, when the voltage of the power source 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 56 disconnects the switch 57 so that no charging current flows through the current path of the power source 51. The overcharge detection voltage is not particularly limited, but specifically, it is 4.20V ± 0.05V, and the overdischarge detection voltage is not particularly limited, but specifically, it is 2.40V ± 0.1V.

[0150] Switch 57 includes a charging control switch, a discharging control switch, a charging diode, a discharging diode, etc., and switches the connection between the power supply 51 and the external device according to the instruction of the control unit 56. This switch 57 includes a field effect transistor (MOSFET) using a metal oxide semiconductor, etc., and the charging and discharging current is detected based on the ON resistance of the switch 57.

[0151] 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 measurement result of the temperature to the control unit 56. The measurement result of the temperature measured by the temperature detection unit 59 is used when the control unit 56 performs charging and discharging control during abnormal heat generation and when the control unit 56 performs correction processing during calculation of the remaining capacity.

Example

[0152] An example of this technology will be described.

[0153] <Examples 1 to 9 and Comparative Examples 1 to 4> As described below, after manufacturing the electrolytic solution, the characteristics of the electrolytic solution were evaluated.

[0154] [Manufacture of Electrolytic Solution] After adding an electrolyte salt (lithium salt) to a solvent (sulfonyl compound), the solvent was stirred.

[0155] As the sulfonyl compound (cyclic compound), sulfolane (SL) and 3-methylsulfolane (MSL) were used. As the sulfonyl compound (chain compound), dimethyl sulfone (DMS) and ethyl methyl sulfone (EMS) were used. The specific composition of the sulfonyl compound is as shown in Table 1. Here, two types of cyclic compounds and chain compounds were used as the sulfonyl compound.

[0156] As the lithium salt, lithium bis(fluorosulfonyl)imide (LiFSI) was used.

[0157] In this case, as shown in Table 1, the mixing ratio of the lithium salt and the sulfonyl compound was set. That is, the molar ratio M was changed by varying the amount of substance (mol) of each of the lithium salt and the sulfonyl compound (cyclic compound and chain compound).

[0158] Thereby, an electrolytic solution containing a lithium salt and a sulfonyl compound was prepared.

[0159] For comparison, an electrolytic solution was prepared by the same procedure except that only one of the cyclic compound and the chain compound was used as the sulfonyl compound, as shown in Table 1.

[0160] [Evaluation of Characteristics of Electrolytic Solution] When the characteristics (state) of the electrolytic solution were evaluated, the results shown in Table 1 were obtained.

[0161] Specifically, in a freezer (temperature = -10 °C), after storing the mixture obtained by the above-described electrolytic solution production procedure for a period of time (storage time = 1 week), the state (liquid or solid) of the mixture was visually determined.

[0162] In Table 1, for reference, the concentration (mol / dm 3 (= mol / l)), density (g / cm 3 ), viscosity (mPa·s), and ionic conductivity (mS / cm) of the mixture are also shown. The concentration is the content of the electrolyte salt (lithium salt) with respect to the solvent (sulfonyl compound). The density and viscosity were measured using a viscometer (Stabinger viscometer SVM3000 manufactured by Anton Paar). Also, an alternating current impedance measuring device (VMP3 alternating current impedance measuring device manufactured by Biologic) was connected to an electric conductivity cell (CG-511B electric conductivity cell manufactured by Toa DKK Corporation), and the ionic conductivity was measured using the alternating current impedance method.

[0163]

Table 1

[0164] [Investigation] As shown in Table 1, the state of the mixture varied depending on the composition of the mixture.

[0165] Specifically, when only one type of sulfonyl compound was used as the solvent (Comparative Examples 1 to 4), the state of the mixture became solid. When a chain compound was used as the sulfonyl compound, depending on the molar ratio M, a part of the mixture had already become solid at room temperature, so each of the concentration, density, viscosity, and ionic conductivity was not measured.

[0166] On the other hand, when two types of sulfonyl compounds were used as the solvent and the molar ratio M was set to 2 to 4 (Examples 1 to 9), the state of the mixture became liquid, so the mixture became a liquid electrolyte (electrolyte solution).

[0167] In this case (Examples 1 to 9), in particular, a series of tendencies described below were obtained.

[0168] First, when two types of cyclic compounds were used as the sulfonyl compound (Examples 1 to 3), the state of the mixture became a stable liquid. In this case, when the first cyclic compound was sulfolane (SL) and the second cyclic compound was a derivative of sulfolane (MSL), the state of the mixture became a sufficiently stable liquid.

[0169] Second, when one type of cyclic compound and one type of chain compound were used as the sulfonyl compound (Examples 4 to 9), the state of the mixture became a stable liquid. In this case, when the cyclic compound was sulfolane (SL) and the chain compound was either dimethyl sulfone (DMS) or ethyl methyl sulfone (EMS), the state of the mixture became a sufficiently stable liquid.

[0170] <Examples 10 to 14> As shown in Table 2, an electrolytic solution was produced by the same procedure as in Examples 2 and 5, except that a fluorinated ether compound was further added to the solvent (sulfonyl compound), and then the properties of the electrolytic solution were evaluated.

[0171] Here, hydrofluoroether (CHF2-CF2-O-CH2-CF2-CHF2 (HFE)) was used as the fluorinated ether compound. The addition amount (amount of substance (mol)) of the fluorinated ether compound is as shown in Table 2.

[0172]

Table 2

[0173] As shown in Table 2, even when a fluorinated ether compound was used (Examples 10 to 14), the state of the mixture became liquid, and thus a liquid electrolyte (electrolytic solution) was obtained.

[0174] In this case, in particular, compared with the case where no fluorinated ether compound was used (Examples 2 and 5), the viscosity decreased and the ionic conductivity increased.

[0175] <Example 15> As described below, after manufacturing a test secondary battery using the electrolytic solution of Example 13, the battery characteristics of the secondary battery were evaluated.

[0176] Figure 4 shows the cross-sectional configuration of the test secondary battery, and the test secondary battery is a so-called coin-type lithium-ion secondary battery. In this secondary battery, as shown in Figure 4, the test electrode 61 is housed inside the exterior cup 64, and the counter electrode 62 is housed inside the exterior can 65. The test electrode 61 and the counter electrode 62 are laminated with each other via a separator 63, and the exterior cup 64 and the exterior can 65 are clamped to each other via a gasket 66. The electrolytic solution is impregnated in each of the test electrode 61, the counter electrode 62, and the separator 63.

[0177] [Manufacture of Secondary Battery] When fabricating the test electrode 61, first, 90 parts by mass of a positive electrode active material (LiNi which is a lithium-containing compound (oxide)) 0.8 Co 0.15 Al 0.05 O2), 5 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 5 parts by mass of a positive electrode conductive agent (Ketjen black) were mixed with each other to obtain a positive electrode mixture. Subsequently, after adding the positive electrode mixture to a solvent (N-methyl-2-pyrrolidone which is an organic solvent), the solvent was stirred to obtain a paste-like positive electrode mixture slurry. Subsequently, using a coating device, the positive electrode mixture slurry was applied to one side of a positive electrode current collector (aluminum foil with a thickness of 15 μm), and then the positive electrode mixture slurry was dried to form a positive electrode active material layer. Finally, the positive electrode active material layer was compression-molded using a roll press machine.

[0178] When fabricating the counter electrode 62, first, 90 parts by mass of a negative electrode active material (elemental silicon which is a metal-based material), 5 parts by mass of a negative electrode binder (polyvinylidene fluoride), and 5 parts by mass of a negative electrode conductive agent (Ketjen black) were mixed with each other to obtain a negative electrode mixture. Subsequently, after adding the negative electrode mixture to a solvent (N-methyl-2-pyrrolidone which is an organic solvent), the solvent was dried to obtain a paste-like negative electrode mixture slurry. Subsequently, using a coating device, the negative electrode mixture slurry was applied to one side of a negative electrode current collector (copper foil with a thickness of 15 μm), and then the negative electrode mixture slurry was dried to form a negative electrode active material layer. Finally, the negative electrode active material layer was compression-molded using a roll press machine.

[0179] When preparing the electrolytic solution, the same procedure as in Example 13 was used, except that a fluorinated cyclic carbonate was further added to a solvent (sulfonyl compound) as required. As the fluorinated cyclic carbonate, fluoroethylene carbonate (FEC) was used. The addition amount (amount of substance (mol)) of the fluorinated cyclic carbonate is as shown in Table 3.

[0180] When assembling the secondary battery, first, the test electrode 61 was punched out into a pellet shape and then the test electrode 61 was housed inside the outer cup 64. Subsequently, after punching out the counter electrode 62 into a pellet shape, the counter electrode 62 was housed inside the outer can 65. Finally, through the separator 63 (a porous polyolefin film with a thickness of 7 μm) impregnated with the electrolytic solution, the test electrode 61 housed in the outer cup 64 and the counter electrode 62 housed in the outer can 65 were laminated on each other, and then the outer cup 64 and the outer can 65 were clamped to each other through the gasket 66.

[0181] When stabilizing the assembled secondary battery, the secondary battery was charged and discharged for 1 cycle in a normal temperature environment (temperature = 23°C). During charging, it was first charged at a constant current until the voltage reached 4.2V at a current density of 1 mA / cm 2 , and then charged at a constant voltage until the current density reached 0.02 mA / cm 2 at that voltage of 4.2V. During discharging, it was discharged at a constant current until the voltage reached 3.0V at a current density of 1 mA / cm 2 .

[0182] As a result, the test secondary battery shown in Fig. 4 was completed.

[0183] [Evaluation of Battery Characteristics] When evaluating the cycle characteristics as the battery characteristics, the results shown in Table 3 were obtained.

[0184] In this case, first, the discharge capacity (the discharge capacity of the first cycle) was measured by charging and discharging the secondary battery in a normal temperature environment. Subsequently, the secondary battery was repeatedly charged and discharged until the total number of cycles reached 50 cycles in the same environment, and again the discharge capacity (the discharge capacity of the 50th cycle) was measured. Finally, based on the calculation formula of capacity retention rate (%) = (discharge capacity of the 50th cycle / discharge capacity of the first cycle) × 100, the capacity retention rate, which is an index for evaluating the cycle characteristics, was calculated. The charge and discharge conditions were the same as those during the stabilization of the secondary battery.

[0185]

Table 3

[0186] [Investigation] As shown in Table 3, when an electrolytic solution containing a lithium salt and a sulfonyl compound was used (Example 13), a high capacity retention rate was obtained. In this case, when the electrolytic solution contained a fluorinated cyclic carbonate (Example 15), the capacity retention rate further increased.

[0187] [Summary] From the results shown in Tables 1 to 3, when the electrolytic solution contained a lithium salt and a sulfonyl compound, and the sulfonyl compound contained two or more of a cyclic compound and a chain compound, and the molar ratio M was 2 to 4, the state (liquid) of the electrolytic solution was ensured. Therefore, a mixture of a lithium salt and a sulfonyl compound could be used as a liquid electrolyte (electrolytic solution). As a result, a secondary battery having excellent battery characteristics could be realized using the electrolytic solution.

[0188] As described above, the present technology has been described with one embodiment and examples, but the configuration of the present technology is not limited to the configuration described in one embodiment and examples, and thus can be variously modified.

[0189] Specifically, the case where the battery structure of the secondary battery is a laminate film type has been described. However, since the battery structure of the secondary battery is not particularly limited, it may be a cylindrical type, a square type, a button type, or the like.

[0190] Also, 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, it may be a stacked type, a ninety-nine fold type, or the like. In the stacked type, the positive electrode and the negative electrode are alternately stacked via a separator, and in the ninety-nine fold type, the positive electrode and the negative electrode are folded in a zigzag while facing each other via a separator.

[0191] Furthermore, although the electrode reactant has been described in the case where it is lithium, 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. In addition, the electrode reactant may be other light metals such as aluminum.

[0192] The effects described in this specification are merely illustrative, and thus 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.

Claims

1. A lithium salt, Sulfonyl compounds and Including, the sulfonyl compound includes two or more compounds selected from the cyclic compound represented by formula (1) and the chain compound represented by formula (2), and also includes at least the cyclic compound represented by formula (1), The concentration of the lithium salt is 1.159 mol / L or more, a ratio of the number of moles of the sulfonyl compound to the number of moles of the lithium salt is 2 or more and 4 or less; Further, the fluorinated ether compound represented by formula (3) is contained. Electrolyte for secondary batteries. 【Chemical 1】 (R1 is an alkylene group.) [Chemical Formula 2] (Each of R2 and R3 is an alkyl group.) R4-O-R5...(3) (Each of R4 and R5 is a fluorinated alkyl group.)

2. The sulfonyl compound contains two of the cyclic compounds. The electrolyte for a secondary battery according to claim 1.

3. The sulfonyl compound includes sulfolane. The electrolyte for a secondary battery according to claim 2.

4. The sulfonyl compound further includes 3-methylsulfolane. The electrolyte for a secondary battery according to claim 3.

5. the sulfonyl compound includes one type of the cyclic compound and one type of the chain compound; The electrolyte for a secondary battery according to claim 1.

6. The sulfonyl compound includes sulfolane. The electrolyte for a secondary battery according to claim 5.

7. The sulfonyl compound further includes any one of dimethyl sulfone and ethyl methyl sulfone. The electrolyte for a secondary battery according to claim 6.

8. Further, fluorinated cyclic carbonates are included. The electrolyte solution for a secondary battery according to claim 1 .

9. A positive electrode and a negative electrode; The electrolyte solution for a secondary battery according to any one of claims 1 to 8, A secondary battery comprising:

10. It is a lithium-ion secondary battery. The secondary battery according to claim 9.

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