Electrolyte for secondary battery and secondary battery

Abstract

This secondary battery comprises a positive electrode, a negative electrode, and an electrolyte solution including an electrolyte salt containing an imide anion represented by formula (1).

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 an imide compound represented by R F 1 -S(=O)2-NH-S(=O)2-NH-S(=O)2-R F 2 (see, for example, Patent Document 1). Further, the electrolyte salt of the electrolyte contains an imide anion represented by F-S(=O)2-N - -C(=O)-N - -S(=O)2-F or F-S(=O)2-N - -S(=O)2-C6H4-S(=O)2-N - -S(=O)2-F (see, for example, Non-Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

[0006] Although various studies have been conducted on the configuration of secondary batteries, there is still room for improvement because the battery characteristics of the secondary batteries are not yet sufficient.

[0007] Therefore, an electrolyte for a secondary battery and a secondary battery that can obtain excellent battery characteristics are desired.

[0008] The electrolyte for a secondary battery according to an embodiment of the present technology contains an electrolyte salt, and the electrolyte salt contains an imide anion represented by the formula (1).

[0009] [Chemical Formula] (Each of R1 and R2 is either a fluorine group or a fluorinated alkyl group. R3 is a fluorinated alkylene group. Each of W, X, Y, and Z is either a carbonyl group (>C=O), a sulfinyl group (>S=O), or a sulfonyl group (>S(=O)2).)

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

[0011] According to the electrolytic solution for a secondary battery or the secondary battery according to one embodiment of the present technology, since the electrolyte salt of the electrolytic solution for a secondary battery contains an imide anion, 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 the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0014] Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. The order of description is as follows. 1. Electrolytic solution 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. Electrolytic solution for secondary battery> First, an electrolyte for a secondary battery according to an embodiment of the present technology (hereinafter simply referred to as "electrolyte") will be described.

[0016] <1-1. Configuration> The electrolyte is a liquid electrolyte used in a secondary battery, which is an electrochemical device. However, the electrolyte may be used in other electrochemical devices. The type of other electrochemical devices is not particularly limited, but specifically, other electrochemical devices include capacitors and the like.

[0017] This electrolyte contains an electrolyte salt. More specifically, the electrolyte contains, together with the electrolyte salt, a solvent for dispersing (ionizing) the electrolyte salt.

[0018] [Electrolyte Salt] The electrolyte salt contains an anion and a cation.

[0019] (Anion) The anion contains an imide anion represented by formula (1). However, the type of imide anion may be only one type or two or more types.

[0020] [Chemical Formula] (Each of R1 and R2 is either a fluorine group or a fluorinated alkyl group. R3 is a fluorinated alkylene group. Each of W, X, Y, and Z is either a carbonyl group, a sulfinyl group, or a sulfonyl group.)

[0021] The reason why the anion contains an imide anion is as described below. First, when a secondary battery using a positive electrode and a negative electrode is charged and discharged with an electrolytic solution, a high-quality film derived from an electrolyte salt is formed on the surfaces of the positive electrode and the negative electrode, respectively. Therefore, the decomposition reaction of the electrolytic solution (particularly, the solvent described later) is suppressed. Second, by using the above-described film, the migration rate of cations is improved in the vicinity of the surfaces of the positive electrode and the negative electrode, respectively. Third, the migration rate of cations is also improved in the electrolytic solution.

[0022] As shown in the formula (1), this imide anion is a chain anion (divalent minus ion) having two nitrogen atoms (N) and four functional groups (W, X, Y, and Z).

[0023] Each of R1 and R2 is not particularly limited as long as it is either a fluorine group (-F) or a fluorinated alkyl group. That is, each of R1 and R2 may be the same group as each other or different groups from each other. Accordingly, each of R1 and R2 is not a hydrogen group (-H) or an alkyl group.

[0024] The fluorinated alkyl group is a group in which one or more hydrogen groups (-H) in the alkyl group are substituted by fluorine groups. However, the fluorinated alkyl group may be linear or branched having one or more side chains.

[0025] The number of carbon atoms of the fluorinated alkyl group is not particularly limited, but specifically, it is 1 to 10. This is because the solubility and ionization of the electrolyte salt containing the imide anion are improved.

[0026] Specific examples of the fluorinated alkyl group include a perfluoromethyl group (-CF3) and a perfluoroethyl group (-C2F5).

[0027] The fluorinated alkylene group which is R3 is a group in which one or more hydrogen groups of the alkylene group are substituted by fluorine groups. However, the fluorinated alkylene group may be linear or branched having one or more side chains.

[0028] The carbon number of the fluorinated alkylene group is not particularly limited, but specifically, it is 1 to 10. This is because the solubility and ionizability of the electrolyte salt containing the imide anion are improved.

[0029] Specific examples of the fluorinated alkylene group are a perfluoromethylene group (-CF2-), a perfluoroethylene group (-C2F4-), a perfluoropropylene group (-C3F6-), and the like.

[0030] Each of W, X, Y, and Z is not particularly limited as long as it is any one of a carbonyl group, a sulfinyl group, and a sulfonyl group. That is, each of W to Z may be the same group as each other or different groups from each other. Of course, only any two of W to Z may be the same group as each other, or only any three of W to Z may be the same group as each other.

[0031] (Specific examples of anions) Specific examples of the imide anion are anions represented by each of Formula (1-1) to Formula (1-56) and the like.

[0032]

Chemical formula

[0033]

Chemical formula

[0034]

Chemical formula

[0035]

Chemical formula

[0036] [Chemical formula]

[0037] [Chemical formula]

[0038] (Cation) The type of cation is not particularly limited. Specifically, the cation contains any one or two or more of light metal ions. That is, the electrolyte salt contains light metal ions as cations. This is because a high voltage can be obtained in a secondary battery using the electrolyte solution.

[0039] The type of light metal ion is not particularly limited. Specifically, the light metal ion is an alkali metal ion, an alkaline earth metal ion, etc. Specific examples of alkali metal ions are lithium ion, sodium ion, potassium ion, etc. Specific examples of alkaline earth metal ions are beryllium ion, magnesium ion, calcium ion, etc. In addition, the type of light metal ion may be aluminum ion, etc.

[0040] Among them, it is preferable that the light metal ion contains lithium ion. This is because a sufficiently high voltage can be obtained in a secondary battery using the electrolyte solution.

[0041] (Content) Since the content of the electrolyte salt in the electrolyte solution is not particularly limited, it can be arbitrarily set. Among them, the content of the electrolyte salt is preferably 0.20 mol / kg to 2.00 mol / kg with respect to the solvent. This is because high ionic conductivity can be obtained.

[0042] [Solvent] The solvent contains any one or two or more of non-aqueous solvents (organic solvents), and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte. The non-aqueous solvents include esters and ethers, and more specifically, carbonate-based compounds, carboxylic acid ester-based compounds, lactone-based compounds, etc.

[0043] The carbonate-based 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.

[0044] The carboxylic acid ester-based compounds include chain carboxylic acid esters. Specific examples of chain carboxylic acid esters are methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl trimethylacetate, methyl butyrate, and ethyl butyrate.

[0045] The lactone-based compounds include lactones. Specific examples of lactones are γ-butyrolactone and γ-valerolactone.

[0046] In addition, the ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.

[0047] [Other electrolyte salts] In addition, the electrolyte may further contain any one or two or more of other electrolyte salts. This is because the migration rate of cations is further improved near the surfaces of the positive electrode and the negative electrode, and the migration rate of cations is also further improved in the electrolyte solution. Since the content of other electrolyte salts in the electrolyte solution is not particularly limited, it can be set arbitrarily.

[0048] The types of other electrolyte salts are not particularly limited. Specifically, other electrolyte salts are light metal salts such as lithium salts. However, the above-described electrolyte salts are excluded from the lithium salts described herein.

[0049] Specific examples of lithium salts include 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)phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalatophosphate (LiPF4(C2O4)), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2).

[0050] Among them, other electrolyte salts preferably contain any one or two or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate. This is because the migration rate of cations is sufficiently improved near the surface of each of the positive electrode and the negative electrode, and the migration rate of cations is also sufficiently improved in the electrolyte solution.

[0051] [Additive] Furthermore, the electrolyte solution may further contain any one or two or more of the additives. This is because a film derived from the additive is formed on the surface of each of the positive electrode and the negative electrode during charge and discharge of the secondary battery using the electrolyte solution, thereby suppressing the decomposition reaction of the electrolyte solution. Note that the content of the additive in the electrolyte solution is not particularly limited and can be arbitrarily set.

[0052] The type of the additive is not particularly limited. Specifically, the additive is an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, a sulfonic acid ester, a dicarboxylic anhydride, a disulfonic anhydride, a sulfate ester, a nitrile compound, an isocyanate compound, or the like.

[0053] (Unsaturated cyclic carbonate) The unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated carbon bond (carbon-carbon double bond). The number of unsaturated carbon bonds is not particularly limited, so it may be only 1 or 2 or more. Specific examples of the unsaturated cyclic carbonate include vinylene carbonate, vinyl ethylene carbonate, and methylene ethylene carbonate.

[0054] (Fluorinated cyclic carbonate) The fluorinated cyclic carbonate is a cyclic carbonate containing fluorine as a constituent element. That is, the fluorinated cyclic carbonate is a compound in which one or more hydrogen groups of the cyclic carbonate are substituted by fluorine groups. Specific examples of the fluorinated cyclic carbonate include ethylene monofluorocarbonate and ethylene difluorocarbonate.

[0055] (Sulfonic acid ester) The sulfonic acid ester is a cyclic monosulfonic acid ester, a cyclic disulfonic acid ester, a chain monosulfonic acid ester, a chain disulfonic acid ester, or the like. Specific examples of the cyclic monosulfonic acid ester include 1,3-propanesultone, 1-propene-1,3-sultone, 1,4-butanesultone, 2,4-butanesultone, and propargyl methanesulfonate. Specific examples of the cyclic disulfonic acid ester include cyclodison.

[0056] (Dicarboxylic anhydride) Specific examples of the dicarboxylic anhydride include succinic anhydride, glutaric anhydride, and maleic anhydride.

[0057] (Disulfonic anhydride) Specific examples of the disulfonic anhydride include ethanedisulfonic anhydride and propanedisulfonic anhydride.

[0058] (Sulfuric acid ester) Specific examples of the sulfuric acid ester include ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide).

[0059] (Nitrile compound) The nitrile compound is a compound having 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(dicyanomethylene) indane.

[0060] (Isocyanate compound) The isocyanate compound is a compound having one or more isocyanate groups (-NCO). Specific examples of the isocyanate compound include hexamethylene diisocyanate.

[0061] <1-2. Manufacturing method> When producing the electrolyte solution, the electrolyte salt is added to the solvent. In this case, another electrolyte salt may be further added to the solvent, or an additive may be further added to the solvent. Thereby, since the electrolyte salt and the like are dispersed or dissolved in the solvent, the electrolyte solution is prepared.

[0062] <1-3. Action and effect> According to this electrolyte solution, the electrolyte solution contains an electrolyte salt, and the electrolyte salt contains an imide anion.

[0063] In this case, as described above, compared with the case where the electrolyte salt contains other anions, in a secondary battery using the electrolyte, the decomposition reaction of the electrolyte is suppressed and the migration rate of cations is improved. Therefore, excellent battery characteristics can be obtained in a secondary battery using the electrolyte.

[0064] The above-mentioned "other anions" refer to phosphate hexafluoride ions (PF6 - ) that do not correspond to imide anions. Further, the "other anions" do not correspond to imide anions but are anions similar to the imide anions, specifically, anions represented by each of Formula (2-1) to Formula (2-7).

[0065]

Chemical formula

[0066] In the anions shown in each of Formula (2-1) and Formula (2-2), when each of R1 and R2 is either a fluorine group or a fluorinated alkyl group and each of W to Z is a carbonyl group, R3 is a phenylene group.

[0067] In the anions shown in each of Formula (2-3) and Formula (2-4), when each of R1 and R2 is either a fluorine group or a fluorinated alkyl group and each of W to Z is a sulfinyl group, R3 is a phenylene group.

[0068] In the anions shown in each of Formula (2-5) and Formula (2-6), when each of R1 and R2 is either a fluorine group or a fluorinated alkyl group and each of W to Z is a sulfonyl group, R3 is a phenylene group.

[0069] In the anion represented by the formula (2-7), when each of R1 and R2 is a fluorine group, each of W, Y and Z is a sulfonyl group, and X is a carbonyl group, R3 is a phenylene group.

[0070] In particular, if the electrolyte salt contains a light metal ion as a cation, a high voltage can be obtained in the secondary battery using the electrolyte salt, so that a higher effect can be obtained. In this case, if the light metal ion contains a lithium ion, a higher voltage can be obtained, so that an even higher effect can be obtained.

[0071] Further, if the content of the electrolyte salt is 0.20 mol / kg to 2.00 mol / kg with respect to the solvent, high ionic conductivity can be obtained, so that a higher effect can be obtained.

[0072] Further, if the electrolytic solution further contains any one or two or more of an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, a sulfonic acid ester, a dicarboxylic acid anhydride, a disulfonic acid anhydride, a sulfuric acid ester, a nitrile compound and an isocyanate compound, the decomposition reaction of the electrolytic solution is suppressed in the secondary battery using the electrolytic solution, so that a higher effect can be obtained.

[0073] Further, if the electrolytic solution further contains any one or two or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate and lithium difluorophosphate as another electrolyte salt, the migration rate of the cation is further improved, so that a higher effect can be obtained.

[0074] <2. Secondary battery> Next, a secondary battery using the above-described electrolytic solution will be described.

[0075] The secondary battery described here is a secondary battery in which a battery capacity is obtained by utilizing the occlusion and release of electrode reactants, and includes an electrolytic solution together with a positive electrode and a negative electrode.

[0076] 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 deposition of electrode reaction substances on the surface of the negative electrode during charging.

[0077] The type of the electrode reaction substance is not particularly limited. Specifically, the electrode substance is a light metal such as an alkali metal and an alkaline earth metal. Specific examples of the alkali metal include lithium, sodium, potassium, etc., and specific examples of the alkaline earth metal include beryllium, magnesium, calcium, etc. However, the type of the electrode reaction substance may also be other light metals such as aluminum.

[0078] Hereinafter, the case where the electrode reaction substance is lithium will be taken as an example. A secondary battery that obtains battery capacity by utilizing the occlusion and release of lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is occluded and released in an ionic state.

[0079] <2-1. Configuration> FIG. 1 shows the perspective configuration of the secondary battery, and FIG. 2 shows the 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 the cross-section of the battery element 20 along the XZ plane is shown by a broken line. In FIG. 2, only a part of the battery element 20 is shown.

[0080] 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.

[0081] [Exterior Film and Sealing 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 with the battery element 20 housed inside. Thus, the exterior film 10 houses an electrolytic solution together with the positive electrode 21 and the negative electrode 22 described later.

[0082] Here, the exterior film 10 is a single film-like member and is folded in the folding direction F. The exterior film 10 is provided with a recessed portion 10U (so-called deep drawing portion) for accommodating the battery element 20.

[0083] 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 a 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.

[0084] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and thus it may be one layer or two layers, or four layers or more.

[0085] 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.

[0086] This sealing film 41 is a sealing member that prevents outside air and the like from entering the interior of the exterior film 10. The sealing film 41 contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and the polyolefin is polypropylene or the like.

[0087] 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.

[0088] [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.

[0089] This battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are laminated on each other with the separator 23 interposed therebetween, and the positive electrode 21, the negative electrode 22, and the separator 23 are wound around a winding axis P which is a virtual axis extending in the Y-axis direction. Thereby, the positive electrode 21 and the negative electrode 22 are wound around each other with the separator 23 interposed therebetween.

[0090] 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 (cross section along the XZ plane) of the battery element 20 intersecting the winding axis P 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.

[0091] (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.

[0092] 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 metal material include aluminum and the like.

[0093] 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.

[0094] 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 any one or two or more of coating methods and the like.

[0095] The type of the positive electrode active material is not particularly limited, but specifically, it is a lithium-containing compound and 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 elements, but specifically, the other element is an element 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, and the like.

[0096] 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 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33Co 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 phosphate compounds are LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0097] The positive electrode binder contains any one or two or more of synthetic rubber and polymer compounds. Specific examples of synthetic rubber are styrene-butadiene rubber, fluorine rubber, and ethylene propylene diene, etc. Specific examples of polymer compounds are polyvinylidene fluoride, polyimide, and carboxymethyl cellulose, etc.

[0098] The positive electrode conductive agent contains any one or two or more of conductive materials such as carbon materials. 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 and a polymer compound, etc.

[0099] (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.

[0100] 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 metal material are copper, etc.

[0101] 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.

[0102] 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).

[0103] The type of the negative electrode active material is not particularly limited, but specifically, it is one or both of a carbon material and 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 one or both of silicon and tin. This metal-based material may be a single substance, an alloy, a compound, a mixture of two or more thereof, or a material containing two or more phases thereof. Specific examples of the metal-based material are TiSi2 and SiO x (0 < x ≤ 2, or 0.2 < x < 1.4), etc.

[0104] 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.

[0105] (Separator) As shown in Fig. 2, the separator 23 is an insulating porous membrane 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.

[0106] (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 an electrolyte salt, and the electrolyte salt contains an imide anion.

[0107] [Positive electrode lead and negative electrode lead] As shown in Fig. 1, 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 metal 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.

[0108] As shown in Fig. 1, 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 metal material are copper and the like. Here, the leading-out direction of the negative electrode lead 32 is the same as the leading-out 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.

[0109] <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 electrolyte. 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 electrolyte. During these charging and discharging processes, lithium is occluded and released in an ionic state.

[0110] <2-3. Manufacturing method> When manufacturing a secondary battery, each of the positive electrode 21 and the negative electrode 22 is produced according to the procedure of an example described below, and after assembling the secondary battery using the electrolyte together with the positive electrode 21 and the negative electrode 22, a stabilization treatment of the secondary battery is performed. Note that the procedure for preparing the electrolyte is as described above.

[0111] [Manufacture 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, the 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 the compression molding may be repeated a plurality of times. As a result, since the positive electrode active material layer 21B is formed on both surfaces of the positive electrode current collector 21A, the positive electrode 21 is produced.

[0112] [Manufacture of negative electrode] The negative electrode 22 is formed by the same procedure as the above-described procedure for manufacturing the positive electrode 21. 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 manufactured.

[0113] [Assembly of the 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.

[0114] Subsequently, after laminating the positive electrode 21 and the negative electrode 22 with each other via the separator 23, a wound body (not shown) is manufactured 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.

[0115] 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, the outer peripheral edge portions of two sides of the fusion layers facing each other are adhered to each other using an adhesion method such as a heat fusion method, thereby accommodating the wound body inside the bag-shaped exterior film 10.

[0116] Finally, after injecting the electrolytic solution into the bag-shaped exterior film 10, the outer peripheral edges of the remaining one side of the facing fusion layers are adhered to each other using an adhesion method such as heat fusion. 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.

[0117] As a result, the wound body is impregnated with the electrolytic solution, so that the battery element 20, which is a wound electrode body, is produced. Therefore, since the battery element 20 is sealed inside the bag-shaped exterior film 10, a secondary battery is assembled.

[0118] [Stabilization of Secondary Battery] The assembled secondary battery is charged and discharged. Various conditions such as the ambient 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, so that the state of the secondary battery is electrochemically stabilized. Therefore, the secondary battery is completed.

[0119] [2-4. Action and Effect] According to this secondary battery, the secondary battery is provided with an electrolytic solution, and the electrolytic solution has the above-described configuration. Therefore, excellent battery characteristics can be obtained for the reasons described above.

[0120] In particular, 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, so that a higher effect can be obtained.

[0121] Other actions and effects of this secondary battery are the same as the other actions and effects of the above-described electrolytic solution.

[0122] [3. Modification Example] 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.

[0123] [Modification Example 1] A separator 23 which is a porous membrane was used. However, although not specifically illustrated here, a laminated separator including a polymer compound layer may also be used.

[0124] 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, suppressing the displacement (warping) of the battery element 20. As a result, even if side reactions such as the decomposition reaction of the electrolytic solution occur, 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.

[0125] 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, 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 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.

[0126] When producing the laminated separator, after preparing a precursor solution containing a polymer compound, a solvent, etc., the precursor solution is applied to one or both surfaces of the porous membrane. In this case, if necessary, a plurality of insulating particles may be added to the precursor solution.

[0127] Even when this laminated separator is used, since lithium ions can move between the positive electrode 21 and the negative electrode 22, the same effect can be obtained. In this case, in particular, as described above, since the safety of the secondary battery is improved, a higher effect can be obtained.

[0128] [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-like electrolyte may be used.

[0129] 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.

[0130] 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 composition of the electrolytic solution is as described above. The polymer compound includes polyvinylidene fluoride and the like. 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 side or both sides of each of the positive electrode 21 and the negative electrode 22.

[0131] Even when this electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 through the electrolyte layer, so the same effects can be obtained. In this case, in particular, as described above, since leakage of the electrolytic solution is prevented, higher effects can be obtained.

[0132] <4. Applications of the Secondary Battery> The applications (application examples) of the secondary battery are not particularly limited. The secondary battery used as a power source may be the main power source for electronic devices, electric vehicles, etc., or may be an auxiliary power source. 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 is a power source used in place of the main power source or a power source that can be switched from the main power source.

[0133] Specific examples of the uses 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 supplies and memory cards. Electric tools such as electric drills and electric saws. Battery packs mounted on electronic devices and the like. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles (including hybrid vehicles). Power storage systems such as household or industrial battery systems that store power for emergencies and the like. In these applications, one secondary battery may be used, or a plurality of secondary batteries may be used.

[0134] The battery pack may use a single cell or a battery pack. An electric vehicle is a vehicle that operates (runs) using a secondary battery as a driving power source, and may also be a hybrid vehicle that is equipped with other driving sources in addition to the secondary battery. In a household power storage system, household electrical appliances and the like can be used by utilizing the power stored in the secondary battery that is the power storage source.

[0135] Here, a specific example of an application example of a secondary battery will be described. The configuration of the application example described below is merely an example and can be changed as appropriate.

[0136] FIG. 3 shows the block configuration of the 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.

[0137] As shown in FIG. 3, this battery pack includes a power supply 51 and a circuit board 52. This circuit board 52 is connected to the power supply 51 and includes a positive electrode terminal 53, a negative electrode terminal 54, and a temperature detection terminal 55.

[0138] Power supply 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 supply 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.

[0139] 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 supply 51 as necessary.

[0140] Note that when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 56 cuts off the switch 57 so that no charging current flows through the current path of the power supply 51. The overcharge detection voltage is not particularly limited, but specifically, it is 4.20V ± 0.05V, and the overdischarge detection voltage is not particularly limited, but specifically, it is 2.40V ± 0.1V.

[0141] The switch 57 includes a charge control switch, a discharge 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 metal-oxide-semiconductor field-effect transistor (MOSFET), etc., and the charge and discharge current is detected based on the ON resistance of the switch 57.

[0142] The temperature detection unit 59 includes a temperature detection element such as a thermistor, 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 charge and discharge control during abnormal heat generation and when the control unit 56 performs correction processing during calculation of the remaining capacity.

Example

[0143] An embodiment of the present technology will be described.

[0144] <Examples 1 to 19 and Comparative Examples 1 to 16> As described below, after manufacturing a secondary battery, the battery characteristics of the secondary battery were evaluated.

[0145] [Manufacture of Secondary Battery] A laminated film type secondary battery (lithium ion secondary battery) shown in FIGS. 1 and 2 was manufactured according to the following procedure.

[0146] [Manufacture of Positive Electrode] First, 91 parts by mass of a positive electrode active material (LiNi 0.82 Co 0.14 Mn 0.04 O2), 3 parts by mass of a positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of a positive electrode conductive agent (carbon black) were mixed with each other to obtain a positive electrode mixture. Subsequently, after the positive electrode mixture was put into a solvent (N-methyl-2-pyrrolidone which is an organic solvent), the organic 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 then the positive electrode mixture slurry was dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B was compression-molded using a roll press machine. Thereby, the positive electrode 21 was manufactured.

[0147] [Manufacture of Negative Electrode] First, 93 parts by mass of a negative electrode active material (artificial graphite, which is a carbon material) and 7 parts by mass of a negative electrode binder (polyvinylidene fluoride) were mixed with each other to obtain a negative electrode mixture. Subsequently, after the negative electrode mixture was put into a solvent (N-methyl-2-pyrrolidone, which is an organic solvent), the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Subsequently, after the negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector 22A (a strip-shaped copper foil with a thickness of 15 μm) using a coating device, the negative electrode mixture slurry was dried to form a negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B was compression-molded using a roll press. Thereby, the negative electrode 22 was produced.

[0148] (Preparation of Electrolyte Solution) First, a solvent was prepared. As this solvent, ethylene carbonate (EC) and propylene carbonate (PC), which are cyclic carbonates, propyl propionate (PrPr), which is a chain carboxylic acid ester, and γ-butyrolactone (GBL), which is a lactone, were used. The mixing ratio (weight %) of the solvent is as shown in Tables 1 and 2.

[0149] Subsequently, an electrolyte salt was added to the solvent, and then the solvent was stirred. As the cation of the electrolyte salt, lithium ion (Li + ) was used. As the anion of the electrolyte salt, the imide anion shown in formula (1-1), the imide anion shown in formula (1-37), and the imide anion shown in formula (1-55) were used. The content (mol / kg) of the electrolyte salt with respect to the solvent is as shown in Tables 1 and 2.

[0150] Thereby, an electrolyte solution containing the electrolyte salt was prepared. This electrolyte salt is a lithium salt containing an imide anion as an anion.

[0151] For comparison, as shown in Table 2, as the anion, hexafluorophosphate ion (PF6 -An electrolytic solution was prepared in the same procedure except that [[ID=]] was used. Also, for comparison, as shown in Tables 2 and 3, an electrolytic solution was prepared in the same procedure except that an anion shown in any of Formula (2-1), Formula (2-5), and Formula (2-7) was used as the anion.

[0152] (Assembly of secondary battery) First, a positive electrode lead 31 (aluminum foil) was welded to the positive electrode current collector 21A of the positive electrode 21, and a negative electrode lead 32 (copper foil) was welded to the negative electrode current collector 22A of the negative electrode 22.

[0153] Subsequently, the positive electrode 21 and the negative electrode 22 were laminated on each other via a separator 23 (a microporous polyethylene film having a thickness of 15 μm), and then the positive electrode 21, the negative electrode 22, and the separator 23 were wound to produce a wound body. Subsequently, the wound body was pressed using a press machine to form the wound body into a flat shape.

[0154] Subsequently, the exterior film 10 (fusion layer / metal layer / surface protection layer) was folded so as to sandwich the wound body accommodated in the recessed portion 10U, and then the outer peripheral edge portions of two sides of the fusion layer were thermally fused to each other to store the wound body inside the bag-shaped exterior film 10. As the exterior film 10, an aluminum laminate film in which a fusion layer (a polypropylene film having a thickness of 30 μm), a metal layer (an aluminum foil having a thickness of 40 μm), and a surface protection layer (a nylon film having a thickness of 25 μm) were laminated in this order from the inside was used.

[0155] Finally, after injecting an electrolytic solution into the bag-shaped exterior film 10, the outer peripheral edge portions of the remaining one side of the fusion layer were thermally fused to each other in a reduced-pressure environment. In this case, a sealing film 41 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film having a thickness of 5 μm) was inserted between the exterior film 10 and the negative electrode lead 32. As a result, since the wound body was impregnated with the electrolytic solution, the battery element 20 was produced.

[0156] Therefore, since the battery element was encapsulated inside the exterior film 10, a secondary battery was assembled.

[0157] (Stabilization of the secondary battery) The secondary battery was charged and discharged for one cycle in a normal temperature environment (temperature = 23°C). During charging, it was charged at a constant current with a current of 0.1C until the voltage reached 4.1V, and then charged at a constant voltage with the voltage of 4.1V until the current reached 0.05C. During discharging, it was discharged at a constant current with a current of 0.1C until the voltage reached 2.5V. 0.1C is the current value that can completely discharge the battery capacity (theoretical capacity) in 10 hours, and 0.05C is the current value that can completely discharge the battery capacity in 20 hours.

[0158] As a result, a film was formed on the surfaces of the positive electrode 21 and the negative electrode 22, so the state of the secondary battery was electrochemically stabilized. Thus, a laminate film type secondary battery was completed.

[0159] Note that after the completion of the secondary battery, the electrolytic solution was analyzed using inductively coupled plasma (ICP) emission spectrometry. As a result, it was confirmed that the type and mixing ratio (weight %) of the solvent and the type and content (mol / kg) of the electrolyte salt (cation and anion) were as shown in Tables 1 to 3.

[0160] [Evaluation of battery characteristics] When the battery characteristics were evaluated, the results shown in Tables 1 to 3 were obtained. Here, the high-temperature cycle characteristics, high-temperature storage characteristics, and low-temperature load characteristics were evaluated.

[0161] (High-temperature cycle characteristics) First, by charging and discharging the secondary battery in a high-temperature environment (temperature = 60°C), the discharge capacity (the discharge capacity of the first cycle) was measured. The charge and discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0162] Subsequently, the secondary battery was repeatedly charged and discharged in the same environment until the total number of cycles reached 100 cycles, and the discharge capacity (the discharge capacity at the 100th cycle) was measured. The charge and discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0163] Finally, based on the calculation formula of cycle retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the 1st cycle) × 100, the cycle retention rate, which is an index for evaluating the high-temperature cycle characteristics, was calculated.

[0164] (High-temperature storage characteristics) First, the secondary battery was charged and discharged once in a normal-temperature environment (temperature = 23°C), and the discharge capacity (the discharge capacity before storage) was measured. The charge and discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0165] Subsequently, the secondary battery was charged in the same environment, and the charged secondary battery was stored in a high-temperature environment (temperature = 80°C) for 10 days. Then, the secondary battery was discharged in a normal-temperature environment, and the discharge capacity (the discharge capacity after storage) was measured. The charge and discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0166] Finally, based on the calculation formula of storage retention rate (%) = (discharge capacity after storage / discharge capacity before storage) × 100, the capacity retention rate, which is an index for evaluating the high-temperature storage characteristics, was calculated.

[0167] (Low-temperature load characteristics) First, the secondary battery was charged and discharged once in a normal-temperature environment (temperature = 23°C), and the discharge capacity (the discharge capacity at the 1st cycle) was measured. The charge and discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0168] Subsequently, in a low-temperature environment (temperature = -10°C), the secondary battery was repeatedly charged and discharged until the total number of cycles reached 100 cycles, and the discharge capacity (discharge capacity at the 100th cycle) was measured. The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above, except that the current during discharge was changed to 1C. 1C is the current value that can completely discharge the battery capacity in one hour.

[0169] Finally, based on the calculation formula of load retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the 1st cycle) × 100, the load retention rate, which is an index for evaluating the low-temperature load characteristics, was calculated.

[0170] [Table 1]

[0171] [Table 2]

[0172] [Table 3]

[0173] [Discussion] As shown in Tables 1 to 3, each of the cycle retention rate, storage retention rate, and load retention rate varied significantly depending on the composition of the electrolyte.

[0174] Specifically, when the electrolyte salt did not contain imide anions (Comparative Examples 1 to 4), all of the cycle retention rate, storage retention rate, and load retention rate decreased.

[0175] Also, similarly, when the electrolyte salt contained anions similar to imide anions (Comparative Examples 5 to 16), all of the cycle retention rate, storage retention rate, and load retention rate decreased.

[0176] On the other hand, when the electrolyte salt contains an imide anion (Examples 1 to 19), the cycle retention rate, storage retention rate, and load retention rate all increased.

[0177] The above-mentioned tendency, that is, the tendency that the cycle retention rate, storage retention rate, and load retention rate all increase in response to the use of an imide anion, was obtained regardless of the composition (type and mixing ratio) of the solvent.

[0178] In particular, when the electrolyte salt contains an imide anion (Examples 1 to 19), the following tendencies were obtained. First, when the electrolyte salt contains a light metal ion (lithium ion) as a cation, each of the cycle retention rate, storage retention rate, and load retention rate became sufficiently high. Second, when the content of the electrolyte salt was 0.20 mol / kg to 2.00 mol / kg with respect to the solvent, each of the cycle retention rate, storage retention rate, and load retention rate became sufficiently high.

[0179] <Examples 20 to 37> As shown in Tables 4 and 5, after manufacturing a secondary battery by the same procedure as in Example 3 except that either an additive or another electrolyte salt was added to the electrolytic solution, the battery characteristics were evaluated.

[0180] Details of the additives are as described below. As the unsaturated cyclic carbonates, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and methylene ethylene carbonate (MEC) were used. As the fluorinated cyclic carbonates, fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC) were used. As the sulfonic acid esters, propane sultone (PS) and propene sultone (PRS), which are cyclic monosulfonic acid esters, and cyclodisone (CD), which is a cyclic disulfonic acid ester, were used. As the dicarboxylic acid anhydride, succinic anhydride (SA) was used. As the disulfonic acid anhydride, propane disulfonic anhydride (PSAH) was used. As the sulfate ester, ethylene sulfate (DTD) was used. As the nitrile compound, succinonitrile (SN) was used. As the isocyanate compound, hexamethylene diisocyanate (HMI) was used.

[0181] As other electrolyte salts, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), and lithium difluorophosphate (LiPF2O2) were used.

[0182] The respective contents (weight %) of the additives and other electrolyte salts in the electrolyte are as shown in Tables 4 and 5. In this case, after the completion of the secondary battery, by analyzing the electrolyte using inductively coupled plasma optical emission spectrometry (ICP-OES), it was confirmed that the respective contents of the additives and other electrolyte salts are as shown in Tables 4 and 5.

[0183] [Table 4]

[0184] [Table 5]

[0185] As shown in Table 1 and Table 4, when the electrolytic solution contains additives (Examples 20 to 32), the cycle retention rate, storage retention rate, and load retention rate each increased more compared to the case where the electrolytic solution does not contain additives (Examples 1 to 3).

[0186] Also, as shown in Table 1 and Table 5, when the electrolytic solution contains other electrolyte salts (Examples 33 to 37), the cycle retention rate and storage retention rate each increased compared to the case where the electrolytic solution does not contain other electrolyte salts (Examples 1 to 3), and in some cases, the load retention rate also increased.

[0187] [Summary] From the results shown in Tables 1 to 5, when the electrolyte salt of the electrolytic solution contains an imide anion, the cycle retention rate, storage retention rate, and load retention rate were all improved. Therefore, excellent high-temperature cycle characteristics, excellent high-temperature storage characteristics, and excellent low-temperature load characteristics were obtained in the secondary battery, and thus excellent battery characteristics could be obtained.

[0188] Specifically, the case where the element structure of the battery element is a wound type was described. However, since the element structure of the battery element is not particularly limited, it may be a laminated type, a ninety-nine-fold type, or the like. In the laminated type, the positive electrode and the negative electrode are alternately laminated via a separator, and in the ninety-nine-fold type, the positive electrode and the negative electrode are folded in a zigzag while facing each other via a separator.

[0189] Also, although the case where the electrode reactant is lithium was described, the electrode reactant is not particularly limited. Specifically, as described above, the electrode reactant may be another alkali metal such as sodium and potassium, or an alkaline earth metal such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be another light metal such as aluminum.

[0190] The effects described in this specification are merely examples, 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 positive electrode, a negative electrode, and an electrolytic solution containing an electrolyte salt are provided, wherein the electrolyte salt contains an imide anion represented by formula (1), a secondary battery. 【Chemical Formula 1】 Each of R1 and R2 is a fluorine group. R3 is a fluorinated alkylene group. Each of W, X, Y, and Z is any one of a carbonyl group (>C=O), a sulfinyl group (>S=O), and a sulfonyl group (>S(=O) 2 )).

2. The electrolyte salt contains a light metal ion as a cation, The secondary battery according to claim 1.

3. The light metal ion contains a lithium ion, The secondary battery according to claim 2.

4. The electrolytic solution contains a solvent, The content of the electrolyte salt in the electrolytic solution is 0.20 mol / kg or more and 2.00 mol / kg or less with respect to the solvent, The secondary battery according to any one of claims 1 to 3.

5. The electrolytic solution further contains at least one of an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, a sulfonic acid ester, a dicarboxylic acid anhydride, a disulfonic acid anhydride, a sulfuric acid ester, a nitrile compound, and an isocyanate compound, The secondary battery according to any one of claims 1 to 3.

6. The electrolytic solution further contains at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate, The secondary battery according to any one of claims 1 to 3.

7. It is a lithium ion secondary battery, The secondary battery according to any one of claims 1 to 3.

8. containing an electrolyte salt, wherein the electrolyte salt contains an imide anion represented by formula (1), an electrolytic solution for a secondary battery. [Chemical 2] (Each of R1 and R2 is a fluorine group. R3 is a fluorinated alkylene group. Each of W, X, Y, and Z is any one of a carbonyl group, a sulfinyl group, and a sulfonyl group.)

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