Secondary battery

Abstract

This secondary battery is provided with a positive electrode, a negative electrode, and an electrolytic solution containing a first electrolytic salt and a second electrolytic salt. The first electrolytic salt contains first anions and first cations, and the second electrolytic salt contains second anions and second cations. The first anions include at least one type of anion among first imide anions represented by formula (1), second imide anions represented by formula (2), third imide anions represented by formula (3), and fourth imide anions represented by formula (4). The second anions include at least one type of ion among hexafluorophosphate ions (PF6 -), tetrafluoroborate ions (BF4 -), and bis(fluorosulfonyl) imide ions (N(FSO2 )2 -). The sum of the content of the first cations in the electrolytic solution and the content of the second cations in the electrolytic solution is 0.7-2.2 mol / kg. The ratio of the number of moles of the second anions in the electrolytic solution to the number of moles of the first anions in the electrolytic solution is 13-6000 mol%.

Description

Technical Field

[0001] The present technology relates to secondary batteries.

Background Art

[0002] Due to the widespread use of various electronic devices such as mobile phones, the development of secondary batteries as a power source that is small and lightweight and can obtain a high energy density is underway. This secondary battery includes an electrolyte 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, the battery characteristics of the secondary batteries are still not sufficient, so there is room for improvement.

[0007] Therefore, a secondary battery capable of obtaining excellent battery characteristics is desired.

[0008] The secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolytic solution containing a first electrolyte salt and a second electrolyte salt. The first electrolyte salt contains a first anion and a first cation, and the second electrolyte salt contains a second anion and a second cation. The first anion contains at least one of a first imide anion represented by formula (1), a second imide anion represented by formula (2), a third imide anion represented by formula (3), and a fourth imide anion represented by formula (4). The second anion is hexafluorophosphate ion (PF6 - ), tetrafluoroborate ion (BF4 - ), and bis(fluorosulfonyl)imide ion (N(FSO2)2 -It contains at least one of them. The sum of the content of the first cation in the electrolytic solution and the content of the second cation in the electrolytic solution is 0.7 mol / kg or more and 2.2 mol / kg or less. The ratio of the number of moles of the second anion in the electrolytic solution to the number of moles of the first anion in the electrolytic solution is 13 mol% or more and 6000 mol% or less.

[0009]

Chemical formula

[0010]

Chemical formula

[0011]

Chemical formula

[0012]

Chemical formula

[0013] According to the secondary battery of one embodiment of the present technology, the electrolytic solution contains a first electrolyte salt (a first anion and a first cation) and a second electrolyte salt (a second anion and a second cation), the first anion contains at least one of a first imide anion, a second imide anion, a third imide anion, and a fourth imide anion, the second anion contains at least one of a hexafluorophosphate ion, a tetrafluoroborate ion, and a bis(fluorosulfonyl)imide ion, the above-described conditions are satisfied with respect to the sum of the content of the first cation in the electrolytic solution and the content of the second cation in the electrolytic solution, and the above-described conditions are satisfied with respect to the ratio of the number of moles of the first anion in the electrolytic solution and the number of moles of the second anion in the electrolytic solution. Therefore, excellent battery characteristics can be obtained.

[0014] 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

[0015]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0016] 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. Secondary battery 1-1. Configuration 1-2. Operation 1-3. Manufacturing method 1-4. Action and effect 2. Modification example 3. Applications of secondary batteries

[0017] <1. Secondary battery> First, a secondary battery according to an embodiment of the present technology will be described.

[0018] The secondary battery described herein is a secondary battery in which 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.

[0019] 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 the electrode reactant on the surface of the negative electrode during charging.

[0020] The type of the electrode reactant is not particularly limited, but specifically, it 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 reactant may be other light metals such as aluminum.

[0021] Hereinafter, the case where the electrode reactant is lithium will be taken as an example. A secondary battery in which battery capacity is obtained 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.

[0022] <1-1. Configuration> FIG. 1 shows a perspective configuration of the secondary battery, and FIG. 2 shows a partial cross-sectional configuration of the battery element 20 shown in FIG. 1. However, in FIG. 1, a state in which 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 indicated by a broken line.

[0023] 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 herein is a laminated film type secondary battery using a flexible or pliable exterior film 10.

[0024] In the following description, the upper side in each of FIGS. 1 and 2 is defined as the upper side of the secondary battery, and the lower side in each of FIGS. 1 and 2 is defined as the lower side of the secondary battery.

[0025] [Exterior Film and Sealing Films] 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. Thus, the exterior film 10 houses the electrolyte together with the positive electrode 21 and the negative electrode 22.

[0026] 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 accommodating the battery element 20 is provided in the exterior film 10.

[0027] 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.

[0028] However, the configuration (number of layers) of the exterior film 10 is not particularly limited, and it may be one layer or two layers, or four layers or more.

[0029] 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.

[0030] This sealing film 41 is a sealing member that prevents outside air and the like from entering the interior of the exterior film 10. Further, the sealing film 41 contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and specific examples of such polymer compounds are polypropylene and the like.

[0031] The configuration of the sealing film 42 is the same as that of the sealing film 41, except that it is a sealing member that has adhesiveness to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has adhesiveness to the negative electrode lead 32.

[0032] [Battery element] As shown in FIGS. 1 and 2, the battery element 20 is a power generation element that includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolytic solution (not shown), and is housed inside the exterior film 10.

[0033] 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 the winding axis P while facing each other with the separator 23 interposed therebetween. Note that the winding axis P is a virtual axis extending in the Y-axis direction.

[0034] 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 shape of the cross-section of the battery element 20 that intersects the winding axis P (the cross-section along the XZ plane) is a flat shape defined by the major axis J1 and the minor axis J2. This major axis J1 is a virtual axis that extends in the X-axis direction and has a length greater than the length of the minor axis J2. The minor axis J2 is a virtual axis that extends in the Z-axis direction intersecting the X-axis direction and has a length smaller than the length of 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 approximate ellipse.

[0035] (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.

[0036] 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.

[0037] The positive electrode active material layer 21B contains any one or two or more kinds of positive electrode active materials that occlude and release lithium. However, the positive electrode active material layer 21B may further contain any one or two or more kinds of other materials such as a positive electrode binder and a positive electrode conductive agent.

[0038] 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.

[0039] The type of the positive electrode active material is not particularly limited, but specifically, it is a lithium-containing compound. This lithium-containing compound is a compound containing one or more transition metal elements as constituent elements together with lithium, and may further contain one 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, it 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, it is an oxide, a phosphate compound, a silicate compound, a borate compound, and the like.

[0040] 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 0.33 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.

[0041] The positive electrode binder contains any one or more of synthetic rubbers 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.

[0042] 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, ketjen black, etc. However, the conductive material may also be a metal material, a polymer compound, etc.

[0043] (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.

[0044] 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.

[0045] The negative electrode active material layer 22B contains any one or two or more of negative electrode active materials that occlude and release 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.

[0046] Here, the negative electrode active material layer 22B is provided on both surfaces 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, a firing method (sintering method), etc.

[0047] 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. Note that the negative electrode active material may contain only one of the carbon material and the metal-based material, or may contain both.

[0048] Specific examples of the carbon material include graphitizable carbon, non-graphitizable carbon, and graphite. This graphite may be natural graphite, artificial graphite, or both.

[0049] The metal-based material is a material containing, as constituent elements, any one or two or more of metal elements and metalloid elements capable of forming an alloy with lithium. Specific examples of the metal elements and metalloid elements include silicon and tin. This metal-based material may be a single substance, an alloy, a compound, a mixture of two or more thereof, or a material containing two or more phases thereof. Specific examples of the metal-based material include TiSi2 and SiO x (0 < x ≤ 2 or 0.2 < x < 1.4), etc.

[0050] Details regarding each of the negative electrode binder and the negative electrode conductive agent are the same as the details regarding each of the positive electrode binder and the positive electrode conductive agent.

[0051] (Separator) As shown in FIG. 2, the separator 23 is an insulating porous film disposed between the positive electrode 21 and the negative electrode 22. This separator 23 allows each of the first cation and the second cation described later to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. Note that the separator 23 contains a polymer compound such as polyethylene.

[0052] (Electrolyte) The electrolyte is a liquid electrolyte. This electrolyte is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23, and contains a first electrolyte salt and a second electrolyte salt. More specifically, the electrolyte contains, together with the first electrolyte salt and the second electrolyte salt, a solvent for dispersing (ionizing) each of the first electrolyte salt and the second electrolyte salt.

[0053] (First electrolyte salt) The first electrolyte salt is a compound that ionizes in a solvent and contains a first anion and a first cation.

[0054] The first anion contains an imide anion. Specifically, the imide anion contains any one or two or more of a first imide anion represented by formula (1), a second imide anion represented by formula (2), a third imide anion represented by formula (3), and a fourth imide anion represented by formula (4). That is, the first electrolyte salt contains an imide anion as the first anion.

[0055] However, the type of the first imide anion may be only one type or two or more types. The fact that the type may be one type or two or more types is the same for each of the second imide anion, the third imide anion, and the fourth imide anion.

[0056]

Chemical formula

[0057]

Chemical formula

[0058]

Chemical formula

[0059]

Chemical formula

[0060] The reason why the first anion contains an imide anion is as described below. First, when the secondary battery is charged and discharged, a high-quality film derived from the first electrolyte salt is formed on the surface of each of the positive electrode 21 and the negative electrode 22. Thereby, the decomposition reaction of the electrolytic solution (especially the solvent) due to the reaction with each of the positive electrode 21 and the negative electrode 22 is suppressed. Second, using the above-described film, the migration rate of the first cation is improved in the vicinity of the surface of each of the positive electrode 21 and the negative electrode 22. Third, the migration rate of the first cation is also improved in the electrolytic solution.

[0061] As shown in formula (1), the first imide anion is a chain anion (divalent minus ion) containing two nitrogen atoms (N) and three functional groups (W1 to W3).

[0062] 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. Thereby, each of R1 and R2 is not a hydrogen group (-H) or an alkyl group or the like.

[0063] 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 two or more side chains.

[0064] 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 ionizability of the electrolyte salt containing the first imide anion are improved.

[0065] Specific examples of the fluorinated alkyl group include a perfluoromethyl group (-CF3) and a perfluoroethyl group (-C2F5), etc.

[0066] Each of W1 to W3 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 W1 to W3 may be the same group as each other or different groups from each other. Of course, only any two of W1 to W3 may be the same group as each other.

[0067] As shown in formula (2), the second imide anion is a chain anion (trivalent minus ion) containing three nitrogen atoms and four functional groups (X1 to X4).

[0068] Details regarding each of R3 and R4 are the same as those regarding each of R1 and R2.

[0069] Each of X1 to X4 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 X1 to X4 may be the same group as each other or different groups from each other. Of course, only any two of X1 to X4 may be the same group as each other, or only any three of X1 to X4 may be the same group as each other.

[0070] As shown in formula (3), the third imide anion is a cyclic anion (divalent minus ion) containing two nitrogen atoms, three functional groups (Y1 to Y3), and one connecting group (R5).

[0071] The fluorinated alkylene group which is R5 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 two or more side chains.

[0072] The number of carbon atoms in 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 third imide anion are improved.

[0073] Specific examples of the fluorinated alkylene group include a perfluoromethylene group (-CF2-) and a perfluoroethylene group (-C2F4-).

[0074] Each of Y1 to Y3 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 Y1 to Y3 may be the same group as each other or different groups from each other. Of course, only any two of Y1 to Y3 may be the same group as each other.

[0075] As shown in formula (4), the fourth imide anion is a chain anion (divalent minus ion) containing two nitrogen atoms (N), four functional groups (Z1 to Z4), and one connecting group (R8).

[0076] Details regarding each of R6 and R7 are the same as those regarding each of R1 and R2.

[0077] R8 is not particularly limited as long as it is any one of an alkylene group, a phenylene group, a fluorinated alkylene group, and a fluorinated phenylene group.

[0078] The alkylene group may be linear or branched having one or two or more side chains. The number of carbon atoms in the 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 fourth imide anion are improved. Specific examples of the alkylene group include a methylene group (-CH2-), an ethylene group (-C2H4-), and a propylene group (-C3H6-).

[0079] Details regarding the fluorinated alkylene group which is R8 are the same as those regarding the fluorinated alkylene group which is R5.

[0080] The fluorinated phenylene group is a group in which one or more hydrogen groups in the phenylene group are substituted by fluorine groups. Specific examples of the fluorinated phenylene group include a monofluorophenylene group (-C6H3F-), etc.

[0081] Each of Z1 to Z4 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 Z1 to Z4 may be the same group as each other or different groups from each other. Of course, only any two of Z1 to Z4 may be the same group as each other, or only any three of Z1 to Z4 may be the same group as each other.

[0082] Specific examples of the first imide anion include anions represented by each of formulas (1-1) to (1-30), etc.

[0083]

Chemical formula

[0084]

Chemical formula

[0085]

Chemical formula

[0086] Specific examples of the second imide anion include anions represented by each of formulas (2-1) to (2-22), etc.

[0087]

Chemical formula

[0088]

Chemical formula

[0089] Specific examples of the third imide anion include anions represented by each of Formula (3-1) to Formula (3-15).

[0090]

Chem.

[0091] Specific examples of the fourth imide anion include anions represented by each of Formula (4-1) to Formula (4-65).

[0092]

Chem.

[0093]

Chem.

[0094]

Chem.

[0095]

Chem.

[0096]

Chem.

[0097]

Chem.

[0098]

Chem.

[0099] The type of the first cation is not particularly limited. Specifically, the first cation contains any one or two or more of light metal ions. That is, the first electrolyte salt contains a light metal ion as the first cation. This is because a high voltage can be obtained.

[0100] The type of the light metal ion is not particularly limited, but specifically, it is an alkali metal ion, an alkaline earth metal ion, etc. Specific examples of the alkali metal ion are a sodium ion, a potassium ion, etc. Specific examples of the alkaline earth metal ion are a beryllium ion, a magnesium ion, a calcium ion, etc. In addition, the light metal ion may be an aluminum ion or the like.

[0101] Among them, the light metal ion preferably contains a lithium ion. This is because a sufficiently high voltage can be obtained.

[0102] (Second electrolyte salt) The second electrolyte salt is a compound that ionizes in a solvent, similarly to the first electrolyte salt. This second electrolyte salt contains a second anion and a second cation.

[0103] The second anion contains a specific type of ion different from the imide anion (hereinafter referred to as "specific anion"). Specifically, the specific anion contains any one or two or more of hexafluorophosphate ion (PF6 - ), tetrafluoroborate ion (BF4 - ), and bis(fluorosulfonyl)imide ion (N(FSO2)2 - ).

[0104] Details regarding the second cation are as described above. The type of the second cation may be the same as the type of the first cation or may be different from the type of the first cation.

[0105] Among them, it is preferable that the type of the second cation is the same as that of the first cation. More specifically, each of the first cation and the second cation preferably contains lithium ions, which are light metal ions, for the reasons described above.

[0106] (Content) Regarding the relationship between the content of the first electrolyte salt (first anion and first cation) in the electrolytic solution and the content of the second electrolyte salt (second anion and second cation) in the electrolytic solution, predetermined conditions are satisfied.

[0107] Specifically, the sum T (mol / kg) of the content C1 of the first cation and the content C2 of the second cation in the electrolytic solution is 0.7 mol / kg to 2.2 mol / kg. Also, the ratio R (mol%) of the number of moles M2 of the second anion to the number of moles M1 of the first anion in the electrolytic solution is 13 mol% to 6000 mol%. This is because the moving speeds of the first cation and the second cation are sufficiently improved near the surfaces of the positive electrode 21 and the negative electrode 22, and the moving speeds of the first cation and the second cation are also sufficiently improved in the electrolytic solution.

[0108] The "content of the first cation in the electrolytic solution" described here is the content of the first cation with respect to the solvent, and the "content of the second cation in the electrolytic solution" is the content of the second cation with respect to the solvent. The sum T is calculated based on the calculation formula T = C1 + C2, and the ratio R is calculated based on the calculation formula R = (M2 / M1) × 100.

[0109] When specifying the respective contents C1 and C2 and the number of moles M1 and M2, the electrolytic solution is recovered by disassembling the secondary battery, and then the electrolytic solution is analyzed using inductively coupled plasma (ICP) emission spectrometry. As a result, since the weight of the solvent, the weight of the first electrolyte salt (the first anion and the first cation), and the weight of the second electrolyte salt (the second anion and the second cation) are each specified, the respective contents C1 and C2 are calculated, and the respective number of moles M1 and M2 are calculated.

[0110] The procedure for specifying the content described here is the same also for specifying the content of the components of the electrolytic solution (excluding the first electrolyte salt and the second electrolyte salt) described later.

[0111] (Solvent) The solvent contains any one or two or more of non-aqueous solvents (organic solvents), and the electrolytic solution containing the non-aqueous solvent is a so-called non-aqueous electrolytic solution. The non-aqueous solvent is esters, ethers, etc., and more specifically, carbonate-based compounds, carboxylic acid ester-based compounds, lactone-based compounds, etc.

[0112] The carbonate-based compounds are cyclic carbonates, chain carbonates, etc. Specific examples of the cyclic carbonate are ethylene carbonate, propylene carbonate, etc. Specific examples of the chain carbonate are dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.

[0113] The carboxylic acid ester-based compounds are chain carboxylic acid esters, etc. Specific examples of the chain carboxylic acid ester are methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl trimethylacetate, methyl butyrate, ethyl butyrate, etc.

[0114] The lactone-based compounds are lactones, etc. Specific examples of the lactone are γ-butyrolactone, γ-valerolactone, etc.

[0115] The ethers may be, for example, 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.

[0116] (Other electrolyte salts) The electrolytic solution may further contain any one or two or more of other electrolyte salts. This is because the migration speeds of the first cation and the second cation are further improved near the surfaces of the positive electrode 21 and the negative electrode 22, and the migration speeds of the first cation and the second cation are also further improved in the electrolytic solution. Since the content of other electrolyte salts in the electrolytic solution is not particularly limited, it can be arbitrarily set.

[0117] The types of other electrolyte salts are not particularly limited, but specifically, they are light metal salts such as lithium salts. However, the above-described first electrolyte salt and second electrolyte salt are excluded from the lithium salts described here.

[0118] Specific examples of the lithium salts include lithium trifluoromethanesulfonate (LiCF3SO3), 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), lithium difluorophosphate (LiPF2O2), etc.

[0119] Among them, other electrolyte salts preferably contain one or both of lithium bis(oxalato)borate and lithium difluorophosphate. This is because the migration rates of the first cation and the second cation are sufficiently improved near the surfaces of the positive electrode 21 and the negative electrode 22, and the migration rates of the first cation and the second cation are also sufficiently improved in the electrolyte solution.

[0120] (Additive) Further, 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 surfaces of the positive electrode 21 and the negative electrode 22 during charge and discharge of the secondary battery, 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.

[0121] The type of the additive is not particularly limited. Specifically, it includes unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonic acid esters, dicarboxylic anhydrides, disulfonic anhydrides, sulfuric acid esters, nitrile compounds, isocyanate compounds, and the like.

[0122] 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 1 or 2 or more. Specific examples of the unsaturated cyclic carbonate include vinylene carbonate, vinyl ethylene carbonate, and methylene ethylene carbonate.

[0123] 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 in the cyclic carbonate are substituted by fluorine groups. Specific examples of the fluorinated cyclic carbonate include monofluoroethylene carbonate and difluoroethylene carbonate.

[0124] Sulfonic acid esters include cyclic monosulfonic acid esters, cyclic disulfonic acid esters, chain monosulfonic acid esters, chain disulfonic acid esters, and the like. Specific examples of cyclic monosulfonic acid esters include 1,3-propanesultone, 1-propene-1,3-sultone, 1,4-butanesultone, 2,4-butanesultone, and propargyl methanesulfonate. Specific examples of cyclic disulfonic acid esters include cyclodisone and the like.

[0125] Specific examples of dicarboxylic acid anhydrides include succinic anhydride, glutaric anhydride, maleic anhydride, and the like.

[0126] Specific examples of disulfonic acid anhydrides include ethanedisulfonic anhydride, propanedisulfonic anhydride, and the like.

[0127] Specific examples of sulfuric acid esters include ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide) and the like.

[0128] Nitrile compounds are compounds containing one or more cyano groups (-CN). Specific examples of nitrile compounds 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.

[0129] Isocyanate compounds are compounds containing one or more isocyanate groups (-NCO). Specific examples of isocyanate compounds include hexamethylene diisocyanate and the like.

[0130] [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 conductive material are aluminum and the like. The shape of the positive electrode lead 31 is not particularly limited, but specifically, it is any one of a thin plate shape and a mesh shape.

[0131] 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 conductive 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.

[0132] <1-2. 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 charging and discharging, lithium is occluded and released in an ionic state.

[0133] <1-3. Manufacturing Method> When manufacturing a secondary battery, each of the positive electrode 21 and the negative electrode 22 is produced according to an example procedure described below. After preparing the electrolytic solution, the secondary battery is assembled using the positive electrode 21, the negative electrode 22, and the electrolytic solution, and a stabilization treatment for the assembled secondary battery is performed.

[0134] [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. Note that the 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 the compression molding may be repeated a plurality of times. Thereby, 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.

[0135] [Fabrication of Negative Electrode] The 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. Thereby, 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.

[0136] [Preparation of Electrolyte Solution] A first electrolyte salt (a first anion and a first cation) and a second electrolyte salt (a second anion and a second cation) are introduced into a solvent. In this case, the input amounts of the first electrolyte salt and the second electrolyte salt are adjusted so that the above-described conditions are satisfied for each of the sum T and the ratio R. Note that 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.

[0137] [Assembly of Secondary Battery] First, using a joining method such as a welding method, the positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21, and using a joining method such as a welding method, the negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22.

[0138] Subsequently, after laminating the positive electrode 21 and the negative electrode 22 with each other via the separator 23, the positive electrode 21, the negative electrode 22, and the separator 23 are wound to produce a wound body (not shown). This wound body has the same configuration as that 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 form the wound body into a flat shape.

[0139] Subsequently, after accommodating the wound body inside the recessed portion 10U, the outer packaging film 10 (fusion layer / metal layer / surface protection layer) is folded so that the outer packaging films 10 face each other. Subsequently, using an adhesion method such as a thermal fusion method, the outer peripheral edge portions of two sides of the fusion layers facing each other are adhered to each other to accommodate the wound body inside the bag-shaped outer packaging film 10.

[0140] Finally, after injecting the electrolytic solution inside the bag-shaped outer packaging film 10, using an adhesion method such as a thermal fusion method, the outer peripheral edge portions of the remaining one side of the fusion layers facing each other are adhered to each other. In this case, a sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32.

[0141] As a result, since the wound body is impregnated with the electrolytic solution, the battery element 20, which is a wound electrode body, is produced. Therefore, since the battery element 20 is enclosed inside the bag-shaped outer packaging film 10, a secondary battery is assembled.

[0142] [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, and the charge and discharge conditions can be arbitrarily set. As a result, a film is formed on the surface of each of the positive electrode 21 and the negative electrode 22, and the state of the secondary battery is electrochemically stabilized. Thus, the secondary battery is completed.

[0143] <1-4. Action and effect> According to this secondary battery, the electrolytic solution contains a first electrolyte salt (a first anion and a first cation) and a second electrolyte salt (a second anion and a second cation), the first anion contains an imide anion, the second anion contains a specific anion, and the above-described conditions regarding the sum T and the ratio R are satisfied.

[0144] In this case, as described above, since the first anion contains an imide anion, a high-quality film derived from the first electrolyte salt is formed on the surface of each of the positive electrode 21 and the negative electrode 22 during the charge and discharge of the secondary battery. Thereby, the decomposition reaction of the electrolytic solution on the surface of each of the positive electrode 21 and the negative electrode 22 is suppressed. Moreover, the migration speed of the first cation is improved in the vicinity of the surface of each of the positive electrode 21 and the negative electrode 22, and the migration speed of the first cation is also improved in the electrolytic solution.

[0145] In addition, since the second anion contains a specific anion, the migration speed of the second cation is improved in the vicinity of the surface of each of the positive electrode 21 and the negative electrode 22, and the migration speed of the second cation is also improved in the electrolytic solution.

[0146] Furthermore, the total amount (the sum T of the contents C1 and C2) of the first electrolyte salt and the second electrolyte salt is optimized, and the mixing ratio (the ratio R of the number of moles M1 and M2) of the first electrolyte salt and the second electrolyte salt is also optimized. Thereby, the migration speeds of the first cation and the second cation are further improved in the vicinity of the surface of each of the positive electrode 21 and the negative electrode 22, and the migration speeds of the first cation and the second cation are also further improved in the electrolytic solution.

[0147] Therefore, excellent battery characteristics can be obtained.

[0148] In particular, if each of the first cation and the second cation contains a light metal ion, a high voltage can be obtained, 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.

[0149] Further, if the electrolytic solution further contains an additive, and the additive contains any one 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, so that a higher effect can be obtained.

[0150] Further, if the electrolytic solution further contains another electrolyte salt, and the other electrolyte salt contains one or both of lithium bis(oxalato)borate and lithium difluorophosphate, the migration rate of the cation is further improved, so that a higher effect can be obtained.

[0151] Further, if the secondary battery is a lithium-ion secondary battery, a sufficient battery capacity can be stably obtained by utilizing the intercalation and deintercalation of lithium, so that a higher effect can be obtained.

[0152] <2. 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.

[0153] [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.

[0154] 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, thereby suppressing the displacement (winding displacement) of the battery element 20. As a result, even if a side reaction such as a decomposition reaction of the electrolyte occurs, 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.

[0155] Note that one or both of the porous membrane and the polymer compound layer may contain a plurality of insulating particles. This is because when the secondary battery generates heat, the plurality of insulating particles promote heat dissipation, thereby improving the safety (heat resistance) of the secondary battery. The insulating particles contain any one or two or more of insulating materials such as inorganic materials and resin materials. Specific examples of the inorganic material include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of the resin material include acrylic resin and styrene resin.

[0156] When producing the laminated separator, a precursor solution containing a polymer compound, a solvent, etc. is prepared, and then 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.

[0157] 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 swelling of the secondary battery is suppressed, a higher effect can be obtained.

[0158] [Modification 2] An electrolyte 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.

[0159] In the battery element 20 using an 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.

[0160] Specifically, the electrolyte layer contains a polymer compound together with an 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 an electrolytic solution, a 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.

[0161] Even when this electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, so the same effect can be obtained. In this case, in particular, as described above, since leakage of the electrolytic solution is prevented, a higher effect can be obtained.

[0162] <3. Applications of Secondary Batteries> The applications (application examples) of secondary batteries are not particularly limited. The secondary battery used as a power source may be a main power source such as an electronic device and an electric vehicle, or 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 may be a power source used in place of the main power source or a power source that can be switched from the main power source.

[0163] 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.

[0164] 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 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, which is a power storage source.

[0165] 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.

[0166] FIG. 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.

[0167] As shown in FIG. 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.

[0168] 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. 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.

[0169] Control unit 56 includes a central processing unit (CPU), a memory, etc., and controls the operation of the entire battery pack. This control unit 56 detects and controls the usage state of power source 51 as necessary.

[0170] Note that when the voltage of power source 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, control unit 56 disconnects switch 57 so that no charging current flows through the current path of that 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.

[0171] Switch 57 includes a charge control switch, a discharge control switch, a charging diode, a discharging diode, etc., and switches the connection between power source 51 and an external device according to an instruction from 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 switch 57.

[0172] Temperature detection unit 59 includes a temperature detection element such as a thermistor, measures the temperature of power source 51 using temperature detection terminal 55, and outputs the measurement result of that temperature to control unit 56. The measurement result of the temperature measured by temperature detection unit 59 is used when control unit 56 performs charge and discharge control during abnormal heat generation and when control unit 56 performs correction processing during calculation of the remaining capacity.

Example

[0173] An embodiment of the present technology will be described.

[0174] <Examples 1 to 26 and Comparative Examples 1 to 12> As described below, after manufacturing a secondary battery, the battery characteristics of the secondary battery were evaluated.

[0175] [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.

[0176] [Manufacture of Positive Electrode] First, 91 parts by mass of a positive electrode active material (a lithium-containing compound (oxide) (LiNi 0.82 Co 0.14 Al 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 introducing the positive electrode mixture into a solvent (N-methyl-2-pyrrolidone, an organic solvent), the solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector 21A (a strip-shaped aluminum foil having a thickness of 12 μm) using a coating device, and 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. Thus, the positive electrode 21 was manufactured.

[0177] [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 sides 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. Thus, the negative electrode 22 was fabricated.

[0178] (Preparation of Electrolyte Solution) After adding a first electrolyte salt and a second electrolyte salt to the solvent, the solvent was stirred.

[0179] As the solvent, ethylene carbonate, which is a cyclic carbonate ester, and γ-butyrolactone, which is a lactone, were used. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:γ-butyrolactone = 30:70.

[0180] As the first cation, lithium ions (Li + ) were used, and as the first anion, an imide anion was used. Specifically, as the imide anion, a first imide anion represented by Formula (1-21), a second imide anion represented by Formula (2-5), a third imide anion represented by Formula (3-5), and a fourth imide anion represented by Formula (4-37) were used.

[0181] As the second cation, lithium ions (Li + ) were used, and as the second anion, a specific anion was used. Specifically, as the specific anion, hexafluorophosphate ions (PF6 - ) were used.

[0182] The content (mol / kg) of the first electrolyte salt, the content (mol / kg) of the second electrolyte salt, the sum T (mol / kg), and the ratio R (mol%) were as shown in Tables 1 to 3.

[0183] Thereby, an electrolytic solution containing the first electrolyte salt and the second electrolyte salt was prepared. This first electrolyte salt is a lithium salt containing an imide anion as the first anion, and the second electrolyte salt is a lithium salt containing a specific anion as the second anion.

[0184] (Assembly of the 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.

[0185] Subsequently, after laminating the positive electrode 21 and the negative electrode 22 with each other via a separator 23 (a microporous polyethylene film with a thickness of 15 μm), 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.

[0186] Subsequently, after folding the exterior film 10 (fusion layer / metal layer / surface protection layer) so as to sandwich the wound body housed inside the recessed portion 10U, the outer peripheral edge portions of two sides of the fusion layer were heat-fused to each other, and the wound body was stored inside the bag-shaped exterior film 10. As the exterior film 10, an aluminum laminate film in which a fusion layer (a polypropylene film with a thickness of 30 μm), a metal layer (an aluminum foil with a thickness of 40 μm), and a surface protection layer (a nylon film with a thickness of 25 μm) were laminated in this order from the inside was used.

[0187] Finally, after injecting the electrolyte inside the bag-shaped exterior film 10, the outer peripheral edges of the remaining one side of the fusion layer were heat-sealed to each other in a reduced-pressure environment. In this case, a sealing film 41 (a polypropylene film with 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 with 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 electrolyte, the battery element 20 was fabricated.

[0188] Therefore, since the battery element was encapsulated inside the exterior film 10, the secondary battery was assembled.

[0189] (Stabilization of the secondary battery) The secondary battery was charged and discharged once in a normal-temperature environment (temperature = 23°C). During charging, it was first charged at a constant current with a current of 0.1C until the voltage reached 4.2V, and then charged at a constant voltage with the voltage of 4.2V 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.

[0190] As a result, a film was formed on the surfaces of the positive electrode 21 and the negative electrode 22 respectively, so the state of the secondary battery was electrochemically stabilized. Therefore, the laminate film type secondary battery was completed.

[0191] [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.

[0192] (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.

[0193] Subsequently, in the same environment, the secondary battery was repeatedly charged and discharged until the total number of cycles reached 100 cycles, and the discharge capacity (the 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.

[0194] 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.

[0195] (High-temperature storage characteristics) First, in a normal-temperature environment (temperature = 23°C), the secondary battery was charged and discharged for 1 cycle to measure the discharge capacity (the discharge capacity before storage). The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0196] 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 to measure the discharge capacity (the discharge capacity after storage). The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0197] Finally, based on the calculation formula of storage retention rate (%) = (discharge capacity after storage / discharge capacity before storage) × 100, the storage retention rate, which is an index for evaluating the high-temperature storage characteristics, was calculated.

[0198] (Low-temperature load characteristics) First, in a normal-temperature environment (temperature = 23°C), the secondary battery was charged and discharged for 1 cycle to measure the discharge capacity (the discharge capacity at the 1st cycle). The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0199] 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 (the 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 1 hour.

[0200] 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.

[0201] [Table 1]

[0202] [Table 2]

[0203] [Table 3]

[0204] [Discussion] As shown in Tables 1 to 3, in the secondary battery using an imide anion as the first anion and a specific anion (phosphate hexafluoride ion) as the second anion, the cycle retention rate, storage retention rate, and load retention rate all varied significantly depending on the composition of the electrolyte.

[0205] Specifically, when the appropriate conditions where the sum T is 0.7 mol / kg to 2.2 mol / kg or less and the ratio R is 13 mol% to 6000 mol% are not satisfied (Comparative Examples 1 to 12), the cycle retention rate, storage retention rate, and load retention rate all decreased.

[0206] On the other hand, when the appropriate conditions that the sum T is 0.7 mol / kg to 2.2 mol / kg or less and the ratio R is 13 mol% to 6000 mol% are satisfied (Examples 1 to 26), the cycle retention rate, storage retention rate, and load retention rate all increased. In this case, in particular, when each of the first cation and the second cation contains a light metal ion (lithium ion), the cycle retention rate, storage retention rate, and load retention rate all became sufficiently high.

[0207] <Examples 27 to 52 and Comparative Examples 13 to 24> As shown in Tables 4 to 6, except that tetrafluoroborate ion (BF4 - ) was used instead of hexafluorophosphate ion as the specific anion, secondary batteries were fabricated by the same procedure as in Examples 1 to 26 and Comparative Examples 1 to 12, and then the battery characteristics were evaluated.

[0208]

Table 4

[0209]

Table 5

[0210]

Table 6

[0211] As shown in Tables 4 to 6, similar tendencies were obtained also in the secondary batteries using the specific anion (tetrafluoroborate ion) as the anion of the second electrolyte salt.

[0212] Specifically, when the appropriate conditions that the sum T is 0.7 mol / kg or more and 2.2 mol / kg or less and the ratio R is 13 mol% or more and 6000 mol% or less are not satisfied (Comparative Examples 13 to 24), all of the cycle retention rate, storage retention rate, and load retention rate decreased, whereas when the appropriate conditions are satisfied (Examples 27 to 52), all of the cycle retention rate, storage retention rate, and load retention rate increased.

[0213] <Examples 53 to 78 and Comparative Examples 25 to 36> As shown in Tables 7 to 9, secondary batteries were fabricated by the same procedure as in Examples 1 to 26 and Comparative Examples 1 to 12, except that bis(fluorosulfonyl)imide ion (N(FSO2)2 - ) was used as the specific anion instead of hexafluorophosphate ion, and then the battery characteristics were evaluated.

[0214]

Table 7

[0215]

Table 8

[0216]

Table 9

[0217] As shown in Tables 7 to 9, a similar tendency was obtained also in the secondary battery using the specific anion (bis(fluorosulfonyl)imide ion) as the anion of the second electrolyte salt.

[0218] Specifically, when the proper conditions that the sum T is 0.7 mol / kg to 2.2 mol / kg or less and the ratio R is 13 mol% to 6000 mol% are not satisfied (Comparative Examples 25 to 36), all of the cycle retention rate, storage retention rate, and load retention rate decreased, whereas when the proper conditions are satisfied (Examples 53 to 78), all of the cycle retention rate, storage retention rate, and load retention rate increased.

[0219] <Examples 79 to 123> As shown in Tables 10 to 12, after manufacturing a secondary battery by the same procedure as in Example 8 except that either an additive or another electrolyte salt was included in the electrolyte, the battery characteristics were evaluated. In this case, after adding either an additive or another electrolyte salt to the solvent containing the electrolyte salt, the solvent was stirred.

[0220] Details regarding the additives are as described below. As the unsaturated cyclic carbonates, vinylene carbonate (VC), vinyl ethylene carbonate (VC), 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.

[0221] As the other electrolyte salts, lithium bis(oxalato)borate (LiBOB) and lithium difluorophosphate (LiPF2O2) were used.

[0222] The content (weight %) of each of the additives and other electrolyte salts in the electrolytic solution was as shown in Tables 10 to 12.

[0223]

Table 10

[0224]

Table 11

[0225]

Table 12

[0226] As shown in Tables 10 to 12, when the electrolytic solution contains an additive (Examples 79 to 91, 94 to 106, 109 to 121), the cycle retention rate and the storage retention rate each increased more while maintaining a high load retention rate as compared with the case where the electrolytic solution does not contain an additive (Example 8).

[0227] Also, as shown in Tables 10 to 12, when the electrolytic solution contains another electrolyte salt (Examples 92, 93, 107, 108, 122, 123), the cycle retention rate, the storage retention rate, and the load retention rate each increased more as compared with the case where the electrolytic solution does not contain another electrolyte salt (Example 8).

[0228] [Summary] From the results shown in Tables 1 to 12, when the electrolytic solution contains a first electrolyte salt (a first anion and a first cation) and a second electrolyte salt (a second anion and a second cation), the first anion contains an imide anion, the second anion contains a specific anion, and the above-described conditions regarding the sum T and the ratio R are satisfied, the cycle retention rate, the storage retention rate, and the load retention rate are 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.

[0229] The above has described the present technology by giving one embodiment and examples. However, since the configuration of the present technology is not limited to the configuration described in the one embodiment and examples, it can be variously modified.

[0230] Specifically, the case where the element structure of the battery element is a wound type has been described. However, since the element structure of the battery element is not particularly limited, 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.

[0231] 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 positive electrode, a negative electrode, and an electrolytic solution containing a first electrolyte salt and a second electrolyte salt provided with, the first electrolyte salt contains a first anion and a first cation, the second electrolyte salt contains a second anion and a second cation, the electrolytic solution further contains at least one of an unsaturated cyclic carbonate, a fluorinated cyclic carbonate, a sulfonic acid ester, a dicarboxylic anhydride, a disulfonic anhydride, a sulfate ester, a nitrile compound, and an isocyanate compound, the first anion contains at least one of a first imide anion represented by formula (1), a second imide anion represented by formula (2), a third imide anion represented by formula (3), and a fourth imide anion represented by formula (4), the second anion contains at least one of hexafluorophosphate ion (PF 6 - ), tetrafluoroborate ion (BF 4 - ), and bis(fluorosulfonyl)imide ion (N(FSO 2 )) 2 - ), the sum of the content of the first cation in the electrolytic solution and the content of the second cation in the electrolytic solution is 0.7 mol / kg or more and 2.2 mol / kg or less, the ratio of the number of moles of the second anion in the electrolytic solution to the number of moles of the first anion in the electrolytic solution is 13 mol% or more and 6000 mol% or less, a secondary battery. 【Chemical Formula 1】 (Each of R1 and R2 is either a fluorine group or a fluorinated alkyl group. Each of W1, W2, and W3 is either a carbonyl group (>C=O), a sulfinyl group (>S=O), or a sulfonyl group (>S(=O) 2 ).)) [Chemical Formula 2] (Each of R3 and R4 is either a fluorine group or a fluorinated alkyl group. Each of X1, X2, X3, and X4 is either a carbonyl group, a sulfinyl group, or a sulfonyl group.) [Chemical Formula 3] (R5 is a fluorinated alkylene group. Each of Y1, Y2, and Y3 is either a carbonyl group, a sulfinyl group, or a sulfonyl group.) [Chemical Formula 4] (Each of R6 and R7 is either a fluorine group or a fluorinated alkyl group. R8 is either an alkylene group, a phenylene group, a fluorinated alkylene group, or a fluorinated phenylene group. Each of Z1, Z2, Z3, and Z4 is either a carbonyl group, a sulfinyl group, or a sulfonyl group.)

2. Each of the first cation and the second cation contains a light metal ion. 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 further contains at least one of lithium bis(oxalato)borate and lithium difluorophosphate. The secondary battery according to any one of Claims 1 to 3.

5. It is a lithium ion secondary battery. The secondary battery according to any one of Claims 1 to 3.

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