Secondary battery

Abstract

A secondary battery that comprises: a positive electrode including a positive electrode active material; a negative electrode; and an electrolytic solution containing an electrolyte salt. The positive electrode active material includes a lithium-containing compound, lithium carbonate, and lithium hydroxide. The lithium carbonate content in the positive electrode active material is 0.2%–0.7% by mass and the lithium hydroxide content in the positive electrode active material is 0.2%–0.7% by mass. The electrolyte salt includes at least one imide anion from 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).

Description

Technical Field

[0001] This 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 while achieving a high energy density has been underway. This secondary battery includes an electrolytic solution together with a positive electrode and a negative electrode, and various studies have been made regarding the configuration of this secondary battery.

[0003] Specifically, the electrolytic solution 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 electrolytic solution 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 these secondary batteries are not yet sufficient.

[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 containing a positive electrode active material, a negative electrode, and an electrolytic solution containing an electrolyte salt. The positive electrode active material includes a lithium-containing compound, lithium carbonate, and lithium hydroxide. The content of lithium carbonate in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less, and the content of lithium hydroxide in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less. The electrolyte salt contains an imide anion, and the imide 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).

[0009] [Chemical Formula] (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).)

[0010]

Chemical formula

[0011]

Chemical formula

[0012]

Chemical formula

[0013] The above-mentioned "lithium-containing compound" is a general term for compounds containing lithium as a constituent element. Details of the lithium-containing compound will be described later.

[0014] According to the secondary battery of an embodiment of the present technology, the cathode active material of the cathode contains a lithium-containing compound, lithium carbonate, and lithium hydroxide, the content of lithium carbonate in the cathode active material is 0.2 wt% or more and 0.7 wt% or less, the content of lithium hydroxide in the cathode active material is 0.2 wt% or more and 0.7 wt% or less, and the electrolyte salt of the electrolytic solution contains at least one of a first imide anion, a second imide anion, a third imide anion, and a fourth imide anion as an imide anion, so that excellent battery characteristics can be obtained.

[0015] 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

[0016]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0017] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The order of description is as follows. 1. 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

[0018] <1. Secondary battery> First, the secondary battery of an embodiment of the present technology will be described.

[0019] 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.

[0020] 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.

[0021] 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 also be other light metals such as aluminum.

[0022] 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.

[0023] <1-1. Configuration> FIG. 1 shows a perspective configuration of the secondary battery, and FIG. 2 shows a cross-sectional configuration of the battery element 20 shown in FIG. 1. However, in FIG. 1, a state where the exterior film 10 and the battery element 20 are separated from each other is shown, and a cross-section of the battery element 20 along the XZ plane is indicated by a broken line. In FIG. 2, only a part of the battery element 20 is shown.

[0024] 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 laminate film type secondary battery using a flexible or pliable exterior film 10.

[0025] [Outer film and sealing film] As shown in Fig. 1, the outer film 10 is an outer member that houses the battery element 20, and has a bag-like structure that is sealed with the battery element 20 housed inside. Thereby, the outer film 10 stores the electrolytic solution together with the positive electrode 21 and the negative electrode 22 described later.

[0026] Here, the outer 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 outer film 10.

[0027] Specifically, the outer film 10 is a three-layer laminated film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside. In the state where the outer 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 outer 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 outer film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer 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 inside of the outer film 10. The sealing film 41 contains a polymer compound such as polyolefin that has adhesiveness to the positive electrode lead 31, and specific examples of the polymer compound are polypropylene and the like.

[0031] The structure 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.

[0032] [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.

[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 via the separator 23, and are wound around the winding axis P while facing each other via the separator 23. 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 (cross section along the XZ plane) intersecting the winding axis P is a flat shape defined by the major axis J1 and the 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 substantially flat 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 a positive electrode active material that intercalates and deintercalates lithium. However, the positive electrode active material layer 21B may further contain any one or more 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 sides 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 may be any one or more of coating methods.

[0039] The positive electrode active material contains a lithium-containing compound, lithium carbonate (Li2CO3), and lithium hydroxide (LiOH).

[0040] As described above, the lithium-containing compound is a general term for compounds containing lithium as a constituent element and intercalates and deintercalates lithium. The type of the lithium-containing compound may be only one type or two or more types. Since the average particle size (median diameter D50) of the lithium-containing compound is not particularly limited, it can be arbitrarily set.

[0041] Each of lithium carbonate and lithium hydroxide is a component remaining in the lithium-containing compound because it is formed unintentionally in the manufacturing process of the lithium-containing compound. Hereinafter, lithium carbonate and lithium hydroxide are collectively referred to simply as "residual lithium components". This residual lithium component is an unnecessary component contained in the lithium-containing compound due to reasons in the manufacturing process and is a factor that degrades the battery characteristics of the secondary battery.

[0042] Therefore, the content (remaining amount) of the residual lithium component is set to be sufficiently small within the range that can ensure the battery characteristics of the secondary battery. Specifically, the content of lithium carbonate in the positive electrode active material is 0.2% by weight to 0.7% by weight, and the content of lithium hydroxide in the positive electrode active material is 0.2% by weight to 0.7% by weight.

[0043] The reason why the content of the residual lithium component is within the above-mentioned range is that the surface state of the positive electrode active material, that is, the elemental distribution on the surface of the lithium-containing compound, is optimized. Specifically, on the surface of the lithium-containing compound, the occupancy ratio of the constituent elements of the lithium-containing compound becomes sufficiently larger than the occupancy ratio of the constituent elements of the residual lithium component. As a result, while the generation of gas caused by the presence of the residual lithium component is suppressed, lithium ions are easily input and output in the lithium-containing compound, and the electrolyte is less likely to be decomposed on the surface of the lithium-containing compound. In this case, in particular, even when the secondary battery is used (charged and discharged) or stored in a severe environment such as a high-temperature environment or a low-temperature environment, the above-mentioned advantages can be stably obtained.

[0044] The content of the residual lithium component can be measured using the Warder method according to the procedure described below.

[0045] First, after weighing a predetermined amount (Sg) of the positive electrode active material, the positive electrode active material is placed in a sample bottle. Here, S = 10 (g). Subsequently, after adding ultrapure water (50 ml = 50 cm 3 ) together with a stir bar into the sample bottle, the ultrapure water is stirred (stirring time = 1 hour) using a stirrer. Subsequently, after allowing the stirred ultrapure water to stand (standing time = 1 hour), the supernatant of the ultrapure water is collected using a syringe with a filter, and then the supernatant is filtered. Subsequently, after collecting the supernatant (10 ml = 10 cm 3 ) after filtration using a volumetric pipette, the supernatant is placed in an Erlenmeyer flask with a stopper.

[0046] Subsequently, after adding one drop of phenolphthalein solution to the supernatant, while stirring the supernatant using a stirrer, titrate with a titrant solution (hydrochloric acid (HCl) having a concentration of M) until the liquid color (red color) disappears, and read the amount of hydrochloric acid dropped (A ml = A cm 3 ). Here, the concentration M = 0.02 mol / l (= 0.02 mol / dm 3 ). Subsequently, after adding two drops of bromophenol blue solution to the supernatant, while stirring the supernatant using a stirrer, titrate with the above-described titrant solution until the liquid color changes from blue to yellow-green (the blue color disappears), and read the amount of hydrochloric acid dropped (B ml = B cm 3 ). As the titration apparatus, an automatic titrator COM-1600 manufactured by Hiranuma Sangyo Co., Ltd. can be used.

[0047] Finally, calculate the lithium carbonate content (weight%) using the following formula (11) and calculate the lithium hydroxide content (weight%) using the following formula (12).

[0048] Lithium carbonate content (weight%) = [(M × 2B × (f / 1000) × 0.5 × 73.892 × 5) / S] × 100 ··· (11) (S is the weight (g) of the positive electrode active material. B is the amount of drop (ml = cm 3 ) from the end point of the first time using the phenolphthalein solution to the end point of the second time using the bromophenol blue solution. f is a factor depending on the concentration of the titrant solution. M is the concentration of the titrant solution (mol / l = mol / dm 3 ).)

[0049] Lithium hydroxide content (weight%) = [(M × (A - B) × (f / 1000) × 23.941 × 5) / S] × 100 ··· (12) (S is the weight (g) of the positive electrode active material. A is the amount of drop (ml = cm 3 ) until the end point of the first time using the phenolphthalein solution. B is the amount of drop (ml = cm3 ) where f is a factor depending on the concentration of the titrant solution and M is the concentration of the titrant solution (mol / l = mol / dm 3 ).)

[0050] Specifically, the 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.

[0051] Among them, the lithium-containing compound may contain a first lithium composite oxide represented by the formula (5), may contain a second lithium composite oxide represented by the formula (6), or may contain both.

[0052] Li x Ni 1-y M1 y O 2-a X1 b ···(5) (M1 is at least one of Co, Mn, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X1 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0.9 ≦ x ≦ 1.1, 0.005 ≦ y ≦ 0.5, -0.1 ≦ a ≦ 0.2, and 0 ≦ b ≦ 0.1.)

[0053] Li x Mn 1-x-y-z Ni y M2 z O 2-a X2 b ···(6) (M2 is at least one of Co, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X2 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, z, a, and b satisfy 0 < x ≤ 0.3, 0.3 ≤ y ≤ 0.9, 0 ≤ z ≤ 0.5, -0.1 ≤ a ≤ 0.2, and 0 ≤ b ≤ 0.1.)

[0054] As is clear from formula (5), the first lithium composite oxide is a binary composite oxide that can contain two or more main elements (Ni and M1) together with lithium as constituent elements. Specific examples of the first lithium composite oxide are LiNi 0.82 Co 0.14 Al 0.04 O2 and the like.

[0055] As is clear from formula (6), the second lithium composite oxide is a ternary composite oxide that can contain three or more main elements (Mn, Ni, and M2) together with lithium as constituent elements. Specific examples of the second lithium composite oxide are LiMn 0.30 Ni 0.50 Co 0.20 O2, LiMn 0.33 Ni 0.33 Co 0.33 Al 0.01 O2, and LiMn 0.04 Ni 0.87 Co 0.08 Al 0.01 O2 and the like.

[0056] Note that the positive electrode active material may further contain any one or two or more of other lithium-containing compounds. The types of other lithium-containing compounds are not particularly limited, but specifically include oxides, phosphate compounds, silicate compounds, borate compounds, and the like. However, the above-described first lithium composite oxide and second lithium composite oxide are excluded from the oxides described here.

[0057] Specific examples of the oxide include LiNiO2, LiCoO2, and LiMn2O4. Specific examples of the phosphate compound include LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4 and the like.

[0058] The positive electrode binder contains any one or two or more of materials such as synthetic rubber and polymer compounds. Specific examples of the synthetic rubber include styrene-butadiene rubber, fluorine rubber, and ethylene propylene diene. Specific examples of the polymer compound include polyvinylidene fluoride, polyimide, and carboxymethyl cellulose.

[0059] 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 include graphite, carbon black, acetylene black, and ketjen black. However, the conductive material may also be a metal material, a polymer compound, or the like.

[0060] (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.

[0061] The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. The negative electrode current collector 22A contains a conductive material such as a metal material, and specific examples of the conductive material include copper.

[0062] 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.

[0063] 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).

[0064] 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.

[0065] Specific examples of the carbon material are graphitizable carbon, non-graphitizable carbon, and graphite. This graphite may be natural graphite or artificial graphite.

[0066] The metal-based material is a general term for materials containing any one or two or more of metal elements and metalloid elements that can form an alloy with lithium as constituent elements. Specific examples of the metal elements and metalloid elements are silicon, tin, etc. This metal-based material may be a single substance, an alloy, a compound, a mixture of two or more of them, or a material containing two or more phases of them. Specific examples of the metal-based material are TiSi2 and SiO x (0 < x ≤ 2 or 0.2 < x < 1.4), etc.

[0067] Details regarding the negative electrode binder are the same as those regarding the positive electrode binder, and details regarding the negative electrode conductive agent are the same as those regarding the positive electrode conductive agent.

[0068] (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.

[0069] (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 an electrolyte salt. More specifically, the electrolyte contains a solvent for dispersing (ionizing) the electrolyte salt together with the electrolyte salt.

[0070] The electrolyte salt is a compound that ionizes in a solvent and contains an anion and a cation.

[0071] The anion contains an imide anion. Specifically, the imide anion contains any one or two or more of the first imide anion represented by formula (1), the second imide anion represented by formula (2), the third imide anion represented by formula (3), and the fourth imide anion represented by formula (4). That is, the electrolyte salt contains an imide anion as an anion.

[0072] 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.

[0073]

Chem.

[0074]

Chem.

[0075]

Chem.

[0076] [Chemical formula] (Each of R6 and R7 is any one of a fluorine group and a fluorinated alkyl group. R8 is any one of an alkylene group, a phenylene group, a fluorinated alkylene group, and a fluorinated phenylene group. Each of Z1, Z2, Z3, and Z4 is any one of a carbonyl group, a sulfinyl group, and a sulfonyl group.)

[0077] The reason why the anion contains an imide anion is as follows. First, during charge and discharge of the secondary battery, a high-quality film derived from the electrolyte salt is formed on the surface of each of the positive electrode 21 and the negative electrode 22, so that the decomposition reaction of the electrolytic solution (especially the solvent) is suppressed. Second, by using the above-mentioned film, the migration rate of lithium ions 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 lithium ions is also improved in the electrolytic solution.

[0078] 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).

[0079] Each of R1 and R2 is not particularly limited as long as it is any one of a fluorine group (-F) and 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, etc.

[0080] The fluorinated alkyl group is a group in which one or more hydrogen groups (-H) in the alkyl group are replaced by fluorine groups. However, the fluorinated alkyl group may be linear or branched with one or more side chains.

[0081] The number of carbon atoms in 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.

[0082] Specific examples of the fluorinated alkyl group include a perfluoromethyl group (-CF3) and a perfluoroethyl group (-C2F5).

[0083] 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.

[0084] 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).

[0085] Details regarding each of R3 and R4 are the same as those regarding each of R1 and R2.

[0086] 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.

[0087] 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).

[0088] 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 more side chains.

[0089] The number of carbon atoms 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 third imide anion are improved.

[0090] Specific examples of the fluorinated alkylene group are a perfluoromethylene group (-CF2-) and a perfluoroethylene group (-C2F4-), etc.

[0091] 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.

[0092] 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).

[0093] Details regarding each of R6 and R7 are the same as the details regarding each of R1 and R2.

[0094] 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.

[0095] The alkylene group may be linear or branched with one 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-), etc.

[0096] Details regarding the fluorinated alkylene group that is R8 are the same as the details regarding the fluorinated alkylene group that is R5.

[0097] 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.

[0098] 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.

[0099] (Specific examples of anions) Specific examples of the first imide anion include anions represented by each of Formula (1-1) to Formula (1-30), etc.

[0100]

Chemical formula

[0101]

Chemical formula

[0102]

Chemical formula

[0103] Specific examples of the second imide anion include anions represented by each of formulas (2-1) to (2-22).

[0104]

Chemical formula

[0105]

Chemical formula

[0106] Specific examples of the third imide anion include anions represented by each of formulas (3-1) to (3-15).

[0107]

Chemical formula

[0108] Specific examples of the fourth imide anion include anions represented by each of formulas (4-1) to (4-65).

[0109]

Chemical formula

[0110]

Chemical formula

[0111]

Chemical formula

[0112]

Chemical formula

[0113]

Chemical formula

[0114] [Chemical formula]

[0115] [Chemical formula]

[0116] (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.

[0117] The type of light metal ion is not particularly limited, but specifically, it is an alkali metal ion and 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 light metal ion may be aluminum ion, etc.

[0118] Among them, the light metal ion preferably contains lithium ion. This is because a sufficiently high voltage can be obtained.

[0119] (Content) The content of the electrolyte salt in the electrolytic solution is not particularly limited, so it can be arbitrarily set. Among them, the content of the electrolyte salt is preferably 0.2 mol / kg to 2 mol / kg. This is because high ionic conductivity can be obtained. The "content of the electrolyte salt" described here is the content of the electrolyte salt with respect to the solvent.

[0120] When specifying the content of the electrolyte salt, the secondary battery is disassembled to recover the electrolytic solution, and then the electrolytic solution is analyzed using inductively coupled plasma (ICP) emission spectrometry. As a result, the weight of the solvent and the weight of the electrolyte salt are specified respectively, and thus the content of the electrolyte salt is calculated.

[0121] [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.

[0122] 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.

[0123] 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.

[0124] The lactone-based compounds are lactones, etc. Specific examples of the lactone are γ-butyrolactone, γ-valerolactone, etc.

[0125] Note that the ethers may be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.

[0126] [Other electrolyte salts] Incidentally, the electrolytic solution may further contain any one or two or more of other electrolyte salts. This is because the migration rate of lithium ions is further improved near the surface of each of the positive electrode 21 and the negative electrode 22, and the migration rate of lithium ions is 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.

[0127] The type of other electrolyte salts is not particularly limited, but specifically, it is a light metal salt such as a lithium salt. However, the above-described electrolyte salt is excluded from the lithium salts described herein.

[0128] Specific examples of the lithium salt 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 difluorooxalatoborate (LiBF2(C2O4)), lithium difluorodi(oxalato)phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalatophosphate (LiPF4(C2O4)), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2).

[0129] Among them, it is preferable that the other electrolyte salt contains 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 lithium ions is sufficiently improved near the surface of each of the positive electrode 21 and the negative electrode 22, and the migration rate of lithium ions is also sufficiently improved in the electrolytic solution.

[0130] [Additive] Further, the electrolytic solution may further contain any one or two or more of the additives. During charging and discharging of the secondary battery, a film derived from the additive is formed on the surfaces of the positive electrode 21 and the negative electrode 22, respectively, so that the decomposition reaction of the electrolytic solution is suppressed. Note that the content of the additive in the electrolytic solution is not particularly limited and can be arbitrarily set.

[0131] The type of the additive is not particularly limited. Specifically, it is 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, an isocyanate compound, or the like.

[0132] (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, and thus 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.

[0133] (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 two or more hydrogen groups of the cyclic carbonate are substituted with fluorine groups. Specific examples of the fluorinated cyclic carbonate include ethylene monofluorocarbonate and ethylene difluorocarbonate.

[0134] (Sulfonic acid ester) The sulfonic acid ester includes a cyclic monosulfonic acid ester, a cyclic disulfonic acid ester, a chain monosulfonic acid ester, a chain disulfonic acid ester, and 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.

[0135] (Dicarboxylic acid anhydride) Specific examples of the dicarboxylic acid anhydride include succinic anhydride, glutaric anhydride, maleic anhydride, and the like.

[0136] (Disulfonic acid anhydride) Specific examples of the disulfonic acid anhydride include ethanedisulfonic anhydride, propanedisulfonic anhydride, and the like.

[0137] (Sulfuric acid ester) Specific examples of the sulfuric acid ester include ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide), and the like.

[0138] (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, and the like.

[0139] (Isocyanate compound) The isocyanate compound is a compound having one or more isocyanate groups (-NCO). Specific examples of the isocyanate compound include hexamethylene diisocyanate, and the like.

[0140] [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, the positive electrode lead 31 is either in a thin plate shape or a mesh shape or the like.

[0141] 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 direction 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.

[0142] <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 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 charging and discharging, lithium is occluded and released in an ionic state.

[0143] <1-3. Manufacturing Method> When manufacturing a secondary battery, each of the positive electrode 21 and the negative electrode 22 is produced according to a procedure of an example described below, and after preparing the electrolyte, the secondary battery is assembled using the positive electrode 21, the negative electrode 22, and the electrolyte, and a stabilization treatment of the secondary battery is performed.

[0144] [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 containing a lithium-containing compound, a positive electrode binder, and a positive electrode conductive agent are mixed with each other into a solvent. As described above, this positive electrode active material contains lithium carbonate and lithium hydroxide together with the lithium-containing compound for reasons in the production of the lithium-containing compound. Note that the solvent may be an aqueous solvent or an organic solvent.

[0145] Subsequently, a positive electrode active material layer 21B is formed by applying the positive electrode mixture slurry to both sides 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 layers 21B are formed on both sides of the positive electrode current collector 21A, the positive electrode 21 is produced.

[0146] [Fabrication of Negative Electrode] A negative electrode 22 is formed by the same procedure as the procedure for fabricating 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 sides 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 sides of the negative electrode current collector 22A, the negative electrode 22 is produced.

[0147] [Preparation of Electrolyte Solution] An electrolyte salt containing an imide anion is introduced into a solvent. In this case, another electrolyte salt may be further added to the solvent, or an additive may be further added to the solvent. As a result, since the electrolyte salt and the like are dispersed or dissolved in the solvent, an electrolyte solution is prepared.

[0148] [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.

[0149] 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.

[0150] 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 heat 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.

[0151] Finally, after injecting the electrolytic solution inside the bag-shaped outer packaging film 10, using an adhesion method such as a heat 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.

[0152] 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 sealed inside the bag-shaped outer packaging film 10, the secondary battery is assembled.

[0153] [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, so that the state of the secondary battery is electrochemically stabilized. Thus, the secondary battery is completed.

[0154] <1-4. Action and effect> According to this secondary battery, the positive electrode active material of the positive electrode 21 contains a lithium-containing compound, lithium carbonate, and lithium hydroxide. The content of lithium carbonate in the positive electrode active material is 0.2% by weight to 0.7% by weight, and the content of lithium hydroxide in the positive electrode active material is 0.2% by weight to 0.7% by weight. The electrolyte salt of the electrolytic solution contains an imide anion.

[0155] In this case, as described above, when the positive electrode active material contains residual lithium components (lithium carbonate and lithium hydroxide) together with the lithium-containing compound, the element distribution on the surface of the positive electrode active material is optimized. As a result, while suppressing the generation of gas caused by the presence of the residual lithium components, lithium ions are more easily input and output in the lithium-containing compound, and the electrolytic solution is less likely to be decomposed on the surface of the lithium-containing compound.

[0156] Moreover, as described above, a high-quality film derived from the 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, so that the decomposition reaction of the electrolytic solution is suppressed. In addition, the migration speed of lithium ions 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 lithium ions is also improved in the electrolytic solution.

[0157] Therefore, excellent battery characteristics can be obtained.

[0158] In particular, if the lithium-containing compound contains one or both of the first lithium composite oxide and the second lithium composite oxide, a high voltage can be obtained, so that a higher effect can be obtained.

[0159] In addition, if the electrolyte salt contains light metal ions as cations, a high voltage can be obtained, so a higher effect can be achieved. In this case, if the light metal ions contain lithium ions, a higher voltage can be obtained, so an even higher effect can be achieved.

[0160] Also, if the content of the electrolyte salt in the electrolytic solution is 0.2 mol / kg to 2 mol / kg, high ionic conductivity can be obtained, so a higher effect can be achieved.

[0161] In addition, if the electrolytic solution further contains any one or more of unsaturated cyclic carbonates, fluorinated cyclic carbonates, sulfonic acid esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfuric acid esters, nitrile compounds, and isocyanate compounds as additives, the decomposition reaction of the electrolytic solution is suppressed, so a higher effect can be obtained.

[0162] In addition, if the electrolytic solution further contains any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate as other electrolyte salts, the migration rate of lithium ions is further improved, so a higher effect can be obtained.

[0163] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the intercalation and deintercalation of lithium, so a higher effect can be achieved.

[0164] <2. Modification Example> As described above, the configuration of the secondary battery can be appropriately changed as described below. However, a series of modification examples described below may be combined with each other.

[0165] [Modification Example 1] As described above, the electrolytic solution may contain other electrolyte salts together with the electrolyte salt containing imide anions.

[0166] Among them, the electrolytic solution preferably contains lithium hexafluorophosphate as another electrolyte salt, and the content of the electrolyte salt in the electrolytic solution is optimized in relation to the content of other electrolyte salts in the electrolytic solution.

[0167] Specifically, the electrolyte salt contains a cation and an imide anion. Also, the hexafluorophosphate ion contains a lithium ion and a hexafluorophosphate ion.

[0168] In this case, the sum T (mol / kg) of the content C1 of the cation in the electrolytic solution and the content C2 of the lithium ion 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 hexafluorophosphate ion in the electrolytic solution to the number of moles M1 of the imide anion in the electrolytic solution is 13 mol% to 6000 mol%. This is because the moving speeds of the cation and the lithium ion are sufficiently improved near the surfaces of the positive electrode 21 and the negative electrode 22 respectively, and the moving speeds of the cation and the lithium ion are also sufficiently improved in the liquid of the electrolytic solution.

[0169] The "content of the cation in the electrolytic solution" described here is the content of the electrolyte salt of the cation with respect to the solvent, and the "content of the lithium ion in the electrolytic solution" is the content of the lithium ion with respect to the solvent. Note that 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.

[0170] When calculating each of the sum T and the ratio R, the electrolytic solution is recovered by disassembling the secondary battery, and then the electrolytic solution is analyzed using ICP emission spectrometry. As a result, since each of the contents C1, C2 and the number of moles M1, M2 is specified, each of the sum T and the ratio R is calculated.

[0171] Even in this case, since the electrolytic solution contains an electrolyte salt, the same effect can be obtained. In this case, in particular, when the electrolyte salt is used in combination with another electrolyte salt (lithium hexafluorophosphate), the total amount (sum T) of the two is optimized, and the mixing ratio (ratio R) of the two is also optimized. As a result, the moving speeds of cations and lithium ions are further improved near the surfaces of the positive electrode 21 and the negative electrode 22, respectively, and the moving speeds of cations and lithium ions are further improved even in the electrolytic solution. Therefore, a higher effect can be obtained.

[0172] [Modification Example 2] The separator 23 which is a porous membrane was used. However, although not specifically shown here, a laminated separator including a polymer compound layer may be used.

[0173] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both surfaces of the porous membrane. This is because the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, and the displacement (winding displacement) of the battery element 20 is suppressed. Thereby, even if a side reaction such as a decomposition reaction of the electrolytic solution occurs, the swelling of the secondary battery is suppressed. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because excellent physical strength and excellent electrochemical stability can be obtained.

[0174] 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, and thus the safety (heat resistance) of the secondary battery is improved. The insulating particles contain one or more of insulating materials such as inorganic materials and resin materials. 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.

[0175] When manufacturing a laminated separator, after preparing a precursor solution containing a polymer compound, a solvent, etc., the precursor solution is applied to one or both sides of a porous membrane. In this case, if necessary, a plurality of insulating particles may be added to the precursor solution.

[0176] Even when using this laminated separator, since lithium ions can move between the positive electrode 21 and the negative electrode 22, the same effects can be obtained. In this case, in particular, as described above, since the safety of the secondary battery is improved, higher effects can be obtained.

[0177] [Modification Example 3] An electrolytic solution that is a liquid electrolyte was used. However, although not specifically illustrated here, an electrolyte layer that is a gel electrolyte may also be used.

[0178] 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.

[0179] Specifically, the electrolyte layer contains a polymer compound together with the electrolytic solution, and the electrolytic solution is held by the polymer compound. This is because leakage of the electrolytic solution is prevented. The composition of the electrolytic solution is as described above. The polymer compound contains polyvinylidene fluoride, etc. When forming the electrolyte layer, after preparing a precursor solution containing the electrolytic solution, the polymer compound, a solvent, etc., the precursor solution is applied to one or both sides of each of the positive electrode 21 and the negative electrode 22.

[0180] Even when using this electrolyte layer, since lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, 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.

[0181] <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 or 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 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.

[0182] Specific examples of the applications of secondary batteries are as follows. Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals. Storage devices such as backup power sources and memory cards. Power tools such as electric drills and electric saws. Battery packs mounted on electronic devices, etc. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid cars). Power storage systems such as household or industrial battery systems that store power for emergencies. In these applications, one secondary battery may be used, or a plurality of secondary batteries may be used.

[0183] 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 the power storage source.

[0184] Here, a specific example regarding 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.

[0185] Figure 3 shows the block configuration of a battery pack. The battery pack described here is a battery pack (so-called soft pack) using one secondary battery, and is mounted on an electronic device typified by a smartphone.

[0186] 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.

[0187] The power source 51 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to the positive electrode terminal 53, and the negative electrode lead is connected to the negative electrode terminal 54. Since this power source 51 can be connected to the outside via the positive electrode terminal 53 and the negative electrode terminal 54, it can be charged and discharged. The circuit board 52 includes a control unit 56, a switch 57, a PTC element 58, and a temperature detection unit 59. However, the PTC element 58 may be omitted.

[0188] The 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 the power source 51 as necessary.

[0189] In addition, when the voltage of the power source 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 56 disconnects the switch 57 so that no charging current flows through the current path of the power source 51. The overcharge detection voltage is not particularly limited, but specifically, it is 4.20V ± 0.05V, and the overdischarge detection voltage is not particularly limited, but specifically, it is 2.40V ± 0.1V.

[0190] 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 source 51 and an external device according to an instruction from 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.

[0191] 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

[0192] The embodiments of the present technology will be described.

[0193] <Examples 1 to 46 and Comparative Examples 1 to 28> As described below, after manufacturing a secondary battery, the battery characteristics of the secondary battery were evaluated.

[0194] [Manufacture of secondary battery] The laminated film type secondary battery (lithium ion secondary battery) shown in FIGS. 1 and 2 was manufactured according to the following procedure.

[0195] (Manufacture of positive electrode) First, 91 parts by mass of a positive electrode active material (lithium-containing compound), 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. As the lithium-containing compound, LiNi 0.82 Co 0.14 Al 0.04 O2 (LNCA) as the first lithium composite oxide and LiMn 0.30 Ni 0.50 Co 0.20 O2 (LMNC) were used. The average particle size (median diameter D50 (μm)) of the lithium-containing compound is as shown in Tables 1 to 6.

[0196] In addition, when the content (weight%) of the residual lithium component in the positive electrode active material was examined according to the above procedure, the content of lithium carbonate (Li2CO3) and the content of lithium hydroxide (LiOH) were as shown in Tables 1 to 6.

[0197] Subsequently, after adding the positive electrode mixture to a solvent (N-methyl-2-pyrrolidone, an organic solvent), the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, after applying the positive electrode mixture slurry to both sides of a positive electrode current collector 21A (a strip-shaped aluminum foil with a thickness of 12 μm) using a coating device, 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. Thereby, the positive electrode 21 was fabricated.

[0198] (Fabrication of negative electrode) First, 93 parts by mass of a negative electrode active material (artificial graphite, 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 adding the negative electrode mixture to a solvent (N-methyl-2-pyrrolidone, an organic solvent), the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Subsequently, after applying the negative electrode mixture slurry 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. Thereby, the negative electrode 22 was fabricated.

[0199] (Preparation of electrolyte) First, an electrolyte salt was added to a solvent, and then the solvent was stirred.

[0200] As the solvent, ethylene carbonate, a cyclic carbonate ester, and γ-butyrolactone, a lactone, were used. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:γ-butyrolactone = 30:70.

[0201] As the cation of the electrolyte salt, lithium ion (Li +) was used. As the anion of the electrolyte salt, the first imide anion shown in each of Formula (1-5), Formula (1-6), Formula (1-21) and Formula (1-22), the second imide anion shown in Formula (2-5), the third imide anion shown in Formula (3-5), and the fourth imide anion shown in Formula (4-37) were used. The content (mol / kg) of the electrolyte salt was as shown in Tables 1 to 6.

[0202] Thereby, an electrolytic solution containing the electrolyte salt was prepared. This electrolyte salt is a lithium salt containing an imide anion as an anion.

[0203] For comparison, an electrolytic solution was prepared by the same procedure except that hexafluorophosphate ion (PF6 - ) was used as the anion.

[0204] (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.

[0205] Subsequently, the positive electrode 21 and the negative electrode 22 were laminated on each other via a separator 23 (a microporous polyethylene film with a thickness of 15 μm), and then the positive electrode 21, the negative electrode 22, and the separator 23 were wound to produce a wound body. Subsequently, the wound body was pressed using a press machine to form the wound body into a flat shape.

[0206] Subsequently, after folding the outer film 10 (fusion layer / metal layer / surface protection layer) so as to sandwich the wound body accommodated in the recessed portion 10U, the outer peripheral edge portions of two sides of the fusion layer were heat-sealed to each other, and the wound body was stored inside the bag-shaped outer film 10. As the outer 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.

[0207] Finally, after injecting the electrolytic solution into the interior of the bag-shaped exterior film 10, the outer peripheral edges 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 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 electrolytic solution, the battery element 20 was fabricated.

[0208] Therefore, since the battery element was encapsulated inside the exterior film 10, the secondary battery was assembled.

[0209] (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 that 4.2V voltage 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.

[0210] As a result, films were 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 laminated film type secondary battery was completed.

[0211] [Evaluation of battery characteristics] When the battery characteristics were evaluated, the results shown in Tables 1 to 6 were obtained. Here, the high-temperature cycle characteristics, high-temperature storage characteristics, and low-temperature load characteristics were evaluated.

[0212] (High-temperature cycle characteristics) First, the secondary battery was charged and discharged in a high-temperature environment (temperature = 60 °C) to measure the discharge capacity (the discharge capacity of the first cycle). The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0213] Subsequently, in the same environment, the secondary battery was repeatedly charged and discharged until the total number of cycles reached 100 cycles to measure the discharge capacity (the discharge capacity of the 100th cycle). The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0214] Finally, based on the calculation formula of cycle retention rate (%) = (discharge capacity of the 100th cycle / discharge capacity of the first cycle) × 100, the cycle retention rate, which is an index for evaluating the high-temperature cycle characteristics, was calculated.

[0215] (High-temperature storage characteristics) First, the secondary battery was charged and discharged once in a normal-temperature environment (temperature = 23 °C) 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.

[0216] Subsequently, in the same environment, the secondary battery was charged, and then the charged secondary battery was stored in a high-temperature environment (temperature = 80 °C) for a storage time of 10 days. After that, 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.

[0217] 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.

[0218] (Low-temperature load characteristics) First, the secondary battery was charged and discharged once in a normal-temperature environment (temperature = 23 °C) to measure the discharge capacity (the discharge capacity of the first cycle). The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above.

[0219] 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 discharge the battery capacity in 1 hour.

[0220] 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.

[0221] [Table 1]

[0222] [Table 2]

[0223] [Table 3]

[0224] [Table 4]

[0225] [Table 5]

[0226] [Table 6]

[0227] [Discussion] As shown in Tables 1 to 6, each of the cycle retention rate, storage retention rate, and load retention rate varied significantly depending on the composition of the positive electrode 21 and the composition of the electrolytic solution.

[0228] Specifically, in the secondary batteries (Tables 1 to 3) using the first lithium composite oxide as the lithium-containing compound, the following tendencies were obtained.

[0229] Even when the content of lithium carbonate was 0.2% by weight to 0.7% by weight and the content of lithium hydroxide was 0.2% by weight to 0.7% by weight, when the electrolyte salt did not contain an imide anion (Comparative Examples 1 to 14), all of the cycle retention rate, storage retention rate, and load retention rate decreased.

[0230] On the other hand, when the content of lithium carbonate was 0.2% by weight to 0.7% by weight and the content of lithium hydroxide was 0.2% by weight to 0.7% by weight, and the electrolyte salt contained an imide anion (Examples 1 to 23), all of the cycle retention rate, storage retention rate, and load retention rate increased.

[0231] Also, in the secondary batteries (Tables 4 to 6) using the second lithium composite oxide as the lithium-containing compound, the same tendencies were obtained.

[0232] Even when the content of lithium carbonate was 0.2% by weight to 0.7% by weight and the content of lithium hydroxide was 0.2% by weight to 0.7% by weight, when the electrolyte salt did not contain an imide anion (Comparative Examples 15 to 28), all of the cycle retention rate, storage retention rate, and load retention rate decreased.

[0233] On the other hand, when the content of lithium carbonate was 0.2% by weight to 0.7% by weight and the content of lithium hydroxide was 0.2% by weight to 0.7% by weight, and the electrolyte salt contained an imide anion (Examples 24 to 46), all of the cycle retention rate, storage retention rate, and load retention rate increased.

[0234] In particular, when the electrolyte salt contains an imide anion (Examples 1 to 46), the following tendencies were also 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 0.2 mol / kg to 2 mol / kg with respect to the solvent, each of the cycle retention rate, storage retention rate, and load retention rate became sufficiently high.

[0235] <Examples 47 to 64> As shown in Tables 7 and 8, after manufacturing a secondary battery by the same procedure as in Example 3 except that either an additive or another electrolyte salt was contained in the electrolytic solution, 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.

[0236] Details regarding the additive are as described below. As the unsaturated cyclic carbonate, vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and methylene ethylene carbonate (MEC) were used. As the fluorinated cyclic carbonate, fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC) were used. As the sulfonic acid ester, propane sultone (PS) and propene sultone (PRS), which are cyclic monosulfonic acid esters, and cyclodison (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.

[0237] 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.

[0238] The respective contents (weight %) of the additives and other electrolyte salts in the electrolyte solution were as shown in Tables 7 and 8.

[0239]

Table 7

[0240]

Table 8

[0241] As shown in Tables 1 and 7, when the electrolyte solution contained additives (Examples 47 to 59), one or more of the cycle retention rate and the storage retention rate increased more compared with the case where the electrolyte solution did not contain additives (Example 3).

[0242] Also, as shown in Tables 1 and 8, when the electrolyte solution contained other electrolyte salts (Examples 60 to 64), one or more of the cycle retention rate and the storage retention rate increased more compared with the case where the electrolyte solution did not contain other electrolyte salts (Example 3).

[0243] <Examples 65 to 96> As shown in Tables 9 and 10, after manufacturing a secondary battery by the same procedure as in Example 3 except that the electrolyte solution contained another electrolyte salt (lithium hexafluorophosphate (LiPF6)), the battery characteristics were evaluated.

[0244] In this case, after adding another electrolyte salt together with the electrolyte salt to the solvent, the solvent was stirred. The content (mol / kg) of the electrolyte salt, the content (mol / kg) of the other electrolyte salt, the sum T (mol / kg), and the ratio R (mol%) were as shown in Tables 9 and 10.

[0245] [Table 9]

[0246] [Table 10]

[0247] As shown in Tables 9 and 10, when the two conditions that the sum T is 0.7 mol / kg to 2.2 mol / kg and the ratio R is 13 mol% to 6000 mol% are satisfied (such as Example 69), the cycle retention rate, the storage retention rate, and the load retention rate are each increased as compared with the case where the two conditions are not satisfied (such as Example 65).

[0248] [Summary] From the results shown in Tables 1 to 10, when the positive electrode active material of the positive electrode 21 contains a lithium-containing compound, lithium carbonate, and lithium hydroxide, the content of lithium carbonate in the positive electrode active material is 0.2% by weight to 0.7% by weight, the content of lithium hydroxide in the positive electrode active material is 0.2% by weight to 0.7% by weight, and the electrolyte salt of the electrolytic solution contains an imide anion, 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.

[0249] As described above, the present technology has been described with one embodiment and examples, but the configuration of the present technology is not limited to the configuration described in one embodiment and examples, and thus can be variously modified.

[0250] 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 with a separator interposed therebetween, and in the ninety-nine-fold type, the positive electrode and the negative electrode are folded in a zigzag while facing each other with a separator interposed therebetween.

[0251] 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 containing a positive electrode active material, a negative electrode, and an electrolytic solution containing an electrolyte salt provided with, the positive electrode active material includes a lithium-containing compound, lithium carbonate, and lithium hydroxide, the content of the lithium carbonate in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less, the content of the lithium hydroxide in the positive electrode active material is 0.2% by weight or more and 0.7% by weight or less, the electrolyte salt contains an imide anion, and the imide 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), a secondary battery. 【Chemical Formula 1】 (Each of R1 and R2 is any one of a fluorine group and a fluorinated alkyl group. Each of W1, W2, and W3 is any one of a carbonyl group (>C=O), a sulfinyl group (>S=O), and a sulfonyl group (>S(=O) 2 )). 【Chemical Formula 2】 (Each of R3 and R4 is any one of a fluorine group and a fluorinated alkyl group. Each of X1, X2, X3, and X4 is any one of a carbonyl group, a sulfinyl group, and a sulfonyl group.). 【Chemical Formula 3】 (R5 is a fluorinated alkylene group. Each of Y1, Y2, and Y3 is any one of a carbonyl group, a sulfinyl group, and 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. The lithium-containing compound contains at least one of a first lithium composite oxide represented by formula (5) and a second lithium composite oxide represented by formula (6). The secondary battery according to claim 1. Li x Ni 1-y M1 y O 2-a X1 b ... (5) (M1 is at least one of Co, Mn, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X1 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0.9 ≤ x ≤ 1.1, 0.005 ≤ y ≤ 0.5, -0.1 ≤ a ≤ 0.2, and 0 ≤ b ≤ 0.1.) Li x Mn 1-x-y-z Ni y M2 z O 2-a X2 b ... (6) (M2 is at least one of Co, Mg, Ba, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr, W, Na, K, Nb, Ta, and rare earth elements. X2 is at least one of F, Cl, Cr, I, P, S, and Si. x, y, a, and b satisfy 0 < x ≤ 0.3, 0.3 ≤ y ≤ 0.9, 0 ≤ z ≤ 0.5, -0.1 ≤ a ≤ 0.2, and 0 ≤ b ≤ 0.1.)

3. The electrolyte contains light metal ions as cations. The secondary battery according to claim 1.

4. The light metal ion includes a lithium ion. The secondary battery according to claim 3.

5. The content of the electrolyte salt in the electrolyte is 0.2 mol / kg or more and 2 mol / kg or less. The secondary battery according to any one of claims 1 to 4.

6. The electrolyte further includes lithium hexafluorophosphate. The electrolyte salt includes a cation and the imide anion. The lithium hexafluorophosphate includes a lithium ion and a hexafluorophosphate ion. The sum of the content of the cation in the electrolyte and the content of the lithium ion in the electrolyte is 0.7 mol / kg or more and 2.2 mol / kg or less. The ratio of the number of moles of the hexafluorophosphate ion in the electrolyte to the number of moles of the imide anion in the electrolyte is 13 mol% or more and 6000 mol% or less. The secondary battery according to any one of claims 1 to 4.

7. The electrolyte further includes 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 sulfate ester, a nitrile compound, and an isocyanate compound. The secondary battery according to any one of claims 1 to 4.

8. The electrolyte further includes 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 4.

9. It is a lithium ion secondary battery. The secondary battery according to any one of claims 1 to 4.

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