Secondary batteries

Abstract

This secondary battery is provided with a positive electrode, a negative electrode containing a negative-electrode active material layer, and an electrolytic solution containing an electrolyte salt. The negative-electrode active material layer contains a carbon material. The thickness of the negative-electrode active material layer is 30-100 μm, inclusive. The volume density of the negative-electrode active material layer is 1.4 g / cm3 or more and 2 g / cm3 or less. The electrolyte salt contains imide anions. The imide anions include 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).

Description

[Technical Field]

[0001] This technology relates to secondary batteries. [Background technology]

[0002] With the widespread use of various electronic devices such as mobile phones, development of rechargeable batteries is progressing as a power source that is small, lightweight, and provides high energy density. These rechargeable batteries contain an electrolyte along with a positive electrode and a negative electrode, and various studies are being conducted on the configuration of these batteries.

[0003] Specifically, the electrolyte is R F 1 -S(=O)2-NH-S(=O)2-NH-S(=O)2-R F 2 It contains an imide compound represented by (see, for example, Patent Document 1). In addition, the electrolyte salt of the electrolyte is FS(=O)2-N - -C(=O)-N - -S(=O)2-F or FS(=O)2-N - -S(=O)2-C6H4-S(=O)2-N - It contains an imide anion represented by -S(=O)2-F (see, for example, Non-Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Chinese Patent No. 102786443 Specification [Non-patent literature]

[0005] [Non-Patent Document 1] Faiz Ahmed et al., "Novel divalent organo-lithium salts with high electrochemical and thermal stability for aqueous rechargeable Li-Ion batteries", Electrochimica Acta, 298, 2019, 709-716 [Non-Patent Document 2] Faiz Ahmed et al., "Highly conductive divalent fluorosulfonyl imide based electrolytes improving Li-ion battery performance: Additive potentiating", Journal of Power Sources, 455, 2020, 227980 [Summary of the Invention]

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

[0007] 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 including a negative electrode active material layer, and an electrolytic solution including an electrolyte salt. The negative electrode active material layer includes a carbon material, the thickness of the negative electrode active material layer is 30 μm or more and 100 μm or less, and the volume density of the negative electrode active material layer is 1.4 g / cm 3 or more and 2 g / cm 3 or less. The electrolyte salt includes an imide anion, and the imide anion includes 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] [ka] (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.)

[0011] [ka] (R5 is a fluorinated alkylene group. Y1, Y2, and Y3 are each one of the following: a carbonyl group, a sulfinyl group, or a sulfonyl group.)

[0012] [ka] (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.)

[0013] According to one embodiment of this technology, the negative electrode active material layer of the negative electrode contains a carbon material, the thickness of the negative electrode active material layer is 30 μm or more and 100 μm or less, and the volume density of the negative electrode active material layer is 1.4 g / cm³. 3 More than 2g / cm 3 As described below, since the electrolyte salt of the electrolyte solution contains at least one of the first, second, third, and fourth imid anions as imid anions, excellent battery characteristics can be obtained.

[0014] Furthermore, the effects of this technology are not necessarily limited to those described herein, but may include any of the series of effects related to this technology described later. [Brief explanation of the drawing]

[0015] [Figure 1] This is a perspective view showing the configuration of a secondary battery in one embodiment of this technology. [Figure 2] Figure 1 is a cross-sectional view showing the configuration of the battery element. [Figure 3] This is a block diagram showing the configuration of an example application of a secondary battery. [Modes for carrying out the invention]

[0016] An embodiment of this technology will be described in detail below with reference to the drawings. The order of description is as follows. 1. Secondary battery 1-1. Composition 1-2.Operation 1-3. Manufacturing method 1-4. Mechanism of Action and Effects 2. Variations 3. Applications of rechargeable batteries

[0017] <1. Secondary battery> First, we will describe a secondary battery according to one embodiment of this technology.

[0018] The secondary battery described here is a secondary battery that obtains its capacity by utilizing the intercalation and deintercalation of electrode reactants, and is equipped with an electrolyte along with a positive electrode and a negative electrode.

[0019] In this secondary battery, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. In other words, the electrochemical capacity per unit area of ​​the negative electrode is set to be greater than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent the deposition of electrode reactants on the surface of the negative electrode during charging.

[0020] The type of electrode reactant is not particularly limited, but specifically, it is a light metal such as alkali metals and alkaline earth metals. Specific examples of alkali metals include lithium, sodium, and potassium, while specific examples of alkaline earth metals include beryllium, magnesium, and calcium. However, the type of electrode reactant may also be other light metals such as aluminum.

[0021] In the following example, we will consider the case where lithium is the electrode reactant. A secondary battery that obtains battery capacity by utilizing the intercalation and deintercalation of lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is intercalated and deintercalated in an ionic state.

[0022] <1-1. Structure> Figure 1 shows a perspective view of the secondary battery, while Figure 2 shows a cross-sectional view of the battery element 20 shown in Figure 1. However, in Figure 1, the outer film 10 and the battery element 20 are shown separated from each other, and the cross-section of the battery element 20 along the XZ plane is shown with a dashed line. In Figure 2, only a portion of the battery element 20 is shown.

[0023] As shown in Figures 1 and 2, this secondary battery comprises an outer film 10, a battery element 20, a positive electrode lead 31, a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminate film type secondary battery using a flexible or pliable outer film 10.

[0024] [Outer packaging film and sealing film] As shown in Figure 1, the outer film 10 is an outer component that houses the battery element 20, and has a sealed bag-like structure in which the battery element 20 is housed. In this way, the outer film 10 houses the electrolyte together with the positive electrode 21 and negative electrode 22, which will be described later.

[0025] Here, the outer film 10 is a single film-like component that is folded in the folding direction F. The outer film 10 is provided with a recessed portion 10U (a so-called deep-drawn portion) for housing the battery element 20.

[0026] Specifically, the outer film 10 is a three-layer laminate film in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order from the inside out. When the outer film 10 is folded, the outer edges of the opposing fusion layers are fused together. The fusion layer contains a polymer compound such as polypropylene. The metal layer contains a metallic material such as aluminum. The surface protection layer contains a polymer compound such as nylon.

[0027] However, the composition (number of layers) of the outer film 10 is not particularly limited; it may consist of one or two layers, or four or more layers.

[0028] The sealing film 41 is inserted between the outer film 10 and the positive lead 31, and the sealing film 42 is inserted between the outer film 10 and the negative lead 32. However, one or both of the sealing films 41 and 42 may be omitted.

[0029] This sealing film 41 is a sealing member that prevents outside air and other elements from entering the interior of the outer film 10. The sealing film 41 also contains a polymer compound such as polyolefin that has good adhesion to the positive electrode lead 31, and a specific example of such a polymer compound is polypropylene.

[0030] The structure of the sealing film 42 is the same as that of the sealing film 41, except that it is a sealing member that adheres to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as a polyolefin that adheres to the negative electrode lead 32.

[0031] [Battery element] As shown in Figures 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 electrolyte (not shown), and is housed inside the outer film 10.

[0032] This battery element 20 is a so-called wound electrode body. That is, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23, and are wound around a 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.

[0033] 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 flattened, the shape of the cross-section of the battery element 20 intersecting the winding axis P (cross-section along the XZ plane) is a flattened shape defined by the major axis J1 and the minor axis J2. The major axis J1 is a virtual axis that extends in the X-axis direction and has a longer length than the minor axis J2, while the minor axis J2 is a virtual axis that extends in the Z-axis direction intersecting the X-axis direction and has a shorter length than the major axis J1. Here, since the three-dimensional shape of the battery element 20 is a flattened cylinder, the shape of the cross-section of the battery element 20 is a flattened, approximately elliptical shape.

[0034] (positive electrode) As shown in Figure 2, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B.

[0035] 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, a specific example of which is aluminum.

[0036] The positive electrode active material layer 21B contains one or more types of positive electrode active materials that intercalate and deintercalate lithium. However, the positive electrode active material layer 21B may further contain one or more types of other materials such as positive electrode binders and positive electrode conductive agents.

[0037] 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 on only one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically, it is one or more of the following methods, such as coating.

[0038] The type of positive electrode active material is not particularly limited, but specifically it is a lithium-containing compound. This lithium-containing compound is a compound that contains lithium along with one or more transition metal elements as constituent elements, and may further contain one or more other elements as constituent elements. The type of other element is not particularly limited as long as it is an element other than lithium and the transition metal elements, but specifically it is an element belonging to groups 2 to 15 of the long-period periodic table. The type of lithium-containing compound is not particularly limited, but specifically it is an oxide, a phosphoric acid compound, a silicate compound, and a borate compound, etc.

[0039] Specific examples of oxides include LiNiO2, LiCoO2, and LiCo 0.98 Al 0.01 Mg 0.01 O2, LiLiLi 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.82 Co 0.14 Al 0.04 O2, LiLiLi 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 Examples include O2 and LiMn2O4. Specific examples of phosphorylated compounds include LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 Examples include PO4.

[0040] The positive electrode binder contains one or more of the following: synthetic rubber and polymer compounds. Specific examples of synthetic rubber include styrene-butadiene rubber, fluorine-based rubber, and ethylene-propylenediene. Specific examples of polymer compounds include polyvinylidene fluoride, polyimide, and carboxymethylcellulose.

[0041] The positive electrode conductive agent contains one or more types of conductive materials, such as carbon materials. Specific examples of carbon materials include graphite, carbon black, acetylene black, and Ketjenblack. However, the conductive material may also be a metallic material or a polymer compound.

[0042] (Negative electrode) As shown in Figure 2, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0043] 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 metallic material, a specific example of which is copper.

[0044] The negative electrode active material layer 22B contains one or more types of negative electrode active materials that intercalate and deintercalate lithium. However, the negative electrode active material layer 22B may further contain one or more types of other materials such as negative electrode binders, thickeners, and negative electrode conductive agents.

[0045] 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 on only 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 one or more of the following: coating, gas phase, liquid phase, thermal spraying, and firing (sintering).

[0046] Specifically, the negative electrode active material contains one or more types of carbon materials. This is because the crystal structure of the carbon material does not change easily during lithium intercalation and deintercalation, thus allowing for a stable high energy density. Furthermore, the carbon material also functions as a negative electrode conductive agent. As a result, the negative electrode 22 achieves improved conductivity while stably obtaining a high energy density.

[0047] The type of carbon material is not particularly limited, but specifically includes easily graphitizable carbon, poorly graphitizable carbon, and graphite. This graphite may be natural graphite, artificial graphite, or both. The interplanar spacing of the (002) plane of the carbon material measured using X-ray diffraction is not particularly limited. A specific example of X-ray diffraction is wide-angle X-ray diffraction.

[0048] In particular, carbon materials contain graphite, and it is preferable that the interplanar spacing of the (002) planes of graphite, as measured by X-ray diffraction, is 0.3372 nm or less. This is because both the charging capacity and the discharging capacity increase.

[0049] The carbon material may include one or more of the following: pyrolysis carbons, cokes, glassy carbon fibers, calcined organic polymer compounds, activated carbon, and carbon blacks. The cokes are one or more of the following: pitch coke, needle coke, and petroleum coke. The calcined organic polymer compounds are substances obtained by calcining (carbonizing) polymer compounds at an appropriate temperature, and specific examples of such polymer compounds are one or more of the following: phenolic resins and furan resins. In addition, the carbon material may be low-crystalline carbon heat-treated at approximately 1000°C or below, or amorphous carbon heat-treated in the same manner. The shape of the carbon material is not particularly limited, but specifically, it may be one or more of the following: fibrous, spherical, granular, and flaky.

[0050] Here, the negative electrode active material layer 22B has a thickness T (μm) and a volume density V (g / cm³). 3) has the following characteristics. The thickness T and volume density V are optimized in relation to the composition of the electrolyte salt (imido anion) described later. The thickness T described here is the dimension of the negative electrode active material layer 22B in the direction (Z axis direction) in which the positive electrode 21 and the negative electrode 22 face each other via the separator 23, and more specifically, it is the thickness of one negative electrode active material layer 22B provided on one surface of the negative electrode current collector 22A.

[0051] Specifically, the thickness T is 30 μm to 100 μm, and the volume density V is 1.4 g / cm³. 3 ~2g / cm 3 This is because, when the negative electrode active material layer 22B contains carbon material, both the thickness T and the volume density V are optimized, thereby ensuring energy density while improving the chemical stability of the electrolyte.

[0052] In detail, when the thickness T is within the range described above, the volume density V is 1.4 g / cm³. 3 When the value becomes smaller than this, the energy density decreases. Also, when the thickness T is within the above range, the volume density V is 2 g / cm³. 3 If the value exceeds this, the lithium ion absorption and desorption efficiency decreases, and the impregnation of the electrolyte into the negative electrode active material layer 22B decreases. In contrast, when the thickness T is within the above range, the volume density V is 1.4 g / cm³. 3 ~2g / cm 3 This increases the energy density, improves the lithium ion absorption and desorption efficiency, and enhances the impregnation of the electrolyte into the negative electrode active material layer 22B.

[0053] The procedure for calculating the thickness T and volume density V is as follows.

[0054] To calculate the thickness T, first, the negative electrode 22 is recovered by disassembling the secondary battery. Then, the negative electrode 22 is cut in the thickness direction (Z-axis direction) using a cutting instrument such as a microtome, thereby exposing the cross-section of the negative electrode 22.

[0055] Next, the cross-section of the negative electrode 22 (negative electrode active material layer 22B) is observed using an electron microscope to obtain observation results (electron microscope image). Either a scanning electron microscope (SEM) or a transmission electron microscope (TEM), or both, can be used. The observation magnification can be set arbitrarily.

[0056] Next, the thickness T (μm) of the negative electrode active material layer 22B is measured based on electron microscope images. In this case, ten different thicknesses T are obtained by measuring the thickness T at ten different locations. Finally, the average value of the ten thicknesses T is calculated.

[0057] To determine the volume density V, first, the negative electrode 22 is recovered by disassembling the secondary battery. Next, the negative electrode 22 is cut using a cutting instrument such as a microtome to a predetermined length L (mm) and width W (mm). This length L is the dimension of the negative electrode 22 in the X-axis direction, and the width W is the dimension of the negative electrode 22 in the Y-axis direction. Furthermore, the thickness T (μm) of the negative electrode active material layer 22B is calculated using the procedure described above.

[0058] Next, the weight M1 (g) of the cut negative electrode 22 is measured. Then, using the cut negative electrode 22, the negative electrode current collector 22A is peeled off from the negative electrode active material layer 22B and recovered. Next, the weight M2 (g) of the recovered negative electrode current collector 22A is measured, and the weight M3 (g) of the negative electrode active material layer 22B is calculated by subtracting weight M2 from weight M1. Finally, the volume density V is calculated based on the length L, width W, thickness T and weight M3.

[0059] Furthermore, when recovering the negative electrode current collector 22A from the negative electrode 22 which contains a negative electrode binder, instead of peeling the negative electrode current collector 22A from the negative electrode active material layer 22B, the negative electrode active material layer 22B may be dissolved and removed from the negative electrode 22 using an organic solvent such as dimethyl carbonate. In this case, the negative electrode binder in the negative electrode active material layer 22B is dissolved by the organic solvent, and the negative electrode active material and other materials are removed from the negative electrode current collector 22A along with the negative electrode binder. As a result, the negative electrode current collector 22A is recovered from the negative electrode 22.

[0060] Furthermore, the negative electrode active material may also contain one or more metallic materials, as this allows for a higher energy density to be obtained.

[0061] This metallic material is a general term for materials that contain one or more metallic elements and metalloid elements capable of forming alloys with lithium as constituent elements. Specific examples of these metallic and metalloid elements include silicon and tin. Furthermore, metallic materials may be elements, alloys, compounds, mixtures of two or more of these, or materials containing two or more of these phases. Specific examples of metallic materials include TiSi2 and SiO2. x (0 <x≦2、または0.2<x<1.4)などである。

[0062] 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.

[0063] In particular, the negative electrode binder is preferably made of styrene-butadiene rubber rather than polyvinylidene fluoride. When the negative electrode active material contains a carbon material, the presence of styrene-butadiene rubber in the negative electrode binder ensures excellent binding properties while improving the dispersibility of the carbon material in the negative electrode mixture slurry described later. As a result, the negative electrode active material (carbon material) is sufficiently dispersed within the negative electrode active material layer 22B, and the negative electrode active materials are sufficiently bound to each other via the negative electrode binder (styrene-butadiene rubber).

[0064] The type of thickener is not particularly limited, but specifically, it is carboxymethylcellulose, etc. This is because, when the negative electrode active material layer 22B contains a negative electrode binder (styrene-butadiene rubber), the presence of a thickener in the negative electrode active material layer 22B makes it easy to adjust the viscosity of the negative electrode mixture slurry described later. This makes it easier to form the negative electrode active material layer 22B easily and stably using a coating method.

[0065] (Separator) As shown in Figure 2, the separator 23 is an insulating porous membrane interposed between the positive electrode 21 and the negative electrode 22, allowing 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.

[0066] (electrolyte) The electrolyte is a liquid electrolyte. This electrolyte is impregnated into the positive electrode 21, the negative electrode 22, and the separator 23, and contains an electrolyte salt. More specifically, the electrolyte contains an electrolyte salt along with a solvent that disperses (ionizes) the electrolyte salt.

[0067] Electrolyte salts are compounds that ionize in a solvent and contain anions and cations.

[0068] The anion contains an imid anion. Specifically, the imid anion contains one or more of the following: the first imid anion represented by formula (1), the second imid anion represented by formula (2), the third imid anion represented by formula (3), and the fourth imid anion represented by formula (4). In other words, the electrolyte salt contains one imid anion.

[0069] However, the first imid anion may be of only one type or of two or more types. This limitation of having one or more types also applies to the second, third, and fourth imid anions.

[0070] [ka] (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, a sulfinyl group, or a sulfonyl group.)

[0071] [ka] (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.)

[0072] [ka] (R5 is a fluorinated alkylene group. Y1, Y2, and Y3 are each one of the following: a carbonyl group, a sulfinyl group, or a sulfonyl group.)

[0073] [ka] (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.)

[0074] The reason why the anion contains an imide anion is explained below. Firstly, during charging and discharging of the secondary battery, a good quality film derived from the electrolyte salt is formed on the surfaces of the positive electrode 21 and the negative electrode 22, thereby suppressing the decomposition reaction of the electrolyte (especially the solvent) on the surfaces of the positive electrode 21 and the negative electrode 22. Secondly, the migration speed of lithium ions is improved near the surfaces of the positive electrode 21 and the negative electrode 22 by utilizing the above-mentioned film. Thirdly, the migration speed of lithium ions is also improved in the electrolyte solution.

[0075] The first imide anion is a chain-like anion (a divalent negative ion) containing two nitrogen atoms (N) and three functional groups (W1-W3), as shown in formula (1).

[0076] Each of R1 and R2 is not particularly limited, as long as they are either a fluorine group (-F) or a fluorinated alkyl group. That is, each of R1 and R2 may be the same group or different groups. Thus, each of R1 and R2 is not a hydrogen group (-H) or an alkyl group, etc.

[0077] A fluorinated alkyl group is an alkyl group in which one or more hydrogen groups (-H) are substituted with a fluorine group. However, a fluorinated alkyl group may be linear or branched, having one or more side chains.

[0078] The number of carbon atoms in the fluorinated alkyl group is not particularly limited, but specifically it is between 1 and 10. This is because it improves the solubility and ionization of the electrolyte salt containing the primary imidone anion.

[0079] Specific examples of fluorinated alkyl groups include perfluoromethyl (-CF3) and perfluoroethyl (-C2 F5) groups.

[0080] Each of W1 to W3 is not particularly limited, as long as it is one of the carbonyl group, sulfinyl group, or sulfonyl group. That is, each of W1 to W3 may be the same group or may be different groups. Of course, any two of W1 to W3 may be the same group.

[0081] The second imidone anion is a chain-like anion (a trivalent negative ion) containing three nitrogen atoms and four functional groups (X1 to X4), as shown in formula (2).

[0082] The details for R3 and R4 are the same as the details for R1 and R2.

[0083] Each of X1 to X4 is not particularly limited as long as it is one of the carbonyl group, sulfinyl group, or sulfonyl group. That is, each of X1 to X4 may be the same group or may be different groups. Of course, any two of X1 to X4 may be the same group, or any three of X1 to X4 may be the same group.

[0084] The third imide anion is a cyclic anion (a divalent negative ion) containing two nitrogen atoms, three functional groups (Y1-Y3), and one connecting group (R5), as shown in formula (3).

[0085] A fluorinated alkylene group, designated as R5, is an alkylene group in which one or more hydrogen groups are substituted with fluorine groups. However, the fluorinated alkylene group may be linear or branched, having one or more side chains.

[0086] The number of carbon atoms in the fluorinated alkylene group is not particularly limited, but specifically it is 1 to 10. This is because it improves the solubility and ionization of the electrolyte salt containing the tertiary imide anion.

[0087] Specific examples of fluorinated alkylene groups include perfluoromethylene groups (-CF2-) and perfluoroethylene groups (-C2F4-).

[0088] Each of Y1 to Y3 is not particularly limited as long as it is one of the carbonyl group, sulfinyl group, or sulfonyl group. That is, each of Y1 to Y3 may be the same group or may be different groups. Of course, any two of Y1 to Y3 may be the same group.

[0089] The fourth imide anion, as shown in formula (4), is a chain-like anion (a divalent negative ion) containing two nitrogen atoms, four functional groups (Z1-Z4), and one connecting group (R8).

[0090] The details for R6 and R7 are the same as the details for R1 and R2.

[0091] R8 is not particularly limited as long as it is any of the alkylene group, phenylene group, fluorinated alkylene group, and fluorinated phenylene group.

[0092] The alkylene group may be linear or branched, having one or more side chains. The number of carbon atoms in the alkylene group is not particularly limited, but is specifically 1 to 10. This is because it improves the solubility and ionization of the electrolyte salt containing the quaternary imide anion. Specific examples of alkylene groups include the methylene group (-CH2-), the ethylene group (-C2H4-), and the propylene group (-C3H6-).

[0093] The details regarding the fluorinated alkylene group R8 are the same as those regarding the fluorinated alkylene group R5.

[0094] A fluorinated phenylene group is a phenylene group in which one or more hydrogen groups are replaced by fluorine groups. A specific example of a fluorinated phenylene group is the monofluorophenylene group (-C6H3F-).

[0095] Each of Z1 to Z4 is not particularly limited as long as it is one of the carbonyl group, sulfinyl group, or sulfonyl group. That is, each of Z1 to Z4 may be the same group or different groups. Of course, any two of Z1 to Z4 may be the same group, or any three of Z1 to Z4 may be the same group.

[0096] (Specific examples of anions) Specific examples of the first imide anion include the anions represented by formulas (1-1) to (1-30), respectively.

[0097] [ka]

[0098] [ka]

[0099] [ka]

[0100] Specific examples of secondary imide anions include the anions represented by equations (2-1) to (2-22), respectively.

[0101] [ka]

[0102] [ka]

[0103] Specific examples of third imide anions include the anions represented by formulas (3-1) to (3-15), respectively.

[0104] [ka]

[0105] Specific examples of the fourth imide anion include the anions represented by formulas (4-1) to (4-65), respectively.

[0106] [ka]

[0107] [ka]

[0108] [ka]

[0109] [ka]

[0110] [ka]

[0111] [ka]

[0112] [ka]

[0113] (cation) The type of cation is not particularly limited. Specifically, the cation contains one or more types of light metal ions. That is, the electrolyte salt contains light metal ions as cations because a high voltage can be obtained.

[0114] The types of light metal ions are not particularly limited, but specifically include alkali metal ions and alkaline earth metal ions. Specific examples of alkali metal ions include lithium ions, sodium ions, and potassium ions. Specific examples of alkaline earth metal ions include beryllium ions, magnesium ions, and calcium ions. Other light metal ions may include aluminum ions, etc.

[0115] In particular, light metal ions that contain lithium ions are preferable because they allow for a sufficiently high voltage to be obtained.

[0116] (Content) The electrolyte salt content in the electrolyte solution is not particularly limited and can be set arbitrarily. However, an electrolyte salt content of 0.2 mol / kg to 2 mol / kg is preferred because it provides high ionic conductivity. The "electrolyte salt content" described here refers to the electrolyte salt content relative to the solvent.

[0117] To determine the electrolyte salt content, the secondary battery is disassembled, the electrolyte is recovered, and then the electrolyte is analyzed using inductively coupled plasma (ICP) emission spectroscopy. This allows the weight of the solvent and the weight of the electrolyte salt to be determined, and the electrolyte salt content can then be calculated.

[0118] [solvent] The solvent contains one or more non-aqueous solvents (organic solvents), and the electrolyte containing such non-aqueous solvents is a so-called non-aqueous electrolyte. Non-aqueous solvents include esters and ethers, and more specifically, carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds.

[0119] Carbonate ester compounds include cyclic carbonate esters and linear carbonate esters. Specific examples of cyclic carbonate esters include ethylene carbonate and propylene carbonate. Specific examples of linear carbonate esters include dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate.

[0120] Carboxylic acid ester compounds include chain-like carboxylic acid esters. Specific examples of chain-like carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl trimethylacetate, methyl butyrate, and ethyl butyrate.

[0121] Lactone compounds include lactones, among others. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0122] The ethers may also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

[0123] [Other electrolyte salts] Furthermore, the electrolyte may also contain one or more of the other electrolyte salts. This is because the migration rate of lithium ions is further improved near the surfaces of the positive electrode 21 and the negative electrode 22, as well as within the electrolyte. The amount of other electrolyte salts in the electrolyte is not particularly limited and can be set arbitrarily.

[0124] Other types of electrolyte salts are not particularly limited, but specifically include light metal salts such as lithium salts. However, the electrolyte salts mentioned above are excluded from the lithium salts described here.

[0125] Specific examples of lithium salts include lithium hexafluoride phosphate (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)borate (LiPF2(C2O4)2), lithium tetrafluorooxalatophosphate (LiPF4(C2O4)), lithium monofluorophosphate (Li2PFO3), and lithium difluorophosphate (LiPF2O2).

[0126] In particular, it is preferable that the other electrolyte salts include one or more of the following: lithium hexafluoride phosphate, 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 surfaces of the positive electrode 21 and the negative electrode 22, as well as in the electrolyte solution.

[0127] [Additives] Furthermore, the electrolyte may also contain one or more of the additives. This is because, during charging and discharging of the secondary battery, a film derived from the additives is formed on the surfaces of the positive electrode 21 and the negative electrode 22, thereby suppressing the decomposition reaction of the electrolyte. The amount of additives in the electrolyte is not particularly limited and can be set arbitrarily.

[0128] The types of additives are not particularly limited, but specifically include unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, sulfonic acid esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfate esters, nitrile compounds, and isocyanate compounds.

[0129] (Unsaturated cyclic carbonate ester) Unsaturated cyclic carbonate esters are cyclic carbonate esters that contain unsaturated carbon bonds (carbon-carbon double bonds). The number of unsaturated carbon bonds is not particularly limited; there may be one or two or more. Specific examples of unsaturated cyclic carbonate esters include vinylene carbonate, vinylethylene carbonate, and methyleneethylene carbonate.

[0130] (Fluorinated cyclic carbonate) Fluorinated cyclic carbonates are cyclic carbonates that contain fluorine as a constituent element. That is, fluorinated cyclic carbonates are compounds in which one or more hydrogen groups in a cyclic carbonate are replaced by fluorine groups. Specific examples of fluorinated cyclic carbonates include monofluoroethylene and difluoroethylene.

[0131] (Sulfonic acid ester) Sulfonic acid esters include cyclic monosulfonic acid esters, cyclic disulfonic acid esters, linear monosulfonic acid esters, and linear disulfonic acid esters. Specific examples of cyclic monosulfonic acid esters include 1,3-propanesultone, 1-propene-1,3-sultone, 1,4-butanesultone, 2,4-butanesultone, and propargyl methanesulfonic acid ester. Specific examples of cyclic disulfonic acid esters include cyclodison.

[0132] (Dicarboxylic acid anhydride) Specific examples of dicarboxylic acid anhydrides include succinic anhydride, glutaric anhydride, and maleic anhydride.

[0133] (Disulfonic anhydride) Specific examples of disulfonic anhydrides include ethanedisulfonic anhydride and propanedisulfonic anhydride.

[0134] (Sulfate ester) Specific examples of sulfate esters include ethylene sulfate (1,3,2-dioxathiolane 2,2-dioxide).

[0135] (Nitrile compounds) Nitrile compounds are compounds having one or more cyano groups (-CN). Specific examples of nitrile compounds include octanenitrile, benzonitrile, phthalonitrile, succinonitrile, glutalonitrile, adiponitrile, sebaconitrile, 1,3,6-hexanetricarbonite, 3,3'-oxydipropionitrile, 3-butoxypropionitrile, ethylene glycol bispropionitrile ether, 1,2,2,3-tetracyanopropane, tetracyanopropane, fumaronitrile, 7,7,8,8-tetracyanoquinodimethane, cyclopentanecarbonite, 1,3,5-cyclohexanetricarbonite, and 1,3-bis(dicyanomethylidene)indan.

[0136] (Isocyanate compounds) Isocyanate compounds are compounds having one or more isocyanate groups (-NCO). Specific examples of isocyanate compounds include hexamethylene diisocyanate.

[0137] [Positive lead and negative lead] As shown in Figures 1 and 2, the positive electrode lead 31 is a positive electrode terminal connected to the positive electrode current collector 21A of the positive electrode 21, and is led out from the inside to the outside of the outer film 10. This positive electrode lead 31 contains a conductive material such as a metal material, a specific example of which is aluminum. The shape of the positive electrode lead 31 is not particularly limited, but specifically, the positive electrode lead 31 is either plate-shaped or mesh-shaped.

[0138] As shown in Figures 1 and 2, the negative electrode lead 32 is a negative electrode terminal connected to the negative electrode current collector 22A of the negative electrode 22, and is led out from the inside to the outside of the outer film 10. This negative electrode lead 32 contains a conductive material such as a metal material, a specific example of which is copper. Here, the direction of lead generation of the negative electrode lead 32 is the same as the direction of lead generation of the positive electrode lead 31. Details regarding the shape of the negative electrode lead 32 are the same as details regarding the shape of the positive electrode lead 31.

[0139] <1-2. Operation> During charging of the secondary battery, lithium is released from the positive electrode 21 in the battery element 20, and this lithium is absorbed into the negative electrode 22 via the electrolyte. Conversely, during discharging of the secondary battery, lithium is released from the negative electrode 22 in the battery element 20, and this lithium is absorbed into the positive electrode 21 via the electrolyte. During charging and discharging, lithium is absorbed and released in an ionic state.

[0140] <1-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and the negative electrode 22 are prepared according to the example procedure described below, and the electrolyte is prepared. The secondary battery is then assembled using the electrolyte along with the positive electrode 21 and the negative electrode 22, and the secondary battery is subjected to a stabilization treatment.

[0141] [Fabrication of the positive electrode] First, a paste-like positive electrode slurry is prepared by adding a mixture (positive electrode mixture) containing positive electrode active material, positive electrode binder, and positive electrode conductive agent to a solvent. The solvent may be an aqueous solvent or an organic solvent. Next, the positive electrode slurry is applied to both sides of the positive electrode current collector 21A to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B is compressed and molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or the compression molding may be repeated multiple times. As a result, a positive electrode 21 is fabricated as positive electrode active material layers 21B are formed on both sides of the positive electrode current collector 21A.

[0142] [Fabrication of the negative electrode] The negative electrode 22 is formed using the same procedure as the positive electrode 21 fabrication procedure described above. Specifically, first, a paste-like negative electrode slurry is prepared by adding a mixture (negative electrode mixture) containing a carbon material and a negative electrode binder to a solvent. Details regarding the solvent are as described above. Next, the negative electrode slurry is applied to both sides of the negative electrode current collector 22A to form the negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B is compression molded. As a result, the negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A, thus fabricating the negative electrode 22.

[0143] When manufacturing this negative electrode 22, conditions such as the concentration and amount of the negative electrode mixture slurry applied during the negative electrode active material layer 22B formation process are adjusted so that the thickness T and volume density V satisfy the above-mentioned conditions.

[0144] [Preparation of electrolyte solution] An electrolyte salt containing an imido anion is added to the solvent. In this case, other electrolyte salts may be added to the solvent, or additional additives may be added to the solvent. As a result, the electrolyte salts and other components are dispersed or dissolved in the solvent, and an electrolyte solution is prepared.

[0145] [Assembly of rechargeable batteries] First, the positive electrode lead 31 is connected to the positive electrode current collector 21A of the positive electrode 21 using a joining method such as welding, and the negative electrode lead 32 is connected to the negative electrode current collector 22A of the negative electrode 22 using a joining method such as welding.

[0146] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to produce a wound body (not shown). This wound body has the same configuration as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with electrolyte. Subsequently, the wound body is pressed using a press or the like to form a flattened shape.

[0147] Next, after housing the wound body inside the recessed portion 10U, the outer film 10 (fusion layer / metal layer / surface protection layer) is folded so that the outer films 10 face each other. Subsequently, using an adhesive method such as heat fusion, the outer edges of two sides of the opposing fusion layers are bonded together, thereby housing the wound body inside the bag-shaped outer film 10.

[0148] Finally, after injecting the electrolyte into the bag-shaped outer film 10, the outer edges of the remaining sides of the opposing fused layers are bonded together using an adhesive method such as heat fusion. In this case, a sealing film 41 is inserted between the outer film 10 and the positive electrode lead 31, and a sealing film 42 is inserted between the outer film 10 and the negative electrode lead 32.

[0149] As a result, the electrolyte is impregnated into the wound material, thus creating the battery element 20, which is a wound electrode body. Therefore, the battery element 20 is sealed inside the bag-shaped outer film 10, and the secondary battery is assembled.

[0150] [Stabilization of secondary batteries] The assembled secondary battery is then charged and discharged. Various conditions such as ambient temperature, number of charge / discharge cycles, and charge / discharge conditions can be set arbitrarily. As a result, a coating is formed on the surfaces of the positive electrode 21 and the negative electrode 22, thereby electrochemically stabilizing the state of the secondary battery. Thus, the secondary battery is completed.

[0151] <1-4. Mechanism and Effects> According to this secondary battery, the negative electrode active material layer 22B of the negative electrode 22 contains a carbon material, the thickness T of the negative electrode active material layer 22B is 30 μm to 100 μm, and the volume density V of the negative electrode active material layer 22B is 1.4 g / cm³. 3 ~2g / cm 3 The electrolyte salt in the electrolyte solution contains imid anions.

[0152] In this case, as described above, when the negative electrode active material layer 22B contains carbon material, the thickness T and volume density V are optimized, thereby ensuring energy density while improving the chemical stability of the electrolyte. This increases energy density, improves lithium ion absorption and desorption efficiency, and improves the impregnation of the electrolyte into the negative electrode active material layer 22B.

[0153] Furthermore, as described above, during the charging and discharging of the secondary battery, a high-quality film derived from the electrolyte salt is formed on the surfaces of the positive electrode 21 and the negative electrode 22, thereby suppressing the decomposition reaction of the electrolyte. In addition, the migration speed of lithium ions is improved near the surfaces of the positive electrode 21 and the negative electrode 22, and also within the electrolyte.

[0154] Therefore, excellent battery characteristics can be obtained.

[0155] In particular, if the negative electrode active material layer 22B of the negative electrode 22 further contains styrene-butadiene rubber, the negative electrode active material (carbon material) is sufficiently dispersed within the negative electrode active material layer 22B, and the negative electrode active materials are sufficiently bonded to each other via the negative electrode binder (styrene-butadiene rubber), thus achieving a higher effect.

[0156] Furthermore, if the carbon material contains graphite and the interplanar spacing of the (002) planes of that graphite is 0.3372 nm or less, both the charging capacity and discharging capacity will increase, resulting in a greater effect.

[0157] Furthermore, if the electrolyte salt contains light metal ions as cations, a higher voltage can be obtained, resulting in a greater effect. In this case, if the light metal ions contain lithium ions, a sufficiently high voltage can be obtained, resulting in an even greater effect.

[0158] Furthermore, if the electrolyte salt content in the electrolyte solution is between 0.2 mol / kg and 2 mol / kg, high ionic conductivity can be obtained, resulting in a greater effect.

[0159] Furthermore, if the electrolyte also contains one or more of the following as additives: unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, sulfonic acid esters, dicarboxylic acid anhydrides, disulfonic acid anhydrides, sulfate esters, nitrile compounds, and isocyanate compounds, the decomposition reaction of the electrolyte is suppressed, thereby achieving a higher effect.

[0160] Furthermore, if the electrolyte also contains one or more of the following electrolyte salts: lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate, the lithium ion migration rate will be further improved, resulting in a greater effect.

[0161] Furthermore, 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, thus achieving a higher level of efficiency.

[0162] <2. Variant> The configuration of the secondary battery can be modified as appropriate, as described below. However, the variations described below may be combined with each other.

[0163] [Example 1] As described above, the electrolyte may contain other electrolyte salts along with the electrolyte salt containing the imid anion.

[0164] In particular, it is preferable that the electrolyte contains lithium hexafluoride phosphate as another electrolyte salt, and that the content of the electrolyte salt in the electrolyte is optimized in relation to the content of other electrolyte salts in the electrolyte.

[0165] Specifically, the electrolyte salt contains cations and imid anions. Furthermore, the hexafluoride phosphate ion contains lithium ions and hexafluoride phosphate ions.

[0166] In this case, the sum T (mol / kg) of the cation content C1 and the lithium ion content C2 in the electrolyte is 0.7 mol / kg to 2.2 mol / kg. Furthermore, the ratio R (mol%) of the moles of hexafluoride phosphate ions M2 in the electrolyte to the moles of imido anions M1 in the electrolyte is 13 mol% to 6000 mol%. This is because the migration velocities of cations and lithium ions are sufficiently improved near the surfaces of the positive electrode 21 and the negative electrode 22, as well as within the electrolyte.

[0167] The "cation content in the electrolyte" described here refers to the content of the cation electrolyte salt relative to the solvent, while the "lithium ion content in the electrolyte" refers to the content of lithium ions relative to the solvent. The sum T is calculated based on the formula T = C1 + C2, and the ratio R is calculated based on the formula R = (M2 / M1) × 100.

[0168] To calculate the sum T and the proportion R, the secondary battery is disassembled, the electrolyte is recovered, and then analyzed using ICP emission spectrometry. This allows the content of C1 and C2 and the number of moles M1 and M2 to be determined, and thus the sum T and the proportion R can be calculated.

[0169] In this case as well, since the electrolyte solution contains an electrolyte salt, a similar effect can be obtained. In particular, when the electrolyte salt is used in combination with another electrolyte salt (lithium hexafluoride phosphate), the total amount (sum T) of both is optimized, and the mixing ratio (ratio R) of the two is also optimized. As a result, the migration velocities of cations and lithium ions near the surfaces of the positive electrode 21 and the negative electrode 22 are further improved, as are the migration velocities of cations and lithium ions in the electrolyte solution. Therefore, an even greater effect can be obtained.

[0170] [Differentiation 2] A porous membrane separator 23 was used. However, although not specifically shown in the diagram, a laminated separator containing a polymer compound layer may also be used.

[0171] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer provided on one or both sides of the porous membrane. This improves the adhesion of the separator to the positive electrode 21 and the negative electrode 22, thereby suppressing misalignment (winding misalignment) of the battery element 20. As a result, swelling of the secondary battery is suppressed even if side reactions such as electrolyte decomposition occur. The polymer compound layer contains a polymer compound such as polyvinylidene fluoride. This is because it provides excellent physical strength and excellent electrochemical stability.

[0172] Furthermore, one or both of the porous membrane and the polymer compound layer may contain multiple insulating particles. This is because the multiple insulating particles promote heat dissipation when the secondary battery generates heat, thereby improving the safety (heat resistance) of the secondary battery. The insulating particles consist of one or more types of insulating materials, such as inorganic materials and resin materials. Specific examples of inorganic materials include aluminum oxide, aluminum nitride, boehmite, silicon oxide, titanium oxide, magnesium oxide, and zirconium oxide. Specific examples of resin materials include acrylic resin and styrene resin.

[0173] When fabricating a laminated separator, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is applied to one or both sides of a porous membrane. In this case, if necessary, multiple insulating particles may be added to the precursor solution.

[0174] Even when using this stacked separator, lithium ions can move between the positive electrode 21 and the negative electrode 22, thus achieving a similar effect. In this case, as mentioned above, the safety of the secondary battery is improved, resulting in an even greater effect.

[0175] [Difference 3] A liquid electrolyte solution was used. However, although not specifically illustrated here, a gel-like electrolyte layer may also be used.

[0176] In the battery element 20 using an electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23 and the electrolyte layer, and the positive electrode 21, negative electrode 22, separator 23, and electrolyte layer are wound together. This electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

[0177] Specifically, the electrolyte layer contains a polymer compound along with the electrolyte, and the electrolyte is held in place by the polymer compound. This prevents leakage of the electrolyte. The composition of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolyte, polymer compound, and solvent is prepared, and then the precursor solution is applied to one or both sides of the positive electrode 21 and the negative electrode 22, respectively.

[0178] 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, thus achieving a similar effect. In this case, in particular, as mentioned above, leakage of the electrolyte is prevented, resulting in an even greater effect.

[0179] <3. Applications of rechargeable batteries> The uses (application examples) of secondary batteries are not particularly limited. Secondary batteries used as power sources may be the primary power source or auxiliary power source for electronic devices and electric vehicles. A primary power source is a power source that is used preferentially regardless of the presence or absence of other power sources. An auxiliary power source is a power source used in place of the primary power source, or a power source that can be switched to from the primary power source.

[0180] Specific examples of secondary battery applications are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals; backup power supplies and storage devices such as memory cards; power tools such as electric drills and electric saws; battery packs installed in electronic devices; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles); and power storage systems such as household or industrial battery systems that store power in preparation for emergencies. In these applications, one secondary battery may be used, or multiple secondary batteries may be used.

[0181] The battery pack may use individual cells or a battery pack. An electric vehicle is a vehicle that operates (drives) using a secondary battery as a power source, and may also be a hybrid vehicle equipped with other power sources in addition to the secondary battery. In a household power storage system, the electricity stored in the secondary battery, which is the power storage source, can be used to power household electrical appliances, etc.

[0182] Here, we will specifically explain one example of a secondary battery application. The configuration of the application example described below is merely an example and can be modified as needed.

[0183] Figure 3 shows the block configuration of the battery pack. The battery pack described here is a single rechargeable battery pack (a so-called soft pack) and is installed in electronic devices such as smartphones.

[0184] As shown in Figure 3, this battery pack comprises a power supply 51 and a circuit board 52. The circuit board 52 is connected to the power supply 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55.

[0185] The power supply 51 includes one secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. Since the power supply 51 can be connected to the outside via the positive terminal 53 and the negative 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.

[0186] The control unit 56 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. The control unit 56 also detects and controls the usage status of the power supply 51 as needed.

[0187] Furthermore, when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or over-discharge detection voltage, the control unit 56 disconnects the switch 57 to prevent charging current from flowing through the current path of the power supply 51. The overcharge detection voltage is not particularly limited, but specifically it is 4.20V ± 0.05V, and the over-discharge detection voltage is not particularly limited, but specifically it is 2.40V ± 0.1V.

[0188] Switch 57 includes a charge control switch, a discharge control switch, a charging diode, and a discharging diode, and switches the connection between the power supply 51 and external equipment according to the instructions of the control unit 56. This switch 57 includes a field-effect transistor (MOSFET) using a metal oxide semiconductor, and the charge / discharge current is detected based on the ON resistance of switch 57.

[0189] The temperature detection unit 59 includes a temperature detection element such as a thermistor and measures the temperature of the power supply 51 using the temperature detection terminal 55, and outputs the temperature measurement result to the control unit 56. The temperature measurement result measured by the temperature detection unit 59 is used when the control unit 56 performs charge / discharge control in the event of abnormal heat generation, and when the control unit 56 performs correction processing when calculating the remaining capacity. [Examples]

[0190] An example of this technology will be described below.

[0191] <Examples 1-24 and Comparative Examples 1-12> As explained below, after fabricating a secondary battery, its battery characteristics were evaluated.

[0192] [Manufacturing of secondary batteries] The laminate film type secondary battery (lithium-ion secondary battery) shown in Figures 1 and 2 was fabricated using the following procedure.

[0193] (Fabrication of the positive electrode) First, the positive electrode active material (LiNi, a lithium-containing compound (oxide)) 0.82 Co 0.14 Al 0.04 A positive electrode mixture was prepared by mixing 91 parts by mass of 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). Next, the positive electrode mixture was added to a solvent (an organic solvent, N-methyl-2-pyrrolidone), and the solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to both sides of the positive electrode current collector 21A (a strip of aluminum foil with a thickness of 12 μm) using a coating apparatus, and 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. This completed the production of the positive electrode 21.

[0194] (Fabrication of the negative electrode) First, 93 parts by mass of negative electrode active material (artificial graphite, a carbon material) and 7 parts by mass of negative electrode binder (polyvinylidene fluoride) were mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture was added to a solvent (N-methyl-2-pyrrolidone, an organic solvent), and the solvent was stirred to prepare a paste-like negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (a strip of copper foil with a thickness of 15 μm) using a coating apparatus, and 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. This completed the production of the negative electrode 22.

[0195] Thickness T (μm) and volume density V (g / cm³) 3 The interplanar spacing (nm) of the (002) plane of the carbon material (artificial graphite) was as shown in Tables 1 and 2.

[0196] (Preparation of electrolyte solution) First, the electrolyte salt was added to the solvent, and then the solvent was stirred.

[0197] The solvents used were ethylene carbonate, a cyclic carbonate ester, and γ-butyrolactone, a lactone. In this case, the solvent mixing ratio (by weight) was ethylene carbonate:γ-butyrolactone = 30:70.

[0198] As a cation of the electrolyte salt, lithium ions (Li + The following imid anions were used as the electrolyte salts: the first imid anions shown in formulas (1-5), (1-6), (1-21), and (1-22), respectively; the second imid anion shown in formula (2-5); the third imid anion shown in formula (3-5); and the fourth imid anion shown in formula (4-37). The electrolyte salt content (mol / kg) is as shown in Tables 1 and 2.

[0199] This resulted in the preparation of an electrolyte solution containing an electrolyte salt. This electrolyte salt is a lithium salt containing an imido anion as the anion.

[0200] For comparison, the electrolyte was prepared using the same procedure, except that hexafluoride phosphate ions (PF6-) were used as the anion, as shown in Table 3.

[0201] (Assembly of secondary batteries) First, the positive electrode lead 31 (aluminum foil) was welded to the positive electrode current collector 21A of the positive electrode 21, and the negative electrode lead 32 (copper foil) was welded to the negative electrode current collector 22A of the negative electrode 22.

[0202] Next, the positive electrode 21 and the negative electrode 22 were laminated together 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 together to create a wound body. Subsequently, the wound body was pressed using a press machine to form a flattened shape.

[0203] Next, the outer film 10 (fusion layer / metal layer / surface protection layer) was folded so as to sandwich the wound body housed in the recess 10U, and then the outer edges of two sides of the fusion layer were heat-fused together to house the wound body inside the bag-shaped outer film 10. As the outer film 10, an aluminum laminate film was used in which a fusion layer (polypropylene film with a thickness of 30 μm), a metal layer (aluminum foil with a thickness of 40 μm), and a surface protection layer (nylon film with a thickness of 25 μm) were laminated in this order from the inside.

[0204] Finally, after injecting the electrolyte into the bag-shaped outer film 10, the outer edges of the remaining side of the fusion layer were heat-fused together in a reduced-pressure environment. In this case, a sealing film 41 (polypropylene film with a thickness of 5 μm) was inserted between the outer film 10 and the positive electrode lead 31, and a sealing film 42 (polypropylene film with a thickness of 5 μm) was inserted between the outer film 10 and the negative electrode lead 32. As a result, the electrolyte was impregnated into the wound material, and the battery element 20 was fabricated.

[0205] Therefore, since the battery elements were sealed inside the outer film 10, a secondary battery was assembled. The rated capacity (mAH) of the secondary battery was as shown in Tables 1 to 3.

[0206] (Stabilization of secondary batteries) A secondary battery was subjected to one charge-discharge cycle in a normal temperature environment (temperature = 23°C). During charging, constant current charging was performed at a current of 0.1C until the voltage reached 4.2V, and then constant voltage charging was performed at that voltage of 4.2V until the current reached 0.05C. During discharging, constant current discharge was performed at a current of 0.1C until the voltage reached 2.5V. 0.1C is the current value required to completely discharge the battery capacity (theoretical capacity) in 10 hours, and 0.05C is the current value required to completely discharge the battery capacity in 20 hours.

[0207] As a result, a coating was formed on the surfaces of both the positive electrode 21 and the negative electrode 22, thereby electrochemically stabilizing the state of the secondary battery. Thus, a laminate film type secondary battery was completed.

[0208] [Evaluation of battery characteristics] The battery characteristics were evaluated, and the results shown in Tables 1 to 3 were obtained. Here, high-temperature cycle characteristics, high-temperature storage characteristics, and low-temperature load characteristics were evaluated.

[0209] (High-temperature cycle characteristics) First, the discharge capacity (discharge capacity in the first cycle) was measured by charging and discharging the secondary battery in a high-temperature environment (temperature = 60°C). The charge and discharge conditions were the same as those used during the stabilization of the secondary battery described above.

[0210] Next, the secondary battery was repeatedly charged and discharged in the same environment until the total number of cycles reached 100, and the discharge capacity (discharge capacity at the 100th cycle) was measured. The charge and discharge conditions were the same as those used during the stabilization of the secondary battery described above.

[0211] Finally, the cycle maintenance rate (%) was calculated based on the formula: Cycle Maintenance Rate (%) = (Discharge Capacity at Cycle 100 / Discharge Capacity at Cycle 1) × 100, which is an index for evaluating high-temperature cycle characteristics.

[0212] (High temperature storage characteristics) First, the discharge capacity (discharge capacity before storage) was measured by performing one charge-discharge cycle on a secondary battery in a room temperature environment (temperature = 23°C). The charge-discharge conditions were the same as those used during the stabilization of the secondary battery described above.

[0213] Next, the secondary battery was charged in the same environment, stored in a charged state in a high-temperature environment (temperature = 80°C) for 10 days, and then discharged in a room-temperature environment to measure the discharge capacity (discharge capacity after storage). The charge and discharge conditions were the same as those used during the stabilization of the secondary battery described above.

[0214] Finally, the storage retention rate (%) was calculated based on the formula: Storage Retention Rate (%) = (Discharge Capacity after Storage / Discharge Capacity before Storage) × 100, which is an index for evaluating high-temperature storage characteristics.

[0215] (Low-temperature load characteristics) First, the discharge capacity (discharge capacity in the first cycle) was measured by charging and discharging the secondary battery for one cycle in a room temperature environment (temperature = 23°C). The charging and discharging conditions were the same as those used during the stabilization of the secondary battery described above.

[0216] Next, the secondary battery was repeatedly charged and discharged in a low-temperature environment (temperature = -10°C) until the total number of cycles reached 100, and the discharge capacity (discharge capacity at 100 cycles) was measured. The charge and discharge conditions were the same as those for the stabilization of the secondary battery described above, except that the discharge current was changed to 1C. 1C is the current value required to completely discharge the battery capacity in one hour.

[0217] 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.

[0218]

Table 1

[0219]

Table 2

[0226] <Examples 25-42> As shown in Tables 4 and 5, secondary batteries were prepared using the same procedure as in Example 4, except that the electrolyte contained either an additive or another electrolyte salt, and then the battery characteristics were evaluated. In this case, either the additive or another electrolyte salt was added to the solvent containing the electrolyte salt, and then the solvent was stirred.

[0227] Details regarding the additives are as follows: As unsaturated cyclic carbonate esters, vinylene carbonate (VC), vinylethylene carbonate (VEC), and methyleneethylene carbonate (MEC) were used. As fluorinated cyclic carbonate esters, monofluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC) were used. As sulfonic acid esters, propanesultone (PS) and propensultone (PRS), which are cyclic monosulfonic acid esters, and cyclodison (CD), which is a cyclic disulfonic acid ester, were used. As dicarboxylic acid anhydride, succinic anhydride (SA) was used. As disulfonic acid anhydride, propanedisulfonic anhydride (PSAH) was used. As sulfate ester, ethylene sulfate (DTD) was used. As nitrile compound, succinonitrile (SN) was used. As isocyanate compound, hexamethylene diisocyanate (HMI) was used.

[0228] Other electrolyte salts used included lithium hexafluoride phosphate (LiPF6), lithium tetraborate tetrafluoride (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), and lithium difluorophosphate (LiPF2O2).

[0229] The respective content (by weight %) of additives and other electrolyte salts in the electrolyte solution are shown in Tables 4 and 5.

[0230] [Table 4]

[0231] [Table 5]

[0232] As shown in Tables 1 and 4, when the electrolyte contained additives (Examples 25-37), at least one of the cycle retention rate and storage retention rate increased compared to when the electrolyte did not contain additives (Example 4).

[0233] Furthermore, as shown in Tables 1 and 5, when the electrolyte contained other electrolyte salts (Examples 38-42), at least one of the cycle retention rate and storage retention rate increased compared to when the electrolyte did not contain other electrolyte salts (Example 4).

[0234] <Examples 43-74> As shown in Tables 6 and 7, secondary batteries were fabricated using the same procedure as in Example 4, except that another electrolyte salt (lithium hexafluoride phosphate (LiPF6)) was included in the electrolyte solution, and then the battery characteristics were evaluated.

[0235] 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 6 and 7.

[0236]

Table 6

[0237]

Table 7

[0238] As shown in Tables 6 and 7, 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 47), each of the cycle retention rate, storage retention rate, and load retention rate increased more compared to the case where the two conditions are not satisfied (such as Example 43).

[0239] <Examples 75 to 78 and Comparative Example 13> As shown in Table 8, after manufacturing a secondary battery by the same procedure as in Examples 4, 19, 20, 23 and Comparative Example 4 except that the type of the negative electrode binder was changed, the battery characteristics were evaluated. As this negative electrode binder, styrene-butadiene rubber (SBR) was used instead of polyvinylidene fluoride.

[0240] The manufacturing procedure of the negative electrode 22 is the same as that of Example 4 except for the procedure described below. When obtaining the negative electrode mixture, 96.5 parts by mass of a negative electrode active material (artificial graphite which is a carbon material), 1.5 parts by mass of a negative electrode binder (styrene-butadiene rubber (SBR)), and 2 parts by mass of a thickener (carboxymethyl cellulose) were mixed with each other.

[0241]

Table 8

[0242] As shown in Table 8, changing the type of negative electrode binder yielded similar trends to those seen in Tables 1 to 3.

[0243] In other words, even when the negative electrode 22 contained a negative electrode active material (carbon material) and a negative electrode binder (styrene-butadiene rubber), the cycle retention rate, storage retention rate, and load retention rate all decreased when the electrolyte salt did not contain an imid anion (Comparative Example 13).

[0244] In contrast, when the negative electrode 22 contained a negative electrode active material (carbon material) and a negative electrode binder (styrene-butadiene rubber), and the electrolyte salt contained an imid anion (Examples 75-78), the cycle retention rate, storage retention rate, and load retention rate all increased.

[0245] In particular, when styrene-butadiene rubber was used as the negative electrode binder (Examples 75-78), at least one of the cycle retention rate and storage retention rate increased compared to when polyvinylidene fluoride was used as the negative electrode binder (Examples 4, 19, 20, 23).

[0246] [summary] The results shown in Tables 1 to 8 indicate that the negative electrode 22 contains carbon material, has a thickness T of 30 μm to 100 μm, and a volume density V of 1.4 g / cm³. 3 ~2g / cm 3 Furthermore, when the electrolyte salt of the electrolyte solution contained imid anions, the cycle retention rate, storage retention rate, and load retention rate were all improved. Therefore, excellent high-temperature cycle characteristics, excellent high-temperature storage characteristics, and excellent low-temperature load characteristics were obtained in the secondary battery, resulting in excellent battery characteristics.

[0247] Although the present technology has been described above with reference to one embodiment and one example, the configuration of the present technology is not limited to the configuration described in the one embodiment and one example, and can be modified in various ways.

[0248] Specifically, the case where the element structure of the battery element is of the wound type has been described. However, the element structure of the battery element is not particularly limited, and may also be of the stacked type or the zigzag type. In the stacked type, the positive electrode and negative electrode are stacked alternately with a separator in between, while in the zigzag type, the positive electrode and negative electrode are folded in a zigzag pattern facing each other with a separator in between.

[0249] The effects described herein are illustrative only, and therefore the effects of this technology are not limited to those described herein. Accordingly, other effects may be obtained with respect to this technology.

Claims

1. Positive electrode and, A negative electrode containing a negative electrode active material layer, Electrolyte containing electrolyte salts and Equipped with, The aforementioned negative electrode active material layer contains a carbon material, The thickness of the negative electrode active material layer is 30 μm or more and 80 μm or less. The volume density of the negative electrode active material layer is 1.4 g / cm³. 3 1.8g / cm or more 3 The following: The electrolyte salt comprises an imid anion, and the imid anion comprises at least one of a first imid anion represented by formula (1) and a second imid anion represented by formula (2). The electrolyte further comprises lithium hexafluoride phosphate, The electrolyte salt comprises a cation and the imid anion, The lithium hexafluoride phosphate comprises lithium ions and hexafluoride phosphate ions. The sum of the cation content in the electrolyte and the lithium ion content 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 hexafluoride phosphate ion in the electrolyte to the number of moles of the imido anion in the electrolyte is 13 mol% or more and 6000 mol% or less. Secondary battery. 【Chemistry 1】 (Each of R1 and R2 is either a fluorine group or a fluorinated alkyl group. Each of W1, W2 and W3 is a carbonyl group (>C=O), a sulfinyl group (>S=O), and a sulfonyl group (>S(=O)) 2 ) is one of the following. 【Chemistry 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.)

2. The negative electrode further comprises styrene-butadiene rubber, The secondary battery according to claim 1.

3. The carbon material contains graphite, The interplanar spacing of the (002) planes of the graphite, as measured by X-ray diffraction, is 0.3372 nm or less. The secondary battery according to claim 1.

4. The aforementioned electrolyte salt contains light metal ions as cations. The secondary battery according to claim 1.

5. The aforementioned light metal ions include lithium ions. The secondary battery according to claim 4.

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

7. The electrolyte further comprises at least one of lithium hexafluoride phosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, and lithium difluorophosphate. A secondary battery according to any one of claims 1 to 5.

8. Lithium-ion rechargeable batteries, A secondary battery according to any one of claims 1 to 5.

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