Secondary batteries

Abstract

This secondary battery comprises: a positive electrode that includes a positive electrode active substance layer; a negative electrode that includes a negative electrode active substance layer; a separator and a heat resistant layer which are disposed between the positive electrode and the negative electrode; and an electrolytic solution containing an electrolyte salt. The heat resistant layer is disposed at least in a region in which the positive electrode active substance layer and the negative electrode active substance layer oppose each other, and has a melting point or a decomposition temperature that is higher than the melting point or the decomposition temperature of the separator. The electrolyte salt contains imide anions. The imide anions include at least one of 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 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 [Overview of the Initiative]

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

[0007] There is a need for a secondary battery that can achieve excellent battery characteristics.

[0008] A secondary battery according to one embodiment of this technology comprises a positive electrode containing a positive electrode active material layer, a negative electrode containing a negative electrode active material layer, a separator and a heat-resistant layer disposed between the positive electrode and the negative electrode, and an electrolyte containing an electrolyte salt. The heat-resistant layer is disposed in a region where at least the positive electrode active material layer and the negative electrode active material layer face each other, and has a melting point or decomposition temperature higher than the melting point or decomposition temperature of the separator. The electrolyte salt contains an imid anion, the imid anion containing at least one of 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).

[0009] [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 (>C=O), a sulfinyl group (>S=O), or a sulfonyl group (>S(=O)2).)

[0010]

Chem.

[0011]

Chem.

[0012]

Chem.

[0013] According to one embodiment of the secondary battery of this technology, a separator and a heat-resistant layer are arranged between the positive electrode and the negative electrode, and the heat-resistant layer is arranged in a region where at least the positive electrode active material layer and the negative electrode active material layer face each other and has a melting point or decomposition temperature higher than the melting point or decomposition temperature of the separator, and the electrolyte salt of the electrolyte solution contains at least one of the first imid anion, second imid anion, third imid anion and fourth imid anion as an imid anion, so that 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] This is a cross-sectional view showing a part of the configuration of the battery element shown in Figure 1. [Figure 3] This is a cross-sectional view showing the overall configuration of the battery element shown in Figure 1. [Figure 4] This is a cross-sectional view showing the configuration of the battery element in Modification Example 1. [Figure 5] This is a cross-sectional view showing the configuration of the battery element in modified example 2. [Figure 6] This is a cross-sectional view showing the configuration of the battery element in modified example 3. [Figure 7] This is a cross-sectional view showing the configuration of the battery element in modified example 4. [Figure 8] This is a cross-sectional view showing the configuration of the battery element in modified example 5. [Figure 9] This is a cross-sectional view showing the configuration of the battery element in modified example 6. [Figure 10] This is a cross-sectional view showing the configuration of the battery element in modified example 7. [Figure 11] This is a cross-sectional view showing the configuration of the battery element in modified example 8. [Figure 12]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. 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. Figure 2 shows a partial cross-sectional view of the battery element 20 shown in Figure 1. Figure 3 shows the overall cross-sectional view of the battery element 20 shown in Figure 1.

[0023] However, Figure 1 shows the outer film 10 and the battery element 20 separated from each other, and the cross-section of the battery element 20 along the XZ plane is shown by a dashed line. In Figure 3, the positive electrode 21, negative electrode 22, separator 23, and heat-resistant layer 24 are shown separated from each other before winding.

[0024] As shown in Figures 1 to 3, 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.

[0025] In the following explanation, the upper side in each of Figures 1 to 3 will be considered the upper side of the secondary battery, and the lower side in each of Figures 1 to 3 will be considered the lower side of the secondary battery.

[0026] [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 inside. Thus, the outer film 10 houses the electrolyte together with the positive electrode 21 and the negative electrode 22.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] [Battery element] As shown in Figures 1 to 3, the battery element 20 is a power generation element that includes a positive electrode 21, a negative electrode 22, a separator 23, a heat-resistant layer 24, and an electrolyte (not shown), and is housed inside the outer film 10.

[0034] 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 a heat-resistant layer 24, and are wound around a winding axis P while facing each other via the separator 23 and the heat-resistant layer 24. The winding axis P is a virtual axis extending in the Y-axis direction.

[0035] 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 a major axis J1 and a minor axis J2. This major axis J1 is a virtual axis that extends in the X-axis direction and has a longer length than the minor axis J2. The minor axis J2 is a virtual axis that extends in the Z-axis direction intersecting the X-axis direction and has a 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.

[0036] (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.

[0037] 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.

[0038] 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.

[0039] Here, the positive electrode active material layer 21B is provided on both surfaces of the positive electrode current collector 21A. However, the positive electrode active material layer 21B may be provided only on one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically, it is a coating method or the like.

[0040] The type of the positive electrode active material is not particularly limited, but specifically, it is a lithium-containing compound. This lithium-containing compound is a compound containing one or more transition metal elements as constituent elements together with lithium, and further may 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 element, but specifically, it is an element belonging to Groups 2 to 15 in the long-period type periodic table. The type of the lithium-containing compound is not particularly limited, but specifically, it is an oxide, a phosphate compound, a silicate compound, a borate compound, or the like.

[0041] Specific examples of the oxide are LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2 and LiMn2O4, etc. Specific examples of the phosphate compound are LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0042] 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.

[0043] 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.

[0044] (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.

[0045] 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.

[0046] 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 and negative electrode conductive agents.

[0047] 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).

[0048] The type of negative electrode active material is not particularly limited, but specifically, it can be carbon materials or metallic materials, because they provide a high energy density. The negative electrode active material may contain only one of the carbon materials or metallic materials, or it may contain both.

[0049] Specific examples of carbon materials include readily graphitizable carbon, non-graphitizable carbon, and graphite. This graphite may be natural graphite, artificial graphite, or both.

[0050] Metallic materials are 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. These 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。

[0051] Details regarding the negative electrode binder and negative electrode conductive agent are the same as those regarding the positive electrode binder and positive electrode conductive agent.

[0052] (Opposite region and non-opposite region) Here, as shown in Figure 3, the positive electrode active material layer 21B is provided on a portion of the surface of the positive electrode current collector 21A, and the negative electrode active material layer 22B is provided on a portion of the surface of the negative electrode current collector 22A.

[0053] Specifically, the positive electrode active material layer 21B is located in the central region of the surface of the positive electrode current collector 21A in the longitudinal direction (left-right direction in Figure 3) when the positive electrode current collector 21A extends in the longitudinal direction. As a result, the central region of the surface of the positive electrode current collector 21A is covered by the positive electrode active material layer 21B. In contrast, the inner end region of the surface of the positive electrode current collector 21A is exposed and not covered by the positive electrode active material layer 21B, and the outer end region of the surface of the positive electrode current collector 21A is also exposed and not covered by the positive electrode active material layer 21B.

[0054] Furthermore, when the negative electrode current collector 22A extends in the longitudinal direction (left-right direction in Figure 3), the negative electrode active material layer 22B is positioned in the central region of the surface of the negative electrode current collector 22A in the longitudinal direction. As a result, the central region of the surface of the negative electrode current collector 22A is covered by the negative electrode active material layer 22B. In contrast, the inner end region of the surface of the negative electrode current collector 22A is exposed and not covered by the negative electrode active material layer 22B, while the outer end region of the surface of the negative electrode current collector 22A is also exposed and not covered by the negative electrode active material layer 22B.

[0055] However, the area where the negative electrode active material layer 22B is arranged in the longitudinal direction extends inward from the area where the positive electrode active material layer 21B is arranged in the longitudinal direction, and also extends outward from the area where the positive electrode active material layer 21B is arranged in the longitudinal direction. As a result, in the positive electrode 21 and the negative electrode 22, there are regions where the positive electrode active material layer 21B and the negative electrode active material layer 22B face each other (opposing region R), and regions where the positive electrode active material layer 21B and the negative electrode active material layer 22B do not face each other (non-opposing region). In the negative electrode active material layer 22B, the portion located in the opposing region R is involved in charging and discharging, but the portion not located in the opposing region R is hardly involved in charging and discharging.

[0056] Because the area where the negative electrode active material layer 22B is installed is extended beyond the area where the positive electrode active material layer 21B is installed, the presence of opposing regions R and non-opposing regions in the positive electrode 21 and negative electrode 22 is intended to prevent unintended deposition of lithium metal on the surface of the negative electrode current collector 22A while ensuring a chargeable and dischargeable region (opposing region R).

[0057] (Separator) As shown in Figures 2 and 3, the separator 23 is an insulating porous membrane placed 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.

[0058] (electrolyte) The electrolyte is a liquid electrolyte. This electrolyte is impregnated into the positive electrode 21, the negative electrode 22, the separator 23, and the heat-resistant layer 24, and contains an electrolyte salt. More specifically, the electrolyte contains an electrolyte salt along with a solvent that disperses (ionizes) the electrolyte salt.

[0059] (Electrolyte salts) Electrolyte salts are compounds that ionize in a solvent and contain anions and cations.

[0060] (Anion) 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 an imid anion as anion.

[0061] However, the first imid anion may be of one type or two or more types. This limitation of having one or more types also applies to the second, third, and fourth imid anions.

[0062] [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.)

[0063] [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.)

[0064] [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.)

[0065] [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.)

[0066] 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. This suppresses the decomposition reaction of the electrolyte (especially the solvent) caused by the reaction with 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.

[0067] 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).

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Specific examples of fluorinated alkyl groups include perfluoromethyl (-CF3) and perfluoroethyl (-C2F5) groups.

[0072] 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.

[0073] 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).

[0074] The details for R3 and R4 are the same as the details for R1 and R2.

[0075] 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.

[0076] 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).

[0077] 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.

[0078] 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.

[0079] Specific examples of fluorinated alkylene groups include perfluoromethylene groups (-CF2-) and perfluoroethylene groups (-C2F4-).

[0080] 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.

[0081] The fourth imide anion is a chain-like anion (a divalent negative ion) containing two nitrogen atoms (N), four functional groups (Z1-Z4), and one connecting group (R8), as shown in formula (4).

[0082] The details for R6 and R7 are the same as the details for R1 and R2.

[0083] R8 is not particularly limited as long as it is any of the alkylene group, phenylene group, fluorinated alkylene group, and fluorinated phenylene group.

[0084] 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-).

[0085] The details regarding the fluorinated alkylene group R8 are the same as those regarding the fluorinated alkylene group R5.

[0086] 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-).

[0087] 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.

[0088] Specific examples of the first imide anion include the anions represented by formulas (1-1) to (1-30), respectively.

[0089] [ka]

[0090] [ka]

[0091] [ka]

[0092] Specific examples of secondary imide anions include the anions represented by equations (2-1) to (2-22), respectively.

[0093] [ka]

[0094] [ka]

[0095] Specific examples of third imide anions include the anions represented by formulas (3-1) to (3-15), respectively.

[0096] [ka]

[0097] Specific examples of the fourth imide anion include the anions represented by formulas (4-1) to (4-65), respectively.

[0098] [ka]

[0099] [ka]

[0100] [ka]

[0101] [ka]

[0102] [ka]

[0103] [ka]

[0104] [ka]

[0105] (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.

[0106] 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 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.

[0107] In particular, light metal ions that contain lithium ions are preferable because they allow for a sufficiently high voltage to be obtained.

[0108] (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.

[0109] 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.

[0110] The procedure for determining the content described here is also applicable when determining the content of electrolyte components other than electrolyte salts, which will be discussed later.

[0111] (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.

[0112] 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.

[0113] 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.

[0114] Lactone compounds include lactones, among others. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0115] The ethers may also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane.

[0116] (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 content of the other electrolyte salts in the electrolyte is not particularly limited and can be set arbitrarily.

[0117] 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.

[0118] 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).

[0119] 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.

[0120] (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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

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

[0126] Specific examples of disulfonic anhydrides include ethanedisulfonic anhydride and propanedisulfonic anhydride.

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

[0128] Nitrile compounds are compounds containing 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.

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

[0130] (Heat-resistant layer) As shown in Figure 2, the heat-resistant layer 24 is positioned between the positive electrode 21 and the negative electrode 22 to prevent short circuits between the positive electrode 21 and the negative electrode 22.

[0131] This heat-resistant layer 24 is positioned between the positive electrode 21 and the negative electrode 22, at least in the opposing region R. That is, the area in which the heat-resistant layer 24 is provided may be limited to the opposing region R, or it may be an area extended beyond that opposing region R.

[0132] Here, as shown in Figure 3, the heat-resistant layer 24 is positioned in a region extended from the opposing region R. In this case, the area where the heat-resistant layer 24 is provided extends both inward from the opposing region R and outward from the opposing region R. This is because it better prevents short circuits between the positive electrode 21 and the negative electrode 22.

[0133] Furthermore, as shown in Figure 3, the heat-resistant layer 24 is provided on the separator 23. As will be described later, this improves the handling of the heat-resistant layer 24 compared to the case where the heat-resistant layer 24 is provided on the positive electrode 21 or the negative electrode 22, thus simplifying the manufacturing process of the secondary battery.

[0134] Specifically, the separator 23 has a pair of surfaces on which a heat-resistant layer 24 is provided, and this heat-resistant layer 24 is provided on both sides of the separator 23. These two sides of the separator 23 are the surface of the separator 23 facing the positive electrode 21 and the surface of the separator 23 facing the negative electrode 22. As a result, the heat-resistant layer 24 is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23.

[0135] This heat-resistant layer 24 contains one or more types of heat-resistant materials. This is because, even if the separator 23 melts or breaks in a high-temperature environment caused by heat generation in a secondary battery, the heat-resistant layer 24 remains interposed between the positive electrode 21 and the negative electrode 22, thereby preventing a short circuit between the positive electrode 21 and the negative electrode 22.

[0136] This heat-resistant material is a material that has a melting point or decomposition temperature higher than the melting point or decomposition temperature of the separator 23. In other words, the heat-resistant layer 24 has a melting point or decomposition temperature higher than the melting point or decomposition temperature of the separator 23. In contrast, a material that has a melting point or decomposition temperature lower than the melting point or decomposition temperature of the separator 23 is a non-heat-resistant material.

[0137] The type of heat-resistant material is not particularly limited, but among them, the melting point or decomposition temperature of the heat-resistant material is preferably about 200°C or higher, and more preferably about 210°C to 2100°C. As described above, the separator 23 contains a polymer compound, so if the melting point or decomposition temperature of the heat-resistant material is within the above range, the condition that the melting point or decomposition temperature of the heat-resistant layer 24 is higher than that of the separator 23 is more easily met. Furthermore, since the temperature of the lithium-ion secondary battery reaches about 200°C or higher during thermal runaway, if the melting point or decomposition temperature of the heat-resistant material is within the above range, the conditions regarding the heat-resistant layer 24 are more easily met.

[0138] Furthermore, the temperature at which thermal runaway occurs in lithium-ion secondary batteries may vary depending on the combination of positive electrode active material and negative electrode active material. Specifically, thermal runaway is more likely to occur when the positive electrode active material contains a lithium-containing compound having a layered rock salt-type crystalline structure, and the negative electrode active material contains a material that intercepts and deintercepts lithium. Specific examples of positive electrode active material (lithium-containing compound having a layered rock salt-type crystalline structure) include oxides such as LiCoO2 mentioned above, while specific examples of negative electrode active material (material that intercepts and deintercepts lithium) include the carbon materials and metallic materials mentioned above. For this reason, the physical properties of heat-resistant materials, such as having a melting point or decomposition temperature of approximately 200°C or higher, are suitable as constituent materials for the heat-resistant layer 24 used in lithium-ion secondary batteries, which are prone to thermal runaway.

[0139] The thickness of the heat-resistant layer 24 is not particularly limited, but specifically it is 0.1 μm to 10 μm, preferably 0.5 μm to 5 μm. This is because excellent heat resistance can be obtained in the heat-resistant layer 24 while suppressing the increase in electrical resistance. The density of the heat-resistant layer 24 is also not particularly limited, but specifically it is 0.01 mg / cm³ for the same reasons as the thickness mentioned above. 2 ~10 mg / cm³ 2 That is the case.

[0140] (Heat-resistant material (polymer compound)) More specifically, the heat-resistant material contains one or more types of polymer compounds. This is because it provides excellent thermal stability in the heat-resistant layer 24 and allows for easy formation of the heat-resistant layer 24.

[0141] The type of polymer compound is not particularly limited, but specifically includes polyamides, polystyrenes, polyacrylic acid esters, polymethacrylic acid esters, polycarbonates, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfones, polyethersulfones, polyetheretherketones, polytetrafluoroethylenes, polyimides, polyetherimides, melamines, benzoguanamines, and polytetrafluoroethylenes. This is because sufficient thermal stability can be obtained in the heat-resistant layer 24. Note that the polyamide may be an aliphatic polyamide or an aromatic polyamide.

[0142] The type of polyacrylic acid ester is not particularly limited. Specific examples of polyacrylic acid esters include methyl polyacrylate, ethyl polyacrylate, butyl polyacrylate, 2-ethylhexyl polyacrylate, glycidyl polyacrylate, and hydroxyethyl polyacrylate. Similarly, the type of polymethacrylate ester is not particularly limited. Specific examples of polymethacrylate esters include methyl polymethacrylate, ethyl polymethacrylate, butyl polymethacrylate, 2-ethylhexyl polymethacrylate, glycidyl polymethacrylate, and hydroxyethyl polymethacrylate.

[0143] In particular, the polymer compound is preferably a polymer compound having an amide bond (-C(=O)-NH-) (hereinafter referred to as "amide polymer compound"). This is because amide polymer materials generally have a melting point or decomposition temperature higher than 200°C.

[0144] The type of amide polymer material is not particularly limited, but specifically, it includes the aliphatic polyamides and aromatic polyamides mentioned above. Among these, aromatic polyamides are preferred because they provide better thermal stability in the heat-resistant layer 24.

[0145] Specifically, aromatic polyamides include para-type aromatic polyamides represented by formula (5-1) and meta-type aromatic polyamides represented by formula (5-2). The melting or decomposition temperature of para-type aromatic polyamides is approximately 600°C, while the melting or decomposition temperature of meta-type aromatic polyamides is higher than 600°C, and more specifically, unmeasurable.

[0146] [ka] (Each of n1 and n2 is an integer between 100 and 10000.)

[0147] (Heat-resistant material (oxide)) Alternatively, the heat-resistant material contains one or more types of oxides. This is because it provides excellent thermal stability in the heat-resistant layer 24 and allows for easy formation of the heat-resistant layer 24.

[0148] The type of oxide is not particularly limited, but specifically, it is one or more types of oxides that contain elements belonging to groups 4, 13, and 14 of the long-period periodic table as constituent elements. This is because the melting points of these oxides are generally higher than 200°C.

[0149] Specific examples of oxides include metallic oxides (or inorganic oxides) such as aluminum oxide, titanium oxide, silicon oxide, and zirconium oxide. This is because sufficient thermal stability can be obtained in the heat-resistant layer 24. Among these, aluminum oxide, titanium oxide, and silicon oxide are preferred, with aluminum oxide being more preferred, because it further improves the thermal stability of the heat-resistant layer 24.

[0150] To give examples of typical oxides, the melting or decomposition temperature of aluminum oxide is approximately 2054°C, the melting or decomposition temperature of titanium oxide is approximately 1870°C, and the melting or decomposition temperature of silicon oxide is approximately 1650°C.

[0151] When the oxide consists of multiple particles, the average particle size (median diameter D50) of these multiple particles is not particularly limited, but is specifically 0.001 μm to 10 μm, preferably 0.01 μm to 1 μm. This is because the thickness of the heat-resistant layer 24 can be reduced while ensuring the penetration of the electrolyte into the heat-resistant layer 24.

[0152] Furthermore, if the heat-resistant material contains oxides, it is preferable that the heat-resistant layer 24 also contains a retaining material that holds the oxides. This is because it makes it easier to maintain the dispersion state of multiple particles (oxides) within the heat-resistant layer 24.

[0153] The holding material contains one or more polymer compounds that hold oxides. Specific examples of polymer compounds that are holding materials include polyamide, polystyrene, polyacrylic acid ester, polymethacrylic acid ester, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyetherimide, melamine, benzoguanamine, polytetrafluoroethylene, and polyvinylidene fluoride. Further details regarding polyacrylic acid ester and polymethacrylic acid ester are as described above.

[0154] In this case, the heat-resistant layer 24's function (heat resistance) is achieved by the heat-resistant oxide material, so the holding material does not necessarily have to be heat-resistant. That is, when the heat-resistant layer 24 contains a heat-resistant material (oxide) and a holding material, the melting point or decomposition temperature of the holding material is not particularly limited. For this reason, the melting point or decomposition temperature of the holding material may be higher than or equal to the melting point or decomposition temperature of the separator 23. However, in order to further prevent short circuits, it is preferable that the melting point or decomposition temperature of the holding material be higher than the melting point or decomposition temperature of the separator 23.

[0155] When the heat-resistant material contains an oxide, the heat-resistant layer 24 containing the heat-resistant material is formed using a coating method or the like. In this case, a solution is prepared in which the oxide is dispersed and the retaining material is dissolved using a solvent such as an organic solvent. This solution is then applied to both sides of the separator 23 and dried. This forms a heat-resistant layer 24 containing both the heat-resistant material (oxide) and the retaining material.

[0156] The oxide content in the solution is not particularly limited. In this case, by adjusting the oxide content, it is possible to prevent problems such as "repellency" from occurring when the solution is applied.

[0157] The solution may also contain one or more other materials, such as surfactants. The amount of surfactant in the solution is not particularly limited, but is specifically 0.01% to 3% by weight, preferably 0.05% to 1% by weight. This is because it improves the dispersibility of oxides and other substances in the solution, as well as the coatability (wettability) of the solution.

[0158] When a heat-resistant layer 24 containing a retaining material along with a heat-resistant material (oxide) is formed, the retaining material concentrates near the contact interfaces between the oxide particles, as well as near the contact interfaces between the oxide particles and the negative electrode active material particles. In this case, the amount of retaining material decreases in areas other than those near the aforementioned contact interfaces, so that these areas appear as if they have voids (pores). As a result, the heat-resistant layer 24 is considered to become a so-called porous state (a porous interconnected structure), and even if the heat-resistant layer 24 is provided on the separator 23, the electrolyte can easily be impregnated into the separator 23.

[0159] [Positive lead and negative lead] As shown in Figure 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 outer film 10. This positive electrode lead 31 contains a conductive material such as a metal material, and a specific example of such a conductive material is aluminum. The shape of the positive electrode lead 31 is not particularly limited, but specifically it can be either a thin plate shape or a mesh shape.

[0160] As shown in Figure 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 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.

[0161] <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.

[0162] <1-3. Manufacturing method> When manufacturing a secondary battery, the positive electrode 21 and 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 negative electrode 22, and the assembled secondary battery is subjected to stabilization treatment.

[0163] [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.

[0164] [Fabrication of the negative electrode] The negative electrode 22 is formed using the same procedure as that used to fabricate the positive electrode 21 described above. Specifically, first, a paste-like negative electrode slurry is prepared by adding a mixture (negative electrode mixture) containing the negative electrode active material, negative electrode binder, and negative electrode conductive agent 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.

[0165] [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.

[0166] [Formation of a heat-resistant layer] When using a polymer compound as the heat-resistant material, a solution is prepared by adding the polymer compound to a solvent, and then the solution is applied to both sides of the separator 23. Details regarding the solvent are as described above. This forms a heat-resistant layer 24 containing the heat-resistant material (polymer compound).

[0167] When using an oxide as the heat-resistant material, a solution is prepared by adding the oxide and the retaining material to a solvent, in which the oxide is dispersed by the solvent and the retaining material is dissolved. This solution is then applied to both sides of the separator 23. Details regarding the solvent are as described above. This forms a heat-resistant layer 24 containing the heat-resistant material (oxide) and the retaining material.

[0168] This explanation describes the case where a retaining material is used, but it is not necessary to use that material. The procedure for forming the heat-resistant layer 24 when a retaining material is not used is the same as the procedure for forming the heat-resistant layer 24 when a retaining material is used, except that the solution is prepared without using the retaining material.

[0169] [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.

[0170] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23 on which a heat-resistant layer 24 is formed. Then, the positive electrode 21, the negative electrode 22, the separator 23, and the heat-resistant layer 24 are wound together to produce a wound body (not shown). In this case, since the heat-resistant layer 24 is provided on the separator 23 in advance, the handling of the heat-resistant layer 24 is improved as described above. The wound body has the same configuration as the battery element 20, except that the electrolyte is not impregnated into the positive electrode 21, the negative electrode 22, the separator 23, and the heat-resistant layer 24. Next, the wound body is pressed using a press or the like to form a flattened shape.

[0171] 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.

[0172] 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.

[0173] 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.

[0174] [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.

[0175] <1-4. Mechanism and Effects> In this secondary battery, a separator 23 and a heat-resistant layer 24 are arranged between the positive electrode 21 and the negative electrode 22, the heat-resistant layer 24 is located in at least the opposing region R and contains a heat-resistant material, and the electrolyte salt of the electrolyte solution contains an imid anion.

[0176] In this case, as described above, even if the separator 23 melts or breaks in a high-temperature environment, the heat-resistant layer 24 remains interposed between the positive electrode 21 and the negative electrode 22, thus preventing a short circuit between the positive electrode 21 and the negative electrode 22.

[0177] 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.

[0178] Therefore, excellent battery characteristics can be obtained.

[0179] In particular, if the heat-resistant layer 24 contains a polymer compound, and that polymer compound contains one or more of the following: polyamide, polystyrene, polyacrylic acid ester, polymethacrylic acid ester, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyetherimide, melamine, benzoguanamine, and polytetrafluoroethylene, then excellent thermal stability can be obtained in the heat-resistant layer 24, thus providing a higher effect.

[0180] Furthermore, if the heat-resistant layer 24 contains oxides, and those oxides include one or more of the following: aluminum oxide, titanium oxide, silicon oxide, and zirconium oxide, then excellent thermal stability can be obtained in the heat-resistant layer 24, resulting in a higher effect. In this case, if the heat-resistant layer 24 further contains a holding material that retains oxides, and that holding material includes one or more of the following: polyamide, polystyrene, polyacrylic acid ester, polymethacrylic acid ester, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyetherimide, melamine, benzoguanamine, polytetrafluoroethylene, and polyvinylidene fluoride, then the dispersion state of multiple particles (oxides) within the heat-resistant layer 24 is more easily maintained, resulting in an even higher effect.

[0181] Furthermore, if the heat-resistant layer 24 is provided on the separator 23, the handling of the heat-resistant layer 24 is improved, and the manufacturing process of secondary batteries using the heat-resistant layer 24 becomes easier, thus achieving a higher level of effectiveness.

[0182] 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, an even higher voltage can be obtained, resulting in an even greater effect.

[0183] 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.

[0184] Furthermore, if the electrolyte also contains additives, and these additives include one or more of the following: 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.

[0185] Furthermore, if the electrolyte solution contains other electrolyte salts, and these 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, the lithium ion migration rate will be further improved, resulting in a greater effect.

[0186] 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.

[0187] <2. Variant> The configuration of the secondary battery described above can be modified as appropriate, as explained below. However, any two or more of the variations described below may be combined with each other.

[0188] [Modified examples 1, 2] As described above, the heat-resistant layer 24 only needs to be positioned in at least the opposing region R between the positive electrode 21 and the negative electrode 22. Accordingly, the arrangement range of the heat-resistant layer 24 can be arbitrarily changed.

[0189] In Figure 3, the area where the heat-resistant layer 24 is provided is extended beyond the opposing region R. More specifically, the area where the heat-resistant layer 24 is provided is extended both on the inside and outside of the winding compared to the area where the negative electrode active material layer 22B is provided.

[0190] In contrast, as shown in Figure 4, which corresponds to Figure 3, the area where the heat-resistant layer 24 is provided is extended beyond the opposing region R, and more specifically, the area where the heat-resistant layer 24 is provided may coincide with the area where the negative electrode active material layer 22B is provided (modification 1).

[0191] Alternatively, as shown in Figure 5, which corresponds to Figure 3, the area where the heat-resistant layer 24 is provided may coincide with the opposing region R, and more specifically, the area where the heat-resistant layer 24 is provided may be narrower than the area where the negative electrode active material layer 22B is provided and coincide with the area where the positive electrode active material layer 21B is provided (modification 2).

[0192] In these cases as well, the same effect can be obtained because the heat-resistant layer 24 is used to prevent short circuits between the positive electrode 21 and the negative electrode 22.

[0193] [Modified examples 3, 4] In Figure 3, the heat-resistant layer 24 is provided on the separator 23, and more specifically, the heat-resistant layer 24 is provided on both sides of the separator 23. However, as long as the heat-resistant layer 24 is arranged in at least the opposing region R between the positive electrode 21 and the negative electrode 22, the number of heat-resistant layers 24 can be arbitrarily changed.

[0194] Specifically, as shown in Figure 6, which corresponds to Figure 3, the heat-resistant layer 24 may be provided only on one surface of the separator 23, i.e., the side of the separator 23 facing the negative electrode 22 (modification 3).

[0195] Alternatively, as shown in Figure 7, which corresponds to Figure 3, the heat-resistant layer 24 may be provided only on one side of the separator 23 on its lower surface, i.e., the side facing the positive electrode 21 (modification 4).

[0196] In these cases as well, the same effect can be obtained because the heat-resistant layer 24 is used to prevent short circuits between the positive electrode 21 and the negative electrode 22.

[0197] In particular, as shown in Figure 6, even when the secondary battery is stored under harsh conditions such as high temperature or high voltage, the reaction between the negative electrode 22 and the separator 23 is suppressed while ensuring a lithium ion transport path (diffusion path). Therefore, it is possible to prevent the reaction products between the negative electrode 22 and the separator 23 from accumulating on the surface of the negative electrode 22.

[0198] Furthermore, as shown in Figure 7, even if the secondary battery is stored under harsh conditions such as high temperature or high voltage, the reaction between the positive electrode 21 and the separator 23 can be suppressed, and the physical strength of the separator 23 can be prevented from decreasing due to oxidation.

[0199] [Modifications 5-8] In Figure 3, the heat-resistant layer 24 is provided on the separator 23. However, as long as the heat-resistant layer 24 is located in at least the opposing region R between the positive electrode 21 and the negative electrode 22, the location of the heat-resistant layer 24 can be arbitrarily changed.

[0200] Specifically, as shown in Figure 8, which corresponds to Figure 3, the heat-resistant layer 24 may be provided on both the positive electrode 21 and the negative electrode 22 (modification 5). In this case, the heat-resistant layer 24 is placed between the positive electrode 21 and the separator 23, and the heat-resistant layer 24 is placed between the negative electrode 22 and the separator 23.

[0201] Alternatively, as shown in Figure 9, which corresponds to Figure 3, the heat-resistant layer 24 may be provided only on the negative electrode 22 (modification 6), or as shown in Figure 10, which corresponds to Figure 3, the heat-resistant layer 24 may be provided only on the positive electrode 21 (modification 7).

[0202] In addition, as shown in Figure 11, which corresponds to Figure 3, the heat-resistant layer 24 may be provided on both sides of the separator 23, and the heat-resistant layer 24 may also be provided on the positive electrode 21 and the negative electrode 22 respectively (modification 8).

[0203] In these cases as well, the same effect can be obtained because the heat-resistant layer 24 is used to prevent short circuits between the positive electrode 21 and the negative electrode 22.

[0204] [Modification 9] As described above, the electrolyte may contain other electrolyte salts along with the electrolyte salt containing the imid anion.

[0205] 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.

[0206] Specifically, the electrolyte salt contains cations and imid anions. Furthermore, the hexafluoride phosphate ion contains lithium ions and hexafluoride phosphate ions.

[0207] 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.

[0208] 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.

[0209] 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.

[0210] 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.

[0211] [Example 10] 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.

[0212] 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.

[0213] 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.

[0214] 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.

[0215] 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, in particular, as mentioned above, swelling of the secondary battery is suppressed, resulting in an even greater effect.

[0216] [Example 11] A liquid electrolyte solution was used. However, although not specifically illustrated here, a gel-like electrolyte layer may also be used.

[0217] 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, a heat-resistant layer 24, and the electrolyte layer, and the positive electrode 21, negative electrode 22, separator 23, heat-resistant layer 24, 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.

[0218] 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.

[0219] 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.

[0220] <3. Applications of rechargeable batteries> The uses (examples of applications) 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 may be a power source used in place of the primary power source, or a power source that can be switched from the primary power source.

[0221] 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.

[0222] 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.

[0223] 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.

[0224] Figure 12 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.

[0225] As shown in Figure 12, 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.

[0226] Power supply 51 includes one secondary battery. In this secondary battery, the positive electrode lead is connected to the positive electrode terminal 53, and the negative electrode lead is connected to the negative electrode terminal 54. Since this power supply 51 can be connected to the outside via the positive electrode terminal 53 and the negative electrode terminal 54, it can be charged and discharged. 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.

[0227] 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 supply 51 as necessary.

[0228] In addition, when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 56 cuts off the switch 57 so that no charging current flows through the current path of the power supply 51. The overcharge detection voltage is not particularly limited, but specifically, it is 4.20V ± 0.05V, and the overdischarge detection voltage is not particularly limited, but specifically, it is 2.40V ± 0.1V.

[0229] The switch 57 includes a charge control switch, a discharge control switch, a charging diode, a discharging diode, etc., and switches the connection between the power supply 51 and an external device according to the instruction of the control unit 56. This switch 57 includes a metal-oxide-semiconductor field-effect transistor (MOSFET), etc., and the charge and discharge current is detected based on the ON resistance of the switch 57.

[0230] [[ID=十六]]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

[0231] An example of this technology will be described below.

[0232] <Examples 1-24 and Comparative Examples 1-6> As explained below, after fabricating a secondary battery, its battery characteristics were evaluated.

[0233] [Manufacturing of secondary batteries] A laminate film type secondary battery (lithium-ion secondary battery) shown in Figures 1 and 2 was fabricated using the following procedure. In this case, a separator 23 shown in Figure 3, i.e., a separator 23 with a heat-resistant layer 24 provided on both sides, was used to fabricate the secondary battery.

[0234] (Fabrication of the positive electrode) First, the positive electrode active material is a lithium-containing compound (oxide) (LiNi 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.

[0235] (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 organic 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.

[0236] (Formation of a heat-resistant layer) First, a solution for forming the heat-resistant layer 24 was prepared.

[0237] When using polymer compounds as heat-resistant materials, the polymer compound was added to a solvent (the organic solvent N-methyl-2-pyrrolidone), and then the solvent was stirred. As polymer compounds, the para-type aromatic polyamide (PA1) shown in formula (5-1) and the meta-type aromatic polyamide (PA2) shown in formula (5-2) were used.

[0238] When using oxides as heat-resistant materials, the solvent (organic solvent N-methyl-2-pyrrolidone) is used to dissolve the oxide (central particle size = 0.3 μm, specific surface area = 13 m²). 2 After adding the oxide ( / g) and the retaining material, the solvent was stirred. Aluminum oxide (Al2O3), titanium oxide (TiO2), and silicon oxide (SiO2) were used as oxides. Polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA) were used as retaining materials. The mixing ratio (by weight) of oxide to retaining material was oxide:retaining material = 20:1.

[0239] Next, a coating film was formed by applying the solution to both sides of the separator 23 (a polyethylene microporous membrane with an average pore size of 17.9 nm) using a tabletop coater. Finally, the coating film was phase-separated by immersing the separator 23 in a water bath, and then the coating film was dried with hot air.

[0240] As a result, as shown in Tables 1 and 2, a heat-resistant layer 24 (thickness = 2 μm, density = 0.3 mg / cm³) is applied to both sides of the separator 23. 2 ) was formed.

[0241] The procedure for producing the polyethylene microporous membrane, which is the separator 23, is as follows: First, a polyethylene solution was prepared by melt-kneading polyethylene and a plasticizer (liquid paraffin) using a twin-screw extruder. Next, a gel-like sheet was formed by extruding the polyethylene solution from a T-die attached to the tip of the twin-screw extruder and winding the polyethylene solution using a cooling roll. Subsequently, a thin film was obtained by biaxial stretching of the gel-like sheet. Finally, the thin film was washed with a solvent (hexane) to extract and remove any remaining liquid paraffin, and then the thin film was dried and heat-treated. As a result, the thin film was made microporous, and a polyethylene microporous membrane was obtained.

[0242] For comparison, as shown in Table 2, a heat-resistant layer 24 was formed using the same procedure, except that a non-heat-resistant material (polyethylene (PE), a polymer compound) was used instead of a heat-resistant material.

[0243] (Preparation of electrolyte solution) First, the electrolyte salt was added to the solvent, and then the solvent was stirred.

[0244] 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.

[0245] 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 Table 1 and Table 2.

[0246] Thereby, an electrolytic solution containing the electrolyte salt was prepared. This electrolyte salt is a lithium salt containing an imide anion as an anion.

[0247] For comparison, as shown in Table 2, an electrolytic solution was prepared by the same procedure except that hexafluorophosphate ion (PF6 - ) was used as the anion.

[0248] (Assembly of secondary battery) First, a positive electrode lead 31 (aluminum foil) was welded to the positive electrode current collector 21A of the positive electrode 21, and a negative electrode lead 32 (copper foil) was welded to the negative electrode current collector 22A of the negative electrode 22.

[0249] Subsequently, the positive electrode 21 and the negative electrode 22 were laminated on each other through a separator 23 provided with a heat-resistant layer 24, and then the positive electrode 21, the negative electrode 22, the separator 23 and the heat-resistant layer 24 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.

[0250] 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.

[0251] 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.

[0252] Therefore, since the battery elements were sealed inside the outer film 10, a secondary battery was assembled.

[0253] (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.

[0254] 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.

[0255] [Evaluation of battery characteristics] The battery characteristics were evaluated, and the results shown in Tables 1 and 2 were obtained. Here, high-temperature cycle characteristics, high-temperature storage characteristics, and low-temperature load characteristics were evaluated.

[0256] (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.

[0257] 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.

[0258] 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.

[0259] (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.

[0260] 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.

[0261] 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.

[0262] (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.

[0263] 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.

[0264] Finally, the load maintenance rate (%) was calculated based on the formula: Load Maintenance Rate (%) = (Discharge capacity at 100th cycle / Discharge capacity at 1st cycle) × 100, which is an index for evaluating low-temperature load characteristics.

[0265] [Table 1]

[0266] [Table 2]

[0267] [Consideration] As shown in Tables 1 and 2, the cycle retention rate, storage retention rate, and load retention rate varied considerably depending on the electrolyte composition and the heat-resistant layer 24.

[0268] Specifically, even when the heat-resistant layer 24 contained a heat-resistant material, the cycle retention rate, storage retention rate, and load retention rate all decreased when the electrolyte salt did not contain an imid anion (Comparative Examples 1-5).

[0269] Furthermore, even when the electrolyte salt contained imid anions, if the heat-resistant layer 24 contained a non-heat-resistant material (Comparative Example 6), the cycle retention rate, storage retention rate, and load retention rate all decreased.

[0270] In contrast, when the heat-resistant layer 24 contained a heat-resistant material and the electrolyte salt contained an imid anion (Examples 1-24), the cycle retention rate, storage retention rate, and load retention rate all increased.

[0271] In particular, when the electrolyte salt contained an imid anion (Examples 1-24), the following tendencies were also observed. Firstly, when the electrolyte salt contained a light metal ion (lithium ion) as a cation, the cycle retention rate, storage retention rate, and load retention rate were all sufficiently high. Secondly, when the electrolyte salt content was 0.2 mol / kg to 2 mol / kg relative to the solvent, the cycle retention rate, storage retention rate, and load retention rate were all sufficiently high.

[0272] <Examples 25-42> As shown in Tables 3 and 4, secondary batteries were prepared using the same procedure as in Example 3, 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.

[0273] 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.

[0274] 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).

[0275] The respective content (by weight %) of additives and other electrolyte salts in the electrolyte solution are shown in Tables 3 and 4.

[0276] [Table 3]

[0277] [Table 4]

[0278] As shown in Tables 3 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 3).

[0279] Furthermore, as shown in Tables 3 and 4, 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 3).

[0280] <Examples 43-74> As shown in Tables 5 and 6, secondary batteries were fabricated using the same procedure as in Example 3, except that another electrolyte salt (lithium hexafluoride phosphate (LiPF6)) was included in the electrolyte solution, and then the battery characteristics were evaluated.

[0281] In this case, the other electrolyte salt was added to the solvent along with the electrolyte salt, and then the solvent was stirred. The content of the electrolyte salt (mol / kg), the content of the other electrolyte salt (mol / kg), the sum T (mol / kg), and the percentage R (mol%) are as shown in Tables 5 and 6.

[0282] [Table 5]

[0283] [Table 6]

[0284] As shown in Tables 5 and 6, when the two conditions were met—a sum T of 0.7 mol / kg to 2.2 mol / kg and a proportion R of 13 mol% to 6000 mol% (e.g., Example 47)—the cycle retention rate, storage retention rate, and load retention rate were all increased compared to when these two conditions were not met (e.g., Example 43).

[0285] [summary] The results shown in Tables 1 to 6 indicate that when a heat-resistant layer 24 is placed in at least the opposing region R between the positive electrode 21 and the negative electrode 22, and when the heat-resistant layer 24 contains a heat-resistant material, and the electrolyte salt of the electrolyte contains an imido anion, the cycle retention rate, storage retention rate, and 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, resulting in excellent battery characteristics.

[0286] 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.

[0287] 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.

[0288] 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. A positive electrode containing a positive electrode active material layer, A negative electrode containing a negative electrode active material layer, A separator and a heat-resistant layer are disposed between the positive electrode and the negative electrode. Electrolyte containing electrolyte salts and Equipped with, The heat-resistant layer is arranged in a region where at least the positive electrode active material layer and the negative electrode active material layer face each other, and has a melting point or decomposition temperature higher than the melting point or decomposition temperature of the separator. 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. The electrolyte further comprises at least one of the following: unsaturated cyclic carbonate esters, fluorinated cyclic carbonate esters, disulfonic anhydrides, sulfate esters, nitrile compounds, and isocyanate compounds. 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】 (R3 and R4 are each fluorine groups. X1, X2, X3, and X4 are each one of the following: a carbonyl group, a sulfinyl group, or a sulfonyl group.)

2. The heat-resistant layer contains a polymer compound, The polymer compound includes at least one of the following: polyamide, polystyrene, polyacrylic acid ester, polymethacrylic acid ester, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyetherimide, melamine, benzoguanamine, and polytetrafluoroethylene. The secondary battery according to claim 1.

3. The heat-resistant layer contains an oxide, The oxide comprises at least one of aluminum oxide, titanium oxide, silicon oxide, and zirconium oxide. The secondary battery according to claim 1.

4. The heat-resistant layer further comprises a polymer compound that retains the oxide, The polymer compound includes at least one of the following: polyamide, polystyrene, polyacrylic acid ester, polymethacrylic acid ester, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyetherimide, melamine, benzoguanamine, polytetrafluoroethylene, and polyvinylidene fluoride. The secondary battery according to claim 3.

5. The heat-resistant layer is provided in the separator. A secondary battery according to any one of claims 1 to 4.

6. The aforementioned electrolyte salt contains light metal ions as cations. A secondary battery according to any one of claims 1 to 4.

7. The aforementioned light metal ions include lithium ions. The secondary battery according to claim 6.

8. 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 4.

9. 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 4.

10. Lithium-ion rechargeable batteries, A secondary battery according to any one of claims 1 to 4.

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