Electrolyte for secondary battery and secondary battery

Abstract

The secondary battery comprises: a positive electrode; a negative electrode; and an electrolyte comprising a solvent, an electrolyte salt, a first unsaturated compound containing at least one of the compounds represented by formulas (1) to (4), and a second unsaturated compound containing at least one of the compounds represented by formulas (5) to (19).

Description

Technical Field

[0001] This technology relates to electrolytes for secondary batteries and secondary batteries themselves. Background Technology

[0002] With the widespread adoption of mobile phones and other electronic devices, secondary batteries are being developed as small, lightweight power sources capable of delivering high energy density. These secondary batteries include a positive electrode, a negative electrode, and an electrolyte (for secondary batteries), and various studies have been conducted regarding their structure.

[0003] Specifically, to obtain high charging efficiency, the electrolyte contains α-substituted oxy-γ-butyrolactone derivatives (e.g., see Patent Document 1). To obtain excellent cycling characteristics, the electrolyte contains cyclic esters with intramolecular unsaturated carbon bonds (e.g., see Patent Document 2). To suppress gas generation during continuous charging at high charging voltages, the electrolyte contains lactones with unsaturated carbon bonds (e.g., see Patent Document 3). To obtain good high-temperature cycling characteristics, the electrolyte contains acrylic compounds with intramolecular cyclic carbonate or lactone structures (e.g., see Patent Document 4). To obtain excellent durability at high temperatures, the electrolyte contains acrylic compounds with intramolecular lactone structures (e.g., see Patent Document 5).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2003-163031

[0007] Patent Document 2: Japanese Patent Application Publication No. 11-273723

[0008] Patent Document 3: Japanese Patent Application Publication No. 2005-340151

[0009] Patent Document 4: Japanese Patent Application Publication No. 2014-026886

[0010] Patent document 5: Japanese Patent Application Publication No. 2017-174543. Summary of the Invention

[0011] Various studies have been conducted on the battery characteristics of the secondary battery, but the cycle characteristics of this secondary battery are still insufficient, so there is room for improvement.

[0012] Therefore, there is a need for electrolytes and secondary batteries that can achieve excellent cycle characteristics.

[0013] An embodiment of the present technology provides an electrolyte for a secondary battery comprising a solvent, an electrolyte salt, a first unsaturated compound containing at least one of the compounds represented by formulas (1) to (4), and a second unsaturated compound containing at least one of the compounds represented by formulas (5) to (19).

[0014] [Chemical Formula 1]

[0015] 1

[0016]

[0017] (R1 to R6 are any one of hydrogen (H), alkyl, acrylate and methacrylate, and at least one of R1 to R6 is either acrylate or methacrylate.)

[0018] R7 to R14 are any one of hydrogen (H), alkyl, acrylate and methacrylate, and at least one of R7 to R14 is either acrylate or methacrylate.

[0019] R15 is an alkenyl group.

[0020] [Chemical Formula 2]

[0021] 2

[0022]

[0023] (R21 and R22 are alkenyl groups, respectively;

[0024] R23 and R24 are alkenyl groups, respectively;

[0025] R25 to R30 are either hydrogen (H) or an alkenyl group, and two or more of R25 to R30 are alkenyl groups.

[0026] R31 to R36 are either hydrogen (H) or an alkenyl group, and two or more of R31 to R36 are alkenyl groups.

[0027] R37 is an alkylene group with an ether bond, while R38 and R39 are alkenyl groups, respectively.

[0028] R40 is an alkylene group, while R41 and R42 are alkenyl groups, respectively.

[0029] R43 is any one of alkylene and alkylene with ether bond, and R44 and R45 are any one of acrylate and methacrylate, respectively.

[0030] R46 to R48 are alkenyl groups;

[0031] R49 to R51 are either alkyl or alkenyl groups, and two or more of R49 to R51 are alkenyl groups.

[0032] R52 to R54 are alkenyl groups;

[0033] R55 is any one of alkylene and arylene;

[0034] R56 is a tetravalent hydrocarbon group, R57 to R60 are alkylene groups, R61 to R64 are any one of hydroxyl, acrylic, and methacrylic groups, and two or more of R61 to R64 are any one of acrylic and methacrylic groups.

[0035] R65 is any one of hydrogen (H) and alkyl groups, and R66 is an alkenyl group;

[0036] R67 and R68 are alkenyl groups, respectively;

[0037] R69 and R70 are alkenyl groups, respectively.

[0038] One embodiment of the present technology provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte having the same composition as the electrolyte for a secondary battery described in one embodiment of the present technology.

[0039] It should be noted that the details (definitions) of "acrylic acid group" and "methacrylic acid group" will be described later.

[0040] According to one embodiment of the present technology, the electrolyte for a secondary battery or the secondary battery contains a first unsaturated compound and a second unsaturated compound, thus achieving excellent cycle characteristics.

[0041] It should be noted that the effects of this technology are not necessarily limited to those described herein, but can be any of the series of effects associated with this technology described later. Attached Figure Description

[0042] Figure 1 This is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0043] Figure 2 It means Figure 1 A cross-sectional view of the structure of the battery element is shown.

[0044] Figure 3 This is a block diagram illustrating the structure of a secondary battery application example. Detailed Implementation

[0045] The following is a detailed description of one embodiment of the present technology with reference to the accompanying drawings. It should be noted that the description is presented in the following order.

[0046] 1. Electrolyte for secondary batteries

[0047] 1-1. Composition

[0048] 1-2. Manufacturing method

[0049] 1-3. Functions and Effects

[0050] 2. Secondary battery

[0051] 2-1. Composition

[0052] 2-2. Actions

[0053] 2-3. Manufacturing method

[0054] 2-4. Functions and Effects

[0055] 3. Variations

[0056] 4. Uses of secondary batteries

[0057] <1. Electrolyte for Secondary Batteries>

[0058] First, an electrolyte for a secondary battery (hereinafter referred to as "electrolyte") according to one embodiment of the present technology will be described.

[0059] This electrolyte is used in secondary batteries. Additionally, it can also be used in electrochemical devices other than secondary batteries. The type of electrochemical device is not particularly limited; specifically, it can be a capacitor, etc.

[0060] <1-1. Composition>

[0061] The electrolyte comprises a solvent, an electrolyte salt, a first unsaturated compound, and a second unsaturated compound. The first unsaturated compound comprises any one or more compounds represented by formulas (1) to (4), and the second unsaturated compound comprises any one or more compounds represented by formulas (5) to (19).

[0062] [Chemical Formula 3]

[0063] Transformation 3

[0064]

[0065] (R1 to R6 are any one of hydrogen (H), alkyl, acrylate and methacrylate, and at least one of R1 to R6 is either acrylate or methacrylate.)

[0066] R7 through R14 are any one of hydrogen (H), alkyl, acrylate, and methacrylate, respectively, at least one of R7 through R14 is either acrylate or methacrylate, and R15 is an alkenyl group.

[0067] [Chemical Formula 4]

[0068] Transformation 4

[0069]

[0070] (R21 and R22 are alkenyl groups, respectively;

[0071] R23 and R24 are alkenyl groups, respectively;

[0072] R25 to R30 are either hydrogen (H) or an alkenyl group, and two or more of R25 to R30 are alkenyl groups.

[0073] R31 to R36 are either hydrogen (H) or an alkenyl group, and two or more of R31 to R36 are alkenyl groups.

[0074] R37 is an alkylene group with an ether bond, while R38 and R39 are alkenyl groups, respectively.

[0075] R40 is an alkylene group, while R41 and R42 are alkenyl groups, respectively.

[0076] R43 is any one of alkylene and alkylene with ether bond, and R44 and R45 are any one of acrylate and methacrylate, respectively.

[0077] R46 to R48 are alkenyl groups;

[0078] R49 to R51 are either alkyl or alkenyl groups, and two or more of R49 to R51 are alkenyl groups.

[0079] R52 to R54 are alkenyl groups;

[0080] R55 is any one of alkylene and arylene;

[0081] R56 is a tetravalent hydrocarbon group, R57 to R60 are alkylene groups, R61 to R64 are any one of hydroxyl, acrylic, and methacrylic groups, and two or more of R61 to R64 are any one of acrylic and methacrylic groups.

[0082] R65 is any one of hydrogen (H) and alkyl groups, and R66 is an alkenyl group;

[0083] R67 and R68 are alkenyl groups, respectively;

[0084] R69 and R70 are alkenyl groups, respectively.

[0085] The reason why the electrolyte contains both the first unsaturated compound and the second unsaturated compound is that, compared to the case where the electrolyte contains only one of the first and second unsaturated compounds, the durability of the coating formed on the electrode surface is improved when this electrolyte is used in a secondary battery. The "electrode" refers to one or both of the positive electrode 21 and the negative electrode 22, which will be described later. Therefore, during charging and discharging, the decomposition reaction of the electrolyte on the electrode surface can be suppressed, and thus the discharge capacity is less likely to decrease even with repeated charging and discharging. Details of the reasons explained here will be described later.

[0086] [The first unsaturated compound]

[0087] As shown in formulas (1) to (4), the first unsaturated compound is a cyclic compound with an lactone-type ring structure and unsaturated carbon bonds (carbon-to-carbon double bonds).

[0088] The unsaturated carbon bond can exist inside the lactone-type ring structure, outside the lactone-type ring structure, or both. Furthermore, the number of unsaturated carbon bonds can be only one or more.

[0089] A lactone-type ring structure refers to a carbon ring structure with -C(=O)-O- as part of the ring, and the number of carbon atoms forming the ring together with this -C(=O)-O- is not particularly limited. Therefore, a lactone-type ring structure can be a five-membered ring, a six-membered ring, or other types of rings.

[0090] Hereinafter, the compound shown in formula (1) will be referred to as "the first unsaturated compound A", the compound shown in formula (2) will be referred to as "the first unsaturated compound B", the compound shown in formula (3) will be referred to as "the first unsaturated compound C", and the compound shown in formula (4) will be referred to as "the first unsaturated compound D".

[0091] (First unsaturated compound A)

[0092] As shown in formula (1), the first unsaturated compound A is a cyclic compound having a lactone-type ring structure as a five-membered ring and having unsaturated carbon bonds on the outside of the lactone-type ring structure.

[0093] R1 through R6 can each be any one of hydrogen (H), alkyl, acrylate, and methacrylate groups, without particular limitation. However, any one or more of R1 through R6 must be either acrylate or methacrylate. This is because, as mentioned above, the first unsaturated compound A must have unsaturated carbon bonds. Therefore, compounds where R1 through R6 are either hydrogen (H) or alkyl groups do not have unsaturated carbon bonds and are therefore not considered the first unsaturated compound A.

[0094] There is no particular limitation on the number of carbon atoms in an alkyl group. Furthermore, alkyl groups can be straight-chain or branched, having one or more side chains. Specific examples of alkyl groups include methyl, ethyl, propyl, and butyl.

[0095] The acrylate group is represented by -OC(=O)-CH=CH2. That is, the acrylate group is obtained by removing the terminal hydrogen (the hydrogen atom bonded to the oxygen atom) from acrylic acid (CH2=CH-C(=O)-OH).

[0096] The methacrylate group is represented by -OC(=O)-C(-CH3)=CH2. That is, the methacrylate group is obtained by removing the terminal hydrogen from methacrylic acid (CH2=C(-CH3)-C(=O)-OH).

[0097] (First unsaturated compound B)

[0098] As shown in formula (2), the first unsaturated compound B is a cyclic compound having a lactone-type ring structure as a six-membered ring and having unsaturated carbon bonds on the outside of the lactone-type ring structure.

[0099] R7 through R14 can each be any one of hydrogen (H), alkyl, acrylate, and methacrylate groups, without particular limitation. However, any one or more of R7 through R14 must be either acrylate or methacrylate. This is because, as mentioned above, the first unsaturated compound B must have unsaturated carbon bonds. Therefore, compounds R7 through R14 that are either hydrogen (H) or alkyl groups do not have unsaturated carbon bonds and are therefore not considered first unsaturated compounds B. Details regarding alkyl, acrylate, and methacrylate groups are as described above.

[0100] (First unsaturated compound C)

[0101] As shown in formula (3), the first unsaturated compound C is a cyclic compound having a lactone-type ring structure as a five-membered ring and having unsaturated carbon bonds on the outside of the lactone-type ring structure.

[0102] The first unsaturated compound C contains one methylene group (CH2=CH-) with an unsaturated carbon bond. That is, formula (3) shows that a methylene group is bonded to any one of the three carbon atoms (C) that form a lactone-type ring structure (five-membered ring) together with -C(=O)-O-. Therefore, the methylene group is bonded to any one of the carbon atoms at the α-position, β-position, and γ-position.

[0103] (First unsaturated compound D)

[0104] As shown in formula (4), the first unsaturated compound D is a cyclic compound having an lactone-type ring structure and having unsaturated carbon bonds on the inside of the lactone-type ring structure.

[0105] R15 can be any alkenyl group; there are no particular restrictions. In this case, the number of carbon atoms in the alkenyl group is not particularly limited. Therefore, the shape of the lactone structure (whether it is a membered ring) is determined by the number of carbon atoms in the alkenyl group. Furthermore, the alkenyl group can be linear or branched.

[0106] Specific examples of linear alkenyl groups are -CH=CH-, -CH=CH-CH2-, -CH2-CH=CH-, -CH=CH-CH2-CH2-, -CH2-CH2-CH=CH-, and -CH=CH-CH=CH-, etc.

[0107] Specific examples of branched alkenyl groups are -C(-CH3)=CH-CH2-, -CH=C(-CH3)-CH2-, -CH2-CH2-C(-CH3)=CH-, -CH2-CH2-CH=C(-CH3)-, -C(-CH3)=CH-CH2-CH2-, -CH=C(-CH3)-CH2-CH2-, -CH2-CH2-C(-CH3)=CH-, -CH2-CH2-CH=C(-CH3)-, -C(-CH3)=CH-CH=CH-, -CH=C(-CH3)-CH=CH-, -CH=CH-C(-CH3)=CH-, and -CH=CH-CH=C(-CH3)-, etc.

[0108] The first unsaturated compound D preferably comprises one or more of the compounds represented by formulas (21) to (24). This is because it can sufficiently improve the durability of the coating formed on the electrode surface.

[0109] [Chemical Formula 5]

[0110] 5

[0111]

[0112] (R81 to R98 are any one of hydrogen (H) and alkyl groups, respectively.)

[0113] The compounds represented by formulas (21) and (22) respectively have a lactone-type ring structure as a five-membered ring, and have one unsaturated carbon bond inside the lactone-type ring structure. In addition, the positions of the unsaturated carbon bond are different in the compounds represented by formulas (21) and (22).

[0114] The compound shown in formula (23) has a lactone-type ring structure as a six-membered ring, and has one unsaturated carbon bond on the inside of the lactone-type ring structure.

[0115] The compound shown in formula (24) has a lactone-type ring structure as a six-membered ring, and has two unsaturated carbon bonds on the inside of the lactone-type ring structure.

[0116] R81 through R98 can each be any one of hydrogen (H) or an alkyl group; there are no particular restrictions. Details regarding alkyl groups are as described above.

[0117] (Specific examples of the first unsaturated compound)

[0118] Specific examples of the first unsaturated compound A are compounds represented by formulas (1-1) to (1-4), etc. Specific examples of the first unsaturated compound B are compounds represented by formula (2-1), etc. Specific examples of the first unsaturated compound C are compounds represented by formulas (3-1) and (3-2), etc. Specific examples of the first unsaturated compound D are compounds represented by formulas (4-1) to (4-6), etc.

[0119] Here, the compounds represented by formulas (4-1) to (4-3) correspond to the compounds represented by formula (21). The compound represented by formula (4-4) corresponds to the compound represented by formula (22). The compound represented by formula (4-5) corresponds to the compound represented by formula (23). The compound represented by formula (4-6) corresponds to the compound represented by formula (24).

[0120] [Chemical Formula 6]

[0121] Transformation 6

[0122]

[0123] More specifically, the compound represented by formula (1-1) is 2-oxotetrahydrofuran-3-yl acrylate. The compound represented by formula (1-2) is 2-oxotetrahydrofuran-3-yl methacrylate. The compound represented by formula (1-3) is 5-oxotetrahydrofuran-3-yl acrylate. The compound represented by formula (1-4) is 5-oxotetrahydrofuran-3-yl methacrylate.

[0124] The compound shown in formula (2-1) is 4-methyl-2-oxotetrahydro-2H-pyran-4-yl methacrylate.

[0125] The compound shown in formula (3-1) is α-methylene-γ-butyrolactone. The compound shown in formula (3-2) is γ-methylene-γ-butyrolactone.

[0126] The compound represented by formula (4-1) is γ-crotonic acid lactone. The compound represented by formula (4-2) is 3-methyl-2(5H)-furanone. The compound represented by formula (4-3) is 4-methyl-2(5H)-furanone. The compound represented by formula (4-4) is α-angelicinolone. The compound represented by formula (4-5) is 5,6-dihydro-2H-pyran-2-one. The compound represented by formula (4-6) is α-pyranone.

[0127] (Content of the first unsaturated compound)

[0128] The content of the first unsaturated compound in the electrolyte is not particularly limited, but is preferably 0.1% to 2% by weight. This is because it can sufficiently improve the durability of the coating. In the case where the electrolyte contains two or more first unsaturated compounds, the content described herein is the sum of the contents of each first unsaturated compound.

[0129] [Second unsaturated compound]

[0130] As shown in formulas (5) to (19), the second unsaturated compound is a chain or cyclic compound that does not have a lactone-type ring structure and has unsaturated carbon bonds (carbon-to-carbon double bonds).

[0131] Hereinafter, the compound shown in formula (5) will be referred to as "second unsaturated compound A", the compound shown in formula (6) will be referred to as "second unsaturated compound B", the compound shown in formula (7) will be referred to as "second unsaturated compound C", the compound shown in formula (8) will be referred to as "second unsaturated compound D", the compound shown in formula (9) will be referred to as "second unsaturated compound E", the compound shown in formula (10) will be referred to as "second unsaturated compound F", the compound shown in formula (11) will be referred to as "second unsaturated compound G", the compound shown in formula (12) will be referred to as "second unsaturated compound H", the compound shown in formula (13) will be referred to as "second unsaturated compound I", the compound shown in formula (14) will be referred to as "second unsaturated compound J", the compound shown in formula (15) will be referred to as "second unsaturated compound K", the compound shown in formula (16) will be referred to as "second unsaturated compound L", the compound shown in formula (17) will be referred to as "second unsaturated compound M", the compound shown in formula (18) will be referred to as "second unsaturated compound N", and the compound shown in formula (19) will be referred to as "second unsaturated compound O".

[0132] (Second unsaturated compound A)

[0133] As shown in formula (5), the second unsaturated compound A is a chain compound having a sulfonyl group (-S(=O)2-) and an unsaturated carbon bond.

[0134] R21 and R22 can both be alkenyl groups; there are no particular restrictions. The number of carbon atoms in the alkenyl group is not particularly limited. Furthermore, the alkenyl group can be linear or branched. The type of alkenyl group is not particularly limited; specifically, it can be vinyl or allyl, etc.

[0135] (Second unsaturated compound B)

[0136] As shown in formula (6), the second unsaturated compound B is a cyclic compound with a spirobis(m-dioxane) ring structure and unsaturated carbon bonds.

[0137] R23 and R24 can both be alkenyl groups; there are no specific restrictions. Details regarding alkenyl groups are as described above.

[0138] (Second unsaturated compound C)

[0139] As shown in formula (7), the second unsaturated compound C is a cyclic compound with a benzene ring structure and unsaturated carbon bonds.

[0140] R25 through R30 can each be either hydrogen (H) or an alkenyl group; there are no special restrictions. Two or more of R25 through R30 must be alkenyl groups. Details regarding alkenyl groups are as described above.

[0141] (Second unsaturated compound D)

[0142] As shown in formula (8), the second unsaturated compound D is a cyclic compound with a cyclohexane-type ring structure and unsaturated carbon bonds.

[0143] R31 through R36 can each be either hydrogen (H) or an alkenyl group; there are no particular restrictions, but two or more of R31 through R36 must be alkenyl groups. This is because, as mentioned above, the second unsaturated compound D must have unsaturated carbon bonds. Therefore, compounds R31 through R36 that are each hydrogen (H) do not have unsaturated carbon bonds and are therefore not considered second unsaturated compounds D. Details regarding alkenyl groups are as described above.

[0144] (Second unsaturated compound E)

[0145] As shown in formula (9), the second unsaturated compound E is a chain compound with a diethylene glycol-type structure and unsaturated carbon bonds.

[0146] R37 can be any alkylene group with an ether bond (-O-), without any particular limitation. The alkylene group with an ether bond refers to a chain group with one or more ether bonds introduced in the middle of the alkylene group.

[0147] There is no particular limitation on the number of carbon atoms in an alkylene group. Furthermore, alkylene groups can be straight-chain or branched. Specific examples of alkylene groups include methylene, ethylene, propylene, and butylene. Therefore, specific examples of alkylene groups with ether bonds are -CH2-O-CH2-, -CH2-O-CH2-CH2-, -CH2-CH2-O-CH2-, and -CH2-CH2-O-CH2-CH2-.

[0148] R38 and R39 can both be alkenyl groups; there are no specific restrictions. Details regarding alkenyl groups are as described above.

[0149] (Second unsaturated compound F)

[0150] As shown in formula (10), the second unsaturated compound F is a chain compound with an adipic acid-type structure and unsaturated carbon bonds.

[0151] R40 can be any alkylene group; there are no special restrictions. Details regarding alkylene groups are as described above. R41 and R42 can each be any alkenyl group; there are no special restrictions. Details regarding alkenyl groups are as described above.

[0152] (Second unsaturated compound G)

[0153] As shown in formula (11), the second unsaturated compound G is a chain compound with a polyethylene glycol-type structure and unsaturated carbon bonds.

[0154] R43 can be any one of alkylene groups or alkylene groups with ether bonds; there are no particular limitations. Details regarding alkylene groups and alkylene groups with ether bonds are as described above. R44 and R45 can each be any one of acrylate groups or methacrylate groups; there are no particular limitations. Details regarding acrylate groups and methacrylate groups are as described above.

[0155] (Second unsaturated compound H)

[0156] As shown in formula (12), the second unsaturated compound H is a cyclic compound with a pyromellitic acid-type structure and unsaturated carbon bonds.

[0157] R46 through R48 can be any alkenyl group; there are no specific restrictions. Details regarding alkenyl groups are as described above.

[0158] (Second unsaturated compound I)

[0159] As shown in formula (13), the second unsaturated compound I is a cyclic compound with an isocyanuric acid-type structure and unsaturated carbon bonds.

[0160] R49 through R51 can each be either an alkyl group or an alkenyl group; there are no particular restrictions, but two or more of R49 through R51 must be alkenyl groups. This is because, as mentioned above, second unsaturated compound I must have unsaturated carbon bonds. Therefore, compounds where R49 through R51 are alkyl groups do not have unsaturated carbon bonds and thus do not belong to second unsaturated compound I. Details regarding alkyl and alkenyl groups are as described above.

[0161] (Second unsaturated compound J)

[0162] As shown in formula (14), the second unsaturated compound J is a cyclic compound with a triazine structure and unsaturated carbon bonds.

[0163] R52 to R54 can each be an alkenyl group; there are no particular restrictions. Details regarding alkenyl groups are as described above.

[0164] (Second unsaturated compound K)

[0165] As shown in formula (15), the second unsaturated compound K is a cyclic compound with a dimaleimide-type structure and unsaturated carbon bonds.

[0166] R55 can be any of alkylene or aryl groups; there are no particular limitations. Details regarding alkylene groups are as described above. Specific examples of alkylene groups include ethylene, propylene, and butylene. Specific examples of aryl groups include phenylene and naphthylene.

[0167] (Second unsaturated compound L)

[0168] As shown in formula (16), the second unsaturated compound L is a cyclic compound with a pentaerythritol-type structure and unsaturated carbon bonds.

[0169] R56 requires only a tetravalent hydrocarbon group; there are no specific restrictions. This tetravalent hydrocarbon group refers to a group formed by the removal of four hydrogen atoms from alkanes, alkenes, alkynes, cycloalkanes, and aromatic hydrocarbons. Specific examples of alkanes include butane and pentane. Specific examples of alkenes include butene and pentene. Specific examples of alkynes include butyne and pentyne. Specific examples of cycloalkanes include cyclobutane, cyclopentane, and cyclohexane. Specific examples of aromatic hydrocarbons include benzene and naphthalene.

[0170] R57 through R60 can be any alkylene group; there are no specific limitations. Details regarding alkylene groups are as described above.

[0171] R61 to R64 can each be any one of hydroxyl, acrylic, or methacrylic groups; there are no special restrictions. However, two or more of R61 to R64 must be either acrylic or methacrylic groups. Details regarding acrylic and methacrylic groups are as described above.

[0172] (Second unsaturated compound M)

[0173] As shown in formula (17), the second unsaturated compound M is a chain compound with an acrylic structure and unsaturated carbon bonds.

[0174] R65 can be any of hydrogen (H) or an alkyl group; there are no particular restrictions. Details regarding alkyl groups are provided above. R66 can be any of an alkenyl group; there are no particular restrictions. Details regarding alkenyl groups are provided above.

[0175] (Second unsaturated compound N)

[0176] As shown in formula (18), the second unsaturated compound N is a chain compound with a maleic acid-type structure and unsaturated carbon bonds.

[0177] R67 and R68 can both be alkenyl groups; there are no specific restrictions. Details regarding alkenyl groups are as described above.

[0178] (Second unsaturated compound O)

[0179] As shown in formula (19), the second unsaturated compound O is a chain compound having ether bonds and unsaturated carbon bonds.

[0180] R69 and R70 can both be alkenyl groups; there are no specific restrictions. Details regarding alkenyl groups are as described above.

[0181] (Specific examples of second unsaturated compounds)

[0182] Specific examples of the second unsaturated compound A are compounds represented by formula (5-1), etc. Specific examples of the second unsaturated compound B are compounds represented by formula (6-1), etc. Specific examples of the second unsaturated compound C are compounds represented by formulas (7-1) and (7-2), etc. Specific examples of the second unsaturated compound D are compounds represented by formula (8-1), etc.

[0183] Specific examples of the second unsaturated compound E are compounds represented by formula (9-1), etc. Specific examples of the second unsaturated compound F are compounds represented by formula (10-1), etc. Specific examples of the second unsaturated compound G are compounds represented by formulas (11-1) to (11-3), etc. Specific examples of the second unsaturated compound H are compounds represented by formula (12-1), etc.

[0184] Specific examples of the second unsaturated compound I are compounds represented by formula (13-1), etc. Specific examples of the second unsaturated compound J are compounds represented by formula (14-1), etc. Specific examples of the second unsaturated compound K are compounds represented by formulas (15-1) to (15-3), etc. Specific examples of the second unsaturated compound L are compounds represented by formulas (16-1) and (16-2), etc.

[0185] Specific examples of the second unsaturated compound M are compounds represented by formulas (17-1) and (17-2), respectively. Specific examples of the second unsaturated compound N are compounds represented by formula (18-1), etc. Specific examples of the second unsaturated compound O are compounds represented by formula (19-1), etc.

[0186] [Chemical Formula 7]

[0187] Transformation 7

[0188]

[0189] [Chemical Formula 8]

[0190] Transformation 8

[0191]

[0192] More specifically, the compound shown in formula (5-1) is divinyl sulfone.

[0193] The compound shown in formula (6-1) is 3,9-divinylspirobis(m-dioxane).

[0194] The compound shown in formula (7-1) is p-divinylbenzene. The compound shown in formula (7-2) is m-divinylbenzene.

[0195] The compound shown in formula (8-1) is 1,2,4-trivinylcyclohexane.

[0196] The compound shown in formula (9-1) is diethylene glycol divinyl ether.

[0197] The compound shown in formula (10-1) is divinyl adipate.

[0198] The compound represented by formula (11-1) is ethylene glycol dimethacrylate. The compound represented by formula (11-2) is triethylene glycol dimethacrylate. The compound represented by formula (11-3) is tetraethylene glycol dimethacrylate.

[0199] The compound shown in formula (12-1) is trimenyl pyromellitic acid.

[0200] The compound shown in formula (13-1) is diallyl propyl isocyanurate.

[0201] The compound shown in formula (14-1) is 1,3,5-triacryloylhexahydro-1,3,5-triazine.

[0202] The compound represented by formula (15-1) is 1,4-bis(maleimide)butane. The compound represented by formula (15-2) is 1,6-bis(maleimide)hexane. The compound represented by formula (15-3) is N,N-1,3-phenylene dimaleimide.

[0203] The compound shown in formula (16-1) is pentaerythritol tetraacrylate. The compound shown in formula (16-2) is pentaerythritol triacrylate.

[0204] The compound represented by formula (17-1) is vinyl methacrylate. The compound represented by formula (17-2) is allyl acrylate.

[0205] The compound represented by formula (18-1) is diallyl maleate.

[0206] The compound shown in formula (19-1) is diallyl ether.

[0207] (Content of the second unsaturated compound)

[0208] The content of the second unsaturated compound in the electrolyte is not particularly limited, but is preferably 0.01% to 1% by weight. This is because the durability of the coating is sufficiently improved. In cases where the electrolyte contains two or more second unsaturated compounds, the content described herein is the sum of the contents of each second unsaturated compound.

[0209] [solvent]

[0210] The solvent includes any one or more non-aqueous solvents (organic solvents), and the electrolyte containing such non-aqueous solvents is called a non-aqueous electrolyte. The non-aqueous solvent is an ester or ether, and more specifically, a carbonate compound, a carboxylic acid ester compound, or a lactone compound.

[0211] Carbonate compounds include cyclic carbonates and chain carbonates. Specific examples of cyclic carbonates are ethylene carbonate and propylene carbonate, while specific examples of chain carbonates are dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0212] Carboxylic acid esters are chain-like carboxylic acid esters. Specific examples of chain-like carboxylic acid esters include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, and ethyl trimethylacetate.

[0213] Lactone compounds include lactones. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0214] It should be noted that, in addition to the lactone compounds mentioned above, ethers can also be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, and 1,4-dioxane, etc.

[0215] The non-aqueous solvent is preferably a high dielectric constant solvent having a relative dielectric constant of 20 or higher at temperatures ranging from -30°C to 60°C. This is because high battery capacity can be obtained when the electrolyte is used in a secondary battery. This high dielectric constant solvent is the aforementioned cyclic carbonates and lactones, etc. It should be noted that the aforementioned chain carbonates and chain carboxylic esters, etc., are low dielectric constant solvents having a lower relative dielectric constant than the high dielectric constant solvent.

[0216] The high dielectric constant solvent includes a lactone, and the ratio R of the weight W2 of the lactone to the weight W1 of the high dielectric constant solvent is more preferably 30% to 100% by weight. This is because the discharge capacity is not easily reduced even when charging and discharging a secondary battery using an electrolyte. This ratio R is calculated based on the formula R (wt%) = (W2 / W1) × 100.

[0217] [Electrolyte salts]

[0218] Electrolyte salts are light metal salts such as lithium salts. Specific examples of lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium tri(trifluoromethanesulfonyl)methylide (LiC(CF3SO2)3), and lithium bis(oxalate)borate (LiB(C2O4)2), etc.

[0219] There is no particular limitation on the content of the electrolyte salt, but specifically, it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent. This is because high ionic conductivity can be obtained.

[0220] [additive]

[0221] It should be noted that the electrolyte may further contain any one or more of the additives.

[0222] Specifically, the additive is one or both of unsaturated cyclic carbonates and halocyclic carbonates. This is because, when the electrolyte is used in a secondary battery, it can suppress the decomposition reaction of the electrolyte. The content of each of the unsaturated cyclic carbonates and halocyclic carbonates in the electrolyte can be arbitrarily set.

[0223] Unsaturated cyclic carbonates are cyclic carbonates containing unsaturated bonds (carbon-to-carbon double bonds). Specific examples of unsaturated cyclic carbonates include vinylene carbonate (1,3-dioxacyclopenten-2-one), vinylene carbonate (4-vinyl-1,3-dioxacyclopenten-2-one), and methylene ethylene carbonate (4-methylene-1,3-dioxacyclopenten-2-one).

[0224] Halogenated cyclic carbonates are cyclic carbonates containing halogens as constituent elements; that is, compounds obtained by replacing one or more hydrogen atoms in a cyclic carbonate with halogen groups. The type of halogen group is not particularly limited, but specifically, it can be any one or more of fluorine, chloro, bromine, and iodine groups. Specific examples of halogenated cyclic carbonates include fluoroethylene carbonate (4-fluoro-1,3-dioxolane-2-one) and difluoroethylene carbonate (4,5-difluoro-1,3-dioxolane-2-one).

[0225] In addition, the additives are any one or more of sulfonates, sulfates, sulfites, dicarboxylic anhydrides, disulfonic anhydrides, and sulfonic acid carboxylic anhydrides. This is because, when the electrolyte is used in a secondary battery, it can suppress the decomposition reaction of the electrolyte. The content of each of the sulfonates, sulfates, sulfites, dicarboxylic anhydrides, disulfonic anhydrides, and sulfonic acid carboxylic anhydrides in the electrolyte can be arbitrarily set.

[0226] Specific examples of sulfonates are 1,3-propanesulfonyl lactone, 1-propen-1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, 2,4-butanesulfonyl lactone, and propargyl methanesulfonate.

[0227] Specific examples of sulfate esters include 1,3,2-dioxazothiophene 2,2-dioxide, 1,3,2-dioxothiacyclohexane 2,2-dioxide, and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxazothiophene.

[0228] Specific examples of sulfites include 1,3-propanesulfonyl lactone, 1-propen-1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, 2,4-butanesulfonyl lactone, and propargyl methanesulfonate. Specific examples of sulfites include 1,3,2-dioxazolthiophene 2-oxide and 4-methyl-1,3,2-dioxazolthiophene 2-oxide.

[0229] Specific examples of dicarboxylic anhydrides include 1,4-dioxane-2,6-dione, succinic anhydride, and glutaric anhydride.

[0230] Specific examples of disulfonic anhydrides include 1,2-ethanedisulfonic anhydride, 1,3-propanedisulfonic anhydride, and hexafluoro-1,3-propanedisulfonic anhydride.

[0231] Specific examples of sulfonic acid carboxylic anhydrides include 2-sulfobenzoic anhydride and 2,2-dioxothiazophen-5-one.

[0232] In addition, the other compounds are nitrile compounds. This is because, when the electrolyte is used in a secondary battery, the decomposition reaction of the electrolyte can be suppressed. The content of nitrile compounds in the electrolyte can be arbitrarily set.

[0233] This nitrile compound is a compound having one or more cyano groups (-CN). Specific examples of nitrile compounds are octanoic acid, benzyl nitrile, phthalonitrile, succinic acid, glutaronitrile, adiponitrile, sebaconitrile, 1,3,6-hexanetrionitrile, 3,3'-oxydipropionitrile, 3-butoxypropionitrile, ethylene glycol dipropionitrile ether, 1,2,2,3-tetracyanopropane, tetracyanopropane, fumaric acid, 7,7,8,8-tetracyanoquinone dimethyl ether, cyclopentaneformitrile, 1,3,5-cyclohexanetrionitrile, and 1,3-bis(dicyanomethylene)indane, etc.

[0234] <1-2. Manufacturing Method>

[0235] In the manufacture of an electrolyte, an electrolyte salt is added to a solvent, and then a first unsaturated compound and a second unsaturated compound are added to the solvent. Thus, since the electrolyte salt, the first unsaturated compound, and the second unsaturated compound are dispersed or dissolved in the solvent, an electrolyte is prepared.

[0236] <1-3. Functions and Effects>

[0237] The electrolyte contains both a first unsaturated compound and a second unsaturated compound.

[0238] In this case, as described above, the durability of the coating formed on the electrode surface is improved in a secondary battery using an electrolyte compared to a case where the electrolyte contains only one of the first unsaturated compound and the second unsaturated compound.

[0239] Specifically, the first unsaturated compound, which is a cyclic compound incorporating unsaturated carbon bonds (intercarbon double bonds) into a lactone-type ring structure, possesses the property of forming a coating on the electrode surface through decomposition and reaction during charging and discharging. Thus, when the electrolyte contains the first unsaturated compound, the electrode surface is protected by this coating. Consequently, on the reactive electrode surface, the decomposition reaction of the electrolyte is suppressed, and therefore the discharge capacity is less likely to decrease.

[0240] However, the coating derived from the first unsaturated compound has high solvent affinity and therefore low solvent resistance. In this case, if repeated charge-discharge cycles occur, the coating derived from the first unsaturated compound is easily decomposed, thus reducing the coverage of the electrode formed by this coating. Consequently, if the secondary battery is used repeatedly, the decomposition reaction of the electrolyte cannot be adequately suppressed, and the discharge capacity tends to decrease.

[0241] The same applies to the case where the electrolyte contains only the second unsaturated compound. That is, when the electrolyte contains only the second unsaturated compound, similarly to the case where the electrolyte contains only the first unsaturated compound, the coating derived from the second unsaturated compound has low solvent resistance and cannot sufficiently suppress the decomposition reaction of the electrolyte, thus the discharge capacity tends to decrease during repeated charge and discharge.

[0242] In contrast, when the electrolyte contains both a first unsaturated compound and a second unsaturated compound, the solvent resistance of the first unsaturated compound is dramatically improved due to the synergistic effect of the two compounds. Therefore, even with repeated charge-discharge cycles, the coating derived from the first unsaturated compound is less prone to decomposition, thus easily maintaining the coating's coverage of the electrode. Consequently, even with repeated use of the rechargeable battery, electrolyte decomposition reactions can be sufficiently suppressed, thus minimizing the reduction in discharge capacity.

[0243] Based on the above, when the electrolyte contains both a first unsaturated compound and a second unsaturated compound, compared to when the electrolyte contains only one of the first and second unsaturated compounds, the decomposition reaction of the electrolyte can be sufficiently suppressed. Therefore, even with repeated charge and discharge cycles, the discharge capacity is less likely to decrease. Thus, excellent cycle characteristics can be obtained in secondary batteries containing an electrolyte.

[0244] In particular, in this embodiment, if the first unsaturated compound D includes any one or more of the compounds represented by each of formulas (21) to (24), the durability of the coating can be sufficiently improved, thereby sufficiently suppressing the decomposition reaction of the electrolyte, and thus achieving a higher effect.

[0245] Furthermore, if the content of the first unsaturated compound in the electrolyte is 0.1% to 2% by weight and the content of the second unsaturated compound in the electrolyte is 0.01% to 1% by weight, the durability of the coating can be significantly improved, thereby effectively suppressing the decomposition reaction of the electrolyte and thus achieving a higher effect.

[0246] In addition, if the solvent (high dielectric constant solvent) contains lactone and the proportion R is 30% to 100% by weight, a high battery capacity can be obtained, and a high discharge capacity can be obtained even with repeated charge and discharge, thus achieving better performance.

[0247] Furthermore, if the electrolyte further contains one or both of unsaturated cyclic carbonates and halocyclic carbonates, the decomposition reaction of the electrolyte can be further suppressed, thus achieving even better results.

[0248] Furthermore, if the electrolyte further contains any one or more of sulfonates, sulfates, sulfites, dicarboxylic anhydrides, disulfonic anhydrides, and sulfonic acid anhydrides, the decomposition reaction of the electrolyte can be further suppressed, thus achieving a higher effect.

[0249] Furthermore, if the electrolyte further contains nitrile compounds, the decomposition reaction of the electrolyte can be further suppressed, thus achieving even better results.

[0250] <2. Secondary batteries>

[0251] Next, we will explain the secondary battery that uses the electrolyte described above.

[0252] The secondary battery described here is a secondary battery in which battery capacity is obtained by the intercalation and deintercalation of electrode reactants. It has a positive electrode, a negative electrode, and an electrolyte in liquid form. In this secondary battery, in order to prevent the electrode reactants from depositing on the surface of the negative electrode during charging, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. That is, 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.

[0253] There are no particular restrictions on the types of substances used in the electrode reactions; specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

[0254] The following example uses lithium as the electrode reactant. A secondary battery that utilizes the insertion and extraction of lithium to obtain battery capacity is called a lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is inserted and extracted in an ionic state.

[0255] <2-1. Composition>

[0256] Figure 1 The three-dimensional structure of a secondary battery is shown. Figure 2 It shows Figure 1 The cross-sectional structure of the battery element 20 is shown. However, Figure 1 The outer packaging film 10 and the battery element 20 are shown in a state where they are separated from each other, and the cross-section of the battery element 20 along the XZ plane is shown by dashed lines. Figure 2 Only a portion of battery element 20 is shown.

[0257] like Figure 1 as well as Figure 2 As shown, the secondary battery includes an outer packaging film 10, a battery element 20, a positive electrode lead 31 and a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminated film type secondary battery that uses a flexible (or pliable) outer packaging film 10.

[0258] [Outer packaging film and sealing film]

[0259] like Figure 1 As shown, the outer packaging film 10 is a flexible outer packaging component that houses the battery element 20, and has a bag-like structure that is sealed when the battery element 20 is housed inside. Therefore, the outer packaging film 10 houses the positive electrode 21, the negative electrode 22, and the electrolyte, which will be described later.

[0260] Here, the outer packaging film 10 is a film-shaped component that can be folded along the folding direction F. A recess 10U (so-called deep stretch portion) for accommodating the battery element 20 is provided on the outer packaging film 10.

[0261] Specifically, the outer packaging film 10 is a laminated film consisting of three layers stacked sequentially from the inside: a welding layer, a metal layer, and a surface protective layer. When the outer packaging film 10 is folded, the outer peripheries of the opposing welding layers are welded together. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon.

[0262] In addition, there is no particular limitation on the structure (number of layers) of the outer packaging film 10; it can be 1 layer, 2 layers, or more than 4 layers.

[0263] Sealing film 41 is inserted between outer packaging film 10 and positive lead 31, and sealing film 42 is inserted between outer packaging film 10 and negative lead 32. Alternatively, one or both of sealing films 41 and 42 may be omitted.

[0264] The sealing film 41 is a sealing component that prevents external air from entering the interior of the outer packaging film 10. Furthermore, the sealing film 41 contains a polymer compound such as a polyolefin, which has a tight adhesion to the positive electrode lead 31. This polyolefin is polypropylene, etc.

[0265] The structure of the sealing membrane 42 is the same as that of the sealing membrane 41, except that it is a sealing component that adheres tightly to the negative electrode lead 32. That is, the sealing membrane 42 contains a polymer compound such as polyolefin that adheres tightly to the negative electrode lead 32.

[0266] [Battery Components]

[0267] like Figure 1 as well as Figure 2 As shown, the battery element 20 is a power generation element including a positive electrode 21, a negative electrode 22, a separator 23 and an electrolyte (not shown), and is housed inside the outer packaging film 10.

[0268] The battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23, and the positive electrode 21, the negative electrode 22, and the separator 23 are wound around a winding axis P, which is an imaginary axis extending along the Y-axis direction. Thus, the positive electrode 21 and the negative electrode 22 are wound relative to each other via the separator 23.

[0269] The three-dimensional shape of the battery element 20 is not particularly limited. Here, since the battery element 20 is flat, the cross-section of the battery element 20 intersecting the winding axis P (the cross-section along the XZ plane) has a flat shape defined by the major axis J1 and the minor axis J2. The major axis J1 is an imaginary axis extending in the X-axis direction and having a length greater than the minor axis J2, while the minor axis J2 is an imaginary axis extending in the Z-axis direction intersecting the X-axis direction and having a length less than the major axis J1. Here, the three-dimensional shape of the battery element 20 is a flattened cylindrical shape, therefore the cross-sectional shape of the battery element 20 is a flattened, approximately elliptical shape.

[0270] (positive electrode)

[0271] like Figure 2 As shown, the positive electrode 21 includes a positive current collector 21A and a positive active material layer 21B.

[0272] The positive current collector 21A has one side with a positive active material layer 21B disposed thereon. The positive current collector 21A contains a conductive material such as a metal, which is aluminum, etc.

[0273] Here, the positive electrode active material layer 21B is disposed on both sides of the positive electrode current collector 21A, and includes any one or more positive electrode active materials capable of lithium intercalation and deintercalation. Alternatively, the positive electrode active material layer 21B may be disposed only on one side of the positive electrode current collector 21A, opposite to the negative electrode 22. Furthermore, the positive electrode active material layer 21B may further include a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited; specifically, it may be any one or more methods such as coating.

[0274] There are no particular limitations on the type of positive electrode active material; specifically, it can be lithium-containing compounds. These lithium-containing compounds are compounds that contain one or more transition metal elements as constituent elements along with lithium, and may further contain one or more other elements as constituent elements. The other elements can be any elements other than lithium and transition metal elements; there are no particular limitations. Specifically, they must belong to groups 2 to 15 of the long-period periodic table. There are no particular limitations on the type of lithium-containing compound; specifically, it can be oxides, phosphoric acid compounds, silicate compounds, and borate compounds, etc.

[0275] Specific examples of oxides are LiNiO2, LiCoO2, and LiCo. 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co0.15 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 phosphoric acid compounds are LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0276] The positive electrode binder includes any one or more of synthetic rubbers and polymeric compounds. Synthetic rubbers include styrene-butadiene rubber, fluorinated rubbers, and ethylene propylene diene monomer (EPDM) rubber. Polymeric compounds include polyvinylidene fluoride (PVDF), polyimide, and carboxymethyl cellulose.

[0277] The positive electrode conductive agent includes any one or more conductive materials such as carbon materials, including graphite, carbon black, acetylene black, and Ketjen black. Alternatively, the conductive material can also be a metal or a polymer compound.

[0278] (negative electrode)

[0279] like Figure 2 As shown, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0280] The negative current collector 22A has one side with a negative active material layer 22B disposed thereon. The negative current collector 22A contains a conductive material such as a metal, which is copper, etc.

[0281] Here, the negative electrode active material layer 22B is disposed on both sides of the negative electrode current collector 22A, and includes any one or more negative electrode active materials capable of lithium insertion / extraction. Alternatively, the negative electrode active material layer 22B may be disposed only on one side of the negative electrode current collector 22A on the side opposite to the positive electrode 21. Furthermore, the negative electrode active material layer 22B may further include a negative electrode binder and a negative electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited; specifically, it can be any one or more of the following: coating method, vapor phase method, liquid phase method, thermal spraying method, and sintering method.

[0282] The type of negative electrode active material is not particularly limited, but specifically it can be one or both of carbon materials and metallic materials. This is because high energy density can be obtained. Carbon materials include easily graphitized carbon, difficult-to-graphitize carbon, and graphite (natural and artificial graphite). Metallic materials are a general term for materials containing one or more metallic elements and half-metallic elements that can form alloys with lithium as constituent elements. These metallic elements and half-metallic elements are one or both of silicon and tin. Metallic materials can be monomers, alloys, compounds, mixtures of two or more of them, or materials containing two or more of their phases. Specific examples of metallic materials are TiSi2 and SiO. x (0 < x ≤ 2, or 0.2 < x < 1.4), etc.

[0283] The 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.

[0284] (Diaphragm)

[0285] like Figure 2 As shown, the separator 23 is an insulating porous membrane located between the positive electrode 21 and the negative electrode 22, which prevents contact (short circuit) between the positive electrode 21 and the negative electrode 22 while allowing lithium ions to pass through. The separator 23 contains a polymer compound such as polyethylene.

[0286] (electrolyte)

[0287] The electrolyte is respectively immersed in the positive electrode 21, the negative electrode 22, and the separator 23, and has the above-described structure. That is, the electrolyte contains a solvent, an electrolyte salt, and both a first unsaturated compound and a second unsaturated compound.

[0288] [Positive and negative leads]

[0289] like Figure 1 As shown, the positive lead 31 is the positive terminal connected to the battery element 20 (positive electrode 21), and more specifically, to the positive current collector 21A. The positive lead 31 extends from the inside of the outer packaging film 10 to the outside and contains a conductive material such as aluminum. The shape of the positive lead 31 is not particularly limited; specifically, it can be any of the following: a thin plate shape or a mesh shape.

[0290] like Figure 1As shown, the negative electrode lead 32 is the negative terminal connected to the battery element 20 (negative electrode 22), and more specifically, to the negative current collector 22A. This negative electrode lead 32 extends from the inside of the outer packaging film 10 to the outside and contains a conductive material such as copper. Here, the lead-out direction of the negative electrode lead 32 is the same as that of the positive electrode lead 31. It should be noted that the details regarding the shape of the negative electrode lead 32 are the same as the details regarding the shape of the positive electrode lead 31.

[0291] <2-2. Actions>

[0292] During charging, lithium is deintercalated from the positive electrode 21 in the battery element 20 and intercalated into the negative electrode 22 via the electrolyte. Conversely, during discharging, lithium is deintercalated from the negative electrode 22 in the battery element 20 and intercalated into the positive electrode 21 via the electrolyte. During these charging and discharging processes, lithium is intercalated and deintercalated in an ionic state.

[0293] <2-3. Manufacturing Method>

[0294] In the case of manufacturing a secondary battery, a positive electrode 21 and a negative electrode 22 were fabricated through the steps described below. Then, the positive electrode 21 and the negative electrode 22 were used together with an electrolyte to fabricate the secondary battery. It should be noted that the steps for preparing the electrolyte are as described above.

[0295] [The production of the positive electrode]

[0296] First, a mixture of positive electrode active material, positive electrode binder, and positive electrode conductive agent (positive electrode paste) is added to a solvent to prepare a paste-like positive electrode paste slurry. This solvent can be an aqueous solvent or an organic solvent. Next, the positive electrode paste slurry is coated onto both sides of the positive electrode current collector 21A, thereby forming a positive electrode active material layer 21B. Subsequently, the positive electrode active material layer 21B can be compressed and molded using a roller press or similar device. In this case, the positive electrode active material layer 21B can be heated, or the compression molding process can be repeated multiple times. Thus, the positive electrode 21 is manufactured.

[0297] [Making the negative electrode]

[0298] The negative electrode 22 is formed using the same steps as those described for the positive electrode 21. Specifically, first, a mixture (negative electrode paste) consisting of a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent is added to a solvent to prepare a paste-like negative electrode paste slurry. Next, the negative electrode paste slurry is coated onto both sides of the negative electrode current collector 22A to form a negative electrode active material layer 22B. Subsequently, the negative electrode active material layer 22B may be compressed and molded. Thus, the negative electrode 22 is manufactured.

[0299] (Assembly of a secondary battery)

[0300] First, the positive lead 31 is connected to the positive electrode 21 (positive current collector 21A) using a welding method or the like, and the negative lead 32 is connected to the negative electrode 22 (negative current collector 22A).

[0301] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via the separator 23, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to form a wound body. This wound body has the same structure as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with electrolyte. Next, the wound body is pressed using a press or the like to form a flat shape.

[0302] Next, the wound body is housed inside the recess 10U, and then the outer packaging film 10 (welded layer / metal layer / surface protective layer) is folded so that the outer packaging films 10 are facing each other. Next, using a heat fusion method or the like, the outer peripheral portions of two sides of the facing outer packaging films 10 (welded layers) are joined together, thereby housing the wound body inside the bag-shaped outer packaging film 10.

[0303] Finally, electrolyte is injected into the inside of the pouch-shaped outer packaging film 10, and then the outer periphery of the remaining edge of the outer packaging film 10 (welded layer) is joined together using a heat fusion method or the like. In this case, sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32. Thus, electrolyte is impregnated into the wound body, thereby creating a battery element 20 as a wound electrode body, and the battery element 20 is sealed inside the pouch-shaped outer packaging film 10, thereby assembling a secondary battery.

[0304] (Stabilization of secondary batteries)

[0305] The assembled secondary battery is charged and discharged. Various conditions, such as ambient temperature, number of charge / discharge cycles, and charge / discharge conditions, can be arbitrarily set. As a result, a coating is formed on the surface of both the positive electrode 21 and the negative electrode 22, thereby stabilizing the state of the secondary battery electrochemically. Thus, a laminated film type secondary battery using the outer packaging film 10 is completed.

[0306] <2-4. Functions and Effects>

[0307] The secondary battery described above contains the electrolyte. In this case, for the reasons stated above, the decomposition reaction of the electrolyte can be sufficiently suppressed, and therefore the discharge capacity is not easily reduced even after repeated charge-discharge cycles. Therefore, excellent cycle characteristics can be obtained.

[0308] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the insertion and extraction of lithium, thus achieving higher performance.

[0309] The other functions and effects of this secondary battery are the same as those of the electrolyte described above.

[0310] <3. Variations>

[0311] As explained below, the structure of the secondary battery described above can be modified appropriately. However, any two or more of the variations described below can also be combined with each other.

[0312] [Variation Example 1]

[0313] A septum 23 was used as a porous membrane. However, although not specifically illustrated here, a laminated septum comprising layers of polymer compounds may be used instead of the porous membrane 23.

[0314] Specifically, the laminated separator comprises a porous membrane with one and two faces and a polymer compound layer disposed on one or both faces of the porous membrane. This is because, due to the improved adhesion of the separator to the positive electrode 21 and the negative electrode 22, the positional displacement of the battery element 20 is less likely to occur. Therefore, even if electrolyte decomposition reactions occur, the secondary battery is less likely to expand. The polymer compound layer comprises a polymer compound such as polyvinylidene fluoride (PVDF). This is because PVDF and the like have excellent physical strength and electrochemical stability.

[0315] It should be noted that one or both of the porous membrane and the polymer compound layer may contain any one or more types of insulating particles. This is because multiple insulating particles dissipate heat when the secondary battery heats up, thus improving the safety (heat resistance) of the secondary battery. Insulating particles include inorganic particles and resin particles. Specific examples of inorganic particles include alumina, aluminum nitride, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, and zirconium oxide. Specific examples of resin particles include acrylic resin and styrene resin.

[0316] In the case of fabricating a layered membrane, a precursor solution containing a polymer compound and a solvent is prepared, and then the precursor solution is coated onto one or both sides of the porous membrane. In this case, multiple insulating particles can also be added to the precursor solution as needed.

[0317] With the use of this layered separator, lithium ions can also move between the positive electrode 21 and the negative electrode 22, thus achieving the same effect.

[0318] [Variation Example 2]

[0319] An electrolyte solution, which is a liquid electrolyte, was used. However, although not specifically illustrated here, an electrolyte layer, which is a gel electrolyte, can also be used instead of the electrolyte solution.

[0320] In the battery element 20 using an electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23 and an electrolyte layer, and the positive electrode 21, the negative electrode 22, the separator 23 and the electrolyte layer are wound around each other. The electrolyte layer is located between the positive electrode 21 and the separator 23, and between the negative electrode 22 and the separator 23.

[0321] Specifically, the electrolyte layer comprises an electrolyte and a polymer compound, and the electrolyte is held in place by the polymer compound. This is to prevent leakage of the electrolyte. The composition of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. In the case of forming the electrolyte layer, a precursor solution comprising the electrolyte, the polymer compound, and a solvent is prepared, and then the precursor solution is coated onto one or both sides of the positive electrode 21 and the negative electrode 22, respectively.

[0322] When this electrolyte layer is used, lithium ions can also move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, thus achieving the same effect.

[0323] <4. Uses of Secondary Batteries>

[0324] There are no particular limitations on the uses (application examples) of secondary batteries. Secondary batteries used as a power source can be the main power source for electronic devices and electric vehicles, or they can be an auxiliary power source. The main power source is the power source used preferentially, regardless of the availability of other power sources. An auxiliary power source is a power source used in place of the main power source, or a power source switched from the main power source.

[0325] Specific examples of applications for rechargeable batteries include: electronic devices such as camcorders, digital still cameras, mobile phones, laptops, stereo headphones, portable radios, and portable information terminals; backup power supplies and storage devices such as memory cards; power tools such as electric drills and chainsaws; battery packs integrated into 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 pre-store power in preparation for emergencies. In these applications, one or multiple rechargeable batteries can be used.

[0326] Battery packs can use single cells or battery packs. Electric vehicles are vehicles that operate (drive) using a secondary battery as a power source, and can also be hybrid vehicles that have a power source other than the secondary battery. In household electricity storage systems, electricity stored in a secondary battery that serves as an electricity storage source can be used to operate household electrical products, etc.

[0327] Here, we will specifically illustrate one application example of a secondary battery. The structure of the application example described below is only one example and can therefore be modified as appropriate.

[0328] Figure 3 This describes the modular structure of the battery pack. The battery pack described here is a pouch cell that uses a secondary battery and is used in electronic devices such as smartphones.

[0329] like Figure 3 As shown, the battery pack includes 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.

[0330] The power supply 51 includes a secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. Since the power supply 51 can be connected to an external source through the positive terminal 53 and the negative terminal 54, it can be charged and discharged. The circuit board 52 includes a control unit 56, a switch 57, a thermistor element (PTC element) 58, and a temperature detection unit 59. Alternatively, the PTC element 58 may be omitted.

[0331] The control unit 56 includes a central processing unit (CPU) and memory, etc., and controls the operation of the battery pack as a whole. The control unit 56 detects and controls the usage status of the power supply 51 as needed.

[0332] It should be noted that when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or the over-discharge detection voltage, the control unit 56 cuts off the switch 57 to prevent the charging current from flowing through the current path of the power supply 51. The overcharge detection voltage is not particularly limited, but is specifically 4.2V ± 0.05V, and the over-discharge detection voltage is also not particularly limited, but is specifically 2.4V ± 0.1V.

[0333] Switch 57 includes a charging control switch, a discharging control switch, a charging diode, and a discharging diode, etc., and switches the connection between power supply 51 and external devices according to the instructions of control unit 56. Switch 57 includes a field-effect transistor (MOSFET) using metal-oxide-semiconductor, and the charging and discharging current is detected based on the on-resistance of switch 57.

[0334] 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 temperature measurement result to the control unit 56. The temperature measurement result measured by the temperature detection unit 59 is used for charging and discharging control by the control unit 56 when abnormal heating occurs, and for correction processing by the control unit 56 when calculating the remaining capacity.

[0335] Example

[0336] The embodiments of this technology are described below.

[0337] <Experimental Examples 1-1 to 1-37>

[0338] As described below, a secondary battery was fabricated, and its battery characteristics were then evaluated.

[0339] [Making a Second-hand Battery]

[0340] The following steps were used to create Figure 1 as well as Figure 2 The image shows a laminated film type lithium-ion secondary battery.

[0341] (The production of the positive electrode)

[0342] First, 91 parts by mass of the positive electrode active material (LiCoO2 as a lithium-containing compound (oxide)), 3 parts by mass of the positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of the positive electrode conductive agent (graphite) are mixed together to prepare a positive electrode mixture. Next, the positive electrode mixture is added to a solvent (N-methyl-2-pyrrolidone as an organic solvent), and the organic solvent is stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated onto both sides of the positive electrode current collector 21A (a strip of aluminum foil with a thickness of 12 μm) using a coating device, and then the positive electrode mixture slurry is dried to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B is compressed and molded using a roller press. Thus, the positive electrode 21 is produced.

[0343] (Making the negative electrode)

[0344] First, 93 parts by mass of the negative electrode active material (artificial graphite as a carbon material) and 7 parts by mass of the negative electrode binder (polyvinylidene fluoride) are mixed together to prepare a negative electrode mixture. Next, the negative electrode mixture is added to a solvent (N-methyl-2-pyrrolidone as an organic solvent), and the organic solvent is stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is coated onto both sides of the negative electrode current collector 22A (a strip of copper foil with a thickness of 15 μm) using a coating device, and then the negative electrode mixture slurry is dried to form a negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B is compressed and molded using a roller press. Thus, the negative electrode 22 is produced.

[0345] (Preparation of electrolyte)

[0346] An electrolyte salt (LiPF6 as a lithium salt) was added to a solvent, and the solvent was then stirred. γ-Butyrolactone (GBL) was used as a high-dielectric-constant solvent (lactone), ethylene carbonate (EC) was used as a high-dielectric-constant solvent (cyclic carbonate), and dimethyl carbonate (DMC) was used as a low-dielectric-constant solvent (chain carboxylic acid ester). The ratio R (wt%) was 50 wt% by making the solvent mixing ratio (GBL∶EC∶DMC) = 10∶10∶80. The content of the electrolyte salt relative to the solvent was 1.2 mol / kg. Next, the first unsaturated compound and the second unsaturated compound were added to the solvent containing the electrolyte salt, and the solvent was stirred. Thus, an electrolyte was prepared.

[0347] The types of the first unsaturated compound and its content (wt%) in the electrolyte, and the types of the second unsaturated compound and its content (wt%) in the electrolyte are shown in Table 1 and Table 2.

[0348] (Assembly of a secondary battery)

[0349] First, the aluminum positive lead 31 is soldered to the positive electrode 21 (positive current collector 21A), and the copper negative lead 32 is soldered to the negative electrode 22 (negative current collector 22A).

[0350] Next, the positive electrode 21 and the negative electrode 22 are stacked together via a separator 23 (a microporous polyethylene membrane with a thickness of 15 μm), and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to create a wound body. Next, the wound body is pressed using a press to form a flat wound body.

[0351] Next, the outer packaging film 10 is folded by clamping the coil housed in the recess 10U. The outer packaging film 10 is an aluminum laminate film in which a welding layer (30 μm thick polypropylene film), a metal layer (40 μm thick aluminum foil), and a surface protective layer (25 μm thick nylon film) are layered sequentially from the inside. Next, the coil is housed inside the bag-shaped outer packaging film 10 by thermally fusing the outer periphery of two sides of the outer packaging film 10 (welding layer) together.

[0352] Finally, electrolyte is injected into the interior of the pouch-shaped outer packaging film 10, and then the outer periphery of the remaining edge of the outer packaging film 10 (welded layer) is thermally fused together under reduced pressure. In this case, a sealing film 41 (a polypropylene film with a thickness of 5 μm) is inserted between the outer packaging film 10 and the positive electrode lead 31, and a sealing film 42 (a polypropylene film with a thickness of 5 μm) is inserted between the outer packaging film 10 and the negative electrode lead 32. Thus, electrolyte is impregnated into the wound body, thereby forming a battery element 20 as a wound electrode body. Therefore, the battery element 20 is sealed inside the outer packaging film 10, thereby assembling a secondary battery.

[0353] (Stabilization of secondary batteries)

[0354] The secondary battery was subjected to one charge-discharge cycle at room temperature (temperature = 23℃). During charging, a constant current of 0.1C was used until the voltage reached 4.2V, followed by constant voltage charging at that 4.2V until the current reached 0.05C. During discharging, a constant current of 0.1C was used until the voltage reached 3.0V. 0.1C refers to the current value required to fully discharge the battery (theoretical capacity) in 10 hours, and 0.05C refers to the current value required to fully discharge the battery in 20 hours. This completed the laminated film type secondary battery.

[0355] <Comparative Examples 1-1 to 1-3>

[0356] A secondary battery was fabricated using the same steps, except that neither the first nor the second unsaturated compound was used, and its battery characteristics were then evaluated. Alternatively, a secondary battery was fabricated using the same steps, except that only one of the first or the second unsaturated compound was used, and its battery characteristics were then evaluated.

[0357] [Evaluation of Battery Characteristics]

[0358] The battery characteristics (cycle characteristics) of the secondary battery were evaluated, and the results are shown in Table 1 and Table 2.

[0359] In investigating cycle characteristics, the secondary battery was first charged in a high-temperature environment (temperature = 50°C), and then left to rest in the same environment for 3 hours. During charging, it was charged at a constant current of 1C until the voltage reached 4.2V, and then charged at a constant voltage of 4.2V until the current reached 0.05C. 1C refers to the current value required to fully discharge the battery capacity in 1 hour.

[0360] Next, the discharge capacity (discharge capacity of the first cycle) was measured by discharging the secondary battery in the same environment. During discharge, a constant current of 3C was applied until the voltage reached 3.0V. 3C refers to the current value at which the battery capacity is fully discharged in 10 / 3 hours.

[0361] Next, the secondary battery was repeatedly charged and discharged in the same environment until 100 cycles were reached, and the discharge capacity (discharge capacity of the 100th cycle) was measured. The charge and discharge conditions for the 2nd to 100th cycles were the same as those for the 1st cycle.

[0362] Finally, based on the formula that capacity retention (%) = (discharge capacity of the 100th cycle / discharge capacity of the first cycle) × 100, the capacity retention rate, which is used as an indicator to evaluate cycle characteristics, is calculated.

[0363] [Table 1]

[0364]

[0365] [Table 2]

[0366]

[0367] [Inspection]

[0368] As shown in Tables 1 and 2, the capacity retention varies significantly depending on the composition of the electrolyte. Hereinafter, the capacity retention of the electrolyte without either the first unsaturated compound or the second unsaturated compound (Comparative Example 1-1) will be used as a comparison benchmark.

[0369] When the electrolyte contains only the first unsaturated compound (Comparative Examples 1-2), the capacity retention rate increases, and when the electrolyte contains only the second unsaturated compound (Comparative Examples 1-3), the capacity retention rate increases.

[0370] More specifically, when the electrolyte contains only the first unsaturated compound, the capacity retention rate increases by approximately 19%, and when the electrolyte contains only the second unsaturated compound, the capacity retention rate increases by approximately 14%. Therefore, when the electrolyte contains both the first and second unsaturated compounds, the capacity retention rate is expected to increase by approximately 33% (=19%+14%).

[0371] However, in practice, when the electrolyte contains both the first unsaturated compound and the second unsaturated compound (Examples 1-1 to 1-37), the capacity retention rate increases dramatically.

[0372] More specifically, when the electrolyte contains both the first and second unsaturated compounds, the capacity retention rate increases by approximately 52% to approximately 67%. Therefore, contrary to the above prediction, the increase in capacity retention rate (approximately 52% to approximately 67%) is approximately twice the expected value (approximately 33%). It can be assumed that this dramatic increase in capacity retention rate when the electrolyte contains both the first and second unsaturated compounds is due to the synergistic effect of the first and second unsaturated compounds, which significantly inhibits the decomposition reaction of the electrolyte.

[0373] In particular, when the electrolyte contains both a first unsaturated compound and a second unsaturated compound, the capacity retention rate is sufficiently increased when the content of the first unsaturated compound in the electrolyte is 0.1% to 2% by weight and the content of the second unsaturated compound in the electrolyte is 0.01% to 1% by weight.

[0374] <Examples 2-1 to 2-4>

[0375] As shown in Table 3, secondary batteries were fabricated using the same steps, except that unsaturated cyclic carbonates and halocyclic carbonates were added to the electrolyte, respectively. The battery characteristics of the secondary batteries were then evaluated.

[0376] Table 3 shows the types of unsaturated cyclic carbonates and their contents (wt%) in the electrolyte, as well as the types of halogenated cyclic carbonates and their contents (wt%) in the electrolyte. Here, vinylene carbonate (VC) was used as the unsaturated cyclic carbonate, and fluoroethylene carbonate (FEC) was used as the halogenated cyclic carbonate.

[0377] [Table 3]

[0378] The content of the first unsaturated compound is 1.5% by weight, and the content of the second unsaturated compound is 0.2% by weight.

[0379]

[0380] As shown in Table 3, when the electrolyte contains each of the unsaturated cyclic carbonate and the halocyclic carbonate (Examples 2-1 to 2-4), the capacity retention is further increased.

[0381] <Examples 3-1 to 3-18>

[0382] As shown in Tables 4 and 5, secondary batteries were fabricated using the same steps, except that each of the following was added to the electrolyte as an additive: sulfonate, sulfate, sulfite, dicarboxylic anhydride, disulfonic anhydride, and sulfonic acid carboxylic anhydride. The battery characteristics of the secondary batteries were then evaluated.

[0383] The types of sulfonates and their contents (by weight%) in the electrolyte, the types of sulfates and their contents (by weight%) in the electrolyte, the types of sulfites and their contents (by weight%) in the electrolyte, the types of dicarboxylic anhydrides and their contents (by weight%) in the electrolyte, the types of disulfonic anhydrides and their contents (by weight%) in the electrolyte, and the types of sulfonic anhydrides and their contents (by weight%) in the electrolyte are shown in Tables 4 and 5.

[0384] Here, 1,3-propanesulfonyl lactone (PS), 1-propen-1,3-sulfonyl lactone (PRS), 1,4-butanesulfonyl lactone (BS1), 2,4-butanesulfonyl lactone (BS2), and propargyl methanesulfonate (MSP) were used as sulfonates.

[0385] As sulfate esters, 1,3,2-dioxazothiophene 2,2-dioxide (OTO), 1,3,2-dioxothiacyclohexane 2,2-dioxide (OTA) and 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxazothiophene (SOTO) were used.

[0386] As sulfites, 1,3,2-dioxazothiophene 2-oxide (DTO) and 4-methyl-1,3,2-dioxazothiophene 2-oxide (MDTO) were used.

[0387] 1,4-Dioxane-2,6-dione (DOD), succinic anhydride (SA), and glutaric anhydride (GA) were used as dicarboxylic anhydrides.

[0388] As disulfonic anhydrides, 1,2-ethanedisulfonic anhydride (ESA), 1,3-propanedisulfonic anhydride (PSA), and hexafluoro-1,3-propanedisulfonic anhydride (FPSA) were used.

[0389] 2-Sulfobenzoic anhydride (SBA) and 2,2-dioxothiazophen-5-one (DOTO) were used as sulfonic acid carboxylic anhydrides.

[0390] [Table 4]

[0391] The content of the first unsaturated compound is 1.5% by weight, and the content of the second unsaturated compound is 0.2% by weight.

[0392]

[0393] [Table 5]

[0394] The content of the first unsaturated compound is 1.5% by weight, and the content of the second unsaturated compound is 0.2% by weight.

[0395]

[0396] As shown in Tables 4 and 5, when the electrolyte contains each of sulfonate, sulfate, sulfite, dicarboxylic anhydride, disulfonic anhydride and sulfonic acid anhydride (Examples 3-1 to 3-18), the capacity retention is further increased.

[0397] <Examples 4-1 to 4-18>

[0398] As shown in Table 6, secondary batteries were fabricated using the same steps, except that a nitrile compound was added to the electrolyte as an additive. The battery characteristics of the secondary batteries were then evaluated.

[0399] The types of nitrile compounds and their contents (wt%) in the electrolyte are shown in Table 6. Here, the nitrile compounds used are octanoic acid (ON), benzyl nitrile (BN), phthalonitrile (PN), succinic acid (SN), glutaronitrile (GN), adiponitrile (AN), sebaconitrile (SBN), 1,3,6-hexanetrionitrile (HCN), 3,3'-oxydipropionitrile (OPN), 3-butoxypropionitrile (BPN), ethylene glycol dipropionitrile ether (EGPN), 1,2,2,3-tetracyanopropane (TCP), tetracyanoethylene (TCE), fumaric acid (FN), 7,7,8,8-tetracyanoquinone dimethane (TCQ), cyclopentaneformitrile (CPCN), 1,3,5-cyclohexanetrionitrile (CHCN), and 1,3-bis(dicyanomethylene)indane (BCMI).

[0400] [Table 6]

[0401] The content of the first unsaturated compound is 1.5% by weight, and the content of the second unsaturated compound is 0.2% by weight.

[0402]

[0403] As shown in Table 6, when the electrolyte contains nitrile compounds (Examples 4-1 to 4-18), the capacity retention rate is further increased.

[0404] <Examples 5-1 to 5-15>

[0405] As shown in Table 7, except for changing the composition of the solvent, a secondary battery was fabricated using the same steps, and then the battery characteristics of the secondary battery were evaluated.

[0406] The types of solvents, the mixing ratios (content (wt%)) of each solvent, and the proportion R (wt%) are shown in Table 7. Here, propylene carbonate (PC) was newly used as a high dielectric constant solvent (cyclic carbonate), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) as low dielectric constant solvents (chain carbonates), and propyl propionate (PrPr) as a low dielectric constant solvent (chain carboxylic acid ester). In this case, the proportion R was changed by altering the types of solvents and the mixing ratios of each solvent.

[0407] Here, as battery characteristics, not only cycle characteristics (capacity retention) were evaluated, but also additional charge-discharge characteristics were evaluated.

[0408] In investigating additional charge-discharge characteristics, the secondary battery was first subjected to repeated charge-discharge cycles using the same procedures as those used in investigating the cycle characteristics described above, and the discharge capacity of the 100th cycle was measured.

[0409] Next, the secondary battery was charged in the same environment (temperature = 50°C), and then left to rest (rest time = 3 hours). The charging conditions were the same as those of the first cycle. Next, the charged secondary battery was left to rest in a low-temperature environment (temperature = -20°C) (rest time = 3 hours), thereby allowing the charged secondary battery to cool completely to its interior.

[0410] Next, the secondary battery was discharged under the same conditions (temperature = -20°C), and the discharge capacity (discharge capacity of the 101st cycle) was determined. The discharge conditions were the same as those for the first cycle.

[0411] Finally, based on the formula that additional maintenance rate (%) = (discharge capacity of the 101st cycle / discharge capacity of the 100th cycle) × 100, the additional maintenance rate, which is used as an indicator to evaluate the additional charge and discharge characteristics, is calculated.

[0412] [Table 7]

[0413] The content of the first unsaturated compound (formula (1-1)) is 1.5% by weight, and the content of the second unsaturated compound (formula (5-1)) is 0.2% by weight.

[0414]

[0415] As shown in Table 7, the same results as in Table 1 can be obtained even by changing the composition of the solvent. That is, when the electrolyte contains both the first unsaturated compound and the second unsaturated compound, the high capacity retention rate increases. In this case, especially when the ratio R is 30% to 100% (Examples 1-1, etc.), the additional retention rate also increases.

[0416] [Summarize]

[0417] Based on the results shown in Tables 1 to 7, a high capacity retention rate was obtained when the electrolyte contained both the first and second unsaturated compounds. Therefore, excellent cycling characteristics were achieved in the secondary battery.

[0418] The present invention has been described above by listing one implementation method and embodiment, but the structure of the present invention is not limited to the structure described in one implementation method and embodiment, and various modifications are possible.

[0419] Although the laminated film type battery structure has been described, there is no particular limitation on the type of battery structure. Specifically, the battery structure can be cylindrical, square, coin-shaped, or button-shaped, etc.

[0420] Furthermore, the case where the battery element structure is a wound type has been explained, but the type of element structure is not particularly limited. Specifically, the element structure can be a stacked type where the electrodes (positive and negative electrodes) are stacked together, or a zigzag type where the electrodes (positive and negative electrodes) are folded into a Z-shape, etc.

[0421] Furthermore, while the use of lithium as the electrode reactant has been mentioned, it is not specifically limited. Specifically, as described above, the electrode reactant can be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. Additionally, other light metals such as aluminum can also be used as the electrode reactant.

[0422] The effects described in this specification are merely illustrative, and therefore the effects of this technology are not limited to those described herein. Thus, other effects can also be obtained with this technology.

Claims

1. A secondary battery, comprising: positive electrode; Negative electrode; and An electrolyte comprising a solvent, an electrolyte salt, and a combination of at least one of a first unsaturated compound represented by formula (1) and a second unsaturated compound represented by formulas (5) to (16), a combination of a first unsaturated compound represented by formula (2) and a second unsaturated compound represented by formula (5), or a combination of a first unsaturated compound represented by formula (3) and a second unsaturated compound represented by formula (5). R1 through R6 are any one of hydrogen (H), alkyl, acrylate, and methacrylate groups, and at least one of R1 through R6 is either an acrylate group or a methacrylate group. R7 to R14 are any one of hydrogen (H), alkyl, acrylate and methacrylate, and at least one of R7 to R14 is either acrylate or methacrylate. R21 and R22 are alkenyl groups, respectively. R23 and R24 are alkenyl groups, respectively. R25 to R30 are either hydrogen (H) or an alkenyl group, and two or more of R25 to R30 are alkenyl groups. R31 to R36 are either hydrogen (H) or an alkenyl group, and two or more of R31 to R36 are alkenyl groups. R37 is an alkylene group with an ether bond, while R38 and R39 are alkenyl groups, respectively. R40 is an alkylene group, while R41 and R42 are alkenyl groups, respectively. R43 is any one of an alkylene group and an alkylene group having an ether bond, and R44 and R45 are any one of an acrylate group and a methacrylate group, respectively. R46 to R48 are alkenyl groups, respectively. R49 to R51 are any one of alkyl and alkenyl groups, and two or more of R49 to R51 are alkenyl groups. R52 to R54 are alkenyl groups, respectively. R55 is any one of alkylene and arylene. R56 is a tetravalent hydrocarbon group, R57 to R60 are alkylene groups, R61 to R64 are any one of hydroxyl, acrylic, and methacrylic groups, and two or more of R61 to R64 are any one of acrylic and methacrylic groups.

2. The secondary battery according to claim 1, wherein, The content of the first unsaturated compound in the electrolyte is more than 0.1% by weight and less than 2% by weight. The content of the second unsaturated compound in the electrolyte is more than 0.01% by weight and less than 1% by weight.

3. The secondary battery according to claim 1, wherein, The solvent is a high dielectric constant solvent having a relative dielectric constant of 20 or higher at temperatures ranging from -30°C to less than 60°C. The high dielectric constant solvent contains lactones. The weight ratio of the lactone to the weight of the high dielectric constant solvent is more than 30% by weight and less than 100% by weight.

4. The secondary battery according to claim 1, wherein, The electrolyte further comprises at least one of unsaturated cyclic carbonates and halocyclic carbonates.

5. The secondary battery according to claim 1, wherein, The electrolyte further comprises at least one of sulfonate, sulfate, sulfite, dicarboxylic anhydride, disulfonic anhydride, and sulfonic acid carboxylic anhydride.

6. The secondary battery according to claim 1, wherein, The electrolyte further contains nitrile compounds.

7. The secondary battery according to claim 1, wherein, The secondary battery is a lithium-ion secondary battery.

8. An electrolyte for a secondary battery, comprising: Solvent; Electrolyte salts; and The combination of the first unsaturated compound represented by formula (1) and at least one of the second unsaturated compounds represented by formulas (5) to (16), the combination of the first unsaturated compound represented by formula (2) and the second unsaturated compound represented by formula (5), or the combination of the first unsaturated compound represented by formula (3) and the second unsaturated compound represented by formula (5), R1 through R6 are any one of hydrogen (H), alkyl, acrylate, and methacrylate groups, and at least one of R1 through R6 is either an acrylate group or a methacrylate group. R7 to R14 are any one of hydrogen (H), alkyl, acrylate and methacrylate, and at least one of R7 to R14 is either acrylate or methacrylate. R21 and R22 are alkenyl groups, respectively. R23 and R24 are alkenyl groups, respectively. R25 to R30 are either hydrogen (H) or an alkenyl group, and two or more of R25 to R30 are alkenyl groups. R31 to R36 are either hydrogen (H) or an alkenyl group, and two or more of R31 to R36 are alkenyl groups. R37 is an alkylene group with an ether bond, while R38 and R39 are alkenyl groups, respectively. R40 is an alkylene group, while R41 and R42 are alkenyl groups, respectively. R43 is any one of an alkylene group and an alkylene group having an ether bond, and R44 and R45 are any one of an acrylate group and a methacrylate group, respectively. R46 to R48 are alkenyl groups, respectively. R49 to R51 are any one of alkyl and alkenyl groups, and two or more of R49 to R51 are alkenyl groups. R52 to R54 are alkenyl groups, respectively. R55 is any one of alkylene and arylene. R56 is a tetravalent hydrocarbon group, R57 to R60 are alkylene groups, R61 to R64 are any one of hydroxyl, acrylic, and methacrylic groups, and two or more of R61 to R64 are any one of acrylic and methacrylic groups.

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