Electrolyte for secondary batteries and secondary batteries

Abstract

The secondary battery comprises: a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte contains at least one of a solvent, an electrolyte salt, a diester compound represented by formula (1), and a sulfur-containing compound represented by formulas (2) to (14).

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, the development of secondary batteries—small, lightweight power sources capable of delivering high energy density—is underway. These secondary batteries comprise 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 excellent high-temperature lifespan performance and low-temperature discharge characteristics, the non-aqueous electrolyte contains one or both of ethylene carbonate and propylene carbonate, chain carboxylic acid esters, and carbonyl ester compounds (e.g., see Patent Document 1). To obtain excellent initial and high-rate discharge characteristics after storage, the non-aqueous electrolyte contains alkylene dicarbonate compounds (e.g., see Patent Document 2). To suppress the reduction of discharge capacity during charge-discharge cycles and obtain good low-temperature discharge characteristics, the non-aqueous electrolyte contains cyclic carbonates, chain carboxylic acid esters, and diester compounds (e.g., see Patent Document 3). To improve low-temperature cycling characteristics, the non-aqueous electrolyte contains cyclic carbonates, chain carbonates, and compounds derived from R1-OC(=O)-O-(CR3R4). n -OC(=O)-R2 represents the additive, monofluorophosphate or difluorophosphate (for example, see Patent Document 4.).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-220313

[0007] Patent Document 2: Japanese Patent Application Publication No. 07-282849

[0008] Patent Document 3: Japanese Patent Application Publication No. 2006-080008

[0009] Patent Document 4: Japanese Patent Application Publication No. 2018-133290 Summary of the Invention

[0010] Various studies have been conducted on the battery characteristics of the secondary battery, but since the storage characteristics of this secondary battery are not yet fully developed, there is room for improvement.

[0011] Therefore, there is a need for electrolytes for secondary batteries and secondary batteries that can achieve excellent preservation properties.

[0012] An embodiment of the present technology provides an electrolyte for a secondary battery comprising a solvent, an electrolyte salt, a diester compound represented by formula (1), and at least one of sulfur-containing compounds represented by formulas (2) to (14).

[0013] [Chemical Formula 1]

[0014]

[0015] (R1 and R2 are any one of halogen group, alkyl group, alkoxy group, haloalkyl group, and haloalkoxy group, respectively, and R3 to R6 are any one of hydrogen group, halogen group, alkyl group, and haloalkyl group, respectively.)

[0016] [Chemical Formula 2]

[0017]

[0018] (R11 and R12 are any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl and haloaryl, and R11 and R12 can be bonded to each other.)

[0019] R13 is any one of alkyl, aryl, hydroxyalkyl, lithium alkanol, haloalkyl, and haloaryl, and R14 is any one of hydrogen, lithium, alkyl, and haloalkyl.

[0020] R15 and R16 are any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl groups, and R15 and R16 can be bonded to each other.

[0021] [Chemical Formula 3]

[0022]

[0023] (R17 and R18 are any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl and haloaryl, respectively, and R17 and R18 can be bonded to each other.)

[0024] R19 and R20 are either alkyl or haloalkyl, and R21 is either alkylene or haloalkylene.

[0025] R22 is any one of alkyl and haloalkyl, R23 is any one of hydrogen, lithium, alkyl and haloalkyl, and R24 is any one of alkylene and haloalkylene.

[0026] R25 and R26 are any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, respectively, and R27 is any one of alkylene and haloalkylene groups.

[0027] [Chemical Formula 4]

[0028]

[0029] (R28 and R29 are any one of hydrogen-based, lithium-based, alkyl, hydroxyalkyl, lithium alkanol-based, and haloalkyl, respectively, and R28 and R29 can be bonded to each other. Among them, 1,2-vinyl sulfate and 1-methyl-1,2-vinyl sulfate are not included in the sulfur-containing compounds represented by formula (9).

[0030] R30 and R31 are any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl, and R30 and R31 can be bonded to each other.

[0031] R32 is any one of hydrogen-based, lithium-based, alkyl, and haloalkyl, R33 is any one of alkyl and haloalkyl, and R34 is any one of alkylene and haloalkylene.

[0032] R35 and R36 are any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, respectively, and R37 is any one of alkylene and haloalkylene groups.

[0033] R38 and R39 are any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, respectively, and R40 is any one of alkylene and haloalkylene groups.

[0034] [Chemical Formula 5]

[0035]

[0036] (R41 to R44 are any one of hydrogen-based, alkyl, haloalkyl, groups represented by formula (15), and groups represented by formula (16), and at least one of R41 to R44 is any one of groups represented by formula (15) and groups represented by formula (16). R45 and R46 are any one of alkylene and haloalkylene, and can be omitted. R47 is any one of alkyl and haloalkyl. In formulas (15) and (16), the asterisks (*) indicate bonding bonds.)

[0037] One embodiment of the present technology provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte having the same structure as the electrolyte for a secondary battery described in one embodiment of the present technology.

[0038] According to one embodiment of the present technology, the electrolyte for secondary batteries or the secondary battery contains diester compounds and sulfur-containing compounds, thus achieving excellent storage characteristics.

[0039] 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

[0040] Figure 1 This is a perspective view showing the structure of a secondary battery in one embodiment of the present technology.

[0041] Figure 2 It means Figure 1 The diagram shows a cross-sectional view of the structure of the battery element.

[0042] Figure 3 This is a block diagram illustrating the structure of a secondary battery application example. Detailed Implementation

[0043] 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.

[0044] 1. Electrolyte for secondary batteries

[0045] 1-1. Structure

[0046] 1-2. Manufacturing method

[0047] 1-3. Functions and Effects

[0048] 2. Secondary battery

[0049] 2-1. Structure

[0050] 2-2. Actions

[0051] 2-3. Manufacturing method

[0052] 2-4. Functions and Effects

[0053] 3. Variations

[0054] 4. Uses of secondary batteries

[0055] <1. Electrolyte for Secondary Batteries>

[0056] First, an electrolyte for a secondary battery (hereinafter referred to as "electrolyte") according to one embodiment of the present technology will be described.

[0057] This electrolyte is used in secondary batteries. Furthermore, the electrolyte described herein can be used in other electrochemical devices besides secondary batteries. The types of other electrochemical devices are not particularly limited; specifically, they include capacitors, etc.

[0058] <1-1. Structure>

[0059] The electrolyte comprises a solvent, an electrolyte salt, a diester compound, and a sulfur-containing compound. The diester compound comprises a compound represented by formula (1), and the sulfur-containing compound comprises any one or more of the compounds represented by formulas (2) to (14).

[0060] [Chemical Formula 6]

[0061]

[0062] (R1 and R2 are any one of halogen group, alkyl group, alkoxy group, haloalkyl group, and haloalkoxy group, respectively, and R3 to R6 are any one of hydrogen group, halogen group, alkyl group, and haloalkyl group, respectively.)

[0063] [Chemical Formula 7]

[0064]

[0065] (R11 and R12 are any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl and haloaryl, and R11 and R12 can be bonded to each other.)

[0066] R13 is any one of alkyl, aryl, hydroxyalkyl, lithium alkanol, haloalkyl, and haloaryl, and R14 is any one of hydrogen, lithium, alkyl, and haloalkyl.

[0067] R15 and R16 are any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl groups, and R15 and R16 can be bonded to each other.

[0068] [Chemical Formula 8]

[0069]

[0070] (R17 and R18 are any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl and haloaryl, respectively, and R17 and R18 can be bonded to each other.)

[0071] R19 and R20 are either alkyl or haloalkyl, and R21 is either alkylene or haloalkylene.

[0072] R22 is any one of alkyl and haloalkyl, R23 is any one of hydrogen, lithium, alkyl and haloalkyl, and R24 is any one of alkylene and haloalkylene.

[0073] R25 and R26 are any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, respectively, and R27 is any one of alkylene and haloalkylene groups.

[0074] [Chemical Formula 9]

[0075]

[0076] (R28 and R29 are any one of hydrogen-based, lithium-based, alkyl, hydroxyalkyl, lithium alkanol-based, and haloalkyl, respectively, and R28 and R29 can be bonded to each other. Among them, 1,2-vinyl sulfate and 1-methyl-1,2-vinyl sulfate are not included in the sulfur-containing compounds represented by formula (9).

[0077] R30 and R31 are any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl, and R30 and R31 can be bonded to each other.

[0078] R32 is any one of hydrogen-based, lithium-based, alkyl, and haloalkyl, R33 is any one of alkyl and haloalkyl, and R34 is any one of alkylene and haloalkylene.

[0079] R35 and R36 are any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, respectively, and R37 is any one of alkylene and haloalkylene groups.

[0080] R38 and R39 are any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, respectively, and R40 is any one of alkylene and haloalkylene groups.

[0081] [Chemical Formula 10]

[0082]

[0083] (R41 to R44 are any one of hydrogen-based, alkyl, haloalkyl, groups represented by formula (15), and groups represented by formula (16), and at least one of R41 to R44 is any one of groups represented by formula (15) and groups represented by formula (16). R45 and R46 are any one of alkylene and haloalkylene, and can be omitted. R47 is any one of alkyl and haloalkyl. In formulas (15) and (16), the asterisks (*) indicate bonding bonds.)

[0084] The reason the electrolyte contains both diester compounds and sulfur-containing compounds is that, during the charging and discharging of a secondary battery using this electrolyte, a high-quality coating derived from both diester compounds and sulfur-containing compounds forms on the electrode surface. This electrochemically protects the electrode surface, thus suppressing electrolyte decomposition reactions on the electrode surface. In this case, in particular, electrolyte decomposition reactions can be effectively suppressed even when the secondary battery is stored in a high-temperature environment.

[0085] [Diester compounds]

[0086] Diester compounds, as shown in formula (1), are chain-like compounds having two ester groups (R1-C(=O)-O- and R2-C(=O)-O-).

[0087] R1 and R2 can be any one of halogen groups, alkyl groups, alkoxy groups, haloalkyl groups, and haloalkoxy groups, without any particular limitation. R1 and R2 can be the same group or different groups.

[0088] There is no particular limitation on the type of halogen group; specifically, it can be any one of fluorine, chlorine, bromine, and iodine groups.

[0089] Alkyl groups can be straight-chain, branched with one or more side chains, planar cyclic, or three-dimensional cross-linked cyclic. The number of rings in a cyclic alkyl group is not particularly limited, and can be one or more. The number of carbon atoms in the alkyl group is not particularly limited, but preferably 1 to 4, more preferably 1 to 3. This is because it ensures the solubility and compatibility of the diester compound. Specific examples of alkyl groups are methyl, ethyl, propyl, and butyl.

[0090] The alkoxy group can be linear or branched with one or more side chains. The number of carbon atoms in the alkoxy group is not particularly limited, but is preferably 1 to 4, more preferably 1 to 3. This is because it ensures the solubility and compatibility of the diester compound. Specific examples of alkoxy groups include methoxy, ethoxy, propoxy, and butoxy groups.

[0091] A haloalkyl group is a group in which one or more hydrogen groups of the aforementioned alkyl groups are substituted by one or more halogen groups. A haloalkoxy group is a group in which one or more hydrogen groups of the aforementioned alkoxy groups are substituted by one or more halogen groups.

[0092] R3 to R6 can be any one of the following: hydrogen group, halogen group, alkyl group, and haloalkyl group; there are no particular limitations. R3 to R6 can be the same group or different groups. Of course, it is also possible for only some of R3 to R6 to be the same group. Details regarding halogen groups, alkyl groups, and haloalkyl groups are as described above.

[0093] (Specific examples of diester compounds)

[0094] Specific examples of diester compounds are compounds represented by formulas (1-1) to (1-46), respectively. This is because it is easy to form a coating with sufficient electrochemical durability on the surface of the electrode.

[0095] [Chemical Formula 11]

[0096]

[0097] [Chemical Formula 12]

[0098]

[0099] (Content of diester compounds)

[0100] The content of diester compounds in the electrolyte is not particularly limited, but is preferably 0.001% to 5% by weight. This is because it is easy to form a coating with sufficient electrochemical durability on the surface of the electrode.

[0101] [Sulfur-containing compounds]

[0102] Sulfur-containing compounds, as shown in formulas (2) to (14), are chain or cyclic compounds containing sulfur as a constituent element.

[0103] Hereinafter, the compound shown in formula (2) will be referred to as "the first sulfur-containing compound", the compound shown in formula (3) will be referred to as "the second sulfur-containing compound", the compound shown in formula (4) will be referred to as "the third sulfur-containing compound", the compound shown in formula (5) will be referred to as "the fourth sulfur-containing compound", the compound shown in formula (6) will be referred to as "the fifth sulfur-containing compound", the compound shown in formula (7) will be referred to as "the sixth sulfur-containing compound", the compound shown in formula (8) will be referred to as "the seventh sulfur-containing compound", the compound shown in formula (9) will be referred to as "the eighth sulfur-containing compound", the compound shown in formula (10) will be referred to as "the ninth sulfur-containing compound", the compound shown in formula (11) will be referred to as "the tenth sulfur-containing compound", the compound shown in formula (12) will be referred to as "the eleventh sulfur-containing compound", the compound shown in formula (13) will be referred to as "the twelfth sulfur-containing compound", and the compound shown in formula (14) will be referred to as "the thirteenth sulfur-containing compound".

[0104] (First sulfur-containing compound)

[0105] The first sulfur-containing compound, as shown in formula (2), is a chain or cyclic compound having a sulfonyl group (-S(=O)2-).

[0106] R11 and R12 can be any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl groups, without any particular limitation. R11 and R12 can be the same group or different groups. Details regarding alkyl and haloalkyl groups are as described above.

[0107] The alkenyl group can be linear or branched with one or more side chains. Preferably, the alkenyl group has 2 to 4 carbon atoms, more preferably 2 or 3. This is because it ensures the solubility and compatibility of the first sulfur-containing compound. Specific examples of alkenyl groups are vinyl and allyl groups.

[0108] The number of aromatic rings contained in the aryl group is not particularly limited. Therefore, the number of carbon atoms in the aryl group is not particularly limited, but preferably 6 to 10, more preferably 6. This is because it ensures the solubility and compatibility of the first sulfur-containing compound. Specific examples of aryl groups are phenyl, tolyl, and naphthyl.

[0109] A haloalkenyl group is a group in which one or more hydrogen groups of the alkenyl group described above are replaced by one or more halogen groups. A haloaryl group is a group in which one or more hydrogen groups of the aryl group described above are replaced by one or more halogen groups.

[0110] In addition, R11 and R12 can also be bonded to each other. That is, as mentioned above, the first sulfur-containing compound can be a chain compound in which R11 and R12 are not bonded to each other, or it can be a cyclic compound in which R11 and R12 are bonded to each other.

[0111] (Second sulfur-containing compound)

[0112] As shown in formula (3), the second sulfur-containing compound is a chain-like compound having a sulfite group (-S(=O)2-O-).

[0113] R13 can be any one of alkyl, aryl, hydroxyalkyl, lithium alkanolyl, haloalkyl, and haloaryl groups, without any particular limitation. Details regarding alkyl, aryl, haloalkyl, and haloaryl groups are as described above.

[0114] A hydroxyalkyl group is a group in which one or more hydrogen groups of the aforementioned alkyl groups are replaced by hydroxyl groups. The hydroxyl group can be introduced at the end of the alkyl group or in the middle of the alkyl group. The number of carbon atoms in the hydroxyalkyl group is not particularly limited, but is preferably 1 to 4, more preferably 1 to 3. This is because it ensures the solubility and compatibility of the second sulfur-containing compound. Specific examples of hydroxyalkyl groups are hydroxymethyl (-CH2-OH), hydroxyethyl (-C2H4-OH), hydroxypropyl (-C3H6-OH), and hydroxybutyl (-C4H8-OH), etc.

[0115] Lithium alkanols are groups in which the hydrogen group of the hydroxyl group contained in the above-mentioned hydroxyalkyl group is replaced by a lithium group. Specific examples of lithium alkanols are lithium methoxide (-CH2-OLi), lithium ethanol (-C2H4-OLi), lithium propoxide (-C3H6-OLi), and lithium butoxide (-C4H8-OLi), etc.

[0116] R14 can be any of the following: hydrogen-based, lithium-based, alkyl, and haloalkyl; there are no particular restrictions. Details regarding alkyl and haloalkyl groups are as described above.

[0117] (Third sulfur-containing compound)

[0118] As shown in formula (4), the third sulfur-containing compound is a chain or cyclic compound having a sulfonylcarboxylic acid group (-S(=O)2-OC(=O)-).

[0119] R15 and R16 can be any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl groups, without any particular limitation. R15 and R16 can be the same group or different groups. The details of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl groups are as described above.

[0120] In addition, R15 and R16 can also be bonded to each other. That is, as mentioned above, the third sulfur-containing compound can be a chain compound in which R15 and R16 are not bonded to each other, or it can be a cyclic compound in which R15 and R16 are bonded to each other.

[0121] (4th sulfur-containing compound)

[0122] As shown in formula (5), the fourth sulfur-containing compound is a chain or cyclic compound having two sulfonyl groups (-S(=O)2-) and the two sulfonyl groups being bonded to each other via an ether bond (-O-).

[0123] R17 and R18 can be any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl groups, without any particular limitation. R17 and R18 can be the same group or different groups. The details of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl groups are as described above.

[0124] In addition, R17 and R18 can also be bonded to each other. That is, as mentioned above, the fourth sulfur-containing compound can be a chain-like compound in which R17 and R18 are not bonded to each other, or it can be a cyclic compound in which R17 and R18 are bonded to each other.

[0125] (Fifth sulfur-containing compound)

[0126] As shown in formula (6), the fifth sulfur-containing compound is a chain-like compound having two sulfite groups bonded together by a linker (-R21-). In this fifth sulfur-containing compound, the two sulfite groups are arranged in a left-right symmetrical manner.

[0127] R19 and R20 can be either alkyl or haloalkyl groups, with no particular limitation. R19 and R20 can be the same group or different groups. Details regarding alkyl and haloalkyl groups are as described above.

[0128] R21 can be any of the alkylene or haloalkylene groups; there are no special restrictions.

[0129] The alkylene group can be linear or branched with one or more side chains. The number of carbon atoms in the alkylene group is not particularly limited, but is preferably 1 to 4, more preferably 1 to 3. This is because it ensures the solubility and compatibility of the fifth sulfur-containing compound. Specific examples of alkylene groups are methylene, ethylene, propylene, and butylene.

[0130] A haloalkylene group is a group in which one or more hydrogen groups of the aforementioned alkylene groups are replaced by one or more halogen groups.

[0131] (Sixth sulfur-containing compound)

[0132] As shown in formula (7), the sixth sulfur-containing compound is a chain-like compound having two sulfite groups bonded together by a linker (-R24-). In this sixth sulfur-containing compound, the two sulfite groups are arranged in a left-right asymmetric manner.

[0133] R22 can be any of alkyl or haloalkyl groups without particular limitation, and R23 can be any of hydrogen-based, lithium-based, alkyl, or haloalkyl groups without particular limitation. Details regarding alkyl and haloalkyl groups are as described above.

[0134] R24 can be any of the alkylene or haloalkylene groups; there are no particular restrictions. Details regarding alkylene and haloalkylene groups are as described above.

[0135] (7th sulfur-containing compound)

[0136] As shown in formula (8), the seventh sulfur-containing compound is a chain-like compound having two sulfite groups bonded together by a linker (-R27-). In this seventh sulfur-containing compound, the two sulfite groups are arranged in a left-right symmetrical manner.

[0137] R25 and R26 can be any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, without any particular limitation. R25 and R26 can be the same group or different groups. Details regarding alkyl and haloalkyl groups are as described above.

[0138] R27 can be any of the alkylene or haloalkylene groups; there are no particular restrictions. Details regarding alkylene and haloalkylene groups are as described above.

[0139] (8th sulfur-containing compound)

[0140] As shown in formula (9), the eighth sulfur-containing compound is a chain or cyclic compound having a sulfate group (-OS(=O)2-O-).

[0141] R28 and R29 can be any one of the following: hydrogen-based, lithium-based, alkyl, hydroxyalkyl, lithium alkanol-based, and haloalkyl. There are no particular restrictions. R28 and R29 can be the same group or different groups. Details regarding alkyl, hydroxyalkyl, lithium alkanol-based, and haloalkyl groups are as described above.

[0142] In addition, R28 and R29 can also be bonded to each other. That is, as mentioned above, the eighth sulfur-containing compound can be a chain-like compound in which R28 and R29 are not bonded to each other, or it can be a cyclic compound in which R28 and R29 are bonded to each other.

[0143] Here, among the series of compounds having the structure shown in formula (9), 1,2-vinyl sulfate and 1-methyl-1,2-vinyl sulfate are not included in the 8th sulfur-containing compound. That is, even if 1,2-vinyl sulfate and 1-methyl-1,2-vinyl sulfate have the structure shown in formula (9) respectively, they are not among the 8th sulfur-containing compounds described herein. This is because it is difficult to form a high-quality coating on the surface of the electrode, and therefore the surface of the electrode is difficult to be electrochemically protected.

[0144] (Ninth sulfur-containing compound)

[0145] As shown in formula (10), the ninth sulfur-containing compound is a chain or cyclic compound having two sulfite groups bonded together by an ether bond. In this ninth sulfur-containing compound, the two sulfite groups are arranged in a left-right symmetrical manner.

[0146] R30 and R31 can be any one of alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, or haloaryl groups, without any particular limitation. R30 and R31 can be the same group or different groups. Details regarding alkyl, alkenyl, aryl, haloalkyl, haloalkenyl, and haloaryl groups are as described above.

[0147] In addition, R30 and R31 can also be bonded to each other. That is, as mentioned above, the ninth sulfur-containing compound can be a chain-like compound in which R30 and R31 are not bonded to each other, or it can be a cyclic compound in which R30 and R31 are bonded to each other.

[0148] (10th sulfur-containing compound)

[0149] As shown in formula (11), the 10th sulfur-containing compound is a chain-like compound having a sulfate group and a sulfite group, wherein the sulfate group and the sulfite group are bonded to each other via a linker (-R34).

[0150] R32 can be any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, without any particular limitation, and R33 can be any one of alkyl and haloalkyl groups, without any particular limitation. Details regarding alkyl and haloalkyl groups are as described above.

[0151] R34 can be any of the alkylene or haloalkylene groups; there are no particular restrictions. Details regarding alkylene and haloalkylene groups are as described above.

[0152] (11th sulfur-containing compound)

[0153] As shown in formula (12), the 11th sulfur-containing compound is a chain-like compound having a sulfate group and a sulfite group, wherein the sulfate group and the sulfite group are bonded to each other via a linker (-R37).

[0154] R35 and R36 can be any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, without any particular limitation. R35 and R36 can be the same group or different groups. Details regarding alkyl and haloalkyl groups are as described above.

[0155] R37 can be any of the alkylene or haloalkylene groups; there are no particular restrictions. Details regarding alkylene and haloalkylene groups are as described above.

[0156] (12th sulfur-containing compound)

[0157] As shown in formula (13), the 12th sulfur-containing compound is a chain-like compound having two sulfate groups that are bonded to each other via a linker (-R40-).

[0158] R38 and R39 can be any one of hydrogen-based, lithium-based, alkyl, and haloalkyl groups, without any particular limitation. R38 and R39 can be the same group or different groups. Details regarding alkyl and haloalkyl groups are as described above.

[0159] R40 can be any of the alkylene or haloalkylene groups; there are no particular restrictions. Details regarding alkylene and haloalkylene groups are as described above.

[0160] (13th sulfur-containing compound)

[0161] As shown in formula (14), the 13th sulfur-containing compound is a cyclic compound having a sulfate group.

[0162] R41 to R44 can be any one of the following: hydrogen group, alkyl group, haloalkyl group, group represented by formula (15), and group represented by formula (16), without any particular limitation. R41 to R44 can be the same group or different groups. Of course, it is also possible for only some of R41 to R44 to be the same group. The details of alkyl and haloalkyl groups are as described above.

[0163] The group shown in formula (15) is a cyclic group with a structure of 1,2-vinyl sulfate type, and the asterisk (*) shown in formula (15) indicates a bonding bond. Therefore, the group shown in formula (15) can be R41 to R44 as shown in formula (14).

[0164] R45 can be any of the alkylene or haloalkylene groups; there are no particular restrictions. Details regarding alkylene and haloalkylene groups are as described above. Alternatively, R45 can be omitted.

[0165] The group shown in formula (16) is a chain-like group having a sulfite group, and the asterisk (*) shown in formula (16) represents a bond. Therefore, the group shown in formula (16) can be R41 to R44 as shown in formula (14).

[0166] R46 can be any of alkylene or haloalkylene, without particular limitation. Details regarding alkylene and haloalkylene are as described above. Furthermore, R46, like R45 mentioned above, can be omitted.

[0167] R47 can be any of alkyl or haloalkyl groups; there are no particular limitations. Details regarding alkyl and haloalkyl groups are as described above.

[0168] Here, one or more of R41 to R44 are any one of the groups shown in formula (15) and formula (16). Thus, the 13th sulfur-containing compound contains one or both of the groups shown in formula (15) and formula (16), and is therefore different from the 8th sulfur-containing compound when it is a cyclic compound.

[0169] (Specific examples of sulfur-containing compounds)

[0170] Specific examples of sulfur-containing compounds 1 through 13 are as follows. This is because it is easy to form a coating with sufficient electrochemical durability on the electrode surface.

[0171] Specific examples of the first sulfur-containing compounds are compounds represented by formulas (2-1) to (2-7), respectively.

[0172] [Chemical Formula 13]

[0173]

[0174] Specific examples of the second sulfur-containing compounds are compounds represented by formulas (3-1) to (3-10), respectively.

[0175] [Chemical Formula 14]

[0176]

[0177] Specific examples of the third sulfur-containing compounds are compounds represented by formulas (4-1) to (4-18), respectively.

[0178] [Chemical Formula 15]

[0179]

[0180] Specific examples of the fourth sulfur-containing compounds are compounds represented by formulas (5-1) to (5-17), respectively.

[0181] [Chemical Formula 16]

[0182]

[0183] Specific examples of the fifth sulfur-containing compounds are compounds represented by formulas (6-1) to (6-8), respectively.

[0184] [Chemical Formula 17]

[0185]

[0186] Specific examples of the sixth sulfur-containing compounds are compounds represented by formulas (7-1) to (7-10), respectively.

[0187] [Chemical Formula 18]

[0188]

[0189] Specific examples of the seventh sulfur-containing compounds are compounds represented by formulas (8-1) to (8-10), respectively.

[0190] [Chemical Formula 19]

[0191]

[0192] Specific examples of the eighth sulfur-containing compounds are compounds represented by formulas (9-1) to (9-20), respectively.

[0193] [Chemical Formula 20]

[0194]

[0195] Specific examples of the ninth sulfur-containing compounds are compounds represented by formulas (10-1) to (10-13), respectively.

[0196] [Chemical Formula 21]

[0197]

[0198] Specific examples of sulfur-containing compounds in the 10th category are compounds represented by formulas (11-1) to (11-10), respectively.

[0199] [Chemical Formula 22]

[0200]

[0201] Specific examples of sulfur-containing compounds in section 11 are compounds represented by formulas (12-1) to (12-10), respectively.

[0202] [Chemical Formula 23]

[0203]

[0204] Specific examples of sulfur-containing compounds in section 12 are compounds represented by formulas (13-1) to (13-10), respectively.

[0205] [Chemical Formula 24]

[0206]

[0207] Specific examples of sulfur-containing compounds in the 13th category are compounds represented by formulas (14-1) to (14-3), respectively.

[0208] [Chemical Formula 25]

[0209]

[0210] (Content of sulfur-containing compounds)

[0211] The content of sulfur-containing compounds in the electrolyte is not particularly limited, but is preferably 0.001% to 5% by weight. This is because it is easy to form a coating with sufficient electrochemical durability on the surface of the electrode.

[0212] It should be noted that when the electrolyte contains two or more sulfur-containing compounds, the content stated here is the sum of the contents of each sulfur-containing compound in the electrolyte.

[0213] [solvent]

[0214] 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.

[0215] 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.

[0216] 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.

[0217] Lactone compounds include lactones. Specific examples of lactones include γ-butyrolactone and γ-valerolactone.

[0218] 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.

[0219] [Electrolyte salts]

[0220] 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), lithium bis(oxalate)borate (LiB(C2O4)2), and lithium difluoro(oxalate)borate (LiB(C2O4)F2), etc.

[0221] 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.

[0222] [additive]

[0223] It should be noted that the electrode solution may further contain any one or more additives. The types of additives are not particularly limited, but specifically include unsaturated cyclic carbonates, halocarbonates, phosphate esters, acid anhydrides, nitrile compounds, and isocyanate compounds, etc. This is because they can improve the chemical stability of the electrolyte. Additionally, the sulfur-containing compounds mentioned above are not included in the acid anhydrides described herein.

[0224] 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).

[0225] Specific examples of halogenated carbonates include fluoroethylene carbonate (4-fluoro-1,3-dioxolane-2-one) and difluoroethylene carbonate (4,5-difluoro-1,3-dioxolane-2-one).

[0226] Specific examples of phosphate esters include trimethyl phosphate and triethyl phosphate.

[0227] Anhydrides are cyclic dicarboxylic acid anhydrides, and specific examples of cyclic dicarboxylic acid anhydrides include succinic anhydride, glutaric anhydride, and maleic anhydride.

[0228] Specific examples of nitrile compounds include acetonitrile, succinate, and adiponitrile.

[0229] Specific examples of isocyanate compounds include hexamethylene diisocyanate, etc.

[0230] <1-2. Manufacturing Method>

[0231] In the manufacture of an electrolyte, an electrolyte salt is added to a solvent, followed by a diester compound and a sulfur-containing compound. Thus, the electrolyte salt, diester compound, and sulfur-containing compound are dispersed or dissolved in the solvent, thereby preparing the electrolyte.

[0232] <1-3. Functions and Effects>

[0233] The electrolyte contains both diester compounds and sulfur-containing compounds.

[0234] In this case, compared to cases where the electrolyte does not contain either diester compounds or sulfur-containing compounds, or cases where the electrolyte contains diester compounds and other compounds, in secondary batteries using an electrolyte, a coating derived from both diester compounds and sulfur-containing compounds is formed on the surface of the electrode, thus the surface of the electrode is electrochemically protected.

[0235] Other compounds described herein are propane sulpholactone represented by formula (17-1), propene sulpholactone represented by formula (17-2), ethylene glycol sulfate (1,2-ethylene sulfate) represented by formula (17-3), and propylene glycol sulfate (1-methyl-1,2-ethylene sulfate) represented by formula (17-4).

[0236] [Chemical Formula 26]

[0237]

[0238] Therefore, even when storing the secondary battery in a high-temperature environment, the decomposition reaction of the electrolyte can be effectively suppressed, thus minimizing the reduction in the discharge capacity of the secondary battery. This results in excellent storage characteristics.

[0239] In particular, if the number of carbon atoms in alkyl groups is 1 to 4, in alkenyl groups is 2 to 4, in aryl groups is 6 to 10, and in alkylene groups is 1 to 4, the solubility and compatibility of both diester compounds and sulfur-containing compounds can be guaranteed, thus achieving better results.

[0240] In addition, if the content of diester compounds in the electrolyte is 0.001% to 5% by weight, it is easy to form a coating with sufficient electrochemical durability on the surface of the electrode, thus achieving better results.

[0241] In addition, if the content of sulfur-containing compounds in the electrolyte is 0.001% to 5% by weight, it is easy to form a coating with sufficient electrochemical durability on the surface of the electrode, thus achieving better results.

[0242] <2. Secondary batteries>

[0243] Next, the secondary battery using electrolyte described above will be explained.

[0244] The secondary battery described herein is a secondary battery in which battery capacity is obtained by the intercalation and deintercalation of electrode reactants. It includes a positive electrode, a negative electrode, and an electrolyte in liquid form. In this secondary battery, 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.

[0245] 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.

[0246] 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.

[0247] <2-1. Structure>

[0248] 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. Additionally, 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.

[0249] 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.

[0250] [Outer packaging film and sealing film]

[0251] 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.

[0252] Here, the outer packaging film 10 is a thin film 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.

[0253] 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.

[0254] 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.

[0255] 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.

[0256] The sealing film 41 is a sealing component that prevents external gases 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 seal with respect to the positive electrode lead 31. This polyolefin is polypropylene, etc.

[0257] 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 provides a tight seal relative to the negative electrode lead 32. That is, the sealing membrane 42 contains a polymer compound such as polyolefin that provides a tight seal relative to the negative electrode lead 32.

[0258] [Battery Components]

[0259] like Figure 1 as well as Figure 2 As shown, the battery element 20 is a power generation element that includes a positive electrode 21, a negative electrode 22, a separator 23 and an electrolyte (not shown), and is housed inside the outer packaging film 10.

[0260] 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 with a separator 23 in between, 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 opposite each other with a separator 23 in between.

[0261] 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.

[0262] (positive electrode)

[0263] like Figure 2 As shown, the positive electrode 21 includes a positive current collector 21A and a positive active material layer 21B.

[0264] 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.

[0265] 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 on only one side of the positive electrode current collector 21A. 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.

[0266] There are no particular limitations on the type of positive electrode active material; specifically, it can be a lithium-containing compound. This lithium-containing compound is a compound that contains 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 only need to be 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.

[0267] 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 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2, Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 O2 and LiMn2O4, etc. Specific examples of phosphoric acid compounds are LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4, etc.

[0268] 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.

[0269] 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.

[0270] (negative electrode)

[0271] like Figure 2 As shown, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0272] 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.

[0273] 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 on only one side of the negative electrode current collector 22A. 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 may be any one or more of the following: coating method, vapor phase method, liquid phase method, spraying method, and firing method (sintering method).

[0274] 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.

[0275] 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.

[0276] (Septum)

[0277] 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.

[0278] (electrolyte)

[0279] The electrolyte is immersed in the positive electrode 21, the negative electrode 22, and the separator 23, and has the structure described above. That is, the electrolyte contains both diester compounds and sulfur-containing compounds.

[0280] [Positive and negative leads]

[0281] 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.

[0282] like Figure 1 As 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.

[0283] <2-2. Actions>

[0284] During charging of the secondary battery, 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 of the secondary battery, 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.

[0285] <2-3. Manufacturing Method>

[0286] In the case of manufacturing a secondary battery, a positive electrode 21 and a negative electrode 22 were fabricated through the steps described below, and 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.

[0287] [The production of the positive electrode]

[0288] 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 active material layer 21B is formed on both sides of the positive electrode current collector 21A, thereby forming the positive electrode 21.

[0289] [Making the negative electrode]

[0290] 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. The type of solvent is as described above. 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 active material layer 22B is formed on both sides of the negative electrode current collector 22A, thereby fabricating the negative electrode 22.

[0291] (Assembly of a secondary battery)

[0292] First, the positive lead 31 is connected to the positive electrode 21 (positive current collector 21A) using a soldering method or the like, and the negative lead 32 is connected to the negative electrode 22 (negative current collector 22A).

[0293] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with the separator 23 in between, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound together to form a wound body (not shown). 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 into a flat shape using a press or the like.

[0294] 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.

[0295] Finally, the electrolyte is injected into the inside of the pouch-shaped outer packaging film 10, and then the outer periphery of the remaining side of the outer packaging film 10 (welded layer) is joined together using a heat fusion method or the like. In this case, the sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32.

[0296] Thus, an electrolyte is impregnated in the wound body to produce a battery element 20 as a wound electrode body, and the battery element 20 is sealed inside the bag-shaped outer packaging film 10, thereby assembling a secondary battery.

[0297] (Stabilization of secondary batteries)

[0298] 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.

[0299] <2-4. Functions and Effects>

[0300] The secondary battery is equipped with the electrolyte described above. In this case, as described above, during charging and discharging, a coating derived from both the diester compound and the sulfur-containing compound is formed on the surfaces of the positive electrode 21 and the negative electrode 22, respectively, thus electrochemically protecting the surfaces of the positive electrode 12 and the negative electrode 22. Therefore, even when storing the secondary battery in a high-temperature environment, the decomposition reaction of the electrolyte can be effectively suppressed, thereby achieving excellent storage characteristics.

[0301] In particular, 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.

[0302] The other functions and effects of this secondary battery are the same as those of the electrolyte described above.

[0303] <3. Variations>

[0304] As explained below, the structure of the aforementioned secondary battery can be modified appropriately. Furthermore, any two or more of the variations described below can be combined with each other.

[0305] [Variation Example 1]

[0306] 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.

[0307] 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 relative to the positive electrode 21 and the negative electrode 22, it is less likely to cause positional displacement (winding displacement) of the battery element 20. 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 similar compounds possess excellent physical strength and electrochemical stability.

[0308] 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 particles of alumina, aluminum nitride, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, and zirconium oxide. Specific examples of resin particles include particles of acrylic resin and styrene resin.

[0309] 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.

[0310] 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.

[0311] [Variation Example 2]

[0312] 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.

[0313] 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 with the separator 23 and the electrolyte layer in between, 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.

[0314] 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 structure of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. In 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.

[0315] 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.

[0316] <4. Uses of Secondary Batteries>

[0317] 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.

[0318] Specific examples of applications for rechargeable batteries are as follows: 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 such as electric cars (including hybrid vehicles). 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.

[0319] Battery packs can use single cells or battery arrays. 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.

[0320] 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.

[0321] Figure 3 This describes the frame structure of the battery pack. The battery pack described here is a pouch cell that uses a rechargeable battery and is used in electronic devices such as smartphones.

[0322] 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.

[0323] 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.

[0324] 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.

[0325] 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.

[0326] 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.

[0327] 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 the remaining capacity is calculated.

[0328] Example

[0329] The embodiments of this technology are described below.

[0330] <Examples 1-17 and Comparative Examples 1-7>

[0331] As described below, a secondary battery was fabricated, and its battery characteristics were then evaluated.

[0332] [Making a Second-hand Battery]

[0333] The following steps were used to create it. Figure 1 as well as Figure 2 The image shows a laminated film type secondary battery (lithium-ion secondary battery).

[0334] (The production of the positive electrode)

[0335] First, 91 parts by mass of the positive electrode active material (lithium cobalt oxide (LiCoO2)), 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 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.

[0336] (Making the negative electrode)

[0337] 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 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.

[0338] (Preparation of electrolyte)

[0339] First, a solvent was prepared. Ethyl carbonate and diethyl carbonate, as carbonate compounds (cyclic and chain carbonates), and propyl propionate and ethyl propionate, as carboxylic acid ester compounds (chain carboxylic acid esters), were used as the solvent. The mixing ratio (by weight) of the solvent was ethylene carbonate : diethyl carbonate : propyl propionate : ethyl propionate = 30 : 10 : 30 : 30.

[0340] Next, an electrolyte salt (lithium hexafluorophosphate (LiPF6)) was added to the solvent, and the solvent was then stirred. The concentration of the electrolyte salt relative to the solvent was 1 mol / kg.

[0341] Next, additives (ethylene carbonate as an unsaturated cyclic carbonate and fluoroethylene carbonate as a halocarbonate) were added to the solvent, and then the solvent was stirred.

[0342] Finally, the diester compound and the sulfur-containing compound were added to the solvent, and the solvent was stirred. The types of the diester compound and the sulfur-containing compound are shown in Table 1. Thus, the electrolyte salt, additives, diester compound, and sulfur-containing compound were dispersed or dissolved in the solvent, thereby preparing the electrolyte.

[0343] It should be noted that, for the purpose of comparison, the electrolyte was prepared using the same steps, except that neither the diester compound nor the sulfur-containing compound was used.

[0344] In addition, for comparison purposes, electrolytes were prepared using the same steps, except that other compounds were used instead of sulfur-containing compounds. The types of other compounds are shown in Table 1.

[0345] (Assembly of a secondary battery)

[0346] 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).

[0347] Next, the positive electrode 21 and the negative electrode 22 are stacked together with a separator 23 (a microporous polyethylene membrane with a thickness of 15 μm) in between, 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.

[0348] Next, the outer packaging film 10 (welding layer / metal layer / surface protective layer) is folded in such a way that the rolled body housed in the recess 10U is clamped, and then the outer peripheral portions of two sides of the outer packaging film 10 (welding layer) are heat-fused together, thereby housing the rolled body inside the bag-shaped outer packaging film 10. As the outer packaging film 10, an aluminum laminate film is used, which is stacked sequentially from the inside: 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).

[0349] 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 the battery element 20.

[0350] Therefore, the battery components are sealed inside the outer packaging film 10, thereby assembling a secondary battery.

[0351] (Stabilization of secondary batteries)

[0352] 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's theoretical capacity in 10 hours, and 0.05C refers to the current value required to fully discharge the battery's capacity in 20 hours.

[0353] Thus, due to the coating formed on the surfaces of both the positive electrode 21 and the negative electrode 22, the secondary battery is electrochemically stable. Therefore, a laminated film type secondary battery has been completed.

[0354] It should be noted that after the secondary battery was completed, the electrolyte was analyzed using inductively coupled plasma (ICP) emission spectroscopy. The results showed that the content of unsaturated cyclic carbonates and halocarbonates in the electrolyte was 1 wt%. Furthermore, the determination results of the contents (wt%) of diester compounds, sulfur-containing compounds, and other compounds in the electrolyte are shown in Table 1.

[0355] [Evaluation of Battery Characteristics]

[0356] The battery characteristics (high-temperature storage characteristics) of the secondary battery were evaluated, and the results are shown in Table 1.

[0357] In investigating the high-temperature storage characteristics, the discharge capacity (discharge capacity before storage) of the secondary battery was first measured by charging and discharging it for one cycle at room temperature (temperature = 25°C). The charge and discharge conditions were the same as those used during the stabilization treatment of the secondary battery described above.

[0358] Next, the rechargeable batteries were stored in a high-temperature environment (temperature = 60°C) for 4 weeks.

[0359] Next, the secondary battery was subjected to three charge-discharge cycles at room temperature, and the discharge capacity (discharge capacity after storage) was measured in the fourth cycle. The charge-discharge conditions were the same as those used during the stabilization treatment of the secondary battery, except that the charging current and discharging current were changed to 1 / 3C. 1 / 3C refers to the current value required to fully discharge the battery within 3 hours.

[0360] Finally, based on the formula that capacity retention rate (%) = (discharge capacity after storage / discharge capacity before storage) × 100, the capacity retention rate, which is used as an indicator to evaluate the high-temperature storage characteristics, is calculated.

[0361] [Table 1]

[0362] Table 1

[0363] [Inspection]

[0364] As shown in Table 1, the capacity retention varies significantly depending on the composition of the electrolyte. Hereinafter, the capacity retention of electrolytes that do not contain either diester compounds or sulfur-containing compounds (Comparative Example 1) will be used as a comparison benchmark.

[0365] When the electrolyte contains diester compounds and other compounds (Comparative Examples 2-7), the capacity retention rate only increases slightly, and therefore a high capacity retention rate cannot be obtained. In contrast, when the electrolyte contains diester compounds and sulfur-containing compounds (Examples 1-17), the capacity retention rate increases significantly, and therefore a significantly high capacity retention rate is obtained.

[0366] <Examples 18-25>

[0367] As shown in Table 2, secondary batteries were fabricated using the same steps, except for changing the contents of diester compounds and sulfur-containing compounds in the electrolyte. The battery characteristics of the secondary batteries were then evaluated.

[0368] [Table 2]

[0369] Table 2

[0370]

[0371] As shown in Table 2, when the content of diester compounds in the electrolyte is 0.001% to 5% by weight (Examples 8, 19, 20), the capacity retention rate is further increased, and when the content of sulfur-containing compounds in the electrolyte is 0.001% to 5% by weight (Examples 8, 23, 24), the capacity retention rate is further increased.

[0372] [Summarize]

[0373] The results shown in Tables 1 and 2 indicate that a high capacity retention rate can be obtained when the electrolyte contains both diester compounds and sulfur-containing compounds. Therefore, excellent storage characteristics can be achieved in secondary batteries.

[0374] The above description, which presents the present technology through one implementation method and embodiment, does not limit the structure of the present technology to the structure described in one implementation method and embodiment, and various modifications are possible.

[0375] Specifically, the case where the secondary battery structure is a laminated film type has been described. However, since the battery structure of a secondary battery is not particularly limited, it can also be cylindrical, square, coin-shaped, or button-shaped, etc.

[0376] Furthermore, the case where the battery element structure is a wound type has been explained. However, since the battery element structure is not particularly limited, it can be a stacked type where the positive and negative electrodes are stacked on top of each other, or a repeatedly folded type where the positive and negative electrodes are folded into a Z-shape, etc.

[0377] Furthermore, while the use of lithium as the electrode reactant has been described, it is not particularly limited. Specifically, as mentioned 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.

[0378] It should be noted that the above-mentioned electrolyte is not limited to secondary batteries, and therefore it can also be used in other electrochemical devices such as capacitors.

[0379] 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 The electrolyte comprises a solvent, an electrolyte salt, a diester compound represented by formula (1), and a sulfur-containing compound represented by formula (5). R1 is any one of a halogen group and an alkyl group, R2 is an alkoxy group, and R3 to R6 are any one of a hydrogen group and an alkyl group, respectively. R17 and R18 are alkyl groups, and R17 and R18 are bonded to each other.

2. The secondary battery according to claim 1, wherein, The alkyl group is methyl or ethyl. The alkoxy group is ethoxy or propoxy.

3. The secondary battery according to claim 1 or 2, wherein, The content of the diester compound in the electrolyte is more than 0.001% by weight and less than 5% by weight.

4. The secondary battery according to claim 1 or 2, wherein, The content of the sulfur-containing compound in the electrolyte is more than 0.001% by weight and less than 5% by weight.

5. The secondary battery according to claim 1 or 2, wherein, The secondary battery is a lithium-ion secondary battery.

6. An electrolyte for a secondary battery, comprising: Solvent; Electrolyte salts; Diester compounds represented by formula (1); and The sulfur-containing compound represented by formula (5), R1 is any one of a halogen group and an alkyl group, R2 is an alkoxy group, and R3 to R6 are any one of a hydrogen group and an alkyl group, respectively. R17 and R18 are alkyl groups, and R17 and R18 are bonded to each other.

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