Lithium battery electrolyte and lithium battery

Abstract

In order to solve the deficiency of 1,3-propanesultone as an additive, the application provides a lithium battery electrolyte and a lithium battery. The electrolyte comprises an organic solvent, a lithium salt and an additive, and the additive comprises a thiophene compound as shown in general formula (I), wherein R1 is a non-hydrogen group, R2-R3 are H or an organic group, and at least one of R1-R3 is a halogen-substituted or unsubstituted pinacol borate group. The thiophene compound in the electrolyte of the application can replace 1,3-propanesultone, and can participate in the film formation of the positive and negative electrodes, improve the electrode kinetic and thermodynamic properties, reduce the impedance of the interface film, reduce the gas production during battery formation and storage, improve the voltage drop of the battery during full charge storage, and improve the stability of the electrolyte.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a lithium battery electrolyte and a lithium battery. Background Technology

[0002] Lithium-ion batteries have a wide range of applications in power batteries, energy storage, and 3C products due to their inherent advantages such as high specific capacity, high cycle performance, and environmental friendliness.

[0003] Electrolytes, one of the four main components of lithium-ion batteries, are typically composed of non-aqueous organic solvents, lithium salts, and additives. Conventional non-aqueous organic solvents, due to differences in their physical properties, are typically composed of chain carbonates, chain carboxylic esters, and cyclic carbonates, used in combination depending on the specific application. Lithium salts are composed of lithium hexafluorophosphate or a composite lithium salt of lithium hexafluorophosphate and lithium difluorosulfonylimide. Additives are substances added in small quantities but with single or multiple functions, forming a solid interfacial film on the positive and negative electrode surfaces, significantly improving battery performance. For example, 1,3-propanesulfonate lactone, widely used in the industry, can improve the battery's high-temperature storage and high-temperature cycling performance; however, its addition increases the battery's internal resistance, which is detrimental to low-temperature and high-rate charge / discharge operations. Furthermore, like other activated esters, 1,3-propanesulfonate lactone is a toxic, teratogenic, and mutagenic alkylating agent, which will inevitably have a significant impact on human health and the environment. The European Union is planning to ban batteries or related products containing 1,3-propanesulfonate lactone, and will gradually implement this ban over the next 5-10 years.

[0004] Therefore, it is necessary to develop some new additives to partially or completely replace the above-mentioned additives, thereby further improving battery performance. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium battery electrolyte and a lithium battery that can reduce or eliminate the addition of 1,3-propanesulfonate lactone.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A first aspect of this invention provides a lithium battery electrolyte comprising an organic solvent, a lithium salt, and an additive, wherein the additive comprises a thiophene compound as shown in general formula (I).

[0008]

[0009] Wherein, R1 is a non-hydrogen group, R2 to R3 are H or organic groups, and at least one of R1 to R3 is a halogen-substituted or unsubstituted pinacol ester group of borate.

[0010] According to some specific implementations, R1 is an organic group.

[0011] According to some specific embodiments, the organic group is a halogen-substituted or unsubstituted alkyl group with 1-5 carbon atoms, a halogen-substituted or unsubstituted alkenyl group with 3-5 carbon atoms, a halogen-substituted or unsubstituted ester group with 2-5 carbon atoms, a halogen-substituted or unsubstituted alkynyl group with 3-5 carbon atoms, a halogen-substituted or unsubstituted cyano group with 1-3 carbon atoms, or Si(CH3)3(CH2). n - A substituted or unsubstituted pinacol ester group of borate or a halogenated or unsubstituted alkyl ether group with 1 to 3 carbon atoms.

[0012] According to some specific embodiments, the halogen is fluorine, chlorine, bromine or iodine.

[0013] According to some specific embodiments, the substitution means that the hydrogen on the organic group is partially or completely replaced by a halogen.

[0014] According to some specific embodiments, the organic group is methyl, fluoromethyl, ethyl, fluoroethyl, propyl, fluoropropyl, propenyl, fluoropropenyl, methyl ester, fluoromethyl ester, ethyl ester, fluoroethyl ester, propynyl, fluoropropynyl, pinacol ester, methyl ether, fluoromethyl ether, ethyl ether, or fluoroethyl ether.

[0015] Furthermore, the fluorine substitution is either complete or partial.

[0016] According to some more specific and preferred embodiments, the thiophene compound is selected from one or more of the following compounds:

[0017]

[0018] According to some specific embodiments, the thiophene compound accounts for 0.01% to 5% of the total mass of the lithium battery electrolyte, for example, 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%... %, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, etc.

[0019] Further, the thiophene compound accounts for 0.01% to 3% of the total mass of the lithium battery electrolyte. Even further, the thiophene compound accounts for 0.5% to 3% of the total mass of the lithium battery electrolyte. Still further, the thiophene compound accounts for 0.5% to 1.8% of the total mass of the lithium battery electrolyte.

[0020] According to some specific embodiments, the additive also includes other additives selected from one or more of the following: fluoroethylene carbonate (FEC), succinate (SN), adiponitrile (ADN), 1,3,6-hexanetrionitrile (HTCN), 1,2-bis(cyanoethoxy)ethane, 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone, vinylene carbonate (VEC), vinyl sulfate (DTD), tris(trimethyl)silylborate (TMSB), triallyl isocyanurate (TAIC), tris(trimethylsilyl)phosphate (TMSP), lithium difluorophosphate (LiPO2F2), and vinylene carbonate (VC).

[0021] Further, the other additives in the lithium battery electrolyte have a mass percentage of 2% to 10%, specifically 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, and 5.6%. %, 5.7%, 5.8%, 5.9%, 6%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5%, 9.6%, 9.7%, 9.8%, 9.9%, 10%.

[0022] Furthermore, the other additives include lithium difluorophosphate, vinylene carbonate, and vinyl sulfate in a mass ratio of 0.5–1:0.2–0.8:1.

[0023] According to some specific embodiments, the lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium hexafluorophosphate (LiPF6), lithium carbonate, lithium sulfate, lithium sulfite, lithium nitrate (LiNO3), lithium bis(fluorosulfonyl)imide (LiFSi), lithium bis(trifluoromethylsulfonyl)imide (LiTFSi), lithium difluorophosphate (LiPO2F2), and lithium difluorobis(oxalate) phosphate (LiDFOP).

[0024] Furthermore, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium difluorophosphate, and lithium nitrate.

[0025] According to some specific embodiments, the lithium salt accounts for 8% to 20% of the total mass of the lithium battery electrolyte, for example, 8%, 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0026] According to some specific embodiments, the organic solvent is selected from one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl butyrate, methyl acrylate, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, N,N-dimethylformamide, sulfolane, dimethyl sulfoxide, dimethyl sulfide, γ-butyrolactone, and tetrahydrofuran.

[0027] According to some more specific embodiments, the organic solvent is dimethyl carbonate, ethylene carbonate, propylene carbonate and ethyl methyl carbonate in a volume ratio of 2-6:2-6:1:8-15.

[0028] The present invention also provides a lithium battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0029] According to some specific embodiments, the active material of the positive electrode is a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide includes one or more of the following: lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and compounds obtained by adding other transition metals or non-transition metals to the above lithium transition metal composite oxide.

[0030] According to some specific embodiments, the active material of the negative electrode is selected from one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon-carbon composite, lithium titanate, and metals that can form alloys with lithium.

[0031] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0032] The thiophene compounds in the electrolyte of this invention can replace 1,3-propanesulfonic acid lactone, and can participate in the formation of positive and negative electrode films, improve the kinetic and thermodynamic properties of the electrodes, reduce the impedance of the interfacial film, reduce gas generation during battery formation and storage, improve the voltage drop of the battery when stored in a fully charged state, and improve the stability of the electrolyte.

[0033] When used in combination with other additives, the stability of the positive and negative electrode films can be further enhanced, and the cycle performance of the battery under high temperature conditions can be improved. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0035] Unless otherwise specified, the reagents, instruments, etc. used in the following examples and comparative examples are all commercially available products commonly used in the art, or can be prepared using conventional methods in the art. In this invention, unless otherwise specified, all contents are mass contents, "%" is mass percentage, and parts are parts by mass.

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the ranges, the endpoint values ​​of the ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0037] The preparation methods of the lithium-ion battery and electrolyte used in this invention are as follows:

[0038] Example 1

[0039] In a glove box filled with argon (water and oxygen content both less than 0.1 ppm), dimethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 20 / 20 / 5 / 55. 0.8 parts of lithium difluorophosphate (LiPO2F2), 0.5 parts of vinylene carbonate (VC), and 1 part of vinyl sulfate (DTD) were added. LiPF6 was added to bring the lithium salt concentration to 1.0 mol / L. After stirring until homogeneous, 100 parts of the basic electrolyte were obtained.

[0040] Take 99.5 parts of the basic electrolyte and add 0.5 parts of compound 1 to obtain the electrolyte used in this example.

[0041] The positive electrode, separator, and negative electrode are fabricated into a dry cell, which is then installed in a battery casing. The lithium-ion battery electrolyte of this embodiment is injected, followed by formation, degassing, secondary sealing, and volume determination to obtain the final lithium-ion battery. The positive electrode is NCM712, the negative electrode is graphite, the cell design capacity is 2000mAh, and the battery charge / discharge range is 2.75–4.4V.

[0042] Example 2

[0043] It is largely the same as Example 1, except that: the base electrolyte is 99 parts and the amount of compound 1 added is 1 part.

[0044] Example 3

[0045] It is largely the same as Example 1, except that: the base electrolyte is 98 parts and the amount of compound 1 added is 2 parts.

[0046] Example 4

[0047] It is largely the same as Example 1, except that: the base electrolyte is 97 parts and the amount of compound 1 added is 3 parts.

[0048] Example 5

[0049] It is largely the same as Example 1, except that: the base electrolyte is 95 parts and the amount of compound 1 added is 5 parts.

[0050] Example 6

[0051] It is largely the same as Example 1, except that compound 1 is replaced with compound 2 and the amount added is 0.5 parts.

[0052] Example 7

[0053] It is largely the same as Example 2, except that compound 1 is replaced with compound 2 and the amount added is 1 part.

[0054] Example 8

[0055] It is largely the same as Example 3, except that compound 1 is replaced with compound 2 and the amount added is 2 parts.

[0056] Example 9

[0057] It is largely the same as Example 4, except that compound 1 is replaced with compound 2 and the amount added is 3 parts.

[0058] Example 10

[0059] It is largely the same as Example 1, except that compound 1 is replaced with compound 3 and the amount added is 0.5 parts.

[0060] Example 11

[0061] It is largely the same as Example 2, except that compound 1 is replaced with compound 3 and the amount added is 1 part.

[0062] Example 12

[0063] It is largely the same as Example 3, except that compound 1 is replaced with compound 3 and the amount added is 2 parts.

[0064] Example 13

[0065] It is largely the same as Example 4, except that compound 1 is replaced with compound 3 and the amount added is 3 parts.

[0066] Comparative Example 1

[0067] It is largely the same as Example 2, except that compound 1 is replaced with 1,3-propanesulfonic acid lactone and the amount added is 1 part.

[0068] Performance testing

[0069] (1) High-temperature cycling performance test at 45℃:

[0070] At 45℃, the battery is charged at a constant current and constant voltage rate of 1.0C, with a cutoff current of 0.02C, and discharged at a rate of 1.0C, with a voltage range of 2.75~4.4V.

[0071] High-temperature cycle capacity retention rate = High-temperature discharge capacity after 800 cycles / High-temperature discharge capacity after the first cycle × 100%.

[0072] (2) Gas production performance after being placed at 80℃ for 7 hours:

[0073] Charge and discharge the battery at 1.0C rate at room temperature for 5 weeks, and record the discharge capacity as C3. Then charge it at 1.0C rate to 4.4V and record the battery voltage P1. Measure the battery volume V1 before storage using the water displacement method. After storing the battery at 80℃ in an oven for 7 hours, remove it and cool it to room temperature. Measure the battery volume V2 after storage using the water displacement method again and record the battery voltage as P2. Then discharge the battery at 1.0C rate at room temperature and record the discharge capacity as C4.

[0074] The rate of change of volume during storage ΔV: ΔV=(V2-V1) / V1×100%.

[0075] Shelving capacity retention rate: Shelving capacity retention rate = C4 / C3 × 100%.

[0076] Voltage drop during rest: ΔP = P1 - P2

[0077] The high-temperature cycling and storage performance of the lithium-ion batteries of Examples 1-13 and Comparative Example 1 are shown in Table 1.

[0078] Table 1

[0079]

[0080]

[0081] The test results in Table 1 show that compounds 1-3 mentioned in this invention all improve the high-temperature cycling and high-temperature storage performance of the battery to a certain extent compared with 1,3-propanesulfonic acid lactone. Among them, compound 2 shows more significant improvement in the changes in internal resistance during high-temperature cycling and the capacity retention during storage.

[0082] To further illustrate the high-temperature performance of the compounds mentioned in this invention, the combined use of thiazole compounds and 1,3-propanesulfonic acid lactone was also investigated. Specific implementation methods are as follows:

[0083] Comparative Example 2

[0084] It is largely the same as Example 3, except that compound 1 is replaced with 1,3-propanesulfonic acid lactone and the content is 2 parts.

[0085] Example 14

[0086] It is largely the same as Example 3, except that 2 parts of compound 1 are replaced with 1 part of 1,3-propanesulfonic acid lactone and 1 part of compound 1.

[0087] Example 15

[0088] It is largely the same as Example 3, except that 2 parts of compound 1 are replaced with 1 part of 1,3-propanesulfonic acid lactone and 1 part of compound 2.

[0089] Example 16

[0090] Similar to Example 3, except that 2 parts of compound 1 were replaced with 1 part of 1,3-propanesulfonic acid lactone and 1 part of compound 3.

[0091] The battery was tested according to the performance testing method described above; the test results of 1,3-propanesulfonate lactone and the compound are shown in Table 2.

[0092] Table 2

[0093]

[0094]

[0095] The test results in Table 2 show that the compounds mentioned in this invention can be used alone in electrolytes, and can also be used in combination with existing high-temperature additives such as 1,3-propanesulfonic acid lactone (PS) to reduce the amount of PS used and reduce dependence on such toxic and harmful substances.

[0096] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A lithium battery electrolyte, comprising an organic solvent, a lithium salt, and additives, characterized in that: The additives include thiophene compounds as shown in general formula (I). Wherein, R1 is a non-hydrogen group, R2 to R3 are H or organic groups, and at least one of R1 to R3 is a halogen-substituted or unsubstituted pinacol ester group of borate.

2. The lithium battery electrolyte according to claim 1, characterized in that: R1 is an organic group.

3. The lithium battery electrolyte according to claim 1 or 2, characterized in that: The organic group is a halogenated or unsubstituted alkyl group with 1-5 carbon atoms, a halogenated or unsubstituted alkenyl group with 3-5 carbon atoms, a halogenated or unsubstituted ester group with 2-5 carbon atoms, a halogenated or unsubstituted alkynyl group with 3-5 carbon atoms, a halogenated or unsubstituted cyano group with 1-3 carbon atoms, or Si(CH3)3(CH2). n - A substituted or unsubstituted pinacol ester group of borate or a halogenated or unsubstituted alkyl ether group with 1 to 3 carbon atoms.

4. The lithium battery electrolyte according to claim 1, characterized in that: The thiophene compounds are selected from one or more of the following compounds:

5. The lithium battery electrolyte according to claim 1, characterized in that: The thiophene compound accounts for 0.01% to 5% of the total mass of the lithium battery electrolyte.

6. The lithium battery electrolyte according to claim 5, characterized in that: The thiophene compound accounts for 0.5% to 3% of the total mass of the lithium battery electrolyte.

7. The lithium battery electrolyte according to claim 1, characterized in that: The additives also include other additives selected from one or more of the following: fluoroethylene carbonate, succinate, adiponitrile, 1,3,6-hexanetrionitrile, 1,2-bis(cyanoethoxy)ethane, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinylene carbonate, vinyl sulfate, tris(trimethyl)silylborate, triallyl isocyanurate, tris(trimethylsilyl)phosphate, lithium difluorophosphate, and vinylene carbonate. The other additives constitute 2% to 10% of the lithium battery electrolyte by mass.

8. The lithium battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium hexafluorophosphate, lithium carbonate, lithium sulfate, lithium sulfite, lithium nitrate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, and lithium difluorobis(oxalate phosphate), and the mass of the lithium salt accounts for 8% to 20% of the total mass of the lithium battery electrolyte.

9. The lithium battery electrolyte according to claim 1, characterized in that: The organic solvent is selected from one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl butyrate, methyl acrylate, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, N,N-dimethylformamide, sulfolane, dimethyl sulfoxide, dimethyl sulfide, γ-butyrolactone, and tetrahydrofuran.

10. A lithium battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 9.

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