Non-aqueous electrolyte and battery

Abstract

In order to solve the problem that a large number of lithium sources need to be consumed when an existing electrolyte additive forms an interfacial film, the invention provides a non-aqueous electrolyte and a battery, the non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, the lithium salt comprises one or more of compounds shown as a structural formula I, and the structural formula I is # imgabs0 #, r1 to R3 are respectively and independently selected from H, F, CN, CnF2n + 1 or (CF3) mCH2O, n is an integer between 1 and 6, and m is an integer between 1 and 3.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a non-aqueous electrolyte and a battery. Background Art

[0002] Lithium batteries have been increasingly used in household appliances, portable electronic devices, and electric vehicles due to their high energy density and high voltage. However, during the cycle, the growth of lithium dendrites on the negative electrode side of the battery, cracking of the solid electrolyte interface film (SEI film), decomposition of the electrolyte on the positive electrode side, and dissolution of transition metals have led to shortened battery life, which has hindered the development of lithium batteries.

[0003] Electrolyte engineering can adjust the above-mentioned problems on the negative electrode side and the positive electrode side, and is considered to be a key and practical method for achieving high-voltage, high-energy-density lithium batteries. Among them, high-concentration electrolytes can form LiF inorganic compounds that are conducive to SEI enrichment. Invention patent CN112259790A discloses a dual-ion FSI- and TFSI-high-concentration electrolyte for lithium metal batteries; however, the high viscosity of most high-concentration electrolytes is not conducive to wetting electrodes and diaphragms, and the cost of high-concentration electrolytes is also relatively high. Invention patent CN113140792A discloses an additive for lithium batteries. However, the additive must be combined with the existing lithium ions in the positive and negative electrodes to form a lithium-containing compound in order to construct an effective interface film, which will consume a large amount of lithium source and is not conducive to extending the battery life. In contrast, the method of optimizing the type of lithium salt is less expensive. Therefore, it is very necessary to design and synthesize new lithium salts to improve the cycle performance of the battery cell, and to form a good SEI on the negative electrode of the lithium battery and a positive electrode electrolyte interface film (CEI film) on the positive electrode. Summary of the invention

[0004] In view of the problem that existing electrolyte additives need to consume a large amount of lithium source to form an interface film, the present invention provides a non-aqueous electrolyte and a battery.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0006] In one aspect, the present invention provides a non-aqueous electrolyte, comprising a lithium salt, an organic solvent and an additive, wherein the lithium salt comprises one or more compounds represented by structural formula I, wherein structural formula I is

[0007]

[0008] Wherein, each of R1-R3 is independently selected from H, F, CN, C n F 2n+1 or (CF3) m CH2O, n is an integer between 1 and 6, and m is an integer between 1 and 3.

[0009] Optionally, the concentration of the substance of structural formula I in the non-aqueous electrolyte is 0.01M to 2M.

[0010] Optionally, the concentration of the substance of structural formula I in the non-aqueous electrolyte is 0.5M to 1M.

[0011] Optionally, the substance of structural formula I includes one or more of structural formulas I-1 to I-8,

[0012]

[0013] Optionally, the concentration of the lithium salt is 0.1M-2M.

[0014] Optionally, the lithium salt also includes one or more of LiBF4, LiPF6, LiPF2O2, LiAsF6, LiClO4, LiSO3CF3, LiB(C2O4)2, LiBF2C2O4, LiN(SO2CF3)2 and LiN(SO2F)2.

[0015] Optionally, the organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate.

[0016] Optionally, the additive is one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, propylene sulfate, vinyl sulfite and propylene sulfite;

[0017] And / or, the mass content of the additive in the non-aqueous electrolyte is 5% to 20%.

[0018] In another aspect, the present invention provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator and the non-aqueous electrolyte as described in any one of the above.

[0019] Optionally, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel manganese cobalt ternary material, lithium iron phosphate and lithium manganese oxide;

[0020] The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes natural graphite, artificial graphite, mesophase micro carbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 and one or more of Li-Al alloys.

[0021] In the present invention, the imidazole group contains N and has strong water removal and acid removal performance, forming N + ions, and form ion pairs with anions. At the same time, they can also complex transition metal ions, avoiding the damage of HF formed during the use of the battery to SEI and the catalysis of metal ions to the electrolyte system, improving the high temperature and high pressure performance and safety performance of the battery. The active groups in the imidazole ring derivatives can form SEI films at the positive and negative electrodes, improve the uniformity and conductivity of the SEI film, and improve DCR (impedance). In addition, the conjugated structure of the SO2-N-SO2 group makes the anion have negative charge dispersion and good structural flexibility. The -SO2- group effectively shields the negative charge on the N atom. Therefore, the imine anion exhibits weak coordination properties, increases the lithium ion migration number of the electrolyte, and improves the fast charging performance of the battery. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] One embodiment of the present invention provides a non-aqueous electrolyte, including a lithium salt, an organic solvent and an additive, wherein the lithium salt includes one or more compounds represented by structural formula I, wherein structural formula I is

[0024]

[0025] Wherein, each of R1-R3 is independently selected from H, F, CN, C n F 2n+1 or (CF3) m CH2O, n is an integer between 1 and 6, and m is an integer between 1 and 3.

[0026] In the present invention, the imidazole group contains N and has strong water removal and acid removal performance, forming N + ions, and form ion pairs with anions. At the same time, they can also complex transition metal ions, avoiding the damage of HF formed during the use of the battery to SEI and the catalysis of metal ions to the electrolyte system, improving the high temperature and high pressure performance and safety performance of the battery. The active groups in the imidazole ring derivatives can form SEI films at the positive and negative electrodes, improve the uniformity and conductivity of the SEI film, and improve DCR (impedance). In addition, the conjugated structure of the SO2-N-SO2 group makes the anion have negative charge dispersion and good structural flexibility. The -SO2- group effectively shields the negative charge on the N atom. Therefore, the imine anion exhibits weak coordination properties, increases the lithium ion migration number of the electrolyte, and improves the fast charging performance of the battery.

[0027] In some embodiments, the concentration of the substance of formula I in the non-aqueous electrolyte is 0.01 M to 2 M. The electrolyte containing the substance of formula I within the above concentration range can improve the high temperature and high pressure performance and safety performance of the battery cell, reduce impedance, and increase the cycle life of the battery.

[0028] In one embodiment, the concentration of the substance of formula I is 0.01M, 0.05M, 0.1M, 0.3M, 0.5M, 0.7M, 0.9M, 1.1M, 1.3M, 1.5M, 1.7M, 1.9M or 2M.

[0029] In a preferred embodiment, the concentration of the substance of structural formula I in the non-aqueous electrolyte is 0.5 M to 1 M. The electrolyte containing the substance of structural formula I within the above concentration range can further improve the high temperature and high pressure performance and safety performance of the battery cell, reduce impedance, and increase the cycle life of the battery.

[0030] In some embodiments, based on the mass of the non-aqueous electrolyte being 100%, the content of the organic solvent is 35-90%, and the content of the additive is 0.1-20%. The viscosity of the electrolyte is improved by regulating the content of the organic solvent to ensure the migration rate of lithium ions in the electrolyte. By regulating the content of the additive, the occurrence of side reactions of the electrolyte during the charging and discharging process can be suppressed, the generation of gas can be reduced, the expansion rate of the battery can be improved, and the overcharge safety performance of the electrochemical device at high temperature can be improved, effectively improving the storage performance of the battery under high temperature conditions.

[0031] In a specific embodiment, the content of the organic solvent is 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%. The content of the additive is 0.1%, 1%, 2%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%.

[0032] In a preferred embodiment, based on the mass of the non-aqueous electrolyte being 100%, the content of the organic solvent is 35-80%, and the content of the additive is 0.1-15%. The viscosity of the electrolyte is improved by regulating the content of the organic solvent to ensure the migration rate of lithium ions in the electrolyte. By regulating the content of the additive, the occurrence of side reactions of the electrolyte during the charging and discharging process can be further suppressed, the generation of gas can be reduced, the expansion rate of the battery can be improved, and the overcharge safety performance of the electrochemical device at high temperature can be improved, effectively improving the storage performance of the battery under high temperature conditions.

[0033] In some embodiments, the substance of formula I comprises one or more of formulas I-1 to I-8,

[0034]

[0035] By selecting the above-mentioned lithium salts, the high temperature and high pressure performance and safety performance of the battery cell can be further improved, the DCR (impedance) can be reduced, the lithium ion migration number of the electrolyte can be increased, and the fast charging performance of the battery cell can be improved.

[0036] Furthermore, the preparation method of the substance of formula I

[0037] As shown in formula II,

[0038]

[0039] Formula II,

[0040] Specifically, imidazole solution and triethylamine were added to dichloromethane solution, stirred evenly, 1 mol of acyl chloride was added dropwise, and reacted at 60° C. for 2 h to obtain compound a.

[0041] Compound a and allyl alcohol are added to a dichloromethane solvent, triethylamine is added as a catalyst, and the mixture is stirred evenly. A nucleophilic substitution reaction occurs at 60° C. to obtain compound b.

[0042] Compound b and triethylamine (catalyst) were added to dichloromethane solvent, and sulfonyl chloride was added dropwise, stirred evenly, and reacted at 60° C. to obtain compound c.

[0043] Compound c was added to dichloromethane solvent, and after mixing evenly, catalyst triethylamine was added, and the mixture was stirred evenly. The mixture was reacted at 60° C. to obtain compound d.

[0044] Add R1K to the solution of compound d, stir evenly, and react in an ice-water bath for several hours. Collect the reaction product compound e, and then add lithium hydroxide to obtain a substance of structural formula I.

[0045] In some embodiments, the concentration of the lithium salt is 0.1M-2M. The concentration of the lithium salt in the electrolyte is not particularly limited, but when the content of the lithium salt is lower than 0.1M, the number of mobile lithium ions in the electrolyte is insufficient, and when the content of the lithium salt is higher than 2M, the viscosity of the electrolyte may increase, resulting in an increase in the impedance of the electrolyte, which reduces the migration rate of lithium ions and may reduce the performance of the battery.

[0046] In a preferred embodiment, the concentration of the lithium salt is 0.9 M-1 M. The electrolyte that meets the above conditions ensures the migration rate of lithium ions and further improves the electrochemical performance of the battery.

[0047] In some embodiments, the lithium salt further comprises one or more of LiBF4, LiPF6, LiPF2O2, LiAsF6, LiClO4, LiSO3CF3, LiB(C2O4)2, LiBF2C2O4, LiN(SO2CF3)2 and LiN(SO2F)2. By selecting the above ionizable lithium salts, the amount of lithium ions that can migrate in the electrolyte is guaranteed.

[0048] In some embodiments, the organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate. The above solvents are arbitrary within the range that does not significantly damage the effect of the lithium ion battery of the present invention, but when one is used alone, the lower limit of its content is usually 3% or more by volume, preferably 5% or more by volume relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, the conductivity can be reduced due to the reduction in the dielectric constant of the non-aqueous electrolyte, and it is easy to make the large current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery reach a good range. In addition, the upper limit is usually 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby helping to improve the stability during high temperature storage.

[0049] In some embodiments, the additive is one or more of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, propylene sulfate, vinyl sulfite, and propylene sulfite.

[0050] And / or, the mass content of the additive in the non-aqueous electrolyte is 5% to 20%.

[0051] By adding the above-mentioned additives, the occurrence of side reactions in the electrolyte during the charge and discharge process can be further inhibited, gas generation can be reduced, the expansion rate of the battery can be improved, and the overcharge safety performance of the electrochemical device at high temperature can be improved, which can effectively improve the storage performance of the battery under high temperature conditions.

[0052] On the other hand, an embodiment of the present invention provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the non-aqueous electrolyte as described in any one of the above.

[0053] In some embodiments, the positive electrode sheet includes a positive electrode active material, which includes one or more of lithium cobalt oxide, lithium nickel manganese cobalt ternary material, lithium iron phosphate and lithium manganese oxide, which helps to improve the high temperature cycle performance of the battery.

[0054] The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes natural graphite, artificial graphite, mesophase micro carbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 and one or more of Li-Al alloys.

[0055] The present invention is further described below by way of examples.

[0056] Example 1

[0057] This embodiment is used to illustrate the non-aqueous electrolyte and battery disclosed in the present invention, and includes the following operating steps:

[0058] Preparation of non-aqueous electrolyte

[0059] Ethylene carbonate, diethyl carbonate and propyl propionate are mixed in a mass ratio of 1:1:1 as an organic solvent. Add additives and lithium salts in the proportions shown in Table 1 to the organic solvent and mix well to obtain the desired electrolyte. Among them, VC is vinylene carbonate, PS is 1,3-propane sultone, FEC is fluoroethylene carbonate, and SN is succinonitrile;

[0060] Production of positive electrode:

[0061] The positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent CNT, and the binder polyvinylidene fluoride are fully stirred and mixed in N-methylpyrrolidone solvent at a weight ratio of 97:1.5:1.5 to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector Al foil, dried, and cold pressed to obtain a positive electrode sheet. Other positive electrode materials such as lithium manganese oxide (LiMn2O4), 532 ternary (LiNi 0.5 Co 0.3 Mn 0.2 ) is prepared in a similar manner;

[0062] Negative electrode production:

[0063] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in a proper amount of deionized water solvent at a mass ratio of 95:2:2:1 to form a uniform negative electrode slurry. The slurry is coated on the negative electrode current collector Cu foil, dried, and cold pressed to obtain a negative electrode sheet. Other negative electrode materials such as lithium titanate are prepared in a similar manner;

[0064] Lithium-ion battery production:

[0065] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is in the middle of the positive and negative electrodes to play an isolating role, and then they are wound to form a bare cell. The bare cell is placed in an outer packaging bag, and the prepared electrolyte is injected into the dried battery. After vacuum packaging, standing, forming, shaping and other processes, the preparation of a 4Ah lithium-ion battery is completed.

[0066] Example 2-16

[0067] The examples are used to illustrate the non-aqueous electrolyte and battery disclosed in the present invention, and include most of the operating steps in Example 1, except that the formulation in Table 1 is used.

[0068] Comparative Examples 1-7

[0069] The comparative example is used to compare and illustrate the non-aqueous electrolyte and battery disclosed in the present invention, and includes most of the operating steps in Example 1, except that the formula in Table 1 is used.

[0070] Table 1

[0071]

[0072]

[0073] Performance Testing

[0074] 1. The sodium ion batteries prepared in the above examples and comparative examples were subjected to the following performance tests:

[0075] Test 1: 25℃ cyclic charge and discharge test at 1C, record the discharge capacity of the battery in the third week and the 700th week of 25℃ cyclic charge and discharge, and calculate according to the following formula: 700th week capacity / 3rd week capacity × 100%.

[0076] Test 2: 45℃ cyclic charge and discharge test at 1C, record the discharge capacity of the battery at 45℃ cyclic charge and discharge in the third week and the 500th week, and calculate according to the following formula: 500th week capacity / 3rd week capacity × 100%. The test results are shown in Table 2.

[0077] Table 2

[0078]

[0079]

[0080] The results of Examples 1 to 12 and Comparative Examples 1 to 7 show that, under the same solvent and additive components, the battery using the substance of formula I has better cycle performance than the battery using LiPF6. From the results of Examples 13, 14 and Comparative Examples 1 and 4, it can be seen that the substance of formula I and LiPF6 are used as conductive lithium salts, and the cycle performance of the corresponding battery is improved compared with the battery using LiPF6 alone. The results of Examples 15, 16 and Comparative Examples 6 and 7 show that when the content of additives in the electrolyte formula is reduced, the battery performance can be significantly improved by adding the substance of formula I. The main reason for the difference in battery performance that can be seen from the test results of Examples 1 to 13 and Comparative Examples 1 to 5 is that the substance of formula I is more stable than LiPF6, and can maintain excellent stability of the system during battery operation, especially during the cycle process, thereby affecting the cycle life of the battery. The difference in battery performance reflected in Examples 13, 14 and Comparative Examples 1 and 4 is mainly due to the fact that the N-containing group in the structure of the substance of formula I can be adsorbed and freed in hydrofluoric acid, avoiding the damage of hydrofluoric acid to the SEI film and thus affecting the cycle performance of the battery. It can be seen from the test results of Examples 5 and 17-20 that the concentration of the substance of structural formula I within 0.5M to 1M can significantly improve the battery performance.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that: It includes a lithium salt, an organic solvent and an additive, wherein the lithium salt includes one or more compounds shown in structural formula I, wherein structural formula I is Wherein, each of R1-R3 is independently selected from H, F, CN, C n F 2n+1 or (CF3) m CH2O, n is an integer between 1 and 6, and m is an integer between 1 and 3.

2. The non-aqueous electrolyte according to claim 1, characterized in that The concentration of the substance of structural formula I in the non-aqueous electrolyte is 0.01M to 2M.

3. The non-aqueous electrolyte according to claim 2, characterized in that The concentration of the substance of structural formula I in the non-aqueous electrolyte is 0.5M to 1M.

4. The non-aqueous electrolyte according to claim 1, characterized in that The substance of structural formula I includes one or more of structural formulas I-1 to I-8, 5. The non-aqueous electrolyte according to claim 1, characterized in that The concentration of the lithium salt is 0.1M-2.0M.

6. The non-aqueous electrolyte according to claim 1, characterized in that The lithium salt also includes one or more of LiBF4, LiPF6, LiPF2O2, LiAsF6, LiClO4, LiSO3CF3, LiB(C2O4)2, LiBF2C2O4, LiN(SO2CF3)2 and LiN(SO2F)2.

7. The non-aqueous electrolyte according to claim 1, characterized in that The organic solvent is one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate and butyl propionate.

8. The non-aqueous electrolyte according to claim 1, characterized in that The additive is one or more of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, propylene sulfate, vinyl sulfite and propylene sulfite; And / or, the mass content of the additive in the non-aqueous electrolyte is 5% to 20%.

9. A battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the non-aqueous electrolyte according to any one of claims 1 to 8.

10. The battery according to claim 9, characterized in that The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes one or more of lithium cobalt oxide, lithium nickel manganese cobalt ternary material, lithium iron phosphate and lithium manganese oxide; The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes natural graphite, artificial graphite, mesophase micro carbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 and one or more of Li-Al alloys.

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