Non-aqueous electrolyte and battery

Abstract

To solve the problem that a large amount of lithium sources are consumed in forming an interface film by using an existing electrolyte additive, the present application provides a nonaqueous electrolyte and a battery, the nonaqueous electrolyte comprising a lithium salt, an organic solvent and an additive, the lithium salt comprising one or more of compounds shown in structural formula I, the structural formula I being wherein R1-R3 are each independently selected from H, F, CN, C n F 2n+1 or (CF3) m CH2O, n is an integer between 1-6, and m is an integer between 1-3.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a non-aqueous electrolyte and a battery. BACKGROUND

[0002] Lithium batteries have been widely used in household appliances, portable electronic devices and electric vehicles due to their high energy density and high voltage. However, the growth of lithium dendrites on the negative electrode side, the cracking of the solid electrolyte interface film (SEI film) and the decomposition of the electrolyte on the positive electrode side, and the transition metal dissolution during the cycle process hinder 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 to realize high-voltage and high-energy-density lithium batteries. Among them, high-concentration electrolyte can form LiF inorganic compounds 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 the electrode and the separator, and the cost of high-concentration electrolyte 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 to construct an effective interface film, which consumes a large amount of lithium source and is not conducive to the prolongation of the battery life. In contrast, the method of optimizing the type of lithium salt is relatively low in cost. Therefore, it is necessary to design and synthesize new lithium salts to improve the cycle performance of the battery and form a good SEI on the lithium battery negative electrode and a positive electrode electrolyte interface film (CEI film) on the positive electrode. SUMMARY

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

[0005] The technical scheme adopted by the application to solve the above technical problems is as follows:

[0006] In one aspect, the application provides a non-aqueous electrolyte, which comprises a lithium salt, an organic solvent and an additive, wherein the lithium salt comprises one or more of the compounds shown in structural formula I, and the structural formula I is

[0007]

[0008] wherein R1-R3 are each 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 nonaqueous electrolyte is 0.01M-2M.

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

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

[0012]

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

[0014] Optionally, the lithium salt further 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, methyl ethyl 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, ethylene sulfate, propylene sulfate, ethylene sulfite, and propylene sulfite.

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

[0018] In another aspect, the present application provides a battery including a positive electrode sheet, a negative electrode sheet, a separator, and the nonaqueous electrolyte as claimed 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 cobaltate, lithium nickel manganese cobalt ternary material, lithium iron phosphate, and lithium manganate.

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

[0021] In the present application, the imidazole group containing N has strong water and acid removing performance, forms N + ions, and forms ion pairs with anions, and can also complex transition metal ions, avoiding the destruction of SEI by HF formed during battery use and the catalysis of metal ions on electrolyte systems, improving the high temperature and high pressure performance and safety performance of the battery cell. The active groups in the imidazole ring derivative can form SEI films at the positive and negative electrodes, improve the uniformity and conductivity of the SEI film, and improve the DCR (impedance). In addition, the conjugated structure of the SO2-N-SO2 group makes the anion have negative charge dispersibility and good structural flexibility, and the -SO2- group effectively shields the negative charge on the N atom. Therefore, the imine anion exhibits weak coordination performance, improves the lithium ion transference number of the electrolyte, and improves the fast charging performance of the battery cell. DETAILED DESCRIPTION

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

[0023] An embodiment of the present application provides a non-aqueous electrolyte, comprising a lithium salt, an organic solvent and an additive, wherein the lithium salt comprises one or more of compounds shown in structural formula I, and the structural formula I is

[0024]

[0025] wherein, R1-R3 are each 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 application, the imidazole group containing N has strong water and acid removing performance, forms N + ions, and forms ion pairs with anions, and can also complex transition metal ions, avoiding the destruction of SEI by HF formed during battery use and the catalysis of metal ions on electrolyte systems, improving the high temperature and high pressure performance and safety performance of the battery cell. The active groups in the imidazole ring derivative can form SEI films at the positive and negative electrodes, improve the uniformity and conductivity of the SEI film, and improve the DCR (impedance). In addition, the conjugated structure of the SO2-N-SO2 group makes the anion have negative charge dispersibility and good structural flexibility, and the -SO2- group effectively shields the negative charge on the N atom. Therefore, the imine anion exhibits weak coordination performance, improves the lithium ion transference number of the electrolyte, and improves the fast charging performance of the battery cell.

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

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

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

[0030] In some embodiments, the content of the organic solvent is 35% to 90% and the content of the additive is 0.1% to 20%, based on 100% of the mass of the nonaqueous electrolyte. By adjusting the content of the organic solvent, the viscosity of the electrolyte is improved, and the migration rate of lithium ions in the electrolyte is ensured. By adjusting the content of the additive, the occurrence of side reactions of the electrolyte during charging and discharging can be inhibited, the generation of gas is reduced, the swelling rate of the battery is improved, the overcharge safety performance of the electrochemical device at high temperature is improved, and the storage performance of the battery under high-temperature conditions is effectively improved.

[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%, and 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, the content of the organic solvent is 35% to 80% and the content of the additive is 0.1% to 15%, based on 100% of the mass of the nonaqueous electrolyte. By adjusting the content of the organic solvent, the viscosity of the electrolyte is improved, and the migration rate of lithium ions in the electrolyte is ensured. By adjusting the content of the additive, the occurrence of side reactions of the electrolyte during charging and discharging can be further inhibited, the generation of gas is reduced, the swelling rate of the battery is improved, the overcharge safety performance of the electrochemical device at high temperature is improved, and the storage performance of the battery under high-temperature conditions is effectively improved.

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

[0034]

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

[0036] Further, the preparation method of the substance of structural formula I

[0037] As shown in formula II,

[0038]

[0039] Formula II,

[0040] Specifically, imidazole solution and triethylamine are added to dichloromethane solution, stirred uniformly, 1 mol acyl chloride is added dropwise, and the reaction is carried out at 60°C for 2h to obtain compound a.

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

[0042] Compound b and triethylamine (catalyst) are added to dichloromethane solvent, and sulfuryl chloride is added dropwise, stirred uniformly, and reacted at 60°C to obtain compound c.

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

[0044] R1K is added to the solution of compound d, stirred uniformly, reacted in an ice water bath for several hours, and the reaction product compound e is collected, and then lithium hydroxide is added to obtain the 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 is not particularly limited, but when the content of the lithium salt is less than 0.1M, the number of movable 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, a decrease in the migration rate of lithium ions, and a possible decrease in the performance of the battery.

[0046] In a preferred embodiment, the concentration of the lithium salt is 0.9M-1M. The electrolyte meeting 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 salt, the number of lithium ions that can migrate in the electrolyte is ensured.

[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 solvent is arbitrary within a range that does not significantly impair the effects of the lithium ion battery of the present application, but in the case of using one alone, the lower limit of the content is generally 3% by volume or more, preferably 5% by volume or more, relative to the total amount of the solvent of the nonaqueous electrolyte. By setting this range, a decrease in conductivity due to a decrease in the dielectric constant of the nonaqueous electrolyte can be avoided, and it is easy to bring the large-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the nonaqueous electrolyte battery to a good range. In addition, the upper limit is generally 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less. By setting this range, the oxidation / reduction resistance of the nonaqueous electrolyte can be improved, thereby contributing to an improvement in stability at the time of high-temperature storage.

[0049] In some embodiments, 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.

[0050] In some embodiments, the nonaqueous electrolyte further comprises 5% to 20% by mass of the additive.

[0051] By adding the above additive, the occurrence of side reactions of the electrolyte during charge and discharge 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 temperatures can be improved, and the storage performance of the battery at high temperatures can be effectively improved.

[0052] In another aspect, an embodiment of the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and the nonaqueous electrolyte according to any one of the above.

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

[0054] The negative electrode sheet includes a negative electrode active material including one or more of natural graphite, artificial graphite, meso-phase micro carbon sphere, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, Sn02, Ti02-Li4Ti50 12 and Li-Al alloy.

[0055] The application is further illustrated by the following examples.

[0056] Example 1

[0057] This example is used to illustrate the non-aqueous electrolyte and battery disclosed in the present application, including the following operation steps:

[0058] Preparation of non-aqueous electrolyte

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

[0060] Preparation of positive electrode sheet:

[0061] The positive electrode active material lithium cobaltate (LiCo02), conductive agent CNT, and binder polyvinylidene fluoride are mixed in a weight ratio of 97:1.5:1.5 in N-methylpyrrolidone solvent, and stirred sufficiently to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector Al foil, dried, cold-pressed to obtain the positive electrode sheet. Other positive electrode materials such as lithium manganate (LiMn204), 532 ternary (LiNi 0.5 Co 0.3 Mn 0.2 ) are prepared in a similar manner;

[0062] Preparation of negative electrode sheet:

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

[0064] Preparation of lithium ion battery:

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

[0066] Examples 2-16

[0067] Examples are used to illustrate the non-aqueous electrolyte and battery disclosed in the present application, including most of the operation steps in Example 1, the difference is that the formula in Table 1 is used.

[0068] Comparative Examples 1-7

[0069] Comparative examples are used to illustrate the non-aqueous electrolyte and battery disclosed in the present application, including most of the operation steps in Example 1, the difference is that the formula in Table 1 is used.

[0070] Table 1

[0071]

[0072]

[0073] Performance test

[0074] I. The following performance tests were performed on the sodium ion batteries prepared in the above examples and comparative examples:

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

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

[0077] Table 2

[0078]

[0079]

[0080] The results of Examples 1-12 and Comparative Examples 1-7 demonstrate that, given the same solvent and additive components, batteries using the substance of Structural Formula I exhibit better cycle performance than batteries using LiPF6. The results of Examples 13 and 14 and Comparative Examples 1 and 4 demonstrate that the cycling performance of batteries using the substance of Structural Formula I in combination with LiPF6 as a conductive lithium salt is improved compared to batteries using LiPF6 alone. The results of Examples 15 and 16 and Comparative Examples 6 and 7 demonstrate that, when the additive content in the electrolyte formulation is reduced, the addition of the substance of Structural Formula I significantly improves battery performance. The main reason for the difference in battery performance between Examples 1-13 and Comparative Examples 1-5 is that the substance of Structural Formula I is more stable than LiPF6, maintaining excellent system stability during battery operation, especially during cycling, which in turn impacts the battery's cycle life. The difference in battery performance between Examples 13 and 14 and Comparative Examples 1 and 4 is primarily due to the fact that the nitrogen-containing groups in the substance of Structural Formula I can adsorb and dissociate with hydrofluoric acid, preventing hydrofluoric acid from damaging the SEI membrane and thus affecting the battery's cycling performance. The test results of Examples 5 and 17-20 show that the concentration of the substance of formula I within the range of 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 scope of protection of the present invention.

Claims

1. A nonaqueous electrolyte, characterized by comprising: The lithium salt comprises one or more of compounds represented by structural formula I, the structural formula I is wherein R1-R3 are each independently selected from H, F, CN, C n F 2n+1 or (CF3) m CH2O, n is an integer between 1-6, and m is an integer between 1-3.

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

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

4. The nonaqueous electrolyte according to claim 1, characterized by The substance of structural formula I comprises one or more of structural formulas I-1-I-8, 5. The nonaqueous electrolyte according to claim 1, wherein The concentration of the lithium salt is 0.1M-2.0M.

6. The nonaqueous electrolyte according to claim 1, wherein 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.

7. The non-aqueous electrolyte according to claim 1, characterized in that The organic solvent is one or more of vinyl 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 nonaqueous electrolyte according to claim 1, wherein The additive is one or more of vinylene carbonate, vinyl ethylene carbonate, fluoro-vinylene carbonate, difluoro-vinylene carbonate, 1,3-propane sultone, 1,4-butane sultone, ethylene sulfate, propylene sulfate, ethylene sulfite and propylene sulfite. The mass content of the additive in the non-aqueous electrolyte is 5%-20%.

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

10. The battery of claim 9, wherein, The positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises one or more of lithium cobaltate, lithium nickel manganese cobalt ternary material, lithium iron phosphate and lithium manganate; The positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises one or more of lithium cobaltate, lithium nickel manganese cobalt ternary material, lithium iron phosphate and lithium manganate; The negative electrode sheet includes a negative electrode active material including one or more of natural graphite, artificial graphite, meso-phase micro carbon sphere, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, Sn02, Ti02-Li4Ti50 12 and Li-Al alloy.

Images