Electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte and a lithium ion battery. The electrolyte comprises a compound I. The structure of the compound I comprises an isothiocyanate group and variable R1, R2, R3 and R4 groups; wherein R1 is selected from any one of substituted or unsubstituted C1-C5 alkyl groups, silicon atoms, aryl groups and alkenyl groups, substituent groups are at least one of C1-C5 alkyl groups, alkenyl groups and cyano groups, and R2, R3 and R4 are respectively and independently selected from any one of hydrogen atoms, C1-C10 alkyl groups and cyano groups. In the electrolyte provided by the invention, the compound I can reduce contact between metal ions and the electrolyte, reduce generation of side reactions such as gas production and phase change, and promote formation of a positive electrode interface film (CEI) to inhibit continuous oxygenolysis of the electrolyte, so that the structural stability of a positive electrode material is protected; therefore, the positive and negative electrode interface side reaction of the lithium ion battery in a high-temperature working state is effectively reduced, and the application performance of the lithium ion battery at a high temperature is improved.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to an electrolyte and a lithium-ion battery. Background Technology

[0002] With the development of new energy vehicles, wearable devices, and portable mobile devices, the performance requirements for lithium-ion batteries are constantly increasing. There is a growing expectation to develop more stable lithium-ion batteries with higher energy density to meet daily needs. The performance, lifespan, and safety of lithium-ion batteries are highly dependent on the stability of the electrodes and electrolyte.

[0003] The core challenge currently facing lithium-ion battery electrolyte technology lies in how to meet the stringent requirements of high energy density, high voltage, and high temperature. Traditional electrolyte systems are prone to side reactions such as oxidation decomposition, severe gas generation, and transition metal dissolution at high temperatures, leading to serious problems such as battery gas generation, increased internal resistance, and rapid decline in cycle life.

[0004] Therefore, how to improve the overall performance of electrolytes in high-temperature environments, while taking into account the high and low temperature performance, interface stability, and cost-effectiveness of electrolytes, is a problem that needs to be solved. Summary of the Invention

[0005] The purpose of this application is to provide an electrolyte and a lithium-ion battery, aiming to solve the problem of unsatisfactory overall performance of existing electrolytes under high-temperature environments.

[0006] The first embodiment of this application provides an electrolyte comprising compound I, the structural formula of which is shown in Formula I:

[0007] Formula I; Wherein, R1 is selected from any one of substituted or unsubstituted C1-C5 alkyl, silicon, aryl, and alkenyl groups, the substituent is at least one of C1-C5 alkyl, alkenyl, and cyano groups, and R2, R3, and R4 are each independently selected from hydrogen, C1-C5 alkyl, silicon, aryl, and alkenyl groups. 10 Either alkyl or cyano.

[0008] In some embodiments, R1 is selected from any one of substituted or unsubstituted C1-C3 alkyl, silicon atom, phenyl and alkenyl groups, the substituent is at least one of C1-C3 alkyl, alkenyl and cyano groups, and R2, R3 and R4 are each independently selected from any one of hydrogen atom and C1-C3 alkyl groups.

[0009] In some embodiments, the structural formula of compound I is selected from any one of the structures shown in formulas I-1 to I-8:

[0010] In some embodiments, the electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates; The volume ratio of the cyclic carbonate to the chain carbonate is (20~25):(70~80).

[0011] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate.

[0012] In some embodiments, the chain carbonate includes at least one of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0013] In some embodiments, the electrolyte further includes a sulfur-containing compound, a carbonate compound, and a first lithium salt.

[0014] In some embodiments, the mass ratio of compound I, the sulfur-containing compound, the carbonate compound, and the first lithium salt is (0.2~0.5):(0.5~1):(3~5):(1~1.8).

[0015] In some embodiments, the sulfur-containing compound includes at least one of vinyl sulfate, methylene methane disulfonate, and 1,3-propenesulfonate lactone.

[0016] In some embodiments, the carbonate compound includes at least one of fluoroethylene carbonate and vinylene carbonate.

[0017] In some embodiments, the first lithium salt includes at least one of lithium dioxaborate, lithium difluorooxaborate, and lithium difluorophosphate.

[0018] In some embodiments, the electrolyte further includes a second lithium salt, wherein the second lithium salt comprises 12-16% by mass in the electrolyte; The second lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluorosulfonylimide.

[0019] The second embodiment of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte in any of the above embodiments; The capacity retention rate of the electrolyte after 400 cycles at 45°C is 88.3-91.3%.

[0020] This application provides an electrolyte comprising compound I, wherein the structure of compound I includes an isothiocyanate group and variable R1, R2, R3, and R4 groups; wherein R1 is selected from any one of substituted or unsubstituted C1-C5 alkyl, silicon, aryl, and alkenyl groups, the substituent is at least one of C1-C5 alkyl, alkenyl, and cyano groups, and R2, R3, and R4 are each independently selected from hydrogen, C1-C5 alkyl, silicon, aryl, and cyano groups. 10 Any one of alkyl and cyano groups. In the electrolyte provided in this application, compound I can reduce the contact between metal ions and the electrolyte, reduce the occurrence of side reactions such as gas generation and phase transition, promote the formation of a positive electrode interface film (CEI) to inhibit the continuous oxidative decomposition of the electrolyte, thereby protecting the structural stability of the positive electrode material, and thus effectively reducing the positive and negative electrode interface side reactions of lithium-ion batteries under high-temperature operating conditions, improving the application performance of lithium-ion batteries at high temperatures. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0023] Figure 1 The graph shows the test results of batteries prepared with the electrolytes provided in the embodiments and comparative examples of this application. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0025] In the description of this application, it should be noted that "multiple" means two or more, unless otherwise explicitly specified. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include one or more features.

[0026] The compounds of this application can be synthesized via synthetic routes including methods similar to those known in the field of chemistry, particularly with reference to the description contained herein. Starting materials are generally available from commercial sources or can be readily prepared using methods known to those skilled in the art. For illustrative purposes, the reaction schemes described below illustrate possible routes for synthesizing the compounds of this application and key intermediates. For a more detailed description of each reaction step, see the Examples section below. Those skilled in the art will recognize that other suitable starting materials, reagents, and synthetic routes can be used to synthesize the compounds of this application and their various derivatives.

[0027] Unless otherwise stated, the term "alkyl" as used herein refers to a saturated aliphatic hydrocarbon group, which may be straight-chain or branched. For example, the term "C1-C6 alkyl" refers to an alkyl group containing 1, 2, 3, 4, 5, or 6 carbon atoms (e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, neopentyl, hexyl, 2-methylpentyl, etc.). Similarly, the alkyl portion (i.e., alkyl) of alkoxy, alkylacyl, alkylphosphate, alkylsulfonyl, and alkylaminosulfonyl groups has the same definition above. For example, the term "C1-C3 alkyl" refers to an alkyl group containing 1, 2, or 3 carbon atoms (e.g., methyl, ethyl, propyl, and isopropyl). Alkyl groups may be substituted or unsubstituted, and when substituted, the substituents may be substituted at any usable link.

[0028] Unless otherwise stated, the term "alkenyl" as used herein refers to a straight-chain or branched aliphatic hydrocarbon chain having a plurality of carbon atoms and containing at least one carbon-carbon double bond (e.g., -C=C-, -C=CH2). Non-limiting examples of alkenyl groups include: vinyl, 1-propenyl, 2-propenyl, isopropenyl, 1-butenyl, 2-butenyl, 3-butenyl, 2-pentenyl, hexenyl, octenyl, decenyl, myrceneyl, etc.

[0029] Unless otherwise stated, the term "alkoxy" as used herein refers to -O-alkyl, where alkyl is as defined in this application.

[0030] Unless otherwise stated, the term "ester group" as used herein refers to -COO-alkyl, where alkyl is as defined in this application.

[0031] Unless otherwise stated, the term "phenyl" as used herein refers to a functional group having a benzene ring.

[0032] The following disclosure provides many different embodiments or examples for implementing different structures of this application. To simplify the disclosure of this application, the configuration and arrangement of specific examples are described below. Of course, these are merely examples and are not intended to limit this application.

[0033] For lithium-ion batteries, the stability of the electrode / electrolyte depends on whether a highly stable electrode / electrolyte interface film (CEI / SEI) can be constructed to adapt to different scenarios such as high energy density, high voltage, and fast charging.

[0034] When lithium hexafluorophosphate (LiPF6) is used as the lithium salt, along with carbonate solvents and a small amount of functional additives, this composition has significant limitations: While ethylene carbonate (EC) in the electrolyte can undergo redox decomposition on the surfaces of the ternary cathode and graphite anode, respectively, forming a protective cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI), these interfacial films lack stability at high temperatures. Furthermore, EC is more easily oxidized than chain carbonates. At approximately 3.8-4.0V, the H atoms in the EC molecule react with the oxygen atoms of the layered oxide cathode, leading to EC dehydrogenation, transition metal ion reduction, and the formation of ethylene carbonate. The active hydroxyl groups (-OH) formed on the cathode surface can further react with PF6 in the electrolyte. - The reaction releases the strong Lewis acid PF5 gas.

[0035] When the state of charge (SOC) is above approximately 80% (corresponding to a voltage > 4.2V), Ni in a high oxidation state... 4+ It will induce the generation of highly reactive singlet oxygen ( 1 O2) and triplet oxygen ( 3 O2). 1 O2 then nucleophilically attacks the EC molecule, forming a ketone group, which eventually decomposes into CO2, CO, and H2O. Simultaneously, the generated water molecules can also trigger EC hydrolysis through nucleophilic attack, further releasing CO2. On the other hand, electrolytes such as fluoroethylene carbonate (FEC) decompose at high temperatures to produce HF, corroding the positive electrode interface, leading to increased interfacial impedance and the dissolution of transition metal ions. These complex side reactions (EC oxidation and decomposition, FEC decomposition to produce acid, hydrolysis, gas production, and transition metal dissolution) mutually promote each other, forming a vicious cycle, ultimately causing serious problems such as battery gas production, increased internal resistance, and rapid decline in cycle life.

[0036] To address the aforementioned issues, the industry has attempted to improve solvent systems, but all efforts face technological bottlenecks for industrial application. For example, sulfone solvents possess ultra-high oxidation potentials exceeding 4.8V, making them suitable for extremely high-voltage systems, but they exhibit poor compatibility with graphite anodes. While ionic liquids offer advantages such as non-flammability and excellent thermal stability, their high cost and poor low-temperature performance limit their large-scale application. Therefore, using carbonates as electrolyte solvents remains the preferred choice for lithium-ion battery manufacturing processes, and optimizing carbonate solvent systems is currently a key research focus in the industry.

[0037] The applicant discovered through research that by adding special functional additives to the electrolyte, it is possible to combine them with lithium salts and organic solvents in the electrolyte system to form a stable and high-temperature resistant interfacial protective layer, thereby improving the overall performance of the electrolyte in high-temperature environments and enabling it to balance high and low temperature performance, interfacial stability, and cost-effectiveness.

[0038] The first embodiment of this application provides an electrolyte comprising compound I, the structural formula of which is shown in Formula I:

[0039] Formula I; Wherein, R1 is selected from any one of substituted or unsubstituted C1-C5 alkyl, silicon, aryl, and alkenyl groups, the substituent is at least one of C1-C5 alkyl, alkenyl, and cyano groups, and R2, R3, and R4 are each independently selected from hydrogen, C1-C5 alkyl, silicon, aryl, and alkenyl groups. 10 Either alkyl or cyano.

[0040] It is understandable that the sulfur and nitrogen atoms in the isothiocyanate (-NCS) group of compound I can coordinate with transition metals (such as Ni, Co, and Mn) during battery charging and discharging, reducing the contact between metal ions and the electrolyte, decreasing side reactions such as gas generation and phase transition, and forming a positive electrode interfacial film (CEI) to inhibit the continuous oxidative decomposition of the electrolyte. This composite coating can prevent subsequent electrolyte decomposition reactions, suppress side reactions, reduce the dissolution of transition metal ions, and protect the structural stability of the positive electrode material. In addition, the nitrogen atom in compound I contains a lone pair of electrons, which can interact with H+. + It combines with H2O and HF in the electrolyte to achieve the effects of dehydration and acid removal, further improving the high-temperature resistance of the electrolyte.

[0041] In some embodiments, R1 is selected from any one of substituted or unsubstituted C1-C3 alkyl, silicon atom, phenyl and alkenyl groups, the substituent is at least one of C1-C3 alkyl, alkenyl and cyano groups, and R2, R3 and R4 are each independently selected from any one of hydrogen atom and C1-C3 alkyl groups.

[0042] It is understandable that when compound I contains silicon atoms, it can react with HF to generate inert SiF4, blocking the HF corrosion path. Furthermore, silicon atoms contain empty orbitals, which can react with PF5 to inhibit its further decomposition. Therefore, it can improve battery gas generation and capacity retention during high-temperature storage. When compound I contains cyano groups, it can coordinate with positive electrode transition metal ions, inhibiting the dissolution of positive electrode transition metal ions under high-temperature conditions and improving capacity retention.

[0043] In some embodiments, compound I is selected from any one of compounds I-1 to I-8 as shown below:

[0044] In some embodiments, the electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates; The volume ratio of cyclic carbonates to chain carbonates is (20~25):(70~80).

[0045] Understandably, the volume ratio of cyclic carbonates to chain carbonates can be any value from 20:80, 21:88, 22:86, 23:84, 24:82, 25:70, or any value within a range of any two of these. Cyclic carbonates are primarily responsible for dissolving lithium salts and forming a stable protective film on the negative electrode surface; chain carbonates are primarily responsible for reducing electrolyte viscosity and melting point, improving low-temperature performance and ionic conductivity. By controlling the ratio of cyclic carbonates to chain carbonates to meet the above-mentioned range, a balance can be achieved between system viscosity and ionic conductivity.

[0046] In some embodiments, cyclic carbonates include at least one of ethylene carbonate and propylene carbonate.

[0047] In some embodiments, the chain carbonate includes at least one of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

[0048] In some embodiments, the electrolyte further includes a sulfur-containing compound, a carbonate compound, and a first lithium salt.

[0049] In some embodiments, the mass ratio of compound I, sulfur-containing compound, carbonate compound and first lithium salt is (0.2~0.5):(0.5~1):(3~5):(1~1.8).

[0050] Understandably, sulfur-containing compounds are a class of functional components used to protect highly active ternary cathode materials. Their core function is to preferentially undergo oxidation reactions on the cathode surface, forming a stable and dense solid electrolyte interphase (CEI) film. This protective film effectively inhibits the continuous oxidative decomposition of the electrolyte, reduces gas production, and significantly hinders the dissolution of transition metal ions, thereby greatly improving the battery's high-temperature cycle performance, storage stability, and overall lifespan.

[0051] The key role of carbonate compounds is to preferentially undergo reduction reactions on the graphite anode surface, participating in the formation of a denser, more stable, and highly ionicly conductive solid electrolyte interphase (SEI) film. This enhanced SEI film effectively inhibits the continuous decomposition of the electrolyte on the anode side, reducing the loss of active lithium, thereby significantly improving the battery's cycle life and coulombic efficiency. Simultaneously, it also improves the battery's low-temperature performance and rate performance, and helps reduce gas generation during charging and discharging, enhancing the battery's safety and stability.

[0052] The first lithium salt, as an additive, primarily enhances the performance of ternary batteries by synergistically optimizing the electrode interface. Its core function is to preferentially form a stable CEI film rich in LiF and PO / F compounds on the positive electrode surface, effectively inhibiting electrolyte oxidation and the dissolution of transition metal ions, and neutralizing harmful HF, thus significantly improving the battery's high-temperature cycling and storage performance. Simultaneously, it can also participate in the construction of a more robust SEI film on the negative electrode.

[0053] By adding sulfur-containing compounds, carbonate compounds, and a first lithium salt to the electrolyte, and controlling the amount added to meet the above-mentioned range, an ideal synergistic effect can be formed with compound I, thereby improving the overall performance of the battery.

[0054] In some embodiments, the sulfur-containing compound includes at least one of vinyl sulfate (DTD), methylene methane disulfonate (MMDS), and 1,3-propenesulfonate lactone (PST).

[0055] In some embodiments, the carbonate compound includes at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

[0056] In some embodiments, the first lithium salt includes at least one of lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiODFB), and lithium difluorophosphate (LiPO2F2).

[0057] In some embodiments, the electrolyte further includes a second lithium salt, wherein the second lithium salt comprises 12-16% by mass in the electrolyte; It is understandable that the mass percentage of the second lithium salt in the electrolyte can be any value from 12%, 13%, 14%, 15%, 16%, or any value within a range of two. When the mass percentage of the second lithium salt in the electrolyte meets the above-mentioned range, the electrolyte can have relatively ideal conductivity.

[0058] The second lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluorosulfonyl)imide.

[0059] The second embodiment of this application provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte in any of the above embodiments.

[0060] Specifically, the lithium-ion battery provided in this application can be prepared in the following manner: Graphite and silicon carbon were used as the negative electrode active materials. A negative electrode slurry was prepared by mixing graphite and silicon carbon, conductive agent acetylene black, binder CMC, and SBR:CNT in a mass percentage of 96.3:0.5:1.4:1.3:0.5. The negative electrode slurry was coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet. NCM811 was used as the positive electrode active material. A positive electrode slurry was prepared by mixing the positive electrode active material, conductive agent acetylene black, and binder PVDF in a mass ratio of 96.5:1.2:2.3. The positive electrode slurry was coated onto an aluminum foil current collector and vacuum dried to obtain the positive electrode sheet. The electrolytes prepared in the examples and comparative examples were used to assemble the above-mentioned positive electrode sheet, negative electrode sheet, and separator into a pouch battery.

[0061] The electrolyte and lithium-ion battery provided in this application are described below with reference to specific embodiments: Example 1 This embodiment provides an electrolyte, which, based on 100% of the total mass of the electrolyte, comprises the following components: First additive I-1: 0.2%; Fluorinated ethylene carbonate: 3%; Vinylene carbonate: 0.3%; Lithium bis(oxalate)borate: 0.5%; Lithium difluorophosphate: 0.6%; Vinyl sulfate: 0.5%; Lithium hexafluorophosphate: 13%; Organic solvents: 81.9%; The organic solvents, calculated by total volume as 100%, include: ethyl methyl carbonate: 63%; Ethylene carbonate: 17%; Diethyl carbonate: 20%.

[0062] The structural formula of the first additive I-1 is shown in Formula I-1:

[0063] Formula I-1.

[0064] The electrolyte was prepared by the following method: Under an argon atmosphere, the first additive I-1, fluoroethylene carbonate, vinylene carbonate, lithium bis(oxalato)borate, ethylene sulfate, and lithium difluorophosphate were added to an organic solvent formed by mixing ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate, and the mixture was stirred at 10°C to obtain the electrolyte.

[0065] Example 2 This embodiment provides an electrolyte that differs from Example 1 only in that the amount of the first additive I-1 is adjusted to 0.5%, while the rest is the same as Example 1.

[0066] Example 3 This embodiment provides an electrolyte that differs from Example 1 only in that it uses a first additive I-2, the structural formula of which is shown in Formula I-2, and the amount added is 0.5%. Everything else is the same as in Example 1.

[0067]

[0068] Formula I-2.

[0069] Example 4 This embodiment provides an electrolyte that differs from Example 1 only in that it uses a first additive I-3, the structural formula of which is shown in Formula I-3, and the amount added is 0.5%. Everything else is the same as in Example 1.

[0070]

[0071] Formula I-3.

[0072] Example 5 This embodiment provides an electrolyte that differs from Example 1 only in that it uses a first additive I-4, the structural formula of which is shown in Formula I-3, and the amount added is 0.5%. Otherwise, it is the same as Example 1.

[0073]

[0074] Formula I-4.

[0075] Example 6 This embodiment provides an electrolyte that differs from Example 5 only in that vinyl sulfate is replaced with methylene methane disulfonate at a dosage of 0.5%, while the rest is the same as Example 5.

[0076] Example 7 This embodiment provides an electrolyte that differs from Example 5 only in that vinyl sulfate is replaced with 1,3-propenesulfonate lactone at a dosage of 1%, while the rest is the same as in Example 5.

[0077] Example 8 This embodiment provides an electrolyte that differs from Example 5 only in that the mass fraction of the second lithium salt is adjusted to 15%, while the rest is the same as Example 5.

[0078] Example 9 This embodiment provides an electrolyte that differs from Example 5 only in that the amount of vinylene carbonate added in the carbonate compound is adjusted to 0.5%, while the rest is the same as Example 5.

[0079] Example 10 This embodiment provides an electrolyte that differs from that of Example 5 only in that lithium bis(oxalato)borate in the first lithium salt is replaced with lithium bis(oxalato)borate, with an addition amount of 0.5%. Otherwise, it is the same as Example 5.

[0080] Example 11 This embodiment provides an electrolyte that differs from Example 5 only in that the second lithium salt is adjusted to lithium hexafluorophosphate and lithium difluorosulfonylimide, with an addition mass fraction of 16%. Otherwise, it is the same as Example 5.

[0081] Comparative Example 1 This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain the first additive; otherwise, it is the same as Example 1.

[0082] The electrolytes used in the above embodiments and comparative examples were used to prepare batteries, and the steps are as follows: Graphite and silicon carbon were used as the negative electrode active materials. A negative electrode slurry was prepared by mixing graphite and silicon carbon, conductive agent acetylene black, binder CMC, and SBR:CNT in a mass percentage of 96.3:0.5:1.4:1.3:0.5. The negative electrode slurry was coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet. NCM811 was used as the positive electrode active material. A positive electrode slurry was prepared by mixing the positive electrode active material, conductive agent acetylene black, and binder PVDF in a mass ratio of 96.5:1.2:2.3. The positive electrode slurry was coated onto an aluminum foil current collector and vacuum dried to obtain the positive electrode sheet. The electrolytes prepared in the examples and comparative examples were used to assemble the above-mentioned positive electrode sheet, negative electrode sheet, and separator into a pouch battery.

[0083] The electrical performance of the prepared batteries was tested using the following methods: (1) High-temperature cycle performance test: At 45℃, the lithium-ion battery was charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.25V, and then charged at a constant voltage of 4.25V until the current ≤0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to a cutoff voltage of 2.8V. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 400 charge-discharge cycles at 45℃ under the above conditions, and the capacity retention rate was calculated according to the following formula. Capacity retention rate (%) of lithium-ion battery after N cycles = (discharge capacity of Nth cycle / initial discharge capacity) × 100% where N is the number of charge-discharge cycles.

[0084] (2) High-temperature storage performance test of lithium-ion batteries The lithium-ion battery was charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.25V, then charged at a constant voltage of 4.25V until the current ≤0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to 2.8V. This constituted one charge-discharge cycle. The lithium-ion battery was subjected to three charge-discharge cycles at 25℃ with a charge-discharge rate of 1C, and then fully charged at a 1C rate. The capacity Q0 of the lithium-ion battery was recorded. The fully charged lithium-ion battery was stored at 60℃ for 30 days, and the 1C discharge capacity Q1 of the lithium-ion battery was recorded. Then, the lithium-ion battery was charged and discharged at 25℃ with a 1C rate for 2 weeks, and the 1C discharge capacity Q2 was recorded. The experimental data of high-temperature storage capacity retention rate and capacity recovery rate of the lithium-ion battery were calculated.

[0085] The calculation formulas used are as follows: Capacity retention rate (%) = Q1 / Q0 × 100%; Capacity recovery rate (%) = Q2 / Q0 × 100%.

[0086] Test results as follows Figure 1 As shown in Table 1.

[0087] Table 1

[0088] In ternary batteries, LiPF6 decomposes to produce PF5 and HF under high temperature and in the presence of trace amounts of water. HF corrodes the positive electrode material, causing transition metals (such as Ni and Mn) to dissolve, destroying the positive electrode structure and triggering the degradation of the SEI film on the negative electrode.

[0089] The thiocyanate group (-N=C=S) in isothiocyanates (RN=C=S) exhibits strong nucleophilicity, preferentially reacting with PF5 and HF to form stable complexes, thus blocking the HF chain reaction. Furthermore, it scavenges reactive substances (such as O2). - This reduces solvent oxidation and gas production, alleviating battery swelling issues at high temperatures.

[0090] according to Figure 1As shown in Table 1, the electrolytes provided in this application can improve high-temperature storage and high-temperature cycling. The additive content in Example 2 is increased compared to Example 1, therefore Example 2 has a better effect on suppressing gas generation than Example 1. Example 3 contains unsaturated double bonds, which form a cross-linked polymer network on the positive electrode surface, enhancing the toughness and thermal stability (>60℃) of the CEI film, thus achieving the best high-temperature cycling performance. Example 4 contains not only isothiocyanate groups but also silicon groups. The silicon groups react with HF to generate inert SiF4, blocking the HF corrosion path. Furthermore, the silicon atoms contain empty orbitals, which can interact with PF5 to inhibit its further decomposition, thus improving battery gas generation and capacity retention during high-temperature storage. Example 5 contains cyano groups, which can coordinate with the positive electrode transition metal ions, inhibiting the dissolution of the positive electrode transition metal ions under high-temperature conditions and improving capacity retention.

[0091] The battery slurry and preparation method provided in the embodiments of this application have been described in detail above. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An electrolyte, characterized in that, Including compound I, the structural formula of which is shown in Formula I: Formula I; Wherein, R1 is selected from any one of substituted or unsubstituted C1-C5 alkyl, silicon, aryl, and alkenyl groups, the substituent is at least one of C1-C5 alkyl, alkenyl, and cyano groups, and R2, R3, and R4 are each independently selected from hydrogen, C1-C5, and C5, respectively. 10 Either alkyl or cyano.

2. The electrolyte according to claim 1, characterized in that, R1 is selected from any one of substituted or unsubstituted C1-C3 alkyl, silicon atom, phenyl and alkenyl groups, and the substituent is at least one of C1-C3 alkyl, alkenyl and cyano groups. R2, R3 and R4 are each independently selected from any one of hydrogen atom and C1-C3 alkyl groups.

3. The electrolyte according to claim 1, characterized in that, The structural formula of compound I is selected from any one of the structures shown in formulas I-1 to I-8: 。 4. The electrolyte according to claim 1, characterized in that, It also includes organic solvents, including cyclic carbonates and chain carbonates; The volume ratio of the cyclic carbonate to the chain carbonate is (20~25):(70~80).

5. The electrolyte according to claim 4, characterized in that, The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate; and / or, The chain carbonate includes at least one of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.

6. The electrolyte according to claim 1, characterized in that, It also includes sulfur-containing compounds, carbonate compounds, and first lithium salts.

7. The electrolyte according to claim 6, characterized in that, The mass ratio of compound I, the sulfur-containing compound, the carbonate compound, and the first lithium salt is (0.2~0.5):(0.5~1):(3~5):(1~1.8).

8. The electrolyte according to claim 6, characterized in that, The sulfur-containing compound includes at least one of vinyl sulfate, methylene methane disulfonate, and 1,3-propenesulfonate lactone; and / or, The carbonate compounds include at least one of fluoroethylene carbonate and vinylene carbonate; and / or, The first lithium salt includes at least one of lithium dioxaborate, lithium difluorooxaborate, and lithium difluorophosphate.

9. The electrolyte according to claim 1, characterized in that, It also includes a second lithium salt, wherein the second lithium salt comprises 12-16% by mass in the electrolyte; The second lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium bistrifluorosulfonylimide.

10. A lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is any one of claims 1 to 9; The capacity retention rate of the electrolyte after 400 cycles at 45°C is 88.3-91.3%.

Images