Electrolyte and preparation method thereof, and lithium battery

Abstract

The application discloses an electrolyte, a preparation method thereof and a lithium battery. The electrolyte has improved thermal stability due to the addition of halogen-containing isocyanate. The preparation method comprises the following steps: mixing a carbonate solvent, halogen-containing isocyanate and other components, and then adding lithium salt, so that the electrolyte with high stability at the electrode interface is prepared. The mechanism of action mainly embodies the following two aspects: 1. -NCO preferentially reacts with water in the electrolyte and hydrogen contained in the electrode material, thereby inhibiting the decomposition of LiPF6 caused by active hydrogen, and further improving the thermal stability of the electrolyte; 2. The halogen atom with strong electron-withdrawing effect in the molecule can further reduce the electron cloud density of -NCO, so that the reactivity of -NCO with H2O, HF and the like is strengthened. The lithium battery is prepared by using the electrolyte containing halogen-containing isocyanate, so that the cycle stability and safety performance of the battery can be improved when the lithium battery is charged, discharged and recycled.

Description

Technical Field

[0001] This application belongs to the field of lithium battery material technology, and particularly relates to an electrolyte and its preparation method, and a lithium battery. Background Technology

[0002] With the widespread application of lithium-ion batteries in electric vehicles, portable electronic devices, and other fields, increasingly stringent requirements have been placed on battery energy density, cycle life, and safety performance. To improve the energy density of lithium-ion batteries, related research is focusing on high voltage (≥4.5V vs. Li / Li). + High-nickel / lithium-rich manganese-based cathode systems are common. However, with increasing voltage and nickel content, insufficient stability at the electrolyte-electrode interface becomes a key bottleneck restricting battery performance. Lithium hexafluorophosphate (LiPF6) in traditional electrolytes is prone to a hydrolytic chain reaction (LiPF6 + H2O → LiF + 2HF + PF5), leading to increased electrolyte acidity, solvent polymerization and discoloration, and severe corrosion of electrode materials. Furthermore, carbonate-based organic electrolyte solvents themselves pose a flammability risk, resulting in significant thermal safety hazards in high-specific-energy systems, further exacerbating battery safety issues. Therefore, improving the stability of the electrolyte-electrode interface in lithium batteries while simultaneously ensuring good cycle performance is a pressing technical problem to be solved. Summary of the Invention

[0003] The embodiments of this application provide an electrolyte and its preparation method, as well as a lithium battery, which can at least to some extent overcome the technical challenge of synergistic optimization of the kinetics and thermodynamic stability of high-voltage lithium battery systems, thereby improving the stability of the electrolyte-electrode interface in lithium batteries.

[0004] Other features and advantages of this application will become apparent from the following detailed description, or may be learned in part from practice of this application.

[0005] According to a first aspect of the embodiments of this application, an electrolyte is provided, which, by mass parts, comprises 75 to 90 parts of carbonate solvent, 5 to 15 parts of lithium salt, 1 to 8 parts of additives, and 0.1 to 5 parts of stabilizer. The stabilizer includes halogenated isocyanates; The additives include any one or more of the following: fluoroethylene carbonate, lithium difluorophosphate, vinylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate.

[0006] According to a second aspect of the embodiments of this application, a method for preparing an electrolyte as described in any embodiment of the first aspect is provided, comprising the following steps: Provides carbonate solvents, lithium salts, additives, and stabilizers; The carbonate solvent and the lithium salt are first mixed to obtain a first mixture; The additive and the stabilizer are added to the first mixture for a second mixing to obtain the electrolyte. The stabilizer includes halogenated isocyanates.

[0007] In some embodiments of this application, based on the foregoing scheme, the general structural formula of the halogen-containing isocyanate is (X). n -RN=C=O; Wherein, X is a halogen atom, and the halogen atom includes any one or more of F, Cl, Br, and I; The halogen atom is substituted at any one or more of the following positions: ortho position, meta position, para position of the aromatic ring, α position of the alkyl group, and β position of the alkyl group; n is the substitution number, n=1, 2, 3; The R group includes any one or more of aryl and alkyl groups.

[0008] In some embodiments of this application, based on the foregoing scheme, the aryl group includes any one or more of benzene rings and naphthalene rings; The alkyl group includes any one or more of straight-chain alkyl groups containing 1 to 6 carbon atoms and branched alkyl groups containing 1 to 6 carbon atoms.

[0009] In some embodiments of this application, based on the foregoing scheme, the halogen-containing isocyanate includes any one or more of p-bromophenyl isocyanate, 2,4-dichlorophenyl isocyanate, pentafluorophenyl isocyanate, brominated n-butyl isocyanate, and 3,5-bis(trifluoromethyl)phenyl isocyanate.

[0010] In some embodiments of this application, based on the foregoing scheme, the carbonate solvent in the electrolyte comprises 75 to 90 parts by mass; and / or, The lithium salt is present in parts by mass of 5 to 15 parts; and / or, The additive is present in parts by weight of 1 to 8 parts; and / or, The stabilizer is present in parts by weight of 0.1 to 5 parts.

[0011] In some embodiments of this application, based on the foregoing scheme, the carbonate solvent includes any one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, and butyl carbonate.

[0012] In some embodiments of this application, based on the foregoing scheme, the lithium salt includes any one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium dioxalateborate, lithium difluorodioxalate phosphate, lithium tetrafluoroborate, and lithium difluorooxalateborate.

[0013] In some embodiments of this application, based on the foregoing scheme, the additive includes any one or more of fluoroethylene carbonate, lithium difluorophosphate, vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, tris(trimethylsilane)borate, and tris(trimethylsilane) phosphate.

[0014] In some embodiments of this application, based on the foregoing scheme, the following steps are further included: after adding the additive and the stabilizer to the first mixture and performing the second mixing, purification treatment is carried out.

[0015] According to a third aspect of the present application, a lithium battery is provided, the lithium battery comprising: a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode; the electrolyte is selected from any of the electrolytes described in the second aspect.

[0016] In this application, the addition of halogen-containing isocyanates to the electrolyte significantly improves its thermal stability. An electrolyte with high stability at the electrode interface is prepared by mixing carbonate solvents, additives, and stabilizers, followed by the addition of lithium salts, where the stabilizer is a halogen-containing isocyanate. The mechanism of action of using halogen-containing isocyanates as electrolyte stabilizers is mainly reflected in two aspects: First, the isocyanate group (-NCO) has strong electrophilic activity, preferentially reacting with water in the electrolyte and active hydrogen contained in the electrode materials, thereby effectively inhibiting the decomposition of LiPF6 initiated by active hydrogen, and thus significantly improving the thermal stability of the electrolyte. Second, the strong electron-withdrawing effect of halogen atoms in the molecule further reduces the electron cloud density of the isocyanate group, enhances the electrophilicity of the isocyanate group, and strengthens the reactivity of the isocyanate group with harmful substances such as H2O and HF, thereby more efficiently removing active impurities from the electrolyte system. Thus, the provided electrolyte preparation method significantly improves the thermal stability of the electrolyte. Due to the high thermal stability of the electrolyte, when used to prepare lithium batteries, the resulting lithium batteries exhibit excellent cycle performance during long-term charge-discharge cycles, thereby improving the overall stability of the battery and extending its lifespan.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] Unless otherwise specified, the terminology used herein should be understood as having the meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In case of any conflict, this specification shall prevail.

[0020] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0021] It should also be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such uses of these terms can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those described.

[0022] In existing electrolyte technologies, high-concentration lithium salts or film-forming additives are typically used to construct a passivation layer on the cathode surface to improve electrochemical stability under high voltage systems. However, high-concentration electrolytes have high viscosity and poor wettability, severely affecting ionic conductivity and rate performance. Furthermore, some film-forming additives (such as fluoroethylene carbonate) are prone to decomposition and reconstruction under continuous high voltage, leading to continuous thickening of the interfacial film, increasing battery internal resistance and accelerating capacity decay. In addition, conventional carbonate solvents are prone to oxidative decomposition under high voltage, generating gas and causing continuous electrolyte consumption. This not only exacerbates electrode structural damage, but the flammability of their decomposition products can also create an "ignition-supporting combustion" effect in thermal runaway scenarios, seriously threatening the safe operation of the battery system.

[0023] The technical solution provided in this application is to solve the above-mentioned technical problems, and the general idea is as follows: In a first aspect, embodiments of this application provide an electrolyte, which, by mass parts, comprises 75 to 90 parts of carbonate solvent, 5 to 15 parts of lithium salt, 1 to 8 parts of additives, and 0.1 to 5 parts of stabilizer. The stabilizer includes halogenated isocyanates; The additives include any one or more of the following: fluoroethylene carbonate, lithium difluorophosphate, vinylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate.

[0024] It is easy to understand that halogenated isocyanates in the electrolyte significantly improve the thermal stability of the electrolyte.

[0025] Based on the same inventive concept, in a second aspect, embodiments of this application provide a method for preparing an electrolyte as described in any embodiment of the first aspect, the method comprising the following steps: Step 1: Provide carbonate solvents, lithium salts, additives, and stabilizers; Step 2: Mix the carbonate solvent and the lithium salt to obtain a first mixture; Step 3: Add the additive and the stabilizer to the first mixture for a second mixing to obtain the electrolyte; The stabilizer includes halogenated isocyanates.

[0026] Understandably, using halogenated isocyanates as stabilizers in the electrolyte is beneficial because the isocyanate groups in halogenated isocyanates have strong electrophilic activity. They can react with water in the electrolyte system and with the active hydrogen contained in the positive and negative electrodes, thereby effectively inhibiting the decomposition of LiPF6 initiated by active hydrogen. This mechanism significantly enhances the thermal stability of the electrolyte.

[0027] This application prepares an electrolyte with high stability at the electrode interface by mixing carbonate solvents, additives, and stabilizers, and then adding lithium salts, wherein the stabilizer is a halogen-containing isocyanate. The mechanism of action of using a halogen-containing isocyanate as an electrolyte stabilizer is mainly reflected in two aspects. First, the isocyanate group (-NCO) has strong electrophilic activity, preferentially reacting with water in the electrolyte and active hydrogen contained in the electrode materials, thereby effectively inhibiting the decomposition of LiPF6 initiated by active hydrogen, and thus significantly improving the thermal stability of the electrolyte. Moreover, if lithium batteries are subsequently prepared using this electrolyte, it helps to improve the cycle performance of the lithium batteries. Second, the strong electron-withdrawing effect of the halogen atoms in the molecule can further reduce the electron cloud density of -NCO, enhance the electrophilicity of -NCO, and strengthen the reactivity of -NCO with harmful substances such as H2O and HF, thereby more efficiently removing active impurities in the electrolyte system. In summary, the electrolyte provided by this application significantly improves the thermal stability of the electrolyte.

[0028] In some embodiments of this application, the general structural formula of the halogen-containing isocyanate is (X). n -RN=C=O; Wherein, X is a halogen atom; the halogen atom includes any one or more of F, Cl, Br, and I; The halogen atom is substituted at any one or more of the following positions: ortho position, meta position, para position of the aromatic ring, α position of the alkyl group, and β position of the alkyl group; n is the substitution number, n=1, 2, 3; The R group includes any one or more of aryl and alkyl groups.

[0029] In some embodiments of this application, the aryl group includes any one or more of a benzene ring and a naphthalene ring; The alkyl group includes any one or more of straight-chain alkyl groups containing 1 to 6 carbon atoms and branched alkyl groups containing 1 to 6 carbon atoms.

[0030] Preferably, the aryl group includes a benzene ring and a naphthalene ring.

[0031] Thus, 1) the isocyanate groups in halogen-containing isocyanates have strong electrophilic activity, which can react with water in the electrolyte system and the active hydrogen contained in the positive and negative electrodes, thereby effectively inhibiting the decomposition of LiPF6 initiated by active hydrogen. This mechanism significantly enhances the thermal stability of the electrolyte. 2) The strong electron-withdrawing effect of halogen atoms in the molecule can further reduce the electron cloud density of -NCO, enhance the electrophilicity of -NCO, and strengthen the reactivity of -NCO with harmful substances such as H2O and HF, thereby more efficiently removing active impurities in the electrolyte system. At the same time, the steric hindrance effect of halogen substituents can effectively prevent solvent molecules such as ethylene carbonate (EC) and ethyl methyl carbonate (EMC) from undergoing direct oxidation reactions on the positive electrode surface. 3) Halogen ions can participate in the construction of a stable solid electrolyte interphase (SEI) film on the electrode surface, effectively blocking direct contact between the electrolyte and the electrode and reducing the probability of side reactions. 4) Halogenated isocyanates have excellent flame retardant properties. Therefore, introducing halogenated isocyanates into the electrolyte system can effectively suppress the flammability of the electrolyte.

[0032] In some embodiments of this application, the halogen-containing isocyanate includes any one or more of p-bromophenyl isocyanate (p-BrC6H4NCO), 2,4-dichlorophenyl isocyanate (2,4-Cl2C6H3NCO), pentafluorophenyl isocyanate (F5C6NCO), bromobutyl isocyanate (BrC4H8NCO), and 3,5-bis(trifluoromethyl)phenyl isocyanate (C6H3(CF3)2-NCO).

[0033] In some embodiments of this application, the carbonate solvent in the electrolyte is 75 to 90 parts by mass. The lithium salt is in the form of 5 to 15 parts by mass. The additive is present in parts by weight of 1 to 8 parts; The stabilizer is present in parts by weight of 0.1 to 5 parts.

[0034] Thus, through the specific mass ratio combination described above, the electrolyte formulation of this embodiment achieves an optimized ratio of each component. Specifically, the carbonate solvent provides a stable solvation environment and ion transport channels; the lithium salt ensures sufficient lithium-ion concentration and conductivity; the additives effectively modify the electrode interface and suppress side reactions; and the halogen-containing isocyanate, as a stabilizer, preferentially removes moisture and active hydrogen from the system through its highly reactive isocyanate groups, significantly inhibiting the thermal decomposition of LiPF6. The synergistic effect of each component enhances the thermal stability and electrochemical window of the electrolyte, thereby potentially significantly improving the battery's high-temperature cycle performance, rate performance, and long-term storage stability. However, it is worth noting that the mass ratio of the stabilizer in the electrolyte should not be less than 0.1 parts; otherwise, the stabilizer will not be able to adequately remove moisture and active hydrogen impurities from the electrolyte system, making it difficult to effectively inhibit the decomposition of LiPF6, thus affecting the thermal stability of the electrolyte and the cycle life of the battery. The mass ratio of the stabilizer should not exceed 5 parts; otherwise, the increased side reactions will lead to an increase in battery interfacial impedance, affecting the battery's cycle stability.

[0035] In some embodiments of this application, the carbonate solvent includes any one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, and butyl carbonate.

[0036] Thus, the selected carbonate solvents are a blend of high-dielectric-constant and low-viscosity solvents. Therefore, carbonate solvents possess high dielectric constants and excellent lithium-ion solvation capabilities, which facilitates the effective dissociation of lithium salts and the formation of stable lithium-ion transport channels. Simultaneously, the combined use of these solvents maintains suitable viscosity and chemical stability over a wide temperature range, optimizing the electrolyte's conductivity and wettability. By rationally blending solvents with different boiling points, viscosities, and film-forming properties, the electrode / electrolyte interface characteristics can be further synergistically controlled, promoting the formation of a stable and dense solid electrolyte interphase (SEI) film, thereby effectively improving the battery's low-temperature performance, rate performance, and cycle life.

[0037] In some embodiments of this application, the lithium salt includes any one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium dioxaborate, lithium difluorodioxaborate, lithium tetrafluoroborate, and lithium difluorooxaborate.

[0038] Preferably, the lithium salt is lithium hexafluorophosphate.

[0039] Thus, the selected lithium salts possess high ionic conductivity and good electrochemical stability, enabling them to operate stably across a wide voltage window and contributing to improved battery energy density and rate performance. Furthermore, the combined use of different lithium salts can exert synergistic effects, such as optimizing the lithium-ion solvation structure by modulating the anion structure, promoting the formation of a stable electrode / electrolyte interface film (SEI / CEI), and effectively suppressing the oxidative decomposition of the electrolyte and the dissolution of transition metal ions at high voltages. In addition, some fluorinated lithium salts (such as LiPF6) can also provide a fluorine source to some extent, assisting in the construction of a stable LiF-rich interface layer, thereby further improving battery cycle life, high-temperature storage performance, and safety.

[0040] In some embodiments of this application, the additive includes any one or more of fluoroethylene carbonate, lithium difluorophosphate, vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate.

[0041] Thus, the selected additives preferentially undergo reduction or oxidation reactions on the electrode surface, participating in the construction of a stable, dense solid electrolyte interphase (SEI) and positive electrode electrolyte interphase (CEI) film with suitable ionic conductivity. For example, fluorine / sulfur-containing additives help form an interface layer rich in inorganic components such as LiF, Li2, and SO3, effectively inhibiting the continuous decomposition of the electrolyte and the dissolution of transition metal ions; cyclic sulfonate additives can improve the flexibility and stability of the interface film; while silane additives can remove trace amounts of water and HF from the system and promote the formation of an organic-inorganic composite interface structure. Through the synergistic effect of different functional additives, this embodiment can significantly improve the battery's initial coulombic efficiency, cycle life, high and low temperature performance, and safety.

[0042] In some embodiments of this application, the following steps are also included: after adding the additive and the stabilizer to the first mixture and performing the second mixing, purification treatment is carried out.

[0043] The purification process includes sequentially performing a first filtration, removing residual water, and a second filtration on the second mixture.

[0044] The method for removing residual moisture includes using a 5wt% molecular sieve; The first filter removes solid impurities; the second filter removes the filtered water.

[0045] Based on the same inventive concept, in a third aspect, embodiments of this application provide a lithium battery, the lithium battery comprising: a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode; the electrolyte is selected from the electrolyte described in the first aspect.

[0046] This application utilizes an electrolyte containing halogen-containing isocyanates to prepare lithium batteries. When charging, discharging, and cycling the lithium batteries (especially those with high voltage and high-nickel / lithium-rich manganese-based cathode systems), the isocyanate groups (-NCO) in the electrolyte preferentially react with water and active hydrogen in the electrode materials, effectively inhibiting LiPF6 decomposition caused by active hydrogen and significantly improving the electrolyte's thermal stability. Secondly, the strong electron-withdrawing effect of halogen atoms further reduces the electron cloud density of -NCO, enhancing its electrophilicity and strengthening its reactivity with harmful substances such as H2O and HF, thus more efficiently removing active impurities from the electrolyte system. Therefore, applying this electrolyte to lithium battery preparation significantly improves the battery's cycle performance. Furthermore, the halide ions in the stabilizer participate in the construction of a stable solid electrolyte interphase (SEI) film on the electrode surface, effectively preventing direct contact between the electrolyte and the electrode, reducing the probability of side reactions, and further improving the battery's cycle stability and safety. Halogenated isocyanates possess excellent flame-retardant properties and can effectively suppress the flammability of the electrolyte, thereby significantly improving battery safety. In summary, this lithium battery exhibits excellent cycle performance during long-term charge-discharge cycles, maintaining a capacity retention of 84% or higher after 300 cycles.

[0047] Based on the same inventive concept, in a fourth aspect, embodiments of this application provide an automobile equipped with any of the lithium batteries described in the third aspect. The lithium batteries described in the third aspect are particularly suitable for new energy vehicles; these new energy vehicles include, but are not limited to, pure electric vehicles, hybrid electric vehicles, and range-extended electric vehicles. In practical applications, the lithium battery can be specifically adapted and optimized according to the vehicle's power requirements, overall vehicle space layout, and range target.

[0048] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0049] Example 1 This embodiment provides a method for preparing an electrolyte, including the following steps: Step 1: Provide carbonate solvents, lithium salts, additives, and stabilizers by weight. The carbonate solvents include 9.5 parts ethylene carbonate, 13.2 parts propylene carbonate, 53 parts methyl ethyl carbonate, and 3.8 parts diethyl carbonate; The lithium salt comprises 8 parts lithium hexafluorophosphate and 6 parts lithium difluorosulfonylimide; The additives include 3 parts fluoroethylene carbonate, 0.5 parts vinylene carbonate, 1 part vinyl sulfate, and 1.5 parts 1,3-propanesulfonic acid lactone. The stabilizer includes 0.5 parts of p-BrC6H4NCO; Step 2: Mix the carbonate solvent and lithium salt to obtain a first mixture; Step 3: Add additives and stabilizers to the first mixture for a second mixture, and then purify to obtain the electrolyte.

[0050] An electrolyte was prepared using the above preparation method.

[0051] Comparative Example 1 Comparative Example 1 provides a method for preparing an electrolyte, which differs from Example 1 in that no stabilizer is added.

[0052] The remaining steps are the same as in Example 1, and will not be repeated here.

[0053] An electrolyte was prepared using the above preparation method.

[0054] Comparative Example 2 Comparative Example 2 provides a method for preparing an electrolyte, which differs from Example 1 in that the mass fraction of the stabilizer is different. The stabilizer used in Comparative Example 1 was 6 parts by mass.

[0055] The remaining steps are the same as in Example 1, and will not be repeated here.

[0056] An electrolyte was prepared using the above preparation method.

[0057] Example 2 Example 2 provides a method for preparing an electrolyte, which differs from Example 1 in that the stabilizer composition is different. The stabilizer used in Example 2 is F5C6NCO.

[0058] The remaining steps are the same as in Example 1, and will not be repeated here.

[0059] An electrolyte was prepared using the above preparation method.

[0060] Example 3 Example 3 provides a method for preparing an electrolyte, which differs from Example 1 in that the composition and content of the stabilizer are different. The stabilizer used in Example 3 is 0.2 parts of BrC4H8NCO.

[0061] The remaining steps are the same as in Example 1, and will not be repeated here.

[0062] An electrolyte was prepared using the above preparation method.

[0063] Example 4 This embodiment provides a method for preparing an electrolyte, including the following steps: Step 1: Provide carbonate solvents, lithium salts, additives, and stabilizers by weight. The carbonate solvents include 9.5 parts ethylene carbonate, 13.2 parts propylene carbonate, 52.5 parts methyl ethyl carbonate, and 3.8 parts diethyl carbonate; The lithium salt comprises 8 parts lithium hexafluorophosphate and 6 parts lithium difluorosulfonylimide; The additives include 3 parts fluoroethylene carbonate, 0.5 parts vinylene carbonate, 1 part vinyl sulfate, and 1.5 parts 1,3-propanesulfonic acid lactone. The stabilizer includes 1 part of 2,4-Cl2C6H3NCO; Step 2: Mix the carbonate solvent and lithium salt to obtain a first mixture; Step 3: Add additives and stabilizers to the first mixture for a second mixture, and then purify to obtain the electrolyte.

[0064] An electrolyte was prepared using the above preparation method.

[0065] Example 5 This embodiment provides a method for preparing an electrolyte, including the following steps: Step 1: Provide carbonate solvents, lithium salts, additives, and stabilizers by weight. The carbonate solvents include 9.5 parts ethylene carbonate, 13.2 parts propylene carbonate, 52.5 parts methyl ethyl carbonate, and 3.8 parts diethyl carbonate; The lithium salt comprises 8 parts lithium hexafluorophosphate and 6 parts lithium difluorosulfonylimide; The additives include 3 parts fluoroethylene carbonate, 0.5 parts vinylene carbonate, 1 part vinyl sulfate, and 1.5 parts 1,3-propanesulfonic acid lactone. The stabilizer consists of 1 part C6H3(CF3)2-NCO; Step 2: Mix the carbonate solvent and lithium salt to obtain a first mixture; Step 3: Add additives and stabilizers to the first mixture for a second mixture, and then purify to obtain the electrolyte.

[0066] An electrolyte was prepared using the above preparation method.

[0067] The electrolytes prepared in each embodiment and comparative example were subjected to color and acidity tests. The tests specifically included the following steps: The electrolytes prepared in the examples and comparative examples were transferred to sealed aluminum bottles, and several sealed aluminum bottles containing different electrolytes were placed in an environment with a water content of <0.01ppm and an oxygen content of <0.01ppm. After storing the aforementioned sealed aluminum bottles for 3 weeks, samples were taken from the glove box to test the acidity and color of the electrolyte. After storing the aforementioned sealed aluminum bottles for 6 weeks, samples were taken from a glove box to test the acidity and color of the electrolyte.

[0068] The colorimetric test method uses the platinum-cobalt colorimetric method, with the colorimetric unit being Hazen; the acidity test method uses the triethylamine titration method, with the acidity unit being ppm.

[0069] The test results are shown in Table 1.

[0070] As shown in Table 1, the addition of halogenated isocyanate stabilizers can significantly slow down the changes in acidity and color of electrolytes after long-term storage; and a very significant inhibitory effect can be achieved with a relatively low addition amount.

[0071] Table 1. Color and acidity test results of the electrolytes prepared in each example and comparative example.

[0072] The electrolytes obtained in each embodiment and comparative example are used to prepare lithium batteries, and the specific steps include the following: 1) Preparation of positive electrode sheet: LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) powder, carbon black, polyvinylidene fluoride (PVDF), and N,N Dimethylpyrrolidone (NMP) is mixed evenly to obtain a slurry; The slurry was uniformly coated onto the aluminum foil current collector (coating thickness 100 μm), and then placed in a vacuum oven at 120℃ for 12 h (until the NMP solvent was completely removed) to obtain the positive electrode sheet; in the positive electrode sheet, by mass fraction, LiNi 0.8 Co 0.1 Mn 0.1 O2 accounts for 96 parts, PVDF accounts for 2 parts, and carbon black accounts for 2 parts; The obtained positive electrode sheet is cut into round pieces with a diameter of 8mm for later use.

[0073] (ii) Preparation of the negative electrode sheet: The silicon-carbon composite powder (active material), carbon black, and polyvinylidene fluoride (PVDF) were mixed evenly at a mass ratio of 85:10:5. Then, N,N-methylpyrrolidone (NMP) (solvent) was added and mixed evenly to obtain a black slurry. The black paste was uniformly coated onto the copper foil current collector (coating thickness of 100μm), and then placed in a vacuum oven at 120℃ for 12h (until the NMP solvent was completely removed) to obtain the negative electrode sheet. In the negative electrode sheet, by mass parts, silicon-carbon composite material accounted for 85 parts, carbon black accounted for 10 parts, and PVDF accounted for 5 parts. The obtained negative electrode sheet was cut into round pieces with a diameter of 12mm for later use.

[0074] (iii) Button battery assembly: Assemble the negative electrode shell, gasket, negative electrode plate, diaphragm, electrolyte, positive electrode plate, gasket, spring, and positive electrode shell in order from bottom to top, and then seal them with a sealing machine; let stand for 4 hours.

[0075] All of these operations were performed in a pure argon glove box.

[0076] The electrolytes prepared in each embodiment and comparative example were used to prepare lithium batteries for cycle performance testing, including the following steps: Remove the battery that has been left to stand for 4 hours and place it under a constant temperature of 25°C. First, the process is cycled twice using a 0.1C charging and 0.1C discharging cycle; then, the process is cycled 350 times using a 0.2C charging and 0.2C discharging cycle, with the cycle voltage range set to 2.8V~4.5V. Calculate the capacity retention rate of the battery after 100 and 300 cycles respectively; The calculation formula is as follows: Capacity retention rate = specific capacity of the last discharge cycle ÷ specific capacity of the third discharge cycle.

[0077] The cycle performance test results of the lithium batteries prepared in each embodiment and comparative example are shown in Table 2.

[0078] Table 2. Cycle performance test results of lithium batteries prepared in each embodiment and comparative example.

[0079] As shown in Table 2, under constant temperature conditions of 25℃, the battery containing halogen isocyanate stabilizer still has a high capacity retention rate after 100 cycles and 300 cycles. This fully demonstrates that halogen groups help to induce the construction of a stable SEI / CEI film, which can effectively prevent direct contact between the electrolyte and the electrode, reduce the occurrence of side reactions, increase the stability of the electrode interface, and thus effectively improve the cycle performance of the battery.

[0080] In addition, comparing Examples 1-2 and Comparative Examples 1-2, it can be seen that the content of stabilizer is also crucial to the cycle stability of the battery. This is because excessive halogenated isocyanates can lead to an increase in interfacial side reactions, thereby increasing the interfacial impedance of the battery and reducing the stable cycle performance of the battery.

[0081] In summary, this application provides an electrolyte, its preparation method, and a lithium battery. The electrolyte exhibits significantly improved thermal stability due to the addition of a halogen-containing isocyanate. The preparation method involves mixing a carbonate solvent, additives, and a stabilizer, followed by the addition of a lithium salt. The stabilizer is a halogen-containing isocyanate, thus producing an electrolyte with high stability at the electrode interface. The use of a halogen-containing isocyanate as an electrolyte stabilizer has two main mechanisms of action. First, the isocyanate group (-NCO) has strong electrophilic activity, preferentially reacting with water in the electrolyte and active hydrogen in the electrode materials, effectively inhibiting the decomposition of LiPF6 initiated by active hydrogen, thereby significantly improving the thermal stability of the electrolyte. Second, the strong electron-withdrawing effect of the halogen atoms in the molecule further reduces the electron cloud density of -NCO, enhancing its electrophilicity and strengthening its reactivity with harmful substances such as H2O and HF, thereby more efficiently removing active impurities from the electrolyte system. This lithium battery is manufactured using an electrolyte containing halogen-containing isocyanates. Therefore, during charging, discharging, and cycling, the -NCO in the electrolyte preferentially reacts with water and active hydrogen in the electrode materials, effectively inhibiting LiPF6 decomposition caused by active hydrogen and significantly improving the electrolyte's thermal stability. Secondly, the strong electron-withdrawing effect of halogen atoms further reduces the electron cloud density of -NCO, enhancing its electrophilicity and strengthening its reactivity with harmful substances such as H2O and HF. This more efficiently removes active impurities from the electrolyte system, thus significantly improving the stable cycle performance of lithium batteries when used in their fabrication. Furthermore, the halide ions in the stabilizer participate in the construction of a stable solid electrolyte interphase (SEI) film on the electrode surface, effectively preventing direct contact between the electrolyte and the electrode, reducing the probability of side reactions, and further improving the battery's cycle stability and safety. Halogen-containing isocyanates possess excellent flame-retardant properties and can effectively suppress the flammability of the electrolyte, thereby significantly improving battery safety. In summary, this lithium battery exhibits excellent cycle performance during long-term charge-discharge cycles; after 300 cycles, its capacity retention rate reaches 84% ​​or higher, thus extending the battery's lifespan.

[0082] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0083] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. For associations of three or more related objects described using "and / or", it means that any one of the three related objects can exist alone, or at least two of them can exist simultaneously. For example, for A, and / or B, and / or C, it can mean that any one of A, B, and C exists alone, or any two of them exist simultaneously, or all three of them exist simultaneously. In this document, "at least one" means one or more, and "more" means two or more. "At least one", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0084] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises, by weight, 75 to 90 parts of carbonate solvent, 5 to 15 parts of lithium salt, 1 to 8 parts of additives, and 0.1 to 5 parts of stabilizer. The stabilizer includes halogenated isocyanates; The additives include any one or more of the following: fluoroethylene carbonate, lithium difluorophosphate, vinylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate.

2. A method for preparing an electrolyte, characterized in that, Includes the following steps: Provides carbonate solvents, lithium salts, additives, and stabilizers; The carbonate solvent and the lithium salt are first mixed to obtain a first mixture; The additive and the stabilizer are added to the first mixture for a second mixing to obtain the electrolyte. The stabilizer includes halogenated isocyanates.

3. The preparation method according to claim 2, characterized in that, The general structural formula of the halogen-containing isocyanate is (X). n -RN=C=O; Wherein, X is a halogen atom, and the halogen atom includes any one or more of F, Cl, Br, and I; The halogen atom is substituted at any one or more of the following positions: ortho position, meta position, para position of the aromatic ring, α position of the alkyl group, and β position of the alkyl group; n is the substitution number, n=1, 2, 3; The R group includes any one or more of aryl and alkyl groups.

4. The preparation method according to claim 3, characterized in that, The aryl group includes any one or more of benzene rings and naphthalene rings; The alkyl group includes any one or more of straight-chain alkyl groups containing 1 to 6 carbon atoms and branched alkyl groups containing 1 to 6 carbon atoms.

5. The preparation method according to claim 3, characterized in that, The halogenated isocyanate includes any one or more of p-bromophenyl isocyanate, 2,4-dichlorophenyl isocyanate, pentafluorophenyl isocyanate, brominated n-butyl isocyanate, and 3,5-bis(trifluoromethyl)phenyl isocyanate.

6. The preparation method according to claim 2, characterized in that, In the electrolyte, the carbonate solvent comprises 75 to 90 parts by mass; and / or, The lithium salt is present in parts by mass of 5 to 15 parts; and / or, The additive is present in parts by weight of 1 to 8 parts; and / or, The stabilizer is present in parts by weight of 0.1 to 5 parts.

7. The preparation method according to claim 3, characterized in that, The carbonate solvents include any one or more of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, and butyl carbonate.

8. The preparation method according to claim 3, characterized in that, The lithium salt includes any one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium di(oxalato)borate, lithium di(fluorodi(oxalato)phosphate), lithium tetra(fluoroborate), and lithium di(fluorooxalato)borate.

9. The preparation method according to claim 3, characterized in that, The additives include any one or more of the following: fluoroethylene carbonate, lithium difluorophosphate, vinylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, tris(trimethylsilane)borate, and tris(trimethylsilane)phosphate.

10. The preparation method according to claim 2, characterized in that, It also includes the following steps: after adding the additive and the stabilizer to the first mixture and performing a second mixing, purification treatment is carried out.

11. A lithium battery, characterized in that, The lithium battery includes: a positive electrode, a negative electrode, an electrolyte, and a separator disposed between the positive electrode and the negative electrode; the electrolyte is selected from the electrolyte prepared by the preparation method according to any one of claims 2 to 10.

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