High-performance lithium ion battery electrolyte and preparation process thereof

Abstract

The application discloses a high-performance lithium ion battery electrolyte and a preparation process thereof, and belongs to the technical field of lithium ion battery electrolytes. The electrolyte comprises a lithium salt, an organic solvent and an additive. The organic solvent comprises nitrile solvents composed of acetonitrile and alkoxy nitrile, fluorine-containing solvents composed of fluoroether and fluorocarboxylic acid ester, and auxiliary solvents. The additive comprises a first additive, a second additive, a third additive and a fourth additive. The electrolyte provided by the application constructs a solvation system synergized by double nitrile and double fluorine-containing solvents, and cooperates with multiple additives to perform stage-by-stage interface regulation, so that the electrolyte can keep high ion transmission capacity and low viscosity, and can also consider positive and negative electrode interface stability and wide temperature adaptability, can effectively reduce side reactions and impedance growth, and can improve the rate performance, cycle life, high and low temperature operation stability and storage stability of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrolyte technology, specifically relating to a high-performance lithium-ion battery electrolyte and its preparation process. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage systems, and high-rate electronic devices, lithium-ion batteries are placing higher demands on electrolytes. On the one hand, electrolytes need to possess high ionic conductivity and low viscosity to meet the requirements of fast charging and low-temperature operation. On the other hand, electrolytes should also form stable interfacial films with low impedance on the surfaces of the positive and negative electrodes, thereby suppressing side reactions, reducing gas production, slowing down impedance growth, and improving cycle life. Although existing carbonate-based electrolytes have mature technology, they are still prone to problems such as repeated damage and repair of the negative electrode interfacial film, continuous consumption of active lithium, increased oxidation side reactions on the positive electrode side, and decreased system stability during high-rate charge and discharge, wide-temperature operation, and long-term cycling. It is difficult to simultaneously achieve fast charging performance, interfacial stability, and wide-temperature adaptability.

[0003] Invention CN120709469A discloses an electrolyte and a battery. The electrolyte includes acetonitrile, carboxylic acid ester, lithium salt, and first, second, and third additives. A gradient film-forming strategy is used to improve the interfacial stability of the acetonitrile-based electrolyte, and it is applied to a fast-charging lithium iron phosphate battery system. However, this invention mainly addresses the problems of pre-charge gas generation and negative electrode side reactions in acetonitrile-based fast-charging systems. While it can improve fast-charging performance and interfacial stability to a certain extent, it still falls short in simultaneously ensuring continuous stability of the negative electrode interface, positive electrode tolerance, and long-term cycle consistency over a wider temperature range, making it difficult to achieve a further balance between high ion conductivity and low side reactions.

[0004] Invention CN118867399A discloses an electrolyte, a secondary battery, and an electronic device for a secondary battery, comprising ethyl fluorocarbonate, ethylene fluorocarbonate, and lithium difluorophosphate. By controlling the content of these components, the invention aims to reduce the positive electrode interface reaction, alleviate the continuous reduction reaction at the negative electrode, and reduce the increase in cycle impedance. However, this invention primarily focuses on improving the interface stability of the ethyl fluorocarbonate system under high voltage. It still has shortcomings in enhancing ion transport capabilities with nitrile solvents under fast charging conditions, synergistically regulating the solvation structure with different nitrile solvents, and constructing the interface film in stages with multiple additives. Therefore, it is difficult to simultaneously achieve fast charging, wide-temperature range, and long-term cycle performance.

[0005] Therefore, how to provide a high-performance lithium-ion battery electrolyte and its preparation process to solve or overcome the technical problems of existing electrolytes that are difficult to simultaneously achieve fast charging performance, interface stability and wide temperature adaptability, and to achieve the technical effect of improving the cycle life, rate performance and operational stability of lithium-ion batteries, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention provides a high-performance lithium-ion battery electrolyte and its preparation process. This process involves constructing a nitrile solvent system composed of acetonitrile and alkoxynitrile, and a fluorinated solvent system composed of fluorinated ethers and fluorinated carboxylic esters, and using various additives for staged interface regulation. This enhances the electrolyte's ion transport capacity, interface stability, and wide temperature adaptability, thereby improving the rate performance, cycle life, and operational stability of lithium-ion batteries.

[0007] In a first aspect, the present invention provides a high-performance lithium-ion battery electrolyte, comprising lithium salt, organic solvent and additives; The organic solvent includes nitrile solvents, fluorinated solvents, and auxiliary solvents. The nitrile solvents include acetonitrile and alkoxynitrile, and the fluorinated solvents include fluorinated ethers and fluorinated carboxylic esters. The volume ratio of the fluorinated ether to the fluorinated carboxylic ester is 1:(0.2-1.2), and the volume ratio of the acetonitrile to the alkoxynitrile is 1:(1-3.5). Based on the total volume of the organic solvents being 100%, the volume fraction of the nitrile solvents is 25%-60%, the volume fraction of the fluorinated solvents is 25%-55%, and the remainder is an auxiliary solvent; The additives include a first additive, a second additive, a third additive, and a fourth additive, based on the total mass of the electrolyte: The first additive has a mass fraction of 0.2%-1.5%, including at least one of lithium difluorophosphate, lithium difluorooxalate borate, and lithium tetrafluoroborate; The second additive has a mass fraction of 0.1%-1.2%, including at least one of vinylene sulfate, methylene disulfonate, 1,3-propanesulfonate lactone and 1,3-propenylsulfonate lactone; The third additive has a mass fraction of 1.5%-5.0%, and includes at least one of vinylene carbonate and fluoroethylene carbonate; The fourth additive has a mass fraction of 0.1%-1.0%, and includes at least one of tris(trimethylsilane) phosphate and tris(trimethylsilyl) phosphate.

[0008] This invention combines acetonitrile with alkoxynitrile to achieve both rapid ion transport and good lithium salt solubility stability. Acetonitrile helps reduce system viscosity and improve bulk ion conduction efficiency, while alkoxynitrile helps mitigate the problem of strong interfacial side reactions when acetonitrile is used alone. Furthermore, by introducing fluoroethers and fluorocarboxylic esters into the same fluorinated solvent system, the excessive coordination of the solvent to lithium ions is weakened at the solvation structure level, making it easier for anions and fluorinated film-forming components to participate in interfacial reactions, thereby promoting the formation of a dense, stable, and low-impedance interfacial film. Simultaneously, the first additive preferentially constructs an inorganic-enriched initial interface, the second additive strengthens and stabilizes the interfacial structure during cycling, the third additive forms and repairs the negative electrode protective film, and the fourth additive inhibits adverse reactions initiated by trace amounts of aqueous acid and improves the interfacial chemical environment. Therefore, the overall system maintains good interfacial and operational stability at high rates, over a wide temperature range, and during long cycles.

[0009] Preferably, the lithium salt comprises lithium hexafluorophosphate and lithium difluorosulfonylimide, wherein the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is (6-15):1, and the total concentration of the lithium salt is 1-1.4 mol / L.

[0010] By employing a composite lithium salt system of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, ion dissociation and interfacial film composition can be improved while ensuring compatibility with conventional aluminum foil and system stability. Specifically, lithium hexafluorophosphate helps maintain the basic conductivity and industrial suitability of the electrolyte, while lithium bis(fluorosulfonyl)imide helps increase the proportion of inorganic fluorine-containing components at the interface and reduce polarization.

[0011] Preferably, the alkoxynitrile satisfies the general structural formula R1O-R2-CN, wherein R1 is selected from an alkyl group with 1-3 carbon atoms, and R2 is selected from an alkylene group with 2-4 carbon atoms or an alkylene group with 1-2 carbon atom side chains; the alkoxynitrile includes at least one of methoxyacetonitrile, ethoxyacetonitrile, propoxyacetonitrile, and 3-methoxypropionitrile.

[0012] The above-mentioned alkoxynitrile structure has both nitrile group and ether bond structural units. The nitrile group is beneficial to improve the solubility of lithium salts and improve stability under high voltage, while the ether bond structure is beneficial to adjust molecular polarity and fluidity, so that the solvent can maintain good solubility without excessively enhancing the binding of lithium ions.

[0013] Preferably, the fluoroether comprises at least one selected from hexafluoroisopropylmethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether. The fluorocarboxylic acid esters include at least one of 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2-difluoroethyl propionate.

[0014] Preferably, the auxiliary solvent includes at least one selected from dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, and ethyl propionate.

[0015] Preferably, the mass ratio of the second additive to the first additive is (0.3-2.5):1, the mass ratio of the third additive to the first additive is (2-15):1, and the mass ratio of the fourth additive to the first additive is (0.2-2):1.

[0016] It should be noted that while fluorinated solvents are beneficial for suppressing interfacial side reactions and promoting the formation of fluorinated interfacial films, if their proportion in the system is too low, it is difficult to fully exert their regulatory effect on the solvation structure and interfacial film composition; if their proportion is too high, it may lead to insufficient effective dissolution environment for lithium salts, decreased system polarity, or reduced mass transfer efficiency at low temperatures. Therefore, this invention combines fluorinated ethers with fluorinated carboxylic esters and limits their proportions with nitrile solvents and auxiliary solvents, allowing the fluorinated solvents to participate in interfacial regulation without excessively weakening the overall salt-dissolving capacity and wetting properties of the system. In particular, compared to some completely inert weakly coordinating fluorinated solvents, fluorinated carboxylic esters retain a certain degree of polarity and intermolecular interaction ability, thus enabling more precise regulation of the interfacial reaction environment without excessively sacrificing processing adaptability.

[0017] Preferably, the electrolyte has a water content of no more than 20 ppm and a free acid content of no more than 50 ppm.

[0018] Controlling the moisture and free acid levels in the electrolyte within the aforementioned ranges helps to suppress lithium salt decomposition, reduce the corrosive effect on the positive and negative electrode interfaces, and lower the risks of gas generation and impedance growth. Especially in systems containing nitrile solvents, fluorinated solvents, and various functional additives, lower moisture and free acid levels help ensure the stable coexistence of all components, avoid adverse interference induced by impurities during interface film formation, and thus improve the storage and operational stability of the electrolyte.

[0019] Secondly, the present invention also provides a process for preparing the electrolyte, comprising the following steps: S1. Raw material pretreatment: Dehydration treatment of nitrile solvents, fluorinated solvents and auxiliary solvents, and drying pretreatment of lithium salts and additives; S2, Solvent premixing: A nitrile solvent, a fluorinated solvent, and an auxiliary solvent are mixed under an inert atmosphere to obtain a mixed solvent; S3. Additive addition: Add the first additive, the second additive, the third additive and the fourth additive to the mixed solvent and stir to mix; S4. Salt dissolution and solution preparation: Add lithium salt to the system obtained in step S3 and continue stirring until completely dissolved to obtain electrolyte mother liquor; S5. Purification and Packaging: The electrolyte mother liquor is filtered and degassed before being sealed and packaged to obtain the electrolyte.

[0020] Preferably, in step S1, the nitrile solvent, fluorinated solvent and auxiliary solvent are dehydrated by molecular sieve adsorption and / or vacuum distillation, and the lithium salt and additives are pretreated by vacuum drying.

[0021] Thirdly, the present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and the electrolyte; The positive electrode includes at least one of lithium iron phosphate and lithium manganese iron phosphate, and the negative electrode includes at least one of graphite and silicon carbide.

[0022] The high-performance lithium-ion battery electrolyte and its preparation process provided by this invention have at least the following beneficial effects: (1) This invention constructs a nitrile solvent system composed of acetonitrile and alkoxynitrile and a fluorinated solvent system composed of fluorinated ether and fluorinated carboxylic acid ester, and uses a first additive, a second additive, a third additive and a fourth additive to perform staged interface regulation, so that the electrolyte can maintain high ion transport capacity and low viscosity while taking into account the stability of the positive and negative electrode interface and wide temperature adaptability. Among them, acetonitrile is beneficial to improve ion conduction capacity, alkoxynitrile is beneficial to improve the dissolution stability of lithium salt and mitigate interface side reactions, fluorinated ether and fluorinated carboxylic acid ester are beneficial to optimize solvation structure and promote the formation of stable interface film, and multiple additives are beneficial to achieve initial film formation, cycle reinforcement, interface repair and impurity suppression respectively, thereby improving the rate performance, cycle life and operating stability of lithium-ion batteries.

[0023] (2) The present invention further limits the lithium salt system, the types of alkoxynitriles, the types of fluorinated solvents, the types of auxiliary solvents, and the proportions of various additives, so that the electrolyte system can form a more reasonable balance between conductivity, interfacial film composition, wettability, low-temperature fluidity and high-temperature stability. Among them, the composite lithium salt is beneficial to take into account both basic conductivity and fluorinated inorganic interface construction, the alkoxynitrile with a specific structure is beneficial to coordinate salt solubility and interfacial stability, the auxiliary solvent is beneficial to improve processing adaptability and electrode wetting effect, and the proportion control between various additives is beneficial to avoid the problems of interfacial film being too thin or too thick or mutual interference between film-forming components, thereby further improving the comprehensive electrochemical performance and batch stability of the electrolyte. Detailed Implementation

[0024] To better understand the above technical solutions, a detailed description of the specific implementation methods will be provided below. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” used in the embodiments of this invention are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0026] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0027] This invention provides a high-performance lithium-ion battery electrolyte, composed of lithium salt, organic solvent, and additives. The organic solvent serves as a continuous liquid medium in the electrolyte, dissolving the lithium salt and providing a transport environment for lithium-ion migration. The additives are dissolved or dispersed in the continuous liquid medium to regulate the formation and stability of the electrode interface film. The lithium salt provides the transportable lithium ions. Functionally, this electrolyte can be divided into a solvation regulation system, a lithium-conducting salt system, and an interface regulation system, specifically including: (1) An organic solvent system, wherein the organic solvent includes nitrile solvents, fluorinated solvents, and auxiliary solvents, wherein the nitrile solvents include acetonitrile and alkoxynitrile, and the fluorinated solvents include fluorinated ethers and fluorinated carboxylic esters; the volume ratio of the fluorinated ether to the fluorinated carboxylic ester is 1:0.2-1.2, and the volume ratio of the acetonitrile to the alkoxynitrile is 1:1-3.5; based on the total volume of the organic solvents as 100%, the volume fraction of the nitrile solvents is 25%-60%, the volume fraction of the fluorinated solvents is 25%-55%, and the remainder is auxiliary solvent. In the above organic solvent system, acetonitrile is used to reduce the viscosity of the system and improve the bulk ion conduction efficiency; alkoxynitrile is used to improve the dissolution stability of lithium salts and mitigate the tendency of interfacial side reactions when acetonitrile is used alone; fluorinated ether is used to reduce the excessive coordination of the solvent to lithium ions and promote the preferential participation of fluorinated interfacial components in film formation; fluorinated carboxylic ester is used to further regulate the solvation structure and interfacial reaction activity; and auxiliary solvent is used to improve wettability, processing adaptability, and system homogeneity. Through the synergistic effect of the above components, the electrolyte can maintain good ion transport capacity and interfacial stability under high rate and wide temperature range conditions.

[0028] In one preferred embodiment, the alkoxynitrile satisfies the general structural formula R1O-R2-CN, wherein R1 is selected from an alkyl group with 1-3 carbon atoms, and R2 is selected from an alkylene group with 2-4 carbon atoms or an alkylene group with 1-2 carbon atom side chains. By defining the R1 and R2 structures as described above, it is beneficial for the alkoxynitrile to simultaneously possess appropriate polarity, good fluidity, and the ability to dissolve lithium salts, thereby maintaining ion-conducting ability without excessively enhancing the binding effect on lithium ions.

[0029] In a more preferred embodiment, the alkoxynitrile includes at least one selected from methoxyacetonitrile, ethoxyacetonitrile, propoxyacetonitrile, and 3-methoxypropionitrile. These specific alkoxynitrile species exhibit good industrial availability and solubility compatibility. Methoxyacetonitrile and 3-methoxypropionitrile offer a balance of low viscosity and good salt solubility, while ethoxyacetonitrile and propoxyacetonitrile are beneficial for adjusting the polarity and volatility of the system. Therefore, they can be selected or compounded according to different cell rate and temperature requirements.

[0030] In one preferred embodiment, the fluorinated ether comprises at least one selected from hexafluoroisopropylmethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether; the fluorinated carboxylic acid ester comprises at least one selected from 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2-difluoroethyl propionate. The aforementioned fluorinated ethers possess weak coordination and high chemical stability, which is beneficial for suppressing disordered reactions of free solvent molecules at the interface. The introduction of electron-withdrawing fluorinated groups into the aforementioned fluorinated carboxylic acid esters can further reduce interfacial side reaction activity and improve mass transfer and desolvation behavior at low temperatures. When used in combination, these two ethers help to establish a more reasonable balance between solvation regulation and interfacial protection.

[0031] In one preferred embodiment, the auxiliary solvent includes at least one selected from dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, and ethyl propionate. Linear carbonates are beneficial for improving the wettability and conductivity of the electrolyte to the electrodes and diaphragm, while carboxylic acid esters are beneficial for reducing system viscosity and improving flowability. This gives the electrolyte of the present invention good processing adaptability during actual electrolyte injection and wetting processes.

[0032] (2) A lithium salt system, wherein the lithium salt comprises lithium hexafluorophosphate and lithium difluorosulfonylimide, wherein the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is 6-15:1, and the total concentration of the lithium salt is 1.0-1.4 mol / L. In the above-mentioned composite lithium salt system, lithium hexafluorophosphate is used to maintain the basic conductivity of the system and its compatibility with conventional battery systems, while lithium difluorosulfonylimide is used to improve the proportion of inorganic fluorine-containing components in the interface and reduce polarization. Controlling the ratio of the two within the above range is beneficial to balance conductivity, interfacial film-forming ability, and compatibility with aluminum current collectors, avoiding an excessively high proportion of lithium difluorosulfonylimide leading to an increase in side reactions, and also avoiding insufficient conductivity or increased system viscosity due to excessively low or high total concentration.

[0033] In one preferred embodiment, the lithium salt is preferentially dissolved in a pre-mixed organic solvent system to avoid uneven dissolution, localized salt precipitation, or premature adverse reactions of some additives caused by excessively high local concentrations of a single solvent. By first establishing a homogeneous solvent environment and then introducing the composite lithium salt, it is beneficial to improve system homogeneity and batch consistency.

[0034] (3) An additive system comprising a first additive, a second additive, a third additive, and a fourth additive. The first additive has a mass fraction of 0.2%-1.5% and includes at least one of lithium difluorophosphate, lithium difluorooxalate borate, and lithium tetrafluoroborate; the second additive has a mass fraction of 0.1%-1.2% and includes at least one of vinylene sulfate, methanedisulfonate, 1,3-propanesulfonate lactone, and 1,3-propenylsulfonate lactone; the third additive has a mass fraction of 1.5%-5.0% and includes at least one of vinylene carbonate and fluorovinyl carbonate; the fourth additive has a mass fraction of 0.1%-1.0% and includes at least one of tris(trimethylsilane) phosphate and tris(trimethylsilyl) phosphate. The first additive is preferentially used to construct an inorganic enriched initial interfacial membrane; the second additive is used to reinforce and stabilize the interfacial structure during cycling; the third additive is used to construct and repair the negative electrode side protective membrane; and the fourth additive is used to absorb or mitigate the adverse effects of trace amounts of water and acid in the system and improve the interfacial chemical environment. By combining the functions of the additives mentioned above, the interfacial film formation process can be made more balanced, reducing initial side reactions and improving subsequent cycle stability.

[0035] In one preferred embodiment, the mass ratio of the second additive to the first additive is 0.3-2.5:1, the mass ratio of the third additive to the first additive is 2-15:1, and the mass ratio of the fourth additive to the first additive is 0.2-2:1. These ratios facilitate synergistic effects among the various additives in initial film formation, cycle reinforcement, interface repair, and impurity suppression. This avoids situations where an excessively high proportion of a single additive leads to an overly thick interfacial film, increased impedance, or enhanced side reactions, while also preventing situations where an excessively low proportion fails to fully realize its corresponding function.

[0036] In a more preferred embodiment, the first additive preferably includes at least one of lithium difluorophosphate and lithium difluorooxalate borate; the second additive preferably includes at least one of vinylene sulfate and 1,3-propanesulfonate lactone; the third additive preferably includes at least one of vinylene carbonate and fluorovinyl carbonate; and the fourth additive preferably includes tris(trimethylsilane) phosphate. This preferred combination helps to further balance the initial film-forming efficiency, subsequent cycle stability, and the inhibitory effect of trace amounts of water and acid in the system.

[0037] (4) Purity control system: The water content of the electrolyte is not higher than 20 ppm, and the free acid content is not higher than 50 ppm. In a system containing nitrile solvents, fluorine solvents, various interfacial additives, and composite lithium salts, high water and free acid content can easily induce lithium salt decomposition, uneven interfacial film, gas generation, and increased impedance. Controlling these indicators within the appropriate range is beneficial to improving the storage stability, preparation stability, and practical application stability of the electrolyte.

[0038] The preparation process of the aforementioned high-performance lithium-ion battery electrolyte specifically includes the following steps: S1. Raw material pretreatment: Dehydration treatment of nitrile solvents, fluorinated solvents and auxiliary solvents, and drying pretreatment of lithium salts and additives.

[0039] This step is used to reduce the moisture and impurity content of the raw materials, thereby minimizing lithium salt decomposition and interfacial side reactions caused by trace amounts of moisture and acidic substances during subsequent solution preparation. For liquid raw materials, testing can be performed first, followed by processing as needed; for solid lithium salts and additives, drying can be carried out without inducing decomposition.

[0040] In one preferred embodiment, the nitrile solvent, fluorinated solvent and auxiliary solvent are dehydrated by molecular sieve adsorption and / or vacuum distillation, and the lithium salt and additives are pretreated by vacuum drying.

[0041] Among them, molecular sieve adsorption is suitable for the mild dehydration treatment of solvents with high heat sensitivity, vacuum distillation is suitable for reducing trace amounts of water in some volatile solvents, and vacuum drying is beneficial for removing adsorbed water on the surface of solid components, thereby improving the purity and batch consistency of the system.

[0042] S2. Solvent premixing: A nitrile solvent, a fluorinated solvent, and an auxiliary solvent are mixed under an inert atmosphere to obtain a mixed solvent.

[0043] This step is used to establish a homogeneous basic liquid environment, allowing solvents with different polarities, volatility, and coordination abilities to mix thoroughly, thus providing a stable medium for subsequent additive dispersion and lithium salt dissolution. An inert atmosphere helps reduce interference from moisture and oxygen in the air on the system.

[0044] In one preferred embodiment, the nitrile solvent, the fluorinated solvent, and the auxiliary solvent are added sequentially to a stirred tank in a predetermined ratio and mixed for 10-60 minutes at room temperature or below 30°C to form a clear and homogeneous mixed solvent. For acetonitrile, which has high volatility, it is preferable to add it under sealed conditions to reduce evaporation loss.

[0045] S3. Additive addition: Add the first additive, the second additive, the third additive and the fourth additive to the mixed solvent and stir to mix.

[0046] This step is used to pre-disperse various functional additives uniformly in the base solvent system, thereby reducing component inhomogeneity, local side reactions, or dissolution fluctuations caused by excessively high local concentrations when lithium salts are added subsequently. Adding the additives first and mixing them thoroughly facilitates the formation of a more homogeneous interface control system.

[0047] In one preferred embodiment, the first and second additives can be added and stirred first to ensure preferential and uniform dispersion of the initial interface-regulating components; then the third and fourth additives are added to reduce the possibility of local concentration of volatile or active components. This order of addition is not unique, but it is preferable to ensure that each component is fully stirred and dispersed after addition.

[0048] S4. Salt dissolution and solution preparation: Add lithium salt to the system obtained in step S3 and continue stirring until completely dissolved to obtain the electrolyte mother liquor.

[0049] This step is used to establish the final lithium-conducting system. Since the electrolyte of this invention contains a complex lithium salt and various solvents and additives of different polarities, the system must be continuously stirred after the lithium salt is added until it is completely clear to ensure the homogeneity and stability of the electrolyte. Dissolving the lithium salt in a pre-formed homogeneous solvent-additive system helps improve dissolution efficiency and reduces the risk of salt precipitation or localized side reactions.

[0050] In one preferred embodiment, the lithium salt is added in batches, with stirring for 10-30 minutes after each addition, and then the next batch is added, until all the salt has been added. This batch addition method helps avoid localized high salt concentrations that could cause delayed dissolution or localized precipitation.

[0051] In a more preferred embodiment, the stirring time in step S4 is 30-180 min, preferably with no visible suspended matter, no visible crystals, and a clear and transparent appearance.

[0052] S5. Purification and Packaging: The electrolyte mother liquor is filtered and degassed before being sealed and packaged to obtain the electrolyte.

[0053] This step removes trace particulate impurities and air bubbles trapped during dissolution, improving electrolyte cleanliness and storage stability. Filtration reduces the adverse effects of particulate impurities on subsequent electrolyte filling and interface formation, degassing reduces the impact of residual air bubbles after packaging on solution preparation accuracy and storage safety, and sealed packaging helps maintain the electrolyte in a low-water, low-acid state.

[0054] In one preferred embodiment, filtration may be performed using a filter membrane with a pore size of 0.2-1 μm, and degassing may be performed using at least one of static degassing, vacuum degassing, or inert gas bubbling degassing.

[0055] In a more preferred embodiment, the purified electrolyte is filled into a sealed container under an inert atmosphere and stored in a low-water, low-oxygen environment to reduce compositional fluctuations before subsequent use.

[0056] The following is a supplement to the specific implementation methods: In S1, the dehydration treatment of liquid raw materials is preferably carried out by first detecting the moisture content. When the detection result is higher than the preset threshold, molecular sieve adsorption or vacuum distillation is then used. The drying pretreatment of solid raw materials is preferably carried out under conditions not higher than their thermal decomposition temperature to avoid deactivation of effective components.

[0057] In S2, it is preferable to add the auxiliary solvent first, followed by the nitrile solvent and the fluorinated solvent, so as to utilize the fluidity and wettability of the auxiliary solvent to accelerate the uniform dispersion of the subsequent solvent.

[0058] In S3, if an additive dissolves slowly in the mixed solvent, it can be pre-dispersed in a small amount of mixed solvent before being added to the main system to improve the overall mixing efficiency.

[0059] In S4, it is preferable to add lithium hexafluorophosphate first, followed by lithium bisfluorosulfonylimide, to control the local coordination environment and dissolution rate of the system.

[0060] In S5, the electrolyte after filtration and degassing can be tested again for moisture, free acid, and appearance to confirm that the obtained electrolyte meets the usage requirements.

[0061] Example 1

[0062] This invention provides a high-performance lithium-ion battery electrolyte, which is composed of the following materials: Based on the preparation of 500 mL of electrolyte, the following components were used: acetonitrile 58.9 g, 3-methoxypropionitrile 142.5 g, hexafluoroisopropyl methyl ether 152.1 g, 2,2,2-trifluoroethyl acetate 68.4 g, methyl ethyl carbonate 50.5 g, dimethyl carbonate 53.5 g, lithium hexafluorophosphate 82.8 g, lithium difluorosulfonyl imide 10.3 g, lithium difluorophosphate 2.0 g, lithium difluorooxalate borate 2.0 g, vinylene sulfate 2.0 g, 1,3-propanesulfonate lactone 1.2 g, vinylene carbonate 10.0 g, fluoroethylene carbonate 8.0 g, and tris(trimethylsilane) phosphate 1.8 g.

[0063] The volume ratio of acetonitrile to 3-methoxypropionitrile is approximately 1:2, and the volume ratio of hexafluoroisopropyl methyl ether to 2,2,2-trifluoroethyl acetate is approximately 1:0.5. Based on the total volume of organic solvents, the volume fraction of nitrile solvents is approximately 45%, the volume fraction of fluorinated solvents is approximately 35%, and the remainder is auxiliary solvent. The molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is approximately 10:1, and the total concentration of lithium salt is approximately 1.2 mol / L.

[0064] The preparation method of the above electrolyte specifically includes the following steps: S1. Raw material pretreatment: Acetonitrile, 3-methoxypropionitrile, hexafluoroisopropylmethyl ether, 2,2,2-trifluoroethyl acetate, methyl ethyl carbonate and dimethyl carbonate were placed in a sealed container containing 3A molecular sieve and allowed to stand at room temperature for 48 h for dehydration treatment; lithium hexafluorophosphate, lithium difluorosulfonylimide, lithium difluorophosphate, lithium difluorooxalate borate, vinylene sulfate, 1,3-propanesulfonate lactone, vinylene carbonate, fluoroethylene carbonate and tris(trimethylsilane) phosphate were dried in a vacuum drying oven at 60℃ for 12 h.

[0065] S2. Solvent premixing: Under argon protection, acetonitrile, 3-methoxypropionitrile, hexafluoroisopropylmethyl ether, 2,2,2-trifluoroethyl acetate, methyl ethyl carbonate and dimethyl carbonate are sequentially added to a dry mixing vessel equipped with mechanical stirring. The mixture is stirred at 25°C and 300 rpm for 20 min to obtain a clear and transparent mixed solvent.

[0066] S3. Additive addition: Add lithium difluorophosphate, lithium difluorooxalate borate, vinylene sulfate, 1,3-propanesulfonate lactone, vinylene carbonate, fluoroethylene carbonate and tris(trimethylsilane) phosphate to the mixed solvent obtained in step S2, and continue stirring at 25°C and 400 rpm for 30 min to fully disperse the additives.

[0067] S4. Salt solution preparation: Add lithium hexafluorophosphate to the system obtained in step S3 in three batches. Stir for 20 minutes after each batch is added, then add lithium difluorosulfonylimide and continue stirring at 25°C and 500 rpm for 90 minutes until the system is completely clear and transparent to obtain the electrolyte mother liquor.

[0068] S5. Purification and Packaging: The electrolyte mother liquor obtained in step S4 is filtered through a 0.22 μm polytetrafluoroethylene filter membrane, then degassed under vacuum at -0.08 MPa for 30 min, and subsequently dispensed and sealed in an argon atmosphere to obtain the electrolyte.

[0069] Unless otherwise specified, the preparation steps used in the other embodiments and comparative examples are the same as those in Example 1, and the battery assembly and testing conditions are also the same. The specific differences are as follows:

[0070] Example 2

[0071] The difference between this embodiment and Example 1 is that the volume ratio of acetonitrile to 3-methoxypropionitrile is adjusted to 1:1; the total integral of nitrile solvent is adjusted to 40%, while the rest remain the same.

[0072] Example 3

[0073] The difference between this embodiment and Example 1 is that the volume ratio of acetonitrile to 3-methoxypropionitrile is adjusted to 1:3.5, while the rest remains the same.

[0074] Example 4

[0075] The difference between this embodiment and Example 1 is that the total integral of the fluorinated solvent is adjusted to 25%, the volume ratio of hexafluoroisopropyl methyl ether to 2,2,2-trifluoroethyl acetate is adjusted to 1:0.2, and the rest remain the same.

[0076] Example 5

[0077] The difference between this embodiment and Example 1 is that the total integral of the fluorinated solvent is adjusted to 55%, the volume ratio of hexafluoroisopropyl methyl ether to 2,2,2-trifluoroethyl acetate is adjusted to 1:1.2, and the rest remain the same.

[0078] Example 6

[0079] The difference between this embodiment and Example 1 is that 3-methoxypropionitrile is replaced with a mixture of ethoxyacetonitrile and 3-methoxypropionitrile in a volume ratio of 1:1, while the rest remains the same.

[0080] Example 7

[0081] The difference between this embodiment and Example 1 is that hexafluoroisopropyl methyl ether is replaced with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 2,2,2-trifluoroethyl acetate is replaced with 2,2-difluoroethyl acetate, while the rest remain the same.

[0082] Example 8

[0083] The difference between this embodiment and Example 1 is that the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is adjusted to 6:1, the total concentration of lithium salt is adjusted to 1.0 mol / L, and the rest remain the same.

[0084] Example 9

[0085] The difference between this embodiment and Example 1 is that the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is adjusted to 15:1, the total concentration of lithium salt is adjusted to 1.4 mol / L, and the rest remain the same.

[0086] Example 10

[0087] The difference between this embodiment and Embodiment 1 is that the mass ratio of the second additive to the first additive is adjusted to 0.3:1, the mass ratio of the third additive to the first additive is adjusted to 2:1, and the mass ratio of the fourth additive to the first additive is adjusted to 0.2:1, while the rest remain the same.

[0088] Example 11

[0089] The difference between this embodiment and Embodiment 1 is that the mass ratio of the second additive to the first additive is adjusted to 2.4:1, the mass ratio of the third additive to the first additive is adjusted to 10:1, and the mass ratio of the fourth additive to the first additive is adjusted to 2:1, while the rest remain the same.

[0090] Comparative Example 1 This comparative example uses a standard commercial system benchmark, specifically: a standard electrolyte with an EC / EMC / DMC volume ratio of 1:1:1, 1.1 mol / L LiPF6, and 2.0 wt% VC.

[0091] Comparative Example 2 The difference between this comparative example and Example 1 is that alkoxynitrile and fluorinated solvent are removed, and only acetonitrile and auxiliary solvent are retained, with the third additive remaining as the main additive.

[0092] Comparative Example 3 The difference between this comparative example and Example 1 is that the fluorinated solvent is removed, while acetonitrile, 3-methoxypropionitrile and auxiliary solvent are retained, and the additive system remains the same.

[0093] Comparative Example 4 The difference between this comparative example and Example 1 is that all solvents are retained, but the first additive, the second additive, and the fourth additive are removed, and only the third additive is retained.

[0094] Comparative Example 5 The difference between this comparative example and Example 1 is that, based on Example 1, the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is adjusted to 3:1.

[0095] Test methods To compare the performance of different electrolytes, all examples and comparative examples used the same cell system for testing. The test cells were 1.2 Ah aluminum-plastic film pouch cells. The positive electrode uses lithium manganese iron phosphate electrode sheets, with an active material, conductive agent Super P, and PVDF mass ratio of 96:2:2 and a single-sided areal density of 17.5 mg / cm³. 2 ; The negative electrode adopts a graphite / silicon-carbon composite negative electrode, with the mass ratio of graphite, silicon-carbon, Super P, CMC and SBR being 90:5:1:1.5:2.5, and the N / P ratio controlled at 1.08-1.12; the separator is a 12 μm ceramic-coated polyolefin separator; the liquid injection volume is controlled at 2.6 g / Ah; The formation process is as follows: charge at 0.1C constant current to 4.35V at 25℃, maintain constant voltage to 0.05C, let stand for 24 hours, and then discharge at 0.2C to 2.5V to complete 2 cycles of formation.

[0096] The specific test metrics include: 1. Ionic conductivity κ (mS / cm): Refer to GB / T 5545-2008 "Electrochemical Analysis Methods - Conductivity Method". Place the electrolyte in a conductivity cell at a constant temperature of 25℃, and use the AC impedance method to test the resistance corresponding to the high-frequency intercept. Combine this with the cell constant to calculate the ionic conductivity.

[0097] 2. 25℃ Fast Charging Cycle Capacity Retention Rate (%): Refer to the room temperature rate charging test method in GB / T 31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles"**. The cell is charged at 25℃ with a constant current and constant voltage of 4C to 4.35V and then cut off at 0.05C, followed by discharging at 1C to 2.5V, cycling 300 times. The capacity retention rate is calculated as the ratio of the discharge capacity on the 300th cycle to the initial discharge capacity.

[0098] 3. -20℃ Capacity Retention Rate (%): Refer to the low-temperature capacity test method in GB / T 31486-2015. After the cell is fully charged at 25℃, it is placed in a -20℃ environment for 12 hours, and then discharged at 0.5C to 2.5V. The low-temperature capacity retention rate is calculated by the ratio of the discharge capacity to the discharge capacity at 0.5C at 25℃.

[0099] 4. 60℃ High Temperature Storage Capacity Retention Rate (%): Refer to the storage performance test method in GB / T 31486-2015. The cell is fully charged at 25℃ and stored in a 60℃ environment for 7 days. After being restored to 25℃, it is discharged at 1C to 2.5V. The capacity retention rate is calculated as the ratio of the discharge capacity after storage to the discharge capacity before storage.

[0100] The specific test results are shown in Table 1: Table 1 Example 1 12.8 82.4 88.6 94.2 Example 2 13.3 79.1 84.7 92.1 Example 3 11.9 84.1 87.4 94.8 Example 4 13 76.8 80.9 90.3 Example 5 11.1 83 86.1 95 Example 6 12.5 81 87.2 93.9 Example 7 12.1 80.5 86.8 94.1 Example 8 12.2 78.4 84.9 92.8 Example 9 12 81.2 85.5 93.3 Example 10 13 77.2 81.6 91 Example 11 11.6 79.6 84.2 93.6 Comparative Example 1 9.4 58.3 71.5 86.9 Comparative Example 2 13.7 61.2 63.8 81.4 Comparative Example 3 13.1 69.5 76.4 88.7 Comparative Example 4 12.6 73.1 78.1 89.5 Comparative Example 5 11.4 76 79.3 88.9 As can be seen from Table 1, Example 1 showed the most balanced performance in four indicators: ionic conductivity, low-temperature capacity retention, fast-charge cycle capacity retention, and high-temperature storage capacity retention. This indicates that the electrolyte system formed by combining acetonitrile with 3-methoxypropionitrile, fluoroether with fluorocarboxylic acid ester, lithium hexafluorophosphate with lithium difluorosulfonylimide, and synergistic regulation by multiple additives can effectively balance ion conduction capability, low-temperature adaptability, fast-charge cycle stability, and high-temperature storage stability.

[0101] Examples 2 and 3 show that variations in the ratio of acetonitrile to alkoxynitrile significantly affect the system's performance. A higher proportion of acetonitrile results in higher ionic conductivity at 25°C, which is more conducive to rapid initial transport, but reduces low-temperature capacity retention and long-term cycling retention. A higher proportion of alkoxynitrile leads to greater stability at low temperatures and during cycling, but slightly lower ionic conductivity. Therefore, a balance needs to be struck between rapid transport capability and interfacial stability between acetonitrile and alkoxynitrile.

[0102] Examples 4 and 5 show that the overall amount of fluorinated solvent and the coordination relationship between fluorinated ethers and fluorinated carboxylic esters significantly affect the system performance. When the proportion of fluorinated solvent is low and the participation of fluorinated carboxylic esters is insufficient, the interfacial protection is weak, leading to a decrease in fast-charge cycling performance and high-temperature storage performance. When the proportion of fluorinated solvent is further increased, although the high-temperature storage stability is improved, the ionic conductivity at 25°C decreases, indicating that excessive weakly coordinated fluorinated solvents can weaken the bulk ion transport capability to some extent. Therefore, the formulation of fluorinated solvents needs to balance interfacial protection and bulk transport capability.

[0103] Examples 6 and 7 show that, under the condition that the remaining components are basically the same, the electrolyte can still maintain a high level of comprehensive performance after changing the specific species of alkoxynitrile and fluorinated solvent. This indicates that the synergistic system of dual nitrile and dual fluorinated solvent constructed in this invention is not only applicable to a single material, but also has good adaptability and universality for replacing similar species.

[0104] Examples 8 and 9 show that the composition of the composite lithium salt has a significant impact on the system performance. Under different ratios, the electrolyte can maintain good overall performance. However, as the composition of the composite lithium salt changes, the ionic conductivity, low-temperature capacity retention, and fast-charge cycle capacity retention fluctuate to varying degrees, indicating that the composition of the composite lithium salt needs to be balanced between ion conduction capability, interfacial film formation behavior, and system stability.

[0105] Examples 10 and 11 demonstrate that the various additives are not simply additive; their synergistic effects also significantly impact electrolyte performance. When the proportions of the second, third, and fourth additives relative to the first additive are low, the interfacial reinforcement and continuous repair capabilities are insufficient, leading to a decline in fast-charge cycle performance and high-temperature storage performance. Conversely, as the proportions of these additives increase, the interfacial protection is enhanced, and high-temperature storage performance improves, but ionic conductivity and rate cycle performance are somewhat affected. This indicates a clear synergistic and restrictive relationship among the various additives, necessitating a rational combination to achieve comprehensive performance optimization.

[0106] Comparative Examples 1 to 5 further illustrate that the technical effect of the present invention is not due to a single component, but rather to the solvation structure formed by the synergistic interaction of the two nitrile compounds and the two fluorinated solvents, the composite lithium salt system, and the staged interface regulation by multiple additives. Only when the above factors work together can the electrolyte achieve a good overall balance between ion conduction capability, low-temperature adaptability, fast-charge cycle stability, and high-temperature storage stability.

[0107] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Clearly, those skilled in the art can make various alterations and variations to the invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the invention and its equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A high-performance lithium-ion battery electrolyte, characterized in that, Including lithium salts, organic solvents, and additives; The organic solvents include nitrile solvents, fluorinated solvents, and auxiliary solvents. The nitrile solvents include acetonitrile and alkoxynitrile, and the fluorinated solvents include fluorinated ethers and fluorinated carboxylic esters. The volume ratio of the fluorinated ethers to the fluorinated carboxylic esters is 1:(0.2-1.2), and the volume ratio of the acetonitrile to the alkoxynitrile is 1:(1-3.5). Based on the total volume of organic solvents as 100%, the volume fraction of the nitrile solvent is 25%-60%, the volume fraction of the fluorinated solvent is 25%-55%, and the remainder is an auxiliary solvent; The additives include a first additive, a second additive, a third additive, and a fourth additive, based on the total mass of the electrolyte: The first additive has a mass fraction of 0.2%-1.5%, including at least one of lithium difluorophosphate, lithium difluorooxalate borate, and lithium tetrafluoroborate; The second additive has a mass fraction of 0.1%-1.2%, including at least one of vinylene sulfate, methylene disulfonate, 1,3-propanesulfonate lactone and 1,3-propenylsulfonate lactone; The third additive has a mass fraction of 1.5%-5.0%, and includes at least one of vinylene carbonate and fluoroethylene carbonate; The fourth additive has a mass fraction of 0.1%-1.0% and includes tris(trimethylsilane) phosphate; The lithium salt comprises lithium hexafluorophosphate and lithium difluorosulfonylimide, wherein the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide is (6-15):1, and the total concentration of the lithium salt is 1-1.4 mol / L.

2. The high-performance lithium-ion battery electrolyte as described in claim 1, characterized in that, The alkoxynitrile includes at least one of methoxyacetonitrile, ethoxyacetonitrile, propoxyacetonitrile, and 3-methoxypropionitrile.

3. The high-performance lithium-ion battery electrolyte as described in claim 1, characterized in that, The fluoroethers include at least one of hexafluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether. The fluorocarboxylic acid esters include at least one of 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2-difluoroethyl propionate.

4. The high-performance lithium-ion battery electrolyte as described in claim 1, characterized in that, The auxiliary solvent includes at least one of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, and ethyl propionate.

5. The high-performance lithium-ion battery electrolyte as described in claim 1, characterized in that, The mass ratio of the second additive to the first additive is (0.3-2.5):1, the mass ratio of the third additive to the first additive is (2-15):1, and the mass ratio of the fourth additive to the first additive is (0.2-2):

1.

6. The high-performance lithium-ion battery electrolyte as described in claim 1, characterized in that, The electrolyte has a water content of no more than 20 ppm and a free acid content of no more than 50 ppm.

7. A process for preparing the electrolyte as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Raw material pretreatment: Dehydration treatment of nitrile solvents, fluorinated solvents and auxiliary solvents, and drying pretreatment of lithium salts and additives; S2, Solvent premixing: A nitrile solvent, a fluorinated solvent, and an auxiliary solvent are mixed under an inert atmosphere to obtain a mixed solvent; S3. Additive addition: Add the first additive, the second additive, the third additive and the fourth additive to the mixed solvent and stir to mix; S4. Salt dissolution and solution preparation: Add lithium salt to the system obtained in step S3 and continue stirring until completely dissolved to obtain electrolyte mother liquor; S5. Purification and Packaging: The electrolyte mother liquor is filtered and degassed before being sealed and packaged to obtain the electrolyte.

8. The preparation process according to claim 7, characterized in that, In step S1, nitrile solvents, fluorinated solvents and auxiliary solvents are dehydrated by molecular sieve adsorption and / or vacuum distillation, and lithium salts and additives are pretreated by vacuum drying.

9. A lithium-ion battery, characterized in that, Includes a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1-6; The positive electrode includes at least one of lithium iron phosphate and lithium manganese iron phosphate, and the negative electrode includes at least one of graphite and silicon carbide.