A fast-charging lithium-ion battery electrolyte, its preparation method, and the battery itself.

Abstract

This invention relates to the field of electrolyte technology, and more particularly to a fast-charging lithium-ion battery electrolyte, its preparation method, and the battery itself. The electrolyte comprises 75%–82% of a composite organic solvent, which includes cyclic carbonates, chain carbonates, and short-chain carboxylic acid esters; 12%–16% of a composite lithium salt, which includes a main lithium salt and an auxiliary lithium salt. The main lithium salt is lithium hexafluorophosphate, and the auxiliary lithium salt is at least one selected from lithium difluorooxalate borate, lithium bis(oxalate borate), and lithium tetrafluoroborate; and 2%–9% of functional composite additives, which include film-forming additives, salt-stabilizing and anti-decomposition additives, and flame-retardant and gas-suppressing additives. This invention discloses a fast-charging lithium-ion battery electrolyte, its preparation method, and the battery, which can balance lithium salt dissociation, ion conductivity, and electrode wettability, and is suitable for the harsh conditions of ultra-high-rate fast charging.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, and in particular to a fast-charging lithium-ion battery electrolyte, its preparation method, and the battery itself. Background Technology

[0002] With the rapid development of portable energy storage, small intelligent electronic devices, and precision testing equipment, lithium iron phosphate (LFP) lithium-ion batteries have become the mainstream system in small energy storage and precision power supply fields due to their advantages of high safety, long cycle life, and low cost. Meanwhile, the continuous upgrading of fast charging technology also requires LFP coin cells to possess ultra-high rate fast charging capabilities of 4C and above, high-temperature operating stability, and wide temperature range adaptability. As the core carrier for lithium-ion migration and transport, the electrolyte's physicochemical properties and composition directly determine the fast-charging kinetics, interface stability, and high-temperature lifespan of LFP batteries.

[0003] Lithium iron phosphate (LFP) materials inherently suffer from low electronic conductivity, small electrode porosity, and poor electrolyte wettability. Under ultra-high rate fast charging conditions, severe high-current polarization, large voltage drop, and sluggish lithium-ion insertion / extraction kinetics easily lead to problems such as low charging efficiency, high polarization heat generation, and significant cell temperature rise. Conventional commercial LFP coin cell electrolytes generally use traditional binary carbonate solvents combined with a single lithium hexafluorophosphate salt, which is only suitable for 1C to 2C conventional charge / discharge rates. They have significant technical shortcomings under 4C to 8C ultra-high rate fast charging and high-temperature conditions. First, conventional solvent systems have high viscosity and limited ion transport rates, which cannot meet the kinetic requirements of high-current fast charging for lithium iron phosphate (LFP) systems, resulting in severe polarization losses. Second, LFP has many active sites at the interface, making the electrolyte prone to continuous side reactions under high-temperature fast charging conditions. This leads to SEI film passivation, pulverization, and a surge in impedance, continuously consuming active lithium and causing rapid capacity decay. Third, single lithium hexafluorophosphate has poor resistance to hydrolysis and thermal decomposition. The small, sealed cavity of the coin cell makes it difficult for heat to dissipate, easily causing heat accumulation and temperature rise. Under high-temperature conditions, lithium salts are prone to decomposition, producing corrosive impurities, leading to internal pressure accumulation, electrode corrosion, and interface failure, seriously affecting battery safety and cycle life. Finally, conventional electrolytes have insufficient wettability on LFP electrodes, poor adaptability to high and low temperatures, low capacity utilization during low-temperature fast charging, and easy decomposition and failure at high temperatures, making them unsuitable for ultra-high rate, wide-temperature-range fast charging scenarios for LFP systems. Most improvement solutions for fast-charging electrolytes of lithium iron phosphate involve adding a single film-forming aid, resulting in poor formulation synergy. These solutions cannot simultaneously address issues such as high polarization, poor wetting, easy passivation at high-temperature interfaces, numerous side reactions, and internal pressure accumulation in the lithium iron phosphate system. Even under ultra-high-rate fast charging, problems such as low charging efficiency, rapid cycle decay, and poor high-temperature stability still exist, making it difficult to meet the application requirements of high-end lithium iron phosphate coin cells for ultra-high rates, long lifespan, and high safety.

[0004] Therefore, developing an electrolyte that is compatible with lithium iron phosphate systems, can stably achieve ultra-high rate fast charging from 4C to 8C, and has high wettability, high interface stability, high temperature resistance, and low side reaction is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, the present invention provides a fast-charging lithium-ion battery electrolyte, a preparation method, and a battery.

[0006] One objective of this invention is to disclose a fast-charging lithium-ion battery electrolyte, comprising: The composite organic solvent comprises cyclic carbonates, chain carbonates, and short-chain carboxylic esters; wherein: cyclic carbonates have ultra-high dielectric constants, which can effectively improve lithium salt dissociation efficiency and increase the concentration of free lithium ions in the system; chain carbonates have extremely low viscosity, which can significantly reduce the ion migration resistance of the electrolyte and meet the requirements of high-current fast charging and rapid ion transport; short-chain carboxylic esters have both low viscosity and excellent low-temperature fluidity, which can greatly improve the wettability of the electrolyte to the electrode plates, while improving the low-temperature fast charging performance of the electrolyte and broadening the operating temperature range of the system.

[0007] A composite lithium salt, comprising a main lithium salt and an auxiliary lithium salt, wherein the main lithium salt is lithium hexafluorophosphate, which has advantages such as high ionic conductivity, low raw material cost, and wide compatibility with electrodes; the auxiliary lithium salt is at least one of lithium difluorooxalate borate, lithium bis(oxalate borate), and lithium tetrafluoroborate, which can significantly improve the thermal stability and hydrolysis resistance of the electrolyte, inhibit the high-temperature hydrolysis and decomposition of lithium hexafluorophosphate, and participate in the formation of the electrode interface film, optimize the microstructure of the SEI film, reduce the interfacial contact impedance, and further improve the fast-charging cycle stability.

[0008] The functional composite additives include film-forming additives, salt-stabilizing and anti-decomposition additives, and flame-retardant and gas-suppressing additives. The film-forming additives preferentially undergo redox reactions with the electrolyte during the initial stage of fast charging, forming a thin, dense, highly flexible, and highly ion-conductive composite SEI film in situ on the positive and negative electrode surfaces. This effectively blocks continuous side reactions between the electrolyte and electrodes, reduces interfacial impedance, minimizes active lithium-ion loss, and improves fast-charging cycle stability. The salt-stabilizing and anti-decomposition additives complex trace amounts of moisture and acidic impurities in the electrolyte system, fundamentally inhibiting lithium salt hydrolysis and electrolyte thermal decomposition, reducing corrosive gas generation, and maintaining long-term stability of the electrolyte system. The flame-retardant and gas-suppressing additives improve the flame-retardant performance of the electrolyte, reduce the risk of battery thermal runaway, and effectively suppress electrolyte decomposition and gas generation under high-temperature fast-charging conditions, preventing battery bulging and electrode corrosion failure, thus comprehensively improving battery safety performance.

[0009] By mass percentage, the composite organic solvent accounts for 75% to 82% of the electrolyte mass, the composite lithium salt accounts for 12% to 16% of the electrolyte mass, and the functional composite additive accounts for 2% to 9% of the electrolyte mass.

[0010] Preferably, the cyclic carbonate is at least one of ethylene carbonate and propylene carbonate.

[0011] Preferably, the chain carbonate is at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0012] Preferably, the short-chain carboxylic acid ester is at least one selected from ethyl acetate, methyl propionate, and ethyl propionate.

[0013] Preferably, the mass ratio of the cyclic carbonate, the chain carbonate, and the short-chain carboxylic acid ester is 20-30:40-55:10-20.

[0014] Preferably, the main lithium salt accounts for 11% to 14% of the mass of the electrolyte, and the auxiliary lithium salt accounts for 1% to 2% of the mass of the electrolyte.

[0015] Preferably, the film-forming additive is at least one of fluoroethylene carbonate, vinylene carbonate, and lithium alkyl sulfonate; the salt-stabilizing and decomposition-resistant additive is at least one of triethyl phosphite and trimethyl phosphate; and the flame-retardant and gas-suppressing additive is at least one of dimethyl methylphosphonate and cyclophosphonitrile flame retardants.

[0016] Preferably, the mass ratio of the film-forming additive, the salt-stabilizing and anti-decomposition additive, and the flame-retardant and gas-suppressing additive is 1-3:0.5-2:0.5-4.

[0017] The second objective of this invention is to disclose a method for preparing a fast-charging lithium-ion battery electrolyte, comprising the following steps: S1 Inert Environment Pretreatment: All raw materials are pretreated to remove water and impurities in an argon-protected glove box with a moisture content of ≤10ppm and an oxygen content of ≤20ppm, and the moisture content of the raw materials is controlled to be below 5ppm. S2. Preparation of composite solvent: Weigh cyclic carbonate, chain carbonate and short-chain carboxylic acid ester according to the preset mass ratio, mix and stir at room temperature for 20 to 30 minutes to obtain a uniform, transparent and non-layered composite organic solvent. S3. Dissolution of composite lithium salt: Slowly add the composite lithium salt to the composite organic solvent in batches, stir for 40-60 minutes under constant temperature conditions in an ice-water bath, and control the system temperature to not exceed 30°C, until the lithium salt is completely dissolved and the system is free of precipitation and turbidity. S4. Functional additive compounding: Add film-forming additive, salt-stabilizing and anti-decomposition additive, and flame-retardant and gas-suppressing additive to the system in sequence, and stir at room temperature for 30-40 minutes to ensure that the components are evenly dispersed and fully synergistic. S5. Precision filtration and purification: The mixture is precisely filtered using a 0.22μm organic microporous membrane to remove trace impurities and insoluble matter, thus obtaining a high-rate fast-charging lithium-ion battery electrolyte.

[0018] The third objective of this invention is to disclose a lithium-ion battery using an electrolyte obtained by the above-described preparation method.

[0019] The present invention has the following technical effects: 1. The composite organic solvent adopts a high-dielectric, low-viscosity, wide-temperature-range ternary compound system, composed of cyclic carbonates, chain carbonates, and short-chain carboxylic esters. Specifically: the cyclic carbonates possess ultra-high dielectric constants, effectively improving lithium salt dissociation efficiency and increasing the concentration of free lithium ions in the system; the chain carbonates have extremely low viscosity, significantly reducing electrolyte ion migration resistance and meeting the requirements of high-current fast charging and rapid ion transport; the short-chain carboxylic esters combine low viscosity and excellent low-temperature fluidity, greatly improving the electrolyte's wettability on the electrode plates, while also improving the electrolyte's low-temperature fast charging performance and broadening the system's operating temperature range. These three components work synergistically to balance lithium salt dissociation, ion conduction rate, and electrode wettability, making it suitable for the demanding conditions of ultra-high-rate fast charging.

[0020] 2. The precise and synergistic combination of film-forming additives, salt-stabilizing and anti-decomposition additives, and flame-retardant and gas-suppressing additives can construct a composite SEI film with uniform structure, density, stability, and high ion conductivity on the electrode surface. Compared with traditional loose SEI films, the electrode interface impedance is reduced by more than 30%, effectively reducing the irreversible loss of active lithium ions during fast charging and significantly extending the battery life. After 500 cycles of 8C ultra-high rate fast charging, the battery capacity retention rate is ≥85%, and the cycle stability far exceeds that of conventional electrolytes.

[0021] 3. The electrolyte of this invention has excellent low-temperature adaptability. It can still maintain excellent ion conduction and wetting performance at a low temperature of -20℃, and the capacity utilization rate of low-temperature fast charging is greatly improved.

[0022] 4. The main-auxiliary composite lithium salt synergistic system retains the core advantage of high ionic conductivity of lithium hexafluorophosphate, while significantly improving the thermal stability, hydrolysis resistance and interfacial film formation performance of the electrolyte through trace amounts of auxiliary lithium salt. This fundamentally inhibits lithium salt decomposition and electrolyte deterioration under the high temperature environment of fast charging, greatly reduces the generation of corrosive gases, and reduces the rate of gas bulging and electrode corrosion in fast charging batteries. Attached Figure Description

[0023] Figure 1Line graph showing the degradation trend of 8C room temperature fast charging cycle life of lithium iron phosphate button batteries. Detailed Implementation

[0024] The principles and features of the present invention are described below with reference to embodiments; the examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0025] Example 1 A fast-charging lithium-ion battery electrolyte comprises the following mass percentages: 79% composite organic solvent, 14% composite lithium salt, and 7% composite additives. The composite organic solvent includes 25% ethylene carbonate, 45% methyl ethyl carbonate, and 9% ethyl propionate; the composite lithium salt includes 13% lithium hexafluorophosphate and 1% lithium difluorooxalate borate; and the composite additives include 2% fluoroethylene carbonate, 1.5% triethyl phosphite, and 3.5% dimethyl methylphosphonate. The above are the mass percentages of the battery electrolyte.

[0026] The preparation method of the above electrolyte is as follows: S1. Inert environment pretreatment: All raw materials are pretreated to remove water and impurities in an argon-protected glove box with a moisture content of ≤10ppm and an oxygen content of ≤20ppm, and the moisture content of the raw materials is controlled to be below 5ppm. S2. Preparation of composite solvent: Weigh cyclic carbonate, chain carbonate and short-chain carboxylic acid ester according to the preset mass ratio, mix and stir at room temperature for 25 minutes to obtain a uniform, transparent and non-layered composite organic solvent. S3. Dissolution of composite lithium salt: Slowly add the composite lithium salt to the composite organic solvent in batches, stir for 50 minutes under constant temperature conditions in an ice-water bath, and control the system temperature to not exceed 30℃, until the lithium salt is completely dissolved and the system is free of precipitation and turbidity. S4. Functional additive compounding: Add film-forming additive, salt-stabilizing and anti-decomposition additive, and flame-retardant and gas-suppressing additive to the system in sequence, and stir at room temperature for 35 minutes to ensure that the components are evenly dispersed and fully synergistic. S5. Precision filtration and purification: The mixture is precisely filtered using a 0.22μm organic microporous membrane to remove trace impurities and insoluble matter, thus obtaining a high-rate fast-charging lithium-ion battery electrolyte.

[0027] Example 2 A high-rate fast-charging lithium-ion battery electrolyte comprises the following components by mass percentage: 80% composite organic solvent, 13% composite lithium salt, and 7% functional composite additives. The composite organic solvent includes 22% propylene carbonate, 50% diethyl carbonate, and 8% ethyl acetate; the composite lithium salt includes 12% lithium hexafluorophosphate, 1% lithium bis(oxalato)borate, 2.5% vinylene carbonate, 2% trimethyl phosphate, and 2.5% cyclophosphonitrile compounds. The above are the mass percentages of the battery electrolyte.

[0028] The preparation method of the electrolyte in this embodiment is the same as that in Example 1.

[0029] Example 3 A high-rate fast-charging lithium-ion battery electrolyte comprises the following components by mass percentage: 76% composite organic solvent, 15% composite lithium salt, and 9% functional composite additives. The composite organic solvent includes 28% ethylene carbonate, 42% dimethyl carbonate, and 6% methyl propionate; the composite lithium salt includes 14% lithium hexafluorophosphate and 1% lithium tetrafluoroborate; and the composite additives include 3% lithium alkyl sulfonate, 2% triethyl phosphite, and 4% dimethyl methylphosphonate. The above are the mass percentages of the battery electrolyte.

[0030] The preparation method of the electrolyte in this embodiment is the same as that in Example 1.

[0031] Comparative Example The system uses a conventional binary carbonate solvent system with the following components: 30% ethylene carbonate, 58% dimethyl carbonate, and 12% lithium hexafluorophosphate. This system uses a single lithium salt formulation and has no composite functional additives.

[0032] The electrolytes used in all the above examples and comparative examples were prepared using CR-2032 stainless steel button battery casings. Lithium-ion batteries were assembled in an argon-protected glove box (water and oxygen content ≤0.01 ppm) with no water or oxygen. Assembly followed the order of positive electrode casing, positive electrode plate, electrolyte, separator, negative electrode plate, gasket, and negative electrode casing. The devices were sealed under a pressure ≤0.5 MPa, resulting in lithium-ion batteries assembled using the electrolytes prepared in Examples 1 to 3 and Comparative Example 1. The performance of these batteries under various operating conditions (room temperature (25℃), high temperature (55℃), and low temperature (-20℃)) was tested using a NEWARE BTS-5 V-type battery charge / discharge testing system.

[0033] The electrolytes from Examples 1 to 3 and the comparative conventional electrolyte were assembled into lithium-ion cells based on lithium iron phosphate. Under unified testing standards and environments, performance tests were conducted on 8C ultra-high rate fast charging efficiency, 8C fast charging cycle life, and low-temperature capacity retention at 55℃ / -20℃. Specific test results are shown in Table 1 below. Figure 1 As shown.

[0034] Table 1. Performance comparison of electrolytes and comparative examples in Examples 1 to 3 Test sample 8C fast charging efficiency 8C cycle 500 cycles capacity retention 8C high temperature (55℃) 500 cycles capacity retention -20℃ Low temperature capacity retention Example 1 96.2% 87.5% 83.2% 83.1% Example 2 95.8% 86.9% 82.6% 82.5% Example 3 95.1% 85.8% 81.5% 81.9% Comparative Example 1 78.5% 62.3% 45.7% 65.2% The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fast-charging lithium-ion battery electrolyte, characterized in that, include: A composite organic solvent, wherein the composite organic solvent comprises cyclic carbonates, chain carbonates and short-chain carboxylic acid esters; A composite lithium salt, comprising a main lithium salt and an auxiliary lithium salt, wherein the main lithium salt is lithium hexafluorophosphate, and the auxiliary lithium salt is at least one of lithium difluorooxalate borate, lithium bis(oxalate borate), and lithium tetrafluoroborate. Functional composite additives, including film-forming additives, salt-stabilizing and decomposition-resistant additives, and flame-retardant and gas-suppressing additives. By mass percentage, the composite organic solvent accounts for 75% to 82% of the electrolyte mass, the composite lithium salt accounts for 12% to 16% of the electrolyte mass, and the functional composite additive accounts for 2% to 9% of the electrolyte mass.

2. The fast-charging lithium-ion battery electrolyte according to claim 1, characterized in that, The cyclic carbonate is at least one of ethylene carbonate and propylene carbonate.

3. The fast-charging lithium-ion battery electrolyte according to claim 1, characterized in that, The chain carbonate is at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

4. The fast-charging lithium-ion battery electrolyte according to claim 1, characterized in that, The short-chain carboxylic acid ester is at least one of ethyl acetate, methyl propionate, and ethyl propionate.

5. The fast-charging lithium-ion battery electrolyte according to claim 1, characterized in that, The mass ratio of the cyclic carbonate, the chain carbonate, and the short-chain carboxylic acid ester is 20-30:40-55:10-20.

6. The fast-charging lithium-ion battery electrolyte according to claim 1, characterized in that, The main lithium salt accounts for 11% to 14% of the mass of the electrolyte, and the auxiliary lithium salt accounts for 1% to 2% of the mass of the electrolyte.

7. The fast-charging lithium-ion battery electrolyte according to claim 1, characterized in that, The film-forming additive is at least one of fluoroethylene carbonate, vinylene carbonate, and lithium alkyl sulfonate; the salt-stabilizing and decomposition-resistant additive is at least one of triethyl phosphite and trimethyl phosphate; and the flame-retardant and gas-suppressing additive is at least one of dimethyl methylphosphonate and cyclophosphonitrile flame retardants.

8. The fast-charging lithium-ion battery electrolyte according to claim 1, characterized in that, The mass ratio of the film-forming additive, the salt-stabilizing and anti-decomposition additive, and the flame-retardant and gas-suppressing additive is 1-3:0.5-2:0.5-4.

9. A method for preparing the fast-charging lithium-ion battery electrolyte according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1 Inert Environment Pretreatment: All raw materials are pretreated to remove water and impurities in an argon-protected glove box with a moisture content of ≤10ppm and an oxygen content of ≤20ppm, and the moisture content of the raw materials is controlled to be below 5ppm. S2. Preparation of composite solvent: Weigh cyclic carbonate, chain carbonate and short-chain carboxylic acid ester according to the preset mass ratio, mix and stir at room temperature for 20 to 30 minutes to obtain a uniform, transparent and non-layered composite organic solvent. S3. Dissolution of composite lithium salt: Slowly add the composite lithium salt to the composite organic solvent in batches, stir for 40-60 minutes under constant temperature conditions in an ice-water bath, and control the system temperature to not exceed 30°C, until the lithium salt is completely dissolved and the system is free of precipitation and turbidity. S4. Functional additive compounding: Add film-forming additive, salt-stabilizing and anti-decomposition additive, and flame-retardant and gas-suppressing additive to the system in sequence, and stir at room temperature for 30-40 minutes to ensure that the components are evenly dispersed and fully synergistic. S5. Precision filtration and purification: The mixture is precisely filtered using a 0.22μm organic microporous membrane to remove trace impurities and insoluble matter, thus obtaining a high-rate fast-charging lithium-ion battery electrolyte.

10. A lithium-ion battery comprising the fast-charging lithium-ion battery electrolyte as described in any one of claims 1 to 8.

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