Electrolyte, lithium ion battery containing the electrolyte

Abstract

The application discloses an electrolyte, a lithium ion battery containing the electrolyte and belongs to the technical field of lithium ion batteries. The electrolyte comprises a lithium salt, an organic solvent and a basic additive; further comprises 1-2 wt.% of a first additive and 1-2 wt.% of a second additive in terms of mass percentage; the first additive is at least one of a sulfuric acid ester compound or a sulfonic acid ester compound, can optimize a negative electrode interface film formation, and improves the high-temperature stability of the film layer; the second additive is at least one of a chain or cyclic polyfluorinated anhydride, can promote the enrichment of lithium fluoride in a negative electrode solid electrolyte interface film, reduce the interface impedance, and stabilize the high-temperature interface structure; meanwhile, the non-cyclic ester compound is used as the organic solvent, the viscosity of the electrolyte is reduced, and the lithium ion migration efficiency at low temperature is ensured. Through the synergistic cooperation between the components, the battery has excellent high-temperature stability and low-temperature adaptability, so that the fast charging capacity and the cycle service life of the battery under extreme working conditions are improved.

Description

Technical Field

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

[0002] With the rapid development of the new energy industry, lithium-ion batteries, with their superior energy density, long cycle life, and environmental friendliness, have been widely applied in new energy vehicles, large-scale energy storage, and various digital energy storage devices, playing a crucial role in the low-carbon energy transition. Currently, the application scenarios for new energy equipment are continuously expanding, requiring batteries not only to have efficient fast-charging capabilities but also to adapt to complex and extreme operating conditions such as frigid temperatures and extreme heat. The market is placing more stringent demands on battery fast-charging efficiency, high and low temperature adaptability, and long-term cycle stability.

[0003] Currently, commercial lithium-ion battery systems still have significant performance shortcomings, making it difficult to balance fast charging requirements with a comfortable user experience across all temperature ranges. Under high-temperature operating conditions, the electrolyte is prone to severe side reactions, and the solid electrolyte interfacial film structure at the negative electrode is easily damaged and destabilized, leading to a surge in interfacial impedance, electrode corrosion, and other problems that severely limit the battery's high-temperature cycle life. Conversely, under low-temperature conditions, the electrolyte's ion conductivity decreases significantly, lithium-ion migration kinetics deteriorate, and lithium-ion precipitation is highly likely during fast charging, inducing continuous lithium dendrite growth. This not only reduces the battery's low-temperature charge / discharge efficiency but also seriously affects battery safety and service life.

[0004] Electrolyte, as the core medium for ion transport within a battery, is crucial for regulating the negative electrode interface morphology, optimizing ion conduction rate, and balancing the battery's overall performance at high and low temperatures. Existing conventional electrolyte formulations struggle to simultaneously meet the dual requirements of high-temperature interface stability and low-temperature high-efficiency fast charging, making them unsuitable for practical applications involving high-power charging and discharging under extreme conditions. Therefore, developing a wide-temperature, fast-charging electrolyte that enhances high-temperature interface stability, optimizes the low-temperature ion transport environment, and effectively suppresses low-temperature lithium plating and lithium dendrite growth is of significant research importance and practical application value for improving the adaptability of power batteries and energy storage batteries across various scenarios. Summary of the Invention

[0005] To address the technical challenge of existing lithium-ion batteries simultaneously achieving high-temperature interface stability and low-temperature high-efficiency fast charging, this invention proposes an electrolyte and a lithium-ion battery containing this electrolyte. By adding additives with specific structures and functions to the electrolyte, this invention enables the battery to possess both excellent high-temperature stability and low-temperature adaptability, thereby effectively improving the battery's fast charging capability and cycle life under extreme operating conditions.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention is to provide an electrolyte comprising a lithium salt, an organic solvent, and a base additive; said organic solvent being an acyclic ester compound; and further comprising, by weight percentage, 1-2 wt.% of a first additive and 1-2 wt.% of a second additive; wherein: The first additive is a sulfate ester or sulfonate ester compound having the structure of Formula 1; Formula 1; where: X is selected from C or O, n is 0 or 1, Ra is selected from H, alkanes with 1-3 carbon atoms, , , or ; The second additive is at least one of chain polyfluoroanhydride or cyclic polyfluoroanhydride; The electrolyte meets the following condition: 0.5 ≤ ≤1.5, and 2 ≤ a ≤ 4, 5 ≤ b ≤ 8, 1 ≤ c ≤ 2; where: 'a' represents the sum of the mass percentages of the first and second additives in the electrolyte, expressed in wt.%. The proportion of 'a' in the electrolyte affects the thickness and density of the negative electrode interfacial film. If the value of 'a' is too small, the negative electrode film will not be dense, leading to solvent decomposition and gas generation at the negative electrode, and the resulting film will have poor performance. If the value of 'a' is too large, the interfacial film will be very thick, resulting in increased impedance. b represents the number of hydrogen atoms at the α-position of the sulfate or sulfonate groups in the first additive. The number of hydrogen atoms at the α-position determines the reactivity of the first additive; a larger b value indicates stronger reactivity. It is important to keep the value within a reasonable range because the first additive needs to form a film at the negative electrode, so its activity cannot be too low. However, if the activity is too high, the film will be very thick, which is not conducive to Li ion transport. For cases containing multiple first additives, the b value is calculated using a weighted average with the mass ratio of each additive as the weight. For example, if additive A accounts for 1% and has 6 hydrogen atoms at the α-position, and additive B accounts for 1% and has 8 hydrogen atoms at the α-position, then the b value is calculated using the formula (1%*6+1%*8) / (1%+1%)=7.

[0007] c represents the F / C molar ratio in the second additive. The c value affects the proportion of inorganic LiF components and organic components in the negative electrode interface film. Excessive inorganic components lead to poor Li-ion conductivity, while excessive organic components result in poor interface film stability. Therefore, the proportion should be within a reasonable range. For cases containing multiple second additives, the c value is calculated using a weighted average with the mass ratio of each additive as the weight. For example, if additive M accounts for 1% and its structure contains 4 C and 4 F, and additive N accounts for 2% and its structure contains 5 C and 6 F, then the c value is calculated using the formula (1%*4+2%*6) / (1%*4+2%*5).

[0008] As a preferred technical solution, the structure of the chain-like polyfluoroanhydride is shown in Formula 2: Equation 2; where R1 and R2 are each independently selected from fluoroalkyl groups with 1 to 3 carbon atoms; the fluoroalkyl groups in the chain polyfluoroanhydride have high electrochemical stability and can preferentially reduce and decompose on the electrode surface to form a LiF-rich solid electrolyte interfacial film, i.e., an SEI film. This SEI film has excellent density and ionic conductivity, and can effectively inhibit the continuous reduction and decomposition of the electrolyte on the negative electrode surface. At the same time, the anhydride groups in the chain polyfluoroanhydride can spontaneously absorb trace amounts of water and HF in the electrolyte, inhibiting lithium salt hydrolysis and avoiding corrosion of the positive electrode material by HF. On this basis, the chain polyfluoroanhydride also has a synergistic effect with the first additive. The first additive optimizes the film-forming characteristics of the negative electrode interface on the electrode surface, and the chain polyfluoroanhydride forms a fluorine-rich SEI film on the electrode surface. The two work together to improve the electrode interface characteristics, thereby significantly improving the cycle life and high-temperature storage performance of the lithium-ion battery.

[0009] The structure of the cyclic polyfluoroanhydride is shown in Formula 3: Equation 3; where m is 0 or 1. Cyclic polyfluoroanhydrides can enhance the functionality of additives by utilizing the special reactivity brought by their cyclic structure. The cyclic structure of cyclic polyfluoroanhydrides gives them stronger adsorption capacity and faster reduction decomposition kinetics on the electrode surface, enabling them to preferentially undergo reduction reactions over solvents at lower potentials, thereby forming a more uniform and dense SEI film on the negative electrode surface. At the same time, the anhydride groups in cyclic polyfluoroanhydrides can effectively remove trace amounts of water and HF in the electrolyte, inhibiting the corrosion of the positive electrode material by HF and the dissolution of transition metal ions. Similar to chain polyfluoroanhydrides, cyclic polyfluoroanhydrides can produce synergistic effects with the first additive, and the combined effect of the two significantly improves the long-term cycle performance and high-temperature stability of lithium-ion batteries.

[0010] As a preferred technical solution, the first additive is selected from at least one of compound 1-1, compound 1-2, and compound 1-3 having the following structures; ; These sulfate / sulfonate compounds with specific structures possess suitable molecular size and reactivity. The sulfate or sulfonate groups can undergo oxidative polymerization on the positive electrode surface, forming a dense and robust passivation film that effectively inhibits the oxidative decomposition of the electrolyte on the positive electrode surface and the dissolution of transition metal ions from the positive electrode material. Simultaneously, these compounds can participate in the formation of the SEI film on the negative electrode surface, working synergistically with the second additive to form a dense and stable SEI film on the negative electrode surface, effectively preventing the reduction reaction of the electrolyte on the negative electrode surface. By selecting these specific compounds as the first additive, the film-forming properties of the electrolyte can be made more stable and controllable, thereby effectively improving the battery's cycle performance and high-temperature storage performance.

[0011] As a preferred technical solution, the second additive is selected from at least one of compounds 2-1, 2-2, 2-3, 2-4, and 2-5 having the following structures;

[0012] .

[0013] These chain- or cyclic polyfluoroanhydride compounds with specific structures have different fluorine contents and molecular structures, allowing for flexible adjustment of the fluorination degree and anhydride functional group content of the electrolyte according to actual needs.

[0014] As a preferred technical solution, the acyclic ester compound is at least one of a chain carbonate or a chain carboxylic acid ester. Preferably, the acyclic ester compound includes a chain carbonate with 3-5 carbon atoms and a chain carboxylic acid ester with 3-5 carbon atoms. These substances can provide the electrolyte with lower viscosity and higher dielectric constant, which is beneficial to the complete dissociation of lithium salt and the rapid migration of lithium ions. Compared with cyclic ester solvents, acyclic ester compounds have lower viscosity and higher ion mobility, which can effectively improve the conductivity and lithium ion transport rate of the electrolyte, thereby improving the rate performance and low-temperature discharge performance of the battery. At the same time, acyclic ester compounds have lower freezing points and wider operating temperature ranges, which helps to broaden the operating temperature range of lithium-ion batteries. In addition, acyclic ester solvents have good compatibility with the first and second additives, which can ensure that the additives are uniformly dispersed in the electrolyte and fully exert their interface protection function, thereby synergistically improving the overall electrochemical performance of the battery.

[0015] As a preferred technical solution, the non-cyclic ester compound has a mass percentage content of 70-90 wt.% in the electrolyte. Within this content range, the electrolyte can not only have excellent ion transport performance, but also work synergistically with the first and second additives to form a stable interface protective film on the electrode surface, thereby effectively improving the cycle life and rate performance of the lithium-ion battery.

[0016] As a preferred technical solution, the basic additive is at least one selected from vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), lithium difluorooxalate borate (LiODFB), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), and methanedisulfonate (MMDS); the basic additive has a mass percentage content of 0.1-3 wt.% in the electrolyte. The basic additive can further optimize the film-forming performance and interfacial stability of the electrolyte. VC, as a classic film-forming additive, can preferentially reduce and form a stable SEI film on the negative electrode surface; PS can form a protective film on the positive electrode surface, inhibiting the oxidative decomposition of the positive electrode material; LiODFB, as a lithium salt additive, can participate in the formation of the SEI film and improve the interfacial ionic conductivity; TMSB and TMSP can remove HF and moisture from the electrolyte, inhibiting the hydrolysis of lithium salts; MMDS can improve the stability of the electrode interface. These basic additives, together with the first and second additives, can comprehensively improve the electrode interface characteristics from multiple aspects, further enhancing the cycle performance and safety performance of lithium-ion batteries. By controlling the content of basic additives at 0.1-3 wt.%, their functional effects can be fully utilized without affecting the overall performance of the electrolyte due to excessive addition.

[0017] As a preferred technical solution, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(trifluorosulfonyl)imide, and lithium bis(fluorosulfonyl)imide. The concentration of the lithium salt in the electrolyte is controlled at 0.7-1.3 mol / L to ensure that the electrolyte has excellent ionic conductivity and electrochemical stability. Specifically, lithium hexafluorophosphate is currently the most commonly used lithium salt in commercial lithium-ion batteries, possessing high ionic conductivity and good film-forming properties; lithium tetrafluoroborate has excellent thermal stability and oxidation resistance; lithium bis(oxalato)borate can form a stable interface film on the electrode surface; and lithium bis(trifluorosulfonyl)imide and lithium bis(fluorosulfonyl)imide have even higher thermal stability and hydrolytic stability. Controlling the lithium salt concentration within the range of 0.7-1.3 mol / L ensures that the electrolyte has sufficiently high ionic conductivity to support the high-current charging and discharging of the battery, while avoiding the problems of increased viscosity and cost caused by excessively high lithium salt concentrations. Within this lithium salt concentration range, the lithium salt exhibits good compatibility with the first additive, the second additive, and the basic additive, enabling them to synergistically leverage their respective performance advantages, thereby comprehensively improving the cycle performance, rate performance, and high-temperature stability of lithium-ion batteries.

[0018] A second objective of this invention is to provide a lithium-ion battery comprising the electrolyte described in the first aspect above. The battery provided by this invention exhibits both excellent high-temperature stability and low-temperature adaptability, thereby improving the battery's fast-charging capability and cycle life under extreme operating conditions.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention significantly improves the overall performance of the battery over a wide temperature range by adding a first additive and a second additive as functional additives to the electrolyte. Through the synergistic effect between the first and second additives, and the combined effect of the functional additives and other components in the electrolyte, the overall performance is enhanced. The cyclic sulfonic acid / sulfuric acid compounds in the first additive act as film-forming aids, effectively optimizing the film-forming characteristics of the negative electrode interface and significantly improving the high-temperature structural stability of the negative electrode solid electrolyte interface film. The second additive, when combined, promotes the enrichment of highly stable lithium fluoride active components in the negative electrode interface film, inhibits the continuous occurrence of side reactions in the electrolyte, constructs a dense and thin interface passivation film, and effectively reduces the electrode interface impedance. Simultaneously, this invention uses acyclic esters as organic solvents, which can reduce the viscosity of the electrolyte at low temperatures, significantly accelerate the lithium-ion migration rate under low-temperature conditions, fully meet the requirements of low-temperature, high-power, fast charging and discharging of the battery, and effectively suppress lithium plating and lithium dendrite growth during low-temperature charging and discharging. The proportions of each component must be 0.5 ≤ Under the conditions of ≤1.5 and 2≤a≤4, 5≤b≤8, 1≤c≤2, the components form a highly efficient synergistic effect, enabling the electrolyte system to simultaneously possess excellent high-temperature interface stability and low-temperature fast charging capability. This effectively overcomes the technical defects of traditional electrolytes that cannot simultaneously meet the requirements of high and low temperature performance, thereby significantly improving the fast charging performance and long-term cycle life of lithium-ion batteries and broadening the practical application scenarios of batteries. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail. The raw materials used in the present invention are all commercially available products and can be obtained from public commercial channels.

[0021] The structural formulas of compounds 1-1, 1-2, and 1-3 used are as follows: .

[0022] The CAS number for compound 1-1 is 1431298-10-0, the CAS number for compound 1-2 is 201419-80-9, and the CAS number for compound 1-3 is 62822-68-8.

[0023] The structural formulas of compounds 2-1, 2-2, 2-3, 2-4, and 2-5 are as follows;

[0024] .

[0025] The CAS number of compound 2-1 is 407-25-0, the CAS number of compound 2-2 is 356-42-3, the CAS number of compound 2-3 is 336-59-4, the CAS number of compound 2-4 is 669-30-9, and the CAS number of compound 2-5 is 376-68-1.

[0026] Example 1 1. Preparation of electrolyte: In an inert atmosphere glove box with both water and oxygen levels <0.1 ppm, dimethyl carbonate (DMC) and ethyl acetate (EA) were uniformly mixed at a mass ratio of DMC:EA = 7:3 to form an organic solvent. After mixing, 1 mol / L of thoroughly dried lithium hexafluorophosphate (LiPF6) was added as the lithium salt. After the lithium salt was completely dissolved, 1% of compound 1-1, 1% of compound 2-1, and basic additives were added. The basic additives were 0.5% vinylene carbonate (VC) and 0.5% lithium difluorooxalate borate (LiODFB) to prepare the electrolyte.

[0027] 2. Preparation of the positive electrode: Lithium iron phosphate (LiFePO4) positive electrode active material, conductive agent Super P, conductive carbon black KS-6, and binder PVDF were mixed uniformly at a mass ratio of 93.2:3.3:1.5:2. A nitrogen-methylpyrrolidone solvent was added, and the mixture was homogenized using a gradient homogenization process to prepare a uniform positive electrode slurry. The slurry was then uniformly coated onto the surface of a 9 μm thick aluminum foil current collector, with the areal density controlled at 294 g / m². 2 After coating, pre-dry in an 80℃ forced-air drying oven for 18 hours, then cold-press to a density of 2.32 g / cm³. 3 After being punched, the cathode material is dried in a vacuum glass dryer at 120°C for 12 hours to obtain a lithium-ion battery cathode sheet that meets the requirements.

[0028] 3. Preparation of the negative electrode: A negative electrode slurry was prepared by mixing graphite with conductive agent Super P, thickener CMC, and binder SBR in a mass ratio of 95.5:1.0:1.0:2.5. This slurry was then uniformly coated onto both sides of a copper foil, with the coating surface density controlled at 108 g / m². 2 After coating, the material is first pre-dried in an 80℃ forced-air drying oven for 18 hours, then rolled, slit, and sliced, and finally placed in a vacuum oven at 100℃ for 12 hours to obtain a lithium-ion battery negative electrode sheet that meets the requirements.

[0029] 4. Preparation of the diaphragm: The commercially available 35 μm polyolefin microporous membrane, model SEP35PE single-layer polyethylene membrane, was selected.

[0030] 5. Preparation of lithium-ion batteries: The positive electrode, negative electrode, and separator prepared by the above process are stacked to form a lithium-ion battery with a thickness of about 7 mm, a width of about 50 mm, and a length of about 50 mm, with a capacity of 2.4 Ah. The battery is then vacuum baked at 85°C for 48 hours and injected with the above electrolyte to complete the battery fabrication.

[0031] Examples 2-12 and Comparative Examples 1-6 The differences between Examples 2-12, Comparative Examples 1-6 and Example 1 lie in the types and contents of the first and second additives in the electrolyte, and the composition of the organic solvent, as detailed in Table 1. In Table 1, DEC represents diethyl carbonate, MA represents methyl acetate, and EC represents ethylene carbonate; the preparation methods of the positive electrode, negative electrode, electrolyte, separator, and lithium-ion battery are the same as in Example 1.

[0032] Table 1. Parameter table for Examples 1-13 and Comparative Examples 1-6

[0033] Performance testing The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests.

[0034] (1) High-temperature cycling performance test Under a test condition of 60℃, the lithium-ion batteries obtained in each embodiment and comparative example were charged at a constant current of 1C to 3.65V, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 2.0V. This constitutes one charge-discharge cycle, and the discharge capacity D1 is recorded. This charge-discharge cycle is repeated 300 times, and the discharge capacity D2 of the 300th cycle is recorded. At this point, the high-temperature cycle capacity retention rate (%) = D2 / D1 × 100%.

[0035] (2) High-temperature storage performance test The experimental battery was charged and discharged at 0.33C for 3 weeks at room temperature, and the average discharge capacity was recorded as C1. Then, it was fully charged and placed in a constant temperature oven at 60℃ for 28 days. After removal, it was placed at room temperature for 6 hours and discharged at 0.33C, with the discharge capacity recorded as C2. This process was repeated for another 3 weeks at 0.33C, and the average discharge capacity was recorded as C3. The capacity retention rate (%) after 28 days of high-temperature storage is calculated as C2 / C1 × 100%, and the capacity recovery rate (%) is calculated as C3 / C1 × 100%.

[0036] (3) Low-temperature DC internal resistance (DCR) test After capacity testing, the experimental batteries were charged to 50% SOC at room temperature. After resting at -25℃ for 10 hours, the sampling voltage V0 at the start of discharge was recorded. Then, the batteries were discharged at a current of 2C I1 for 30 seconds, and the sampling voltage V1 at the end of discharge was recorded. The DC discharge impedance DCR of the experimental battery at low temperature was calculated as DCR = (V0 - V1) / I1.

[0037] (4) Low-temperature rate discharge performance test After capacity testing, the experimental battery was charged and discharged at 0.33C for three weeks at room temperature, and the average discharge capacity was recorded as C1. It was then fully charged at 0.33C current I2, left to stand at -25℃ for 10 hours, and then discharged at 2C current I2 until empty. The discharge capacity was recorded as C4. The low-temperature rate discharge capacity retention rate of the experimental battery was calculated as C4 / C1 × 100%.

[0038] The test results are shown in Table 2.

[0039] Table 2 Performance test results of Examples 1-13 and Comparative Examples 1-6

[0040] Table 2 shows the test results from Examples 1-13 and Comparative Examples 1-6. It is evident that a reasonable combination of cyclic sulfonic acid / sulfuric acid compounds and polyfluoroanhydrides, using a non-cyclic ester solvent system, and with the properties and proportions of each component satisfying the relationship 0.5 ≤ When the coefficients are ≤1.5, and 2≤a≤4, 5≤b≤8, and 1≤c≤2, the high-temperature interface stability, low-temperature rate discharge capability, and long-term cycle life of lithium iron phosphate batteries can be significantly improved. Specifically, the capacity retention rate after 300 cycles at 60°C, the capacity retention rate after 28 days of rest at 60°C, and the recovery rate are all significantly better than those of comparative examples 1-6, with an improvement of approximately 10% in each performance aspect. In terms of low-temperature performance, the low-temperature DCR of the batteries in examples 1-13 is 30~50 mΩ lower than that of comparative examples 1-6, and the low-temperature rate discharge capacity retention rate is more than 15% higher. The above performance improvements are attributed to the fact that cyclic sulfonic acid / sulfuric acid compounds can optimize the film formation effect at the negative electrode interface and enhance the high-temperature structural stability of the negative electrode solid electrolyte interface film; the combination with polyfluoroanhydrides can promote the enrichment of lithium fluoride components in the interface film, suppress electrolyte side reactions, and form a dense and low-resistivity passivation film. Using non-cyclic ester solvents can reduce the viscosity of the electrolyte at low temperatures and accelerate the lithium-ion conduction speed, which can not only ensure the battery's ability to charge and discharge at low temperatures and high power, but also suppress lithium plating and lithium dendrite growth under low-temperature conditions.

[0041] Furthermore, the test results of Example 1 and Comparative Examples 1-2 show that the first and second additives have a synergistic effect. When either additive is missing from the system, the stability and tolerance of the battery under extreme conditions decrease significantly, and its high-temperature cycling, high-temperature storage, and low-temperature discharge performance all show significant deterioration. The test results of Examples 1-13 and Comparative Examples 3-4 show that when the properties and proportions of the relevant components in the lithium-ion battery system deviate by 0.5 ≤ When the temperature range is limited to ≤1.5, 2≤a≤4, 5≤b≤8, and 1≤c≤2, the overall high and low temperature performance of the battery will degrade. Comparison of Examples 1-13 and Comparative Examples 5-6 shows that introducing the cyclic ester component ethylene carbonate into the solvent system increases the low-temperature interface impedance of the battery, resulting in a significant deterioration in its low-temperature rate discharge performance.

[0042] In summary, by optimizing the combination of functional additives, matching the non-cyclic ester solvent system, and strictly controlling the properties and ratio range of each component, this invention can synergistically balance the high-temperature interface stability and low-temperature fast charging and discharging performance of the battery, effectively solving the pain point that traditional electrolytes are difficult to adapt to extreme operating conditions in a wide temperature range, and significantly improving the full-temperature range performance and practical application value of lithium-ion batteries.

[0043] Although the present invention has been disclosed above with reference to preferred embodiments, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solutions and inventive concepts of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An electrolyte comprising a lithium salt, an organic solvent, and a basic additive, characterized in that, The organic solvent is an acyclic ester compound; by mass percentage, it also includes 1-2 wt.% of a first additive and 1-2 wt.% of a second additive; wherein: The first additive is a sulfate ester or sulfonate ester compound having the structure of Formula 1; Formula 1, where: X is selected from C or O, n is 0 or 1, and Ra is selected from H, alkanes with 1-3 carbon atoms, , , or ; The second additive is at least one of chain polyfluoroanhydride or cyclic polyfluoroanhydride; The electrolyte meets the following condition: 0.5 ≤ ≤1.5, and 2 ≤ a ≤ 4, 5 ≤ b ≤ 8, 1 ≤ c ≤ 2; where: a is the sum of the mass percentages of the first additive and the second additive in the electrolyte; b is the number of α-hydrogen atoms in the sulfate ester group or sulfonate ester group of the first additive; c is the F / C molar ratio in the second additive.

2. The electrolyte according to claim 1, characterized in that, The structure of the chain-like polyfluoroanhydride is shown in Formula 2: Formula 2, in which R1 and R2 are each independently selected from fluoroalkyl groups having 1 to 3 carbon atoms.

3. The electrolyte according to claim 1, characterized in that, The structure of the cyclic polyfluoroanhydride is shown in Formula 3: Equation 3, where m is 0 or 1.

4. The electrolyte according to claim 1, characterized in that, The first additive is selected from at least one of compound 1-1, compound 1-2, and compound 1-3 having the following structures; 。 5. The electrolyte according to claim 1, characterized in that, The second additive is selected from at least one of compounds 2-1, 2-2, 2-3, 2-4, and 2-5 having the following structures; 。 6. The electrolyte according to claim 1, characterized in that, The acyclic ester compound is at least one of chain carbonates and chain carboxylic acid esters.

7. The electrolyte according to claim 6, characterized in that, The acyclic ester compounds include chain carbonates with 3-5 carbon atoms and chain carboxylic acid esters with 3-5 carbon atoms.

8. The electrolyte according to claim 1, characterized in that, The noncyclic ester compound has a mass percentage of 70-90 wt.% in the electrolyte.

9. The electrolyte according to any one of claims 1 to 5, characterized in that, The basic additive is at least one selected from vinylene carbonate, 1,3-propanesulfonyl lactone, lithium difluorooxalate borate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and methanedisulfonate; the basic additive has a mass percentage content of 0.1-3 wt.% in the electrolyte.

10. The electrolyte according to any one of claims 1 to 5, characterized in that, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(trifluorosulfonyl)imide, and lithium bis(fluorosulfonyl)imide; the concentration of the lithium salt in the electrolyte is 0.7-1.3 mol / L.

11. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 1 to 10.

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