Electrolyte and battery

Abstract

The invention provides an electrolyte and a battery, and belongs to the technical field of batteries, the electrolyte is applied to the battery, and the battery comprises a positive plate. The electrolyte comprises an additive, a lithium salt and an organic solvent, and the lithium salt comprises lithium bis (fluorosulfonyl) imide. The mass percent of the additive in the electrolyte is X%, the mass percent of the lithium bis (fluorosulfonyl) imide in the electrolyte is Y%, the mass percent of the low-viscosity solvent in the electrolyte is B%, and (X + Y) / (A * B) is larger than or equal to 0.04 and smaller than or equal to 0.3. Wherein A represents the compaction density of the positive plate, and the unit is g / cm < 3 >. According to the electrolyte provided by the embodiment of the invention, the electrical performance, the cycle performance and the safety performance of an electrolyte system can be ensured, and meanwhile, when the electrolyte is applied to a battery, the wettability of the electrolyte to a positive plate is improved, the impedance of a solid electrolyte interface is effectively reduced, the charge-discharge energy efficiency of the battery is improved, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to an electrolyte and a battery. Background Technology

[0002] With the rapid development of lithium-ion batteries, they are increasingly widely used in people's lives, becoming the main energy source for electronic devices such as mobile phones and computers. Currently, the development of high-capacity lithium-ion batteries is accelerating, and their widespread application in passenger vehicles, commercial vehicles, construction machinery, and energy storage has made them the mainstream. However, as the capacity of lithium-ion batteries increases significantly, their energy density also rises, leading to a marked increase in the compaction density of the positive electrode. This increased compaction density makes it more difficult for the electrolyte to wet the positive electrode, resulting in a deterioration in battery efficiency and cycle performance. Summary of the Invention

[0003] The embodiments of this application provide an electrolyte and a battery. The electrolyte can improve the wetting performance of the positive electrode, effectively reduce the impedance of the solid electrolyte interface, improve the charge and discharge efficiency of the battery, and improve the cycle performance of the battery.

[0004] In a first aspect, embodiments of this application provide an electrolyte applied to a battery, the battery including a positive electrode sheet; The electrolyte includes additives, lithium salts, low-viscosity solvents, and organic solvents; the lithium salts include lithium bis(fluorosulfonyl)imide. The additive has a mass percentage of X% in the electrolyte, lithium bis(fluorosulfonyl)imide has a mass percentage of Y% in the electrolyte, and the low-viscosity solvent has a mass percentage of B% in the electrolyte, satisfying the following: 0.04≤(X+Y) / (A×B)≤0.3; Where A represents the compaction density of the positive electrode, in g / cm³. 3 .

[0005] In some embodiments, 0 < X ​​≤ 15; And / or, 0 < Y ≤ 10; And / or, 10≤B≤70; And / or, 1.9≤A≤2.6.

[0006] In some embodiments, 2 < X < 6; And / or, 2≤Y<8; And / or, 15≤B≤70; And / or, 2.4≤A≤2.6.

[0007] In some embodiments, the lithium salt further includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium dioxalate borate, lithium difluorooxalate phosphate, and lithium difluorooxalate borate.

[0008] In some embodiments, the lithium salt in the electrolyte is 10%-16% by mass.

[0009] In some embodiments, the lithium salt includes lithium hexafluorophosphate and lithium difluorosulfonylimide; The mass percentage of lithium hexafluorophosphate in the electrolyte is 7%-12%, and / or the mass percentage of lithium bisfluorosulfonylimide in the electrolyte is 2%-8%.

[0010] In some embodiments, the mass percentage of lithium bis(fluorosulfonyl)imide in the lithium salt is >20%.

[0011] In some embodiments, the additive includes at least one selected from vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, ethylene sulfate, ethylene sulfite, and methane dithiomethyl ester.

[0012] In some embodiments, the additives include vinylene carbonate, vinylene carbonate and methane disulfide; The mass percentage of vinylene carbonate in the electrolyte is 1%-10%; And / or, the mass percentage of fluoroethylene carbonate in the electrolyte is 0.1%-1%; And / or, the mass percentage of methane dithiosulfinate in the electrolyte is 0.1%-1%.

[0013] In some embodiments, the viscosity value of the low-viscosity solvent is ≤1 cP.

[0014] In some embodiments, the low-viscosity solvent includes at least one of dimethyl carbonate and carboxylic acid esters; And / or, the organic solvent includes at least one of ethylene carbonate, propylene carbonate and ethyl methyl carbonate.

[0015] In some embodiments, the organic solvent includes ethylene carbonate and ethyl methyl carbonate; The mass percentage of ethylene carbonate in the electrolyte is 10%-40%, and / or the mass percentage of methyl ethyl carbonate in the electrolyte is 10%-30%.

[0016] Secondly, embodiments of this application provide a battery comprising the electrolyte as described above.

[0017] In some embodiments, after battery formation, the content of hydrogen fluoride in the electrolyte is 1ppm-300ppm.

[0018] In some embodiments, after battery formation, the content of hydrogen fluoride in the electrolyte is 5ppm-200ppm.

[0019] The beneficial effects of the embodiments of this application are as follows: In embodiments of this application, the electrolyte is used in a battery, which includes a positive electrode. The electrolyte includes additives, a lithium salt, a low-viscosity solvent, and an organic solvent. The lithium salt includes lithium bis(fluorosulfonyl)imide. The mass percentage of the additives in the electrolyte is X%, the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte is Y%, and the mass percentage of the low-viscosity solvent in the electrolyte is B%, satisfying: 0.04 ≤ (X + Y) / (A × B) ≤ 0.3. Wherein, A represents the compaction density of the positive electrode, in g / cm³. 3 By ensuring that the mass percentages of additives in the electrolyte (X%), lithium bis(fluorosulfonyl)imide in the electrolyte (Y%), low-viscosity solvent in the electrolyte (B%), and the compaction density (A) of the positive electrode sheet satisfy the above formula, it is possible to guarantee the electrical performance, cycle performance, and safety performance of the electrolyte system. This also helps to improve the wetting performance of the electrolyte on the positive electrode sheet when the electrolyte is applied to the battery, effectively reduce the impedance of the solid electrolyte interface, improve the charge-discharge efficiency of the battery, and enhance the battery's cycle performance. Detailed Implementation

[0020] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific implementation methods described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0021] In a first aspect, embodiments of this application provide an electrolyte used in a battery, the battery including a positive electrode. The electrolyte includes additives, a lithium salt, a low-viscosity solvent, and an organic solvent. The lithium salt is lithium bis(fluorosulfonyl)imide. The additives have a mass percentage of X% in the electrolyte, the lithium bis(fluorosulfonyl)imide has a mass percentage of Y% in the electrolyte, and the low-viscosity solvent has a mass percentage of B% in the electrolyte, satisfying: 0.04 ≤ (X + Y) / (A × B) ≤ 0.3. Wherein, A represents the compaction density of the positive electrode, in g / cm³. 3By ensuring that the mass percentages of additives in the electrolyte (X%), lithium bis(fluorosulfonyl)imide in the electrolyte (Y%), low-viscosity solvent in the electrolyte (B%), and the compaction density (A) of the positive electrode sheet satisfy the above formula, it is possible to guarantee the electrical performance, cycle performance, and safety performance of the electrolyte system. This also helps to improve the wetting performance of the electrolyte on the positive electrode sheet when the electrolyte is applied to the battery, effectively reduce the impedance of the solid electrolyte interface, improve the charge-discharge efficiency of the battery, and enhance the battery's cycle performance.

[0022] Additives in the electrolyte help form a solid electrolyte interphase (SEI) film, reducing solvent molecule penetration while allowing lithium ions to migrate freely, thereby improving battery charge-discharge efficiency and extending battery cycle life. The content of additives in the electrolyte affects its viscosity, internal resistance, thermal stability, low-temperature performance, and safety, and also impacts the cost. Lithium salts provide lithium ions to form a conductive network; lithium bis(fluorosulfonyl)imide, with its high degree of dissociation, can improve electrolyte conductivity and reduce battery internal resistance. The synergistic effect of lithium salts and additives contributes to the formation of a stable SEI film. Low-viscosity solvents, acting as carriers for dissolving lithium salts and additives in the electrolyte, can control the concentration of lithium salts and additives within a suitable range and adjust the electrolyte viscosity. The compaction density of the positive electrode has a significant impact on the energy density, cycle life, and safety of the battery. As the energy density of the battery increases, the compaction density of the positive electrode in the battery also increases significantly. The increase in compaction density can make it more difficult for the electrolyte to wet, thus affecting the cycle life and charge / discharge efficiency of the battery.

[0023] This application embodiment correlates the mass percentage of additives (X%), lithium bis(fluorosulfonyl)imide (Y%), and low-viscosity solvent (B%) in the electrolyte with the compaction density (A) of the positive electrode. This allows for dynamic control of the electrolyte performance over a wide range. Under different positive electrode compaction densities, by adjusting the contents of additives, lithium bis(fluorosulfonyl)imide, and low-viscosity solvent in the electrolyte, a suitable electrolyte can be obtained, ensuring the battery's charge-discharge efficiency and cycle performance. By ensuring that each parameter satisfies the above formula, a suitable electrolyte can be obtained based on the positive electrode compaction density. Through the synergistic effect of multiple components in the electrolyte, the battery's performance is maximized.

[0024] In some embodiments, 0 < X ​​≤ 15. By ensuring that the mass percentage of the additive in the electrolyte is greater than 0% and less than or equal to 15%, it is possible to guarantee that the additive contributes to SEI film formation, conductivity optimization, and electrolyte safety improvement. It is also possible to control the viscosity of the electrolyte within a suitable range, reduce the internal resistance and gas expansion rate of the electrolyte, and control the cost of the electrolyte.

[0025] For example, X can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15, or any other value within the range of greater than 0% and less than or equal to 15%.

[0026] In some embodiments, 2 < X < 6.

[0027] By keeping the mass percentage of the additive in the electrolyte within the above-mentioned range, it is possible to balance the additive's contribution to SEI film formation, conductivity optimization, and electrolyte safety, and to enhance its synergistic effect with other components in the electrolyte, thereby controlling the electrolyte's viscosity, internal resistance, and gas expansion rate within a suitable range.

[0028] In some embodiments, 0 < Y ≤ 10. By ensuring that the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0% and less than or equal to 10%, the electrolyte can possess good electrical conductivity, excellent thermal and chemical stability, and good low-temperature performance. Furthermore, the viscosity of the electrolyte can be reduced, and the cost of the electrolyte can be controlled. The synergistic effect of lithium bis(fluorosulfonyl)imide and additives helps to form a stable SEI film, thereby reducing side reactions between the electrolyte and the positive and negative electrodes, and improving battery safety and cycle life.

[0029] For example, Y can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, or any other value within the range of greater than 0% and less than or equal to 10%.

[0030] In some embodiments, 2 ≤ Y < 8.

[0031] By keeping the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte within the above-mentioned range, the synergistic effect between lithium bis(fluorosulfonyl)imide and the electrolyte components can be improved, which helps to improve the conductivity, thermal stability and chemical stability of the electrolyte, and gives the electrolyte good low-temperature performance.

[0032] In some embodiments, 10 ≤ B ≤ 70. By ensuring that the mass percentage of the low-viscosity solvent in the electrolyte is greater than 10% and less than or equal to 70%, the low-viscosity solvent acts as a carrier, balancing the electrolyte's conductivity, wettability, cost, and safety, and controlling the electrolyte's viscosity within a reasonable range. Those skilled in the art can adjust the mass percentage of the low-viscosity solvent in the electrolyte as needed, in conjunction with the aforementioned formula.

[0033] For example, B can be 10, 20, 30, 40, 50, 60 or 70, or any other value in the range of 10-70.

[0034] In some embodiments, 15 ≤ B ≤ 70.

[0035] By keeping the mass percentage of the low-viscosity solvent in the electrolyte within the above-mentioned range, the conductivity, wettability, cost, and safety of the electrolyte can be balanced, resulting in a good synergistic effect with other components in the electrolyte and improving the overall performance of the electrolyte.

[0036] In some embodiments, 1.9 ≤ A ≤ 2.6. That is, the compaction density of the positive electrode is 1.9 g / cm³. 3 -2.6 g / cm 3 By setting the compaction density of the positive electrode sheet within the aforementioned range, it is possible to ensure that the positive electrode sheet has suitable porosity, guarantee the wettability of the electrolyte to the positive electrode sheet, reduce the internal resistance of the positive electrode sheet, and ensure a high energy density, thereby increasing the battery capacity in the same volume. The electrolyte provided in this application embodiment can correlate the content of additives, lithium bis(fluorosulfonyl)imide, and low-viscosity solvent in the electrolyte with the compaction density of the positive electrode sheet. It can adaptively adjust the electrolyte for positive electrode sheets with different compaction densities, thereby ensuring the wettability of the electrolyte to the positive electrode sheet, effectively reducing the impedance of the solid electrolyte interface, improving the charge and discharge efficiency of the battery, and improving the cycle performance of the battery.

[0037] For example, A can be 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5 or 2.6, or any other value in the range of 1.9-2.6.

[0038] In some embodiments, 2.4 ≤ A ≤ 2.6.

[0039] By keeping the compaction density of the electrolyte within the above range, the porosity of the positive electrode can be kept within a certain range, ensuring the wettability of the electrolyte on the positive electrode, reducing the internal resistance of the positive electrode, and achieving a high energy density while balancing various performance characteristics.

[0040] In some embodiments, the lithium salt further includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium dioxalate borate (LiBOB), lithium difluorooxalate phosphate (LiODFP), and lithium difluorooxalate borate (LiODFB).

[0041] That is, in addition to lithium difluorosulfonylimide, the electrolyte also includes other lithium salts. Among them, lithium hexafluorophosphate and lithium difluorooxalate phosphate have high conductivity, which helps to improve the conductivity of the electrolyte. Lithium tetrafluoroborate and lithium difluorooxalate borate have high thermal stability, which can improve the high-temperature stability of the electrolyte. Lithium difluorophosphate and lithium difluorooxalate borate have good low-temperature performance, which helps to improve the low-temperature performance of the electrolyte. Those skilled in the art can select one or more of these lithium salts as needed to obtain an electrolyte that meets the requirements.

[0042] In some embodiments, the lithium salt constitutes 10%-16% of the electrolyte by mass. By setting the lithium salt to 10%-16% of the electrolyte by mass, the low-temperature performance of the electrolyte can be guaranteed, the electrochemical performance of the battery can be optimized, and the cost of the electrolyte can be balanced.

[0043] For example, the mass percentage of lithium salt in the electrolyte can be 10%, 11%, 12%, 13%, 14%, 15%, and 16%.

[0044] In some embodiments, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Lithium hexafluorophosphate exhibits high ionic conductivity and high solubility in organic solvents, contributing to improved battery charge-discharge efficiency. It also possesses high chemical stability, is not easily decomposed, and does not readily react with electrode materials, thus extending battery life. Lithium bis(fluorosulfonyl)imide (LiFSI) exhibits high thermal stability and excellent low-temperature performance, and also possesses a wide electrochemical window, contributing to improved battery energy density and cycle stability. The synergistic effect of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide enhances the overall performance of the battery.

[0045] In some embodiments, the mass percentage of lithium hexafluorophosphate in the electrolyte is 7%-12%. By setting the mass percentage of lithium hexafluorophosphate in the electrolyte to 7%-12%, the conductivity of the electrolyte can be guaranteed, the lithium-ion concentration in the electrolyte can be increased, the energy density of the battery can be improved, and the safety and stability of the battery can be guaranteed.

[0046] For example, the mass percentage of lithium hexafluorophosphate in the electrolyte can be 7%, 8%, 9%, 10%, 11%, or 12%.

[0047] In some embodiments, the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte is 2%-8%. Setting the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte to 2%-8% ensures good electrochemical stability and contributes to the electrolyte's conductivity, thermal stability, and low-temperature performance. Furthermore, within this range, it helps to ensure the overall performance of the electrolyte while meeting the requirement of formula 0.04≤(X+Y) / (A×B)≤0.3.

[0048] For example, the mass percentage of lithium bisfluorosulfonylimide in the electrolyte can be 2%, 4%, 5%, 6%, 7% or 8%.

[0049] In some embodiments, the mass percentage of lithium bis(fluorosulfonyl)imide in the lithium salt is >20%.

[0050] By controlling the mass percentage of lithium bis(fluorosulfonyl)imide (LiFSI) in the lithium salt to be above 20%, due to the anionic structure of LiFSI ((FSO2)2N), - Lithium hexafluorophosphate (LiPF6) is highly stable, with strong SN and SF bonds that are not easily broken. It exhibits strong inertness to hydrolysis and produces almost no HF, thus ensuring that the hydrogen fluoride content in the electrolyte can be controlled within a low range after battery formation, reducing the increase in side reactions caused by hydrogen fluoride. In contrast, lithium hexafluorophosphate (LiPF6) has poorer chemical stability; its anion PF6... - It will dissociate into highly active PF5, which can easily cause a hydrolysis chain reaction. As time and temperature increase, it can easily lead to a high hydrogen fluoride content in the electrolyte.

[0051] In some embodiments, the additive includes at least one of vinylene carbonate (VC), ethylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite (ES), and methylene disulfonate (MMDS).

[0052] Among them, vinylene carbonate exhibits excellent film-forming properties, contributing to the formation of a stable SEI film and aiding in improving the high and low temperature performance of the battery, reducing internal resistance, and increasing battery capacity and cycle life. Ethylene carbonate also contributes to the formation of a stable SEI and can inhibit electrolyte decomposition. Fluorinated ethylene carbonate improves the high-voltage stability of the electrolyte and possesses excellent film-forming properties. Ethylene sulfate can suppress capacity decay. Ethylene sulfite has good film-forming properties and helps improve the low-temperature performance and storage stability of the electrolyte. Methylene methane disulfonate improves the high-temperature cycling performance of the electrolyte and helps inhibit manganese dissolution.

[0053] In some embodiments, the additives include vinylene carbonate, vinylene carbonate, and methane disulfide. Through the synergistic effect of vinylene carbonate, vinylene carbonate, and methane disulfide, the film-forming properties of the electrolyte can be improved, high-temperature cycling stability can be enhanced, and the overall performance of the electrolyte can be guaranteed.

[0054] In some embodiments, the mass percentage of vinylene carbonate in the electrolyte is 1%-10%. By setting the mass percentage of vinylene carbonate in the electrolyte to 1%-10%, it is possible to improve the cycle stability, energy density, and safety performance of the battery while ensuring that the viscosity of the electrolyte is within a suitable range and controlling the cost of the electrolyte.

[0055] For example, the mass percentage of vinylene carbonate in the electrolyte can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0056] In some embodiments, the mass percentage of fluoroethylene carbonate in the electrolyte is 0.1%-1%. When the mass percentage of fluoroethylene carbonate in the electrolyte is 0.1%-1%, it helps to form a stable SEI film, repairs the SEI during battery cycling, improves the ionic conductivity of the electrolyte, maintains suitable electrolyte viscosity, optimizes charge / discharge rates, and enhances low-temperature performance. Furthermore, fluoroethylene carbonate can also inhibit electrolyte decomposition and improve thermal stability.

[0057] For example, the mass percentage of fluoroethylene carbonate in the electrolyte may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0058] In some embodiments, the mass percentage of methane disulfide in the electrolyte is 0.1%-1%. When the mass percentage of methane disulfide in the electrolyte is 0.1%-1%, it can suppress impedance rise, increase battery cycle life, improve battery high-temperature cycle performance, and increase battery energy density.

[0059] For example, the mass percentage of methane dithiomethyl ester in the electrolyte may be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0060] In some embodiments, the viscosity value of the low-viscosity solvent is ≤1 cP.

[0061] By keeping the viscosity of the low-viscosity solvent below 1 cp, the viscosity of the electrolyte can be controlled within a reasonable range, reducing the charge transfer resistance between the electrolyte and the electrode, improving the ionic conductivity of the electrolyte, and enhancing the low-temperature performance of the electrolyte.

[0062] For example, the viscosity test method (rotational viscometer method) can be as follows: take 0.5 ml of electrolyte sample into a sample cup, stabilize the water bath temperature at the measurement temperature of 25°C, place the rotor at the bottom of the sample cup, start the instrument, and record the viscosity value after the reading stabilizes.

[0063] In some embodiments, the low-viscosity solvent includes at least one of dimethyl carbonate (DMC) and carboxylic acid esters.

[0064] Dimethyl carbonate (DMC) and carboxylic acid esters have low viscosity, which helps control the electrolyte viscosity within a reasonable range, reducing the charge transfer resistance between the electrolyte and the electrode, improving the ionic conductivity of the electrolyte, and enhancing its low-temperature performance. Specifically, the viscosity of dimethyl carbonate is approximately 0.65 cP, and the viscosity of ethyl acetate (EA) in the carboxylic acid ester is approximately 0.45 cP, both meeting the requirement of viscosity <1 cP. Furthermore, dimethyl carbonate also has high solubility, which helps improve the fluidity of the electrolyte, enhance its low-temperature performance, and reduce the battery's internal resistance.

[0065] The carboxylic acid esters include at least one of ethyl acetate (EA), propylene carbonate (EP), methyl acetate (MA), propyl propionate (PP), and methyl butyrate (MB).

[0066] In some embodiments, the organic solvent includes at least one selected from ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC). Ethyl carbonate contributes to the formation of a stable SEI film, improving the conductivity of the electrolyte. Ethyl methyl carbonate exhibits low viscosity, high conductivity, and a high boiling point, resulting in excellent overall performance. Propylene carbonate has a low melting point, improving the low-temperature performance of the electrolyte and exhibiting stable properties. Ethyl methyl carbonate has low viscosity, a high dielectric constant, and strong solubility for lithium salts, significantly contributing to improved battery energy density and discharge capacity, while also possessing advantages such as low toxicity and low volatility.

[0067] In some embodiments, the organic solvent includes ethylene carbonate and ethyl methyl carbonate. Ethyl carbonate and ethyl methyl carbonate can work synergistically, with ethylene carbonate contributing to the formation of a stable SEI film, while ethyl methyl carbonate helps improve the battery's energy density and discharge capacity. By controlling the ratio of ethylene carbonate to ethyl methyl carbonate, the viscosity, conductivity, and stability of the electrolyte can be adjusted to meet the needs of different application scenarios.

[0068] In some embodiments, the mass percentage of ethylene carbonate in the electrolyte is 10%-40%.

[0069] Ethylene carbonate has a high dielectric constant, which can promote the dissociation of lithium salts in the electrolyte. Furthermore, the reduction products of ethylene carbonate can form a stable SEI film on the electrode surface and influence the viscosity of the electrolyte. By maintaining the mass percentage of ethylene carbonate in the electrolyte at 10%-40%, various properties of the electrolyte can be balanced.

[0070] For example, the mass percentage of ethylene carbonate in the electrolyte can be 10%, 15%, 20%, 25%, 30%, 35%, or 40%.

[0071] In some embodiments, the mass percentage of ethyl methyl carbonate in the electrolyte is 10%-30%.

[0072] Similarly, by making the mass percentage of methyl ethyl carbonate in the electrolyte 10%-30%, the various properties of the electrolyte can also be balanced.

[0073] For example, the mass percentage of methyl ethyl carbonate in the electrolyte can be 10%, 15%, 20%, 25%, or 30%.

[0074] Secondly, embodiments of this application provide a battery comprising the electrolyte as described above.

[0075] The beneficial effects of the battery provided in this application embodiment compared to the prior art are basically the same as the beneficial effects of the electrolyte compared to the prior art, and will not be repeated here.

[0076] In some embodiments, the battery includes a casing, and a cell and an electrolyte contained within the casing. The cell includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrode.

[0077] In some embodiments, after battery formation, the content of hydrogen fluoride in the electrolyte is 1ppm-300ppm.

[0078] By employing the electrolyte provided in this application embodiment, the hydrogen fluoride content in the electrolyte after formation can be reduced. A small amount of hydrogen fluoride helps promote the formation of the SEI film, adjusts the acidity of the electrolyte, improves battery performance, and enhances the compatibility of the electrolyte with other components. Specifically, lithium bis(fluorosulfonyl)imide (LiFSI) in the lithium salt has high dissociation and excellent thermal stability, and is not easily decomposed at high temperatures, reducing HF generated by lithium salt decomposition. The additives help form a stable SEI film and reduce HF generated by side reactions. The low-viscosity solvent, as a carrier for lithium salt and additives, can control the concentration of lithium salt and additives within a suitable range, avoiding side reactions caused by excessively high local concentrations. Furthermore, the low-viscosity solvent can improve lithium ion migration efficiency and reduce local overheating or side reactions caused by hindered ion migration. By ensuring that the mass percentages of additives in the electrolyte (X%), lithium bis(fluorosulfonyl)imide in the electrolyte (Y%), low-viscosity solvent in the electrolyte (B%), and the compaction density (A) of the positive electrode sheet satisfy the above formula, the performance of the electrolyte can be dynamically controlled through the synergistic effect of multiple factors. This reduces the generation of HF caused by side reactions, thereby controlling the hydrogen fluoride content in the electrolyte within the above range after battery formation.

[0079] For example, the test method for hydrogen fluoride content can be as follows: Measure approximately 40 mL of pure water into a clean 250 mL Erlenmeyer flask using a graduated cylinder, add 3-5 drops of bromothymol blue indicator (the water will turn yellow at this point). Titrate with 0.0100 mol / L sodium hydroxide standard solution until blue, adjust the initial reading of the burette, and set aside. Weigh approximately 20 g of electrolyte using the subtraction method, accurate to 0.01 g (electrolyte mass meter: m1), add the electrolyte to the aforementioned Erlenmeyer flask, allowing it to mix rapidly. Titrate this electrolyte rapidly with sodium hydroxide standard solution until it changes from yellow to blue, indicating the endpoint. Record the volume (mL) of sodium hydroxide standard solution consumed.

[0080] Calculation formula: W= ; Where: W----content of free acid in electrolyte (calculated as HF), ppm; C----Concentration of sodium hydroxide standard solution, mol / L; V1----The volume of sodium hydroxide standard solution consumed in the titration of the electrolyte, in mL; M----molar mass of HF; m1----The mass of electrolyte measured, in grams.

[0081] In some embodiments, after battery formation, the hydrogen fluoride content in the electrolyte is 5ppm-200ppm. By ensuring that the hydrogen fluoride content in the electrolyte is 5ppm-200ppm after battery formation, the overall performance of the electrolyte can be improved, thereby enhancing battery performance.

[0082] The embodiments of this application are further illustrated below with reference to specific examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed according to the conditions recommended by the manufacturer.

[0083] Preparation method of positive electrode sheet: The positive electrode active material (lithium iron phosphate), binder (polyvinylidene fluoride), and conductive agent (acetylene black) are mixed in a mass ratio of 97.5:1.8:0.7 to obtain a mixture; the mixture is added to N-methylpyrrolidone (NMP) and stirred until the mixture is uniform to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on aluminum foil, then dried, and then cold-pressed to obtain the positive electrode sheet; Preparation method of negative electrode sheet: The negative electrode active material (artificial graphite), conductive agent (acetylene black) and binder (styrene-butadiene rubber) are dispersed in a solvent at a mass ratio of 97.0:0.9:2.1 to obtain a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying and cold pressing, the negative electrode sheet is obtained. Electrolyte preparation method: Lithium salt, solvent and additives are mixed in proportion to obtain electrolyte; Battery assembly method: The vacuum-dried positive and negative electrode sheets and dry-process single-layer separator are cut, die-cut and slit. The positive electrode sheet is 52mm long and 62mm wide, and the negative electrode sheet is 54mm long and 65mm wide. They are then assembled into a square aluminum shell. Then, electrolyte is injected under high temperature and negative pressure to assemble the battery.

[0084] Unless otherwise specified, in the following examples and comparative examples, the positive electrode active material is lithium iron phosphate, and the compaction density of the positive electrode is 2.5 g / cm³. 3 .

[0085] Example 1 In this embodiment, the organic solvent in the electrolyte comprises 15.5% by mass, of which ethylene carbonate comprises 15.5% by mass. The low-viscosity solvent in the electrolyte comprises 70% by mass, of which dimethyl carbonate (DMC) comprises 40% by mass and ethyl acetate (EA) comprises 30% by mass. The lithium salt in the electrolyte comprises 12% by mass, of which lithium bis(fluorosulfonyl)imide comprises 4.5% by mass and lithium hexafluorophosphate comprises 7.5% by mass. The additives in the electrolyte comprise 2.5% by mass, of which vinylene carbonate (VC) comprises 2.0% by mass and fluoroethylene carbonate (FEC) comprises 0.5% by mass.

[0086] Example 2 In this embodiment, the electrolyte contains 67.4% organic solvent by mass, of which ethylene carbonate accounts for 30%, propylene carbonate for 5%, and ethyl methyl carbonate for 32.4%. The electrolyte also contains 15% low-viscosity solvent by mass, of which dimethyl carbonate (DMC) accounts for 10% and ethyl acetate (EA) accounts for 5%. The electrolyte contains 15% lithium salt by mass, of which lithium bis(fluorosulfonyl)imide accounts for 3% and lithium hexafluorophosphate accounts for 12%. The additives account for 2.6% of the electrolyte by mass, of which vinylene carbonate (VC) accounts for 2% and fluoroethylene carbonate (FEC) accounts for 0.6%.

[0087] Example 3 In this embodiment, the electrolyte contains 59% organic solvent by mass, of which ethylene carbonate accounts for 30%, propylene carbonate for 5%, and methyl ethyl carbonate for 24%. The electrolyte contains 20% low-viscosity solvent by mass, of which dimethyl carbonate (DMC) accounts for 10% and ethyl acetate (EA) accounts for 10%. The electrolyte contains 16% lithium salt by mass, of which lithium bis(fluorosulfonyl)imide accounts for 10% and lithium hexafluorophosphate accounts for 6%. The additives account for 5% of the electrolyte by mass, of which vinylene carbonate (VC) accounts for 3%, fluoroethylene carbonate (FEC) accounts for 1%, and methyl methane disulfide (MMDS) accounts for 1%.

[0088] Comparative Example 1 In this comparative example, the electrolyte contains 76.7% organic solvent by mass, including 30% ethylene carbonate, 5% propylene carbonate, and 41.7% methyl ethyl carbonate. The electrolyte also contains 5% low-viscosity solvent by mass, including 5% dimethyl carbonate (DMC). The electrolyte contains 15% lithium salt by mass, including 4.5% lithium bis(fluorosulfonyl)imide and 10.5% lithium hexafluorophosphate. The additives constitute 3.3% of the electrolyte by mass, including 3.0% vinylene carbonate (VC) and 0.3% propylene carbonate (PS).

[0089] Comparative Example 2 In this comparative example, the mass percentage of organic solvent in the electrolyte is 3.7%, of which ethylene carbonate accounts for 3.7%. The mass percentage of low-viscosity solvent in the electrolyte is 80%, of which dimethyl carbonate (DMC) accounts for 50% and ethyl acetate (EA) accounts for 30%. The mass percentage of lithium salt in the electrolyte is 13%, of which lithium bis(fluorosulfonyl)imide accounts for 3.5% and lithium hexafluorophosphate accounts for 9.5%. The mass percentage of additives in the electrolyte is 3.3%, of which ethylene carbonate (VC) accounts for 3% and methyl methane disulfide (MMDS) accounts for 0.3%.

[0090] Comparative Example 3 In this comparative example, the electrolyte contains 37% organic solvent by mass, of which ethylene carbonate accounts for 30% and ethyl methyl carbonate accounts for 7%. The electrolyte also contains 30% low-viscosity solvent by mass, of which dimethyl carbonate (DMC) accounts for 20% and ethyl carboxylate (ethyl acetate) accounts for 10%. The electrolyte contains 13% lithium salt by mass, of which lithium bis(fluorosulfonyl)imide accounts for 3% and lithium hexafluorophosphate accounts for 10%. The additive ethylene carbonate (VC) accounts for 20% of the electrolyte by mass.

[0091] Comparative Example 4 In this comparative example, the electrolyte contains 49% organic solvent by mass, of which ethylene carbonate accounts for 30% and ethyl methyl carbonate for 19%. The electrolyte contains 20% low-viscosity solvent by mass, of which dimethyl carbonate (DMC) accounts for 10% and ethyl acetate (EA) accounts for 10%. The electrolyte contains 15% lithium salt by mass, of which lithium bis(fluorosulfonyl)imide accounts for 4.5% and lithium hexafluorophosphate accounts for 10.5%. The additive ethylene carbonate (VC) accounts for 16% of the electrolyte by mass.

[0092] Comparative Example 5 In this comparative example, the electrolyte contains 66% organic solvent by mass, including 30% ethylene carbonate, 5% propylene carbonate, and 31% methyl ethyl carbonate. The electrolyte also contains 15% low-viscosity solvent by mass, including 15% dimethyl carbonate (DMC). The electrolyte contains 16% lithium salt by mass, including 12% lithium bis(fluorosulfonyl)imide and 4% lithium hexafluorophosphate. The additives constitute 3% of the electrolyte by mass, including 2.5% vinylene carbonate (VC) and 0.5% fluoroethylene carbonate (FEC).

[0093] Comparative Example 6 In this comparative example, the electrolyte contains 78% organic solvent by mass, including 30% ethylene carbonate, 5% propylene carbonate, and 43% methyl ethyl carbonate. The electrolyte also contains 5% low-viscosity solvent by mass, including 5% dimethyl carbonate (DMC). The electrolyte contains 13.5% lithium salt by mass, including 4.5% lithium bis(fluorosulfonyl)imide and 9% lithium hexafluorophosphate. The additives constitute 3.5% of the electrolyte by mass, including 3.0% vinylene carbonate (VC) and 0.5% fluoroethylene carbonate (FEC).

[0094] The parameters for Examples 1-3 and Comparative Examples 1-6 are shown in Table 1: Table 1. Comparison of parameters in different embodiments and comparative examples

[0095] As can be seen from Table 1, the parameters in Examples 1-3 meet the requirement of 0.04≤(X+Y) / (A×B)≤0.3, while the parameters in Comparative Examples 1-6 do not meet the requirement of 0.04≤(X+Y) / (A×B)≤0.3.

[0096] The batteries in Examples 1-3 and Comparative Examples 1-6 were subjected to room temperature power discharge tests and cycle performance tests.

[0097] The method for testing the power discharge performance at room temperature is as follows: At 25℃, the battery is charged at a constant power of 0.5P, with a cutoff voltage of 3.65V. The battery is then discharged at a constant power of 0.5P, with a cutoff voltage of 2.5V. This cycle is repeated 3 times. The battery is then placed in a 25℃ test chamber and left to stand for 4 hours. The battery is then charged at a constant power of 0.5P, with a cutoff voltage of 3.65V. This cycle is repeated 13 times. The charging energy E1 and discharging energy E2 of the battery in the 13th cycle are recorded. The energy efficiency is then calculated as E2 / E1.

[0098] The cycle performance test method is as follows: after being placed at 25℃ or 45℃ for 1 hour, the battery is subjected to full charge and discharge cycles, and the capacity retention rate is recorded at 200 cycles, 500 cycles, and 1000 cycles. Full charge: the battery is charged at a constant power of 0.5P, with a cutoff voltage of 3.65V; Full discharge: the battery is discharged at a constant power of 0.5P, with a cutoff voltage of 2.5V.

[0099] The test results are shown in Table 2: Table 2. Comparison of battery performance test results in different embodiments and comparative examples.

[0100] As can be seen from Table 2, the batteries in Examples 1-3 of this application have high power discharge performance and excellent room temperature cycle performance and high temperature cycle performance, which are significantly superior to Comparative Examples 1-6.

[0101] A comparison of the data from Example 2 and Comparative Example 5 shows that when the lithium bisfluorosulfonylimide (LiFSI) content meets the formula requirements, it can enhance the ionic conductivity of the electrolyte, greatly improve the thermal and chemical stability of the electrolyte, and help form a more stable solid electrolyte interface film with lower impedance on the negative electrode surface. When the LiFSI content does not meet the formula requirements, the LiFSI electrolyte will corrode the aluminum current collector to a certain extent, causing a short circuit between the positive and negative electrodes, thereby degrading the battery's electrical performance.

[0102] As can be seen from the comparison of the data of Example 3 and Comparative Example 4 in Table 1, when the content of the additive is too high and does not meet the requirements of the formula, it reacts with the active lithium on the negative electrode interface, and the solid electrolyte interface film formed is thickened, which leads to an increase in SEI impedance, deteriorates the power discharge efficiency, and deteriorates the capacity retention rate at room temperature and high temperature cycles.

[0103] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An electrolyte, characterized in that, Applied to a battery, the battery including a positive electrode; The electrolyte includes additives, lithium salts, low-viscosity solvents, and organic solvents, wherein the lithium salts include lithium bis(fluorosulfonyl)imide. The additive has a mass percentage of X% in the electrolyte, the lithium difluorosulfonyl imide has a mass percentage of Y% in the electrolyte, and the low-viscosity solvent has a mass percentage of B% in the electrolyte, satisfying the following: 0.04≤(X+Y) / (A×B)≤0.3; Wherein, A represents the compaction density of the positive electrode sheet, in g / cm³. 3 .

2. The electrolyte according to claim 1, characterized in that, 0＜X≤15； And / or, 0 < Y ≤ 10; And / or, 10≤B≤70; And / or, 1.9≤A≤2.

6.

3. The electrolyte according to claim 2, characterized in that, 2＜X＜6； And / or, 2≤Y<8; And / or, 15≤B≤70; And / or, 2.4≤A≤2.

6.

4. The electrolyte according to claim 1, characterized in that, The lithium salt also includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium dioxalate borate, and lithium difluorooxalate borate.

5. The electrolyte according to claim 4, characterized in that, The lithium salt has a mass percentage of 10%-16% in the electrolyte.

6. The electrolyte according to claim 5, characterized in that, The lithium salt includes the lithium hexafluorophosphate and the lithium difluorosulfonylimide; The lithium hexafluorophosphate has a mass percentage of 7%-12% in the electrolyte, and / or the lithium difluorosulfonamide has a mass percentage of 2%-8% in the electrolyte.

7. The electrolyte according to claim 1, characterized in that, In the lithium salt, the mass percentage of the lithium bisfluorosulfonylimide is >20%.

8. The electrolyte according to claim 1, characterized in that, The additives include at least one of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate, ethylene sulfate, ethylene sulfite, and methane dithiomethyl ester.

9. The electrolyte according to claim 8, characterized in that, The additives include the vinylene carbonate, the fluorovinyl carbonate, and the methane disulfide methyl ester; The vinylene carbonate in the electrolyte has a mass percentage of 1%-10%. And / or, the fluoroethylene carbonate in the electrolyte is 0.1%-1% by mass; And / or, the methane dithiomethyl ester in the electrolyte is 0.1%-1% by mass.

10. The electrolyte according to any one of claims 1-9, characterized in that, The viscosity of the low-viscosity solvent is ≤1 cP.

11. The electrolyte according to claim 10, characterized in that, The low-viscosity solvent includes at least one of dimethyl carbonate and carboxylic acid esters; And / or, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, and ethyl methyl carbonate.

12. The electrolyte according to claim 11, characterized in that, The organic solvent includes the ethylene carbonate and the methyl ethyl carbonate; The ethylene carbonate in the electrolyte has a mass percentage of 10%-40%, and / or the methyl ethyl carbonate in the electrolyte has a mass percentage of 10%-30%.

13. A battery, characterized in that, The battery includes the electrolyte as described in any one of claims 1-12.

14. The battery according to claim 13, characterized in that, After the battery is formed, the content of hydrogen fluoride in the electrolyte is 1ppm-300ppm.

15. The battery according to claim 14, characterized in that, After the battery is formed, the content of hydrogen fluoride in the electrolyte is 5ppm-200ppm.

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