Electrolyte and lithium ion battery

Abstract

An electrolyte and a lithium ion battery. The electrolyte comprises a solvent and an additive, wherein the solvent comprises a carboxylic acid ester; the additive comprises a benzenesulfonyl isocyanate compound, and the benzenesulfonyl isocyanate compound satisfies formula 1: formula 1, wherein R1, R2, R3, R4, and R5 are each independently selected from any one of H, F, Cl, Br, methyl, ethyl, propyl, butyl, pentyl, and hexyl.

Description

Electrolyte, lithium-ion battery

[0001] Cross-reference of related applications

[0002] This application claims priority to Chinese Patent Application No. 202411955155.0, filed on December 27, 2024, entitled "Electrolyte and Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to, but is not limited to, the field of lithium battery technology, specifically to electrolytes and lithium-ion batteries. Background Technology

[0004] Lithium-ion battery technology is one of the most important energy storage technologies in modern society. Lithium-ion batteries are widely used in electric vehicles, military equipment, aerospace, energy storage systems, and many other fields. The electrolyte plays a crucial role in lithium-ion batteries, requiring good compatibility with the electrodes and separators to connect the battery into an organic whole. The composition of the electrolyte directly affects the electrochemical performance of lithium-ion batteries; therefore, optimizing the electrolyte formulation can optimize the performance of lithium-ion batteries.

[0005] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] In a first aspect, this application provides an electrolyte comprising: a solvent and an additive, wherein the solvent comprises a carboxylic acid ester; and the additive comprises a benzenesulfonyl isocyanate compound satisfying Formula 1:

[0008] R1, R2, R3, R4, and R5 are each independently selected from any one of H, F, Cl, Br, methyl, ethyl, propyl, butyl, pentyl, and hexyl.

[0009] Therefore, the electrolyte proposed in this application possesses suitable liquid fluidity and high ionic conductivity. Furthermore, in lithium-ion batteries, after the electrolyte decomposes to form an SEI film, the SEI layer exhibits good stability, reducing lithium-ion loss caused by repeated SEI film rupture and formation, as well as changes in the composition and structure of the SEI layer within the lithium-ion battery. Thus, the electrolyte proposed in this application is beneficial for improving the fast-charging and cycle performance of lithium-ion batteries.

[0010] In some embodiments, R1, R2, R3, R4, and R5 are each independently selected from H, methyl, ethyl, and propyl. In Formula 1, R1, R2, R3, R4, and R5 are within the aforementioned functional group range. The benzene ring in the benzenesulfonyl isocyanate compound exhibits strong reactivity with R1, R2, R3, R4, and R5, and can form a strong interaction with the α-H introduced by the carboxylic acid ester in the electrolyte, thereby reducing the influence of α-H on the SEI film. Therefore, the benzenesulfonyl isocyanate compound additive can improve the stability of the electrolyte in lithium-ion batteries, thereby improving the cycle performance of lithium-ion batteries.

[0011] In some embodiments, the benzenesulfonyl isocyanate compound includes at least one of p-methylbenzenesulfonyl isocyanate, benzenesulfonyl ester isocyanate, o-methylbenzenesulfonyl isocyanate, and m-methylbenzenesulfonyl isocyanate.

[0012] The aforementioned compounds possess hydrogen bond acceptors capable of forming hydrogen bonds, interacting with the α-H atoms introduced by the carboxylic acid esters to form hydrogen bonds, thus resulting in high stability of the electrolyte solvent. Therefore, electrolytes containing the aforementioned compounds and carboxylic acid esters are beneficial for the formation of chemically stable SEI films in lithium-ion batteries.

[0013] In some embodiments, the benzenesulfonyl isocyanate compound has a mass fraction of 0.05% to 2% in the electrolyte. Therefore, the benzenesulfonyl isocyanate compound allows the carboxylic acid ester to fully exert its role as a solvent in the electrolyte, thereby improving the conductivity of the electrolyte and enhancing the stability of the SEI film and the chemical stability of the electrolyte. This is beneficial for improving the cycle performance and high-temperature storage retention of lithium-ion batteries.

[0014] In some embodiments, the carboxylic acid ester includes at least one selected from ethyl acetate, ethyl propionate, methyl acetate, and methyl propionate. Therefore, the aforementioned carboxylic acid esters, when used as electrolyte solvents, can improve the wettability of the electrolyte, increase its conductivity, and thus enhance the fast-charging performance of lithium-ion batteries.

[0015] In some embodiments, the mass fraction of the carboxylic acid ester in the electrolyte is 20% to 60%. This is beneficial for improving the electrolyte conductivity, thereby improving the fast-charging performance of the lithium-ion battery.

[0016] In some embodiments, the solvent may be a carbonate, including at least one selected from ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and dimethyl carbonate. Therefore, carbonates exhibit good chemical stability and good solubility, which is beneficial for improving the chemical stability of lithium-ion batteries.

[0017] In some embodiments, the solvent may be a carbonate, wherein the carbonate has a mass fraction of 37.5% to 62.5%. Thus, the carbonate can form a stable mixed solvent with the carboxylic acid ester.

[0018] In some embodiments, the electrolyte comprises a lithium salt, wherein the lithium salt includes an electrolyte lithium salt and an additive lithium salt. This replenishes the lithium-ion content in the electrolyte, compensates for lithium-ion loss during cycling, and improves the cycle performance of the lithium-ion battery.

[0019] In some embodiments, the electrolyte lithium salt comprises lithium hexafluorophosphate, and the mass fraction of the electrolyte lithium salt in the electrolyte is 8% to 13%. Therefore, in the electrolyte proposed in this application, adding an electrolyte lithium salt can effectively replenish lithium ions, which is beneficial for improving the cycle performance of lithium-ion batteries.

[0020] In some embodiments, the additive lithium salt includes at least one selected from lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate, wherein the mass fraction of the additive lithium salt in the electrolyte is 1% to 5%. This improves the electrolyte conductivity, helps enhance the fast-charging performance of lithium-ion batteries, effectively reduces performance degradation during high-temperature use, and improves the high-temperature storage retention rate of lithium-ion batteries.

[0021] In some embodiments, the additive may be vinylene carbonate, and the mass fraction of vinylene carbonate in the electrolyte is 0.5% to 5%. Thus, vinylene carbonate, as an additive, is beneficial for the formation of a stable SEI film, which can improve the cycle performance of lithium-ion batteries.

[0022] In some embodiments, the additive may be vinyl sulfate, and the mass fraction of vinyl sulfate in the electrolyte is 0.05% to 2%. Thus, vinyl sulfate, as an additive, can reduce polarization in lithium-ion batteries and improve the fast-charging performance of lithium-ion batteries.

[0023] In a second aspect, this application proposes a lithium-ion battery, comprising: an electrolyte, wherein the electrolyte is the electrolyte proposed in this application; and a positive electrode, wherein the positive electrode active material in the positive electrode comprises lithium iron phosphate.

[0024] The lithium-ion battery proposed in this application uses lithium iron phosphate as the positive electrode active material, which gives the lithium-ion battery high stability and safety performance. Combined with the electrolyte proposed in this application, the fast-charging performance and cycle performance of the lithium-ion battery can be improved. Therefore, this lithium-ion battery exhibits good performance in stability, safety, fast-charging performance, and cycle performance.

[0025] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Detailed Implementation

[0026] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or in accordance with the product manual.

[0027] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0028] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0029] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0030] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is also expected that ranges of 60 to 110 and 80 to 120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" have been listed in this article; "0 to 5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0033] Lithium iron phosphate (LiFePO4 or LFP) is widely used in electric vehicles and energy storage systems as the positive electrode active material for lithium-ion batteries due to its high safety, good cycle stability, non-toxicity, environmental friendliness, and low cost. However, compared to ternary materials, lithium iron phosphate has a lower lithium-ion diffusion rate and lower electronic conductivity. Lithium-ion batteries using lithium iron phosphate as the positive electrode active material are prone to polarization during charging and discharging, thus limiting the development and application of lithium iron phosphate as the positive electrode active material in fast-charging applications.

[0034] To reduce the migration resistance of lithium ions in lithium iron phosphate materials and improve the lithium ion diffusion rate, the chemical composition of the electrolyte in lithium iron phosphate batteries can be adjusted. Components with low viscosity and high ionic conductivity can be used to enhance the migration ability of lithium ions. Compared to carbonate solvents in the electrolyte, carboxylic acid esters have lower viscosity and better wettability, which can improve the electrolyte conductivity and thus improve the fast-charging performance of lithium-ion batteries.

[0035] However, adjustments to the electrolyte's chemical composition can also affect the formation and stability of the solid electrolyte interphase (SEI) film in lithium-ion batteries. In lithium iron phosphate batteries, the decomposition of carbonates and lithium ions in the electrolyte can form a stable SEI film on the surface of the negative electrode. Carboxylic acid esters, as solvents, constitute a large proportion of the electrolyte, introducing a large amount of α-H atoms bonded to carbonyl carbons. These α-H atoms are reactive. The presence of a large amount of α-H atoms in the electrolyte causes the formed SEI film to be repeatedly destroyed and regenerated, affecting its stability and thus leading to lithium ion consumption and a decrease in the cycle performance of the lithium-ion battery. To address the aforementioned problems, this application proposes an electrolyte and a lithium-ion battery. The electrolyte proposed in this application has high electrolyte conductivity, which is beneficial for improving the fast-charging performance of lithium-ion batteries. Simultaneously, the electrolyte proposed in this application can react to form a stable SEI film, which is beneficial for improving the cycle performance of lithium-ion batteries.

[0036] In a first aspect, this application provides an electrolyte comprising: a solvent and an additive, wherein the solvent comprises a carboxylic acid ester; and the additive comprises a benzenesulfonyl isocyanate compound satisfying Formula 1:

[0037] R1, R2, R3, R4, and R5 are each independently selected from any one of H, F, Cl, Br, methyl, ethyl, propyl, butyl, pentyl, and hexyl.

[0038] The electrolyte proposed in this application includes a carboxylic acid ester as the electrolyte solvent. The carboxylic acid ester has low viscosity, reducing the steric hindrance of lithium-ion migration in the lithium-ion battery, resulting in higher electrolyte conductivity and thus improving the fast-charging performance of the lithium-ion battery. A benzenesulfonyl isocyanate compound is added to the electrolyte. The isocyanate group (-NCO) contained in the benzenesulfonyl isocyanate compound can react with water and / or acids in the lithium-ion battery to generate urea substances insoluble in the solvent, thereby effectively improving the stability of the SEI film. The benzenesulfonyl isocyanate compound satisfies Formula 1 and can interact with the α-H of the carboxylic acid ester, reducing the activity of α-H, improving the stability of the SEI film, and giving the electrolyte good chemical stability at high temperatures, thereby improving the cycle performance and capacity retention rate of the lithium-ion battery at high temperatures. Therefore, the electrolyte proposed in this application has appropriate liquid flowability and high electrolyte conductivity. Furthermore, in lithium-ion batteries, after the electrolyte decomposes to form an SEI film, the SEI layer exhibits good stability, reducing lithium-ion loss caused by repeated SEI film rupture and formation, as well as changes in the composition and structure of the SEI layer in lithium-ion batteries. Therefore, the electrolyte proposed in this application is beneficial for improving the fast-charging performance and cycle performance of lithium-ion batteries.

[0039] In some embodiments, R1, R2, R3, R4, and R5 are each independently selected from H, methyl, ethyl, and propyl. In Formula 1, R1, R2, R3, R4, and R5 are within the aforementioned functional group range. The benzene ring in the benzenesulfonyl isocyanate compound exhibits strong reactivity with R1, R2, R3, R4, and R5, and can form a strong interaction with the α-H introduced by the carboxylic acid ester in the electrolyte, thereby reducing the influence of α-H on the SEI film. Therefore, the benzenesulfonyl isocyanate compound additive can improve the stability of the electrolyte in lithium-ion batteries, thereby improving the cycle performance of lithium-ion batteries.

[0040] In some embodiments, the benzenesulfonyl isocyanate compound includes at least one of p-methylbenzenesulfonyl isocyanate, benzenesulfonyl ester isocyanate, o-methylbenzenesulfonyl isocyanate, and m-methylbenzenesulfonyl isocyanate.

[0041] include:

[0042] The aforementioned compounds possess hydrogen bond acceptors capable of forming hydrogen bonds, interacting with the α-H atoms introduced by the carboxylic acid esters to form hydrogen bonds, thus resulting in high stability of the electrolyte solvent. Therefore, electrolytes containing the aforementioned compounds and carboxylic acid esters are beneficial for the formation of chemically stable SEI films in lithium-ion batteries.

[0043] In some embodiments, the mass fraction of the benzenesulfonyl isocyanate compound in the electrolyte is 0.05% to 2%. Within this range, the benzenesulfonyl isocyanate compound can interact with the α-H introduced by the carboxylic acid ester, limiting the damage of the SEI film by the α-H. Therefore, the benzenesulfonyl isocyanate compound allows the carboxylic acid ester to fully exert its role as a solvent in the electrolyte, improving the electrolyte conductivity, thereby enhancing the stability of the SEI film and the chemical stability of the electrolyte, which is beneficial for improving the cycle performance and high-temperature storage retention of lithium-ion batteries.

[0044] In some embodiments, the carboxylic acid ester includes at least one selected from ethyl acetate (EA), ethyl propionate (EP), methyl acetate (MA), and methyl propionate (MP). Using the aforementioned carboxylic acid esters as electrolyte solvents results in lower liquid viscosity, lower surface tension, better solubility for lithium salts, and a wider liquid temperature range. Therefore, using these carboxylic acid esters as electrolyte solvents can improve the wettability of the electrolyte, increase its conductivity, and thus enhance the fast-charging performance of lithium-ion batteries.

[0045] In some embodiments, the mass fraction of the carboxylic acid ester in the electrolyte is 20% to 60%. Using the carboxylic acid ester as an electrolyte solvent, with a mass fraction within the aforementioned range, can adjust the viscosity of the electrolyte and the solubility of lithium salts in the electrolyte, which is beneficial for improving the liquid flowability of the electrolyte and increasing the lithium ion content in the electrolyte. This, in turn, helps to improve the conductivity of the electrolyte, thereby improving the fast-charging performance of the lithium-ion battery.

[0046] In some embodiments, the solvent may be a carbonate, including at least one selected from ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC). The aforementioned carbonates, as electrolyte solvents, can react with lithium to form an organic SEI film of alkyl lithium carbonate. Carbonates possess good chemical stability and good solubility, which facilitates the complete dissolution of additives, lithium salts, and other substances added to the electrolyte. Therefore, this contributes to improving the chemical stability of lithium-ion batteries.

[0047] In some embodiments, the solvent may be a carbonate, wherein the carbonate mass fraction is 37.5% to 62.5%. The carbonate mass fraction is within the aforementioned range because carbonates have good versatility and can effectively dissolve additives, lithium salts, and other substances in the electrolyte. Thus, carboxylic acid esters can form stable mixed solvents with other carboxylic acid esters.

[0048] In some embodiments, the electrolyte comprises a lithium salt, wherein the lithium salt includes an electrolyte lithium salt and an additive lithium salt. This replenishes the lithium-ion content in the electrolyte, compensates for lithium-ion loss during cycling, and improves the cycle performance of the lithium-ion battery.

[0049] In some embodiments, the electrolyte lithium salt comprises lithium hexafluorophosphate, and the mass fraction of the electrolyte lithium salt in the electrolyte is 8% to 13%. The electrolyte lithium salt ionizes in the electrolyte solvent, releasing a large amount of lithium ions. This replenishes the lithium ions in the electrolyte, which act as carriers of charge transfer during battery charging and discharging, participating in the redox reaction between the positive and negative electrodes. Furthermore, in the electrolyte proposed in this application, the additive includes benzenesulfonyl isocyanate compounds. These compounds contain sulfonyl groups (-SO2-), which can delocalize the electrons on the nitrogen atoms attached to them. This blocks the reaction of lithium hexafluorophosphate decomposition to PF5 in the presence of moisture or due to increased temperature, reducing the formation of LiF and HF, and thus helping to suppress the activity of carboxylic acid esters at the negative electrode interface. This helps to suppress the decomposition of the electrolyte at the electrode interface. Therefore, in the electrolyte proposed in this application, the addition of electrode electrolyte lithium salt can effectively replenish lithium ions, which is beneficial to improving the cycle performance of lithium-ion batteries.

[0050] In some embodiments, the additive lithium salt includes at least one selected from lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate, wherein the mass fraction of the additive lithium salt in the electrolyte is 1% to 5%. The aforementioned additive lithium salts possess strong ionic conductivity, which can improve the mobility of lithium ions in the electrolyte. The fluoride ions in lithium bis(fluorosulfonyl)imide (LiFSI) have strong electron-withdrawing properties, and the coordination effect between the cations and anions in the lithium salt is weak, which can enhance the mobility of lithium ions in the electrolyte. LiFSI has superior thermal stability, reducing the possibility of side reactions such as thermal decomposition at high temperatures. Therefore, the electrolyte conductivity can be improved, which helps to improve the fast-charging performance of lithium-ion batteries and effectively reduces the performance degradation of batteries during high-temperature use, thereby improving the high-temperature storage retention rate of lithium-ion batteries.

[0051] In some embodiments, the additive may be vinylene carbonate, and the mass fraction of vinylene carbonate in the electrolyte is 0.5% to 5%. In the electrolyte, vinylene carbonate (VC) facilitates the formation of an SEI film with high lithium-ion conductivity and stable chemical properties, reducing side reactions at the negative electrode of the lithium-ion battery and improving the cycle performance of the lithium-ion battery. The formed SEI film helps reduce the interfacial resistance between the lithium-ion battery electrode and the electrolyte, allowing lithium ions to more smoothly intercalate and deintercalate on the electrode surface during charging and discharging. Therefore, it is beneficial to form a stable SEI film, which improves the cycle performance of the lithium-ion battery.

[0052] In some embodiments, the additive may be vinyl sulfate, and the mass fraction of vinyl sulfate in the electrolyte is 0.05% to 2%. Vinyl sulfate (DTD) can coordinate with lithium salts and lithium ions in the solvent to form stable complexes in the electrolyte, further forming a dense SEI film on the electrode surface. This effectively suppresses irreversible reactions between the electrode material and the electrolyte, protects the electrolyte, and improves the cycle life of the battery. DTD can improve the wettability of the electrolyte, which is beneficial for improving the contact and electron transport performance at the electrode-electrolyte interface. Therefore, vinyl sulfate, as an additive, can reduce polarization in lithium-ion batteries and improve their fast-charging performance.

[0053] In some embodiments, the additive includes at least one selected from fluoroethylene carbonate (FEC), methylene disulfonate (MMDS), 1,3-propanesulfonate lactone (PS), tris(trimethylsilane) phosphate (TMSP), tris(trimethylsilane) borate (TMSB), lithium difluorooxalate borate (LiODFB), and lithium difluorophosphate (LiPO2F2). The aforementioned additives facilitate the formation of a more stable SEI film in lithium-ion batteries, and help balance the high-temperature storage performance, high-temperature cycle performance, low-temperature power performance, and low-temperature charging capability of lithium-ion batteries.

[0054] In a second aspect, this application proposes a lithium-ion battery, comprising: an electrolyte, wherein the electrolyte is the electrolyte proposed in this application; and a positive electrode, wherein the positive electrode active material in the positive electrode comprises lithium iron phosphate.

[0055] The lithium-ion battery proposed in this application uses lithium iron phosphate as the positive electrode active material. The stable PO bonds in the lithium iron phosphate crystal give the lithium-ion battery high stability and safety. Combined with the electrolyte proposed in this application, the conductivity and chemical stability of the electrolyte are improved, which is beneficial for enhancing the fast-charging performance of the lithium-ion battery and shortening the charging time at room temperature. Simultaneously, the electrolyte proposed in this application can improve the stability of the SEI film in the lithium-ion battery. Therefore, this lithium-ion battery exhibits good performance in terms of stability, safety, fast-charging performance, and cycle life.

[0056] In some embodiments, the charging cut-off voltage of the lithium-ion battery is less than or equal to 3.75V. Within the aforementioned charging cut-off voltage range, the cycle performance and safety of the lithium-ion battery are at a superior level.

[0057] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0058] Example 1

[0059] S1: Preparation of electrolyte:

[0060] The electrolyte is prepared by mixing the following ingredients according to the aforementioned mass fractions: lithium salt: 3% LiFSI, 10% LiPF6, additives: 2% VC, 1% DTD, 0.5% methylbenzenesulfonyl isocyanate, 1% FEC, carboxylic acid ester: 40% EA, carbonate: 28% EC, 14.5% EMC.

[0061] S2: Preparation of the positive electrode sheet:

[0062] LiFePO4 (positive electrode material), polyvinylidene fluoride (PVDF) (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 94:3:3. N-methylpyrrolidone (NMP) solvent was added until the system became homogeneous and transparent. The mixture was stirred using a vacuum mixer to obtain a positive electrode material slurry. This slurry was then uniformly coated onto a 13 μm thick aluminum foil current collector. After air-drying at room temperature, the foil was transferred to a 120°C oven and dried for 1 hour. Following this, the mixture was cold-pressed (compacted density 2.6 g / cm³). 3 ), cut to obtain positive electrode sheets;

[0063] S3: Preparation of the negative electrode sheet

[0064] A negative electrode material (graphite), a thickener (sodium carboxymethyl cellulose solution), and a binder (styrene-butadiene rubber latex) were mixed at a mass ratio of 96:2:2. Deionized water solvent was added, and the mixture was stirred using a vacuum mixer to obtain a negative electrode material slurry. This slurry was then uniformly coated onto a current collector copper foil (6 μm thick), air-dried at room temperature, and then transferred to a 120°C oven for drying for 1 hour. Afterward, it was cold-pressed (compacted density 1.6 g / cm³). 3 The negative electrode sheet is obtained by cutting.

[0065] S4: Lithium-ion battery manufacturing

[0066] The positive electrode, negative electrode, and polypropylene separator are wound together, wrapped with an aluminum-plastic film, baked to remove moisture, injected with the prepared electrolyte, and sealed. After standing, hot and cold pressing, formation, clamping, and capacity testing, a soft-pack lithium-ion battery is prepared.

[0067] Example 2

[0068] Example 2 is consistent with Example 1, except that in S1, the lithium salt is 1% by mass of LiFSI and 8% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 18.5% by mass of EMC.

[0069] Example 3

[0070] Example 3 is consistent with Example 1, except that in S1, the lithium salt is 5% by mass of LiFSI and 13% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 18.5% by mass of EMC.

[0071] Example 4

[0072] Example 4 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 20% by mass of EA, and the carbonate is 28% by mass of EC and 34.5% by mass of EMC.

[0073] Example 5

[0074] Example 5 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 60% by mass of EA, and the carbonate is 22.5% by mass of EC.

[0075] Example 6

[0076] Example 6 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 0.5% by mass of VC, 2% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 3% by mass of FEC, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 13% by mass of EMC.

[0077] Example 7

[0078] Example 7 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 5% by mass of VC, 0.05% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 12.45% by mass of EMC.

[0079] Example 8

[0080] Example 8 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.05% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 14.05% by mass of EMC.

[0081] Example 9

[0082] Example 9 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 2% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 13% by mass of EMC.

[0083] Example 10

[0084] Example 10 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 40% by mass of EP, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0085] Example 11

[0086] Example 11 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 40% by mass of MA, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0087] Example 12

[0088] Example 12 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate and 1% by mass of FEC, the carboxylic acid ester is 40% by mass of MP, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0089] Example 13

[0090] Example 13 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate, 0.5% by mass of FEC and 0.5% by mass of MMDS, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0091] Example 14

[0092] Example 14 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate, 0.5% by mass of FEC and 0.5% by mass of PS, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0093] Example 15

[0094] Example 15 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate, 0.5% by mass of FEC and 0.5% by mass of TMSP, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0095] Example 16

[0096] Example 16 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate, 0.5% by mass of FEC and 0.5% by mass of TMSB, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0097] Example 17

[0098] Example 17 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate, 0.5% by mass of FEC and 0.5% by mass of LIODFB, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0099] Example 18

[0100] Example 18 is consistent with Example 1, except that in S1, the lithium salt is 3% by mass of LiFSI and 10% by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of DTD, 0.5% by mass of methylbenzenesulfonyl isocyanate, 0.5% by mass of FEC and 0.5% by mass of LIPO2F2, the carboxylic acid ester is 40% by mass of EA, and the carbonate is 28% by mass of EC and 14.5% by mass of EMC.

[0101] Comparative Example 1

[0102] Comparative Example 1 is consistent with Example 1, except that in S1, the lithium salt is 12.5% ​​by mass of LiPF6, the additives are 2% by mass of VC, 1% by mass of FEC, 0.3% by mass of LIPO2F2, and there is no carboxylic acid ester, and the carbonates are 28% by mass of EC, 19.7% by mass of EMC, 5% by mass of PC, and 32% by mass of DMC.

[0103] The electrolyte composition in Examples 1-18 and Comparative Example 1 can be found in Table 1.

[0104] Table 1

[0105] Test method:

[0106] 1. Electrolyte conductivity test

[0107] The prepared electrolyte was placed in a 25°C constant temperature water bath for 30 minutes, and the conductivity was tested using a conductivity meter.

[0108] 2. Cyclic test at 45℃ (1C)

[0109] The prepared lithium-ion battery was first discharged at 1C to 2.0V at 45℃ and then subjected to cycle testing.

[0110] The test process involves first charging at a constant current of 1C to 3.75V, then charging at a constant voltage to a current of 0.05C, and then discharging at a constant current of 1C to 2.0V. This charging / discharging cycle is repeated to calculate the capacity retention rate of the lithium-ion battery after 1000 cycles at 45℃ using 1C / 1C.

[0111] 3. 4C cycle test at 25℃

[0112] The prepared lithium-ion battery was first discharged at 1C to 2.0V at 25℃ and then subjected to cycle testing.

[0113] The test process involves first charging at a constant current of 4C to 3.75V, then charging at a constant voltage to a current of 0.05C, and then discharging at a constant current of 1C to 2.0V. This charging / discharging cycle is repeated to calculate the capacity retention rate of the lithium-ion battery after 500 cycles at 25℃ using 1C / 1C.

[0114] 4. Storage test at 60℃

[0115] At 25°C, the prepared lithium-ion battery was first discharged to 2.0V at 1C, then charged to 3.75V at a constant current of 1C, then charged at a constant voltage to a current of 0.05C, and finally discharged to 2.0V at a constant current of 1C. The discharge capacity is denoted as C. 放 1. Then, charge the lithium-ion battery at a constant current of 1C to 3.75V, and then charge it at a constant voltage to a current of 0.05C. Store the lithium-ion battery in a 60℃ oven for 60 days, then place it at room temperature, first discharge it at 1C to 2.0V, then charge it at a constant current of 1C to 3.75V, then charge it at a constant voltage to a current of 0.05C, and finally discharge it at a constant current of 1C to 2.0V. Record the discharge capacity as C. 放2 C 放2 / C 放1 ×100% = Capacity retention rate (%)

[0116] Test results: See Table 2

[0117] Table 2

[0118] As shown in Table 2:

[0119] Compared with Comparative Example 1, the electrolyte proposed in this application significantly improves the conductivity of lithium-ion batteries, meeting the 6C charging capability. In Comparative Example 1, lithium plating occurred during the 6C cycle, exacerbating the loss of active lithium and causing a significant drop in battery capacity. In Example 1, due to the synergistic effect of additive formula 1-1 and the carboxylic acid ester, the damage of the carboxylic acid ester to the negative electrode interface can be effectively suppressed, thus significantly improving the 1C cycle capacity retention rate at 45°C.

[0120] Compared with Comparative Example 2, Example 1 did not contain additive 1-1, resulting in decreased stability of the SEI film in the lithium-ion battery and a significant decrease in capacity retention during 1C cycling at 45°C and 60D storage at 0°C.

[0121] The changes in lithium salt content in Examples 2 and 3 also resulted in a significant improvement in 6C cycle performance compared to Comparative Example 1.

[0122] Compared to Comparative Example 1, Example 5 has a higher content of carboxylic acid esters, resulting in a significant improvement in electrolyte conductivity.

[0123] Compared to Example 1, Examples 6 and 7 show changes in VC content (decreased and increased), and the lithium-ion battery's capacity remains the same for 1C cycling at 45°C and 60D storage at 0°C, compared to 500cls for 6C cycling at 25°C.

[0124] Compared to Example 1, Examples 8 and 9 show changes in the content of compound 1-1. The decreased content of compound 1-1 indicates a significant deterioration in high-temperature storage and cycling, as well as a marked decline in the 6C cycle retention rate. This suggests that the compound effectively inhibits electrolyte decomposition at the electrode interface, which is beneficial for the formation of a stable SEI layer.

[0125] Examples 10-12 used carboxylic acid esters of EP, MA, and MP, respectively. Compared with Comparative Example 1, the high-temperature cycle capacity retention, high-temperature storage performance, and 6C cycle performance of the lithium-ion batteries were significantly improved.

[0126] Compared to Example 1, Examples 13-18 respectively added the additives MMDS, PS, TMSP, TMSB, LiODFB, and LiPO2F2. This facilitates the formation of a stable SEI film, balancing the high-temperature storage performance, high-temperature cycling performance, and fast-charging performance of lithium-ion batteries.

[0127] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0128] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0129] In this application, the order in which the steps are written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0130] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrolyte comprising: Solvents, additives The solvent includes carboxylic acid esters; The additive includes a benzenesulfonylisocyanate compound satisfying Formula 1: R1, R2, R3, R4, and R5 are each independently selected from any one of H, F, Cl, Br, methyl, ethyl, propyl, butyl, pentyl, and hexyl.

2. The electrolyte according to claim 1, wherein, R1, R2, R3, R4, and R5 are each independently selected from H, methyl, ethyl, and propyl.

3. The electrolyte according to claim 2, wherein, The benzenesulfonyl isocyanate compounds include at least one of p-methylbenzenesulfonyl isocyanate, benzenesulfonyl ester isocyanate, o-methylbenzenesulfonyl isocyanate, and m-methylbenzenesulfonyl isocyanate.

4. The electrolyte according to claim 1, wherein, The mass fraction of the benzenesulfonyl isocyanate compound in the electrolyte is 0.05% to 2%.

5. The electrolyte according to any one of claims 1-4, wherein, The carboxylic acid ester includes at least one of ethyl acetate, ethyl propionate, methyl acetate, and methyl propionate.

6. The electrolyte according to any one of claims 1-4, wherein, The mass fraction of the carboxylic acid ester in the electrolyte is 20% to 60%.

7. The electrolyte according to any one of claims 1-4, wherein, The solvent includes carbonates, which include at least one of ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and dimethyl carbonate.

8. The electrolyte according to any one of claims 1-4, wherein, The solvent comprises carbonate, wherein the carbonate has a mass fraction of 37.5% to 62.5%.

9. The electrolyte according to any one of claims 1-4, wherein, The electrolyte includes lithium salts, which include electrolyte lithium salts and additive lithium salts.

10. The electrolyte according to claim 9, wherein, The electrolyte lithium salt includes lithium hexafluorophosphate, and the mass fraction of the electrolyte lithium salt in the electrolyte is 8% to 13%.

11. The electrolyte according to claim 9, wherein, The additive lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate, and the mass fraction of the additive lithium salt in the electrolyte is 1% to 5%.

12. The electrolyte according to any one of claims 1-4, wherein, The additive includes vinylene carbonate, and the mass fraction of the vinylene carbonate in the electrolyte is 0.5% to 5%.

13. The electrolyte according to any one of claims 1-4, wherein, The additive includes vinyl sulfate, and the mass fraction of the vinyl sulfate in the electrolyte is 0.05% to 2%.

14. A lithium-ion battery, comprising: Electrolyte, wherein the electrolyte is the electrolyte according to any one of claims 1-13; The positive electrode sheet, wherein the positive active material in the positive electrode sheet includes lithium iron phosphate.

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