Electrolyte additive, sodium ion battery electrolyte applying same and sodium ion battery

Abstract

The invention relates to the technical field of battery materials, in particular to an electrolyte additive, a sodium-ion battery electrolyte applying the electrolyte additive and a sodium-ion battery. The electrolyte additive comprises vinylene carbonate, fluoroethylene carbonate, a sodium salt additive and a succinic anhydride-3-sulfonic acid additive with a specific structure. The electrolyte additive is added into an electrolyte consisting of a sodium salt and an organic solvent according to a specific proportion to prepare the high-performance sodium-ion battery electrolyte. The electrolyte can synergistically construct a stable and compact interfacial film on the surfaces of a positive electrode and a negative electrode, electrolyte decomposition is effectively inhibited, HF generation and high-temperature gas production are reduced, and the first efficiency, the cycle life and the high-temperature storage performance of the battery are remarkably improved. The method is particularly suitable for the sodium ion battery of a layered oxide / hard carbon system, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to an electrolyte additive and a sodium-ion battery electrolyte and sodium-ion battery using the additive. Background Technology

[0002] As the global energy structure accelerates its transition to a green and low-carbon model, energy storage technology has become a crucial link supporting the large-scale integration of renewable energy and the development of the electric vehicle industry. Sodium-ion batteries, due to their abundant raw materials, low cost, superior low-temperature performance, and strong compatibility with lithium-ion battery manufacturing processes, are considered an important candidate system for next-generation large-scale energy storage and medium- and low-speed electric vehicles. Regarding cathode materials, layered transition metal oxides (such as NaMO2) have become one of the most commercially promising technologies due to their high specific capacity, suitable voltage platform, and mature synthesis process. However, these materials still face a series of interfacial chemical challenges in practical applications: On the one hand, the material surface usually has a high residual alkali content (such as NaOH, Na2CO3, etc.). These alkaline species readily undergo nucleophilic reactions with carbonate solvents in the electrolyte, catalyzing solvent decomposition and releasing gases such as CO2. Especially under high temperature or high voltage (≥3.95V) conditions, the structural stability of the cathode-electrolyte interface film (CEI) is insufficient, making it difficult to effectively suppress continuous oxidative decomposition reactions, leading to increased battery gas production, reduced cycle life, and decreased safety.

[0003] On the negative electrode side, hard carbon materials, due to their abundant defect structure and large interlayer spacing, provide ample storage sites for sodium ions and promote rapid insertion and extraction, making them the preferred negative electrode material for sodium-ion batteries. However, their highly disordered porous surface structure also presents challenges for interfacial film formation: during the initial charge-discharge process, the solid electrolyte interphase (SEI) film formed by the electrolyte reduction on the negative electrode surface is often uneven, non-dense, and exhibits poor electrochemical stability. During long-term cycling, this unstable SEI film continuously breaks down and reconstructs, constantly consuming active sodium ions and electrolyte, leading to a continuous increase in interfacial impedance, accelerated capacity decay, and potential safety hazards such as dendrite growth.

[0004] To improve the interfacial stability and cycle life of sodium-ion batteries, researchers typically introduce functional additives into the electrolyte to construct efficient and stable SEI / CEI films on the electrode surface. Commonly used additives include vinylene carbonate (VC) and fluoroethylene carbonate (FEC), which can promote the formation of inorganic-organic composite interfacial layers and inhibit electrolyte decomposition to some extent. However, in sodium-ion battery systems, especially high-voltage layered oxide / hard carbon systems, the modification effect of single or small amounts of additives is limited: while VC can participate in the formation of polymeric layers, its antioxidant capacity at high voltages is insufficient; FEC can promote the formation of fluorine-containing interfacial components, but excessive use may lead to increased electrolyte viscosity and low-temperature performance degradation. Furthermore, traditional additives have weak neutralization capabilities for residual alkali on the cathode surface and are ineffective at removing trace amounts of water and HF byproducts from the electrolyte, making it difficult to comprehensively address issues such as gas generation, impedance increase, and cycle degradation.

[0005] Therefore, developing a novel multifunctional electrolyte additive system that can simultaneously stabilize the positive and negative electrode interfaces, suppress side reactions, and improve the structural integrity and ion conduction efficiency of the SEI / CEI film has become a key issue in promoting the long cycle life and high safety applications of sodium-ion batteries. This invention aims to address the aforementioned technical bottlenecks by providing a composite additive scheme with a novel structural design and significant synergistic effects, thereby comprehensively improving the overall electrochemical performance of sodium-ion batteries. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide an electrolyte additive that improves the initial efficiency, enhances cycle performance, reduces gas generation during high-temperature storage, and lowers the rate of increase in internal resistance of sodium-ion batteries, as well as a sodium-ion battery electrolyte and a sodium-ion battery using the additive. This electrolyte additive can be applied to layered oxide / hard carbon systems, effectively ensuring battery cycle performance and extending battery life, thus providing strong support for the practical application of sodium-ion batteries.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides an electrolyte additive comprising vinylene carbonate, fluorovinyl carbonate, sodium salt additive, and succinic anhydride-3-sulfonic acid additive, wherein the succinic anhydride-3-sulfonic acid additive comprises a compound having the structure shown in Formula 1 below: Wherein, R is selected from one of the following: halogen atom, C1-C20 haloalkoxy / haloalkyl, C1-C20 isocyanate / aniline / amino, C1-C20 alkoxy / alkeneoxy / silanoxy, and C1-C20 alkyl / acyl / ether.

[0008] The succinic anhydride-3-sulfonic acid additives in this invention have the following advantages: Firstly, the succinic anhydride structure can form a stable SEI film on the electrode surface, improving battery cycle performance. Secondly, it can react with impurities in the electrolyte, reducing side reactions and thus extending battery life. The sulfonic acid structure can enhance the ionic conductivity and wettability of the electrolyte, promote sodium ion migration, and increase electrolyte conductivity. Furthermore, the sulfur-containing structure can promote the formation of a flexible SEI film on the negative electrode surface, improving the interfacial contact between the electrode and the electrolyte, reducing interfacial impedance, and optimizing battery cycle performance.

[0009] A mixture of fluoroethylene carbonate and vinylene carbonate is used as the main additive. The polycarbonate formed by its reduction can effectively inhibit the continuous growth of the SEI film and improve the high-temperature performance and cycle performance of the battery.

[0010] As a preferred embodiment of the present invention, the succinic anhydride-3-sulfonic acid additive includes at least one of additive A, additive B, or additive C having the structure shown in formulas A, B, and C: In formula A, R is selected from silanoxy groups. Silanoxy groups can react with residual alkali on the positive electrode surface, reduce gas generation at high temperatures in the battery, remove trace amounts of water and HF in the electrolyte, stabilize the NaPF6 structure, prevent the electrolyte from decomposing and generating HF that could damage the SEI / CEI, improve the stability of the positive and negative electrodes, and improve gas generation and cycle performance during high-temperature storage.

[0011] In formula B, R is selected from isocyanate groups. The nitrile group (—C=N—) of its double bond structure can initiate electrochemical polymerization to form free radical cations. These free radical cations can polymerize with carbonate organic solvents to form an SEI that is predominantly organic and rich in sodium nitride, thereby improving the density and uniformity of the SEI film. At the same time, the isocyanate group can inhibit the decomposition of the electrolyte and reduce the generation of CO2 and H2 during cycling, which is beneficial to enhancing the cycle stability of the battery.

[0012] In formula C, R is selected from fluoroalkoxy groups, which possess strong electronegativity and chemical stability, enhancing the electrolyte's antioxidant and anti-reduction capabilities and broadening its electrochemical window. Simultaneously, additives containing F can generate F free radicals at certain temperatures, which can adsorb hydroxyl radicals, thereby blocking chain reactions and improving the safety of ion batteries. Furthermore, fluoroalkoxy groups can synergistically alter the Na+ content in the electrolyte. + The coordination environment promotes the formation of an organic SEI rich in sodium fluoride, sodium alkyl, and sodium alkoxy on the negative electrode surface. The generated SEI film is thin, dense, uniform, and has low impedance, which can reduce sodium ion consumption and thus improve cycle performance.

[0013] As a preferred embodiment of the present invention, the succinic anhydride-3-sulfonic acid additives include additive A, additive B and additive C in a mass ratio of (0.1-2.0):(0.1-2.0):(0.1-2.0).

[0014] As a preferred embodiment of the present invention, the sodium salt additive includes at least one of sodium difluorophosphate, sodium bis(oxalate)borate, sodium di(oxalate)borate, and sodium di(oxalate)phosphate.

[0015] As a preferred embodiment of the present invention, the mass ratio of vinylene carbonate, fluorovinyl carbonate, sodium salt additive and succinic anhydride-3-sulfonic acid additive is (0.5-1.5):(0.5-4.5):(0.5-1.5):(0.5-2.5).

[0016] In a second aspect, the present invention provides a sodium-ion battery electrolyte, comprising, by mass fraction of 100%, the following components in mass fractions: 13-25% sodium salt, 65-85% organic solvent, and 2.0-10.0% electrolyte additive; wherein the electrolyte additive is the electrolyte additive described in any one of claims 1-5.

[0017] As a preferred embodiment of the present invention, the sodium salt comprises at least one selected from sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium perchlorate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, and sodium nitrate. Preferably, the sodium salt may be selected from one or more of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0018] As a preferred embodiment of the present invention, the concentration of the sodium salt in the electrolyte is 0.7 to 1.4 mol / L, and the high concentration of salt can improve the ionic conductivity of the electrolyte.

[0019] In a preferred embodiment of the present invention, the organic solvent comprises carbonate and ether-based solvents, including at least one selected from ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The use of a mixed solvent in this invention can lower the melting point and viscosity of the electrolyte, and improve the ion transport performance of the electrolyte.

[0020] As a preferred embodiment of the present invention, the electrolyte is obtained by uniformly mixing sodium salt, organic solvent, and electrolyte additives under specific temperature, humidity, oxygen content, and water content conditions. During the preparation of the sodium-ion battery electrolyte of the present invention, the ambient temperature is controlled at 10–20°C, humidity ≤1%, oxygen content ≤1 ppm, and water content ≤0.1 ppm to ensure the purity of the organic solvent, maintain the electrochemical stability window, and prevent sodium salt decomposition, which could lead to electrolyte failure.

[0021] Thirdly, the present invention provides a sodium-ion battery comprising the aforementioned sodium-ion battery electrolyte; the sodium-ion battery is a sodium-ion layered oxide system battery. The sodium-ion battery further includes a positive electrode, a negative electrode, and a separator.

[0022] Preferably, the raw material of the positive electrode sheet includes a sodium ion layered oxide active material, including NaMO2, where M is selected from any one or a combination of at least two of Fe, Ni, Co, Mn, Cu, Cr, Al, Mg, Ti, Li, and Zn. As a preferred embodiment of the present invention, the positive electrode active material is NaCu. 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2.

[0023] Preferably, the raw material of the negative electrode sheet includes a carbon-based negative electrode active material, which includes any one or a combination of at least two of graphene, graphene oxide, soft carbon, hard carbon, and expanded graphite. As a preferred embodiment of the present invention, hard carbon is selected as the negative electrode active material.

[0024] Preferably, the sodium-ion battery has an application temperature of -40 to 60°C, and the battery exhibits good cycle performance at high temperatures.

[0025] Compared with the prior art, the beneficial effects of the present invention include: This invention introduces succinic anhydride-3-sulfonic acid additives with specific structures (especially the synergistic use of structures A, B, and C) to construct a dense, uniform composite interfacial film (SEI / CEI) rich in NaF, nitrides, and organic sodium salts on the negative electrode surface. This interfacial film exhibits excellent electrochemical stability and ion conductivity, effectively inhibiting continuous electrolyte decomposition and reducing active sodium loss, thereby significantly extending battery cycle life. The silanoxy structure in the additive can react with trace amounts of water in the electrolyte, residual alkali on the positive electrode surface, and decomposition product HF, blocking the catalytic decomposition chain reaction of sodium salts such as NaPF6, and significantly reducing the HF content during electrolyte storage and cycling. Through the film-forming effect of the succinic anhydride structure and the wetting and ion conduction enhancement effect of the sulfonic acid groups, the side reactions of positive electrode oxidation gas generation and negative electrode reduction are synergistically suppressed. The fluoroalkoxy and isocyanate groups in the additives enhance the electrolyte's antioxidant / reduction resistance and electrochemical polymerization film-forming ability, respectively, and broaden the electrolyte's electrochemical window, enabling the battery to maintain good cycle performance and interface stability in a temperature range of -40℃ to 60℃ and under a high voltage of ≥3.95V.

[0026] Compared with single additives or common composite additive systems, the multifunctional composite additive provided by this invention exhibits comprehensive advantages in terms of initial efficiency, cycle life, HF suppression, and gas generation control, providing a reliable technical path for electrolyte design of high energy density and long life sodium-ion batteries. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, these should not be construed as limiting the present invention and are merely examples.

[0028] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are obtained from conventional commercial sources or prepared by conventional methods.

[0029] This invention provides an electrolyte additive, comprising vinylene carbonate, fluorovinyl carbonate, sodium salt additive, and succinic anhydride-3-sulfonic acid additive, wherein the succinic anhydride-3-sulfonic acid additive comprises compounds having the structure shown in Formula 1 below: Wherein, R is selected from C1 to C20 haloalkoxy / haloalkyl / halogen atom, C1 to C20 isocyanate group / aniline group / amino group, C1 to C20 alkoxy / alkeneoxy / silanoxy group, and C1 to C20 alkyl / acyl / ether group.

[0030] In a preferred embodiment of the present invention, the succinic anhydride-3-sulfonic acid additive includes at least one of additive A, additive B, or additive C having the structure shown in formulas A, B, and C: As an optional embodiment of the present invention, the preparation method of succinic anhydride-3-sulfonic acid additives can be further defined. Succinic anhydride-3-sulfonic acid additives can be prepared using the following raw materials (which can be obtained by searching for their structural formulas on the Gaide Chemicals website) according to the following synthetic route: As an optional embodiment of the present invention, the synthetic route of additive A is as follows: As an optional embodiment of the present invention, the synthetic route of additive B is as follows: As an optional embodiment of the present invention, the synthetic route of additive C is as follows: The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0031] Example 1 This embodiment provides a sodium-ion battery electrolyte: A long-cycle electrolyte based on a layered oxide / hard carbon system comprises an organic solvent, a sodium salt, and electrolyte additives. The organic solvent comprises 75% and consists of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, and ethylene glycol dimethyl ether, with a volume ratio of ethylene carbonate:propylene carbonate:methyl ethyl carbonate:diethyl carbonate:propylene carbonate:ethylene glycol dimethyl ether = 10:35:40:5:10. The sodium salt comprises 18.5% and consists of sodium hexafluorophosphate and sodium difluorosulfonamide, with a mass ratio of sodium hexafluorophosphate:sodium difluorosulfonamide = 5:1. The electrolyte additives include 1.0% vinylene carbonate, 3.0% fluoroethylene carbonate, 1% sodium salt additive (sodium difluorophosphate: sodium difluorooxalate borate = 1:1) and 1.5% succinic anhydride-3-sulfonic acid additive (additive A: additive B: additive C = 1:1:1).

[0032] Example 2 This embodiment provides a sodium-ion battery electrolyte: A long-cycle electrolyte based on a layered oxide / hard carbon system is composed of an organic solvent, a sodium salt, and electrolyte additives. The organic solvent comprises 76% and consists of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, and ethylene glycol dimethyl ether, with a volume ratio of ethylene carbonate:propylene carbonate:methyl ethyl carbonate:diethyl carbonate:propylene carbonate:ethylene glycol dimethyl ether = 10:35:40:5:10. The sodium salt comprises 18.5% and consists of sodium hexafluorophosphate and sodium difluorosulfonamide, with a mass ratio of sodium hexafluorophosphate:sodium difluorosulfonamide = 5:1. The electrolyte additives include 1.0% vinylene carbonate, 3.0% fluoroethylene carbonate, 1% sodium salt additive (sodium difluorophosphate: sodium difluorooxalate borate = 1:1) and 0.5% succinic anhydride-3-sulfonic acid additive (additive A: additive B: additive C = 1:1:1).

[0033] Example 3 This embodiment provides a sodium-ion battery electrolyte: A long-cycle electrolyte based on a layered oxide / hard carbon system comprises an organic solvent, a sodium salt, and electrolyte additives. The organic solvent comprises 74% and consists of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, and ethylene glycol dimethyl ether, with a volume ratio of ethylene carbonate:propylene carbonate:methyl ethyl carbonate:diethyl carbonate:propylene carbonate:ethylene glycol dimethyl ether = 10:35:40:5:10. The sodium salt comprises 18.5% and consists of sodium hexafluorophosphate and sodium difluorosulfonamide, with a mass ratio of sodium hexafluorophosphate:sodium difluorosulfonamide = 5:1. The electrolyte additives include 1.0% vinylene carbonate, 3.0% fluoroethylene carbonate, 1% sodium salt additive (sodium difluorophosphate: sodium difluorooxalate borate = 1:1) and 2.5% succinic anhydride-3-sulfonic acid additive (additive A: additive B: additive C = 1:1:1).

[0034] Example 4 This embodiment provides a sodium-ion battery electrolyte: Replace additive A: additive B: additive C = 1:1:1 with only additive A, and keep all other conditions the same as in Example 1.

[0035] Example 5 This embodiment provides a sodium-ion battery electrolyte: Replace additive A: additive B: additive C = 1:1:1 with only additive B, and keep all other conditions the same as in Example 1.

[0036] Example 6 This embodiment provides a sodium-ion battery electrolyte: Replace additive A: additive B: additive C = 1:1:1 with only additive C, and keep all other conditions the same as in Example 1.

[0037] Example 7 This embodiment provides a sodium-ion battery electrolyte: Replace the additive A: additive B: additive C = 1:1:1 with only additive A: additive B = 1:1, and keep all other conditions the same as in Example 1.

[0038] Example 8 This embodiment provides a sodium-ion battery electrolyte: Replace the additive A: additive B: additive C = 1:1:1 with only additive A: additive C = 1:1, and keep all other conditions the same as in Example 1.

[0039] Example 9 This embodiment provides a sodium-ion battery electrolyte: Replace the ratio of additive A: additive B: additive C = 1:1:1 with only additive B: additive C = 1:1, and keep all other conditions the same as in Example 1.

[0040] Comparative Example 1 This comparative example provides a sodium-ion battery electrolyte (without succinic anhydride-3-sulfonic acid additives): A long-cycle electrolyte based on a layered oxide / hard carbon system is composed of an organic solvent, a sodium salt, and additives. The organic solvent comprises 76.5% and consists of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, and ethylene glycol dimethyl ether, with a volume ratio of ethylene carbonate:propylene carbonate:methyl ethyl carbonate:diethyl carbonate:propylene carbonate:ethylene glycol dimethyl ether = 10:35:40:5:10. The sodium salt comprises 18.5% and consists of sodium hexafluorophosphate and sodium difluorosulfonyl imide, with a mass ratio of sodium hexafluorophosphate:sodium difluorosulfonyl imide = 5:1. The electrolyte additives include 1.0% ethylene carbonate, 3.0% fluoroethylene carbonate, and 1% sodium salt additive (sodium difluorophosphate:sodium difluorooxalate borate = 1:1).

[0041] Comparative Example 2 This comparative example provides a sodium-ion battery electrolyte (with excess succinic anhydride-3-sulfonic acid additive): A long-cycle electrolyte based on a layered oxide / hard carbon system is composed of an organic solvent, a sodium salt, and additives. The organic solvent comprises 73% and consists of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, and ethylene glycol dimethyl ether, with a volume ratio of ethylene carbonate:propylene carbonate:methyl ethyl carbonate:diethyl carbonate:propylene carbonate:ethylene glycol dimethyl ether = 10:35:40:5:10. The sodium salt comprises 18.5% and consists of sodium hexafluorophosphate and sodium difluorosulfonyl imide, with a mass ratio of sodium hexafluorophosphate:sodium difluorosulfonyl imide = 5:1. The electrolyte additives include 1.0% ethylene carbonate, 3.0% fluoroethylene carbonate, 1% sodium salt additive (sodium difluorophosphate:sodium difluorooxalate borate = 1:1), and 3.5% succinic anhydride-3-sulfonic acid additive (additive A:additive B:additive C = 1:1:1).

[0042] Comparative Example 3 This comparative example provides a sodium-ion battery electrolyte: The 1.5% succinic anhydride-3-sulfonic acid additive was replaced with 0.5% tris(trimethylsilane) phosphate, 0.5% propylene sulfate, and 0.5% 1,3-propanesulfonate lactone, while all other conditions remained the same as in Example 1.

[0043] Comparative Example 4 This comparative example provides a sodium-ion battery electrolyte: The 1.5% succinic anhydride-3-sulfonic acid additive was replaced with 1.5% sodium succinic anhydride-3-sulfonate, and all other conditions were the same as in Example 1.

[0044] The sodium-ion battery electrolytes obtained in Examples 1-9 and Comparative Examples 1-4 are used to prepare soft-pack sodium-ion batteries using a soft-pack stacking process. The specific process is as follows: NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 After stacking and assembling O2 positive electrode, hard carbon negative electrode and polyethylene separator (e.g. PE+OBS separator <polyethylene + solvent-coated separator>), the material is baked until the moisture content is within acceptable limits, then the electrolyte is injected, and after hot pressing formation and high-temperature standing, it is packaged. After capacity testing and standing at room temperature, a soft-pack finished battery is obtained. The HF content of the electrolyte is tested, and the electrochemical performance of the sodium-ion battery is tested.

[0045] HF content test: After storing the prepared electrolyte at 60℃ for 0 and 30 days, the electrolyte was dissolved in ice water and titrated with a 0.01 mol / L sodium hydroxide standard solution to obtain the HF content of the electrolyte after storage at 60℃ for 0 and 30 days, as shown in Table 1.

[0046] First-time efficiency: The battery cells were divided at 25°C to obtain the first charge capacity and the first discharge capacity. The first efficiency was recorded as (first discharge capacity / first charge capacity * 100%), as shown in Table 1.

[0047] High-temperature storage gas generation performance: After storing the battery cell at 60℃ for 0 and 30 days, the thickness H1 before storage and the thickness H2 after storage were recorded. The internal resistance DCR1 before storage and the internal resistance DCR2 after storage were also recorded. The cell gas expansion rate = (H2-H1) / H1*100% and the internal resistance growth rate before and after storage = (DCR2-DCR1) / DCR1*100% were recorded, as shown in Table 1.

[0048] High-temperature cycling performance: The battery was tested at 45°C on an electrochemical workstation battery testing system. The test charge / discharge current density was 1C / 1C, and the charge / discharge voltage window was 2.0V to 4.0V, as shown in Table 1.

[0049] Table 1 Based on the performance test data from Examples 1-9, Comparative Examples 1-4, and Table 1, the following core conclusions can be drawn: Succinic anhydride-3-sulfonic acid additives are key components for improving the overall performance of sodium-ion batteries. Comparative Example 1, without such additives, had an electrolyte HF content as high as 435.9 ppm, significantly higher than Examples 1-9 (273.1-361.2 ppm) with such additives. Furthermore, Comparative Example 1's battery had an initial efficiency of only 78.25%, an internal resistance growth rate of 26.58%, a high-temperature storage gas expansion rate of 4.92%, and only 856 cycles to 80% SOH, all significantly inferior to Examples 1-9 (initial efficiency 83.07%-86.36%, internal resistance growth rate 10.56%-19.37%, gas expansion rate 1.40%-2.45%, cycle count 1550-2440). This indicates that such additives can inhibit the decomposition of NaPF6 to produce HF by reacting with trace amounts of water in the electrolyte and residual alkali on the cathode surface through silane groups, thus preventing damage to the SEI / CEI film. At the same time, they can reduce high-temperature gas production, decrease interfacial impedance growth, and improve the battery's initial efficiency and cycle stability.

[0050] The dosage of succinic anhydride-3-sulfonic acid additives needs to be controlled within a reasonable range (0.5%-2.5%), as excessive addition will lead to performance degradation. Data from Examples 2 (0.5%), 1 (1.5%), and 3 (2.5%) show that as the content of this type of additive increases, the HF content of the electrolyte after storage and the high-temperature gas expansion rate of the battery show a decreasing trend. Among them, the HF-30D in Example 3 is as low as 273.1 ppm, and the gas expansion rate is only 1.40%. However, the initial efficiency of Comparative Example 2 (3.5%, excessive) drops to 81.23%, and the number of cycles is only 1428, which is significantly lower than that of Examples 1-3. This indicates that excessive addition will disrupt the electrolyte system balance and affect battery performance. Overall, the addition of about 1.5% (Example 1) performs best, with a number of cycles of 2440, an initial efficiency of 86.36%, and an internal resistance growth rate of only 10.56%, showing balanced and excellent performance.

[0051] Among succinic anhydride-3-sulfonic acid additives, the ternary compound of additives A, B, and C outperforms single-component or binary compound additives. Example 1, using a compound ratio of A:B:C = 1:1:1, achieved the best initial efficiency, internal resistance growth rate, and cycle count among all examples. In contrast, Examples 4 (A only), 5 (B only), and 6 (C only), containing only single components, had cycle counts of only 1550-1674, significantly lower than Example 1. The binary compound additives in Examples 7 (A:B = 1:1), 8 (A:C = 1:1), and 9 (B:C = 1:1) had cycle counts of 1834-1905, also failing to achieve the effect of the ternary compound. This is because the functions of the three components work synergistically: the silanoxy groups of additive A remove moisture and HF, stabilizing the positive electrode surface; the isocyanate groups of additive B improve the density of the SEI film; and the fluoroalkoxy groups of additive C broaden the electrochemical window and optimize the SEI film composition. The combination of these three components comprehensively solves the problem at the positive and negative electrode interfaces.

[0052] The succinic anhydride-3-sulfonic acid additives of the present invention (related structures of formulas A, B, and C) are superior to traditional additives or structural analogs. Comparative Example 3 used a mixed additive of tris(trimethylsilane)phosphate, propylene sulfate, and 1,3-propanesulfonate lactone, achieving an HF-30D of 387.4 ppm, a gas production expansion rate of 3.59%, and a cycle count of 1260. Comparative Example 4 used sodium succinic anhydride-3-sulfonate, achieving an HF-30D of 410.5 ppm, a gas production expansion rate of 4.46%, and a cycle count of only 1032, both significantly inferior to the performance of Example 1. This demonstrates that the succinic anhydride-3-sulfonic acid additives designed in this invention have greater advantages in suppressing side reactions and optimizing interfacial properties.

[0053] The synergistic effect of vinylene carbonate, fluoroethylene carbonate, sodium salt additives, and succinic anhydride-3-sulfonic acid additives is a crucial prerequisite for ensuring the long-cycle and high-temperature stability of the battery. When the four additives coexist, the polycarbonate formed by fluoroethylene carbonate and vinylene carbonate inhibits excessive SEI film growth, the sodium salt additive helps optimize ion transport, and the succinic anhydride-3-sulfonic acid additive improves interfacial reactions. The synergistic effect of these multiple components enables the battery to maintain excellent performance under high-temperature cycling at 45°C and high-temperature storage at 60°C, making it suitable for a wide application temperature range of -40°C to 60°C.

[0054] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An electrolyte additive, characterized in that, This includes vinylene carbonate, fluorovinyl carbonate, sodium salt additives, and succinic anhydride-3-sulfonic acid additives, wherein the succinic anhydride-3-sulfonic acid additives include compounds having the structure shown in Formula 1 below: Wherein, R is selected from one of the following: halogen atom, C1-C20 haloalkoxy / haloalkyl, C1-C20 isocyanate / aniline / amino, C1-C20 alkoxy / alkeneoxy / silanoxy, and C1-C20 alkyl / acyl / ether.

2. The electrolyte additive according to claim 1, characterized in that, The succinic anhydride-3-sulfonic acid additives include at least one of additive A, additive B, or additive C having the structure shown in formulas A, B, and C: 。 3. The electrolyte additive according to claim 2, characterized in that, The succinic anhydride-3-sulfonic acid additives include additives A, B, and C in a mass ratio of (0.1–2.0):(0.1–2.0):(0.1–2.0).

4. The electrolyte additive according to any one of claims 1, characterized in that, The sodium salt additive includes at least one of sodium difluorophosphate, sodium bis(oxalate)borate, sodium di(oxalate)borate, and sodium di(oxalate)phosphate.

5. The electrolyte additive according to any one of claims 1, characterized in that, The mass ratio of vinylene carbonate, fluorovinyl carbonate, sodium salt additive, and succinic anhydride-3-sulfonic acid additive is (0.5-1.5):(0.5-4.5):(0.5-1.5):(0.5-2.5).

6. A sodium-ion battery electrolyte, characterized in that, The electrolyte comprises, by mass fraction of 100%, the following components in mass fraction: sodium salt 13-25%, organic solvent 65-85%, and electrolyte additive 2.0-10.0%; wherein the electrolyte additive is the electrolyte additive according to any one of claims 1-5.

7. The sodium-ion battery electrolyte according to claim 6, characterized in that, The sodium salt includes at least one of sodium hexafluorophosphate, sodium difluorosulfonamide, sodium difluoromethanesulfonamide, sodium perchlorate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, and sodium nitrate.

8. The sodium-ion battery electrolyte according to claim 6 or 7, characterized in that, The concentration of the sodium salt in the electrolyte is 0.7–1.4 mol / L.

9. The sodium-ion battery electrolyte according to claim 6, characterized in that, The organic solvent includes at least one of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

10. A sodium-ion battery, characterized in that, The sodium-ion battery electrolyte comprises any one of claims 6-9; the sodium-ion battery is a sodium-ion layered oxide system battery.

Images