A long-circulation lithium / sodium ion battery electrolyte capable of solubilizing a strong coordination salt, a preparation method and applications thereof

Abstract

The application provides a long-circulation lithium / sodium ion battery electrolyte capable of solubilizing a strong coordination salt, a preparation method and application, and comprises a conventional lithium / sodium salt, a strong coordination salt, an organic solvent and a solubilizer; the strong coordination salt is lithium / sodium nitrate, lithium / sodium trifluoroacetate, lithium / sodium carbonate, lithium / sodium fluoride and lithium / sodium chloride; and the solubilizer is ethylene sulfate, N-methyl acetamide and propylene sulfate. By using the electrolyte, the solubility of the strong coordination salt in the conventional solvent system is significantly improved, the solubility of sodium nitrate can be increased from less than 0.1 mol / L to more than 2.0 mol / L, and high-concentration rapid dissolution can be achieved. When the electrolyte is matched with a polyanion and a layered oxide positive electrode material, the cycle stability is greatly improved, the average coulombic efficiency is close to 100%, and the electrolyte exhibits excellent cycle performance and rate performance in a soft package battery, and is suitable for the field of lithium / sodium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a long-cycle lithium / sodium-ion battery electrolyte that can solubilize strong coordination salts, its preparation method, and its application. Background Technology

[0002] Lithium-ion and sodium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems. The electrolyte, as a key component of the battery, directly affects its cycle life and safety.

[0003] Currently, conventional electrolytes typically use lithium hexafluorophosphate or sodium hexafluorophosphate as electrolyte salts, dissolved in carbonate solvents. However, a single salt system cannot simultaneously meet the requirements of high conductivity, a wide electrochemical window, and good interfacial stability. Therefore, researchers have attempted to introduce functional, highly coordinating salts such as nitrates, trifluoroacetates, and carbonates. These salts can participate in SEI film formation at the electrode interface, improving interfacial stability.

[0004] However, existing technologies have significant shortcomings: strongly coordinated salts generally have low solubility in conventional carbonate solvents. For example, nitrates typically have a solubility of less than 0.1 mol / L in conventional solvents, making effective addition difficult. Furthermore, the introduction of strongly coordinated salts can easily lead to salt precipitation or decomposition, affecting battery cycle performance. Simply mixing conventional salts with strongly coordinated salts is insufficient to achieve synergistic optimization and fully leverage the interfacial regulation advantages of strongly coordinated salts. Therefore, developing an electrolyte system that can significantly improve the solubility of strongly coordinated salts while maintaining good overall electrolyte performance has significant practical value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the prior art and to provide a long-cycle lithium / sodium ion battery electrolyte, preparation method and application that can solubilize strong coordination salts, at least solving one of the problems of low solubility of strong coordination salts in conventional solvent systems, narrow electrochemical window and difficulty in exerting the advantages of interface regulation in the prior art.

[0006] In a first aspect, the present invention provides a long-cycle lithium / sodium-ion battery electrolyte that can solubilize a strong coordination salt, comprising a conventional lithium / sodium salt, a strong coordination salt, an organic solvent, and a solubilizer.

[0007] The conventional lithium / sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaOTF), sodium difluorosulfonamide (NaFSI), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiOTF), and lithium difluorosulfonamide (LiFSI), and its concentration in the electrolyte is 1.0 mol / L.

[0008] The strong coordinating salt is at least one of sodium nitrate (NaNO3), sodium trifluoroacetate (NaTFA), sodium carbonate (Na2CO3), sodium fluoride (NaF), sodium chloride (NaCl), lithium nitrate (LiNO3), lithium trifluoroacetate (LiTFA), lithium carbonate (Li2CO3), lithium fluoride (LiF), and lithium chloride (LiCl), and its concentration in the electrolyte is 0.1–2.0 mol / L.

[0009] The organic solvent is at least one selected from ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl 2,2-difluoroacetate (DFEA), diethyl carbonate (DEC), diethyl sulfate (DES), methyl propionate (MP), ethyl acetate (EA), trimethyl phosphate (TMP), and triethyl phosphate (TEP). The type and ratio of the organic solvent can be adjusted according to actual needs to obtain suitable physicochemical properties.

[0010] The solubilizer is at least one of vinyl sulfate DTD, N-methylacetamide NMA, and propylene sulfate PTD, and its mass percentage in the electrolyte is 3%–10%. The role of the solubilizer is to regulate the charge distribution of the solvent system through intermolecular interactions, improve the solubility of strong coordination salts, and participate in the construction of interfacial films to improve the stability of the electrode interface.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned electrolyte, comprising the following steps: ① Ethylene carbonate is heated to 40-80℃ and melted into a liquid state. It is then mixed with methyl propionate and trimethyl phosphate in a set volume ratio and stirred until homogeneous to obtain a mixed solvent. ② Under an inert atmosphere, add conventional lithium / sodium salts to the mixed solvent in step (1) in 3–5 portions, control the dissolution temperature at 20–100 °C, and the stirring speed at 100–1000 rpm until completely dissolved; ③ Add solubilizer to the solution obtained in step ② and continue stirring for 0.5–24 h until the mixture is homogeneous; ④ Add the strongly coordinating salt to the solution in step ③ in 3-5 portions, stirring until completely dissolved to obtain crude electrolyte; ⑤ Add molecular sieves to the crude electrolyte from step ④, let it stand for 12–48 hours to remove water, and then filter to obtain the electrolyte.

[0012] In the above preparation method, the purpose of adding conventional lithium / sodium salt and solubilizer in stages is to prevent excessively high local concentrations from causing dissolution difficulties and to prevent the exothermic effect from causing hydrolysis of the electrolyte salt. The sequential design of dissolving the conventional salt and solubilizer first, and then adding the strong coordination salt, is beneficial for the solubilizer to interact with the solvent molecules in advance, creating a favorable environment for the dissolution of the strong coordination salt, which can accelerate the dissolution rate.

[0013] Thirdly, the present invention provides a lithium-ion battery or a sodium-ion battery comprising the above-mentioned electrolyte.

[0014] The positive electrode material of the battery is selected from at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), nickel-cobalt-manganese ternary cathode (NCM), sodium vanadium phosphate (Na3V2(PO4)3), sodium vanadium fluoride phosphate (Na3V2O2(PO4)2F), sodium iron sulfate (Na2Fe2(SO4)3), sodium-containing Prussian blue analogue (PB), and sodium-containing layered oxide (NFM).

[0015] The negative electrode material of the battery is selected from at least one of lithium metal, sodium metal, hard carbon, graphite, and silicon-carbon negative electrodes.

[0016] The separator of the battery is selected from at least one of PP, PE or glass fiber separators with a thickness of 1-300 μm.

[0017] Regarding the working principle of solubilizers, the present invention provides the following explanation: The solubilizer selected in this invention contains strongly polar functional groups (such as S=O bonds and amide bonds), which can undergo dipole-dipole interactions with organic solvents, improving miscibility and homogenizing charge distribution. This molecular-level rearrangement generates an entropy increase effect, providing more favorable thermodynamic conditions for the dissolution of strongly coordinated salts, resulting in solubility far exceeding that of conventional systems; simultaneously, it enhances solvation capability, ensuring stable dissolution of high-concentration salts. Furthermore, the solubilizer and the strongly coordinated salt work synergistically at the interface to jointly construct a stable organic-inorganic composite SEI film, effectively suppressing side reactions and improving battery cycle stability.

[0018] Compared with the prior art, the present invention has the following beneficial effects: First, it significantly improves the solubility of strongly coordinated salts. Using the solubilizer of this invention, the solubility of strongly coordinated salts in conventional solvent systems is greatly increased. Taking sodium nitrate as an example, its solubility in conventional carbonate solvents can be increased from less than 0.1 mol / L to more than 2.0 mol / L, achieving high-concentration stable dissolution of strongly coordinated salts and providing a prerequisite for fully leveraging their interfacial regulation effects.

[0019] Second, it broadens the electrochemical stability window. The electrolyte of this invention has an electrochemical stability window exceeding 4.7 V, which can be matched with high-voltage cathode materials and meet the development requirements of high-energy-density batteries. Experiments show that the oxidation decomposition potential of sodium-ion batteries using the electrolyte of this invention can reach 4.8 V, and that of lithium-ion batteries can reach 4.9 V.

[0020] Third, it improves interface stability. The solubilizer and the strong coordinating salt work synergistically at the electrode interface to participate in the construction of a structurally stable SEI film. Experiments show that after cycling, the electrode surface of the battery using the electrolyte of this invention is smooth and dense, without obvious dendrites and corrosion pits, effectively suppressing the side reactions between the electrolyte and the electrode material.

[0021] Fourth, the preparation process is simple. The electrolyte of this invention adopts a conventional mixing and dissolution process, which does not require complex equipment or harsh conditions, making it easy to achieve large-scale production and widespread application.

[0022] Fifth, it has a wide range of applications. The electrolyte of this invention can be used in both lithium-ion and sodium-ion batteries, and is compatible with a variety of positive and negative electrode material systems, exhibiting excellent comprehensive performance in both coin cells and pouch cells. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0024] Figure 1 This is the electrochemical window for the embodiments and comparative examples in this invention; Figure 2 The figures show the long-cycle performance of Na||NVP batteries at 1.0 C rate obtained from the embodiments and comparative examples of the present invention. Figure 3 The graph shows the long-cycle performance of the NFM||HC pouch cell obtained in the embodiment of the present invention at 0.5 A. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] Example 1 This embodiment provides a sodium-ion battery electrolyte that can solubilize a strong coordination salt. The electrolyte composition is as follows: NaPF6 is used as a conventional sodium salt with a concentration of 1.0 mol / L; NaNO3 is used as a strong coordination salt with a concentration of 1.5 mol / L; ethylene carbonate EC, methyl propionate MP, and trimethyl phosphate TMP are used as organic solvents with a volume ratio of EC:MP:TMP = 5:7:8; and ethylene sulfate DTD is used as a solubilizer with a mass percentage of 5%.

[0027] The specific preparation steps of the electrolyte in this embodiment are as follows: (1) Heat EC in a 45 °C metal bath until it is completely melted into a liquid state, and mix it with MP and TMP in a volume ratio of 5:7:8. Stir well to obtain a mixed solvent. (2) In an argon atmosphere glove box, add the conventional sodium salt into the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add the strong coordinating salt to the above solution in three portions and stir at 500 rpm for 30 minutes until completely dissolved; (5) Add an appropriate amount of molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0028] Example 2 This embodiment provides a sodium-ion battery electrolyte that can solubilize a strong coordination salt. The electrolyte composition is as follows: NaPF6 is used as a conventional sodium salt with a concentration of 1.0 mol / L; NaNO3 is used as a strong coordination salt with a concentration of 2.0 mol / L; ethylene carbonate EC, methyl propionate MP, and trimethyl phosphate TMP are used as organic solvents with a volume ratio of EC:MP:TMP = 5:7:8; and ethylene sulfate DTD is used as a solubilizer with a mass percentage of 15%.

[0029] The preparation steps of the electrolyte in this embodiment are the same as those in Example 1.

[0030] Example 3 This embodiment provides a sodium-ion battery electrolyte containing two strong coordination salts. The electrolyte composition is as follows: NaPF6 is used as a conventional sodium salt with a concentration of 1.0 mol / L; NaNO3 and NaF are used as strong coordination salts with concentrations of 0.8 mol / L and 0.3 mol / L, respectively; ethylene carbonate EC, fluoroethylene carbonate FEC, methyl propionate MP, and trimethyl phosphate TMP are used as organic solvents with a volume ratio of EC:FEC:MP:TMP=4:1:7:8; and ethylene sulfate DTD is used as a solubilizer with a mass percentage of 6%.

[0031] The specific preparation steps of the electrolyte in this embodiment are as follows: (1) Heat EC and FEC in a 45°C metal bath until they are completely melted into a liquid state, and mix them with MP and TMP in a volume ratio and stir evenly to obtain a mixed solvent; (2) In an argon atmosphere glove box, add the conventional sodium salt into the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add the strong coordinating salt to the above solution in four alternating portions, and stir at 500 rpm for 30 minutes until completely dissolved; (5) Add molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0032] Example 4 This embodiment provides a low-viscosity sodium-ion battery electrolyte containing different strong coordination salts. The electrolyte composition is as follows: NaFSI is used as a conventional sodium salt with a concentration of 1.0 mol / L; NaTFA is used as a strong coordination salt with a concentration of 1.2 mol / L; ethylene carbonate EC, ethyl acetate EA, and trimethyl phosphate TMP are used as organic solvents with a volume ratio of EC:EA:TMP=5:7:8; and ethylene sulfate DTD is used as a solubilizer with a mass percentage of 5%.

[0033] The preparation steps of the electrolyte in this embodiment are the same as those in Example 1.

[0034] Example 5 This embodiment provides a sodium-ion battery electrolyte with an adjustable solvent ratio. The electrolyte composition is as follows: NaPF6 is used as a conventional sodium salt with a concentration of 1.0 mol / L; NaNO3 is used as a strong coordinating salt with a concentration of 1.5 mol / L; ethylene carbonate EC, methyl propionate MP, and trimethyl phosphate TMP are used as organic solvents with a volume ratio of EC:MP:TMP = 5:5:5; and ethylene sulfate DTD is used as a solubilizer with a mass percentage of 6%.

[0035] The preparation steps of the electrolyte in this embodiment are the same as those in Example 1.

[0036] Example 6 This embodiment provides a sodium-ion battery electrolyte with NaFSI as the conventional electrolyte salt. The electrolyte composition is as follows: NaFSI is used as the conventional sodium salt with a concentration of 1.0 mol / L; NaNO3 and NaTFA are used as strong coordinating salts with concentrations of 1.2 mol / L and 0.3 mol / L, respectively; fluoroethylene carbonate (FEC), methyl propionate (MP), and trimethyl phosphate (TMP) are used as organic solvents with a volume ratio of FEC:MP:TMP = 5:7:8; and ethylene sulfate (DTD) is used as a solubilizer with a mass percentage of 7%.

[0037] The specific preparation steps of the electrolyte in this embodiment are as follows: (1) Mix FEC with MP and TMP in a volume ratio of 5:7:8 and stir until homogeneous to obtain a mixed solvent; (2) In an argon atmosphere glove box, add the conventional sodium salt into the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add the strong coordinating salt to the above solution in four alternating portions, and stir at 500 rpm for 30 minutes until completely dissolved; (5) Add molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0038] Example 7 This embodiment provides a sodium-ion battery electrolyte incorporating a sulfate ester solvent. The electrolyte composition is as follows: NaClO4 is used as a conventional sodium salt with a concentration of 1.0 mol / L; NaNO3 is used as a strong coordinating salt with a concentration of 1.5 mol / L; ethylene carbonate (EC), diethyl sulfate (DES), and trimethyl phosphate (TMP) are used as organic solvents with a volume ratio of EC:DES:TMP = 5:7:8; and N-methylacetamide (NMA) is used as a solubilizer with a mass percentage of 5%.

[0039] The specific preparation steps of the electrolyte in this embodiment are as follows: (1) Heat EC in a 25 °C metal bath until it is completely melted into a liquid state, and mix it with DES and TMP in a volume ratio of 5:7:8. Stir well to obtain a mixed solvent. (2) In an argon atmosphere glove box, add the conventional sodium salt into the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add the strong coordinating salt to the above solution in three portions and stir at 500 rpm for 6 hours until completely dissolved; (5) Add an appropriate amount of molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0040] Example 8 This embodiment provides a lithium-ion battery electrolyte that can be enriched with a strong coordination salt. The electrolyte composition is as follows: LiPF6 is used as a conventional lithium salt with a concentration of 1.0 mol / L; LiNO3 is used as a strong coordination salt with a concentration of 1.2 mol / L; ethylene carbonate EC, diethyl carbonate DEC, and triethyl phosphate TEP are used as organic solvents with a volume ratio of EC:DEC:TEP=5:7:8; and ethylene sulfate DTD is used as a solubilizer with a mass percentage of 4%.

[0041] The specific preparation steps of the electrolyte in this embodiment are as follows: (1) Heat EC in a 40 °C metal bath until it is completely melted into a liquid state, and mix it with DEC and TEP in a volume ratio of 5:7:8. Stir well to obtain a mixed solvent; (2) In an argon atmosphere glove box, add the conventional lithium salt to the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add the strong coordinating salt to the above solution in three portions and stir at 500 rpm for 8 hours until completely dissolved; (5) Add an appropriate amount of molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0042] Example 9 This embodiment provides a lithium-ion battery electrolyte containing a ternary strong coordination salt. The electrolyte composition is as follows: LiPF6 is used as a conventional lithium salt with a concentration of 1.0 mol / L; LiNO3, LiTFA, and LiF are used as strong coordination salts with concentrations of 0.6 mol / L, 0.4 mol / L, and 0.2 mol / L, respectively; ethylene carbonate (EC), diethyl carbonate (DEC), and triethyl phosphate (TEP) are used as organic solvents with a volume ratio of EC:DEC:TEP = 5:7:8; and ethylene sulfate (N-methylacetamide, NMA) is used as a solubilizer with a mass percentage of 20%.

[0043] The specific preparation steps of the electrolyte in this embodiment are as follows: (1) Heat EC in a 50 °C metal bath until it is completely melted into a liquid state, and mix it with DEC and TEP in a volume ratio of 5:7:8. Stir well to obtain a mixed solvent; (2) In an argon atmosphere glove box, add the conventional lithium salt to the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add the strong coordinating salt to the above solution in three portions and stir at 500 rpm for 10 hours until completely dissolved; (5) Add an appropriate amount of molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0044] Example 10 This embodiment provides a lithium-ion battery electrolyte suitable for high-rate applications. The electrolyte composition is as follows: LiFSI is used as a conventional lithium salt with a concentration of 1.0 mol / L; LiNO3 and LiTFA are used as strong coordinating salts with concentrations of 1.0 mol / L and 0.3 mol / L, respectively; ethylene carbonate EC, ethyl acetate EA, and triethyl phosphate TEP are used as organic solvents with a volume ratio of EC:EA:TEP=5:7:8; and propylene sulfate PTD is used as a solubilizer with a mass percentage of 6%.

[0045] The specific preparation steps of the electrolyte in this embodiment are as follows: (1) Heat EC in a 40 °C metal bath until it is completely melted into a liquid state, and mix it with EA and TEP in a volume ratio of 5:7:8. Stir well to obtain a mixed solvent. (2) In an argon atmosphere glove box, add the conventional lithium salt to the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add the strong coordinating salt to the above solution in three portions and stir at 500 rpm for 8 hours until completely dissolved; (5) Add an appropriate amount of molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0046] Example 11 This embodiment provides a lithium-ion battery electrolyte suitable for a wide temperature range. The electrolyte composition is as follows: LiPF6 is used as a conventional lithium salt with a concentration of 1.0 mol / L; LiNO3, LiTFA, and LiF are used as strong coordinating salts with concentrations of 0.8 mol / L, 0.3 mol / L, and 0.2 mol / L, respectively; ethylene carbonate (EC), ethyl 2,2-difluoroacetate (DFEA), and triethyl phosphate (TEP) are used as organic solvents with a volume ratio of EC:DFEA:TEP = 5:7:8; and ethylene sulfate (DTD) and N-methylacetamide (NMA) are used as solubilizers with mass percentages of 4% and 3%, respectively.

[0047] The specific preparation steps of the electrolyte in this embodiment are as follows: (1) Place EC and NMA in a 45 °C metal bath and heat until completely melted into a liquid state. Mix them with DFEA and TEP in a volume ratio of 5:7:8 and stir until homogeneous to obtain a mixed solvent. (2) In an argon atmosphere glove box, add the conventional lithium salt to the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add the strong coordinating salt to the above solution in 5 alternating portions, and stir at 500 rpm for 40 minutes until completely dissolved; (5) Add molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0048] Comparative Example 1 This comparative example provides a conventional sodium-ion battery electrolyte without solubilizers. The electrolyte composition is as follows: NaPF6 as the conventional sodium salt with a concentration of 1.0 mol / L; ethylene carbonate EC, methyl propionate MP, and trimethyl phosphate TMP as organic solvents with a volume ratio of EC:MP:TMP=5:7:8; and NaNO3 with a concentration of 1.5 mol / L.

[0049] The specific preparation steps of the electrolyte in this comparative example are as follows: (1) Heat EC in a 45 °C metal bath until it is completely melted into a liquid state, and mix it with MP and TMP in a volume ratio of 5:7:8. Stir well to obtain a mixed solvent. (2) In an argon atmosphere glove box, add the conventional sodium salt into the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) When NaNO3 was added to the above solution to a concentration of 1.5 mol / L and stirred at 500 rpm for 12 h, there was still obvious precipitation and it could not be effectively dissolved; (4) Add an appropriate amount of molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0050] Comparative Example 2 This comparative example provides a conventional sodium-ion battery electrolyte that does not contain a strong coordinating salt. The electrolyte composition is as follows: NaPF6 is used as the conventional sodium salt with a concentration of 1.0 mol / L; ethylene carbonate EC, methyl propionate MP, and trimethyl phosphate TMP are used as organic solvents, and the volume ratio of the three is EC:MP:TMP=5:7:8.

[0051] The specific preparation steps of the electrolyte in this comparative example are as follows: (1) Heat EC in a 45 °C metal bath until it is completely melted into a liquid state, and mix it with MP and TMP in a volume ratio of 5:7:8. Stir well to obtain a mixed solvent. (2) In an argon atmosphere glove box, add the conventional sodium salt into the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add an appropriate amount of molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0052] Comparative Example 3 This comparative example provides a sodium-ion battery electrolyte with excessively low solubilizer content. The electrolyte composition is as follows: NaPF6 as the conventional sodium salt with a concentration of 1.0 mol / L; ethylene carbonate EC, methyl propionate MP, and trimethyl phosphate TMP as organic solvents with a volume ratio of EC:MP:TMP=5:7:8; ethylene sulfate DTD as the solubilizer with a mass percentage of 1%; and NaNO3 with a concentration of 1.5 mol / L.

[0053] The specific preparation steps of the electrolyte in this comparative example are as follows: (1) Heat EC in a 45 °C metal bath until it is completely melted into a liquid state, and mix it with MP and TMP in a volume ratio of 5:7:8. Stir well to obtain a mixed solvent. (2) In an argon atmosphere glove box, add the conventional sodium salt into the mixed solvent in three portions and stir at 500 rpm until completely dissolved; (3) Add the solubilizer and continue stirring for 30 minutes until the mixture is homogeneous; (4) Add NaNO3 to the above solution until its concentration reaches 1.5 mol / L. After stirring at 500 rpm for 12 hours, the solution is still slightly turbid. After standing, a small amount of precipitate appears at the bottom. The actual concentration of NaNO3 dissolved is about 1.0 mol / L. (5) Add an appropriate amount of molecular sieve, let stand for 24 hours to remove water, and obtain electrolyte.

[0054] Comparative Example 4 This comparative example provides a sodium-ion battery electrolyte with excessive solubilizer content. The electrolyte composition is as follows: NaPF6 as the conventional sodium salt with a concentration of 1.0 mol / L; ethylene carbonate EC, methyl propionate MP, and trimethyl phosphate TMP as organic solvents with a volume ratio of EC:MP:TMP=5:7:8; ethylene sulfate DTD as the solubilizer with a mass percentage of 25%; and NaNO3 with a concentration of 1.5 mol / L.

[0055] The specific preparation steps of the electrolyte in this comparative example are the same as those in comparative example 3. The results show that NaNO3 can be completely dissolved, but the viscosity of the electrolyte increases significantly and the ionic conductivity decreases.

[0056] Performance testing 1. Solubility test The actual dissolution of the strong coordination salts in Examples 1-11 and Comparative Examples 1-4 was tested respectively, and the results are shown in Table 1.

[0057] Table 1. Results of solubility test of strongly coordinated salts As can be seen from Table 1: In Examples 1-11 using the solubilizer of this invention, all strongly coordinated salts were completely dissolved, and the actual dissolved concentration reached the target value. The dissolved concentration of NaNO3 reached 2.0 mol / L, which is more than 20 times higher than the <0.1 mol / L of Comparative Example 1, indicating that the solubilizer has a significant solubilizing effect on strongly coordinated salts.

[0058] Examples 3, 6, 9, and 11 demonstrate that both di- and tri-salt systems can achieve complete dissolution, indicating that the solubilizer of this invention is universally applicable to various strong coordination salt combinations. Examples 4 and 10 use the low-viscosity solvent EA, which reduces system viscosity while achieving complete dissolution, thus improving rate performance. Comparative Example 1 shows that strong coordination salts cannot dissolve without the solubilizer, confirming that the solubilizer is a key component for improving the solubility of strong coordination salts. Comparative Example 3 shows that when the solubilizer content is too low (1%), the solubilization effect is insufficient, with an actual dissolved concentration of only about 1.0 mol / L; Comparative Example 4 shows that while a high solubilizer content (25%) can achieve complete dissolution, it leads to a significant increase in viscosity. Therefore, the preferred solubilizer content range of 3%–20% in this invention achieves a good balance between high solubility and suitable viscosity.

[0059] 2. Battery performance testing 2.1 Cycle performance test of button cells For the sodium-ion battery system, Na||Na3V2(PO4)3 coin cells were assembled using the electrolytes of Examples 1-4 and Comparative Examples 1-4, respectively. Charge-discharge tests were conducted in the voltage range of 2.5-4.0 V and the current density was 1 C (1 C = 117 mAh / g). The results are shown in Table 3.

[0060] For the lithium-ion battery system, Li||LiFePO4 coin cells were assembled using the electrolytes of Examples 8-11 and Comparative Example 2 (sodium salt was replaced with lithium salt), respectively. Charge-discharge tests were conducted in the voltage range of 2.5-4.0 V and the current density was 1 C (1 C = 170 mAh / g). The results are shown in Table 3.

[0061] Table 2 Cycle performance of Na||Na3V2(PO4)3 coin cells Table 3 Cycle performance of Li||LiFePO4 coin cells As can be seen from Table 2: In sodium-ion battery systems, the Na||Na3V2(PO4)3 coin cells assembled using the electrolyte of this invention in Examples 1-7 all exhibited a capacity retention rate of over 97.0% and an average coulombic efficiency of over 99.5% after 300 cycles, demonstrating excellent cycle stability.

[0062] Compared to Comparative Example 2 (without strong coordination salt, capacity retention of 94.1%), the cycling performance of Examples 1-7 was significantly improved, confirming that the introduction of strong coordination salt effectively improved electrode interface stability. In Comparative Example 1, the battery could not charge and discharge normally due to undissolved NaNO3, further demonstrating that complete dissolution of the strong coordination salt is a necessary prerequisite for achieving its interface optimization function. Comparative Example 3 (1% solubilizer content) had a capacity retention of only 84.8%, and Comparative Example 4 (25% solubilizer content) had a capacity retention of 96.0%, both significantly worse than the 99.0% of Example 1, indicating that both excessively low and excessively high solubilizer content have adverse effects on cycling performance.

[0063] As can be seen from Table 3: For lithium-ion battery systems, the Li||LiFePO4 coin cells assembled using the electrolyte of this invention in Examples 8-11 all exhibited a capacity retention rate of over 98% and an average coulombic efficiency of over 99.8% after 200 cycles, demonstrating excellent cycle stability.

[0064] Compared with Comparative Example 2 (lithium system, without strong coordination salt, capacity retention of 90.5%, coulombic efficiency of 96.6%), the cycle performance and coulombic efficiency of Examples 8-11 are significantly improved, confirming that the technical solution of the present invention is also applicable to lithium-ion battery systems.

[0065] From the examples: Example 9 introduced a ternary strong coordination salt system of LiTFA and LiF, increasing the capacity retention to 98.8%; Example 10 used LiFSI and PTD as solubilizers, achieving an initial capacity of 161.4 mAh / g; Example 11 introduced DFEA fluorinated solvent and DTD+NMA composite solubilizers, further increasing the initial capacity to 163.8 mAh / g with a capacity retention of 98.2%. Example 10 used the low-viscosity solvent EA, and Example 11 used the fluorinated solvent DFEA, both exhibiting excellent cycling performance, indicating that the electrolyte of this invention has good adaptability in different solvent systems.

[0066] In summary, the electrolyte provided by this invention, which can dissolve strong coordination salts, significantly improves the solubility of strong coordination salts, enhances interfacial stability, and improves battery cycle performance by introducing an appropriate amount of solubilizer. Moreover, the preparation process is simple and applicable to various systems, salt combinations, and solvent systems of lithium-ion and sodium-ion batteries, thus possessing significant practical value and broad application prospects.

[0067] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A long-cycle lithium / sodium ion battery electrolyte capable of solubilizing strong coordination salts, characterized in that: This includes conventional lithium / sodium salts, strong coordination salts, organic solvents, and solubilizers.

2. The long-cycle lithium / sodium ion battery electrolyte with solubility for strong coordination salts according to claim 1, characterized in that, The conventional lithium / sodium salt is at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaOTF), sodium difluorosulfonamide (NaFSI), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiOTF), and lithium difluorosulfonamide (LiFSI).

3. The long-cycle lithium / sodium ion battery electrolyte with solubility for strong coordination salts according to claim 1, characterized in that, The strong coordinating salt is at least one of sodium nitrate (NaNO3), sodium trifluoroacetate (NaTFA), sodium carbonate (Na2CO3), sodium fluoride (NaF), sodium chloride (NaCl), lithium nitrate (LiNO3), lithium trifluoroacetate (LiTFA), lithium carbonate (Li2CO3), lithium fluoride (LiF), and lithium chloride (LiCl).

4. The long-cycle lithium / sodium ion battery electrolyte with solubility for strong coordination salts according to claim 1, characterized in that, The organic solvent is at least one of ethylene carbonate EC, fluoroethylene carbonate FEC, ethyl 2,2-difluoroacetate DFEA, diethyl carbonate DEC, diethyl sulfate DES, methyl propionate MP, ethyl acetate EA, trimethyl phosphate TMP, and triethyl phosphate TEP.

5. The long-cycle lithium / sodium ion battery electrolyte with solubility for strong coordination salts according to claim 1, characterized in that, The solubilizer is at least one of vinyl sulfate DTD, N-methylacetamide NMA, and propylene sulfate PTD.

6. The long-cycle lithium / sodium ion battery electrolyte with solubility for strong coordination salts according to claim 1, characterized in that, The concentration of the conventional lithium / sodium salt in the electrolyte is 1.0 mol / L; the concentration of the strong coordination salt in the electrolyte is 0.1–2.0 mol / L.

7. The long-cycle lithium / sodium ion battery electrolyte with solubility for strong coordination salts according to claim 1, characterized in that, The solubilizer has a mass percentage content of 3%–20% in the electrolyte.

8. A method for preparing a long-cycle lithium / sodium-ion battery electrolyte as described in any one of claims 1-7, characterized in that, Includes the following steps: ① Ethylene carbonate is heated to 40-80℃ and melted into a liquid state. It is then mixed with methyl propionate and trimethyl phosphate in a set volume ratio and stirred until homogeneous to obtain a mixed solvent. ② Under an inert atmosphere, add conventional lithium / sodium salts to the mixed solvent in step (1) in 3–5 portions, control the dissolution temperature at 20–100 °C, and the stirring speed at 100–1000 rpm until completely dissolved; ③ Add solubilizer to the solution obtained in step ② and continue stirring for 0.5–24 h until the mixture is homogeneous; ④ Add the strongly coordinating salt to the solution in step ③ in 3-5 portions, and stir until completely dissolved to obtain crude electrolyte; ⑤ Add molecular sieves to the crude electrolyte from step ④, let it stand for 12–48 hours to remove water, and then filter to obtain the electrolyte.

9. A lithium-ion battery or sodium-ion battery, characterized in that, Long-cycle lithium / sodium-ion battery electrolyte comprising the solubilizable strong coordination salt as described in any one of claims 1-8.

10. A lithium-ion battery or sodium-ion battery according to claim 9, characterized in that: The positive electrode is selected from at least one of lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), nickel-cobalt-manganese ternary cathode (NCM), sodium vanadium phosphate (Na3V2(PO4)3), sodium vanadium fluoride phosphate (Na3V2O2(PO4)2F), sodium iron sulfate (Na2Fe2(SO4)3), sodium-containing Prussian blue analogue (PB), and sodium-containing layered oxide (NFM); the negative electrode is selected from at least one of lithium metal / sodium, hard carbon, graphite, and silicon-carbon negative electrodes; and the separator is selected from at least one of PP, PE, or glass fiber separators with a thickness of 1–300 μm.

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