Sodium-ion battery electrolyte with low self-discharge

Abstract

The application discloses a low-self-discharge sodium ion battery electrolyte, which comprises an ether organic solvent, an electrolyte sodium salt and an additive, wherein the additive is a carbonate additive, a sulfate additive or a salt additive; the carbonate additive is one or more than two of fluoroethylene carbonate, ethylene carbonate and / or vinylene carbonate; the sulfate additive is one or more than two of 1,3-propane sulfonic acid lactone, 1,3-butane sulfonic acid lactone and / or propylene sulfate; and the salt additive is sodium bis(fluorosulfonyl)imide and / or sodium bis(trifluoromethylsulfonyl)imide. The sodium ion battery assembled by the low-self-discharge electrolyte has the characteristics of high stability, good solvation effect and excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery electrolyte technology, specifically to a sodium-ion battery electrolyte with low self-discharge. Background Technology

[0002] The concept of sodium-ion batteries was proposed in 1970-1980 and, along with lithium-ion batteries, received widespread attention. Compared to lithium-ion batteries, sodium-ion batteries have abundant raw material reserves, lower costs, and higher safety, making them one of the ideal choices for energy storage. To date, many anode materials have been researched and reported, such as metal sulfides, metal oxides, alloys, organic materials, and carbon-based materials. Among these, carbon-based materials offer cost-effectiveness and excellent overall electrochemical performance, showing broad prospects for industrial applications.

[0003] Based on the stacking pattern of carbon layers, carbon materials can be classified into four categories: graphite, graphene, soft carbon, and hard carbon. Among them, hard carbon, with its high reversible capacity and first-efficiency, is considered the most mature and currently the only material potentially commercially viable. Hard carbon possesses abundant sodium storage sites, including sodium ion adsorption at open pores and defects, sodium ion insertion / intercalation between graphite layers, and sodium ion filling within micropores. Existing research has proposed sodium storage mechanisms such as "insertion-adsorption," "adsorption-insertion," "three-stage," and "adsorption-filling" to address the slope and plateau capacities of hard carbon.

[0004] Batteries with charge will experience some capacity loss after being stored at a certain temperature for a period of time, a phenomenon known as self-discharge. Taking hard carbon as an example, when the hard carbon electrode is in a sodium-storage state, the sodium ions filling the micropores are relatively stable, while sodium ions adsorbed on the surface and embedded between graphite layers will automatically detach or undergo side reactions with the electrolyte, resulting in capacity loss. Self-discharge of sodium-ion batteries reduces battery life and hinders their further development.

[0005] In sodium-ion batteries, hard carbon is often used with ester-based electrolytes, while ether-based electrolytes offer superior rate and cycle performance and good compatibility with hard carbon, attracting widespread attention. However, hard carbon exhibits significantly stronger self-discharge in ether-based electrolytes than in ester-based electrolytes, leading to severe capacity loss and shortened battery life. The main reason for this is the loose and complex SEI layer formed by ether-based electrolytes, which causes continuous side reactions between the hard carbon and the electrolyte.

[0006] To effectively suppress the self-discharge of sodium-ion batteries, methods such as purifying electrode materials and modifying electrode surfaces are generally employed. Purifying electrode materials mainly refers to removing impurities from the material, while surface modification primarily includes pre-sodiumization. For hard carbon materials, purification and surface modification are costly, difficult to implement, and have low reproducibility. Summary of the Invention

[0007] The purpose of this invention is to provide a sodium-ion battery electrolyte with low self-discharge, and sodium-ion batteries assembled using this electrolyte have the characteristics of high stability, good solvation effect and excellent electrochemical performance.

[0008] This invention can be achieved through the following technical solutions:

[0009] This invention discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and additives. The additives are carbonate additives, sulfate additives, and / or salt additives. The carbonate additives are one or more of fluoroethylene carbonate, ethylene carbonate, and / or vinylene carbonate. The sulfate additives are one or more of 1,3-propanesulfonate lactone, 1,3-butanesulfonate lactone, and / or propylene sulfate. The salt additives are sodium bis(fluorosulfonyl)imide and / or sodium bis(trifluoromethylsulfonyl)imide.

[0010] This invention addresses electrolytes containing ether-based organic solvents by adding carbonate, sulfate, or salt additives to synergistically form a film with the electrolyte salt on the negative electrode surface. Carbonates can form a C=O-containing organic-inorganic composite SEI film with sodium hexafluorophosphate or sodium perchlorate through ring-opening polymerization or double-bond addition. Sulfate additives can form an S=O-containing organic-inorganic composite SEI film with sodium hexafluorophosphate or sodium perchlorate through ring-opening polymerization. Salt additives can undergo reduction reactions to form an inorganic SEI film containing Na-F or Na-Cl bonds with sodium hexafluorophosphate or sodium perchlorate. After adding these additives, a sodium salt-additive composite SEI film is formed on the hard carbon surface. This type of composite SEI film exhibits higher stability and toughness, more effectively isolating the electrolyte from contact with the hard carbon and reducing side reactions. Meanwhile, due to the addition of additives, sodium ions have an optimized solvation effect. The additional C=O bonds (carbonates), S=O bonds (sulfates), and F-containing functional groups (salts) introduced into the solvation outer layer enhance the interaction between sodium ions and hard carbon, and inhibit the release of sodium ions adsorbed on the surface and embedded in the graphite layers.

[0011] Furthermore, the amount of carbonate additives added is 0.5-5% of the volume of ether organic solvent (liquid additives), the amount of sulfate additives added is 0.5-5% of the mass of ether organic solvent (solid additives), and the molar ratio of the amount of salt additives added to the sodium electrolyte salt is 2:8-5:5.

[0012] Furthermore, the electrolyte sodium salt is sodium hexafluorophosphate and / or sodium perchlorate.

[0013] Furthermore, the ether organic solvent is diethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether.

[0014] Furthermore, the concentration of the sodium electrolyte salt in the electrolyte is 0.5–1.5 mol / L.

[0015] Furthermore, the cathode material of the sodium-ion battery is a Prussian blue-based material, a layered oxide material, and / or a polyanionic cathode material.

[0016] Furthermore, polyanionic cathode materials include phosphate cathode materials, pyrophosphate cathode materials, sulfate cathode materials, silicate cathode materials, and / or borate cathode materials.

[0017] Furthermore, the negative electrode material of sodium-ion batteries is hard carbon or metallic sodium.

[0018] Furthermore, sodium-ion batteries are hard carbon / sodium half-cells, sodium iron pyrophosphate / hard carbon full-cells, and sodium vanadium phosphate / hard carbon full-cells.

[0019] This invention provides a low self-discharge sodium-ion battery electrolyte, which has the following beneficial effects:

[0020] First, the SEI membrane has high stability. It is formed by the synergistic formation of electrolyte salt and additives in ether electrolytes, rather than by solvents. The resulting dense composite SEI membrane has superior mechanical and chemical properties, which can isolate hard carbon from the electrolyte and reduce side reactions.

[0021] Secondly, it has a good solvation effect. The solvation effect generated by adding a composite additive system introduces S=0, C=O and fluorine-containing functional groups, which can enhance the interaction between sodium ions and hard carbon and inhibit the release of sodium ions.

[0022] Third, it has excellent electrochemical performance. When sodium-ion batteries are assembled using the electrolyte of this invention, the self-discharge of hard carbon in ether electrolytes is greatly reduced, the capacity loss of sodium-ion batteries is reduced, and the capacity retention and lifespan of sodium-ion batteries are improved. Attached Figure Description

[0023] Figure 1 Discharge-charge-discharge performance diagram of Na / / 1M NaPF6 (diethylene glycol dimethyl ether) / / Japanese hard carbon battery;

[0024] Figure 2 The charging-discharging-charging performance of Na / / 1M NaPF6 (diethylene glycol dimethyl ether) / / Japanese hard carbon battery after being left to stand at 60℃ for 3 days in the discharge state.

[0025] Figure 3 Performance graph of Na / / 1M NaPF6 (diethylene glycol dimethyl ether) / / Japanese hard carbon battery after being left to stand at 60℃ for 6 days in discharge state;

[0026] Figure 4 Discharge-charge-discharge performance diagram of Na / / 1M NaPF6 (diethylene glycol dimethyl ether) + 2% fluoroethylene carbonate / / Japanese hard carbon battery;

[0027] Figure 5 The charging-discharging-charging performance of a Japanese hard carbon battery after being left to stand at 60°C for 3 days in a discharged state (Na / / 1M NaPF6 (diethylene glycol dimethyl ether) + 2% fluoroethylene carbonate) is shown in the figure.

[0028] Figure 6 The charging-discharging-charging performance of a Japanese hard carbon battery after being left to stand at 60°C for 6 days in a discharged state (Na / / 1M NaPF6 (diethylene glycol dimethyl ether) + 2% fluoroethylene carbonate) is shown in the figure.

[0029] Figure 7 Transmission electron microscope image of Na / / 0.5M NaPF6 (diethylene glycol dimethyl ether) / / Japanese hard carbon battery SEI;

[0030] Figure 8 Transmission electron microscope image of Na / / 0.5M NaPF6+0.5M NaTFSI (diethylene glycol dimethyl ether) / / Japanese hard carbon battery SEI. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0032] This invention discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and additives. The additives are carbonate additives, sulfate additives, and / or salt additives. The carbonate additives are one or more of fluoroethylene carbonate, ethylene carbonate, and / or vinylene carbonate. The sulfate additives are one or more of 1,3-propanesulfonate lactone, 1,3-butanesulfonate lactone, and / or propylene sulfate. The salt additives are sodium bis(fluorosulfonyl)imide and / or sodium bis(trifluoromethylsulfonyl)imide. Carbonates can form an organic-inorganic composite SEI film containing C=O bonds with sodium hexafluorophosphate or sodium perchlorate through ring-opening polymerization or double bond addition. Sulfate additives can form an organic-inorganic composite SEI film containing S=O bonds with sodium hexafluorophosphate or sodium perchlorate through ring-opening polymerization. Salt additives can undergo reduction reactions to form an inorganic SEI film containing Na-F or Na-Cl bonds with sodium hexafluorophosphate or sodium perchlorate. After adding the above additives, a sodium salt-additive composite SEI film is formed on the hard carbon surface. This type of composite SEI film has higher stability and toughness, and can more effectively isolate the electrolyte from the hard carbon, reducing the occurrence of side reactions. At the same time, due to the addition of additives, sodium ions have an optimized solvation effect. The additional C=O bonds (carbonates), S=O bonds (sulfate esters), and F-containing functional groups (salts) introduced into the solvation outer layer enhance the interaction between sodium ions and hard carbon, inhibiting the desorption of sodium ions adsorbed on the surface and embedded in the graphite layers.

[0033] Furthermore, the amount of carbonate additives added is 0.5–5% of the volume of ether organic solvent (liquid additives), the amount of sulfate additives added is 0.5–5% of the mass of ether organic solvent (solid additives), and the molar ratio of salt additives to electrolyte sodium salt is 2:8–5:5. Within a specific range, excessive additive addition results in overly strong film-forming ability and excessively thick films, reducing the battery's initial efficiency; insufficient additive addition prevents the formation of a dense and uniform SEI layer, thus failing to improve self-discharge.

[0034] Furthermore, the electrolyte sodium salt is sodium hexafluorophosphate or sodium perchlorate.

[0035] Furthermore, the ether organic solvent is diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0036] Furthermore, the concentration of the sodium electrolyte salt in the electrolyte is 0.5–1.5 mol / L.

[0037] Furthermore, the cathode material of the sodium-ion battery is a Prussian blue-based material, a layered oxide material, and / or a polyanionic cathode material.

[0038] Furthermore, polyanionic cathode materials include phosphate cathode materials, pyrophosphate cathode materials, sulfate cathode materials, silicate cathode materials, and / or borate cathode materials.

[0039] Furthermore, the negative electrode material of sodium-ion batteries is hard carbon or metallic sodium.

[0040] Furthermore, sodium-ion batteries are hard carbon / sodium half-cells, sodium iron pyrophosphate / hard carbon full-cells, and sodium vanadium phosphate / hard carbon full-cells.

[0041] Compared to existing technologies, this invention addresses the drawbacks of electrode purification and surface modification being unsuitable for industrial production by optimizing the electrolyte composition with a reasonable component ratio, offering ease of operation and feasibility. By adding different types of additives that interact with sodium salts, a dense SEI film is synergistically formed, isolating hard carbon from the electrolyte. The resulting solvation effect weakens the release of sodium ions adsorbed on the surface and embedded in the graphite layers, thereby suppressing self-discharge, reducing capacity loss, and improving the electrochemical performance of sodium-ion batteries.

[0042] Example 1

[0043] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and an additive, wherein the additive is a carbonate additive, specifically fluoroethylene carbonate. The amount of the carbonate additive added is 5% of the volume of the ether-based organic solvent.

[0044] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate; the concentration of the electrolyte sodium salt in the electrolyte is 1.5 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether.

[0045] Example 2

[0046] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and additives. The additives are carbonate additives, specifically ethylene carbonate and vinylene carbonate. The amount of carbonate additives added is 3% of the volume of the ether-based organic solvent.

[0047] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate; the concentration of the electrolyte sodium salt in the electrolyte is 1 mol / L; and the ether organic solvent is tetraethylene glycol dimethyl ether.

[0048] Example 3

[0049] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and additives. The additives are carbonate additives, specifically fluoroethylene carbonate and vinylene carbonate. The amount of carbonate additives added is 0.5% of the volume of the ether-based organic solvent.

[0050] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate or sodium perchlorate; the concentration of the electrolyte sodium salt in the electrolyte is 0.5 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0051] Example 4

[0052] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and an additive, wherein the additive is a sulfate ester additive, specifically 1,3-propanesulfonic acid lactone. The amount of the sulfate ester additive added is 5% of the mass of the ether-based organic solvent.

[0053] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate; the concentration of the electrolyte sodium salt in the electrolyte is 1.5 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether.

[0054] Example 5

[0055] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and an additive, wherein the additive is a sulfate ester additive, specifically 1,3-butanolactone. The amount of the sulfate ester additive added is 3% of the mass of the ether-based organic solvent.

[0056] In this embodiment, the electrolyte sodium salt is sodium perchlorate; the concentration of the electrolyte sodium salt in the electrolyte is 1 mol / L; and the ether organic solvent is tetraethylene glycol dimethyl ether.

[0057] Example 6

[0058] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and additives. The additives are sulfate ester additives, specifically 1,3-propanesulfonic acid lactone and propylene sulfate. The amount of sulfate ester additives added is 0.5% of the mass of the ether-based organic solvent.

[0059] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate or sodium perchlorate; the concentration of the electrolyte sodium salt in the electrolyte is 0.5 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0060] Example 7

[0061] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and an additive, wherein the additive is a salt additive, and the salt additive is sodium bis(fluorosulfonyl)imide; the molar ratio of the amount of salt additive added to the electrolyte sodium salt is 2:8.

[0062] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate; the concentration of the electrolyte sodium salt in the electrolyte is 1.5 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether.

[0063] Example 8

[0064] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and an additive, wherein the additive is a salt additive, and the salt additive is sodium bis(trifluoromethanesulfonyl)imide; the molar ratio of the amount of salt additive added to the electrolyte sodium salt is 5:5.

[0065] In this embodiment, the electrolyte sodium salt is sodium perchlorate; the concentration of the electrolyte sodium salt in the electrolyte is 1 mol / L; and the ether organic solvent is tetraethylene glycol dimethyl ether.

[0066] Example 9

[0067] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and additives. The additives are salt additives, specifically sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethylsulfonyl)imide. The molar ratio of the amount of salt additives added to the electrolyte sodium salt is 3:7.

[0068] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate or sodium perchlorate; the concentration of the electrolyte sodium salt in the electrolyte is 0.5 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0069] Example 10

[0070] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, an electrolyte sodium salt, and additives. The additives are carbonate additives and sulfate additives. The carbonate additives are fluoroethylene carbonate and ethylene carbonate, and the sulfate additive is 1,3-propanesulfonic acid lactone. The amount of carbonate additive added is 5% of the volume of the ether-based organic solvent, and the amount of sulfate additive added is 3% of the mass of the ether-based organic solvent.

[0071] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate; the concentration of the electrolyte sodium salt in the electrolyte is 1.5 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0072] Example 11

[0073] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, a sodium electrolyte salt, and additives. The additives are carbonate additives, sulfate additives, and salt additives. The carbonate additive is fluoroethylene carbonate; the salt additives are sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethanesulfonyl)imide. The amount of carbonate additive added is 3% of the volume of the ether-based organic solvent, and the molar ratio of the salt additive to the sodium electrolyte salt is 2:8.

[0074] In this embodiment, the electrolyte sodium salt is sodium perchlorate; the concentration of the electrolyte sodium salt in the electrolyte is 1 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0075] Example 12

[0076] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, comprising an ether-based organic solvent, a sodium electrolyte salt, and additives. The additives are carbonate additives, sulfate additives, and salt additives. The carbonate additives are fluoroethylene carbonate, ethylene carbonate, and / or vinylene carbonate; the sulfate additives are 1,3-propanesulfonate lactone and 1,3-butanesulfonate lactone; and the salt additives are sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethanesulfonyl)imide. The amount of carbonate additive added is 3% of the volume of the ether-based organic solvent, the amount of sulfate additive added is 3% of the mass of the ether-based organic solvent, and the molar ratio of the salt additive to the sodium electrolyte salt is 3:7.

[0077] In this embodiment, the electrolyte sodium salt is sodium hexafluorophosphate; the concentration of the electrolyte sodium salt in the electrolyte is 1 mol / L; and the ether organic solvent is diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0078] In the above embodiments of the present invention, the electrolyte system has wide applicability; the positive electrode material for sodium-ion batteries can be Prussian blue-based materials, layered oxide materials, and / or polyanionic positive electrode materials. Specifically, polyanionic positive electrode materials include phosphate positive electrode materials, pyrophosphate positive electrode materials, sulfate positive electrode materials, silicate positive electrode materials, and / or borate positive electrode materials. Simultaneously, there is also corresponding adaptability for the negative electrode material; the negative electrode material for sodium-ion batteries is hard carbon or metallic sodium. Accordingly, sodium-ion batteries can be hard carbon / sodium half-cells, sodium iron pyrophosphate / hard carbon full-cells, and sodium vanadium phosphate / hard carbon full-cells.

[0079] Application Example 1

[0080] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, the preparation process of which is as follows:

[0081] Step ①: The ether solvent used in the standard electrolyte is diethylene glycol dimethyl ether (99.8%, Duoduo Chemical Reagent Network), and the electrolyte salt is sodium hexafluorophosphate (99.99%, Guotai Huarong Chemical New Materials Co., Ltd.). Weigh 1.68 g of sodium hexafluorophosphate into 10 mL of diethylene glycol dimethyl ether, heat at 60℃ for 12 h to dissolve it, and shake well to obtain the standard electrolyte.

[0082] Step ②: Take 5 mL of standard electrolyte, add 100 μL of fluoroethylene carbonate (99.9%, Duoduo Chemical Reagent Network), shake well to obtain the optimized electrolyte.

[0083] Step 3: Using Japanese hard carbon as the negative electrode and sodium sheet as the positive electrode, assemble a sodium-ion battery using an optimized electrolyte.

[0084] The blank electrolyte retained 60% of its capacity after standing at 60°C for three days and 42% of its capacity after standing for six days. Figures 1-3 After adding the aforementioned additive, the volume retention rate was 68% after three days and 60% after six days. Figures 4-6 This indicates that self-discharge is suppressed.

[0085] Application Example 2

[0086] This embodiment discloses a low self-discharge sodium-ion battery electrolyte, the preparation process of which is as follows:

[0087] Step ①: The ether solvent used in the standard electrolyte is diethylene glycol dimethyl ether (99.8%, Duoduo Chemical Reagent Network), and the electrolyte salt is sodium hexafluorophosphate (99.99%, Guotai Huarong Chemical New Materials Co., Ltd.). Weigh 1.68g of sodium hexafluorophosphate into 20mL of diethylene glycol dimethyl ether, heat at 60°C for 12 hours to dissolve it, and shake well to obtain the standard electrolyte.

[0088] Step ②: Take 5 mL of standard electrolyte, add 0.76 g of sodium bis(trifluoromethanesulfonyl)imide (99.5%, Duoduo Chemical Reagent Network), heat at 60 degrees Celsius for 12 h to dissolve it, shake evenly, and obtain the optimized additive.

[0089] Step 3: Using Japanese hard carbon as the negative electrode and sodium sheet as the positive electrode, assemble a sodium-ion battery using an optimized electrolyte.

[0090] In addition to the increase in capacity retention, combined with Figure 7 and Figure 8 As can be seen, the SEI layer on the hard carbon surface of the sodium-ion battery assembled with blank electrolyte is disordered and uneven in thickness, with some parts in direct contact with the electrolyte. However, after adding sodium bis(trifluoromethanesulfonyl)imide, the composite SEI layer becomes dense and uniform, effectively isolating the hard carbon from the electrolyte.

[0091] The above embodiments are merely specific examples of the present invention, and their descriptions are quite specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these obvious substitutions all fall within the protection scope of the present invention.

Claims

1. A low self-discharge sodium-ion battery electrolyte, used in sodium-ion batteries, characterized in that: The product includes ether-based organic solvents, sodium electrolyte salts, and additives. The additives are carbonate additives, sulfate additives, and salt additives. The carbonate additives are one or more of fluoroethylene carbonate, ethylene carbonate, and / or vinylene carbonate. The sulfate additives are one or more of 1,3-propanesulfonate lactone, 1,3-butanesulfonate lactone, and / or propylene sulfate. The salt additives are sodium bis(fluorosulfonyl)imide and / or sodium bis(trifluoromethylsulfonyl)imide. The amount of the carbonate additive is 0.5-5% of the volume of the ether organic solvent, and the amount of the sulfate additive is 0.5-5% of the mass of the ether organic solvent; the molar ratio of the amount of the salt additive to the electrolyte sodium salt is 2:8 to 5:

5. The electrolyte sodium salt is sodium hexafluorophosphate and / or sodium perchlorate; The ether organic solvent is diethylene glycol dimethyl ether and / or tetraethylene glycol dimethyl ether; The negative electrode material of the sodium-ion battery is hard carbon.

2. The low self-discharge sodium-ion battery electrolyte according to claim 1, characterized in that: The concentration of the sodium salt of the electrolyte in the electrolyte is 0.5–1.5 mol / L.

3. The low self-discharge sodium-ion battery electrolyte according to claim 1, characterized in that: The positive electrode material of the sodium-ion battery is a Prussian blue-based material, a layered oxide material, and / or a polyanionic positive electrode material.

4. The low self-discharge sodium-ion battery electrolyte according to claim 3, characterized in that: Polyanionic cathode materials include phosphate cathode materials, pyrophosphate cathode materials, sulfate cathode materials, silicate cathode materials, and / or borate cathode materials.

5. The low self-discharge sodium-ion battery electrolyte according to claim 3, characterized in that: The sodium-ion battery is either a sodium iron pyrophosphate / hard carbon full cell or a sodium vanadium phosphate / hard carbon full cell.

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