Electrolyte and battery

Abstract

The application provides an electrolyte and a battery, and relates to the technical field of batteries.The electrolyte comprises an electrolyte, a solvent and an additive, wherein the additive comprises a gas-phase flame-retardant additive and a liquid-phase flame-retardant additive.In the technical scheme of the application, the gas-phase flame-retardant additive and the liquid-phase flame-retardant additive are used to release gas or liquid or form a protective layer to prevent the combustion reaction from further expanding, so that the effect of flame retardation is achieved.Meanwhile, the gas-phase flame-retardant additive and the liquid-phase flame-retardant additive both have a certain degree of heat resistance, which can improve the heat resistance of the electrolyte, so that the battery is not prone to causing the combustion reaction of the electrolyte in the case of short-circuiting and fierce heat release, and the combustion risk of the electrolyte is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrolyte and a battery. BACKGROUND

[0002] Sodium-ion batteries have achieved great application, especially layered oxide sodium-ion batteries, which have great advantages: high energy density, low cost, good rate performance, and higher safety than lithium-ion batteries.

[0003] There is still some risk in extreme use cases. Currently, sodium-ion battery electrolytes generally use organic electrolytes. Common organic solvents in electrolytes are carbonate compounds such as DMC (dimethyl carbonate), EMC (methyl ethyl carbonate), DEC (diethyl carbonate), PC (propylene carbonate), etc. The flash points of these organic solvents are very low, and the electrolyte is highly flammable, so there is still a risk of fire and combustion for sodium-ion batteries. SUMMARY

[0004] The main purpose of the present application is to provide an electrolyte and a battery, which aims to reduce the risk of spontaneous combustion of the battery.

[0005] To achieve the above-mentioned purpose, the present application provides an electrolyte, which comprises an electrolyte, a solvent and an additive, wherein the additive comprises a gas-phase flame-retardant additive and a liquid-phase flame-retardant additive.

[0006] In an embodiment, the electrolyte comprises a sodium salt, and the sodium salt comprises at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium difluoro(oxalato)borate, sodium tetrafluoroborate, sodium bis(oxalato)borate and sodium difluorophosphate.

[0007] In an embodiment, the total molar concentration of the sodium salt is 0.6 mol / L to 1.5 mol / L.

[0008] Preferably, the total molar concentration of the sodium salt is 0.8 mol / L to 1.2 mol / L.

[0009] In an embodiment, the gas-phase flame-retardant additive comprises a phosphazene compound; and / or,

[0010] The liquid-phase flame-retardant additive comprises at least one of 1,3,5-tris[(3,3,3-trifluoropropyl)methyl]cyclotrisiloxane and perfluoro(2-methyl-3-pentanone).

[0011] In an embodiment, the additive further comprises a film-forming additive.

[0012] In an embodiment, in the electrolyte, the mass fraction of the film-forming additive is 1% to 4%; and / or,

[0013] The film-forming additive includes at least two of fluoroethylene carbonate (FEC), acid propylene (PS), ethylene sulfate (DTD), and 1,3-propylene sulfite (PST).

[0014] In an embodiment, the solvent includes diethyl ethylphosphonate, and at least one of a phosphate compound, a fluoroether, and a fluoroester.

[0015] In an embodiment, the mass percentage of diethyl ethylphosphonate in the electrolyte is not less than 15%.

[0016] The application further provides a battery including the electrolyte as described above.

[0017] In an embodiment, the battery is a sodium ion battery including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the material of the positive electrode sheet is a layered oxide, the material of the negative electrode sheet is hard carbon, and the material of the separator is polypropylene, polyethylene, or a composite of polypropylene and polyethylene.

[0018] In the technical solution of the application, the gas-phase flame-retardant additive has a high vapor pressure and can quickly form a flame-retardant vapor group to inhibit gas-phase combustion (a large amount of gas generated by electrolyte volatilization and decomposition); the liquid-phase flame-retardant additive has a low vapor pressure and can retard flame in the liquid phase (unvaporized residual liquid electrolyte), and the two cooperate to play a flame-retardant role, thereby achieving the flame-retardant effect. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments of the application.

[0020] It should be noted that, in the embodiments, the specific conditions not mentioned are implemented according to the conventional conditions or the conditions recommended by the manufacturers. The reagents or instruments not mentioned by the manufacturers are conventional products that can be purchased on the market. In addition, the meaning of “and / or” appearing in the entire text includes three parallel solutions, for example, “A and / or B” includes the A solution, or the B solution, or the solution in which A and B are satisfied at the same time. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person of ordinary skill in the art can realize it, and when the combination of technical solutions appears to be contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the protection scope of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without making creative efforts are within the protection scope of the application.

[0021] Sodium-ion batteries have achieved great application, especially layered oxide sodium-ion batteries, which have great advantages: high energy density, low cost, good rate performance, and higher safety than lithium-ion batteries.

[0022] There is still some danger in extreme use cases, and currently sodium-ion battery electrolytes generally use organic electrolytes. Common organic solvents in electrolytes are carbonate compounds such as DMC (dimethyl carbonate), EMC (methyl ethyl carbonate), DEC (diethyl carbonate), PC (propylene carbonate), etc. The flash points of these organic solvents are very low, and the electrolyte is highly flammable, so there is still a risk of fire and combustion of sodium-ion batteries.

[0023] In view of this, the present application provides an electrolyte, comprising an electrolyte, a solvent and an additive, wherein the additive comprises a gas-phase flame-retardant additive and a liquid-phase flame-retardant additive.

[0024] In the technical solution of the present application, by using a gas-phase flame-retardant additive and a liquid-phase flame-retardant additive, the two synergistically play a flame-retardant role. At the same time, the gas-phase flame-retardant additive and the liquid-phase flame-retardant additive both have a certain degree of heat resistance, can effectively absorb heat, reduce the occurrence of electrolyte evaporation or decomposition at high temperatures, thereby improving the thermal stability of the electrolyte, so that the battery is not easy to cause the combustion reaction of the electrolyte in the case of short-circuiting and severe heat release, thereby reducing the combustion risk of the electrolyte. The vapor pressure of the gas-phase flame-retardant additive is relatively high, which can quickly form a flame-retardant vapor group, thereby effectively inhibiting the combustion process; the liquid-phase flame-retardant additive prevents the combustion of the remaining electrolyte, further improving the flame-retardant performance of the electrolyte.

[0025] In an embodiment, the electrolyte comprises a sodium salt, and the sodium salt comprises at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium difluoro(oxalato)borate, sodium tetrafluoroborate, sodium bis(oxalato)borate and sodium difluorophosphate.

[0026] In the technical solution of the present application, by using a sodium salt as the electrolyte, the electrolyte can be used as the electrolyte of a sodium-ion battery, and can be applied to a sodium-ion battery to reduce the risk of spontaneous combustion of the sodium-ion battery. By using at least one of the above-mentioned sodium salts, the sodium salt has high thermal stability, preventing electrolyte decomposition or evaporation, thereby ensuring the safety and reliability of the battery in a high-temperature environment. In addition, the sodium salt as the electrolyte can form a stable passivation film on the surface of the electrode of the battery during application to the battery, reduce the side reaction between the electrode and the electrolyte, and improve the stability and conductivity of the electrode interface, thereby improving the charge and discharge efficiency and cycle life of the battery.

[0027] In an embodiment, the total molar concentration of the sodium salt is 0.6 mol / L to 1.5 mol / L.

[0028] In the technical scheme of the present application, by limiting the total molar concentration of the sodium salt to 0.6-1.5 mol / L, sufficient ion concentration is provided to ensure that the electrolyte has good conductivity and electrochemical performance, reduce the interaction between ions, improve the flowability of the electrolyte, and enhance the conductivity of the electrolyte.

[0029] Preferably, the total molar concentration of the sodium salt is 0.8-1.2 mol / L.

[0030] In the technical scheme of the present application, by limiting the total molar concentration of the sodium salt to 0.8-1.2 mol / L, the performance of the electrolyte is better, which can ensure sufficient ion concentration and will not cause excessive aggregation of ions, thereby reducing the occurrence of conditions such as excessive viscosity or precipitation of solid from the electrolyte.

[0031] In an embodiment, the gas-phase flame retardant additive includes a phosphazene compound. In the technical scheme of the present application, by using a phosphazene compound as a gas-phase flame retardant additive, a flame-retardant vapor group formed quickly can retard the combustion of volatile combustible substances (combustible gases generated by electrolyte volatilization or decomposition).

[0032] In an embodiment, the liquid-phase flame retardant additive includes at least one of 1,3,5-tris[(3,3,3-trifluoropropyl)methyl]cyclotrisiloxane and perfluoro(2-methyl-3-pentanone). In the technical scheme of the present application, by using at least one of 1,3,5-tris[(3,3,3-trifluoropropyl)methyl]cyclotrisiloxane and perfluoro(2-methyl-3-pentanone) as the liquid-phase flame retardant additive, it has high boiling point and low volatility, can effectively retard the combustion of unvaporized residual electrolyte, and reduce the risk of combustion; at the same time, the liquid-phase flame retardant additive has excellent thermal stability, can maintain its physical and chemical properties at high temperatures, and prevents electrolyte decomposition or volatilization.

[0033] Specifically, in some embodiments of the present application, the phosphazene compound includes ethoxy(pentafluoro)cyclotriphosphazene or hexafluorocyclotriphosphazene.

[0034] In an embodiment, the additive further includes a film-forming additive.

[0035] In the technical scheme of the present application, by adding a film-forming additive, a uniform and stable passivation film can be formed on the surface of the electrode, reducing the side reaction between the electrode and the electrolyte, improving the stability and conductivity of the electrode interface, and further improving the charge-discharge efficiency and cycle life of the battery.

[0036] In an embodiment, the mass percentage of the film-forming additive in the electrolyte is 1-4%. In the technical scheme of the present application, by setting the mass percentage of the film-forming additive to be 1-4%, the film-forming additive can form a uniform and stable passivation film on the surface of the electrode of the battery, effectively reducing the side reaction between the electrode and the electrolyte, improving the stability and conductivity of the electrode interface, and at the same time, the film-forming additive can also reduce the decomposition and gas generation of the electrolyte, reduce the internal pressure of the battery, and improve the overall safety performance of the battery.

[0037] In an embodiment, the film-forming additive includes at least two of fluorine ethylene carbonate (FEC), acid propylene (PS), vinyl sulfate (DTD), and 1,3-propylene sulfone lactone (PST).

[0038] In the technical scheme of the present application, by using at least two film-forming additives, at least two film-forming agents can play a synergistic role and form a protective film on the positive and negative electrodes of the battery, for example, when fluorine ethylene carbonate (FEC) and vinyl sulfate (DTD) are used in combination, FEC can form a stable SEI film on the surface of the negative electrode, and DTD can form a stable passivation film on the surface of the positive electrode, thereby comprehensively improving the electrochemical performance of the battery; wherein, FEC can form a stable SEI film (solid electrolyte interface film) on the surface of the electrode, reduce the side reaction between the electrode and the electrolyte, and improve the cycle stability and rate performance of the battery; PS can form a uniform protective film on the surface of the electrode, reduce the decomposition of the electrolyte, and improve the cycle life and safety of the battery; DTD can form a stable passivation film on the surface of the electrode, reduce the side reaction between the electrode and the electrolyte, and improve the cycle stability and rate performance of the battery; PST can form a uniform and stable passivation film on the surface of the electrode, reduce the decomposition of the electrolyte, and improve the cycle life and safety of the battery.

[0039] In an embodiment, the solvent includes diethyl ethyl phosphonate (DEEP), and at least one of a phosphate compound, a fluorinated ether, and a fluorinated ester.

[0040] In the technical scheme of the present application, by using diethyl ethyl phosphonate, and at least one of a phosphate compound, a fluorinated ether, and a fluorinated ester as a solvent, the thermal stability of the solvent is improved, which can maintain its physical and chemical properties under high temperature conditions, prevent the decomposition or volatilization of the electrolyte, and ensure the stability and safety of the electrolyte under high temperature environment; wherein, DEEP, the phosphate compound, the fluorinated ether, and the fluorinated ester all have good electrochemical stability and high dielectric constant, can provide good ion transport performance, and improve the conductivity of the electrolyte. At the same time, DEEP can form a stable SEI film on the surface of the electrode, reduce the side reaction between the electrode and the electrolyte, and improve the cycle stability and rate performance of the battery;

[0041] In an embodiment, the mass percentage of diethyl ethylphosphonate in the electrolyte is not less than 15%.

[0042] In the technical solution of the present application, DEEP has high thermal stability, high phosphorus content and good flame retardant effect. When the mass percentage of DEEP is not less than 15%, the thermal stability of the electrolyte is significantly improved, ensuring the safety and reliability of the battery in high temperature environment.

[0043] The present application also provides a battery comprising the electrolyte as described above.

[0044] In the technical solution of the present application, by using the electrolyte as described above to prepare the battery, excellent electrochemical performance, thermal stability and safety performance are achieved, the cycle life, charge-discharge efficiency and low temperature performance of the battery are significantly improved, which has important practical significance and broad application prospect.

[0045] In an embodiment, the battery is a sodium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the material of the positive electrode sheet is a layered oxide, the material of the negative electrode sheet is hard carbon, and the material of the separator is polypropylene, polyethylene or a composite of polypropylene and polyethylene.

[0046] In the technical solution of the present application, by using layered oxide as the positive electrode material, high theoretical specific capacity and good cycle stability are achieved, which can be used to provide stable sodium ion intercalation and deintercalation process, improve the overall performance of the battery, and improve the theoretical specific capacity and cycle stability of the sodium ion battery; by using hard carbon as the negative electrode material, the hard carbon material can provide stable sodium ion intercalation and deintercalation sites during the charge and discharge process, reduce the volume change of the electrode material, and improve the cycle life and rate performance of the battery; by using a composite material as the material of the separator, the physical and chemical properties of the separator can be maintained under high temperature conditions, preventing short circuit and thermal runaway.

[0047] In an embodiment, the positive electrode coating of the positive electrode sheet comprises a layered oxide, carbon black, carbon nanotubes, polyvinylidene fluoride and a positive electrode solid electrolyte, wherein the mass ratio of the layered oxide, carbon black, carbon nanotubes, polyvinylidene fluoride and positive electrode solid electrolyte is 92:2:1.5:2.5:2. In the technical solution of the present application, the layered oxide serves as a positive electrode active material, has a high theoretical specific capacity and good cycle stability. This material can provide a stable sodium ion intercalation and deintercalation process, improve the overall energy density of the battery; carbon black and carbon nanotubes as conductive agents can be uniformly distributed in the positive electrode active material, improve the conductivity of the positive electrode material, reduce the internal resistance of the electrode, and improve the charge and discharge efficiency of the battery; carbon nanotubes have excellent electrical conductivity and mechanical properties, can form a three-dimensional conductive network, further improve the conductivity and structural stability of the positive electrode material, and improve the rate performance of the battery; polyvinylidene fluoride as a binder can uniformly fix the positive electrode active material, conductive agent and solid electrolyte together to form a stable coating, improve the mechanical strength and conductivity of the positive electrode sheet.

[0048] In an embodiment, the negative electrode coating of the negative electrode sheet comprises hard carbon, carbon black, styrene butadiene rubber, sodium carboxymethyl cellulose and a negative electrode solid electrolyte, wherein the mass ratio of hard carbon, carbon black, styrene butadiene rubber, sodium carboxymethyl cellulose and negative electrode solid electrolyte is 92.5:2:2.5:1:2. In the technical solution of the present application, hard carbon serves as a negative electrode active material, has a high specific capacity and good cycle stability. Hard carbon material can provide stable sodium ion intercalation and deintercalation sites during charging and discharging, reduce the volume change of the electrode material, improve the cycle life and rate performance of the battery; carbon black as a conductive agent can be uniformly distributed in the hard carbon material, improve the conductivity of the negative electrode material, reduce the internal resistance of the electrode, and improve the charge and discharge efficiency of the battery; styrene butadiene rubber (SBR) as a binder has good adhesion and mechanical strength, can uniformly fix the negative electrode active material, conductive agent and solid electrolyte together to form a stable coating, improve the mechanical strength and conductivity of the negative electrode sheet; sodium carboxymethyl cellulose (CMC) as a thickening agent can improve the stability and coating performance of the slurry, ensure uniform distribution of the negative electrode material during coating, reduce particle agglomeration, and improve the consistency and performance of the negative electrode sheet.

[0049] In an embodiment, the positive electrode solid electrolyte and the negative electrode solid electrolyte both comprise a solid electrolyte, and the chemical formula of the solid electrolyte is Na l+x Zr2Si x P 3-x O 12 (0≤x≤3), wherein the solid content of the positive electrode solid electrolyte is 30%, and the dispersing agent is N-methyl pyrrolidone; the solid content of the negative electrode solid electrolyte is 30%, and the dispersing agent is water. In the technical solution of the present application, Na l+xZr2Si x P 3-x O 12 As the solid-state electrolyte, it has high sodium ion conductivity, can provide good ion transmission performance, improve the charge and discharge efficiency and rate performance of the battery; by using N-methyl pyrrolidone as a dispersant for the positive solid-state electrolyte, it can effectively dissolve the polyvinylidene fluoride and other binders, so that the positive active material, conductive agent and binder are uniformly dispersed in the slurry.

[0050] The technical solutions of the application will be further described in detail in combination with specific embodiments. It should be understood that the following embodiments are only used to explain the application and not to limit the application.

[0051] Experimental materials

[0052] Unless otherwise specified, the reagents used without specifying the manufacturer are conventional products that can be purchased on the market.

[0053] DEEP: diethyl ethylphosphonate;

[0054] TMP: trimethyl phosphate;

[0055] TFP: tris(2,2,2-trifluoroethyl) phosphate;

[0056] TTE: 1,1,2,2-tetrafluoroethyl-2,2,3-tetrafluoropropyl ether;

[0057] CDP: cresyl diphenyl phosphate;

[0058] NaPF6: sodium hexafluorophosphate;

[0059] NaFSI: sodium bisfluorosulfonylimide;

[0060] HFPN: hexafluorocyclotriphosphazene;

[0061] D3F: 1,3,5-tris[(3,3,3-trifluoropropyl)methyl]cyclotrisiloxane;

[0062] PFPN: ethoxy(pentafluoro)cyclotriphosphazene;

[0063] PFMP: perfluoro(2-methyl-3-pentanone);

[0064] FEC: fluoroethylene carbonate;

[0065] PS: acid acrylate;

[0066] DTD: vinyl sulfate;

[0067] TMSB: 2-methyl-3-pentanone;

[0068] EMC: ethyl methyl carbonate;

[0069] PC: propylene carbonate.

[0070] Example 1

[0071] This example provides an electrolyte, the composition of which is:

[0072] DEEP: TMP: CDP: NaPF6: NaFSI: PFPN: PFMP: FEC: PS: DTD: TMSB = 15%: 35%: 25.8%: 10%: 4%: 6%: 2%: 1%: 0.5%: 0.5%: 0.2%.

[0073] Example 2

[0074] This example provides an electrolyte, the composition of which is:

[0075] DEEP: TMP: CDP: TTE: NaPF6: NaFSI: HFPN: D3F: FEC: PS: DTD: TMSB = 15%: 25%: 25.8%: 10%: 10%: 4%: 5%: 3%: 1%: 0.5%: 0.5%: 0.2%.

[0076] Example 3

[0077] This example provides an electrolyte, the composition of which is:

[0078] DEEP: TFP: CDP: TTE: NaPF6: NaFSI: HFPN: D3F: FEC: PS: DTD: TMSB = 15%: 35%: 25.8%: 10%: 4%: 5%: 3%: 1%: 0.5%: 0.5%: 0.2%.

[0079] Comparative Example 1

[0080] This comparative example provides an electrolyte, the composition of which is:

[0081] EMC: PC: NaPF6: NaFSI: PFPN: PFMP: FEC: PS: DTD: TMSB = 50%: 10%: 15.8%: 10%: 4%: 6%: 2%: 1%: 0.5%: 0.5%: 0.2%.

[0082] The electrolyte provided in this comparative example does not have diethyl ethylphosphonate and a phosphoric acid ester compound, a fluorinated ether, a fluorinated ester, or the like solvent.

[0083] Comparative Example 2

[0084] This comparative example provides an electrolyte, the composition of which is:

[0085] TFP: PC: EMC: NaPF6: NaFSI: PFPN: PFMP: FEC: PS: DTD: TMSB = 50%: 10%: 15.8%: 10%: 4%: 6%: 2%: 1%: 0.5%: 0.5%: 0.2%.

[0086] The electrolyte provided by the present comparative example does not contain diethyl ethylphosphonate solvent.

[0087] Comparative Example 3

[0088] The electrolyte provided by the present comparative example has the following composition:

[0089] TMP: CDP: NaPF6: NaFSI: PFPN: FEC: PS: DTD: TMSB = 58%: 25.8%: 10%: 4%: 2%: 1%: 0.5%: 0.5%: 0.2%.

[0090] The electrolyte provided by the present comparative example does not contain diethyl ethylphosphonate and liquid-phase flame retardant additive.

[0091] Comparative Example 4

[0092] The electrolyte provided by the present comparative example has the following composition:

[0093] DEEP: TMP: CDP: NaPF6: NaFSI: PFPN: FEC: PS: DTD: TMSB = 16%: 38%: 27.5%: 10%: 4%: 2%: 1%: 0.6%: 0.6%: 0.3%.

[0094] The present comparative example does not contain PFMP compared with Example 1.

[0095] The electrolyte of Comparative Example 4 is in the form of emulsion, and there are insoluble particles, which cannot be directly applied.

[0096] Comparative Example 5

[0097] The electrolyte provided by the present comparative example has the following composition:

[0098] DEEP: TMP: CDP: NaPF6: NaFSI: PFMP: FEC: PS: DTD: TMSB = 16%: 37.5%: 26%: 10%: 6%: 2%: 1%: 0.6%: 0.6%: 0.3%.

[0099] The present comparative example does not contain PFMP compared with Example 1.

[0100] The electrolyte of Comparative Example 5 is in the form of slurry, and there are insoluble particles, which cannot be directly applied.

[0101] The electrolyte prepared in Examples 1-3 and Comparative Examples 1-3 was injected into the same batch of cylindrical sodium ion batteries, the material of the positive electrode of the cylindrical sodium ion battery was layered oxide, the material of the negative electrode of the cylindrical sodium ion battery was hard carbon, and the material of the separator of the cylindrical sodium ion battery was polypropylene, polyethylene, a composite of polypropylene and polyethylene; the composition of the positive electrode slurry of the cylindrical sodium ion battery was: 92% layered oxide, 2% carbon black, 1.5% carbon nanotube, 2.5% polyvinylidene fluoride, and 2% positive electrolyte dispersion liquid; the composition of the negative electrode slurry of the cylindrical sodium ion battery was: 92.5% hard carbon, 2% carbon black, 2.5% butadiene-styrene rubber, 1% sodium carboxymethyl cellulose, and 2% negative electrolyte dispersion liquid; wherein the solid-state electrolyte of the positive electrolyte dispersion liquid and the negative electrolyte dispersion liquid was Na3Zr2Si2PO 12 , the mass ratio of the solid-state electrolyte in the positive electrolyte dispersion liquid was 30%, the dispersing agent was N-methyl pyrrolidone, the mass ratio of the solid-state electrolyte in the negative electrolyte dispersion liquid was 30%, and the dispersing agent was water.

[0102] The capacity of the batteries prepared using the electrolyte of Examples 1-3 and Comparative Examples 1-3 was detected, and the batteries were respectively subjected to needle puncture experiments after formation and capacity test, and the experimental results are shown in Table 1.

[0103] Table 1: Battery capacity and needle puncture experiment results

[0104]

[0105]

[0106] As can be seen from Table 1, Examples 1-3 did not catch fire, and Comparative Examples 1-3 caught fire and burned; in addition, as can be seen from Comparative Example 1, the battery capacity was slightly higher when using a carbonate solvent, and the battery capacity was slightly reduced when using a flame-retardant solvent such as phosphate ester.

[0107] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structural transformation made according to the content of the present application, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. An electrolyte, characterized in that, The mixture includes electrolytes, solvents, and additives, wherein the additives include gas-phase flame retardant additives and liquid-phase flame retardant additives, the gas-phase flame retardant additives include phosphazene compounds, the phosphazene compounds include ethoxy(pentafluoro)cyclotriphosphazene or hexafluorocyclotriphosphazene, the liquid-phase flame retardant additives include at least one of 1,3,5-tris[(3,3,3-trifluoropropyl)methyl]cyclotrisiloxane and perfluoro(2-methyl-3-pentanone), and the solvent includes diethyl ethylphosphonate, and at least one of phosphate ester compounds, fluorinated ethers, and fluorinated esters.

2. The electrolyte as described in claim 1, characterized in that, The electrolyte includes a sodium salt, which includes at least one of sodium hexafluorophosphate, sodium bis(fluorosulfonyl)imide, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium bis(oxalate)borate, and sodium difluorophosphate.

3. The electrolyte as described in claim 2, characterized in that, The total molar concentration of the sodium salt is 0.6 mol / L to 1.5 mol / L.

4. The electrolyte as described in claim 2, characterized in that, The total molar concentration of the sodium salt is 0.8 mol / L to 1.2 mol / L.

5. The electrolyte as described in claim 1, characterized in that, The additives also include film-forming additives.

6. The electrolyte as described in claim 5, characterized in that, In the electrolyte, the film-forming additive accounts for 1% to 4% by mass; and / or, The film-forming additives include at least two of the following: fluoroethylene ester (FEC), propylene ester (PS), ethylene sulfate (DTD), and 1,3-propenesulfonate lactone (PST).

7. The electrolyte as described in claim 1, characterized in that, In the electrolyte, the mass percentage of diethyl ethylphosphonate is not less than 15%.

8. A battery, characterized in that, Includes the electrolyte as described in any one of claims 1 to 7.

9. The battery as claimed in claim 8, characterized in that, The battery is a sodium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is made of layered oxide, the negative electrode is made of hard carbon, and the separator is made of polypropylene, polyethylene, or a composite of polypropylene and polyethylene.

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