Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The invention provides a sodium-ion battery electrolyte and a sodium-ion battery, and relates to the technical field of sodium-ion batteries. The sodium-ion battery electrolyte comprises sodium salt, an organic solvent and an additive, the additive is selected from one or more of a thioimide functional additive and a film-forming additive. The sodium-ion battery electrolyte provided by the invention can inhibit the dissolution of an SEI membrane and a CEI membrane and improve the cycling stability of a sodium-ion battery under high voltage, so that the energy density and the service life of the sodium-ion battery are improved.

Description

TECHNICAL FIELD

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

[0002] With the increasing demand for energy by mankind, the resources of traditional fossil energy such as oil, coal and natural gas are limited, and the world is facing a new trend of energy transformation. Secondary batteries have become an important technology for energy transformation, among which lithium ion battery technology is mature and dominates the market, and is widely used in new energy vehicles, aerospace, energy storage and other fields. In recent years, the demand for power batteries and energy storage has rapidly expanded, and the global demand for lithium resources has rapidly grown, but the distribution of lithium resources in the earth's crust is uneven and limited, and there is a technical risk that the supply cannot meet the development demand. Sodium ion batteries have similar working principles to lithium ion batteries and are abundant in resources, and are the most potential alternative and complementary products of lithium ion batteries.

[0003] Sodium ion batteries have great advantages in material cost and resource reserves, but compared with lithium batteries, there is still a certain gap in energy density. High voltage is very important to improve energy density, and electrolyte is an important component of the SEI film and CEI film of sodium ion batteries, and has an important influence on the energy density of sodium ion batteries. For the ester electrolyte used in traditional lithium ion batteries, it has poor compatibility with the electrode interface in sodium ion batteries. In addition, under high voltage, part of the components in the SEI film and CEI film formed during the working process of the sodium ion battery will continue to dissolve, thereby causing the cycle performance of the sodium ion battery to deteriorate and the capacity to decrease continuously. Therefore, it is of great importance to solve the problem of SEI film and CEI film dissolution in the high-voltage charging and discharging process of sodium ion batteries and to develop a high-voltage electrolyte suitable for sodium ion batteries. SUMMARY

[0004] Based on the technical problems existing in the background art, the present application provides a sodium ion battery electrolyte and a sodium ion battery.

[0005] The sodium ion battery electrolyte provided by the present application comprises a sodium salt, an organic solvent and an additive.

[0006] The sodium ion battery electrolyte provided by the present application helps to improve the problems of poor cycle stability and capacity decay in the high-voltage charging and discharging process of sodium ion batteries.

[0007] Preferably, the sodium ion battery electrolyte comprises 5-40 parts by mass of sodium salt, 70-95 parts by mass of organic solvent and 0.1-8 parts by mass of additive.

[0008] The prepared sodium ion battery electrolyte of the application can form relatively complete SEI film and CEI film by controlling the proportion of raw materials, improve the energy density of the battery, and prolong the service life of the battery.

[0009] Preferably, the thioimide functional additive is N-cyclohexyl thio-phthalimide.

[0010] The basic imide group in the thioimide functional additive in the application can react with hydrofluoric acid and trace water in the electrolyte, which can effectively avoid the damage of hydrofluoric acid and trace water to the SEI film, and the benzene ring and imide ring structure can help to form a flat and dense SEI film on the negative electrode, which can help to improve the energy density and cycle stability of the sodium ion battery.

[0011] Preferably, the film-forming additive is selected from one or more of 1,3-propanesulfonic acid lactone, fluorinated ethylene carbonate, vinyl sulfate, and sodium bis-trifluoromethanesulfonimide.

[0012] The film-forming additive can form a flat, dense and stable solid electrolyte interface (SEI) film on the electrode surface, effectively inhibit the occurrence of harmful side reactions and reduce the consumption of electrolyte, thereby improving the cycle stability of the sodium ion battery.

[0013] Preferably, the mass ratio of the thioimide functional additive and the film-forming additive is (0.05-0.2):6.

[0014] The thioimide functional additive and the film-forming additive synergistically prevent the electrolyte from being oxidized on the positive electrode, prevent the dissolution of transition metal ions, and at the same time, construct stable CEI film and SEI film, avoid the continuous consumption of electrolyte, solve the problem of continuous capacity decay of the battery in the process of high-voltage charging and discharging cycle, and improve the service life of the sodium ion battery.

[0015] Preferably, the organic solvent is an ether organic solvent; and the ether organic solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

[0016] The electrolyte prepared by the ether organic solvent has better compatibility with the negative electrode hard carbon; the weak solvation structure of the ether organic solvent can form a uniform and stable CEI film on the positive electrode, solving the problem of dissolution of the CEI film under high pressure; and the ether organic solvent and the additive synergistically construct a uniform and stable SEI film and CEI film.

[0017] Preferably, the sodium salt is selected from one or more of sodium hexafluorophosphate and sodium perchlorate.

[0018] The coordination between the ether organic solvent and the sodium salt can improve the stability of the sodium ion battery in the high-voltage charging and discharging process, and a sodium ion battery with excellent performance is prepared.

[0019] The application further provides a sodium ion battery, which comprises a positive electrode sheet, a separator, a negative electrode sheet and the sodium ion battery electrolyte.

[0020] Preferably, the positive electrode sheet comprises a positive electrode current collector and a positive electrode coating layer coated on the positive electrode current collector, and the positive electrode coating layer comprises the following raw materials in parts by mass: 90-96 parts of a positive electrode active material, 0.5-2 parts of oxalic acid, 1-3 parts of a conductive agent and 1-3 parts of a binder.

[0021] More preferably, the positive electrode active material is selected from one or more of NaNi 1 / 3 Fe 1 / 3 Mn l / 3 O2, NaNi 0.25 Fe 0.25 Mn 0.5 O2.

[0022] More preferably, the preparation of the positive electrode sheet comprises: adding the positive electrode active material, the oxalic acid, the conductive agent and the binder into a solvent, uniformly dispersing to obtain a positive electrode slurry, uniformly coating the positive electrode slurry on the positive electrode current collector, performing baking drying, roller pressing and die cutting, and the positive electrode slurry forms a positive electrode coating layer, so that the positive electrode sheet is obtained.

[0023] More preferably, the solvent is N-methyl pyrrolidone, and the positive electrode current collector is a carbon-coated aluminum foil.

[0024] Preferably, the negative electrode sheet comprises a negative electrode current collector and a negative electrode coating layer coated on the negative electrode current collector, and the negative electrode coating layer comprises the following raw materials in parts by mass: 90-96 parts of a negative electrode active material, 1-4 parts of a conductive agent and 1-5 parts of a binder.

[0025] More preferably, the negative electrode active material is hard carbon.

[0026] More preferably, the preparation of the negative electrode sheet comprises: adding the negative electrode active material, the conductive agent and the binder into a solvent, uniformly dispersing to obtain a negative electrode slurry, uniformly coating the negative electrode slurry on the negative electrode current collector, performing baking drying, roller pressing and die cutting, and the negative electrode slurry forms a negative electrode coating layer, so that the negative electrode sheet is obtained.

[0027] More preferably, the solvent is water, and the negative electrode current collector is a carbon-coated aluminum foil.

[0028] Preferably, the separator is a PP and PE mixed separator.

[0029] A preparation method of a sodium ion battery, comprising the following steps: stacking a positive electrode sheet, a diaphragm and a negative electrode sheet into an electric core, packaging, drying, injecting the above-mentioned sodium ion battery electrolyte, carrying out infiltration, formation, aging, air extraction sealing, and distribution, and obtaining the sodium ion battery.

[0030] The preparation method of the sodium ion battery can prepare the sodium ion battery with excellent charge-discharge performance and long service life.

[0031] The present application has the following advantages:

[0032] The film-forming additive of the present application can form a good SEI film on the electrode surface. The thioimide functional additive has a basic group, which can combine with hydrofluoric acid and trace water in the fluorine-containing electrolyte, thereby removing the hydrofluoric acid and water, preventing damage to the SEI film, and the electronegativity of the sulfur atom is stronger, more inclined to preferentially undergo an electrochemical reduction reaction, improving the film-forming effect of the SEI film of the electrolyte, and improving the occurrence of side reactions. The present application selects an ether organic solvent to solve the problem that the CEI film formed by the ester carbonate solvent in the positive electrode of the sodium ion battery is unstable and some substances will continuously dissolve.

[0033] The sodium ion battery electrolyte used in the present application can form a relatively complete SEI film and CEI film, inhibit the dissolution of the SEI film and CEI film, inhibit the occurrence of harmful side reactions in the battery, improve the dissolution of the SEI film and CEI film under high pressure, improve the cycle stability of the battery under high pressure, and thereby improve the energy density and service life of the sodium ion battery. DETAILED DESCRIPTION

[0034] The technical solutions of the present application are described in detail through specific embodiments.

[0035] The materials, reagents and the like used in the following examples and comparative examples can be obtained from commercial channels unless otherwise specified.

[0036] Example 1

[0037] A preparation method of a sodium ion battery electrolyte, comprising the following steps:

[0038] In an argon atmosphere glove box with a water oxygen content of less than 0.01 ppm, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and 1,3-dioxolane are mixed in a mass ratio of 6:3:1 to obtain an organic solvent; sodium hexafluorophosphate, 1,3-propanesultone and fluoroethylene carbonate are dissolved in the organic solvent to obtain the sodium ion battery electrolyte; the concentration of sodium hexafluorophosphate in the sodium ion battery electrolyte is 1 mol / L, the mass percentage of fluoroethylene carbonate in the total mass of the sodium ion battery electrolyte is 5%, and the mass percentage of 1,3-propanesultone in the total mass of the sodium ion battery electrolyte is 1%.

[0039] Example 2

[0040] A preparation method of a sodium ion battery electrolyte, comprising the following steps:

[0041] In an argon atmosphere glove box with water oxygen content less than 0.01 ppm, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and 1,3-dioxolane are mixed according to a mass ratio of 6:3:1 to obtain an organic solvent; sodium hexafluorophosphate, 1,3-propane sultone, fluoroethylene carbonate and N-cyclohexylthiophthalimide are dissolved in the organic solvent to obtain the sodium ion battery electrolyte; the concentration of sodium hexafluorophosphate in the sodium ion battery electrolyte is 1 mol / L, the mass percentage of fluoroethylene carbonate in the total mass of the sodium ion battery electrolyte is 5%, the mass percentage of 1,3-propane sultone in the total mass of the sodium ion battery electrolyte is 1%, and the mass percentage of N-cyclohexylthiophthalimide in the total mass of the sodium ion battery electrolyte is 0.05%.

[0042] Example 3

[0043] A preparation method of a sodium ion battery electrolyte, comprising the following steps:

[0044] In an argon atmosphere glove box with water oxygen content less than 0.01 ppm, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and 1,3-dioxolane are mixed according to a mass ratio of 6:3:1 to obtain an organic solvent; sodium hexafluorophosphate, 1,3-propane sultone, fluoroethylene carbonate and N-cyclohexylthiophthalimide are dissolved in the organic solvent to obtain the sodium ion battery electrolyte; the concentration of sodium hexafluorophosphate in the sodium ion battery electrolyte is 1 mol / L, the mass percentage of fluoroethylene carbonate in the total mass of the sodium ion battery electrolyte is 5%, the mass percentage of 1,3-propane sultone in the total mass of the sodium ion battery electrolyte is 1%, and the mass percentage of N-cyclohexylthiophthalimide in the total mass of the sodium ion battery electrolyte is 0.1%.

[0045] Example 4

[0046] A preparation method of a sodium ion battery electrolyte, comprising the following steps:

[0047] In an argon atmosphere glove box with water and oxygen content less than 0.01 ppm, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and 1,3-dioxolane were mixed according to a mass ratio of 6:3:1 to obtain an organic solvent; sodium hexafluorophosphate, 1,3-propanesultone, fluoroethylene carbonate and N-cyclohexylthiophthalimide were dissolved in the organic solvent to obtain a sodium ion battery electrolyte; the concentration of sodium hexafluorophosphate in the sodium ion battery electrolyte was 1 mol / L, the mass percentage of fluoroethylene carbonate in the total mass of the sodium ion battery electrolyte was 5%, the mass percentage of 1,3-propanesultone in the total mass of the sodium ion battery electrolyte was 1%, and the mass percentage of N-cyclohexylthiophthalimide in the total mass of the sodium ion battery electrolyte was 0.2%.

[0048] Comparative Example 1

[0049] The difference between the present comparative example and Example 1 is only that 1,3-propanesultone is not added, and the remaining steps are the same as those of Example 1.

[0050] Comparative Example 2

[0051] The difference between the present comparative example and Example 1 is only that the organic solvent is a mixture of ethylene carbonate, dimethyl carbonate and propylene carbonate according to a mass ratio of 1:1:1, and the remaining steps are the same as those of Example 1.

[0052] The above electrolyte, a positive electrode sheet, a separator and a negative electrode sheet were assembled to obtain a sodium ion battery, specifically as follows.

[0053] Preparation of the positive electrode sheet: NaNi 1 / 3 Fe 1 / 3 Mn l / 3 O2, oxalic acid, conductive agent SP, conductive agent GOs and PVDF were mixed according to a mass ratio of 93.5:0.5:1.75:1.25:3, N-methyl pyrrolidone was added, and the mixture was fully stirred according to the homogenization process to obtain a positive electrode slurry with a solid content of 57%, which was then coated on a positive electrode current collector carbon-coated aluminum foil with a coating thickness of 340 μm, and then dried, rolled, die-cut, and the positive electrode slurry formed a positive electrode coating to obtain the positive electrode sheet.

[0054] Preparation of the negative electrode sheet: hard carbon, SP, CMC and SBR were mixed according to a mass ratio of 94:2.4:1.4:2.4, deionized water was added, and the mixture was fully stirred according to the homogenization process to obtain a negative electrode slurry with a solid content of 50%, which was then coated on a negative electrode current collector carbon-coated aluminum foil with a coating thickness of 150 μm, and then dried, rolled, die-cut, and the negative electrode slurry formed a negative electrode coating to obtain the negative electrode sheet.

[0055] Sodium ion battery preparation: the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive and negative electrodes to act as a barrier, to obtain a dry battery; the dry battery is placed in an aluminum plastic film, dried at 80-95°C for 15-30h, then injected with the prepared sodium ion battery electrolyte and packaged, and the battery is subjected to high-temperature infiltration, formation, aging, vacuum sealing, and capacity testing to obtain the sodium ion battery.

[0056] The sodium ion battery prepared above is tested for first charge-discharge efficiency and 25°C cycle capacity retention rate for 200 cycles. The test results are shown in Table 1.

[0057] Table 1

[0058]

[0059] As can be seen from the data in Table 1, the sodium ion battery prepared by the present application has a higher capacity retention rate under high voltage conditions. In combination with Example 1 and Comparative Example 1, it can be seen that the addition of 1,3 propanesultone to the sodium ion electrolyte can improve the capacity retention rate of the sodium ion battery, because 1,3 propanesultone can prevent the oxidation of the electrolyte on the positive electrode surface, inhibit the dissolution of transition metal ions, and at the same time build a stable SEI film, thereby improving the cycle performance of the sodium ion battery and prolonging the service life of the battery.

[0060] In combination with Example 1 and Comparative Example 2, it can be seen that the sodium ion battery using an ether-based electrolyte has better cycle stability under high voltage, because the ether-based electrolyte has better compatibility with the negative electrode hard carbon than the ester-based electrolyte, and the ether-based electrolyte helps to build a stable CEI film, thereby improving the cycle stability of the sodium ion battery under high voltage.

[0061] In combination with Examples 2-4 and Example 1, it can be seen that the addition of N-cyclohexylthiophthalimide to the sodium ion electrolyte can effectively improve the capacity retention rate of the sodium ion battery under high voltage, because the imide group in N-cyclohexylthiophthalimide can absorb trace amounts of hydrofluoric acid and water in the electrolyte, and the benzene ring and imide ring help to form a flat and stable SEI film, inhibit the occurrence of harmful side reactions, and improve the cycle stability of the sodium ion battery.

[0062] In summary, the present application uses an ether-based organic solvent in combination with the film-forming additives 1,3 propanesultone, fluoroethylene carbonate, and the thiophthalimide functional additive, to obtain a sodium ion battery with stable SEI and CEI films, effectively improving the cycle performance of the sodium ion battery under high voltage, improving the energy density of the battery, and prolonging the service life of the battery.

[0063] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A sodium-ion battery electrolyte, characterized in that, It includes sodium salts, organic solvents, and additives; the additives are selected from one or more of thioimide functional additives and film-forming additives.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, The thioimide functional additive is N-cyclohexylthiophthalimide.

3. The sodium-ion battery electrolyte according to claim 1, characterized in that, The film-forming additive is selected from one or more of 1,3-propanesulfonate lactone, fluoroethylene carbonate, ethylene sulfate, and sodium bis(trifluoromethanesulfonyl)imide.

4. The sodium-ion battery electrolyte according to any one of claims 1-3, characterized in that, The mass ratio of the thioimide functional additive to the film-forming additive is (0.05-0.2):

6.

5. The sodium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent is an ether-based organic solvent; the ether-based organic solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

6. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt is selected from one or more of sodium hexafluorophosphate and sodium perchlorate.

7. The sodium-ion battery electrolyte according to claim 1, characterized in that, By weight, it includes 5-40 parts sodium salt, 70-95 parts organic solvent, and 0.1-8 parts additives.

8. A sodium-ion battery, characterized in that, It includes a positive electrode, a separator, a negative electrode, and the sodium-ion battery electrolyte according to any one of claims 1-7.

9. The sodium-ion battery according to claim 8, characterized in that, The positive electrode active material in the aforementioned positive electrode sheet is selected from NaNi 1 / 3 Fe 1 / 3 Mn l / 3 O2, NaNi 0.25 Fe 0.25 Mn 0.5 One or more of O2.

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