Electrolyte, sodium ion battery and electrical equipment

Abstract

The present invention relates to the field of battery technology and discloses an electrolyte, a sodium ion battery, and an electrical device. The electrolyte contains a sodium salt, an organic solvent, and a first additive, wherein the first additive is a compound represented by formula (I), wherein R1, R2, and R3 are each independently selected from a fluorine-containing substituent. By adding the first additive to the electrolyte, the present invention improves the electrolyte's high-voltage resistance and significantly enhances the cycle performance of the sodium ion battery. #imgabs0#

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrolyte, a sodium ion battery and electrical equipment. Background Art

[0002] Secondary batteries are attracting increasing attention due to their high energy density and excellent cycle performance. To meet the energy density requirements for secondary batteries, the development of secondary batteries is gradually moving towards high energy density and high safety. Currently, one method to improve the energy density of secondary batteries is to increase the charge cutoff voltage of the secondary battery. As the charge cutoff voltage increases, the valence of the transition metal in the secondary battery's positive electrode material also increases, resulting in increased side reactions between the positive electrode material and the electrolyte, which in turn leads to a series of changes such as the decomposition of the electrolyte and the generation of gas.

[0003] Currently, alkali metal secondary batteries primarily use ester electrolytes as electrolytes. However, these electrolytes have weak high-voltage resistance and a low initial oxidation potential. Furthermore, metal ions are easily leached from the electrolyte during use, leading to electrolyte decomposition and increased battery internal resistance, which in turn affects the battery's cycle life. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of low initial oxidation potential of the electrolyte and low cycle capacity retention rate of the sodium ion battery in the prior art, and to provide an electrolyte, a sodium ion battery and an electrical device. By adding a first additive to the system, the high-voltage resistance of the electrolyte can be greatly improved, and the cycle performance of the sodium ion battery is significantly improved.

[0005] In order to achieve the above object, the first aspect of the present invention provides an electrolyte, which contains a sodium salt, an organic solvent and a first additive, wherein the first additive is a compound represented by formula (I):

[0006]

[0007] wherein R1, R2 and R3 are each independently selected from fluorine-containing substituents.

[0008] Optionally, the fluorine-containing substituent is -CF3, -CHF2, -CH2F and -(CH2) n At least one of CH2F, wherein n is an integer from 1 to 6.

[0009] Optionally, the first additive is at least one of p-trifluoromethylbenzyl acetonitrile, 3,5-trifluoromethylbenzyl acetonitrile, 3-trifluoromethylbenzyl acetonitrile and p-3,4,5-trifluoromethylbenzyl acetonitrile.

[0010] Optionally, based on the total weight of the electrolyte, the content of the first additive is 0.5-30 wt%.

[0011] Optionally, based on the total weight of the electrolyte, the content of the first additive is 0.8-10 wt %.

[0012] Optionally, the concentration of the sodium salt is 0.5-3 mol / L.

[0013] Optionally, the electrolyte further contains a second additive, which is a fluorinated carbonate.

[0014] Optionally, the weight ratio of the first additive to the second additive is 1:(0.1-1).

[0015] Optionally, the second additive is selected from one or more of fluoroethylene carbonate, difluoroethylene carbonate and 3,3,3-trifluoropropylene carbonate.

[0016] Optionally, the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium bis(trifluoromethylsulfonyl)imide and sodium bis(fluorosulfonyl)imide.

[0017] Optionally, the organic solvent is selected from one or more of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate.

[0018] A second aspect of the present invention provides a sodium ion battery comprising a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the electrolyte is the above-mentioned electrolyte.

[0019] A third aspect of the present invention provides an electrical device, which includes the above-mentioned sodium ion battery.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention adds a first additive to the electrolyte, thereby increasing the initial oxidation potential of the electrolyte and improving the high-voltage resistance of the electrolyte; and the cycle performance of the sodium ion battery is significantly improved, with the capacity retention rate of the sodium ion battery still exceeding 90% after 100 charge / discharge cycles;

[0022] (2) The present invention adds a first additive to the electrolyte. The acetonitrile groups (-C-CN) attached to the meta and para positions of the benzene ring of the first additive can complex with the metal ions in the positive electrode active material, thereby reducing the decomposition of the electrolyte and inhibiting the dissolution of metal ions.

[0023] (3) The present invention adds a first additive to the electrolyte. The strong electron-withdrawing groups (fluorine-containing substituents) introduced at different positions of the benzene ring of the first additive can lower the energy levels of the highest occupied molecular orbital (HOMO) / lowest unoccupied molecular orbital (LUMO), thereby precisely regulating the initial oxidation potential of the electrolyte.

[0024] (4) The present invention adds a first additive to the electrolyte, which broadens the electrochemical window and inhibits the dissolution of positive electrode metal ions. The monomer can undergo electrochemical polymerization on the surface of the positive electrode to form a dense thin layer of conductive polymer film, which can reduce the internal resistance of the battery, inhibit the further reaction of the electrolyte with the positive electrode material under high voltage conditions, and improve the battery performance. DETAILED DESCRIPTION

[0025] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0026] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0027] A first aspect of the present invention provides an electrolyte comprising a sodium salt, an organic solvent, and a first additive, wherein the first additive is a compound represented by formula (I):

[0028]

[0029] wherein R1, R2 and R3 are each independently selected from fluorine-containing substituents.

[0030] In the present invention, the fluorine-containing substituents are -CF3, -CHF2, -CH2F and -(CH2) n At least one of CH2F, wherein n is an integer from 1 to 6.

[0031] In the present invention, the acetonitrile group (-C-CN) can complex with the metal ions in the positive electrode active material, reducing electrolyte decomposition and inhibiting metal ion dissolution. The introduction of a strong electron-withdrawing group can lower the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), precisely regulating the electrolyte's initial oxidation potential. Therefore, a first additive having a strong electron-withdrawing group is added to the electrolyte. The first additive is at least one of p-trifluoromethylphenylacetonitrile, 3,5-trifluoromethylphenylacetonitrile, 3-trifluoromethylphenylacetonitrile, and p-3,4,5-trifluoromethylphenylacetonitrile.

[0032] In the present invention, in order to precisely control the initial oxidation potential of the electrolyte, the content of the first additive is 0.5-30 wt % based on the total weight of the electrolyte.

[0033] In a specific embodiment of the present invention, the content of the first additive is 0.8-10 wt % based on the total weight of the electrolyte. Within this range, the first additive can effectively improve the high-voltage resistance of the electrolyte. Specifically, the content of the first additive can be 0.8 wt %, 1 wt %, 3 wt %, 5 wt %, or 10 wt %.

[0034] In the present invention, in order to ensure that the electrolyte has good fluidity, wettability and high ionic conductivity, the concentration of the sodium salt is 0.5-3 mol / L. Specifically, the concentration of the sodium salt can be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L.

[0035] In the present invention, the sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium bis(trifluoromethylsulfonyl)imide and sodium bis(fluorosulfonyl)imide.

[0036] In a specific embodiment of the present invention, sodium hexafluorophosphate (NaPF6) is used as the sodium salt due to its high ionic conductivity, stable chemical properties and low price.

[0037] In the present invention, in order to form a dense SEI (solid electrolyte interface) film, the electrolyte further contains a second additive, which is a fluorinated carbonate.

[0038] In the present invention, in order to improve the performance of the formed SEI film, the weight ratio of the first additive to the second additive is 1:(0.1-1). Specifically, the weight ratio of the first additive to the second additive can be 1:0.1, 1:0.5 or 1:1.

[0039] In the present invention, the second additive is selected from one or more of fluoroethylene carbonate, bisfluoroethylene carbonate and 3,3,3-trifluoropropylene carbonate.

[0040] In a specific embodiment of the present invention, the second additive is fluoroethylene carbonate because fluoroethylene carbonate is conducive to forming a SEI film, forming a tight structural layer without increasing impedance, preventing further decomposition of the electrolyte, and improving the low-temperature performance of the electrolyte.

[0041] In a specific embodiment of the present invention, the additive is a combination of fluoroethylene carbonate and p-trifluoromethylbenzyl cyanide, and the weight ratio of p-trifluoromethylbenzyl cyanide to fluoroethylene carbonate is 1:(0.1-1). Specifically, the weight ratio of p-trifluoromethylbenzyl cyanide to fluoroethylene carbonate can be 1:0.1, 1:0.5 or 1:1.

[0042] In another specific embodiment of the present invention, the additive is a combination of fluoroethylene carbonate and 3,5-trifluoromethylbenzyl cyanide, and the weight ratio of 3,5-trifluoromethylbenzyl cyanide to fluoroethylene carbonate is 1:(0.1-1). Specifically, the weight ratio of 3,5-trifluoromethylbenzyl cyanide to fluoroethylene carbonate can be 1:0.1, 1:0.5 or 1:1.

[0043] In another specific embodiment of the present invention, the additive is a combination of fluoroethylene carbonate and 3-trifluoromethylbenzyl cyanide, and the weight ratio of 3-trifluoromethylbenzyl cyanide to fluoroethylene carbonate is 1:(0.1-1). Specifically, the weight ratio of 3-trifluoromethylbenzyl cyanide to fluoroethylene carbonate can be 1:0.1, 1:0.5 or 1:1.

[0044] In another specific embodiment of the present invention, the additive is a combination of fluoroethylene carbonate and 3,4,5-trifluoromethylbenzene acetonitrile, and the weight ratio of 3,4,5-trifluoromethylbenzene acetonitrile to fluoroethylene carbonate is 1:(0.1-1). Specifically, the weight ratio of 3,4,5-trifluoromethylbenzene acetonitrile to fluoroethylene carbonate can be 1:0.1, 1:0.5 or 1:1.

[0045] In the present invention, an organic solvent is also required in the electrolyte. The organic solvent can ensure that the electrolyte has good fluidity, wettability and high ionic conductivity. The organic solvent is selected from one or more of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate.

[0046] In a preferred embodiment of the present invention, since the solvent formed by the combination of ethylene carbonate, propylene carbonate, and diethyl carbonate can better dissolve the sodium salt, the first additive, and the second additive, the solvent is a combination of ethylene carbonate, propylene carbonate, and diethyl carbonate, and the volume ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate is 1:(0.5-1.5):(1-3). Specifically, the volume ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate can be 1:0.5:1, 1:1:2, or 1:1.5:3.

[0047] A second aspect of the present invention provides a sodium ion battery comprising a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the electrolyte is the above-mentioned electrolyte.

[0048] In the present invention, the positive electrode includes a positive electrode current collector and a positive electrode film. The positive electrode film contains a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, and a dispersant. The weight ratio of the positive electrode active material, the positive electrode conductive agent, the positive electrode binder, and the dispersant is (60-100):1:(1-3):(1-3). Specifically, the weight ratio of the positive electrode active material, the positive electrode conductive agent, the positive electrode binder, and the dispersant can be 60:1:1:1, 80:1:2:2, or 100:1:3:3.

[0049] In the present invention, the positive electrode current collector is selected from one or more of aluminum foil, carbon-coated aluminum foil or foamed aluminum.

[0050] In a specific embodiment of the present invention, the positive electrode current collector is aluminum foil.

[0051] In the present invention, the positive electrode active material is selected from one or more of sodium ferric pyrophosphate, sodium ferrous sulfate, sodium nickel iron manganese oxide and Prussian blue.

[0052] In the present invention, the positive electrode conductive agent is selected from one or more of conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, graphene and graphene oxide.

[0053] In the present invention, the positive electrode binder is selected from one or more of polyvinylidene fluoride, sodium hydroxymethyl cellulose, sodium alginate, chitosan, guar gum, lignin, sericin and polyacrylic acid.

[0054] In the present invention, the dispersant is selected from one or more of polyvinyl pyrrolidone, styrene maleic anhydride and polyacrylic acid.

[0055] In a specific embodiment of the present invention, the dispersant is polyvinylpyrrolidone (PVP).

[0056] In a specific embodiment of the present invention, the positive electrode film is a combination of sodium nickel iron manganese oxide, conductive carbon black, polyvinylidene fluoride and PVP, and the weight ratio of sodium nickel iron manganese oxide, conductive carbon black, polyvinylidene fluoride and PVP is 80:1:1:1.

[0057] In the present invention, the negative electrode includes a negative electrode current collector and a negative electrode film. The negative electrode film contains a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and a dispersant. The weight ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode binder, and the dispersant is (60-100):1:(1-3):(1-3). Specifically, the weight ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode binder, and the dispersant can be 60:1:1:1, 80:1:2:2, or 100:1:3:3.

[0058] In the present invention, the negative electrode current collector is selected from one or more of copper foil, aluminum foil and nickel foam.

[0059] In a specific embodiment of the present invention, the negative electrode current collector is aluminum foil.

[0060] In the present invention, the negative electrode active material is selected from one or more of graphite, hard carbon and sodium alloy powder.

[0061] In the present invention, the negative electrode conductive agent is selected from one or more of conductive carbon black, graphene and nanocarbon fibers.

[0062] In the present invention, the negative electrode binder is selected from one or more of sodium polyacrylate, carboxymethyl cellulose, styrene-butadiene rubber and polyacrylonitrile.

[0063] In a specific embodiment of the present invention, the negative electrode film is a combination of graphite, conductive carbon black, sodium polyacrylate and PVP, and the weight ratio of graphite, conductive carbon black, sodium polyacrylate and PVP is 100:1:3:3.

[0064] In the present invention, the separator is selected from one or more of single-layer polypropylene, double-layer polypropylene and three-layer polypropylene-polyethylene-polypropylene.

[0065] In a specific embodiment of the present invention, the separator is a single layer of polypropylene.

[0066] In the present invention, the sodium ion battery further comprises a battery case, which is used to assemble the positive electrode, the separator, the electrolyte and the negative electrode.

[0067] A third aspect of the present invention provides an electrical device, which includes the above-mentioned sodium ion battery.

[0068] The present invention will be described in detail below through examples, comparative examples and test examples. The examples, comparative examples and test examples are implemented based on the technical solution of the present invention and provide specific operating processes, but the scope of protection of the present invention is not limited to the following examples.

[0069] The experimental methods in the following examples, comparative examples and test examples, unless otherwise specified, are conventional methods in the art. The experimental materials used in the following examples, comparative examples and test examples, unless otherwise specified, are all commercially available.

[0070] Example 1

[0071] (1) Preparation of positive electrode: Take positive electrode materials (aluminum foil, sodium nickel iron manganese oxide, conductive carbon black, polyvinylidene fluoride, and PVP), add 80g of sodium nickel iron manganese oxide, 10g of conductive carbon black, and 10g of polyvinylidene fluoride to 10g of PVP and mix them to prepare positive electrode slurry, and evenly coat the positive electrode slurry on aluminum foil with a thickness of 18μm, and then dry, roll, and cut to prepare the positive electrode;

[0072] (2) Preparation of the negative electrode: A negative electrode material (aluminum foil, graphite, conductive carbon black, sodium polyacrylate, and PVP) was prepared by adding 100 g of graphite, 1 g of conductive carbon black, and 3 g of sodium polyacrylate to 3 g of PVP and mixing them to prepare a negative electrode slurry. The negative electrode slurry was evenly coated on an aluminum foil with a thickness of 18 μm, and then dried, rolled, and cut to prepare a negative electrode.

[0073] (3) Preparation of electrolyte: In a glove box with a water content and an oxygen content of less than 0.1 ppm, 168 g of NaPF6 was dissolved in 1000 mL (1200 g) of solvent at room temperature (25°C) to obtain a NaPF6 solution. The solvent was a combination of ethylene carbonate, propylene carbonate, and diethyl carbonate (the volume ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate was 1:1:2). The concentration of the NaPF6 solution was 1 mol / L. Subsequently, 13.7 g of the first additive (p-trifluoromethylbenzeneacetonitrile) and 6.9 g of the second additive (fluoroethylene carbonate) were added to the NaPF6 solution in sequence. After mixing, electrolyte A1 was obtained.

[0074] (4) Assembly of sodium ion battery: The positive electrode, single-layer polypropylene, and negative electrode are stacked in sequence and wound into a bare cell, which is then placed in a battery case, injected with electrolyte, and sealed to form a sodium ion battery B1.

[0075] Example 2

[0076] (1) Preparation of positive electrode: Take positive electrode materials (aluminum foil, sodium nickel iron manganese oxide, conductive carbon black, polyvinylidene fluoride, and PVP), add 80g of sodium nickel iron manganese oxide, 10g of conductive carbon black, and 10g of polyvinylidene fluoride to 10g of PVP and mix them to prepare positive electrode slurry, and evenly coat the positive electrode slurry on aluminum foil with a thickness of 18μm, and then dry, roll, and cut to prepare the positive electrode;

[0077] (2) Preparation of the negative electrode: A negative electrode material (aluminum foil, graphite, conductive carbon black, sodium polyacrylate, and PVP) was prepared by adding 100 g of graphite, 1 g of conductive carbon black, and 1 g of sodium polyacrylate to 3 g of PVP and mixing them to prepare a negative electrode slurry. The negative electrode slurry was evenly coated on an aluminum foil with a thickness of 18 μm, and then dried, rolled, and cut to obtain a negative electrode.

[0078] (3) Preparation of electrolyte: In a glove box with a water content and an oxygen content of less than 0.1 ppm, 336 g of NaPF6 was dissolved in 1000 mL (1200 g) of solvent at room temperature (25°C) to obtain a NaPF6 solution. The solvent was a combination of ethylene carbonate, propylene carbonate, and diethyl carbonate (the volume ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate was 1:1:2). The concentration of the NaPF6 solution was 2 mol / L. Then, 15.4 g of the first additive (p-trifluoromethylbenzeneacetonitrile) and 7.7 g of the second additive (fluoroethylene carbonate) were added to the NaPF6 solution in sequence. After mixing, electrolyte A2 was obtained.

[0079] (4) Assembly of sodium ion battery: The positive electrode, single-layer polypropylene, and negative electrode are stacked in sequence and wound into a bare cell, which is then placed in a battery case, injected with electrolyte, and sealed to form a sodium ion battery B2.

[0080] Example 3

[0081] (1) Preparation of positive electrode: Take positive electrode materials (aluminum foil, sodium nickel iron manganese oxide, conductive carbon black, polyvinylidene fluoride, and PVP), add 80g of sodium nickel iron manganese oxide, 10g of conductive carbon black, and 10g of polyvinylidene fluoride to 10g of PVP and mix them to prepare positive electrode slurry, and evenly coat the positive electrode slurry on aluminum foil with a thickness of 18μm, and then dry, roll, and cut to prepare the positive electrode;

[0082] (2) Preparation of the negative electrode: A negative electrode material (aluminum foil, graphite, conductive carbon black, sodium polyacrylate, and PVP) was prepared by adding 100 g of graphite, 1 g of conductive carbon black, and 3 g of sodium polyacrylate to 3 g of PVP and mixing them to prepare a negative electrode slurry. The negative electrode slurry was evenly coated on an aluminum foil with a thickness of 18 μm, and then dried, rolled, and cut to prepare a negative electrode.

[0083] (3) Preparation of electrolyte: In a glove box with a water content and an oxygen content of less than 0.1 ppm, 420 g of NaPF6 was dissolved in 1000 mL (1200 g) of solvent at room temperature (25°C) to obtain a NaPF6 solution. The solvent was a combination of ethylene carbonate, propylene carbonate, and diethyl carbonate (the volume ratio of ethylene carbonate, propylene carbonate, and diethyl carbonate was 1:1:2). The concentration of the NaPF6 solution was 2.5 mol / L. Subsequently, 16.2 g of the first additive (p-trifluoromethylbenzeneacetonitrile) and 8.1 g of the second additive (fluoroethylene carbonate) were added to the NaPF6 solution in sequence. After mixing, electrolyte A3 was obtained.

[0084] (4) Assembly of sodium ion battery: The positive electrode, single-layer polypropylene, and negative electrode are stacked in sequence and wound into a bare cell, which is then placed in a battery case, injected with electrolyte, and sealed to form a sodium ion battery B3.

[0085] Example 4

[0086] According to the method of Example 1, except that the first additive used in Example 4 is 3,5-trifluoromethylbenzeneacetonitrile, electrolyte A4 is prepared, and finally sodium ion battery B4 is prepared.

[0087] Example 5

[0088] According to the method of Example 1, except that the first additive used in Example 5 is 3-trifluoromethylbenzyl cyanide, electrolyte A5 is prepared, and finally sodium ion battery B5 is prepared.

[0089] Example 6

[0090] The method of Example 1 was followed, except that the first additive used in Example 6 was 3,4,5-trifluoromethylbenzeneacetonitrile, to prepare electrolyte A6, and finally prepare sodium ion battery B6.

[0091] Example 7

[0092] According to the method of Example 1, except that the weight of the first additive (p-trifluoromethylphenylacetonitrile) in Example 7 is 41.1 g, electrolyte A7 is prepared, and finally a sodium ion battery B7 is prepared.

[0093] Example 8

[0094] According to the method of Example 1, except that the weight of the first additive (p-trifluoromethylphenylacetonitrile) in Example 8 is 68.5 g, electrolyte A8 is prepared, and finally a sodium ion battery B8 is prepared.

[0095] Example 9

[0096] According to the method of Example 1, except that the weight of the first additive (p-trifluoromethylphenylacetonitrile) in Example 9 is 137 g, electrolyte A9 is prepared, and finally sodium ion battery B9 is prepared.

[0097] Comparative Example 1

[0098] According to the method of Example 1, except that the first additive used in Comparative Example 1 is benzyl cyanide, an electrolyte C1 is prepared, and finally a sodium ion battery D1 is prepared.

[0099] Comparative Example 2

[0100] According to the method of Example 7, except that the first additive used in Comparative Example 2 is benzyl cyanide, an electrolyte C2 is prepared, and finally a sodium ion battery D2 is prepared.

[0101] Comparative Example 3

[0102] The method of Example 8 was followed, except that the first additive used in Comparative Example 3 was benzyl cyanide, to prepare electrolyte C3, and finally prepare sodium ion battery D3.

[0103] Comparative Example 4

[0104] The method of Example 9 was followed, except that the first additive used in Comparative Example 4 was benzyl cyanide, to prepare electrolyte C4, and finally prepare sodium ion battery D4.

[0105] Comparative Example 5

[0106] According to the method of Example 1, except that the first additive was not used in Comparative Example 5, electrolyte C5 was prepared, and finally a sodium ion battery D5 was prepared.

[0107] Test Example 1

[0108] The onset oxidation potentials of electrolytes A1-A9 and C1-C5 in Examples 1-9 and Comparative Examples 1-5 were tested by linear sweep voltammetry. The testing method included the following steps:

[0109] Testing equipment: Princeton electrochemical workstation;

[0110] Test conditions: scan rate 0.1mV / s, range 0-6V;

[0111] Test battery structure: button battery, model CR2032, stainless steel (positive electrode) / glass fiber separator + experimental electrolyte / sodium sheet (negative electrode);

[0112] The results are shown in Table 1:

[0113] Table 1

[0114]

[0115]

[0116] As can be seen from Table 1, the first additive of the present application is added to the electrolyte system, and the content of the first additive is controlled within the range of 0.5-30wt% based on the total weight of the electrolyte. The initial oxidation potential of electrolytes A1-A9 is higher than the initial oxidation potential of electrolytes C1-C5. Therefore, the first additive of the present application is added to the electrolyte system and the content of the first additive is controlled within the range of 0.5-30wt% based on the total weight of the electrolyte. The high voltage resistance of the electrolyte can be improved.

[0117] Test Example 2

[0118] The cycle performance of the sodium ion batteries B1-B9 and D1-D5 in Examples 1-9 and Comparative Examples 1-5 was tested, and the testing method included the following steps:

[0119] Testing equipment: Blue Power battery testing system;

[0120] Test steps: At 25±1.5℃, charge to 4.2V at 0.2C constant current, then discharge to 1.5V at 0.2C constant current. After 3 cycles, charge to 4.2V at 1C constant current, then discharge to 1.5V at 1C constant current. After 100 charge / discharge cycles, calculate the capacity retention rate of the 100th cycle. The calculation formula is: (discharge capacity of the 100th cycle / discharge capacity of the 1st cycle) × 100%;

[0121] The test results are shown in Table 2:

[0122] Table 2

[0123]

[0124]

[0125] As can be seen from Table 2, the first additive of the present application is added to the electrolyte system, and the content of the first additive is controlled within the range of 0.5-30wt% based on the total weight of the electrolyte. The cycle performance of the sodium ion batteries B1-B9 in Examples 1-9 is higher than the cycle performance of the sodium ion batteries D1-D5 in Comparative Examples 1-5, and the cycle performance of the sodium ion batteries B1-B9 in Examples 1-9 is higher than 90%. Therefore, the use of the electrolyte of the present application can enhance the cycle performance of the sodium ion battery.

[0126] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte contains a sodium salt, an organic solvent and a first additive, wherein the first additive is at least one of 3,5-trifluoromethylbenzyl cyanide, 3-trifluoromethylbenzyl cyanide and p-3,4,5-trifluoromethylbenzyl cyanide; The electrolyte further contains a second additive, which is a fluorinated carbonate; The weight ratio of the first additive to the second additive is 1:(0.1-1).

2. The electrolyte according to claim 1, characterized in that Based on the total weight of the electrolyte, the content of the first additive is 0.5-30 wt %.

3. The electrolyte according to claim 2, characterized in that Based on the total weight of the electrolyte, the content of the first additive is 0.8-10 wt %.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The concentration of the sodium salt is 0.5-3 mol / L.

5. The electrolyte according to claim 4, characterized in that The second additive is selected from one or more of fluoroethylene carbonate, bisfluoroethylene carbonate and 3,3,3-trifluoropropylene carbonate.

6. The electrolyte according to claim 1, characterized in that The sodium salt is selected from one or more of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium difluorooxalatoborate, sodium bisoxalatoborate, sodium bis(trifluoromethylsulfonyl)imide and sodium bis(fluorosulfonyl)imide.

7. The electrolyte according to claim 1, characterized in that The organic solvent is selected from one or more of dimethyl carbonate, ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate.

8. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the electrolyte is the electrolyte according to any one of claims 1 to 7.

9. An electrical device, characterized in that: The electrical equipment includes the sodium ion battery according to claim 8.

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