CN117096435A - Sodium ion battery electrolyte additive, electrolyte and sodium ion battery - Google Patents

Abstract

The invention relates to a sodium ion battery electrolyte additive, electrolyte and a sodium ion battery, belongs to the technical field of sodium ion batteries, and aims to solve at least one of the problems of low first charge and discharge efficiency, low first discharge capacity, poor cycle performance and the like of the sodium ion battery in the prior art. The structural formula of the additive is shown as the formula (I): wherein R is ₁ Selected from one of substituted or unsubstituted C1-C5 alkyl and substituted or unsubstituted C2-C5 unsaturated hydrocarbon. The additive can improve the first charge and discharge efficiency and the first discharge capacity of the sodium ion battery, has better cycle performance, and is particularly characterized by inhibiting the attenuation of the cycle capacity of the battery and reducing the cycle gas production and the impedance increase.

Description

A sodium-ion battery electrolyte additive, electrolyte and sodium-ion battery

Technical field

The invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery electrolyte additive, an electrolyte and a sodium ion battery.

Background technique

Due to the limited global reserves of lithium resources, the cost of lithium-ion batteries has increased significantly. The abundance of sodium resources is high, its material cost is lower, and it can technically achieve similar functions to lithium-ion batteries. Therefore, the development of high-performance sodium-ion batteries can help alleviate resource problems in the new energy industry.

Like lithium-ion batteries, sodium-ion batteries are also composed of positive electrodes, negative electrodes, electrolytes and separators. Among them, the electrolyte, as a carrier for sodium ions to be transported between the positive and negative electrodes, needs to be insulated from the electrons between the positive and negative electrodes to avoid continued redox decomposition reactions in the electrolyte. However, unlike the graphite negative electrode of lithium-ion batteries, sodium-ion battery negative electrodes usually use amorphous carbon materials with large specific surface areas, such as hard carbon, as the negative electrode. The electrolyte forms a film on the surface of the hard carbon, which consumes more electrolyte and creates a passivation film. Thick and not dense enough, resulting in low first charge and discharge efficiency of the battery, and more interface side reactions will occur during cycling, resulting in rapid cycle capacity decay accompanied by gas production and impedance growth, making it impossible to obtain satisfactory electrochemical performance .

Contents of the invention

In view of the above analysis, embodiments of the present invention aim to provide a sodium-ion battery electrolyte additive, electrolyte and sodium-ion battery to solve the problem of low first charge and discharge efficiency, first discharge capacity and poor cycle performance of existing sodium-ion batteries. At least one of the questions.

On the one hand, the present invention provides a sodium ion battery electrolyte additive, the structural formula of the additive is as shown in formula (I):

Among them, R ₁ is selected from one of substituted or unsubstituted C1-C5 alkyl groups and substituted or unsubstituted C2-C5 unsaturated hydrocarbon groups.

Further, the R ₁ is selected from one of substituted or unsubstituted C1-C3 alkyl groups and substituted or unsubstituted C2-C3 unsaturated hydrocarbon groups.

Further, the additive is selected from one or more compounds 1 to 8, and the structural formula of the compounds 1 to 8 is as follows:

In a second aspect, the present invention provides a sodium ion battery electrolyte, which includes the additive, sodium salt and organic solvent.

Further, the mass of the additive accounts for 0.01 to 5% of the total mass of the electrolyte.

Further, the concentration of the sodium salt in the electrolyte is 0.2 to 2 mol/L.

Further, the sodium salt is selected from sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium methanesulfonate, sodium trifluoromethanesulfonate, sodium dioxaloborate, sodium difluoroxaloborate, One or more of sodium difluorophosphate, sodium difluorobisoxalophosphate, sodium bisfluorosulfonimide and sodium bistrifluoromethanesulfonimide.

Further, the organic solvent is selected from one or more types of carboxylic acid esters, ethers, cyclic carbonates, chain carbonates and heterocyclic compounds.

In a third aspect, the present invention provides a sodium ion battery, including the electrolyte, a positive electrode, a negative electrode and a separator.

Further, the charging voltage of the sodium-ion battery is ≤4.5V.

Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

(1) The additive of the present invention can improve the first charge and discharge efficiency and first discharge capacity of sodium-ion batteries, and also has good cycle performance, which is specifically manifested in inhibiting the attenuation of battery cycle capacity and reducing cycle gas production and impedance growth;

(2) The additive of the present invention can form a stable interface film (SEI) at the electrode/electrolyte interface. The interface film is a composite structure of organic matter and inorganic matter. The side close to the electrolyte is loose and porous where organic matter dominates. part, which is conducive to the infiltration of electrolyte and the transmission of sodium ions. The side close to the electrode material is a dense part dominated by inorganic substances, which is conducive to suppressing the occurrence of side reactions of the electrolyte. The additives can reduce the The consumption of active sodium is beneficial to the improvement of first charging efficiency and first capacity. The N-C=O structure in formula (I) has good thermal stability, and the introduction of sulfur, nitrogen, and oxygen elements enriches the electrode/electrolyte interface membrane group points, further improving the chemical stability and thermal stability of the interface film, which is beneficial to inhibiting the impedance growth during the cycling process of sodium-ion batteries. At the same time, N-C=O is not easy to generate gas at high temperatures, which is beneficial to improving the cycling production of sodium-ion batteries. In addition, the sulfonyl imide structure on the side chain of formula (I) can improve the structural toughness and stability of the SEI film, inhibit the "rupture-repair" side reaction of the interface film caused by changes in material volume during cycling, and is beneficial to inhibiting Loss of active sodium during cycling of sodium-ion batteries;

(3) The additive of the present invention is applied to sodium-ion batteries. The sodium-ion battery has better first charge and discharge efficiency and first discharge capacity under high voltage, and also has good cycle performance, which is specifically manifested in inhibiting the attenuation of battery cycle capacity. Reduce cyclic gas production and impedance growth;

(4) The mass of the additives described in the present invention accounts for 0.01 to 5% of the total mass of the electrolyte. This is because when the additive content is less than 0.01%, the film formation of the compound of formula (I) is poor, which affects the electrode electrolyte interface. The protection function is relatively weak, which inhibits the nitrogen-containing heterocyclic groups from improving the film-forming efficiency and cycle performance; when the additive content exceeds 5%, the film of the compound of formula (I) becomes thicker, which inhibits the sulfonamide group from improving the SEI film structure. Toughness and stability lead to the intensification of the "rupture-repair" side reaction of the interface film due to changes in material volume during cycles, resulting in increased impedance and gas production;

(5) The first charge and discharge efficiency of the sodium ion battery of the present invention is ≥83.3%, the first capacity is ≥1454.6mAh, and after 500 cycles, the capacity retention rate is ≥85.8%, the internal resistance growth rate is ≤22.4%, and the inflation rate is 5.8-24.5 %.

In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination solutions. Additional features and advantages of the invention will be set forth in the description which follows, and in part, some advantages will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the present invention may be realized and obtained by means of the contents particularly pointed out in the specification.

Detailed ways

A specific embodiment of the present invention discloses a sodium ion battery electrolyte additive. The structural formula of the additive is as shown in formula (I):

Among them, R ₁ is selected from one of substituted or unsubstituted C1-C5 alkyl groups and substituted or unsubstituted C2-C5 unsaturated hydrocarbon groups.

The additive described in the present invention can form a stable interface film (SEI) at the electrode/electrolyte interface. The interface film is a composite structure of organic matter and inorganic matter. The side close to the electrolyte is a loose porous part dominated by organic matter. It is conducive to the infiltration of the electrolyte and the transmission of sodium ions. The side close to the electrode material is a dense part dominated by inorganic substances, which is conducive to inhibiting the occurrence of side reactions of the electrolyte. The additives can reduce the impact on active sodium during the negative electrode film formation process. consumption, thereby conducive to the improvement of first charging efficiency and first capacity. The N-C=O structure in formula (I) has good thermal stability, and the introduction of sulfur, nitrogen, and oxygen elements enriches the electrode/electrolyte interface membrane components, further The chemical stability and thermal stability of the interface film are improved, which is beneficial to inhibiting the impedance growth during the cycling process of sodium-ion batteries. At the same time, N-C=O is not easy to generate gas at high temperatures, which is beneficial to improving the cycling gas generation of sodium-ion batteries. In addition, , the sulfonimide structure on the side chain of formula (I) can improve the structural toughness and stability of the SEI film, inhibit the "rupture-repair" side reaction of the interface film caused by changes in material volume during cycling, and is beneficial to inhibiting sodium-ion batteries. Loss of active sodium during circulation.

Specifically, the R ₁ is selected from one of substituted or unsubstituted C1-C3 alkyl groups and substituted or unsubstituted C2-C3 unsaturated hydrocarbon groups.

Specifically, the additive is selected from one or more compounds 1 to 8, and the structural formula of the compounds 1 to 8 is as follows:

Another embodiment of the present invention provides a sodium ion battery electrolyte, the electrolyte including the additive, sodium salt and organic solvent.

Specifically, the mass of the additive accounts for 0.01 to 5% of the total mass of the electrolyte.

For example, the mass of the additive accounts for 0.01%, 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55 of the total mass of the electrolyte. %, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.6%, 3.8%, 4.0%, 4.2%, 4.4%, 4.6%, 4.8%, 5.0%.

It should be noted that the inventor found during the experiment that although the compound represented by formula (I) can improve the first charge and discharge efficiency and cycle performance of sodium ion batteries under high voltage and can reduce cycle gas production, when the electrolyte When the mass of the additive accounts for more than 5% or less than 0.01% of the total mass of the electrolyte, the high and low temperature performance of the sodium ion battery under high voltage cannot be optimal. The inventor found through a large number of experiments and analysis that the formula (I ) compound content is too low or too high, it is not conducive to improving the performance of the battery. Especially when the content of the compound of formula (I) is too high, the cycle performance of the battery will be significantly reduced. Comprehensive analysis shows that the quality of the additive of the present invention is selected to account for 0.01 to 5% of the total mass of the electrolyte, which can further improve the first charge and discharge efficiency and cycle performance of the sodium-ion battery, and inhibit the gas production of the battery cycle.

Specifically, the concentration of the sodium salt in the electrolyte is 0.2 to 2 mol/L.

Exemplarily, the concentration of the sodium salt in the organic solvent is 0.2mol/L, 0.4mol/L, 0.6mol/L, 0.8mol/L, 1.0mol/L, 1.2mol/L, 1.4mol/L , 1.6mol/L, 1.8mol/L, 2.0mol/L.

It should be noted that the concentration of sodium salt in the electrolyte in the present invention is 0.2~2 mol/L. This is because the concentration is too low, the conductivity is too low, and the battery impedance is too large, which is not conducive to ion transmission. The concentration is too high, and the viscosity is too high, which is not good. If the electrode pieces are easily wetted, the battery will not be able to charge and discharge or lead to sodium precipitation.

Specifically, the sodium salt is selected from sodium hexafluorophosphate (NaPF ₆ ), sodium perchlorate (NaClO ₄ ), sodium tetrafluoroborate (NaBF ₄ ), sodium methanesulfonate (NaCH ₃ SO ₃ ), trifluoroborate. Sodium fluoromethanesulfonate (NaCF ₃ SO ₃ ), sodium dioxaloborate (NaC ₄ BO ₈ ), sodium difluoromethanesulfonate (NaC ₂ BF ₂ O ₄ ), sodium difluorophosphate (NaPO ₂ F ₂ ), difluoromethanesulfonate One or more of sodium fluorobisoxalophosphate (NaDFBP), sodium bisfluorosulfonyl imide (NaFSI) and sodium bistrifluoromethylsulfonyl imide (NaTFSI).

Specifically, the organic solvent is selected from one or more types of carboxylic acid esters, ethers, cyclic carbonates, chain carbonates and heterocyclic compounds.

Specifically, the electrolyte also includes other raw materials, and the other raw materials are selected from the group consisting of vinylene carbonate (VC), vinylene ethylene carbonate (VEC), fluoroethylene carbonate (FEC), and vinyl sulfite. ester (ES), 1,3-propanesultone (PS), 1,3-propenesultone (PST), 1,4-butanesultone (BS) and vinyl sulfate (DTD), At least one of 4-methyl vinyl sulfate and propylene sulfate (PCS).

It should be noted that when the electrolyte described in the present invention is applied to a sodium-ion battery, the sodium-ion battery has better first charge and discharge efficiency and first discharge capacity under high pressure, and also has better cycle performance. The specific performance is as follows: Suppress battery cycle capacity decay, reduce cycle gas production and impedance growth.

Another embodiment of the present invention discloses a sodium ion battery, including the electrolyte, a positive electrode, a negative electrode and a separator.

It should be noted that the positive electrode, negative electrode and separator in the present invention are all made of materials of the prior art, and are not particularly limited in the present invention.

Exemplarily, _the cathode _material is made of sodium copper iron manganese oxide, and its _{general chemical formula is} : Na is one or more of Li, Ni, Mg, Zn, Co, Al, Zr, and Ti; x, y, z, a, and b are respectively the mole percentage of the corresponding elements, where 0.6＜x＜1.2, 0<y<0.5, 0<z≤0.5, 0<a≤0.8, 0≤b≤0.5; y+z+a+b=1, and each element in the chemical formula satisfies charge balance; preferably x=1, y= z=a=1/3, b=0, and the negative electrode is a hard carbon negative electrode material.

Exemplarily, the positive active material may be at least one of layered oxide, polyanion, and Prussian blue/white material. The negative active material may be at least one of carbon-based materials, titanium-based materials, alloy materials, and organic compounds.

It should be noted that the sodium ion battery of the present invention has better first charge and discharge efficiency and first discharge capacity under a high voltage system, and also has good cycle performance, which is specifically manifested in inhibiting the attenuation of battery cycle capacity and reducing cycle time. Gas production and resistance growth.

Example 1

Compound 1 in this example is prepared by the following method: add 81.5g (0.5mol) acesulfame acid to a 500mL reaction bottle, add 200mL deionized water, add 27.56g (0.26mol) sodium carbonate in batches, and stir the reaction until the system Not acidic. Dry under reduced pressure to obtain a white solid, add 200 mL of dimethyl carbonate, stir to fully dissolve, let stand and filter to obtain a clear liquid, dry under reduced pressure to obtain a white solid, recrystallize from dimethyl carbonate/toluene mixed solvent, filter, and dry under reduced pressure The white solid product obtained is compound 1.

Example 2

Compounds 2 to 4 of this example are prepared by the following method:

Place 100g of Compound 1 prepared in Example 1 into the reaction chamber, mix fluorine gas and nitrogen gas at a ratio of 1:4, and then pass it into the reaction chamber through the fluorine/nitrogen metering device at a flow rate of 500L/h, and adjust the infrared generator. The frequency is 5×10 ¹³ Hz, the reaction temperature is controlled to 80°C, and the pressure is 0.6MPa for fluorination reaction. After the reaction is completed after 20 hours, the product is released, and the incompletely reacted tail gas enters the tail gas treatment device for processing, and the mixed product is dissolved to In 100ml of 5% hydrochloric acid solution, each component was separated through the "cooling-crystallization-filtration" method. Solid substances precipitated at -5~-10℃, -20~-22℃ and -26~-28℃ respectively. After NMR analysis, three temperatures were identified corresponding to compound 4, compound 2 and compound 3 respectively. The obtained compounds were vacuum dried at 60°C to obtain 15.2g of compound 2, 18.1g of compound 3 and 16.7g of compound 4 respectively.

Example 3

Compound 5 in this example is prepared by the following method: 20 g of compound 1 prepared in Example 1 is placed in a reaction chamber, hydrogen and nitrogen are mixed at a ratio of 1:4, and then passed through a hydrogen/nitrogen metering device at a flow rate of 200L/h. Pass into the reaction chamber, adjust the frequency of the infrared generator to 3×10 ¹³ Hz, control the reaction temperature to 100°C, and the pressure to 0.5MPa to carry out hydrogenation reaction. After the reaction is completed in 10 hours, the product is released, and the incompletely reacted tail gas enters The exhaust gas treatment device is used for treatment, and the solid substance is compound 5.

Example 4

Compounds 6 to 8 in this example were prepared by the following method: only the reactant compound 1 was changed and replaced with compound 2, compound 3 or compound 4, and the others were the same as in Example 3. Compound 6, compound 7 or compound were obtained respectively. 8.

Example 5 Preparation of electrolyte

Mix propylene carbonate (PC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) in a mass ratio of PC:DEC:EMC=1:1:1 to obtain a solvent, and then add sodium hexafluorophosphate (NaPF ₆ ), the concentration of sodium hexafluorophosphate (NaPF ₆ ) is 1 mol/L, and then compound 1 accounting for 1% of the total mass of the electrolyte is added to obtain an electrolyte.

Examples 6 and 7

In Examples 6 and 7, only the addition amount of Compound 1 was changed, and the rest were the same as in Example 5. An electrolyte was prepared, and the composition of each raw material was shown in Table 1.

Examples 8 to 17

For the preparation of electrolytes in Examples 8 to 17, please refer to Example 11 for details. The composition of each raw material is shown in Table 1.

Table 1

Group Other raw materials additive Additive mass content Example 5 - Compound 1 1% Example 6 - Compound 1 0.01% Example 7 - Compound 1 5% Example 8 2%FEC Compound 1 1% Example 9 2%FEC Compound 2 1% Example 10 2%FEC Compound 3 1% Example 11 2%FEC Compound 4 1% Example 12 2%FEC Compound 5 1% Example 13 2%FEC Compound 6 1% Example 14 2%FEC Compound 7 1% Example 15 2%FEC Compound 8 1% Example 16 2%FEC Compound 1 0.01% Example 17 2%FEC Compound 1 5% Comparative example 1 - - - Comparative example 2 2%FEC - - Comparative example 3 2%FEC Compound 1 0.001% Comparative example 4 2%FEC Compound 1 6% Comparative example 5 - Compound 1 0.001% Comparative example 6 - Compound 1 6%

Comparative Examples 1 to 6

The preparation method of the electrolyte in Comparative Examples 1 to 6 is the same as that in Example 5, and the differences are shown in Table 1.

Preparation of Sodium Ion Batteries

The electrolytes prepared in Examples 5-17 and Comparative Examples 1-6 are made into sodium ion batteries. The specific preparation method is as follows:

(1) Mix the copper, iron, manganese and sodium ternary material NaCu _1/3 Fe _1/3 Mn _1/3 O ₂ , conductive agent SuperP, adhesive PVDF and carbon nanotubes (CNT) in a mass ratio of 97.5:1.5:1.5: 0.5, mix evenly to prepare a sodium ion battery cathode slurry of a certain viscosity, apply it on the aluminum foil for the current collector, the coating amount is 32 mg/cm ² , dry it at 85°C and then cold press; then trim the edges, Cut the pieces into strips, dry them at 85°C for 4 hours under vacuum conditions, and weld the tabs to make sodium-ion battery cathode sheets that meet the requirements;

(2) Make a slurry of hard carbon, conductive agent SuperP, thickener CMC, and adhesive SBR (styrene-butadiene rubber emulsion) in a mass ratio of 95:1.4:1.4:2.2, mix evenly, and use the mixed After the slurry is coated on both sides of the copper foil, and dried at 85°C, the coating amount is 18 mg/cm ² ; trim, cut, and slit, and then dry at 110°C for 4 hours under vacuum conditions. , welding the tabs to make a sodium-ion battery negative electrode that meets the requirements;

(3) The positive electrode sheet, negative electrode sheet and separator prepared above are made into a sodium ion battery with a thickness of 6mm, a width of 60mm, and a length of 66mm through a lamination process, vacuum-baked at 85°C for 24 hours, and then injected into the embodiments respectively The electrolytes prepared in 5-17 and Comparative Examples 1-6 were left to stand for 24 hours, then charged to 2.5V with a constant current of 0.1C (150mA), and charged to 4.2V with a constant current of 0.3C (450mA). When the current drops to 0.05C (75mA), the sum of the two-step charging capacity is the first charge capacity C0; then discharge to 2.0V at 0.2C (300mA), and the released capacity is the first discharge capacity C1; finally, it is 0.2 C (300mA) charges the battery to 3.5V to complete the sodium ion battery preparation.

The sodium-ion batteries made from the electrolytes of Examples 5-17 and Comparative Examples 1-6 were subjected to battery performance cycle tests. The test results are shown in Table 2, where the first charge and discharge efficiency = first discharge capacity C1/first charge capacity C0*100%.

The battery performance cycle test conditions are as follows:

The prepared sodium-ion battery was placed in a 45°C constant temperature oven and subjected to a 1C constant current and constant voltage charge/1C constant current and discharge cycle test in the voltage range of 2-4.2V. The constant current and constant voltage charge cut-off current was 0.05C. Each step Leave it alone for 2 minutes after charging and discharging. Record the discharge capacity, impedance and volume of the battery before cycling and the discharge capacity, impedance and volume after 500 cycles.

Calculate the capacity retention rate, impedance growth rate and inflation rate of high temperature cycle according to the following formula:

Capacity retention rate = discharge capacity after cycle/discharge capacity before cycle × 100%;

Impedance growth rate = (impedance after cycle - impedance before cycle) / impedance before cycle × 100%;

Inflation rate = (battery volume after cycling - initial battery volume)/initial battery volume × 100%.

Table 2

It can be seen from the results in Table 2 that the performance of the sodium ion battery prepared in Examples 5-17 is better than that of Comparative Examples 1-6, which shows that the compound represented by formula (I) of the present invention has a good performance in the electrode/electrolyte solution. A stable interfacial film (SEI) can be formed at the interface. The interface film is a composite structure of organic and inorganic substances. The side close to the electrolyte is a loose and porous part dominated by organic matter, which is conducive to the infiltration of the electrolyte and the transmission of sodium ions. The side close to the electrode material is the dense part dominated by inorganic substances, which is beneficial to inhibiting the side reactions of the electrolyte. The additives can reduce the consumption of active sodium during the negative electrode film formation process, thereby benefiting the first charging efficiency and first capacity. The N-C=O structure in formula (I) has good thermal stability, and the introduction of sulfur, nitrogen, and oxygen elements enriches the components of the electrode/electrolyte interface film, further improving the chemical stability and thermal stability of the interface film property, which is beneficial to inhibiting the impedance growth during the cycling process of sodium ion batteries. At the same time, N-C=O is not easy to generate gas at high temperatures, which is beneficial to improving the cycling gas generation of sodium ion batteries. In addition, the sulfonyl side chain on the formula (I) The imine structure can improve the structural toughness and stability of the SEI film, inhibit the "rupture-repair" side reaction of the interface film caused by changes in material volume during cycling, and help inhibit the loss of active sodium during the cycling process of sodium-ion batteries.

Comparing Examples 5 to 7 with Comparative Examples 1, 5 and 6, it can be found that when the additive content is less than 0.01%, the first charge and discharge efficiency, first discharge capacity and cycle performance of the sodium ion battery cannot reach the optimal state. This is because when the additive content is less than 0.01%, the film formation of the compound of formula (I) is poor, and the protection of the electrode electrolyte interface is relatively weak, thereby inhibiting the nitrogen-containing heterocyclic group from improving the film formation efficiency and cycle performance; when When the additive content exceeds 5%, the film of the compound of formula (I) becomes thicker, which inhibits the sulfonamide group from improving the structural toughness and stability of the SEI film, resulting in the "rupture-repair" side effect of the interface film due to changes in material volume during cycling. The reaction intensifies and the impedance increases and gas is produced. Based on the above analysis, the mass of the additive in the present invention accounts for 0.01 to 5% of the total mass of the electrolyte.

Comparing Example 8, Examples 16 to 17 and Comparative Examples 2 to 4, the above conclusion can also be obtained.

Comparing Examples 8 to 15 with Comparative Example 2, the first charge and discharge efficiency and first discharge capacity of the sodium-ion battery containing the additive of the present invention are significantly increased, and the cycle performance is significantly improved, indicating that the additive of the present invention improves film formation. quality.

The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can easily think of changes or modifications within the technical scope disclosed in the present invention. All substitutions are within the scope of the present invention.

Claims (10)

1. A sodium ion battery electrolyte additive, characterized in that the structural formula of the additive is as shown in formula (I): Among them, R ₁ is selected from one of substituted or unsubstituted C1-C5 alkyl groups and substituted or unsubstituted C2-C5 unsaturated hydrocarbon groups. 2. A sodium ion battery electrolyte additive according to claim 1, characterized in that said _R1 is selected from substituted or unsubstituted C1-C3 alkyl, substituted or unsubstituted C2-C3 unsaturated One of the hydrocarbon groups. 3. A sodium ion battery electrolyte additive according to claim 1 or 2, characterized in that the additive is selected from one or more compounds 1 to 8, and the structural formula of the compounds 1 to 8 is As follows: 4. A sodium ion battery electrolyte, characterized in that the electrolyte includes the additive described in any one of claims 1 to 3, a sodium salt and an organic solvent. 5. A sodium ion battery electrolyte according to claim 4, characterized in that the mass of the additive accounts for 0.01 to 5% of the total mass of the electrolyte. 6. A sodium ion battery electrolyte according to claim 4, characterized in that the concentration of the sodium salt in the electrolyte is 0.2 to 2 mol/L. 7. A kind of sodium ion battery electrolyte according to claim 4, characterized in that the sodium salt is selected from the group consisting of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium methanesulfonate, sodium trifluorophosphate. Sodium fluoromethanesulfonate, sodium difluoromethanesulfonate, sodium difluoromethanesulfonate, sodium difluorophosphate, sodium difluorobisoxalophosphate, sodium bisfluorosulfonimide and sodium bistrifluoromethylsulfonimide One or several. 8. A sodium ion battery electrolyte according to any one of claims 4 to 7, characterized in that the organic solvent is selected from carboxylic acid esters, ethers, cyclic carbonates, and chain carbonic acids. One or more of esters and heterocyclic compounds. 9. A sodium-ion battery, characterized by comprising the electrolyte, positive electrode, negative electrode and separator according to any one of claims 4-8. 10. The sodium-ion battery according to claim 9, wherein the charging voltage of the sodium-ion battery is ≤4.5V.