Electrolyte for high-voltage-resistant sodium-ion battery and preparation method and application thereof

Abstract

The application belongs to the technical field of energy storage materials, and specifically discloses an electrolyte for a high-voltage-resistant sodium ion battery, a preparation method and application thereof.The functional additive in the electrolyte for the high-voltage-resistant sodium ion battery is a trifluoromethyl pyrazole compound, which can preferentially undergo redox reactions on the positive electrode and the negative electrode of the sodium ion battery, respectively, and then form CEI interface films and SEI interface films rich in nitrogen elements and trifluoromethyl derivatives.The interface films are dense and thin, and have excellent ion conduction capacity.The functional additive can not only improve the oxidation potential of the electrolyte for the high-voltage-resistant sodium ion battery, but also reduce the interface impedance under high voltage, thereby improving the cycle stability of the battery under high voltage and low temperature.

Description

Technical Field

[0001] This invention belongs to the field of energy storage materials technology, and specifically relates to an electrolyte for high-voltage sodium-ion batteries, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries have made significant progress in electrode material development due to their enormous potential in large-scale energy storage. For example, substantial progress has been made in the research of polyanionic compounds with excellent cycle stability, high-capacity Prussian blue analogs, and layered metal oxides. However, compared to the rapid development of electrode materials, the development of sodium-ion battery electrolyte systems has lagged behind, making it difficult to meet the diverse needs of practical applications. This is especially true at low temperatures, where battery kinetic hysteresis is particularly prominent. This is mainly attributed to the increased electrolyte viscosity and decreased ionic conductivity caused by low temperatures, as well as the significant increase in the sodium ion desolvation barrier, resulting in a substantial reduction in the rate of ion transport at the interface and through the SEI film. Furthermore, the extended ion diffusion path inside thick electrodes further exacerbates mass transfer resistance, leading to severe capacity decay. Simultaneously, uncontrollable solvent decomposition at low temperatures often leads to the formation of unstable SEI films, causing a sharp deterioration in cycle performance. As a crucial bridge connecting the positive and negative electrodes, the electrolyte is essential for interfacial dynamics and thermodynamic stability. Therefore, it is urgent to develop an electrolyte system that can optimize low-temperature reaction kinetics and synergistically regulate high-voltage interfacial stability to ensure the long-term cycle life of the battery. Summary of the Invention

[0003] In view of this, the present invention provides an electrolyte for high-voltage sodium-ion batteries, its preparation method and application.

[0004] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: This invention provides an electrolyte for high-voltage sodium-ion batteries, wherein the high-voltage sodium-ion battery electrolyte contains a functional additive shown in Formula I: Formula I; R is selected from any one of phenyl, substituted phenyl, naphthyl, thiophene, or furanyl.

[0005] Compared to existing technologies, the electrolyte for high-voltage sodium-ion batteries provided by this invention uses trifluoromethylpyrazole compounds as functional additives, effectively overcoming the problem of poor cycle performance of existing sodium-ion battery electrolytes under high voltage and low temperature conditions. In the trifluoromethylpyrazole compounds provided by this invention, the phenyl, substituted phenyl, thiophene, or furanyl groups have a planar conjugation effect with the pyrazole, and the trifluoromethyl group on the pyrazole ring has a strong electron-withdrawing effect. These two elements synergistically balance the electron cloud structure of the pyrazole ring, endowing the functional additive with higher HOMO and lower LUMO energy levels. During charge and discharge, this functional additive preferentially undergoes oxidation and reduction reactions at the positive and negative electrodes compared to the solvent, and participates in film formation, thereby forming a nitrogen-rich CEI and SEI interface film rich in trifluoromethyl derivatives. This interface film is dense and thin, and possesses excellent ion conductivity. In addition, specific functional additives can effectively capture HF in the electrolyte, inhibit the dissolution of transition metals in the cathode material, prevent material structure collapse and corrosion of the CEI and SEI interface films, thereby significantly reducing the battery internal resistance at low temperatures and the increase in interface impedance during high-voltage cycling.

[0006] The functional additives in the electrolyte for high-voltage sodium-ion batteries provided by this invention can significantly improve the poor battery performance under high voltage and low temperature conditions caused by existing functional additives, and significantly improve the low-temperature cycle performance and high-voltage cycle performance of sodium-ion batteries.

[0007] Preferably, the substituted phenyl group includes any one of methyl-substituted phenyl, methoxy-substituted phenyl, tert-butyl-substituted phenyl, fluorinated substituted phenyl, trifluoromethyl-substituted phenyl, or cyano-substituted phenyl.

[0008] More preferably, the functional additive is at least one of the compounds shown in Formulas 1-14: Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6 Formula 7 Formula 8 Formula 9 Formula 10 Formula 11 Formula 12 Formula 13 Equation 14.

[0009] Selected functional additives can further improve the high voltage and low temperature resistance of sodium-ion batteries.

[0010] Preferably, the electrolyte for high-voltage sodium-ion batteries further includes sodium salt, non-aqueous organic solvent, and auxiliary additives; wherein the concentration of the sodium salt in the electrolyte for high-voltage sodium-ion batteries is 0.8 mol / L-1.5 mol / L.

[0011] Preferably, the functional additive has a mass content of 0.5%-2% in the electrolyte for high-voltage sodium-ion batteries, based on the sum of the mass of the non-aqueous organic solvent and the sodium salt being 100%.

[0012] Preferably, the mass content of the auxiliary additive in the electrolyte for high-voltage sodium-ion batteries is 0.5%-2%, based on the sum of the mass of the non-aqueous organic solvent and the sodium salt being 100%.

[0013] Preferably, the non-aqueous organic solvent includes at least one of chain carbonates, cyclic carbonates, or carboxylic acid esters.

[0014] Preferably, the auxiliary additives include at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, sodium difluorooxalate borate, sodium difluorophosphate, vinylene carbonate, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0015] Preferably, the sodium salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, or sodium dioxolaneborate.

[0016] Preferably, the chain carbonate is at least one of methyl ethyl carbonate or diethyl carbonate.

[0017] Preferably, the cyclic carbonate is at least one of ethylene carbonate, propylene carbonate, or fluoroethylene carbonate.

[0018] Preferably, the carboxylic acid ester is at least one of ethyl acetate, methyl propionate, or ethyl butyrate.

[0019] This invention provides a method for preparing the electrolyte for high-voltage sodium-ion batteries, comprising the following steps: Weigh each component according to the design ratio, and mix the weighed non-aqueous organic solvent and sodium salt evenly to obtain the primary electrolyte. The functional additives and auxiliary additives are added to the primary electrolyte and mixed evenly to obtain an electrolyte for high-voltage sodium-ion batteries.

[0020] The present invention also provides a high-voltage resistant sodium-ion battery, the high-voltage resistant sodium-ion battery comprising a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte for high-voltage resistant sodium-ion batteries.

[0021] Preferably, the negative electrode is hard carbon.

[0022] Preferably, the positive electrode is any one of sodium electrode positive electrode materials such as sodium nickel manganate or sodium vanadium phosphate.

[0023] The high-voltage sodium-ion battery electrolyte provided by this invention, when applied to sodium-ion batteries, enables the sodium-ion battery to achieve a capacity retention rate of 96.4% at 0℃ and 0.2C rate, 94.1% at -10℃ and 0.2C rate, 92.0% at -20℃ and 0.2C rate, and 85.2% at -40℃ and 0.2C rate. After 400 cycles at room temperature (25℃), the capacity retention rate reaches 93.5%; and after 200 cycles at -10℃, the capacity retention rate reaches 87.8%. By adding the high-voltage sodium-ion battery electrolyte of this invention, the cycle capacity retention rate of sodium-ion batteries under high voltage and low temperature conditions can be significantly improved. Attached Figure Description

[0024] Figure 1 TEM image of the positive electrode of the battery prepared in Example 7 of this invention after 200 cycles at -10°C; Figure 2 TEM image of the positive electrode of the battery prepared in Comparative Application Example 6 of the present invention after 200 cycles at -10°C; Figure 3 The TEM image shows the negative electrode of the battery prepared in Example 7 of this invention after 200 cycles at -10°C. Figure 4 The TEM image shows the negative electrode of the battery prepared in Comparative Application Example 6 of this invention after 200 cycles at -10°C. Figure 5 SEM image of the positive electrode of the battery prepared in Application Example 7 of the present invention after 200 cycles at -10°C; Figure 6 SEM image of the positive electrode of the battery prepared in Comparative Application Example 6 of the present invention after 200 cycles at -10°C; Figure 7 SEM image of the negative electrode of the battery prepared in Application Example 7 of the present invention after 200 cycles at -10°C; Figure 8 The image shows the negative electrode of the battery prepared in Comparative Application Example 6 of this invention after 200 cycles at -10°C. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] This invention provides a positive electrode sheet, specifically comprising the following preparation steps: Sodium nickel iron manganese oxide material, polyvinylidene fluoride (PVDF) binder, carbon nanotubes, and Super P (SP) conductive agent were dispersed in N-methylpyrrolidone at a mass ratio of 94.5:2:1:2.5. After thorough stirring and uniform mixing, the mixture was coated onto Al foil current collector. The areal density of the positive electrode material was 30.0 mg / cm³. 2 After drying and rolling, the positive electrode sheet is obtained.

[0027] The present invention also provides a negative electrode sheet, which specifically includes the following preparation steps: The negative electrode active material (hard carbon), thickener (sodium carboxymethyl cellulose (CMC), binder (styrene-butadiene rubber (SBR), and conductive agent (SuperP (SP))) were dispersed in deionized water at a mass ratio of 96:1.5:0.5:1.5. After thorough stirring and uniform mixing, the mixture was coated onto the current collector Al foil. The areal density of the negative electrode material was 15.3 mg / cm³. 2 After drying and rolling, the negative electrode sheet is obtained.

[0028] The synthetic routes and methods for the compounds shown in Formulas 1 to 14 of this invention and the compounds provided in Comparative Example 7 are as follows: R2 is a phenyl group.

[0029] In a clean, dry round-bottom flask, a magnetic stir bar was added. 1 mmol of the hydrazide chloride compound of formula a with different substituents was dissolved in xylene (10 mL), 2-bromo-3,3,3-trifluoropropene (BTP) (2 mmol), and 1,4-diazabicyclo[2.2.2]octane (DABCO, 3 mmol). The mixture was stirred vigorously at room temperature for 24 h. Then, stirring was stopped, water (15 mL) was added, and the mixture was extracted with ethyl acetate (15 mL × 3). The organic phases were combined, dried over anhydrous Na2SO4, filtered, concentrated under reduced pressure, and further purified by silica gel column chromatography (using petroleum ether / ethyl acetate as eluent) to obtain the product shown in formula b.

[0030] The functional additives in Formulas 1 to 14 and Comparative Example 7 of this invention can be synthesized according to the above-described synthesis method, only requiring adjustment of the R1 substituent according to the product.

[0031] The method for synthesizing the compound provided in Comparative Example 3 includes the following steps: Weigh 2.002 g (10 mmol) of 4-phenyl-1,1,1-trifluoro-3-buten-2-one and 1.73 g (12 mmol) of methylhydrazine sulfate, place them in a dry 100 mL round-bottom flask, add 30 mL of anhydrous ethanol and stir to dissolve. Then, under ice bath cooling, slowly add 1.67 mL (12 mmol) of triethylamine to release free methylhydrazine in situ. After the addition is complete, remove the ice bath, connect a condenser, and heat under reflux in an oil bath at 85 °C~90 °C for 4 to 10 minutes. The reaction was carried out for 6 hours, during which the reaction process was monitored by TLC (petroleum ether: ethyl acetate = 5:1) until the starting material spot completely disappeared. After the reaction solution was cooled, the ethanol was removed by rotary evaporation under reduced pressure. The crude product was dissolved in ethyl acetate, washed with saturated brine, dried with anhydrous sodium sulfate, and concentrated. The concentrate was purified by silica gel column chromatography (eluent: petroleum ether: ethyl acetate = 10:1). The target fractions were combined and the solvent was evaporated to dryness, and finally 3-phenyl-1-methyl-5-trifluoromethyl-1H-pyrazole white solid was obtained.

[0032] The method for synthesizing the compound provided in Comparative Example 4 includes the following steps: Will 1 mmol of p-toluenesulfonyl hydrazine (1.2 mmol), toluene (6 mL), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) (3 mmol), and 2-bromo-3,3,3-trifluoropropene (2 mmol) were added to a 25 mL round-bottom flask equipped with a magnetic stir bar and a reflux condenser; the resulting mixture was stirred vigorously at 60°C for 6 h; subsequently, water (15 mL) was added to the mixture, and extraction was performed with ethyl acetate (15 mL × 3). The organic phases were combined, dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure. The crude product was purified by silica gel rapid column chromatography (using petroleum ether / ethyl acetate = 6 / 1 as eluent) to obtain... .

[0033] The method for synthesizing the compound provided in Comparative Example 5 includes the following steps: Using phenylhydrazine and 4-methyl-1,1,1-trifluoro-2-pentanone as equimolar starting materials (1:1), a two-stage dehydration reaction is carried out under acidic conditions or in a heated polar solvent (such as ethanol). First, an hydrazone intermediate is generated, followed by intramolecular electrophilic cyclization, and finally the target product is obtained with high regioselectivity.

[0034] The synthetic route for the compound provided in Comparative Example 5 is as follows: The method for synthesizing the compound provided in Comparative Example 6 includes the following steps: Starting with equimolar amounts of phenylhydrazine and 1-cyclohexyl-4,4,4-trifluoro-1,3-butanedione (molecular weight 222.20), a two-stage dehydration condensation reaction was carried out in an acidic catalyst (such as acetic acid) or a heated polar solvent (such as ethanol). The reaction first involved the amino group of phenylhydrazine attacking the carbonyl group of the diketone to generate a monohydrazone intermediate. Subsequently, an intramolecular nucleophilic cyclization occurred under acidic conditions, and the second water molecule was removed. Finally, a pyrazole ring was constructed with high regioselectivity, yielding the compound provided in Comparative Example 6. The synthetic route for the compound provided in Comparative Example 6 is as follows: Where Ph represents phenyl and Cy represents cyclohexyl.

[0035] Compounds for which no synthetic method is described are all commercially available products.

[0036] Example 1 This embodiment provides an electrolyte for high-voltage sodium-ion batteries, and the specific preparation method includes the following: In an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), sodium hexafluorophosphate was added to ethyl methyl carbonate, fluoroethylene carbonate, and ethyl acetate (mass ratio 1:1:1), followed by the addition of functional additives and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. The mixture was stirred until homogeneous to obtain an electrolyte suitable for high-voltage sodium-ion batteries. The concentration of sodium hexafluorophosphate in the electrolyte is 0.8 mol / L; Based on the total mass of methyl ethyl carbonate, fluoroethylene carbonate, ethyl acetate, and sodium hexafluorophosphate (100%), the content of the functional additive in the electrolyte is 0.5 wt%, and the content of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether in the electrolyte is 2 wt%. The functional additive is the compound shown in Formula 1, with the following structure: .

[0037] Example 2 This embodiment provides an electrolyte for high-voltage sodium-ion batteries, and the specific preparation method includes the following: In an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), sodium hexafluorophosphate was added to ethyl methyl carbonate, fluoroethylene carbonate, and ethyl acetate (mass ratio 1:1:1), followed by the addition of functional additives and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. The mixture was stirred until homogeneous to obtain an electrolyte suitable for high-voltage sodium-ion batteries. The concentration of sodium hexafluorophosphate in the electrolyte is 1 mol / L; Based on the total mass of methyl ethyl carbonate, fluoroethylene carbonate, ethyl acetate, and sodium hexafluorophosphate being 100%, the content of the functional additive in the electrolyte is 1 wt%, and the content of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether in the electrolyte is 1 wt%. The functional additive is the compound shown in Formula 2, with the following structure: .

[0038] Example 3 This embodiment provides an electrolyte for high-voltage sodium-ion batteries, and the specific preparation method includes the following: In an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm), sodium hexafluorophosphate was added to ethyl methyl carbonate, fluoroethylene carbonate, and ethyl acetate (mass ratio 1:1:1), followed by the addition of functional additives and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. The mixture was stirred until homogeneous to obtain an electrolyte suitable for high-voltage sodium-ion batteries. The concentration of sodium hexafluorophosphate in the electrolyte is 1.2 mol / L; Based on the total mass of methyl ethyl carbonate, fluoroethylene carbonate, ethyl acetate, and sodium hexafluorophosphate being 100%, the content of the functional additive in the electrolyte is 1.5 wt%, and the content of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether in the electrolyte is 1.5 wt%. The functional additive is the compound shown in Formula 3, with the following structure: .

[0039] Example 4 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 4, whose structure is as follows: Other operating steps are the same as in Example 1.

[0040] Example 5 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 5, whose structure is as follows: Other operating steps are the same as in Example 1.

[0041] Example 6 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 6, whose structure is as follows: Other operating steps are the same as in Example 1.

[0042] Example 7 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 7, whose structure is as follows: Other operating steps are the same as in Example 1.

[0043] Example 8 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 8, whose structure is as follows: Other operating steps are the same as in Example 1.

[0044] Example 9 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 9, whose structure is as follows: Other operating steps are the same as in Example 1.

[0045] Example 10 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 10, whose structure is as follows: Other operating steps are the same as in Example 1.

[0046] Example 11 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 11, whose structure is as follows: Other operating steps are the same as in Example 1.

[0047] Example 12 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 12, whose structure is as follows: Other operating steps are the same as in Example 1.

[0048] Example 13 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 13, whose structure is as follows: Other operating steps are the same as in Example 1.

[0049] Example 14 This embodiment provides an electrolyte for high-voltage sodium-ion batteries. The difference between this embodiment and Embodiment 1 is that the functional additive is replaced with an equal amount of the compound shown in Formula 14, whose structure is as follows: Other operating steps are the same as in Example 1.

[0050] Application Example 1 This application example provides a sodium-ion battery, and the specific preparation method includes the following: The prepared positive electrode, separator, and negative electrode are stacked in sequence, packaged with aluminum-plastic film, baked, injected with the electrolyte for sodium-ion batteries prepared in Example 1, left to stand, formed, shaped with fixtures, resealed, and capacity tested to complete the preparation of the sodium-ion battery.

[0051] Application Example 2 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 2. Other operating steps are the same as in application example 1.

[0052] Application Example 3 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 3. Other operating steps are the same as in application example 1.

[0053] Application Example 4 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 4. Other operating steps are the same as in application example 1.

[0054] Application Example 5 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 5. Other operating steps are the same as in application example 1.

[0055] Application Example 6 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 6. Other operating steps are the same as in application example 1.

[0056] Application Example 7 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 7. Other operating steps are the same as in application example 1.

[0057] Application Example 8 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 8. Other operating steps are the same as in application example 1.

[0058] Application Example 9 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 9. Other operating steps are the same as in application example 1.

[0059] Application Example 10 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 10. Other operating steps are the same as in application example 1.

[0060] Application Example 11 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 11. Other operating steps are the same as in application example 1.

[0061] Application Example 12 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 12. Other operating steps are the same as in application example 1.

[0062] Application Example 13 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 13. Other operating steps are the same as in application example 1.

[0063] Application Example 14 This application example provides a sodium-ion battery. The difference between this application example and application example 1 is that the electrolyte for the sodium-ion battery prepared in example 1 is replaced with an equal amount of the electrolyte for the sodium-ion battery prepared in example 14. Other operating steps are the same as in application example 1.

[0064] Comparative Example 1 This comparative example provides an electrolyte. The difference between this comparative example and Example 1 is that the compound shown in Formula 1 is replaced with an equal amount of... Other operating steps are the same as in Example 1.

[0065] Comparative Example 2 This comparative example provides an electrolyte. The difference between this comparative example and Example 1 is that the compound shown in Formula 1 is replaced with an equal amount of... Other operating steps are the same as in Example 1.

[0066] Comparative Example 3 This comparative example provides an electrolyte. The difference between this comparative example and Example 1 is that the compound shown in Formula 1 is replaced with an equal amount of... Other operating steps are the same as in Example 1.

[0067] Comparative Example 4 This comparative example provides an electrolyte. The difference between this comparative example and Example 1 is that the compound shown in Formula 1 is replaced with an equal amount of... Other operating steps are the same as in Example 1.

[0068] Comparative Example 5 This comparative example provides an electrolyte. The difference between this comparative example and Example 1 is that the compound shown in Formula 1 is replaced with an equal amount of... Other operating steps are the same as in Example 1.

[0069] Comparative Example 6 This comparative example provides an electrolyte. The difference between this comparative example and Example 1 is that the compound shown in Formula 1 is replaced with an equal amount of... Other operating steps are the same as in Example 1.

[0070] Comparative Example 7 This comparative example provides an electrolyte. The difference between this comparative example and Example 1 is that the compound shown in Formula 1 is replaced with an equal amount of... Other operating steps are the same as in Example 1.

[0071] Comparative Application Example 1 This comparative application example provides a sodium-ion battery. The difference between this comparative application example and application example 1 is that the electrolyte prepared in example 1 is replaced with an equal amount of the electrolyte prepared in comparative example 1, while the other operating steps are the same as in application example 1.

[0072] Comparative Application Example 2 This comparative application example provides a sodium-ion battery. The difference between this comparative application example and application example 1 is that the electrolyte prepared in example 1 is replaced with an equal amount of the electrolyte prepared in comparative example 2, while the other operation steps are the same as in application example 1.

[0073] Comparative Application Example 3 This comparative application example provides a sodium-ion battery. The difference between this comparative application example and application example 1 is that the electrolyte prepared in example 1 is replaced with an equal amount of the electrolyte prepared in comparative example 3, while the other operation steps are the same as in application example 1.

[0074] Comparative Application Example 4 This comparative application example provides a sodium-ion battery. The difference between this comparative application example and application example 1 is that the electrolyte prepared in example 1 is replaced with an equal amount of the electrolyte prepared in comparative example 4, while the other operation steps are the same as in application example 1.

[0075] Comparative Application Example 5 This comparative application example provides a sodium-ion battery. The difference between this comparative application example and application example 1 is that the electrolyte prepared in example 1 is replaced with an equal amount of the electrolyte prepared in comparative example 5, while the other operation steps are the same as in application example 1.

[0076] Comparative Application Example 6 This comparative application example provides a sodium-ion battery. The difference between this comparative application example and application example 1 is that the electrolyte prepared in example 1 is replaced with an equal amount of the electrolyte prepared in comparative example 6, while the other operation steps are the same as in application example 1.

[0077] Comparative Application Example 7 This comparative application example provides a sodium-ion battery. The difference between this comparative application example and application example 1 is that the electrolyte prepared in example 1 is replaced with an equal amount of the electrolyte prepared in comparative example 7, while the other operation steps are the same as in application example 1.

[0078] The sodium-ion batteries prepared in the application examples and comparative application examples of this invention were tested after being sealed and allowed to stand, pre-charged and formed, and then sealed and tested again. The specific operations are as follows: Low-temperature discharge performance test: The sodium-ion battery was charged and discharged at room temperature using a constant current-constant voltage method. First, it was charged to 4.0V at a 0.1C rate, then allowed to stand at room temperature for 5 minutes, and then discharged to 1.5V at a constant current of 0.1C. This charge-discharge cycle was repeated three times. Next, it was charged to 4.0V at a 0.2C rate, allowed to stand at room temperature for 5 minutes, and then discharged to 1.5V at a constant current of 0.2C. The discharge capacity at room temperature (C1) was recorded. Then, the battery was charged again to 4.0V at a 0.2C current rate, bringing it to a fully charged state (100% SOC). Finally, after standing at 0℃, -10℃, -20℃, and -40℃ for 16 hours, the discharge capacity (C2) at different temperatures and 0.2C current rates was tested. The low-temperature discharge capacity retention rate was calculated. Low-temperature capacity retention (%) = C2 / C1 × 100%; The specific test results are shown in Table 1.

[0079] Room temperature high pressure cycling performance test: At 25℃, the battery was charged to 4.0V at a rate of 0.1C, then left to stand at room temperature for 5 minutes, and discharged to 1.5V at a constant current of 0.1C. This charge-discharge cycle was repeated 3 times to activate the battery. The battery was then charged to 4.0V at a rate of 1C, and then discharged to 1.5V at a constant current of 1C to complete one charge-discharge cycle. The above charge-discharge process was repeated to perform 400 charge-discharge cycle tests. The capacity retention rate (%) of the 400th cycle was calculated as (400th discharge capacity / first discharge capacity) × 100%. The specific test results are shown in Table 2.

[0080] Low-temperature cycling performance test: At -10℃, the battery was charged to 4.0V at a rate of 0.1C, then left to stand at room temperature for 5 minutes, and discharged to 1.5V at a constant current of 0.1C. This charge-discharge cycle was repeated 3 times to activate the battery. The battery was then charged to 4.0V at a rate of 0.5C, and then discharged to 1.5V at a constant current of 0.5C to complete one charge-discharge cycle. The battery was subjected to 200 charge-discharge cycle tests by repeating the above charge-discharge process. The capacity retention rate (%) of the 200th cycle was calculated as (200th discharge capacity / first discharge capacity) × 100%. The specific test results are shown in Table 2.

[0081] Table 1 Table 2 As shown in Table 1, the high-voltage sodium-ion battery electrolytes provided in Examples 1-14 of this invention exhibit excellent low-temperature discharge performance and high-voltage resistance when applied to sodium-ion batteries. As shown in Table 2, the cycle performance data at high voltage and ambient temperature and high voltage and low temperature show that the capacity retention rate of Examples 25℃ after 400 cycles and the capacity retention rate after 200 cycles at -10℃ are significantly better than those of the comparative examples. The sodium-ion battery using the electrolyte for sodium-ion batteries provided in Example 7 of this invention, i.e., the sodium-ion battery provided in Example 7, exhibits capacity retention rates of 96.4%, 94.1%, 92.0%, and 85.2% at 0°C, -10°C, -20°C, and -40°C at a 0.2C rate, respectively. After 400 cycles at 1C rate at 25°C, its capacity retention rate reaches 93.5%; and after 200 cycles at 0.5C rate at -10°C, its capacity retention rate reaches 87.8%. This demonstrates that the electrolyte for sodium-ion batteries provided in this invention enables sodium-ion batteries to possess both excellent high-voltage resistance and low-temperature resistance.

[0082] The functional additives in the sodium-ion battery electrolytes provided in Comparative Application Examples 1, 5, and 6 all use aliphatic groups as R groups. The functional additives in the sodium-ion battery electrolyte provided in Comparative Application Example 3 use methyl groups as nitrogen-atom-linked groups. The functional additives in the sodium-ion battery electrolyte provided in Comparative Application Example 4 omit the nitrogen-atom-linked phenyl groups. These functional additives will disrupt the conjugated structure of the overall structure, forming a thicker and more unstable interfacial film on the electrode surface. This increases electrode polarization under low-temperature conditions, reduces the capacity retention rate of the sodium-ion battery under low-temperature conditions, and results in a significant decrease in the battery's low-temperature performance.

[0083] Compared with the functional additives in the sodium-ion battery electrolyte provided in Application Example 2, the decomposition products formed under high voltage are unstable, resulting in continuous thickening of the interfacial film, which in turn makes the sodium-ion battery have poor cycle stability under high voltage and low temperature.

[0084] In contrast to Application Example 7, when a compound with multiple benzene ring substitutions is used as a functional additive, a thicker interfacial film is generated, which increases the impedance and causes a sharp increase in internal polarization of the battery during low-temperature cycling, resulting in a decrease in the cycling performance of the sodium-ion battery under high voltage and low temperature.

[0085] Figure 1 , Figure 3 , Figure 5 and Figure 7 This indicates that after low-temperature cycling, the electrolyte in the battery provided in Example 7 forms a dense and thin interfacial film on the surface of the positive and negative electrode materials. At the same time, the functional additive provided in Example 7 decomposes to form a dense and thin SEI film and CEI film. This interfacial film has excellent ion conductivity. In addition, this functional additive can effectively capture HF in the electrolyte, inhibit the dissolution of transition metals in the positive electrode material and the corrosion of the CEI and SEI interfacial films by transition metals, thereby significantly reducing the battery internal resistance under low-temperature conditions, suppressing the increase of interfacial impedance during high-voltage cycling, and thus improving the cycling stability of sodium-ion batteries at low temperatures.

[0086] Figure 2 , Figure 4 , Figure 6 and Figure 8 This indicates that after low-temperature cycling, compared with the battery provided in Application Example 6, both the positive and negative electrode materials have a thick and uneven layer of deposits. This interface film cannot effectively prevent the electrolyte from eroding the materials under high voltage, leading to the collapse of the positive electrode material structure and increasing the battery impedance, resulting in a significant decrease in the battery's cycle performance.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte for high-voltage sodium-ion batteries, characterized in that, The electrolyte for high-voltage sodium-ion batteries contains the functional additive shown in Formula I: Formula I; R is selected from any one of phenyl, substituted phenyl, naphthyl, thiophene, or furanyl.

2. The electrolyte for high-voltage sodium-ion batteries as described in claim 1, characterized in that, The substituted phenyl group includes any one of methyl-substituted phenyl, methoxy-substituted phenyl, tert-butyl-substituted phenyl, fluorinated substituted phenyl, trifluoromethyl-substituted phenyl, or cyano-substituted phenyl.

3. The electrolyte for high-voltage sodium-ion batteries as described in claim 2, characterized in that, The functional additive is at least one of the compounds shown in Formulas 1-14: Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6 Formula 7 Formula 8 Formula 9 Formula 10 Formula 11 Formula 12 Formula 13 Equation 14.

4. The electrolyte for high-voltage sodium-ion batteries as described in claim 3, characterized in that, The electrolyte for high-voltage sodium-ion batteries further includes sodium salt, non-aqueous organic solvent, and auxiliary additives; wherein the concentration of the sodium salt in the electrolyte for high-voltage sodium-ion batteries is 0.8 mol / L-1.5 mol / L.

5. The electrolyte for high-voltage sodium-ion batteries as described in claim 4, characterized in that, With the sum of the non-aqueous organic solvent and sodium salt as 100%, the mass content of the functional additive in the electrolyte for high-voltage sodium-ion batteries is 0.5%-2%.

6. The electrolyte for high-voltage sodium-ion batteries as described in claim 4, characterized in that, With the sum of the non-aqueous organic solvent and sodium salt as 100%, the mass content of the auxiliary additive in the electrolyte for high-voltage sodium-ion batteries is 0.5%-2%.

7. The electrolyte for high-voltage sodium-ion batteries as described in claim 4, characterized in that, The non-aqueous organic solvent includes at least one of chain carbonates, cyclic carbonates, or carboxylic acid esters; The auxiliary additives include at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 1,4-butanesulfonate lactone, sodium difluorooxalate borate, sodium difluorophosphate, vinylene carbonate, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. The sodium salt includes at least one of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, or sodium dioxolaneborate.

8. A method for preparing the electrolyte for a high-voltage sodium-ion battery according to any one of claims 1-7, characterized in that, Includes the following steps: Weigh each component according to the design ratio, and mix the weighed non-aqueous organic solvent and sodium salt evenly to obtain the primary electrolyte. The functional additives and auxiliary additives are added to the primary electrolyte and mixed evenly to obtain an electrolyte for high-voltage sodium-ion batteries.

9. A high-voltage resistant sodium-ion battery, characterized in that, The high-voltage resistant sodium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte for a high-voltage resistant sodium-ion battery as described in any one of claims 1-7.

10. The high-voltage sodium-ion battery as described in claim 9, characterized in that, The negative electrode is hard carbon.

Images