A secondary battery electrolyte and a secondary sodium ion battery containing the same

Abstract

The application belongs to the technical field of sodium ion batteries, and discloses a secondary battery electrolyte and a secondary sodium ion battery containing the electrolyte. The secondary battery electrolyte contains a non-aqueous organic solvent, an inorganic salt and an additive, and the additive contains an acid anhydride compound A containing a silicon-based functional group. The compound A in the electrolyte can form a stable SEI passivation film at the negative electrode interface, inhibit the continuous reaction of the solvent with the negative electrode interface, can be partially decomposed at the positive electrode interface before the solvent to form a cathode CEI film, inhibit the oxidative decomposition of the electrolyte at the positive electrode interface, improve the cycle and high-temperature performance of the battery, and can eliminate the active proton hydrogen in the battery system by using the acid anhydride and the silicon-based functional group contained in the compound, so as to reduce the decomposition of the electrolyte, and further improve the comprehensive performance of the secondary sodium ion battery.

Description

TECHNICAL FIELD

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

[0002] Secondary sodium ion batteries have been widely applied in the fields of power, energy storage and 3C digital products, wherein, in the field of power batteries, longer endurance and longer cycle life are pursued, and the specific energy density of the battery is mainly improved by increasing the charging voltage of the battery or increasing the nickel content of the positive electrode material. At present, layered oxides are used as positive electrode materials in the high-nickel and high-voltage ternary route, and the specific energy is relatively high, the rate performance is good, and the cycle life is good. However, with the continuous increase of voltage and nickel content, the performance of the sodium ion battery faces great challenges. First, after the voltage or the nickel content of the layered system is increased, the surface activity of the positive electrode material is high, which easily causes the oxidation and decomposition of the electrolyte; second, during the use of the battery, the material structure changes, the positive electrode material is more likely to dissolve transition metal ions and produce hydrogen evolution behavior, thereby further catalyzing the decomposition of the electrolyte, causing the internal resistance of the sodium ion battery to increase, and the cycle life and high-temperature performance to be obviously poor.

[0003] At present, the material system represented by layered oxides is developing rapidly and can be used as a supplement to sodium ion batteries. The layered oxide sodium ion battery has many common characteristics in terms of structure characteristics, surface properties, working principles, alkaline properties and performance and failure modes of secondary sodium ion batteries, but it is more complex, mainly in that it is prone to produce gas during the cycle and storage process, the high-temperature cycle life and calendar life are insufficient, the internal resistance increases rapidly, and the battery is prone to sodium precipitation during use. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a secondary battery electrolyte and a secondary sodium ion battery containing the electrolyte. The secondary battery electrolyte of the present application comprises a non-aqueous organic solvent, an inorganic salt and an additive, the additive comprises an acid anhydride compound A containing a silicon-based functional group, the compound A can form a stable SEI passivation film at the negative electrode interface to inhibit the continuous reaction of the solvent with the negative electrode interface, and can also decompose at the positive electrode interface before the solvent to form a cathode CEI film, thereby inhibiting the oxidation and decomposition of the electrolyte at the positive electrode interface, improving the cycle and high-temperature performance of the battery, and at the same time, the acid anhydride and silicon-based functional group contained in the compound can eliminate the active proton hydrogen in the battery system, thereby reducing the decomposition of the electrolyte and improving the comprehensive performance of the secondary sodium ion battery.

[0005] To achieve the purpose of the present application, the secondary battery electrolyte of the present application comprises a non-aqueous organic solvent, an inorganic salt and an additive, the additive comprises an acid anhydride compound A containing a silicon-based functional group, and the structure of the compound A is M is -CH2-CH2- or -CH2-CH-CH2-, n is an integer from 1 to 5, R1, R2, R3 are independently selected from alkyl, alkenyl, alkynyl, isocyanate, nitrile with 1 to 5 carbons.

[0006] Further, in some embodiments of the application, the compound A is at least one of compounds A1-A10:

[0007]

[0008]

[0009] Further, in some embodiments of the application, the compound A is added in an amount of 0.05-2% of the total weight of the electrolyte.

[0010] Preferably, in some embodiments of the application, the compound A is added in an amount of 0.2-2%, for example 0.2-1%, or for example 0.2-0.5% of the total weight of the electrolyte.

[0011] Further, in some embodiments of the application, the additive further comprises an additive other than compound A, the additive other than compound A is selected from two or more of vinyl sulfonate, 3-tert-butyldimethylsilyloxy glutaric anhydride, propylene sulfite, 1,3-propane sultone, 1,3-propene sultone, 2,4-butane sultone, tris(trimethylsilyl) phosphate, tetra-vinyl silane, triallyl isocyanurate, tripropargyl phosphate, pentaerythritol tetraacrylate, 1,3,6-hexane tricarbonitrile, 3,3-bis vinyl sulfite, 2,4,6-triallyloxy-1,3,5-triazine; preferably, the additive other than compound A is added in an amount of 0.5-5% of the total weight of the electrolyte.

[0012] Preferably, in some embodiments of the application, the additive other than compound A is selected from other additives in the examples shown in Table 1 of the application, and the specific combination is the combination in Example 1 of Table 1.

[0013] Further, in some embodiments of the application, the non-aqueous organic solvent comprises one or a mixture of two or more of propylene carbonate, vinylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, difluoroethyl acetate, ethyl difluoroacetate.

[0014] Preferably, in some embodiments of the application, the non-aqueous organic solvent is selected from the combination of non-aqueous organic solvents in Example 1 of Table 1 of the application.

[0015] Preferably, in some embodiments of the application, the amount of the carbonate added in the non-aqueous organic solvent accounts for 60-85% of the total weight of the electrolyte.

[0016] Further, in some embodiments of the application, the inorganic salt is an inorganic sodium salt, and the inorganic sodium salt is selected from one or more of sodium hexafluorophosphate, sodium difluorophosphate, sodium difluoro oxalate borate, sodium difluoro bisoxalate phosphate, sodium bisfluorosulfonylimide, sodium bis-trifluorosulfonylimide, and sodium bisoxalate borate.

[0017] Preferably, in some embodiments of the application, the inorganic salt is selected from the inorganic sodium salt combination in Example 1 shown in Table 1 of the application.

[0018] Preferably, in some embodiments of the application, the mass percentage of the inorganic salt in the electrolyte is 10-20%.

[0019] In another aspect, the application also provides a secondary sodium ion battery comprising the aforementioned secondary battery electrolyte.

[0020] The complex functional group contained in Compound A in the application has multiple functional properties. The anhydride functional group can form a stable SEI passivation film at the negative electrode interface, inhibit the continuous reaction of the solvent with the negative electrode interface, and improve the stability of the negative electrode interface. The anhydride functional group can also decompose prior to the solvent at the positive electrode interface to form a cathode CEI film to passivate the positive electrode activity, thereby inhibiting the oxidative decomposition of the electrolyte at the positive electrode interface and improving the cycle and high-temperature performance of the battery. In addition, both the anhydride functional group and the silicon-based functional group can react with trace amounts of water and HF in the electrolyte, reducing the damage of HF to the positive and negative electrode materials.

[0021] In addition, the silicon-based functional group in Compound A can regulate the impedance of the additive and the degree of reactivity on the positive and negative electrode surfaces. When R1, R2, and R3 are saturated alkanes, the impedance increase caused by the presence of anhydride in Compound A can be reduced. When R1, R2, and R3 are unsaturated groups, the complex reaction at the positive electrode interface can be further increased, further enhancing the effect of positive electrode protection. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the application more clear and apparent, the application will be further described in detail below in combination with embodiments. Additional aspects and advantages of the application will be partially given in the following description, partially will become apparent from the following description, or will be understood by the practice of the application. It should be understood that the following description is only used to explain the application, and is not used to limit the application.

[0023] When equivalent, concentration, or other value or parameter is expressed in a range or a preferred range or a series of upper preferred values and lower preferred values, it is to be understood that all ranges formed by any pair of any upper range limit or preferred value and any lower range limit or preferred value, even if the range is not explicitly stated, are to be specifically disclosed. For example, when a range "1 to 5" is disclosed, then the description is to be interpreted to include ranges such as "1 to 4," "1 to 3," "1 to 2," "1 to 2 and 4 to 5," "1 to 3 and 5," etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include the endpoints and all integers and fractions within that range.

[0024] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. "Optional" or "any of" means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not.

[0025] The indefinite articles "a" and "an" preceding an element or component of the application are intended to be non-limiting regarding the number of elements or components. The recitation of "a" or "an" should therefore be interpreted to mean "one or at least one" and the singular form "the" includes the plural unless the number is obviously meant to be singular.

[0026] In addition, the terms "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" as described throughout this specification are not necessarily to be construed as applying to the same embodiment or example, unless the context clearly dictates otherwise. Furthermore, the foregoing description is not to be interpreted in an exclusionary sense, namely, not to mean that various aspects or features of the application are mutually exclusive or that a feature or aspect of the application cannot be used in combination with another feature or aspect of the application. Rather, the foregoing description is to be interpreted as describing various embodiments of the application.

[0027] For the convenience of description, some materials involved in the examples and comparative examples of the present application are described using alphabetical abbreviation or English abbreviation: propylene carbonate (PC), propyl propionate (PP), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,3-propene sultone (PST), vinylene carbonate (VC), ethylene sulfate (DTD), tetra-vinylsilane (TVSI), triallyl isocyanurate (TAIC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (D2), sodium difluoro(oxalato)borate (NaODFB), sodium difluorophosphate (NaPO2F2), difluoroethyl acetate (DFEA), tris(trimethylsilyl)phosphate (TMSP).

[0028] Example 1

[0029] Preparation of electrolyte: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), propylene carbonate (PC), dimethyl carbonate (DEC), ethyl methyl carbonate (EMC) were mixed uniformly in a mass ratio of 30:20:50 to obtain a mixed solution, 10.0% NaPF6 and 3% sodium bisfluorosulfonylimide (NaFSI) based on the total mass of the electrolyte were added to the mixed solution, stirred until it was completely dissolved, then 0.5% vinylene carbonate (VC), 1% fluoroethylene carbonate (FEC), 1% 1,3-propane sultone (PS), 0.5% 1,3-propylene sultone (PST) based on the total mass of the electrolyte were added, and stirred uniformly to obtain the sodium ion battery electrolyte of Example 1.

[0030] Examples 2-31

[0031] Examples 2-31 are also specific embodiments of electrolyte preparation, except that the composition and ratio of each component of the electrolyte are added as shown in Table 1, and other parameters and preparation methods are the same as those of Example 1. The specific electrolyte formula is shown in Table 1.

[0032] Comparative Example 1

[0033] Preparation of electrolyte: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), propylene carbonate (PC), dimethyl carbonate (DEC), ethyl methyl carbonate (EMC) were mixed uniformly in a mass ratio of 30:20:50 to obtain a mixed solution, 10.0% NaPF6 and 3% sodium bisfluorosulfonylimide (NaFSI) based on the total mass of the electrolyte were added to the mixed solution, stirred until it was completely dissolved, then 0.5% vinylene carbonate (VC), 1% fluoroethylene carbonate (FEC), 2% 1,3-propane sultone based on the total mass of the electrolyte were added, and stirred uniformly to obtain the sodium ion battery electrolyte of Comparative Example 1.

[0034] Comparative Example 2

[0035] Preparation of electrolyte: In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), propylene carbonate (PC), dimethyl carbonate (DEC), ethyl methyl carbonate (EMC) were mixed uniformly in a mass ratio of 30:20:50 to obtain a mixed solution, 10.0% NaPF6 and 3% sodium bisfluorosulfonylimide (NaFSI) based on the total mass of the electrolyte were added to the mixed solution, stirred until it was completely dissolved, then 0.5% vinylene carbonate (VC), 1% fluoroethylene carbonate (FEC), 1% 1,3-propylene sultone based on the total mass of the electrolyte were added, and stirred uniformly to obtain the sodium ion battery electrolyte of Comparative Example 2.

[0036] Comparative Example 3

[0037] Preparation of electrolyte: In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), propylene carbonate (PC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:20:50 to obtain a mixed solution, 10.0% NaPF6 and 3% sodium bisfluorosulfonylimide (NaFSI) based on the total mass of the electrolyte were added to the mixed solution, stirred until they were completely dissolved, then 0.5% vinylene carbonate (VC), 1% fluoroethylene carbonate (FEC), 1% 1,3-propane sultone (PS), and 0.5% 1,3-propene sultone (PST) based on the total mass of the electrolyte were added, and stirred to obtain the sodium-ion battery electrolyte of Comparative Example 3.

[0038] Comparative Example 4

[0039] Preparation of electrolyte: In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), propylene carbonate (PC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:20:50 to obtain a mixed solution, 10.0% NaPF6 and 3% sodium bisfluorosulfonylimide (NaFSI) based on the total mass of the electrolyte were added to the mixed solution, stirred until they were completely dissolved, then 0.5% vinylene carbonate (VC), 1% fluoroethylene carbonate (FEC), 1% 1,3-propane sultone (PS), and 0.5% 1,3-propene sultone (PST) based on the total mass of the electrolyte were added, and stirred to obtain the sodium-ion battery electrolyte of Comparative Example 3.

[0040] Comparative Example 5

[0041] Preparation of electrolyte: In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), propylene carbonate (PC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:20:50 to obtain a mixed solution, 10.0% NaPF6 and 3% sodium bisfluorosulfonylimide (NaFSI) based on the total mass of the electrolyte were added to the mixed solution, stirred until they were completely dissolved, then 0.5% vinylene carbonate (VC), 1% fluoroethylene carbonate (FEC), 1% 1,3-propane sultone (PS), and 0.5% 1,3-propene sultone (PST) based on the total mass of the electrolyte were added, and stirred to obtain the sodium-ion battery electrolyte of Comparative Example 3.

[0042] Comparative Example 6

[0043] Preparation of electrolyte: In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), propylene carbonate (PC), dimethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 30:20:50 to obtain a mixed solution. Then, 10.0% of NaPF6, 3% of sodium bisfluorosulfonylimide (NaFSI), 0.5% of sodium difluoro(oxalato)borate (NaDFOB), and 0.5% of sodium difluorophosphate (NaPO2F2) based on the total mass of the electrolyte were added to the mixed solution and stirred until they were completely dissolved. Then, 0.5% of vinylene carbonate (VC), 1% of fluoroethylene carbonate (FEC), 1% of 1,3-propane sultone (PS), and 1% of vinyl sulfate (DTD) based on the total mass of the electrolyte were added and stirred until they were uniformly mixed to obtain the sodium-ion battery electrolyte of Comparative Example 6.

[0044] Comparative Example 7

[0045] Preparation of electrolyte: In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), propylene carbonate (PC), dimethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 30:20:50 to obtain a mixed solution. Then, 10.0% of NaPF6, 3% of sodium bisfluorosulfonylimide (NaFSI), 0.5% of sodium difluoro(oxalato)borate (NaDFOB), and 0.5% of sodium difluorophosphate (NaPO2F2) based on the total mass of the electrolyte were added to the mixed solution and stirred until they were completely dissolved. Then, 0.5% of vinylene carbonate (VC), 1% of fluoroethylene carbonate (FEC), 1% of 1,3-propane sultone (PS), and 1% of vinyl sulfate (DTD) based on the total mass of the electrolyte were added and stirred until they were uniformly mixed to obtain the sodium-ion battery electrolyte of Comparative Example 6.

[0046] Table 1 Composition of electrolytes of Comparative Examples 1-7 and Examples 1-31

[0047]

[0048]

[0049] Effect Example

[0050] A soft pack battery was prepared using the improved O3-type layered oxide NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 as the positive electrode material, hard carbon as the negative electrode material, aluminum foil as the positive and negative electrode current collector, and a polypropylene film as the separator. Then, the electrolytes of Examples 1-31 and Comparative Examples 1-7 described above were injected, and the processes of packaging, storage, formation, aging, sodium ion packaging, and capacity distribution were performed to obtain sodium-ion soft pack batteries for testing.

[0051] 1. Room temperature cycling performance

[0052] The above sodium ion battery was charged to 4.0 V at 1C constant current constant voltage, with a cutoff current of 0.05C, under room temperature (25±2℃) conditions, and then left to stand for 5 min, and then discharged to 2.0 V at constant current, and left to stand for 5 min, and the process was repeated for charging and discharging. The average of the capacities of the first three weeks was the initial capacity A1, and the capacity after the n th cycle was An, and the capacity retention rate at the n th cycle could be calculated by (An / A1)*100%.

[0053] 2. High temperature cycling performance

[0054] The above sodium ion battery was charged to 4.0 V at 1C constant current constant voltage, with a cutoff current of 0.05C, under high temperature (45±2℃) conditions, and then left to stand for 5 min, and then discharged to 2.0 V at constant current, and left to stand for 5 min, and the process was repeated for charging and discharging. The average of the capacities of the first three weeks was the initial capacity C1, and the capacity after the n th cycle was Cn, and the capacity retention rate at the 600 th cycle could be calculated by (C 600 / C1)*100%.

[0055] 3. Low temperature -20℃ performance

[0056] The above sodium ion battery was charged to 4.0 V at 1C constant current constant voltage, with a cutoff current of 0.05C, under room temperature (25±2℃) conditions, and then left to stand for 5 min, and then discharged to 2.0 V at 1C rate constant current, and the discharge capacity was recorded as B1. The battery was again charged to 4.0 V at 1C constant current constant voltage, with a cutoff current of 0.05C, and then placed in a low temperature -20℃ environment, and left to stand for 4 h, and then discharged to 1.5 V at 1C rate constant current, and the discharge capacity was recorded as B2. The 1C discharge ratio at low temperature -20℃ could be calculated by (B2 / B1)*100%.

[0057] 4. High temperature storage performance

[0058] The above sodium ion battery was charged and discharged once at 1C / 1C (the discharge capacity was recorded as DC0) under high temperature (60±2℃) conditions, and the initial thickness was recorded as D1, and the initial internal resistance R1, and then the above sodium ion soft package battery was charged to 4.0 V at 1C constant current constant voltage. The above full sodium ion battery was placed in a 60℃ high temperature oven for 7 days, and immediately after taking out, the thickness was measured as D2, and 1C discharge was carried out under room temperature conditions (the discharge capacity was recorded as DC1). The internal resistance was tested by an alternating current resistance meter as R2, and then 1C / 1C charging and discharging was carried out (the discharge capacity was recorded as DC2), and the thickness change rate, internal resistance change rate, DCR change rate, capacity retention rate and capacity recovery rate of the sodium ion battery were calculated using the following formula:

[0059]

[0060]

[0061]

[0062]

[0063] Table 2 Battery performance test results of Comparative Examples 1-7 and Examples 1-31

[0064]

[0065]

[0066] From the above Table 2, it can be seen that the high and low temperature performance and cycle performance of the electrolyte solution in which the negative electrode film-forming additives VC and FEC and the high-temperature additive PS are added to the electrolyte solution of the mixed salt of sodium hexafluorophosphate and sodium bisfluorosulfonylimide, and the PC / DEC / EMC = 3 / 2 / 5 solvent system are all poor, the thickness of the battery increases more during high-temperature storage, and the capacity retention rate is low. Disassembling the battery found that the sodium precipitation phenomenon existed in the battery during the cycle process, indicating that there was a large negative effect on improving the high-temperature performance of the battery by increasing PS. In Comparative Example 2, PST was used to replace PS, and the comprehensive performance of the battery was improved compared with that of the battery in Comparative Example 1. In Comparative Example 3, PS and PST were used as high-temperature additives, and the cycle performance was further improved. Too high a content of PST and PS is not conducive to the low temperature and cycle performance of sodium batteries, and there is a risk of sodium precipitation. By further adding vinyl sulfate (Comparative Example 5), sodium difluoro oxalate borate and sodium difluorophosphate (Comparative Examples 6 / 7) and other low-impedance materials to the sodium battery electrolyte solution, the room temperature cycle life of the sodium battery was significantly improved, and the high-temperature performance was also strengthened. The low-temperature discharge ratio was increased from 70% to more than 80%, indicating that inorganic salt additives have good ability to improve the cycle and high and low temperature performance of the layered sodium battery.

[0067] Example 1, based on Comparative Example 3, 0.5% of A1 is added to the additive, the room temperature and high temperature cycle life are both improved, the low temperature discharge performance is close, the high temperature storage capacity retention and recovery rate are both improved, by adding 0.5% of sodium difluoro(oxalato)borate and 0.5% of sodium difluorophosphate to the electrolyte based on Example 1, the comprehensive performance of the sodium ion battery is further strengthened, and the low temperature performance is also significantly improved. Due to the presence of anhydride functional groups in compound A, a film can be formed on the negative electrode preferentially to the solvent, and at the same time, partial decomposition occurs on the surface of the positive electrode, increasing the positive electrode interfacial impedance, thereby reducing the low temperature performance. Through the combined use of new inorganic salts, the proportion of the inorganic SEI film at the positive and negative electrode interfaces can be adjusted, the sodium ion charge transfer resistance can be reduced, and the transport performance of sodium ions can be improved. By comparing the battery data of the addition amount of compound A1 (Examples 3-7), it can be found that when the addition amount of compound A1 is 0.1%, the comprehensive performance of the relative reference group is limited, indicating that when the addition amount of compound A1 is too small, a dense interface film cannot be formed at the interface. When the addition amount of compound A1 is increased to 1-2%, the high temperature energy storage performance of the sodium battery decreases, which may be due to the fact that the residual part is unstable and decomposes at high temperature, causing the high temperature performance to decrease. At the same time, the excessive introduction of the compound will further increase the interfacial impedance, deteriorate the room temperature cycle performance and low temperature discharge capacity, and increase the risk of sodium precipitation in sodium batteries. By comparing the performance of different structural compounds A (Examples 9-17), it is found that the comprehensive performance of compound A is better than that of 1,3 propylene sulfone. When the silicon-based functional group substituent in compound A is a saturated alkane (methyl, ethyl), the room temperature performance is better than that of the additive with an unsaturated group, and the high temperature performance is slightly inferior to that of the additive containing an unsaturated bond. When R1, R2, R3 in compound A are saturated alkanes, the impedance increase caused by the presence of anhydride in compound A can be reduced, and when R1, R2, R3 are unsaturated groups, the complexation reaction at the positive electrode interface can be further increased, further enhancing the effect of positive electrode protection.

[0068] Further, by optimizing the solvent system, the comprehensive performance of sodium batteries can also be further improved. After introducing part of the carboxylic acid ester PP in the solvent system of the electrolyte, the high-temperature gas production is reduced, the room temperature and high-temperature cycle life is enhanced, and it is found that the carboxylic acid ester PP can rapidly react with trace Na metal precipitated in the sodium battery system, inhibit the precipitation of sodium dendrites, and thus reduce the continuous reduction of sodium metal and the solvent. The room temperature cycle performance and low temperature discharge capacity of fluorinated ether and fluorinated carboxylic acid ester in the battery system are further improved, showing the performance advantage of fluorinated solvent in the sodium battery system. It is found that fluorinated compounds can improve the composition of sodium fluoride interface film in the sodium battery system, reduce the impedance of the battery, and enhance the stability of the interface. At the same time, fluorinated solvents also have an inhibitory effect on the precipitation of sodium metal, and controlling the precipitation of sodium metal in the sodium battery system is the key to improving the performance of sodium batteries.

[0069] In summary, by introducing compound A in the sodium battery electrolyte of layered oxides, the high-temperature and high-temperature cycle life of layered sodium ion batteries can be significantly improved, and the storage performance of sodium ion batteries can be enhanced. By modifying the new inorganic sodium salt with sodium hexafluorophosphate, the cycle stability and high and low temperature performance of sodium batteries are further improved. The introduction of carboxylic acid ester and fluorinated solvent reduces the risk of sodium precipitation in layered sodium ion batteries, improves the interface dynamics performance, and thus improves the comprehensive performance of sodium ion batteries. The complex functional groups contained in the above compound A have multifunctional properties. The anhydride functional group can form a stable SEI passivation film at the negative electrode interface, inhibit the continuous reaction of the solvent with the negative electrode interface, and improve the stability of the negative electrode interface. It can also decompose at the positive electrode interface before the solvent to form a cathode CEI film to passivate the positive active material, thereby inhibiting the oxidative decomposition of the electrolyte at the positive electrode interface and improving the cycle and high-temperature performance of the battery. In addition, the anhydride functional group and the silicon-based functional group can react with trace water and HF in the electrolyte, which can reduce the damage of HF to the positive and negative electrode materials. The silicon-based functional group in compound A can regulate the impedance of the additive and the reaction activity degree on the positive and negative electrode surfaces. When R1, R2 and R3 are saturated alkanes, the impedance increase caused by the anhydride in compound A can be reduced. When R1, R2 and R3 are unsaturated groups, the complex reaction at the positive electrode interface is further increased, and the effect of positive electrode protection is further enhanced.

[0070] Those skilled in the art will readily understand that the above description is only an embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A secondary battery electrolyte, characterized by comprising: The secondary battery electrolyte comprises a non-aqueous organic solvent, an inorganic salt, and an additive, wherein the additive comprises an acid anhydride compound A containing a silicon group functional group, and the structure of the compound A is at least one of compounds A1-A10:

2. The secondary battery electrolyte according to claim 1, characterized by The amount of the compound A added is 0.05-2% of the total weight of the electrolyte.

3. The secondary battery electrolyte according to claim 1, characterized by The amount of the compound A added is 0.2-2% of the total weight of the electrolyte.

4. The secondary battery electrolyte according to claim 1, characterized by, The amount of the compound A added is 0.2-1% of the total weight of the electrolyte.

5. The secondary battery electrolyte according to claim 1, wherein The amount of the compound A added is 0.2-0.5% of the total weight of the electrolyte.

6. The secondary battery electrolyte according to claim 1, wherein The additive further comprises an additive other than the compound A, and the additive other than the compound A is selected from two or more of vinyl sulfate, 3-tert-butyldimethylsilyloxy glutaric anhydride, propylene sulfate, vinylene carbonate, 1,3-propane sulfonate lactone, 1,3-propylene sulfonate lactone, 2,4-butane sulfonate lactone, tris(trimethylsilyl) phosphate, tetra-vinyl silane, triallyl isocyanurate, tripropargyl phosphate, pentaerythritol tetraacrylate, 1,3,6-hexane trinitrile, 3,3-bis vinyl sulfite, 2,4,6-triallyloxy-1,3,5-triazine.

7. The secondary battery electrolyte according to claim 6, characterized by The amount of the additive other than the compound A added is 0.5-5% of the total weight of the electrolyte.

8. The secondary battery electrolyte according to claim 1, characterized by, The non-aqueous organic solvent comprises one or more than two kinds of mixture of propylene carbonate, vinylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoro-vinylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, difluoroethyl acetate, and ethyl difluoroacetate.

9. The secondary battery electrolyte according to claim 1, characterized by, The inorganic salt is an inorganic sodium salt, and the inorganic sodium salt is selected from one or more of sodium hexafluorophosphate, sodium difluorophosphate, sodium difluoro oxalate borate, sodium difluoro bis-oxalate phosphate, sodium bis-fluorosulfonyl imide, sodium bis-trifluorosulfonyl imide, and sodium bis-oxalate borate.

10. The secondary battery electrolyte according to claim 1, characterized by, The mass percentage of the inorganic salt in the electrolyte is 10-20%.

11. A secondary sodium-ion battery, characterized in that, The secondary sodium ion battery comprises the secondary battery electrolyte according to any one of claims 1-10.

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