Lithium / sodium ion battery electrolyte and secondary battery thereof

Abstract

The invention discloses a lithium / sodium ion battery electrolyte and a secondary battery thereof, the electrolyte comprises an electrolyte salt, a non-aqueous solvent and an additive, the additive at least comprises a novel composite metal salt compound as a first additive, a cyclic anhydride compound as a second additive, and a low impedance ester additive, the specific structure of the additive is shown in the specification. Through the mutual synergistic effect of the first additive and the second additive with specific contents, the high-temperature storage performance of the battery is improved, and the high-temperature cycle performance of the battery is further improved; meanwhile, the introduction of the third additive further inhibits the impedance increase in the cycle process, and improves the low-temperature performance and the quick-charge performance of the battery, so that the quick-charge performance, the high-temperature cycle performance and the high-temperature storage performance of the battery are considered at the same time.

Description

Technical Field

[0001] This invention relates to the field of electrolytes, and in particular to a lithium / sodium-ion battery electrolyte that achieves good high-temperature cycling performance, high-temperature storage performance, and low-temperature fast charging performance, and its application in secondary batteries. Background Technology

[0002] In recent years, rechargeable batteries, as a new type of energy source, have been widely used in important fields such as next-generation information and communication, electric vehicles, energy storage power stations, and the energy internet. With the continuous deepening of research and technological development of rechargeable batteries, in order to promote and apply them in various fields, rechargeable batteries need to simultaneously meet requirements such as high specific energy, long cycle life, high safety, high power, and low cost, possessing excellent comprehensive performance. The electrolyte, as the medium for ion transport, is the fundamental guarantee for the battery's charge and discharge performance and is also one of the most important factors affecting the battery's main performance characteristics, especially rate performance, high and low temperature performance, cycle life, and storage performance.

[0003] To improve battery capacity retention and reduce capacity decay during repeated charging and discharging, Donghe New Energy Co., Ltd.'s patent CN116323628A discloses a cyclic dihalophosphate compound that can improve battery cycle life and output characteristics. Hebei Shengtai Materials Co., Ltd.'s patent CN116143666A also discloses a method for preparing lithium triethylamine difluorophosphate of vinyl sulfonate. This compound can undergo a redox reaction on the electrode surface before the electrolyte, generating a stable and dense protective film, preventing continuous decomposition of the electrolyte on the positive electrode material surface, thereby improving the cycle performance and charge-discharge cycle stability of the lithium battery. However, during the research process, this invention found that using this type of compound alone easily leads to electrolyte decomposition and gas generation, especially after long-term storage, resulting in poor high-temperature storage performance and deteriorated high-temperature cycle performance.

[0004] Therefore, developing an electrolyte with good overall performance to achieve long-term storage stability, high-temperature cycling stability, and improve low-temperature fast charging performance is an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a lithium / sodium ion battery electrolyte that balances storage performance, cycle performance, and fast charging performance.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A lithium / sodium ion battery electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives, wherein the additives include at least:

[0008] The first additive is selected from novel composite metal salts with the structure shown in formula (I):

[0009]

[0010] In formula (I), L is a straight bond or oxygen; R1 is selected from C1-C6 alkyl, C1-C6 haloalkyl, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, C3-C6 cycloalkyl, C3-C6 halocycloalkyl, C3-C6 cycloalkenyl or C3-C6 halocycloalkenyl; R2, R3, and R4 are independently selected from C1-C6 alkyl; M is selected from Li, Na or K.

[0011] The second additive is an acid anhydride additive, selected from at least one of the compounds with the structures shown in formulas (II) and (III):

[0012]

[0013] In formula (II), X is selected from C2-C6 alkenyl or C2-C6 haloalkenyl;

[0014] In formula (III), Y is selected from methylene, O or S; R5 and R6 are independently selected from hydrogen, halogen, C1-C3 alkyl, C1-C3 haloalkyl, C2-C4 alkenyl or C2-C4 haloalkenyl; n1 and n2 are independently selected from 0, 1 or 2.

[0015] The first additive accounts for A1 of the total mass of the electrolyte, and 0.05% ≤ A1 ≤ 4.0%;

[0016] The second additive accounts for A2 of the total mass of the electrolyte, and 0.05% ≤ A2 ≤ 3.0%.

[0017] The first additive of this invention is a good film-forming additive that preferentially oxidizes and decomposes on the electrode surface to form a stable solid electrolyte interface film. Simultaneously, during charging, it generates components with high ionic conductivity, such as fluorophosphates, on the electrode surface, improving the ion-conducting properties of the interface film, reducing the inorganic lithium salt content in the interface film, thereby reducing battery impedance and improving battery cycle performance. However, when the first additive exists alone, the NH groups in its structure accelerate the increase in electrolyte acidity, leading to electrolyte decomposition and gas production, resulting in deterioration of the battery's long-term storage performance. This invention incorporates a second additive containing anhydride groups, which not only combines with the NH groups in the first additive to inhibit NH decomposition but also reacts with trace amounts of water and hydrofluoric acid in the electrolyte, preventing metal ion dissolution and electrolyte decomposition and gas production caused by increased electrolyte acidity, thus improving electrolyte stability. However, if the second additive is used alone, it induces a thickening of the electrolyte interface film formed on the electrode surface during charging, increasing interface impedance, especially in fast-charging battery systems, leading to deterioration of battery cycle performance. When the first and second additives are used together, the presence of electron-withdrawing groups in the structure of the second additive (III) increases the number of ring-opening sites, or the unsaturated bonds in the structure of the second additive (II), making the second additive more prone to polymerization and generating complex S / O-based organic products. Simultaneously, taking advantage of the first additive's preferential film-forming characteristic of inorganic components such as fluorophosphates, the two work synergistically to form a stable organic-inorganic multi-component composite SEI film on the electrode.

[0018] This invention achieves the regulation of the reaction intensity on the electrode by controlling the amount and ratio of the first and second additives, thereby adjusting the production ratio of organic and inorganic components, optimizing the composition of the SEI film, and enabling the SEI film to have both excellent ion transport capability and structural / thermal stability. This can further improve the film formation effect, improve the high-temperature storage stability of the battery, and further enhance the high-temperature cycling performance.

[0019] Therefore, regarding the amount of the first additive and the second additive, preferably, 0.1% ≤ A1 ≤ 3.0% and 0.1% ≤ A2 ≤ 2.0%. More preferably, 0.2 ≤ A1 / A2 ≤ 8; even more preferably, 0.25 ≤ A1 / A2 ≤ 6.

[0020] Regarding the structure of the first additive and the second additive, preferably, in formula (I), R1 is selected from C1-C3 alkyl, C1-C3 haloalkyl, C2-C3 alkenyl, C2-C3 haloalkenyl, C2-C3 ynyl or C2-C3 haloynyl; R2, R3, and R4 are independently selected from C1-C3 alkyl; M is selected from Li or Na;

[0021] In formula (II), X is selected from vinyl, methyl-substituted vinyl, dimethyl-substituted vinyl, allyl, and methyl-substituted allyl;

[0022] In formula (III), Y is selected from O or S; R5 and R6 are independently selected from hydrogen, fluorine, methyl, ethyl, vinyl or allyl; n1 and n2 are both 1.

[0023] More preferably, the first additive is selected from at least one of the novel composite metal salts shown in the following structure:

[0024]

[0025] The second additive is selected from at least one of the following acid anhydride compounds with the structure shown below:

[0026]

[0027] To further suppress impedance growth during cycling and improve the battery's low-temperature and fast-charging performance, the additive also includes a low-impedance ester third additive. The third additive is selected from at least one of fluoroethylene carbonate, ethylene sulfate, 4,4'-diethylene sulfate, 1,4-dioxane disulfate, tris(trimethylsilyl)phosphate, or tris(trimethylsilyl)borate, and any one of the third additives accounts for 0.1 to 10.0 wt% of the total mass of the electrolyte.

[0028] Preferably, the third additive is selected from at least one of fluoroethylene carbonate, ethylene sulfate, or tris(trimethylsilyl)phosphate, and any one of the third additives accounts for 0.2 to 5.0 wt% of the total mass of the electrolyte.

[0029] By simultaneously introducing a low-resistance ester-based third additive in addition to the first and second additives, the impedance growth during cycling can be further suppressed, thereby further improving the battery's low-temperature and fast-charging performance. By adjusting the amount and ratio of the first, second, and third additives, the battery can achieve excellent fast-charging, cycling, and storage performance.

[0030] Preferably, the ratio of (amount of the first additive + amount of the second additive) to the amount of the third additive is 0.1 to 10. More preferably, the ratio of (amount of the first additive + amount of the second additive) to the amount of the third additive is 0.2 to 6.

[0031] The electrolyte described above can be used in both lithium-ion and sodium-ion batteries.

[0032] When the electrolyte is used in a lithium-ion battery, the electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium tri(oxalate) phosphate, or lithium difluorobis(oxalate) phosphate.

[0033] When the electrolyte is used in a sodium-ion battery, the electrolyte salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, or sodium difluorophosphate.

[0034] The amount of electrolyte salt added accounts for 6.0 to 22.5 wt% of the total mass of the electrolyte, preferably 10.0 to 18.0 wt%.

[0035] The non-aqueous solvent used in this invention can be any solvent commonly used in electrolytes. Preferably, the non-aqueous solvent is selected from at least one of C3-C6 carbonates or fluorocarbonates, C3-C8 carboxylic acids or fluorocarboxylic acids, sulfones, or ethers.

[0036] Specifically, the C3-C6 carbonate or fluorocarbonate compound is selected from at least one of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate, fluoropropylene carbonate, fluoromethyl ethyl carbonate, fluorodimethyl carbonate, or fluorodiethyl carbonate; the C3-C8 carboxylic acid ester or fluorocarboxylic acid ester compound is selected from at least one of γ-butyrolactone, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl acetate, propyl propionate, and 2,2-difluoroethyl acetate; the sulfone compound is selected from at least one of sulfolane, dimethyl sulfoxide, dimethyl sulfone, or diethyl sulfone; and the ether compound is selected from at least one of triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol dimethyl ether, dioxolane, and tetrahydrofuran.

[0037] Preferably, the non-aqueous solvent is selected from one of the following: a mixed solvent of EC and DMC; a mixed solvent of EC and EMC; a mixed solvent of EC, EMC, and DEC; a mixed solvent of FEC and EMC; a mixed solvent of methyltrifluoroethyl carbonate and EMC; a mixed solvent of EC, FEC, and EMC; a mixed solvent of EC, FEC, and DEC; a mixed solvent of FEC, methyltrifluoroethyl carbonate, and 2,2-difluoroethyl acetate; a mixed solvent of EC, DEC, and EP; a mixed solvent of EC, DEC, and PP; a mixed solvent of EC, EMC, and MP; a mixed solvent of EC, EMC, and 2,2-difluoroethyl acetate; a mixed solvent of PC and DEC; a mixed solvent of EMC and PC; a mixed solvent of DEC, EMC, and PC; a mixed solvent of PC and DME; a mixed solvent of PC, DME, and DOL; or a mixed solvent of PC, DME, and THF.

[0038] To further improve the overall performance of the battery, the additive also includes a basic additive, which is different from the electrolyte salt and is selected from at least one of vinylene carbonate, 1,3-propanesulfonyl lactone, 1,3-propenesulfonyl lactone, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, adiponitrile, cyclohexylbenzene, lithium bis(oxalate) difluorophosphate, lithium bis(fluorooxalate) borate, sodium bis(fluorooxalate) borate, sodium difluorophosphate, sodium bis(fluorosulfonyl)imide, and sodium bis(oxalate) difluorophosphate. Any one of the basic additives accounts for 0.1 to 5.0 wt% of the total mass of the electrolyte, and is used to meet the application scenarios of different electrolytes and the electrochemical performance requirements of the battery.

[0039] In one specific embodiment, a lithium-ion battery electrolyte is provided, wherein the electrolyte salt is preferably LiPF6, and the amount used accounts for 10.0-15.0 wt% of the total mass of the electrolyte; the non-aqueous solvent is preferably at least one of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), more preferably a mixed solvent of EC, EMC, and DEC, and the mass ratio of the three is EC:EMC:DEC = 3:5:2; the first additive is compound (I-1), and the amount used accounts for 0.1-3.0 wt% of the total mass of the electrolyte; the second additive is preferably compound (II-1), and the amount used accounts for 0.1-2.0 wt% of the total mass of the electrolyte; the third additive is preferably FEC, and the amount used accounts for 0.2-5.0 wt% of the total mass of the electrolyte; the basic additive includes at least: vinylene carbonate, 1,3-propanesulfonyl lactone, and lithium difluorooxalate borate, and the amount used accounts for 0.5-2 wt% of the total mass of the electrolyte.

[0040] In another specific embodiment, a sodium-ion battery electrolyte is provided, wherein the electrolyte salt is preferably NaPF6, and the amount used accounts for 10.0-18.0 wt% of the total mass of the electrolyte; the non-aqueous solvent is preferably at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and propylene carbonate (PC), more preferably a mixed solvent of DEC, EMC, and PC, and the mass ratio of the three is PC:EMC:DEC = 3:5:2; the first additive is compound (I-2), and the amount used accounts for 0.1-3.0 wt% of the total mass of the electrolyte; the second additive is preferably compound (II-1), and the amount used accounts for 0.1-2.0 wt% of the total mass of the electrolyte; the third additive is preferably FEC, and the amount used accounts for 0.2-5.0 wt% of the total mass of the electrolyte; the basic additive includes at least 1,3-propenyl sulfonyl lactone and sodium difluorosulfonyl imide, and the amount used accounts for 0.5-2 wt% of the total mass of the electrolyte.

[0041] The present invention also provides a lithium / sodium ion secondary battery, comprising a positive electrode, a negative electrode, and a separator, as well as the electrolyte described above.

[0042] Specifically, the active material of the positive electrode is selected from lithium cobalt oxide, lithium iron phosphate, lithium nickel manganese oxide, ternary materials of nickel cobalt manganese lithium, sodium-containing layered oxides, Prussian blue / white or polyanions (sodium iron phosphate, sodium vanadium phosphate, etc.), and the active material of the negative electrode is selected from graphite, silicon-carbon composite materials, lithium titanate, lithium metal, hard carbon, anthracite soft carbon, hard-soft composite carbon and their composite materials.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] 1. The first and second additives of this invention work synergistically. The second additive inhibits the decomposition of NH groups in the first additive, suppresses the decomposition and gas production of the electrolyte, and inhibits the acidity increase of the electrolyte during long-term storage, thereby improving the storage performance of the battery and the stability of the electrolyte. At the same time, by controlling the amount and ratio of the first and second additives, the SEI film composition is adjusted, forming an organic-inorganic multi-component composite SEI film with excellent ion transport capability and structural / thermal stability on the electrode surface. This effectively reduces interfacial impedance and suppresses impedance growth during cycling, further improving the high-temperature cycling performance of the battery.

[0045] 2. This invention proposes the combined use of a first additive, a second additive, and a third additive with specific structures, while regulating the content distribution of the three additives. Through the synergistic effect between the three additives, not only is the impedance growth during battery cycling suppressed, effectively improving the low-temperature and fast-charging performance of the battery, but also the high-temperature storage performance and high-temperature cycling performance of the battery are further improved, thus improving the overall performance of the battery. Detailed Implementation

[0046] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0047] I. Electrolyte Preparation

[0048] Preparation of basic lithium-ion battery electrolyte 1: In an argon-filled glove box (moisture content < 5 ppm, oxygen content < 10 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of EC:EMC:DEC = 3:5:2. Then, lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution until the molar concentration reached 1.0 mol / L to obtain basic electrolyte 1.

[0049] Preparation of sodium basic electrolyte 2: In an argon-filled glove box (moisture < 5 ppm, oxygen < 10 ppm), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and propylene carbonate (PC) were uniformly mixed at a mass ratio of PC:EMC:DEC = 3:5:2. Then, sodium hexafluorophosphate (NaPF6) was slowly added to the mixed solution until the molar concentration reached 1.0 mol / L to obtain basic electrolyte 2.

[0050] Add the first additive, second additive, third additive, and basic additive quantitatively according to the data in Table 1 below, and mix thoroughly to form an electrolyte:

[0051] Table 1 Electrolyte Formulation

[0052]

[0053]

[0054] Note: After adjusting the amount of additives, only the amount of solvent in the base electrolyte is adjusted, and the distribution ratio of each component in the solvent remains unchanged.

[0055] II. Electrolyte Storage Acidity Test

[0056] The electrolytes of the above examples and comparative examples were transferred to sealed aluminum bottles and stored in a constant temperature oven at 45°C. Samples of the electrolytes were taken in a glove box before storage, after 7 days of storage, and after 14 days of storage to test the acidity value. The acidity test method was non-aqueous titration, and the acidity unit was ppm. The test results are shown in Table 2 below.

[0057] III. Electrochemical Performance Testing

[0058] The electrolytes from Examples 1-20 and Comparative Examples 1-5 were used to fabricate 1260mAh lithium-ion batteries in soft-pack form. Each lithium-ion battery includes a positive electrode, a negative electrode, a separator, an electrolyte, and battery auxiliary materials. The positive electrode active material is a ternary lithium-ion cathode material (LiNi). 0.6 Co 0.2 Mn 0.2 O2, the negative electrode active material is high-capacity graphite. The preparation process is as follows: the positive electrode sheet, separator and negative electrode sheet are wound together into a core, sealed with aluminum-plastic film and then baked to ensure that the electrode moisture meets the requirements. After baking, the cell is injected with electrolyte, and after standing, formation, capacity testing and aging processes, the finished lithium-ion battery soft pack cell is obtained.

[0059] The electrolytes from Examples 21-24 and Comparative Examples 6-8 were used to prepare 1000mAh soft-pack sodium-ion batteries. Each sodium-ion battery includes a positive electrode, a negative electrode, a separator, an electrolyte, and battery auxiliary materials. The positive electrode active material is a ternary cathode material (NaNi). 0.33 Fe 0.33 Mn 0.33 O2, with hard carbon as the negative electrode active material. The preparation process is as follows: the positive electrode, separator, and negative electrode are wound together into a core, sealed with aluminum-plastic film, and then baked to ensure that the electrode moisture content meets the requirements. After baking, the cell is injected with electrolyte, and after standing, formation, capacity testing, and aging processes, the finished sodium ion soft-pack cell is obtained.

[0060] The performance of the lithium-ion and sodium-ion batteries prepared above was tested, mainly including:

[0061] (1) Initial impedance test:

[0062] During the battery capacity grading stage: At room temperature (25℃), charge the battery with a constant current of 0.2C until the charging cutoff voltage, and then charge it with a constant voltage until the current drops to 0.05C; then discharge the battery with a constant current of 0.2C until the discharge cutoff voltage, and record the discharge capacity C1, which is the initial capacity of the battery.

[0063] Then charge at a constant current of 0.2C until the charging cutoff voltage, and charge at a constant voltage until the current drops to 0.05C; then discharge at a constant current of 0.2C until the capacity reaches 0.5*C1, which is 50% SOC state of charge, let stand for 2 hours, and record the voltage U1.

[0064] Finally, discharge the battery at a constant current of 4C for 30 seconds, record the voltage U2, and calculate the initial impedance of the battery:

[0065] Initial impedance = (U1 - U2) / 4 * 1000

[0066] (2) Low-temperature discharge performance test

[0067] The battery was discharged to 80% of its lower limit voltage at a discharge current of 1C in an oven at -20±1℃. This was taken as the low-temperature discharge capacity, and the percentage of this capacity to the 1C discharge capacity at 25℃ was calculated and recorded as the low-temperature discharge capacity retention rate.

[0068] (3) High-temperature storage performance test

[0069] At room temperature (25℃), the battery was charged at a constant current of 1C to the charging cutoff voltage (4.4V), and then charged at a constant voltage until the current dropped to 0.05C. It was then placed in a 60℃ constant temperature oven for 60 days. After storage, the battery was cooled to room temperature, and the initial volume V1 and the volume V2 after storage were recorded. The battery was then discharged at a constant current of 1C to the discharge cutoff voltage, and the initial discharge capacity C1 and the discharge capacity C2 after storage were recorded. The high-temperature storage volume expansion rate and capacity retention rate were calculated using the following formula:

[0070] High-temperature storage volume expansion rate = (V2 / V1-1)*100%

[0071] High-temperature storage capacity retention rate = C2 / C1 * 100%

[0072] (4) High-temperature cycling performance test

[0073] The battery was cycled in an oven at 45±1℃ with a charge / discharge current of 1C / 1C. The discharge capacity was calculated per cycle. The cycle was stopped after 500 cycles, and the capacity retention rate after the cycle was calculated.

[0074] The specific test results are shown in Table 2 below:

[0075] Table 2 Results of electrolyte storage acidity and electrochemical tests

[0076]

[0077]

[0078] Based on the data in Tables 1 and 2 above, a comparison of Comparative Examples 1 and 2 / 3 shows that using the first additive alone can reduce battery impedance, improve low-temperature discharge performance, and enhance high-temperature cycling performance, but it increases electrolyte acidity and degrades high-temperature storage performance. Using the second additive alone can suppress electrolyte acidity growth and electrolyte storage gas generation, improving high-temperature storage performance, but it slightly increases initial impedance and degrades low-temperature and high-temperature cycling performance. Furthermore, a comparison of Comparative Examples 6 and 7 / 8 shows that the first and second additives exhibit similar effects in sodium-ion batteries.

[0079] Comparing Examples 1-8 with Comparative Examples 4 and 5, it can be seen that only when the first additive and the second additive satisfy the relationships 0.05% ≤ A1 ≤ 4.0%, 0.05% ≤ A2 ≤ 3.0%, and 0.2 ≤ A1 / A2 ≤ 8, can the secondary battery possess good low-temperature discharge performance, high-temperature cycle performance, and high-temperature storage performance. When A1 / A2 is too large, on the one hand, it leads to an increase in electrolyte acidity, resulting in a deterioration in high-temperature storage performance; on the other hand, the content of the first additive is much higher than that of the second additive, resulting in an excessive amount of inorganic components in the formed SEI film, which has poor structural / thermal stability and deteriorates high-temperature cycle performance. When A1 / A2 is too small, it leads to an excessive amount of organic components in the formed SEI film, increasing battery impedance and deteriorating both low-temperature discharge performance and high-temperature cycle performance.

[0080] Comparative examples 1-8 show that controlling the content of the first additive and the second additive, especially when the two satisfy the relationship 0.5≤A1 / A2≤4, can further improve the high-temperature cycle performance of the battery, while also having good low-temperature discharge and high-temperature storage performance.

[0081] Comparing Examples 2 and 16-18, it can be seen that further introducing a low-resistance ester-based third additive into the electrolyte can significantly improve the low-temperature discharge performance of the battery, and further enhance the high-temperature storage and cycle performance, thus improving the overall performance of the battery. Meanwhile, comparing Examples 21 and 22 shows that the combined use of these three additives in sodium-ion batteries also exhibits a consistent improvement effect.

[0082] Comparing Examples 2 and Examples 9-18, it can be seen that compounds II-1, II-2, II-3, III-1, III-2, III-3, III-4, III-5, and compounds FEC, DTD, and TMSP all have the functions of the additives they represent and can be used interchangeably.

[0083] Comparing Examples 16 and 19, 20, it can be seen that, based on the addition of the first, second, and third additives, the combined use of basic additives such as VC, PS, and LiDFOB can further improve the high and low temperature performance and storage performance of the battery. Meanwhile, comparing Examples 22 and 23, 24, it can be seen that adding basic additives to sodium-ion batteries can achieve the same effect.

Claims

1. A lithium / sodium ion battery electrolyte, comprising an electrolyte salt, a non-aqueous solvent, and additives, characterized in that: The additives include: The first additive is selected from novel composite metal salts with the structure shown in formula (I): In formula (I), L is a straight bond or oxygen; R1 is selected from C1-C6 alkyl, C1-C6 haloalkyl, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, C3-C6 cycloalkyl, C3-C6 halocycloalkyl, C3-C6 cycloalkenyl or C3-C6 halocycloalkenyl; R2, R3, and R4 are independently selected from C1-C6 alkyl; M is selected from Li, Na or K; The second additive is an acid anhydride additive, selected from at least one of the compounds with the structures shown in formulas (II) and (III): In formula (II), X is selected from C2-C6 alkenyl or C2-C6 haloalkenyl; In formula (III), Y is selected from methylene, O or S; R5 and R6 are independently selected from hydrogen, halogen, C1-C3 alkyl, C1-C3 haloalkyl, C2-C4 alkenyl or C2-C4 haloalkenyl; n1 and n2 are independently selected from 0, 1 or 2. The first additive accounts for A1 of the total mass of the electrolyte, and 0.05% ≤ A1 ≤ 4.0%; The second additive accounts for A2 of the total mass of the electrolyte, and 0.05% ≤ A2 ≤ 3.0%.

2. The lithium / sodium ion battery electrolyte according to claim 1, characterized in that: 0.1% ≤ A1 ≤ 3.0%, 0.1% ≤ A2 ≤ 2.0%.

3. The lithium / sodium ion battery electrolyte according to claim 1 or 2, characterized in that: 0.2≤A1 / A2≤8.

4. The lithium / sodium ion battery electrolyte according to claim 1, characterized in that: In formula (I), R1 is selected from C1-C3 alkyl, C1-C3 haloalkyl, C2-C3 alkenyl, C2-C3 haloalkenyl, C2-C3 ynyl or C2-C3 haloynyl; R2, R3, and R4 are independently selected from C1-C3 alkyl; M is selected from Li or Na; In formula (II), X is selected from vinyl, methyl-substituted vinyl, dimethyl-substituted vinyl, allyl, and methyl-substituted allyl; In formula (III), Y is selected from O or S; R5 and R6 are independently selected from hydrogen, fluorine, methyl, ethyl, vinyl or allyl; n1 and n2 are both 1.

5. The lithium / sodium ion battery electrolyte according to claim 4, characterized in that: The first additive is selected from at least one of the novel composite metal salts shown in the following structures: The second additive is selected from at least one of the following acid anhydride compounds with the structure shown below:

6. The lithium / sodium ion battery electrolyte according to any one of claims 1-5, characterized in that: The additive also includes a third additive, which is selected from at least one of fluoroethylene carbonate, ethylene sulfate, 4,4'-diethylene sulfate, 1,4-dioxane disulfate, tris(trimethylsilyl)phosphate, or tris(trimethylsilyl)borate, and any one of the third additives accounts for 0.1 to 10.0 wt% of the total mass of the electrolyte.

7. The lithium / sodium ion battery electrolyte according to claim 6, characterized in that: The third additive is selected from at least one of fluoroethylene carbonate, ethylene sulfate, or tris(trimethylsilyl)phosphate, and any one of the third additives accounts for 0.5 to 5.0 wt% of the total mass of the electrolyte.

8. The lithium / sodium ion battery electrolyte according to claim 6 or 7, characterized in that: The ratio of (amount of the first additive + amount of the second additive) to the amount of the third additive is 0.1 to 10.

9. The lithium / sodium ion battery electrolyte according to claim 1, characterized in that: When the electrolyte is used in a lithium-ion battery, the electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalate phosphate, lithium tri(oxalate) phosphate, or lithium difluorobis(oxalate) phosphate. When the electrolyte is used in a sodium-ion battery, the electrolyte salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, or sodium difluorophosphate.

10. The lithium / sodium ion battery electrolyte according to claim 1, characterized in that: The non-aqueous solvent is selected from at least one of C3-C6 carbonates or fluorocarbonates, C3-C8 carboxylic acids or fluorocarboxylic acids, sulfones, or ethers.

11. The lithium / sodium ion battery electrolyte according to any one of claims 1-10, characterized in that: The additives also include basic additives, which are selected from at least one of vinylene carbonate, 1,3-propanesulfonyl lactone, 1,3-propenesulfonyl lactone, lithium difluorophosphate, lithium difluorosulfonylimide, adiponitrile, cyclohexylbenzene, lithium difluorophosphate bis(oxalate), lithium difluorooxalate borate, sodium difluorooxalate borate, sodium difluorophosphate, sodium difluorosulfonylimide, and sodium difluorophosphate bis(oxalate), and any one of the basic additives accounts for 0.1 to 5.0 wt% of the total mass of the electrolyte; the basic additives are different from electrolyte salts.

12. A lithium / sodium-ion secondary battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that: The lithium / sodium ion secondary battery is filled with the electrolyte according to any one of claims 1-11.

13. The lithium / sodium ion secondary battery according to claim 12, characterized in that: The active material of the positive electrode is selected from lithium cobalt oxide, lithium iron phosphate, lithium nickel manganese oxide, ternary materials of nickel cobalt manganese lithium, sodium-containing layered oxides, Prussian blue / white or polyanions (sodium iron phosphate, sodium vanadium phosphate), and the active material of the negative electrode is selected from graphite, silicon-carbon composite material, lithium titanate, lithium metal, hard carbon, anthracite soft carbon, hard-soft composite carbon and their composite materials.

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