Use of a thiazole ester additive in a secondary battery electrolyte

Abstract

The application discloses application of a thiazole ester additive in a secondary battery electrolyte, wherein the thiazole ester additive comprises at least one compound shown in a structural formula (I), and the specific structure of the thiazole ester additive is shown in the specification. The thiazole ester additive disclosed by the application is applied in the secondary battery electrolyte, so that the low-temperature discharge, normal-temperature cycle, high-temperature cycle and high-temperature storage performance of the battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery electrolytes, and in particular to the application of a thiazole ester additive in secondary battery liquid electrolytes. Background Technology

[0002] Batteries are prone to increased internal resistance, capacity decay, and decreased safety performance under high or low temperature environments. This not only affects battery lifespan and efficiency but also limits their application in cold regions, tropical regions, and special industrial scenarios such as aerospace. In recent years, to improve battery performance under high and low temperature environments, researchers have developed a series of novel electrolytes by adjusting the additives and solvents in the electrolyte.

[0003] However, existing electrolytes still cannot simultaneously meet the performance requirements of batteries under both high and low temperature conditions. For example, while fluoroethylene carbonate (FEC) can significantly improve the low-temperature performance of batteries as a low-temperature additive, its stability at high temperatures is poor, and the HF produced by its decomposition severely degrades the high-temperature performance of the battery. Similarly, the 1,3-propanesulfonate lactone (PS) additive mentioned in patent CN102244296B can improve the high-temperature storage performance of batteries, but its high impedance degrades the low-temperature performance of the battery. In addition, patent CN118336110A proposes a low-temperature electrolyte using low-melting-point and low-viscosity carboxylic esters as solvents. Although it significantly improves low-temperature performance, the carboxylic ester solvent is prone to causing gas generation in the battery at high temperatures, thus affecting high-temperature performance.

[0004] Therefore, developing a multifunctional additive and electrolyte that can simultaneously achieve both high and low temperature performance is an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes the application of thiazole ester compounds as additives in liquid electrolytes. The inventors have experimentally determined that liquid electrolytes containing thiazole ester compounds, when used in secondary batteries, can improve the low-temperature discharge, room-temperature cycling, high-temperature cycling, and high-temperature storage performance of the secondary batteries. Furthermore, this invention introduces a second additive, which can suppress the increase in battery impedance caused by excessively thick thiazole ester compound films, thus changing the effect of thiazole ester compounds on battery impedance from increasing to decreasing, and further improving the low-temperature discharge performance of the battery.

[0006] The electrolyte described in this invention is a liquid electrolyte.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] In a first aspect, the application of a thiazole ester additive in a secondary battery electrolyte, said thiazole ester additive comprising at least one of the compounds shown in structural formula (I):

[0009]

[0010] In structural formula (I), R1 and R2 are each independently selected from hydrogen, fluorine, 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, and R3 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.

[0011] Preferably, in formula (I), R1 and R2 are each independently selected from hydrogen atom, methyl, tert-butyl, vinyl or ethynyl, and R3 is selected from methyl, tert-butyl, n-butyl, cyclopentyl or trifluoromethyl.

[0012] More preferably, the thiazole ester additive is selected from at least one of compounds of formula (I-1) to (I-9):

[0013]

[0014] The use of the thiazole ester additives described in this invention in secondary battery electrolytes can balance high and low temperature performance of the battery. The sulfonate groups and thiazole rings in the thiazole ester additives of this invention form a stable and dense interfacial film on the positive and negative electrode surfaces, effectively suppressing side reactions and significantly improving the battery's room-temperature cycle performance. However, the high electronegativity of sulfur and nitrogen atoms in the thiazole ring structure leads to uneven electron cloud distribution, making thiazole ring-containing compounds prone to ring-opening decomposition under high-temperature conditions, thus degrading the battery's high-temperature storage performance. The thiazole ester additives of this invention improve the problem of uneven electron cloud distribution by introducing carboxylic acid ester groups to modify the thiazole ring, thereby improving the stability of the compound under high-temperature environments. This design allows thiazole ester compounds to form films on the positive and negative electrode surfaces even at high temperatures, thereby improving the battery's cycle and storage performance at high temperatures. Furthermore, this design reduces the electron cloud density of the carboxylic acid ester groups, making them easier to electrochemically reduce and thus participate in negative electrode film formation. Thiazole ester compounds contain thiazole rings and carboxylic acid ester groups, which can generate an inorganic lithium salt layer rich in S, N and O at the positive and negative electrode interfaces, thereby improving the lithium ion transport rate and thus improving the low-temperature discharge performance of the battery.

[0015] Secondly, the present invention also provides a non-aqueous electrolyte for secondary batteries, wherein the electrolyte comprises the thiazole ester additives described in the first aspect of the present invention, and the amount of the additives is 0.001 to 5.0 wt% of the total mass of the electrolyte. When the content of the thiazole ester additives is low (e.g., less than 0.001%), the film formation effect of the positive and negative electrodes is poor, and the battery's room temperature cycling, high temperature cycling, and high temperature storage performance cannot be improved. When the content of the thiazole ester additives is high (e.g., greater than 5%), the film formation of the positive and negative electrodes is thicker, the impedance is higher, and the effect of improving the battery's room temperature cycling, high temperature cycling, and high temperature storage performance decreases.

[0016] Preferably, the content of the thiazole ester additive accounts for 0.01 to 3.0 wt% of the total mass of the electrolyte; more preferably, 0.1 to 2.0 wt%.

[0017] In some embodiments, the thiazole ester additive accounts for 0.001 to 5.0 wt% of the total mass of the electrolyte. Therefore, using this amount of thiazole ester additive in the electrolyte can form a stable, dense, and highly ion-conducting interfacial film on the positive and negative electrode surfaces, improving the battery's low-temperature discharge, room-temperature cycling, high-temperature cycling, and high-temperature storage performance.

[0018] In some embodiments, the thiazole ester additive accounts for 0.01 to 3.0 wt% of the total electrolyte mass. This effectively improves the battery's low-temperature discharge, room-temperature cycling, high-temperature cycling, and high-temperature storage performance.

[0019] In some embodiments, the thiazole ester additive accounts for 0.1 to 2.0 wt% of the total electrolyte mass. This effectively improves the battery's low-temperature discharge, room-temperature cycling, high-temperature cycling, and high-temperature storage performance.

[0020] Furthermore, the non-aqueous electrolyte for the secondary battery also contains a second additive, which is selected from at least one of 1,3-propanesulfonyl lactone (PS) or 1,3-propenesulfonyl lactone (PST), and the amount of the second additive is 0.001 to 5.0 wt% of the total mass of the electrolyte.

[0021] Preferably, the contents of the thiazole ester additive and the second additive account for a% and b% of the total mass of the electrolyte, respectively, and conform to the following relationship:

[0022] 0.2≤a+b≤10;

[0023] 0.1≤a / b≤10.

[0024] Furthermore, the contents of the thiazole ester additive and the second additive satisfy the following relationship:

[0025] 0.5≤a+b≤5;

[0026] 0.2≤a / b≤5.

[0027] This invention innovatively introduces a second additive with a reduction potential similar to that of the thiazole ester additive. When the second additive and the thiazole ester additive are used in combination, they can compete for reduction on the negative electrode surface, thereby mutually inhibiting each other's film-forming effect and avoiding the formation of an excessively thick SEI. This mechanism allows the inorganic lithium salt layer constructed with the thiazole ester additive to achieve a thinner thickness while maintaining a high ion transport rate, thus changing the effect of the thiazole ester additive on battery impedance from increasing to decreasing. Compared with using the thiazole ester additive or the second additive alone, the synergistic effect of the two can significantly reduce battery impedance and significantly improve low-temperature discharge performance.

[0028] When the ratio of the two components does not meet the above conditions, the battery impedance cannot be reduced.

[0029] In some implementations, 0.2 ≤ a + b ≤ 10; 0.1 ≤ a / b ≤ 10. This improves the battery's performance in room temperature cycling, high temperature cycling, and high temperature storage, and significantly enhances its impedance and low-temperature discharge performance.

[0030] In some implementations, 0.5 ≤ a + b ≤ 5; 0.2 ≤ a / b ≤ 5. This improves the battery's performance in room temperature cycling, high temperature cycling, and high temperature storage, and significantly enhances its impedance and low-temperature discharge performance.

[0031] Specifically, in the electrolyte, the sum of the contents of thiazole ester additives and the second additive is between 0.2 and 10, preferably between 0.5 and 5. If the sum of the contents of the two is too small (e.g., less than 0.2), the film-forming effect is poor, and the battery impedance and low-temperature discharge performance are not significantly improved. If the sum of the contents of the two is too large (e.g., greater than 10), it will lead to a thicker interfacial film, thereby deteriorating the impedance, low-temperature discharge, room temperature cycling, high temperature cycling and high-temperature storage performance.

[0032] Specifically, in the electrolyte, the ratio of the content of thiazole ester additives and the second additive is between 0.1 and 10, preferably between 0.2 and 5. If the ratio of the two is too small (e.g., less than 0.1), the second additive will significantly inhibit the film-forming effect of the thiazole ester additives, resulting in insignificant improvement in the battery's room temperature cycling, high temperature cycling, and high temperature storage performance. If the ratio of the two is too large (e.g., greater than 10), the second additive cannot inhibit the film-forming effect of the thiazole ester additives, resulting in a thicker interfacial film that cannot reduce the battery's impedance.

[0033] Furthermore, the non-aqueous electrolyte for secondary batteries also contains a third additive, which is selected from at least one of vinylene carbonate, fluoroethylene carbonate (FEC), vinyl sulfate (DTD), vinyl sulfite, pentaerythritol dicyclic sulfate, 4,4'-diethylene sulfate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, adiponitrile, cyclohexylbenzene, lithium dioxalate borate, lithium difluorooxalate borate, sodium dioxalate borate, and sodium difluorooxalate borate. The content of any one of the third 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 requirements of battery electrochemical performance.

[0034] Furthermore, the non-aqueous electrolyte for the secondary battery also contains a non-aqueous solvent, which is selected from at least one of C3-C6 carbonate or fluorocarbonate compounds, C3-C8 carboxylic acid esters or fluorocarboxylic acid ester compounds, sulfone compounds or ether compounds.

[0035] Specifically, the C3-C6 carbonate or fluorocarbonate compound is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, fluoroethylene carbonate (FEC), fluoropropylene carbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, or diethyl fluorocarbonate; the C3-C8 carboxylic acid ester or fluorocarboxylic acid ester compound is selected from at least one of γ-butyrolactone, methyl acetate, methyl propionate (MP), methyl butyrate, ethyl acetate, ethyl propionate (EP), ethyl butyrate, propyl acetate, propyl propionate (PP), or 2,2-difluoroethyl acetate. The sulfone compound is selected from at least one of sulfolane, dimethyl sulfoxide, dimethyl sulfone, or diethyl sulfone. The ether compound is selected from at least one of triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol dimethyl ether (DME), dioxolane (DOL), and tetrahydrofuran (THF).

[0036] Preferably, the non-aqueous solvent is selected from a mixture of EC and DMC, EC and EMC, EC, EMC and DEC, FEC and EMC, methyltrifluoroethyl carbonate and EMC, EC, FEC and EMC, EC, FEC and DEC, FEC, methyltrifluoroethyl carbonate and 2,2-difluoroethyl acetate, EC, DEC and EP, EC, DEC and PP, EC, EMC and MP, EC, EMC and 2,2-difluoroethyl acetate, PC and DEC, EMC and PC, DEC, EMC and PC, PC and DME, PC, DME and DOL, or PC, DME and THF.

[0037] Furthermore, the non-aqueous electrolyte for the secondary battery also contains an electrolyte salt. When the electrolyte is used in a lithium-ion battery, the electrolyte salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethanesulfonyl)imide. When the electrolyte is used in a sodium-ion battery, the electrolyte salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonyl)imide, or sodium bis(trifluoromethanesulfonyl)imide.

[0038] In one specific embodiment, a non-aqueous electrolyte for lithium-ion secondary batteries is provided, comprising an electrolyte salt, a non-aqueous solvent, a thiazole ester additive, a second additive, and a third additive. The electrolyte salt is LiPF6, and its content accounts for 5.0–15.0 wt% of the total mass of the electrolyte, preferably 12.5 wt%. The non-aqueous solvent is selected from at least one of EC, EMC, and DEC, preferably a mixture of EC, EMC, and DEC, and the mass ratio of the three is EC:EMC:DEC = 3:5:2. The thiazole ester additive is selected from at least one of the compounds shown in formulas (I-1) to (I-9), and its content accounts for 0.001–5.0 wt% of the total mass of the electrolyte. The second additive is selected from at least one of PS or PST, and its content accounts for 0.001–5.0 wt% of the total mass of the electrolyte. The third additive is DTD, and its content accounts for 0.1–2.0 wt% of the total mass of the electrolyte, preferably 2.0 wt%.

[0039] In another specific embodiment, a non-aqueous electrolyte for sodium-ion secondary batteries is provided, comprising an electrolyte salt, a non-aqueous solvent, a thiazole ester additive, a second additive, and a third additive. The electrolyte salt is NaPF6, and its content accounts for 5.0–15.0 wt% of the total mass of the electrolyte, preferably 12.5 wt%. The non-aqueous solvent is selected from at least one of DEC, EMC, and PC, preferably a mixed solvent of DEC, EMC, and PC, and the mass ratio of the three is PC:EMC:DEC = 3:5:2. The thiazole ester additive is selected from at least one of the compounds shown in formulas (I-1) to (I-9), preferably the compound shown in formula (I-1), and its content accounts for 0.001–5.0 wt% of the total mass of the electrolyte, preferably 0.5 wt%. The second additive is selected from PS, and its content accounts for 0.001–5.0 wt% of the total mass of the electrolyte, preferably 0.5 wt%. The third additive is FEC, and its content accounts for 0.1–5.0 wt% of the total mass of the electrolyte, preferably 2.0 wt%.

[0040] Thirdly, the present invention also provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the secondary battery is filled with the non-aqueous electrolyte for secondary batteries described in the second aspect of the present invention.

[0041] Specifically, the positive electrode is selected from at least one of lithium cobalt oxide, lithium iron phosphate, lithium nickel manganese oxide, ternary materials of nickel cobalt manganese lithium, sodium-containing layered oxides, Prussian blue / white, and polyanions, and the negative electrode is selected from at least one of graphite, silicon-carbon composite material, lithium titanate, lithium metal, hard carbon, anthracite soft carbon, and hard-soft composite carbon.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] This invention provides an application of thiazole ester additives in non-aqueous electrolytes for secondary batteries. When used in non-aqueous electrolytes for secondary batteries, the thiazole ester additives can improve the battery's low-temperature discharge, room-temperature cycling, high-temperature cycling, and high-temperature storage performance. Adding a second additive to the thiazole ester additives can also significantly improve battery impedance and low-temperature discharge performance. Detailed Implementation

[0044] 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.

[0045] I. Electrolyte Preparation

[0046] The solvents were mixed uniformly according to the data in Table 1 below. Then, the electrolyte salts were slowly added to the mixed solution. After mixing evenly, the additive compounds were added quantitatively and mixed evenly to form an electrolyte.

[0047] Table 1 Electrolyte Formulation

[0048]

[0049]

[0050] 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.

[0051] II. Electrochemical Performance Testing

[0052] The electrolytes from Examples 1-29 and Comparative Examples 1-6 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.

[0053] The electrolytes from Examples 30-32 and Comparative Examples 7-8 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 positive electrode (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.

[0054] The performance of the lithium-ion and sodium-ion batteries prepared above was tested, mainly including:

[0055] (1) Cyclic test at 25℃:

[0056] The battery was charged and discharged at a current of 1C / 1C in a room temperature environment of 25±1℃. The discharge capacity of the first cycle was recorded as C1, the discharge capacity of the 300th cycle was recorded as C2, and the capacity retention rate of the 300-cycle cycle was (C2 / C1)×100%.

[0057] (2) 60℃ cycle test:

[0058] The battery was charged and discharged at a current of 1C / 1C in a room temperature environment of 60±1℃. The discharge capacity of the first cycle was recorded as C1, the discharge capacity of the 300th cycle was recorded as C2, and the capacity retention rate of the 300-cycle cycle was (C2 / C1)×100%.

[0059] (3) High-temperature storage test:

[0060] Before storage, the battery was cycled once at room temperature (0.5C / 0.5C), then charged at a constant current of 0.5C to 4.20V, and then charged at a constant voltage until the current dropped to 0.05C. The battery impedance R1 and volume V1 were recorded. The battery was then stored in a 60℃ constant temperature oven for 30 days, and the impedance R2 and volume V2 after high-temperature storage were recorded. The impedance growth rate and volume expansion rate during high-temperature storage were calculated using the following formula:

[0061] High-temperature storage impedance growth rate = (R2-R1) / R1×100%.

[0062] High-temperature storage volume expansion rate = (V2-V1) / V1×100%.

[0063] (4) Impedance test:

[0064] 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.

[0065] 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.

[0066] Finally, discharge the battery at a constant current of 4C for 30 seconds, record the voltage U2, and calculate the battery impedance R:

[0067] Impedance R = (U1 - U2) / (4 × C1)

[0068] (5) Low-temperature discharge test:

[0069] At room temperature (25℃), the battery was charged at a constant current of 0.5C to the charging cutoff voltage, and then charged at a constant voltage until the current dropped to 0.05C. It was then discharged at a constant current of 0.5C to the discharge cutoff voltage, and the discharge capacity C1 was recorded. Subsequently, the battery was placed in a -20℃ constant temperature oven for 6 hours and then discharged at a constant current of 0.5C to 2.24V, and the discharge capacity C2 was recorded. The low-temperature discharge capacity retention rate of the battery was calculated using the following formula:

[0070] Low-temperature discharge capacity retention rate = (C2 / C1) × 100%.

[0071] The specific test results are shown in Table 2 below:

[0072] Table 2 Battery Test Results

[0073]

[0074]

[0075] A comparison of Comparative Example 1 and Examples 1-8 shows that using an electrolyte containing thiazole ester additives in lithium-ion batteries can, on the one hand, improve the battery's cycling performance at both room temperature and high temperature, and suppress impedance growth and volume expansion during long-term high-temperature storage; on the other hand, it can improve the battery's low-temperature discharge capacity retention rate. Similarly, a comparison of Example 30 and Comparative Example 7 shows that using an electrolyte containing thiazole ester additives in sodium-ion batteries exhibits the same effect.

[0076] Comparing Examples 1 to 8, it can be seen that as the amount of thiazole ester additives increases, the overall battery performance improves first, but as the amount of additives increases further, the battery performance cannot be improved further. The preferred amount of thiazole ester additives is 0.1 to 2.0 wt%.

[0077] Comparisons of Comparative Examples 1, 4-6, and Example 10 show that compounds containing only thiazole rings lead to a significant increase in battery impedance and volume expansion during high-temperature storage; while compounds containing only carboxylic acid ester groups do not significantly improve battery impedance, low-temperature discharge, room-temperature cycling, high-temperature cycling, or impedance growth and volume expansion during high-temperature storage. When compounds containing only thiazole rings are used in combination with compounds containing only carboxylic acid ester groups, the battery performance is similar to that of compounds containing only thiazole rings, indicating that the combination does not produce a synergistic effect. When these two functional groups are combined into a single substance, not only are the low-temperature discharge, room-temperature cycling, and high-temperature cycling performance of the battery significantly improved, but the impedance growth and volume expansion during long-term high-temperature storage are also effectively suppressed.

[0078] Comparing Examples 2-8 and Examples 17-28 shows that, based on the presence of thiazole ester additives, further adding a second additive can change the effect of thiazole ester additives on battery impedance from increasing to decreasing. Comparing Examples 17-20, Examples 23-26, Examples 21-22, and Examples 27-28 shows that only when the thiazole ester additive and the second additive satisfy the following relationship: 0.2≤a+b≤10; 0.1≤a / b≤10, can the secondary battery impedance be significantly reduced and the low-temperature discharge performance further improved. When the sum of the contents of the thiazole ester additive and the second additive is too small, the negative electrode film formation effect is poor, and the improvement in battery impedance and low-temperature discharge performance is not significant; once the sum of their contents is too large, it leads to a thicker interfacial film, and the improvement in battery impedance and low-temperature discharge performance is not significant. When the ratio of thiazole ester additive to the second additive is too small, the film-forming effect of the second additive significantly inhibits that of the thiazole ester additive, resulting in minimal improvement in battery impedance and low-temperature discharge performance. Conversely, when the ratio is too large, the second additive fails to inhibit the film-forming effect of the thiazole ester additive, leading to a thicker interfacial film and an inability to reduce battery impedance. Furthermore, a comparison of Examples 30 and 31 shows that introducing a second additive into the sodium-ion battery electrolyte, based on the thiazole ester additive, exhibits the same effect.

[0079] Comparative Examples 7, 19, 25 and Comparative Examples 2-3 show that, compared with using thiazole ester additives or the second additive alone, the synergistic effect of both significantly improves the battery impedance and low-temperature discharge performance. Similarly, comparing Example 31 and Comparative Example 8 shows that, in sodium-ion batteries, the synergistic effect of both thiazole ester additives and the second additive can also significantly improve the battery impedance and low-temperature discharge performance.

[0080] By comparing Examples 4 and Examples 9-16, it can be seen that compounds I-1, I-2, I-3, I-4, I-5, I-6, I-7, I-8, and I-9 all have the functions of the thiazole ester additives they represent and can be used interchangeably.

[0081] A comparison of Examples 4 and 29 shows that, based on thiazole ester additives, the addition of a third additive, DTD, can further improve battery performance. Similarly, a comparison of Examples 30 and 32 shows that adding a third additive, FEC, to sodium-ion batteries achieves the same effect.

Claims

1. The application of a thiazole ester additive in a secondary battery electrolyte, characterized in that: The thiazole ester additives include at least one of the compounds shown in structural formula (I): In structural formula (I), R1 and R2 are each independently selected from hydrogen, fluorine, 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, and R3 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.

2. The application of the thiazole ester additive according to claim 1 in the electrolyte of a secondary battery, characterized in that: In structural formula (I), R1 and R2 are each independently selected from hydrogen atom, methyl, tert-butyl, vinyl or ethynyl, and R3 is selected from methyl, tert-butyl, n-butyl, cyclopentyl or trifluoromethyl.

3. The application of the thiazole ester additive according to claim 2 in the electrolyte of a secondary battery, characterized in that: The thiazole ester additive is selected from at least one of compounds of formula (I-1) to (I-9):

4. A non-aqueous electrolyte for secondary batteries, characterized in that: The electrolyte contains any of the thiazole ester additives described in claims 1-3, and the amount of the additive is 0.001 to 5.0 wt% of the total mass of the electrolyte.

5. The non-aqueous electrolyte for secondary batteries according to claim 4, characterized in that: The amount of the thiazole ester additive is 0.01 to 3.0 wt% of the total mass of the electrolyte.

6. The non-aqueous electrolyte for secondary batteries according to any one of claims 4-5, characterized in that: The electrolyte further comprises a second additive, which is selected from at least one of 1,3-propanesulfonyl lactone or 1,3-propenesulfonyl lactone, and the amount of the second additive is 0.001 to 5.0 wt% of the total mass of the electrolyte.

7. The non-aqueous electrolyte for secondary batteries according to claim 6, characterized in that: The thiazole ester additive and the second additive account for a% and b% of the total mass of the electrolyte, respectively, and conform to the following relationship: 0.2≤a+b≤10; 0.1≤a / b≤10.

8. The non-aqueous electrolyte for secondary batteries according to claim 7, characterized in that: The contents of the thiazole ester additive and the second additive satisfy the following relationship: 0.5≤a+b≤5; 0.2≤a / b≤5.

9. The non-aqueous electrolyte for secondary batteries according to claim 6, characterized in that: The electrolyte further comprises a third additive selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, vinyl sulfite, pentaerythritol dicyclic sulfate, 4,4'-diethylene sulfate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, adiponitrile, cyclohexylbenzene, lithium dioxalate borate, lithium difluorooxalate borate, sodium dioxalate borate, and sodium difluorooxalate borate, and the content of any one of the third additives accounts for 0.1 to 5.0 wt% of the total mass of the electrolyte.

10. The non-aqueous electrolyte for secondary batteries according to claim 9, wherein the electrolyte further comprises an electrolyte salt and a non-aqueous solvent, characterized in that: The electrolyte salt is lithium hexafluorophosphate, and its content accounts for 5.0 to 15.0 wt% of the total mass of the electrolyte; the non-aqueous solvent is a mixture of ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate, and the mass ratio of the three is ethylene carbonate: methyl ethyl carbonate: diethyl carbonate = 3:5:2; the thiazole ester additive is selected from at least one of the compounds shown in formulas (I-1) to (I-9), and its content accounts for 0.001 to 5.0 wt% of the total mass of the electrolyte; the second additive is selected from at least one of 1,3-propanesulfonyl lactone or 1,3-propenesulfonyl lactone, and its content accounts for 0.001 to 5.0 wt% of the total mass of the electrolyte; the third additive is ethylene sulfate, and its content accounts for 0.1 to 2.0 wt% of the total mass of the electrolyte.

11. The non-aqueous electrolyte for secondary batteries according to claim 9, wherein the electrolyte further comprises an electrolyte salt and a non-aqueous solvent, characterized in that: The electrolyte salt is sodium hexafluorophosphate, and its content accounts for 5.0–15.0 wt% of the total mass of the electrolyte; the non-aqueous solvent is a mixture of diethyl carbonate, methyl ethyl carbonate, and propylene carbonate, and the mass ratio of the three is propylene carbonate: methyl ethyl carbonate: diethyl carbonate = 3:5:2; the thiazole ester additive is selected from at least one of the compounds shown in formulas (I-1) to (I-9), and its content accounts for 0.001–5.0 wt% of the total mass of the electrolyte; the second additive is selected from at least one of 1,3-propanesulfonyl lactone or 1,3-propenesulfonyl lactone, and its content accounts for 0.001–5.0 wt% of the total mass of the electrolyte; the third additive is fluoroethylene carbonate, and its content accounts for 0.1–5.0 wt% of the total mass of the electrolyte.

12. A secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that: The secondary battery is filled with the non-aqueous electrolyte for secondary batteries according to any one of claims 4-11.

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