An electrolyte additive, an electrolyte containing the additive and a lithium ion battery

Abstract

The application specifically discloses an electrolyte additive, an electrolyte containing the additive and a lithium ion battery. The structural formula of the electrolyte additive is as follows: wherein R1 and R2 independently include an unsaturated six-membered nitrogen heterocycle. The N=C=N contained in the electrolyte additive can eliminate the consumption of active lithium and the destructive effect on the SEI film of hydrofluoric acid and water in the electrolyte. Moreover, the pyridine nitrogen contained in the electrolyte additive can coordinate with transition metal ions, further improving the stability of the CEI film and the SEI film, thereby improving the cycle performance of the lithium battery and relieving the problem of fast voltage attenuation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to an electrolyte additive, an electrolyte containing the additive and a lithium ion battery. BACKGROUND

[0002] The continuous prosperity of computers, communications and consumer electronics has brought rapid development of the lithium ion battery industry, especially in recent years with the rise of new energy vehicles, which not only promotes the development of power lithium ion batteries, but also puts forward higher requirements for energy density and safety performance. The endurance capability of electric vehicles has become one of the performance indicators that consumers are most concerned about, and the energy density of the battery determines the single mileage of the electric vehicle. How to improve the energy density of the battery in a limited space and weight has become a hot research topic.

[0003] At present, increasing the working voltage of the positive electrode material is the most important way to improve the energy density of the lithium ion battery. Therefore, high-voltage positive electrode materials such as LNMO, high-voltage ternary, high-voltage lithium cobaltate, layered lithium-rich oxide (LLO) and the like have become a research hotspot. As the voltage of the lithium ion battery continues to increase, the positive electrode material will have a higher electrode potential. At this time, the oxidation decomposition of the electrolyte at the positive electrode and the reaction at the positive electrode interface will be more intense. As the lithium battery continues to cycle, the internal resistance of the lithium battery gradually increases, which will lead to a decrease in the performance of the lithium battery or even failure.

[0004] Therefore, how to improve the high-voltage resistance of the electrolyte and reduce the reaction degree of the electrolyte at the positive electrode interface is a research focus for improving the performance of lithium batteries using high-voltage positive electrode materials. SUMMARY

[0005] In order to solve the problems and deficiencies in the prior art, the present application provides an electrolyte additive, an electrolyte containing the additive and a lithium ion battery.

[0006] In a first aspect, the present application provides an electrolyte additive, which adopts the following technical solution:

[0007] An electrolyte additive, the structural formula of the electrolyte additive is as follows:

[0008]

[0009] Among them, R1, R2independently includes an unsaturated six-membered nitrogen heterocycle.

[0010] Firstly, the electrolyte additive of the present application has the effect of promoting the formation of a positive electrode film, which can not only form a uniform and dense CEI film at the positive electrode, but also inhibit the dissolution of TM (excessive metal sulfide) metal ions and the release of oxygen, thereby inhibiting its reduction at the negative electrode surface, further reducing the interface reaction degree at the positive and negative electrodes, avoiding the increase of internal resistance of the lithium battery during the cycle process, and significantly improving the cycle performance of the lithium battery. Secondly, the presence of water and hydrofluoric acid in the electrolyte will consume active lithium in the lithium battery, and the "N=C=N" contained in the electrolyte additive of the present application can eliminate water and hydrofluoric acid in the electrolyte, which can not only reduce the consumption of lithium ions during the cycle process, but also help to improve the cycle life of the lithium battery, and can avoid the destructive effect of hydrofluoric acid on the SEI film, which helps to improve the cycle stability of the lithium battery and alleviate the problem of fast voltage decay. Thirdly, the transition metal ions present in the electrolyte will migrate to the negative electrode surface during the cycle process of the lithium battery, and the reduction at the negative electrode surface will cause the SEI film to thicken or destroy the structure of the SEI film, which will be detrimental to the capacity of the lithium battery and the cycle stability; and the pyridine nitrogen in the electrolyte additive of the present application can coordinate with the transition metal ions, thereby reducing the damage of the transition metal ions in the electrolyte to the negative electrode SEI film, further improving the high-voltage cycle performance of the lithium battery and alleviating the problem of fast voltage decay.

[0011] Preferably, the electrolyte additive comprises at least one of the following structural formulas:

[0012]

[0013] Secondly, the present application provides an electrolyte, which adopts the following technical scheme:

[0014] An electrolyte comprises an organic solvent, a lithium salt, a carbonate additive, and an electrolyte additive as described above.

[0015] Preferably, the mass ratio of the electrolyte additive in the electrolyte is 0.3%-1%.

[0016] If the electrolyte additive of the present application is too little, it will affect the interface density and uniformity of the CEI film generated at the interface, at this time the electrolyte additive cannot cooperate with other additives to effectively alleviate the degree of reaction between the positive electrode interface and the electrolyte, and due to the mutual influence between the positive and negative electrode sheets, the severe interface reaction at the positive electrode will also have a negative impact on the interface stability at the negative electrode, thereby leading to the performance degradation of the lithium battery. If the electrolyte additive is too much, on the one hand, it will reduce the stability of the electrolyte, which is not conducive to improving the stability of the positive and negative electrode interfaces, and on the other hand, it will inhibit the performance of other types of additives, thereby having a negative impact on the performance of the electrolyte and further reducing the cycle performance of the lithium battery.

[0017] Preferably, the electrolyte further comprises a sulfur-containing additive, the sulfur-containing additive comprising at least one of propylene-1,3-propanesultone PST, 1,3-propanesultone PS, and vinyl sulfate DTD.

[0018] The mass ratio of the sulfur-containing additive in the electrolyte is 0.5%-3%.

[0019] The use of the above-mentioned selected sulfur-containing additives can play an auxiliary film-forming role at the interface of the positive and negative electrodes, and has high thermal stability and will not cause side reactions that are not conducive to the stability of the electrolyte under high pressure and high temperature, thereby significantly improving the capacity and cycle performance of the lithium battery. If the amount of the sulfur-containing additive is too small, it is not conducive to the formation of a dense CEI film at the positive electrode and a dense SEI film at the negative electrode, which affects the cycle performance of the lithium battery. If the amount of the sulfur-containing additive is too large, it will form an excessive film, increase the impedance of the lithium battery, and cause the cycle performance of the lithium battery to decrease.

[0020] Preferably, the sulfur-containing additive comprises the propylene-1,3-propanesultone PST and the 1,3-propanesultone PS; or, the sulfur-containing additive comprises the propylene-1,3-propanesultone PST and the vinyl sulfate DTD; or, the sulfur-containing additive comprises the 1,3-propanesultone PS and the vinyl sulfate DTD.

[0021] Preferably, the organic solvent comprises a cyclic carbonate, a chain carbonate, and a chain carboxylic acid ester; the mass ratio of the organic solvent in the electrolyte is 80%-90%.

[0022] Preferably, the mass ratio of the cyclic carbonate, the chain carbonate, and the chain carboxylic acid ester is 1-15:20-70:5-20.

[0023] Preferably, the cyclic carbonate comprises at least one of fluoroethylene carbonate FEC and vinyl carbonate VC; the chain carbonate comprises diethyl carbonate; and the chain carboxylic acid ester comprises ethyl difluoroacetate.

[0024] The use of the cyclic carbonate, the chain carbonate, and the chain carboxylic acid ester can help improve the stability of the electrolyte, provide a stable environment for the respective roles and cooperation of the lithium salt additive, the sulfur-containing additive, and the electrolyte additive, thereby improving the high-pressure and high-temperature resistance of the electrolyte, and further improving the cycle performance of the lithium battery.

[0025] Preferably, the carbonate-based additive comprises at least one of vinylene carbonate and fluoroethylene carbonate; the mass ratio of the carbonate-based additive in the electrolyte is 0.01%-1%.

[0026] The carbonate additive helps the reaction at the negative electrode interface to form a dense and uniform SEI film, which cooperates with the electrolyte additive to simultaneously improve the stability at the positive electrode and negative electrode interfaces, thereby further optimizing the cycle stability of the lithium battery, especially significantly improving the room temperature and high temperature cycle performance of the lithium battery. If the amount of the carbonate additive is too small, it will be difficult to form a dense SEI film at the negative electrode, and it will be difficult to cooperate with the positive and negative electrodes in the lithium battery, thereby reducing the cycle performance of the lithium battery. If the amount of the carbonate additive is too large, it will result in an excessively large thickness of the SEI film at the negative electrode, which will result in an excessively large resistance of the lithium battery, and the lithium battery is prone to produce gas under high pressure and high temperature during the cycle process, which will damage the structure of the lithium battery, and in severe cases, it will even cause the internal pressure of the lithium battery to rise, the battery to swell, and the phenomenon of liquid leakage, which will greatly affect the cycle performance and safety performance of the lithium battery.

[0027] Preferably, the lithium salt additive includes at least one of lithium bisfluorosulfonylimide, lithium difluorophosphate, lithium bisoxalate borate, and lithium difluorodioxalate phosphate.

[0028] The mass percentage of the lithium salt additive in the electrolyte is 0.5%-1%.

[0029] Preferably, the lithium salt includes lithium hexafluorophosphate, and the mass percentage of the lithium salt in the electrolyte is 10%-15%.

[0030] By doping a suitable lithium salt additive in the electrolyte, not only can the consumption of active lithium during the cycle process of the lithium battery be compensated, but also the dissolution of the positive electrode metal ions can be inhibited, the damage degree of the dissolution of the metal ions to the SEI film can be reduced, and the stability of the SEI film can be improved.

[0031] In a third aspect, the present application provides a lithium ion battery, which adopts the following technical solution:

[0032] A lithium ion battery includes the electrolyte described above. DETAILED DESCRIPTION

[0033] In order to better understand and implement, the technical solutions of the present application will be clearly and completely described below in combination with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the present application.

[0035] Unless otherwise indicated, all numerical values of parameters (e.g. of quantities, of reaction conditions, etc.) in the specification and claims are to be understood as approximations as opposed to being fixed. Accordingly, unless indicated otherwise, the numerical parameters set forth in the specification and claims are approximations that can vary depending upon the requirements of the desired properties.

[0036] As used herein, "and / or" means one or all of the listed items.

[0037] As used herein "comprises" and "comprising" are to be construed as including only the recited elements among the "only" and "at least" recited elements.

[0038] All percentages in the present application are by weight, unless otherwise indicated.

[0039] As used in the present specification, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. For example, the term "a component" means one or more components.

[0040] The electrolyte additives used in the following examples and comparative examples are as follows:

[0041] A1, A2, A3, A4, respectively, the synthesis method of A1-A4 is as follows: room temperature, the reaction kettle is added in turn solvent and 1, 3-diphenyl urea derivatives, stirring uniformity after adding solid phosgene, then add the catalyst composed of copper salt, nickel salt and cerium nitrate ammonium and reaction aids, heating to 40-80 DEG C after incubation and stirring, after stirring, the above reaction system into the ammonia gas to adjust the pH to 7.5-9 after suction filtration, the filtrate first normal pressure evaporation of solvent, then under reduced pressure distillation at 1.35-1.54 kPa pressure, collect 153-156 DEG C between the fraction, vacuum drying oven to get higher purity of A1-A4.

[0042] Example 1

[0043] 1. Electrolyte and preparation of electrolyte

[0044] The electrolyte in the present embodiment includes organic solvent, carbonate additive, lithium salt, lithium salt additive, electrolyte additive, sulfur-containing additive in a mass ratio of 81.5%:0.5%:15%:0.5%:0.5%:2%;

[0045] The organic solvent is composed of cyclic carbonate (mass ratio of 1:1 of fluoroethylene carbonate and vinyl carbonate), chain carbonate (diethyl carbonate), chain carboxylate (ethyl difluoroacetate) with a mass ratio of 15:65:10,

[0046] The carbonate-based additive is vinylene carbonate VC,

[0047] The lithium salt is lithium hexafluorophosphate LiPF6,

[0048] The lithium salt additive is lithium difluorophosphate LiPO2F2,

[0049] The electrolyte additive (with a structural formula of

[0050] The sulfur-containing additive is 1,3-propanesulfonic acid lactone PS.

[0051] The preparation steps of the electrolyte are as follows: under an argon atmosphere, the formula amount of the carbonate-based additive, the sulfur-containing additive, the lithium salt additive, and the electrolyte additive are added to the organic solvent, and then the lithium salt is added, and the mixture is stirred at 10°C to obtain the electrolyte.

[0052] 2. Preparation of a lithium battery

[0053] The lithium battery of the present embodiment comprises a positive electrode, a negative electrode, a separator, and the above electrolyte.

[0054] Preparation of a positive electrode sheet: the positive electrode active material (0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2), a conductive agent (acetylene black), and a binder (PVDF) are prepared into a positive electrode slurry with a mass ratio of 94:3:3; the positive electrode slurry is coated on an aluminum foil current collector, vacuum dried, and a positive electrode sheet is prepared.

[0055] Preparation of a negative electrode sheet: the negative electrode active material (graphite), the conductive agent (acetylene black), and the binder (CMC), the binder (SBR) are prepared into a negative electrode slurry with a mass percentage of 94:1:2:3; the negative electrode slurry is coated on a copper foil current collector, vacuum dried, and a negative electrode sheet is prepared.

[0056] After the above positive electrode sheet, negative electrode sheet, and Celgard2400 separator are assembled into an electric core, the electric core is transferred into a shell, and then the electrolyte prepared in the present embodiment is injected, formed, and constant volume, and a battery of the present embodiment is obtained.

[0057] Example 2

[0058] 1. Electrolyte and preparation of an electrolyte

[0059] The electrolyte in the embodiment includes organic solvent, carbonate additive, lithium salt, lithium salt additive, electrolyte additive, sulfur-containing additive in a mass ratio of 85%:0.8%:10%:0.8%:0.9%:2.5%;

[0060] The organic solvent is composed of cyclic carbonate (fluoroethylene carbonate and vinyl carbonate in a mass ratio of 1:1), chain carbonate (diethyl carbonate), and chain carboxylic acid ester (ethyl difluoroacetate) in a mass ratio of 2:20:6,

[0061] The carbonate additive is fluoroethylene carbonate FEC,

[0062] The lithium salt is lithium hexafluorophosphate LiPF,

[0063] The lithium salt additive is lithium bisfluorosulfonylimide LiFSI,

[0064] The electrolyte additive (with a structural formula of

[0065] The sulfur-containing additive is propenyl-1,3-propane sulfite PST.

[0066] The preparation steps of the electrolyte are as follows: under an argon atmosphere, the formula amount of the carbonate additive, the sulfur-containing additive, the lithium salt additive, and the electrolyte additive are added to the organic solvent, and then the lithium salt is added, and the mixture is stirred at 10°C to obtain the electrolyte.

[0067] 2. Preparation of lithium battery

[0068] The preparation of the lithium battery is consistent with that in Embodiment 1.

[0069] Embodiment 3

[0070] 1. Electrolyte and preparation of electrolyte

[0071] The electrolyte in the embodiment includes organic solvent, carbonate additive, lithium salt, lithium salt additive, electrolyte additive, sulfur-containing additive in a mass ratio of 84%:0.1%:11.6%:1%:0.3%:3%;

[0072] The organic solvent is composed of cyclic carbonate (fluoroethylene carbonate and vinyl carbonate in a mass ratio of 1:1), chain carbonate (diethyl carbonate), and chain carboxylic acid ester (ethyl difluoroacetate) in a mass ratio of 10:50:20,

[0073] The carbonate additive is vinylene carbonate VC,

[0074] The lithium salt is lithium hexafluorophosphate LiPF,

[0075] The lithium salt additive is lithium bisoxalate borate LiBOB,

[0076] Electrolyte additive (structure formula

[0077] The sulfur-containing additive is vinyl sulfonate DTD.

[0078] The preparation steps of the electrolyte are as follows: under an argon atmosphere, the formula amount of the carbonate additive, the sulfur-containing additive, the lithium salt additive and the electrolyte additive are added into the organic solvent, then the lithium salt is added, and the mixture is stirred at 10°C to obtain the electrolyte.

[0079] 2. Preparation of lithium battery

[0080] The preparation of the lithium battery is consistent with that in Example 1.

[0081] Example 4

[0082] 1. Electrolyte and preparation of electrolyte

[0083] The electrolyte in the present example is different from that in Example 1 in that the mass fraction of the electrolyte additive in the electrolyte is adjusted to 0.1%, and the part less than 100% in the electrolyte can be obtained by adjusting the amount of the organic solvent (one or more of the organic solvents can be adjusted); the other steps and parameter settings are consistent with those in Example 1.

[0084] 2. Preparation of lithium battery

[0085] The preparation of the lithium battery is consistent with that in Example 1.

[0086] Example 5

[0087] 1. Electrolyte and preparation of electrolyte

[0088] The electrolyte in the present example is different from that in Example 1 in that the mass fraction of the electrolyte additive in the electrolyte is adjusted to 1.8%, and the part more than 100% in the electrolyte can be obtained by adjusting the amount of the organic solvent (one or more of the organic solvents can be adjusted); the other steps and parameter settings are consistent with those in Example 1.

[0089] 2. Preparation of lithium battery

[0090] The preparation of the lithium battery is consistent with that in Example 1.

[0091] Example 6

[0092] 1. Electrolyte and preparation of electrolyte

[0093] The electrolyte in the embodiment is different from that in embodiment 1 in that the sulfur-containing additive is composed of propylene-1,3-sulfinic acid lactone PST and 1,3-propane sulfonate lactone PS, and the mass proportions of PST and PS in the electrolyte are 1.5% and 0.5% respectively; and other steps and parameter settings remain consistent with those in embodiment 1.

[0094] 2. Preparation of lithium battery

[0095] The preparation of the battery in the embodiment remains consistent with that in embodiment 1.

[0096] Embodiment 7

[0097] 1. Electrolyte and preparation of electrolyte

[0098] The electrolyte in the embodiment is different from that in embodiment 1 in that the sulfur-containing additive is composed of 1,3-propane sulfonate lactone PS and vinyl sulfate DTD, and the mass proportions of PS and DTD in the electrolyte are 1.5% and 1% respectively; and other steps and parameter settings remain consistent with those in embodiment 1.

[0099] 2. Preparation of lithium battery

[0100] The preparation of the battery in the embodiment remains consistent with that in embodiment 1.

[0101] Embodiment 8

[0102] 1. Electrolyte and preparation of electrolyte

[0103] The electrolyte in the embodiment is different from that in embodiment 1 in that the sulfur-containing additive is composed of propylene-1,3-sulfinic acid lactone PST and vinyl sulfate DTD, and the mass proportions of PST and DTD in the electrolyte are 0.5% and 1.5% respectively. Other steps and parameter settings remain consistent with those in embodiment 1.

[0104] 2. Preparation of lithium battery

[0105] The preparation of the battery in the embodiment remains consistent with that in embodiment 1.

[0106] Embodiment 9

[0107] 1. Electrolyte and preparation of electrolyte

[0108] The electrolyte in the embodiment is different from that in embodiment 1 in that the electrolyte additive is adjusted Other steps and parameter settings remain consistent with those in embodiment 1.

[0109] 2. Preparation of lithium battery

[0110] The preparation of the battery in the embodiment remains consistent with that in embodiment 1.

[0111] Example 10

[0112] 1. Electrolyte and preparation of electrolyte

[0113] The electrolyte in this example is different from example 1 in that the electrolyte additive is adjusted to be The other steps and parameter settings are consistent with example 1.

[0114] 2. Preparation of lithium battery

[0115] The preparation of the battery in this example is consistent with example 1.

[0116] Example 11

[0117] 1. Electrolyte and preparation of electrolyte

[0118] The electrolyte in this example is different from example 1 in that the electrolyte additive is adjusted to be The other steps and parameter settings are consistent with example 1.

[0119] 2. Preparation of lithium battery

[0120] The preparation of the battery in this example is consistent with example 1.

[0121] Comparative Example 1

[0122] 1. Electrolyte and preparation of electrolyte

[0123] The electrolyte in this example is different from example 1 in that the electrolyte does not contain electrolyte additives, and the part of the electrolyte less than 100% can be obtained by adjusting the amount of organic solvent (one or more of the organic solvents can be adjusted); the other steps and parameter settings are consistent with example 1.

[0124] 2. Preparation of lithium battery

[0125] Consistent with the preparation of lithium battery in example 1.

[0126] Comparative Example 2

[0127] 1. Electrolyte and preparation of electrolyte

[0128] The electrolyte in this example is different from example 1 in that the electrolyte additive is adjusted to be The other steps and parameter settings are consistent with example 1.

[0129] 2. Preparation of lithium battery

[0130] The preparation of the battery in this example is consistent with example 1.

[0131] Test method

[0132] I. Normal temperature cycle performance test of lithium battery

[0133] At 25°C, the lithium ion battery is charged at 0.5C (nominal capacity) to a voltage of 4.6V, then charged at 4.6V to a current ≤0.05C, and after 10 min of rest, discharged at 1C to a cutoff voltage of 2.5V. The above is one charge-discharge cycle. The lithium ion battery is subjected to 1000 charge-discharge cycles at 25°C according to the above conditions.

[0134] The capacity retention rate (%) of the lithium ion battery after N cycles = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, and N is the cycle number of the lithium ion battery.

[0135] The average voltage (V) of the lithium ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, and N is the cycle number of the lithium ion battery.

[0136] II. High temperature cycle performance test of lithium battery

[0137] At 45°C, the lithium ion battery is charged at 1.0C (nominal capacity) to a voltage of 4.6V, then charged at 4.6V to a current ≤0.05C, and after 10 min of rest, discharged at 1C to a cutoff voltage of 2.5V. The above is one charge-discharge cycle. The lithium ion battery is subjected to 800 charge-discharge cycles at 45°C according to the above conditions.

[0138] The capacity retention rate (%) of the lithium ion battery after N cycles = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, and N is the cycle number of the lithium ion battery.

[0139] The average voltage (V) of the lithium ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, and N is the cycle number of the lithium ion battery.

[0140] Table 1

[0141]

[0142]

[0143] In combination with Examples 1-3, 9-11 and Comparative Examples 1-2 and Table 1, it can be seen that the electrolyte additive of the present application can improve the high-voltage stability of the electrolyte after being added to the electrolyte. On the one hand, it can simultaneously act on the positive electrode surface and the negative electrode surface to generate a dense and stable CEI film and SEI film. On the other hand, it can also consume water and hydrofluoric acid in the electrolyte, avoid the destructive effect of the electrolyte on the CEI film and SEI film during the cycling of the lithium battery, reduce the occurrence of side reactions in the electrolyte, and effectively improve the problems of fast cycling capacity decay and fast voltage decay of the lithium battery under the high-voltage material system. In Comparative Example 1, no electrolyte additive is used, and the cycling performance of the lithium battery at room temperature and high temperature is poor, and the voltage decay is significant. In Comparative Example 2, other types of additives are used, and the cycling performance of the lithium battery at room temperature and high temperature is poor, and the voltage decay is significant.

[0144] In combination with Examples 1-3, 4-5 and Table 1, it can be seen that the mass fraction of the electrolyte additive in the electrolyte is too small (Example 4), the CEI film formed at the positive electrode is unstable, and cannot effectively reduce the side reactions; the mass fraction of the electrolyte additive in the electrolyte is too large (Example 5), the interface films formed at the positive electrode and the negative electrode are too thick, which will be detrimental to the cycling performance of the lithium battery, manifested as a decrease in the cycling capacity retention rate and a fast voltage decay. Further comparison of Examples 1-3 shows that when the mass fraction of the electrolyte additive in the electrolyte is 0.5%, the high-temperature cycling performance of the lithium battery is better.

[0145] In combination with Examples 1, 6-8 and Table 1, it can be seen that by adjusting the collocation of the sulfur-containing additive, the sulfur-containing additive can act together with the electrolyte additive to further improve the cycling performance of the lithium battery, especially the high-temperature cycling performance of the lithium battery. Specifically, when the sulfur-containing additive is selected as 1,3-propanesulfonic acid lactone PS, the sulfur-containing additive and the electrolyte additive have the best cooperation effect, and make the most significant contribution to improving the high-temperature cycling capacity retention rate of the lithium battery and reducing the high-temperature voltage decay of the lithium battery.

[0146] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, but these modifications or replacements are within the protection scope of the present application.

Claims

1. An electrolyte additive, characterized in that: The structural formula of the electrolyte additive is as follows: ， Among them, R1 and R2 independently include unsaturated six-membered nitrogen heterocycles.

2. The electrolyte additive according to claim 1, characterized in that: The electrolyte additive includes at least one of the following structural formulas: 、 、 、 。 3. An electrolyte, characterized in that: It includes organic solvents, carbonate additives, lithium salts, lithium salt additives, and electrolyte additives as described in any one of claims 1-2; the electrolyte additives account for 0.3%-1% of the mass of the electrolyte.

4. The electrolyte according to claim 3, characterized in that: The electrolyte also includes sulfur-containing additives, which include at least one of propylene-1,3-propanesulfonate lactone, 1,3-propanesulfonate lactone, and vinyl sulfate. The sulfur-containing additive accounts for 0.5%-3% of the mass of the electrolyte.

5. The electrolyte according to claim 4, characterized in that: The sulfur-containing additive includes the propenyl-1,3-propanesulfonate lactone and the 1,3-propanesulfonate lactone. Alternatively, the sulfur-containing additive may include propylene-1,3-propanesulfonic acid lactone or the vinyl sulfate; Alternatively, the sulfur-containing additive may include 1,3-propanesulfonic acid lactone or the vinyl sulfate.

6. The electrolyte according to claim 3, characterized in that: The organic solvents include cyclic carbonates, linear carbonates, and linear carboxylic acid esters; The organic solvent accounts for 80%-90% of the mass of the electrolyte.

7. The electrolyte according to claim 6, characterized in that: In the organic solvent, the mass ratio of the cyclic carbonate, the chain carbonate, and the chain carboxylic acid ester is 1-15:20-70:5-20.

8. The electrolyte according to claim 3, characterized in that: The carbonate additives include at least one of vinylene carbonate and fluoroethylene carbonate; The carbonate additives constitute 0.01%-1% of the electrolyte by mass.

9. The electrolyte according to claim 3, characterized in that: The lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalate)borate, and lithium difluoro(oxalate)phosphate. The lithium salt additive accounts for 0.5%-1% of the mass of the electrolyte.

10. A lithium-ion battery, characterized in that: Includes the electrolyte as described in any one of claims 3-9.

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