Electrolyte additive, electrolyte containing additive and lithium ion battery

Abstract

The invention 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: # imgabs0 #, wherein R1 and R2 independently comprise unsaturated six-membered nitrogen heterocyclic rings. N = C = N contained in the electrolyte additive can eliminate the consumption of water and hydrofluoric acid in the electrolyte on active lithium and the destructive effect on an SEI film, and pyridine nitrogen contained in the electrolyte additive can be coordinated with transition metal ions, so that the stability of the CEI film and the SEI film is further improved, and the service life of the electrolyte is prolonged. Therefore, the cycle performance of the lithium battery is improved, and the problem of fast voltage attenuation is relieved.

Description

Technical Field

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

[0002] The continued prosperity of computers, communications and consumer electronics has brought about the rapid development of the lithium-ion battery industry. In particular, the rise of new energy vehicles in recent years has not only promoted the development of power lithium-ion batteries, but also put forward higher energy density and safety performance requirements. The endurance of electric vehicles has become one of the performance indicators that consumers pay most attention to, and the energy density of the battery determines the single mileage of the electric vehicle. How to improve the energy density of the battery under limited space and weight has become a hot topic of research for all parties.

[0003] At present, increasing the working voltage of the positive electrode material is the most important way to increase the energy density of lithium-ion batteries. Therefore, high-voltage positive electrode materials such as LNMO, high-voltage ternary, high-voltage lithium cobalt oxide, layered lithium-rich oxide (LLO), etc. have become research hotspots. As the voltage of lithium-ion batteries continues to increase, the positive electrode material will have a higher electrode potential. At this time, the oxidative decomposition of the electrolyte at the positive electrode and the reaction at the positive electrode interface will be more intense. As the lithium battery charge and discharge cycle continues, the internal resistance of the lithium battery gradually increases, which will cause the performance of the lithium battery to decline or even fail.

[0004] Therefore, how to improve the electrolyte's ability to withstand high voltage and reduce the degree of electrolyte reaction at the positive electrode interface is the research focus of improving the performance of lithium batteries using high-voltage positive electrode materials. Summary of the invention

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

[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] Wherein, R1 and R2 independently include unsaturated six-membered nitrogen heterocyclic ring.

[0010] First, the electrolyte additive of the present application has the function of promoting the film formation of the positive electrode, which can not only form a uniform and dense CEI film at the positive electrode, but also inhibit the dissolution of TMs (transition metal sulfide) metal ions and the release of oxygen, thereby inhibiting its reduction on the surface of the negative electrode, thereby reducing the degree of interfacial reaction at the positive and negative electrodes, avoiding the increase of internal resistance of the lithium battery during the cycle, and significantly improving the cycle performance of the lithium battery. Second, the presence of water and hydrofluoric acid in the electrolyte will consume the active lithium in the lithium battery and cause side reactions that are harmful to the capacity and cycle performance of the lithium battery. The "N=C=N" contained in the electrolyte additive of the present application can eliminate the water and hydrofluoric acid in the electrolyte, which can not only reduce the consumption of lithium ions during the cycle, which helps to improve the cycle life of the lithium battery, but also 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 rapid voltage decay. Third, the transition metal ions present in the electrolyte will migrate to the surface of the negative electrode during the cycle of the lithium battery, and reduction at the surface of the negative electrode will cause the SEI film to thicken or destroy the structure of the SEI film, which will be detrimental to the capacity and cycle stability of the lithium battery; 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 rapid voltage decay.

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

[0012]

[0013] In a second aspect, the present application provides an electrolyte, which adopts the following technical solution:

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

[0015] Preferably, the electrolyte additive accounts for 0.3%-1% by mass in the electrolyte.

[0016] Too little electrolyte additive in the present application 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. Moreover, due to the certain mutual influence between the positive and negative electrodes, the violent interface reaction at the positive electrode will also have a negative impact on the interface stability at the negative electrode, thereby causing the performance degradation of the lithium battery. Too much electrolyte additive, on the one hand, will reduce the stability of the electrolyte, which is not conducive to improving the stability of the positive and negative electrode interfaces. 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, wherein the sulfur-containing additive comprises at least one of propenyl-1,3-propane sultone PST, 1,3-propane sultone PS, and vinyl sulfate DTD;

[0018] The sulfur-containing additive accounts for 0.5%-3% by mass in the electrolyte.

[0019] The combination of the above-selected sulfur-containing additives can play a role in assisting film formation at the interface between 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 conditions, thereby significantly improving the capacity and cycle performance of lithium batteries. Too little addition of sulfur-containing additives is not conducive to the formation of a dense CEI film at the positive electrode and a dense SEI film at the negative electrode, affecting the performance of the lithium battery cycle; too much addition of sulfur-containing additives will cause excessive film formation, increase the module impedance in the lithium battery, and lead to a decrease in the cycle performance of the lithium battery.

[0020] Preferably, the sulfur-containing additive includes the propenyl-1,3-propane sultone PST and the 1,3-propane sultone PS; or, the sulfur-containing additive includes the propenyl-1,3-propane sultone PST and the vinyl sulfate DTD; or, the sulfur-containing additive includes the 1,3-propane sultone PS and the vinyl sulfate DTD.

[0021] Preferably, the organic solvent comprises cyclic carbonate, chain carbonate, and chain carboxylic acid ester; the mass proportion 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 includes at least one of fluoroethylene carbonate FEC and vinyl carbonate VC; the chain carbonate includes diethyl carbonate; and the chain carboxylic acid ester includes ethyl difluoroacetate.

[0024] By using a combination of cyclic carbonates, chain carbonates, and chain carboxylates, it helps to improve the stability of the electrolyte, and provide a stable environmental basis for the lithium salt additives, sulfur-containing additives, and electrolyte additives to play their respective roles and cooperate with each other, thereby improving the electrolyte's resistance to high voltage and high temperature, and further improving the cycle performance of lithium batteries.

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

[0026] Carbonate additives help to generate a dense and uniform SEI film at the negative electrode interface. When combined with electrolyte additives, they can simultaneously improve the stability of the positive and negative electrode interfaces, thereby further optimizing the cycle stability of lithium batteries, especially for the normal temperature and high temperature cycle performance of lithium batteries. Too little addition of carbonate additives will not be conducive to the formation of a dense SEI film at the negative electrode, which will be detrimental to the coordination of the positive and negative electrodes in the lithium battery, and will reduce the cycle performance of the lithium battery; while too much addition of carbonate additives will lead to excessive thickness of the SEI film at the negative electrode, which will lead to a large resistance of the lithium battery, and the lithium battery is prone to gasification under high pressure and high temperature during the cycle process, which will damage the structure of the lithium battery. In severe cases, it may even cause the internal pressure of the lithium battery to increase, the battery to swell, and the leakage of liquid, 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 bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalatoborate), and lithium difluorobis(oxalatophosphate);

[0028] The lithium salt additive accounts for 0.5%-1% by mass in the electrolyte.

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

[0030] By doping the electrolyte with suitable lithium salt additives, it is not only possible to compensate for the consumption of active lithium during the lithium battery cycle, but also possible to inhibit the dissolution of positive electrode metal ions, reduce the degree of damage to the SEI film caused by the dissolution of metal ions, and improve the stability of the SEI film.

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

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

[0033] For better understanding and implementation, the technical solution of the present application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

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

[0035] Unless otherwise indicated, all numerical values ​​expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that can vary depending upon the desired properties desired to be obtained.

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

[0037] As used herein, “including” and “comprising” encompasses the case where only the stated elements are present as well as the case where there are other elements other than the stated elements.

[0038] All percentages in this application are by weight unless otherwise stated.

[0039] Unless otherwise indicated, "a", "an", "an" and "the" used in this specification are intended to include "at least one" or "one or more". For example, "a component" means one or more components, so more than one component may be considered and may be employed or used in the implementation of the embodiment.

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

[0041] They are denoted as A1, A2, A3, and A4 respectively. The synthesis method of A1-A4 is as follows: a solvent and a 1,3-diphenylurea derivative are added to a reaction kettle in sequence at room temperature, solid phosgene is added after stirring evenly, and then a catalyst composed of a copper salt, a nickel salt and ammonium cerium nitrate and a reaction aid are added, the temperature is raised to 40-80°C, and then the temperature is kept and stirred. After stirring, ammonia is introduced into the above reaction system to adjust the pH to 7.5-9 and then filtered, the obtained filtrate is first evaporated to remove the solvent at normal pressure, and then reduced pressure distillation is performed at a pressure of 1.35-1.54 kPa, and the fraction between 153-156°C is collected and vacuum dried in an oven to obtain A1-A4 with higher purity.

[0042] Example 1

[0043] 1. Electrolyte and preparation of electrolyte

[0044] The electrolyte in this embodiment includes an organic solvent, a carbonate additive, a lithium salt, a lithium salt additive, an electrolyte additive, and a 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 (fluoroethylene carbonate and ethylene carbonate in a mass ratio of 1:1) with a mass ratio of 15:65:10, chain carbonate (diethyl carbonate) and chain carboxylic acid ester (ethyl difluoroacetate).

[0046] The carbonate additive is vinylene carbonate VC,

[0047] The lithium salt is lithium hexafluorophosphate LiPF6,

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

[0049] Electrolyte additive (structural formula:

[0050] The sulfur-containing additive is 1,3-propane sultone PS.

[0051] The preparation steps of the electrolyte are as follows: in an argon atmosphere, add a formulated amount of carbonate additives, sulfur-containing additives, lithium salt additives and electrolyte additives to an organic solvent, then add lithium salt, and stir and mix at 10°C to obtain an electrolyte.

[0052] 2. Preparation of lithium batteries

[0053] The lithium battery of this embodiment includes a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte.

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

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

[0056] After assembling the above-mentioned positive electrode plate, negative electrode plate and Celgard2400 separator to obtain a battery cell, the battery cell is transferred into a casing, and then the electrolyte prepared in this embodiment is injected, formed, and constant in volume to obtain the battery of this embodiment.

[0057] Example 2

[0058] 1. Electrolyte and preparation of electrolyte

[0059] The electrolyte in this embodiment includes an organic solvent, a carbonate additive, a lithium salt, a lithium salt additive, an electrolyte additive, and a 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 ethylene 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 bis(fluorosulfonyl)imide LiFSI.

[0064] Electrolyte additive (structural formula:

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

[0066] The preparation steps of the electrolyte are as follows: in an argon atmosphere, add a formulated amount of carbonate additives, sulfur-containing additives, lithium salt additives and electrolyte additives to an organic solvent, then add lithium salt, and stir and mix at 10°C to obtain an electrolyte.

[0067] 2. Preparation of lithium batteries

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

[0069] Example 3

[0070] 1. Electrolyte and preparation of electrolyte

[0071] The electrolyte in this embodiment includes an organic solvent, a carbonate additive, a lithium salt, a lithium salt additive, an electrolyte additive, and a 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 ethylene carbonate in a mass ratio of 1:1) with a mass ratio of 10:50:20, chain carbonate (diethyl carbonate) and chain carboxylic acid ester (ethyl difluoroacetate).

[0073] The carbonate additive is vinylene carbonate VC,

[0074] The lithium salt is lithium hexafluorophosphate LiPF,

[0075] The lithium salt additive is lithium bis(oxalatoborate) LiBOB.

[0076] Electrolyte additive (structural formula:

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

[0078] The preparation steps of the electrolyte are as follows: in an argon atmosphere, add a formulated amount of carbonate additives, sulfur-containing additives, lithium salt additives and electrolyte additives to an organic solvent, then add lithium salt, and stir and mix at 10°C to obtain an electrolyte.

[0079] 2. Preparation of lithium batteries

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

[0081] Example 4

[0082] 1. Electrolyte and preparation of electrolyte

[0083] The electrolyte in this embodiment is different from that in Embodiment 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 adaptively 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 Embodiment 1.

[0084] 2. Preparation of lithium batteries

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

[0086] Example 5

[0087] 1. Electrolyte and preparation of electrolyte

[0088] The electrolyte in this embodiment is different from that in Embodiment 1 in that: the mass fraction of the electrolyte additive in the electrolyte is adjusted to 1.8%, and the portion exceeding 100% in the electrolyte can be obtained by adaptively 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 Embodiment 1.

[0089] 2. Preparation of lithium batteries

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

[0091] Example 6

[0092] 1. Electrolyte and preparation of electrolyte

[0093] The electrolyte in this embodiment is different from that in Embodiment 1 in that the sulfur-containing additive is adjusted to consist of propenyl-1,3-sultone PST and 1,3-propanesultone PS, and the mass proportions of PST and PS in the electrolyte are 1.5% and 0.5%, respectively; the other steps and parameter settings are consistent with those in Embodiment 1.

[0094] 2. Preparation of lithium batteries

[0095] The preparation of the battery in this example is consistent with that in Example 1.

[0096] Example 7

[0097] 1. Electrolyte and preparation of electrolyte

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

[0099] 2. Preparation of lithium batteries

[0100] The preparation of the battery in this example is consistent with that in Example 1.

[0101] Example 8

[0102] 1. Electrolyte and preparation of electrolyte

[0103] The electrolyte in this embodiment is different from that in Embodiment 1 in that the sulfur-containing additive is adjusted to consist of propenyl-1,3-sultone PST and vinyl sulfate DTD, and the mass proportions of PST and DTD in the electrolyte are 0.5% and 1.5%, respectively. The other steps and parameter settings are consistent with those in Embodiment 1.

[0104] 2. Preparation of lithium batteries

[0105] The preparation of the battery in this example is consistent with that in Example 1.

[0106] Example 9

[0107] 1. Electrolyte and preparation of electrolyte

[0108] The electrolyte in this embodiment is different from that in embodiment 1 in that: the electrolyte additive is adjusted The other steps and parameter settings are consistent with those in Example 1.

[0109] 2. Preparation of lithium batteries

[0110] The preparation of the battery in this example is consistent with that in Example 1.

[0111] Example 10

[0112] 1. Electrolyte and preparation of electrolyte

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

[0114] 2. Preparation of lithium batteries

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

[0116] Embodiment 11

[0117] 1. Electrolyte and preparation of electrolyte

[0118] The electrolyte in this embodiment is different from that in embodiment 1 in that: the electrolyte additive is adjusted The other steps and parameter settings are consistent with those in Example 1.

[0119] 2. Preparation of lithium batteries

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

[0121] Comparative Example 1

[0122] 1. Electrolyte and preparation of electrolyte

[0123] The electrolyte in this comparative example is different from that in Example 1 in that: the electrolyte does not contain electrolyte additives, and the portion of the electrolyte that is less than 100% can be obtained by adaptively 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 those in Example 1.

[0124] 2. Preparation of lithium batteries

[0125] The preparation of lithium battery is consistent with that in Example 1.

[0126] Comparative Example 2

[0127] 1. Electrolyte and preparation of electrolyte

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

[0129] 2. Preparation of lithium batteries

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

[0131] Test Method

[0132] 1. Lithium battery room temperature cycle performance test

[0133] At 25°C, the lithium-ion battery is charged at a constant current of 0.5C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current ≤ 0.05C, left for 10 minutes, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery is charged and discharged 1000 times at 25°C under the above conditions.

[0134] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

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

[0136] 2. Lithium battery high temperature cycle performance test

[0137] At 45°C, the lithium-ion battery is charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current ≤ 0.05C, left for 10 minutes, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery is subjected to 800 charge and discharge cycles at 45°C under the above conditions.

[0138] The capacity retention rate (%) of a lithium-ion battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the lithium-ion battery.

[0139] The average voltage (V) of a lithium-ion battery after N cycles = discharge energy of the Nth cycle / discharge capacity of the Nth cycle, where N is the number of cycles 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 act on the positive electrode surface and the negative electrode surface at the same time 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, avoiding the electrolyte from damaging the CEI film and SEI film during the lithium battery cycle, reducing the occurrence of side reactions in the electrolyte, and effectively improving the problem of fast capacity decay and voltage decay of lithium batteries under high-voltage material systems. In Comparative Example 1, no electrolyte additive is used, and the cycle performance of the lithium battery at room temperature and high temperature deteriorates, and the voltage decay is significant. In Comparative Example 2, other types of additives are used, and the cycle performance of the lithium battery at room temperature and high temperature deteriorates, and the voltage decay is significant.

[0144] Combining Examples 1-3, 4-5 and Table 1, it can be seen that when 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 the side reaction cannot be effectively reduced; when the mass fraction of the electrolyte additive in the electrolyte is too large (Example 5), the interface film formed at the positive electrode and the negative electrode is too thick, which will be detrimental to the cycle performance of the lithium battery, manifested as a decrease in the cycle capacity retention rate and a fast voltage decay. And further comparing Examples 1-3, it can be found that when the mass fraction of the electrolyte additive in the electrolyte is 0.5%, the high temperature cycle 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 combination of the sulfur-containing additive, the sulfur-containing additive can work together with the electrolyte additive to further improve the cycle performance of the lithium battery, especially the improvement of the high-temperature cycle performance of the lithium battery is most significant. Specifically, when the sulfur-containing additive selects 1,3-propane sultone PS, the sulfur-containing additive and the electrolyte additive have the best coordination effect, and contribute most significantly to improving the high-temperature cycle capacity retention rate of the lithium battery and reducing the high-temperature voltage decay of the lithium battery.

[0146] The above embodiments are only used to illustrate the technical solution of the present application rather than to limit the protection scope of the present application. Although the present application is described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the technical solution of the present application can be modified or equivalently replaced, but these modifications or replacements are all 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: Wherein, R1 and R2 independently include unsaturated six-membered nitrogen heterocyclic ring.

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: The electrolyte comprises an organic solvent, a carbonate additive, a lithium salt, a lithium salt additive and the electrolyte additive as claimed in any one of claims 1 to 2.

4. The electrolyte according to claim 3, characterized in that: The electrolyte additive accounts for 0.3%-1% by mass in the electrolyte.

5. The electrolyte according to claim 3, characterized in that: The electrolyte further includes a sulfur-containing additive, wherein the sulfur-containing additive includes at least one of propenyl-1,3-propane sultone, 1,3-propane sultone, and vinyl sulfate; The sulfur-containing additive accounts for 0.5%-3% by mass in the electrolyte.

6. The electrolyte according to claim 5, characterized in that: The sulfur-containing additive includes the propenyl-1,3-propane sultone and the 1,3-propane sultone; Or, the sulfur-containing additive includes propenyl-1,3-propane sultone and the vinyl sulfate; Alternatively, the sulfur-containing additive includes 1,3-propane sultone and the vinyl sulfate.

7. The electrolyte according to claim 3, characterized in that: The organic solvent includes cyclic carbonate, chain carbonate, and chain carboxylic acid ester; The mass proportion of the organic solvent in the electrolyte is 80%-90%.

8. The electrolyte according to claim 7, 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.

9. The electrolyte according to claim 3, characterized in that: The carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate; The carbonate additive accounts for 0.01%-1% by mass in the electrolyte.

10. 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(oxalatoborate), and lithium difluorobis(oxalatophosphate); The lithium salt additive accounts for 0.5%-1% by mass in the electrolyte.

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

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