Electrolyte and lithium battery using same

Abstract

The invention provides an electrolyte and a lithium battery using the same. The electrolyte comprises a functional additive A, and the molecular structure of the functional additive A meets the formula I; wherein R1, R2, R3 and R4 are independently selected from at least one of hydrogen, alkyl, alkenyl, alkenyloxy, alkynyl and alkynyloxy, and at least one group of R1, R2, R3 and R4 comprises at least one of alkenyl, alkenyloxy, alkynyl and alkynyloxy. By adopting the electrolyte, the gas production condition of the battery can be improved, and the cycle capacity retention ratio and the high-temperature storage performance of the lithium battery can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery electrolytes, in particular to an electrolyte and a lithium battery using the electrolyte. Background Art

[0002] With the rapid development of portable electronic devices, electric vehicles and smart grids, people have an increasing demand for high-performance electrochemical storage devices. Among them, lithium batteries have always occupied an important position in the commercial market with their high energy density, high operating voltage, long cycle life and minimal memory effect. In terms of power batteries, the energy density of traditional lithium batteries is close to the theoretical limit, but it still cannot meet the needs of existing applications. At present, the spinel nickel manganese oxide cathode material (LNMO) has a high operating voltage of 4.75V (relative to Li / Li+) and a high theoretical specific capacity of 146.7mAh / g. The material composition does not contain Co elements, the preparation process is relatively simple, the cost is low and it has the advantages of high safety. It has become the most promising next-generation commercial high-energy density lithium battery cathode material.

[0003] However, spinel nickel manganese oxide (LNMO) cathode material as a positive electrode active material also faces some technical challenges. Specifically, the surface of the spinel nickel manganese oxide (LNMO) cathode material has exposed Ni 4+ It will catalyze the oxidative decomposition of the electrolyte. Conventional electrolytes under high potential and high temperature conditions will cause LiPF6 to decompose to produce PF5. PF5 reacts with trace water in the electrolyte system to generate HF, which will accelerate the oxidation of Mn in the LNMO structure. 2+ Dissolution not only causes instability in the positive electrode structure, but also the dissolved Mn 2+ Being reduced at the negative electrode will also lead to capacity decay during electrolyte circulation. Summary of the invention

[0004] The object of the present invention is to provide an electrolyte and a lithium battery using the same, wherein the electrolyte can improve the gas production of the battery and enhance the cycle capacity retention rate and high-temperature storage performance of the lithium battery.

[0005] According to one aspect of the present invention, an electrolyte is provided, the electrolyte comprising a functional additive A, the molecular structure of the functional additive A satisfies Formula I: Formula I; wherein R1, R2, R3, and R4 are independently selected from at least one of hydrogen, alkyl, alkenyl, alkenyloxy, alkynyl, and alkynyloxy, and at least one of R1, R2, R3, and R4 includes at least one of alkenyl, alkenyloxy, alkynyl, and alkynyloxy.

[0006] This solution can improve the cycle capacity retention rate and high-temperature storage performance of the battery using the electrolyte by introducing a functional additive A whose molecular structure meets the above requirements into the electrolyte, and can also reduce the acidic substances in the electrolyte, improve the stability of the electrolyte during use, and reduce unexpected interface reactions. The molecular structure of the functional additive A not only needs to satisfy Formula I, but also includes unsaturated functional groups such as alkenyl, alkenyloxy, alkynyl or alkynyloxy, that is, the functional additive A also includes cyano, unsaturated functional groups and pyridine structures. Under the influence of the aforementioned multiple functional groups, the functional additive A has a higher occupied molecular orbital (HOMO) energy level and a lower occupied molecular orbital (LUMO), so the functional additive A can preferentially undergo redox reactions on the electrode surface to form an interface film with good density and uniform film formation, thereby improving the cycle stability and high-temperature storage performance of the battery.

[0007] On the one hand, by introducing the functional additive A containing unsaturated functional groups into the electrolyte, it is beneficial to improve the structural stability of the CEI membrane and the SEI membrane, thereby achieving effective inhibition of the dissolution of transition metal ions (TMs metal ions) from the positive electrode, which not only improves the cycle stability of the positive electrode during the cycle, but also reduces the concentration of TMs metal ions in the electrolyte, thereby preventing a large amount of TMs metal deposition at the negative electrode, thereby achieving the purpose of simultaneously improving the stability of the positive and negative electrodes during the battery cycle and improving the cycle capacity retention rate of the battery. Especially when the battery is in a high temperature environment, the transition metal elements in the positive electrode material are more easily dissolved into the electrolyte in the form of TMs ions under high temperature conditions, and the present application introduces the functional additive A into the electrolyte to improve the compactness of the interface film, greatly improve the dissolution of the transition metal elements under high temperature conditions, and improve the high temperature storage performance and high temperature cycle stability of the battery. On the other hand, due to the influence of the lone pair of electrons in the cyano and pyridine structures in the functional additive A, the functional additive A can react with acidic substances such as PF5, HF and CO2 to neutralize, which not only reduces the acidity of the electrolyte and improves the stability of the battery, but also reduces the gas production of the battery, helps maintain the stability of the internal structure of the battery, and reduces the safety risks caused by internal overpressure. Especially when the battery is in a high temperature environment, the use of functional additive A to reduce the generation of acidic substances can effectively reduce the unexpected reaction of the electrolyte and prevent the corrosion of electrode materials.

[0008] Preferably, R1 is an alkenyloxy group. Compared with other unsaturated functional groups (alkenyl, alkynyl, alkynyloxy), the functional additive A that satisfies R1 as an alkenyloxy group on the basis of Formula I not only has good reactivity, can participate in the electrode film formation process, regulate the physical structure and chemical composition of the interface film, thereby improving the cycle performance of the battery, but also has better stability, can maintain its own molecular structure stability, and is not prone to unexpected reactions during the processing process. At the same time, compared with the functional additive A in which R2, R3, and R4 are alkenyloxy groups, the alkenyloxy group at the R1 position provides a special chemical environment for the N atom and cyano group on the pyridine in the adjacent position. Therefore, the functional additive A in which R1 is an alkenyloxy group has a higher reactivity and is more conducive to improving the electrochemical performance of the battery.

[0009] Preferably, the functional additive A includes 2-vinyloxy-4-methoxymethyl-3-cyano-6-methylpyridine. When 2-vinyloxy-4-methoxymethyl-3-cyano-6-methylpyridine is selected as the functional additive A, R1 is vinyloxy, R2 is methoxymethyl, R3 is hydrogen, and R4 is methyl, the electrolyte prepared thereby can effectively improve the cycle capacity stability, high temperature storage stability and gas generation of the battery using the electrolyte.

[0010] Preferably, based on the total mass of the electrolyte, the content of the functional additive A is 0.3-1%. The functional additive A within the above content range can improve the compactness and structural stability of the interface film, effectively reduce the interface impedance, improve the battery cycle performance, delay battery aging, and extend the battery cycle life without limiting the role of other components in the electrolyte.

[0011] Preferably, a sulfur-containing additive is also included, and the sulfur-containing additive includes at least one of 1,3-propane sultone (PS), sulfite (ES), methylene disulfonate (MMDS), and ethylene sulfate (DTD); based on the total mass of the electrolyte, the content of the sulfur-containing additive is 0.5-2%. Furthermore, the introduction of the sulfur-containing additive into the electrolyte can not only promote the electrolyte to form a dense, flexible, low-impedance SEI film on the negative electrode surface, but also help improve the gas production of the battery and improve the cycle performance of the lithium battery.

[0012] Preferably, a carbonate additive is also included, and the carbonate additive includes at least one of vinylene carbonate (VC) and fluoroethylene carbonate (FEC); based on the total mass of the electrolyte, the content of the carbonate additive is 0.2-1%. By introducing the carbonate additive into the electrolyte containing the functional additive A, the cycle stability of the positive electrode and the negative electrode is improved.

[0013] Preferably, the electrolyte includes a sulfur-containing additive and a carbonate additive, the sulfur-containing additive includes methylene methanedisulfonate (MMDS) and ethylene sulfate (DTD), and the carbonate additive includes fluoroethylene carbonate (FEC). Combining the functional additive A with the sulfur-containing additive and carbonate additive that meet the above requirements can make the CEI film and SEI film formed by the battery have good flexibility and mechanical strength, and effectively improve the cycle performance of the battery.

[0014] Preferably, the electrolyte further comprises a lithium salt additive, which comprises at least one of lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiBOB), and lithium difluorobis(oxalatoborate) (LiODFB); the content of the lithium salt additive is 0.5% to 1% based on the total mass of the electrolyte. Introducing the lithium salt additive in the above-mentioned addition amount into the electrolyte is conducive to the lithium salt additive participating in the film formation on the surface of the positive and negative electrodes, which not only improves the stability of the interface film, thereby improving the capacity retention rate and cycle performance of the battery, but also improves the overall performance of the electrolyte and the uniformity of the electrolyte distribution in the battery, so as to ensure that the battery has good chemical stability and long life.

[0015] Preferably, an organic solvent is also included, and the organic solvent includes at least two of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0016] Preferably, the organic solvent includes ethylene carbonate and ethyl methyl carbonate.

[0017] Preferably, when the organic solvent includes ethylene carbonate and ethyl methyl carbonate, calculated by volume fraction, the volume fractions of ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate in the organic solvent are 20-40%, 0-20%, 0-20% and 30-50%, respectively.

[0018] Preferably, the electrolyte solution includes an electrolyte salt, and the concentration of the electrolyte salt in the electrolyte solution is 1.0 to 1.3 mol / L.

[0019] Preferably, the electrolyte salt is lithium hexafluorophosphate.

[0020] According to another aspect of the present invention, a lithium battery is provided, comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, and also comprising the above-mentioned electrolyte, wherein the active material of the positive electrode contains a transition metal element. The positive electrode active material containing transition metal elements is used in combination with the above-mentioned electrolyte to form a uniform and dense interface film on the electrode surface of the battery, which greatly optimizes the stability of the interface reaction, reduces the dissolution of transition metal ions, and improves the gas production of the battery, thereby enabling the battery to maintain excellent cycle stability under high potential and high temperature conditions.

[0021] Preferably, the active material of the positive electrode comprises a spinel lithium nickel manganese oxide positive electrode (LNMO). DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0023] Example 1

[0024] This embodiment provides an electrolyte solution, including a functional additive A, a sulfur-containing additive, a carbonate additive, a lithium salt additive, an electrolyte salt, and an organic solvent.

[0025] The mass fraction of functional additive A in the electrolyte is 0.3%. Functional additive A is 2-vinyloxy-4-methoxymethyl-3-cyano-6-methylpyridine, its CAS number is 113614-06-5, and its structural formula is:

[0026]

[0027] The sulfur-containing additive is methylene disulfonate (MMDS) and ethylene sulfate (DTD) in a mass ratio of 1:1, with a mass fraction of 1.0% in the electrolyte. The carbonate additive is fluoroethylene carbonate (FEC), with a mass fraction of 0.5% in the electrolyte. The lithium salt additive is lithium difluorophosphate (LiPO2F2), with a mass fraction of 0.0% in the electrolyte. The electrolyte salt is lithium hexafluorophosphate (LiPF6), and its concentration in the electrolyte is 1.0 mol / L. The organic solvent is composed of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate. Taking the total volume of the organic solvent as 100%, the volume fraction of ethylene carbonate is 30%, the volume fraction of diethyl carbonate is 20%, and the volume fraction of ethyl methyl carbonate is 50%.

[0028] Prepare the raw materials according to the above-mentioned raw material composition, and prepare the electrolyte according to the following steps: in a glove box filled with argon, first mix the above-mentioned functional additive A, sulfur-containing additives, carbonate additives, lithium salt additives and organic solvents, then add electrolyte salt to the organic solvent, mix well at 10°C, and obtain an electrolyte.

[0029] Example 2

[0030] This embodiment prepares an electrolyte with reference to the preparation method provided in Example 1. The difference between this embodiment and Example 1 is that in the process of preparing the electrolyte, an equal mass of 2-propyleneoxy-3-cyano-4,6-dimethylpyridine is used to replace the functional additive A used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0031] Among them, the CAS number of 2-propyleneoxy-3-cyano-4,6-dimethylpyridine is 949572-47-8, and its structural formula is

[0032] Example 3

[0033] This example prepares an electrolyte by referring to the preparation method provided in Example 1. The difference between this example and Example 1 is that in the process of preparing the electrolyte, an equal mass of 2-vinyl nicotinoonitrile is used to replace the functional additive A used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0034] Among them, the CAS number of 2-vinyl nicotinonitrile is 100949-39-1, and its structural formula is

[0035] Example 4

[0036] This example prepares an electrolyte with reference to the preparation method provided in Example 1. The difference between this example and Example 1 is that in the process of preparing the electrolyte, an equal mass of 6-vinyl nicotinoonitrile is used to replace the functional additive A used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0037] Among them, the CAS number of 6-vinyl nicotinonitrile is 16173-99-2, and its structural formula is

[0038] Example 5

[0039] This example prepares an electrolyte by referring to the preparation method provided in Example 1. The difference between this example and Example 1 is that in the process of preparing the electrolyte, an equal mass of 2-ethynyl nicotinonitrile is used to replace the functional additive A used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0040] Among them, the CAS number of 2-ethynylnicotinonitrile is 132898-81-8, and its structural formula is

[0041] Example 6

[0042] This embodiment refers to the preparation method provided in Example 1 to prepare an electrolyte. The difference between this embodiment and Example 1 is that in the process of preparing the electrolyte, an equal mass of carbonate additive fluoroethylene carbonate (FEC) is used to replace the sulfur-containing additive used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with Example 1.

[0043] Example 7

[0044] This embodiment prepares an electrolyte with reference to the preparation method provided in Example 1. The difference between this embodiment and Example 1 is that in the process of preparing the electrolyte, an equal mass of sulfur-containing additive ethylene sulfate (DTD) is used to replace the carbonate additive used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0045] Example 8

[0046] This embodiment prepares an electrolyte with reference to the preparation method provided in Example 1. The difference between this embodiment and Example 1 is that in the process of preparing the electrolyte, an equal mass of vinylene carbonate (VC) is used to replace the fluoroethylene carbonate (FEC) used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0047] Example 9

[0048] This embodiment prepares an electrolyte with reference to the preparation method provided in Example 1. The difference between this embodiment and Example 1 is that in the process of preparing the electrolyte, an equal mass of methylene disulfonate (MMDS) is used instead of ethylene sulfate (DTD) used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0049] Example 10

[0050] This embodiment refers to the preparation method provided in Example 1 to prepare an electrolyte. The difference between this embodiment and Example 1 is that in the process of preparing the electrolyte, an equal mass of ethylene sulfate (DTD) is used instead of methylene disulfonate (MMDS) used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0051] Comparative Example 1

[0052] This comparative example refers to the preparation method provided in Example 1 to prepare an electrolyte. The difference between this comparative example and Example 1 is that in the process of preparing the electrolyte, an equal mass of organic solvent is used to replace the functional additive A used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with Example 1.

[0053] Comparative Example 2

[0054] This comparative example refers to the preparation method provided in Example 1 to prepare an electrolyte. The difference between this comparative example and Example 1 is that in the process of preparing the electrolyte, an equal mass of 3-cyanopyridine is used to replace the functional additive A used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with Example 1.

[0055] Among them, the CAS number of 3-cyanopyridine is 100-54-9, and its structural formula is

[0056] Comparative Example 3

[0057] This comparative example refers to the preparation method provided in Example 1 to prepare an electrolyte. The difference between this comparative example and Example 1 is that in the process of preparing the electrolyte, an equal mass of 2-vinyloxypyridine is used to replace the functional additive A used in Example 1, and the remaining raw material ratios and preparation methods are strictly consistent with Example 1.

[0058] Among them, the CAS number of 2-vinyloxypyridine is 21636-73-7, and its structural formula is

[0059] Preparation Example 1

[0060] The electrolytes provided in the above-mentioned Examples 1 to 10 and the electrolytes provided in Comparative Examples 1 to 3 were respectively used to prepare lithium batteries. The positive electrode, Celgard 2400 separator, and negative electrode were stacked in order to obtain a battery cell through a lamination process, and the battery cell was placed in an outer packaging shell, dried, and injected with electrolyte, and a lithium battery was obtained through vacuum packaging, standing, formation, and capacity separation processes.

[0061] The positive electrode includes a positive electrode current collector and a positive electrode active coating. The positive electrode current collector is aluminum foil. The positive electrode active coating includes a positive electrode active material spinel lithium nickel manganese oxide positive electrode (LNMO), a conductive agent acetylene black, and a binder polyvinylidene fluoride (PVDF); in the positive electrode active coating, the mass ratio of the positive electrode active material, the conductive agent and PVDF is 94:3:3. The negative electrode includes a negative electrode current collector and a negative electrode active coating. The negative electrode current collector is copper foil. The negative electrode active coating includes a negative electrode active material graphite, a conductive agent acetylene black, carboxymethyl cellulose (CMC), and styrene butadiene rubber (SBR); in the negative electrode active coating, the mass ratio of graphite, conductive agent, CMC and SBR is 94:1:2:3.

[0062] Test Example 1

[0063] Test subjects: the electrolytes provided in Examples 1 to 10 and Comparative Examples 1 to 3 and lithium batteries prepared using the electrolytes respectively. The specific battery preparation method is shown in Preparation Example 1.

[0064] Test items and test methods:

[0065] (1) Electrolyte HF content test: The electrolyte was stored at 45°C, and the HF content at 0d and 15d was tested by ice water titration, respectively, and recorded as HF-0d and HF-15d.

[0066] (2) Battery high temperature storage performance: At 25°C, the lithium battery was charged at a constant current of 1C to a voltage of 4.4V, and then charged at a constant voltage of 4.4V to a current of 0.05C. The volume of the test lithium battery was V0 and the initial capacity was C0. The lithium batteries provided by the test subjects were then placed in a constant temperature box at 60°C and stored for 90 days. The volume of the test lithium battery was taken out and recorded as V1, the capacity was maintained at C1, and the capacity was restored to C2.

[0067] The volume expansion rate (%) of the lithium battery after being stored at 60°C for 90 days = (Vn-V0) / V0×100%.

[0068] The capacity retention rate of lithium battery after 90 days of storage at 60°C (%) = (C1 / C0) × 100%,

[0069] The capacity recovery rate (%) of the lithium battery after storage at 60°C for 90 days = (C2 / C0)×100%.

[0070] (3) Battery room temperature cycle performance: At 25°C, the lithium battery is charged at a constant current of 5C (nominal capacity) to a voltage of 4.4V, then charged at a constant voltage of 4.4V to a current ≤0.05C, left for 10 minutes, and then discharged at a constant current of 5C to a cut-off voltage of 2.8V. The above is one charge and discharge cycle. The lithium battery is subjected to 1000 charge and discharge cycles at 25°C under the above conditions.

[0071] The capacity retention rate (%) of a lithium battery after N cycles = (discharge capacity at the Nth cycle / first discharge capacity) × 100%, where N is the number of cycles of the lithium battery.

[0072] (4) Battery high temperature cycle performance: At 45°C, the lithium battery was charged at a constant current of 5C (nominal capacity) to a voltage of 4.4V, and then charged at a constant voltage of 4.4V to a current of ≤0.05C. The lithium batteries provided by the test subjects were then placed in a constant temperature box at 60°C. After storage for 90 days, they were discharged at a constant current of 5C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium battery was subjected to 1000 charge and discharge cycles at 45°C under the above conditions.

[0073] The capacity retention rate (%) of a lithium battery after N cycles = (discharge capacity at the Nth cycle / first discharge capacity) × 100%, where N is the number of cycles of the lithium battery.

[0074] Test results: as shown in Table 1.

[0075] Table 1. Performance test results of this test case

[0076]

[0077]

[0078] Result analysis:

[0079] By comparing the test performance of Examples 1 to 10 with Comparative Examples 1 to 3 in Table 1, it can be found that the lithium batteries provided by Examples 1 to 10 have good cycle stability and thermal stability compared with the lithium batteries provided by Comparative Examples 1 to 3. Among them, the electrolyte provided by Example 1 has a small amount of gas production, and the lithium battery has a good cycle capacity retention rate and high temperature storage rate.

[0080] By comparing the test performance of the lithium battery provided by Examples 1 to 5 with that provided by Comparative Examples 1 to 3, it can be found that the capacity retention rate of the lithium battery of Examples 1 to 5 after 1000 cycles at room temperature is 94.87% to 95.31%, the capacity retention rate after 1000 cycles at high temperature is 85.14% to 85.57%, the capacity retention rate after 90 days of storage at 60°C is 91.42% to 91.72%, the capacity recovery rate after 90 days of storage at 60°C is 94.41% to 94.55%, and the volume expansion rate after 90 days of storage at 60°C is 6.42% to 6.64%. Compared with the lithium battery of Comparative Examples 1 to 3, the lithium battery provided by Examples 1 to 5 has better comprehensive performance, which is because the functional additive A including cyano, unsaturated functional group and pyridine structure in the molecular structure is introduced into the electrolyte provided by Examples 1 to 5, which can significantly improve the cycle stability of the battery at room temperature and high temperature, improve the retention rate and recovery rate of the battery after high temperature storage, and reduce gas generation.

[0081] Among them, the electrolyte provided in Comparative Example 1 does not introduce functional additive A or materials with similar structures thereto, Comparative Example 2 introduces a compound including cyano and pyridine structures but without carbon-carbon unsaturated bonds into the electrolyte, and Comparative Example 3 introduces a compound including alkenyl and pyridine structures but without cyano into the electrolyte. Comparing the experimental data of Comparative Examples 1 to 3 with those of Example 1 in Table 2, it can be found that compared with the lithium battery of Comparative Example 1, the electrolyte provided by Comparative Examples 2 to 3 has less gas production, and the lithium battery cycle capacity retention rate and high-temperature storage rate are higher; but the gas production of the electrolyte of Examples 1 to 5, the lithium battery cycle capacity retention rate and high-temperature storage rate are all higher than those of the lithium battery of Comparative Examples 2 to 3. This shows that when the molecular structure of the functional additive A introduced into the electrolyte includes cyano, unsaturated functional groups and pyridine structures at the same time, the gas production of the battery can be improved, and the normal temperature cycle stability, high temperature cycle stability, and the retention rate and recovery rate after high temperature storage of the battery can be improved.

[0082] Comparing the test performance of the lithium battery provided by Example 1 with that of Examples 8 to 10, it can be seen that the comprehensive performance of the battery of Example 1 is better than that of Examples 8 to 10, and the comprehensive performance of the battery of Examples 8 to 10 is better than that of Examples 7 and 6, which shows that FEC, MMDS and DTD in the electrolyte have a certain synergistic effect, which can make the CEI film and SEI film formed by the battery have good flexibility and mechanical strength, and effectively improve the room temperature cycle performance, high temperature storage performance and high temperature cycle stability of the battery. And under the premise that the electrolyte contains functional additive A, FEC, MMDS and DTD are conducive to the reaction of functional additive A with HF in the electrolyte, effectively improving the gas production of the battery.

[0083] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a functional additive A, and the molecular structure of the functional additive A satisfies Formula I: Formula I; wherein R1, R2, R3, and R4 are independently selected from at least one of hydrogen, alkyl, alkenyl, alkenyloxy, alkynyl, and alkynyloxy, and at least one of R1, R2, R3, and R4 includes at least one of alkenyl, alkenyloxy, alkynyl, and alkynyloxy.

2. The electrolyte according to claim 1, characterized in that The R1 is an alkenyloxy group.

3. The electrolyte according to claim 2, characterized in that The functional additive A includes 2-vinyloxy-4-methoxymethyl-3-cyano-6-methylpyridine.

4. The electrolyte according to claim 1, characterized in that Based on the total mass of the electrolyte, the content of the functional additive A is 0.3-1%.

5. The electrolyte according to claim 1, characterized in that The electrolyte further comprises a sulfur-containing additive, wherein the sulfur-containing additive comprises at least one of 1,3-propane sultone, sulfite, methylene methanedisulfonate and ethylene sulfate; based on the total mass of the electrolyte, the content of the sulfur-containing additive is 0.5-2%.

6. The electrolyte according to claim 1, characterized in that The electrolyte further comprises a carbonate additive, wherein the carbonate additive comprises at least one of vinylene carbonate and fluoroethylene carbonate; based on the total mass of the electrolyte, the content of the carbonate additive is 0.2-1%.

7. The electrolyte according to any one of claims 5 to 6, characterized in that: The electrolyte includes a sulfur-containing additive and a carbonate additive, wherein the sulfur-containing additive includes methylene methanedisulfonate and ethylene sulfate, and the carbonate additive includes fluoroethylene carbonate.

8. The electrolyte according to claim 1, characterized in that It also includes a lithium salt additive, which includes at least one of lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(oxalatoborate), and lithium difluorobis(oxalatoborate); based on the total mass of the electrolyte, the content of the lithium salt additive is 0.5% to 1%.

9. The electrolyte according to claim 1, characterized in that: The invention also includes an organic solvent, wherein the organic solvent includes at least two of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

10. A lithium battery, characterized in that: The invention comprises a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, and also comprises the electrolyte according to any one of claims 1 to 9, wherein the active material of the positive electrode contains a transition metal element.

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