Cyano electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention belongs to the technical field of lithium ion batteries, and relates to a cyano electrolyte additive, an electrolyte and a lithium ion battery. The cyano electrolyte additive comprises a nitrile additive and a functional additive; the structural formula of the functional additive is shown in the specification. The nitrile additive and the functional additive are compounded, the functional additive has a cyano group and a triazine ring, the triazine ring is chelated with transition metal ions and cooperates with the cyano group to form a film, and a benzene ring rigid structure can enhance the thermal stability. The nitrile additive and the functional additive have a cyano complementation effect, three phenyl groups in the functional additive are connected with a triazine ring, so that the functional additive has a larger structure and steric hindrance and cannot be completely complexed with transition metal ions on the surface of the positive electrode, and the short-chain nitrile additive has a smaller structure and can make up the space of the functional additive; and the two synergistically form a complementary effect to form a compact interfacial film on the surface of the positive electrode so as to improve the high-temperature performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a cyano-based electrolyte additive, an electrolyte, and a lithium-ion battery. Background Technology

[0002] In the field of lithium-ion battery technology, ternary lithium batteries have high energy density and have become the core power source for new energy vehicles, aerospace, and medical devices. However, performance degradation and safety hazards under high-temperature environments severely restrict their application, specifically in the following aspects: Material and interface instability: High-nickel ternary materials are prone to lattice oxygen release at temperatures above 60°C, triggering a transformation of the layered structure to the spinel / rock salt phase, leading to a sharp drop in capacity; simultaneously, high-valence nickel (Ni 4+ The battery reacts violently with the electrolyte, producing gases such as CO / CO2, which causes the battery to swell. Electrolyte thermal decomposition: Conventional lithium hexafluorophosphate (LiPF6) based electrolytes decompose at temperatures above 75°C, producing highly corrosive phosphorus pentafluoride (PF5) and hydrofluoric acid, which corrode the cathode material and dissolve transition metals (such as Ni). 2+ Co 3+ These molecules migrate to the negative electrode, damaging the SEI film and accelerating the loss of active lithium. Thermal runaway risk: High temperature triggers electrolyte decomposition → membrane melting → internal short-circuit chain reaction. The thermal runaway initiation temperature of the ternary system (about 170℃) is significantly lower than that of lithium iron phosphate (>200℃), and the heat release is greater.

[0003] Although existing technologies improve heat resistance by coating the positive electrode or adding additives, there is still a problem of capacity decay during high-temperature storage.

[0004] Therefore, the development of ternary lithium batteries that combine high energy density and high-temperature stability urgently requires breakthroughs in material interface control and electrolyte design to meet the rigid requirements of high-temperature battery storage in extreme scenarios such as new energy vehicles and oil exploration. Summary of the Invention

[0005] The purpose of this invention is to provide a cyano-based electrolyte additive, an electrolyte, and a lithium-ion battery, which solves the problem of capacity decay in ternary lithium batteries during high-temperature storage in the prior art.

[0006] This invention is achieved through the following technical solution: This invention discloses a cyano electrolyte additive, comprising nitrile additives and functional additives; the structural formula of the functional additive is: .

[0007] Furthermore, the nitrile additives include at least one of butadionitrile, adiponitrile, fluoroacetonitrile, and 1,2-bis(2-cyanoethoxy)ethane.

[0008] The present invention also discloses an electrolyte comprising a lithium salt and an electrolyte additive, wherein the electrolyte additive comprises the cyano electrolyte additive described above. Based on the total mass of the electrolyte as 100%, nitrile additives account for 0.3% to 1%; functional additives account for 0.3% to 0.5%; and lithium salts account for 12.5% ​​to 15%.

[0009] Furthermore, the electrolyte additives also include sulfur-containing additives, carbonate additives, and lithium salt additives.

[0010] Furthermore, based on the total mass of the electrolyte being 100%, the sulfur-containing additive accounts for 0.5% to 2%, the carbonate additive accounts for 0.3% to 0.5%, and the lithium salt additive accounts for 0.3% to 1%.

[0011] Furthermore, the sulfur-containing additive includes at least one of 1,3-propenesulfonate lactone, 1,3-propanesulfonate lactone, and vinyl sulfate. The carbonate additives include vinylene carbonate; The lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium tetrafluoroborate, and lithium bis(oxalato)borate.

[0012] Furthermore, the electrolyte also includes an organic solvent, which includes cyclic carbonates and chain carbonates, and the chain carbonates include diethyl carbonate and methyl ethyl carbonate.

[0013] Furthermore, based on the total mass of the organic solvent being 100%, the total mass of the cyclic carbonate is 20%–25%, the mass of the diethyl carbonate is 10%–20%, and the mass of the methyl ethyl carbonate is 55%–65%.

[0014] Furthermore, the cyclic carbonate includes fluoroethylene carbonate, ethylene carbonate, and propylene carbonate. Calculated based on the total mass of the organic solvent as 100%, the mass percentage of fluoroethylene carbonate is 4%, the mass percentage of ethylene carbonate is 14%, and the mass percentage of propylene carbonate is 6%.

[0015] Furthermore, the lithium salt is lithium hexafluorophosphate.

[0016] The present invention also discloses a lithium-ion battery, including a positive electrode, a negative electrode, and the electrolyte mentioned above.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a cyano-based electrolyte additive, which combines nitrile additives and functional additives. The cyano group in the nitrile additive has strong electron-withdrawing properties, lowering the lowest unoccupied molecular orbital (LUMO) energy level. The cyano group preferentially oxidizes to form a film, improving the thermal stability of the electrolyte and reducing interfacial impedance. The functional additive has a cyano group and a triazine ring. The triazine ring chelates transition metal ions and synergistically forms a film with the cyano group. The rigid structure of the benzene ring enhances thermal stability. The cyano group of the nitrile additive and the functional additive have a complementary effect. The three phenyl groups and the triazine ring in the functional additive are linked, resulting in a larger structure and steric hindrance, which cannot completely complex the transition metal ions on the positive electrode surface. The short-chain nitrile additive has a smaller structure, which can compensate for the space of the functional additive. The two work synergistically to form a dense interfacial film on the positive electrode surface, thereby improving high-temperature storage performance. The cyano group in nitrile additives and functional additives can react with water and hydrofluoric acid in the electrolyte, effectively reducing the concentration of these harmful substances and providing dual purification capabilities. Water and hydrofluoric acid are prone to side reactions with the cathode material under high voltage conditions, leading to interfacial instability and decreased electrochemical performance. The presence of nitrile additives and functional additives can significantly reduce these side reactions and improve the stability of the electrolyte.

[0018] This invention also provides an electrolyte comprising a lithium salt and electrolyte additives, wherein the electrolyte additives include nitrile additives and functional additives. In the electrolyte, the mass ratio of nitrile additives to functional additives is (0.3-1):(0.3-0.5). By limiting the mass ratio of nitrile additives to functional additives, the chemical properties of the electrolyte and the physical structure of the protective film can be optimized, improving the battery's performance at high temperatures.

[0019] Furthermore, electrolyte additives also include sulfur-containing additives, carbonate additives, and lithium salt additives. Sulfur-containing additives and their decomposition products can react with transition metals (such as Ni) in the cathode material. 2+ Mn 2+ / Mn 3+ Complexation enhances the stability of the positive electrode electrolyte interface and, to some extent, inhibits the dissolution of transition metals. Furthermore, compared to carbon-containing compounds, sulfur-containing compounds with similar molecular structures possess lower LUMO orbitals. Therefore, theoretically, sulfur-containing compounds have high reduction potentials and are easily reduced to form films on the negative electrode surface.

[0020] Carbonate additives construct stable electrode interfaces in ternary lithium batteries, forming a low-resistance, expansion-resistant solid electrolyte interphase (SEI) film on the negative electrode side and assisting in the formation of a cathode-electrolyte interface (CEI) film on the positive electrode side, thus improving high-voltage stability. Due to their high oxidation potential and good chemical and thermal stability, carbonate additives effectively improve electrolyte performance, primarily in two ways: they help broaden the electrochemical window of the electrolyte, allowing it to remain stable over a wider voltage range, directly enhancing the battery's performance stability under high-voltage operation; and they optimize electrolyte volatility, reducing volatilization losses at high temperatures or during charge / discharge processes. This not only improves the battery's thermal stability but also significantly enhances overall safety.

[0021] Lithium salt additives construct a stable, dense, and ionicly conductive CEI film at the positive electrode interface through preferential oxidation decomposition and / or chelation. This CEI film isolates the highly active delithiated positive electrode material from direct contact with the electrolyte, inhibits the continuous oxidation decomposition and gas production of the electrolyte, stabilizes the positive electrode material structure, and reduces the dissolution of transition metal ions. It also chelates the dissolved metal ions, preventing them from migrating to the negative electrode and damaging the SEI film, thus improving the battery's stability at high temperatures. Attached Figure Description

[0022] Figure 1 The free acid content inside the batteries prepared in Examples 1-6, Comparative Examples 1 and 2 after 28 days of storage; Figure 2 The battery volume change rate of the batteries prepared in Examples 1-4, Comparative Example 1, and Comparative Example 2 after storage at 60°C for 28 days; Figure 3 The growth rate of cycle resistance at 35°C for the batteries prepared in Examples 1-6, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are only a part of the embodiments of the present invention, and not all of them.

[0024] The detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely to illustrate one selected embodiment of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] This invention provides a cyano electrolyte additive, comprising nitrile additives and functional additives, wherein the structural formula of the functional additive is:

[0026] The above formula is called 2,2',2'-((1,3,5-triazine-2,4,6-triyl)tri(phenyl-4,1-diyl))triacetonitrile).

[0027] This invention does not limit the specific type of nitrile additive, and can be any nitrile additive conventional in the art. For example, in some preferred embodiments, the nitrile additive includes at least one selected from butadionitrile, adiponitrile, fluoroacetonitrile, and 1,2-bis(2-cyanoethoxy)ethane.

[0028] This invention also provides an electrolyte comprising a lithium salt and electrolyte additives, wherein the electrolyte additives include nitrile additives and functional additives. Based on the total mass of the electrolyte (100%), the nitrile additives comprise 0.3%–1%; and the functional additives comprise 0.3%–0.5%. By limiting the mass ratio of nitrile additives to functional additives, the chemical properties of the electrolyte and the physical structure of the protective film can be optimized, improving the battery's performance at high temperatures.

[0029] Preferably, the lithium salt is lithium hexafluorophosphate (LiPF6), and the mass percentage of the lithium salt in the electrolyte is 12.5% ​​to 15%.

[0030] Preferably, the electrolyte further includes an organic solvent, which includes cyclic carbonates and chain carbonates. The cyclic carbonates include fluoroethylene carbonate, ethylene carbonate, and propylene carbonate, and the chain carbonates include diethyl carbonate and methyl ethyl carbonate.

[0031] Based on the total mass of the organic solvent being 100%, the total mass of the cyclic carbonate is 20% to 25%, the mass of the diethyl carbonate is 10% to 20%, and the mass of the methyl ethyl carbonate is 55% to 65%.

[0032] Preferably, the electrolyte additives further include sulfur-containing additives, carbonate additives, and lithium salt additives. Based on the total mass of the electrolyte (100%), the sulfur-containing additives account for 0.5% to 2%, the carbonate additives account for 0.3% to 0.5%, and the lithium salt additives account for 0.3% to 1%.

[0033] The sulfur-containing additives include at least one of 1,3-propenesulfonate lactone, 1,3-propanesulfonate lactone, and vinyl sulfate; the carbonate additives include vinylene carbonate; and the lithium salt additives include at least one of lithium difluorosulfonylimide, lithium difluorophosphate, lithium tetrafluoroborate, and lithium bis(oxalato)borate.

[0034] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0035] Example 1 Based on the mass percentage of the components, the electrolyte formulation used in this embodiment is as follows: adiponitrile: 0.5%, functional additives: 0.3%, lithium difluorophosphate (LiPO2F2): 0.8%, vinylene carbonate: 0.5%, vinyl sulfate: 1%, lithium hexafluorophosphate (LiPF6): 15%, and the balance is organic solvent, with the organic solvent having a mass fraction of 81.9% in the electrolyte.

[0036] The organic solvent in the electrolyte formulation consists of fluoroethylene carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate. Based on the total mass of the organic solvents being 100%, fluoroethylene carbonate accounts for 4% of the mass, ethylene carbonate for 14%, propylene carbonate for 6%, diethyl carbonate for 15%, and methyl ethyl carbonate for 61%.

[0037] Under an argon atmosphere, adiponitrile, vinylene carbonate, lithium difluorophosphate, vinyl sulfate, and functional additives were added to the organic solvent according to the above mass fractions. Then, lithium hexafluorophosphate was added, and the mixture was stirred and mixed at 10°C to obtain the electrolyte of this embodiment.

[0038] Example 2 This embodiment provides an electrolyte that differs from Example 1 only in that the amount of functional additive added to the electrolyte is 0.4%, and the mass fraction of organic solvent in the electrolyte is 81.8%. Everything else is the same as in Example 1.

[0039] Example 3 This embodiment provides an electrolyte that differs from Embodiment 1 only in that the amount of functional additive added to the electrolyte is 0.5%, and the mass fraction of organic solvent in the electrolyte is 81.7%. Everything else is the same as in Embodiment 1.

[0040] Example 4 This embodiment provides an electrolyte that differs from Example 1 only in that the type of nitrile additive is changed to fluoroacetonitrile, the amount added is adjusted to 0.3%, and the mass fraction of the organic solvent in the electrolyte is 82.1%. Everything else is the same as in Example 1.

[0041] Example 5 This embodiment provides an electrolyte that differs from Example 1 only in that the type of nitrile additive is changed to succinic anhydride, the amount added is 0.5%, and the mass fraction of the organic solvent in the electrolyte is 81.9%. Everything else is the same as in Example 1.

[0042] Example 6 This embodiment provides an electrolyte that differs from Example 1 only in that: the nitrile additive is replaced with 1,2-bis(2-cyanoethoxy)ethane, and the addition amount is 1%; the mass fraction of the organic solvent in the electrolyte is 81.4%, and the rest is the same as in Example 1.

[0043] Example 7 This embodiment provides an electrolyte that differs from Example 1 only in that the sulfur-containing additive is changed to 1,3-propanesulfonate lactone, and the addition amount is 2%; the mass fraction of the organic solvent in the electrolyte is 80.9%, and the rest is the same as in Example 1.

[0044] Example 8 This embodiment provides an electrolyte that differs from Example 1 only in that: the type of sulfur-containing additive is adjusted to 1,3-propenesulfonate lactone, and the amount added is 0.5%; the mass fraction of the organic solvent in the electrolyte is 82.4%, and the rest is the same as in Example 1.

[0045] Example 9 This embodiment provides an electrolyte that differs from Example 1 only in that the amount of vinylene carbonate added is adjusted to 0.3%, and the mass fraction of the organic solvent in the electrolyte is 82.1%. Everything else is the same as in Example 1.

[0046] Example 10 This embodiment provides an electrolyte that differs from Example 1 only in that the amount of lithium hexafluorophosphate added is adjusted to 12.5%, and the mass fraction of the organic solvent in the electrolyte is 84.4%. Everything else is the same as in Example 1.

[0047] Example 11 This embodiment provides an electrolyte that differs from Example 1 only in that the amount of lithium hexafluorophosphate added is adjusted to 14%, and the mass fraction of organic solvent in the electrolyte is 82.9%. Everything else is the same as in Example 1.

[0048] Example 12 This embodiment provides an electrolyte that differs from Example 1 only in that the lithium salt additive type is changed to lithium bis(fluorosulfonyl)imide, the addition amount is 1%, and the mass fraction of organic solvent in the electrolyte is 81.7%. Everything else is the same as in Example 1.

[0049] Example 13 This embodiment provides an electrolyte that differs from Example 1 only in that the lithium salt additive type is changed to lithium tetrafluoroborate, the addition amount is 0.3%, and the mass fraction of organic solvent in the electrolyte is 82.4%. Everything else is the same as in Example 1.

[0050] Comparative Example 1 This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain functional additives; otherwise, it is the same as Example 1.

[0051] Comparative Example 2 This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain nitrile additives or functional additives; otherwise, it is the same as Example 1.

[0052] This invention provides a battery comprising the electrolyte described above, and further comprising a negative electrode sheet containing a negative electrode active material and a positive electrode sheet containing a positive electrode active material. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer formed of a negative electrode active material disposed on the surface of the negative electrode current collector.

[0053] In the specific preparation of the negative electrode sheet, the negative electrode active material, the first conductive agent, and the first binder can be dispersed in an appropriate amount of solvent and thoroughly stirred to form a uniform negative electrode slurry; the negative electrode slurry is uniformly coated on the negative electrode current collector, and after drying, rolling and cutting, the negative electrode sheet is obtained.

[0054] In one specific embodiment, the negative electrode active layer comprises, by weight percentage, 70% to 99% graphite negative electrode material, 0.5% to 15% of a first conductive agent, and 0.5% to 15% of a first binder.

[0055] This invention does not limit the specific type of negative electrode active material in the negative electrode sheet; it can be a negative electrode active material commonly used in batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, or silicon-based negative electrode materials. The first conductive agent can be carbon black or graphene, and the first binder can be polyvinylidene fluoride or polyacrylic acid.

[0056] The positive electrode sheet includes a positive current collector and a positive active layer formed of positive active material disposed on the surface of the positive current collector. In the specific preparation of the positive electrode sheet, the positive active material, a second conductive agent, and a second binder can be dispersed in an appropriate amount of solvent and thoroughly stirred to form a uniform positive slurry; the positive slurry is uniformly coated on the positive current collector, and after drying, rolling and cutting, the positive electrode sheet is obtained.

[0057] In one specific embodiment, the positive electrode active layer comprises, by weight percentage, 70% to 99% of positive electrode active material, 0.5% to 15% of a second conductive agent, and 0.5% to 15% of a second binder.

[0058] This invention does not limit the specific type of positive electrode active material in the positive electrode sheet; it can be any positive electrode active material commonly used in batteries, such as lithium cobalt oxide nickel-cobalt-manganese ternary materials or nickel-cobalt-aluminum ternary materials. The second conductive agent can be carbon black or graphene, and the second binder can be polyvinylidene fluoride or polytetrafluoroethylene.

[0059] The battery also includes a separator. This invention does not limit the specific selection of separator material. It can be a separator material commonly used in batteries, such as polypropylene separator, polyethylene separator, polypropylene / polyethylene double-layer composite separator, etc.

[0060] The electrolytes prepared in the examples and comparative examples were used to assemble batteries with the above-mentioned positive electrode, negative electrode and separator. The electrical performance of the batteries was tested and the results are shown in Table 1.

[0061] Table 1

[0062] As can be seen from Examples 1-13 and Comparative Examples 1 and 2, the introduction of the functional additives of the present invention helps to significantly improve the high-temperature performance of ternary batteries. This is mainly because the added nitrile additives and functional additives have cyano complementary effects. The functional additives have larger structures and steric hindrance, and cannot completely complex the transition metal ions on the positive electrode surface. The short-chain nitrile additives have smaller structures and can make up for the space of the functional additives. The two work together to form a complementary effect and form a dense interface film on the positive electrode surface to improve high-temperature performance.

[0063] The batteries prepared in Examples 1-6, Comparative Examples 1 and 2 were subjected to electrical performance tests, and the results were as follows: Figure 1 The image shows the free acid content inside the battery after 28 days of storage. From... Figure 1 It can be seen that Examples 1-6 contain both nitrile additives and functional additives, which have a more obvious effect on inhibiting acidity during storage. In contrast, Comparative Example 1 contains only nitrile additives, and its effect on inhibiting acidity is not as good as that of Examples 1-6. Comparative Example 2 does not contain either nitrile additives or functional additives, and therefore cannot effectively capture free acid in the electrolyte, resulting in the most significant increase in acidity.

[0064] The batteries prepared in Examples 1-4, Comparative Examples 1 and 2 were subjected to electrical performance tests at 60°C, and the results were as follows: Figure 2 The battery volume change rate is shown as the rate of change after 28 days of storage at 60°C. From... Figure 2 It can be seen that Examples 1-4 have a significant inhibitory effect on gas generation during high-temperature storage. This is mainly attributed to the effective suppression of free acid in the battery, thereby avoiding the corrosion of the positive electrode interface by free acid and the resulting gas generation. However, Comparative Examples 1 and 2 cannot effectively suppress the acidity in the battery, thus increasing the gas generation of the battery during high-temperature storage.

[0065] The batteries prepared in Examples 1-6, Comparative Examples 1 and 2 were subjected to cycle tests at 35°C to obtain the resistance growth rate. Figure 3 The growth rate of cyclic resistance is shown at 35°C. From... Figure 3 It can be seen that the DC resistance growth rate during high-temperature cycling in Examples 1-4 is relatively low, mainly because the nitrile additive and the functional additive have a cyano complementary effect. The functional additive has three phenyl and triazine rings connected together, which has a larger structure and steric hindrance, and cannot completely complex the transition metal ions on the positive electrode surface. The short-chain nitrile additive has a smaller structure, which can make up for the space of the functional additive. The two work together to form a complementary effect, forming a dense interfacial film on the positive electrode surface to improve the high-temperature cycling performance. However, Comparative Examples 1 and 2 cannot form a synergistic complementary effect, resulting in a faster increase in DC resistance and a slight deterioration in high-temperature cycling.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A cyano electrolyte additive, characterized in that, It includes nitrile additives and functional additives; the structural formula of the functional additive is: 。 2. The cyano electrolyte additive according to claim 1, characterized in that, Nitrile additives include at least one of butadionitrile, adiponitrile, fluoroacetonitrile, and 1,2-bis(2-cyanoethoxy)ethane.

3. An electrolyte, characterized in that, The electrolyte includes a lithium salt and an electrolyte additive, wherein the electrolyte additive includes the cyano electrolyte additive as described in claim 1 or 2. Based on the total mass of the electrolyte as 100%, nitrile additives account for 0.3% to 1%; functional additives account for 0.3% to 0.5%; and lithium salts account for 12.5% ​​to 15%.

4. The electrolyte according to claim 3, characterized in that, The electrolyte additives also include sulfur-containing additives, carbonate additives, and lithium salt additives.

5. The electrolyte according to claim 4, characterized in that, Based on the total mass of the electrolyte as 100%, the sulfur-containing additive accounts for 0.5% to 2%, the carbonate additive accounts for 0.3% to 0.5%, and the lithium salt additive accounts for 0.3% to 1%.

6. The electrolyte according to claim 4, characterized in that, The sulfur-containing additive includes at least one of 1,3-propenesulfonate lactone, 1,3-propanesulfonate lactone, and vinyl sulfate. The carbonate additives include vinylene carbonate; The lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium tetrafluoroborate, and lithium bis(oxalato)borate.

7. The electrolyte according to claim 3, characterized in that, The electrolyte also includes an organic solvent, which includes cyclic carbonates and chain carbonates, and the chain carbonates include diethyl carbonate and methyl ethyl carbonate.

8. The electrolyte according to claim 7, characterized in that, Based on the total mass of the organic solvent being 100%, the total mass of the cyclic carbonate is 20% to 25%, the mass of the diethyl carbonate is 10% to 20%, and the mass of the methyl ethyl carbonate is 55% to 65%.

9. An electrolyte according to claim 3, characterized in that, The lithium salt is lithium hexafluorophosphate.

10. A lithium-ion battery, comprising a positive electrode and a negative electrode, characterized in that, It also includes the electrolyte as described in any one of claims 3 to 9.

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