Lithium ion battery electrolyte and application thereof

Abstract

This invention proposes a lithium-ion battery electrolyte and its application. The electrolyte comprises at least the following components: a fluorocarbonate solvent, including 2,2,2-trifluoroethyl methyl carbonate and fluoroethylene carbonate; a lithium salt, including a first lithium salt, the first lithium salt including lithium hexafluorophosphate; and an additive, including a first additive, the first additive having the following general structural formula: wherein R1 and R2 are each independently selected from substituents having 1-6 carbon atoms, an unsaturation degree of 0-4, and a heteroatom number of 0-3, wherein the heteroatom is selected from at least one of oxygen, nitrogen, or sulfur. Through the lithium-ion battery electrolyte and its application proposed in this invention, the high-voltage resistance of the electrolyte can be improved, the high-temperature cycle stability of the battery can be significantly enhanced, and the impedance growth and gas generation during high-temperature storage can be suppressed.

Description

Technical Field

[0001] This invention relates to the field of power battery technology, specifically to a lithium-ion battery electrolyte and its application. Background Technology

[0002] With the rapid development of the new energy vehicle market, the demand for high-energy-density lithium-ion batteries is becoming increasingly urgent. Increasing battery voltage is a straightforward and feasible method to improve energy density. However, as battery voltage increases, higher demands are placed on the high-voltage resistance of the electrolyte. While using fluorinated solvents can improve the high-voltage resistance of the electrolyte, it corrodes the solid electrolyte interphase (SEI) and chemical-electrochemical interface (CEI) films, leading to interface damage and continuous side reactions. This ultimately manifests as a series of problems such as high-temperature gas generation, high-temperature capacity loss, and increased DC resistance, affecting battery performance. Summary of the Invention

[0003] This invention proposes a lithium-ion battery electrolyte and its application. The lithium-ion battery electrolyte and its application provided by this invention can improve the high voltage resistance of the electrolyte, significantly enhance the high temperature cycle stability of the battery, and suppress the battery impedance growth and high temperature storage gas generation.

[0004] To address the aforementioned technical problems, the present invention provides a lithium-ion battery electrolyte, comprising at least the following components:

[0005] Fluorinated carbonate solvents, including 2,2,2-trifluoroethyl methyl carbonate and fluoroethylene carbonate;

[0006] Lithium salts, including a first lithium salt comprising lithium hexafluorophosphate; and

[0007] Additives, including a first additive, the first additive having the following general structural formula:

[0008]

[0009] R1 and R2 are each independently selected from substituents having 1-6 carbon atoms, an unsaturation degree of 0-4, and a heteroatom number of 0-3, wherein the heteroatom is selected from at least one of oxygen, nitrogen, or sulfur.

[0010] In one embodiment of the present invention, the substituent is selected from at least one of alkyl, alkenyl, alkynyl, carbonyl, ester, amino, or heterocyclic groups.

[0011] In one embodiment of the present invention, the first additive is selected from... Compound 1 Compound 2 or At least one of compound 3.

[0012] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.05wt%-3wt%.

[0013] In one embodiment of the present invention, the content of 2,2,2-trifluoroethyl methyl carbonate in the electrolyte is 10wt%-85wt%.

[0014] In one embodiment of the present invention, in the fluorocarbonate solvent, the mass ratio of 2,2,2-trifluoroethyl methyl carbonate to fluoroethylene carbonate is 9:1-7:3.

[0015] In one embodiment of the present invention, the lithium salt further includes a second lithium salt, the second lithium salt being selected from at least one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide.

[0016] In one embodiment of the present invention, the content of the lithium salt in the electrolyte is 12wt%-20wt%, and the content of the first lithium salt in the electrolyte is 8wt%-20wt%.

[0017] The present invention also provides a lithium-ion battery, comprising at least:

[0018] The positive electrode sheet includes a positive electrode active material, wherein the structural formula of the positive electrode active material is Li. a Ni x Mn y O 4-z M z Wherein, 0.9≤a≤1.1, 0.4≤x≤0.6, 1.4≤y≤1.6, 0≤z≤0.1, and M is selected from at least one of Cl, Br, I, S, Se, Te, or F;

[0019] Negative electrode plate;

[0020] A diaphragm is disposed between the positive electrode and the negative electrode; and

[0021] The electrolyte is selected from the lithium-ion battery electrolytes mentioned above.

[0022] The present invention also provides an electronic device comprising the above-described lithium-ion battery.

[0023] In summary, this invention proposes a lithium-ion battery electrolyte and its application. Fluorinated carbonate solvents can improve the high-voltage resistance of the electrolyte, making it suitable for high-voltage battery systems. The synergistic effect of the fluorinated carbonate solvents and the first additive can form a stable SEI film at the interface between the negative electrode and the electrolyte, and a stable CEI film at the interface between the positive electrode and the electrolyte, ensuring the stability of the electrode-electrolyte interface at high temperatures. This significantly improves the high-temperature cycle stability of the battery and suppresses impedance growth and gas generation during high-temperature storage. Detailed Implementation

[0024] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0026] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention proposes a lithium-ion battery electrolyte, comprising at least a fluorinated carbonate solvent, a lithium salt, and additives, wherein the lithium salt includes a first lithium salt, which includes lithium hexafluorophosphate (LiPF6), and the additives include a first additive, the structural formula of which is: R1 and R2 are each independently selected from substituents having 1-6 carbon atoms, an unsaturation degree of 0-4, and a heteroatom number of 0-3. The heteroatoms are, for example, selected from at least one of oxygen or sulfur. In the lithium-ion battery electrolyte provided by this invention, the fluorocarbonate solvent can improve the electrolyte's high-voltage resistance, making it suitable for high-voltage battery systems. Furthermore, the fluorocarbonate solvent and the first additive work synergistically to form a stable SEI film at the interface between the negative electrode and the electrolyte, and a stable CEI film at the interface between the positive electrode and the electrolyte, ensuring the stability of the electrode-electrolyte interface at high temperatures. This significantly improves the high-temperature cycle stability of the battery and suppresses impedance growth and gas generation during high-temperature storage.

[0028] In one embodiment of the present invention, fluorocarbonate solvents exhibit good high-pressure stability, ensuring the interfacial stability of the electrolyte on the positive electrode side. Furthermore, due to the strong electron-withdrawing properties of fluorine atoms, the fluorocarbonate solvents reduce the dissociation ability of lithium salts, thereby promoting the binding of lithium ions and anions. This results in a solvation structure dominated by the salt anion, increasing the inorganic components in the interfacial phase and thus enhancing its stability. Specifically, in this embodiment, the fluorocarbonate solvents include methyl 2,2,2-trifluoroethyl ester (FEMC) and fluoroethylene carbonate (FEC), etc. The content of FEMC in the electrolyte is, for example, 10wt%-85wt%, or, for example, 55wt%-75wt%, and the mass ratio of FEMC to FEC is, for example, 9:1-7:3. By controlling the mass ratio of FEMC and FEC, it is possible to reduce battery impedance while avoiding the problem of increased interfacial byproducts between the electrode and electrolyte caused by excessive FEC content, thereby improving the battery's high-temperature storage gas generation rate and high-temperature cycle stability.

[0029] In one embodiment of the present invention, in the first additive, the substituents of R1 and R2 are each independently selected from alkyl, alkenyl, alkynyl, carbonyl, ester, amino, or heterocyclic groups, etc. Specifically, in this embodiment, the first additive is, for example, selected from... Compound 1 Compound 2 or At least one of compound 3, etc. In fluorocarbonate solvent systems, many lithium salts decompose rapidly, causing a localized temperature increase at the interface between the electrode and the electrolyte. Furthermore, the presence of trace amounts of water in the electrolyte accelerates the hydrolysis of the first lithium salt, leading to an increase in electrolyte acidity. By introducing a first additive into the fluorocarbonate solvent, the first additive and the fluorocarbonate solvent work synergistically, especially under high temperature and high pressure, significantly suppressing the rate of acid rise in the electrolyte. This reduces the damage to the interfacial phase caused by acidic substances such as HF, thereby significantly alleviating electrolyte decomposition under high temperature and high pressure systems. This suppresses gas generation and impedance growth during high-temperature storage of the battery, improving the high-temperature cycle stability of the battery.

[0030] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.05wt%-3wt%, and further, for example, 0.3wt%-1.5wt%. By controlling the content of the first additive, it is possible to suppress gas generation during high-temperature storage of the battery while avoiding the problem of increased interfacial by-products between the electrode and the electrolyte caused by excessive content of the first additive, thereby improving the battery impedance and high-temperature cycle stability.

[0031] In one embodiment of the present invention, the additive further includes a second additive, such as a negative electrode film-forming additive, which is selected from at least one of vinylene carbonate (VC), 1,3-propanesultone (PS), or ethylene sulfate (DTD), and the content of the second additive in the electrolyte is, for example, 0.1 wt% to 5 wt%.

[0032] In one embodiment of the present invention, the content of lithium salt in the electrolyte is, for example, 12wt%-20wt%. The content of the first lithium salt in the electrolyte is, for example, 8wt%-20wt%.

[0033] In one embodiment of the present invention, the lithium salt further includes a second lithium salt, which is selected from at least one of lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the content of the second lithium salt is, for example, 0.1 wt% to 3 wt%. By introducing the second lithium salt, the conductivity of the electrolyte can be improved due to the stronger dissociation ability of the second lithium salt, thereby improving the impedance of the battery.

[0034] In one embodiment of the present invention, when preparing the electrolyte, battery-grade FEMC and FEC are mixed uniformly in a glove box under a stable gas atmosphere such as argon according to a mass ratio to obtain a fluorocarbonate mixed solvent. Lithium salt and additives are then added to the above-mentioned fluorocarbonate mixed solvent and mixed uniformly to prepare a lithium-ion battery electrolyte. The moisture content in the glove box is, for example, less than 10 ppm.

[0035] This invention also proposes a lithium-ion battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte. The separator is located between the positive and negative electrodes to prevent short circuits between them, allowing lithium ions to pass through. The electrolyte fills the space between the positive electrode, separator, and negative electrode, and is the aforementioned lithium-ion battery electrolyte, serving to conduct ions. The lithium-ion battery can be, for example, a primary or secondary battery. A secondary battery can be, for example, a pouch battery, a hard-case battery, or a cylindrical battery. This invention does not specifically limit the type or category of lithium-ion batteries.

[0036] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active layer coated on at least one surface of the positive current collector. The positive current collector is, for example, a foil formed by surface treatment of materials such as nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or nonwoven fabric.

[0037] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder. The ratio of the positive electrode active material, the conductive agent, and the binder can be selected according to actual needs. In this embodiment, the positive electrode active material includes, for example, lithium nickel manganese oxide, with the chemical formula, for example, Li. a Ni x Mn y O 4-z M z Wherein, 0.90≤a≤1.10, 0.4≤x≤0.6, 1.4≤y≤1.6, 0≤z≤0.1, and M is selected from at least one of Cl, Br, I, S, Se, Te, or F. Further, in this embodiment, the surface of the positive electrode active material is, for example, provided with a coating layer. The material of the coating layer includes, for example, carbon, and the mass of the coating layer is 1% to 3% of the mass of the positive electrode active material.

[0038] In one embodiment of the present invention, the conductive agent is selected from at least one of conductive carbon black (SuperP), acetylene black, carbon nanotubes, or graphene, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), poly(ethylene oxide) (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate (polyacrylate), polyvinyl ether (polyvinyl ether), polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexanefluoropropylene (polyhexafluoropropylene), or polymerized styrene-butadiene rubber (SBR).

[0039] In one embodiment of the present invention, the positive electrode current collector is, for example, aluminum foil, the conductive agent is, for example, SuperP, the binder is, for example, PVDF, and the chemical formula of the positive electrode active material is, for example, Li. 0.95 Ni 0.45 Mn 1.54 O4, and the surface of the positive electrode active material is coated with a carbon coating layer. Specifically, when preparing Li containing a carbon coating layer... 0.95 Ni 0.45 Mn 1.54 When using O4 as the positive electrode active material, the carbon source is first pre-sintered in a stable gas atmosphere such as nitrogen to obtain the carbon material. Then, the carbon material and Li... 0.95 Ni 0.45 Mn 1.54The O4 positive electrode active material is mixed evenly and then subjected to a secondary sintering process to obtain Li containing a carbon coating layer. 0.95 Ni 0.45 Mn 1.54 O4 positive electrode active material. The carbon source is selected from at least one of fructose, polyethylene glycol, galactose, polyvinylpyrrolidone, or tannic acid. The pre-sintering temperature is, for example, 550°C, and the pre-sintering time is, for example, 5 hours. The secondary sintering temperature is, for example, 350°C, and the secondary sintering time is, for example, 12 hours.

[0040] In one embodiment of the present invention, when preparing the positive electrode, Li containing a carbon coating layer is used... 0.95 Ni 0.45 Mn 1.54 O4 positive electrode active material, PVDF, and Super P are mixed in a mass ratio of 98:1:1, dissolved in an organic solvent, and stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto aluminum foil, air-dried at room temperature, and then transferred to an oven for drying. After cold pressing and slitting, the positive electrode sheet is obtained. The organic solvent is, for example, N-methylpyrrolidone (NMP).

[0041] In one embodiment of the present invention, the negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is selected from, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector.

[0042] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material, a conductive agent, a thickener, and a binder. The proportions of the negative electrode active material, conductive agent, thickener, and binder can be selected according to actual needs. In this embodiment, the negative electrode active material is selected from at least one of graphite, silicon, or carbon dioxide. Further, the negative electrode active material is, for example, selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, pure silicon, silicon oxides, and silicon carbide compounds.

[0043] In one embodiment of the present invention, the conductive agent is selected from at least one of SuperP, acetylene black, Ketjen black, carbon nanotubes, or graphene. The thickener includes, for example, sodium carboxymethyl cellulose (CMC-Na). The binder is selected from at least one of PVDF, PEO, PA, polypropylene, polyacrylate, polyethylene ether, PMMA, polyhexamethylene propylene, or SBR.

[0044] In one embodiment of the present invention, the negative electrode current collector is, for example, copper foil, the negative electrode active material is, for example, artificial graphite, the conductive agent is, for example, SuperP, the thickener is, for example, CMC-Na, and the binder is, for example, SBR. Specifically, the negative electrode active material, conductive agent, thickener, and binder are mixed in a mass ratio of 96:1:1:2, and deionized water solvent is added. The mixture is then thoroughly stirred and mixed under the action of a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, and after being dried at room temperature, it is transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet is obtained.

[0045] In one embodiment of the present invention, the separator is, for example, a conventional separator, a ceramic separator, a polymer separator, a non-woven fabric separator, or an inorganic-organic composite separator. Specifically, the separator is, for example, a single-layer polypropylene (PP) membrane, a single-layer polyethylene (PE) membrane, a double-layer PP / PE membrane, a double-layer PP / PP membrane, or a triple-layer PP / PE / PP membrane, wherein the thickness of the separator is, for example, 9μm-15μm. In this embodiment, for example, a single-layer PP membrane with a thickness of 12μm is selected as the separator.

[0046] In one embodiment of the present invention, the positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. Then, an aluminum-plastic film is wrapped around the separator, and the mixture is dried in a vacuum oven at 120°C. Afterward, the prepared lithium-ion battery electrolyte is injected at a rate of 3.0 g / Ah, and the mixture is sealed. Following electrolyte formation, a soft-pack lithium-ion battery with a capacity of 1 Ah is obtained.

[0047] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0048] Example 1

[0049] Preparation of the positive electrode: Fructose is pre-sintered in a stable gas atmosphere such as nitrogen to obtain carbon material, and then the carbon material and Li... 0.95 Ni 0.45 Mn 1.54 The O4 positive electrode active material is mixed evenly and then subjected to a secondary sintering process to obtain Li containing a carbon coating layer. 0.95 Ni 0.45 Mn 1.54 O4 positive electrode active material. Li containing a carbon coating layer... 0.95 Ni 0.45 Mn 1.54O4 positive electrode active material, PVDF and SuperP are mixed in a mass ratio of 98:1:1, dissolved in NMP solvent, and stirred under vacuum until the system is homogeneous to obtain positive electrode slurry. The positive electrode slurry is then uniformly coated on aluminum foil, dried at room temperature and then transferred to an oven for drying. After cold pressing and slitting, positive electrode sheet is obtained.

[0050] Preparation of negative electrode sheet: Artificial graphite, SuperP, CMC-Na and SBR are mixed in a mass ratio of 96:1:1:2, and deionized water solvent is added. The mixture is then stirred and mixed thoroughly under vacuum to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil, and then dried at room temperature before being transferred to an oven for drying. After rolling and cutting, the negative electrode sheet is obtained.

[0051] Electrolyte preparation: In an argon-atmosphere glove box with a moisture content of less than 10 ppm, battery-grade FEMC and FEC were mixed uniformly at a mass ratio of 9:1 according to the electrolyte composition described in Table 1 to obtain a fluorocarbonate solvent. LiPF6 and Compound 1 were then added to the fluorocarbonate solvent and mixed uniformly to prepare the lithium-ion battery electrolyte. The contents of LiPF6 and Compound 1 in the electrolyte were 13 wt% and 0.5 wt%, respectively.

[0052] Membrane selection: A single-layer PP membrane with a thickness of 12μm was selected as the membrane.

[0053] Battery preparation: The positive electrode, separator and negative electrode are placed in sequence and wrapped with aluminum-plastic film. After drying in a vacuum oven at 120°C, the lithium-ion battery electrolyte prepared above is injected at 3.0 g / Ah and then sealed. After electrolyte formation, a soft-pack lithium-ion battery with a capacity of 1Ah is obtained.

[0054] Example 2

[0055] The mass ratio of FEMC to FEC is 8:2, and the other steps are the same as in Example 1.

[0056] Example 3

[0057] The mass ratio of FEMC to FEC is 7:3, and the other steps are the same as in Example 1.

[0058] Example 4

[0059] The content of compound 1 in the electrolyte was 0.1 wt%, and the other steps were the same as in Example 2.

[0060] Example 5

[0061] The content of compound 1 in the electrolyte is 1 wt%, and the other steps are the same as in Example 2.

[0062] Example 6

[0063] The electrolyte contains compound 2, and the contents of compound 1 and compound 2 in the electrolyte are 0 and 0.5 wt%, respectively. Other steps are the same as in Example 2.

[0064] Example 7

[0065] The electrolyte contains compound 3, and the contents of compound 1 and compound 3 in the electrolyte are 0 and 0.5 wt%, respectively. Other steps are the same as in Example 2.

[0066] Example 8

[0067] The electrolyte includes LiFSI, and the contents of LiPF6 and LiFSI in the electrolyte are 12.5 wt% and 0.5 wt%, respectively. The other steps are the same as in Example 2.

[0068] Comparative Example 1

[0069] The content of compound 1 in the electrolyte was 0, and the other steps were the same as in Example 2.

[0070] Comparative Example 2

[0071] The electrolyte contains methyl ethyl carbonate (EMC) but no FEMC, and the mass ratio of EMC to FEC is 8:2. The other steps are the same as in Example 2.

[0072] Comparative Example 3

[0073] The electrolyte contains the additive tris(trimethylsilyl)phosphate (TMSP), and the contents of compound 1 and TMSP in the electrolyte are 0 and 0.5 wt%, respectively. Other steps are the same as in Example 2.

[0074] The content of raw material components and the mass ratio of raw materials required for the electrolytes prepared in each embodiment and comparative example are shown in Table 1.

[0075] Table 1. Composition of electrolytes in Examples 1-8 and Comparative Examples 1-3

[0076]

[0077]

[0078] In this invention, the lithium-ion batteries prepared with different electrolyte ratios in Examples 1-8 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in Table 2.

[0079] In one embodiment of the present invention, for example, a direct current resistance (DCR) test is performed on a lithium-ion battery. Specifically, at 25°C, the battery is discharged at a 1C current to 50% state of charge (SOC), and the battery voltage is detected and recorded as the initial voltage. Then, the current is increased to 4C and maintained for 30 seconds. After the battery voltage stabilizes, the stable voltage is recorded as the final voltage, and the difference between the final voltage and the initial voltage is calculated. The ratio of this difference to the 4C current value is the battery's DCR.

[0080] In one embodiment of the present invention, for example, a high-temperature storage gas production rate test is performed on a lithium-ion battery. Specifically, after the battery is fully charged, it is stored in a constant temperature chamber at 60°C for 15 days, and the volume of the battery is tested. The difference between the volume and the original volume of the battery is calculated, and the percentage of the difference to the original volume is taken as the high-temperature storage gas production rate of the battery.

[0081] In one embodiment of the present invention, a high-temperature cycle stability test is performed on a lithium-ion battery. Specifically, the battery is cycled at 45°C with a charge / discharge rate of 1C / 1C within a charge / discharge cutoff voltage range of 3.4V-4.85V. The test ends when the battery capacity reaches 80% of the first cycle capacity (State of Health (SOH)), and the number of high-temperature cycles is recorded.

[0082] Table 2 shows the performance test results of lithium-ion batteries in Examples 1-8 and Comparative Examples 1-3.

[0083] Group 25℃ DCR ​​(mOhm) Gas production rate (%) at 60℃ storage High-temperature cycling cycles (80% SOH) Example 1 114.7 47 432 Example 2 108.3 38 478 Example 3 101.2 42 401 Example 4 107.3 43 437 Example 5 127.3 33 409 Example 6 118.1 41 445 Example 7 121.8 38 463 Example 8 103.8 33 474 Comparative Example 1 103.4 63 342 Comparative Example 2 160.7 75 278 Comparative Example 3 106.3 57 389

[0084] Please refer to Tables 1 and 2. Comparing Examples 1-3, it can be seen that in the total solvent composed of FEC and FEMC, when the content of FEC in the total solvent increases from 10 wt% to 20 wt%, the battery's DCR and storage gas generation rate decrease, while the number of high-temperature cycles increases. This indicates that FEC can enhance the conductivity of the electrolyte and preferentially decompose into a film at the negative electrode, enhancing interfacial stability, thereby reducing battery impedance and high-temperature storage gas generation rate, and improving high-temperature cycle stability. When the content of FEC in the total solvent continues to increase from 20 wt% to 30 wt%, although the battery's DCR decreases, the number of high-temperature cycles also decreases significantly, while the storage gas generation rate increases. This indicates that excessive decomposition of FEC leads to excessive interfacial byproducts, thus affecting the battery's high-temperature cycle stability and high-temperature storage gas generation rate. Therefore, by controlling the mass ratio of FEC to FEMC, it is possible to balance battery impedance, high-temperature storage gas generation rate, and high-temperature cycle stability.

[0085] Please refer to Tables 1 and 2. Comparing Examples 2, 4, and 5, it can be seen that when the content of compound 1 in the electrolyte increases from 0.1 wt% to 0.5 wt%, although the battery's DCR increases, the storage gas generation rate decreases, and the number of high-temperature cycles increases. When the content of compound 1 in the electrolyte continues to increase from 0.5 wt% to 1 wt%, although the battery's storage gas generation rate decreases, the number of high-temperature cycles also decreases significantly, and the impedance increases significantly. This indicates that when the content of compound 1 is too high, the excess compound 1 may transform into a nucleophile that attacks cyclic compounds in the electrolyte system, leading to the polymerization of cyclic compound 1 and an increase in interfacial byproducts, thereby affecting the battery's impedance and high-temperature cycling stability. Therefore, by controlling the content of compound 1 in the electrolyte, it is possible to balance the battery's impedance, high-temperature storage gas generation rate, and high-temperature cycling stability.

[0086] Please refer to Tables 1 and 2. Comparing Examples 2, 6-7, and Comparative Example 1, it can be seen that when the electrolyte contains compound 1, compound 2, or compound 3 as the first additive, although the battery's DCR increases slightly, the storage gas generation rate decreases significantly, and the number of high-temperature cycles increases significantly. This indicates that the first additive can suppress high-temperature storage gas generation and improve the battery's high-temperature cycle stability. Moreover, among the three first additives, compound 1, compound 2, and compound 3, the battery's DCR and storage gas generation rate are the lowest, and the number of high-temperature cycles is the highest when compound 1 is present in the electrolyte. This indicates that compound 1 has the most significant effect on improving the battery's high-temperature storage gas generation rate and high-temperature cycle stability.

[0087] Please refer to Tables 1 and 2. Comparing Example 2 and Comparative Example 2, it can be seen that when the total solvent mainly contains EMC, the battery has a higher DCR and storage gas generation rate, and fewer high-temperature cycle times, compared to when the total solvent mainly contains FEMC. This indicates that fluorocarbonate solvents such as FEMC can significantly improve the battery's impedance, high-temperature storage gas generation rate, and high-temperature cycle stability, thus ensuring that the battery can work normally under high-voltage systems.

[0088] Please refer to Tables 1 and 2. Comparing Example 2, Comparative Example 1, and Comparative Example 3, it can be seen that when using conventional acid-removing additives such as TMSP in fluorocarbonate solvents, the battery's DCR increases, while the storage gas generation rate decreases slightly, and the number of high-temperature cycles increases slightly. However, when using Compound 1 in fluorocarbonate solvents, the battery's storage gas generation rate decreases significantly, and the number of high-temperature cycles increases significantly. This indicates that the combined use of fluorocarbonate solvents and TMSP cannot effectively improve the battery's high-temperature storage gas generation rate and high-temperature cycle stability. Only the synergistic effect of fluorocarbonate solvents and the first additive, such as Compound 1, can comprehensively improve the battery's high-temperature storage gas generation rate and high-temperature cycle stability.

[0089] Please refer to Tables 1 and 2. Comparing Examples 2 and 8, it can be seen that when the electrolyte contains the second lithium salt LiFSI, the number of high-temperature cycles of the battery does not change significantly, but the impedance and storage gas generation rate are significantly reduced. This indicates that the introduction of the second lithium salt can not only reduce the viscosity of the electrolyte, but also enhance the stability of the interface by producing sulfur- and fluorine-containing inorganic compounds, thereby effectively reducing the battery impedance and high-temperature storage gas generation rate.

[0090] This invention also provides an electronic device comprising at least one of the aforementioned lithium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the aforementioned lithium-ion battery, and therefore the advantages of including the aforementioned lithium-ion battery are not elaborated here.

[0091] In summary, this invention proposes a lithium-ion battery electrolyte and its application. By introducing fluorocarbonate solvents into the electrolyte, its high-voltage resistance can be improved, making it suitable for high-voltage battery systems. By introducing a first additive into the electrolyte, the fluorocarbonate solvent and the first additive work synergistically to form a stable SEI film at the interface between the negative electrode and the electrolyte, and a stable CEI film at the interface between the positive electrode and the electrolyte. This ensures the stability of the electrode-electrolyte interface at high temperatures, thereby significantly improving the high-temperature cycle stability of the battery and suppressing impedance growth and gas generation during high-temperature storage.

[0092] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0093] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A lithium-ion battery electrolyte, characterized in that, It includes at least the following components: Fluorinated carbonate solvents, including 2,2,2-trifluoroethyl methyl carbonate and fluoroethylene carbonate; Lithium salts, including a first lithium salt comprising lithium hexafluorophosphate; and Additives, including a first additive, the first additive having the following general structural formula: R1 and R2 are each independently selected from substituents having 1-6 carbon atoms, an unsaturation degree of 0-4, and a heteroatom number of 0-3, wherein the heteroatom is selected from at least one of oxygen, nitrogen, or sulfur.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The substituent is selected from at least one of alkyl, alkenyl, alkynyl, carbonyl, ester, amino, or heterocyclic groups.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first additive is selected from At least one of them.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the first additive in the electrolyte is 0.05wt%-3wt%.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of 2,2,2-trifluoroethyl methyl carbonate in the electrolyte is 10wt%-85wt%.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that, In the fluorocarbonate solvent, the mass ratio of 2,2,2-trifluoroethyl methyl carbonate to fluoroethylene carbonate is 9:1 to 7:

3.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt further includes a second lithium salt selected from at least one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide.

8. The lithium-ion battery electrolyte according to claim 7, characterized in that, The lithium salt in the electrolyte contains 12wt%-20wt%, and the first lithium salt in the electrolyte contains 8wt%-20wt%.

9. A lithium-ion battery, characterized in that, include: The positive electrode sheet includes a positive electrode active material, wherein the structural formula of the positive electrode active material is Li. a Ni x Mn y O 4-z M z Wherein, 0.9≤a≤1.1, 0.4≤x≤0.6, 1.4≤y≤1.6, 0≤z≤0.1, and M is selected from at least one of Cl, Br, I, S, Se, Te or F; Negative electrode plate; A diaphragm is disposed between the positive electrode and the negative electrode; and The electrolyte is selected from the lithium-ion battery electrolyte according to any one of claims 1-8.

10. An electronic device, characterized in that, Including the lithium-ion battery as described in claim 9.

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