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 fluorinated solvent, including 2,2-difluoroethyl ethyl carbonate and fluoroethylene carbonate; a lithium salt, including a first lithium salt, wherein the first lithium salt comprises lithium hexafluorophosphate; and an additive, including a first additive, wherein the first additive comprises tripropynyl phosphate. The lithium-ion battery electrolyte and its application proposed in this invention can improve the high-voltage resistance of the electrolyte and enhance the cycle stability and rate performance of the battery.

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] The rapid development of the new energy vehicle market has driven explosive growth in the lithium metal battery market, and has also placed higher demands on the energy density of lithium metal batteries to address users' range anxiety. Increasing battery voltage, as a straightforward and feasible method, can indeed improve battery energy density, but it places higher demands on the high-voltage resistance of the electrolyte. Using fluorinated solvents as the main solvent, while improving the electrolyte's high-voltage resistance, can also lead to interface damage and continuous side reactions, as well as a series of problems such as high-temperature gas generation, high-temperature capacity loss, and increased impedance, thus 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 and improve the cycle stability and rate performance of the battery.

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

[0005] Fluorinated solvents, including 2,2-difluoroethyl ethyl carbonate and fluoroethylene carbonate;

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

[0007] Additives, including a first additive, wherein the first additive includes tripropynyl phosphate.

[0008] In one embodiment of the present invention, the content of 2,2-difluoroethyl ethyl carbonate in the electrolyte is 20wt%-85wt%, and the content of fluoroethylene carbonate in the electrolyte is 5wt%-20wt%.

[0009] In one embodiment of the present invention, the content of 2,2-difluoroethyl ethyl carbonate in the electrolyte is 35wt%-70wt%.

[0010] In one embodiment of the present invention, the mass ratio of the 2,2-difluoroethyl ethyl carbonate to the fluoroethylene carbonate is 9:1-7:3.

[0011] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.01wt%-1wt%.

[0012] In one embodiment of the present invention, the additive further includes a second additive, the second additive including propylene-1,3-sulfonyl lactone, and the content of the second additive in the electrolyte is 0.01wt%-1wt%.

[0013] In one embodiment of the present invention, the mass ratio of the first additive to the second additive is (0.375-1):1.

[0014] In one embodiment of the present invention, the lithium salt content in the electrolyte is 12wt%-20wt%.

[0015] In one embodiment of the present invention, the content of the first lithium salt in the electrolyte is 11wt%-20wt%, and 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, and the content of the second lithium salt in the electrolyte is 0.1wt%-1wt%.

[0016] The present invention also provides a lithium-ion battery, comprising at least:

[0017] 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, 0.90≤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;

[0018] Negative electrode plate;

[0019] A diaphragm is disposed between the positive electrode and the negative electrode; and

[0020] The electrolyte is selected from the lithium-ion battery electrolytes mentioned above.

[0021] In summary, this invention proposes a lithium-ion battery electrolyte and its application. Fluorinated solvents can improve the high-voltage resistance of the electrolyte, thereby increasing the battery's voltage and energy density. The synergistic effect of the fluorinated solvent and the first additive forms a uniform and stable organic-inorganic composite interfacial phase, ensuring the stability of the electrode-electrolyte interface, reducing electrolyte decomposition at the interface and dissolution of the positive electrode transition metal, mitigating the increase in interfacial impedance, and thus significantly improving the battery's cycle stability and rate performance. The second additive participates in the film-forming reaction, generating sulfur-containing compounds with high ionic conductivity, which helps to further generate a stable interfacial phase, reduce interfacial side reactions, mitigate impedance growth, and further improve the battery's cycle stability and rate performance. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] This invention proposes a lithium-ion battery electrolyte, comprising at least a fluorinated solvent, a lithium salt, and additives. The fluorinated solvent includes 2,2-difluoroethylethylcarbonate (DFDEC) and fluoroethylene carbonate (FEC). The lithium salt includes a first lithium salt, specifically lithium hexafluorophosphate (LiPF6). The additive includes a first additive, specifically tripropargyl phosphate (TPP). In the lithium-ion battery electrolyte provided by this invention, the fluorinated solvent improves the electrolyte's high-voltage resistance. Furthermore, the fluorinated solvent and the first additive work synergistically to form a uniform and stable organic-inorganic composite interfacial phase, reducing electrolyte decomposition at the interface and the dissolution of the positive electrode transition metal, mitigating the increase in interfacial impedance, thereby improving the battery's cycle performance and rate performance.

[0026] In one embodiment of the present invention, the fluorinated solvent has a high boiling point and oxidation stability, which can significantly improve the high voltage resistance of the electrolyte. At the same time, the fluorinated solvent has a weak solvation effect, which will cause more salt anions to decompose at the interface between the electrode and the electrolyte, generating phosphorus- and fluorine-containing inorganic interface phases, thereby significantly improving the cycle stability and rate performance of the battery.

[0027] In one embodiment of the present invention, for the fluorinated solvent, the content of DDFEC in the electrolyte is, for example, 20wt%-85wt%, or more specifically, 35wt%-70wt%, and the content of FEC in the electrolyte is, for example, 5wt%-20wt%, and the mass ratio of DDFEC to FEC is, for example, 9:1-7:3. By controlling the mass ratio of DDFEC to FEC, problems such as high electrolyte viscosity, low conductivity, and poor wettability caused by excessive DDFEC content can be avoided, as can interfacial phase instability caused by excessive FEC content, thereby improving the cycle stability and rate performance of the battery.

[0028] In one embodiment of the present invention, the structural formula of TPP in the first additive is as follows: The first additive, acting as a film-forming additive in the electrolyte, possesses unsaturated bonds in its structure. It preferentially decomposes at the electrode interface, generating phosphorus-containing oligomers, which participate in the formation of a uniform and dense interfacial phase. Simultaneously, the preferential decomposition and film formation of the first additive can, to some extent, mitigate the decomposition rate of salt anions, promoting a more uniform and dense interfacial phase. Therefore, the synergistic effect of the first additive and the fluorinated solvent can form a uniform and stable organic-inorganic composite interfacial phase, reducing electrolyte decomposition at the interface and the dissolution of the positive electrode transition metal, mitigating the increase in interfacial impedance, and thus improving the battery's cycle stability and rate performance.

[0029] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.01 wt%-1 wt%. Since the phosphorus-containing polymer generated by the decomposition of the first additive has low ionic conductivity, by controlling the content of the first additive, the problem of increased battery interface impedance and deterioration of kinetic performance caused by excessive phosphorus-containing polymer can be avoided, thereby improving the kinetic performance and cycle stability of the battery.

[0030] In one embodiment of the present invention, the additive further includes a second additive, such as propenyl-1,3-sulfonyl lactone (Prop-1-ene-1,3-sultone, PST). By introducing the second additive, it participates in the film-forming reaction to generate a sulfur-containing compound with high ionic conductivity, which helps to further generate a stable interfacial phase, reduce interfacial side reactions, alleviate impedance growth, and further improve the cycle stability and rate performance of the battery.

[0031] In one embodiment of the present invention, the content of the second additive in the electrolyte is, for example, 0.01 wt%-1 wt%. By controlling the content of the second additive, it is possible to avoid the degradation of the battery's rate performance caused by excessive content of the second additive, thereby balancing the battery's rate performance and cycle stability.

[0032] In one embodiment of the present invention, the mass ratio of the first additive to the second additive is, for example, (0.375-1):1. By controlling the mass ratio of the first additive to the second additive, both the rate performance and cycle stability of the battery can be balanced.

[0033] In one embodiment of the present invention, the additive further includes a third additive, such as a 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 third additive in the electrolyte is, for example, 0.1wt%-5wt%.

[0034] 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, 11wt%-20wt%.

[0035] 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). By introducing the second lithium salt, its stronger water absorption can alleviate the hydrolysis of the lithium salt, thereby improving the rate performance and cycle stability of the battery. The content of the second lithium salt in the electrolyte is, for example, 0.1 wt%-1 wt%. By controlling the content of the second lithium salt, it is possible to avoid the degradation of the battery's rate performance and cycle stability caused by excessive content of the second lithium salt.

[0036] In one embodiment of the present invention, when preparing the electrolyte, battery-grade DFDEC 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 fluorinated solvent. Lithium salt and additives are then added to the fluorinated 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.

[0037] 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.

[0038] 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.

[0039] 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 which includes, for example, carbon, and the mass ratio of the coating layer to the positive electrode active material is, for example, (1-3):1.

[0040] 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).

[0041] 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 1.54O4, 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 pre-sintered in a stable gas atmosphere such as nitrogen to obtain carbon material. 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. 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.

[0042] In one embodiment of the present invention, when preparing the positive electrode, Li containing a carbon coating layer is used... a Ni x Mn y O 4-z M z 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).

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] In one embodiment of the present invention, the above-mentioned positive electrode, separator and negative electrode are placed in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation, and is put into an aluminum-plastic film, transferred to a vacuum oven at 120°C for drying, and then injected with the lithium-ion battery electrolyte prepared above at 3.0 g / Ah and sealed. After electrolyte formation, a soft-pack lithium-ion battery with a capacity of 1Ah is obtained.

[0049] 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.

[0050] Example 1

[0051] 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 1.54The O4 highly active material is mixed evenly and then subjected to a secondary sintering process to obtain Li containing a carbon coating. 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 1.54 O4 positive electrode active material, PVDF and Super P 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.

[0052] 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.

[0053] Electrolyte preparation: In an argon atmosphere glove box with a moisture content of less than 10 ppm, DDFEC and FEC were mixed uniformly at a mass ratio of 9:1 according to the electrolyte composition described in Table 1 to obtain a fluorinated solvent. LiPF6 and TPP were then added to the fluorinated solvent and mixed uniformly to prepare the lithium-ion battery electrolyte. The contents of LiPF6 and TPP in the electrolyte were 13 wt% and 0.3 wt%, respectively.

[0054] Membrane selection: A single-layer PP membrane with a thickness of 12μm was selected as the membrane.

[0055] Battery preparation: The positive electrode, separator and negative electrode are placed in sequence and placed in an 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.

[0056] Example 2

[0057] The mass ratio of DFDEC to FEC is 8:2, and the other steps are the same as in Example 1.

[0058] Example 3

[0059] The mass ratio of DFDEC to FEC is 7:3, and the other steps are the same as in Example 1.

[0060] Example 4

[0061] The content of TPP in the electrolyte is 0.01 wt%, and the other steps are the same as in Example 2.

[0062] Example 5

[0063] The content of TPP in the electrolyte is 1 wt%, and the other steps are the same as in Example 2.

[0064] Example 6

[0065] The electrolyte contains PST, and the content of PST in the electrolyte is 0.01 wt%. Other steps are the same as in Example 2.

[0066] Example 7

[0067] The PST content in the electrolyte is 1 wt%, and the other steps are the same as in Example 6.

[0068] Example 8

[0069] The electrolyte contains LiFSI, and the content of LiFSI in the electrolyte is 0.1 wt%. The other steps are the same as in Example 2.

[0070] Example 9

[0071] The content of LiFSI in the electrolyte is 1 wt%, and the other steps are the same as in Example 8.

[0072] Example 10

[0073] The LiFSI content in the electrolyte is 1.2 wt%, and the other steps are the same as in Example 8.

[0074] Example 11

[0075] The mass ratio of TPP to PST is 0.5:1, and the other steps are the same as in Example 7.

[0076] Example 12

[0077] The mass ratio of TPP to PST is 1:1, and the other steps are the same as in Example 7.

[0078] Example 13

[0079] The electrolyte contains VC and DTD, and the content of VC and DTD in the electrolyte is 0.5 wt%. Other steps are the same as in Example 2.

[0080] Comparative Example 1

[0081] The electrolyte does not contain TPP, and the other steps are the same as in Example 2.

[0082] Comparative Example 2

[0083] The electrolyte contains 2,2,2-trifluoroethyl carbonate (TFDEC), and the mass ratio of TFDEC, FDEC and FEC is 0:8:2. The other steps are the same as in Example 2.

[0084] Comparative Example 3

[0085] The electrolyte contains DTD, and the content of DTD in the electrolyte is 0.5 wt%. Other steps are the same as those in Comparative Example 1.

[0086] Comparative Example 4

[0087] The electrolyte contains vitamin C, and the content of vitamin C in the electrolyte is 0.5 wt%. The other steps are the same as those in Comparative Example 3.

[0088] Comparative Example 5

[0089] The positive electrode active material is lithium cobalt oxide, and the other steps are the same as those in Comparative Example 1.

[0090] Comparative Example 6

[0091] The positive electrode active material is lithium cobalt oxide, and the other steps are the same as in Example 2.

[0092] Comparative Example 7

[0093] The electrolyte does not contain TPP, and the other steps are the same as in Example 7.

[0094] Comparative Example 8

[0095] The electrolyte did not contain TPP, and the other steps were the same as in Comparative Example 2.

[0096] 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. The contents of the first lithium salt, second lithium salt, first additive, second additive, and third additive are mass percentages calculated based on the total mass of the electrolyte.

[0097] Table 1. Composition of electrolytes in Examples 1-13 and Comparative Examples 1-8

[0098]

[0099]

[0100] In this invention, the lithium-ion batteries prepared with different electrolyte ratios and positive electrode active materials in Examples 1-13 and Comparative Examples 1-8 were subjected to performance tests, and the test results are shown in Table 2.

[0101] In one embodiment of the present invention, for example, a room temperature cycle stability test is performed on a lithium-ion battery. Specifically, the battery is cycled at 25°C with a charge / discharge rate of 0.5C / 1C, and the battery capacity is measured. The test ends when the battery capacity reaches 80% of the first cycle capacity (State of Health (SOH), and the number of cycles at 25°C is recorded.

[0102] In one embodiment of the present invention, for example, a rate performance test is performed on a lithium-ion battery. Specifically, at 25°C, the battery is sequentially charged at different rates (0.33C, 1C, 2C, and 3C) to the upper limit cutoff voltage, then charged at the upper limit cutoff voltage with a constant voltage until the current is less than 0.05C. After resting for 10 minutes, it is discharged at a constant current of 0.33C to the lower limit cutoff voltage. Each charging rate cycle is repeated twice, and then the cycle is adjusted to the next rate. The charging capacity of the second cycle at 0.33C and the second cycle at 3C are recorded as the charging capacity of the lithium-ion battery at 0.33C and 3C, respectively. The capacity retention rate at the high-rate 3C charging is calculated using the following formula:

[0103] 3C capacity retention rate (%) = (3C charging capacity / 0.33C charging capacity) × 100%.

[0104] Among them, the upper limit cutoff voltage of the lithium nickel manganese oxide / graphite battery in Examples 1-13, Comparative Examples 1-4 and Comparative Examples 7-8 is 4.85V and the lower limit cutoff voltage is 3.4V. For the lithium cobalt oxide / graphite battery in Comparative Examples 5-6, the upper limit cutoff voltage is 4.45V and the lower limit cutoff voltage is 2.8V.

[0105] In one embodiment of the present invention, a high-temperature cycle stability test is performed on a lithium-ion battery, for example. Specifically, the battery is charged and discharged at 45°C with a charge / discharge rate of 1C / 1C within the charge / discharge cutoff voltage, and the battery capacity is measured. The test ends when the battery capacity reaches 80% of the first cycle capacity (State of Health (SOH), and the number of cycles at 45°C is recorded.

[0106] In the examples 1-13, 1-4 and 7-8, the charge / discharge cutoff voltage was 3.4V-4.85V, and in the examples 5-6, the charge / discharge cutoff voltage was 2.8V-4.45V.

[0107] Table 2 shows the performance test results of lithium-ion batteries in Examples 1-13 and Comparative Examples 1-8.

[0108]

[0109]

[0110] Please refer to Tables 1 and 2. Comparing Example 2 and Comparative Example 2, it can be seen that when DDFEC is used instead of TFDEC in the fluorinated solvent, the number of cycles at 25°C, the 3C capacity retention, and the number of cycles at 45°C all increase significantly. This indicates that although TFDEC has a higher degree of fluorination, which enhances the intrinsic oxidation stability of the electrolyte and improves its high-voltage resistance, it also leads to a significant increase in electrolyte viscosity and a significant decrease in electrolyte conductivity and wettability, thus affecting the battery's cycle stability and rate performance. Therefore, by controlling the type of fluorinated solvent, it is possible to improve the electrolyte's high-voltage resistance while simultaneously ensuring the battery's cycle stability and rate performance.

[0111] Please refer to Tables 1 and 2. Comparing Example 2, Comparative Example 1, Comparative Examples 3-4, and Comparative Example 7, it can be seen that compared with adding the first additive TPP to the fluorinated solvent, adding the second additive PST or the third additive DTD and / or VC to the fluorinated solvent increases the number of cycles at 25°C, the 3C capacity retention rate, and the number of cycles at 45°C, but the increase is very small. This indicates that using the second or third additive in combination with the fluorinated solvent does not significantly improve the cycle stability and rate performance of the battery, but using the first additive in combination with the fluorinated solvent can significantly improve the cycle stability and rate performance of the battery.

[0112] Please refer to Tables 1 and 2. Comparing Example 2, Comparative Examples 1-2, and Comparative Example 8, it can be seen that in the fluorinated solvent composed of TFDEC and FEC, the addition of the first additive TPP increases the number of cycles at 25°C, 3C capacity retention, and 45°C, but the increase is very small. However, in the fluorinated solvent composed of DFDEC and FEC, the addition of the first additive TPP significantly increases the number of cycles at 25°C, 3C capacity retention, and 45°C. This indicates that when TFDEC is used as the main solvent in the fluorinated solvent in combination with the first additive, its effect on improving the cycle stability and rate performance of the battery is not significant. However, when DFDEC is used as the main solvent in the fluorinated solvent in combination with the first additive, it can significantly improve the cycle stability and rate performance of the battery.

[0113] Please refer to Tables 1 and 2. Comparing Examples 1-3, it can be seen that in the fluorinated solvent, when the mass ratio of DDFEC to FEC is greater than 8:2, the number of cycles at 25°C, 3C capacity retention, and 45°C all decrease. This indicates that because DDFEC has high viscosity and poor dissociation ability, excessively high DDFEC content leads to a decrease in electrolyte conductivity and affects electrolyte wettability, thereby compromising battery cycle stability and rate performance. When the mass ratio of DDFEC to FEC is less than 8:2, the number of cycles at 25°C, 3C capacity retention, and 45°C all decrease. This indicates that because FEC is unstable at high temperatures and produces a large number of interfacial byproducts, the interfacial phase is unstable, thus affecting battery cycle stability and rate performance. Therefore, by controlling the mass ratio of DDFEC to FEC in the fluorinated solvent, the cycle stability and rate performance of the battery can be improved.

[0114] Please refer to Tables 1 and 2. Comparing Examples 2 and 4-5, it can be seen that as the content of the first additive TPP increases from 0.01 wt% to 0.3 wt%, the number of cycles at 25°C, the 3C capacity retention, and the number of cycles at 45°C all increase significantly. This indicates that the first additive TPP can promote the formation of a more uniform and stable interfacial phase, effectively reducing the reaction at the solid-liquid interface, thereby improving the cycle stability and rate performance of the battery. However, when the content of the first additive TPP continues to increase from 0.3 wt% to 1 wt%, although the number of cycles at 45°C continues to increase, the number of cycles at 25°C and the 3C capacity retention decrease significantly. This indicates that as the content of the first additive TPP continues to increase, although the high-temperature cycle stability continues to improve, the room-temperature cycle stability and rate performance of the battery are significantly affected. Therefore, by controlling the content of the first additive TPP, it is possible to balance the room-temperature cycle stability, rate performance, and high-temperature cycle stability of the battery.

[0115] Please refer to Tables 1 and 2. Comparing Examples 2, 6, 1, and 7, it can be seen that when the electrolyte contains only PST (the first additive), the increase in the number of cycles at 25°C, 3C capacity retention, and 45°C is relatively small, indicating that PST has little effect on improving the cycle stability and rate performance of the battery. However, when the electrolyte contains both PST and PPP, the increase in the number of cycles at 25°C, 3C capacity retention, and 45°C is the largest, indicating that the combined use of PST and PPP helps to generate a more stable interfacial phase, reduce interfacial side reactions, alleviate impedance growth, and thus further improve the cycle stability and rate performance of the battery.

[0116] Please refer to Tables 1 and 2. Comparing Examples 6-7, it can be seen that as the content of the second additive PST increases from 0.01 wt% to 1 wt%, although the number of cycles at 25°C and 45°C increases, the 3C capacity retention decreases. This indicates that while the cycle stability of the battery improves with increasing the content of the second additive PST, the rate performance is affected. Therefore, by controlling the content of the second additive PST, it is possible to balance the rate performance and cycle stability of the battery.

[0117] Please refer to Tables 1 and 2. Comparing Examples 2, 13, 1, and 4, it can be seen that for the first and third additives, when the electrolyte contains only the third additives VC and DTD, the increase in the number of cycles at 25°C, 3C capacity retention, and 45°C is relatively small, indicating that the third additive has no significant effect on improving the cycle performance and rate performance of the battery. When the electrolyte contains the first additive TPP, the third additive VC, and the third additive DTD simultaneously, the increase in the number of cycles at 25°C, 3C capacity retention, and 45°C is the largest, indicating that the first and third additives work synergistically to further improve the cycle stability and rate performance of the battery.

[0118] Please refer to Tables 1 and 2. Comparing Examples 7 and 11-12, it can be seen that when the mass ratio of the first additive TPP to the second additive PST increases from 0.3:1 to 0.5:1, the number of cycles at 25°C, the 3C capacity retention, and the number of cycles at 45°C significantly increase. This indicates that increasing the mass ratio of the first additive to the second additive improves the battery's high-temperature cycle stability and rate performance. However, when the mass ratio of the first additive TPP to the second additive continues to increase from 0.5:1 to 1:1, although the number of cycles at 45°C continues to increase, the number of cycles at 25°C and the 3C capacity retention decrease. This indicates that while an excessively high mass ratio of the first additive to the second additive can improve the battery's high-temperature cycle stability, too much of the first additive participating in film formation can affect the battery's kinetic performance, thus impacting its high-temperature cycle stability and rate performance. Therefore, by controlling the mass ratio of the first additive to the second additive, both the battery's rate performance and high-temperature cycle stability can be balanced.

[0119] Please refer to Tables 1 and 2. Comparing Examples 2 and 8, it can be seen that when the electrolyte contains a second lithium salt, LiFSI, the battery's 25°C cycle count, 3C capacity retention, and 45°C cycle count all increase. This indicates that because the second lithium salt, LiFSI, has stronger water absorption, it can alleviate the hydrolysis of lithium salts, thereby improving the battery's rate performance and cycle stability. Therefore, the second lithium salt, LiFSI, can further improve the battery's rate performance and cycle stability.

[0120] Please refer to Tables 1 and 2. Comparing Examples 8-10, it can be seen that when the content of the second lithium salt LiFSI increases from 0.1 wt% to 1 wt%, although the number of cycles at 25°C and the 3C capacity retention rate increase, the number of cycles at 45°C decreases. This indicates that increasing the content of the second lithium salt LiFSI from 0.1 wt% to 1 wt% can improve the battery's room temperature cycle stability and rate performance, but the high-temperature cycle stability is affected. When the content of the second lithium salt LiFSI continues to increase from 1 wt% to 1.2 wt%, the number of cycles at 25°C, the 3C capacity retention rate, and the number of cycles at 45°C all decrease. This indicates that when the content of the second lithium salt LiFSI continues to increase from 1 wt% to 1.2 wt%, under high voltage, the second lithium salt LiFSI easily reacts with the aluminum foil, causing continuous decomposition of the electrolyte, thereby affecting the battery's room temperature cycle stability, rate performance, and high-temperature cycle stability. Therefore, by controlling the content of the second lithium salt LiFSI, the rate performance and cycle stability of the battery can be avoided.

[0121] Please refer to Tables 1 and 2. Comparing Example 2, Comparative Example 1, and Comparative Examples 5-6, it can be seen that in the lithium cobalt oxide cathode active material, the synergistic effect of the fluorinated solvent and the first additive TPP can also improve the number of cycles at 25°C, the 3C capacity retention rate, and the number of cycles at 45°C, but the improvement is very small. This indicates that for the lithium cobalt oxide cathode active material system, the combined use of the fluorinated solvent and the first additive has no significant effect on improving the cycle stability and rate performance of the battery. Therefore, compared with the lithium cobalt oxide cathode active material, the fluorinated solvent and the first additive have a more significant effect on improving the lithium nickel manganese oxide cathode active material system.

[0122] 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.

[0123] In summary, this invention proposes a lithium-ion battery electrolyte and its application. By introducing a fluorinated solvent into the electrolyte, the high-voltage resistance of the electrolyte can be improved, thereby increasing the battery's voltage and energy density. By introducing a first additive into the electrolyte, the fluorinated solvent and the first additive work synergistically to form a uniform and stable organic-inorganic composite interfacial phase, ensuring the stability of the electrode-electrolyte interface, reducing electrolyte decomposition at the interface and dissolution of the positive electrode transition metal, mitigating the increase in interfacial impedance, and thus significantly improving the battery's cycle stability and rate performance. By introducing a second additive into the electrolyte, the second additive can participate in the film-forming reaction, generating a sulfur-containing compound with high ionic conductivity, which helps to further generate a stable interfacial phase, reduce interfacial side reactions, mitigate impedance growth, and further improve the battery's cycle stability and rate performance.

[0124] 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.

[0125] 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 solvents, including 2,2-difluoroethyl ethyl carbonate and fluoroethylene carbonate; Lithium salts, including a first lithium salt comprising lithium hexafluorophosphate; and Additives, including a first additive, wherein the first additive includes tripropynyl phosphate.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of 2,2-difluoroethyl ethyl carbonate in the electrolyte is 20wt%-85wt%, and the content of fluoroethylene carbonate in the electrolyte is 5wt%-20wt%.

3. The lithium-ion battery electrolyte according to claim 2, characterized in that, The content of 2,2-difluoroethyl ethyl carbonate in the electrolyte is 35wt%-70wt%.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The mass ratio of the 2,2-difluoroethyl ethyl carbonate to the fluoroethylene carbonate is 9:1-7:

3.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the first additive in the electrolyte is 0.01wt%-1wt%.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additive also includes a second additive, which comprises propylene-1,3-sulfonyl lactone, and the content of the second additive in the electrolyte is 0.01wt%-1wt%.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that, The mass ratio of the first additive to the second additive is (0.375-1):

1.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt content in the electrolyte is 12wt%-20wt%.

9. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first lithium salt has a content of 11wt%-20wt% in the electrolyte, and the lithium salt further includes a second lithium salt, which is selected from at least one of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide, and the content of the second lithium salt in the electrolyte is 0.1wt%-1wt%.

10. 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, 0.90≤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; Negative electrode sheet; 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 1-9.

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