Electrolyte and battery containing the electrolyte

Abstract

PURPOSE: To provide an electrolyte and a battery including the electrolyte.SOLUTION: An electrolyte includes a solvent, a lithium salt, and an additive. The solvent is composed of a fluorinated solvent, the fluorinated solvent includes fluorinated ethylene carbonate (FEC), and the additive includes diethyl 2-thiophene methyl phosphonate (DTYP). A content of DTYP is 0.01% to 1.2% based on a total mass of the electrolyte. The electrolyte of the present invention, on basis of using fluorinated solvent as solvent to provide a battery with good high voltage resistance performance, also through a synergistic effect of FEC and DTYP with specific content, forms SEI and CEI films with excellent thermal stability at positive and negative electrode interfaces, thus enabling the battery to have both good high-temperature storage performance and high-temperature cycling performance.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention is in the field of lithium-ion battery technology and relates to electrolytes and batteries containing such electrolytes. [Background technology]

[0002] In recent years, the rapid development of the new energy vehicle market has led to an explosive growth in the market value of power batteries, primarily secondary alkali metal-ion batteries. However, the energy density of currently commercially available secondary lithium-ion batteries is already approaching its theoretical limit. Increasing the battery voltage has become an intuitive and feasible solution to fundamentally address electric vehicle buyers' concerns about driving range. However, as the battery voltage increases, the oxidation activity of the cathode material also increases, making it more susceptible to structural damage. Electrolytes are prone to decomposition at high voltages. Especially at high temperatures, side reactions within the electrolyte and at the interfaces between the electrolyte and the positive and negative electrodes intensify, resulting in rapid battery expansion, capacity loss, and poor cycling performance. Summary of the Invention [Problem to be solved by the invention]

[0003] Therefore, how to make a battery have both high voltage and excellent high temperature performance has become a technical problem to be solved urgently in this field. [Means for solving the problem]

[0004] The present invention provides an electrolyte solution that provides excellent high-voltage resistance by using a fluorinated solvent as a solvent, and forms a CEI film and SEI film with excellent thermal stability at the positive electrode interface and negative electrode interface, respectively, due to the synergistic effect of fluoroethylene carbonate (FEC) and a specific content of diethyl (thiophen-2-ylmethyl)phosphonate (DTYP), thereby enabling the battery to have both excellent high-temperature storage performance and high-temperature cycle performance.

[0005] The present invention further provides a battery containing the above-described electrolyte, which not only has high voltage resistance but also has excellent high-temperature storage performance and high-temperature cycle performance.

[0006] A first aspect of the present invention provides an electrolyte solution comprising a solvent, a lithium salt, and an additive, wherein the solvent is a fluorinated solvent, the fluorinated solvent includes fluoroethylene carbonate, and the additive includes diethyl 2-thienylmethylphosphonate. The content of the diethyl 2-thienylmethylphosphonate is 0.01% to 1.2% based on the total mass of the electrolyte solution.

[0007] In one alternative embodiment, the content of the fluoroethylene carbonate is 8% to 12% based on the mass of the fluorinated solvent.

[0008] In one alternative embodiment, the additive further comprises tetravinyl silane (TVSI).

[0009] In one alternative embodiment, the content of the tetravinylsilane is 0.01% to 1% based on the total mass of the electrolyte solution.

[0010] In one alternative embodiment, the mass ratio of the diethyl 2-thienylmethylphosphonate to the tetravinylsilane is (3 to 30):(1 to 10).

[0011] In one alternative embodiment, the fluorinated solvent further comprises fluoroethyl methyl carbonate (FEMC) and / or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0012] In one alternative embodiment, the fluorinated solvents include fluoroethylene carbonate, fluoroethyl methyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0013] In one alternative embodiment, the mixing mass ratio of the fluoroethylene carbonate, fluoroethyl methyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 1:4:3.

[0014] In one alternative embodiment, the content of the lithium salt is 12% to 20% based on the total mass of the electrolyte solution.

[0015] In one alternative embodiment, the lithium salt comprises lithium hexafluorophosphate. The content of the lithium hexafluorophosphate relative to the total mass of the electrolyte solution is 8% to 20%.

[0016] A second aspect of the present invention provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the electrolyte is the electrolyte provided by the first aspect of the present invention.

[0017] In one alternative embodiment, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a lithium manganese nickel oxide material having a carbon coating layer. The chemical formula of the lithium manganese nickel oxide material is Li a Ni x Mn y O4, where 0.90≦a≦1.10, 0.4≦x≦0.6, and 1.4≦y≦1.6. [Effects of the Invention]

[0018] The embodiments of the present invention have at least the following beneficial effects. 1) The electrolyte of the present invention uses a fluorinated solvent as a solvent, thereby providing the electrolyte with a relatively high fluorine content, where the strong electron-withdrawing ability of fluorine atoms is advantageous for providing the electrolyte with higher oxidation stability, thereby significantly improving the high-voltage resistance of the electrolyte. 2) The electrolyte of the present invention uses a specific content of fluoroethylene carbonate and 2-thienylmethylphosphonic acid diethyl in combination to form an SEI film and a CEI film on the negative electrode side and the positive electrode side, respectively, which have excellent thermal stability, thereby improving the high-temperature storage performance and high-temperature cycle performance of the battery. 3) The 2-thienylmethylphosphonic acid diethyl ester used in the electrolyte of the present invention has a phosphate ester moiety in its structure that is liberated into the electrolyte. - Because the ions can be trapped, the thermal decomposition activity of the lithium salt can be reduced, thereby suppressing side reactions caused by the decomposition of the lithium salt, improving the thermal stability of the electrolyte, and avoiding the problems of gas generation in the battery at high temperatures, which leads to increased capacity loss and DC resistance, thereby further improving the high-temperature storage performance and high-temperature cycle performance of the battery. DETAILED DESCRIPTION OF THE INVENTION

[0019] In order to clarify the purpose, technical solutions and advantages of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Any other embodiments obtained based on the embodiments of the present invention without requiring creative work by those skilled in the art shall also fall within the protection scope of the present invention.

[0020] A first aspect of the present invention provides an electrolyte solution comprising a solvent, a lithium salt, and an additive, wherein the solvent is a fluorinated solvent, the fluorinated solvent comprising fluoroethylene carbonate, and the additive comprises diethyl 2-thienylmethylphosphonate. The content of diethyl 2-thienylmethylphosphonate is 0.01% to 1.2% based on the total mass of the electrolyte.

[0021] Fluorinated solvents can provide electrolytes with a relatively high fluorine content. The strong electron-withdrawing ability of fluorine atoms can provide electrolytes with relatively high oxidation stability, thereby significantly improving the high-voltage capability of the electrolyte. However, the carbon-fluorine bonds in fluorinated solvents are easily broken at high temperatures. The broken fluorine atoms react with active hydrogen in the electrolyte to generate hydrofluoric acid, which increases the acidity of the electrolyte and corrodes the alkaline materials in the SEI and CEI, causing destruction of the positive and negative electrode interfaces and continuous side reactions. This results in problems such as gas generation in batteries at high temperatures, capacity loss, and increased direct current resistance (DCR).

[0022] The present invention uses a fluorinated solvent containing fluoroethylene carbonate (FEC) in combination with an additive called diethyl 2-thienylmethylphosphonate (DTYP, structural formula shown in Formula I). ​​Here, FEC is reduced on the negative electrode side to form an SEI film, which is advantageous for protecting the negative electrode interface. The thiophene moiety in the DTYP molecular structure is preferentially oxidized on the positive electrode side to form a stable CEI film, which can protect the electrolyte from continuous oxidation side reactions. The phosphate ester moiety in the molecular structure is used to convert PF6, which is freed in the electrolyte, into PF6. - The ability to trap ions reduces the thermal decomposition activity of the lithium salt, thereby suppressing side reactions caused by the decomposition of the lithium salt and improving the thermal stability of the electrolyte, thereby avoiding the problems of gas generation, capacity loss, and increased DCR at high temperatures. Furthermore, research has found that when the DTYP content in the electrolyte is less than 0.01%, it is difficult to form a stable CEI film, and when the DTYP content in the electrolyte is greater than 1.2%, the high-temperature cycle performance of the battery is significantly degraded. [ka]

[0023] As described above, the electrolyte of the present invention provides a battery with excellent high voltage resistance by selecting a fluorinated solvent as the solvent. Furthermore, the synergistic effect of FEC and a specific amount of DTYP forms SEI and CEI films at the positive and negative electrode interfaces, which have excellent thermal stability, thereby enabling the battery to simultaneously exhibit excellent high-temperature storage performance and high-temperature cycle performance.

[0024] In one specific embodiment, the content of diethyl 2-thienylmethylphosphonate relative to the total mass of the electrolyte may be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, or a range consisting of any two of these values.

[0025] The inventors have found through research that when the content of DTYP is greater than 1%, the high-temperature cycling performance of the battery begins to deteriorate slightly. Therefore, the content of diethyl 2-thienylmethylphosphonate is more preferably ≦1% based on the total mass of the electrolyte.

[0026] The present invention does not specifically limit the content of the fluorinated solvent in the electrolyte solution, and the usual content of the solvent in the electrolyte solution can be used as a reference.

[0027] Furthermore, the content of fluoroethylene carbonate relative to the mass of the fluorinated solvent is 8% to 12%, and within this content range, it is advantageous for the battery to have both better high-voltage resistance and high-temperature performance.

[0028] In one preferred embodiment, the additive further comprises tetravinylsilane (TVSI). The structural formula of tetravinylsilane is shown in Formula II. Because its molecular structure contains an unsaturated carbon-carbon double bond, oxidative decomposition of tetravinylsilane occurs preferentially on the positive electrode side, and together with DTYP, it participates in the formation of a CEI film. Furthermore, the formed CEI film is a silicon-rich polymer and is resistant to swelling by fluorinated solvents, which is advantageous for further enhancing the stability of the CEI film, thereby further improving the high-temperature storage performance and cycle performance of the battery. [ka]

[0029] Furthermore, the content of tetravinylsilane relative to the total mass of the electrolyte solution is 0.01% to 1%. For example, the content of tetravinylsilane relative to the total mass of the electrolyte solution is 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, or a range consisting of any two of these values.

[0030] When the content of tetravinylsilane is less than 0.01%, it is difficult to form a stable CEI film together with DTYP. However, when the amount of tetravinylsilane is excessive, i.e., more than 1%, the thickness of the CEI film becomes too large, which increases the DCR of the battery, thereby deteriorating the storage performance of the battery at high temperatures and shortening the cycle life.

[0031] More specifically, the mass ratio of diethyl 2-thienylmethylphosphonate to tetravinylsilane is (3 to 30):(1 to 10). By mixing DTYP and TVSI within the above mass ratio range, the battery can be provided with superior high-temperature cycle performance and high-temperature storage performance.

[0032] In one preferred embodiment, the fluorinated solvent further comprises fluoroethyl methyl carbonate (FEMC) and / or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (D2). FEMC can enter the solvation layer of lithium ions, thereby participating in the formation of an SEI or CEI film, introducing F-containing components to the electrode-electrolyte interface and enhancing the stability of the interface, thereby improving the oxidation stability of the electrolyte on the positive electrode side. Furthermore, FEMC itself is a fluorinated solvent and is resistant to decomposition even at high voltages, thereby improving the oxidation stability of the electrolyte itself. D2 is advantageous in reducing the viscosity of the electrolyte, thereby improving the fluidity and conductivity of the electrolyte.

[0033] The research found that when fluoroethylene carbonate (FEC), fluoroethyl methyl carbonate (FEMC), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (D2) were mixed, the high-temperature storage performance and high-temperature cycling performance of the battery were improved compared to when FEC and FEMC or FEC and D2 were mixed.

[0034] Furthermore, the mixing mass ratio of fluoroethylene carbonate, fluoroethyl methyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 1:4:3, which can further improve the high-temperature storage performance and high-temperature cycle performance of the battery.

[0035] The present invention does not specifically limit the type of lithium salt, and lithium salts commonly used in this field can be selected, including one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium hexafluoroarsenate, but the present invention is not limited thereto. Furthermore, the content of the lithium salt is 12% to 20% of the total mass of the electrolyte. Illustratively, the content of the lithium salt is 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of these values, relative to the total mass of the electrolyte.

[0036] In one preferred embodiment, the lithium salt includes lithium hexafluorophosphate, and the content of lithium hexafluorophosphate is 8% to 20% relative to the total mass of the electrolyte. Illustratively, the content of lithium hexafluorophosphate relative to the total mass of the electrolyte is 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of these values. Compared to other types of lithium salts, lithium hexafluorophosphate is less susceptible to corrosion even at high voltages.

[0037] A second aspect of the present invention provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the electrolyte is the electrolyte provided by the first aspect of the present invention.

[0038] The battery of the present invention contains the above-mentioned electrolyte solution, and therefore can withstand high voltages and also have excellent high-temperature cycle performance and high-temperature storage performance.

[0039] The positive electrode sheet of the present invention includes a current collector and a positive electrode active material layer disposed on the current collector surface. Here, the positive electrode active material layer mainly contains a positive electrode active material, and further contains usual components such as a binder and a conductive agent.

[0040] The present invention does not specifically limit the type of positive electrode active material, and positive electrode active materials commonly used in this field can be selected, including one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese nickel oxide, and lithium iron phosphate, but the present invention is not limited thereto.

[0041] In one preferred embodiment, the positive electrode active material comprises a lithium manganese nickel oxide material having a carbon coating layer, and the chemical formula of the lithium manganese nickel oxide material is Li a Ni x Mn y O4, where 0.90≦a≦1.10, 0.4≦x≦0.6, and 1.4≦y≦1.6.

[0042] The present invention does not limit the form in which the surface of the lithium manganese nickel oxide inner core is coated with the carbon coating layer, and therefore, the surface of the inner core may be partially coated, or the entire surface may be coated.

[0043] It should be understood that if the mass ratio of the carbon coating layer in the lithium manganese nickel oxide material is too low, it is difficult to effectively protect the inner core, and if the mass ratio is too high, it is detrimental to the energy density of the battery. In one preferred embodiment, the mass of the carbon coating layer accounts for 1% to 3% of the mass of the lithium manganese nickel oxide material. Here, the mass of the lithium manganese nickel oxide material refers to the mass of the inner core and does not include the mass of the carbon coating layer.

[0044] In one specific embodiment, the carbon source of the carbon coating layer includes one or more of fructose, polyethylene glycol, galactose, polyvinylpyrrolidone, and tannic acid. The carbon coating layer formed by the above carbon sources can effectively protect the surface of the inner core and at the same time form a large number of conductive carbon dots on the surface of the inner core, which is advantageous for improving the conductive performance of the material.

[0045] The present invention does not particularly limit the conductive agent in the positive electrode sheet, and conductive agents commonly used in this field can be selected, including one or more of acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, and graphene, but the present invention is not limited thereto.

[0046] The present invention does not particularly limit the binder in the positive electrode sheet, and binders commonly used in this field can be selected, including one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene butadiene rubber, and polyethylene oxide, but the present invention is not limited thereto.

[0047] The present invention does not particularly limit the current collector in the positive electrode sheet, and a positive electrode current collector commonly used in this field, such as aluminum foil, can be selected.

[0048] The positive electrode sheet of the present invention can be produced by a conventional method in this field, for example, by dispersing a positive electrode active material, a conductive agent, and a binder in a solvent to obtain a positive electrode active material layer slurry, applying the slurry onto a positive electrode current collector, and drying the slurry to obtain a positive electrode sheet.

[0049] The negative electrode sheet in the present invention can be selected from negative electrode sheets commonly used in this field, and includes a current collector and a negative electrode active material layer disposed on the current collector surface.

[0050] For the negative electrode current collector, a negative electrode current collector commonly used in this field, for example, a copper foil, can be selected.

[0051] The negative electrode active material layer mainly consists of a negative electrode active material, and further contains ordinary components such as a binder, a thickener, and a conductive agent.

[0052] The present invention does not particularly limit the type of the negative electrode active material, and a negative electrode active material commonly used in this field can be selected, which includes one or more of artificial graphite, natural graphite, hard carbon, soft carbon, nano-silicon (Si), silicon oxide negative electrode material (SiO x (0 < x < 2)), and silicon-carbon negative electrode materials, but the present invention is not limited thereto.

[0053] The present invention does not particularly limit the types of the conductive agent and the binder in the negative electrode sheet. Since the selection range can refer to the types of the conductive agent and the binder in the positive electrode sheet, it will not be repeatedly described here.

[0054] The present invention does not particularly limit the type of the thickener in the negative electrode sheet, and a thickener commonly used in this field can be selected, which includes one or more of sodium carboxymethyl cellulose, sodium polyacrylate, or polyvinyl alcohol, but the present invention is not limited thereto.

[0055] The negative electrode sheet of the present invention can be manufactured by using a common method in this field. For example, after dispersing a negative electrode active material, a conductive agent, a thickener, and a binder in a solvent to form a negative electrode active material layer slurry, the negative electrode active material layer slurry is coated on the negative electrode current collector, and a negative electrode sheet can be obtained after drying.

[0056] The function of the separator is to separate the positive and negative electrode sheets and provide a path for lithium ions to move. The present invention does not specifically limit the type of separator, and separators commonly used in this field, such as polypropylene separators and polyethylene separators, can be selected.

[0057] The present invention does not specifically limit the manufacturing method of a lithium ion battery, and a lithium ion battery can be manufactured using a manufacturing method commonly used in this field. For example, a positive electrode sheet, a separator, and a negative electrode sheet are stacked in order so that the separator is located between the positive electrode sheet and the negative electrode sheet, and a battery cell is obtained by a stacking or winding process, and then the lithium ion battery of the present invention can be obtained by processes such as firing, liquid injection, chemical conversion, and packaging.

[0058] The electrolyte and battery provided by the present invention will be described in more detail below with reference to specific examples.

[0059] Unless otherwise specified, the reagents, materials, and equipment used in the following examples are all common reagents, materials, and equipment in the art, and are all commercially available. Related reagents can also be synthesized by common methods in the art. [Example]

[0060] The lithium ion batteries of Examples 1 to 14 and Comparative Examples 1 to 10 are all fabricated according to the following method.

[0061] 1. Preparation of the electrolyte In a glove box with an argon gas atmosphere and a moisture content of less than 10 ppm, the lithium salt and additives are added to the solvent and mixed uniformly to obtain an electrolyte solution. Here, the lithium salt is LiPF6, and its added mass is 13% of the total mass of the electrolyte. The specific types and contents of the solvents and additives used in the electrolyte are as shown in Table 1. In Table 1, the content of the additive is expressed as mass % based on the total mass of the electrolyte. The mass percentage content of the solvent in the electrolyte solution is 100% - mass percentage content of the lithium salt - mass percentage content of the additive, but is not listed in Table 1.

[0062] 2. Preparation of the positive electrode sheet Lithium-ion cathode active material with carbon coating structure 0.98 Ni 0.45 Mn 1.55 O4, the binder polyvinylidene fluoride, and the conductive agent Super P are mixed in a weight ratio of 98:1:1, and N-methylpyrrolidone is added. The mixture is stirred under a vacuum mixer until the mixture becomes uniform and transparent, yielding a positive electrode slurry. The positive electrode slurry is then evenly applied to aluminum foil, which is then dried at room temperature and then transferred to an oven for drying. The foil is then cold-pressed and cut to obtain a positive electrode sheet.

[0063] 3. Preparation of negative electrode sheet The negative electrode active material, artificial graphite, conductive agent Super P, thickener carboxymethylcellulose sodium CMC-Na, and binder styrene butadiene rubber SBR are mixed in a mass ratio of 96:1:1:2, and deionized water is added to obtain negative electrode slurry under the action of a vacuum mixer. The negative electrode slurry is evenly coated onto the negative electrode current collector copper foil, which is then dried at room temperature and then transferred to a drying oven for drying. The negative electrode sheet is then obtained through cold pressing and cutting.

[0064] 4. Lithium-ion battery assembly A 12 μm thick polypropylene film was used as the separator. The positive electrode sheet, separator, and negative electrode sheet obtained above were stacked in order, with the separator positioned between the positive and negative electrode sheets to act as an insulator, to obtain a laminated core. The laminated core was then placed in an aluminum plastic film package and transferred to a vacuum oven where it was dried at 120°C. 3 g of the electrolyte obtained above was then injected, sealed, and the electrolyte was converted, resulting in a soft-pack lithium-ion battery with a capacity of 1 Ah.

[0065] [Table 1]

[0066] Test Example The lithium ion batteries of the above examples and comparative examples were subjected to the following performance tests.

[0067] (1) 25°C DC resistance (DCR) test for lithium-ion batteries Place the battery in a thermostatic chamber and adjust the temperature to 25°C. Use a current of 0.33C to charge and discharge the battery three times, and record the discharge capacity of the last cycle as C0. At the specified temperature (25°C), discharge the battery to 50% SOC (State of Charge, reflecting the remaining capacity of the battery) at a current of 1C0. When the current is increased to 4C0 and maintained for 30 seconds, measure the difference between the updated stable voltage and the original plateau voltage. The ratio of this value to the 4C0 current value is the battery's DC resistance. The DCR test result after the first full charge of the battery is the initial DCR of the battery.

[0068] (2) Capacity retention rate of lithium-ion batteries when stored at high temperatures (60°C) At room temperature, the battery is discharged at a rate of 0.3C to the cut-off voltage, and the discharged capacity is designated as the initial discharge capacity C0. The battery is then fully charged and stored in a constant temperature bath at 60°C for 15 days. After storage, it is removed and cooled to room temperature, and then discharged at a rate of 0.3C to the cut-off voltage, and the discharge capacity is designated as C1. The storage capacity retention rate of this battery at a high temperature of 60°C is C1 / C0 × 100%.

[0069] (3) High temperature 45℃ cycle test The battery is cycled at 45°C. The voltage range is 3.4V to 4.85V, and the charge / discharge rate is 1C / 1C. The discharge capacity for each cycle is recorded. The test is terminated when the remaining battery capacity is 80% SOC, and the number of cycles actually achieved is recorded.

[0070] The test results are shown in Table 2.

[0071] [Table 2]

[0072] From the data in Table 2, the following conclusions can be drawn from the analysis: 1) Comparing Examples 1-4 and Comparative Examples 7 and 8, when the DTYP content in the electrolyte was between 0.01% and 1.2%, the 25°C DCR was low and the 60°C high-temperature storage capacity retention rate was high. Among these, the overall battery performance was best when the DTYP content was 0.3%, and the 60°C storage capacity recovery rate of the battery increased when the DTYP content in the electrolyte was increased from 0.01% to 0.3%, suggesting that the DTYP additive better maintains thermodynamic stability and reduces reactions at the solid-liquid interface, even at high temperatures. However, when the DTYP content in the electrolyte reached 1% or above, some deterioration in the number of high-temperature 45°C cycles of the battery was observed. When the DTYP content in the electrolyte was less than 0.01% or more than 1.2%, the number of high-temperature 45°C cycles of the battery was significantly reduced, and when the DTYP content was greater than 1.2%, the 25°C DCR resistance of the battery also significantly increased.

[0073] 2) Comparing Examples 2, 5-7, and 13-14, without changing the solvent system, when DTYP and TVSI were used in combination and the TVSI content in the electrolyte was controlled to 0.01% to 1%, the 25°C DCR of the corresponding battery decreased, and both the 60°C storage capacity retention rate and the number of high-temperature 45°C cycles improved to some extent. However, when the TVSI content in the electrolyte was less than 0.01%, the 25°C DCR and high-temperature storage performance of the battery were equivalent to those of Example 2, which did not contain TVSI, but the number of high-temperature cycles of the battery slightly deteriorated. When the TVSI content in the electrolyte was greater than 1%, the 60°C storage capacity retention rate of the battery was slightly improved compared to Example 2, but the 25°C DCR of the battery significantly increased and the number of high-temperature 45°C cycles also slightly decreased.

[0074] 3) Comparing Example 6 with Examples 8 to 12, when a mixture of FEC, FEMC, and D2 was used as a solvent, the battery's DCR at 25°C was lowest, its storage capacity retention at 60°C, and the number of high-temperature 45°C cycles were highest, compared to when only FEC was used as a solvent or when FEC was mixed with any one of FPC, D2, or FEMC and used as a solvent, and thus the battery's performance was better in all respects.

[0075] 4) As can be seen from Comparative Examples 1 to 3, when DTYP was not added to the electrolyte and only common electrolyte additives such as VC and DTD were used, the battery performance was significantly worse.Also, when DTD and TVSI were used in combination, the battery had difficulty maintaining a balance between kinetics and thermodynamics, which resulted in a significant increase in the DCR of the battery and a significant decrease in the number of high-temperature 45°C cycles.

[0076] 5) As can be seen from Comparative Examples 4 and 5, when only D2 was used as a solvent in the electrolyte, the battery could not be charged and discharged normally. This is because D2 has a relatively high viscosity and low solubility in lithium salts, making it impossible for the battery to operate normally as an electrolyte. When only FEMC was used as a solvent in the electrolyte, the battery showed an extremely high 25°C DCR value and clearly poor high-temperature 45°C cycle performance.

[0077] 6) As can be seen from Comparative Examples 6, 9, and 10, when only a conventional carbonate ester was used as the solvent, the carbonate ester solvent had difficulty withstanding the high voltage of the battery system, and a large amount of electrolyte oxidation occurred during the chemical formation stage, preventing the battery from being cycled normally. Even when FEC was mixed with the conventional carbonate ester solvents DMC or EC, the electrolyte was unable to withstand the high voltage, resulting in a very high initial impedance and very poor 60°C storage performance and high-temperature 45°C cycle performance. [Industrial Applicability]

[0078] The electrolyte of the present invention provides excellent high-pressure resistance by using a fluorinated solvent as a solvent, and forms a CEI film and an SEI film with excellent thermal stability at the positive electrode interface and the negative electrode interface, respectively, due to the synergistic effect of FEC and a specific content of DTYP, thereby enabling the battery to have both excellent high-temperature storage performance and high-temperature cycle performance.

[0079] The above embodiments are merely for explaining the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art will understand that modifications can still be made to the technical solutions described in the above embodiments, or that equivalent replacements can be made for some or all of the technical features. Furthermore, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. a solvent, a lithium salt, and an additive, wherein the solvent is a fluorinated solvent, the fluorinated solvent comprises fluoroethylene carbonate, and the additive comprises diethyl 2-thienylmethylphosphonate; The content of the diethyl 2-thienylmethylphosphonate is 0.01% to 1.2% based on the total mass of the electrolyte solution.

2. 2. The electrolyte solution according to claim 1, wherein the content of the fluoroethylene carbonate is 8% to 12% by mass of the fluorinated solvent.

3. The electrolyte solution according to claim 1 or 2, wherein the additive further comprises tetravinylsilane.

4. The electrolyte solution according to claim 3, wherein the content of the tetravinylsilane is 0.01% to 1% by weight of the total weight of the electrolyte solution.

5. 5. The electrolyte solution according to claim 4, wherein the mass ratio of the 2-thienylmethylphosphonic acid diethyl ester to the tetravinylsilane is (3 to 30):(1 to 10).

6. 2. The electrolyte solution according to claim 1, wherein the fluorinated solvent further comprises fluoroethyl methyl carbonate and / or 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

7. 7. The electrolyte of claim 6, wherein the fluorinated solvent comprises fluoroethylene carbonate, fluoroethyl methyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

8. 8. The electrolyte solution according to claim 7, wherein the mixing mass ratio of the fluoroethylene carbonate, the fluoroethyl methyl carbonate, and the 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 1:4:

3.

9. 2. The electrolyte solution according to claim 1, wherein the content of the lithium salt is 12% to 20% based on the total mass of the electrolyte solution.

10. the lithium salt comprises lithium hexafluorophosphate; 10. The electrolyte solution according to claim 9, wherein the content of the lithium hexafluorophosphate is 8% to 20% based on the total mass of the electrolyte solution.

11. A battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte solution, wherein the electrolyte solution is the electrolyte solution according to any one of claims 1 to 10.

12. The positive electrode sheet includes a positive electrode active material, the positive electrode active material including a lithium manganese nickel oxide material having a carbon coating layer, and the lithium manganese nickel oxide material has a chemical formula of Li ａ Ni ｘ Mn ｙ O ４ 12. The battery of claim 11, wherein 0.90≦a≦1.10, 0.4≦x≦0.6, and 1.4≦y≦1.6.

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