High-temperature-resistant and high-pressure-resistant sulfuryl electrolyte as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium battery electrolyte, in particular to high-temperature-resistant and high-voltage-resistant sulfuryl electrolyte as well as a preparation method and application thereof. The invention provides a high-temperature-resistant and high-pressure-resistant sulfuryl electrolyte. The high-temperature-resistant and high-pressure-resistant sulfuryl electrolyte comprises conductive lithium salt, a sulfone solvent, a fluorine-containing diluent and a phosphate functional additive, wherein the conductive lithium salt is one or more of bis (trifluoromethylsulfonyl) or bis (fluoromethylsulfonyl) imide lithium. The electrolyte has excellent thermal stability at high temperature, a stable interface protection layer can be generated at the positive electrode and the negative electrode of the battery, the coulombic efficiency of the battery under the high-voltage condition is greatly improved, the cycle life of the battery under the high-voltage condition is greatly prolonged, the cycle life of a formed lithium metal soft package is 300 circles or above under the charging cut-off voltage of 4.4 V, and the service life of the lithium metal soft package is prolonged. The lithium metal soft package can still normally circulate under the charging cut-off voltage of 4.6 V, and in an actual circulation test, the lithium metal soft package hardly generates gas, so that the safety performance of the battery is obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery electrolytes, and in particular to a high temperature and high pressure resistant sulfone-based electrolyte and a preparation method and application thereof. Background Art

[0002] With the widespread use of various portable electronic consumer products, new energy vehicles and industrial equipment, lithium-ion batteries are playing an increasingly important role in people's daily lives. Due to the needs of special scenarios, many electronic devices and industrial equipment need to be used in high-temperature environments, such as manufacturing plants, medical disinfection equipment, aerospace systems, and oil drilling operations. In addition, with the frequent occurrence of high-temperature extreme weather in recent years, batteries are required to be able to operate stably in high-temperature environments. At the same time, with the increasing demand for energy storage systems, people's requirements for battery life and energy density are also increasing. Lithium metal has attracted widespread attention from researchers due to its extremely high theoretical specific capacity and lowest electrode potential. However, the application of traditional LiPF6 / EC-based electrolytes on lithium metal electrode materials has essential problems: (1) Poor low-potential stability. Carbonate-based solvents have high reactivity with lithium metal, especially under high temperature conditions, resulting in continuous consumption of lithium metal and electrolyte, and even serious safety hazards due to the growth of lithium dendrites; (2) LiPF6 has poor thermal stability and is prone to hydrolysis at high temperatures, as well as the dissolution of transition metal ions from the surface of the positive electrode material, making it difficult for lithium-ion batteries to exhibit excellent performance at high temperatures; (3) LiPF6 / EC-based electrolytes have low oxidative stability and are generally decomposed at potentials above 4.5V. In comparison, organic sulfone compounds have a high oxidative stability because the sulfur atom in the molecule is already in the highest oxidation state (S 6+ ), and the S=O bond has an extremely high bond energy, which makes it have excellent antioxidant stability and thermal stability, so it is regarded as a very promising high-voltage and high-temperature electrolyte solvent. However, sulfone compounds have poor compatibility with lithium metal, and the high melting point, high viscosity and low wettability of sulfone solvents generally hinder the practical application of sulfone solvents.

[0003] In order to improve the stability of lithium metal high temperature cycles, many researchers have made unremitting efforts, but many formulas are modified from LiPF6 / EC-based electrolytes. For example: CN115425292B provides a high temperature resistant electrolyte, which includes polyfluorobenzene compounds, lithium salts and solvents. The use of electrolytes containing polyfluorobenzene compounds can alleviate the decomposition of electrolytes to produce hydrofluoric acid at high temperatures, reduce the dissolution of positive electrode transition metal ions, and improve the high temperature cycle performance and high temperature storage stability of batteries. However, this formula uses a LiPF6 / EC-based electrolyte, which cannot fundamentally solve the problem that LiPF6 is easily decomposed to produce hydrofluoric acid at high temperatures. CN117374400A discloses a high temperature lithium ion battery electrolyte and a lithium ion battery. The electrolyte includes a solvent, a lithium salt and a functional additive, and the functional additive includes lithium bis(fluorosulfonyl)imide (LiFSI), a sulfonate additive, fluoroethylene carbonate (FEC) and a fluoropyridine compound. This invention improves the cycle performance of lithium batteries at high operating voltages by adding FEC, improves the high-temperature instability of FEC by adding LiFSI and sulfonate additives, inhibits the corrosion of aluminum foil by LiFSI under high voltage and inhibits gas production under high temperature conditions by adding fluoropyridine compounds, and improves the poor high-voltage stability of fluoropyridine compounds by adding sulfonate additives. The addition of LiFSI and FEC can indeed improve the high-temperature stability of LiPF6 / EC-based electrolytes, but the gas production of FEC and the poor compatibility of sulfonates with lithium metal negative electrodes have hindered the application of this electrolyte in high-temperature lithium metal batteries.

[0004] Therefore, there is an urgent need to develop an electrolyte formula that is resistant to high temperature and high pressure and can improve the incompatibility between lithium metal and sulfone solvents. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a high temperature and high pressure resistant sulfone-based electrolyte and a preparation method and application thereof. The electrolyte has excellent thermal stability at high temperature, can generate a stable interface protection layer at the positive and negative electrodes of the battery, greatly improving the coulombic efficiency and cycle life of the battery under high voltage conditions. The composed lithium metal soft pack has a cycle life of more than 300 cycles at a charging cut-off voltage of 4.4V, and can still circulate normally at a charging cut-off voltage of 4.6V. In actual cycle tests, the lithium metal soft pack produces almost no gas, which significantly improves the safety performance of the battery.

[0006] To this end, the present invention provides the following technical solutions:

[0007] In a first aspect, the present invention provides, in an optional embodiment, a high temperature and high pressure resistant sulfone-based electrolyte, comprising a conductive lithium salt, a sulfone solvent, a fluorine-containing diluent, and a phosphate functional additive;

[0008] Wherein, the conductive lithium salt is one or more of lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluoromethylsulfonyl)imide.

[0009] In the present invention, compared with LiPF6, lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) have the advantages of high solubility, good thermal stability, hydrolysis resistance, high temperature resistance, and gas production inhibition, and are therefore selected as conductive lithium salts. Sulfone solvents have higher oxidation stability due to the strong electron-withdrawing property of the sulfone group (-SO2-) compared with ester and ether solvents, and tolerate higher cut-off voltages, and sulfone solvents have high dielectric constants, high boiling points, high flash points, low flammability, low cost, and low toxicity. However, the high viscosity of sulfone solvents and poor compatibility with lithium metal negative electrodes hinder their practical application in lithium metal batteries. The viscosity can be effectively reduced by adding fluorine-containing diluents and phosphate functional additives. In addition, high temperature is also an effective method to reduce the viscosity of the system, improve wettability and conductivity. In terms of negative electrode compatibility, measures such as increasing the concentration of lithium salts, grafting fluorine-containing functional groups in sulfone-based solvents, adding phosphate functional additives and using fluorine-containing diluents are taken to reduce the corrosion of sulfone-based electrolytes on lithium metal negative electrodes. By assembling Li / Cu batteries for testing, it is found that the coulomb efficiency of the electrolyte of the present invention reaches more than 99.2% at 60°C. It is worth noting that all components of the high-temperature resistant sulfone-based electrolyte are selected from materials with high-temperature resistant properties, and each component has an extremely high boiling point. Before reaching the boiling point, almost no decomposition reaction occurs. The reasonable design is matched to fundamentally realize the phenomenon of no gas expansion of the electrolyte during use, thereby simplifying the second sealing process of battery production, eliminating the cumbersome steps of frequently taking the battery out of the mold and re-pressurizing it, effectively avoiding the damage to the solid electrolyte interface (SEI) caused by human operation, and significantly improving the production efficiency and quality stability of the battery.

[0010] The highly polar sulfonyl group of sulfone solvents has strong electron-withdrawing property, which makes sulfone solvents highly resistant to oxidation and allows lithium salts to be fully electrochemically decomposed first, forming a dense positive electrode electrolyte interface (CEI) layer rich in F and S on the positive electrode surface. The CEI layer contains LiSO2F with low electron density S=O bonds, which is compatible with Li + The formed Li + -LiSO2F has the smallest binding energy, which helps in uniform Li + Transfer, while the -S(=O)2- group in the decomposition product of the local high-concentration sulfone-based electrolyte can react with the transition metal (Ni 2+ , Mn 2+ or Mn 3+ ) complexation, improving the interface stability between the positive electrode and the electrolyte and inhibiting the dissolution of transition metals to a certain extent.

[0011] Sulfone solvents have high dielectric constants, high solubility for lithium salts, and good oxidation stability to ensure that they can work at high voltages. Increasing the concentration of lithium salts improves the reduction stability of the electrolyte. At the same time, sulfone solvents have the advantages of high flash point, low flammability, low cost and low toxicity. The electrolyte has excellent thermal stability at high temperatures, can generate a stable interface protection layer at the positive and negative electrodes of the battery, and greatly improves the coulombic efficiency and cycle life of the battery under high voltage conditions. Traditional LiPF6 / EC-based lithium-ion battery electrolytes are not suitable for high-temperature lithium metal batteries. The high-temperature and high-pressure sulfone-based electrolyte provided by the present invention can promote the commercialization of high-temperature and wide-temperature lithium metal batteries. Lithium metal batteries using this high-temperature and high-pressure sulfone-based electrolyte have higher energy density.

[0012] Under high temperature conditions, LiPF6 is prone to thermal decomposition to produce PF5 and HF, etc. HF will corrode SEI and positive and negative electrode materials, resulting in decreased battery performance. In contrast, LiFSI and LiTFSI have higher high temperature stability and hydrolysis stability, and can form a solid SEI layer rich in inorganic components on the positive and negative electrode surfaces of lithium-ion batteries. These inorganic SEI layers have good chemical / electrochemical stability, thereby inhibiting the continuous erosion of the electrode materials by the electrolyte. In addition, phosphate functional additives decompose on the electrode surface to produce a phosphorus-containing organic interface protective layer, which synergizes with the inorganic SEI layer to significantly enhance the mechanical flexibility and chemical stability of the overall SEI layer. This organic-inorganic composite structure SEI layer is particularly important in high temperature environments, which can slow down the decomposition of the electrolyte and reduce the side reactions of the electrode materials, thereby extending the cycle life of the battery.

[0013] Preferably, the molar ratio of the conductive lithium salt, the sulfone solvent and the fluorine-containing diluent is 1:(1.2-3.5):(0.5-10); and / or the added amount of the phosphate functional additive is 0.1-10% of the mass of the electrolyte.

[0014] Preferably, the sulfone solvent is selected from one or more of Formula 1 or Formula 2,

[0015]

[0016] Wherein, R1 and R2 are independently selected from halogen, alkyl having 1-6 carbon atoms, halogenated alkane having 1-6 carbon atoms, alkoxy having 1-6 carbon atoms, cyanoalkyl having 1-6 carbon atoms, alkylene having 1-6 carbon atoms, halogenated alkylene having 1-6 carbon atoms, phenyl, halogenated phenyl or cyanophenyl, and R3 and R4 are independently selected from alkyl having 2-6 carbon atoms, halogenated alkane having 2-6 carbon atoms, alkoxy having 2-6 carbon atoms, nitrile-containing alkyl having 2-6 carbon atoms, alkylene having 2-6 carbon atoms, halogenated alkylene having 2-6 carbon atoms, phenylene, halogenated phenylene or cyanophenylene.

[0017] In the present invention, the sulfone solvent of formula 1 can be the following:

[0018]

[0019]

[0020] The sulfone solvent of formula 2 can be the following:

[0021]

[0022] Preferably, the fluorine-containing diluent is selected from one or more of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, hexafluoroisopropyl methyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether or fluorobenzene; and / or, the phosphate ester functional additive is selected from one or more of tripropargyl phosphate, triallyl phosphate, tris(trimethylsilane) phosphate, acetylene diethyl phosphate, 4-ethynylphenyl diethyl phosphate, tripropargyl phosphite, triallyl phosphite, and tris(trimethylsilane) phosphite.

[0023] Preferably, the electrolyte further comprises an aprotic solvent; the aprotic solvent is selected from one or more of carbonate solvents, carboxylate solvents, ionic liquids, ether solvents or nitrile solvents. The amount of the aprotic solvent added is less than 40% of the mass of the electrolyte.

[0024] In the present invention, the carbonate solvent is selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and ethylene carbonate; the carboxylate solvent is selected from ethyl acetate, propyl acetate, and ethyl propionate; the ionic liquid is selected from 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate; the ether solvent is selected from ethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, and dipropyl ether; the nitrile solvent is selected from acetonitrile, propionitrile, butyronitrile, succinonitrile, and glutaronitrile.

[0025] In a second aspect, the present invention provides, in an optional embodiment, a method for preparing the above-mentioned high temperature and high pressure resistant sulfone-based electrolyte, comprising the following steps:

[0026] Conductive lithium salt is added into a sulfone solvent for dispersion to obtain a high-concentration lithium salt solution, and then a fluorine-containing diluent and a functional additive are sequentially added into the high-concentration lithium salt to obtain a high-temperature and high-pressure resistant sulfone-based electrolyte.

[0027] Preferably, the concentration of the conductive lithium salt in the high-concentration lithium salt solution is higher than 2 mol / L; and / or the concentration of the conductive lithium salt in the high-temperature and high-pressure resistant sulfone-based electrolyte is 0.5-2 mol / L.

[0028] In the present invention, the high temperature and high pressure resistant sulfone-based electrolyte of the present invention has the characteristics of local high energy, and the local high concentration structure of the electrolyte can effectively improve the incompatibility problem between lithium metal and sulfone solvents: the decomposition of lithium salt anions, the preferential reduction of polyfluorinated or perfluorinated diluents on the surface of lithium metal, and the use of functional additives, the three together can effectively reduce the reduction of sulfone solvents on the surface of lithium metal, and the coulombic efficiency of Li / Cu batteries with local high concentration sulfone electrolyte at 60°C can reach 99.2%.

[0029] In a third aspect, the present invention provides a lithium metal secondary battery in an optional embodiment, comprising a positive electrode, a negative electrode, a separator and the above-mentioned high temperature and high pressure resistant sulfone-based electrolyte.

[0030] Preferably, the charging cut-off voltage of the lithium metal secondary battery is higher than 4.2V, preferably 4.4V; and / or the operating temperature is 25-80°C, preferably 35-60°C.

[0031] In the present invention, the material of the positive electrode is selected from one of ternary nickel cobalt manganese (brand NCM622), lithium manganate, lithium iron phosphate, ternary nickel cobalt manganese or ternary nickel cobalt aluminum, the negative electrode is selected from one of lithium metal strip, lithium copper composite strip or lithium-containing alloy, and the material of the diaphragm is selected from one of polypropylene, polyethylene, a composite of polypropylene and polyethylene, ceramic, glass fiber or cellulose.

[0032] Compared with the prior art, the present invention has one of the following beneficial effects:

[0033] 1. The electrolyte provided by the present invention has excellent thermal stability at high temperature, can generate a stable interface protection layer at the positive and negative electrodes of the battery, greatly improving the coulombic efficiency and cycle life of the battery under high voltage conditions. The composed lithium metal soft pack has a cycle life of more than 300 cycles at a charging cut-off voltage of 4.4V, and can still circulate normally at a charging cut-off voltage of 4.6V. In the actual cycle test, the lithium metal soft pack produces almost no gas, which significantly improves the safety performance of the battery.

[0034] 2. The present invention can effectively improve the problem of high viscosity of sulfone solvents and poor wettability to battery cells by adding high temperature conditions and diluents. The capacity of the battery cell at 60°C is 1.1-1.3 times that at 25°C. Under the condition of 3-4.6V cut-off voltage, the energy density of the ternary lithium metal battery system at 60°C with high load can reach 500Wh / kg.

[0035] 3. The electrolyte of the present invention has the characteristic of local high concentration, which can effectively improve the incompatibility problem between lithium metal and sulfone solvents: the decomposition of lithium salt anions, the preferential reduction of polyfluorinated or perfluorinated diluents on the lithium metal surface, and the use of functional additives. The three together can effectively reduce the reduction of sulfone solvents on the lithium metal surface. At 60°C, the coulombic efficiency of the Li / Cu battery with local high-concentration sulfone electrolyte can reach 99.2%.

[0036] 4. The highly polar sulfonyl group of sulfone solvents has strong electron-withdrawing property, which makes sulfone solvents highly resistant to oxidation and allows lithium salts to be fully electrochemically decomposed preferentially, forming a dense positive electrode electrolyte interface (CEI) layer rich in F and S on the positive electrode surface. The CEI layer contains LiSO2F with low electron density S=O bonds, which is compatible with Li + The formed Li + -LiSO2F has the smallest binding energy, which helps in uniform Li + Transfer, while the -S(=O)2- group in the decomposition product of the local high-concentration sulfone-based electrolyte can react with the transition metal (Ni 2+ , Mn 2+ or Mn 3+ ) complexation, improving the interface stability between the positive electrode and the electrolyte and inhibiting the dissolution of transition metals to a certain extent.

[0037] 5. The electrolyte provided by the present invention can effectively inhibit battery gas production at high temperatures. In the preparation process of lithium metal batteries using the electrolyte, there is no need to reserve additional air bags and perform a secondary sealing process after formation, thereby saving costs in the battery production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 Digital photos of gas generation of soft-pack batteries in Example 1 and Comparative Example 1 of the present invention;

[0040] Figure 2 This is a charge and discharge specific capacity-voltage curve of the electrolyte of Example 7 of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] As the global demand for energy storage systems rises sharply, the limitations of lithium-ion batteries in terms of energy density become increasingly prominent, especially in the context of pursuing higher endurance performance and coping with extreme operating environments. Lithium metal has attracted widespread attention from researchers due to its extremely high theoretical specific capacity and lowest electrode potential. However, commercial LiPF6-based electrolytes cannot match lithium metal batteries at high temperatures.

[0043] In terms of electrolyte, LiPF6 is very easy to decompose at temperatures above 55°C, and commonly used carbonate solvents (such as diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate) are highly volatile and have low flash and boiling points, which can easily lead to gas production during the battery cycle. Although most of the gas production can be solved by battery formation, gas is still produced during the cycle, especially when the battery capacity drops, the interfacial side reactions intensify, resulting in a large amount of gas production.

[0044] On the positive electrode side, high temperature conditions accelerate the decomposition of LiPF6-based electrolyte to produce hydrofluoric acid, which in turn causes the transition metal elements of the positive electrode material to dissolve and diffuse to the negative electrode surface, destroying the solid electrolyte interface (SEI) layer, increasing the interface impedance, and catalyzing the continuous decomposition of the electrolyte, resulting in rapid capacity decay of the battery.

[0045] On the negative electrode side, the SEI layer formed by the LiPF6-based electrolyte is prone to rupture above 60°C, and the electrolyte will continue to react with fresh lithium, leading to the formation of lithium dendrites and reduced Coulombic efficiency, which will seriously affect the cycle life of the battery and cause safety hazards.

[0046] In summary, the application of traditional commercial LiPF6-based electrolytes in lithium metal batteries faces severe challenges, especially under high temperature conditions. Therefore, designing a high-temperature resistant electrolyte that is compatible with the electrode can not only stabilize the positive electrode, but also build a stable SEI layer on the negative electrode side, which helps the stable cycle of lithium metal batteries under extreme high temperature conditions.

[0047] To this end, the present invention provides a high temperature and high pressure resistant sulfone-based electrolyte, the lithium metal soft pack composed of which has a cycle life of more than 300 cycles at a charging cut-off voltage of 4.4V, and can still cycle normally at a charging cut-off voltage of 4.6V. In actual cycle tests, the lithium metal soft pack produces almost no gas, which significantly improves the safety performance of the battery.

[0048] The technical solution of the present invention will be described below in conjunction with embodiments.

[0049] Example 1

[0050] The present embodiment provides a high temperature and high pressure resistant sulfone-based electrolyte, in which the molar ratio of lithium bis(fluorosulfonyl)imide, cyclopentane sulfone, methyl ethyl sulfone and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 1:2:0.5:2, and the added amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0051] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(fluorosulfonyl)imide, cyclopentane sulfone, methyl ethyl sulfone and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and in a glove box filled with nitrogen, lithium bis(fluorosulfonyl)imide is added to a mixed solution of cyclopentane sulfone and methyl ethyl sulfone for dispersion to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and tripropargyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent high-temperature and high-pressure resistant sulfone-based electrolyte.

[0052] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0053] Example 2

[0054] This embodiment provides a high temperature and high pressure resistant sulfone-based electrolyte, in which the molar ratio of lithium bis(fluorosulfonyl)imide, cyclopentane, trifluoromethylethyl sulfone and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 1:2:0.5:2, and the added amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0055] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(fluorosulfonyl)imide, cyclopentane, trifluoromethyl ethyl sulfone and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and in a glove box filled with nitrogen, lithium bis(fluorosulfonyl)imide is added to a mixed solution of cyclopentane and trifluoromethyl ethyl sulfone for dispersion to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and tripropargyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent high-temperature and high-pressure resistant sulfone-based electrolyte.

[0056] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0057] Example 3

[0058] The present embodiment provides a high temperature and high pressure resistant sulfone-based electrolyte, in which the molar ratio of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, cyclopentane and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 0.5:0.5:2.5:2, and the added amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0059] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, cyclopentane and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and in a glove box filled with nitrogen, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide are added to cyclopentane for dispersion to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and tripropargyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent high-temperature and high-pressure resistant sulfone-based electrolyte.

[0060] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0061] Example 4

[0062] This embodiment provides a high temperature and high pressure resistant sulfone-based electrolyte, in which the molar ratio of lithium bis(fluorosulfonyl)imide, cyclopentane sulfone, succinonitrile and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 1:2:0.5:2, and the added amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0063] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(fluorosulfonyl)imide, cyclopentane, succinonitrile and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and in a glove box filled with nitrogen, lithium bis(fluorosulfonyl)imide is added to a mixed solution of cyclopentane and succinonitrile for dispersion to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and tripropargyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent high-temperature and high-pressure resistant sulfone-based electrolyte.

[0064] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0065] Example 5

[0066] This embodiment provides a high temperature and high pressure resistant sulfone-based electrolyte, in which the molar ratio of lithium bis(fluorosulfonyl)imide, cyclopentane, trifluoromethylethyl sulfone and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 1:2:0.5:2, and the added amount of triallyl phosphate is 2% of the mass of the electrolyte.

[0067] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(fluorosulfonyl)imide, cyclopentane, trifluoromethyl ethyl sulfone and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and in a glove box filled with nitrogen, lithium bis(fluorosulfonyl)imide is added to a mixed solution of cyclopentane and trifluoromethyl ethyl sulfone for dispersion to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and triallyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent high-temperature and high-pressure resistant sulfone-based electrolyte.

[0068] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0069] Example 6

[0070] The present embodiment provides a high temperature and high pressure resistant sulfone-based electrolyte, in which the molar ratio of lithium bis(trifluoromethylsulfonyl)imide, cyclopentane sulfone, trifluoromethylethyl sulfone and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether is 1:2:0.5:2, and the added amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0071] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(trifluoromethyl)sulfonyl imide, cyclopentane sulfone, trifluoromethyl ethyl sulfone and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether are weighed according to the molar ratio, and in a glove box filled with nitrogen, lithium bis(trifluoromethyl)sulfonyl imide is added to a mixed solution of cyclopentane sulfone and trifluoromethyl ethyl sulfone for dispersion to obtain a high-concentration lithium salt solution, and then 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and tripropargyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent high-temperature and high-pressure resistant sulfone-based electrolyte.

[0072] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0073] Example 7

[0074] The present embodiment provides a high temperature and high pressure resistant sulfone-based electrolyte, in which the molar ratio of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, cyclopentane and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 0.5:0.5:2.5:2, and the added amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0075] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, cyclopentane and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and in a glove box filled with nitrogen, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide are added to cyclopentane for dispersion to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and tripropargyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent high-temperature and high-pressure resistant sulfone-based electrolyte.

[0076] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.6V, a pressure of 500kPa, and an operating temperature of 60°C.

[0077] Comparative Example 1

[0078] This comparative example provides a method for preparing an electrolyte: ethylene carbonate EC and ethyl methyl carbonate EMC are uniformly mixed in a volume ratio of 3:7, LiPF6 with a concentration of 1 mol / L is added, and the mixture is stirred to obtain a transparent electrolyte.

[0079] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0080] Comparative Example 2

[0081] This comparative example provides a method for preparing an electrolyte: ethylene carbonate EC and ethyl methyl carbonate EMC are uniformly mixed in a volume ratio of 3:7, LiPF6 with a concentration of 1 mol / L is added, and the mixture is stirred to obtain a transparent electrolyte.

[0082] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.6V, a pressure of 500kPa, and an operating temperature of 60°C.

[0083] Comparative Example 3

[0084] This comparative example provides a sulfone-based electrolyte, in which the molar ratio of LiPF6, cyclopentane sulfone and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 1:2.5:2, and the added amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0085] The preparation method of the above-mentioned sulfone-based electrolyte is: LiPF6, cyclopentane sulfone and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and LiPF6 is added to cyclopentane sulfone for dispersion in a glove box filled with nitrogen to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and tripropargyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent sulfone-based electrolyte.

[0086] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0087] Comparative Example 4

[0088] This comparative example provides a sulfone-based electrolyte, in which the molar ratio of LiClO4, sulfolane and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 1:2.5:2, and the added amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0089] The preparation method of the sulfone-based electrolyte is as follows: LiClO4, sulfolane and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and LiClO4 is added to sulfolane in a glove box filled with nitrogen for dispersion to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane and tripropargyl phosphate are added to the high-concentration lithium salt solution in sequence and stirred evenly to obtain a transparent sulfone-based electrolyte.

[0090] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0091] Comparative Example 5

[0092] This comparative example provides a sulfone-based electrolyte, in which the molar ratio of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide and sulfolane is 0.5:0.5:2.5, and the addition amount of tripropargyl phosphate is 2% of the mass of the electrolyte.

[0093] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide and sulfolane are weighed according to a molar ratio, and in a glove box filled with nitrogen, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide are added to sulfolane for dispersion to obtain a high-concentration lithium salt solution, and then tripropargyl phosphate is added to the high-concentration lithium salt solution and stirred evenly to obtain a transparent sulfone-based electrolyte.

[0094] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0095] Comparative Example 6

[0096] This comparative example provides a sulfone-based electrolyte, in which the molar ratio of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, cyclopentane and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is 0.5:0.5:2.5:2.

[0097] The preparation method of the sulfone-based electrolyte is as follows: lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, cyclopentane and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane are weighed according to the molar ratio, and in a glove box filled with nitrogen, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide are added to cyclopentane for dispersion to obtain a high-concentration lithium salt solution, and then 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane is added to the high-concentration lithium salt solution and stirred evenly to obtain a transparent sulfone-based electrolyte.

[0098] The ternary nickel-cobalt-manganese (grade NCM622) was selected as the positive electrode, with a loading of 17.8 mg / cm 2 The negative electrode uses a lithium-copper composite strip with a lithium metal thickness of 20μm, and the diaphragm uses Celgard 2500PP diaphragm. After being assembled into a soft-pack battery, the performance of the assembled soft-pack battery is tested under the conditions of a charging cut-off voltage of 4.4V, a pressure of 500kPa, and an operating temperature of 60°C.

[0099] Experimental example

[0100] The soft-pack batteries assembled in Examples 1-7 and Comparative Examples 1-6 were tested for cycle life, energy density and coulombic efficiency of the batteries in each embodiment and comparative example according to the test methods of each embodiment and comparative example. The results are shown in Table 1:

[0101] Table 1 Battery cycle life, energy density and coulombic efficiency

[0102]

[0103]

[0104] in conclusion:

[0105] By comparing and analyzing Examples 1-6, it is found that when lithium bis(trifluoromethylsulfonyl imide) and / or lithium bis(fluoromethylsulfonyl imide), sulfone solvents, fluorine-containing diluents and functional additives are used to prepare electrolytes, and soft-pack batteries are assembled, good cycle performance can be obtained when the charging cut-off voltage is 4.4V, while the battery using commercial electrolyte in Comparative Example 1 rapidly decays in performance at high temperatures; compared with Example 3, after lithium bis(trifluoromethylsulfonyl imide) and lithium bis(fluoromethylsulfonyl imide) are replaced with other lithium salts in Comparative Examples 3 and 4, the battery performance seriously declines; in Comparative Example 5, after the fluorine-containing diluent in the developed high temperature and high pressure electrolyte is removed, the viscosity of the electrolyte is extremely large, the wettability deteriorates, and the ion transport is difficult, making the battery basically unable to cycle; in Comparative Example 6, the functional additives are removed compared to Example 3, and the cycle performance of the battery is significantly deteriorated. The main reason why the performance of the embodiments of the present invention is better than that of the comparative examples is that the developed sulfone-based electrolyte itself has good oxidation resistance and high-temperature stability. At the same time, the lithium salt undergoes redox reaction at the positive and negative electrode interfaces before the solvent during the cycle to form thin and strong CEI and SEI. Combined with functional additives, the adverse reactions between the electrolyte and the electrodes at high temperatures are effectively reduced, thereby slowing down the growth of lithium dendrites and the generation of dead lithium in lithium metal batteries, and improving the battery cycle performance.

[0106] Example 7: By increasing the charge cut-off voltage to 4.6 V, the positive electrode loading was increased to 23 mg / cm 2 The energy density of the battery can reach 510Wh / kg, which is much higher than the energy density of current lithium-ion batteries, and can be cycled stably. However, even with a low-load positive electrode, comparative example 2 can hardly be cycled under high voltage.

[0107] Figure 1The digital photos of the gas production of the soft pack of comparative example 1 (left) and embodiment 3 (right) are shown. The comparative example is a LiPF6 / EC-based electrolyte, which has serious side reactions with the positive and negative electrodes under high temperature conditions. On the positive electrode side, it is manifested as the destruction of the electrode material structure and the instability of the CEI film. On the negative electrode side, the electrolyte continues to corrode the lithium metal negative electrode, resulting in a series of side reactions, such as the re-decomposition of the SEI film, the growth of lithium dendrites, and the shuttle of transition ions dissolved in the positive electrode to the negative electrode to aggravate the degradation of the metal lithium negative electrode. These side reactions are accompanied by the generation of a large amount of gas, resulting in a violent expansion of the battery and even safety problems. Sulfone-based electrolytes are inherently stable at high temperatures, the components are not easily volatile, there are few side reactions during battery cycling, and almost no gas is produced, which has a significant inhibitory effect on the volume expansion of the battery.

[0108] Figure 2 This is the charge and discharge specific capacity-voltage curve of the electrolyte in Example 7. The battery can still maintain good cycle performance at a cut-off voltage of 4.6V, indicating that the developed sulfone-based electrolyte has good compatibility with high-voltage positive electrodes and lithium metal negative electrodes, and can be stably cycled under high temperature and high pressure conditions, greatly improving the energy density of the battery cell. After calculation and experiments, the battery energy density can reach more than 500Wh / kg.

[0109] Although the principles of the present invention are described in detail above in conjunction with the preferred embodiments of the present invention, those skilled in the art should understand that the above embodiments are merely explanations of the exemplary implementations of the present invention, and are not intended to limit the scope of the present invention. The details in the embodiments do not constitute limitations on the scope of the present invention, and any obvious changes such as equivalent transformations, simple replacements, etc. based on the technical solution of the present invention, without departing from the spirit and scope of the present invention, fall within the protection scope of the present invention.

Claims

1. A high temperature and high pressure resistant sulfone-based electrolyte, characterized in that: Including conductive lithium salts, sulfone solvents, fluorine-containing diluents and phosphate functional additives; Wherein, the conductive lithium salt is one or more of lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluoromethylsulfonyl)imide.

2. The high temperature and high pressure resistant sulfone-based electrolyte according to claim 1, characterized in that: The molar ratio of the conductive lithium salt, the sulfone solvent and the fluorine-containing diluent is 1:(1.2-3.5):(0.5-10); and / or, The added amount of the phosphate functional additive is 0.1-10% of the mass of the electrolyte.

3. The high temperature and high pressure resistant sulfone-based electrolyte according to claim 1, characterized in that: The sulfone solvent is selected from one or more of Formula 1 or Formula 2, Wherein, R1 and R2 are independently selected from halogen, alkyl having 1-6 carbon atoms, halogenated alkane having 1-6 carbon atoms, alkoxy having 1-6 carbon atoms, cyanoalkyl having 1-6 carbon atoms, alkylene having 1-6 carbon atoms, halogenated alkylene having 1-6 carbon atoms, phenyl, halogenated phenyl or cyanophenyl, and R3 and R4 are independently selected from alkyl having 2-6 carbon atoms, halogenated alkane having 2-6 carbon atoms, alkoxy having 2-6 carbon atoms, nitrile-containing alkyl having 2-6 carbon atoms, alkylene having 2-6 carbon atoms, halogenated alkylene having 2-6 carbon atoms, phenylene, halogenated phenylene or cyanophenylene.

4. The high temperature and high pressure resistant sulfone-based electrolyte according to claim 1, characterized in that: The fluorine-containing diluent is selected from one or more of 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, hexafluoroisopropyl methyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether or fluorobenzene; and / or, The phosphate functional additive is selected from one or more of tripropargyl phosphate, triallyl phosphate, tris(trimethylsilane) phosphate, diethyl acetylene phosphate, diethyl 4-ethynylphenyl phosphate, tripropargyl phosphite, triallyl phosphite, and tris(trimethylsilane) phosphite.

5. The high temperature and high pressure resistant sulfone-based electrolyte according to claim 1, characterized in that: The electrolyte also includes an aprotic solvent; The aprotic solvent is selected from one or more of carbonate solvents, carboxylate solvents, ionic liquids, ether solvents or nitrile solvents.

6. The high temperature and high pressure resistant sulfone-based electrolyte according to claim 5, characterized in that: The amount of the aprotic solvent added is less than 40% of the mass of the electrolyte.

7. A method for preparing a high temperature and high pressure resistant sulfone-based electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: Conductive lithium salt is added into a sulfone solvent for dispersion to obtain a high-concentration lithium salt solution, and then a fluorine-containing diluent and a functional additive are sequentially added into the high-concentration lithium salt to obtain a high-temperature and high-pressure resistant sulfone-based electrolyte.

8. The method for preparing a high temperature and high pressure resistant sulfone-based electrolyte according to claim 7, characterized in that: The concentration of the conductive lithium salt in the high-concentration lithium salt solution is higher than 2 mol / L; and / or, The concentration of the conductive lithium salt in the high temperature and high pressure resistant sulfone-based electrolyte is 0.5-2 mol / L.

9. A lithium metal secondary battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the high temperature and high pressure resistant sulfone-based electrolyte according to any one of claims 1 to 6.

10. The lithium metal secondary battery according to claim 9, characterized in that: The charging cut-off voltage of the lithium metal secondary battery is higher than 4.2V; and / or, The operating temperature is 25-80℃.

Images