An electrolyte solution, a preparation method thereof, and a lithium battery

Abstract

An electrolyte, a preparation method thereof, and a lithium battery belong to the technical field of energy. The lithium battery includes an electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator. Among them, the electrolyte includes a solvent, a lithium salt, and a 2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxy propenyl compound additive. The lithium battery containing this compound additive can maintain good electrochemical performance while having good flame retardancy.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and more particularly, to an electrolyte, a preparation method thereof, and a lithium battery. Background Art

[0002] Commercial lithium batteries have the advantages of high energy and power density, no memory effect, long cycle life, and environmental friendliness. Their applications are rapidly expanding from the field of consumer electronics to the fields of electric vehicles and new energy energy storage.

[0003] However, in recent years, with the large-scale popularization and application of lithium batteries, a large number of safety accidents related to thermal runaway of lithium batteries occur worldwide every year. The academic and industrial circles have been continuously paying attention to and strengthening the exploration and improvement of the safety of lithium batteries. The abuse conditions that cause thermal runaway (smoking, catching fire and burning, explosion) mainly include mechanical abuse (such as extrusion, puncture), electrical abuse (such as overcharging, internal short circuit), and thermal abuse (such as overheat shock), etc. The role played by the electrolyte in the thermal runaway process of lithium batteries is very crucial.

[0004] Therefore, developing a highly safe flame-retardant electrolyte is the most economical and simple strategy, which can effectively reduce the risk (probability) of thermal runaway combustion and explosion of lithium batteries, and greatly reduce the personal and property damage caused by thermal runaway. Summary of the Invention

[0005] Based on the above deficiencies, the present application provides an electrolyte, a preparation method thereof, and a lithium battery to partially or completely improve the problem of thermal runaway of lithium batteries in related technologies.

[0006] The present application is implemented as follows:

[0007] In a first aspect, an example of the present application provides an electrolyte, including a solvent, a lithium salt, and an additive; the additive includes a 2-(bis(2-oxo-1,3-dioxo-4-yl)methoxy)phosphoryloxy propenyl compound represented by formula (1):

[0008]

[0009] Wherein, R1 and R2 are each independently selected from one of a hydrogen atom, a fluorine-substituted or unsubstituted C1-C6 linear alkyl group, a C3-C12 cycloalkyl group, a C2-C6 alkene group or alkyne group, a C6-C12 cyclic alkene group, a cyano group, a C1-C5 nitrile group, a methoxy group, an ethoxy group, a phenyl group, a benzene ring derivative group, and a five- or six-membered heterocyclic group.

[0010] In the above implementation process, 2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxy propenyl compound is added to the electrolyte, which has good flame retardant effect and compatibility with the negative electrode of the lithium-ion battery. It can improve the flame retardancy of the lithium-ion battery while reducing the negative impact of the additive on the electrochemical performance of the lithium-ion battery. Moreover, the additive contains carbon-carbon double bonds, which can polymerize to form high molecular compounds at high temperatures, covering the surfaces of the positive and negative electrodes and the separator of the lithium-ion battery, increasing the interfacial impedance, blocking the transmission of lithium ions, causing the battery to open circuit, and preventing the further progress of battery thermal runaway.

[0011] Combined with the first aspect, in an alternative embodiment of the present application, in the additive, R1 and R2 are each independently selected from a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, an alkenyl or alkynyl group having 2 to 6 carbon atoms, or a cyclic alkenyl group having 6 to 12 carbon atoms;

[0012] Optionally, in the additive, R1 and R2 are each independently selected from a hydrogen atom, a linear alkyl group having 1 to 6 carbon atoms, or a cycloalkyl group having 3 to 12 carbon atoms;

[0013] Optionally, in the additive, R1 and R2 are both selected from a hydrogen atom;

[0014] Optionally, the additive accounts for 0.1% to 20% of the total mass of the electrolyte.

[0015] In the above implementation process, the additive accounts for 0.1% to 20% of the total mass of the electrolyte, which can ensure the flame retardant effect while reducing the adverse impact of the additive on the electrochemical performance of the lithium battery.

[0016] Combined with the first aspect, in an alternative embodiment of the present application, the solvent is a carbonate, a carboxylate, or a sulfate and their fluorinated derivative solvents;

[0017] Optionally, the solvent is selected from at least one of ethylene carbonate, fluorinated ethylene carbonate, propylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, ethyl methyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, (2,2,2)-trifluoroethyl carbonate, ethyl acetate, difluoroethyl acetate, propyl propionate, sultone, vinylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, methyl formate, methyl acrylate, and methyl butyrate.

[0018] Combined with the first aspect, in an alternative embodiment of the present application, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium difluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium hexafluoroaluminate, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluoroarsenate, and lithium perfluoroalkylsulfonylmethyl;

[0019] Optionally, the lithium salt accounts for 10-20% of the total mass of the electrolyte.

[0020] In combination with the first aspect, in an optional embodiment of the present application, the electrolyte further includes an auxiliary additive; the auxiliary additive is at least one of 1,3-propane sultone, 1,4-butane sultone, allyl-1,3-sulfonic acid lactone, ethylene sulfate, propylene sulfate, butene sulfite, vinylene carbonate, fluoroethylene carbonate, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium difluorophosphate, and lithium tetrafluoroborate.

[0021] In the above implementation process, adding an auxiliary additive can further improve the electrochemical performance of a lithium battery containing this electrolyte.

[0022] In a second aspect, an embodiment of the present application provides a method for preparing an electrolyte, and the preparation method includes: mixing a solvent, a lithium salt, and an additive to form an electrolyte. The additive includes a 2-(bis(2-oxy-1,3-dioxo-4-yl)methoxy)phosphoryloxypropenyl compound represented by formula (1):

[0023]

[0024] The preparation method further includes the preparation of the additive:

[0025] Step A: Obtain an intermediate represented by formula (2):

[0026]

[0027] Step B: Mix the intermediate with formula (3), and at a temperature of 23-27°C, the chloro group of formula (2) reacts with the hydroxyl group of formula (3); the structure of formula (3) is as follows:

[0028]

[0029] Among them, R1 and R2 in formula (1) correspond to R1 and R2 in formula (3) one by one, and R1 and R2 are each independently selected from a hydrogen atom, a fluorine-substituted or unsubstituted C1-C6 linear alkyl group, a C3-C12 cycloalkyl group, a C2-C6 alkene group or alkyne group, a C6-C12 cyclic alkene group, a cyano group, a C1-C5 nitrile group, a methoxy group, an ethoxy group, a phenyl group, a benzene ring derivative group, and a five- or six-membered heterocyclic group.

[0030] According to the above preparation method, an electrolyte containing 2-(bis(2-oxido-1,3-dioxido-4-yl)methoxy)phosphoryloxy propenyl compound additive can be prepared, which has good flame retardant effect and compatibility with the negative electrode of lithium-ion battery, and can improve the flame retardancy of lithium-ion battery while reducing the negative impact of the additive on the electrochemical performance of lithium-ion battery. Moreover, the additive contains carbon-carbon double bond functional groups, which can polymerize to form high molecular compounds at high temperature, covering the surfaces of the positive and negative electrodes and the separator of the lithium-ion battery, increasing the interfacial impedance, blocking the transmission of lithium ions, resulting in battery open circuit, and preventing the further progress of battery thermal runaway.

[0031] Combined with the second aspect, in an alternative embodiment of the present application, step A includes:

[0032] React POCl3 with 1,2-carbonic glycerol at 0-3°C;

[0033] Optionally, react POCl3, 1,2-carbonic glycerol, chloroform and triethylamine under the action of 4-dimethylaminopyridine (DMAP) catalyst at a temperature of 0-3°C; distill and remove impurities from the reaction stock solution, and wash.

[0034] In step (B), formula (3) is vinyl alcohol;

[0035] Optionally, react the intermediate, vinyl alcohol, chloroform and triethylamine under the action of 4-dimethylaminopyridine (DMAP) catalyst at a temperature of 23-27°C.

[0036] In the above implementation process, by reacting POCl3 with 1,2-carbonic glycerol at 0-3°C and under the action of a catalyst, an intermediate can be obtained, so as to use the intermediate to react with the compound shown in the structure of formula (3) to prepare 2-(bis(2-oxido-1,3-dioxido-4-yl)methoxy)phosphoryloxy propenyl compound additive.

[0037] In the third aspect, an embodiment of the present application provides a lithium battery, including the electrolyte provided in the first aspect, a positive electrode sheet, a negative electrode sheet and a separator.

[0038] In the above implementation process, the lithium battery contains the electrolyte provided in the first aspect, which has good flame retardant effect and compatibility with the negative electrode of lithium-ion battery, and can improve the flame retardancy of lithium-ion battery while reducing the negative impact of the additive on the electrochemical performance of lithium-ion battery. Moreover, the additive in the electrolyte contains carbon-carbon double bond functional groups, which can polymerize to form high molecular compounds at high temperature, covering the surfaces of the positive and negative electrode sheets and the separator of the lithium-ion battery, increasing the interfacial impedance, blocking the transmission of lithium ions, resulting in battery open circuit, and preventing the further progress of battery thermal runaway.

[0039] In combination with the third aspect, in an alternative embodiment of the present application, the positive electrode active material of the positive electrode sheet is selected from at least one of transition metal phosphates, lithium salts of transition metal oxides, and lithium titanate Li4Ti5O 12 , and at least one of transition metal sulfides.

[0040] In combination with the third aspect, in an alternative embodiment of the present application, the negative electrode active material of the negative electrode sheet is selected from at least one of carbon materials, silicon materials, silicon-tin alloy materials, silicon-carbon materials, and silicon-oxygen materials.

[0041] In the above implementation process, the above-mentioned positive electrode active material and negative electrode active material provided by the embodiments of the present application can improve the compatibility between the positive electrode sheet and the negative electrode sheet and the electrolyte, and improve the electrochemical performance of the lithium battery. Specific embodiments

[0042] The following will describe the implementation schemes of the present application in detail in conjunction with embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0043] The following specifically describes the electrolyte and lithium battery provided by the examples of the present application:

[0044] With the large-scale popularization and application of lithium batteries, a large number of safety accidents related to the abuse and thermal runaway of lithium batteries are likely to occur. The abuse conditions that cause thermal runaway (smoking, catching fire and burning, explosion) mainly include mechanical abuse (such as extrusion, puncture), electrical abuse (such as overcharging, internal short circuit), and thermal abuse (such as overheat shock), etc.

[0045] At present, there are many safety improvement strategies to prevent the thermal runaway, fire, combustion and explosion of lithium batteries, such as using flame-retardant electrolytes, flame-retardant heat-shrinkable diaphragms, solid electrolytes, electrode materials with high structural stability (such as lithium iron phosphate LFP), etc.

[0046] Among them, the electrolyte affects the thermal runaway of lithium batteries. Developing high-safety flame-retardant electrolytes is the most economical and simple strategy, which can effectively reduce the risk (probability) of thermal runaway, combustion and explosion of lithium batteries, and greatly reduce the personal and property damage caused by thermal runaway.

[0047] The inventors attempted to improve the electrolyte by using flame retardant phosphate compounds (triethyl phosphate, trimethyl phosphate, dimethyl methylphosphonate, etc.) and phosphazene compounds (ethoxy pentafluorocyclotriphosphazene, hexafluorocyclotriphosphazene, etc.). At high temperatures, the flame retardants decompose and catalyze the attachment of polymers to the surfaces of the positive and negative electrode materials and the separator, resulting in an internal circuit break in the battery, preventing further thermal runaway. At the same time, the formed polymers can also act as an oxygen and combustible isolator. The PO· free radicals generated by the decomposition of the phosphorus-based flame retardants can capture the free radicals of flammable gases such as H·, HO· generated by the high-temperature decomposition of the electrolyte and O2 released by the positive electrode material at high temperatures, forming HPO, thereby preventing or slowing down the progress of the combustion chain reaction and enhancing the flame retardant effect. And the flame retardants decompose at high temperatures to produce non-combustible gases such as P, PO, and HPO, reducing the concentration of combustible gases, thereby delaying the thermal runaway of the battery.

[0048] However, the inventors found that adding compounds such as phosphates and phosphazenes to the electrolyte would cause the electrolyte to be incompatible with the graphite negative electrode, making it difficult to form a stable SEI film on the surface of the negative electrode and co-inserting with Li + and damaging the layered structure of graphite.

[0049] Therefore, the inventors attempted to reduce the amount of compounds such as phosphates and phosphazenes. However, when the concentration of flame retardant additives such as organic phosphates is too low (<10%), there is almost no obvious flame retardant effect, while when the concentration is too high (>20%), it significantly affects the lithium intercalation performance of the graphite negative electrode.

[0050] Therefore, the inventors provide a lithium battery to improve the problems of low flame retardancy and poor electrochemical performance of the lithium battery.

[0051] The lithium battery includes an electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator.

[0052] Among them, the electrolyte includes a solvent, a lithium salt, and an additive. Among them, the additive includes a 2-(bis(2-oxy-1,3-dioxo-4-yl)methoxy)phosphoryloxypropenyl compound represented by formula (1):

[0053]

[0054] Among them, R1 and R2 are each independently selected from a hydrogen atom, a fluorine-substituted or unsubstituted C1-C6 linear alkyl group, a C3-C12 cycloalkyl group, a C2-C6 alkenyl or alkynyl group, a C6-C12 cyclic alkenyl group, a cyano group, a C1-C5 nitrile group, a methoxy group, an ethoxy group, a phenyl group, a benzene ring derivative group, and a five- or six-membered heterocyclic group.

[0055] The electrolyte is added with 2-(bis(2-oxo-1,3-dioxo-4-yl)methoxy)phosphoryloxy propenyl compound, which has good flame retardant effect and compatibility with the negative electrode of lithium-ion battery. It can improve the flame retardancy of lithium-ion battery while reducing the negative impact of the additive on the electrochemical performance of lithium-ion battery. Moreover, the additive contains carbon-carbon double bond functional groups, which can polymerize to form high molecular compounds at high temperature, covering the surfaces of the positive and negative electrodes and the separator of the lithium-ion battery, increasing the interfacial impedance, blocking the transmission of lithium ions, resulting in battery open circuit, and preventing the further progress of battery thermal runaway.

[0056] This application does not limit the specific types of R1 and R2. Exemplarily, R1 is selected from H, and R2 is selected from any one of linear alkyls with C1-C6.

[0057] In a possible implementation manner, both R1 and R2 are independently selected from a hydrogen atom, a linear alkyl with C1-C6, a cycloalkyl with C3-C12, an alkenyl or alkynyl with C2-C6, a cyclic alkenyl with C6-C12. Exemplarily, R1 is selected from hydrogen, and R2 is selected from a linear alkyl with C6. Exemplarily, R1 is selected from a cycloalkyl with C3, and R2 is selected from a linear alkyl with C2.

[0058] Exemplarily, both R1 and R2 are selected from H. Further, this application also provides a preparation method of the additive, including:

[0059] S1. Obtain an intermediate, and the intermediate is shown in formula (2):

[0060]

[0061] S2. Mix the intermediate with the compound shown in formula (3), and at a temperature of 23-27 °C, react the chloro group of formula (2) with the hydroxyl group of formula (3); the structure of formula (3) is as follows:

[0062]

[0063] Wherein, R1 and R2 in formula (3) correspond to R1 and R2 in formula (1), and both R1 and R2 are independently selected from a hydrogen atom, a fluorine-substituted or unsubstituted linear alkyl with C1-C6, a cycloalkyl with C3-C12, an alkenyl or alkynyl with C2-C6, a cyclic alkenyl with C6-C12, a cyano group, a nitrile group with C1-C5, a methoxy group, an ethoxy group, a phenyl group, a benzene ring derivative group, and a five-membered or six-membered heterocyclic group.

[0064] Exemplarily, R1 is selected from one of fluorine-substituted linear alkyls with C1-C6, and R2 is selected from one of cyclic alkenyls with C6-C12. For example, R1 is selected from a fluorine-substituted linear alkyl with C6, and R2 is selected from a cyclic alkenyl with C6.

[0065] Exemplarily, R1 is selected from one of the cyano groups having 1 to 5 carbon atoms, and R2 is selected from methoxy. Exemplarily, R1 is selected from phenyl, and R2 is selected from one of the five- or six-membered heterocyclic groups. For example, if R1 is selected from phenyl, R2 is selected from the five-membered heterocyclic group of the benzene ring.

[0066] Further, the method for preparing the intermediate includes:

[0067] React POCl3 with 1,2-glycerol carbonate at 0 to 3 °C.

[0068] Further, POCl3, 1,2-glycerol carbonate, chloroform, triethylamine, and 4-dimethylaminopyridine (DMAP) catalyst can be mixed and reacted at a temperature of 0 to 3 °C to obtain the intermediate.

[0069] Further, during the reaction, the reactants can be stirred.

[0070] Exemplarily, nitrogen bubbling can be employed. The waste gas generated during the nitrogen bubbling process is absorbed using a NaOH solution.

[0071] Further, the reaction stock solution after the reaction can be distilled to remove impurities and washed.

[0072] Exemplarily, ether can be used for washing.

[0073] Exemplarily, in step S2, dichloromethane, the intermediate, vinyl alcohol, triethylamine, and 4-dimethylaminopyridine (DMAP) catalyst are placed into a reaction kettle, stirred, and nitrogen is bubbled until the atmosphere in the kettle is nitrogen, and the tail gas is absorbed using a 2 mol / L NaOH solution. The reaction stock solution after the reaction is heated to 100 °C and distilled under reduced pressure to remove impurities, and the product is washed and filtered with ether, and the washing solvent is removed under reduced pressure at room temperature to obtain the additive.

[0074] Further, in the electrolyte, the additive accounts for 0.1% to 20% of the total mass of the electrolyte.

[0075] Exemplarily, the additive accounts for one of 0.1%, 1%, 5%, 10%, or 20% of the weight of the electrolyte or within the range between any two of them.

[0076] Further, the electrolyte further contains an auxiliary additive.

[0077] The auxiliary additive is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, allyl-1,3-sulfonic acid lactone, ethylene sulfate, propylene sulfate, butene sulfite, vinylene carbonate, fluoroethylene carbonate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium difluorophosphate, and lithium tetrafluoroborate.

[0078] The present application does not limit the specific type of solvent. In some possible embodiments, the solvent is a carbonate, a carboxylate, a sulfate, or a fluorinated derivative thereof.

[0079] Exemplarily, the solvent is selected from at least one of ethylene carbonate, fluorinated ethylene carbonate, propylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, ethyl methyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, (2,2,2)-trifluoroethyl carbonate, ethyl acetate, ethyl difluoroacetate, propyl propionate, sultone, vinylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, methyl formate, methyl acrylate, and methyl butyrate.

[0080] The present application does not limit the specific type of lithium salt. In some possible embodiments, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium difluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium hexafluoroaluminate, lithium bis(trifluoromethylsulfonyl)imide, lithium hexafluoroarsenate, and perfluoroalkylsulfonylmethyl lithium.

[0081] Furthermore, the lithium salt accounts for 10-20% of the total mass of the electrolyte.

[0082] Exemplarily, the lithium salt accounts for any one or the range between any two of 10%, 11%, 15%, 18%, or 20% of the total mass of the electrolyte.

[0083] Furthermore, the present application does not limit the specific type of the positive electrode active material in the positive electrode sheet. In one possible embodiment, the positive electrode active material is a transition metal phosphate, a transition metal oxide lithium salt, lithium titanate Li4Ti5O 12 , or a combination of one or more of transition metal sulfides.

[0084] Furthermore, the materials for preparing the positive electrode sheet further include a binder and a conductive agent.

[0085] The preparation method of the positive electrode sheet includes a coating method.

[0086] Exemplarily, the positive electrode preparation steps include: mixing a high-nickel ternary material, conductive carbon black, and a binder polyvinylidene fluoride in a mass ratio of 96.8:2.0:1.2, dispersing in N-methyl-2-pyrrolidone to obtain a positive electrode slurry, uniformly coating the positive electrode slurry on both sides of an aluminum foil, drying, rolling, and vacuum drying, and then welding an aluminum positive electrode tab with an ultrasonic welder to obtain a positive electrode sheet with a thickness between 100 and 150 μm.

[0087] Furthermore, the present application does not limit the specific type of the negative electrode active material in the negative electrode sheet. In one possible embodiment, the negative electrode active material of the negative electrode sheet is at least one of a carbon material, a silicon material, a silicon-tin alloy material, a silicon-carbon material, and a silicon-oxygen material.

[0088] Exemplarily, the steps for preparing the negative electrode are as follows: Graphite, conductive carbon black, binder styrene-butadiene rubber, and carboxymethyl cellulose are mixed in a mass ratio of 95:1.5:1.5:2, dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil, dried, rolled, and vacuum-dried. After welding a nickel negative electrode tab with an ultrasonic welder, a negative electrode sheet with a thickness between 150 and 250 μm is obtained.

[0089] Furthermore, the present application does not limit the specific type of the separator. In some possible embodiments, the separator includes a porous polymer membrane, a non-woven fabric separator, and an inorganic composite membrane.

[0090] Furthermore, the method for preparing the lithium-ion battery further includes battery assembly. Exemplarily, a positive electrode sheet, a negative electrode sheet, and a PE ceramic separator are wound to obtain an electrode core. The electrode core is placed in an aluminum-plastic film for encapsulation, dried, injected with an electrolyte and sealed, and then subjected to processes such as standing, formation, secondary sealing, and grading.

[0091] The following further describes the electrolyte and the lithium battery of the present application in detail with reference to embodiments.

[0092] Example 1

[0093] Example 1 of the present application provides a lithium battery, including an electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator, which is obtained by the following method:

[0094] (1) Preparation of the electrolyte

[0095] Ethylene carbonate (abbreviated as EC): Diethyl carbonate (abbreviated as DEC): Dimethyl carbonate (abbreviated as EMC) are mixed in a weight ratio of 1:1:1 to obtain a mixed solvent; then 0.5% by mass of an additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxy)allyl compound), 0.5% vinylene carbonate (abbreviated as VC), 1% fluoroethylene carbonate (abbreviated as FEC), and 1% 1,3-propane sultone (abbreviated as PS) are added to obtain a battery electrolyte; the lithium salt LiPF6 is 1 mol / L. The specific components of the electrolyte are shown in Table 1.

[0096] (2) Preparation of the positive electrode sheet

[0097] Mix high-nickel ternary material, conductive carbon black, and binder polyvinylidene fluoride in a mass ratio of 96.8:2.0:1.2, disperse them in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. Coat the positive electrode slurry evenly on both sides of aluminum foil, dry, calender, and vacuum dry it. After welding an aluminum positive electrode tab with an ultrasonic welder, a positive electrode sheet with a thickness between 100 and 150 μm is obtained. Among them, the positive electrode active material is a high-nickel ternary material purchased from Guizhou Zhenhua or Shenzhen BTR.

[0098] (3) Preparation of negative electrode sheet

[0099] Mix graphite, conductive carbon black, binder styrene-butadiene rubber, and carboxymethyl cellulose in a mass ratio of 95:1.5:1.5:2, disperse them in deionized water to obtain a negative electrode slurry. Coat the negative electrode slurry on both sides of copper foil, dry, calender, and vacuum dry it. After welding a nickel negative electrode tab with an ultrasonic welder, a negative electrode sheet with a thickness between 150 and 250 μm is obtained.

[0100] Among them, the negative electrode active material is artificial graphite purchased from Shenzhen BTR.

[0101] (4) Battery assembly

[0102] The assembly steps of the high-nickel ternary lithium battery are as follows: Wind the positive electrode sheet, negative electrode sheet, and PE ceramic separator to obtain an electrode core, place the electrode core in an aluminum-plastic film for encapsulation, dry it, inject electrolyte and seal it. After processes such as standing, formation, secondary sealing, and grading, a lithium-ion battery is obtained.

[0103] Among them, the separator is purchased from Xingyuan Materials, and it is a PE-coated ceramic separator with a thickness of 20 μm.

[0104] Example 2

[0105] The lithium battery provided in Example 2 of this application is different from that in Example 1 in that:

[0106] In the electrolyte, adjust the addition amount of the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxy)propenyl compound) to 1%, reduce the solvent ratio, and adjust the ratio of (EC:EMC:DEC = 1:1:1) to the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxy)propenyl compound) to 99:1, and keep other reagents and lithium salts unchanged. The specific components of the electrolyte are shown in Table 1.

[0107] Example 3

[0108] The lithium battery provided in Example 3 of this application is different from that in Example 1 in the electrolyte in that:

[0109] Adjust the addition amount of the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxypropyl acrylate) to 3%, reduce the solvent ratio, and adjust the ratio of (EC:EMC:DEC = 1:1:1) to the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxypropyl acrylate) to 97:3, while keeping other reagents and lithium salts unchanged. The specific composition of the electrolyte is shown in Table 1.

[0110] Example 4

[0111] Example 4 of this application provides a lithium battery. The difference in the electrolyte from that of Example 1 is as follows:

[0112] Adjust the addition amount of the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxypropyl acrylate) to 5%, reduce the solvent ratio, and adjust the ratio of (EC:EMC:DEC = 1:1:1) to the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxypropyl acrylate) to 95:5, while keeping other reagents and lithium salts unchanged. The specific composition of the electrolyte is shown in Table 1.

[0113] Example 5

[0114] Example 5 of this application provides a lithium battery. The difference in the electrolyte from that of Example 1 is as follows:

[0115] Adjust the addition amount of the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxypropyl acrylate) to 10%, reduce the solvent ratio, and adjust the ratio of (EC:EMC:DEC = 1:1:1) to the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxypropyl acrylate) to 90:10, while keeping other reagents and lithium salts unchanged. The specific composition of the electrolyte is shown in Table 1.

[0116] Example 6

[0117] Example 6 of this application provides a lithium battery. The difference in the electrolyte from that of Example 1 is as follows:

[0118] Adjust the addition amount of the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxypropyl acrylate) to 15%. Adjust the solvent ratio, and adjust the ratio of (EC:EMC:DEC = 1:1:1) to the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxypropyl acrylate) to 85:15, while keeping other reagents and lithium salts unchanged. The specific composition of the electrolyte is shown in Table 1.

[0119] Example 7

[0120] Example 7 of this application provides a lithium battery. The difference in the electrolyte from that of Example 1 is as follows:

[0121] Adjust the addition amount of the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxy)propenyl compound) to 20%. Adjust the solvent ratio, and adjust the ratio of (EC:EMC:DEC = 1:1:1) to the additive (2-(bis(2-oxo-1,3-dioxolan-4-yl)methoxy)phosphoryloxy)propenyl compound) to 80:20, and keep other reagents and lithium salts unchanged. The specific components of the electrolyte are shown in Table 1.

[0122] Example 8

[0123] Example 8 of this application provides a lithium battery. The difference in the electrolyte from that of Example 5 is only as follows:

[0124] Adjust the mixed solvent to EC:DEC:FEMC (the Chinese name of FEMC is methyl trifluoroethyl carbonate) = 1:1:1, and keep other conditions unchanged. The specific components of the electrolyte are shown in Table 1.

[0125] Example 9

[0126] This application example provides a lithium battery. The difference in the electrolyte from that of Example 5 is only as follows:

[0127] Adjust the mixed solvent to EC:DEC = 1:2, and keep other conditions unchanged. The specific components of the electrolyte are shown in Table 1.

[0128] Comparative Example 1

[0129] Comparative Example 1 of this application provides a lithium battery. The difference in the electrolyte from that of Example 1 is as follows:

[0130] The electrolyte solvent is EC:EMC:DEC = 1:1:1, without adding compound additives, and keep other conditions unchanged. The specific components of the electrolyte are shown in Table 1.

[0131] Comparative Example 2

[0132] Comparative Example 2 of this application provides a lithium battery. The difference in the electrolyte from that of Example 1 is as follows:

[0133] The electrolyte solvent is EC:EMC:DEC = 1:1:1, adding 10% of triethyl phosphate, and keep other conditions unchanged. The specific components are shown in Table 1.

[0134] Comparative Example 3

[0135] Comparative Example 3 of this application provides a lithium battery. The difference in the electrolyte from that of Example 1 is as follows:

[0136] The electrolyte solvent is EC:EMC:DEC = 1:1:1, 10% of pentafluoroethoxyphosphazene is added, and the others remain unchanged. The specific components of the electrolyte are shown in Table 1.

[0137] Table 1

[0138]

[0139]

[0140] Test Example 1: Cycle performance test of lithium-ion battery

[0141] At 25 °C and 45 °C respectively, the lithium-ion batteries of Examples 1-9 and Comparative Examples 1-3 are first charged at a constant current of 1C to a voltage of 4.4 V, then charged at a constant voltage until the current is 0.05C, and then discharged at a constant current of 1C to 2.75 V, and a 500-cycle charge-discharge test is carried out to detect the discharge capacity of the 500th cycle. The test results are shown in Table 2.

[0142] Among them, the capacity retention rate = (the discharge capacity of the 500th cycle / the first discharge capacity) * 100%.

[0143] Test Example 2: Self-extinguishing time test of electrolyte

[0144] Take a PP or PE separator with a length * width size of 20 cm * 40 cm, immerse the entire separator in the electrolyte sample for 5 min, then use tweezers to take out the separator soaked in the electrolyte, use a lighter to ignite the separator soaked in the electrolyte, and record the combustion situation of the separator soaked in the electrolyte and the time from combustion to automatic extinguishing. The test results are shown in Table 2.

[0145] Table 2

[0146]

[0147] Result analysis: In the lithium battery provided by the present application, the self-extinguishing time of the electrolyte is relatively fast or non-combustible, and it has good flame retardancy. At the same time, by using the electrolyte provided by the present application, the lithium battery can also maintain high cycle stability.

[0148] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrolyte, characterized in that, The electrolyte includes a solvent, a lithium salt, and an additive; the additive is a 2-(bis(2-oxo-1,3-dioxo-4-yl)methoxy)phosphoryloxypropenyl compound represented by formula (1): ； Wherein, R1 and R2 are each independently selected from a hydrogen atom, a fluorine-substituted or unsubstituted C1-C6 linear alkyl group, a C3-C12 cycloalkyl group, a C2-C6 alkenyl or alkynyl group, a C6-C12 cyclic alkenyl group, a cyano group, a C1-C5 nitrile group, a methoxy group, an ethoxy group, a phenyl group, a benzene ring derivative group, and a five- or six-membered heterocyclic group; The additive accounts for 0.1% to 20% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that In the additive, R1 and R2 are each independently selected from a hydrogen atom, a C1-C6 linear alkyl group, a C3-C12 cycloalkyl group, a C2-C6 alkenyl or alkynyl group, a C6-C12 cyclic alkenyl group.

3. The electrolyte according to claim 2, characterized in that In the additive, R1 and R2 are each independently selected from a hydrogen atom, a C1-C6 linear alkyl group, a C3-C12 cycloalkyl group.

4. The electrolyte according to claim 2, characterized in that, In the additive, R1 and R2 are both selected from a hydrogen atom.

5. The electrolyte according to claim 2, wherein The solvent is a carbonate, a carboxylate, a sulfate, or a fluorinated derivative solvent thereof.

6. The electrolyte according to claim 5, characterized in that, The solvent is selected from at least one of ethylene carbonate, fluorinated ethylene carbonate, propylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate, ethyl methyl carbonate, methyl trifluoroethyl carbonate, diethyl carbonate, (2,2,2)-trifluoroethyl carbonate, ethyl acetate, difluoroethyl acetate, propyl propionate, sultone, vinylene sulfite, propylene sulfite, methyl sulfide, diethyl sulfite, methyl formate, methyl acrylate, and methyl butyrate.

7. The electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium difluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium hexafluoroaluminate, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluoroarsenate, and lithium perfluoroalkylsulfonylmethyl.

8. The electrolyte according to claim 7, characterized in that, The lithium salt accounts for 10 to 20% of the total mass of the electrolyte.

9. The electrolyte according to claim 1, wherein The electrolyte further includes an auxiliary additive; the auxiliary additive is at least one of 1,3-propane sultone, 1,4-butane sultone, allyl-1,3-sultone, vinylene sulfate, propylene sulfate, butene sulfite, vinylene carbonate, fluorinated ethylene carbonate, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium difluorophosphate, and lithium tetrafluoroborate.

10. A method for preparing an electrolyte, characterized in that, The preparation method includes: mixing a solvent, a lithium salt, and an additive to form an electrolyte; the additive is a 2-(bis(2-oxo-1,3-dioxo-4-yl)methoxy)phosphoryloxypropenyl compound represented by formula (1): ； The preparation method further includes the preparation of the additive: Step A: Obtain an intermediate represented by formula (2): ； Step B: React the intermediate with formula (3) at a temperature of 23 to 27 °C, and the chloro group of formula (2) reacts with the hydroxyl group of formula (3); the structure of formula (3) is: ； Among them, R1 and R2 in formula (1) correspond one by one to R1 and R2 in formula (3), and both R1 and R2 are independently selected from a hydrogen atom, a fluorine-substituted or unsubstituted C1-C6 linear alkyl group, a C3-C12 cycloalkyl group, a C2-C6 alkenyl or alkynyl group, a C6-C12 cyclic alkenyl group, a cyano group, a C1-C5 nitrile group, a methoxy group, an ethoxy group, a phenyl group, a benzene ring derivative group, and a five- or six-membered heterocyclic group; The additive accounts for 0.1% to 20% of the total mass of the electrolyte.

11. The preparation method according to claim 10, wherein The step A includes: Reacting POCl3 with 1,2-carbonic glycerol at 0 to 3 °C; In the step B, the formula (3) is vinyl alcohol.

12. The preparation method according to claim 11, characterized in that, Reacting the POCl3, the 1,2-carbonic glycerol, chloroform, and triethylamine under the action of a 4-dimethylaminopyridine (DMAP) catalyst at a temperature of 0 to 3 °C; distilling and removing impurities from the reaction stock solution, and washing.

13. The preparation method according to claim 11, wherein, Reacting the intermediate, the vinyl alcohol, chloroform, and triethylamine under the action of a 4-dimethylaminopyridine (DMAP) catalyst at a temperature of 23 to 27 °C.

14. A lithium battery, characterized in that, The lithium battery includes the electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator according to any one of claims 1-9.

15. The lithium battery according to claim 14, characterized in that, The positive active material of the positive electrode sheet is selected from at least one of transition metal phosphates, transition metal oxide lithium salts, lithium titanate Li4Ti5O 12 , and transition metal sulfides.

16. The lithium battery according to claim 15, wherein, The negative electrode active material of the negative electrode sheet is selected from at least one of a carbon material, a silicon material, a silicon-tin alloy material, a silicon-carbon material, and a silicon-oxygen material.

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