Lithium ion battery and preparation method thereof

Abstract

The invention provides a lithium ion battery and a preparation method thereof. According to the battery and the preparation method, a composite lithium metal negative electrode comprises lithium metal and lithium nitrate attached to the surface of the lithium metal; the gel polymer electrolyte is prepared from the following components in percentage by mass: 1 to 10 weight percent of comonomer, 60 to 85 weight percent of organic solvent, 5 to 20 weight percent of lithium salt and 0 to 10 weight percent of additive, the organic solvent comprises cyclic fluorocarbonate, chain fluorocarbonate and a fluoroether compound; the comonomer is an acrylate monomer; and the mass ratio of lithium nitrate in the composite lithium metal negative electrode is less than or equal to 25%. According to the lithium ion battery, lithium nitrate attached to the surface of lithium metal can be decomposed into Li3N on the surface of the negative electrode, and a stable and uniform Li3N-rich SEI film is formed. And the three solvents are fluorinated solvents, so that the lithium ion battery has high energy density and excellent normal-temperature and high-temperature cycle performance at the same time under the action of the two aspects.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and more particularly, to a lithium-ion battery and a method for preparing the same. Background Art

[0002] With the popularization of consumer electronic products such as laptop computers, mobile phones, handheld game consoles, tablet computers, mobile power supplies, and drones, people's requirements for the electrochemical devices (e.g., batteries) therein are becoming increasingly stringent. For example, people not only require the battery to be lightweight, but also require the battery to have a short charging time and a long working life. Among various batteries, lithium metal batteries have attracted much attention in the R & D field due to their highest energy density. At present, how to improve the cycle performance of lithium metal batteries has become the focus of research and development in the field of lithium metal batteries.

[0003] By using a combination of an artificial solid electrolyte membrane (SEI) composite lithium metal anode, a gel electrolyte, and a novel lithium metal electrolyte solution, it is possible to achieve a high energy density of a lithium-ion battery while achieving long cycles at room temperature (25 °C) and high temperature (45 °C).

[0004] The specific capacity of lithium metal as the anode can reach 3860 mAh / g, which is more than ten times higher than the theoretical specific capacity of current graphite, 372 mAh / g. However, lithium metal has the lowest chemical potential (-3.04 V) and very high reactivity, and will react with the electrolyte solution in the battery, consuming the lithium source lithium, increasing the impedance of the battery, and finally leading to cycle failure. Therefore, although the energy density can be greatly improved when using metal as the anode material of the battery, the cycle life will also be sharply shortened.

[0005] There are two important directions for improving the cycle performance of lithium metal batteries: 1. Form a stable solid electrolyte membrane (SEI) on the surface of the lithium metal anode. A uniform and stable SEI can reduce the reactivity between lithium metal and the electrolyte solution, and can also inhibit the formation of lithium dendrites, effectively improving the cycle performance of the battery. The formation of SEI can be obtained by adjusting the components of the electrolyte solution after reduction on the surface of the anode, or can be artificially synthesized on the surface of the anode. 2. Develop an electrolyte with a lower reactivity with the lithium metal anode. The electrolyte can be liquid, gel, or all-solid. After the reactivity between the electrolyte and lithium metal is reduced, the cycle Coulomb efficiency and cycle life of the battery can be effectively improved. Summary of the Invention

[0006] The main object of the present invention is to provide a lithium-ion battery and a method for preparing the same, so as to solve the problem in the prior art that it is difficult for a lithium-ion battery to simultaneously achieve both a high energy density and excellent cycle performance at room temperature and high temperature.

[0007] To achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a lithium-ion battery, comprising a composite lithium metal negative electrode, a positive electrode plate and a gel polymer electrolyte, wherein the composite lithium metal negative electrode comprises lithium metal and lithium nitrate attached to the surface of the lithium metal; in terms of mass percentage, the gel polymer electrolyte comprises: 1 to 10 wt% of a comonomer, 60 to 85 wt% of an organic solvent, 5 to 20 wt% of a lithium salt and 0 to 10 wt% of an additive; wherein the organic solvent comprises a cyclic fluorocarbonate, a chain fluorocarbonate and a fluoroether compound; the comonomer is an acrylate monomer; and the mass proportion of lithium nitrate in the composite lithium metal negative electrode is ≤25%.

[0008] Furthermore, the mass proportion of lithium nitrate in the above-mentioned composite lithium metal negative electrode is 2-20%.

[0009] Furthermore, the organic solvent comprises, by mass percentage, 1 to 40 parts of cyclic fluorocarbonate, 1 to 70 parts of chain fluorocarbonate and 1 to 40 parts of fluoroether compound; wherein the chemical formula of the cyclic fluorocarbonate is as shown in Formula I:

[0010]

[0011] R 1 , R 2 , R 3 and R 4 are independently selected from hydrogen, fluorine, C 1 ~C 12 Alkyl, C 1 ~C 12 Fluorinated alkyl, C 3 ~C 12 Cycloalkyl, C 3 ~C 12 Fluorinated cycloalkyl, C 2 ~C 12 The alkenyl group, C 2 ~C 12 Fluoroalkenyl, C 3 ~C 12 The heterocyclic group and C 3 ~C 12 Any one of the fluorinated heterocyclic groups of 1 , R 2 , R 3 and R 4 At least one of which is selected from fluorine atoms, C 1 ~C 12 Fluorinated alkyl, C 3 ~C 12 Fluorinated cycloalkyl, C 2 ~C 12 Fluoroalkenyl and C 3 ~C12 Any one of the substituents in the fluoroheterocyclic group; preferably, R 1 , R 2 , R 3 and R 4 each independently selected from hydrogen, fluorine atom, C 1 to C 6 alkyl, C 1 to C 6 fluoroalkyl, C 3 to C 6 cycloalkyl, C 3 to C 6 fluoro-cycloalkyl, C 2 to C 6 alkenyl, C 2 to C 6 fluoroalkenyl, C 3 to C 6 heterocyclic group and C 3 to C 6 fluoroheterocyclic group, and at least one of R 1 , R 2 , R 3 and R 4 is selected from fluorine atom, C 1 to C 6 fluoroalkyl, C 3 to C 6 fluoro-cycloalkyl, C 2 to C 6 fluoroalkenyl and C 3 to C 6 any one of the substituents in the fluoroheterocyclic group; preferably, the cyclic fluorocarbonate is selected from any one or more of ; and / or, the chemical general formula of the chain fluorocarbonate is shown in Formula II:

[0012]

[0013] Wherein, R 5 and R 6 each independently selected from hydrogen, fluorine atom, C 1 to C 12 alkyl, C 1 to C 12 fluoroalkyl, C 1 to C 12 alkoxy, C 1 to C 12 fluoroalkoxy, C 2 to C 12 alkenyl, C 2 to C 12 fluoroalkenyl, C 6 to C26 aryl, C 6 ~C 26 any one of fluoroaryl, and R 5 and R 6 at least one of them is selected from C 1 ~C 12 fluoroalkyl, C 1 ~C 12 fluoroalkoxy, C 2 ~C 12 fluoroalkenyl and C 6 ~C 26 any one of fluoroaryl substituents; preferably, R 5 and R 6 each independently selected from hydrogen, fluorine atom, C 1 ~C 6 alkyl, C 1 ~C 6 fluoroalkyl, C 1 ~C 6 alkoxy, C 1 ~C 6 fluoroalkoxy, C 2 ~C 6 alkenyl, C 2 ~C 6 fluoroalkenyl, C 6 ~C 12 aryl, C 6 ~C 12 any one of fluoroaryl, and R 5 and R 6 at least one of them is selected from C 1 ~C 6 fluoroalkyl, C 1 ~C 6 fluoroalkoxy, C 2 ~C 6 fluoroalkenyl and C 6 ~C 12 any one of fluoroaryl substituents; preferably, the chain fluoro carbonate is selected from

[0014] any one or more of them; and / or, the chemical general formula of the fluoroether compound is shown in Formula III:

[0015]

[0016] R 7 and R 8 each independently selected from C 1 ~C 10 haloalkyl, C 1 ~C10 any one of haloalkoxy groups having C 2 ~C 10 ; preferably, R 7 and R 8 are each independently selected from haloalkyl groups having C 1 ~C 6 , haloalkoxy groups having C 1 ~C 6 , and haloalkenyl groups having C 2 ~C 6 ; preferably, the fluoroether compound is

[0017] Further, the above-mentioned comonomer includes an acrylate monomer with a network crosslinked structure and a chain-like acrylate monomer. Among them, the acrylate monomer with a network crosslinked structure is ethoxylated trimethylolpropane triacrylate and / or trimethylolpropane triacrylate; and / or, the chain-like acrylate monomer is selected from any one or more of ethyl acetoacetate methacrylate, methyl methacrylate, ethyl acrylate, and decyl acrylate; and / or, the mass ratio of the acrylate monomer with a network crosslinked structure to the chain-like acrylate monomer is 1:(0.1~20).

[0018] Further, the above-mentioned lithium salt is selected from any one or more of lithium perchlorate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium dioxalate borate, lithium difluorooxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium difluorophosphate.

[0019] Further, the above-mentioned additive is selected from any one or more of fluorinated ethylene carbonate, vinylene ethylene carbonate, lithium dioxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, methylene methanedisulfonate, 4-trifluoromethyl ethylene carbonate, 1,3,2-dioxazolothiophene-2,2-dioxide, fluorinated ethylene carbonate, ethylene sulfite, vinylene carbonate, succinic anhydride, propylene sulfite, allyl-1,3-sultone, bis(trimethylsilyl) sulfate, lithium nitrate, N-methyl-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt, N-methyl-propylpiperidinium bis(trifluoromethanesulfonyl)imide salt, 1,3-dioxane, 1,4-dioxane, 1,2-bis(cyanoethoxy)ethane, adiponitrile, 1,3,5-pentanetricarbonitrile, fumarodinitrile, and 1,2,3-tris(2-cyanoethoxy)propane.

[0020] According to another aspect of the present invention, there is provided a method for preparing the above-mentioned lithium-ion battery. The preparation method includes: Step S1, mixing lithium nitrate with oil to obtain a mixed solution, coating the mixed solution on a rolling device, and mechanically rolling a lithium metal elemental matrix with the rolling device to obtain a composite lithium metal negative electrode; Step S2, mixing raw materials including a comonomer, an organic solvent, a lithium salt, and an additive to obtain a mixed liquid; Step S3, stacking the positive electrode, the separator, and the composite lithium metal negative electrode in sequence to obtain a stacked component, welding the electrode tabs, placing the stacked component in an aluminum plastic film, and successively performing vacuum packaging, injecting the mixed liquid, standing and in-situ polymerization, and formation to obtain a lithium-ion battery.

[0021] Further, in the above-mentioned Step S1, the mass ratio of lithium nitrate in the mixed solution is 2-20%; and / or, the oil is selected from Group I base oil and / or fatty oil; and / or, during the mechanical rolling process, the total deformation amount of the thickness of the lithium metal elemental matrix is 5-100%, and the water content in the mechanical rolling environment is <0.5 ppm.

[0022] Further, in the above-mentioned Step S2, the raw materials further include an initiator, and the initiator is azobisisobutyronitrile and / or azobisisoheptonitrile.

[0023] Further, in the above-mentioned Step S3, the temperature of the in-situ polymerization is 45-80 °C, and / or the time of the in-situ polymerization is 2-24 h.

[0024] Applying the technical solution of the present application, on the one hand, lithium nitrate attached to the surface of the lithium metal in the lithium-ion battery can decompose into Li 3 N on the surface of the negative electrode to form a stable and uniform SEI film rich in Li 3 N. This SEI film rich in Li 3 N is considered to be able to effectively promote uniform lithium deposition / stripping, inhibit the formation of lithium dendrites and dead lithium due to its high lithium ion conduction amount, low resistance conductivity, and high Young's modulus, thereby improving the cycle stability of the battery. On the other hand, all three solvents are fluorinated solvents. Among them, cyclic fluorinated carbonate has good solubility for lithium salts and can also form an organic polymer SEI containing C and O on the surface of the negative electrode. It can exhibit good performance when combined with inorganic LiF and Li 3 N. Chain-like fluorinated carbonate can participate in forming a film rich in F on the positive electrode and the negative electrode, and can also adjust the viscosity of the electrolyte. When used in combination with cyclic fluorinated carbonate, it helps to reduce the reaction activity of the electrolyte on the positive electrode and is beneficial to the long cycle of the battery. Fluoroether compounds have very good solubility for lithium ions and are the main solvents for transporting lithium. When solvating lithium, they form a stable five-membered ring structure, which is beneficial to improving the ability of the battery to solvate lithium. Through the above two aspects of effects, the lithium-ion battery can simultaneously achieve high energy density and excellent normal temperature and high temperature cycle performance. Detailed implementation manners

[0025] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0026] As analyzed in the background art of the present application, in the prior art, lithium-ion batteries have the problem that it is difficult to simultaneously achieve high energy density and excellent room-temperature and high-temperature cycle performance. To solve this problem, the present application provides a lithium-ion battery and a preparation method thereof.

[0027] In a typical implementation manner of the present application, a lithium-ion battery is provided, which includes a composite lithium metal negative electrode, a positive electrode sheet, and a gel polymer electrolyte. The composite lithium metal negative electrode includes lithium metal and lithium nitrate attached to the surface of the lithium metal. By mass percentage, the gel polymer electrolyte includes: 1-10 wt% of a comonomer; 60-85 wt% of an organic solvent; 5-20 wt% of a lithium salt; 0-10 wt% of an additive. The organic solvent includes cyclic fluorinated carbonates, chain-like fluorinated carbonates, and fluoroether compounds; the comonomer is an acrylate monomer; the mass percentage of lithium nitrate in the composite lithium metal negative electrode ≤ 25%.

[0028] On the one hand, lithium nitrate attached to the surface of the lithium metal in the lithium-ion battery can decompose into Li 3 N on the surface of the negative electrode, forming a stable and uniform Li 3 N-rich SEI film. This Li 3 N-rich SEI film is considered to be able to effectively promote uniform lithium deposition / stripping, inhibit the formation of lithium dendrites and dead lithium due to its high lithium ion conduction amount, low resistance conductivity, and high Young's modulus, thereby improving the cycle stability of the battery. On the other hand, all three solvents are fluorinated solvents. Among them, cyclic fluorinated carbonates have good solubility for lithium salts and can also form an organic polymer SEI containing C and O on the surface of the negative electrode, which can exhibit good performance when combined with inorganic LiF and Li 3 N. Chain-like fluorinated carbonates can participate in forming an F-rich film on the positive and negative electrodes, and can also adjust the viscosity of the electrolyte. When used in combination with cyclic fluorinated carbonates, it helps to reduce the reaction activity of the electrolyte at the positive electrode, which is beneficial to the long cycle of the battery. Fluoroether compounds have very good solubility for lithium ions and are the main solvents for transporting lithium. When solvating lithium, they form a stable five-membered ring structure, which is beneficial to improving the ability of the battery to solvate lithium. Through the above two aspects of effects, the lithium-ion battery can simultaneously achieve high energy density and excellent room-temperature and high-temperature cycle performance.

[0029] In some embodiments of the present application, the mass percentage of lithium nitrate in the composite lithium metal negative electrode is 2-20%.

[0030] Lithium nitrate on the surface of the composite lithium metal anode decomposes during the electrochemical process after battery assembly to generate Li 3 N, which is an efficient and stable SEI film component. If the mass ratio of lithium nitrate is less than 2%, the amount of Li 3 N generated by its decomposition is not sufficient to form a dense SEI film, and cannot effectively inhibit the formation of lithium dendrites, resulting in poor cycling performance. On the contrary, if the mass ratio exceeds 20%, lithium nitrate will precipitate on the surface of lithium, which may not only reduce the stability of the electrolyte, but also lead to a locally too thick SEI film inside the battery, increasing the internal resistance of the battery and affecting the kinetic performance of the battery. Controlling the mass ratio of lithium nitrate at 2-20% helps to further optimize the surface structure of the composite lithium metal anode, form a more uniform and stable SEI film, effectively reduce the risk of electrolyte decomposition, and improve the cycling stability and energy efficiency of the battery.

[0031] In addition, the mass ratio of lithium nitrate in the composite lithium metal anode can be 2%, 3%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 13%, 15%, 18%, 19% or 20%. Of course, the mass ratio of lithium nitrate in the composite lithium metal anode can be any point value within 2%-20%. Preferably, the mass ratio of lithium nitrate in the composite lithium metal anode can be any point value within 2%-10%, which will not be elaborated here. In some embodiments of the present application, by mass percentage, the organic solvent includes: 1-40 parts of cyclic fluorocarbonate; 1-70 parts of linear fluorocarbonate; 1-40 parts of fluoroether compound; wherein, the chemical general formula of the cyclic fluorocarbonate is as shown in Formula I:

[0032]

[0033] R 1 、R 2 、R 3 and R 4 are each independently selected from any one of hydrogen, fluorine atom, C 1 -C 12 alkyl, C 1 -C 12 fluoroalkyl, C 3 -C 12 cycloalkyl, C 3 -C 12 fluorocycloalkyl, C 2 -C 12 alkenyl, C 2 -C 12 fluoroalkenyl, C 3 -C 12 heterocyclic group and C 3 -C 12 fluorinated heterocyclic group, and R1 , R 2 , R 3 and R 4 at least one of which is selected from a fluorine atom, C 1 ~C 12 fluorinated alkyl, C 3 ~C 12 fluorinated cycloalkyl, C 2 ~C 12 fluorinated alkenyl and C 3 ~C 12 fluorinated heterocyclic group of any one of the substituents; preferably, R 1 , R 2 , R 3 and R 4 each independently selected from hydrogen, a fluorine atom, C 1 ~C 6 alkyl, C 1 ~C 6 fluorinated alkyl, C 3 ~C 6 cycloalkyl, C 3 ~C 6 fluorinated cycloalkyl, C 2 ~C 6 alkenyl, C 2 ~C 6 fluorinated alkenyl, C 3 ~C 6 heterocyclic group and C 3 ~C 6 fluorinated heterocyclic group of any one, and R 1 , R 2 , R 3 and R 4 at least one of which is selected from a fluorine atom, C 1 ~C 6 fluorinated alkyl, C 3 ~C 6 fluorinated cycloalkyl, C 2 ~C 6 fluorinated alkenyl and C 3 ~C 6 fluorinated heterocyclic group of any one of the substituents; preferably, the cyclic fluorinated carbonate is selected from any one or more of; and / or, the chemical general formula of the chain fluorinated carbonate is shown in Formula II:

[0034]

[0035] wherein, R 5 and R 6 each independently selected from hydrogen, a fluorine atom, C 1 ~C 12 alkyl, C1 ~C 12 fluoroalkyl, C 1 ~C 12 alkoxy, C 1 ~C 12 fluoroalkoxy, C 2 ~C 12 alkenyl, C 2 ~C 12 fluoroalkenyl, C 6 ~C 26 aryl, C 6 ~C 26 fluoroaryl, any one of them, and R 5 and R 6 at least one of them is selected from C 1 ~C 12 fluoroalkyl, C 1 ~C 12 fluoroalkoxy, C 2 ~C 12 fluoroalkenyl and C 6 ~C 26 fluoroaryl, any one of them; preferably, R 5 and R 6 are each independently selected from hydrogen, fluorine atom, C 1 ~C 6 alkyl, C 1 ~C 6 fluoroalkyl, C 1 ~C 6 alkoxy, C 1 ~C 6 fluoroalkoxy, C 2 ~C 6 alkenyl, C 2 ~C 6 fluoroalkenyl, C 6 ~C 12 aryl, C 6 ~C 12 fluoroaryl, any one of them, and R 5 and R 6 at least one of them is selected from C 1 ~C 6 fluoroalkyl, C 1 ~C 6 fluoroalkoxy, C 2 ~C 6 fluoroalkenyl and C 6 ~C 12 fluoroaryl, any one of them; preferably, the chain - like fluorinated carbonate is selected from any one or more of; and / or, the general chemical formula of the fluoroether compound is shown in Formula III:

[0036]

[0037] R 7 and R 8 each independently selected from any one of C 1 ~C 10 haloalkyl, C 1 ~C 10 haloalkoxy, C 2 ~C 10 haloalkenyl; preferably, R 7 and R 8 each independently selected from any one of C 1 ~C 6 haloalkyl, C 1 ~C 6 haloalkoxy, C 2 ~C 6 haloalkenyl; preferably, the fluoroether compound is

[0038] The organic solvent system with the above specific ratio plays an important role in the gel polymer electrolyte, which affects the electrochemical performance and cycling stability of the lithium-ion battery. The specific technical effects and principles are as follows:

[0039] The cyclic fluorinated carbonate forms a SEI film rich in LiF and organic polymer on the surface of the negative electrode. LiF has good conductivity for lithium ions and high impedance for electrons, which helps to improve the stability of the SEI film and reduce the formation of lithium dendrites. The organic polymer component ensures the flexibility of the SEI film and reduces the rupture of the SEI film caused by volume changes during the charge and discharge process of the battery. However, too high a content of the cyclic fluorinated carbonate will increase the viscosity of the electrolyte and affect the transport of lithium ions, while too low a content may lead to insufficient formation of the SEI film, limiting its improvement effect on the battery performance. Therefore, controlling the content of the cyclic fluorinated carbonate within 1 to 40 parts is an important parameter for optimizing the SEI film components and maintaining the fluidity and electrochemical stability of the electrolyte. Among them, the content control of the cyclic fluorinated carbonate can be 1 part, 2 parts, 5 parts, 8 parts, 10 parts, 12 parts, 13 parts, 15 parts, 17 parts, 19 parts, 20 parts, 22 parts, 25 parts, 30 parts, 32 parts, 35 parts, 38 parts or 40 parts. Of course, the content of the cyclic fluorinated carbonate can be any point value within 1 to 40 parts, which will not be elaborated here.

[0040] An excessively high content of chain fluorinated carbonates may lead to a decrease in the solubility of other components (such as lithium salts) in the electrolyte, affecting the conductivity of the electrolyte and battery performance. Controlling the chain fluorinated carbonate content to 1 - 70 parts can effectively regulate the physical and chemical properties of the electrolyte, including reducing viscosity, increasing the solubility of lithium salts, and maintaining the supply of F elements required for SEI film formation. Among them, the content of chain fluorinated carbonates can be 1 part, 2 parts, 5 parts, 8 parts, 10 parts, 12 parts, 13 parts, 15 parts, 17 parts, 19 parts, 20 parts, 22 parts, 25 parts, 30 parts, 32 parts, 35 parts, 38 parts, 39 parts, 40 parts, 41 parts, 45 parts, 50 parts, 53 parts, 55 parts, 60 parts, 65 parts, 67 parts or 70 parts. Of course, the content of chain fluorinated carbonates can be any point value within 1 - 70 parts, which will not be elaborated here.

[0041] An excessively high content of fluoroether compounds may lead to an increase in the volatility of fluoroether compounds inside the battery, while an excessively low content of fluoroether compounds may affect the lithium ion transport rate. Maintaining the fluoroether compound content at 1 - 40 parts can make the electrolyte have a sufficiently high conductivity while reducing volatilization, enabling the battery to maintain excellent performance under different temperature conditions. Among them, the content of fluoroether compounds can be 1 part, 2 parts, 5 parts, 8 parts, 10 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 19 parts, 20 parts, 22 parts, 25 parts, 30 parts, 32 parts, 35 parts, 38 parts or 40 parts. Of course, the content of fluoroether compounds can be any point value within 1 - 40 parts, which will not be elaborated here.

[0042] In summary, controlling the specific content ratios of cyclic fluorinated carbonates, chain fluorinated carbonates, and fluoroether compounds within the above ranges not only optimizes the formation of the SEI film, improves the stability and flexibility of the SEI film, reduces the internal impedance of the battery, but also regulates the physical and chemical properties of the electrolyte, including viscosity, conductivity, and stability, thereby significantly improving the cycling performance and safety of lithium ion batteries under normal and high temperature conditions.

[0043] Furthermore, the specific types of the preferred cyclic fluorinated carbonates, chain fluorinated carbonates, and fluoroether compounds are more conducive to enhancing the synergistic cooperation among the three, thereby facilitating the improvement of the lithium solvation ability of the battery.

[0044] In some embodiments of the present application, the comonomer includes an acrylate monomer with a network crosslinked structure and a chain-like acrylate monomer. Among them, the acrylate monomer with a network crosslinked structure is ethoxylated trimethylolpropane triacrylate, and / or trimethylolpropane triacrylate; and / or, the chain-like acrylate monomer is selected from any one or more of ethyl acetoacetate methacrylate, methyl methacrylate, ethyl acrylate, and decyl acrylate; and / or, the mass ratio of the acrylate monomer with a network crosslinked structure to the chain-like acrylate monomer is 1:(0.1 - 20).

[0045] The acrylate monomer with a network crosslinked structure forms a three-dimensional network structure through self-crosslinking. This structure endows the gel polymer electrolyte with good mechanical strength and stability. This structure can effectively prevent the penetration of lithium dendrites and reduce the adverse effects of lithium dendrites on battery performance and safety. At the same time, the three-dimensional network structure can restrict the movement of the electrolyte, reduce the volatilization of the electrolyte, improve the retention rate of the electrolyte in the battery, and thus improve the stability of the battery under different temperature conditions. The chain-like acrylate monomer is mainly responsible for providing a path for lithium ions to transport in the electrolyte. Their chain-like structure allows lithium ions to flow freely in the polymer backbone, improving the conductivity of the electrolyte. However, if the proportion of the chain-like monomer is too high, the rigidity of the polymer framework may be insufficient, and it may not be able to effectively prevent the growth of lithium dendrites; while if the proportion of the chain-like monomer is too low, the flexibility of the copolymer is insufficient, and the ability to conduct lithium ions is insufficient, which may reduce the lithium ion transport ability and affect the kinetic performance of the battery. This solution can achieve a balance between flexibility and rigidity by optimizing the structure and proportion of the comonomer. Specifically, the flexible segment is used to transport lithium ions, and the rigid segment provides the hardness of the overall framework, thereby not only improving the effective transport of lithium ions but also providing sufficient mechanical strength to inhibit lithium dendrites, achieving the balance between the stability of the gel polymer electrolyte structure and the lithium ion transport performance, and further improving the cycle performance, kinetic performance, and safety of the battery, especially its performance at room temperature and high temperature, providing strong technical support for the development of high-energy-density lithium-ion batteries.

[0046] In addition, the copolymer framework formed by the above acrylate monomers can trap the electrolyte within the framework, reducing the reactivity of the electrolyte with the positive and negative electrodes, thereby improving the interfacial stability of the positive and negative electrodes, and can also reduce the usage amount of the electrolyte, thereby improving the long-cycle performance of the battery.

[0047] In some embodiments of the present application, the mass ratio of the acrylate monomer with the above-mentioned network cross-linked structure to the chain-like acrylate monomer can be 1:0.1, 1:0.5, 1:1, 1:2, 1:5, 1:8, 1:10, 1:12, 1:15, 1:18 or 1:20. Of course, the mass ratio of the acrylate monomer with the network cross-linked structure to the chain-like acrylate monomer can be any point value within 5% to 100%. Preferably, the total deformation amount of the thickness of the lithium metal elemental matrix can be any point value within 1:(0.1 to 20). Further preferably, the total deformation amount of the thickness of the lithium metal elemental matrix can be any point value within 1:(1 to 10), which will not be elaborated here. In some embodiments of the present application, the lithium salt is selected from any one or more of lithium perchlorate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate and lithium difluorophosphate.

[0048] The lithium salt mainly plays a role of providing lithium ions in the electrolyte, and its type and content directly affect the conductivity of the electrolyte. The preferably above-mentioned types of lithium salts have high lithium ion conductivity, which helps to improve the transmission rate of lithium ions inside the battery, thereby improving the charge-discharge performance and kinetic performance of the battery, reducing the internal resistance of the battery, and increasing the energy density and power density of the battery.

[0049] In some embodiments of the present application, the additive is selected from any one or more of fluorinated ethylene carbonate, ethylene carbonate, vinylene carbonate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, methylene methanedisulfonate, 4-trifluoromethyl ethylene carbonate, 1,3,2-dioxazolothiophene-2,2-dioxide, fluorinated ethylene carbonate, ethylene sulfite, vinylene carbonate, succinic anhydride, propylene sulfite, propylene-1,3-sultone, bis(trimethylsilyl) sulfate, lithium nitrate, N-methyl-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt, N-methyl-propylpiperidinium bis(trifluoromethanesulfonyl)imide salt, 1,3-dioxane, 1,4-dioxane, 1,2-bis(cyanoethoxy)ethane, adiponitrile, 1,3,5-pentanetricarbonitrile, fumarodinitrile and 1,2,3-tris(2-cyanoethoxy)propane.

[0050] The selection and use of the above-mentioned additive types have an important impact on the electrochemical performance, cycle stability and safety of the lithium-ion battery. By improving the characteristics of the SEI film and optimizing the electrolyte performance, the cycle performance, kinetic performance and safety of the battery are improved. The synergistic effect of these additives with the lithium salt, copolymer framework and artificial solid electrolyte membrane realizes the comprehensive improvement of the battery in terms of energy density, cycle stability and safety, and is an important part of the design of high-performance lithium metal batteries.

[0051] In another typical embodiment of the present application, a method for preparing a lithium-ion battery is provided. In step S1, lithium nitrate is mixed with oil to obtain a mixed solution. The mixed solution is coated on a rolling device, and after mechanically rolling a lithium metal single-element matrix using the rolling device, a composite lithium metal negative electrode is obtained. In step S2, raw materials including a comonomer, an organic solvent, a lithium salt, and an additive are mixed to obtain a mixed liquid. In step S3, a positive electrode, a separator, and the composite lithium metal negative electrode are stacked in sequence to obtain a stacked component. After welding the electrode tabs, the stacked component is placed in an aluminum-plastic film, and through vacuum packaging, injecting the mixed liquid, standing, in-situ polymerization, and formation in sequence, a lithium-ion battery is obtained.

[0052] In step S1, by dissolving lithium nitrate in a specific oil and uniformly coating it on the rolling device, the lithium metal matrix is processed by mechanical rolling. The key to this process is to uniformly distribute lithium nitrate on the surface of the lithium metal negative electrode, thereby laying the foundation for forming a SEI film rich in Li 3 N on the surface of the lithium metal negative electrode. This step can ingeniously solve the problems in the prior art that the solubility of lithium nitrate in the electrolyte is extremely low, resulting in insufficient formation of a SEI film rich in Li 3 N, and excessive addition will precipitate in the electrolyte. In step S2, the mixed liquid obtained by mixing the comonomer, the organic solvent, the lithium salt, and the additive provides a balance between rigidity and flexibility, effectively preventing the penetration of lithium dendrites while maintaining the fluidity of the electrolyte. In step S3, through the processes of vacuum packaging, injecting the mixed liquid, standing, and in-situ polymerization, a gel polymer electrolyte is formed, and the structure of the lithium-ion battery is improved. The formation process further improves the stability of the SEI film and the electrochemical performance of the battery. This series of assembly and preparation steps ensure the close contact between the components inside the battery and the uniform distribution of the electrolyte inside the battery. The lithium-ion battery obtained by the above preparation method can take into account both high energy density and excellent normal-temperature and high-temperature cycle performance.

[0053] In some embodiments of the present application, in step S1, the mass ratio of lithium nitrate in the mixed solution is 2-20%; and / or, the oil is selected from Group I base oil and / or fatty oil; and / or, during the mechanical rolling process, the total deformation of the thickness of the lithium metal single-element matrix is 5-100%, and the water content in the mechanical rolling environment is <0.5 ppm.

[0054] If the addition amount of lithium nitrate is too small, its concentration is insufficient to form a SEI film rich in Li 3The SEI film of N will limit the protective effect of the SEI film on the lithium metal surface, increase the probability of side reactions inside the battery, and thus affect the cycle performance and safety of the battery; if the addition amount of lithium nitrate is too large, lithium nitrate may precipitate on the lithium surface, which not only affects the uniformity and stability of the SEI film, but also may cause damage to the internal structure of the battery and reduce the performance consistency of the battery. Class I base oil, fatty oil or their mixed oil can provide good coating property and compatibility on the lithium metal surface, promote the uniform distribution of lithium nitrate, and form an effective SEI film. By precisely controlling the mass ratio of lithium nitrate, the selection of oils, the deformation amount of the lithium metal matrix, and the water content in the mechanical rolling environment, lithium nitrate is added to the oil that must be used when rolling the lithium strip, and lithium nitrate is uniformly coated on the lithium metal surface through the process of preparing the lithium strip. After the battery is assembled, lithium nitrate can decompose into Li 3 N on the negative electrode surface to form a stable and uniform SEI, thereby improving the cycle stability of the battery. If the deformation amount of the matrix is too small, the mechanical heat during rolling is too small to uniformly coat the rolling oil dissolved with lithium nitrate; if the deformation amount of the matrix is too large, the strip is likely to break during rolling, affecting the production efficiency. Therefore, when rolling the lithium metal material matrix, control the total thickness deformation amount of the matrix to be 5-100%, so that the lithium metal undergoes appropriate deformation during the mechanical rolling process, so that uniform coating of the lithium metal can be achieved, the risk of forming lithium dendrites can be reduced, and the lithium metal will not break due to excessive deformation, affecting the assembly and performance of the battery. Lithium metal is extremely reactive with water, generating hydrogen and corrosive by-products, which will not only consume the lithium source, but also increase the internal impedance of the battery, ultimately leading to a significant decline in the cycle performance of the battery. Controlling the water content in the operating environment <0.5 ppm helps to reduce the risk of reaction between lithium metal and water.

[0055] In addition, the mass ratio of lithium nitrate in the mixed solution can be 2%, 3%, 5%, 6%, 7%, 9%, 10%, 11%, 13%, 15%, 18%, 19% or 20%. Of course, the mass ratio of lithium nitrate in the mixed solution can be any point value within 2% to 20%. Preferably, the mass ratio of lithium nitrate in the mixed solution can be any point value within 2% to 10%. Further preferably, the mass ratio of lithium nitrate in the mixed solution can be any point value within 2% to 5%. Details are not described herein again.

[0056] In addition, the total deformation amount of the thickness of the lithium metal single - element matrix can be 5%, 6%, 7%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%. Of course, the total deformation amount of the thickness of the lithium metal single - element matrix can be any point value within 5% - 100%. Preferably, the total deformation amount of the thickness of the lithium metal single - element matrix can be any point value within 5% - 50%. Further preferably, the total deformation amount of the thickness of the lithium metal single - element matrix can be any point value within 5% - 10%. Details are not elaborated here.

[0057] In some embodiments of the present application, in step S2, the raw materials further include an initiator, and the initiator is azobisisobutyronitrile and / or azobis - 2,4 - dimethylvaleronitrile.

[0058] An initiator such as azobisisobutyronitrile decomposes to generate free radicals, initiating the polymerization of comonomers, ensuring the efficient initiation and precise regulation of the polymerization reaction. The formed gel polymer electrolyte has good mechanical strength, conductivity, and electrochemical stability, forming a synergistic effect with other battery components, effectively improving the cycling performance and safety of lithium - ion batteries under normal and high - temperature conditions.

[0059] In some embodiments of the present application, in step S3, the temperature of in - situ polymerization is 45 - 80 °C, and / or the time of in - situ polymerization is 2 - 24 h.

[0060] The control of temperature during the in - situ polymerization process is an important parameter to ensure the formation of the gel polymer electrolyte. At a temperature of 60 °C, the polymerization reaction can proceed stably, promoting the effective combination between comonomers and forming a gel polymer framework with a three - dimensional network structure. The selection of this temperature range aims to balance the polymerization reaction rate and product quality. Too low a temperature will slow down the polymerization reaction, possibly resulting in incomplete formation of the gel polymer electrolyte, affecting the uniformity and stability of the electrolyte; while too high a temperature may trigger side reactions, leading to the destruction of the structure of the gel polymer electrolyte, affecting the cycling performance and safety of the battery. Sufficient time ensures the full progress of the polymerization reaction, enabling the comonomers to form a uniform and dense gel polymer electrolyte, improving its mechanical strength and conductivity. Insufficient polymerization time may lead to incomplete polymerization, with a loose electrolyte structure, affecting the lithium - ion transport efficiency and the cycling stability of the battery; while too long a time may cause over - polymerization, resulting in excessive curing of the electrolyte, reducing its fluidity and affecting the kinetic performance of the battery. By precisely controlling the temperature and time of in - situ polymerization, this technical solution can ensure the formation quality of the gel polymer electrolyte, achieving high mechanical strength, good conductivity, and stable electrochemical performance of the electrolyte. These meticulous process control parameters ensure good compatibility of the gel polymer electrolyte among the internal components of the battery, improving the cycling performance, kinetic performance, and safety of the battery.

[0061] In addition, the temperature of in-situ polymerization can be 45°C, 46°C, 47°C, 49°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C. Of course, the temperature of in-situ polymerization can be any point value within the range of 45°C to 80°C. Preferably, the temperature of in-situ polymerization can be any point value within the range of 45°C to 60°C. Further preferably, the temperature of in-situ polymerization can be any point value within the range of 45°C to 50°C, which will not be elaborated here.

[0062] In addition, the time of in-situ polymerization can be 2h, 3h, 4h, 5h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 23h or 24h. Of course, the time of in-situ polymerization can be any point value within the range of 2h to 24h. Preferably, the time of in-situ polymerization can be any point value within the range of 2h to 10h. Further preferably, the time of in-situ polymerization can be any point value within the range of 2h to 6h, which will not be elaborated here.

[0063] The beneficial effects of the present application will be further described below in conjunction with embodiments.

[0064] Example 1

[0065] 1. Preparation of composite lithium metal anode

[0066] Dissolve X wt.% of lithium nitrate in type I base oil, stir evenly, then coat it on a rolling equipment. By means of physical rolling, compound the metallic lithium onto the negative electrode current collector copper foil with a thickness of about 12μm. By adjusting the pressure of the roller, make the copper current collector coated with lithium on one side, and control the thickness to be about 50μm. Then, after cutting and slitting, place it in a dry argon atmosphere glove box for storage. The water content in the environment of mechanical rolling is <0.5ppm. During the process of mechanical rolling, the total deformation of the thickness of the lithium metal single matrix is 80%.

[0067] 2. Preparation of positive electrode

[0068] Mix nickel cobalt manganese (NCM) positive electrode active material, conductive agent (conductive carbon of Super P), and binder polyvinylidene fluoride according to a weight ratio of about 97:1.4:1.6, add N-methylpyrrolidone (NMP), and stir in a vacuum mixer until the system is homogeneous to obtain a positive electrode slurry, where the solid content of the positive electrode slurry is about 72wt%; uniformly coat the positive electrode slurry on the positive electrode current collector aluminum foil; dry it, and then after cold pressing, cutting and slitting, dry it under vacuum conditions at about 85°C for about 4h to obtain a positive electrode.

[0069] 3. Preparation of separator

[0070] Use polyethylene (PE) with a thickness of about 15μm as the separator.

[0071] 4. Gel Polymer

[0072] In a dry argon atmosphere, a fluorinated organic solvent containing a cyclic fluorinated carbonate shown by formula A, a linear fluorinated carbonate shown by formula B, and a fluoroether compound shown by formula C is uniformly mixed. Then, a lithium salt shown by formula D and an additive shown by formula E are added to the obtained mixed solution and dissolved uniformly to obtain a mixed liquid. Then, ethoxylated trimethylolpropane triacrylate with a network cross-linked structure and ethyl acetoacetate methacrylate in a linear form with a mass ratio of 1:Y are added thereto, and azobisisobutyronitrile accounting for 0.5 wt% of the total mass of the total monomers is added as an initiator. After stirring evenly, wait for liquid injection.

[0073]

[0074] 5. Preparation and Testing of Lithium Metal Battery

[0075] The positive electrode, separator, artificial solid electrolyte membrane composite lithium metal negative electrode are stacked in sequence and then superimposed; after welding the electrode tabs, they are placed in an outer packaging aluminum-plastic film, vacuum packaged, injected with the mixed liquid, left standing at room temperature for 24 hours, and heated at 60 °C for 12 h for in-situ polymerization to obtain a gel polymer electrolyte, followed by processes such as formation (constant current charging at 0.02C to 3.75V, and then constant current charging at 0.1C to 4.3V), shaping, and capacity testing to obtain a soft-pack laminated lithium metal battery.

[0076] The operation methods of the remaining examples and comparative examples refer to Example 1, and the differences lie in some parameters, as shown in Table 1 specifically.

[0077] Table 1

[0078]

[0079]

[0080] Comparative Example 9

[0081] The difference from Example 1 is that the contents of the cyclic fluorinated carbonate of formula A, the linear fluorinated carbonate of formula B, and the fluoroether compound of formula C (wt%), and the lithium salt D are 13 wt%, 65 wt%, 14 wt%, and 4 wt% in sequence, and finally a soft-pack laminated lithium metal battery is obtained.

[0082] Example 7

[0083] The difference from Example 1 is that the network cross-linked structure / linear structure 1:Y = 1:0.1, and finally a soft-pack laminated lithium metal battery is obtained.

[0084] Example 8

[0085] The difference from Example 1 is that for the network cross-linked structure / chain structure 1: Y = 1:20, and a soft-pack laminated lithium metal battery is finally obtained.

[0086] Example 9

[0087] The difference from Example 1 is that during the mechanical roll pressing process, the total deformation of the thickness of the lithium metal single-substrate is 5%, and a soft-pack laminated lithium metal battery is finally obtained.

[0088] Example 10

[0089] The difference from Example 1 is that during the mechanical roll pressing process, the total deformation of the thickness of the lithium metal single-substrate is 100%, and a soft-pack laminated lithium metal battery is finally obtained.

[0090] Example 11

[0091] The difference from Example 1 is that during the mechanical roll pressing process, the total deformation of the thickness of the lithium metal single-substrate is 4%, and a soft-pack laminated lithium metal battery is finally obtained.

[0092] Example 12

[0093] The difference from Example 1 is that during the mechanical roll pressing process, the total deformation of the thickness of the lithium metal single-substrate is 105%, and a soft-pack laminated lithium metal battery is finally obtained.

[0094] The obtained lithium metal battery is subjected to a cycle test on a charge-discharge device, charged to 4.3 V at a charge rate of 0.3C, and then discharged to 3 V at a discharge rate of 1C, and cycles are carried out in this way. Table 2 shows the test results of the examples and comparative examples.

[0095] Table 2

[0096]

[0097]

[0098] From the test results of Examples 1 to 4, it can be seen that using the artificial solid electrolyte membrane composite lithium metal anode and the gel polymer electrolyte provided by the present invention in a lithium metal battery is beneficial to improving the room-temperature cycle performance and high-temperature cycle performance of the lithium metal battery.

[0099] Comparing Example 2 with Examples 1, 3, and 4, it can be seen that adding the additive has some improvement in the cycle performance of the lithium metal battery, but since the additive forms a film on the negative electrode, it is beneficial to the deposition of lithium.

[0100] Comparing Comparative Example 1 with Example 1, it can be seen that if lithium nitrate is not added during the preparation of the lithium metal anode to form a SEI film rich in Li 3 N, it will greatly affect the cycle performance of the battery.

[0101] Comparing Comparative Example 2 with Example 1, it can be seen that if the addition amount is too large, lithium nitrate will precipitate on the surface of lithium, which will not only affect the cycle performance of the battery, but also affect the consistency of the battery.

[0102] Comparing Comparative Example 3 with Example 1, it can be seen that if the copolymer monomer is not added and the gel polymer electrolyte is not formed, it will greatly affect the cycle performance of the battery, especially the high-temperature cycle performance, because the copolymer framework will trap the electrolyte in the framework, reducing the reaction activity between the electrolyte and the positive and negative electrodes, thereby improving the interfacial stability of the positive and negative electrodes, and further improving the long-cycle performance of the battery.

[0103] Comparing Comparative Example 4 with Example 1, it can be seen that if too much copolymer monomer is added and the degree of electrolyte solidification is too high, the kinetic performance of the battery will decrease, which will greatly affect the normal-temperature cycle performance of the battery.

[0104] Comparing Examples 5 and 6 with Example 1, it can be seen that the mass ratio of the network cross-linked structure / chain structure in the copolymer should be appropriate. If the mass ratio of the chain monomer is too low, the flexibility of the copolymer is insufficient and the lithium-ion conduction ability is insufficient. If the mass ratio of the chain monomer is too high, the rigidity of the copolymer is insufficient and it cannot effectively prevent the penetration of lithium dendrites.

[0105] Comparing Comparative Examples 5, 6, and 7 with Example 1, it can be seen that these three solvents need to be used in combination to achieve a better cycle effect. The fluorinated solvent forms an SEI of LiF component on the surface of the negative electrode and is more resistant to oxidation on the positive electrode side, which is beneficial to the long-cycle performance of the lithium metal battery.

[0106] Comparing Comparative Example 8 with Example 1, it can be seen that the content of the lithium salt cannot be too high. If it is too high, the viscosity of the electrolyte is too large and the battery is difficult to cycle normally.

[0107] Comparing Comparative Example 9 with Example 1, it can be seen that the concentration of the lithium salt cannot be too low. If it is too low, the lithium-ion strength is not sufficient to support the charge-discharge cycle, thus affecting the cycle performance.

[0108] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0109] On the one hand, lithium nitrate attached to the surface of lithium metal in the lithium-ion battery can decompose into Li 3 N on the surface of the negative electrode to form a stable and uniform SEI film rich in Li 3 N. This Li-rich 3The SEI film of N is considered to be able to effectively promote uniform lithium deposition / stripping, inhibit the formation of lithium dendrites and dead lithium, and thus improve the cycle stability of the battery due to its high lithium ion conductivity, low resistance conductivity, and high Young's modulus. On the other hand, all three solvents are fluorinated solvents. Among them, cyclic fluorinated carbonates have good solubility in lithium salts and can also form an organic polymer SEI containing C and O on the negative electrode surface. When combined with inorganic LiF and Li 3 N, it can exhibit excellent performance. Linear fluorinated carbonates can participate in forming an F-rich film on the positive and negative electrodes, and can also adjust the viscosity of the electrolyte. When used in combination with cyclic fluorinated carbonates, it helps to reduce the reaction activity of the electrolyte at the positive electrode, which is beneficial to the long cycle of the battery. Fluoroether compounds have very good solubility for lithium ions and are the main solvents for transporting lithium. When solvating lithium, they form a stable five-membered ring structure, which is beneficial to improving the ability of the battery to solvate lithium. Through the above two aspects of effects, lithium ion batteries can simultaneously achieve high energy density and excellent room temperature and high temperature cycle performance.

[0110] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery comprising a composite lithium metal negative electrode, a positive electrode plate and a gel polymer electrolyte, characterized in that: The composite lithium metal negative electrode includes lithium metal and lithium nitrate attached to the surface of the lithium metal; the gel polymer electrolyte includes, by mass percentage: 1 to 10 wt% of a comonomer; 60-85wt% of an organic solvent; 5-20wt% lithium salt; 0-10wt% additives; Wherein, the organic solvent includes cyclic fluorinated carbonate, chain fluorinated carbonate and fluorinated ether compound; The comonomer is an acrylate monomer; The mass proportion of the lithium nitrate in the composite lithium metal negative electrode is ≤25%.

2. The lithium-ion battery according to claim 1, characterized in that The mass proportion of the lithium nitrate in the composite lithium metal negative electrode is 2-20%.

3. The lithium ion battery according to claim 1 or 2, characterized in that: In parts by weight, the organic solvent comprises: 1 to 40 parts of the cyclic fluorinated carbonate; 1 to 70 parts of the chain fluorinated carbonate; 1 to 40 parts of the fluoroether compound; Wherein, the chemical formula of the cyclic fluorocarbonate is as shown in Formula I: R1, R2, R3 and R4 are each independently selected from hydrogen, fluorine, C1-C 12 Alkyl, C1~C 12 Fluorinated alkyl, C3~C 12 Cycloalkyl, C3~C 12 Fluorinated cycloalkyl, C2~C 12 Alkenyl, C2~C 12 Fluoroalkenyl, C3~C 12 The heterocyclic group and C3~C 12 any one of the fluorinated heterocyclic groups, and at least one of the R1, R2, R3 and R4 is selected from a fluorine atom, a C1-C 12 Fluorinated alkyl, C3~C 12 Fluorinated cycloalkyl, C2~C 12 Fluoroalkenyl and C3~C 12 Any substituent in the fluorinated heterocyclic group; Preferably, R1, R2, R3 and R4 are each independently selected from any one of hydrogen, fluorine atom, C1-C6 alkyl, C1-C6 fluoroalkyl, C3-C6 cycloalkyl, C3-C6 fluorocycloalkyl, C2-C6 alkenyl, C2-C6 fluoroalkenyl, C3-C6 heterocyclic group and C3-C6 fluoroheterocyclic group, and at least one of R1, R2, R3 and R4 is selected from any one of fluorine atom, C1-C6 fluoroalkyl, C3-C6 fluorocycloalkyl, C2-C6 fluoroalkenyl and C3-C6 fluoroheterocyclic group; Preferably, the cyclic fluorinated carbonate is selected from Any one or more of the following; And / or, the general chemical formula of the chain fluorinated carbonate is as shown in Formula II: Wherein, R5 and R6 are each independently selected from hydrogen, fluorine, C1-C 12 Alkyl, C1~C 12 Fluorinated alkyl, C1~C 12 Alkoxy, C1~C 12 Fluorinated alkoxy, C2~C 12 Alkenyl, C2~C 12 Fluoroalkenyl, C6~C 26 Aryl, C6~C 26 any one of the fluorinated aromatic groups, and at least one of the R5 and the R6 is selected from C1 to C 12 Fluorinated alkyl, C1~C 12 Fluorinated alkoxy, C2~C 12 Fluoroalkenyl and C6~C 26 Any substituent in the fluorinated aryl group; Preferably, R5 and R6 are each independently selected from hydrogen, a fluorine atom, a C1-C6 alkyl group, a C1-C6 fluoroalkyl group, a C1-C6 alkoxy group, a C1-C6 fluoroalkoxy group, a C2-C6 alkenyl group, a C2-C6 fluoroalkenyl group, a C6-C 12 Aryl, C6~C 12 any one of the fluorinated aryl groups, and at least one of the R5 and the R6 is selected from the group consisting of C1-C6 fluorinated alkyl groups, C1-C6 fluorinated alkoxy groups, C2-C6 fluorinated alkenyl groups and C6-C 12 Any substituent in the fluorinated aryl group; Preferably, the linear fluorinated carbonate is selected from Any one or more of kind; And / or, the chemical formula of the fluoroether compound is as shown in Formula III: R7 and R8 are each independently selected from C1 to C 10 haloalkyl, C1~C 10 Halogenated alkoxy, C2~C 10 Any one of the halogenated alkenyl groups; Preferably, the R7 and R8 are each independently selected from any one of a C1-C6 haloalkyl group, a C1-C6 haloalkoxy group, and a C2-C6 haloalkenyl group; Preferably, the fluoroether compound is and / or 4. The lithium ion battery according to any one of claims 1 to 3, characterized in that The comonomers include acrylate monomers with a network cross-linked structure and chain acrylate monomers, wherein the acrylate monomers with a network cross-linked structure are ethoxylated trimethylolpropane triacrylate and / or trimethylolpropane triacrylate; And / or, the chain acrylate monomer is selected from any one or more of acetoacetoxyethyl methacrylate, methyl methacrylate, ethyl acrylate and decaacrylate; And / or, the mass ratio of the acrylate monomer having a network cross-linked structure to the chain acrylate monomer is 1:(0.1-20).

5. The lithium ion battery according to any one of claims 1 to 4, characterized in that: The lithium salt is selected from any one or more of lithium perchlorate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium trifluoromethylsulfonate and lithium difluorophosphate.

6. The lithium ion battery according to any one of claims 1 to 5, characterized in that The additive is selected from any one or more of fluoroethylene carbonate carbonate, ethylene ethylene carbonate, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium tetrafluoroborate, methylene disulfonate, 4-trifluoromethylethylene carbonate, 1,3,2-dioxazole thiophene-2,2-dioxide, fluoroethylene carbonate, ethylene sulfite, vinyl carbonate, succinic anhydride, propylene sulfite, propylene-1,3-sultone, bis(trimethylsilyl) sulfate, lithium nitrate, N-methyl-butylpyrrolidine bis(trifluoromethanesulfonyl imide salt), N-methyl-propylpiperidinium bis(trifluoromethanesulfonyl imide salt, 1,3-dioxane, 1,4-dioxane, 1,2-bis(cyanoethoxy)ethane, adiponitrile, 1,3,5-pentanetricarbonitrile, trans-butylene dinitrile and 1,2,3-tris(2-cyanoethoxy)propane.

7. A method for preparing the lithium ion battery according to any one of claims 1 to 6, the method comprising: Step S1, mixing lithium nitrate with oil to obtain a mixed solution, coating the mixed solution on a rolling device, and using the rolling device to mechanically roll a lithium metal single substance matrix to obtain a composite lithium metal negative electrode; Step S2, mixing raw materials including comonomers, organic solvents, lithium salts and additives to obtain a mixed solution; Step S3, stacking the positive electrode, the separator and the composite lithium metal negative electrode in order to obtain a stacked component, placing the stacked component in an aluminum-plastic film after welding the pole ears, and sequentially performing vacuum packaging, injection of the mixed solution, standing and in-situ polymerization, and formation to obtain the lithium-ion battery.

8. The preparation method according to claim 7, characterized in that: In the step S1, the mass percentage of the lithium nitrate in the mixed solution is 2-20%; and / or, the oil is selected from Group I base oil and / or lipid oil; And / or, during the mechanical rolling process, the total deformation amount of the thickness of the lithium metal single substance matrix is ​​5-100%, and the water content in the mechanical rolling environment is less than 0.5 ppm.

9. The preparation method according to claim 7 or 8, characterized in that: In the step S2, the raw materials further include an initiator, and the initiator is azobisisobutyronitrile and / or azobisisoheptanenitrile.

10. The preparation method according to any one of claims 7 to 9, characterized in that: In the step S3, the temperature of the in-situ polymerization is 45 to 80° C., and / or the time of the in-situ polymerization is 2 to 24 hours.

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