Slow-release polymer coating as well as preparation method and application thereof

Abstract

The embodiment of the invention relates to a slow-release polymer coating as well as a preparation method and application thereof, and the preparation method comprises the following steps: mixing a polymer monomer, a polymer monomer initiator, a solvent, a cross-linking agent and an electrolyte initiator in proportion to obtain coating precursor slurry; wherein the polymer monomer comprises a fluorinated acrylate compound; the polymer monomer initiator includes: a radical initiator; the solvent comprises an ether compound; the cross-linking agent comprises one or more of a polyethylene glycol derivative and an acrylate compound; the electrolyte initiator comprises lithium salt which can generate protonic acid with trace water and is resistant to high temperature; and coating the surface of an object to be covered with the coating precursor slurry, and carrying out heating polymerization treatment to obtain the slow-release polymer coating. The slow-release polymer coating can protect the lithium metal negative electrode and enhance the high-temperature safety performance of the lithium metal battery.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and in particular to a sustained-release polymer coating and a preparation method and application thereof. Background Art

[0002] The rapid development of electronic devices and electric vehicles has put forward higher requirements for the energy density of batteries. Lithium metal anodes have attracted extensive research due to their high theoretical specific capacity (3860 mAh / g) and low redox potential (3.04 V vs. standard hydrogen potential).

[0003] The solvents used in traditional commercial electrolytes are carbonate and ether solvents. The solid electrolyte interphase (SEI) formed by the reaction with lithium metal cannot effectively hinder parasitic reactions, resulting in low battery coulombic efficiency, continuous electrolyte consumption, and the inability of lithium ions to deposit evenly on the lithium metal, resulting in severe dendrite growth.

[0004] At high temperatures, liquid electrolytes are volatile and release flammable gases such as CO2 and CH3F. When these gases mix with air and reach a certain concentration, they can cause fire or explosion when exposed to open flames or sparks. At high temperatures, SE I decomposes severely, exposing fresh active lithium. This active lithium further reacts with the small-molecule electrolyte, releasing heat and raising the battery temperature. High temperatures also exacerbate dendrite growth, potentially piercing the separator and short-circuiting the positive and negative electrodes, leading to thermal runaway.

[0005] Therefore, in order to solve the high temperature resistance problem of liquid electrolytes, researchers have proposed the following solutions:

[0006] First, high-concentration or locally high-concentration electrolytes (maintaining a higher salt concentration on the electrode surface or near the interface, and a relatively low overall electrolyte concentration) can significantly reduce solvent volatility and enhance the thermal stability of the electrolyte. However, high-concentration or locally high-concentration electrolytes cannot hinder the growth of dendrites at high temperatures, posing a huge safety hazard.

[0007] Second, by designing polymer-based solid electrolytes with high thermal stability, dendrite growth can be inhibited and side reactions between the electrolyte and lithium metal at high temperatures can be reduced. However, most polymer-based solid electrolytes have low ionic conductivity at room temperature, resulting in insufficient charge transfer capacity of the battery, affecting the battery's charge and discharge performance.

[0008] Third, by constructing a stable SEI, parasitic reactions at room temperature can be reduced and heat generation from high-temperature reactions can be suppressed. However, SEI will inevitably undergo thermal decomposition at high temperatures. In this way, the interfacial reaction between the electrolyte and the electrode causes the battery temperature to further increase, causing battery failure.

[0009] Fourth, gel electrolytes, typically composed of a polymer matrix and an electrolyte solution, combine the high ionic conductivity of liquid electrolytes with the high safety of solid electrolytes, enhancing the safety of lithium batteries while maintaining electrochemical performance. Although the solvent volatility of gel electrolytes is lower than that of liquid electrolytes, at high temperatures, the solvent will still evaporate, causing changes in electrolyte concentration and volume shrinkage. This volatilization can affect the electrolyte's ionic conductivity and the overall performance of the battery.

[0010] Therefore, how to improve the cycle life of the battery at room temperature while also improving the high-temperature safety of the battery is an urgent problem to be solved in this field. Summary of the Invention

[0011] The purpose of the present invention is to address the defects of the existing technology and provide a slow-release polymer coating and its preparation method and application. The slow-release polymer coating can protect the negative electrode of the lithium battery and enhance the high-temperature safety performance of the lithium battery.

[0012] To achieve the above object, the present invention provides a method for preparing a sustained-release polymer coating, the preparation method comprising:

[0013] A polymer monomer, a polymer monomer initiator, a solvent, a crosslinking agent, and an electrolyte initiator are mixed in proportion to obtain a coating precursor slurry; wherein the polymer monomer comprises a fluorinated acrylate compound; the polymer monomer initiator comprises a free radical initiator; the solvent comprises an ether compound; the crosslinking agent comprises one or more of a polyethylene glycol derivative and an acrylate compound; and the electrolyte initiator comprises a high-temperature-resistant lithium salt capable of generating protonic acid with trace water;

[0014] The coating precursor slurry is applied to the surface of the object to be covered, and subjected to a heating polymerization treatment to obtain a slow-release polymer coating.

[0015] Preferably, the volume ratio of the solvent to the polymer monomer is 100:1-1:1; the mass ratio of the polymer monomer to the electrolyte initiator is 1:1-3:1; the volume of the cross-linking agent is 0.5%-3% of the volume of the polymer monomer; and the mass of the polymer monomer initiator is not more than 1% of the mass of the polymer monomer.

[0016] Preferably, the conditions for the heat polymerization treatment are: heat polymerization at 60°C-70°C for 2 hours-20 hours; the atmosphere for heat polymerization includes one or more of an inert atmosphere, a vacuum drying atmosphere, and a waterless drying chamber drying atmosphere; the thickness of the sustained-release polymer coating is 1 μm-100 μm.

[0017] Preferably, the fluorinated acrylate compound includes one or more of trifluoroethyl acrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, heptafluorobutyl acrylate, heptafluoroisobutyl acrylate, nonafluoropentyl acrylate, tridecafluorooctyl acrylate and dodecafluoroheptyl methacrylate;

[0018] The free radical initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and dibenzoyl peroxide;

[0019] The ether compound includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dimethyl ether;

[0020] The lithium salt includes one or more of lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium bis(fluorosulfonyl)imide;

[0021] The polyethylene glycol derivatives include: one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diglycidyl ether, polyethylene glycol diacrylamide, and tri(ethylene glycol) diacrylate;

[0022] The acrylate compound includes one or more of pentaerythritol triacrylate and pentaerythritol tetraacrylate.

[0023] In a second aspect, the present invention provides a sustained-release polymer coating prepared by any of the preparation methods described in the first aspect.

[0024] In a third aspect, the present invention provides a lithium metal comprising the sustained-release polymer coating described in the second aspect.

[0025] In a fourth aspect, the present invention provides a lithium metal battery, wherein the negative electrode of the lithium metal battery is the lithium metal described in the third aspect.

[0026] Preferably, the electrolyte of the lithium metal battery includes lithium salts and cyclic compounds that do not cause cationic ring-opening polymerization and are resistant to high temperatures; wherein the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium bromide, and lithium iodide; the cyclic compound includes a cyclic ether compound and a cyclic carbonate; the cyclic ether compound includes one or more of: 1,3-dioxolane, ethylene oxide, tetrahydrofuran, propylene oxide, epichlorohydrin, 1,2-butylene oxide, oxetane, 1,4-dioxane, and 1,3,5-trioxane.

[0027] In a fifth aspect, the present invention provides a method for preparing the lithium metal battery according to the fourth aspect, the method comprising:

[0028] A lithium salt and a cyclic compound that do not cause cationic ring-opening polymerization and are resistant to high temperatures are mixed in proportion to obtain an electrolyte;

[0029] A polymer monomer, a polymer monomer initiator, a solvent, a crosslinking agent, and an electrolyte initiator are mixed in proportion to obtain a coating precursor slurry; wherein the polymer monomer comprises a fluorinated acrylate compound; the polymer monomer initiator comprises a free radical initiator; the solvent comprises an ether compound; the crosslinking agent comprises one or more of a polyethylene glycol derivative and an acrylate compound; and the electrolyte initiator comprises a high-temperature-resistant lithium salt capable of generating protonic acid with trace water;

[0030] Applying the coating precursor slurry to the surface of lithium metal and performing a heating polymerization treatment to obtain a lithium negative electrode with a slow-release polymer coating;

[0031] The electrolyte is injected between the positive and negative electrodes inside the battery so that the electrolyte fully infiltrates the positive electrode, negative electrode and separator of the battery, and then the packaging is completed to obtain the lithium metal battery.

[0032] In a sixth aspect, the present invention provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the sustained-release polymer coating described in the third aspect.

[0033] The present invention provides a method for preparing a sustained-release polymer coating. By screening a polymer monomer initiator, an electrolyte initiator, a solvent, a polymer monomer, and a cross-linking agent, optimizing the coating precursor slurry ratio and the coating thickness, and using an in-situ polymerization process to heat the prepared sustained-release polymer coating, the sustained-release polymer coating can be applied to a lithium battery to enhance the high-temperature safety of the lithium battery. The details are as follows:

[0034] By using polymer monomers with soft, long side chains, the electrolyte initiator molecules can be effectively anchored between polymer chains at room temperature, reducing leakage of the electrolyte initiator molecules and allowing the cyclic compound electrolyte to maintain a liquid state with high ionic conductivity. The electrolyte initiator molecules are preferentially reduced by the negative electrode, thereby deriving an inorganic-rich solid electrolyte interface and inhibiting side reactions between the negative electrode and the electrolyte. The slow-release polymer coating can uniformly deposit lithium ions or ensure the insertion and extraction of lithium ions, reducing the probability of lithium dendrite formation and avoiding internal short circuit failure of the battery caused by lithium dendrites piercing the diaphragm, thereby improving the battery's cycle life. At high temperatures, the electrolyte initiator in the slow-release polymer coating is released to trigger the ring-opening polymerization of the cyclic compound electrolyte, thereby improving the electrolyte's tolerance to high temperatures and reducing side reactions between the electrolyte and the negative electrode. At the same time, the SEI generated by reducing the electrolyte initiator at room temperature can inhibit heat generation between the electrolyte and the negative electrode, thereby improving the safety of the lithium battery at high temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flow chart of a method for preparing a sustained-release polymer coating according to an embodiment of the present invention;

[0036] Figure 2-a This is one of the SEM images of the sustained-release polymer coating provided in Example 1 of the present invention;

[0037] Figure 2-b This is the second SEM image of the sustained-release polymer coating provided in Example 1 of the present invention;

[0038] Figure 3 Graph showing the long cycle polarization test results of batteries provided in Example 2 of the present invention and Comparative Examples 1 and 2;

[0039] Figure 4 Graph showing the room temperature cycling performance test results of the lithium metal half-cells provided in Example 2 of the present invention and Comparative Examples 1 and 2;

[0040] Figure 5 A graph showing the high temperature cycle test results of the lithium metal half-cell provided in Example 2 of the present invention;

[0041] Figure 6 This is a diagram showing the differential scanning calorimetry test results of lithium metal provided in Example 2 of the present invention and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0043] The present invention provides a method for preparing a sustained-release polymer coating, the process of which is as follows: Figure 1 As shown, the following steps are included:

[0044] Step 110: Mixing polymer monomers, polymer monomer initiators, solvents, crosslinking agents, and electrolyte initiators in proportion to obtain a coating precursor slurry;

[0045] The polymer monomer may include a fluorinated acrylate compound. The fluorinated acrylate compound preferably includes one or more of trifluoroethyl acrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, heptafluoroisobutyl acrylate, nonafluoropentyl acrylate, tridecafluorooctyl acrylate, and dodecafluoroheptyl methacrylate. The mass of the polymer monomer initiator is no more than 1%, preferably 1%, of the mass of the polymer monomer.

[0046] The polymer monomer initiator may include a free radical initiator, and preferably includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and dibenzoyl peroxide.

[0047] The solvent may include an ether compound. The ether compound preferably includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dimethyl ether. The volume ratio of the solvent to the polymer monomer may be 100:1 to 1:1, preferably 99:1.

[0048] The crosslinking agent may include one or more of polyethylene glycol derivatives and acrylate compounds. Polyethylene glycol derivatives preferably include one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diglycidyl ether, polyethylene glycol diacrylamide, and triethylene glycol diacrylate. Acrylate compounds preferably include one or more of pentaerythritol triacrylate and pentaerythritol tetraacrylate. The volume of the crosslinking agent may specifically be 0.5% to 3%, preferably 2%, of the volume of the polymer monomer.

[0049] The electrolyte initiator may include a high temperature resistant lithium salt that can generate protonic acid with trace water, preferably one or more of lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium bis(fluorosulfonyl)imide.

[0050] It is well known in the art that trace water refers to a very small amount of water (water vapor or adsorbed water) present in a gas, liquid or solid. + ) to other substances (molecules or ions), its core feature is the proton transfer ability. High temperature resistance (the high temperature involved in this application refers to not less than 60°C), that is, it will not decompose in an environment of not less than 60°C and remains chemically inert. Therefore, the lithium salt has the characteristics of hydrolysis with trace water and stability at high temperatures. In this embodiment, the decomposition temperature of the lithium salt is not less than 120°C. The mass ratio of the polymer monomer to the electrolyte initiator can be 1:1-3:1, preferably 2:1.

[0051] Step 120 : coating the coating precursor slurry onto the surface of the object to be covered, and performing a heating polymerization treatment to obtain a slow-release polymer coating.

[0052] Specifically, the conditions for the thermal polymerization treatment can be: thermal polymerization at 60°C-70°C for 2-20 hours, preferably at 60°C for 12 hours. The thermal polymerization atmosphere can include one or more of an inert atmosphere, a vacuum drying atmosphere, or an anhydrous drying chamber. The water content of the thermal polymerization environment is preferably less than 20 ppm. The thickness of the sustained-release polymer coating can be 1 μm-100 μm, preferably 1.5 μm.

[0053] During this process, the solvent dissolves the electrolyte initiator and is evenly miscible with the polymer monomer, adjusting the reaction environment so that the reactants are evenly distributed and the reaction efficiency is improved. The free radical initiator thermally decomposes to generate free radicals, forming active centers, thereby initiating the polymerization of the polymer monomer. The cross-linker connects linear or branched polymers into a three-dimensional network structure through chemical bonds, improving the mechanical properties and heat resistance of the polymer, and the electrolyte initiator is anchored between the polymer chains.

[0054] At room temperature, the electrolyte initiator can be preferentially reduced to form a solid electrolyte interface. It is well known to those skilled in the art that inorganic solid electrolyte interfaces are superior to organic solid electrolyte interfaces. In this application, the main component of the inorganic solid electrolyte interface is LiF, which has good heat resistance and mechanical properties.

[0055] At temperatures of 60°C and above, polymerization continues between polymer chains, releasing the electrolyte initiator, which can react with trace water in the battery's electrolyte to produce proton acid. The proton acid acts as an initiator for cationic polymerization, and the released protons combine with the oxygen atoms of the cyclic compounds in the electrolyte to form protonated oxonium ions, which can reduce the ring tension of the cyclic ether and make the carbon-oxygen bond of the cyclic ether more easily break. The protonated oxonium ions further react with the carbon atoms in the cyclic ether, causing the cyclic ether to open its ring and form a linear or branched macromolecule. Furthermore, the solid electrolyte interface formed at room temperature can suppress heat generation between the electrolyte and the negative electrode, improving the safety of the battery at high temperatures.

[0056] The present invention provides a method for preparing a sustained-release polymer coating. By screening a polymer monomer initiator, an electrolyte initiator, a solvent, a polymer monomer, and a cross-linking agent, optimizing the coating precursor slurry ratio and the coating thickness, and using an in-situ polymerization process to heat the prepared sustained-release polymer coating, the sustained-release polymer coating can be applied to a lithium battery to enhance the high-temperature safety of the lithium battery. The details are as follows:

[0057] By using polymer monomers with soft, long side chains, the electrolyte initiator molecules can be effectively anchored between polymer chains at room temperature, reducing leakage of the electrolyte initiator molecules and allowing the cyclic compound electrolyte to maintain a liquid state with high ionic conductivity. The electrolyte initiator molecules are preferentially reduced by the negative electrode, thereby deriving an inorganic-rich solid electrolyte interface and inhibiting side reactions between the negative electrode and the electrolyte. The slow-release polymer coating can uniformly deposit lithium ions or ensure the insertion and extraction of lithium ions, reducing the probability of lithium dendrite formation and avoiding internal short circuit failure of the battery caused by lithium dendrites piercing the diaphragm, thereby improving the battery's cycle life. At high temperatures, the electrolyte initiator in the slow-release polymer coating is released to trigger the ring-opening polymerization of the cyclic compound electrolyte, thereby improving the electrolyte's tolerance to high temperatures and reducing side reactions between the electrolyte and the negative electrode. At the same time, the SEI generated by reducing the electrolyte initiator at room temperature can inhibit heat generation between the electrolyte and the negative electrode, thereby improving the safety of the lithium battery at high temperatures.

[0058] The sustained-release polymer coating provided by the present invention can be applied to electrode materials of energy storage devices such as lithium batteries.

[0059] When it is applied to lithium metal batteries, it can be prepared as follows:

[0060] Step 210 , mixing a lithium salt and a cyclic compound that do not cause cationic ring-opening polymerization and are resistant to high temperatures in proportion to obtain an electrolyte;

[0061] Specifically, the lithium salt may include one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium bromide, and lithium iodide. The cyclic compound may include a cyclic ether compound and a cyclic carbonate, preferably a cyclic ether compound. The cyclic ether compound may include one or more of 1,3-dioxolane, ethylene oxide, tetrahydrofuran, propylene oxide, epichlorohydrin, 1,2-butylene oxide, oxetane, 1,4-dioxane, and 1,3,5-trioxane.

[0062] Here, cationic ring-opening polymerization refers to a chain polymerization reaction in which a cyclic monomer is opened to form a linear polymer through a cationic active center (such as a carbon cation, an oxonium ion, etc.). The cation is the initiator of the ring opening, such as a proton acid (H + ), Lewis acids (AlCl3, BF3), or stable carbon cations. High-temperature resistance means it will not decompose at temperatures above 60°C and remains chemically inert. Therefore, the lithium salt here does not have the ability to generate cationic active centers to initiate the ring-opening of cyclic monomers to form polymers (i.e., it will not produce protonic acids with trace amounts of water), but it can maintain stability at high temperatures.

[0063] In this embodiment, the decomposition temperature of the lithium salt is not lower than 360°C, and the ring opening of the cyclic ether compound will not be caused at room temperature, so that the electrolyte remains in a liquid state at room temperature, can maintain a high ionic conductivity, and still maintain the stability of its own properties at high temperatures, thereby ensuring the high temperature resistance of the electrolyte.

[0064] Step 220 , mixing a polymer monomer, a polymer monomer initiator, a solvent, a cross-linking agent, and an electrolyte initiator to obtain a coating precursor slurry;

[0065] The polymer monomer may include a fluorinated acrylate compound; the polymer monomer initiator may include a free radical initiator; the solvent may include an ether compound; the crosslinker may include one or more of a polyethylene glycol derivative and an acrylate compound; and the electrolyte initiator may include a high-temperature-resistant lithium salt capable of reacting with trace amounts of water to generate a protonic acid. The polymer monomer, polymer monomer initiator, solvent, crosslinker, and electrolyte initiator are the same as those described above for the preparation of the sustained-release polymer coating and are not further described.

[0066] Step 230 , coating the coating precursor slurry onto the surface of the lithium metal and performing a heating polymerization treatment to obtain a lithium negative electrode having a slow-release polymer coating;

[0067] Specifically, the thermal polymerization treatment can be performed at 60°C-70°C for 2-20 hours. The thermal polymerization atmosphere can include one or more of an inert atmosphere, a vacuum drying atmosphere, or a dry drying chamber. The water content in the thermal polymerization environment is preferably less than 20 ppm. The thickness of the sustained-release polymer coating can be 1 μm-100 μm.

[0068] The slow-release polymer coating can protect lithium metal, avoid non-uniform deposition of lithium ions during repeated charge and discharge, and reduce the formation of lithium dendrites. In addition, the electrolyte initiator molecules in the slow-release polymer coating can first be reduced by lithium metal to generate an inorganic-rich solid electrolyte interface. The solid electrolyte interface can inhibit side reactions between lithium metal and solvents or lithium salts in the electrolyte, thereby improving the cycle life of the battery.

[0069] In step 240, the electrolyte is injected between the positive and negative electrodes inside the battery so that the electrolyte fully infiltrates the positive electrode, negative electrode and separator of the battery, and then the packaging is completed to obtain a lithium metal battery.

[0070] Specifically, the positive electrode active material may include one or more of a layered oxide, a polyanionic compound, or a Prussian blue compound. The layered oxide includes one or more of lithium cobalt oxide, lithium nickel cobalt manganese oxide, and sodium nickel iron manganese oxide. The polyanionic compound includes lithium iron phosphate and / or sodium vanadium phosphate. The Prussian blue compound includes Prussian white. The negative electrode is lithium metal with a slow-release polymer coating.

[0071] The diaphragm can be specifically realized by using a polyolefin diaphragm (polyethylene, polypropylene, etc.) or an inorganic ceramic diaphragm (aluminum oxide, silicon oxide, etc.).

[0072] At high temperatures (not less than 60°C), the electrolyte initiator in the sustained-release polymer coating is released, and the cyclic ether compound can undergo ring-opening polymerization under the action of the electrolyte initiator, causing the electrolyte to change from liquid to solid, thereby improving the electrolyte's tolerance to high temperatures and reducing side reactions between the electrolyte and lithium metal.

[0073] To make the objectives, technical solutions, and advantages of the present invention more apparent, the present invention will be further described in detail below with reference to the accompanying drawings. It is apparent that the embodiments described are only some, not all, of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0074] Example 1

[0075] This example prepares a lithium metal with a sustained-release polymer coating.

[0076] Preparation of coating precursor slurry: The polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinker polyethylene glycol diacrylate (PEGDA) are mixed in a volume ratio of 50:1 to obtain solution A, and the solution A is mixed with the electrolyte initiator lithium difluorooxalatoborate (LiDFOB) in a mass ratio of 2:1 to obtain solution B. Then, the solvent ethylene glycol dimethyl ether (DME) with a volume 99 times that of the polymer monomer is added to solution B to obtain solution C. Then, the polymer monomer initiator azobisisobutyronitrile (AIBN) is added to solution C in an amount of 1% of the mass of the polymer monomer to obtain solution D. The solution D is mixed evenly to obtain the coating precursor slurry.

[0077] Preparation of lithium metal: The above coating precursor slurry is added dropwise to one side of a lithium metal surface with a thickness of 300μm. The coating precursor slurry is evenly applied to the lithium metal surface using a doctor blade technique, wherein the doctor blade height is 350μm. Under an argon atmosphere, the lithium metal is heated at a temperature of 60°C for 12 hours to evaporate the solvent ethylene glycol dimethyl ether (DME) and fully polymerize the polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinking agent polyethylene glycol diacrylate (PEGDA), thereby obtaining a lithium metal with a sustained-release polymer coating.

[0078] Afterwards, the lithium metal with the sustained-release polymer coating was subjected to scanning electron microscopy (SEM) testing, and the surface morphology of the coating was captured at a magnification of 2000 times ( Figure 2-a ), the cross-sectional morphology of the coating was captured by scanning at a magnification of 5000 times ( Figure 2-b ),according to Figure 2-a and 2-b As shown, it can be seen that the surface of the lithium metal is covered with a uniform and dense coating, and the coating thickness is 1.5 μm. The coating thicknesses involved in the following examples and comparative examples can be obtained by SEM testing and will not be repeated here.

[0079] Example 2

[0080] This embodiment prepares a lithium metal battery having a lithium metal negative electrode with a slow-release polymer coating.

[0081] Preparation of coating precursor slurry: The polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinker polyethylene glycol diacrylate (PEGDA) are mixed in a volume ratio of 50:1 to obtain solution A, and the solution A is mixed with the electrolyte initiator lithium difluorooxalatoborate (LiDFOB) in a mass ratio of 2:1 to obtain solution B. Then, the solvent ethylene glycol dimethyl ether (DME) with a volume 99 times that of the polymer monomer is added to solution B to obtain solution C. Then, the polymer monomer initiator azobisisobutyronitrile (AIBN) is added to solution C in an amount of 1% of the mass of the polymer monomer to obtain solution D. The solution D is mixed evenly to obtain the coating precursor slurry.

[0082] Preparation of lithium metal: The above coating precursor slurry was added dropwise to one side of a lithium metal surface with a thickness of 300μm. The coating precursor slurry was evenly applied to the lithium metal surface using a doctor blade technique, wherein the doctor blade height was 350μm. Under an argon atmosphere, the lithium metal was heated at a temperature of 60°C for 12 hours to evaporate the solvent ethylene glycol dimethyl ether (DME) and fully polymerize the polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinking agent polyethylene glycol diacrylate (PEGDA), thereby obtaining a lithium metal with a sustained-release polymer coating with a coating thickness of 1.5μm.

[0083] Preparation of the electrolyte: 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to 1,3-dioxolane (DOL) and stirred at 30°C for about 2 hours until completely dissolved to obtain the electrolyte.

[0084] Assembly of lithium metal battery: Take 25μL of electrolyte and drop it on the lithium iron phosphate (LiFePO4) positive electrode, then cover it with a polypropylene separator, add 25μL of electrolyte again to soak the separator, then stack the lithium metal negative electrode with a sustained-release polymer coating and nickel foam, and finally encapsulate the battery into a shell to obtain a lithium metal battery.

[0085] Preparation of lithium-lithium symmetrical battery: Replace the lithium iron phosphate (LiFePO4) positive electrode with lithium metal, assemble the lithium-lithium symmetrical battery for testing in this embodiment as described above, and test the assembled lithium-lithium symmetrical battery on a blue battery charge and discharge instrument at 0.5 mA cm -2 The current density controls the charge and discharge rate, 1mAh cm -2 The capacity density limits the total charge and discharge capacity for long cycle polarization testing.

[0086] Preparation of a lithium metal half-cell: A half-cell was assembled using LiFePO4 as the positive electrode and lithium metal protected by a coating containing an electrolyte initiator (a slow-release polymer coating) as the negative electrode. Charge and discharge cycle performance was then tested at room temperature on a BlueDian battery charge and discharge instrument at a rate of 1C in the 2.5V to 3.8V range. It should be noted that the lithium metal half-cell described here is essentially the lithium metal battery described above, assembled for testing purposes only.

[0087] Example 3

[0088] This embodiment prepares a lithium metal soft-pack battery having a lithium metal negative electrode with a slow-release polymer coating.

[0089] Preparation of coating precursor slurry: The polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinker polyethylene glycol diacrylate (PEGDA) are mixed in a volume ratio of 50:1 to obtain solution A, and the solution A is mixed with the electrolyte initiator lithium difluorooxalatoborate (LiDFOB) in a mass ratio of 2:1 to obtain solution B. Then, the solvent ethylene glycol dimethyl ether (DME) with a volume 99 times that of the polymer monomer is added to solution B to obtain solution C. Then, the polymer monomer initiator azobisisobutyronitrile (AIBN) is added to solution C in an amount of 1% of the mass of the polymer monomer to obtain solution D. The solution D is mixed evenly to obtain the coating precursor slurry.

[0090] Preparation of lithium metal: The above coating precursor slurry was added dropwise to one side of a lithium metal surface with a thickness of 300μm. The coating precursor slurry was evenly applied to the lithium metal surface using a doctor blade technique, wherein the doctor blade height was 350μm. Under an argon atmosphere, the lithium metal was heated at a temperature of 60°C for 12 hours to evaporate the solvent ethylene glycol dimethyl ether (DME) and fully polymerize the polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinking agent polyethylene glycol diacrylate (PEGDA), thereby obtaining a lithium metal with a sustained-release polymer coating with a coating thickness of 1.5μm.

[0091] Preparation of the electrolyte: 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to 1,3-dioxolane (DOL) and stirred at 30°C for about 2 hours until completely dissolved to obtain the electrolyte.

[0092] Assembly of lithium metal soft-pack batteries: The cut lithium metal negative electrode containing a slow-release polymer coating and the LiFePO4 positive electrode are stacked into a battery cell through a stacking machine, the positive electrode is welded with an aluminum current collector, and the negative electrode is welded with a nickel current collector. The battery cell is then encapsulated with an aluminum-plastic film. After that, electrolyte is added to the aluminum-plastic film, and finally sealed and aged to obtain a lithium metal soft-pack battery with a lithium metal negative electrode with a slow-release polymer coating.

[0093] Example 4

[0094] This embodiment prepares a lithium metal battery having a lithium metal negative electrode with a slow-release polymer coating.

[0095] Preparation of coating precursor slurry: The polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinker polyethylene glycol diacrylate (PEGDA) are mixed in a volume ratio of 50:1 to obtain solution A, and the solution A is mixed with the electrolyte initiator lithium difluorooxalatoborate (LiDFOB) in a mass ratio of 4:1 to obtain solution B. Then, the solvent ethylene glycol dimethyl ether (DME) with a volume 1.3 times that of the polymer monomer is added to solution B to obtain solution C. Then, the polymer monomer initiator azobisisobutyronitrile (AIBN) is added to solution C in an amount of 1% of the mass of the polymer monomer to obtain solution D. The solution D is mixed evenly to obtain the coating precursor slurry.

[0096] Preparation of lithium metal: The above coating precursor slurry was added dropwise to one side of a lithium metal surface with a thickness of 300μm. The coating precursor slurry was evenly applied to the lithium metal surface using a doctor blade technique, wherein the doctor blade height was 350μm. Under an argon atmosphere, the lithium metal was heated at a temperature of 60°C for 12 hours to evaporate the solvent ethylene glycol dimethyl ether (DME) and fully polymerize the polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinking agent polyethylene glycol diacrylate (PEGDA), thereby obtaining a lithium metal with a sustained-release polymer coating with a coating thickness of 1.5μm.

[0097] Preparation of the electrolyte: 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to 1,3-dioxolane (DOL) and stirred at 30°C for about 2 hours until completely dissolved to obtain the electrolyte.

[0098] Assembly of lithium metal battery: Take 25μL of electrolyte and drop it on the lithium iron phosphate (LiFePO4) positive electrode, then cover it with a polypropylene separator, add 25μL of electrolyte again to soak the separator, then stack the lithium metal negative electrode with a sustained-release polymer coating and nickel foam, and finally encapsulate the battery into a shell to obtain a lithium metal battery.

[0099] At 30°C and a charge-discharge rate of 1C, the lithium metal battery's discharge capacity decayed to 80% after 250 cycles, reaching a discharge capacity of approximately 113 mAh / g. At 60°C and a charge-discharge rate of 1C, the discharge capacity decayed to 80% after 20 cycles, reaching a discharge capacity of approximately 110 mAh / g.

[0100] Example 5

[0101] This embodiment prepares a lithium metal battery having a lithium metal negative electrode with a slow-release polymer coating.

[0102] Preparation of coating precursor slurry: polymer trifluoroethyl acrylate and crosslinker tri(ethylene glycol) diacrylate are mixed in a volume ratio of 50:1 to obtain solution A, solution A is mixed with electrolyte initiator lithium tetrafluoroborate in a mass ratio of 1:1 to obtain solution B, and then solvent ethylene glycol diethyl ether with a volume 99 times that of the polymer monomer is added to solution B to obtain solution C, and then polymer monomer initiator azobisisoheptanenitrile is added in an amount of 1% of the mass of the polymer monomer to obtain solution D, and solution D is mixed evenly to obtain coating precursor slurry.

[0103] Preparation of lithium metal: The above coating precursor slurry was added dropwise to one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was evenly applied to the lithium metal surface using a doctor blade technique, wherein the doctor blade height was 350 μm. The lithium metal was heated at 70°C for 10 hours in a vacuum drying atmosphere with a water content of 15 ppm to evaporate the solvent ethylene glycol diethyl ether and fully polymerize the polymer trifluoroethyl acrylate and the crosslinking agent tri(ethylene glycol) diacrylate, thereby obtaining a lithium metal with a sustained-release polymer coating with a coating thickness of 5 μm.

[0104] Preparation of electrolyte: Add 1 mol / L lithium perchlorate to ethylene oxide and stir at 30°C for about 2 hours until it is completely dissolved to obtain the electrolyte.

[0105] Assembly of lithium metal battery: Take 25μL of electrolyte and drop it on the lithium iron phosphate (LiFePO4) positive electrode, then cover it with a polypropylene separator, add 25μL of electrolyte again to soak the separator, then stack the lithium metal negative electrode with a sustained-release polymer coating and nickel foam, and finally encapsulate the battery into a shell to obtain a lithium metal battery.

[0106] Example 6

[0107] This embodiment prepares a lithium metal battery having a lithium metal negative electrode with a slow-release polymer coating.

[0108] Preparation of coating precursor slurry: polymer heptafluoroisobutyl acrylate and crosslinker pentaerythritol triacrylate are mixed in a volume ratio of 50:1 to obtain solution A, solution A is mixed with electrolyte initiator lithium bis(fluorosulfonyl)imide in a mass ratio of 2:1 to obtain solution B, and then solvent ethylene glycol dibutyl ether with a volume 99 times that of the polymer monomer is added to solution B to obtain solution C. Subsequently, polymer monomer initiator dibenzoyl peroxide is added to solution C in an amount of 1% of the mass of the polymer monomer to obtain solution D, and solution D is mixed evenly to obtain coating precursor slurry.

[0109] Preparation of lithium metal: The above coating precursor slurry was dropwise added to one side of a 300μm-thick lithium metal surface. The coating precursor slurry was evenly applied to the lithium metal surface using a doctor blade technique with a blade height of 350μm. The lithium metal was heated at 65°C in a dry drying chamber with a water content of 10ppm for 18 hours to volatilize the solvent, ethylene glycol dibutyl ether, and fully polymerize the polymer heptafluoroisobutyl acrylate and the crosslinker pentaerythritol triacrylate, resulting in a lithium metal with a sustained-release polymer coating having a thickness of 7μm.

[0110] Preparation of electrolyte: 1 mol / L lithium bromide was added to 1,4-dioxane and stirred at 30°C for about 2 hours until it was completely dissolved to obtain the electrolyte.

[0111] Assembly of lithium metal battery: Take 25μL of electrolyte and drop it on the lithium iron phosphate (LiFePO4) positive electrode, then cover it with a polypropylene separator, add 25μL of electrolyte again to soak the separator, then stack the lithium metal negative electrode with a sustained-release polymer coating and nickel foam, and finally encapsulate the battery into a shell to obtain a lithium metal battery.

[0112] Example 7

[0113] This embodiment prepares a lithium metal battery having a lithium metal negative electrode with a slow-release polymer coating.

[0114] Preparation of coating precursor slurry: polymer dodecafluoroheptyl methacrylate and crosslinker pentaerythritol tetraacrylate are mixed in a volume ratio of 50:1 to obtain solution A, solution A is mixed with electrolyte initiator lithium difluorooxalatoborate in a mass ratio of 4:1 to obtain solution B, and then solvent diethylene glycol dimethyl ether with a volume 99 times that of the polymer monomer is added to solution B to obtain solution C. Then, polymer monomer initiator azobisisobutyronitrile is added to solution C in an amount of 1% of the mass of the polymer monomer to obtain solution D, and solution D is mixed evenly to obtain coating precursor slurry.

[0115] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropwise added to one side of a 300μm-thick lithium metal surface. The coating precursor slurry was evenly applied to the lithium metal surface using a doctor blade technique with a blade height of 350μm. Under an argon atmosphere, the lithium metal was heated at 60°C for 12 hours to evaporate the solvent diethylene glycol dimethyl ether and fully polymerize the polymer dodecafluoroheptyl methacrylate and the crosslinker pentaerythritol tetraacrylate, thereby obtaining a lithium metal with a sustained-release polymer coating having a thickness of 4μm.

[0116] Preparation of electrolyte: 1 mol / L lithium iodide was added to 1,3,5-trioxane and stirred at 30°C for about 2 hours until completely dissolved to obtain the electrolyte.

[0117] Assembly of lithium metal battery: Take 25μL of electrolyte and drop it on the lithium iron phosphate (LiFePO4) positive electrode, then cover it with a polypropylene separator, add 25μL of electrolyte again to soak the separator, then stack the lithium metal negative electrode with a sustained-release polymer coating and nickel foam, and finally encapsulate the battery into a shell to obtain a lithium metal battery.

[0118] Comparative Example 1

[0119] In this comparative example, a lithium metal battery having a lithium metal negative electrode without a sustained-release polymer coating was prepared.

[0120] Preparation of the electrolyte: 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to 1,3-dioxolane (DOL) and stirred at 30°C for about 2 hours until completely dissolved to obtain the electrolyte.

[0121] Assembly of a lithium-lithium symmetrical battery: 25 μL of electrolyte is dropped onto lithium metal, then a polypropylene separator is covered on it, and 25 μL of electrolyte is added again to wet the separator. Then, a lithium metal negative electrode without a sustained-release polymer coating and nickel foam are stacked, and finally the battery is encapsulated in a shell to obtain a lithium-lithium symmetrical battery.

[0122] The assembled lithium-lithium symmetrical battery was charged and discharged on a blue battery charge and discharge instrument at 0.5 mA cm -2 The current density controls the charge and discharge rate, 1mAh cm -2 The capacity density limits the total charge and discharge capacity for long cycle polarization testing.

[0123] Assembly of a lithium metal half-cell: A half-cell was assembled using LiFePO4 as the positive electrode and bare lithium metal as the negative electrode. The half-cell was then cycled at room temperature on a BlueDian battery charger and discharge instrument at a rate of 1C between 2.5V and 3.8V.

[0124] Comparative Example 2

[0125] In this comparative example, a lithium metal battery having a coated lithium metal negative electrode was prepared.

[0126] Preparation of coating precursor slurry: The polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinker polyethylene glycol diacrylate (PEGDA) are mixed in a volume ratio of 50:1 to obtain solution A, and ethylene glycol dimethyl ether (DME) with a volume 99 times that of the polymer monomer is added to obtain solution C, and azobisisobutyronitrile (AIBN) with a mass fraction of 1% of solution C is added to obtain solution D. The coating precursor slurry is obtained by mixing solution D evenly.

[0127] Preparation of lithium metal: The above coating precursor slurry was added dropwise to one side of a lithium metal surface with a thickness of 300μm. The coating precursor slurry was evenly applied to the lithium metal surface using a doctor blade technique, wherein the doctor blade height was 350μm. Under an argon atmosphere, the lithium metal was heated at a temperature of 60°C for 12 hours to evaporate the solvent ethylene glycol dimethyl ether (DME) and fully polymerize the polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinking agent polyethylene glycol diacrylate (PEGDA), thereby obtaining a lithium metal with a sustained-release polymer coating with a coating thickness of 1.5μm.

[0128] Preparation of the electrolyte: 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to 1,3-dioxolane (DOL) and stirred at 30°C for about 2 hours until completely dissolved to obtain the electrolyte.

[0129] Assembly of a lithium-lithium symmetrical battery: 25 μL of electrolyte is dropped onto lithium metal, then a polypropylene separator is covered on it, and 25 μL of electrolyte is added again to wet the separator. Then, a coated lithium metal negative electrode and nickel foam are stacked, and finally the battery is encapsulated in a shell to obtain a lithium-lithium symmetrical battery.

[0130] The assembled lithium-lithium symmetrical battery was charged and discharged on a blue battery charge and discharge instrument at 0.5 mA cm -2 The current density controls the charge and discharge rate, 1mAh cm -2 The capacity density limits the total charge and discharge capacity for long cycle polarization testing.

[0131] Assembly of a lithium metal half-cell: A half-cell was assembled using LiFePO4 as the positive electrode and a coated lithium metal (without the electrolyte initiator) as the negative electrode. The half-cell was then cycled at room temperature on a BlueDian battery charger and discharge meter at a rate of 1C between 2.5V and 3.8V.

[0132] Comparative Example 3

[0133] In this comparative example, a lithium metal battery having lithium metal protected by a slow-release polymer coating was prepared.

[0134] Preparation of coating precursor slurry: The polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinker polyethylene glycol diacrylate (PEGDA) are mixed in a volume ratio of 50:1 to obtain solution A, and the solution A is mixed with the electrolyte initiator lithium difluorooxalatoborate (LiDFOB) in a mass ratio of 8:1 to obtain solution B. Then, the solvent ethylene glycol dimethyl ether (DME) with a volume 1.3 times that of the polymer monomer is added to solution B to obtain solution C. Then, the polymer monomer initiator azobisisobutyronitrile (AIBN) is added to solution C in an amount of 1% of the mass of the polymer monomer to obtain solution D. The solution D is mixed evenly to obtain the coating precursor slurry.

[0135] Preparation of lithium metal: The above coating precursor slurry was added dropwise to one side of a lithium metal surface with a thickness of 300μm. The coating precursor slurry was evenly applied to the lithium metal surface using a doctor blade technique, wherein the doctor blade height was 350μm. Under an argon atmosphere, the lithium metal was heated at a temperature of 60°C for 12 hours to evaporate the solvent ethylene glycol dimethyl ether (DME) and fully polymerize the polymer monomer pentafluoropropyl acrylate (PFA) and the crosslinking agent polyethylene glycol diacrylate (PEGDA), thereby obtaining a lithium metal with a sustained-release polymer coating with a coating thickness of 1.5μm.

[0136] Preparation of the electrolyte: 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to 1,3-dioxolane (DOL) and stirred at 30°C for about 2 hours until completely dissolved to obtain the electrolyte.

[0137] Assembly of lithium metal battery: Take 25μL of electrolyte and drop it on the lithium iron phosphate (LiFePO4) positive electrode, then cover it with a polypropylene separator, add 25μL of electrolyte again to soak the separator, then stack the lithium metal negative electrode with a sustained-release polymer coating and nickel foam, and finally encapsulate the battery into a shell to obtain a lithium metal battery.

[0138] At 30°C and a charge-discharge rate of 1C, the lithium metal battery's discharge capacity decays to 80% after 200 cycles, with a discharge capacity of approximately 113 mAh / g. At 60°C and a charge-discharge rate of 1C, the electrolyte and electrode reactions after activation cause the battery to fail due to severe charging problems.

[0139] according to Figure 3 As shown, the polarization voltage of the battery of Comparative Example 1 is the largest during long cycles, followed by that of the battery of Comparative Example 2. The battery of Example 2 of the present invention has the smallest polarization voltage during long cycles because the electrolyte initiator in the coating is preferentially reduced on the negative electrode side, thereby generating an inorganic-rich, low-impedance interface layer.

[0140] Figure 4 The results of the room temperature cycle performance test of the lithium metal half-cell provided in Example 2 of the present invention and Comparative Examples 1 and 2 are shown in FIG. Figure 4 As shown, the cycling performance of the lithium metal half-cell of Example 2 of the present invention is much higher than that of the lithium metal half-cells of Comparative Examples 1 and 2. Because the electrolyte initiator in the coating is preferentially reduced on the negative electrode side, the lithium metal half-cell of Example 2 of the present invention forms an inorganic-rich interface layer, which has good mechanical properties, adapts to the volume changes of lithium metal during cycling, and hinders side reactions between the electrolyte and lithium metal. As a result, at 30°C and a charge-discharge rate of 1C, the discharge capacity decays to 78.3% after 470 cycles, with a discharge capacity of approximately 111 mAh / g. In contrast, the discharge capacity of the lithium metal half-cell of Comparative Example 1 decayed to 80.6% after 130 cycles under the same test conditions, with a discharge capacity of approximately 116 mAh / g. The discharge capacity of the lithium metal half-cell of Comparative Example 2 decayed to 86.0% after 280 cycles under the same test conditions, with a discharge capacity of approximately 128 mAh / g.

[0141] Figure 5 The high temperature cycle test results of the lithium metal half-cell provided in Example 2 of the present invention are shown in FIG. Figure 5As shown, the lithium metal half-cell of Example 2 of the present invention can be cycled at 60°C-100°C. This is because when the battery is operated at high temperature, the electrolyte initiator in the coating is released, triggering electrolyte ring-opening polymerization, which can improve the electrolyte's tolerance to high temperatures. However, Comparative Example 1 (a half-cell assembled with a bare lithium metal negative electrode) and Comparative Example 2 (a half-cell assembled with a lithium metal negative electrode protected by a coating without an electrolyte initiator) cannot be cycled stably for a long time at 60°C (not shown in the figure).

[0142] The half-cells of Example 2, Comparative Example 1 (a half-cell assembled with a bare lithium metal negative electrode), and Comparative Example 2 (a half-cell assembled with a lithium metal negative electrode protected by a coating without an electrolyte initiator) were disassembled after cycling at room temperature. The lithium metal and the electrolyte were mixed in a mass ratio of 1:2.5 and placed in a crucible. The mixture was heated at 10°C / min under an argon atmosphere. -1 The temperature was raised from 10°C to 420°C for differential scanning calorimetry (DSC) test. Figure 6 As shown, it can be seen that the lithium metal protected by the coating containing the electrolyte initiator in Example 2 of the present invention can suppress the heat generated by the reaction between the lithium metal and the electrolyte during the temperature rise process. This is because the solid electrolyte interface formed by the reduction of the electrolyte initiator can suppress the heat generated between the electrolyte and the lithium metal.

[0143] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a sustained-release polymer coating, characterized in that: The preparation method comprises: A polymer monomer, a polymer monomer initiator, a solvent, a crosslinking agent, and an electrolyte initiator are mixed in proportion to obtain a coating precursor slurry; wherein the polymer monomer comprises a fluorinated acrylate compound; the polymer monomer initiator comprises a free radical initiator; the solvent comprises an ether compound; the crosslinking agent comprises one or more of a polyethylene glycol derivative and an acrylate compound; and the electrolyte initiator comprises a high-temperature-resistant lithium salt capable of generating protonic acid with trace water; The coating precursor slurry is applied to the surface of the object to be covered, and subjected to a heating polymerization treatment to obtain a slow-release polymer coating.

2. The preparation method according to claim 1, characterized in that The volume ratio of the solvent to the polymer monomer is 100:1-1:1; the mass ratio of the polymer monomer to the electrolyte initiator is 1:1-3:1; the volume of the cross-linking agent is 0.5%-3% of the volume of the polymer monomer; and the mass of the polymer monomer initiator is not more than 1% of the mass of the polymer monomer.

3. The preparation method according to claim 1, characterized in that The conditions for the thermal polymerization treatment are: thermal polymerization at 60°C-70°C for 2 hours-20 hours; the atmosphere for the thermal polymerization includes one or more of an inert atmosphere, a vacuum drying atmosphere, and a waterless drying chamber drying atmosphere; the thickness of the sustained-release polymer coating is 1 μm-100 μm.

4. The preparation method according to claim 1, characterized in that The fluorinated acrylate compound includes one or more of trifluoroethyl acrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, hexafluorobutyl acrylate, heptafluorobutyl acrylate, heptafluoroisobutyl acrylate, nonafluoropentyl acrylate, tridecafluorooctyl acrylate and dodecafluoroheptyl methacrylate; The free radical initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and dibenzoyl peroxide; The ether compound includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dimethyl ether; The lithium salt includes one or more of lithium tetrafluoroborate, lithium difluorooxalatoborate, and lithium bis(fluorosulfonyl)imide; The polyethylene glycol derivatives include: one or more of polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diglycidyl ether, polyethylene glycol diacrylamide, and tri(ethylene glycol) diacrylate; The acrylate compound includes one or more of pentaerythritol triacrylate and pentaerythritol tetraacrylate.

5. A sustained-release polymer coating prepared by the preparation method according to any one of claims 1 to 4.

6. A lithium metal, characterized in that The lithium metal comprises the sustained-release polymer coating according to claim 5.

7. A lithium metal battery, characterized in that: The negative electrode of the lithium metal battery is the lithium metal according to claim 6.

8. The lithium metal battery according to claim 7, characterized in that The electrolyte of the lithium metal battery includes lithium salts and cyclic compounds that do not cause cationic ring-opening polymerization and are resistant to high temperatures; wherein the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium bromide, and lithium iodide; the cyclic compound includes a cyclic ether compound and a cyclic carbonate; the cyclic ether compound includes one or more of: 1,3-dioxolane, ethylene oxide, tetrahydrofuran, propylene oxide, epichlorohydrin, 1,2-butylene oxide, oxetane, 1,4-dioxane, and 1,3,5-trioxane.

9. A method for preparing a lithium metal battery according to any one of claims 7 to 8, characterized in that: The preparation method comprises: A lithium salt and a cyclic compound that do not cause cationic ring-opening polymerization and are resistant to high temperatures are mixed in proportion to obtain an electrolyte; A polymer monomer, a polymer monomer initiator, a solvent, a crosslinking agent, and an electrolyte initiator are mixed in proportion to obtain a coating precursor slurry; wherein the polymer monomer comprises a fluorinated acrylate compound; the polymer monomer initiator comprises a free radical initiator; the solvent comprises an ether compound; the crosslinking agent comprises one or more of a polyethylene glycol derivative and an acrylate compound; and the electrolyte initiator comprises a high-temperature-resistant lithium salt capable of generating protonic acid with trace water; Applying the coating precursor slurry to the surface of lithium metal and performing a heating polymerization treatment to obtain a lithium negative electrode with a slow-release polymer coating; The electrolyte is injected between the positive and negative electrodes inside the battery so that the electrolyte fully infiltrates the positive electrode, negative electrode and separator of the battery, and then the packaging is completed to obtain the lithium metal battery.

10. A lithium ion battery, characterized in that: The negative electrode of the lithium-ion battery comprises the sustained-release polymer coating according to claim 5.

Images