A sustained-release polymer coating and its preparation method and application

Abstract

The embodiment of the present application relates to a slow-release polymer coating and a preparation method and application thereof, wherein the preparation method comprises: mixing polymer monomers, polymer monomer initiators, solvents, cross-linking agents and electrolyte initiators in proportion to obtain a coating precursor slurry; wherein the polymer monomers comprise fluorinated acrylate compounds; the polymer monomer initiators comprise free radical initiators; the solvents comprise ether compounds; the cross-linking agents comprise one or more of polyethylene glycol derivatives and acrylate compounds; and the electrolyte initiators comprise lithium salts that can produce protonic acids with trace amounts of water and are resistant to high temperatures; the coating precursor slurry is coated onto the surface of the object to be covered, and a heating polymerization process is performed to obtain a 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] This invention relates to the field of solid-state battery technology, and in particular to a slow-release polymer coating, its preparation method, and its application. Background Technology

[0002] The rapid development of electronic devices and electric vehicles has placed higher demands on 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] Traditional commercial electrolytes use carbonate and ether solvents, which, when reacted with lithium metal, form a solid electrolyte interphase (SEI) that cannot effectively inhibit parasitic reactions. This results in low battery coulombic efficiency, continuous electrolyte consumption, and the inability of lithium ions to deposit uniformly on lithium metal, leading to severe dendrite growth.

[0004] At high temperatures, liquid electrolytes are prone to volatilization and release flammable gases such as CO2 and CH3F. When these gases mix with air and reach a certain concentration, they may ignite or explode upon contact with an open flame or electrical spark. Simultaneously, at high temperatures, SEI (Sediment I) undergoes severe decomposition, exposing fresh active lithium. The active lithium reacts further with the small-molecule electrolyte, releasing heat and increasing the battery temperature. Furthermore, dendrite growth is more severe at high temperatures, potentially puncturing the separator and causing a short circuit between the positive and negative electrodes, leading to thermal runaway.

[0005] Therefore, researchers have proposed the following strategies to address the high-temperature resistance problem of liquid electrolytes:

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

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

[0008] Third, constructing a stable SEI can reduce parasitic reactions at room temperature and suppress heat generation from high-temperature reactions. However, at high temperatures, the SEI will inevitably undergo thermal decomposition. As a result, the interfacial reaction between the electrolyte and the electrode further increases the battery temperature, leading to battery failure.

[0009] Fourth, gel electrolytes typically consist of a polymer matrix and an electrolyte solution, combining the high ionic conductivity of liquid electrolytes with the high safety of solid electrolytes. This allows for improved safety performance of lithium batteries while maintaining electrochemical performance. Although the solvent volatility of gel electrolytes is lower than that of liquid electrolytes, the solvent will still evaporate at high temperatures, leading to changes in electrolyte concentration and volume shrinkage. This evaporation affects the ionic conductivity of the electrolyte and the overall performance of the battery.

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

[0011] The purpose of this invention is to address the shortcomings of existing technologies by providing a slow-release polymer coating, its preparation method, and its application. This slow-release polymer coating can protect the negative electrode of a lithium battery and enhance the high-temperature safety performance of the lithium battery.

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

[0013] A coating precursor slurry is prepared by mixing polymer monomers, polymer monomer initiators, solvents, crosslinking agents, and electrolyte initiators in a specific ratio. The polymer monomers include fluorinated acrylate compounds; the polymer monomer initiators include free radical initiators; the solvents include ether compounds; the crosslinking agents include one or more of polyethylene glycol derivatives and acrylate compounds; and the electrolyte initiators include lithium salts capable of producing protic acids with trace amounts of water and resistant to high temperatures.

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

[0015] Preferably, the volume ratio of the solvent to the polymer monomer is 100:1 to 1:1; the mass ratio of the polymer monomer to the electrolyte initiator is 1:1 to 3:1; the volume of the crosslinking agent is 0.5% to 3% of the volume of the polymer monomer; and the mass of the polymer monomer initiator is no more than 1% of the mass of the polymer monomer.

[0016] Preferably, the conditions for the heating polymerization treatment are: heating polymerization at 60℃-70℃ for 2-20 hours; the atmosphere for heating polymerization includes one or more of inert atmosphere, vacuum drying atmosphere, and anhydrous drying chamber drying atmosphere; and the thickness of the slow-release polymer coating is 1μm-100μm.

[0017] Preferably, the fluorinated acrylate compounds include one or more of the following: trifluoroethyl acrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, butyl hexafluoroacrylate, heptafluorobutyl acrylate, heptafluoroisobutyl acrylate, nonafluoropentyl acrylate, tridecylfluorooctyl acrylate, and dodecafluoroheptyl methacrylate.

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

[0019] The ether compounds include one or more of the following: 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 difluorooxalate borate, and lithium difluorosulfonylimide.

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

[0022] The acrylate compounds include 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 above.

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

[0025] Fourthly, 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 comprises a lithium salt and a cyclic compound that do not cause cation ring-opening polymerization and are resistant to high temperatures; wherein the lithium salt comprises one or more of lithium bis(trifluoromethanesulfonylimide), lithium perchlorate, lithium bromide, and lithium iodide; the cyclic compound comprises cyclic ether compounds and cyclic carbonates; the cyclic ether compound comprises one or more of 1,3-dioxolane, ethylene oxide, tetrahydrofuran, epichlorohydrin, epichlorohydrin, 1,2-epoxybutane, oxetane, 1,4-dioxane, and 1,3,5-trioxane.

[0027] Fifthly, the present invention provides a method for preparing the lithium metal battery described in the fourth aspect above, the method comprising:

[0028] An electrolyte is obtained by mixing lithium salts and cyclic compounds that do not cause cationic ring-opening polymerization and are resistant to high temperatures in a certain proportion.

[0029] A coating precursor slurry is prepared by mixing polymer monomers, polymer monomer initiators, solvents, crosslinking agents, and electrolyte initiators in a specific ratio. The polymer monomers include fluorinated acrylate compounds; the polymer monomer initiators include free radical initiators; the solvents include ether compounds; the crosslinking agents include one or more of polyethylene glycol derivatives and acrylate compounds; and the electrolyte initiators include lithium salts capable of producing protic acids with trace amounts of water and resistant to high temperatures.

[0030] The coating precursor slurry is coated onto the surface of lithium metal and then subjected to heat polymerization treatment to obtain a lithium anode 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 wets the positive electrode, negative electrode and separator of the battery, and then the encapsulation 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 slow-release polymer coating described in the third aspect above.

[0033] This invention provides a method for preparing a slow-release polymer coating. By screening polymer monomer initiators, electrolyte initiators, solvents, polymer monomers, and crosslinking agents, and optimizing the coating precursor slurry ratio and coating thickness, a slow-release polymer coating is prepared using an in-situ polymerization process. When this slow-release polymer coating is applied to lithium batteries, it can enhance the high-temperature safety of the lithium batteries, as detailed below:

[0034] By using polymer monomers with flexible long side chains, electrolyte initiator molecules can be effectively anchored between polymer chains at room temperature, reducing leakage and maintaining the cyclic electrolyte in a liquid state with high ionic conductivity. The preferential reduction of electrolyte initiator molecules at the negative electrode generates an inorganic-rich solid electrolyte interface, suppressing side reactions between the negative electrode and the electrolyte. The slow-release polymer coating ensures uniform lithium ion deposition or guarantees lithium ion insertion and extraction, reducing the probability of lithium dendrite formation and preventing short circuits caused by lithium dendrites piercing the separator, thus improving battery cycle life. At high temperatures, the release of the electrolyte initiator from the slow-release polymer coating initiates ring-opening polymerization of the cyclic electrolyte, improving the electrolyte's high-temperature tolerance and reducing side reactions between the electrolyte and the negative electrode. Simultaneously, the SEI generated by reducing the electrolyte initiator at room temperature suppresses heat generation between the electrolyte and the negative electrode, thereby improving the safety of lithium batteries at high temperatures. Attached Figure Description

[0035] Figure 1 A flowchart illustrating the preparation method of the sustained-release polymer coating provided in this embodiment of the invention;

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

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

[0038] Figure 3 The graph shows the battery long-cycle polarization test results provided in Embodiment 2 and Comparative Examples 1 and 2 of the present invention.

[0039] Figure 4 The graph shows the room temperature cycling performance test results of the lithium metal half-cells provided in Embodiment 2 and Comparative Examples 1 and 2 of the present invention.

[0040] Figure 5 This is a graph showing the high-temperature cycling test results of the lithium metal half-cell provided in Embodiment 2 of the present invention;

[0041] Figure 6 The graph shows the differential scanning calorimetry test results of lithium metal provided in Embodiment 2 and Comparative Examples 1 and 2 of the present invention. Detailed Implementation

[0042] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

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

[0044] Step 110: Mix the polymer monomer, polymer monomer initiator, solvent, crosslinking agent and electrolyte initiator in proportion to obtain coating precursor slurry;

[0045] The polymer monomer may include fluorinated acrylate compounds. The fluorinated acrylate compounds preferably include one or more of the following: trifluoroethyl acrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, butyl hexafluoroacrylate, heptafluorobutyl acrylate, heptafluoroisobutyl acrylate, nonafluoropentyl acrylate, tridecafluorooctyl acrylate, and dodecafluoroheptyl methacrylate. The mass of the polymer monomer initiator is not greater than 1% of the mass of the polymer monomer, preferably 1%.

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

[0047] The solvent may include ether compounds. Preferably, the ether compounds include 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 solvent to polymer monomer can 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. Preferred 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. Preferred acrylate compounds include one or more of pentaerythritol triacrylate and pentaerythritol tetraacrylate. The volume of the crosslinking agent may specifically be 0.5%-3% of the polymer monomer volume, preferably 2%.

[0049] The electrolyte initiator may include a lithium salt that can produce a protic acid with trace amounts of water and is heat-resistant. Preferably, the lithium salt includes one or more of lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(fluorosulfonyl)imide.

[0050] Trace water, as is known in the art, refers to extremely small amounts of water (water vapor or adsorbed water) present in a gas, liquid, or solid. A protic acid is a substance that can donate a proton (H+). + The core characteristic of lithium salts as compounds (molecules or ions) to other substances is their proton transfer capability. They are heat-resistant (high temperatures in this application refer to temperatures not lower than 60°C), meaning they do not decompose at temperatures not lower than 60°C and remain chemically inert. Therefore, lithium salts possess the characteristics of hydrolysis with trace amounts of water and stability at high temperatures. In this embodiment, the decomposition temperature of the lithium salts is not less than 120°C. The mass ratio of polymer monomer to electrolyte initiator can be 1:1 to 3:1, preferably 2:1.

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

[0052] Specifically, the conditions for the heat polymerization treatment can be: heating and polymerization at 60℃-70℃ for 2-20 hours, preferably at 60℃ for 12 hours. The atmosphere for heat polymerization includes one or more of the following: inert atmosphere, vacuum drying atmosphere, and anhydrous drying chamber. The ambient water content for heat polymerization is preferably less than 20 ppm. The thickness of the slow-release polymer coating can be 1 μm-100 μm, preferably 1.5 μm.

[0053] In this process, the solvent dissolves the electrolyte initiator and is uniformly miscible with the polymer monomers, adjusting the reaction environment to ensure uniform distribution of reactants and improve reaction efficiency. The free radical initiator pyrolyzes to generate free radicals, forming active centers that initiate the polymerization of polymer monomers. The crosslinking agent connects linear or branched polymers into a three-dimensional network structure through chemical bonds, improving the mechanical properties and heat resistance of the polymers. Furthermore, the electrolyte initiator is anchored between the polymer chains.

[0054] At room temperature, electrolyte initiators 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 possesses good heat resistance and mechanical properties.

[0055] At temperatures of 60°C and above, polymerization continues between polymer chains, releasing the electrolyte initiator. This initiator reacts with trace amounts of water in the electrolyte to form protic acids. These protic acids act as initiators for cationic polymerization, releasing protons that combine with oxygen atoms in cyclic compounds within the electrolyte to form protonated oxonium ions. These ions reduce the ring strain of the cyclic ether, making it easier to break the carbon-oxygen bonds. The protonated oxonium ions further react with carbon atoms in the cyclic ether, causing ring opening and generating linear or branched macromolecules. Furthermore, the solid electrolyte interface formed at room temperature suppresses heat generation between the electrolyte and the negative electrode, improving battery safety at high temperatures.

[0056] This invention provides a method for preparing a slow-release polymer coating. By screening polymer monomer initiators, electrolyte initiators, solvents, polymer monomers, and crosslinking agents, and optimizing the coating precursor slurry ratio and coating thickness, a slow-release polymer coating is prepared using an in-situ polymerization process. When this slow-release polymer coating is applied to lithium batteries, it can enhance the high-temperature safety of the lithium batteries, as detailed below:

[0057] By using polymer monomers with flexible long side chains, electrolyte initiator molecules can be effectively anchored between polymer chains at room temperature, reducing leakage and maintaining the cyclic electrolyte in a liquid state with high ionic conductivity. The preferential reduction of electrolyte initiator molecules at the negative electrode generates an inorganic-rich solid electrolyte interface, suppressing side reactions between the negative electrode and the electrolyte. The slow-release polymer coating ensures uniform lithium ion deposition or guarantees lithium ion insertion and extraction, reducing the probability of lithium dendrite formation and preventing short circuits caused by lithium dendrites piercing the separator, thus improving battery cycle life. At high temperatures, the release of the electrolyte initiator from the slow-release polymer coating initiates ring-opening polymerization of the cyclic electrolyte, improving the electrolyte's high-temperature tolerance and reducing side reactions between the electrolyte and the negative electrode. Simultaneously, the SEI generated by reducing the electrolyte initiator at room temperature suppresses heat generation between the electrolyte and the negative electrode, thereby improving the safety of lithium batteries at high temperatures.

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

[0059] When used in lithium metal batteries, it can be prepared as follows:

[0060] Step 210: Mix lithium salt and cyclic compound in a certain proportion to obtain electrolyte;

[0061] Specifically, the lithium salt may include one or more of lithium bis(trifluoromethanesulfonylimide), lithium perchlorate, lithium bromide, and lithium iodide. The cyclic compound may include cyclic ether compounds and cyclic carbonates, preferably cyclic ether compounds, which may include one or more of 1,3-dioxolane, ethylene oxide, tetrahydrofuran, epichlorohydrin, epichlorohydrin, 1,2-epoxybutane, 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 initiated by a cationic active center (such as a carbocation or oxonium ion) to open the ring, forming a linear polymer. The cation is the ring-opening initiator, for example, an initiator capable of producing a protic acid (H+). + Lithium salts are substances that are Lewis acids (AlCl3, BF3) or stable carbocations. They are heat-resistant, meaning they do not decompose at temperatures not lower than 60°C and remain chemically inert. Therefore, these lithium salts do not possess the ability to generate cationic active centers to initiate the ring-opening of cyclic monomers to form polymers (i.e., they do not form protic acids with trace amounts of water), but they maintain stability at high temperatures.

[0063] In this embodiment, the decomposition temperature of lithium salts is not lower than 360°C. At room temperature, the ring-opening of cyclic ether compounds will not be caused, so that the electrolyte remains in a liquid state at room temperature, which can maintain a high ionic conductivity. Furthermore, it maintains the stability of its properties at high temperatures, thus ensuring the high-temperature resistance of the electrolyte.

[0064] Step 220: Mix the polymer monomer, polymer monomer initiator, solvent, crosslinking agent and electrolyte initiator to obtain coating precursor slurry;

[0065] The polymer monomers may include fluorinated acrylate compounds; the polymer monomer initiators include free radical initiators; the solvents include ether compounds; the crosslinking agents include one or more of polyethylene glycol derivatives and acrylate compounds; and the electrolyte initiators include lithium salts that can produce protic acids with trace amounts of water and are heat-resistant. The descriptions of polymer monomers, polymer monomer initiators, solvents, crosslinking agents, and electrolyte initiators are the same as those used in the preparation of the sustained-release polymer coating above, and will not be repeated here.

[0066] Step 230: The coating precursor slurry is coated onto the lithium metal surface and subjected to heat polymerization treatment to obtain a lithium anode with a slow-release polymer coating.

[0067] Specifically, the conditions for heat polymerization treatment can be: heating and polymerization at 60℃-70℃ for 2-20 hours. The atmosphere for heat polymerization includes one or more of the following: inert atmosphere, vacuum drying atmosphere, and anhydrous drying chamber atmosphere. The ambient water content for heat polymerization is preferably less than 20 ppm. The thickness of the slow-release polymer coating can be 1 μm-100 μm.

[0068] Slow-release polymer coatings can protect lithium metal, preventing non-uniform deposition of lithium ions during repeated charging and discharging, reducing the formation of lithium dendrites. Furthermore, the electrolyte initiator molecules in the slow-release polymer coating can be reduced by lithium metal first, generating an inorganic-rich solid electrolyte interface. The solid electrolyte interface can suppress side reactions between lithium metal and solvents or lithium salts in the electrolyte, thereby improving the cycle life of the battery.

[0069] Step 240: Inject the electrolyte between the positive and negative electrodes inside the battery, so that the electrolyte fully wets the positive electrode, negative electrode and separator of the battery, and then complete the encapsulation to obtain a lithium metal battery.

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

[0071] The diaphragm can be made using polyolefin diaphragms (polyethylene, polypropylene, etc.) or inorganic ceramic diaphragms (alumina, silicon dioxide, etc.).

[0072] At high temperatures (not lower than 60°C), the electrolyte initiator in the slow-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 a liquid state to a solid state, 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 this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0074] Example 1

[0075] This embodiment prepares lithium metal with a slow-release polymer coating.

[0076] Preparation of coating precursor slurry: Polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) are mixed at a volume ratio of 50:1 to obtain solution A. Solution A is mixed with electrolyte initiator lithium difluorooxalate borate (LiDFOB) at a mass ratio of 2:1 to obtain solution B. Then, ethylene glycol dimethyl ether (DME) solvent with a volume 99 times that of polymer monomer is added to solution B to obtain solution C. After that, azobisisobutyronitrile (AIBN) polymer monomer initiator with a mass of 1% of polymer monomer is added to solution C to obtain solution D. Solution D is mixed evenly to obtain coating precursor slurry.

[0077] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropped onto one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. Under an argon atmosphere, the lithium metal was heated at 60°C for 12 hours to allow the solvent dimethyl glycol ether (DME) to evaporate, and the polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating.

[0078] Subsequently, scanning electron microscopy (SEM) was performed on the lithium metal with the slow-release polymer coating, and the surface morphology of the coating was captured at 2000x magnification. Figure 2-a The cross-sectional morphology of the coating was captured by scanning at a magnification of 5000x. Figure 2-b ),according to Figure 2-a and 2-b As shown, the surface of the lithium metal is covered with a uniform and dense coating, and the coating thickness was measured to be 1.5 μm. The coating thicknesses mentioned in the following examples and comparative examples were all obtained by SEM testing and will not be repeated here.

[0079] Example 2

[0080] This embodiment demonstrates the preparation of a lithium metal battery with a lithium metal anode having a slow-release polymer coating.

[0081] Preparation of coating precursor slurry: Polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) are mixed at a volume ratio of 50:1 to obtain solution A. Solution A is mixed with electrolyte initiator lithium difluorooxalate borate (LiDFOB) at a mass ratio of 2:1 to obtain solution B. Then, ethylene glycol dimethyl ether (DME) solvent with a volume 99 times that of polymer monomer is added to solution B to obtain solution C. After that, azobisisobutyronitrile (AIBN) polymer monomer initiator with a mass of 1% of polymer monomer is added to solution C to obtain solution D. Solution D is mixed evenly to obtain coating precursor slurry.

[0082] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropped onto one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. Under an argon atmosphere, the lithium metal was heated at 60°C for 12 hours to allow the solvent dimethyl glycol ether (DME) to evaporate, and the polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating and a coating thickness of 1.5 μm.

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

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

[0085] Preparation of a lithium-ion symmetric battery: The lithium iron phosphate (LiFePO4) cathode was replaced with lithium metal, and the test lithium-ion symmetric battery of this embodiment was assembled as described above. The assembled lithium-ion symmetric battery was then tested on a Blue Battery Charge-Discharge Instrument at 0.5 mA cm⁻¹. -2 The current density controls the charge and discharge rate, 1mAh cm⁻¹ -2 The total charge and discharge capacity was limited by the capacity density and subjected to long-cycle polarization testing.

[0086] Preparation of lithium metal half-cells: A half-cell was assembled using LiFePO4 as the positive electrode and lithium metal protected by a coating containing an electrolyte initiator (slow-release polymer coating) as the negative electrode. Then, charge-discharge cycle performance was tested at room temperature using a Blue Battery Charge-Discharge Instrument at a 1C rate within the range of 2.5V to 3.8V. It should be noted that the lithium metal half-cells described here are essentially the lithium metal batteries mentioned above, assembled only for testing convenience.

[0087] Example 3

[0088] This embodiment demonstrates the preparation of a lithium metal pouch cell with a lithium metal anode having a slow-release polymer coating.

[0089] Preparation of coating precursor slurry: Polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) are mixed at a volume ratio of 50:1 to obtain solution A. Solution A is mixed with electrolyte initiator lithium difluorooxalate borate (LiDFOB) at a mass ratio of 2:1 to obtain solution B. Then, ethylene glycol dimethyl ether (DME) solvent with a volume 99 times that of polymer monomer is added to solution B to obtain solution C. After that, azobisisobutyronitrile (AIBN) polymer monomer initiator with a mass of 1% of polymer monomer is added to solution C to obtain solution D. Solution D is mixed evenly to obtain coating precursor slurry.

[0090] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropped onto one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. Under an argon atmosphere, the lithium metal was heated at 60°C for 12 hours to allow the solvent dimethyl glycol ether (DME) to evaporate, and the polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating and a coating thickness of 1.5 μm.

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

[0092] Assembly of lithium metal pouch batteries: The cut lithium metal anode with a slow-release polymer coating and LiFePO4 cathode are stacked into a cell using a stacking machine. An aluminum current collector is welded to the cathode and a nickel current collector is welded to the anode. The cell is then encapsulated with an aluminum-plastic film. Electrolyte is added to the aluminum-plastic film, and finally the cell is sealed and aged to obtain a lithium metal pouch battery with a lithium metal anode with a slow-release polymer coating.

[0093] Example 4

[0094] This embodiment demonstrates the preparation of a lithium metal battery with a lithium metal anode having a slow-release polymer coating.

[0095] Preparation of coating precursor slurry: Polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) are mixed at a volume ratio of 50:1 to obtain solution A. Solution A is mixed with electrolyte initiator lithium difluorooxalate borate (LiDFOB) at a mass ratio of 4:1 to obtain solution B. Then, ethylene glycol dimethyl ether (DME) solvent with a volume of 1.3 times that of polymer monomer is added to solution B to obtain solution C. After that, azobisisobutyronitrile (AIBN) polymer monomer initiator with a mass of 1% of polymer monomer is added to solution C to obtain solution D. Solution D is mixed evenly to obtain coating precursor slurry.

[0096] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropped onto one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. Under an argon atmosphere, the lithium metal was heated at 60°C for 12 hours to allow the solvent dimethyl glycol ether (DME) to evaporate, and the polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating and a coating thickness of 1.5 μm.

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

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

[0099] At 30°C and a 1C charge / discharge rate, this lithium metal battery experiences a capacity decay to 80% after 250 cycles, with a discharge capacity of approximately 113 mAh / g. At 60°C and a 1C charge / discharge rate, the capacity decays to 80% after 20 cycles, with a discharge capacity of approximately 110 mAh / g.

[0100] Example 5

[0101] This embodiment demonstrates the preparation of a lithium metal battery with a lithium metal anode having a slow-release polymer coating.

[0102] Preparation of coating precursor slurry: Mix the polymer trifluoroethyl acrylate and the crosslinking agent tri(ethylene glycol) diacrylate at a volume ratio of 50:1 to obtain solution A. Mix solution A with the electrolyte initiator lithium tetrafluoroborate at a mass ratio of 1:1 to obtain solution B. Add ethylene glycol diethyl ether solvent with a volume of 99 times that of the polymer monomer to solution B to obtain solution C. Then add 1% of the polymer monomer initiator azobisisoheptanenitrile by mass of the polymer monomer to obtain solution D. Mix solution D evenly to obtain the coating precursor slurry.

[0103] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropped onto one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. Under a vacuum drying atmosphere with a water content of 15 ppm, the lithium metal was heated at 70°C for 10 hours to allow the solvent ethylene glycol diethyl ether to evaporate, and the polymer trifluoroethyl acrylate and the crosslinking agent tri(ethylene glycol) diacrylate to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating and 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 completely dissolved to obtain electrolyte.

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

[0106] Example 6

[0107] This embodiment demonstrates the preparation of a lithium metal battery with a lithium metal anode having a slow-release polymer coating.

[0108] Preparation of coating precursor slurry: Heptafluoroisobutyl acrylate polymer and pentaerythritol triacrylate crosslinking agent are mixed at a volume ratio of 50:1 to obtain solution A. Solution A is mixed with lithium difluorosulfonyl imide electrolyte in a mass ratio of 2:1 to obtain solution B. Then, ethylene glycol dibutyl ether solvent with a volume of 99 times that of the polymer monomer is added to solution B to obtain solution C. After that, benzoyl peroxide polymer monomer initiator with a mass of 1% of the polymer monomer is added to solution C to obtain solution D. Solution D is mixed evenly to obtain coating precursor slurry.

[0109] Preparation of lithium metal: The above-mentioned coating precursor slurry was drop-added to one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. In an anhydrous drying chamber with a water content of 10 ppm, the lithium metal was heated at 65°C for 18 hours to allow the solvent ethylene glycol dibutyl ether to evaporate and the polymer heptafluoroisobutyl acrylate and crosslinking agent pentaerythritol triacrylate to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating and a coating thickness of 7 μm.

[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 completely dissolved to obtain the electrolyte.

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

[0112] Example 7

[0113] This embodiment demonstrates the preparation of a lithium metal battery with a lithium metal anode having a slow-release polymer coating.

[0114] Preparation of coating precursor slurry: Mix the polymer dodecafluoroheptyl methacrylate and the crosslinking agent pentaerythritol tetraacrylate at a volume ratio of 50:1 to obtain solution A. Mix solution A with the electrolyte initiator lithium difluorooxalate borate at a mass ratio of 4:1 to obtain solution B. Add diethylene glycol dimethyl ether solvent with a volume 99 times that of the polymer monomer to solution B to obtain solution C. Then, add 1% of the polymer monomer initiator azobisisobutyronitrile to solution C to obtain solution D. Mix solution D evenly to obtain the coating precursor slurry.

[0115] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropped onto one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. Under an argon atmosphere, the lithium metal was heated at 60°C for 12 hours to allow the solvent diethylene glycol dimethyl ether to evaporate, and the polymer dodecafluoroheptyl methacrylate and the crosslinking agent pentaerythritol tetraacrylate to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating and a coating thickness of 4 μm.

[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 onto the lithium iron phosphate (LiFePO4) positive electrode, then cover it with a polypropylene separator, add another 25μL of electrolyte to wet the separator, then stack a lithium metal negative electrode with a slow-release polymer coating and nickel foam, and finally encapsulate the battery with a casing to obtain a lithium metal battery.

[0118] Comparative Example 1

[0119] This comparative example demonstrates the preparation of a lithium metal battery with a lithium metal anode that does not have a slow-release polymer coating.

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

[0121] Assembly of lithium-lithium symmetric battery: Take 25μL of electrolyte and drop it onto lithium metal, then cover it with a polypropylene separator, add another 25μL of electrolyte to wet the separator, then stack a lithium metal anode without a slow-release polymer coating and nickel foam, and finally encapsulate the battery with a casing to obtain a lithium-lithium symmetric battery.

[0122] The assembled lithium-ion symmetric battery was tested on a Blue Battery Charge-Discharge Tester at 0.5 mA cm⁻¹. -2 The current density controls the charge and discharge rate, 1mAh cm⁻¹ -2 The total charge and discharge capacity was limited by the capacity density and subjected to long-cycle polarization testing.

[0123] Assembly of lithium metal half-cells: A half-cell was assembled using LiFePO4 as the positive electrode and exposed lithium metal as the negative electrode. Then, it was charged and discharged at room temperature using a Blue Battery Charge-Discharge Tester at a 1C rate within the range of 2.5V to 3.8V.

[0124] Comparative Example 2

[0125] This comparative example demonstrates the preparation of a lithium metal battery with a coated lithium metal anode.

[0126] Preparation of coating precursor slurry: Polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) are mixed at a volume ratio of 50:1 to obtain solution A. Dimethyl ethylene glycol ether (DME) solvent with a volume of 99 times that of polymer monomer is added to obtain solution C. Azobisisobutyronitrile (AIBN) with a mass fraction of 1% of solution C is added to obtain solution D. Solution D is mixed evenly to obtain coating precursor slurry.

[0127] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropped onto one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. Under an argon atmosphere, the lithium metal was heated at 60°C for 12 hours to allow the solvent dimethyl glycol ether (DME) to evaporate, and the polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating and a coating thickness of 1.5 μm.

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

[0129] Assembly of lithium-lithium symmetric battery: Take 25μL of electrolyte and drop it onto lithium metal, then cover it with a polypropylene separator, add another 25μL of electrolyte to wet the separator, then stack a coated lithium metal anode and nickel foam, and finally encapsulate the battery with a casing to obtain a lithium-lithium symmetric battery.

[0130] The assembled lithium-ion symmetric battery was tested on a Blue Battery Charge-Discharge Tester at 0.5 mA cm⁻¹. -2 The current density controls the charge and discharge rate, 1mAh cm⁻¹ -2 The total charge and discharge capacity was limited by the capacity density and subjected to long-cycle polarization testing.

[0131] Assembly of lithium metal half-cells: A half-cell was assembled using LiFePO4 as the positive electrode and lithium metal with a coating (but without an electrolyte initiator in the coating) as the negative electrode. Then, it was charged and discharged at room temperature on a Blue Battery Charge-Discharge Tester at a rate of 1C within the range of 2.5V to 3.8V.

[0132] Comparative Example 3

[0133] This comparative example demonstrates the preparation of a lithium metal battery with lithium metal protected by a slow-release polymer coating.

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

[0135] Preparation of lithium metal: The above-mentioned coating precursor slurry was dropped onto one side of a lithium metal surface with a thickness of 300 μm. The coating precursor slurry was then uniformly coated onto the lithium metal surface using a blade coating technique with a blade height of 350 μm. Under an argon atmosphere, the lithium metal was heated at 60°C for 12 hours to allow the solvent dimethyl glycol ether (DME) to evaporate, and the polymer monomer pentafluoropropyl acrylate (PFA) and crosslinking agent polyethylene glycol diacrylate (PEGDA) to fully polymerize, thus obtaining lithium metal with a slow-release polymer coating and a coating thickness of 1.5 μm.

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

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

[0138] At 30°C and a charge / discharge rate of 1C, the discharge capacity of this lithium metal battery 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 become severe after activation, preventing it from being charged and causing it to fail.

[0139] according to Figure 3 As shown, the battery in Comparative Example 1 has the highest polarization voltage during long-cycle operation, followed by the battery in Comparative Example 2. The battery in Example 2 of this invention achieves the lowest polarization voltage during long-cycle operation because the electrolyte initiator in the coating is preferentially reduced on the negative electrode side, thereby generating a low-impedance interface layer rich in inorganic matter.

[0140] Figure 4 The graph shows the room temperature cycling performance test results of the lithium metal half-cells provided in Embodiment 2 and Comparative Examples 1 and 2 of the present invention. Figure 4 As shown, the lithium metal half-cell of Example 2 of this invention exhibits significantly higher cycle performance than the lithium metal half-cells of Comparative Examples 1 and 2. The lithium metal half-cell of Example 2 benefits from the preferential reduction of the electrolyte initiator in the coating on the negative electrode side, resulting in an inorganic-rich interface layer with excellent mechanical properties. This layer adapts to changes in lithium metal volume during cycling and inhibits side reactions between the electrolyte and lithium metal. Consequently, at 30°C and a 1C charge / discharge rate, the discharge capacity decays to 78.3% after 470 cycles, with a discharge capacity of approximately 111 mAh / g. In contrast, the lithium metal half-cell of Comparative Example 1, under the same test conditions, already exhibits a discharge capacity decay to 80.6% after 130 cycles, with a discharge capacity of approximately 116 mAh / g. The lithium metal half-cell of Comparative Example 2, under the same test conditions, exhibits a discharge capacity decay to 86.0% after 280 cycles, with a discharge capacity of approximately 128 mAh / g.

[0141] Figure 5 The graph shows the high-temperature cycling test results of the lithium metal half-cell provided in Embodiment 2 of the present invention. Figure 5As shown, the lithium metal half-cell of Example 2 of this invention can cycle at 60°C-100°C. This is because when the battery is running at high temperatures, the electrolyte initiator in the coating is released, initiating ring-opening polymerization of the electrolyte, 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 lithium metal protected by a coating without electrolyte initiator as the negative electrode) cannot cycle stably for a long time at 60°C (not shown in the figure).

[0142] The half-cells of Example 2, Comparative Example 1 (half-cell assembled with bare lithium metal anode), and Comparative Example 2 (half-cell assembled with lithium metal protected by a coating without electrolyte initiator as anode) were disassembled after being cycled at room temperature. The lithium metal and electrolyte were mixed at a mass ratio of 1:2.5 and placed in a crucible. The mixture was then incubated at 10°C for 1 minute under an argon atmosphere. -1 The heating rate was measured from 10℃ to 420℃ using differential scanning calorimetry (DSC), and the results are as follows: Figure 6 As shown in the figure, the lithium metal protected by the coating containing the electrolyte initiator in Embodiment 2 of the present invention can suppress the heat generated by the reaction between lithium metal and electrolyte during the heating process. This is because the solid electrolyte interface generated by the reduction of the electrolyte initiator can suppress the heat generation between the electrolyte and lithium metal.

[0143] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment 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 within 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 includes: A coating precursor slurry is prepared by mixing polymer monomers, polymer monomer initiators, solvents, crosslinking agents, and electrolyte initiators in a specific ratio. The polymer monomers include fluorinated acrylate compounds; the polymer monomer initiators include free radical initiators; the solvents include ether compounds; the crosslinking agents include one or more of polyethylene glycol derivatives and acrylate compounds; and the electrolyte initiator includes a first lithium salt capable of producing a protic acid with trace amounts of water and resistant to high temperatures. The first lithium salt includes one or more of lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium difluorosulfonylimide. The coating precursor slurry is applied to the surface of the object to be covered and then subjected to heat polymerization 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 to 1:1; the mass ratio of the polymer monomer to the electrolyte initiator is 1:1 to 3:1; the volume of the crosslinking agent is 0.5% to 3% of the volume of the polymer monomer; and the mass of the polymer monomer initiator is no 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 heating polymerization treatment are: heating polymerization at 60℃-70℃ for 2-20 hours; the atmosphere for heating polymerization includes one or more of the following: inert atmosphere, vacuum drying atmosphere, and anhydrous drying chamber drying atmosphere; the thickness of the slow-release polymer coating is 1μm-100μm.

4. The preparation method according to claim 1, characterized in that, The fluorinated acrylate compounds include one or more of the following: trifluoroethyl acrylate, hexafluoroisopropyl acrylate, pentafluoropropyl acrylate, butyl hexafluoroacrylate, heptafluorobutyl acrylate, heptafluoroisobutyl acrylate, nonafluoropentyl acrylate, tridecafluorooctyl acrylate, and dodecafluoroheptyl methacrylate. The free radical initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide; The ether compounds include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dimethyl ether; The polyethylene glycol derivatives include one or more of the following: polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diglycidyl ether, polyethylene glycol diacrylamide, and tri(ethylene glycol) diacrylate; The acrylate compounds include one or more of pentaerythritol triacrylate and pentaerythritol tetraacrylate.

5. A sustained-release polymer coating prepared by any of the preparation methods described in claims 1-4.

6. A lithium metal, characterized in that, The lithium metal includes the slow-release polymer coating as described in 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 comprises a second lithium salt that does not cause cationic ring-opening polymerization and is heat-resistant, and a cyclic compound; wherein the second lithium salt comprises one or more of lithium bis(trifluoromethanesulfonylimide), lithium perchlorate, lithium bromide, and lithium iodide; the cyclic compound comprises cyclic ether compounds and cyclic carbonates; the cyclic ether compound comprises one or more of 1,3-dioxolane, ethylene oxide, tetrahydrofuran, epichlorohydrin, epichlorohydrin, 1,2-epoxybutane, oxetane, 1,4-dioxane, and 1,3,5-trioxane.

9. A method for preparing a lithium metal battery according to any one of claims 7-8, characterized in that, The preparation method includes: The electrolyte is obtained by mixing a second lithium salt that does not cause cationic ring-opening polymerization and is heat-resistant with a cyclic compound in a certain proportion. A coating precursor slurry is prepared by mixing polymer monomers, polymer monomer initiators, solvents, crosslinking agents, and electrolyte initiators in a specific ratio. The polymer monomers include fluorinated acrylate compounds; the polymer monomer initiators include free radical initiators; the solvents include ether compounds; the crosslinking agents include one or more of polyethylene glycol derivatives and acrylate compounds; and the electrolyte initiator includes a first lithium salt capable of producing a protic acid with trace amounts of water and resistant to high temperatures. The coating precursor slurry is coated onto the surface of lithium metal and then subjected to heat polymerization treatment to obtain a lithium anode with a slow-release polymer coating. The electrolyte is injected between the positive and negative electrodes inside the battery, so that the electrolyte fully wets the positive electrode, negative electrode and separator of the battery, and then the encapsulation is completed to obtain the lithium metal battery.

10. A lithium-ion battery, characterized in that, The negative electrode of the lithium-ion battery includes the slow-release polymer coating as described in claim 5.

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