A boron-rich single-ion polymer artificial SEI film, and a preparation method and application thereof

Abstract

The application relates to the technical field of artificial solid electrolyte interface (SEI) layers, and discloses a boron-rich single-ion polymer artificial SEI film as well as a preparation method and application thereof. The artificial SEI film is a boron-rich three-dimensional cross-linked network structure with single-ion and self-healing functions; a large amount of boron in the structure can act as a Lewis acid to accelerate the dissociation of lithium salt anions and cations, so that the ion conductivity and migration number of the polymer artificial SEI film are improved; and the dynamic covalent bond behavior of borate ester bonds in the structure endows the polymer with self-healing performance, endows the artificial SEI film with self-healing performance, and improves the safety and electrochemical performance of a polymer lithium metal battery. The boron-rich single-ion polymer artificial SEI film provided by the application has high safety and good electrochemical performance, and can provide a new method for preparing a novel artificial SEI film.

Description

Technical Field

[0001] This invention relates to the field of artificial solid electrolyte interlayer (SEI) technology, and in particular to a boron-rich single-ion artificial SEI membrane, its preparation method, and its application. Background Technology

[0002] Lithium metal batteries (LMBs) possess extremely high theoretical specific capacity (3860 mA h g⁻¹) and the lowest reduction potential (-3.040 V vs SHE), making them a viable next-generation rechargeable battery for practical application. However, due to the high reactivity of lithium metal with organic electrolytes, a natural solid electrolyte interphase (SEI) forms on the lithium anode side during battery cycling. Theoretically, the natural SEI film can act as a lithium-ion conductor and electronic insulator, protecting the lithium metal anode and suppressing electrolyte consumption. However, natural SEIs are typically fragile and unstable. After the SEI breaks down, a new SEI film forms, a process that consumes electrolyte and metallic lithium. This ultimately leads to low coulombic efficiency, short cycle life, and the continuous growth of lithium dendrites that can pierce the separator between the positive and negative electrodes, causing internal short circuits and potentially leading to fires and explosions. These problems severely hinder the practical application of lithium metal batteries. Constructing a polymer-based artificial SEI film on the lithium anode surface is a highly effective measure to suppress lithium dendrite growth and mitigate the reaction between lithium metal and the electrolyte.

[0003] However, reported polymer-based artificial SEI films often exhibit low conductivity, hindering lithium-ion transport and leading to uneven deposition and distribution on the electrodes, resulting in lithium dendrite formation. Furthermore, most artificial SEI films are dual-ion conductors; according to the Brissot-Chazalviel theory, ion conduction in dual-ion conductors easily generates an electric field near the electrode, thus promoting lithium dendrite formation. In addition, if the constructed artificial SEI film ruptures during battery cycling, it causes irreversible damage, not only losing its function of protecting the lithium anode but also accelerating lithium dendrite growth. The continuous growth of these lithium dendrites can puncture the battery separator, causing short circuits, and potentially leading to fires and explosions. Summary of the Invention

[0004] This invention aims to overcome at least one of the shortcomings and deficiencies of the prior art, and provides a boron-rich single-ion polymer artificial SEI membrane, its preparation method, and its applications. By improving the key structure and related composition of the boron-rich polymer artificial SEI membrane (especially the key chemical structural formulas, functional groups, and related ratios of the polymer monomers), as well as the overall synthetic route design and reaction conditions of each step of the corresponding preparation method, a series of polymer skeletons with boron-rich crosslinked networks are prepared.

[0005] The objective of this invention is achieved based on the following technical solution:

[0006] The first aspect of this invention provides a boron-rich single-ion polymer artificial SEI membrane, wherein the boron-rich polymer is composed of a crosslinking compound consisting of a pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, a boron ester dithiol compound BDB, and a linear boron-containing monomer LBM, wherein the chemical structural formula of the LBM is as follows:

[0007]

[0008] Where n is an integer from 5 to 15.

[0009] Boron esters, due to the empty orbitals of boron atoms, can act as Lewis acids to immobilize anions. Lithium boron ester salts exhibit high ionic conductivity, good thermal stability, and are simple and inexpensive to prepare. Therefore, we used an olefin click reaction to polymerize the linear boron-containing monomer LBM and the boron ester dithiol compound BDB via pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP to prepare a single-ion polymer artificial SEI film LBP. This effectively improves the conductivity and transport number of the artificial SEI film. Furthermore, boron esters are groups formed by dynamic covalent bonds, and this dynamic covalent bond property also endows the polymer network with self-healing properties. This characteristic allows the SEI film to heal itself after rupture, providing continuous protection for the lithium anode.

[0010] Compared to existing technologies, this polymer network has two main advantages. First, it contains a large number of borate ester groups. The boron atoms in these borate ester groups have empty orbitals, allowing them to accept electrons as Lewis acids. This immobilizes the anions, forming an anion network that enables rapid migration and dissociation of lithium ions within the interface layer. Furthermore, it ensures uniform distribution of lithium ions on the surface layer during lithium ion deposition, effectively preventing lithium dendrite formation and improving the cycle life and safety performance of lithium metal batteries. Second, the numerous dynamic covalent bonds in the borate esters within the polymer network endow the artificial SEI film with excellent self-healing properties. Even if the SEI film ruptures during electrochemical cycling, it will subsequently self-repair, thus continuously protecting the lithium anode.

[0011] Preferably, the crosslinking compound is formed by photoinitiated polymerization, which promotes the formation of a boron-rich crosslinking network by three reactants: pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, borate ester dimercapto compound BDB, and linear boron-containing monomer LBM. This polymer network contains a large number of borate ester groups.

[0012] Preferably, the chemical structural formula of the borate ester dithiol compound BDB is as follows:

[0013]

[0014] The chemical structural formula of pentaerythritol tetra-3-mercaptopropionate PETMP is as follows:

[0015]

[0016] Preferably, the sum of the molar ratios of the linear boron-containing monomer LBM to the borate ester dithiol compound BDB and the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, LBM / (BDB+PETMP), is 1 / 2 to 1 / 25; the molar ratio of the linear boron-containing monomer LBM to the borate ester dithiol compound BDB is 1 / 1 to 1 / 10; and the molar ratio of the linear boron-containing monomer LBM to the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP is 1 / 1 to 1 / 15.

[0017] Preferably, the polymer artificial SEI membrane is a thin film with a thickness of 0.01 to 1.5 micrometers.

[0018] A second aspect of this invention provides a method for preparing a boron-rich single-ion polymer artificial SEI membrane, comprising the following steps:

[0019] 1) Trimethyl borate (TMB) and glyceryl methacrylate (GMMA) were mixed in the first solvent and stirred under an inert atmosphere; then PEG was injected into the reaction solution, heated and stirred, the solvent was removed under reduced pressure, and dried to obtain the product LBM.

[0020] 2) The pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, borate ester dimercapto compound BDB, linear boron-containing monomer LBM obtained in step 1) and initiator are dissolved in a second solvent and mixed evenly. The resulting mixture is then uniformly dropped onto the lithium metal surface and irradiated under ultraviolet light to react. After drying, a polymer artificial SEI film is obtained.

[0021] This invention improves the overall synthetic route design and reaction conditions of each step in the preparation method to prepare a series of boron-rich polymer single-ion artificial SEI membranes.

[0022] Preferably, in step 1):

[0023] The molecular structure of the trimethyl borate is as follows:

[0024] The molecular structure of the methylpropionic acid glyceride is as follows:

[0025] The molecular structure of the polyethylene glycol is as follows: Molecular weight M W =400-2000;

[0026] The molar ratio of trimethyl borate to methacrylic acid is 1 / 0.1 to 1 / 1;

[0027] The molar ratio of trimethyl borate to polyethylene glycol is 2 / 1 to 2 / 5.

[0028] The reaction temperature is 10–80°C, and the reaction time is 2–10 hours;

[0029] The first solvent includes at least one of tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, and acetonitrile.

[0030] Preferably, in step 2):

[0031] The molar ratio of the linear boron-containing monomer LBM to the boron ester dithiol compound BDB is 1 / 1 to 1 / 10, and the molar ratio of the linear boron-containing monomer LBM to the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP is 1 / 1 to 1 / 15; the sum of the molar ratios of LBM to BDB and PETMP, LBM / (BDB+PETMP), is 1 / 2 to 1 / 25.

[0032] The second solvent is any one or more of dimethyl carbonate, ethylene carbonate, 1,3-dioxolane, ethylene glycol dimethyl ether, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide;

[0033] The photoinitiator is one of 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, and 2-hydroxy-2-methylpropanone;

[0034] The mass ratio of the photoinitiator to the linear boron-containing monomer LBM is 1 / 10 to 1 / 20;

[0035] The irradiation reaction time under ultraviolet light is 5 to 30 minutes.

[0036] Preferably, the borate ester dithiol compound BDB described in step 2) is prepared as follows: 1,4-phenyldiboron and 1-thioglycerol are dissolved in a first solvent, deionized water and magnesium sulfate are added, and the mixture is stirred at 10-70°C for 12-36 hours; the reaction product is filtered, distilled under reduced pressure, washed and dried to obtain the borate ester dithiol compound BDB.

[0037] This invention also improves the electrochemical properties of single-ion polymer artificial SEI films, such as conductivity and mobility number, by optimizing and controlling the parameters of each process step in the preparation method (including the molecular weight control of LBM, the ratio between different monomers, reaction time and temperature, etc.).

[0038] The boron-rich single-ion polymer artificial SEI film provided by this invention has good applications in lithium metal batteries.

[0039] Compared with existing technologies, the boron-rich single-ion polymer artificial SEI film prepared by photoinitiated polymerization, based on the linear boron-containing monomer LBM, the boron ester dithiol compound BDB, and the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, can significantly improve the electrochemical performance of lithium metal battery polymer artificial SEI films, such as conductivity and mobility number. This polymer network contains a large number of boron ester groups. The boron atoms in these boron ester groups have empty orbitals and can accept electrons as Lewis acids, fixing the anions and forming an anion network. This allows lithium ions to migrate and dissociate rapidly within the interface layer and ensures uniform distribution of lithium ions on the surface layer during lithium ion deposition. This effectively prevents the formation of lithium dendrites and improves the cycle life and safety performance of lithium metal batteries. Furthermore, the numerous dynamic covalent bonds in the boron esters within the polymer network endow the artificial SEI film with excellent self-healing properties. Even if the SEI film ruptures during electrochemical cycling, it will subsequently self-repair, thus continuously protecting the lithium anode.

[0040] The boron-rich single-ion polymer artificial SEI membrane and its preparation method provided by this invention are rarely reported in the prior art. In particular, the introduction of a large number of borate ester groups into the polymer system, based on the Lewis acid characteristics of boron and the dynamic covalent bond properties of borate ester groups, provides a new method and idea for developing novel polymer artificial SEI membranes (especially single-ion and self-healing materials) with high safety and excellent electrochemical performance.

[0041] This invention is the first to introduce the linear boron-containing monomer LBM and the borate ester bis-thiol compound BDB into a polymer crosslinking network, realizing a boron-rich polymer single-ion polymer artificial SEI membrane in the field of polymer artificial SEI membranes for lithium metal batteries. The large number of borate ester groups improves the lithium-ion conductivity and migration number of the artificial SEI membrane and endows the polymer with self-healing properties, with a very significant improvement effect.

[0042] In summary, the present invention can achieve the following beneficial effects:

[0043] (1) This invention utilizes photoinitiated polymerization to efficiently prepare boron-rich single-ion polymer artificial SEI membranes based on linear boron-containing monomer LBM, boron ester dithiol compound BDB, and pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP. Currently, no methods have been reported to improve the ionic conductivity and transport number of polymer artificial SEIs by introducing linear boron-containing monomer LBM and boron ester dithiol compound BDB.

[0044] (2) This invention uses LBM, BDB, and PETMP as raw materials. After adding an initiator, a single-ion conductor polymer artificial SEI film LBP with a three-dimensional cross-linked network structure and rich in borate ester groups was constructed by ultraviolet light polymerization. This polymer contains a large number of borate ester groups. The boron atoms in these borate ester groups have empty orbitals and can accept electrons as Lewis acids. Anions can be fixed on them to form an anion network, allowing lithium ions to migrate and dissociate rapidly within the interface layer. Furthermore, during lithium ion deposition, lithium ions can be uniformly distributed on the surface layer, thus effectively preventing the formation of lithium dendrites and improving the cycle life and safety performance of lithium metal batteries.

[0045] (3) The numerous borate ester groups introduced in this invention represent a special type of dynamic covalent bond. Based on this unique chemical bond property, the polymer artificial SEI possesses excellent self-healing properties. Although other artificial SEI films can improve electrode interface stability to some extent, the volume change of the electrode during electrochemical cycling usually leads to a certain degree of SEI film rupture. The artificial SEI of this invention has self-healing properties, which can effectively repair the ruptured SEI in a timely manner, allowing the artificial SEI film to continuously and effectively protect the lithium anode, thereby improving the safety performance of lithium metal batteries. Simultaneously, by controlling the ratio of the linear boron-containing monomer LBM, the boron-containing ester dithiol compound BDB, and the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP in the structure, a polymer backbone with stable structure and excellent mechanical properties can be formed.

[0046] In summary, compared with existing technologies, this invention improves the ionic conductivity and transport number of the polymer artificial SEI film by introducing a large number of borate ester groups and utilizing the Lewis acid properties of boron to fix the anions and accelerate the dissociation of lithium salts. Furthermore, based on the dynamic covalent bond characteristics of the borate ester groups, the polymer is endowed with self-healing properties, improving the safety and electrochemical performance of lithium batteries. The boron-rich single-ion polymer artificial SEI film described in this invention possesses high conductivity, transport number, and excellent electrochemical performance, providing a new method for preparing novel single-ion polymer artificial SEIs. Attached Figure Description

[0047] Figure 1 This is a physical image of the boron-rich single-ion polymer artificial SEI film prepared in Example 1 of the present invention, wherein the inset is a scanning electron microscope (SEM) image of the SEI film prepared on lithium metal.

[0048] Figure 2 This is the NMR spectrum of the linear boron-containing monomer LBM synthesized in Example 1 of this invention;

[0049] Figure 3 This is the NMR spectrum of the borate ester dithiol compound BDB synthesized in Example 2 of this invention;

[0050] Figure 4 This is a graph showing the change in conductivity of the boron-rich single-ion polymer artificial SEI membrane prepared in Example 3 of this invention as a function of temperature.

[0051] Figure 5 This is an experimental diagram showing the self-healing performance of the boron-rich single-ion polymer artificial SEI membrane prepared in Example 4 of this invention. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] A preferred embodiment of the present invention provides a boron-rich single-ion polymer artificial SEI membrane, which is composed of a crosslinking compound consisting of a linear boron-containing monomer LBM, a boron ester dithiol compound BDB, and a pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, wherein the molar ratio of LBM to BDB is 1 / 1 to 1 / 10, and the chemical structural formula of the linear boron-containing monomer LBM is as follows: Where n = 5 to 15.

[0054] The crosslinked compound is formed by photoinitiated polymerization, which promotes the formation of a boron-rich mono-ion polymer crosslinked network by three reactants: linear boron-containing monomer LBM, boron ester dithiol compound BDB, and pentaerythritol tetra-3-mercaptopropionate ester PETMP. This network structure has a large number of boron ester groups, which improves the lithium-ion conductivity and mobility number.

[0055] The method for preparing the boron-rich single-ion polymer artificial SEI membrane includes the following steps:

[0056] 1) Trimethyl borate (TMB) and glyceryl methacrylate (GMMA) were mixed in a first solvent and reacted under an inert atmosphere with stirring. Then, PEG (molecular weight MW = 400-2000) was injected into the solution, and the mixture was heated and stirred. After removing the solvent under reduced pressure, the product LBM was obtained by drying.

[0057] 2) The pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, the linear boron-containing monomer LBM obtained in step 1), the boron ester dimercapto compound BDB and the initiator are dissolved in a third solvent and mixed evenly. The mixture is then dropped onto the lithium metal surface using a pipette and irradiated under ultraviolet light to react. After drying, the polymer artificial LBP-SEI is obtained.

[0058] The first, second, and third reagents can be of similar types, as long as they can dissolve the reactants in their respective steps. The order of steps 1) and 2) can be changed; there are no specific requirements.

[0059] The following are specific examples.

[0060] Example 1

[0061] 4.16 g of trimethyl borate (TMB) and 5.76 g of glyceryl methacrylate (GMMA) were mixed in 80 mL of anhydrous acetonitrile, and dry argon gas was introduced while the solution was stirred at 70 °C for 7 h. Then, 40 g of PEG (molecular weight MW = 2000) was injected into the solution, and the reaction was carried out at 70 °C for 9 h. After vacuum distillation and drying, LBM was obtained. The NMR spectrum of LBM is shown in Figure 2. 2.22 g of 1,4-phenyldiboron, 2.5 g of 1-thioglycerol, and 2.2 mL of deionized water were added to 60 mL of tetrahydrofuran and stirred until dissolved. Then, 1.2 g of magnesium sulfate was added, and the reaction was carried out with vigorous stirring at 10 °C for 12 hours. After filtration, vacuum distillation, washing, and drying, BDB was obtained. The NMR spectrum of BDB is shown in Figure 2. Figure 3 .

[0062] 85.2 mg of linear boron-containing monomer LBM, 15.6 mg of boron-containing ester dithiol compound BDB, and 21.6 mg of crosslinking agent pentaerythritol tetra-3-mercaptopropionate (PETMP) were mixed in a reaction flask, and 2 mL of DOL / DME (1:1) was added. The mixture was stirred until all components were uniformly dispersed. Then, 15 μL of initiator 2-hydroxy-2-methylphenylacetone was added to obtain the precursor solution. 5 μL of the precursor solution was pipetted onto lithium metal and irradiated under a UV lamp for 5 min to obtain the polymer artificial SEI film. The entire operation must be performed inside a glove box. The conductivity versus temperature graph is shown below. Figure 4 Compared with a boron-free SEI membrane in a polymer network (by replacing the linear boron-containing monomer LBM in the structure with polyethylene glycol diacrylate PEGDA), the boron-rich single-ion polymer artificial SEI membrane exhibits higher ionic conductivity, indicating that the introduction of boron can improve the ionic conductivity of the artificial SEI membrane.

[0063] The thickness of the boron-rich single-ion polymer artificial SEI film obtained in this embodiment is 50 nanometers, such as Figure 1 As shown. The self-healing properties of the LBP membrane are shown in the figure. Figure 5 After being cut, the polymer artificial SEI membrane can self-heal after being placed at 30°C for 1 hour. This is because the polymer structure contains a large number of borate ester groups formed by dynamic covalent bonds, and the polymer membrane has good self-healing properties.

[0064] Example 2

[0065] 4.16 g of trimethyl borate (TMB) and 1.92 g of glyceryl methacrylate (GMMA) were mixed in 50 mL of tetrahydrofuran, and dry argon gas was introduced while the solution was stirred at 30 °C for 4 h. Then, 8 g of PEG (molecular weight MW = 800) was injected into the solution, and the reaction was carried out at 30 °C for 6 h. LBM was obtained after vacuum distillation and drying. 0.44 g of 1,4-phenyldiboron, 0.5 g of 1-thioglycerol, and 0.02 mL of deionized water were added to 10 mL of dimethyl sulfoxide and stirred until dissolved. Then, 0.48 g of magnesium sulfate was added, and the mixture was stirred vigorously at 20 °C for 20 hours. After filtration, vacuum distillation, washing, and drying, BDB was obtained.

[0066] 85.2 mg of linear boron-containing monomer LBM, 46.8 mg of boron-containing ester dithiol compound BDB, and 64.8 mg of crosslinking agent pentaerythritol tetra-3-mercaptopropionate (PETMP) were mixed in a reaction flask, and 2 mL of EC / DMC (1:1) was added. The mixture was stirred until all components were uniformly dispersed. Then, 20 μL of initiator 2-hydroxy-2-methylphenylacetone was added to obtain the precursor solution. 10 μL of the precursor solution was pipetted onto lithium metal and irradiated under a UV lamp for 10 min to obtain a polymer artificial SEI film. The entire operation must be performed inside a glove box. The thickness of the boron-rich single-ion polymer artificial SEI film obtained in this embodiment is 100 nm. Similar to Example 1, the polymer film obtained in this embodiment exhibits good self-healing properties.

[0067] Example 3

[0068] 2.08 g of trimethyl borate (TMB) and 1.60 g of glyceryl methacrylate (GMMA) were mixed in 70 mL of dimethyl sulfoxide, and dry argon gas was introduced while the solution was stirred at 50 °C for 4 h. Then, 4 g of PEG (molecular weight MW = 800) was injected into the solution, and the reaction was carried out at 50 °C for 8 h. LBM was obtained after vacuum distillation and drying. 0.88 g of 1,4-phenyldiboron, 0.98 g of 1-thioglycerol, and 0.05 mL of deionized water were added to 10 mL of N,N-dimethylformamide and stirred until dissolved. Then, 1.44 g of magnesium sulfate was added, and the mixture was stirred vigorously at 30 °C for 16 hours. After filtration, vacuum distillation, washing, and drying, BDB was obtained.

[0069] 85.2 mg of linear boron-containing monomer LBM, 78.0 mg of boron-containing ester dithiol compound BDB, and 108.0 mg of crosslinking agent pentaerythritol tetra-3-mercaptopropionate (PETMP) were mixed in a reaction flask, and 3 mL of tetrahydrofuran was added. The mixture was stirred until all components were uniformly dispersed. Then, 30 μL of initiator 1-hydroxycyclohexylphenyl ketone was added to obtain the precursor solution. 20 μL of the precursor solution was pipetted onto lithium metal and irradiated under a UV lamp for 15 min to obtain a polymeric artificial SEI film. The entire process had to be performed inside a glove box. The boron-rich single-ion polymeric artificial SEI film obtained in this embodiment had a thickness of 200 nm. Similar to Example 1, the polymer film obtained in this embodiment exhibited good self-healing properties.

[0070] Example 4

[0071] 2.08 g of trimethyl borate (TMB) and 1.92 g of glyceryl methacrylate (GMMA) were mixed in 50 mL of anhydrous acetonitrile, and the solution was stirred at 65 °C for 5 h under dry argon gas. Then, 20 g of PEG (molecular weight MW = 1000) was injected into the solution, and the reaction was carried out at 65 °C for 7 h. LBM was obtained after vacuum distillation and drying. 0.88 g of 1,4-phenyldiboron, 0.98 g of 1-thioglycerol, and 0.06 mL of deionized water were added to 10 mL of tetrahydrofuran and stirred until dissolved. Then, 1.58 g of magnesium sulfate was added, and the mixture was stirred vigorously at 40 °C for 16 hours. BDB was obtained after filtration, vacuum distillation, washing, and drying.

[0072] 42.6 mg of linear boron-containing monomer LBM, 46.8 mg of boron-containing ester dithiol compound BDB, and 64.8 mg of crosslinking agent pentaerythritol tetra-3-mercaptopropionate (PETMP) were mixed in a reaction flask, and 8 mL of DMF was added. The mixture was stirred until all components were uniformly dispersed. Then, 30 μL of initiator 2-hydroxy-2-methylphenylacetone was added to obtain the precursor solution. 20 μL of the precursor solution was pipetted onto lithium metal and irradiated under a UV lamp for 20 min to obtain a polymeric artificial SEI film. The entire process must be performed inside a glove box. The thickness of the boron-rich single-ion polymeric artificial SEI film obtained in this embodiment is 500 nm. Similar to Example 1, the polymer film obtained in this embodiment exhibits good self-healing properties.

[0073] Example 5

[0074] 0.42 g of trimethyl borate (TMB) and 0.45 g of glyceryl methacrylate (GMMA) were mixed in 30 mL of anhydrous acetonitrile, and the solution was stirred at 70 °C for 7 h under dry argon gas. Then, 8 g of PEG (molecular weight MW = 400) was injected into the solution, and the reaction was carried out at 70 °C for 9 h. LBM was obtained after vacuum distillation and drying. 0.44 g of 1,4-phenyldiboron, 0.5 g of 1-thioglycerol, and 0.03 mL of deionized water were added to 10 mL of acetonitrile and stirred until dissolved. Then, 0.2 g of magnesium sulfate was added, and the mixture was stirred vigorously at 50 °C for 20 hours. BDB was obtained after filtration, vacuum distillation, washing, and drying.

[0075] 28.4 mg of linear boron-containing monomer LBM, 36.4 mg of boron-containing ester dithiol compound BDB, and 50.4 mg of crosslinking agent pentaerythritol tetra-3-mercaptopropionate (PETMP) were mixed in a reaction flask, and 10 mL of acetonitrile was added. The mixture was stirred until all components were uniformly dispersed. Then, 60 μL of initiator 2-hydroxy-2-methylphenylacetone was added to obtain the precursor solution. 70 μL of the precursor solution was pipetted onto lithium metal and irradiated under a UV lamp for 20 min to obtain a polymeric artificial SEI film. The entire process had to be performed inside a glove box. The thickness of the boron-rich single-ion polymeric artificial SEI film obtained in this embodiment was 700 nm. Similar to Example 1, the polymer film obtained in this embodiment exhibited good self-healing properties.

[0076] Example 6

[0077] 4.16 g of trimethyl borate (TMB) and 0.64 g of glyceryl methacrylate (GMMA) were mixed in 30 mL of anhydrous acetonitrile, and dry argon gas was introduced while the solution was stirred at 10 °C for 2 h. Then, 8 g of PEG (molecular weight MW = 400) was injected into the solution, and the reaction was carried out at 10 °C for 4 h. LBM was obtained after vacuum distillation and drying. 2.22 g of 1,4-phenyldiboron, 1.23 g of 1-thioglycerol, and 1.6 mL of deionized water were added to 30 mL of N,N-dimethylformamide and stirred until dissolved. Then, 1.8 g of magnesium sulfate was added, and the mixture was stirred vigorously at 60 °C for 25 hours. After filtration, vacuum distillation, washing, and drying, BDB was obtained.

[0078] 85.2 mg of linear boron-containing monomer LBM, 140.4 mg of boron-containing ester dithiol compound BDB, and 194.4 mg of crosslinking agent pentaerythritol tetra-3-mercaptopropionate (PETMP) were mixed in a reaction flask, and 2 mL of tetrahydrofuran was added. The mixture was stirred until all components were uniformly dispersed. Then, 70 μL of initiator 2-hydroxy-2-methylphenylacetone was added to obtain the precursor solution. 80 μL of the precursor solution was pipetted onto lithium metal and irradiated under a UV lamp for 25 min to obtain a polymeric artificial SEI film. The entire process had to be performed inside a glove box. The boron-rich single-ion polymeric artificial SEI film obtained in this embodiment had a thickness of 800 nm. Similar to Example 1, the polymer film obtained in this embodiment exhibited good self-healing properties.

[0079] Example 7

[0080] 4.16 g of trimethyl borate (TMB) and 6.40 g of glyceryl methacrylate (GMMA) were mixed in 30 mL of anhydrous acetonitrile, and the solution was stirred at 80 °C for 10 h under dry argon gas. Then, 40 g of PEG (molecular weight MW = 400) was injected into the solution, and the reaction was carried out at 80 °C for 10 h. LBM was obtained after vacuum distillation and drying. 2.22 g of 1,4-phenyldiboron, 2.46 g of 1-thioglycerol, and 1.1 mL of deionized water were added to 60 mL of tetrahydrofuran and stirred until dissolved. Then, 0.12 g of magnesium sulfate was added, and the mixture was stirred vigorously at 10 °C for 12 hours. BDB was obtained after filtration, vacuum distillation, washing, and drying.

[0081] 85.2 mg of linear boron-containing monomer LBM, 156 mg of boron-containing ester dithiol compound BDB, and 324 mg of crosslinking agent pentaerythritol tetra-3-mercaptopropionate (PETMP) were mixed in a reaction flask, and 2 mL of DOL / DME (1:1) was added. The mixture was stirred until all components were uniformly dispersed. Then, 30 μL of initiator 2-hydroxy-2-methylphenylacetone was added to obtain a precursor solution. 50 μL of the precursor solution was pipetted onto lithium metal and irradiated under a UV lamp for 30 min to obtain a polymer artificial SEI film. The entire operation must be performed inside a glove box. The thickness of the boron-rich single-ion polymer artificial SEI film obtained in this embodiment is 1 μm. Similar to Example 1, the polymer film obtained in this embodiment exhibits good self-healing properties.

[0082] The flame-retardant polymer electrolyte membrane prepared by the preferred embodiment of the present invention has significantly improved electrochemical performance, self-healing ability, high safety and good electrochemical performance, and can provide a new method for preparing novel flame-retardant polymer electrolytes.

[0083] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A boron-rich single-ion polymer artificial SEI membrane, characterized in that, The boron-rich single-ion polymer artificial SEI membrane LBP is composed of a crosslinking compound consisting of pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, linear boron-containing monomer LBM, and boron ester dithiol compound BDB. The chemical structural formula of LBM is as follows: ； Where n is an integer from 5 to 15.

2. The boron-rich single-ion polymer artificial SEI membrane according to claim 1, characterized in that, The crosslinking compound is formed by photoinitiated polymerization, which promotes the formation of a three-dimensional polymer crosslinking network from three reactants: pentaerythritol tetra-3-mercaptopropionate (PETMP), linear boron-containing monomer (LBM), and boron ester dimercapto compound (BDB).

3. The boron-rich single-ion polymer artificial SEI membrane according to claim 1, characterized in that, The chemical structural formula of the borate ester dithiol compound BDB is as follows: ； The chemical structural formula of the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP is as follows: 。 4. The boron-rich single-ion polymer artificial SEI membrane according to claim 1, characterized in that, The sum of the molar ratios of the linear boron-containing monomer LBM to the boron ester dithiol compound BDB and the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, LBM / (BDB+PETMP), is 1 / 2 to 1 / 25; the molar ratio of the linear boron-containing monomer LBM to the boron ester dithiol compound BDB is 1 / 1 to 1 / 10; and the molar ratio of the linear boron-containing monomer LBM to the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP is 1 / 1 to 1 / 15.

5. The boron-rich single-ion polymer artificial SEI membrane according to claim 1, characterized in that, The polymer artificial SEI membrane is a thin film with a thickness of 0.01~1.5 micrometers.

6. A method for preparing a boron-rich single-ion polymer artificial SEI membrane, characterized in that, Includes the following steps: 1) Trimethyl borate (TMB) and glyceryl methacrylate (GMMA) were mixed in the first solvent and stirred under an inert atmosphere. Then, polyethylene glycol (PEG) was injected into the reaction solution, heated and stirred, and the solvent was removed under reduced pressure. The product LBM was then dried. 2) The pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP, borate ester dimercapto compound BDB, linear boron-containing monomer LBM obtained in step 1) and initiator are dissolved in a second solvent and mixed evenly. Then, the resulting precursor solution is uniformly dropped onto the lithium metal surface and irradiated under ultraviolet light to react. After drying, a polymer artificial SEI film is obtained.

7. The method for preparing a boron-rich single-ion polymer artificial SEI membrane according to claim 6, characterized in that, In step 1): The molecular weight M of the polyethylene glycol PEG W =400-2000; The molar ratio of trimethyl borate to methacrylic acid is 1 / 0.1 to 1 / 1; The molar ratio of trimethyl borate to polyethylene glycol is 2 / 1 to 2 / 5; The reaction temperature is 10~80 °C, and the reaction time is 2~10 hours; The first solvent includes at least one of tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, and acetonitrile.

8. The method for preparing a boron-rich single-ion polymer artificial SEI membrane according to claim 6, characterized in that, In step 2): The molar ratio of the linear boron-containing monomer LBM to the boron ester dithiol compound BDB is 1 / 1 to 1 / 10, and the molar ratio of the linear boron-containing monomer LBM to the pentaerythritol tetra-3-mercaptopropionate crosslinking agent PETMP is 1 / 1 to 1 / 15. The second solvent is any one or more of dimethyl carbonate, ethylene carbonate, 1,3-dioxolane, ethylene glycol dimethyl ether, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide; The initiator is one of 2-hydroxy-methylphenylpropane-1-one, 1-hydroxycyclohexylphenyl ketone, and 2-hydroxy-2-methylpropanone; The mass ratio of the initiator to the linear boron-containing monomer LBM is 1 / 1 to 1 / 20; The irradiation reaction time under ultraviolet light is 5 to 30 minutes.

9. The method for preparing a boron-rich single-ion polymer artificial SEI membrane according to claim 6, characterized in that, The borate ester dithiol compound BDB described in step 2) is prepared as follows: 1,4-phenyldiboron and 1-thioglycerol are dissolved in a first solvent, deionized water and magnesium sulfate are added, and the mixture is stirred at 10~70 °C for 12~36 hours; the reaction product is filtered, distilled under reduced pressure, washed and dried to obtain the borate ester dithiol compound BDB.

10. The application of a boron-rich single-ion polymer artificial SEI membrane according to any one of claims 1-5 or a boron-rich single-ion polymer artificial SEI membrane prepared by any one of claims 6-9 in lithium metal batteries.

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