Dynamic self-adaptive polymer artificial SEI layer based on DA bond and preparation and application of dynamic self-adaptive polymer artificial SEI layer

Abstract

The invention belongs to the technical field of lithium metal batteries, and relates to the technical field of artificial SEI layers, in particular to a dynamic self-adaptive polymer artificial SEI layer based on a DA bond and preparation and application thereof. Linear polyurethane serves as a framework, a dynamic DA bond is introduced into a polymer system, a topological network structure is formed through in-situ reaction of the linear polyurethane and bismaleimide on the surface of a lithium metal negative electrode, and therefore the artificial SEI layer based on the DA bond is prepared. The artificial SEI layer is a three-dimensional topological structure polymer material with a dynamic adaptive characteristic. A DA dynamic covalent bond and a hydrogen bond introduced into the structure endow the artificial protection layer with excellent mechanical properties and dynamic characteristics, so that the artificial protection layer can adapt to the volume change of a lithium metal negative electrode in a battery cycle process, thereby realizing long-term stability of the electrode, and remarkably improving the safety and electrochemical performance of the lithium metal battery. Therefore, the invention provides an innovative method for preparing the novel artificial SEI layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium metal batteries, relates to the technical field of artificial SEI layers, and particularly relates to a dynamic adaptive polymer artificial SEI layer based on DA bonds and its preparation and application. Background Art

[0002] Lithium metal is an alkali metal with the lowest reduction potential (-3.04V vs standard hydrogen electrode), and its theoretical specific capacity is as high as 3860 mAh·g-1, which is known as the "holy grail" material. Compared with traditional lithium-ion batteries, lithium metal batteries use lithium metal as the negative electrode, enabling higher energy storage efficiency. Although lithium metal batteries perform excellently in terms of energy density and performance, they still face many challenges in practical applications. In particular, the high reactivity of lithium metal with organic electrolytes leads to the formation of an unstable natural solid electrolyte interface (SEI) on the surface of the lithium negative electrode during battery cycling. However, the natural SEI is usually fragile and unstable, easily rupturing and regenerating during cycling. This process not only consumes the electrolyte and lithium metal but also results in low Coulombic efficiency and short cycle life of the battery. In addition, the growth of lithium dendrites during charge and discharge may cause safety problems such as battery short circuit, overheating, and even fire. Therefore, the systematic research on lithium metal batteries has become a major scientific problem that needs to be solved urgently.

[0003] Constructing a polymer artificial SEI layer on the surface of the lithium negative electrode is a very effective measure to inhibit the growth of lithium dendrites and slow down the reaction between lithium metal and the electrolyte. However, the artificial SEI layers reported so far usually dissolve the synthesized polymer in a solvent and use the doctor blade method to prepare it on the surface of the lithium metal negative electrode, which results in poor interfacial compatibility between the lithium metal negative electrode and the protective layer. In addition, most artificial SEI layers have poor mechanical properties and flexibility, and will rupture and lose the ability to protect the electrode due to the volume change of the lithium metal negative electrode during battery cycling, thus enabling the electrolyte to react with active lithium, accelerating the growth of lithium dendrites. The continuous growth of lithium dendrites will pierce the battery separator, causing the battery to short circuit and fail, and even triggering battery thermal runaway, resulting in fire and explosion in severe cases, posing a safety hazard.

[0004] The Diels-Alder (DA) bond is a common dynamic covalent bond with thermally reversible reactivity. It can undergo bond cleavage when heated above the reverse DA reaction temperature (TrDA) and reform during cooling. When the DA bond is introduced into the polymer crosslinked network, the network can undergo bond cleavage and depolymerization when heated to TrDA, resulting in a decrease in the system viscosity, and the crosslinked network reforms during cooling, achieving the reorganization of the polymer topological structure. It can be seen that if the dynamic DA bond can be introduced into the polymer system and a polymer artificial SEI layer with dynamic self-adaptive ability is designed and prepared based on this, it will surely be beneficial to improve the safety and electrochemical performance of lithium metal batteries. Summary of the Invention

[0005] To overcome the deficiencies of the above-mentioned prior art, the present invention uses linear polyurethane as the backbone, introduces the dynamic DA bond into the polymer system, and designs and prepares a polymer artificial SEI layer based on the DA bond and having dynamic self-adaptive ability. This artificial SEI layer is a topological network structure formed by the in-situ reaction of two reactants (linear polyurethane and bismaleimide) on the surface of lithium metal. This topological network structure can enhance the interfacial interaction and reduce the interfacial impedance; the hydrogen bonds and DA bonds in this structure can endow the artificial SEI layer with strong and tough mechanical characteristics, enabling it to offset the stress generated by the volume change of the electrode and adapt to the electrode volume change process, thereby protecting the lithium metal negative electrode stably for a long time.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of the present invention provides a dynamic self-adaptive polymer artificial SEI layer based on the DA bond. The polymer artificial SEI layer is a dynamic three-dimensional crosslinked topological structure, and its structural formula is as follows:

[0008]

[0009] Among them, n is an integer from 3 to 27.

[0010] The second aspect of the present invention provides a preparation method of the dynamic self-adaptive polymer artificial SEI layer based on the DA bond described in the first aspect. Specifically, it is obtained by promoting two reactants, namely linear polyurethane compound (PU) and bismaleimide (BMI), to form a three-dimensional crosslinked network topological structure at high temperature through the Diels-Alder (DA) reaction. The specific steps are as follows:

[0011] S1. Mix polytetrahydrofuran (PTMEG), an isocyanate compound, and a catalyst in a first solvent. After stirring and reacting under an inert atmosphere, dissolve furan dimethanol (FDT) in the first solvent and inject it into the above solution. Then, heat and stir the reaction mixture. After the reaction, evaporate the solvent to dryness and then dry to obtain a linear polyurethane compound (PU); that is, PU is formed by the condensation polymerization of polytetrahydrofuran (PTMEG), an isocyanate compound, and furan dimethanol (FDT) under the action of a catalyst.

[0012] S2. Dissolve the linear polyurethane compound (PU) and bismaleimide (BMI) in a second solvent. After heating and stirring the reaction under an inert atmosphere, evaporate the solvent in the reaction solution to dryness and then dry to obtain a dynamic adaptive polymer (DACP).

[0013] Through the design of the key structure, related composition (especially the key chemical structural formula, functional groups, related ratios, etc. of the polymer monomers), corresponding preparation methods, overall synthesis routes of the dynamic adaptive polymer artificial SEI layer, and the improvement of the reaction conditions for each step, the present invention prepares a polymer artificial SEI layer with a DA bond cross-linked network as the polymer backbone.

[0014] Compared with the prior art, on the one hand, a large number of dynamic DA covalent bonds and hydrogen bonds are contained in the polymer network. The introduction of DA bonds and hydrogen bonds ensures the high tensile strength and flexibility of the polymer network, providing a prerequisite for the long-term and effective protection of the lithium metal anode. It can dynamically adapt to the influence of the volume change of the lithium metal electrode during the cycling process, thereby effectively inhibiting the growth of lithium dendrites and improving the cycling life and safety performance of the lithium metal battery. On the other hand, the formation of the dynamic adaptive polymer network is obtained by the in-situ reaction of a mixed precursor solution of linear polyurethane and bismaleimide on the surface of the lithium metal anode. This method can obtain better interfacial compatibility, thereby enhancing the interfacial interaction and reducing the interfacial impedance.

[0015] Preferably, the structural formula of the linear polyurethane compound is as follows:

[0016]

[0017] Where: n = 3 - 27, and n is a natural number.

[0018] Preferably, the structural formula of the bismaleimide (BMI) is as follows:

[0019]

[0020] Preferably, the structural formula of the polytetrahydrofuran is: Where: n = 3 - 27, and n is a natural number; the structural formula of the furan dimethanol is: The structural formula of the isocyanate compound is as follows: It includes at least one of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and toluene diisocyanate.

[0021] More preferably, the molecular weight of the polytetrahydrofuran is 250 - 2000.

[0022] Preferably, the first solvent includes at least one of N,N - dimethylformamide, dimethyl sulfoxide, N,N - dimethylacetamide, toluene, and acetonitrile; the second solvent is at least one of N,N - dimethylformamide, dimethyl sulfoxide, N,N - dimethylacetamide, toluene, and acetonitrile; the catalyst includes at least one of dibutyltin dilaurate, stannous octoate, potassium acetate, and lead octoate.

[0023] Preferably, the molar ratio of the polytetrahydrofuran to the isocyanate compound is 1 / 0.5 - 1 / 3; the molar ratio of the polytetrahydrofuran to the catalyst is 1000 / 1 - 10 / 1; the molar ratio of the polytetrahydrofuran to furan dimethanol is 1 / 0.5 - 1 / 2; the functional group ratio of the linear polyurethane to the bismaleimide is 10 / 1 - 1 / 2.

[0024] Preferably, the reaction temperature of S1 is 40 - 120 °C, and the reaction time is 4 - 24 hours; the reaction temperature of S2 is 40 - 120 °C, and the reaction time is 4 - 12 hours.

[0025] The present invention further controls the parameter conditions of each process step of the preparation method (including the molecular weight control of PU, the ratio between different reactants, reaction time and temperature, etc.), thereby further improving the electrochemical properties such as the conductivity and transference number of the dynamic adaptive polymer artificial SEI layer.

[0026] The third aspect of the present invention provides the application of the dynamic adaptive polymer artificial SEI layer based on the DA bond described in the first aspect in a lithium metal battery.

[0027] Preferably, the specific application method is as follows: Dissolve the linear polyurethane compound (PU) and bismaleimide (BMI) in a third solvent, heat and stir to mix evenly to obtain a precursor solution of the artificial SEI layer, then drop the precursor solution onto the surface of the lithium metal negative electrode, and after volatilizing the solvent, obtain a lithium metal negative electrode modified with a dynamic adaptive protective layer.

[0028] More preferably, the third solvent includes at least one of N,N - dimethylformamide, dimethyl sulfoxide, N,N - dimethylacetamide, toluene, and acetonitrile.

[0029] More preferably, the temperature for volatilizing the solvent is 40 - 120 °C.

[0030] More preferably, the artificial SEI layer is in the form of an extremely thin film with a thickness of about 0.1 to 50 microns.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] The dynamic self-adaptive polymer artificial SEI layer based on linear polyurethane (PU) and bismaleimide (BMI) prepared by the Diels-Alder (DA) reaction of the present invention can significantly improve the electrochemical performance and cycle life of lithium metal batteries. In this polymer structure, polyurethane is used as the main chain, and a three-dimensional dynamic cross-linked network structure is formed by the DA reaction. The presence of DA bonds and hydrogen bonds in the structure ensures that the polymer has sufficient mechanical strength and flexibility, enabling it to adapt to the volume change process of the lithium metal negative electrode, thereby stabilizing the electrode in the long term, inhibiting the growth of lithium dendrites, and improving the cycle life and safety performance of the battery. On the other hand, different from the artificial SEI layers prepared by other flow methods, the formation of the dynamic self-adaptive polymer network in this layer is obtained by the in-situ reaction of a mixed precursor solution of linear polyurethane and bismaleimide on the surface of the lithium metal negative electrode. This method can achieve better interfacial compatibility, thereby enhancing the interfacial interaction and reducing the interfacial impedance.

[0033] Specifically, the present invention can achieve the following beneficial effects:

[0034] (1) The present invention first prepares a dynamic self-adaptive polymer artificial SEI layer based on linear polyurethane and bismaleimide through the Diels-Alder (DA) reaction. Currently, there is no report on the method of using DA dynamic covalent bonds and hydrogen bonds to improve the mechanical self-adaptive ability of polymer artificial SEI layers.

[0035] (2) The dynamic self-adaptive polymer artificial SEI layer based on linear polyurethane and bismaleimide prepared by the Diels-Alder (DA) reaction of the present invention can significantly improve the electrochemical performance and cycle life of lithium metal batteries. This polymer network contains a large number of dynamic DA covalent bonds and hydrogen bonds. The introduction of DA bonds and hydrogen bonds ensures the high tensile strength and flexibility of the polymer network, providing a prerequisite for the long-term and effective protection of the lithium metal negative electrode, enabling it to dynamically adapt to the influence of volume changes during the cycling process of the lithium metal electrode, thereby effectively inhibiting the growth of lithium dendrites and improving the cycle life and safety performance of lithium metal batteries.

[0036] (3) The Diels-Alder (DA) bond introduced into the polymer structure in the present invention is a common dynamic covalent bond with thermally reversible reactivity. It can undergo bond cleavage when heated above the reverse DA reaction temperature (TrDA), and reform during the cooling process. When the DA bond is introduced into the polymer crosslinked network, the network can undergo bond cleavage and depolymerization when heated to TrDA, resulting in a decrease in the system viscosity, and the crosslinked network reforms during cooling, thus achieving the reorganization of the polymer topological structure. Moreover, the formation of this artificial SEI layer is obtained by the in-situ reaction of two reactants (linear polyurethane and bismaleimide) on the lithium metal surface to form a topological network structure, which can enhance the interfacial interaction and reduce the interfacial impedance.

[0037] In summary, compared with the prior art, the present invention uses linear polyurethane as the backbone, introduces dynamic DA bonds into the polymer system, and designs and prepares a polymer artificial SEI layer with dynamic self-adaptive ability. The formation of this artificial SEI layer is obtained by the in-situ reaction of two reactants (linear polyurethane and bismaleimide) on the lithium metal surface to form a topological network structure, which can enhance the interfacial interaction and reduce the interfacial impedance; in addition, the hydrogen bonds and DA bonds in this structure can endow the artificial SEI layer with strong and tough mechanical characteristics, enabling it to offset the stress generated by the volume change of the electrode and adapt to the process of electrode volume change, thereby stably protecting the lithium metal anode in the long term, and providing a new method for the preparation of a novel dynamic self-adaptive polymer artificial SEI layer. Description of the Drawings

[0038] Figure 1 Schematic diagram of the chemical structure of the dynamic self-adaptive polymer artificial SEI layer prepared in Example 1;

[0039] Figure 2 Battery cycle performance graph of the dynamic self-adaptive polymer artificial SEI layer prepared in Example 3;

[0040] Figure 3 Rheological behavior graph of the DACP polymer of the dynamic self-adaptive polymer artificial SEI layer synthesized in Example 4;

[0041] Figure 4 Cross-sectional thickness of the DACP of the dynamic self-adaptive polymer artificial SEI layer prepared in Example 5;

[0042] Figure 5 Experimental graph of the mechanical tensile properties of the dynamic self-adaptive polymer artificial SEI layer prepared in Example 7;

[0043] Figure 6 Scanning electron microscope graph of the dynamic self-adaptive polymer DACP film prepared in Example 7. Detailed Description of the Invention

[0044] The specific embodiments of the present invention will be further described below. It should be noted here that the description of these embodiments is for helping to understand the present invention, but does not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0045] In the experimental methods in the following embodiments, unless otherwise specified, they are all conventional methods. In the test materials used in the following embodiments, unless otherwise specified, they can all be obtained through conventional commercial channels.

[0046] The present invention provides a dynamic self-adaptive polymer artificial SEI layer based on DA bonds. The dynamic self-adaptive polymer artificial SEI layer is composed of linear polyurethane (PU) and bismaleimide (BMI), and the functional group ratio of linear polyurethane to bismaleimide is 10 / 1 to 1 / 2. The cross-linked compound is obtained by Diels-Alder (DA) reaction, which promotes the formation of a dynamic self-adaptive polymer cross-linked network from two reactants, linear polyurethane (PU) and bismaleimide. The presence of DA bonds and hydrogen bonds in the structure improves the mechanical strength and flexibility of the polymer, enabling it to adapt to the volume change of the lithium metal anode during the process, thereby stabilizing the electrode in the long term, inhibiting the growth of lithium dendrites, and improving the cycle life and safety performance of the battery.

[0047] The chemical structural formula of the linear polyurethane (PU) is as follows:

[0048]

[0049] Among them, n is an integer from 3 to 27.

[0050] The chemical structural formula of the bismaleimide BMI is as follows:

[0051]

[0052] The chemical structural formula of the dynamic self-adaptive polymer artificial SEI layer in the present invention is as follows:

[0053]

[0054] Among them, n is an integer from 3 to 27.

[0055] The preparation method of the dynamic self-adaptive polymer artificial SEI layer includes the following steps:

[0056] 1) Poly(tetramethylene ether) glycol (PTMEG), an isocyanate compound, and a catalyst are mixed in a first solvent. After stirring and reacting under an inert atmosphere, furan dimethanol (FDT) is dissolved in the first solvent and injected into the above solution, followed by heating and stirring for reaction. After the reaction, the solvent is evaporated to dryness, and then dried to obtain a linear polyurethane compound PU.

[0057] 2) The linear polyurethane compound (PU) and bismaleimide (BMI) are dissolved in a second solvent. After heating and stirring for reaction under an inert atmosphere, the solvent in the reaction solution is evaporated to dryness, and then dried to obtain a dynamic self-adaptive polymer (DACP).

[0058] Or: The linear polyurethane compound (PU) and bismaleimide (BMI) are dissolved in a third solvent. After heating and stirring to mix evenly, an artificial SEI layer precursor solution is obtained. Then, the precursor solution is dropped onto the surface of a lithium metal negative electrode. After the solvent is evaporated, a lithium metal negative electrode modified with a dynamic self-adaptive protective layer, DACP@Li, is obtained. The entire operation process is completed in a glove box filled with an argon atmosphere.

[0059] To make the present invention clearer, the following further elaborates through Examples 1-7 on how the present invention constructs a dynamic self-adaptive polymer artificial SEI layer based on DA bonds, and further illustrates the significant progress achieved by the present invention in combination with test or characterization data.

[0060] Example 1

[0061] 0.5 g of poly(tetramethylene ether) glycol PTMEG (molecular weight MW = 250) and 0.168 g of hexamethylene diisocyanate are dissolved in 15 mL of toluene, stirred for 0.5 h to mix evenly, and then 2 μL of dibutyltin dilaurate is injected into the above solution, and stirred and reacted at 40 °C for 2 h under an inert atmosphere. Then, 0.128 g of furan dimethanol (FDT) is dissolved in 2 mL of toluene and injected into the above solution, and then heated and stirred at 40 °C for 4 h. After the reaction, the product is placed in a forced-air drying oven to evaporate the solvent to dryness, and then transferred to a vacuum drying oven for drying to obtain a linear polyurethane compound (PU).

[0062] 0.464 g of the dried linear polyurethane compound (PU, n = 3 in the structural formula) and 0.0358 g of bismaleimide (BMI) are dissolved in 1 mL of tetrahydrofuran, heated and stirred at 50 °C to mix evenly to obtain an artificial SEI layer DACP precursor solution. Then, 20 μL of the precursor solution is taken with a pipette and dropped onto the surface of a lithium metal negative electrode with a diameter of 15.6 mm, and the lithium metal is placed on a hot stage and heated at 40 °C to evaporate the solvent to obtain a lithium metal negative electrode modified with a dynamic self-adaptive protective layer, denoted as DACP@Li. The entire operation process needs to be completed in a glove box filled with an argon atmosphere.

[0063] The thickness of the dynamically adaptive polymer artificial SEI layer obtained in this example is 0.1 μm. As Figure 1 shown, it is a schematic chemical structure diagram of DACP, where n = 3.

[0064] Example 2

[0065] Dissolve 4.0 g of polytetrahydrofuran PTMEG (molecular weight MW = 1000) and 2.0 g of isophorone diisocyanate in 30 mL of N,N-dimethylacetamide, stir for 0.5 h to mix evenly, then inject 24 μL of dibutyltin dilaurate into the above solution, and stir and react at 80 °C for 3 h under an inert atmosphere. Then dissolve 0.512 g of furandimethanol (FDT) in 2 mL of N,N-dimethylacetamide and inject it into the above solution, and then heat and stir at 60 °C for 12 h. After the reaction is completed, place the product in a blast drying oven to evaporate the solvent completely, and then transfer it to a vacuum drying oven for drying to obtain a linear polyurethane compound (PU).

[0066] Dissolve 0.820 g of the dried linear polyurethane compound (PU, n = 13 in the structural formula) and 0.18 g of bismaleimide (BMI) in 1 mL of tetrahydrofuran, heat and stir at 50 °C to mix evenly to obtain a precursor solution for the artificial SEI layer DACP. Then use a pipette to take 60 μL of the precursor solution and drop it on the surface of a lithium metal negative electrode with a diameter of 15.6 mm, and place the lithium metal on a hot stage, heat at 40 °C to evaporate the solvent to obtain a lithium metal negative electrode modified with a dynamically adaptive protective layer, denoted as DACP@Li. The whole operation process needs to be completed in a glove box filled with an argon atmosphere.

[0067] The thickness of the dynamically adaptive polymer artificial SEI layer obtained in this example is 25 μm, and n = 13 in the structure. As Figure 2 shown, assemble the DACP@Li prepared in this example with the ternary high-voltage positive electrode NCM811 into a full cell, and use the bare lithium Brae-Li without a protective layer as a control experiment to evaluate the performance of the DACP@Li||NCM battery. It is found that it can stably cycle 300 times at a charge-discharge rate of 1.0 C, and its discharge specific capacity at this time still remains at 106 mAh·g -1 , which proves that the modification of the lithium metal negative electrode with the artificial protective layer DACP can improve the cycling performance of the lithium metal battery.

[0068] Example 3

[0069] Dissolve 1 g of polytetrahydrofuran PTMEG (molecular weight MW = 2000) and 0.791 g of dicyclohexylmethane diisocyanate in 30 mL of N,N-dimethylformamide, stir for 0.5 h to mix evenly, then inject 30 μL of stannous octoate into the above solution, and stir and react at 120 °C for 4 h under an inert atmosphere. Then dissolve 0.256 g of furan dimethanol FDT in 2 mL of N,N-dimethylformamide and inject it into the above solution, and then heat and stir at 120 °C for 24 h. After the reaction is completed, place the product in a blast drying oven to evaporate the solvent completely, and then transfer it to a vacuum drying oven for drying to obtain a linear polyurethane compound (PU).

[0070] Dissolve 1.682 g of the dried linear polyurethane compound (PU, n = 27 in the structural formula) and 0.432 g of bismaleimide (BMI) in 1 mL of acetonitrile, heat and stir at 50 °C to mix evenly to obtain a precursor solution for the artificial SEI layer DACP. Then use a pipette to take 200 μL of the precursor solution and drop it on the surface of a lithium metal negative electrode with a diameter of 15.6 mm, and place the lithium metal on a hot stage, heat at 40 °C to evaporate the solvent to obtain a lithium metal negative electrode modified with a dynamic adaptive protective layer, denoted as DACP@Li. The entire operation process needs to be completed in a glove box filled with an argon atmosphere.

[0071] The thickness of the dynamic adaptive polymer artificial SEI layer obtained in this example is 50 μm, and n = 27 in the structure.

[0072] Example 4

[0073] Dissolve 2.0 g of polytetrahydrofuran PTMEG (molecular weight MW = 1000) and 0.435 g of toluene diisocyanate in 20 mL of acetonitrile, stir for 0.5 h to mix evenly, then inject 40 μL of potassium acetate into the above solution, and stir and react at 60 °C for 4 h under an inert atmosphere. Then dissolve 0.128 g of furan dimethanol (FDT) in 1 mL of acetonitrile and inject it into the above solution, and then heat and stir at 40 °C for 4 h. After the reaction is completed, place it in a blast drying oven to evaporate the solvent completely, and then transfer it to a vacuum drying oven for drying to obtain a linear polyurethane compound PU.

[0074] Dissolve 0.064 g of the dried linear polyurethane compound (PU, n = 13 in the structural formula) and 0.036 g of bismaleimide (BMI) in 1 mL of dimethyl sulfoxide, heat and stir at 50 °C to mix evenly to obtain a precursor solution for the artificial SEI layer DACP. Then use a pipette to take 60 μL of the precursor solution and drop it on the surface of a lithium metal negative electrode with a diameter of 15.6 mm, and place the lithium metal on a hot stage, heat at 120 °C to evaporate the solvent to obtain a lithium metal negative electrode modified with a dynamic adaptive protective layer, denoted as DACP@Li. The entire operation process needs to be completed in a glove box filled with an argon atmosphere.

[0075] The thickness of the dynamically adaptive polymer artificial SEI layer obtained in this example is 5 μm, and n = 13 in the structure. As Figure 3 shown, the rheological behavior of the DACP polymer was evaluated, and it was found that within the range of 30 - 90 °C, DACP was within the elastic response range of the polymer segments, demonstrating its broad temperature operating range.

[0076] Example 5

[0077] Dissolve 2.0 g of polytetrahydrofuran PTMEG (molecular weight MW = 2000) and 0.084 g of hexamethylene diisocyanate in 30 mL of toluene, stir for 0.5 h to mix evenly, then inject 25 μL of stannous octoate into the above solution, and stir and react at 80 °C for 4 h under an inert atmosphere. Then dissolve 0.128 g of furan dimethanol (FDT) in 1 mL of toluene and inject it into the above solution, and then heat and stir at 60 °C for 12 h. After the reaction is completed, place the product in a blast drying oven to evaporate the solvent completely, and then transfer it to a vacuum drying oven for drying to obtain a linear polyurethane compound PU.

[0078] Dissolve 0.642 g of the dried linear polyurethane compound (PU, n = 27 in the structural formula) and 0.358 g of bismaleimide (BMI) in 10 mL of dimethyl sulfoxide, heat and stir at 50 °C to mix evenly to obtain the precursor solution of the artificial SEI layer DACP. Then use a pipette to take 50 μL of the precursor solution and drop it on the surface of a lithium metal negative electrode with a diameter of 15.6 mm, and place the lithium metal on a hot stage, heat at 80 °C to evaporate the solvent to obtain a lithium metal negative electrode modified with a dynamically adaptive protective layer, denoted as DACP@Li. The entire operation process needs to be completed in a glove box filled with an argon atmosphere.

[0079] The thickness of the dynamically adaptive polymer artificial SEI layer obtained in this example is 4 μm, where n = 27, as Figure 4 shown.

[0080] Example 6

[0081] Dissolve 1.0 g of polytetrahydrofuran PTMEG (molecular weight MW = 250) and 0.084 g of hexamethylene diisocyanate in 15 mL of toluene, stir for 0.5 h to mix evenly, then inject 25 μL of lead acetate into the above solution, and stir and react at 70 °C for 6 h under an inert atmosphere. Then dissolve 0.256 g of furan dimethanol (FDT) in 2 mL of toluene and inject it into the above solution, and then heat and stir at 50 °C for 20 h. After the reaction is completed, place the product in a blast drying oven to evaporate the solvent completely, and then transfer it to a vacuum drying oven for drying to obtain a linear polyurethane compound (PU).

[0082] Dissolve 6.444 g of the dried linear polyurethane compound (PU, n = 3 in the structural formula) and 0.716 g of bismaleimide (BMI) in 1 mL of dimethyl sulfoxide, heat and stir at 50 °C until evenly mixed to obtain the precursor solution of the artificial SEI layer DACP. Then, use a pipette to take 40 μL of the precursor solution and drop it onto the surface of a lithium metal anode with a diameter of 15.6 mm, and place the lithium metal on a hot stage, heat at 80 °C to evaporate the solvent to dryness, obtaining a lithium metal anode modified with a dynamic adaptive protective layer, denoted as DACP@Li. The entire operation process needs to be completed in a glove box filled with an argon atmosphere.

[0083] The thickness of the dynamic adaptive polymer artificial SEI layer obtained in this example is 15 μm, and n = 3 in the structure.

[0084] Example 7

[0085] Dissolve 4.0 g of polytetrahydrofuran PTMEG (molecular weight MW = 1000) and 0.444 g of isophorone diisocyanate in 50 mL of N,N-dimethylacetamide, stir for 0.5 h until evenly mixed, then inject 30 μL of dibutyltin dilaurate into the above solution, and stir and react at 80 °C under an inert atmosphere for 6 h. Then, dissolve 0.256 g of furan dimethanol (FDT) in 1 mL of toluene and inject it into the above solution, and then heat and stir at 60 °C for 12 h. After the reaction is completed, place the product in a blast drying oven to evaporate the solvent to dryness, and then transfer it to a vacuum drying oven for drying to obtain a linear polyurethane compound (PU).

[0086] Dissolve 6.444 g of the dried linear polyurethane compound (PU, n = 13 in the structural formula) and 0.716 g of bismaleimide (BMI) in 10 mL of tetrahydrofuran, heat and stir at 50 °C until evenly mixed to obtain the precursor solution of the artificial SEI layer DACP. Then, use a pipette to take 150 μL of the precursor solution and drop it onto the surface of a lithium metal anode with a diameter of 15.6 mm, and place the lithium metal on a hot stage, heat at 50 °C to evaporate the solvent to dryness, obtaining a lithium metal anode modified with a dynamic adaptive protective layer, denoted as DACP@Li. The entire operation process needs to be completed in a glove box filled with an argon atmosphere.

[0087] The thickness of the dynamic adaptive polymer artificial SEI layer obtained in this example is 20 μm, and n = 13 in the structural formula. As Figure 5 shown, the influence of introducing DA bonds and linear polyurethane (without DA bonds) on the mechanical properties of the polymer was tested through stress-strain experiments, and it was found that the polymer with DA bonds has ultra-high tensile strength and elongation at break. As Figure 6 , the morphology of the DACP film formed in a polytetrafluoroethylene mold was observed under a scanning electron microscope, and the surface of the DACP film was very dense and uniform.

[0088] In summary, through the optimized design of the overall process flow of the key chemical structure, functional groups, and preparation method of the dynamic self-adaptive artificial protective layer, the present invention uses linear polyurethane as the backbone, introduces dynamic DA bonds into the polymer system, and forms a topological network structure through the in-situ reaction of two reactants (linear polyurethane and bismaleimide) on the surface of lithium metal, thereby preparing an artificial SEI layer based on Diels-Alder (DA) bonds. This artificial SEI layer is a three-dimensional topological structure polymer material with dynamic self-adaptive characteristics. The introduced DA dynamic covalent bonds and hydrogen bonds in the structure endow the artificial protective layer with excellent mechanical properties and dynamic characteristics, enabling it to adapt to the volume change of the lithium metal negative electrode during the battery cycle, thereby achieving long-term stability of the electrode and significantly improving the safety and electrochemical performance of the lithium metal battery. Therefore, the dynamic self-adaptive artificial SEI layer (DACP) provided by the present invention combines high safety and excellent electrochemical performance, providing an innovative method for the preparation of a new artificial SEI layer.

[0089] The above detailed description of the embodiments of the present invention, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principle and spirit of the present invention, various changes, modifications, substitutions, and variations of these embodiments still fall within the protection scope of the present invention.

Claims

1. A dynamic adaptive polymer artificial SEI layer based on DA bonds, characterized in that: The polymer artificial SEI layer is a dynamic three-dimensional cross-linked topological structure, and its structural formula is as follows: Here, n is an integer from 3 to 27.

2. The method for preparing the artificial SEI layer of a dynamic adaptive polymer based on DA bonds according to claim 1, characterized in that: The Diels-Alder reaction is used to induce the linear polyurethane compound and the bismaleimide reactants to form a three-dimensional cross-linked network topology structure at high temperature, which specifically includes the following steps: S1, mixing polytetrahydrofuran, an isocyanate compound and a catalyst in a first solvent, stirring and reacting under an inert atmosphere, dissolving furandimethanol in the first solvent and injecting the mixture into the above solution, heating and stirring the mixture, volatilizing the solvent after the reaction, and drying the mixture to obtain a linear polyurethane compound; S2. Dissolving the linear polyurethane compound and bismaleimide in a second solvent, heating and stirring the reaction under an inert atmosphere to evaporate the solvent in the reaction solution, and then drying to obtain a dynamic adaptive polymer.

3. The method for preparing a dynamic adaptive polymer artificial SEI layer based on DA bonds according to claim 2, characterized in that: The structural formula of the linear polyurethane compound is as follows: Wherein: n=3~27, n is a natural number.

4. The method for preparing a dynamic adaptive polymer artificial SEI layer based on DA bonds according to claim 2, characterized in that: The structural formula of the bismaleimide (BMI) is as follows:

5. The method for preparing a dynamic adaptive polymer artificial SEI layer based on DA bonds according to claim 2, characterized in that: The structural formula of the polytetrahydrofuran is: Wherein: n=3-27, n is a natural number; the structural formula of furandimethanol is: The structural formula of the isocyanate compound is: The invention comprises at least one of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate and toluene diisocyanate.

6. The method for preparing a dynamic adaptive polymer artificial SEI layer based on DA bonds according to claim 2, characterized in that: The first solvent includes at least one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, toluene, and acetonitrile; the second solvent is at least one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, toluene, and acetonitrile; the catalyst includes at least one of dibutyltin dilaurate, stannous octoate, potassium acetate, and lead octoate.

7. The method for preparing a dynamic adaptive polymer artificial SEI layer based on DA bonds according to claim 2, characterized in that: The molar ratio of the polytetrahydrofuran to the isocyanate compound is 1 / 0.5 to 1 / 3; the molar ratio of the polytetrahydrofuran to the catalyst is 1000 / 1 to 10 / 1; the molar ratio of the polytetrahydrofuran to furandimethanol is 1 / 0.5 to 1 / 2; and the ratio of the isocyanate group of the linear polyurethane to the double bond functional group of bismaleimide is 10 / 1 to 1 / 2.

8. The method for preparing a dynamic adaptive polymer artificial SEI layer based on DA bonds according to claim 2, characterized in that: The reaction temperature of S1 is 40-120°C, and the reaction time is 4-24 hours; the reaction temperature of S2 is 40-120°C, and the reaction time is 4-12 hours.

9. Application of the DA bond-based dynamic adaptive polymer artificial SEI layer according to claim 1 in lithium metal batteries.

10. The use according to claim 9, characterized in that: The specific application method is: dissolving a linear polyurethane compound and bismaleimide in a third solvent, heating and stirring to mix evenly to obtain an artificial SEI layer precursor solution, and then dropping the precursor solution on the surface of a lithium metal negative electrode. After evaporating the solvent, a lithium metal negative electrode modified with a dynamic adaptive protective layer is obtained.

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