Boronic ester bond / hydrogen bond synergistic self-healing polymer electrolyte, preparation method and application thereof

Abstract

The application belongs to the technical field of lithium ion battery energy storage materials, and particularly relates to a borate bond / hydrogen bond synergistic self-repairing polymer electrolyte, a preparation method and application. The application first dissolves fluoroalcohol, isocyanate, polycaprolactone diol and a first initiator in an electrolyte to generate a nucleophilic addition reaction, obtains an intermediate solution containing urethane groups, then adds lithium salt to the intermediate solution containing urethane groups, uniformly mixes, and then adds borate monomer and a second initiator to generate an addition reaction, forms a self-repairing precursor solution, and finally heats and in-situ polymerizes the self-repairing precursor solution to obtain the borate bond / hydrogen bond synergistic self-repairing polymer electrolyte. The borate bond / hydrogen bond synergistic self-repairing polymer electrolyte prepared by the application can repair cracks or electrode deformation generated in the cycle process, and contains rich fluorine elements in the inside, which can improve the electrochemical window of the self-repairing solid electrolyte.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery energy storage materials, and particularly relates to a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte, a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of electronic devices and electric vehicles, there is an increasing demand for high-performance and high-safety energy storage systems. Lithium ion batteries have become one of the mainstream energy storage technologies due to their high energy density and long cycle life. However, most traditional lithium ion batteries use organic carbonate liquid electrolytes, which are flammable and prone to form lithium dendrites during use, leading to short circuits and even fires, posing a serious safety hazard. To solve this problem, solid-state electrolytes have gradually attracted attention. Solid-state electrolytes are non-flammable, non-leaking and have good thermal stability, and are considered an important way to improve battery safety. However, existing solid-state electrolytes still face some challenges, such as deficiencies in mechanical strength, interface stability and electrochemical performance, especially in wearable electronic device and electric vehicle application scenarios, where solid-state electrolytes may be damaged due to bending, twisting or impact, thereby affecting the performance and life of lithium ion batteries.

[0003] In recent years, the development of self-healing functional materials has provided a new way to solve this problem. Self-healing solid-state electrolytes can automatically repair after damage, restoring their original physical and electrochemical properties, thereby significantly improving the safety and reliability of lithium ion batteries. However, recent research has found that the introduction of self-healing functions also negatively affects the oxidation resistance and ion transport performance of the electrolyte, and the self-healing groups are sensitive to the complex chemical and electrochemical reaction mechanisms inside the lithium ion battery and external physical and mechanical changes, making it impossible to guarantee the cycle stability of the lithium ion battery. These problems have seriously hindered the development of self-healing solid-state electrolytes. SUMMARY

[0004] In view of the above existing problems, the application provides a borate bond / hydrogen bond synergistic self-repairing polymer electrolyte, a preparation method and application. The application first uses fluorinated alcohol, isocyanate ester, polycaprolactone diol and a first initiator as raw materials to perform nucleophilic addition reaction to obtain an intermediate solution containing urethane groups. Then, the intermediate solution containing urethane groups is mixed with lithium salt, borate monomer and a second initiator to perform addition reaction to obtain a self-repairing precursor solution. Finally, the self-repairing precursor solution is heated and in-situ polymerized to obtain the borate bond / hydrogen bond synergistic self-repairing polymer electrolyte. The borate bond / hydrogen bond synergistic self-repairing polymer electrolyte prepared by the method has excellent mechanical strength, interface stability, electrochemical performance, oxidation resistance, ion transport performance and cycle stability, and solves the technical defects of existing solid electrolytes and self-healing functional materials.

[0005] To solve the above technical problems, the application adopts the following technical solutions:

[0006] The first object of the application is to provide a preparation method of a borate bond / hydrogen bond synergistic self-repairing polymer electrolyte, which comprises the following steps:

[0007] The fluorinated alcohol, isocyanate ester, polycaprolactone diol and first initiator are dissolved in an electrolyte to perform nucleophilic addition reaction to obtain an intermediate solution containing urethane groups. The hydroxyl groups in the fluorinated alcohol and polycaprolactone diol react with the isocyanate groups in the isocyanate ester to easily generate urethane, which is the most important group in the intermediate solution containing urethane groups. The urethane groups can also form intermolecular hydrogen bonds with each other. Therefore, the borate bond / hydrogen bond synergistic self-repairing polymer electrolyte prepared by using the intermediate solution containing urethane groups has good mechanical properties and self-healing properties. In addition, the introduction of fluorine can also improve the redox potential of the borate bond / hydrogen bond synergistic self-repairing polymer electrolyte, so that it can match high-voltage positive electrode materials.

[0008] Lithium salt is added to the intermediate solution containing urethane groups and stirred and dissolved to obtain a functional electrolyte.

[0009] The borate monomer and the second initiator are added to the functional electrolyte to perform addition reaction. The double bond of the functional electrolyte performs electrophilic addition with the mercapto group or double bond of the borate monomer. The second initiator is cleaved to generate free radicals under heating. The free radicals take the hydrogen atoms of the mercapto group or the carbon-carbon double bond of the borate monomer to generate mercapto radicals or alkyl radicals. The generated mercapto radicals or alkyl radicals attack the carbon-carbon double bond of the isocyanate ester to transfer the active center and generate alkyl radicals. The alkyl radicals attack the borate monomer again, and the cycle continues. Finally, the free radicals are annihilated and the free radical reaction is completed to obtain a self-repairing precursor solution.

[0010] The self-repairing precursor solution is heated and in-situ polymerized to obtain a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte, and the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte is a solid-state electrolyte.

[0011] In a preferred embodiment of the present application, the fluoroalcohol is selected from one of 1H, 1H, 2H, 2H-perfluoro-1-octanol, 1H, 1H, 2H, 2H-perfluoro-1-hexanol, 1H, 1H, 2H, 2H-perfluoro-1-dodecanol, and 1H, 1H, 2H, 2H-perfluoro-1-decanol; wherein the mass of the fluoroalcohol accounts for 5% to 30% of the mass of the electrolyte.

[0012] In a preferred embodiment of the present application, the isocyanate ester is selected from one of isocyanatoethyl methacrylate, isocyanatoallyl, and isocyanatoethyl acrylate; wherein the mass ratio of the fluoroalcohol to the isocyanate ester is 1 to 10:1.

[0013] In a preferred embodiment of the present application, the polycaprolactone diol is selected from one of polycaprolactone diol-1000, polycaprolactone diol-2000, polycaprolactone diol-3000, polycaprolactone diol-6000, and polycaprolactone diol-10000; wherein the mass ratio of the polycaprolactone diol to the isocyanate ester is 1 to 10:1.

[0014] In a preferred embodiment of the present application, the first initiator is selected from one of dibutyltin dilaurate, triethylamine, N,N-dimethylbenzylamine, stannous octoate, triphenylphosphine, and 2-methylimidazole; wherein the mass ratio of the fluoroalcohol to the first initiator is 50 to 500:1.

[0015] In a preferred embodiment of the present application, the electrolyte is selected from one of KLD-1230C electrolyte, LB301 electrolyte, LB302 electrolyte, LB303 electrolyte, and LB313 electrolyte.

[0016] In a preferred embodiment of the present application, the conditions of the nucleophilic addition reaction are heating at 40°C to 100°C for 1h.

[0017] In a preferred embodiment of the present application, the lithium salt is selected from one or more of lithium nitrate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bistrifluoromethylsulfonylimide, and lithium bisfluorosulfonylimide; wherein the mass of the lithium salt accounts for 0.1% to 10% of the total amount of the functional electrolyte.

[0018] In a preferred embodiment of the present application, the borate monomer is selected from one of 2,2'-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxaborolane], 2,2'-(1,4-phenylene)-bis(4-allyloxy-1,3,2-dioxaborolane), 4-((allyloxy)methyl)-2-(4-vinylphenyl)-1,3,2-dioxaborolane; wherein the molar ratio of the borate monomer to the isocyanate is 1:1-4.

[0019] In a preferred embodiment of the present application, the second initiator is selected from one of azobisisobutyronitrile, azobisisoheptyl nitrile, di-tert-butyl peroxide, diisopropylbenzene hydroperoxide, benzoyl peroxide, triphenylphosphine; wherein the mass of the second initiator is 0.05%-1% of the mass of the fluorinated alcohol.

[0020] In a preferred embodiment of the present application, the conditions of the addition reaction are heating at 40-100℃ for 0.5-1h.

[0021] A second object of the present application is to provide a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte prepared by the above preparation method.

[0022] A third object of the present application is to provide the use of the boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte in the preparation of a high-voltage lithium metal battery, wherein the voltage range of the high-voltage lithium metal battery is 4.2-4.7V.

[0023] In a preferred embodiment of the present application, the self-healing precursor solution is added dropwise between the positive electrode and the negative electrode, and then heated and in-situ polymerized to obtain a high-voltage lithium metal battery.

[0024] In a preferred embodiment of the present application, the positive electrode is a lithium cobaltate positive electrode, and the negative electrode is a lithium metal negative electrode.

[0025] In a preferred embodiment of the present application, the heating conditions of the in-situ polymerization are heating at 40-100℃ for 0.5-24h.

[0026] Compared with the prior art, the present application has the beneficial effects that:

[0027] 1、The application first takes fluorinated alcohol, isocyanate, polycaprolactone diol and first initiator as raw materials to carry out nucleophilic addition reaction to obtain intermediate solution containing urethane groups; then the intermediate solution containing urethane groups is mixed with lithium salt, borate monomer and second initiator to carry out addition reaction to obtain self-repairing precursor solution; finally, the self-repairing precursor solution is heated and in-situ polymerization is carried out to obtain boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte. The boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte prepared by the application can form a solid CEI film rich in F elements and B elements on the positive electrode side, the CEI film is a positive electrolyte interface film, which effectively inhibits the interface side reaction of the positive electrode side, prevents the generation of cracks and the generation of phase change; forms a SEI film rich in LiF and Li3N on the negative electrode side, the SEI is a solid-state electrolyte interface layer rich in LiF, the solid SEI film prevents further reaction of metal lithium and electrolyte, inhibits dendrite growth and lithium metal pulverization, and can also quickly conduct lithium ions, greatly improving the cycle life and safety performance of high-voltage lithium metal batteries.

[0028] The boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte is a self-repairing solid-state electrolyte applied to high-voltage lithium metal batteries. The application takes borate monomer as raw material, the borate monomer contains boron ester bond, and the boron ester bond contained in the self-repairing solid-state electrolyte realizes dynamic crosslinking and self-healing through ester exchange reaction, so as to repair the interface damage generated in the cycle process of high-voltage lithium metal batteries and restore the original physical performance and electrochemical performance, thereby significantly improving the safety and reliability of high-voltage lithium metal batteries. The Lewis acidity of the boron ester bond can also interact with lithium salt anions, promote uniform deposition of lithium ions, and improve the interface stability and electrochemical performance of high-voltage lithium metal batteries. At the same time, the self-repairing solid-state electrolyte also contains a large number of hydrogen bonds formed between the urethane groups, and these hydrogen bonds have the characteristics of reversibility, directionality and high sensitivity, so that the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte can first break the weak hydrogen bond after being damaged by external force, the new interface generated contains many uncombined hydrogen bond donors or acceptors, these groups form active sites on the fracture surface, when the fracture surfaces contact, these active sites will re-form hydrogen bonds, gradually restore the integrity and function of the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte, and through the joint action of hydrogen bonds and boron ester bonds, the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte has excellent self-healing performance.

[0029] 2、The fluorinated alcohol has rich fluorine elements in the molecular structure, strong electronegativity and high oxidation stability, can significantly improve the electrochemical stability of the self-repairing solid electrolyte, so that the self-repairing solid electrolyte can match the high-voltage positive electrode material, at the same time, the fluorine element also promotes the formation of SEI film, can effectively inhibit the growth of lithium dendrites, and prevent the side reaction between the electrode and the electrolyte, significantly improve the cycle life of the high-voltage lithium metal battery, and improve the electrochemical window of the self-repairing solid electrolyte.

[0030] 3、The polycaprolactone diol is a flexible polymer segment, which can be used as a supporting skeleton of the self-repairing solid electrolyte, and can also effectively alleviate the volume change of the positive electrode and the negative electrode generated in the charging and discharging process, release stress, so as to maintain the stability of the electrode structure. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is a film physical map; wherein, (a) is a borate ester bond / hydrogen bond synergistic self-repairing polymer film physical map prepared by replacing the KLD-1230C electrolyte of example 1 with dimethylacetamide, (b) is a hydrogen bond self-repairing polymer film physical map prepared by replacing the KLD-1230C electrolyte of comparative example 1 with dimethylacetamide.

[0032] Figure 2 It is a scanning electron microscope image; wherein, a graph and b graph are scanning electron microscope images of the surface of the borate ester bond / hydrogen bond synergistic self-repairing polymer film under different magnifications, c graph and d graph are scanning electron microscope images of the surface of the hydrogen bond self-repairing polymer film under different magnifications.

[0033] Figure 3 It is a scanning electron microscope image and an element distribution graph; wherein, a graph~b graph in A graph are surface scanning electron microscope images of the lithium metal negative electrode of the high-voltage lithium metal battery after cycling of example 1 under different magnifications; B graph is a cross-section scanning electron microscope image of the lithium metal negative electrode of the high-voltage lithium metal battery after cycling of example 1 and C, N, O, F element distribution graphs.

[0034] Figure 4 It is a self-healing performance graph of the borate ester bond / hydrogen bond synergistic self-repairing polymer film.

[0035] Figure 5 It is a cycle performance graph; wherein, (a) is a cycle performance graph of a button high-voltage lithium metal battery assembled by using the borate ester bond / hydrogen bond synergistic self-repairing polymer electrolyte of example 1; (b) is a cycle performance graph of a button high-voltage lithium metal battery assembled by using the hydrogen bond self-repairing polymer electrolyte of comparative example 1.

[0036] Figure 6Figure (a) is a rate capability graph of a button high-voltage lithium metal battery assembled using the boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte of Example 1; and Figure (b) is a rate capability graph of a button high-voltage lithium metal battery assembled using the hydrogen bond self-healing polymer electrolyte of Comparative Example 1.

[0037] Figure 7 Figure (a) is a self-healing precursor solution, and Figure (b) is a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0039] In view of the problem that in the prior art self-healing solid-state electrolyte, due to the introduction of self-healing functional materials, the oxidation resistance and ion transport performance of the electrolyte are negatively affected, and the self-healing groups are sensitive to the complex chemical and electrochemical reaction mechanisms inside the lithium ion battery and external physical and mechanical changes, so that the cycle stability of the lithium ion battery cannot be guaranteed, the present application provides a novel boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte. The boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte has high ionic conductivity, solving the problem of ion transport performance; the high-voltage lithium metal battery prepared using the boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte has excellent electrochemical performance, solving the problem of sensitivity; and the present application uses a fluorinated alcohol as a raw material, and the fluorine element of the fluorinated alcohol has a strong electron-withdrawing effect, improving the oxidation resistance, solving the problem of oxidation resistance.

[0040] The technical solutions of the present application are studied below using examples and comparative examples, and the specific research methods and results are shown as follows:

[0041] Example 1

[0042] The preparation method of the boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte comprises the following steps:

[0043] S1, 0.58 g of polycaprolactone diol-2000 was weighed and dissolved in 2 mL of KLD-1230C electrolyte to obtain a mixed solution, then 0.21 mL of isocyanatoethyl methacrylate and 0.22 mL of 1H, 1H, 2H, 2H-perfluoro-1-octanol were added to the mixed solution, and a uniform transparent solution was obtained after stirring, then 10 μL of the first initiator dibutyltin dilaurate was added, and the solution was fully stirred at 50°C for 1 h to obtain an intermediate solution containing urethane groups.

[0044] S2, 20 mg of lithium nitrate was added to the intermediate solution containing urethane groups, and then fully stirred at 50°C for 3 h to obtain a functional electrolyte.

[0045] S3, 0.09 g of 2,2'-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxaborinane] and 5 mg of the second initiator azobisisobutyronitrile were added to the functional electrolyte, and the solution was stirred at 50°C for 0.5 h to obtain a self-repairing precursor solution.

[0046] S4, the self-repairing precursor solution was heated in an oven at 55°C for 1 h to obtain a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte.

[0047] A method for preparing a high-voltage lithium metal battery, comprising the following steps:

[0048] The self-repairing precursor solution was added dropwise between the lithium cobaltate positive electrode and the lithium metal negative electrode, and then heated in an oven at 55°C for 1 h to obtain a high-voltage lithium metal battery.

[0049] Example 2

[0050] A method for preparing a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte, comprising the following steps:

[0051] S1, 0.6 g of polycaprolactone diol-3000 was weighed and dissolved in 2 mL of LB301 electrolyte to obtain a mixed solution, then 0.18 mL of allyl isocyanate and 0.3 mL of 1H, 1H, 2H, 2H-perfluoro-1-hexanol were added to the mixed solution, and a uniform transparent solution was obtained after stirring, then 10 μL of the first initiator triethylamine was added, and the solution was fully stirred at 50°C for 1 h to obtain an intermediate solution containing urethane groups.

[0052] S2, 40 mg of lithium difluoro(oxalato)borate and 20 mg of lithium nitrate were added to the intermediate solution containing urethane groups, and then fully stirred at 50°C for 3 h to obtain a functional electrolyte.

[0053] S3, 0.06 g of 4-((allyloxy)methyl)-2-(4-vinylphenyl)-1,3,2-dioxaborolane and 7 mg of the second initiator azobisisoheptane nitrile were added into the functional electrolyte, and stirred at 50 °C for 1 h to obtain a self-repairing precursor solution.

[0054] S4, the self-repairing precursor solution was heated in a 50 °C oven for 1 h to obtain a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte.

[0055] The preparation method of the high-voltage lithium metal battery comprises the following steps:

[0056] The self-repairing precursor solution was added dropwise between the lithium cobaltate positive electrode and the lithium metal negative electrode, and then heated in a 50 °C oven for 1 h to obtain a high-voltage lithium metal battery.

[0057] Example 3

[0058] The preparation method of the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte comprises the following steps:

[0059] S1, 1.0 g of polycaprolactone diol-10000 was weighed and dissolved in 4 mL of LB302 electrolyte to obtain a mixed solution, then 0.35 mL of isocyanatoethyl acrylate and 0.54 mL of 1H,1H,2H,2H-perfluoro-1-dodecanol were added to the mixed solution, and after stirring, a uniform transparent solution was obtained, then 20 μL of the first initiator N,N-dimethylbenzylamine was added, and the mixture was fully stirred at 50 °C for 1 h to obtain an intermediate solution containing urethane groups.

[0060] S2, 60 mg of lithium bistrifluoromethylsulfonylimide and 40 mg of lithium tetrafluoroborate were added to the intermediate solution containing urethane groups, and then fully stirred at 50 °C for 2 h to obtain a functional electrolyte.

[0061] S3, 0.34 g of 2,2'-(1,4-phenylene)-bis(4-allyloxy-1,3,2-dioxaborolane) and 15 mg of the second initiator diisopropylbenzene peroxide were added into the functional electrolyte, and stirred at 50 °C for 1 h to obtain a self-repairing precursor solution.

[0062] S4, the self-repairing precursor solution was heated in a 60 °C oven for 0.5 h to obtain a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte.

[0063] The preparation method of the high-voltage lithium metal battery comprises the following steps:

[0064] The self-repairing precursor solution was added dropwise between the lithium cobaltate positive electrode and the lithium metal negative electrode, and then heated in a 60 °C oven for 0.5 h to obtain a high-voltage lithium metal battery.

[0065] Example 4

[0066] The preparation method of the boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte comprises the following steps:

[0067] S1, 0.74 g of polycaprolactone diol-6000 is weighed and dissolved in 4 mL of LB303 electrolyte to obtain a mixed solution, then 0.3 mL of isocyanatoethyl methacrylate and 0.48 mL of 1H, 1H, 2H, 2H-perfluoro-1-decanol are added to the mixed solution, and a uniform transparent solution is obtained after stirring, then 20 μL of the first initiator stannous octoate is added, and the mixture is stirred at 50°C for 1 h to obtain an intermediate solution containing urethane groups.

[0068] S2, 40 mg of lithium difluoroborate is added to the intermediate solution containing urethane groups, and then the mixture is stirred at 50°C for 1 h to obtain a functional electrolyte.

[0069] S3, 0.25 g of 4-((allyloxy)methyl)-2-(4-vinylphenyl)-1,3,2-dioxaborolane and 12 mg of the second initiator benzoyl peroxide are added to the functional electrolyte, and the mixture is stirred at 50°C for 1 h to obtain a self-repairing precursor solution.

[0070] S4, the self-repairing precursor solution is heated in a 60°C oven for 4 h to obtain a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte.

[0071] The preparation method of the high-voltage lithium metal battery comprises the following steps:

[0072] The self-repairing precursor solution is added dropwise between the lithium cobalt oxide positive electrode and the lithium metal negative electrode, and then heated in a 60°C oven for 4 h to obtain a high-voltage lithium metal battery.

[0073] Example 5

[0074] The preparation method of the boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte comprises the following steps:

[0075] S1, 0.4 g of polycaprolactone diol-1000 is weighed and dissolved in 4 mL of LB313 electrolyte to obtain a mixed solution, then 0.2 mL of isocyanatoethyl acrylate and 0.25 mL of 1H, 1H, 2H, 2H-perfluoro-1-octanol are added to the mixed solution, and a uniform transparent solution is obtained after stirring, then 10 μL of the first initiator 2-methylimidazole is added, and the mixture is stirred at 50°C for 1 h to obtain an intermediate solution containing urethane groups.

[0076] S2, 2.3 mg of lithium nitrate was added to the intermediate solution containing carbamate groups, and then fully stirred at 50 °C for 3 h to obtain a functional electrolyte.

[0077] S3, 0.2 g of 2,2'-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxaborinane] and 2 mg of the second initiator azobisisobutyronitrile were added to the functional electrolyte, and stirred at 100 °C for 0.5 h to obtain a self-repairing precursor solution.

[0078] S4, the self-repairing precursor solution was heated in an oven at 100 °C for 0.5 h to obtain a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte.

[0079] A method for preparing a high-voltage lithium metal battery, comprising the following steps:

[0080] The self-repairing precursor solution was added dropwise between the lithium cobalt oxide positive electrode and the lithium metal negative electrode, and then heated in an oven at 55 °C for 2 h to obtain a high-voltage lithium metal battery.

[0081] Example 6

[0082] A method for preparing a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte, comprising the following steps:

[0083] S1, 0.1 g of polycaprolactone diol-2000 was weighed and dissolved in 2 mL of KLD-1230C electrolyte to obtain a mixture, then 0.1 mL of isocyanatoethyl methacrylate and 0.1 mL of 1H,1H,2H,2H-perfluoro-1-octanol were added to the mixture, and after stirring a uniform transparent solution was obtained, then 5 μL of the first initiator dibutyltin dilaurate was added, and fully stirred at 40 °C for 1 h to obtain an intermediate solution containing carbamate groups.

[0084] S2, 2.3 mg of lithium nitrate was added to the intermediate solution containing carbamate groups, and then fully stirred at 50 °C for 3 h to obtain a functional electrolyte.

[0085] S3, 0.2 g of 2,2'-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxaborinane] and 2 mg of the second initiator azobisisobutyronitrile were added to the functional electrolyte, and stirred at 100 °C for 0.5 h to obtain a self-repairing precursor solution.

[0086] S4, the self-repairing precursor solution was heated in an oven at 100 °C for 0.5 h to obtain a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte.

[0087] A method for preparing a high-voltage lithium metal battery, comprising the following steps:

[0088] The self-repairing precursor solution is added dropwise between the lithium cobalt oxide anode and the lithium metal cathode, and then heated in an oven at 100°C for 0.5h to obtain a high-voltage lithium metal battery.

[0089] Example 7

[0090] A preparation method of a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte includes the following steps:

[0091] S1, 0.2g of polycaprolactone diol-2000 is weighed and dissolved in 6mL of KLD-1230C electrolyte to obtain a mixed solution, then 0.02mL of isocyanatoethyl methacrylate and 0.2mL of 1H,1H,2H,2H-perfluoro-1-octanol are added to the mixed solution, and a uniform transparent solution is obtained after stirring, and 5μL of first initiator dibutyltin dilaurate is added, and the solution is stirred at 100°C for 1h to obtain an intermediate solution containing urethane groups.

[0092] S2, 64mg of lithium nitrate is added to the intermediate solution containing urethane groups, and then stirred at 50°C for 3h to obtain a functional electrolyte.

[0093] S3, 0.04g of 2,2'-(1,4-phenylene)-bis[4-thiol-1,3,2-dioxaborinane] and 5mg of second initiator azobisisobutyronitrile are added to the functional electrolyte, and stirred at 10°C for 1h to obtain a self-repairing precursor solution.

[0094] S4, the self-repairing precursor solution is heated in an oven at 40°C for 24h to obtain a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte.

[0095] A preparation method of a high-voltage lithium metal battery includes the following steps:

[0096] The self-repairing precursor solution is added dropwise between the lithium cobalt oxide anode and the lithium metal cathode, and then heated in an oven at 40°C for 24h to obtain a high-voltage lithium metal battery.

[0097] Comparative Example 1

[0098] A preparation method of a hydrogen bond self-repairing polymer electrolyte is the same as the preparation steps of Example 1, except that no borate monomer is added in step S3, including the following steps:

[0099] S1, 0.58 g of polycaprolactone diol-2000 was weighed and dissolved in 2 mL of KLD-1230C electrolyte to obtain a mixed solution, then 0.21 mL of isocyanatoethyl methacrylate and 0.22 mL of 1H, 1H, 2H, 2H-perfluoro-1-octanol were added to the mixed solution, and a uniform transparent solution was obtained after stirring, then 10 μL of the first initiator dibutyltin dilaurate was added, and the solution was stirred at 50°C for 1 h to obtain an intermediate solution containing urethane groups.

[0100] S2, 20 mg of lithium nitrate was added to the intermediate solution containing urethane groups, and then stirred at 50°C for 3 h to obtain a functional electrolyte.

[0101] S3, 5 mg of the second initiator azobisisobutyronitrile was added to the functional electrolyte, and stirred until a clear solution was obtained to obtain a self-repairing precursor solution.

[0102] S4, the self-repairing precursor solution was heated in a 55°C oven for 1 h to obtain a hydrogen bond self-repairing polymer electrolyte.

[0103] The preparation method of the high-voltage lithium metal battery comprises the following steps:

[0104] The self-repairing precursor solution was added dropwise between the lithium cobaltate positive electrode and the lithium metal negative electrode, and then heated in a 55°C oven for 1 h to obtain a high-voltage lithium metal battery.

[0105] Result analysis:

[0106] Examples 1 to 7 of the present application all obtained hydrogen bond self-repairing polymer electrolytes with excellent self-healing performance and electrochemical performance, and the hydrogen bond self-repairing polymer electrolyte and high-voltage lithium metal battery of Example 1 were taken as examples, and compared with the hydrogen bond self-repairing polymer electrolyte and high-voltage lithium metal battery of Comparative Example 1, and the specific research methods and results are shown as follows:

[0107] 1, morphology test:

[0108] (1) Macroscopic morphology test:

[0109] In order to facilitate film formation, the KLD-1230C electrolyte of Example 1 and Comparative Example 1 was replaced with dimethylacetamide respectively, and then the same operation was carried out until the self-repairing precursor solution was obtained, and finally the self-repairing precursor solution was dried at 60°C for 24 h under an inert atmosphere to obtain a borate ester bond / hydrogen bond synergistic self-repairing polymer film and a hydrogen bond self-repairing polymer film, and the macroscopic morphology of the two was tested, and the test results are shown as Figure 1 Figure 1 ​The results show that under the macro state, the surface of the borate ester bond / hydrogen bond synergistic self-healing polymer film and the hydrogen bond self-healing polymer film is very smooth and flat, but the borate ester bond / hydrogen bond synergistic self-healing polymer film is more flexible and elastic than the hydrogen bond self-healing polymer film. The hydrogen bond self-healing polymer film only contains hydrogen bonds, and due to the directionality of hydrogen bonds, the hydrogen bond self-healing polymer film has a higher crystallinity and a harder texture, and thus has a poor self-healing performance, almost no self-healing performance.

[0110] (2) Micro-morphology test:

[0111] The micro-morphology of the surface of the borate ester bond / hydrogen bond synergistic self-healing polymer film and the hydrogen bond self-healing polymer film was tested, and the test results are shown in Figure 2 As can be seen from Figure 2 , the introduction of borate ester monomers makes the surface of the borate ester bond / hydrogen bond synergistic self-healing polymer film smoother and flatter, while the surface of the hydrogen bond self-healing polymer film has many small cracks and wrinkles.

[0112] The lithium metal negative electrode of the high-voltage lithium metal battery after cycling was taken as an example for research, Figure 3 , and the A figure in the figure is a surface diagram of the lithium metal negative electrode, and the B figure is a cross-sectional diagram and an element distribution diagram of the lithium metal negative electrode. As can be seen from the A figure, the surface of the lithium metal negative electrode after cycling is smooth and flat, and no lithium dendrite is generated, indicating that a firm SEI film has been formed on the surface of the lithium metal negative electrode; as can be seen from the B figure, the C, N, O and F elements in the SEI film are uniformly distributed, indicating that the borate ester bond / hydrogen bond synergistic self-healing polymer electrolyte has good interfacial compatibility with the lithium metal negative electrode, and a uniform SEI film is formed on the surface of the lithium metal negative electrode after cycling.

[0113] 2. Self-healing performance:

[0114] Figure 4 The self-healing performance test diagram of the borate ester bond / hydrogen bond synergistic self-healing polymer film. As can be seen from Figure 4 , under the dual action of dynamic borate ester bond and hydrogen bond, the polymer network has excellent self-healing performance, and it can complete self-healing within 3h at 30℃.

[0115] 3. Cycle performance test:

[0116] The borate ester bond / hydrogen bond synergistic self-healing polymer electrolyte of Example 1 and the hydrogen bond self-healing polymer electrolyte of Comparative Example 1 were respectively assembled into high-voltage lithium metal batteries, and the cycle performance of the two high-voltage lithium metal batteries was tested according to the following test method, and the test results are shown in Figure 5 .

[0117] Test method: lithium sheet with a diameter of 16 mm was used as the negative electrode, lithium cobalt oxide sheet with a diameter of 8 mm was used as the positive electrode, lithium cobalt oxide was loaded on aluminum foil to prepare lithium cobalt oxide sheet, and the loading amount of lithium cobalt oxide on the lithium cobalt oxide sheet was 5.5 mg cm -2 ; Whatman® filter was used as the separator, the Whatman® filter was 100% borosilicate glass fiber, model GF / A, 1.6 µm pore size, diameter 16 mm, 150 µL of the self-repairing precursor solution was uniformly dropped on the Whatman® filter, the Whatman® filter was clamped between the positive electrode and the negative electrode, and then heated in a 55°C oven for 1 h to obtain a high-voltage lithium metal battery, and the battery shell model was CR2032.

[0118] Test conditions: the first two circles were charged and discharged at a rate of 0.1C to activate the high-voltage lithium metal battery, and then the rate was 0.5C for the charge and discharge cycle test, and the charge and discharge voltage interval was 3.0V~4.6V.

[0119] From the test results of Figure 5 , after 180 cycles, the high-voltage lithium metal battery assembled with the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte of Example 1 still had a specific capacity retention rate of 83%, which was greatly improved compared to the 44% specific capacity retention rate of the high-voltage lithium metal battery assembled with the hydrogen bond self-repairing polymer electrolyte of Comparative Example 1, indicating that the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte can improve the cycle stability of the high-voltage lithium metal battery.

[0120] 4. Rate performance test:

[0121] According to the following method, the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte of Example 1 and the hydrogen bond self-repairing polymer electrolyte of Comparative Example 1 were respectively assembled with lithium metal negative electrode and lithium cobalt oxide positive electrode to form button cells, and the rate performance of each was tested, and the test results are shown in Figure 6 .

[0122] Test method: lithium sheet with a diameter of 16 mm was used as the negative electrode, lithium cobalt oxide sheet with a diameter of 8 mm was used as the positive electrode, lithium cobalt oxide was loaded on aluminum foil to prepare lithium cobalt oxide sheet, and the loading amount of lithium cobalt oxide on the lithium cobalt oxide sheet was 5.5 mg cm -2 ; Whatman® filter was used as the separator, the Whatman® filter was 100% borosilicate glass fiber, model GF / A, 1.6 µm pore size, diameter 16 mm, 150 µL of the self-repairing precursor solution was uniformly dropped on the Whatman® filter, the Whatman® filter was clamped between the positive electrode and the negative electrode, and then heated in a 55°C oven for 1 h to obtain a high-voltage lithium metal battery, and the battery shell model was CR2032.

[0123] Test conditions: under the conditions of 0.2C, 0.5C, 1C, 1.5C, 2C, 4C, respectively, the current density is increased first and then decreased, 1C=180 mAh / g, and the charge and discharge voltage interval is 3.0V~4.3V.

[0124] From the test results of Figure 6 It can be seen from the test results that the high-voltage lithium metal battery assembled by using the boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte of Example 1 has good rate performance, which greatly alleviates the specific capacity decay of the high-voltage lithium metal battery under high-rate charge and discharge.

[0125] Figure 7 The results show that the self-repairing precursor solution can be cured to form a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte after heating.

[0126] In summary, the present application provides a self-repairing solid electrolyte applied to a high-voltage positive electrode and a lithium metal negative electrode, i.e., a boron ester bond / hydrogen bond synergistic self-repairing polymer electrolyte. The self-repairing solid electrolyte is a flexible cross-linked polymer, contains fluorine functional groups in the molecule, can improve the electrochemical window of the self-repairing solid electrolyte, effectively buffers the volume change generated by the positive electrode and the negative electrode during the charge and discharge process, and releases the reaction stress. The boron ester structure in the polymer skeleton can realize dynamic cross-linking and self-healing through ester exchange reaction, combined with the reversible transformation of a large number of hydrogen bonds in the skeleton, both of which synergistically act to repair the interface damage generated by the high-voltage lithium metal battery during the cycle process, restore its original physical properties and electrochemical properties, thereby significantly improving the safety and reliability of the high-voltage lithium metal battery; at the same time, it can also form a CEI film rich in F and B on the positive electrode side, and form a SEI film rich in LiF and Li3N on the negative electrode side, thereby significantly improving the cycle stability of the high-voltage lithium metal battery.

[0127] It should be noted that when numerical ranges are involved in the present application, both endpoints of each numerical range and any number between the two endpoints can be selected. Since the same steps and examples are used, the preferred embodiments are described in the present application to prevent redundancy. Although the preferred embodiments of the present application have been described, those skilled in the art can make additional changes and modifications to these embodiments once they understand the basic inventive concept. Therefore, the appended claims are intended to include the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0128] Obviously, those skilled in the art can make various modifications and changes to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and changes of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and changes.

Claims

1. A method for preparing a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte, characterized by, The method comprises the following steps: The fluorinated alcohol, the isocyanate ester, the polycaprolactone diol and the first initiator are dissolved in an electrolyte to perform a nucleophilic addition reaction, the hydroxyl groups in the fluorinated alcohol and the polycaprolactone diol react with the isocyanate groups in the isocyanate ester to obtain an intermediate solution containing urethane groups; The lithium salt is added to the intermediate solution containing urethane groups and stirred and dissolved to obtain a functional electrolyte; The borate monomer and the second initiator are added to the functional electrolyte to perform an addition reaction to obtain a self-repairing precursor solution; The self-repairing precursor solution is heated and in-situ polymerized to obtain a borate bond / hydrogen bond synergistic self-repairing polymer electrolyte.

2. The method for preparing a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte according to claim 1, characterized in that, The mass of the fluorinated alcohol accounts for 5% to 30% of the mass of the electrolyte.

3. The method for preparing a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte according to claim 1, characterized in that, The mass ratio of the fluorinated alcohol, the isocyanate ester and the polycaprolactone diol is 1 to 10:1:1 to 10.

4. The method for preparing a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte according to claim 1, characterized in that, The nucleophilic addition reaction is performed at 40 to 100 degrees Celsius for 1 hour.

5. The method for preparing a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte according to claim 1, characterized in that, The mass of the lithium salt accounts for 0.1% to 10% of the total mass of the functional electrolyte.

6. The method for preparing a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte according to claim 1, characterized in that, The molar ratio of the borate monomer to the isocyanate ester is 1:1 to 4.

7. The method for preparing a boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte according to claim 1, characterized in that, The addition reaction is performed at 40 to 100 degrees Celsius for 0.5 to 1 hour.

8. A boron ester bond / hydrogen bond cooperative self-healing polymer electrolyte, characterized by, The self-repairing precursor solution is prepared by the preparation method in any one of claims 1 to 7.

9. Use of the boron ester bond / hydrogen bond synergistic self-healing polymer electrolyte of claim 8 in the preparation of high-voltage lithium metal batteries, characterized in that, The voltage range of the high-voltage lithium metal battery is 4.2V to 4.7V.

10. Use according to claim 9, characterized in that, The self-repairing precursor solution is added dropwise between the positive electrode and the negative electrode, and the self-repairing precursor solution is in-situ polymerized by heating to obtain the high-voltage lithium metal battery.

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