Lithium battery polymer protective coating as well as preparation method and application thereof

Abstract

The invention discloses a lithium battery polymer protective coating as well as a preparation method and application thereof, and belongs to the technical field of lithium batteries, the preparation method of the coating comprises the following steps: adding a macromolecular fluorine-containing polymer, boric acid ester-containing branched polyether and a lithiated mesoporous molecular sieve into a solvent, and stirring and dispersing to obtain a coating; coating the coating on the surface of a metal lithium negative electrode, and performing vacuum drying to form a lithium battery polymer protective coating; the boric acid ester-containing branched polyether is obtained by sequentially reacting hyperbranched polyglycidyl with long-chain alkyl succinic anhydride and trimethyl borate; according to the invention, a high-efficiency and stable lithium battery negative electrode protection system is constructed by introducing functional groups such as long-chain alkyl, carbonyl, borate group and the like on the structure of hyperbranched polyglycerol and utilizing the characteristics of the branched structure and the lithiated mesoporous molecular sieve. The system can effectively inhibit the growth of lithium dendrites, improve the safety of the battery and prolong the cycle life of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a lithium battery polymer protective coating and a preparation method and application thereof. Background Art

[0002] In the field of lithium batteries, the negative electrode material is a key factor affecting battery performance and safety. Traditional lithium battery negative electrode materials such as graphite, as well as emerging high-capacity negative electrode materials such as silicon or lithium metal, all have some problems that need to be solved urgently. On the one hand, the negative electrode of lithium batteries is prone to electrolyte decomposition. During the battery charging and discharging process, the electrochemical environment on the negative electrode surface is complex. In particular, high-capacity negative electrode materials undergo large volume changes during charging and discharging, and their surface potential fluctuates significantly, which will promote the reduction and decomposition of solvent molecules in the electrolyte (such as carbonate solvents). For example, common solvents such as ethylene carbonate (EC) will adsorb on the negative electrode surface and undergo electron transfer, decomposing to produce byproducts such as alkyl lithium carbonate and lithium carbonate. This not only consumes electrolyte, but also hinders lithium ion transmission, affecting the battery cycle life. On the other hand, the negative electrode is prone to dendrite formation. Taking the lithium metal negative electrode as an example, when lithium ions are reduced and deposited on its surface, due to factors such as local uneven lithium ion concentration, branch-like metal lithium protrusions (dendrites) will form. As dendrites continue to grow, they may pierce the separator, causing internal short circuits in the battery, leading to serious safety problems such as overheating, fire, and even explosion, greatly reducing the safety of the battery.

[0003] While some coating technologies are currently used to protect lithium battery anodes, these coatings lack compatibility with high-capacity anodes. High-capacity anodes, such as silicon anodes, experience significant volume expansion during charge and discharge, potentially reaching as much as 300%, and existing coatings struggle to adapt to this volume change. As a result, the coatings easily break when the silicon anode expands, losing their ability to provide sustained protection. Furthermore, existing coatings are unable to effectively inhibit the growth of lithium metal dendrites, resulting in poor stability and failing to meet the stability and safety requirements of high-capacity anodes.

[0004] Among the existing solutions to solve the negative electrode problem of lithium batteries, some solutions use traditional chemical synthetic materials as coatings, which have limited effects in inhibiting dendrite growth and stabilizing the solid electrolyte interface (SEI), and cannot significantly improve battery safety and cycle life. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium battery polymer protective coating and its preparation method and application, so as to solve the problem of poor stability of the negative electrode protective coating.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] The first aspect of the present application provides a method for preparing a lithium battery polymer protective coating, comprising the following steps:

[0008] A high molecular weight fluoropolymer, a borate-containing branched polyether, and a lithiated mesoporous molecular sieve are added to a solvent and stirred and dispersed to obtain a coating. The coating is then applied to the surface of a metallic lithium anode and vacuum dried at 50-60°C to form a lithium battery polymer protective coating. The borate-containing branched polyether is obtained by sequentially reacting hyperbranched polyglycidol with long-chain alkyl succinic anhydride and trimethyl borate. The mass ratio of the high molecular weight fluoropolymer, borate-containing branched polyether, and lithiated mesoporous molecular sieve is 1:4-5:4.

[0009] Furthermore, the usage ratio of the hyperbranched polyglycidol, the long-chain alkyl succinic anhydride and the trimethyl borate is 12 g: 0.02-0.04 mol: 0.02-0.04 mol.

[0010] Hyperbranched poly(glycidol) contains numerous ether-oxygen bonds, which can promote the dissociation of lithium salts and weakly coordinate with free lithium ions, forming active migration sites and accelerating the migration of lithium ions along the borate-containing branched polyether segments. However, hyperbranched poly(glycidol) itself has certain limitations. Its hydrophilicity may interfere with the transport of lithium ions due to water molecules when in contact with electrolytes and other systems, affecting transport efficiency and interfacial stability. Its structural rigidity is also insufficient, making it ineffective in suppressing lithium dendrite growth or optimizing the electrode / electrolyte interface.

[0011] Therefore, in the present invention, by introducing long-chain alkyl groups into hyperbranched polyglycidol and long-chain alkyl succinic anhydride, the introduced long-chain alkyl groups serve as hydrophobic segments to form a certain hydrophobic barrier. This weakens the interference of impurities such as water molecules and provides a relatively stable environment for the transmission of lithium ions.

[0012] In addition, the long-chain alkyl succinic anhydride reacts with the hyperbranched polyglycidol to introduce a carbonyl group, thereby constructing an internal lithium ion transport channel. Functional groups such as ether oxygen bonds and carbonyl groups construct the internal lithium ion transport channel. The hyperbranched polyglycidol in the present invention reacts with the long-chain alkyl succinic anhydride and trimethyl borate in sequence to obtain a borate-containing branched polyether, which can optimize the interface layer structure, ensure efficient lithium ion transport at the interface, and thus inhibit the growth of lithium dendrites.

[0013] The present invention also further increases the crosslinking density of the borate-containing branched polyether by reacting trimethyl borate with hyperbranched polyglycidol, introduces borate groups, and imparts dynamic properties to the borate-containing branched polyether, thereby promoting the transport of lithium ions and effectively suppressing the phenomenon of concentration polarization at the electrode interface, thereby inhibiting the formation of lithium dendrites.

[0014] Lithiated mesoporous molecular sieves can serve as a lithium ion storage and transport medium. They possess a rich internal pore structure that allows for the adsorption and release of lithium ions. In the system of the present invention, the branched structure of the borate-containing branched polyether can sterically hinder the aggregation of the lithiated mesoporous molecular sieves, thereby improving the dispersibility of the lithiated mesoporous molecular sieves and promoting the dispersion and wetting of inorganic particles. The synergistic effect of the lithiated mesoporous molecular sieve and the borate-containing branched polyether further optimizes the lithium ion transmission pathway and storage environment, improving the overall performance of the battery.

[0015] Furthermore, the thickness of the lithium battery polymer protective coating is 3-6 μm.

[0016] Furthermore, the high molecular weight fluorine-containing polymer is at least one of PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), FEP (fluorinated ethylene propylene copolymer) and PFA (perfluoroalkyl).

[0017] Furthermore, the solvent is at least one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, triethyl phosphate, acetone, and dioxane. The solvent serves to disperse the raw materials. Preferably, the total mass of the solvent in the present invention is equal to the total mass of the high molecular weight fluoropolymer, borate-containing branched polyether, and lithiated mesoporous molecular sieve.

[0018] The lithiated mesoporous molecular sieve is obtained by soaking SBA-15 molecular sieve in a 2 mol / L lithium-containing solution (lithium hydroxide solution), and then drying and washing with water.

[0019] Furthermore, the borate-containing branched polyether is prepared by the following steps:

[0020] Mixing hyperbranched polyglycidol, N,N-dimethylformamide, long-chain alkyl succinic anhydride and sulfuric acid, stirring and reacting at a temperature of 65-70°C for 3-4 hours, adding the reaction solution into glacial ether for sedimentation, and vacuum drying at 35-40°C to obtain a carboxyl-terminated branched polyether;

[0021] The ratio of hyperbranched polyglycidol, N,N-dimethylformamide, long-chain alkyl succinic anhydride and sulfuric acid is 12 g: 20 mL: 0.02-0.04 mol: 0.08 g;

[0022] Under an inert atmosphere, trimethyl borate and the carboxyl-terminated branched polyether were added to anhydrous acetonitrile, the temperature was set at 60-65°C, and the reaction was stirred for 4-5 hours. After the reaction was completed, the acetonitrile was removed by rotary evaporation to obtain the borate branched polyether;

[0023] The mass ratio of trimethyl borate to the carboxyl-terminated branched polyether is 0.02-0.04 mol:12 g.

[0024] Hyperbranched polyglycidol glycidol is prepared according to a conventional preparation method:

[0025] Trimethylolpropane and N-methylpyrrolidone are mixed, potassium tert-butoxide is added at 60-65°C, potassium tert-butoxide is dissolved in tetrahydrofuran, stirred for 50-60 minutes, then heated to 120°C, glycidol is added dropwise, and the mixture is reacted for 2-3 hours after the addition is complete. After the reaction is completed, anhydrous methanol is added for dissolution, the mixture is neutralized with a cationic resin, rotary evaporated at 50°C, and finally dried to a constant temperature at 60°C under vacuum conditions to obtain a hyperbranched polyglycidol; the mass ratio of glycidol, trimethylolpropane, N-methylpyrrolidone and potassium tert-butoxide is 46-50:1-1.5:1.7-2:0.2.

[0026] Furthermore, the long-chain alkyl succinic anhydride is one of dodecyl succinic anhydride, dodecenyl succinic anhydride and octenyl succinic anhydride.

[0027] In a second aspect, the present application provides a lithium battery polymer protective coating prepared by the above method.

[0028] A third aspect of the present application provides an application of a lithium battery polymer protective coating in a lithium battery.

[0029] Beneficial effects of the present invention:

[0030] A high-molecular-weight fluorinated polymer, a borate-containing branched polyether, and a lithiated mesoporous molecular sieve are added to a solvent and stirred and dispersed to obtain a coating. The coating is then applied to the surface of a metallic lithium anode and vacuum-dried to form a lithium battery polymer protective coating. By introducing functional groups such as long-chain alkyl, carbonyl, and borate groups into the structure of hyperbranched polyglycidol, and utilizing the branched structure and the properties of the lithiated mesoporous molecular sieve, the present invention constructs a highly efficient and stable lithium battery anode protection system. This system can effectively inhibit the growth of lithium dendrites, improving battery safety and cycle life. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] The following is a detailed description of a lithium battery polymer protective coating, its preparation method, and application in accordance with an embodiment of the present application.

[0033] The following is a detailed description with reference to the embodiments.

[0034] Example 1

[0035] The embodiment provides a preparation method of a lithium battery polymer protective coating, and comprises the following steps:

[0036] Polyvinylidene fluoride (PVDF, Mw=1500000), borate branched polyether and lithiated mesoporous molecular sieve are added into N,N dimethylformamide, and after stirring and dispersion, a coating is obtained; the coating is coated on the surface of a metal lithium negative electrode, vacuum drying is performed at 50 DEG C, and a lithium battery polymer protective coating is formed; the borate branched polyether is obtained by sequentially reacting hyperbranched polyglycidol with long-chain alkyl succinic anhydride and trimethyl borate. The mass ratio of polyvinylidene fluoride, borate branched polyether and lithiated mesoporous molecular sieve is 1:4:4; the thickness of the lithium battery polymer protective coating is 6 microns; wherein the lithiated mesoporous molecular sieve is obtained by immersing SBA-15 molecular sieve in a 2 mol / L lithium hydroxide solution, and then drying and washing with water.

[0037] The borate branched polyether is prepared by the following steps:

[0038] Trimethylolpropane and N-methylpyrrolidone are mixed, and then potassium tert-butoxide is added at 65 DEG C; the potassium tert-butoxide is dissolved in tetrahydrofuran; stirring is performed for 60 min; then the temperature is increased to 120 DEG C; epoxypropanol is added dropwise; after the addition is completed, reaction is performed for 3 h; after the reaction is completed, anhydrous methanol is added for dissolution; cationic resin is used for neutralization; rotary evaporation is performed at 50 DEG C; and finally, drying is performed under vacuum at 60 DEG C until the weight is balanced, so that the hyperbranched polyglycidol is obtained; the mass ratio of epoxypropanol, trimethylolpropane, N-methylpyrrolidone and potassium tert-butoxide is 46:1:1.7:0.2.

[0039] The hyperbranched polyglycidol, N,N-dimethylformamide, long-chain alkyl succinic anhydride and sulfuric acid are mixed, stirring is performed at 70 DEG C for 4 h, after the reaction is completed, the reaction solution is added into ice ethyl ether for sedimentation, and after vacuum drying at 40 DEG C, the carboxyl-terminated branched polyether is obtained; the dosage ratio of the hyperbranched polyglycidol, N,N-dimethylformamide, long-chain alkyl succinic anhydride and sulfuric acid is 12 g:20 mL:0.03 mol:0.08 g; the long-chain alkyl succinic anhydride is dodecyl succinic anhydride, dodecenyl succinic anhydride or octenyl succinic anhydride.

[0040] Under a nitrogen atmosphere, trimethyl borate and the carboxyl-terminated branched polyether are added into anhydrous acetonitrile, the temperature is set to 65 DEG C, stirring is performed for 4 h, after the reaction is completed, acetonitrile is removed by rotary evaporation, and the borate branched polyether is obtained; the mass ratio of trimethyl borate and the carboxyl-terminated branched polyether is 0.03 mol:12 g.

[0041] Example 2

[0042] The embodiment provides a preparation method of a lithium battery polymer protective coating, and comprises the following steps:

[0043] Polyvinylidene fluoride (PVDF, Mw = 1500000), a borate-containing branched polyether, and a lithiated mesoporous molecular sieve were added to N,N-dimethylformamide and stirred to disperse to obtain a coating. The coating was applied to the surface of a lithium metal negative electrode and vacuum-dried at 50°C to form a lithium battery polymer protective coating. The borate-containing branched polyether was obtained by sequentially reacting hyperbranched polyglycidol with long-chain alkyl succinic anhydride and trimethyl borate. The mass ratio of polyvinylidene fluoride, borate-containing branched polyether, and lithiated mesoporous molecular sieve was 1:5:4. The thickness of the lithium battery polymer protective coating was 6 μm. The lithiated mesoporous molecular sieve was the same as in Example 1. The borate-containing branched polyether was the same as in Example 1.

[0044] Example 3

[0045] This embodiment provides a method for preparing a lithium battery polymer protective coating, comprising the following steps:

[0046] Polyvinylidene fluoride (PVDF, Mw = 1500000), a borate-containing branched polyether, and a lithiated mesoporous molecular sieve were added to N,N-dimethylformamide and stirred to disperse to obtain a coating. The coating was applied to the surface of a lithium metal negative electrode and vacuum-dried at 50°C to form a lithium battery polymer protective coating. The borate-containing branched polyether was obtained by sequentially reacting hyperbranched polyglycidol with long-chain alkyl succinic anhydride and trimethyl borate. The mass ratio of the high molecular weight fluoropolymer, borate-containing branched polyether, and lithiated mesoporous molecular sieve was 1:6:4. The thickness of the lithium battery polymer protective coating was 6 μm. The lithiated mesoporous molecular sieve was the same as in Example 1. The borate-containing branched polyether was the same as in Example 1.

[0047] Example 4

[0048] This example provides a method for preparing a polymer protective coating for lithium batteries. This example differs from Example 1 in that the preparation process for the borate-containing branched polyether is different, and the long-chain alkyl succinic anhydride in this example is dodecyl succinic anhydride. The remaining raw materials and preparation process remain the same as in Example 1.

[0049] Example 5

[0050] This example provides a method for preparing a polymer protective coating for lithium batteries. This example differs from Example 1 in that the preparation process for the borate-containing branched polyether is different, and the long-chain alkyl succinic anhydride in this example is dodecenyl succinic anhydride. The remaining raw materials and preparation process remain the same as in Example 1.

[0051] Example 6

[0052] This example provides a method for preparing a polymer protective coating for lithium batteries. This example differs from Example 1 in that the preparation process for the borate-containing branched polyether is different. In this example, the mass ratio of trimethyl borate to carboxyl-terminated branched polyether is 0.04 mol:12 g. The remaining raw materials and preparation process remain the same as in Example 1.

[0053] Comparative Example 1

[0054] This comparative example differs from Example 1 in that the borate-containing branched polyether is different. Specifically, no long-chain alkyl succinic anhydride is added during the preparation of the borate-containing branched polyether. The remaining raw materials and preparation process remain the same as in Example 1.

[0055] Comparative Example 2

[0056] This comparative example differs from Example 1 in that the borate-containing branched polyether is different. Specifically, during the preparation of the borate-containing branched polyether, the long-chain alkyl succinic anhydride is replaced with an equal molar amount of succinic acid. The remaining raw materials and preparation process remain the same as in Example 1.

[0057] Comparative Example 3

[0058] This comparative example differs from Example 1 in that the borate-containing branched polyether is replaced with the carboxyl-terminated branched polyether in Example 1. The remaining raw materials and preparation process remain the same as in Example 1.

[0059] Comparative Example 4

[0060] This comparative example is different from Example 1 in that the borate-containing branched polyether is replaced with the hyperbranched polyglycidol in Example 1. The remaining raw materials and preparation process remain the same as in Example 1.

[0061] Performance tests were performed on Examples 1 to 6 and Comparative Examples 1 to 4:

[0062] Charge and discharge test: Using LiFePO4 as the positive electrode and 1M LiPF6, EC:DMC (1:1) as the electrolyte, the lithium metal containing the lithium battery polymer protective coating prepared in Examples 1 to 6 and Comparative Examples 1 to 4 was used as the negative electrode to be tested. The battery was assembled and stable cycles of more than 150 times were performed at a rate of 1C, and the capacity retention rate was recorded.

[0063] In the lithium ion migration number test: the polymer electrolyte was tested using CHI660E and CHI760E electrochemical workstations. Li||Li batteries were assembled with the polarization voltage set to 0.01V and the polarization time set to 14400s.

[0064] The results are shown in Table 1:

[0065] Table 1

[0066]

[0067]

[0068] As can be seen from Table 1, the lithium battery polymer protective coating prepared by the present invention has good stability in the lithium battery field. According to the test results of Examples 1 to 6, it can be seen that the capacity retention rate is still above 85% after 150 stable cycles. It also has a high lithium ion migration number. This solves the problem of poor negative electrode stability. Combining the test results of Example 1 and Comparative Examples 1 to 4, it can be seen that functional groups such as long-chain alkyl groups, carbonyl groups, and borate groups are all beneficial to improving the stability of lithium battery polymer protective coatings in the lithium battery field.

[0069] Combining the test results of Example 1 and Comparative Examples 1-2, it can be seen that the introduction of long-chain alkyl succinic anhydride improves the lithium ion transference number and cycle capacity retention rate. The reason is that the introduction of long-chain alkyl groups can improve the efficiency of lithium ion transmission by changing the interaction between polymer chains. The flexibility of long-chain alkyl groups can reduce the interaction between polymer chains, making the polymer chain segments more easily move and reorganize. This weakened interchain interaction can reduce obstacles in the lithium ion transmission process, improve cycle efficiency, and increase the lithium ion transference number.

[0070] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0071] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a lithium battery polymer protective coating, characterized in that: The steps include: A high molecular weight fluorine-containing polymer, a borate-containing branched polyether and a lithiated mesoporous molecular sieve are added to a solvent, stirred and dispersed to obtain a coating; the coating is applied to the surface of a metallic lithium negative electrode, and vacuum dried to form a lithium battery polymer protective coating; The mass ratio of the high molecular weight fluorine-containing polymer, the borate-containing branched polyether and the lithiated mesoporous molecular sieve is 1:4-5:4; the borate-containing branched polyether is obtained by sequentially reacting hyperbranched polyglycidol with long-chain alkyl succinic anhydride and trimethyl borate.

2. The method for preparing a lithium battery polymer protective coating according to claim 1, characterized in that: The usage ratio of the hyperbranched polyglycidol, the long-chain alkyl succinic anhydride and the trimethyl borate is 12g:0.02-0.04mol:0.02-0.04mol.

3. The method for preparing a lithium battery polymer protective coating according to claim 1, characterized in that: The thickness of the lithium battery polymer protective coating is 3-6 μm.

4. The method for preparing a lithium battery polymer protective coating according to claim 1, characterized in that: The high molecular weight fluorine-containing polymer is at least one of PVDF, PTFE, FEP and PFA.

5. The method for preparing a lithium battery polymer protective coating according to claim 1, characterized in that: The solvent is at least one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylacetamide, triethyl phosphate, acetone and dioxane.

6. The method for preparing a lithium battery polymer protective coating according to claim 1, characterized in that: The borate-containing branched polyether is prepared by the following steps: Mixing hyperbranched polyglycidol, N,N-dimethylformamide, long-chain alkyl succinic anhydride and sulfuric acid, stirring and reacting at a temperature of 65-70°C for 3-4 hours, adding the reaction solution into glacial ether for sedimentation, and vacuum drying at 35-40°C to obtain a carboxyl-terminated branched polyether; Under an inert atmosphere, trimethyl borate and the carboxyl-terminated branched polyether were added to anhydrous acetonitrile, the temperature was set at 60-65° C., and the reaction was stirred for 4-5 hours. After the reaction was completed, the acetonitrile was removed by rotary evaporation to obtain the borate branched polyether.

7. The method for preparing a lithium battery polymer protective coating according to claim 6, characterized in that: The mass ratio of glycidol, trimethylolpropane, N-methylpyrrolidone and potassium tert-butoxide is 46-50:1-1.5:1.7-2:0.

2.

8. The method for preparing a lithium battery polymer protective coating according to claim 6, characterized in that: The long-chain alkyl succinic anhydride is one of dodecyl succinic anhydride, dodecenyl succinic anhydride and octenyl succinic anhydride.

9. A lithium battery polymer protective coating, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the lithium battery polymer protective coating according to claim 9 in a lithium battery.

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