A polypyrrole modified separator, a preparation method and a metal lithium battery

Abstract

This invention discloses a polypyrrole-modified separator, its preparation method, and a lithium metal battery, relating to the field of lithium battery technology. The preparation method involves: dissolving a transition metal compound and PVDF in NMP, stirring until homogeneous to obtain a slurry; coating the slurry onto a clean PP separator, heat-treating to form a pre-coated layer, resulting in a pre-coated separator; immersing the pre-coated separator first in a pyrrole monomer solution for reaction, then immersing it in an initiator solution for further reaction, washing, and drying to obtain the polypyrrole-modified separator; the in-situ polymerization of pyrrole under the induction of the transition metal compound allows for the direct construction of a functional layer rich in nitrogen-polar functional groups on the separator, improving its surface wetting behavior and providing abundant transport channels for lithium ions; the coordination between the transition metal compound and the initiator enhances intermolecular forces, constructing a high-strength framework, which helps suppress lithium dendrite penetration and extend battery cycle life.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a polypyrrole modified separator, its preparation method, and a lithium metal battery. Background Technology

[0002] With a better understanding of the lithium dendrite growth mechanism, various new protection strategies have been developed to construct stable lithium metal anodes. These strategies mainly fall into two directions. The first direction is to optimize the electrolyte composition by adding additives, optimize the lithium salt concentration using different solvents, and use solid electrolytes; however, the solvents or additives used to modify the electrolyte properties are costly and involve complex manufacturing steps. The second direction is anode modification, which involves constructing an ideal artificial SEI with synergistic stabilizing effects through coatings on the anode surface, and creating various 3D porous frameworks to reduce local current density and increase lithium affinity sites; however, due to the high reactivity of lithium and the strict requirements of operating conditions, this is not suitable for large-scale implementation in actual production.

[0003] Therefore, a simpler strategy is needed to achieve the goal, and membrane modification is considered an effective method. Due to its inert nature, it is easier to modify; more importantly, as a barrier in contact with the positive and negative electrodes, the membrane can directly affect the diffusion of lithium ions, regulate the distribution of lithium ions, and thus prevent the irregular growth of lithium dendrites caused by uneven lithium ion distribution.

[0004] Current membrane modification technologies can be mainly summarized into two routes: surface functional coating and the development of novel composite membrane materials. Each route has its own advantages, disadvantages, and common problems.

[0005] For surface functionalization coating, this approach aims to improve the electrochemical performance and safety of commercial polyolefin-based films by adding functional coatings. It is a mainstream and relatively easy-to-implement modification strategy. For example, the core technology of patent document CN119674432A (glassy ZIF 62 hybrid coating) utilizes a grain boundary-free glassy metal-organic framework (MOF) material as a coating. Its continuous and uniform porous structure can efficiently guide the uniform transport of lithium ions, suppressing dendrite growth at its source. Its advantages include precise interface control; the unique grain boundary-free structure avoids the problem of uneven ion transport at grain boundaries in traditional crystalline materials, enabling more effective lithium ion homogenization. It also offers high stability; the structural stability of MOF materials helps maintain the stability of membrane performance during long-term cycling. However, there are still shortcomings and deficiencies, such as poor economic and environmental performance. The synthesis and vitrification of ZIF-62 involve high temperature and high pressure, high energy consumption, and may use toxic ligands and solvents, resulting in high cost and environmental pressure. The process controllability is challenging. Coating MOF materials into uniform and defect-free glassy films requires extremely high process precision, and it is difficult to ensure consistency in large-area preparation.

[0006] The core technology of the patent document with publication number CN119253196A (carboxylated precursor / carbon nanotube composite coating) is through the carboxylation of metal sulfides (GeS / SnS). x A composite coating is constructed using CNTs and silicon nanotubes (SiN), utilizing the former's slow-release function to stabilize interfacial kinetics and the latter to provide a conductive network. Its advantages include high functional integration, simultaneously addressing multiple issues such as ion transport regulation (slow release), electron conduction (CNTs), and mechanical strength (CNT network); furthermore, the kinetics are optimized, with the slow-release mechanism effectively smoothing current fluctuations during charging and discharging and reducing the driving force for dendrite formation. Its disadvantages include high material costs, especially when using germanium (Ge), which is extremely expensive; high-purity carbon nanotubes are also costly; the preparation process is complex, involving multiple steps such as carboxylation treatment, uniform composite with CNTs, and coating, resulting in a narrow process window and significant challenges for industrialization; and its environmental friendliness is poor, with some metal sulfides potentially exhibiting environmental toxicity.

[0007] The development of novel composite membrane materials abandons traditional polyolefin-based membranes and instead focuses on developing entirely new membrane matrix materials to pursue extreme performance breakthroughs. However, this approach is typically accompanied by higher costs and greater process complexity. For example, the core technology of patent document CN120432806A (PBI / PEI modified nanocellulose membrane) uses nanocellulose as a base and performs composite modification with polybenzimidazole (PBI) and polyethyleneimine (PEI) to prepare a novel biomass-based composite membrane. Its advantages include excellent intrinsic safety, with PBI imparting extreme thermal stability and mechanical strength to the membrane, fundamentally improving battery safety; and excellent electrochemical performance, with the composite material providing good ionic conductivity and interfacial compatibility. Its disadvantages and shortcomings are as follows: the raw material cost is extremely high, as PBI, as a special engineering plastic, is priced far higher than ordinary polyolefins; the process is complicated and not environmentally friendly, as the preparation process requires the use of toxic and highly polar solvents (such as NMP and DMAc), and involves multiple discontinuous steps such as solution preparation, ultrasonication, vacuum filtration, solvent exchange, and hot pressing, resulting in low production efficiency, high solvent recovery costs, and significant environmental pressure; and the industrialization is extremely difficult, as the complex multi-step process makes it difficult to improve production efficiency and product yield, and large-scale manufacturing faces enormous challenges. Summary of the Invention

[0008] The present invention aims to solve the problems of complex preparation process and high production cost of existing lithium battery separators when improving the electrochemical performance of lithium batteries.

[0009] To address the aforementioned problems, in a first aspect, the present invention provides a method for preparing a polypyrrole-modified separator, comprising the following steps: Step 1: Dissolve the transition metal compound and polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP), and stir until homogeneous to obtain a slurry; Step 2: Coat the slurry onto a clean polypropylene membrane (PP membrane), and after heat treatment, form a pre-coated membrane. Step 3: First, immerse the pre-coated membrane in a pyrrole monomer solution for reaction, then immerse it in an initiator solution to continue the reaction. After the reaction is complete, remove the membrane, wash and dry it to obtain a polypyrrole modified membrane.

[0010] The method for preparing polypyrrole-modified membranes provided by this invention has, but is not limited to, the following beneficial effects compared to existing technologies: The method for preparing the polypyrrole-modified separator provided by this invention is ingenious and simple. Through in-situ polymerization of pyrrole induced by transition metal compounds, this in-situ polymerization method can directly construct a functional layer on the separator, resulting in a strong and uniformly distributed layer. A functional layer rich in nitrogen-polar functional groups (such as NH) is constructed on the surface of the pre-coated separator. These functional groups significantly enhance the separator's affinity for organic electrolytes, improve its surface wetting behavior, and simultaneously provide abundant transport channels for lithium ions, effectively promoting Li-ion transport. + The migration kinetics enabled a uniform distribution of ion flux. Furthermore, the coordination between the transition metal compound and the initiator enhanced the intermolecular forces, thereby improving the macroscopic mechanical strength of the membrane, constructing a high-strength framework, which helps to suppress lithium dendrite puncture and extend the battery cycle life.

[0011] Moreover, the preparation method is simple and the raw materials are readily available. The raw materials (such as PVDF and PP separators) and solvents (NMP) used are all commonly used materials in the industry. It does not require complex equipment, has high compatibility with existing battery separator production processes, and has good repeatability and potential for large-scale implementation. It is suitable for the industrial production of high-performance lithium metal batteries.

[0012] Preferably, in step 1, the transition metal compound is any one of titanium chloride, vanadium chloride, chromium chloride, copper chloride, cobalt chloride, and ruthenium chloride.

[0013] Specifically, transition metal compounds such as titanium chloride, vanadium, chromium, copper, cobalt, and ruthenium have a highly efficient inducing effect on the in-situ polymerization of pyrrole and can form stable coordination with initiators, effectively enhancing the construction of functional layers and improving the mechanical strength of membranes. Moreover, the raw materials are readily available.

[0014] Preferably, in step 1, the mass ratio of the transition metal compound to polyvinylidene fluoride is (8-12):1.

[0015] Specifically, this mass ratio can achieve the optimal ratio of transition metal compounds to PVDF, ensuring both the induction and coordination effects of the transition metal compounds and enhancing the adhesion between the pre-coating and the PP membrane through PVDF, preventing coating peeling and ensuring the structural stability of the modified membrane.

[0016] Preferably, in step 1, the solid content of the slurry is 20wt% to 40wt%.

[0017] Specifically, the solid content of 20wt% to 40wt% gives the slurry both good fluidity and film-forming properties, making it easy to spread evenly on the PP membrane during coating. This avoids problems such as the coating being too thin and failing to function due to excessive thinness, or the coating being too thick and causing uneven coating and blockage of membrane pores due to excessive thickness, thus ensuring the quality of the pre-coated layer.

[0018] Preferably, in step 2, the coating thickness of the slurry applied to the clean polypropylene diaphragm is 15–30 μm.

[0019] Specifically, a coating thickness of 15–30 μm can form a sufficient functional layer to achieve ion transport optimization and dendrite suppression, without increasing lithium-ion transport resistance or reducing battery rate performance due to excessive coating thickness, thus balancing the modification effect and battery electrochemical performance.

[0020] Preferably, in step 2, the heat treatment temperature is 50℃~80℃ and the time is 2h~5h.

[0021] Specifically, heat treatment conditions of 50℃~80℃ for 2h~5h can efficiently remove NMP solvent from the slurry, allowing the pre-coating to adhere tightly to the PP diaphragm, while avoiding thermal shrinkage and structural damage to the diaphragm caused by long-term high-temperature treatment, thus ensuring the integrity and stability of the pre-coated diaphragm.

[0022] Preferably, in step 3, the concentration of the pyrrole monomer solution is 0.12–0.18 mol / L, and the concentration of the initiator solution is 0.12–0.18 mol / L.

[0023] Specifically, pyrrole monomer solutions and initiator solutions within this concentration range can achieve mild and controllable in-situ polymerization of pyrrole, allowing the polypyrrole coating to grow uniformly on the pre-coated surface. This ensures the complete construction of the functional layer while avoiding excessively high concentrations that lead to rapid polymerization and coating agglomeration, or excessively low concentrations that lead to insufficient polymerization and functional loss.

[0024] Preferably, in step 3, the initiator is either hydrogen peroxide or potassium iodate.

[0025] Specifically, hydrogen peroxide and potassium iodate, as initiators, can efficiently trigger pyrrole polymerization and form stable coordination with transition metal compounds, further enhancing the intermolecular forces of the membrane and improving its mechanical strength. At the same time, the reaction conditions of the two types of initiators are mild, easily adaptable to lithium battery production processes, and no harmful byproducts are generated.

[0026] Secondly, the present invention discloses a polypyrrole-modified membrane, which is prepared by the polypyrrole-modified membrane preparation method described above.

[0027] Specifically, the polypyrrole-modified separator prepared by the above method has excellent electrolyte wettability, high ion transport efficiency and strong mechanical strength. It can guide the uniform deposition of lithium ions, effectively suppress lithium dendrite puncture, and significantly improve the cycle stability and high rate performance of lithium metal batteries.

[0028] Thirdly, the present invention also discloses a lithium metal battery, comprising the polypyrrole-modified separator as described above.

[0029] Specifically, when the polypyrrole-modified separator prepared in this invention is applied to lithium metal batteries, it exhibits excellent cycle stability and high rate performance. This polypyrrole-modified separator can not only guide the uniform deposition of lithium ions and effectively suppress the formation of lithium dendrites, but also significantly reduce the diffusion barrier of lithium ions at the interface, providing a strong guarantee for rapid charging and discharging. Attached Figure Description

[0030] The invention will now be further described with reference to the accompanying drawings.

[0031] Figure 1 This is a flowchart illustrating the preparation process of the polypyrrole-modified separator in Example 1 of the present invention; Figure 2 This is a surface microstructure diagram of the polypyrrole-modified diaphragm of Example 1 of the present invention; Figure 3 This is a comparison chart of the cycle curves of the lithium metal batteries of Embodiment 6 and Comparative Example 1 at different rates. Figure 4 This is a graph showing the capacity retention rate of the lithium metal batteries of Embodiment 6 and Comparative Example 1 at different cycle numbers. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0033] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0034] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0035] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0036] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0037] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application can be purchased commercially or prepared using existing methods; for example, the sources and types of raw materials involved in the following examples and comparative examples are as follows: Copper chloride: Aladdin C433487-10g; Polyvinylidene fluoride: Aladdin P1492342-25g powder; Methylpyrrolidone: Aladdin M103246-100ml; Polypropylene diaphragm: Aladdin P434412 polypropylene (PP); Pyrrole monomer solution: Aladdin V106155-100ml; Potassium iodate solution: Aladdin P111554; Ethanol: Aladdin E1498352-500ml.

[0038] Example 1 This embodiment discloses a polypyrrole-modified separator; please refer to [link / reference]. Figure 1 The preparation is carried out in the following steps: Step 1: Dissolve 2.7g of copper chloride and 0.3g of polyvinylidene fluoride in 7g of N-methylpyrrolidone, and stir at 800rpm for 2h to obtain a uniform slurry. Step 2: Clean the polypropylene membrane with water and ethanol in sequence until it is clean to remove surface impurities; then coat the slurry evenly on the clean polypropylene membrane to a thickness of 20 μm, and then place it in an oven and heat it at 60°C for 4 hours to remove residual N-methylpyrrolidone and form a pre-coated membrane. Step 3: The pre-coated membrane is first immersed in a 0.12 mol / L pyrrole monomer solution for polymerization reaction for 2 hours, and then immersed in a 0.12 mol / L potassium iodate solution for coordination reaction for 2 hours. After the reaction is completed, it is taken out, washed with ethanol, and then placed in an oven to dry at 60℃ for 4 hours to obtain the polypyrrole modified membrane; its morphology characterization is shown in the figure below. Figure 2 As shown, from Figure 2 It can be observed that the surface of the polypyrrole modified diaphragm has a uniform polymer coating.

[0039] Example 2 Compared with Example 1, the only difference is that in step 3, the concentrations of both the pyrrole monomer solution and the potassium iodate solution are changed to 0.15 mol / L; the other steps and conditions remain exactly the same, and the polypyrrole modified membrane is finally obtained.

[0040] Example 3 Compared with Example 1, the only difference is that in step 3, the potassium iodate solution is replaced with a hydrogen peroxide solution of equal concentration; the other steps and conditions are kept exactly the same, and a polypyrrole modified membrane is finally obtained.

[0041] Example 4 Compared with Example 1, the only difference is that in step 3, the concentrations of both the pyrrole monomer solution and the potassium iodate solution are changed to 0.18 mol / L; the other steps and conditions remain exactly the same, and the polypyrrole modified membrane is finally obtained.

[0042] Example 5 Compared with Example 1, the only difference is that in step 2, the coating thickness is changed from 20 μm to 30 μm; the other steps and conditions are kept exactly the same, and a polypyrrole modified membrane is finally obtained.

[0043] Example 6 This embodiment discloses a lithium metal battery, including the polypyrrole-modified separator prepared in Example 1; specifically, the preparation process of the lithium metal battery is as follows: A 100µm thick lithium metal sheet from KELU was used as the negative electrode, and NCM811 (electrode preparation: ① slurry preparation, NCM811, conductive agent, and binder were mixed in a mass ratio of 8:1:1 and added to the solvent NMP, and stirred into a uniform slurry; ② coating, the slurry was coated onto the current collector; aluminum foil was used for the positive electrode, and copper foil for the negative electrode; ③ drying, first drying with forced air, then thoroughly removing water in a vacuum oven; ④ cutting, after rolling and compacting, punching into small round sheets with a diameter of 14mm, weighing and ready for use) was used as the positive electrode. The polypyrrole modified separator prepared in Example 1 was used as the separator, and the electrolyte was a commercial carbonate electrolyte 1M LiPF6 in EC / DEC (1:1) v / v); pouch battery assembly (battery assembly is carried out in the following order: negative electrode shell, spring, gasket, lithium sheet, electrolyte, separator, electrolyte, positive electrode sheet (coating side down), positive electrode shell stacked in sequence, and sealed under pressure with a sealing machine). It is carried out in a glove box under argon protection, where the oxygen and moisture content are both below 0.1 ppm; the final assembly yields a lithium metal battery.

[0044] Example 7 Compared with Example 6, the only difference is that the polypyrrole modified separator prepared in Example 1 is replaced with the polypyrrole modified separator prepared in Example 2; all other steps and conditions are kept exactly the same, and finally, a lithium metal battery is assembled.

[0045] Example 8 Compared with Example 6, the only difference is that the polypyrrole modified separator prepared in Example 1 is replaced with the polypyrrole modified separator prepared in Example 3; all other steps and conditions are kept exactly the same, and finally, a lithium metal battery is assembled.

[0046] Example 9 Compared with Example 6, the only difference is that the polypyrrole modified separator prepared in Example 1 is replaced with the polypyrrole modified separator prepared in Example 4; all other steps and conditions are kept exactly the same, and finally, a lithium metal battery is assembled.

[0047] Example 10 Compared with Example 6, the only difference is that the polypyrrole modified separator prepared in Example 1 is replaced with the polypyrrole modified separator prepared in Example 5; all other steps and conditions are kept exactly the same, and finally, a lithium metal battery is assembled.

[0048] Comparative Example 1 Compared with Example 6, the only difference is that the polypyrrole-modified membrane obtained in Example 1 is replaced with a clean polypropylene membrane; all other steps and conditions are kept exactly the same, and a polypyrrole-modified membrane is finally obtained.

[0049] The conductivity of the lithium metal batteries in Examples 6-10 and Comparative Example 1 was tested using the following method: the assembled batteries were connected to an electrochemical workstation for testing; a dedicated coin cell test fixture was used to ensure a stable and reliable connection. Parameter settings and frequency range were typically set to high frequency 10. -6 From Hz to a low frequency of 0.01 Hz; apply a small sinusoidal voltage of 5 mV to avoid excessive disturbance to the system; after the test, an impedance spectrum is obtained. In the high-frequency region of the impedance spectrum, the intersection of the curve and the real axis is the bulk resistance (R) of the electrolyte, in ohms (Ω). Accurately measure the thickness (L) of the electrolyte (in cm) and the effective contact area (A) with the stainless steel electrode. For liquid electrolytes, the thickness is generally the thickness of the diaphragm. Substitute these values ​​into the formula to calculate the ionic conductivity.

[0050] The test results are listed in Table 1, as follows: Table 1

[0051] Analysis of the data in Table 1 shows that, compared with Comparative Example 1, the lithium metal batteries of Examples 6-10 have significantly higher ionic conductivity. This indicates that the polypyrrole-modified separators of Examples 1-5 used in the lithium metal batteries of Examples 6-10 can improve the electrochemical performance of the lithium metal batteries.

[0052] Next, the cycle performance and capacity retention of the lithium metal batteries of Example 5 and Comparative Example 1 were tested using the following methods: Step 1: Let it sit; Before starting to charge and discharge, let the lithium metal battery sit for 10 minutes to allow the battery to stabilize. Step 2: Constant current and constant voltage charging; First, charge at a constant current of 0.33C until the voltage reaches the cutoff voltage of 4.3V. Then, switch to constant voltage charging at this voltage until the current drops to a minimum to ensure the battery is fully charged. Step 3: Let it sit; after charging is complete, let it sit for another 5 minutes. Step 4: Constant current discharge; Finally, discharge with a constant current of 1C until the voltage drops to the discharge cutoff voltage of 3V. Step 5: Repeat steps 1 to 4 until the set number of cycles of 500 is completed or the battery capacity decreases to 80% of its initial capacity.

[0053] After the above tests, the following results were obtained: Figure 3 The comparison chart of cycle curves at different magnifications and as shown in the figure Figure 4 The capacity retention curves shown are for different number of cycles, from Figure 3It can be observed that the lithium metal battery of Example 1 has superior cycle performance; from Figure 4 It can be observed that the lithium metal battery of Example 1 has a higher capacity retention rate.

[0054] In summary, the test results of the comparative examples and the comparative examples show that the polypyrrole-modified separator prepared by the present invention has the effect of improving the electrochemical performance of lithium metal batteries. This may be because: the coating formed by the slurry first synthesizes a nitrogen-rich separator that releases abundant ion transport channels in the organic electrolyte through in-situ polymerization of pyrrole, providing a pathway for the rapid transport of lithium ions, reducing the diffusion barrier of lithium ions, and promoting the rapid transport of lithium ions; then, through the polymerization of initiator and transition metal compound, the strength of the polymer molecular chain is enhanced, thereby improving the strength of the separator; finally, the polypyrrole-modified separator significantly improves the cycle performance and rate performance of lithium metal batteries.

[0055] The foregoing has described several embodiments of the present invention in detail, but these descriptions are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for producing a polyazole-modified separator, characterized by comprising: a step of applying a polyazole solution to a porous substrate; and a step of drying the porous substrate to which the polyazole solution has been applied. Includes the following steps: Step 1: Dissolve the transition metal compound and polyvinylidene fluoride in N-methylpyrrolidone, and stir until homogeneous to obtain a slurry; Step 2: Coat the slurry onto a clean polypropylene diaphragm, and after heat treatment, form a pre-coated diaphragm. Step 3: First, immerse the pre-coated membrane in a pyrrole monomer solution for reaction, then immerse it in an initiator solution to continue the reaction. After the reaction is complete, remove the membrane, wash and dry it to obtain a polypyrrole modified membrane.

2. The method for producing a polypyrole-modified separator according to claim 1, characterized by, In step 1, the transition metal compound is any one of titanium chloride, vanadium chloride, chromium chloride, copper chloride, cobalt chloride, and ruthenium chloride.

3. The method for preparing the polypyrrole-modified separator according to claim 1, characterized in that, In step 1, the mass ratio of the transition metal compound to polyvinylidene fluoride is (8-12):

1.

4. The method for preparing the polypyrrole-modified separator according to claim 1, characterized in that, In step 1, the solid content of the slurry is 20wt% to 40wt%.

5. The method for preparing the polypyrrole-modified separator according to claim 1, characterized in that, In step 2, the slurry is coated onto a clean polypropylene diaphragm to a thickness of 15–30 μm.

6. The method for preparing the polypyrrole-modified separator according to claim 1, characterized in that, In step 2, the heat treatment temperature is 50℃~80℃ and the time is 2h~5h.

7. The method for preparing the polypyrrole-modified separator according to claim 1, characterized in that, In step 3, the concentration of the pyrrole monomer solution is 0.12–0.18 mol / L, and the concentration of the initiator solution is 0.12–0.18 mol / L.

8. The method for preparing the polypyrrole-modified separator according to claim 1, characterized in that, In step 3, the initiator is either hydrogen peroxide or potassium iodate.

9. A polypyrrole-modified separator, characterized in that, It is prepared by the method for preparing polypyrrole modified membrane according to any one of claims 1-8.

10. A lithium metal battery, characterized in that, Including the polypyrrole-modified diaphragm as described in claim 9.

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