Composite nanofiber membrane current collector, method of making and use thereof

Abstract

This invention relates to the field of battery materials technology, specifically to a composite nanofiber membrane current collector, its preparation method, and its application. The current collector comprises a composite nanofiber membrane consisting of a polymer matrix and a conductive agent dispersed therein. This membrane has a three-dimensional porous structure, with in-situ generated nanoscale LiF particles distributed on its surface and within its internal pores. The preparation method involves first preparing the composite nanofiber membrane via electrospinning, and then using a dual-source synchronous spraying combined with a low-temperature heat treatment process to generate LiF particles in situ on the membrane surface and within its pores. This invention reduces local current density through the three-dimensional porous structure to suppress lithium dendrite growth, constructs a stable artificial SEI layer through in-situ generated LiF to enhance interface stability, and utilizes the porous structure to provide buffer space for lithium deposition to alleviate volume expansion. This significantly improves the initial coulombic efficiency, cycle stability, and safety performance of lithium metal batteries, and the preparation process is mild and controllable, suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a composite nanofiber membrane current collector, its preparation method, and its application. Background Technology

[0002] With the development of technology, people's requirements for battery energy density are constantly increasing. Lithium-ion batteries, currently the mainstream power storage system for electric vehicles and smart grids, can no longer meet the development needs of emerging technologies. Lithium metal, due to its high theoretical specific capacity (3860 mAh / g) and low redox potential (-3.04 V vs standard hydrogen electrode), has become one of the key materials for improving battery energy density. However, lithium metal anodes have many problems, mainly including dendrite growth, unstable interfacial reactions, and infinite volume changes. These problems lead to low coulombic efficiency, short cycle life, and even serious safety hazards.

[0003] Traditional metal current collectors suffer from high density and poor flexibility, making them unsuitable for emerging applications. Existing lithium metal anodes generate numerous lithium dendrites during charge and discharge. With increasing operating time, these dendrites grow and penetrate the separator, posing safety risks. Furthermore, repeated lithium insertion / extraction processes create a large number of "dead lithium" cells, causing unlimited electrode volume expansion, resulting in low battery coulombic efficiency and reduced cycle life.

[0004] To address these issues, researchers have explored various methods, such as optimizing electrolytes, designing artificial solid electrolyte interphase (SEI) films, using solid electrolytes, and introducing three-dimensional current collectors. Among these, three-dimensional current collectors, due to their high specific surface area, can effectively reduce local current density, thus helping to improve lithium dendrite growth. However, these methods still have some drawbacks, such as complex processes, high costs, and susceptibility to delamination. Therefore, developing a novel lithium metal anode material that can improve battery energy density while effectively addressing issues such as dendrite growth, volume expansion, and cycle life has become a key focus and challenge in current research. Summary of the Invention

[0005] To address the problems of high density, poor flexibility, and the tendency to generate large amounts of lithium dendrites and "dead lithium" leading to volume expansion and short cycle life in existing lithium metal anode materials, this invention aims to provide a conductive agent / PAN composite nanofiber membrane current collector for lithium metal battery anodes, its preparation method, and its applications.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a composite nanofiber membrane current collector, comprising a composite nanofiber membrane composed of a polymer matrix and a conductive agent dispersed in the polymer matrix; the composite nanofiber membrane has a three-dimensional porous structure; and lithium compound particles are distributed on the surface and in the internal pores of the composite nanofiber membrane.

[0007] In a preferred embodiment of the present invention, the polymer matrix comprises polyacrylonitrile (PAN). PAN possesses ion-selective permeability or ion enrichment capability, which can regulate the lithium-ion transport rate, avoid lithium-ion enrichment and depletion regions, and prevent localized excessive deposition. PAN can guide lithium ions to deposit in a layered, dense manner, rather than in a dendritic pattern.

[0008] As a preferred embodiment of the present invention, the conductive agent includes one or more of carbon nanotubes, graphene, and carbon black.

[0009] As a preferred embodiment of the present invention, the lithium compound particles are LiF particles with a size of 10-100 nm.

[0010] As a preferred embodiment of the present invention, the composite nanofiber membrane has a thickness of 5-50 μm and a porosity of 30-80%.

[0011] Secondly, the present invention provides a method for preparing the composite nanofiber membrane current collector, comprising the following steps: Preparation of a mixed spinning solution containing polymer and conductive agent; The mixed spinning solution is electrospun to obtain a composite nanofiber membrane; The composite nanofiber membrane is subjected to in-situ lithium compound generation treatment, which generates lithium compound particles on the surface and in the internal pores of the composite nanofiber membrane.

[0012] As a preferred embodiment of the present invention, the step of preparing the mixed spinning solution includes: Polyacrylonitrile is dissolved in a solvent to form a polyacrylonitrile solution; The conductive agent is dispersed in a solvent to form a conductive agent dispersion. The conductive agent dispersion is mixed with the polyacrylonitrile solution and stirred until homogeneous to obtain the mixed spinning solution; The mass ratio of the conductive agent to polyacrylonitrile is 3-15%.

[0013] As a preferred embodiment of the present invention, the in-situ generation process of the lithium compound includes: The lithium source precursor solution and the fluorine source precursor solution are simultaneously sprayed onto both sides of the composite nanofiber membrane using a spraying device. The sprayed composite nanofiber membrane was heat-treated to generate LiF particles through in-situ reaction.

[0014] As a preferred embodiment of the present invention, the in-situ generation treatment of lithium compounds has at least one of the following features a1) to a5): a1) The molar ratio of the lithium source precursor to the fluorine source precursor is 1:1; a2) The lithium source is one or more of LiNO3, LiCl, and LiOH; a3) The fluorine source is one or more of NH4F, HF, and NaF; a4) The spraying time is 1 to 10 seconds, the spraying angle is 30 to 60 degrees, and the spraying pressure is 0.1 to 0.5 MPa; a5) The heat treatment is to heat to 150-250°C at a heating rate of 2-5°C / min under an inert atmosphere and hold at that temperature for 0.1-2 hours.

[0015] Thirdly, the present invention provides a lithium metal battery, including a negative electrode, wherein the negative electrode comprises the composite nanofiber membrane current collector described above, or comprises the composite nanofiber membrane current collector prepared by the preparation method described above.

[0016] Compared with the prior art, the beneficial effects of the present invention include: Summary of the beneficial effects of the composite nanofiber membrane current collector of the present invention 1. This invention achieves precise control of lithium dendrite growth through a dual-technology approach, fundamentally suppressing lithium dendrite growth and significantly improving battery safety. Firstly, a three-dimensional porous composite nanofiber membrane prepared by electrospinning serves as the core structure. Its controllable porosity and high specific surface area effectively reduce the local current density of the electrode, thermodynamically guiding the uniform nucleation of lithium ions and preventing localized enrichment and uneven growth of lithium. This fundamentally suppresses lithium dendrite formation, eliminating safety hazards such as battery short circuits and thermal runaway caused by dendrites penetrating the separator. Secondly, through a dual-source synchronous spraying + low-temperature heat treatment process, nanoscale LiF particles are generated in situ on the surface and internal pores of the fiber membrane. These particles, along with the PAN matrix and conductive agent, form a synergistic effect, precisely controlling the lithium ion flux and further guiding the uniform deposition of lithium metal within the membrane. This prevents disordered lithium growth on the electrode surface, achieving full-cycle suppression of lithium dendrite growth.

[0017] 2. The three-dimensional porous structure of this invention provides dedicated space and buffer margin for lithium metal deposition, completely alleviating the volume expansion during charging and discharging, and solving the industry pain point of "dead lithium" accumulation. The controllable thickness and internal pores of the composite nanofiber membrane provide ample intercalation space for the lithium metal insertion / extraction process, enabling controllable lithium deposition in the membrane's internal pores. This avoids concentrated lithium accumulation and drastic volume expansion on the electrode surface, ensuring the volume stability of the electrode structure during charging and discharging. The stable deposition environment and reversible insertion / extraction pathway significantly reduce the generation and accumulation of "dead lithium" during charging and discharging, solving the core problems of electrode structure damage, continuous decay of coulombic efficiency, and sharp drop in cycle life caused by volume expansion in traditional lithium metal anodes, and significantly improving the utilization rate of lithium metal and the cycle stability of the electrode.

[0018] 3. This invention overcomes the shortcomings of externally added artificial SEI layers, such as easy detachment and poor interfacial adhesion. By constructing a stable artificial SEI layer in situ, it significantly optimizes the stability of the electrode interface. The in-situ generated LiF itself possesses high lithium-ion conductivity, excellent chemical stability, and low electronic conductivity, making it an ideal artificial solid-state electrolyte interface (SEI) material. It can form a uniform and continuous interfacial protective layer on the fiber surface and within the pores, significantly suppressing side reactions between the electrolyte and the lithium metal anode, and reducing irreversible consumption of active lithium. The in-situ generation process enables strong adhesion between LiF particles and the fiber matrix, avoiding the layer detachment and uneven distribution problems caused by traditional coating and encapsulation processes. It can maintain the integrity of the interfacial layer during long-term cycling, greatly improving the long-term stability of the electrode interface and effectively increasing the initial coulombic efficiency and cycle life of the battery.

[0019] 4. This invention establishes a ternary synergistic mechanism of PAN polymer matrix + conductive agent + in-situ LiF, achieving efficient ion / electron dual-channel transport: the PAN polymer matrix provides stable structural support and excellent film-forming ability for the fiber membrane, ensuring the structural integrity of the electrode during long cycles and bending; conductive agents such as carbon nanotubes, graphene, and carbon black form a continuous electron transport network in the matrix, endowing the fiber membrane with excellent conductivity, suitable for high-rate charge and discharge scenarios. The synergy of these three elements achieves an integrated design of structural support, electron transport, and ion regulation, ensuring high-speed electron conduction and achieving uniform diffusion and nucleation of lithium ions, promoting uniform deposition and reversible extraction of lithium metal anodes, ultimately achieving a comprehensive improvement in battery initial efficiency, rate performance, cycle stability, and safety, solving the core pain points of traditional lithium metal batteries such as short cycle life, low coulombic efficiency, and easy short circuit.

[0020] 5. The preparation process of this invention balances performance and industrial feasibility, possessing significant process advantages: It employs a composite process of electrospinning to prepare the fiber matrix + dual-source synchronous spraying + low-temperature heat treatment to generate LiF in situ. The entire process operates under mild reaction conditions, with heat treatment temperatures ranging from 150 to 250°C, eliminating the need for harsh environments such as high temperature and high pressure, ensuring a safe and controllable production process. Process parameters (spraying time, angle, pressure, heat treatment heating rate, holding time, fiber membrane thickness, and porosity, etc.) can be precisely controlled, facilitating the continuous preparation of large-area, highly uniform films and solving the problems of complex, low-yield, and difficult-to-scale existing modification processes. The raw materials used (PAN, carbon nanotubes, lithium salts, fluoride salts, etc.) are all conventional commercial reagents, with wide availability and controllable costs, requiring no special customized materials, thus providing a solid foundation for industrialization. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, these should not be construed as limiting the present invention and are merely examples.

[0022] Unless otherwise specified, the test methods or experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are obtained from conventional commercial sources or prepared by conventional methods.

[0023] This invention provides a method for preparing a conductive agent / PAN composite nanofiber membrane current collector for lithium metal battery anodes, comprising: Step 1: Prepare the PAN matrix solution; Step 2: Prepare the conductive agent dispersion; Step 3: Slowly add the dispersion to the PAN solution and stir to mix; Step 4: Electrospinning to obtain a fiber membrane with a thickness of 50–300 μm; Step 5: Dry at 60–100℃ for 2–24 hours; Step 6: Prepare Li separately + and F - The precursor solution is sprayed onto both sides of the composite nanofiber membrane simultaneously through a spraying device, with a spraying time of 1–10 seconds. Step 7: Perform heat treatment, remove the membrane, rinse repeatedly with deionized water and ethanol to remove unreacted raw materials, and dry to obtain a conductive agent / PAN composite nanofiber membrane with uniformly distributed nanoscale LiF on the surface and in the pores.

[0024] Step 1 includes: Step 101: Add PAN to DMF solvent at a ratio of 15wt% and stir at 60-80℃ for 1-5 hours to ensure complete dissolution; Step 102: Cool the mixed solution to room temperature and set aside.

[0025] Step 2 includes: Step 201: Select a conductive agent, including one or more of carbon nanotubes, graphene, and carbon black (SP); Step 202: Add the conductive agent to a small amount of DMF; Step 203: Disperse ultrasonically for 2-4 hours to form a uniform dispersion.

[0026] Step 3 includes: Step 301: Slowly add the dispersion to the PAN solution; the ratio of conductive agent to PAN is 3-15%. Step 302: Stir at room temperature for 1-2 hours to ensure uniform mixing; Step 4 includes: Step 401: Spin the mixed solution using an electrospinning process; Step 402: Control the spinning parameters to obtain a fiber membrane with a thickness of 50–300 μm and a porosity of 30–80%; Step 403: Place the fiber membrane in a vacuum drying oven.

[0027] The spinning parameters are controlled as follows: The spinning voltage ranges from 15 to 30 kV, the distance between the nozzle and the receiving roller ranges from 15 to 25 cm, the receiving roller speed ranges from 50 to 200 rpm, the solution flow rate ranges from 0.5 to 2.0 mL / h, the ambient temperature ranges from 20 to 30 ℃, the relative humidity ranges from 30 to 60%, the nozzle inner diameter ranges from 0.5 to 1.0 mm, and the receiving method can use a metal roller (stainless steel) or aluminum foil as the receiving body. The spinning time ranges from 1 to 4 hours.

[0028] In step 5, during the drying process, the vacuum level is controlled at 10. -3 Pa to 10 -2 Pa, to ensure the uniformity and stability of the fiber membrane.

[0029] Step 6 includes: Step 601: The lithium source is one or more of LiNO3, LiCl, and LiOH, and the fluorine source is one or more of NH4F, HF, and NaF; Step 602: Spray the precursor solution onto both sides of the composite nanofiber membrane using a spraying device for 1 to 10 seconds to ensure uniform distribution. Step 603: During the spraying process, the spray angle is 30-60° and the spray pressure is 0.1-0.5 MPa to ensure the uniform distribution of the precursor solution.

[0030] Step 7 includes: Step 701: Place the sprayed composite nanofiber membrane in a tube furnace; Step 702: In an inert atmosphere, heat the gas to 150-250°C at a heating rate of 2-5°C / min to avoid oxidation. Step 703: Keep warm for 0.1–2 hours; Step 704: After naturally cooling to room temperature, wash with deionized water and anhydrous ethanol 3 to 5 times in sequence; Step 705: Place the cleaned composite nanofiber membrane in a vacuum drying oven and dry it at 60-80°C for 4-8 hours to obtain the final product.

[0031] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0032] Example 1: Optimal Performance Example This embodiment provides a composite nanofiber membrane current collector, the preparation method of which is as follows: (1) Preparation of a mixed spinning solution containing polymer and conductive agent: Dissolve PAN in DMF to form a PAN solution with a concentration of 15 wt%. Disperse the conductive agent in DMF to form a conductive agent dispersion, wherein the conductive agent is: carbon black (SP) + carbon nanotubes (CNT) + graphene, and the mass ratio of the three is 1:1:1. Mix the conductive agent dispersion with the PAN solution and stir evenly to obtain a mixed spinning solution; wherein the total proportion of conductive agent is 10% (relative to PAN).

[0033] (2) Electrospinning was performed on the mixed spinning solution to obtain a composite nanofiber membrane with a thickness of 20 μm and a porosity of 50%.

[0034] (3) The lithium precursor solution LiNO3 (0.1M) and the fluorine precursor solution NH4F (0.1M) were simultaneously sprayed onto both sides of the composite nanofiber membrane using a spraying device. The spraying time was 5 s, the spraying angle was 45°, and the spraying pressure was 0.3 MPa. The sprayed composite nanofiber membrane was placed in a tube furnace and heated to 200°C at a heating rate of 3°C / min under a nitrogen atmosphere. The temperature was maintained for 1 hour, and after natural cooling to room temperature, it was washed 3 to 5 times with deionized water and anhydrous ethanol. The washed composite nanofiber membrane was then placed in a vacuum drying oven and dried at 70°C for 5 hours to obtain the final product. According to the test analysis, the generated LiF particles had a size of 50 nm and were uniformly distributed on the membrane surface and in the pores.

[0035] Example 2: Different types of conductive agents (carbon black only) The difference between this embodiment and Embodiment 1 is that the conductive agent is only carbon black (SP), the lithium source precursor solution is LiCl solution, and the fluorine source precursor solution is NaF solution; the other conditions are the same as in Embodiment 1.

[0036] Example 3: Low proportion of conductive agent (3%) The difference between this embodiment and Example 1 is that: carbon nanotubes (CNTs) and graphene are used in a mass ratio of 1:1; the lithium source precursor solution is LiOH solution; and the fluorine source precursor solution is HF solution; the other conditions are the same as in Example 1.

[0037] Example 4: Low porosity (30%) The difference between this embodiment and Embodiment 1 is that the porosity of the composite nanofiber membrane is 30%; the other conditions are the same as in Embodiment 1.

[0038] Example 5: Thicker (50μm) The difference between this embodiment and Embodiment 1 is that the thickness of the composite nanofiber membrane is 40 μm; the other conditions are the same as in Embodiment 1.

[0039] Example 6: Thinner thickness (5μm) The difference between this embodiment and Embodiment 1 is that the thickness of the composite nanofiber membrane is 5 μm; the other conditions are the same as in Embodiment 1.

[0040] Example 7: High heat treatment temperature (250℃) The difference between this embodiment and Embodiment 1 is that the heat treatment temperature is raised to 250°C; the other conditions are the same as in Embodiment 1.

[0041] Example 8: Lower heat treatment temperature (150°C) The difference between this embodiment and Embodiment 1 is that the heat treatment temperature is raised to 150°C; the other conditions are the same as in Embodiment 1.

[0042] Comparative Example 1: No conductive agent added The difference between this comparative example and Example 1 is that no conductive agent is added, while other conditions are the same as in Example 1.

[0043] Comparative Example 2: No lithium or fluorine source added (no in-situ LiF generation) The difference between this comparative example and Example 1 is that no lithium source precursor solution and fluorine source precursor solution are added, while other conditions are the same as in Example 1.

[0044] Comparative Example 3: Porosity too low (15%) The difference between this comparative example and Example 1 is that the porosity of the composite nanofiber membrane is only 15%, while the other conditions are the same as in Example 1.

[0045] Experimental Example The materials obtained in the examples and comparative examples were cut and used as negative electrodes, and then combined with commercial lithium iron phosphate positive electrodes, separators, and electrolytes to form batteries.

[0046] The assembled battery was charged at a constant current and constant voltage of 0.1C to 3.65V, and then charged at a constant voltage of 3.65V until the current dropped to 0.01C. The initial charge capacity was recorded. After resting for 30 minutes, the battery was discharged at a constant current of 0.1C to a voltage of 2.5V, and the initial discharge capacity was recorded. The initial coulombic efficiency was calculated. After two cycles of activation at a 0.1C rate, the battery underwent a long-cycle constant current charge-discharge test at a 1C rate, with a voltage range of 2.5–3.65V. The discharge capacity was recorded, and the capacity retention rate after 500 cycles was calculated based on the discharge capacity of the second cycle. The test results are shown in Table 1 below.

[0047] Table 1 Based on the performance test data from Examples 1-8, Comparative Examples 1-3, and Table 1, the following conclusions can be drawn: 1. Example 1 is the optimal implementation scheme, with an initial coulombic efficiency of 92.5% and a capacity retention of 88.2% after 500 cycles, significantly better than other examples and comparative examples. This indicates that, under the combined effect of an appropriate amount of composite conductive agent (carbon black + carbon nanotubes + graphene), moderate porosity (50%), reasonable film thickness (20 μm), and optimized heat treatment conditions (200℃), a current collector with stable structure, excellent conductivity, and strong interfacial compatibility can be constructed, effectively suppressing lithium dendrite growth and "dead lithium" accumulation.

[0048] 2. The type and content of the conductive agent have a significant impact on performance. In Example 2, only carbon black was used, resulting in a discontinuous conductive network, which led to a decrease in electron transport capability, uneven local current density, and slightly lower initial coulombic efficiency and cycle stability than in Example 1. In Example 3, the conductive agent content was only 3%, and the conductive network was incomplete, further aggravating the polarization phenomenon and causing a significant decrease in performance.

[0049] 3. Porosity is one of the key factors affecting lithium deposition behavior. In Example 4, the porosity was only 30%, which limited the lithium deposition space. During charging and discharging, the volume expansion led to high structural stress, which easily formed "dead lithium" and reduced cycle stability. In Comparative Example 3, the porosity was only 15%, and the structure could hardly accommodate lithium deposition, resulting in severe electrode damage and the worst performance.

[0050] 4. Film thickness has a dual impact on lithium-ion diffusion and structural stability. Neither Example 5 (40 μm) nor Example 6 (5 μm) achieved the optimal thickness (20 μm). The former had a longer diffusion path, increased polarization, decreased rate performance, and a more significant impact from volume expansion during cycling, resulting in a slight decrease in capacity retention. The latter, although thin, lacked structural strength, was prone to cracking, and had limited lithium deposition space, making it susceptible to localized over-lithiation during long-term cycling, leading to slightly faster capacity decay. Both examples performed slightly worse than Example 1.

[0051] 5. Heat treatment temperature plays a crucial role in the quality of LiF formation and interfacial stability. Examples 7 (250℃) and 8 (150℃) did not achieve optimal conditions. The former may have led to partial degradation of PAN, decreased mechanical strength of the fiber membrane, slightly coarser LiF particles, and slightly affected interfacial stability; the latter resulted in incomplete LiF formation, small but unevenly distributed particles, and the absence of an effective protective layer in some areas, with numerous side reactions.

[0052] 6. Comparative examples verified the necessity of the structure of each component: Comparative Example 1 (without conductive agent) had an initial coulombic efficiency of only 82% and a cycle retention rate of 65.3%, indicating poor electron transport, uneven lithium deposition, severe electrode polarization, rapid capacity decay, low initial coulombic efficiency, and significantly reduced cycle performance; Comparative Example 2 (without LiF generation) lacked an in-situ LiF layer, making it impossible to form a stable SEI, resulting in continuous side reactions in the electrolyte, severe loss of active lithium, and a significant decrease in cycle life; Comparative Example 3 (too low porosity) had insufficient lithium deposition space, and volume expansion led to film cracking, easy penetration of lithium dendrites, and poor cycle stability.

[0053] In summary, the composite nanofiber membrane current collector proposed in this invention, through multiple means of structural design, material synergy, and interface regulation, successfully suppresses lithium dendrite growth and volume expansion, significantly improving the cycle stability and first-cycle coulombic efficiency of lithium metal batteries. Its preparation process is mild and controllable, and the raw materials are widely available, demonstrating promising industrialization prospects.

[0054] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite nanofiber membrane current collector, characterized by, The composite nanofiber membrane comprises a polymer matrix and a conductive agent dispersed in the polymer matrix; the composite nanofiber membrane has a three-dimensional porous structure; lithium compound particles are distributed on the surface and in the internal pores of the composite nanofiber membrane.

2. The composite nanofiber film current collector of claim 1, wherein, The polymer matrix includes polyacrylonitrile.

3. The composite nanofiber film current collector of claim 1, wherein, The conductive agent includes one or more of carbon nanotubes, graphene, and carbon black.

4. The composite nanofiber film current collector of claim 1, wherein, The lithium compound particles are LiF particles with a diameter of 10–100 nm.

5. The composite nanofiber film current collector of claim 1, wherein, The composite nanofiber membrane has a thickness of 5–50 μm and a porosity of 30–80%.

6. A method for preparing the composite nanofiber film current collector according to any one of claims 1 to 5, characterized by, Includes the following steps: Preparation of a mixed spinning solution containing polymer and conductive agent; The mixed spinning solution is electrospun to obtain a composite nanofiber membrane; The composite nanofiber membrane is subjected to in-situ lithium compound generation treatment, which generates lithium compound particles on the surface and in the internal pores of the composite nanofiber membrane.

7. The preparation method according to claim 6, characterized in that, The steps for preparing the mixed spinning solution include: Polyacrylonitrile is dissolved in a solvent to form a polyacrylonitrile solution; The conductive agent is dispersed in a solvent to form a conductive agent dispersion. The conductive agent dispersion is mixed with the polyacrylonitrile solution and stirred until homogeneous to obtain the mixed spinning solution; The mass ratio of the conductive agent to polyacrylonitrile is 3-15%.

8. The preparation method according to claim 6, characterized in that, The in-situ generation process of the lithium compound includes: The lithium source precursor solution and the fluorine source precursor solution are simultaneously sprayed onto both sides of the composite nanofiber membrane using a spraying device. The sprayed composite nanofiber membrane was heat-treated to generate LiF particles through in-situ reaction.

9. The preparation method according to claim 8, characterized in that, The in-situ lithium compound generation process has at least one of the following characteristics a1) to a5): a1) The molar ratio of the lithium source precursor to the fluorine source precursor is 1:1; a2) The lithium source is one or more of LiNO3, LiCl, and LiOH; a3) The fluorine source is one or more of NH4F, HF, and NaF; a4) The spraying time is 1 to 10 seconds, the spraying angle is 30 to 60 degrees, and the spraying pressure is 0.1 to 0.5 MPa; a5) The heat treatment is to heat to 150-250°C at a heating rate of 2-5°C / min under an inert atmosphere and hold at that temperature for 0.1-2 hours.

10. A lithium metal battery, characterized in that, The negative electrode includes a composite nanofiber membrane current collector as described in any one of claims 1 to 5, or a composite nanofiber membrane current collector prepared by the preparation method according to any one of claims 6 to 9.

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