A composite negative electrode and its preparation method and application in metal secondary battery

Abstract

The present invention discloses a composite negative electrode, a preparation method thereof, and its application in a metal secondary battery, relating to the technical field of electrode materials. The present invention uses a polymer solution with a high carbonization rate as a shell solution and a polymer solution with a low carbonization rate as a core solution. A bimetallic salt is dissolved and dispersed in the shell solution. Through coaxial electrospinning and halogenation, a self-supporting carbon fiber membrane loaded with bimetallic halides and having an endoexilated hollow carbon fiber structure of carbon nanotubes is prepared. This material is then combined with an active metal to prepare a composite negative electrode for a metal secondary battery. The bimetallic halide can guide the active metal to uniformly deposit within the hollow fiber, inhibit dendrite growth, alleviate volume expansion, and simultaneously prevent side reactions between the active metal and the electrolyte. Application of this composite negative electrode in a metal secondary battery can reduce the nucleation overpotential of the active metal and the polarization voltage of the battery cycle, thereby improving the capacity retention rate and cycle life of the metal secondary battery.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and more particularly to a composite negative electrode, a preparation method thereof, and application thereof in a metal secondary battery. Background Art

[0002] With the advancement of science and technology and the rapid development of society, traditional lithium-ion batteries with graphite anodes have reached their theoretical specific capacity limits, making it difficult to meet the demands of high-power facilities and equipment such as long-distance electric vehicles, aerospace equipment, and energy storage grids. Therefore, the development of new high-energy-density chemical energy storage systems is urgent. In recent years, metal secondary batteries, which directly use active metals such as lithium, sodium, potassium, and zinc as anodes, have become a research hotspot in the energy field due to their extremely high specific capacities.

[0003] Although metal secondary batteries have the advantage of high energy density, there are some common problems that need to be solved, especially on the negative electrode side, including the following: (1) Due to uneven current distribution, active metals tend to deposit in the form of dendrites. On the one hand, dendrite breakage will lose electrical contact, thereby losing active materials. On the other hand, dendrites will pierce the diaphragm and directly contact the positive electrode, causing battery short circuit, thermal runaway and even safety hazards; (2) Highly reactive active metals can undergo complex side reactions with the electrolyte, excessively consuming electrolyte and active materials, causing battery capacity decay and reduced cycle life; (3) Active metals will face huge volume expansion during repeated charging and discharging, which will cause repeated rupture and formation of SEI film on the surface of active metals, further consuming electrolyte and reducing coulombic efficiency, while causing electrode pulverization and ultimately battery failure.

[0004] At present, self-supporting carbon fiber skeleton materials are one of the effective means to solve the defects of metal secondary batteries. However, the existing self-supporting carbon fiber skeleton materials mainly solve the volume expansion problem caused by the active metal during repeated charging and discharging, while the problems of capacity attenuation caused by the side reactions between the active metal and the electrolyte, and the growth of metal dendrites have not been comprehensively improved.

[0005] The prior art discloses a self-supporting iron-nickel alloy-decorated nitrogen-doped porous carbon nanofiber lithium metal negative electrode skeleton material. The porous body of the material provides a rich conductive network and open pores to adapt to volume expansion changes and lithium ion transmission during the cycle, thereby improving the rate performance of the lithium battery. However, the active metal in the negative electrode obtained by this material only exists on the outer surface of the carbon fiber or in the gaps between the carbon fibers, and the active metal is not protected. The porous structure of the material increases the specific surface area and increases the contact opportunity between the active metal and the electrolyte. It cannot solve the problem of side reactions between the active metal and the electrolyte, and the dendrite deposition problem also needs further improvement. Summary of the Invention

[0006] In order to overcome the defects and shortcomings of existing metal secondary battery negative electrode materials, that is, active metals tend to deposit in the form of dendrites and are prone to side reactions with the electrolyte, the present invention provides a composite negative electrode. By controlling the content of bimetallic halide in the self-supporting carbon fiber membrane, the active metal is guided to deposit uniformly, the overpotential of active metal deposition nucleation is reduced, the growth of dendrites is inhibited, the inactivation of active substances is prevented, and a thin layer of halide is formed on the surface of the active metal to strengthen the SEI film, avoid side reactions between the active metal and the electrolyte, and improve the capacity retention rate and cycle life.

[0007] Another object of the present invention is to provide a method for preparing the self-supporting carbon fiber membrane in the above-mentioned composite negative electrode.

[0008] Another object of the present invention is to provide a method for preparing the composite negative electrode.

[0009] Another object of the present invention is to provide application of the composite negative electrode in a metal secondary battery.

[0010] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0011] A composite negative electrode comprising a self-supporting carbon fiber membrane and an active metal supported on the self-supporting carbon fiber membrane;

[0012] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains a bimetallic halide; the content of the bimetallic halide is 10 to 50%;

[0013] The active metal is at least one of lithium, sodium, potassium and zinc.

[0014] It should be noted that:

[0015] The self-supporting carbon fiber membrane described in the present invention is a composite material of hollow carbon fiber membrane with epitaxially grown carbon nanotubes, and has a multi-level "core-shell" structure of M1M2X-CNTs@HCF (wherein M1M2X is a double metal halide, CNTs is a carbon nanotube, and HCF is a carbon fiber membrane formed by hollow carbon fibers with a tubular structure). The tubular structure of the hollow carbon fibers can provide a larger space for the deposition of active metals at the negative electrode, thereby alleviating the volume expansion during repeated charging and discharging.

[0016] Compared to bimetallic alloys, bimetallic halides have a stronger affinity for active metals and a lower nucleation barrier. During the preparation of the anode, bimetallic halides act as active sites for the active metal, guiding it into the carbon fiber cavities. The lower the bimetallic halide content, the weaker the guiding ability, preventing the active metal from being injected into the self-supporting carbon fiber membrane. This reduces the active metal content, impairs the electrochemical performance of the anode, and reduces the utilization of the skeleton space. Higher bimetallic halide content leads to the bimetallic occupying the active metal space, reducing the active metal content. Simultaneously, some bimetallic halides convert into elemental bimetallics and form a thin layer of active metal halide on the surface of the active metal, participating in the formation of the solid electrolyte interface (SEI) at the anode. This reinforces the SEI, prevents side reactions between the active metal and the electrolyte that lead to capacity decay, and improves the battery's capacity retention. Therefore, the bimetallic halide content is positively correlated with the SEI film thickness. A too thin SEI film is uneven and prone to rupture, while a too thick SEI film hinders the transport of active metal ions, resulting in sluggish kinetics. This can induce active metal dendrite growth, reduce battery life, and ultimately lead to battery failure.

[0017] In situ epitaxially grown CNTs can regulate the flux of active metal ions, achieve uniform deposition, inhibit the growth of metal dendrites, and at the same time strengthen electrical contact, prevent the inactivation of active materials, and improve battery life; the hollow carbon fiber structure can well encapsulate the active metal inside the hollow carbon fiber, improve space utilization, and provide a buffer space to alleviate the volume expansion of the active metal during repeated deposition / stripping, thereby improving the rate performance of the battery; and the M1M2X-CNTs@HCF multi-level "core-shell" structure carbon fiber membrane is composited with the active metal, and the cross-linked conductive carbon fiber network and CNTs disperse the local current density, which is conducive to the rapid transfer of electrons, reduces the polarization voltage, and is also conducive to the uniform deposition and stripping of active metals.

[0018] The metal secondary battery composite negative electrode prepared by using the self-supporting carbon fiber film of the present invention has the characteristics of high performance, long life, and no dendrites, and the composite negative electrode does not require a binder or a current collector and can achieve self-support.

[0019] Preferably, the content of the double metal halide in the core layer of the self-supporting carbon fiber membrane is 10-50%, more preferably 20-30%, and even more preferably 20%.

[0020] The present invention specifically protects a method for preparing a self-supporting carbon fiber membrane in the above-mentioned composite negative electrode, comprising the following steps:

[0021] S1. dissolving polymer A in an organic solvent to obtain a core solution;

[0022] S2. dissolving two transition metal salt solutions in an organic solvent, and then adding polymer B to dissolve uniformly to obtain a shell solution; wherein the two transition metal salts carry different metals and the molar ratio of the two transition metal salts is (1-4):1; and the number average molecular weight of polymer B is greater than the number average molecular weight of polymer A in S1;

[0023] S3. The core solution in S1 and the shell solution in S2 were coaxially electrospun to obtain core-shell nanofibers, and the core-shell nanofibers were pre-oxidized and carbonized to obtain a material having an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer;

[0024] S4. Annealing the material obtained in S3, and then transferring it to an ammonium halide solution for heat treatment to obtain a self-supporting carbon fiber membrane; wherein the annealing temperature is 150-500°C, and the heat treatment temperature is 80-200°C.

[0025] It should be noted that:

[0026] Controlling the molar ratio of the two transition metal salts in S2 can control the formation of the bimetallic alloy in S3, regulating the catalytic effect on carbon nanotube growth, and successfully obtaining the structure of the self-supporting carbon fiber membrane. In addition, the number average molecular weight of polymer B needs to be greater than the number average molecular weight of polymer A to successfully obtain the self-supporting carbon fiber membrane of the present invention, which includes an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, and has an M1M2X-CNTs@HCF multi-level "core-shell" structure (where M1M2X is a bimetallic halide, CNTs is a carbon nanotube, and HCF is a carbon fiber membrane).

[0027] Specifically, the mass percentage of polymer A in the organic solvent is 45 to 80%; the mass percentage of polymer B in the organic solvent is 30 to 80%.

[0028] Preferably, the mass percentage of the polymer A in the organic solvent is 45-55%, more preferably 55%.

[0029] Preferably, the mass percentage of the polymer B in the organic solvent is 30-40%, more preferably 30%.

[0030] Polymers A and B are the carbon sources of the core layer and the shell layer respectively. Their mass percentage in the organic solvent will affect the coaxial electrospinning in S3. When the mass percentage of the polymer is low, the viscosity of the solution is insufficient and cannot form filaments. When the mass percentage is high, the viscosity of the solution is large, which is not conducive to extrusion into filaments and is easy to clog the needle used for electrospinning. That is, the amount of polymer content will affect the formation of the structure of the self-supporting carbon fiber membrane described in the present invention, and ultimately affect the performance of the supported carbon fiber membrane.

[0031] Specifically, the polymer A is at least one of polystyrene, polyvinyl pyrrolidone, and polymethyl methacrylate.

[0032] Specifically, the polymer B is at least one of polyacrylonitrile, polypyrrole, polyamide, urea, melamine, and asphalt.

[0033] Specifically, the mass percentage of the two transition metal salts in the solvent in S2 is 2 to 45%.

[0034] Preferably, the mass percentage of the two transition metal salts in S2 in the solvent is 2-30%, more preferably 2-10%, and even more preferably 5%.

[0035] The transition metal salt content in S2 also affects the structure and properties of the self-supporting carbon fiber membrane. Too little transition metal salt makes it difficult to catalyze the growth of carbon nanotubes, while too much leads to agglomeration and poor dispersion. Furthermore, the transition metal salt content can affect the viscosity of the shell solution, leading to damage to the final material structure and, in turn, the performance of the self-supporting carbon fiber membrane.

[0036] Specifically, the transition metal salt is at least two of nickel nitrate, cobalt nitrate, iron nitrate, manganese nitrate, nickel acetylacetonate, cobalt acetylacetonate, iron acetylacetonate, manganese acetylacetonate, and complexes formed by the above metal salts.

[0037] Specifically, the organic solvent in S1 and S2 is one of N,N-dimethylformamide, petroleum ether or tetrahydrofuran.

[0038] Specifically, the coaxial electrospinning voltage in S3 is 8 to 30 kV, the spinning speed of the core solution is 0.15 to 8 mL / h, and the spinning speed of the shell solution is 0.2 to 6 mL / h.

[0039] The pre-oxidation and carbonization in S3 are mainly for obtaining the epitaxially grown carbon nanotube core layer and the tubular hollow carbon fiber shell layer. If the temperature is too high and the pre-oxidation degree is too high, the carbon will be oxidized into CO2, and after carbonization, the epitaxially grown carbon nanotube core layer and the tubular hollow carbon fiber shell layer material of the present invention cannot be obtained; and if the temperature is too low, the pre-oxidation and carbonization are insufficient, and the corresponding material cannot be successfully prepared.

[0040] Among them, under the high temperature of carbonization, the high carbonization rate polymer decomposes to produce a carbon-containing atmosphere, and the transition metal salt forms a bimetallic alloy, which can thermally catalyze the inward growth of carbon nanotubes in one step.

[0041] Specifically, the thermo-catalytic bimetallic alloy is at least one of nickel-cobalt, nickel-iron, nickel-manganese, iron-cobalt, iron-manganese, and manganese-cobalt.

[0042] Specifically, the pre-oxidation temperature in S3 is 120-350°C, and the carbonization temperature is 750-1300°C.

[0043] Preferably, the pre-oxidation temperature in S3 is 120°C to 150°C, and the carbonization temperature is 850°C to 1050°C.

[0044] More preferably, the carbonization temperature in S3 is 850-950°C.

[0045] Specifically, the pre-oxidation time is 0.5 to 4 hours, preferably 1 to 2 hours.

[0046] Specifically, the carbonization time is 1 to 6 hours, preferably 4 to 6 hours.

[0047] In S4, annealing treatment is first performed and then transferred to ammonium halide solution for heat treatment. Since the bimetallic alloy is relatively stable and halogenation is difficult, annealing treatment is performed first to oxidize the bimetallic and reduce the difficulty of subsequent halogenation. Among them, if the annealing temperature is too high, carbon materials such as carbon fibers and carbon nanotubes will be oxidized into carbon dioxide and volatilized, and self-supporting carbon fiber membrane materials cannot be successfully obtained. If the temperature is too low, the effect of oxidizing the bimetallic and reducing halogenation cannot be achieved. If the heat treatment temperature is too high, there is a risk of explosion. If the temperature is too low, the halogenation purpose cannot be achieved to obtain bimetallic halides.

[0048] Specifically, the annealing time is 1 to 5 hours; the heat treatment time is 1 to 5 hours.

[0049] Preferably, the annealing temperature in S4 is 250-350°C, more preferably 300°C.

[0050] Preferably, the heat treatment temperature in S4 is 100-200°C, more preferably 150°C.

[0051] Specifically, the solvent of the ammonium halide solution in S4 is water and / or methanol.

[0052] In methanol or water, ammonium halide has good solubility, which can ensure the success of halogenation, and the solubility of bimetallic halide is poor, which ensures that the product is not dissolved and is easy to separate.

[0053] Specifically, the mass percentage of the ammonium halide to the solvent is 20-60%, preferably 30-50%, and more preferably 30-40%.

[0054] Specifically, the ammonium halide solution is at least one of ammonium fluoride, ammonium chloride, ammonium bromide, and ammonium iodide.

[0055] The self-supporting carbon fiber membrane prepared by the present invention is an epitaxially grown carbon nanotube hollow carbon fiber membrane. Compared with traditional electrospinning materials, it has a denser conductive network, can transmit electrons faster and more efficiently, and promote reaction kinetics.

[0056] In addition, the tubular hollow carbon fiber shell obtained by the preparation method of the present invention is loaded with two or more transition metal salts. After the metal salts are decomposed by heat, they will form corresponding metal alloys and catalyze the production of a carbon nanotube core layer that grows inwardly toward the middle of the hollow carbon fiber. This structure can anchor the active metal layer in the negative electrode and prevent the active metal from losing active substances due to loss of electrical contact. After heat treatment, the ammonium halide solution forms a bimetallic halide corresponding to the active metal with the bimetallic, which has a strong affinity for the active metal in the negative electrode and provides a large number of active sites for the nucleation of the active metal, thereby reducing the nucleation barrier of the active metal, helping to inhibit the growth of metal dendrites, and promoting the uniform deposition of active metals. After infiltration of the molten active metal, the bimetallic halide is converted into an active metal halide with high ionic conductivity (SEI film component), which helps to promote the conduction of active metal ions and strengthen the SEI film, prevent the occurrence of side reactions between the active metal and the electrolyte, and effectively alleviate the key problems faced by the negative electrode side of the metal secondary battery, such as dendrites, side reactions, volume expansion, active substance loss and low coulombic efficiency.

[0057] The above preparation method can be industrialized, the preparation method is simple and environmentally friendly, and the obtained self-supporting carbon fiber film can be used as a self-supporting negative electrode for lithium, sodium, potassium, and zinc metal secondary batteries. Compared with traditional metal secondary batteries, the prepared metal secondary batteries show long cycle stability and long cycle life.

[0058] Parts not particularly described in the present invention can be selected within the scope of conventional technology.

[0059] The present invention also provides a method for preparing the composite negative electrode, comprising the following steps:

[0060] The active metal is heated to a molten state in a glove box (oxygen content <0.01 ppm), then fully contacted with and wetted by a self-supporting carbon fiber membrane, and after cooling, a composite negative electrode for a metal secondary battery is obtained.

[0061] The present invention particularly protects the use of the composite negative electrode in a metal secondary battery.

[0062] The self-supporting carbon fiber membrane of the present invention is used in the negative electrode of a metal secondary battery, which can reduce the nucleation overvoltage and polarization voltage of the active metal, inhibit dendrite growth, and prevent the inactivation of the active material; and form a thin layer of halide on the surface of the active metal to strengthen the SEI film, thereby improving the battery's discharge capacity and capacity retention rate, and ultimately improving the battery's long-cycle stability and cycle life.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] The present invention uses a polymer solution with a high carbonization rate as a shell solution and a polymer solution with a low carbonization rate as a core solution, and dissolves and disperses a bimetallic salt in the shell solution. After coaxial electrostatic spinning and halogenation treatment, a self-supporting carbon fiber membrane loaded with bimetallic halides and having an epitaxially grown carbon nanotube hollow carbon fiber structure is prepared. The material is then used to prepare a composite negative electrode. By controlling the content of bimetallic halides in the material, the uniform deposition of active metals can be guided, dendrite growth can be inhibited, and volume expansion can be alleviated. At the same time, side reactions between the active metals and the electrolyte can be avoided. The composite negative electrode is applied to a metal secondary battery, which can reduce the nucleation overvoltage and polarization voltage of the active metal deposition, thereby improving the capacity retention rate and cycle life of the metal secondary battery.

[0065] The self-supporting carbon fiber membrane described in the present invention is applied to the composite negative electrode of a metal secondary battery. The nucleation overvoltage of the first deposition of active metal is below 50 mV, the cycle time of the symmetrical battery is above 830 h, and the polarization voltage is below 36 mV. In the obtained metal secondary battery, the capacity retention rate is above 82% after 500 cycles at a current density of 1 C. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 Schematic diagram and TEM image of the structure of the self-supporting carbon fiber membrane of the present invention.

[0067] Figure 2 This is a performance comparison chart of the composite negative electrode Li||Li symmetric battery of Example 1 and Comparative Examples 1 to 3.

[0068] Figure 3 This is an SEM image of the self-supporting carbon fiber membrane in the composite negative electrode of Example 1. DETAILED DESCRIPTION

[0069] The polymers prepared in the preparation methods S1 and S2 of the present invention were purchased from Aladdin, wherein the number average molecular weight of polymer A was 120,000, and the number average molecular weight of polymer B was 150,000.

[0070] The present invention will be further described below in conjunction with specific embodiments, but the examples do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the examples of the present invention are conventionally purchased raw materials and reagents.

[0071] Example 1

[0072] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0073] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains nickel-iron bimetallic fluoride; the content of the nickel-iron bimetallic fluoride is 20%;

[0074] The active metal is metallic lithium.

[0075] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0076] S1. Dissolving polystyrene in N,N-dimethylformamide to obtain a core solution; the mass percentage of polystyrene in the organic solvent is 55%;

[0077] S2. Nickel nitrate and ferric nitrate in a molar ratio of 1:1 are dissolved in N,N-dimethylformamide, and polyacrylonitrile is added and dissolved with stirring to obtain a shell solution; the mass percentage of the nickel nitrate and ferric nitrate in the organic solvent is 5% in total, and the mass percentage of the polyacrylonitrile in the organic solvent is 30%;

[0078] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 10 kV, a spinning rate of 0.5 mL / h for the core solution, and a spinning rate of 0.8 mL / h for the shell solution; core-shell nanofibers were obtained; the core-shell nanofibers were then pre-oxidized at 120 ° C in air for 1 h and carbonized at 850 ° C in an argon atmosphere for 6 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a nickel-iron alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0079] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 300°C for 3 hours, and then heat-treated in an ammonium fluoride solution at 150°C for 3 hours to obtain a self-supporting carbon fiber membrane with a NiFeFx-CNTs@HCF multi-level "core-shell" structure (the nickel-iron bimetallic fluoride content is 20%); wherein the solvent of the ammonium fluoride solution is methanol, and the mass percentage of ammonium fluoride in the solvent is 30%.

[0080] The self-supporting carbon fiber film is prepared into a composite negative electrode for a metal secondary battery. The specific steps are as follows:

[0081] The metallic lithium is placed on a heating platform with an oxygen value of <0.01ppm and heated to 300℃ to a molten state, fully contacted with and wetted by the self-supporting carbon fiber membrane. After cooling to room temperature, a self-supporting carbon fiber membrane loaded with metallic lithium is obtained, i.e., a self-supporting composite metal lithium battery negative electrode.

[0082] The above composite negative electrode is prepared into a Li||Li symmetric battery:

[0083] The prepared composite negative electrode sheet was cut and used as the counter electrode and the working electrode to assemble a Li||Li symmetrical cell. The button cell model was CR2032, the separator was a polypropylene microporous membrane Celgard 2400, and the electrolyte was 1 mol / L LiTFSI / DOL+DME (V / V=1:1). The electrochemical performance of the assembled symmetrical cell was tested on a Xinwei test system under the test conditions of 1 mA cm -2 1mAh cm -2 .

[0084] The above composite negative electrode is used to prepare a lithium iron phosphate metal secondary battery. The specific steps are as follows:

[0085] Cut the composite negative electrode sheet prepared above as the negative electrode of the lithium metal battery; weigh and mix a certain amount of lithium iron phosphate, superconducting carbon black (Super P) conductive agent and polyvinylidene fluoride (PVDF) binder according to a mass ratio of 8:1:1, and then add an appropriate amount of N-methylpyrrolidone (NMP), stir thoroughly into a paste, apply it on the current collector aluminum foil with a spatula, and then place it in a vacuum drying oven at 60°C for 8 hours, and cut and prepare the electrode sheet as the positive electrode of the lithium metal battery; then transfer them to an argon-filled glove box for assembly of button cells, the button cell model is CR2032, the diaphragm is a polypropylene microporous membrane Celgard 2400, and the electrolyte is 1 mol / L LiPF6 / EC+DMC+EMC (V / V=1:1:1); the assembled lithium metal battery is electrochemically tested on the Xinwei test system, and the voltage range is 2.4~4.2V.

[0086] Example 2

[0087] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0088] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains nickel-cobalt bimetallic fluoride; the content of the nickel-cobalt bimetallic fluoride is 25%;

[0089] The active metal is metallic lithium.

[0090] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0091] S1. Dissolving polyvinyl pyrrolidone in N,N-dimethylformamide to obtain a core solution; the mass percentage of polyvinyl pyrrolidone in the organic solvent is 45%;

[0092] S2. Nickel nitrate and cobalt nitrate are dissolved in N,N-dimethylformamide in a molar ratio of 2:1, and polypyrrole is added and dissolved with stirring to obtain a shell solution; the mass percentage of the nickel nitrate and cobalt nitrate in the organic solvent is 10% in total, and the mass percentage of the polypyrrole in the organic solvent is 40%;

[0093] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 20 kV, a spinning rate of 2 mL / h for the core solution, and a spinning rate of 4 mL / h for the shell solution to obtain core-shell nanofibers; the core-shell nanofibers were then pre-oxidized at 130°C in air for 2 h and carbonized at 950°C in an argon atmosphere for 4 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a nickel-cobalt alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0094] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 250°C for 4 hours, and then heat-treated in an ammonium fluoride solution at 120°C for 4 hours to obtain a self-supporting carbon fiber membrane with a NiCoFx-CNTs@HCF multi-level "core-shell" structure (the nickel-cobalt bimetallic fluoride content is 25%); wherein the solvent of the ammonium fluoride solution is methanol, and the mass percentage of ammonium fluoride in the solvent is 40%.

[0095] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0096] Example 3

[0097] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0098] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains nickel-manganese bimetallic fluoride; the content of the nickel-manganese bimetallic fluoride is 30%;

[0099] The active metal is metallic lithium.

[0100] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0101] S1. Dissolving polymethyl methacrylate in petroleum ether to obtain a core solution; the mass percentage of polymethyl methacrylate in the organic solvent is 55%;

[0102] S2. Nickel nitrate and manganese nitrate in a molar ratio of 3:1 are dissolved in N,N-dimethylformamide, and then polyamide is added and dissolved with stirring to obtain a shell solution; the mass percentage of the nickel nitrate and manganese nitrate in the organic solvent is 15% in total, and the mass percentage of the polyamide in the organic solvent is 50%;

[0103] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 18 kV, a spinning rate of 4 mL / h for the core solution, and a spinning rate of 6 mL / h for the shell solution to obtain core-shell nanofibers; the core-shell nanofibers were then pre-oxidized at 150°C in air for 3 h and carbonized at 1050°C in an argon atmosphere for 4 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a nickel-manganese alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0104] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 500°C for 5 hours, and then heat-treated in an ammonium fluoride solution at 100°C for 5 hours to obtain a self-supporting carbon fiber membrane with a NiMnFx-CNTs@NHCF multi-level "core-shell" structure (the nickel-manganese bimetallic fluoride content is 30%); wherein the solvent of the ammonium fluoride solution is methanol, and the mass percentage of ammonium fluoride in the solvent is 50%.

[0105] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0106] Example 4

[0107] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0108] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains iron-cobalt bimetallic chloride; the content of the iron-cobalt bimetallic chloride is 40%;

[0109] The active metal is metallic lithium.

[0110] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0111] S1. Dissolving polymethyl methacrylate in N,N-dimethylformamide to obtain a core solution; the mass percentage of the polymethyl methacrylate in the organic solvent is 65%;

[0112] S2. A molar ratio of 4:1 of iron acetylacetonate and cobalt acetylacetonate was dissolved in N,N-dimethylformamide, and then a mass ratio of 6:1 of polyacrylonitrile and melamine was added and stirred to dissolve to obtain a shell solution; the mass percentage of the nickel nitrate and cobalt nitrate in the organic solvent was 25% in total, and the mass percentage of the polyacrylonitrile and melamine in the organic solvent was 70%;

[0113] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 25 kV, a spinning rate of 3 mL / h for the core solution, and a spinning rate of 4.5 mL / h for the shell solution to obtain core-shell nanofibers; the core-shell nanofibers were then pre-oxidized at 200°C in air for 2 h and carbonized at 950°C in an argon atmosphere for 3 h to obtain an epitaxially grown carbon nanotube with a core layer catalyzed by an iron-cobalt alloy and a tubular hollow carbon nanofiber shell;

[0114] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 350°C for 2 hours, and then heat-treated in an ammonium chloride solution at 160°C for 2 hours to obtain a self-supporting carbon fiber membrane with a FeCoClx-CNTs@HCF multi-level "core-shell" structure (with an iron-cobalt bimetallic chloride content of 40%); wherein the solvent of the ammonium chloride solution is methanol, and the mass percentage of ammonium chloride in the solvent is 60%.

[0115] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0116] Example 5

[0117] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0118] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains iron-manganese bimetallic bromide; the content of the iron-manganese bimetallic bromide is 30%;

[0119] The active metal is metallic lithium.

[0120] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0121] S1. Dissolving polystyrene in tetrahydrofuran to obtain a core solution; the mass percentage of polystyrene in the organic solvent is 70%;

[0122] S2. A molar ratio of 1:2 of iron acetylacetonate and manganese acetylacetonate was dissolved in tetrahydrofuran, and then a mass ratio of 8:1 of polyacrylonitrile and urea was added and stirred to dissolve to obtain a shell solution; the mass percentage of the iron acetylacetonate and manganese acetylacetonate in the organic solvent was 15% in total, and the mass percentage of the polyacrylonitrile and urea in the organic solvent was 60%;

[0123] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 20 kV, a spinning rate of 2.5 mL / h for the core solution, and a spinning rate of 3.5 mL / h for the shell solution to obtain core-shell nanofibers; the core-shell nanofibers were then pre-oxidized at 260 ° C in air for 2.5 h and carbonized at 850 ° C in an argon atmosphere for 4 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by an iron-manganese alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0124] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 380°C for 1.5 hours, and then heat-treated in an ammonium bromide solution at 180°C for 1.5 hours to obtain a self-supporting carbon fiber membrane with a FeMnBrx-CNTs@HCF multi-level "core-shell" structure (the iron-manganese bimetallic bromide content is 30%); wherein the solvent of the ammonium bromide solution is methanol, and the mass percentage of ammonium bromide in the solvent is 50%.

[0125] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0126] Example 6

[0127] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0128] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains cobalt-manganese bimetallic iodide; the content of the cobalt-manganese bimetallic iodide is 27%;

[0129] The active metal is metallic lithium.

[0130] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0131] S1. Dissolving polyvinyl pyrrolidone in petroleum ether to obtain a core solution; the mass percentage of polyvinyl pyrrolidone in the organic solvent is 70%;

[0132] S2. Cobalt acetylacetonate and manganese acetylacetonate were dissolved in petroleum ether in a molar ratio of 1:3, and polypyrrole and asphalt were added in a mass ratio of 1:6 and dissolved with stirring to obtain a shell solution; the mass percentage of the cobalt acetylacetonate and manganese acetylacetonate in the organic solvent was 13%, and the mass percentage of the polypyrrole and asphalt in the organic solvent was 85%;

[0133] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 25 kV, a spinning rate of 3.5 mL / h for the core solution, and a spinning rate of 5.5 mL / h for the shell solution to obtain core-shell nanofibers; the core-shell nanofibers were then pre-oxidized at 280°C in air for 3.5 h and carbonized at 950°C in an argon atmosphere for 6 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a cobalt-manganese alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0134] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 400°C for 1 hour, and then heat-treated in an ammonium iodide solution at 200°C for 1 hour to obtain a self-supporting carbon fiber membrane with a CoMnIx-CNTs@HCF multi-level "core-shell" structure (the cobalt-manganese bimetallic iodide content is 27%); wherein the solvent of the ammonium iodide solution is water, and the mass percentage of ammonium iodide in the solvent is 40%.

[0135] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0136] Example 7

[0137] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0138] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains nickel-cobalt bimetallic fluoride; the content of the nickel-cobalt bimetallic fluoride is 50%;

[0139] The active metal is metallic lithium.

[0140] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0141] S1. Dissolving polymethyl methacrylate in petroleum ether to obtain a core solution; the mass percentage of polymethyl methacrylate in the organic solvent is 70%;

[0142] S2. Nickel acetylacetonate and cobalt acetamide acetonate were dissolved in petroleum ether in a molar ratio of 1:4, and the polyamide was added and dissolved with stirring to obtain a shell solution; the mass percentage of the nickel acetylacetonate and cobalt acetylacetonate in the organic solvent was 30% in total, and the mass percentage of the polyamide in the organic solvent was 70%;

[0143] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 30 kV, a spinning rate of 2.5 mL / h for the core solution, and a spinning rate of 3.5 mL / h for the shell solution to obtain core-shell nanofibers; the core-shell nanofibers were then pre-oxidized in air at 240°C for 2.5 h and carbonized in an argon atmosphere at 1050°C for 5 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a nickel-cobalt alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0144] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 300°C for 1 hour, and then heat-treated in an ammonium fluoride solution at 100°C for 1 hour to obtain a self-supporting carbon fiber membrane with a NiCoFx-CNTs@HCF multi-level "core-shell" structure (the nickel-cobalt bimetallic fluoride content is 50%); wherein the solvent of the ammonium fluoride solution is water, and the mass percentage of ammonium fluoride in the solvent is 20%.

[0145] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0146] Example 8

[0147] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0148] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains nickel-cobalt bimetallic chloride; the content of the nickel-cobalt bimetallic chloride is 10%;

[0149] The active metal is metallic lithium.

[0150] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0151] S1. Dissolving polymethyl methacrylate in N,N-dimethylformamide to obtain a core solution; the mass percentage of polymethyl methacrylate in the organic solvent is 55%;

[0152] S2. Nickel nitrate and cobalt nitrate were dissolved in petroleum ether in a molar ratio of 1:1, and polyamide was added and dissolved with stirring to obtain a shell solution; the mass percentage of the nickel nitrate and cobalt nitrate in the organic solvent was 2% in total, and the mass percentage of the polyamide in the organic solvent was 40%;

[0153] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 30 kV, a spinning rate of 2.5 mL / h for the core solution, and a spinning rate of 3.5 mL / h for the shell solution to obtain core-shell nanofibers; the core-shell nanofibers were then pre-oxidized at 300 ° C in air for 2.5 h and carbonized at 1000 ° C in an argon atmosphere for 5.5 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a nickel-cobalt alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0154] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 300°C for 1 hour, and then heat-treated in ammonium chloride at 100°C for 2 hours to obtain a self-supporting carbon fiber membrane with a NiCoClx-CNTs@HCF multi-level "core-shell" structure (the nickel-cobalt bimetallic chloride content is 10%); wherein the solvent of the ammonium chloride solution is water, and the mass percentage of ammonium chloride in the solvent is 20%.

[0155] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0156] Comparative Example 1

[0157] A metal secondary battery negative electrode, which is different from the embodiment 1 in that a metal lithium sheet is directly used as the negative electrode sheet.

[0158] The above negative electrode sheet was prepared into a Li||Li symmetrical battery and a lithium iron phosphate metal secondary battery, and the steps were the same as those in Example 1.

[0159] Comparative Example 2

[0160] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a hollow carbon fiber membrane and an active metal supported on the hollow carbon fiber membrane;

[0161] The active metal is metallic lithium.

[0162] The preparation method of the hollow carbon fiber membrane in the negative electrode of the metal secondary battery can refer to the following steps:

[0163] S1. Dissolving polystyrene in N,N-dimethylformamide to obtain a core solution; the mass percentage of polystyrene in the organic solvent is 55%;

[0164] S2. The polyacrylonitrile is added to N,N-dimethylformamide and stirred to dissolve to obtain a shell solution; the mass percentage of the polyacrylonitrile in the organic solvent is 30%;

[0165] S3. The shell solution and the core solution are coaxially electrospun at a voltage of 10 kV, a spinning rate of 0.5 mL / h for the core solution, and a spinning rate of 0.8 mL / h for the shell solution; core-shell nanofibers are obtained; and then the core-shell nanofibers are pre-oxidized in air at 120°C for 1 h and carbonized at 850°C for 6 h in an argon atmosphere to obtain a hollow carbon fiber membrane material.

[0166] The hollow carbon fiber membrane was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0167] Comparative Example 3

[0168] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0169] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer; the core layer contains a nickel-iron bimetallic alloy;

[0170] The active metal is metallic lithium.

[0171] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0172] S1. Dissolving polystyrene in N,N-dimethylformamide to obtain a core solution; the mass percentage of polystyrene in the organic solvent is 55%;

[0173] S2. Nickel nitrate and ferric nitrate in a molar ratio of 1:1 are dissolved in N,N-dimethylformamide, and polyacrylonitrile is added and dissolved with stirring to obtain a shell solution; the mass percentage of the nickel nitrate and ferric nitrate in the organic solvent is 5% in total, and the mass percentage of the polyacrylonitrile in the organic solvent is 30%;

[0174] S3. The core solution of S1 and the shell solution of S2 are coaxially electrospun at a voltage of 10 kV, a spinning liquid outlet rate of the core solution of 0.5 mL / h, and a spinning liquid outlet rate of the shell solution of 0.8 mL / h; core-shell nanofibers are obtained; and the core-shell nanofibers are then pre-oxidized in air at 120°C for 1 h and carbonized at 850°C in an argon atmosphere for 6 h to obtain a self-supporting carbon fiber membrane material in which the core layer is an epitaxially grown carbon nanotube produced by catalysis of nickel-iron alloy and the shell layer is a tubular hollow carbon nanofiber.

[0175] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0176] Comparative Example 4

[0177] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0178] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains nickel fluoride; the content of the nickel fluoride is 20%;

[0179] The active metal is metallic lithium.

[0180] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0181] S1. Dissolving polystyrene in N,N-dimethylformamide to obtain a core solution; the mass percentage of polystyrene in the organic solvent is 55%;

[0182] S2. The nickel nitrate is dissolved in N,N- dimethylformamide, and then polyacrylonitrile is added and dissolved with stirring to obtain a shell solution; the total mass percentage of the nickel nitrate in the organic solvent is 5%, and the mass percentage of the polyacrylonitrile in the organic solvent is 30%;

[0183] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 10 kV, a spinning rate of 0.5 mL / h for the core solution, and a spinning rate of 0.8 mL / h for the shell solution; core-shell nanofibers were obtained; the core-shell nanofibers were then pre-oxidized at 120 ° C in air for 1 h and carbonized at 850 ° C in an argon atmosphere for 6 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a nickel-iron alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0184] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 300°C for 3 hours, and then heat-treated in an ammonium fluoride solution at 150°C for 3 hours to obtain a self-supporting carbon fiber membrane with a NiFx-CNTs@HCF multi-level "core-shell" structure (metal halide content is 20%); wherein the solvent of the ammonium fluoride solution is methanol, and the mass percentage of ammonium fluoride in the solvent is 30%.

[0185] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0186] Comparative Example 5

[0187] A composite negative electrode for a metal secondary battery, the composite negative electrode comprising a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film;

[0188] The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains nickel-iron bimetallic fluoride; the content of the nickel-iron bimetallic fluoride is 20%;

[0189] The active metal is metallic lithium.

[0190] The preparation method of the self-supporting carbon fiber film in the negative electrode of the metal secondary battery can refer to the following steps:

[0191] S1. Dissolving polystyrene in N,N-dimethylformamide to obtain a core solution; the mass percentage of polystyrene in the organic solvent is 55%;

[0192] S2. Nickel nitrate and ferric nitrate in a molar ratio of 1:6 are dissolved in N,N-dimethylformamide, and polyacrylonitrile is added and dissolved with stirring to obtain a shell solution; the mass percentage of the nickel nitrate and ferric nitrate in the organic solvent is 5% in total, and the mass percentage of the polyacrylonitrile in the organic solvent is 30%;

[0193] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 10 kV, a spinning rate of 0.5 mL / h for the core solution, and a spinning rate of 0.8 mL / h for the shell solution; core-shell nanofibers were obtained; the core-shell nanofibers were then pre-oxidized at 120 ° C in air for 1 h and carbonized at 850 ° C in an argon atmosphere for 6 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a nickel-iron alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0194] S4. The material obtained in S3 is placed in a muffle furnace, annealed at 300°C for 3 hours, and then heat-treated in an ammonium fluoride solution at 150°C for 3 hours to obtain a self-supporting carbon fiber membrane with a NiFeFx-CNTs@HCF multi-level "core-shell" structure (the nickel-iron bimetallic fluoride content is 20%); wherein the solvent of the ammonium fluoride solution is methanol, and the mass percentage of ammonium fluoride in the solvent is 30%.

[0195] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0196] Comparative Example 6

[0197] A method for preparing a self-supporting carbon fiber film in a composite negative electrode of a metal secondary battery comprises the following steps:

[0198] S1. Dissolving polystyrene in N,N-dimethylformamide to obtain a core solution; the mass percentage of polystyrene in the organic solvent is 55%;

[0199] S2. Nickel nitrate and ferric nitrate in a molar ratio of 1:6 are dissolved in N,N-dimethylformamide, and polyacrylonitrile is added and dissolved with stirring to obtain a shell solution; the mass percentage of the nickel nitrate and ferric nitrate in the organic solvent is 5% in total, and the mass percentage of the polyacrylonitrile in the organic solvent is 30%;

[0200] S3. The core solution of S1 and the shell solution of S2 were coaxially electrospun at a voltage of 10 kV, a spinning rate of 0.5 mL / h for the core solution, and a spinning rate of 0.8 mL / h for the shell solution; core-shell nanofibers were obtained; the core-shell nanofibers were then pre-oxidized at 120 ° C in air for 1 h and carbonized at 850 ° C in an argon atmosphere for 6 h to obtain a core layer of epitaxially grown carbon nanotubes catalyzed by a nickel-iron alloy and a shell layer of a tubular hollow carbon nanofiber material;

[0201] S4. Place the material obtained in S3 into a muffle furnace, anneal it at 600°C for 1 hour, and then heat treat it in an ammonium fluoride solution at 200°C for 1 hour; wherein the solvent of the ammonium fluoride solution is methanol, and the mass percentage of ammonium fluoride in the solvent is 70%.

[0202] The self-supporting carbon fiber film was prepared into a composite negative electrode for a metal secondary battery, and the composite negative electrode was prepared into a Li||Li symmetric battery and a lithium iron phosphate metal secondary battery, with the same steps as in Example 1.

[0203] Result detection

[0204] The results of the active metal first deposition nucleation overvoltage, polarization voltage, and cycle time of the Li||Li symmetric battery of the above embodiment and comparative example are shown in Table 1;

[0205] The results of the 1C first cycle discharge specific capacity, 1C discharge specific capacity after 500 cycles, and capacity retention rate of the lithium iron phosphate metal secondary batteries of the above examples and comparative examples after activation are shown in Table 2.

[0206] Table 1. Electrochemical performance data of Li||Li symmetric batteries assembled in Examples and Comparative Examples

[0207]

[0208] As can be seen from Table 1, the first deposition nucleation overpotential of the composite negative electrode of Examples 1 to 8 of the present invention does not exceed 50mV, and the polarization voltage does not exceed 36mV. It can be seen that the nucleation barrier of the active metal in the composite negative electrode obtained by the present invention is low, which can inhibit the formation of metal dendrites. On the one hand, it can avoid the loss of active materials of the composite negative electrode, and on the other hand, it can also avoid battery short circuit. In addition, in the composite negative electrode of the present invention, the self-supporting carbon fiber film can form a thin layer of halide on the surface of the active metal, strengthen the SEI film, and avoid the side reaction between the active metal in the negative electrode and the electrolyte, which leads to a decrease in cycle life. It can be seen from Examples 1 to 8 that the cycle life of the composite negative electrode of the present invention is not less than 830h. In Comparative Example 1, a metal lithium sheet is directly used as the electrode, and the active metal nucleation overpotential and polarization voltage are significantly increased. are not less than 150mV, and the cycle time is greatly reduced to only 480h; the hollow carbon fiber membrane used in the composite negative electrode of Comparative Example 2 does not contain bimetallic halide, cannot inhibit the formation of metal dendrites, and cannot strengthen the SEI film; the self-supporting carbon fiber membrane in the composite negative electrode of Comparative Example 3 has not been halogenated, and cannot form a thin layer of halide on the surface of the active metal to strengthen the SEI film, the cycle time is short, and due to the high nucleation barrier, the obtained composite negative electrode active metal nucleation overpotential is large, and metal dendrites are easily formed; in Comparative Example 4, only the molar ratio of the single metal halide and the bimetallic salt in Comparative Example 5 exceed the scope of the present invention, and the performance of the obtained composite negative electrode is also reduced; in Comparative Example 6, due to the high annealing temperature, the carbon material is completely converted into CO2 and volatilized, leaving only the bimetallic alloy, and the subsequent steps cannot be realized.

[0209] Table 2. Electrochemical performance data of metal lithium batteries assembled in Examples and Comparative Examples

[0210]

[0211] As can be seen from Table 2, in Examples 1 to 8, the capacity retention rate of the composite negative electrode obtained by the present invention is above 82%; in Comparative Example 1, a metal lithium sheet is directly used as an electrode, and the capacity retention rate is only 20%; the hollow carbon fiber membrane used in Comparative Example 2 does not contain a bimetallic halide, and the self-supporting carbon fiber membrane in the composite negative electrode of Comparative Example 3 has not been halogenated, and a thin layer of halide cannot be formed on the surface of the active metal, the SEI film cannot be reinforced, and the side reaction between the active metal and the electrolyte cannot be prevented, and the capacity retention rate is only 24.13%; in Comparative Example 4, only a single metal halide and the molar ratio of the bimetallic salt in Comparative Example 5 exceed the scope of the present invention, and the capacity retention rate of the battery prepared by the obtained composite negative electrode is below 80%; and in Comparative Example 6, due to the high annealing temperature, the carbon material is completely converted into CO2 and volatilized, leaving only the bimetallic alloy, and the subsequent steps cannot be realized.

[0212] Figure 1 The structural diagram and TEM image of the self-supporting carbon fiber membrane of the present invention are shown in FIG. Figure 3 This is an SEM image of the self-supporting carbon fiber membrane in the composite negative electrode of Example 1. From the image, the structural morphology of the self-supporting carbon fiber membrane in the composite negative electrode of the present invention can be intuitively observed. The outer layer is a hollow carbon fiber with a tubular structure, and the inner layer is an epitaxially grown carbon nanotube, wherein the black particles are double metal halides.

[0213] Figure 2 The following figure compares the performance of composite negative electrode Li||Li symmetric cells obtained in Example 1 and Comparative Examples 1-3. As can be seen from the figure, the Li||Li symmetric cell obtained in Example 1 cycled stably at a polarization voltage of 22 mV for 985 hours, while the Li||Li symmetric cell obtained in Comparative Example 1 maintained a polarization voltage consistently above 100 mV and experienced a sharp increase in polarization voltage after only 200 hours of cycling, indicating severe dendrite growth in Comparative Example 1. Comparative Examples 2 and 3 also experienced sharp polarization surges and worsening dendrite growth at 360 and 540 hours, respectively, leading to rapid cell failure.

[0214] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A composite negative electrode, characterized in that: The composite negative electrode comprises a self-supporting carbon fiber film and an active metal supported on the self-supporting carbon fiber film; The self-supporting carbon fiber membrane comprises an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer, wherein the core layer contains a double metal halide and the content of the double metal halide is 10-50%; The active metal is at least one of lithium, sodium, potassium and zinc; The bimetallic halide is nickel-iron bimetallic fluoride, nickel-cobalt bimetallic fluoride, nickel-manganese bimetallic fluoride, iron-cobalt bimetallic chloride, iron-manganese bimetallic bromide, cobalt-manganese bimetallic iodide, and nickel-cobalt bimetallic chloride.

2. The composite negative electrode according to claim 1, wherein The content of the double metal halide in the core layer of the self-supporting carbon fiber membrane is 20-25%.

3. A method for preparing a self-supporting carbon fiber membrane in a composite negative electrode according to claim 1 or 2, characterized in that: The steps include: S1. The polymer A is dissolved in an organic solvent to obtain a core solution; S2. Dissolving two transition metal salt solutions in an organic solvent and then adding polymer B to uniformly dissolve the mixture to obtain a shell solution; wherein the two transition metal salts contain different metals and the molar ratio of the two transition metal salts is (1-4):1; and the number average molecular weight of polymer B is greater than the number average molecular weight of polymer A in S1; S3. The core solution in S1 and the shell solution in S2 were coaxially electrospun to obtain core-shell nanofibers, which were pre-oxidized and carbonized to obtain a material having an epitaxially grown carbon nanotube core layer and a tubular hollow carbon fiber shell layer; S4. The material obtained in S3 is annealed and then transferred to an ammonium halide solution for heat treatment to obtain a self-supporting carbon fiber membrane; wherein the annealing temperature is 250~500℃ and the heat treatment temperature is 80~200℃; The polymer A is at least one of polystyrene, polyvinyl pyrrolidone, and polymethyl methacrylate; The polymer B is at least one of polyacrylonitrile, polypyrrole, polyamide, urea, melamine, and asphalt.

4. The preparation method according to claim 3, wherein The mass percentage of polymer A in the organic solvent in S1 is 45-55%.

5. The preparation method according to claim 3, wherein: The mass percentage of polymer B in the organic solvent in S2 is 30-40%.

6. The preparation method according to claim 3, characterized in that: The mass percentage of the two transition metal salts in the solvent in S2 is 2-30%.

7. The preparation method according to claim 3, wherein: The solvent of the ammonium halide solution in S4 is water and / or methanol.

8. The preparation method according to claim 5, characterized in that: The mass percentage of the ammonium halide and the solvent is 20-60%.

9. A method for preparing the composite negative electrode according to claim 1 or 2, characterized in that: The steps include: The active metal is heated to a molten state in a glove box, and then fully contacts and wets the self-supporting carbon fiber membrane. After cooling, a composite negative electrode for a metal secondary battery is obtained. The oxygen content in the glove box is less than 0.01 ppm.

10. Use of the composite negative electrode according to claim 1 or 2 in a metal secondary battery.

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