Porous carbon fiber as well as preparation method and application thereof

Abstract

The invention relates to the technical field of battery negative electrode material preparation, in particular to a porous carbon fiber and a preparation method and application thereof. The porous carbon fiber comprises a porous carbon fiber matrix and lithium-loving functional particles, the porous carbon fiber matrix is provided with holes distributed in the surface and / or the interior of the porous carbon fiber matrix; the lithium-loving functional particles are distributed on the porous carbon fiber matrix in a surface loading and / or embedding manner, and the lithium-loving functional particles are loaded and / or embedded on the surfaces of at least part of holes; based on the total volume of the holes, the volume of the holes with the aperture smaller than or equal to 50 nm in the holes is not smaller than 70%. When the porous carbon fiber provided by the invention is applied to a battery, the problems of non-uniform lithium metal deposition, large volume expansion, poor stability, high cost and the like in the prior art can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of battery anode materials, and particularly relates to a porous carbon fiber and a preparation method and application thereof. Background Art

[0002] Lithium metal is considered to be the most potential anode material for realizing the next-generation high-energy battery due to its ultra-high theoretical specific capacity (3860 mAh·g -1 ) and the lowest reduction potential of -3.04 V (relative to the standard hydrogen electrode). However, when using a lithium metal foil as the lithium metal anode, due to the host-free property of lithium metal and some tip discharge phenomena, it is difficult for lithium metal to undergo a uniform deposition / stripping process, resulting in the gradual formation of lithium dendrites on the electrode surface, leading to an increased contact between the lithium metal and the electrolyte interface, causing side reactions to occur rapidly. As the number of cycles increases, the dendrites continue to grow to form dead lithium, a large amount of active lithium inside the battery is consumed, and the cycle attenuation is serious. In addition, during the deposition process of lithium metal on the anode, there will be a huge volume expansion, resulting in an increase in internal stress of the battery, and even damaging the overall structure of the battery, causing mechanical failure of the battery, which seriously hinders the practical application of the lithium metal anode.

[0003] Some improved methods have been proposed in the prior art. Some researchers have proposed using a porous carbon material as the anode to achieve the purpose of depositing lithium. However, the porosity obtained by the porous carbon material is limited, and the expansion rate of the prepared lithium anode is still relatively large, reaching more than 30%. Moreover, the porous carbon particles do not form physical anchoring, and the large expansion will affect the stability of the electrode and the cycle performance of the battery. There are also some researchers who choose to use carbon fiber as the lithium deposition framework, and the lithiumophilic particles only cover the surface of the carbon fiber. It is easy to detach from the carbon matrix during the electrochemical process, resulting in structural failure. Under the presence of battery pressure, the problem of lithium anode expansion is still severe. How to improve the problems of uneven lithium metal deposition, large volume expansion, poor stability, and high cost is of great significance for improving the battery performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a porous carbon fiber and a preparation method and application thereof, so as to solve the problems in the prior art that it is impossible to improve the uneven lithium metal deposition, large volume expansion, poor stability, and high cost.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present invention is as follows:

[0006] The present invention provides a porous carbon fiber, comprising: a porous carbon fiber matrix and lithiophilic functional particles; the porous carbon fiber matrix has pores distributed on the surface and / or inside the porous carbon fiber matrix; the lithiophilic functional particles are distributed on the porous carbon fiber matrix in a manner of surface loading and / or embedding, and at least part of the pores are surface-loaded and / or embedded with the lithiophilic functional particles; based on the total volume of the pores, the volume proportion of the pores with a pore diameter ≤ 50 nm in the pores is not less than 70%.

[0007] According to the above technical means, in the first aspect, the carbon fiber matrix of the present invention has pores distributed on its surface and / or inside, providing space for lithium ion deposition at the negative electrode, which can greatly relieve the swelling of the lithium metal negative electrode, and the carbon fiber matrix has a carbon fiber skeleton structure, which can reduce the contact area between the lithium metal and the electrolyte and reduce the loss of active lithium caused by side reactions occurring when the lithium metal contacts the electrolyte. In the second aspect, some of the pores in the porous carbon fiber matrix are surface-loaded and / or embedded with lithiophilic functional particles, which can directionally regulate the lithium metal deposition direction, limit the lithium metal deposition in the pores of the porous carbon fiber matrix, relieve the formation of lithium dendrites, and reduce the situation of structural failure caused by the detachment of the lithiophilic functional particles from the porous carbon fiber matrix, which helps to improve stability. When the porous carbon fiber provided by the present invention is applied to a battery, it can improve the problems of uneven lithium metal deposition, large volume expansion, poor stability and high cost in the prior art. In the third aspect, defining the volume content of the pores with a pore diameter ≤ 50 nm in the pores can ensure the ion conduction and metal deposition effect, and prevent the occurrence of failure, collapse, etc. due to unstable structure; if the pore diameter is too large and the volume proportion is too low, the structural stability cannot be guaranteed, and if the pore diameter is too small, the ion conduction is affected.

[0008] Further, the pores include micropores, and the micropores account for 30%-90% of the volume of the pores;

[0009] And / or, the pores further include mesopores and / or macropores.

[0010] The pore diameter of the micropores < 2 nm; mesopores, also known as mesopores, have a pore diameter of 2-50 nm; the pore diameter of macropores > 50 nm.

[0011] According to the above technical means, the pores of the present invention include mesopores and / or macropores, which cooperate with the micropores to make the porous carbon fiber matrix have a hierarchical porous structure. The micropores and mesopores enhance the adsorption of lithium ions or atoms, further induce uniform lithium deposition, and ensure structural stability. The macropores provide effective lithium ion channels to accelerate lithium ion migration. The porous carbon fiber with a hierarchical porous structure can further improve the uniformity of lithium deposition, relieve the formation of lithium dendrites, and improve stability.

[0012] Further, the pore diameter a of the micropores satisfies 0.5 nm ≤ a < 2 nm;

[0013] And / or, the mesopore aperture b satisfies 2 nm ≤ b ≤ 30 nm;

[0014] And / or, the macropore aperture c satisfies 50 nm < c ≤ 200 nm;

[0015] And / or, the mesopores account for 0 - 50% of the pore volume;

[0016] And / or, the macropores account for 0 - 30% of the pore volume.

[0017] When the mesopores or macropores account for 0 of the pore volume, it means that there are no mesopores or macropores.

[0018] According to the above technical means, on the basis of having micropores, the porous carbon fiber matrix of the present invention further has at least one of mesopores and macropores, and regulates the volume ratios of the micropores, mesopores and macropores to make the numbers of the micropores, mesopores and macropores more appropriate, further improving the uniform deposition of lithium, and improving the lithium dendrites and stability.

[0019] Furthermore, the lithiumophilic functional particles include at least one element of magnesium, aluminum, silicon, silver, zinc, tin, germanium, platinum, gold, bismuth, or at least one compound of its oxide, nitride, phosphide, sulfide, chloride;

[0020] And / or, the diameter of the porous carbon fiber matrix is 50 nm - 5000 nm, preferably, the diameter of the porous carbon fiber matrix is 100 nm - 1000 nm;

[0021] And / or, the porous carbon fiber matrix includes a carbon-based material.

[0022] According to the above technical means, the lithiumophilic functional particles of the present invention include the above substances. The lithiumophilic functional particles have a strong lithium ion affinity during the charge and discharge process, induce the accumulation of lithium ions at the negative electrode of the lithiumophilic functional particles, induce the directional deposition of lithium metal, relieve the formation of lithium dendrites, and the above lithiumophilic functional particles are not easily detached from the carbon fiber matrix, improving the stability.

[0023] The porous carbon fiber matrix of the present invention includes a carbon-based material. The porous carbon fiber has a defined diameter of 50 nm - 5000 nm, preferably 100 nm - 1000 nm. The carbon fiber has high strength and plays a supporting role in the lithium metal negative electrode, avoiding the creep of lithium, and at the same time has high conductivity and good rate performance.

[0024] Furthermore, the present invention provides a method for preparing porous carbon fiber, including the following steps:

[0025] (1) Mix the carbon fiber precursor, the lithiumophilic functional particle precursor, the pore-forming agent and the solvent uniformly to obtain a spinning solution;

[0026] (2) Obtain the as-spun fiber filaments through electrospinning;

[0027] (3) Perform pre-oxidation and carbonization on the as-spun fiber filaments.

[0028] According to the above technical means, the carbon fiber precursor is a material for forming a porous carbon fiber matrix. The porous carbon fiber matrix provides functions such as mechanical anchoring and electron conduction in the battery, especially playing an ion conduction role in the solid-state battery system. The pore-forming agent is used to create pores in the carbonized carbon fiber. After pore formation, the carbon fiber has pores on its surface and / or inside, providing a space for lithium deposition. The deposition of lithium metal in the pores will not affect the overall structure of the electrode, providing stability for the electrode. The precursor of the lithiumophilic functional particles is converted into lithiumophilic functional particles after carbonization treatment, and has the function of inducing the directional deposition of lithium metal. The lithiumophilic functional particles are distributed on the porous carbon fiber matrix in a surface loading and / or embedding manner. At least part of the pore surfaces are loaded and / or embedded with lithiumophilic functional particles, restricting the deposition of lithium metal in the pores of the porous carbon fiber matrix, alleviating the formation of lithium dendrites, and reducing the situation of structural failure caused by the detachment of lithiumophilic functional particles from the porous carbon fiber matrix.

[0029] Furthermore, the preparation method satisfies at least one of (1)-(8):

[0030] (1) The mass ratio of the carbon fiber precursor, the precursor of the lithiumophilic functional particles, and the pore-forming agent is (6-10):(0-4):(0-10), but not zero;

[0031] (2) The carbon fiber precursor includes at least one of polyacrylonitrile, polyamide, cellulose, lignin, cellulose, chitosan, polyvinyl alcohol, and polyimide;

[0032] And / or, the particle size of the precursor of the lithiumophilic functional particles is 1 nm - 1000 nm;

[0033] And / or, the precursor of the lithiumophilic functional particles includes at least one element of magnesium, aluminum, silicon, silver, zinc, tin, germanium, platinum, gold, bismuth, or at least one compound of its oxide, nitride, phosphide, sulfide, carbonate, nitrate, phosphate, chlorate, acetate;

[0034] (3) The solid content of the spinning solution is 10 - 25 wt%;

[0035] (4) The parameters of the electrospinning: the voltage is 10 - 20 kV, the receiving distance is 8 - 20 cm; the injection rate is a parameter well-known in the art and no specific limitation is required. As an example, the injection rate is 0.8 - 4.2 mL / h;

[0036] (5) The specific steps of the pre-oxidation include heating at a heating rate of 1-5 °C / min to 200-300 °C and holding for 2-3 h;

[0037] (6) The specific steps of the carbonization include, under a protective atmosphere, heating at a heating rate of 2-10 °C / min to 600-1800 °C and holding for 1-5 h;

[0038] Preferably, the protective atmosphere includes at least one of nitrogen, argon, neon, and krypton;

[0039] More preferably, the temperature of the carbonization is not higher than the melting point of the precursor of the lithiumophilic functional particles;

[0040] (7) The pore-forming agent includes at least one of a gas-releasing pore-forming agent, a soluble-removable pore-forming agent, or a pyrolytic pore-forming agent;

[0041] Preferably, the gas-releasing pore-forming agent includes at least one of ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate, magnesium carbonate, ammonium chloride, silver nitrate, zinc nitrate, and zinc carbonate;

[0042] Preferably, the soluble-removable pore-forming agent includes at least one of potassium chloride, sodium chloride, potassium hydroxide, and sodium hydroxide;

[0043] Preferably, the pyrolytic pore-forming agent includes polyvinylpyrrolidone;

[0044] Preferably, the particle size of the pore-forming agent is 1 nm - 1000 nm;

[0045] (8) After the carbonization, it further includes a pickling step;

[0046] Preferably, the pickling time is 10-30 min;

[0047] More preferably, at least one of hydrochloric acid solution, sulfuric acid solution, and acetic acid solution is used for the pickling.

[0048] According to the above technical means, the present invention helps to regulate the distribution of lithiumophilic functional particles and pore structures by defining the mass ratios of the carbon fiber precursor, the precursor of the lithiumophilic functional particles, and the pore-forming agent. The appropriate distribution of pores and lithiumophilic functional materials helps to induce uniform deposition of lithium metal, improving the battery cycle and rate performance. The carbon fiber precursor includes the above substances and has functional functional groups such as cyano and hydroxyl groups, which helps the lithiumophilic functional particles to migrate to its surface for adsorption or coordination, facilitating the uniform distribution of the lithiumophilic functional particles in the porous carbon fiber matrix, and improving the anchoring effect of the matrix on the lithiumophilic functional particles, reducing the shedding of the lithiumophilic functional particles during battery cycling.

[0049] The present invention regulates the process parameters of electrospinning, which is beneficial to adjusting the fiber diameter of the porous carbon fiber matrix, providing better support, and further enhancing functions such as electron conduction.

[0050] The present invention regulates the carbonization temperature not to be higher than the melting point of the precursor of the lithiumophilic functional particles, which can prevent the melting of the lithiumophilic functional particles and avoid the situation of detachment from the porous carbon fiber matrix.

[0051] Gas-releasing pore-forming agents refer to pore-forming agents that decompose upon heating to generate gas, and the gas escapes to form a porous structure. Soluble-removable pore-forming agents are removed by solvents such as water and acid, leaving pores. Pyrolytic pore-forming agents form pores after pyrolysis at high temperature.

[0052] It should be particularly noted that there is a technical solution in the present invention where the precursor of the lithiumophilic functional particles and the pore-forming agent are the same substance.

[0053] The solvents in the spinning solution include one or more of deionized water, aqueous sodium hydroxide solution, methanol, ethanol, benzene, chloroform, dimethylformamide, and dimethyl sulfoxide.

[0054] Furthermore, the present invention provides a porous carbon fiber material, including the above-mentioned porous carbon fiber or the porous carbon fiber prepared by the above-mentioned preparation method.

[0055] Preferably, the porous carbon fiber material is a porous carbon fiber membrane, and the thickness of the porous carbon fiber membrane is 10 - 50 μm;

[0056] Preferably, the porosity of the porous carbon fiber membrane is 50 - 90%.

[0057] According to the above technical means, the present invention makes the porous carbon fiber into a porous carbon membrane. The porous carbon fiber matrices are stacked on each other to form a non-woven three-dimensional network, and a more stable self-supporting electrode structure is formed through physical anchoring. At the same time, the formed three-dimensional network can also promote the efficient conduction of electrons in the electrode sheet and avoid the addition of insulating binders. The porous carbon fiber membrane material provided by the present invention is beneficial to the solid-solid contact in the all-solid-state battery, forms a stable ion transport channel, avoids the growth of lithium dendrites caused by the tip discharge effect, improves problems such as lithium dendrites, and enhances the battery performance such as cycling.

[0058] The present invention regulates the porosity of the porous carbon fiber membrane to be 50 - 90%, provides space for prelithiation, improves the prelithiation amount, and reduces lithium loss.

[0059] Furthermore, the present invention provides a preparation method of a porous carbon fiber material, including: cutting the porous carbon fiber into short fibers; then mixing with a dispersant and a solvent to prepare a dispersion slurry; and making the dispersion slurry into a membrane material by warm isostatic pressing.

[0060] The solvent includes one or more of water, N-methylpyrrolidone, ethanol, isopropanol, toluene, benzene, ethyl acetate, butyl acetate, methyl ethyl ketone, n-butanol, etc.; the addition amount of the solvent is not specifically limited and the conventional dosage in the art is adopted;

[0061] The dispersant includes but is not limited to one or more of DISPERBYK-2155, DISPERBYK-9076, TNADIS, sodium cholate (and its derivatives, chemically similar chemicals, etc.), polyvinylpyrrolidone (and its derivatives, different molecular weights), polyvinylcaprolactam, sodium dodecylbenzenesulfonate, long-chain alkane octadecanol, hydroxypropyl cellulose, etc.; the addition amount of the dispersant is not specifically limited and the conventional dosage in the art is adopted;

[0062] When preparing the dispersion slurry, the mixing method includes but is not limited to one or more of high-speed stirring, ball milling, ultrasonic oscillation, etc.;

[0063] After removing the solvent and dispersant in the dispersion slurry, a membrane material is made; the solvent removal methods include one or more of vacuum filtration, heating and drying, freeze drying; the dispersant removal methods include one or more of solvent rinsing, vacuum filtration, high-temperature annealing, pickling and soaking, etc., and the solutions used for pickling include one or more of sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, etc.;

[0064] Preferably, the length of the short fiber is 3-10 mm;

[0065] Preferably, the temperature of the warm isostatic pressing is 80-200 °C, the pressure is 100-600 MPa, and the time is 0.1-2 h.

[0066] According to the above technical means, the porous carbon fiber is first uniformly dispersed in the solvent and dispersant to ensure the uniformity of the prepared membrane material. Since the porous carbon fiber has undergone carbonization heat treatment, the polar groups on its surface are not sufficient to uniformly disperse in the solution. Therefore, the addition of the dispersant is beneficial to increasing the compatibility of the carbon fiber in the solvent, thereby forming a uniform dispersion liquid. When forming the membrane material, it is necessary to remove the dispersant because the dispersant affects the overall conductivity of the fiber membrane and will also affect the charge and discharge process of the battery when it is applied to the battery.

[0067] Furthermore, the present invention provides a pole piece, which includes the above porous carbon fiber material or the porous carbon fiber material prepared by the above preparation method.

[0068] Furthermore, when preparing the above pole piece, it also includes pre-lithiation of the porous carbon fiber material to obtain an electrode membrane and rolling to obtain the pole piece.

[0069] The pre-lithiation methods include molten lithium injection pre-lithiation, magnetron sputtering pre-lithiation or physical lamination of lithium foil pre-lithiation.

[0070] When performing roll pressing, the pressure is set to 10 - 50 MPa.

[0071] The thickness of the lithium foil formed after prelithiation is 0 - 20 μm. The prelithiation scheme can reduce the loss of active lithium and improve the cycle performance of the battery. Controlling the thickness of the lithium foil after prelithiation helps to improve the energy density of the battery.

[0072] It should be noted that the electrode can be directly used as the framework for lithium deposition at the negative electrode without prelithiation. This scheme is called "anode-free" or "in-situ lithium metal", which can maximize the energy density of the battery.

[0073] Furthermore, the present invention provides a battery including the above-mentioned electrode.

[0074] The above battery is one of a lithium metal liquid battery, a lithium metal semi-solid battery, and a lithium metal solid battery.

[0075] Advantages of the present invention:

[0076] (1) The porous carbon fiber provided by the present invention includes a porous carbon fiber matrix and a lithiumophilic functional particle; the porous carbon fiber matrix has holes distributed on the surface and / or inside of the porous carbon fiber matrix; the lithiumophilic functional particle is distributed on the porous carbon fiber matrix in a surface loading and / or embedding manner, and at least part of the holes are surface loaded and / or embedded with the lithiumophilic functional particle; based on the total volume of the holes, the volume of the holes with a pore diameter ≤ 50 nm in the holes is not less than 70%. This porous carbon fiber has the advantages of self-supporting, stable structure, uniform holes, high specific surface area, high porosity, etc. First, the carbon fiber matrix of the present invention has holes distributed on its surface and / or inside, providing space for lithium ion deposition at the negative electrode, which can greatly relieve the swelling of the lithium metal negative electrode. And the carbon fiber matrix has a carbon fiber skeleton structure, which can reduce the contact area between the lithium metal and the electrolyte and reduce the loss of active lithium caused by side reactions occurring when the lithium metal contacts the electrolyte. Second, some of the holes in the porous carbon fiber matrix are surface loaded and / or embedded with lithiumophilic functional particles, which can directionally control the lithium metal deposition direction, limit the lithium metal deposition in the holes of the porous carbon fiber matrix, relieve the formation of lithium dendrites, and reduce the situation where the lithiumophilic functional particles fall off from the porous carbon fiber matrix, leading to structural failure, which helps to improve stability. When applying the porous carbon fiber provided by the present invention to a battery, it can improve the problems of uneven lithium metal deposition, large volume expansion, poor stability, and high cost in the prior art. Third, limiting the volume content of the holes with a pore diameter ≤ 50 nm in the holes can ensure ion conduction and metal deposition effects, and prevent structural instability such as failure and collapse; if the pore diameter is too large and the volume ratio is too low, the structural stability cannot be guaranteed, and if the pore diameter is too small, it will affect ion conduction.

[0077] The porous carbon fiber provided by the present invention combines lithiophilic functional particles with high theoretical capacity of 3860 mAh / g and low voltage advantages with a high-porosity and low-density carbon fiber matrix to form a porous carbon fiber. The capacity is much higher than the theoretical capacity of 372 mAh / g of the currently commercial negative electrode graphite, thereby effectively improving the energy density of the battery.

[0078] (2) For the porous carbon fiber provided by the present invention, the pores of the present invention include mesopores and / or macropores, which cooperate with micropores to endow the porous carbon fiber matrix with a hierarchical porous structure. The micropores and mesopores enhance the adsorption of lithium ions or atoms, further inducing uniform lithium deposition. The macropores provide effective lithium ion channels to accelerate lithium ion migration. The porous carbon fiber with a hierarchical porous structure can further improve the uniformity of lithium deposition, alleviate the formation of lithium dendrites, and improve stability. By regulating the volume ratios of the micropores, mesopores and macropores to make the numbers of the micropores, mesopores and macropores more appropriate, the uniform lithium deposition, lithium dendrites and stability are further improved.

[0079] (3) For the porous carbon fiber provided by the present invention, the lithiophilic functional particles include at least one element of magnesium, aluminum, silicon, silver, zinc, tin, germanium, platinum, gold, bismuth, or at least one compound of its oxide, nitride, phosphide, sulfide, chloride. The lithiophilic functional particles have strong lithium ion affinity during charge and discharge processes, inducing the accumulation of lithium ions at the negative electrode of the lithiophilic functional particles and inducing the directional deposition of lithium metal, alleviating the formation of lithium dendrites. The above lithiophilic functional particles are not easily detached from the carbon fiber matrix, improving stability. The porous carbon fiber has a diameter of 50 nm - 5000 nm, preferably 100 nm - 1000 nm. The carbon fiber has high strength and plays a supporting role in the lithium metal negative electrode to prevent lithium from creeping. At the same time, it has high conductivity and good rate performance.

[0080] (4) For the preparation method of the porous carbon fiber provided by the present invention, the carbon fiber precursor is the material for forming the porous carbon fiber matrix. The porous carbon fiber matrix provides functions such as mechanical anchoring and electron conduction in the battery, especially playing an ion conduction role in the solid-state battery system. The pore-forming agent is used to create pores in the carbon fiber after carbonization. The carbon fiber with pores forms pores on its surface and / or inside, providing a lithium deposition space. The deposition of lithium metal in the pores will not affect the overall structure of the electrode, providing stability for the electrode. The lithiophilic functional particle precursor is converted into lithiophilic functional particles after carbonization treatment, and has the function of inducing the directional deposition of lithium metal. The lithiophilic functional particles are distributed on the porous carbon fiber matrix in a surface loading and / or embedding manner, and at least part of the pore surfaces are loaded and / or embedded with lithiophilic functional particles, restricting the deposition of lithium metal in the pores of the porous carbon fiber matrix, alleviating the formation of lithium dendrites, and reducing the situation of structural failure caused by the detachment of lithiophilic functional particles from the porous carbon fiber matrix.

[0081] The preparation method described in the present invention has been widely applied in other fields of the industry. Its preparation process has strong scalability, low process development cost, and strong industrialization potential.

[0082] (5) The present invention provides a method for preparing porous carbon fiber. By defining the mass ratio of the carbon fiber precursor, the lithiumophilic functional particle precursor, and the pore-forming agent, it helps to regulate the distribution of lithiumophilic functional particles and the pore structure. The appropriate distribution of pores and lithiumophilic functional materials helps to induce uniform deposition of lithium metal, improving the battery cycle and rate performance. The carbon fiber precursor includes the above substances and has functional groups such as cyano and hydroxyl, which help the lithiumophilic functional particles migrate to its surface for adsorption or coordination, facilitating the uniform distribution of lithiumophilic functional particles in the porous carbon fiber matrix and enhancing the anchoring effect of the matrix on the lithiumophilic functional particles, reducing the detachment of lithiumophilic functional particles during battery cycling. By regulating the electrospinning process parameters, it is beneficial to adjust the fiber diameter of the porous carbon fiber matrix, providing better support and further enhancing functions such as electron conduction. By regulating the carbonization temperature not higher than the melting point of the lithiumophilic functional particle precursor, it can prevent the melting of lithiumophilic functional particles and the situation of detachment from the porous carbon fiber matrix.

[0083] (6) The present invention provides a porous carbon fiber membrane. The present invention makes the porous carbon fiber into a porous carbon membrane. The porous carbon fiber matrices are stacked on top of each other to form a non-woven three-dimensional network, forming a more stable self-supporting electrode structure through physical anchoring. At the same time, the formed three-dimensional network can also promote the efficient conduction of electrons in the electrode and avoid the addition of insulating binders. The porous carbon fiber membrane material provided by the present invention is beneficial to the solid-solid contact in all-solid-state batteries, forming a stable ion transport channel, avoiding the growth of lithium dendrites caused by the tip discharge effect, improving problems such as lithium dendrites, and enhancing battery cycle performance.

[0084] (7) The present invention provides a method for preparing a porous carbon fiber membrane. First, the porous carbon fiber is uniformly dispersed in a solvent and a dispersant to ensure the uniformity of the prepared membrane material. Since the porous carbon fiber has undergone carbonization heat treatment, the polar groups on its surface are not sufficient to uniformly disperse in the solution. Therefore, the addition of the dispersant is beneficial to increasing the compatibility of the carbon fiber in the solvent, thereby forming a uniform dispersion. When forming the membrane material, the dispersant needs to be removed because the dispersant affects the overall conductivity of the fiber membrane and will also affect the charge and discharge process of the battery when it is applied to the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 It is a schematic structural diagram of the porous carbon fiber provided in Embodiment 1 of the present invention;

[0086] Figure 2 It is a schematic structural diagram of the porous carbon membrane provided in Embodiment 1 of the present invention;

[0087] Figure 3 Schematic structural diagram of the electrode provided in Embodiment 1 of the present invention;

[0088] Figure 4 Charge-discharge curve of the battery made in Embodiment 1 of the present invention;

[0089] Wherein, 100 - porous carbon fiber matrix; 101 - lithiumophilic functional particles; 102 - holes; 103 - porous carbon fiber; 104 - physical anchoring formed between carbon fibers; 105 - pores; 106 - porous carbon film; 107 - second lithium foil; 108 - first lithium foil; 109 - stainless steel. Specific embodiments

[0090] The following will illustrate the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, rather than for limiting the protection scope of the present invention.

[0091] It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0092] Embodiment 1

[0093] This embodiment provides a method for preparing porous carbon fiber, including the following steps:

[0094] (1) Add 15 g of polyacrylonitrile powder and 10 g of polyvinylpyrrolidone powder to 100 mL of dimethylformamide in sequence, and magnetically stir for 12 hours to form a homogeneous solution. Then add 5 g of silver nitrate powder (particle size of 500 - 800 nm) to the solution, and magnetically stir for 12 hours to obtain a spinning solution, and the solid content of the spinning solution is about 24 wt%. The dissolved silver ions are adsorbed on the negative poles of the cyano group of polyacrylonitrile and the nitrogen and oxygen atoms of polyvinylpyrrolidone through electrostatic coordination to form local enrichment of silver ions.

[0095] (2) Electrospinning the spinning solution from bottom to top, setting the voltage to 15 kV and the receiving distance to 15 cm to obtain nanofiber precursor filaments.

[0096] (3) After collecting the nanofiber filaments, they are cut into short fibers with a length of about 5 mm by a fiber cutting machine. The short fibers are placed in a pre-oxidation furnace for the pre-oxidation process, heated in an air atmosphere at a heating rate of 2 °C / min, and held at 200 °C for 2 h. Covalent bond cross-linking is formed between polymer molecular chains after pre-oxidation, improving the structural stability of the fibers during the carbonization process and avoiding the collapse of the carbon fiber structure. After the pre-oxidized fibers are cooled, they are transferred to a tubular furnace under a nitrogen atmosphere and heated to 800 °C at a heating rate of 5 °C / min. After holding at 800 °C for 2 h, they are naturally cooled to complete carbonization to obtain porous carbon fibers containing silver seeds. 200 mL of 0.5 mol / L dilute hydrochloric acid is prepared, and the carbonized porous carbon fibers are placed in the dilute hydrochloric acid and stirred thoroughly for 30 min. After the impurities on the surface of the porous carbon fibers are fully dissolved, the dilute hydrochloric acid is filtered off, and the porous carbon fibers containing silver seeds are repeatedly rinsed and suction-filtered 3 times with pure water. Then, the washed porous carbon fibers containing silver seeds are placed in a blast drying oven and dried for 24 hours to obtain porous carbon fibers containing silver seeds.

[0097] The structure of the porous carbon fibers in this example is shown in Figure 1 , the porous carbon fiber 103 includes a porous carbon fiber matrix 100 and a lithium-philic functional particle Ag 101. The surface and interior of the porous carbon fiber matrix have pores 102. The lithium-philic functional particles are loaded or embedded on the surface of the porous carbon fiber matrix. Some pores are loaded and embedded with the lithium-philic functional particle Ag. The pores include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 10 nm, and macropores with a pore diameter of 50 < c ≤ 100 nm. The volume ratio of the micropores is 56.3%, the volume ratio of the mesopores is 32.8%, and the volume ratio of the macropores is 10.9%. The diameter of the porous carbon fiber matrix is 800 - 1000 nm. The formation mechanism of this porous carbon fiber is that polyacrylonitrile decomposes by heating to form a carbon-based skeleton structure, that is, the porous carbon fiber matrix 100. After polyvinylpyrrolidone decomposes by heating, pores 102 are formed. After silver nitrate decomposes by heating, the lithium-philic functional particle silver 101 is formed and fixed in the porous carbon fiber matrix, playing a role of uniform dispersion and physical anchoring. During the charge and discharge process, the carbon fiber provides mechanical strength, inhibits the expansion and deformation of the negative electrode, the pores provide space for lithium metal deposition, and the lithium-philic functional particle silver induces the directional growth of lithium metal, alleviating the lithium dendrite phenomenon caused by the lack of a host for lithium metal.

[0098] This example also provides a preparation method of a porous carbon fiber material, including the following steps:

[0099] (1) Take 10 g of the above-mentioned porous carbon fibers (cut into short fibers with a length of about 5 mm), 5 g of sodium dodecylbenzenesulfonate, 5 g of polyvinylpyrrolidone, and 200 mL of deionized water and add them to a 1 L ball milling tank. The particle size of the ball milling beads is 3 - 5 mm, and the ball milling beads account for about 1 / 3 of the volume of the ball milling tank. Place the ball milling tank on a horizontal ball mill and blend at a speed of 200 rpm for 12 h. After the dispersion liquid is evenly dispersed, a dispersion slurry is obtained.

[0100] (2) Take out the slurry, take 5 mL of the slurry and dilute it to 50 mL. After ultrasonic oscillation for 30 min, filter the diluted slurry into a film. Place the obtained wet film on a hot stage at 60 °C and dry it for 2 h to obtain a dry film. Then place the dry film in a tubular furnace under a nitrogen atmosphere for heat treatment annealing to remove the dispersant at a temperature of 600 °C and hold for 2 hours. Place the annealed dry film on a hot press and hot press it at 200 MPa and 100 °C for 30 min to finally obtain a porous carbon film with a flat surface and self-supporting silver-containing seeds.

[0101] The structure of the porous carbon film is shown in Figure 2 . The porous carbon film includes a number of carbon fibers 103 that cross to form a three-dimensional network structure. The carbon fibers are fixed by physical anchoring 104. The pores 105 existing between the carbon fibers provide space for subsequent prelithiation treatment and can withstand a certain amount of elastic deformation. The thickness of the porous carbon film is 30 μm and the porosity is 63%.

[0102] This embodiment also provides a pole piece, the structure of which is shown in Figure 3 , including a lithium foil with a thickness of 20 μm and a porous carbon film 106 (the porous carbon film prepared by the above method of this embodiment) provided on one side of the lithium foil. A layer of stainless steel foil 109 is pasted on the other side of the lithium foil as a current collector. Roll it three times repeatedly on a roll press with the pressure set at 20 MPa. After full bonding, the lithium foil forms a first lithium foil 108 and a second lithium foil 107 that is rolled into the pores of the carbon film, increasing the bonding force to obtain a stable self-supporting three-dimensional lithium metal negative electrode. The charge-discharge curve of the self-supporting three-dimensional lithium negative electrode prepared by this method in a soft-pack battery cell is shown in Figure 4 .

[0103] Example 2

[0104] This embodiment provides a pole piece, which is basically the same as that in Example 1, except that: the thickness of the lithium foil in this embodiment is 10 μm.

[0105] Example 3

[0106] This embodiment provides a pole piece, which is basically the same as that in Example 1, except that: this embodiment does not contain lithium foil and stainless steel foil, and directly uses the porous carbon film prepared in Example 1 as the negative electrode.

[0107] Example 4

[0108] This embodiment provides a preparation method of porous carbon fibers, which is basically the same as that in Example 1, except that: when preparing the porous carbon fibers, the addition amount of the pore-forming agent polyvinylpyrrolidone is different; the addition amount of polyvinylpyrrolidone in this embodiment is 5 g.

[0109] In this embodiment, the pores in the porous carbon fiber matrix include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 10 nm, and macropores with a pore diameter of 50 < c ≤ 100 nm. The volume fraction of micropores is 50.3%, the volume fraction of mesopores is 34.9%, and the volume fraction of macropores is 14.8%. The diameter of the porous carbon fiber matrix is 800 - 1000 nm.

[0110] This embodiment also provides a porous carbon film with a thickness of 32 μm and a porosity of 58%. The preparation method is the same as that of Example 1.

[0111] This embodiment also provides a pole piece with the same preparation method as that of Example 1.

[0112] Example 5

[0113] This embodiment provides a method for preparing porous carbon fibers, which is basically the same as that of Example 1, except that the addition amounts of the lithiumophilic functional particle precursors are different. In this embodiment, 15 g of polyacrylonitrile powder, 10 g of polyvinylpyrrolidone, and 3 g of silver nitrate are used.

[0114] In this embodiment, the pores in the porous carbon fiber matrix include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 10 nm, and macropores with a pore diameter of 50 < c ≤ 100 nm. The volume fraction of micropores is 64.8%, the volume fraction of mesopores is 26.9%, and the volume fraction of macropores is 8.3%. The diameter of the porous carbon fiber matrix is 800 - 1000 nm.

[0115] This embodiment also provides a porous carbon film with a thickness of 29 μm and a porosity of 59%. The preparation method is the same as that of Example 1.

[0116] This embodiment also provides a pole piece with the same preparation method as that of Example 1.

[0117] Example 6

[0118] This embodiment provides a method for preparing porous carbon fibers, which is basically the same as that of Example 1, except that during the preparation of the porous carbon fibers, the carbonization temperature is different. The carbonization process in this embodiment includes heating to 1000 °C at a heating rate of 5 °C / min and holding for 2 h.

[0119] In this embodiment, the pores in the porous carbon fiber matrix include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 10 nm, and macropores with a pore diameter of 50 < c ≤ 100 nm. The volume fraction of micropores is 58.1%, the volume fraction of mesopores is 29.6%, and the volume fraction of macropores is 12.3%. The diameter of the porous carbon fiber matrix is 800 - 1000 nm.

[0120] This embodiment also provides a porous carbon film with a thickness of 30 μm and a porosity of 58%.

[0121] This embodiment also provides a pole piece, which is prepared in the same way as in Embodiment 1.

[0122] Embodiment 7

[0123] This embodiment provides a method for preparing porous carbon fibers, which is basically the same as that in Embodiment 1, except that the spinning solution is different. The spinning solution in this embodiment includes 15 g of polyacrylonitrile powder, 10 g of polyvinylpyrrolidone powder, 100 mL of dimethylformamide, and 5 g of calcium carbonate powder (particle size is 50 - 100 nm).

[0124] The porous carbon fibers in this embodiment include a porous carbon fiber matrix and a lithiumophilic functional particle calcium oxide. The surface and interior of the porous carbon fiber matrix have pores. The lithiumophilic functional particles are loaded or embedded on the surface of the porous carbon fiber matrix, and some pores are loaded and embedded with lithiumophilic functional particles. The pores include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 15 nm, and macropores with a pore diameter of 50 < c ≤ 120 nm. The volume ratio of the micropores is 43.9%, the volume ratio of the mesopores is 34.6%, and the volume ratio of the macropores is 21.5%. The diameter of the porous carbon fiber matrix is 600 - 800 nm.

[0125] This embodiment also provides a porous carbon film with a thickness of 34 μm and a porosity of 63%.

[0126] This embodiment also provides a pole piece, which is different from that in Embodiment 1 in that a PET film is used instead of a stainless steel copper foil.

[0127] Embodiment 8

[0128] This embodiment provides a pole piece, which is basically the same as that in Embodiment 7, except that: this embodiment does not contain a lithium foil and a PET film, and directly uses the porous carbon film prepared in Embodiment 7 as the negative electrode.

[0129] Embodiment 9

[0130] This embodiment provides a method for preparing porous carbon fibers, which is basically the same as that in Embodiment 1, except that the spinning solution is different. The spinning solution in this embodiment includes 15 g of polyacrylonitrile powder, 10 g of polyvinylpyrrolidone powder, 100 mL of dimethylformamide, and 5 g of nano-silicon powder (D50 is 100 nm).

[0131] The porous carbon fiber in this embodiment includes a porous carbon fiber matrix and a lithiumophilic functional particle, elemental silicon. The surface and interior of the porous carbon fiber matrix have pores. The lithiumophilic functional particles are loaded or embedded on the surface of the porous carbon fiber matrix, and some pores are loaded with and embedded with lithiumophilic functional particles. The pores include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 10 nm, and macropores with a pore diameter of 100 < c ≤ 150 nm. The volume ratio of the micropores is 73.2%, the volume ratio of the mesopores is 23.3%, and the volume ratio of the macropores is 3.5%. The diameter of the porous carbon fiber matrix is 600 - 900 nm.

[0132] This embodiment also provides a porous carbon film. The thickness of the porous carbon film is 35 μm, and the porosity is 53%. The preparation method is the same as that of Example 1.

[0133] This embodiment also provides an electrode sheet, which is different from that of Example 1 in that a PET film is used instead of a stainless steel copper foil.

[0134] Example 10

[0135] This embodiment provides an electrode sheet, which is basically the same as that of Example 9, except that: this embodiment does not contain a lithium foil and a PET film, and directly uses the porous carbon film prepared in Example 9 as the negative electrode.

[0136] Example 11

[0137] This embodiment provides a preparation method of porous carbon fiber, which is basically the same as that of Example 1, except that the spinning solution is different. The spinning solution in this embodiment includes 15 g of polyacrylonitrile powder, 10 g of polyvinylpyrrolidone powder, 100 mL of dimethylformamide, and 5 g of silicon nitride powder (D50 is 50 nm).

[0138] The porous carbon fiber in this embodiment includes a porous carbon fiber matrix and a lithiumophilic functional particle, silicon nitride. The surface and interior of the porous carbon fiber matrix have pores. The lithiumophilic functional particles are loaded or embedded on the surface of the porous carbon fiber matrix, and some pores are loaded with and embedded with lithiumophilic functional particles. The pores include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 10 nm, and macropores with a pore diameter of 50 < c ≤ 80 nm. The volume ratio of the micropores is 65.2%, the volume ratio of the mesopores is 21.7%, and the volume ratio of the macropores is 13.1%. The diameter of the porous carbon fiber matrix is 800 - 1000 nm.

[0139] This embodiment also provides a porous carbon film. The thickness of the porous carbon film is 25 μm, and the porosity is 75%.

[0140] This embodiment also provides an electrode sheet, which is different from that of Example 1 in that a PET film is used instead of a stainless steel copper foil.

[0141] Example 12

[0142] This embodiment provides a pole piece, which is basically the same as that of Embodiment 11, except that: this embodiment does not contain lithium foil and PET film, and directly uses the porous carbon film obtained in Embodiment 11 as the negative electrode.

[0143] Embodiment 13

[0144] This embodiment provides a method for preparing porous carbon fiber, which is basically the same as that of Embodiment 1, except that the spinning solution and carbonization are different. The spinning solution of this embodiment includes 15 g of water-soluble hydroxypropyl methylcellulose powder, 5 g of silver nitrate powder, 100 mL of water, and 10 g of sodium bicarbonate.

[0145] The carbonization process includes heating to 900 °C at a heating rate of 5 °C / min and holding at 900 °C for 2 h.

[0146] The porous carbon fiber of this embodiment includes a porous carbon fiber matrix and a lithium-philic functional particle silver. The surface and interior of the porous carbon fiber matrix have pores. The lithium-philic functional particles are loaded or embedded on the surface of the porous carbon fiber matrix, and some pores are loaded and embedded with lithium-philic functional particles. The pores include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 20 nm, and macropores with a pore diameter of 50 < c ≤ 200 nm. The volume ratio of the micropores is 44.3%, the volume ratio of the mesopores is 26.8%, the volume ratio of the macropores is 28.9%, and the diameter of the porous carbon fiber matrix is 600 - 1000 nm.

[0147] This embodiment also provides a porous carbon film. The thickness of the porous carbon film is 42 μm, and the porosity is 67%. The preparation method is the same as that of Embodiment 1.

[0148] This embodiment also provides a pole piece, which is different from that of Embodiment 1 in that PET film is used instead of stainless steel copper foil.

[0149] Embodiment 14

[0150] This embodiment provides a method for preparing porous carbon fiber, which is basically the same as that of Embodiment 13, except that the spinning solution is different. The spinning solution of this embodiment includes 15 g of water-soluble hydroxypropyl methylcellulose powder, 5 g of silver nitrate powder, 100 mL of water, and 5 g of sodium bicarbonate.

[0151] The porous carbon fiber of this embodiment includes a porous carbon fiber matrix and a lithium-philic functional particle. The surface and interior of the porous carbon fiber matrix have pores. The lithium-philic functional particles are loaded or embedded on the surface of the porous carbon fiber matrix. The pores include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 20 nm, and macropores with a pore diameter of 50 < c ≤ 200 nm. The volume ratio of the micropores is 41.3%, the volume ratio of the mesopores is 35.8%, and the volume ratio of the macropores is 22.9%.

[0152] This example also provides a porous carbon film and a pole piece, and their preparation methods are the same as those in Example 14. The thickness of the porous carbon film is 35 μm, and the porosity is 67%.

[0153] Example 15

[0154] This example provides a pole piece, which is basically the same as that in Example 13, except that: this example does not contain lithium foil and PET film, and directly uses the porous carbon film prepared in Example 13 as the negative electrode.

[0155] Example 16

[0156] This example provides a preparation method of porous carbon fiber, which is basically the same as that in Example 1, except that the spinning solution and carbonization are different. The spinning solution in this example includes 15 g of water-soluble hydroxypropyl methylcellulose powder, 5 g of zinc chloride powder, 100 mL of water, and 10 g of potassium carbonate.

[0157] The carbonization process includes heating to 900 °C at a heating rate of 5 °C / min and holding at 900 °C for 2 h.

[0158] The porous carbon fiber in this example includes a porous carbon fiber matrix and lithiumophilic functional particles of zinc chloride. The surface and interior of the porous carbon fiber matrix have pores, and the lithiumophilic functional particles are loaded or embedded on the surface of the porous carbon fiber matrix, and some pores are loaded and embedded with lithiumophilic functional particles. The pores include micropores with a pore diameter of 0.5 nm ≤ a < 2 nm, mesopores with a pore diameter of 2 ≤ b ≤ 10 nm, and macropores with a pore diameter of 50 < c ≤ 200 nm. The volume ratio of the micropores is 45.8%, the volume ratio of the mesopores is 28.6%, and the volume ratio of the macropores is 25.6%. The diameter of the porous carbon fiber matrix is 800 - 1000 nm.

[0159] This example also provides a porous carbon film. The thickness of the porous carbon film is 36 μm, the porosity is 69%, and the preparation method is the same as that in Example 1.

[0160] This example also provides a pole piece, which is different from that in Example 1 in that PET film is used instead of stainless steel copper foil.

[0161] Comparative Example 1

[0162] This comparative example provides a pole piece, which is basically the same as that in Example 1, except that: no pore-forming agent is added during the preparation of the porous carbon fiber, and the carbon fiber matrix in the obtained carbon film does not contain pores.

[0163] Comparative Example 2

[0164] This comparative example provides a pole piece, which is basically the same as that in Example 11, except that: no pore-forming agent is added during the preparation of the porous carbon fiber, and the carbon fiber matrix in the obtained carbon film does not contain pores.

[0165] Comparative Example 3

[0166] This comparative example provides a method for preparing carbon fiber, comprising the following steps:

[0167] (1) Mix 15 g of polyacrylonitrile and 75 ml of dimethylformamide to form a homogeneous solution, and perform electrospinning with the voltage set at 15 kV and the receiving distance set at 15 cm to obtain nanofiber precursor filaments. Then, take 5 g of polyvinylpyrrolidone powder, 5 g of silver nitrate powder and 100 ml of dimethylformamide, mix them to obtain a mixed solution, and spray the mixed solution onto the nanofiber precursor filaments by electrospraying. The electrospray voltage is set at 15 kV, the inlet temperature is 150 °C, the inlet pressure is 0.5 MPa, and the feeding rate is 5 mL / min to obtain polyacrylonitrile fiber precursor filaments with polyvinylpyrrolidone and silver nitrate particles on the surface.

[0168] (2) Place the staple fibers in a pre-oxidation furnace for the pre-oxidation process, heat in an air atmosphere at a heating rate of 2 °C / min, and hold at 200 °C for 2 h. After the pre-oxidized fibers are cooled, transfer them to a tube furnace under a nitrogen atmosphere and heat at a heating rate of 5 °C / min to 800 °C. After holding at 800 °C for 2 h, naturally cool to complete carbonization to obtain carbon fibers containing silver seeds. Prepare 200 mL of 0.5 mol / L dilute hydrochloric acid, place the carbonized porous carbon fibers in the dilute hydrochloric acid and stir well for 30 min. After the impurities on the surface of the carbon fibers are fully dissolved, filter off the dilute hydrochloric acid, repeatedly rinse and filter with pure water 3 times, and then place the washed carbon fibers containing silver seeds in a blast drying oven and dry for 24 hours to obtain carbon fibers containing silver seeds, with silver seeds distributed on the fiber surface; the carbon fibers prepared in this comparative example do not have pores.

[0169] This comparative example prepares a porous carbon film with porosity (the pores are formed by the intersection of carbon fibers) and a pole piece according to the method of Example 1.

[0170] Comparative Example 4

[0171] Add 15 g of polyacrylonitrile powder and 10 g of polyvinylpyrrolidone powder to 100 mL of dimethylformamide in sequence, and magnetically stir for 12 hours to form a homogeneous solution. Then add 5 g of silver nitrate powder (particle size 500 - 800 nm) to the solution and magnetically stir for 12 hours to obtain a mixed solution, followed by spray drying and carbonization to obtain a porous carbon material; among them, the electrospray voltage is set at 15 kV, the inlet temperature is 200 °C, the inlet pressure is 0.5 MPa, and the feeding rate is 0.1 mL / min; heat the obtained porous carbon at a heating rate of 5 °C / min to 800 °C, hold at 800 °C for 2 h, and then naturally cool to complete carbonization to obtain porous carbon particles containing silver seeds, which cannot be made into carbon fibers.

[0172] This comparative example prepared the porous carbon film and the electrode sheet according to the method of Example 1.

[0173] Test Example

[0174] In this test example, the electrode sheets provided in the examples and comparative examples were made into batteries to test the battery performance, specifically as follows:

[0175] Battery preparation method: The test batteries were all 1Ah soft-pack battery cells. The positive electrode was a high-nickel ternary positive electrode, and the negative electrode was the negative electrode of each example and comparative example of the present invention. They were assembled in a stacked manner, and the electrolyte was LiPSCl;

[0176] Test method for the first Coulomb efficiency: Charge at 0.1C to the cut-off voltage of 4.25V and then switch to constant voltage of 0.05C to stop, and record it as the charging capacity; then discharge at 0.1C to the cut-off voltage of 2.5V to stop, and record it as the discharge capacity. The first Coulomb efficiency = first discharge capacity / first charging capacity × 100%;

[0177] Test method for the average Coulomb efficiency: Cycle 100 times, calculate the Coulomb efficiency of each cycle, and then take the average value to obtain the average Coulomb efficiency.

[0178] Test method for the lithium intercalation expansion of the negative electrode: Charge at 0.1C to the cut-off voltage of 4.25V and then switch to constant voltage of 0.05C to stop to obtain a fully charged battery, and disassemble it; lithium intercalation expansion of the negative electrode = (thickness of the negative electrode sheet after full charge - thickness of the negative electrode sheet before battery assembly) / thickness of the negative electrode sheet before battery assembly × 100%.

[0179] Test method for the capacity retention rate of 0.33C / 0.33C cycle 100 times: Discharge capacity of the 100th cycle / discharge capacity of the first cycle × 100%.

[0180] Test method for the energy density: Battery capacity × average voltage / battery weight. The battery capacity is the discharge capacity of the first cycle; the average voltage is the average value of the voltage during the test of the discharge capacity.

[0181] Table 1 Performance test results

[0182]

[0183]

[0184] Figure 4 is the charge-discharge curve of the battery made in Example 1. From Figure 4 it can be seen that the battery has good capacity.

[0185] As can be seen from Table 1, the porous carbon fiber provided by the present invention comprises a porous carbon fiber matrix and lithiumophilic functional particles; the porous carbon fiber matrix has pores distributed on the surface and / or inside of the porous carbon fiber matrix; the lithiumophilic functional particles are distributed on the porous carbon fiber matrix in a manner of surface loading and / or embedding, and at least part of the pore surfaces are loaded with and / or embedded with lithiumophilic functional particles, which can alleviate the expansion of the lithium metal anode and the formation of lithium dendrites, reduce the situation of structural failure caused by the detachment of the lithiumophilic functional particles from the porous carbon fiber matrix, contribute to improving the stability, and improve the capacity, cycle performance, energy density and Coulomb efficiency of the battery.

[0186] From the above embodiments, using the self-supporting material porous carbon film provided by the present invention directly as the electrode can further improve the battery energy density and improve the volume expansion. The present invention further regulates the carbonization temperature to be lower than the melting point of the lithiumophilic functional particles, which can improve the battery expansion, energy density and cycle performance.

[0187] The above embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are within the protection scope of the present invention.

Claims

1. A porous carbon fiber, characterized in that, Comprising: A porous carbon fiber matrix and lithiophilic functional particles; the porous carbon fiber matrix has pores distributed on the surface and / or inside the porous carbon fiber matrix; the lithiophilic functional particles are distributed on the porous carbon fiber matrix in a surface-loading and / or embedded manner, and at least part of the surfaces of the pores are loaded and / or embedded with the lithiophilic functional particles; based on the total volume of the pores, the volume ratio of the pores with a pore diameter ≤ 50 nm in the pores is not less than 70%.

2. The porous carbon fiber according to claim 1, wherein The pores include micropores, and the micropores account for 30% - 90% of the volume of the pores; And / or, the pores further include mesopores and / or macropores.

3. The porous carbon fiber according to claim 2, wherein The pore diameter a of the micropores satisfies 0.5 nm ≤ a < 2 nm; And / or, the pore diameter b of the mesopores satisfies 2 nm ≤ b ≤ 30 nm; And / or, the pore diameter c of the macropores satisfies 50 nm < c ≤ 200 nm; And / or, the mesopores account for 0 - 50% of the volume of the pores; And / or, the macropores account for 0 - 30% of the volume of the pores.

4. The porous carbon fiber according to claim 1, characterized in that, The lithiophilic functional particles include at least one element of magnesium, aluminum, silicon, silver, zinc, tin, germanium, platinum, gold, bismuth, or at least one compound of its oxide, nitride, phosphide, sulfide, chloride; And / or, the diameter of the porous carbon fiber matrix is 50 nm - 5000 nm, preferably, the diameter of the porous carbon fiber matrix is 100 nm - 1000 nm; And / or, the porous carbon fiber matrix includes a carbon-based material.

5. A method for preparing porous carbon fiber, characterized in that, Including the following steps: (1) Mixing a carbon fiber precursor, a lithiophilic functional particle precursor, a pore-forming agent, and a solvent uniformly to obtain a spinning solution; (2) Obtaining a fiber precursor by electrospinning; (3) Pre-oxidizing and carbonizing the fiber precursor.

6. The preparation method according to claim 5, wherein The preparation method satisfies at least one of (1) - (8): (1) The mass ratio of the carbon fiber precursor, the lithiophilic functional particle precursor, and the pore-forming agent is (6 - 10):(0 - 4):(0 - 10), but not 0; (2) The carbon fiber precursor includes at least one of polyacrylonitrile, polyamide, cellulose, lignin, cellulose, chitosan, polyvinyl alcohol, polyimide; And / or, the particle size of the lithiophilic functional particle precursor is 1 nm - 1000 nm; And / or, the lithiophilic functional particle precursor includes at least one element of magnesium, aluminum, silicon, silver, zinc, tin, germanium, platinum, gold, bismuth, or at least one compound of its oxide, nitride, phosphide, sulfide, carbonate, nitrate, phosphate, chlorate, acetate; (3) The solid content of the spinning solution is 10 - 25 wt%; (4) The parameters of the electrospinning: the voltage is 10 - 20 kV, and the receiving distance is 8 - 20 cm; (5) The specific steps of the pre-oxidation include heating at a heating rate of 1 - 5 °C / min to 200 - 300 °C and holding for 2 - 3 h; (6) The specific steps of the carbonization include, under a protective atmosphere, heating at a heating rate of 2 - 10 °C / min to 600 - 1800 °C and holding for 1 - 5 h; Preferably, the protective atmosphere includes at least one of nitrogen, argon, neon, krypton; More preferably, the temperature of the carbonization is not higher than the melting point of the precursor of the lithiumophilic functional particles; (7) The pore former includes at least one of a gas-releasing pore former, a soluble-removable pore former, or a pyrolytic pore former; preferably, the gas-releasing pore former includes at least one of ammonium bicarbonate, ammonium carbonate, sodium carbonate, sodium bicarbonate, calcium bicarbonate, calcium carbonate, magnesium bicarbonate, magnesium carbonate, ammonium chloride, silver nitrate, zinc nitrate, and zinc carbonate; Preferably, the soluble-removable pore former includes at least one of potassium chloride, sodium chloride, potassium hydroxide, and sodium hydroxide; Preferably, the pyrolytic pore former includes polyvinylpyrrolidone; (8) After the carbonization, a pickling step is further included; Preferably, the pickling time is 10 - 30 min; More preferably, the pickling is carried out using at least one of hydrochloric acid solution, sulfuric acid solution, and acetic acid solution.

7. A porous carbon fiber material, characterized in that, Comprising the porous carbon fiber according to any one of claims 1 - 4 or the porous carbon fiber prepared by the preparation method according to any one of claims 5 - 6; Preferably, the porous carbon fiber material is a porous carbon fiber membrane, and the thickness of the porous carbon fiber membrane is 10 - 50 μm; Preferably, the porosity of the porous carbon fiber membrane is 50 - 90%; 8. A method for preparing the porous carbon fiber material according to claim 7, characterized in that, Comprising: Cutting the porous carbon fiber into short fibers; then mixing with a dispersant and a solvent to prepare a dispersion slurry; forming the dispersion slurry into a membrane material, and performing warm isostatic pressing; Preferably, the length of the short fibers is 3 - 10 mm; Preferably, the temperature of the warm isostatic pressing is 80 - 200 °C, the pressure is 100 - 600 MPa, and the time is 0.1 - 2 h.

9. A pole piece, characterized in that, Comprising the porous carbon fiber material according to claim 7 or the porous carbon fiber material prepared by the preparation method according to claim 8; 10. A battery, characterized in that, Comprising the electrode sheet according to claim 9.

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