Porous carbon fiber felt, its preparation method, and anode of potassium ion battery

Abstract

The present invention discloses a porous carbon fiber felt, a preparation method thereof, and a negative electrode for a potassium ion battery. The preparation method includes the following steps: S1. Dissolve a high molecular polymer, a magnesium salt, and a nitrogen-containing organic compound in a solvent, and obtain a precursor after stirring; S2. Prepare a nanofiber membrane from the precursor obtained in step S1 by electrospinning; S3. Perform pre-oxidation and calcination treatments on the nanofiber membrane obtained in step S2 to obtain a carbon fiber felt embedded with magnesium nitride; S4. Perform pickling, water washing, and drying on the carbon fiber felt embedded with magnesium nitride obtained in step S3 to obtain a porous carbon fiber felt. When the porous carbon fiber felt is used as the negative electrode for a potassium ion battery, it can promote the reaction kinetics of the battery and provide abundant active sites, thereby obtaining a potassium ion battery with high rate performance, long life, and high capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of potassium ion batteries, and in particular, to a porous carbon fiber felt, a preparation method thereof, and a negative electrode of a potassium ion battery. Background Art

[0002] At present, lithium ion batteries have been widely used in fields such as portable electronic devices and large-scale energy storage devices. Therefore, the demand for lithium shows a rapid growth trend year by year. However, the global reserves of lithium are very limited and unevenly distributed, resulting in a rapid increase in raw material prices, which seriously restricts the rapid development of the field of low-cost and high-performance energy storage devices in China. Potassium element has similar physical and chemical properties to lithium element, and has rich reserves, low cost, easy recovery, and a lower redox potential (-2.91V) compared with sodium (-2.71V), that is, it can have a higher output potential. Therefore, secondary battery systems based on potassium ions have received extensive attention. However, defects such as the large volume and slow kinetics of potassium ions themselves lead to poor rate performance, low specific capacity, and cycling stability of potassium ion batteries. Therefore, it is crucial to design and prepare electrode materials with good electrochemical performance.

[0003] Among many negative electrode materials for potassium ion batteries, carbon materials are still considered to be the most promising electrode materials for commercial potassium ion batteries because of their advantages such as good chemical stability, high conductivity, and environmental friendliness. However, current research on carbon materials shows that although carbon negative electrode materials can obtain a relatively high energy density (273 mA h·g -1 , theoretical value: 279 mAh·g -1 ), their cycling stability and rate performance are relatively poor. This is mainly because the large ionic radius of potassium ions causes the carbon electrode to experience multiple volume expansions / contractions during charge and discharge, resulting in structural collapse. Summary of the Invention

[0004] The present invention provides a porous carbon fiber felt, a preparation method thereof, and a negative electrode of a potassium ion battery to solve the technical problem that the structure of existing carbon materials is prone to collapse when used as negative electrode materials for potassium ion batteries, resulting in poor rate performance and cycling stability of potassium ion batteries.

[0005] According to one aspect of the present invention, a preparation method of a porous carbon fiber felt is provided, including the following steps:

[0006] S1. Dissolve polyacrylonitrile, magnesium salt, and nitrogen-containing organic matter in an N,N-dimethylformamide solvent, and obtain a precursor after stirring,

[0007] Among them, the mass percentage concentration of the polyacrylonitrile in the N,N-dimethylformamide solvent is 35-48%; the mass percentage concentration of the magnesium salt in the N,N-dimethylformamide solvent is 4-16%; the mass percentage concentration of the nitrogen-containing organic matter in the N,N-dimethylformamide solvent is 2-14%.

[0008] S2. Prepare a nanofiber membrane from the precursor obtained in step S1 by electrospinning.

[0009] S3. Subject the nanofiber membrane obtained in step S2 to pre-oxidation and calcination treatments to obtain a carbon fiber felt embedded with magnesium nitride.

[0010] S4. Subject the carbon fiber felt embedded with magnesium nitride obtained in step S3 to pickling, water washing and drying to obtain a porous carbon fiber felt.

[0011] Further, the magnesium salt in step S1 includes magnesium acetate, magnesium chloride, magnesium nitrate or magnesium gluconate.

[0012] Further, the nitrogen-containing organic matter in step S1 includes melamine, urea or biuret.

[0013] Further, the electrospinning conditions in step S2 are as follows: the working voltage is 10-20 kV, the collection distance is 8-20 cm, and the flow rate of the spinning liquid is 0.3-2.0 mL·h -1 .

[0014] Further, the pre-oxidation treatment in step S3 includes: heating from room temperature to 230-280 °C in air and holding for 1-6 h, wherein the heating rate is 1-5 °C·min -1 .

[0015] Further, the calcination treatment in step S3 includes: heating from room temperature to 900-1000 °C under the protection of a mixed gas of argon and hydrogen, holding for 3-6 h, wherein the volume fraction of hydrogen is 6-10%; the heating rate is 1-5 °C·min -1 .

[0016] Further, the pickling in step S4 includes pickling with hydrochloric acid or sulfuric acid for 1-5 h, wherein the mass concentration of hydrochloric acid or sulfuric acid is 5-15%.

[0017] According to another aspect of the present invention, there is also provided a porous carbon fiber felt prepared by the above method.

[0018] Further, the diameter of the carbon fibers in the porous carbon fiber felt is 220-260 nm, and the pore diameter is 20-30 nm.

[0019] In one aspect according to the present invention, a negative electrode for a potassium-ion battery is further provided, and the negative electrode for the potassium-ion battery includes the above-mentioned porous carbon fiber felt.

[0020] The present invention has the following beneficial effects:

[0021] The preparation method of the porous carbon fiber felt provided by the present invention first uses electrospinning technology to prepare a polyacrylonitrile composite fiber membrane with uniformly distributed magnesium salts and nitrogen-containing organic compounds; then the prepared composite fiber membrane is pre-oxidized; and then high-temperature calcination treatment is carried out to obtain carbon fibers with uniformly embedded magnesium nitride. In this process, polyacrylonitrile is carbonized into carbon fibers, and magnesium salts and nitrogen-containing organic compounds are in-situ formed into uniformly distributed magnesium nitride (Mg3N2) in the carbon fibers; finally, the carbon fibers with uniformly embedded magnesium nitride are subjected to dilute acid washing, water washing and drying to finally obtain the porous carbon fiber felt negative electrode material for a potassium-ion battery. In this process, magnesium nitride reacts with dilute acid to generate soluble magnesium salts and volatile ammonia gas, while the carbon skeleton remains unchanged, that is, a porous carbon fiber felt is obtained.

[0022] The carbon fiber diameter in the porous carbon fiber felt prepared in this application is 220-260 nm, the pore diameter is 20-30 nm, and the pore distribution is relatively uniform. When it is used as the negative electrode of a potassium-ion battery, it has the following advantages: (1) The complete one-dimensional fibrous structure of the porous fiber felt is beneficial to the rapid transfer of electrons / K + ions, promotes reaction kinetics, and provides guarantee for the battery to obtain high-rate performance; (2) The porous structure in the porous carbon fiber felt will help to maintain the structural integrity of the electrode during repeated cycling, and provide rich active sites, causing significant pseudocapacitance behavior, so as to obtain a potassium-ion battery with long life and high capacity; (3) The carbon fiber felt can be directly used as an electrode material without using a binder, thereby reducing the internal resistance of the battery and improving the capacity and rate performance of the battery; (4) The relatively uniform pores in the porous carbon fiber felt can guarantee the stability of the structure during cycling, thereby providing guarantee for the stability of the battery.

[0023] In addition to the purposes, features and advantages described above, the present invention has other purposes, features and advantages. The following will refer to the drawings to further describe the present invention in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0025] Figure 1 is the optical digital photo of the porous carbon fiber felt obtained in Example 1;

[0026] Figure 2 is the scanning electron microscope image of the porous carbon fiber felt obtained in Example 1;

[0027] Figure 3 It is the transmission electron microscope image of the porous carbon fiber felt obtained in Example 1;

[0028] Figure 4 It is the transmission electron microscope image of the porous carbon fiber felt obtained in Example 2;

[0029] Figure 5 It is the transmission electron microscope image of the porous carbon fiber felt obtained in Example 3;

[0030] Figure 6 It is the transmission electron microscope image of the carbon fiber felt obtained in Comparative Example 1;

[0031] Figure 7 It is the comparison chart of the potassium storage cycling performance of the porous carbon fiber felt obtained in Example 1 and the carbon fiber felt obtained in Comparative Example 1 as the potassium ion negative electrode at a current density of 0.1 A·g -1 When;

[0032] Figure 8 It is the potassium storage rate performance chart of the porous carbon fiber felt obtained in Example 1 and the carbon fiber felt obtained in Comparative Example 1 as the potassium ion negative electrode. Detailed implementation manners

[0033] In order to make the invention purpose, technical solution and beneficial technical effects of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the embodiments described in this specification are only for explaining the present invention and not for limiting the present invention.

[0034] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, although not explicitly recited, each point or single value between the range endpoints is included in this range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or combined with other lower or upper limits to form a range not explicitly recited.

[0035] In the description herein, it should be noted that unless otherwise specified, "above" and "below" include this number, the "multiple" in "one or more" means two or more, and the "multiple" in "one or more" means two or more.

[0036] The embodiments of the first aspect of the present application provide a preparation method of a porous carbon fiber felt, including the following steps:

[0037] S1. Dissolve polyacrylonitrile, magnesium salt and nitrogen-containing organic compound in N,N-dimethylformamide solvent, and obtain a precursor after stirring.

[0038] Among them, the mass percentage concentration of the polyacrylonitrile in the N,N-dimethylformamide solvent is 35-48%; the mass percentage concentration of the magnesium salt in the N,N-dimethylformamide solvent is 4-16%; the mass percentage concentration of the nitrogen-containing organic compound in the N,N-dimethylformamide solvent is 2-14%.

[0039] S2. Prepare a nanofiber membrane from the precursor obtained in step S1 by electrospinning.

[0040] S3. Perform pre-oxidation and calcination treatments on the nanofiber membrane obtained in step S2 to obtain a carbon fiber felt embedded with magnesium nitride.

[0041] S4. Perform pickling, water washing and drying on the carbon fiber felt embedded with magnesium nitride obtained in step S3 to obtain a porous carbon fiber felt.

[0042] The preparation method of the porous carbon fiber felt provided by the present invention first uses electrospinning technology to prepare a polymer composite fiber membrane with uniformly distributed magnesium salt and nitrogen-containing organic compound; then pre-oxidize the prepared composite fiber membrane; and then perform high-temperature calcination treatment to obtain carbon fibers with uniformly embedded magnesium nitride. In this process, the polymer is carbonized into carbon fibers, and the magnesium salt and nitrogen-containing organic compound generate uniformly distributed magnesium nitride (Mg3N2) in situ in the carbon fibers; finally, perform dilute pickling, water washing and drying on the carbon fibers with uniformly embedded magnesium nitride to finally obtain a porous carbon fiber felt as the anode material for potassium ion batteries. In this process, magnesium nitride reacts with dilute acid to generate soluble magnesium salt and volatile ammonia, while the carbon skeleton remains intact, thus obtaining a porous carbon fiber felt. The above method has low processing cost, simple and easy-to-control process, short cycle, high efficiency and energy saving, and is convenient for further large-scale production.

[0043] According to the embodiments of the present invention, the mass percentage concentration of the magnesium salt in the solvent is 4-16%; the mass percentage concentration of the nitrogen-containing organic compound in the solvent is 2-14%. The magnesium salt and nitrogen-containing organic compound are mainly used to generate magnesium nitride embedded in the carbon fibers. If the content is too high, too many magnesium nitride particles will precipitate on the surface of the carbon fibers, which will not contribute to the formation of a porous structure inside the carbon fibers in the subsequent process; if the content is too low, it is not conducive to the formation of a porous structure.

[0044] In the embodiments of the present invention, the magnesium salt in step S1 includes magnesium acetate, magnesium chloride, magnesium nitrate or magnesium gluconate.

[0045] In the embodiments of the present invention, the nitrogen-containing organic compound in step S1 includes melamine, urea or biuret.

[0046] In an embodiment of the present invention, the electrospinning conditions in step S2 are as follows: the working voltage is 10 - 20 kV, the collection distance is 8 - 20 cm, and the flow rate of the spinning liquid is 0.3 - 2.0 mL·h -1 The carbon fibers obtained from the working voltage, collection distance, and flow rate of the spinning liquid within this range are directly beneficial for obtaining better potassium storage performance. If the diameter is too large, it is not conducive to the transmission of K + and e - transmission, reducing the potassium storage kinetics. If the diameter is too small, it is not conducive to the flexibility of the electrode, and a complete carbon fiber felt cannot be obtained.

[0047] In an embodiment of the present invention, the pre-oxidation treatment in step S3 includes: heating from room temperature to 230 - 280 °C in air and holding for 1 - 6 h, where the heating rate is 1 - 5 °C·min -1 .

[0048] In an embodiment of the present invention, the calcination treatment in step S3 includes: heating from room temperature to 900 - 1000 °C under the protection of a mixed gas of argon and hydrogen, holding for 3 - 6 h, where the volume fraction of hydrogen is 6 - 10%; the heating rate is 1 - 5 °C·min -1 .

[0049] In an embodiment of the present invention, the pickling in step S4 includes pickling with hydrochloric acid or sulfuric acid for 1 - 5 h, where the mass concentration of hydrochloric acid or sulfuric acid is 5 - 15%.

[0050] In an embodiment of the present invention, during the drying process in step S4, the atmosphere is one of air, nitrogen, or argon, the temperature is 50 - 80 °C, and the drying time is 5 - 12 h.

[0051] An embodiment of the second aspect of the present application provides a porous carbon fiber felt prepared by the above method.

[0052] The diameter of the carbon fibers in the porous carbon fiber felt is 220 - 260 nm, and the pore diameter is 20 - 30 nm.

[0053] When it is made into the negative electrode of a potassium ion battery, it has the following advantages:

[0054] (1) The complete one-dimensional fibrous structure of the porous fiber felt is conducive to the rapid transmission of electrons / K + rapid transmission, promoting reaction kinetics, and providing guarantee for the battery to obtain high rate performance.

[0055] (2) The porous structure in the porous carbon fiber felt helps to maintain the structural integrity of the electrode during repeated cycling and provides abundant active sites, resulting in significant pseudocapacitive behavior, thus enabling a long-life and high-capacity potassium-ion battery. The pseudocapacitive behavior caused by ion adsorption on the electrode surface has been proven to bring good rate performance and cycling stability, mainly because the pseudocapacitive behavior does not damage the structure of the electrode material.

[0056] (3) The carbon fiber felt can be directly used as an electrode material without using a binder, thereby reducing the internal resistance of the battery and improving the capacity and rate performance of the battery.

[0057] (4) The relatively uniform pores in the porous carbon fiber felt can ensure the stability of the structure during cycling, thus providing guarantee for the stability of the battery.

[0058] An embodiment of the third aspect of the present application provides a negative electrode for a potassium-ion battery, which is made of the above-mentioned porous carbon fiber felt.

[0059] In the embodiment, the above-mentioned porous carbon fiber felt is assembled as the negative electrode into a potassium-ion battery. Under the condition of a current density of 0.1 A·g -1 , after 120 cycles, the charging specific capacity still remains above 270 mAh·g -1 , and the cycling stability is good.

[0060] Embodiment

[0061] The following embodiments more specifically describe the content disclosed in the present invention. These embodiments are only for illustrative purposes, because various modifications and variations within the scope of the present invention are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0062] Embodiment 1

[0063] S1. Weigh 7 g of polyacrylonitrile (PAN), 3 g of magnesium chloride, and 1.5 g of melamine and add them to 10 mL of N,N-dimethylformamide (DMF) solution. Stir at room temperature for 12 h to obtain a transparent precursor solution.

[0064] S2. Place the precursor solution in a spinning device, set the spinning voltage to 12 kV, the collection distance to 15 cm, and the solution flow rate to 0.4 mL·h -1 . After all the precursor solution is spun, a smooth composite fiber membrane is obtained.

[0065] S3. After drying the composite fiber membrane in a vacuum drying oven for 12 h, place it in a muffle furnace and heat it from room temperature to 230 °C for 1 h of pre-oxidation treatment at a heating rate of 1 °C·min -1 . Subsequently, place the composite fiber membrane in a tubular furnace, introduce an Ar / H2 mixed gas with 8% H2 content to provide protection, heat it from room temperature to 900 °C at a heating rate of 2 °C·min -1 , keep the temperature for 2 h, and naturally cool it to room temperature under the protective gas to obtain a carbon fiber felt embedded with magnesium nitride.

[0066] S4. Immerse the fiber felt in 10% hydrochloric acid, pickle it for 5 h, take it out and wash it with water until neutral, and dry it in an oven at 60 °C to obtain a porous carbon fiber felt.

[0067] Figure 1 is the optical digital photo of the obtained porous carbon fiber felt, from Figure 1 it can be seen that the carbon fiber felt prepared by Example 1 has a complete sheet structure and can be freely bent 180 degrees, indicating that the carbon fiber felt can be directly used as an electrode material.

[0068] Figure 2 is the scanning electron microscope image of the obtained porous carbon fiber felt, from Figure 2 it can be seen that the carbon fiber felt is composed of one-dimensional carbon fibers with a diameter of about 240 nm, and there are relatively large pores reserved between the fibers, which is beneficial to the transfer of electrons and the diffusion of potassium ions, and improves the reaction kinetics.

[0069] Figure 3 is the transmission electron microscope image of the obtained porous carbon fiber felt, from Figure 3 it can be seen that there are a large number of mesopores with a diameter of about 30 nm inside the carbon fibers, which can effectively alleviate problems such as structural collapse caused by volume change during charge and discharge, thereby improving the electrochemical performance.

[0070] After directly assembling the porous carbon fiber felt obtained in Example 1 into a potassium ion battery, under the condition of a current density of 0.1 A·g -1 , after 120 cycles, the charging specific capacity still remains at 276 mAh·g -1 (as shown in Figure 7 ), and when the current density rises to 2 A·g -1 , it still has a charging specific capacity of 188 mAh·g -1 (as shown in Figure 8 ).

[0071] Example 2

[0072] S1. Weigh 7 g of PAN, 3 g of magnesium nitrate, and 1.5 g of melamine respectively and add them to 10 mL of DMF solution, stir at room temperature for 12 h to obtain a transparent precursor solution.

[0073] S2. Place the precursor solution in a spinning device, set the spinning voltage to 12 kV, the collection distance to 15 cm, and the solution flow rate to 0.4 mL·h -1 . After all the precursor solution has been spun, a smooth composite fiber membrane is obtained.

[0074] S3. After drying the composite fiber membrane in a vacuum drying oven for 12 h, place it in a muffle furnace, heat it from room temperature to 230 °C for pre-oxidation treatment for 1 h, with a heating rate of 1 °C·min -1 . Subsequently, place the composite fiber membrane in a tube furnace, introduce an Ar / H2 mixed gas with 8% H2 content to provide protection, heat it from room temperature to 900 °C, with a heating rate of 2 °C·min -1 , keep the temperature for 2 h, and naturally cool it to room temperature under the protective gas to obtain a carbon fiber felt embedded with magnesium nitride.

[0075] S4. Immerse the fiber felt in 10% hydrochloric acid, carry out acid washing for 5 h, take it out and wash it with water until neutral, and dry it in an oven at 60 °C to obtain a porous carbon fiber felt.

[0076] Figure 4 is the transmission electron microscope image of the obtained porous carbon fiber felt. It can be seen from Figure 4 that there are a large number of mesopores with a diameter of about 30 nm inside the carbon fibers.

[0077] Example 3

[0078] S1. Weigh 7 g of PAN, 3 g of magnesium nitrate, and 2 g of urea respectively, add them to 10 mL of DMF solution, and stir at room temperature for 12 h to obtain a transparent precursor solution.

[0079] S2. Place the precursor solution in a spinning device, set the spinning voltage to 12 kV, the collection distance to 15 cm, and the solution flow rate to 0.4 mL·h -1 . After all the precursor solution has been spun, a smooth composite fiber membrane is obtained.

[0080] S3. After drying the composite fiber membrane in a vacuum drying oven for 12 h, place it in a muffle furnace, heat it from room temperature to 230 °C for pre-oxidation treatment for 1 h, with a heating rate of 1 °C·min -1 . Subsequently, place the composite fiber membrane in a tube furnace, introduce an Ar / H2 mixed gas with 8% H2 content to provide protection, heat it from room temperature to 900 °C, with a heating rate of 2 °C·min -1 , keep the temperature for 2 h, and naturally cool it to room temperature under the protective gas to obtain a carbon fiber felt embedded with magnesium nitride.

[0081] S4. Immerse the fiber felt in 10% hydrochloric acid, carry out acid washing for 5 h, take it out and wash it with water until neutral, and dry it in an oven at 60 °C to obtain a porous carbon fiber felt.

[0082] Figure 5 is the transmission electron microscope image of the obtained porous carbon fiber felt. It can be seen from Figure 5 that there are a certain amount of mesopores with a diameter of about 20 nm inside the carbon fibers.

[0083] Example 4

[0084] S1. Weigh 7 g of PAN, 3 g of magnesium nitrate, and 1.5 g of melamine respectively, add them into 10 mL of DMF solution, and stir at room temperature for 12 h to obtain a transparent precursor solution.

[0085] S2. Place the precursor solution in a spinning device, set the spinning voltage to 15 kV, the collection distance to 18 cm, and the solution flow rate to 0.6 mL·h -1 . After all the precursor solution has been spun, a smooth composite fiber membrane is obtained.

[0086] S3. After drying the composite fiber membrane in a vacuum drying oven for 12 h, place it in a muffle furnace, heat it from room temperature to 230 °C for pre-oxidation treatment for 1 h, and the heating rate is 1 °C·min -1 . Subsequently, place the composite fiber membrane in a tubular furnace, introduce an Ar / H2 mixed gas with 8% H2 content to provide protection, heat it from room temperature to 900 °C, the heating rate is 2 °C·min -1 , keep it at a constant temperature for 2 h, and naturally cool it to room temperature under the protective gas to obtain a carbon fiber felt embedded with magnesium nitride.

[0087] S4. Immerse the fiber felt in 10% hydrochloric acid, carry out acid washing for 5 h, take it out, wash it with water until neutral, and dry it in an oven at 60 °C to obtain a porous carbon fiber felt.

[0088] Example 5

[0089] S1. Weigh 7 g of PAN, 3 g of magnesium nitrate, and 1.5 g of melamine respectively, add them into 10 mL of DMF solution, and stir at room temperature for 12 h to obtain a transparent precursor solution.

[0090] S2. Place the precursor solution in a spinning device, set the spinning voltage to 12 kV, the collection distance to 15 cm, and the solution flow rate to 0.4 mL·h -1 . After all the precursor solution has been spun, a smooth composite fiber membrane is obtained.

[0091] S3. After drying the composite fiber membrane in a vacuum drying oven for 12 h, place it in a muffle furnace, heat it from room temperature to 260 °C for pre-oxidation treatment for 1 h, and the heating rate is 1 °C·min -1Subsequently, the composite fiber membrane was placed in a tubular furnace, and an Ar / H2 mixed gas with 8% H2 content was introduced to provide protection. It was heated from room temperature to 900 °C at a heating rate of 2 °C·min -1 , and held for 2 h, and then naturally cooled to room temperature under the protective gas to obtain a carbon fiber felt embedded with magnesium nitride.

[0092] S4. The fiber felt was immersed in 10% hydrochloric acid and pickled for 5 h, taken out, washed with water until neutral, and dried in an oven at 60 °C to obtain a porous carbon fiber felt.

[0093] Example 6

[0094] S1. 7 g of PAN, 3 g of magnesium nitrate, and 1.5 g of melamine were weighed and added to 10 mL of DMF solution, and stirred at room temperature for 12 h to obtain a transparent precursor solution.

[0095] S2. The precursor solution was placed in a spinning device, the spinning voltage was set to 12 kV, the collection distance was 15 cm, and the solution flow rate was 0.4 mL·h -1 . After all the precursor solution was spun, a smooth composite fiber membrane was obtained.

[0096] S3. After drying the composite fiber membrane in a vacuum drying oven for 12 h, it was placed in a muffle furnace and heated from room temperature to 230 °C for pre-oxidation treatment for 1 h at a heating rate of 1 °C·min -1 . Subsequently, the composite fiber membrane was placed in a tubular furnace, and an Ar / H2 mixed gas with 6% H2 content was introduced to provide protection. It was heated from room temperature to 1000 °C at a heating rate of 2 °C·min -1 , and held for 2 h, and then naturally cooled to room temperature under the protective gas to obtain a carbon fiber felt embedded with magnesium nitride.

[0097] S4. The fiber felt was immersed in 10% hydrochloric acid and pickled for 5 h, taken out, washed with water until neutral, and dried in an oven at 60 °C to obtain a porous carbon fiber felt.

[0098] Comparative Example 1

[0099] S1. 7 g of PAN was weighed and added to 10 mL of DMF solution, and stirred at room temperature for 12 h to obtain a transparent precursor solution.

[0100] All other steps were the same as in Example 1 to obtain a carbon fiber felt.

[0101] Figure 6 is the transmission electron microscope image of the obtained carbon fiber felt. It can be seen from Figure 6 that when no magnesium salt and nitrogen-containing organic matter were added to the precursor, the obtained carbon fiber was solid inside, which was not conducive to obtaining a potassium ion battery with a high specific capacity.

[0102] After directly assembling the carbon fiber felt obtained in Comparative Example 1 into a potassium-ion battery, at a current density of 0.1 A·g -1 , after 120 cycles, the charge specific capacity was only 155 mAh·g -1 (as shown in Figure 7 ), and when the current density was increased to 2 A·g -1 , its charge specific capacity was only 89 mAh·g -1 (as shown in Figure 8 ).

[0103] Although the present invention has been described with reference to the preferred embodiments, various modifications can be made thereto and components thereof can be replaced with equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any manner. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A preparation method of a porous carbon fiber felt for the negative electrode of a potassium ion battery, characterized in that, It includes the following steps: S1. Dissolve polyacrylonitrile, magnesium salt and nitrogen-containing organic matter in N,N-dimethylformamide solvent, and obtain a precursor after stirring. Among them, the mass percentage concentration of the polyacrylonitrile in the N,N-dimethylformamide solvent is 35-48%; the mass percentage concentration of the magnesium salt in the N,N-dimethylformamide solvent is 4-16%; the mass percentage concentration of the nitrogen-containing organic matter in the N,N-dimethylformamide solvent is 2-14%; the nitrogen-containing organic matter includes melamine, urea or biuret. S2. Prepare a nanofiber membrane from the precursor obtained in step S1 by electrospinning. S3. Perform pre-oxidation and calcination treatments on the nanofiber membrane obtained in step S2 to obtain a carbon fiber felt embedded with magnesium nitride. S4. Perform pickling, water washing and drying on the carbon fiber felt embedded with magnesium nitride obtained in step S3 to obtain a porous carbon fiber felt.

2. The preparation method of the porous carbon fiber felt for the negative electrode of a potassium ion battery according to claim 1, wherein, The magnesium salt described in step S1 includes magnesium acetate, magnesium chloride, magnesium nitrate or magnesium gluconate.

3. The preparation method of the porous carbon fiber felt for the negative electrode of a potassium ion battery according to claim 1, characterized in that, The electrospinning conditions described in step S2 are as follows: the working voltage is 10 - 20 kV, the collection distance is 8 - 20 cm, and the flow rate of the spinning liquid is 0.3 - 2.0 mL·h -1 .

4. The preparation method of the porous carbon fiber felt for the negative electrode of a potassium ion battery according to claim 1, characterized in that The pre-oxidation treatment described in step S3 includes: heating from room temperature to 230-280 °C in air and holding for 1-6 h, where the heating rate is 1-5 °C·min -1 .

5. The preparation method of the porous carbon fiber felt for the negative electrode of a potassium ion battery according to claim 1, characterized in that, The calcination treatment described in step S3 includes: heating from room temperature to 900 - 1000 °C under the protection of a mixed gas of argon and hydrogen, holding for 3 - 6 h, where the volume fraction of hydrogen is 6 - 10%; the heating rate is 1 - 5 °C·min -1 .

6. The preparation method of the porous carbon fiber felt for the negative electrode of a potassium ion battery according to claim 1, wherein, The pickling described in step S4 includes pickling with hydrochloric acid or sulfuric acid for 1-5 h, where the mass concentration of the hydrochloric acid or sulfuric acid is 5-15%.

7. A porous carbon fiber felt prepared by the preparation method according to any one of claims 1-6.

8. The porous carbon fiber felt according to claim 7, wherein The diameter of the carbon fibers in the porous carbon fiber felt is 220-260 nm, and the pore diameter is 20-30 nm.

9. A negative electrode of a potassium ion battery, characterized in that, The negative electrode of the potassium ion battery includes the porous carbon fiber felt according to claim 7 or 8.

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