Preparation system, method of a hard carbon anode material for a battery and a sodium ion battery

Abstract

The present invention relates to the technical field of sodium-ion battery, and particularly relates to a preparation system, a method for a battery hard carbon negative electrode material and a sodium-ion battery, including a kapok fiber pretreatment module, a kapok fiber precursor preparation module and a hard carbon material preparation module. The kapok fiber pretreatment module is used for treating the outer surface of the kapok fiber and obtaining a solid kapok fiber with a smooth and dry surface. The kapok fiber precursor preparation module is used for crosslinking and modifying the solid kapok fiber obtained by the kapok fiber pretreatment module and obtaining a kapok fiber precursor. The hard carbon material preparation module is used for performing high-temperature carbonization treatment on the kapok fiber precursor to obtain a nitrogen-containing hard carbon material, which is efficient and conducive to high-quality production.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly to a preparation system, a preparation method of a battery hard carbon negative electrode material, and a sodium-ion battery. Background Art

[0002] With the fluctuation of lithium ore prices and resource limitations, the development of new energy storage systems has become the focus. Currently, sodium-ion technology has attracted much attention due to its cost-effectiveness and superior performance. Since sodium ions are larger in size, the negative electrode materials used in sodium-ion batteries require higher requirements. At the same time, the graphite negative electrode used in lithium-ion batteries is not compatible with sodium-ion batteries. Therefore, non-graphitizable hard carbon materials have unique structural features such as large interlayer spacing and short-range order, making them suitable for adsorbing sodium ions and serving as the main negative electrode material.

[0003] The precursors of hard carbon have an oxygen-rich characteristic, and conventional materials are plant-based materials, organic polymers, resins, etc. Among them, the performance of resins and organic compounds is superior to that of biological materials. However, considering cost and sustainability, plant-based materials such as cotton, grass, and leaves are more suitable as precursors for sodium-ion battery-derived carbon negative electrodes. The problem is that for plant-based precursors, the rate performance of the hard carbon materials prepared by pure carbonization is poor, especially at high current densities. In this regard, a large amount of work has focused on improving the rate performance through heteroatom doping, such as doping with nitrogen N, sulfur, and phosphorus P. Among them, N is the most involved heteroatom because doping N at the O site introduces oxygen vacancies, which can increase the "electron-hole" concentration, enhance the conductivity of the hard carbon material, and promote the migration of sodium ions, thus leading to an improvement in its rate performance. The main problem is that the N element inevitably escapes in gaseous form during the high-temperature pyrolysis process, and its functional groups cannot be adjusted during the pyrolysis process. It is not only necessary to increase the content of N after carbonization, but also necessary to optimize the existing form of N after doping to improve the electrochemical performance of biomass material-derived hard carbon negative electrode materials at high rates.

[0004] Of course, there are also many existing patent technologies for battery hard carbon materials. For example, a preparation method of an in-situ oxidation-grown flower-shaped hard carbon sodium-ion battery negative electrode disclosed in a Chinese patent with the application number 202110612080.6: 1. Under an air atmosphere, popcorn is heated to 230 - 280 °C for pre-oxidation treatment; 2. The pre-oxidized popcorn is placed in an atmosphere furnace and carbonized at 800 - 1400 °C for 2 - 3 h to obtain popcorn hard carbon; 3. The popcorn hard carbon is ground and sieved to obtain hard carbon powder with a particle size less than 48 μm; 4. The sieved hard carbon powder is mixed with multi-layer MXene and ball-milled with water as a solvent. Under the action of the huge energy generated by the collision of the ball milling beads, the multi-layer MXene is peeled off and reacts with air to in-situ oxidize to generate TiO2 nanorods, thus forming a flower-shaped TiO2 / MXene / hard carbon composite material.

[0005] As disclosed in a Chinese patent with the application number 202211223124.7, a hard carbon sodium-ion battery anode material derived from reed, its preparation method, and an energy storage battery. In the present invention, the preparation of the hard carbon anode material derived from reed is achieved through a phosphoric acid pyrolysis method. The preparation method mainly includes the following steps: First, wash the dried reed, and after drying, crushing, and sieving, perform concentrated phosphoric acid acid leaching on the material, then heat the material to cause a pyrolysis reaction, and finally obtain a P2O5 composite nitrogen-doped porous hard carbon anode material after crushing and sieving.

[0006] As disclosed in a Chinese patent with the application number 201010203768.0, a composite hard carbon anode material for a lithium-ion battery, with a coating on the hard carbon matrix. The precursor of the hard carbon matrix includes a thermoplastic resin, which pyrolyzes to form the hard carbon matrix, and the precursor of the coating is an organic substance. Its preparation method includes: curing, pyrolysis, crushing, and coating.

[0007] As disclosed in a Chinese patent with the application number 202111627150.1, a preparation method for a hard carbon material precursor, which includes the following steps: In a halogenated hydrocarbon, under the action of a Lewis acid catalyst, perform a Friedel-Crafts alkylation reaction on a high-molecular organic substance of an aryl-containing hard carbon material raw material.

[0008] As disclosed in a Chinese patent with the application number 202410453573.3, a preparation method and application of hard carbon using cotton and linen biomass as raw materials. Use cotton and linen as biomass raw materials, crush and grind the cotton-like carbonized product obtained by primary carbonization of cotton and linen to obtain a carbonized powder precursor, and wash the carbonized powder precursor. Alkali washing can be used to remove impurities such as tar, quinone, and anthracene generated during the first calcination. After washing, perform high-temperature secondary calcination to obtain hard carbon.

[0009] In the above-mentioned patented technologies, in the production and processing of hard carbon precursors, it is difficult to achieve batch processing, the cost is relatively high, and the treatment effect on hard carbon precursor materials is not uniform and thorough enough. This will result in the quality of the final hard carbon materials and batteries not being excellent enough, the performance of the batteries still needing to be improved, and there will also be deficiencies in terms of energy conservation and environmental protection, making them not green and low-carbon enough. Therefore, better improvement schemes are needed for battery preparation and the batteries themselves to better meet the social demand for green and low-carbon. Summary of the Invention

[0010] The object of the present invention is to provide a preparation system, method, and sodium-ion battery for a battery hard carbon anode material that is efficient and conducive to high-quality production.

[0011] The above object of the present invention is achieved by the following technical solutions: A preparation system for a battery hard carbon negative electrode material, including a kapok fiber pretreatment module, a kapok fiber precursor preparation module, and a hard carbon material preparation module. The kapok fiber pretreatment module is used to treat the outer surface of kapok fibers and obtain solid kapok fibers with a smooth and dry surface. The kapok fiber precursor preparation module is used to crosslink and modify the solid kapok fibers obtained by the kapok fiber pretreatment module to obtain kapok fiber precursors. The hard carbon material preparation module is used to perform high-temperature carbonization treatment on the kapok fiber precursors to obtain a nitrogen-containing hard carbon material.

[0012] As a preference of the present invention, the kapok fiber pretreatment module includes an alkalizing agent treatment device including a kapok fiber surface treatment immersion tank for placing kapok fibers. The kapok fiber surface treatment immersion tank is also used to inject an alkalizing solution of sodium hypochlorite and ionized water. A traction cable that can move up and down and make the solution wave is arranged in the kapok fiber surface treatment immersion tank. The traction cable includes a transparent flexible plastic sleeve. A micro camera is arranged in the kapok fiber surface treatment immersion tank. The kapok fiber pretreatment module further includes a processor located outside the kapok fiber surface treatment immersion tank and capable of communicating with the micro camera.

[0013] As a preference of the present invention, the micro camera is built into the flexible plastic sleeve, and ultrasonic transducers are arranged at intervals around the kapok fiber surface treatment immersion tank.

[0014] As a preference of the present invention, the kapok fiber surface treatment immersion tank is in a ring shape or a circular shape. A wave amplitude limiting structure for limiting the up and down movement of the traction cable is arranged in the kapok fiber surface treatment immersion tank. The wave amplitude limiting structure includes a transparent limiting tube installed and connected to the side wall of the kapok fiber surface treatment immersion tank. At least one of the limiting tubes also has a micro camera arranged therein. At least two of the limiting tubes are used as liquid replenishing tubes.

[0015] As a preference of the present invention, a detachable upper filter screen for preventing the upward movement of kapok fibers and a lower filter screen for preventing the downward movement of kapok fibers are arranged in the kapok fiber surface treatment immersion tank. A bottom liquid outlet is arranged at the bottom of the kapok fiber surface treatment immersion tank below the lower filter screen. Both the upper filter screen and the lower filter screen are not less than 800 mesh.

[0016] As a preference of the present invention, the kapok fiber surface treatment immersion tank can also be used to inject a cleaning solution of ionized water and ethanol. The cleaning solution is used to clean the alkalized kapok fibers to obtain clean solid kapok fibers. The kapok fiber pretreatment module further includes a drying device, and the drying device is used to dry the clean solid kapok fibers to obtain the final solid kapok fibers with a smooth and dry surface.

[0017] A preparation method of a hard carbon anode material for a battery, using the aforementioned preparation system for a hard carbon anode material for a battery, includes Step 1: pretreatment of kapok fibers, specifically including Step 1.1, dissolving sodium hypochlorite in ionized water to obtain an alkalization solution; Step 1.2, soaking the kapok fibers in the alkalization solution for at least 4 hours; Step 1.3, washing the kapok fibers soaked and alkalized in Step 1.2 with ionized water and ethanol to obtain clean solid kapok fibers; Step 1.4, drying the clean solid kapok fibers in Step 1.3 to obtain finally smooth and dry solid kapok fibers. Step 2: preparation of a kapok fiber precursor, specifically including Step 2.1, dissolving a pyrolysis auxiliary and a nitrogen source in ionized water for a pre-crosslinking reaction to obtain a crosslinking agent solution; Step 2.2, soaking the solid kapok fibers obtained in Step 1.4 in the crosslinking agent solution obtained in Step 2.1 for at least 12 hours to obtain modified kapok fibers modified by the crosslinking agent; Step 2.3, washing the modified kapok fibers in Step 2.2 with ionized water and absolute ethanol; Step 2.4, drying the modified kapok fibers washed in Step 2.3 to obtain a kapok fiber precursor. Step 3: preparation of a hard carbon material, specifically, subjecting the kapok fiber precursor obtained in Step 2.4 to a high-temperature carbonization process to obtain a hard carbon material.

[0018] As a preference of the present invention, the pyrolysis auxiliary ligand is a zinc-containing compound, including one or more of zinc gluconate, zinc oxide, zinc chloride, zinc nitrate, and zinc carbonate; the nitrogen source is one or more of 2,6-pyridinedicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, 2-methyl-6-pyridinedicarboxylic acid, o-nitrobenzoic acid, m-nitrobenzoic acid, and p-nitrobenzoic acid.

[0019] As a preference of the present invention, in Step 1.2 of Step 1, soaking the kapok fibers in the alkalization solution is carried out in a surface treatment soaking pool for kapok fibers. The internal solution and the kapok fibers follow a circulating flow caused by the undulation of a traction cable. The part of the traction cable in the surface treatment soaking pool for kapok fibers is in a C shape. And during the undulation of the internal solution and the kapok fibers, uniform alkalization is carried out through an image analysis feedback process. The image analysis feedback process specifically includes the following steps: a. acquisition of kapok fiber images; b. preprocessing of kapok fiber images; c. extraction of kapok fiber contours; d. extraction and analysis of kapok fiber features; e. uniform distribution algorithm for kapok fibers; f. feedback and adjustment, where the adjustment step in Step f includes replenishing the solution or adding kapok fibers.

[0020] A sodium-ion battery includes a hard carbon anode material, and the hard carbon anode material is prepared by the aforementioned preparation method of a hard carbon anode material for a battery.

[0021] The beneficial effects of the present invention are as follows: the preparation system can carry out alkalization and cleaning of batches of kapok fibers, with low cost, high efficiency, low carbon and environmental protection; the surface treatment of the kapok fibers is more uniform and the treatment effect is better, which is beneficial to the subsequent cross-linking modification, so that the quality and uniformity of the hard carbon material are improved, which is beneficial to the production of high-quality batteries, the battery performance will be more stable and the service life will be long, and it is green and low-carbon.

[0022] Moreover, in the preparation method, kapok fiber is used as the biomass raw material, combined with 2,6-pyridinedicarboxylic acid as a nitrogen source and zinc chloride as a pyrolysis auxiliary ligand to prepare a high-efficiency hard carbon negative electrode material for sodium ion batteries. The preparation process is relatively environmentally friendly, the raw materials are sufficient, and the increase in the nitrogen content of graphite can effectively improve its first coulombic efficiency and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of the three-dimensional structure of the preparation system of Example 1;

[0024] Figure 2 for Figure 1 Schematic diagram of the three-dimensional structure after the middle structure is optimized and cut open on the side of the immersion pool;

[0025] Figure 3 This is a performance comparison chart of batteries made from the hard carbon materials of the four experimental examples in Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0027] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

[0028] Embodiment 1, as Figure 1 , 2As shown in the figure, a preparation system for a hard carbon anode material of a battery includes a kapok fiber pretreatment module, a kapok fiber precursor preparation module, and a hard carbon material preparation module. The kapok fiber pretreatment module is used to treat the outer surface of kapok fibers and obtain solid kapok fibers with a smooth and dry surface. The kapok fiber precursor preparation module is used to crosslink and modify the solid kapok fibers obtained by the kapok fiber pretreatment module and obtain kapok fiber precursors. The hard carbon material preparation module is used to perform high-temperature carbonization treatment on the kapok fiber precursors to obtain nitrogen-containing hard carbon materials. The design scheme of this embodiment realizes the preparation of hard carbon materials by designing the above-mentioned three major modules. The main idea is to treat the surface of kapok fibers, remove wax, make the surface smooth and expose the active ingredients, and enable the kapok fibers to be better crosslinked and modified, so as to obtain better-quality kapok fiber precursors and produce high-quality hard carbon materials. This is the design idea of the overall preparation system. Under this idea, batch and high-quality production can be better carried out. The specific implementation scheme is as follows: The kapok fiber pretreatment module includes an alkalizing agent treatment device, which includes a kapok fiber surface treatment immersion tank 1 for placing kapok fibers. The kapok fiber surface treatment immersion tank 1 is also used to inject an alkalizing solution of sodium hypochlorite and ionized water. It can be seen that the kapok fiber surface treatment immersion tank 1 soaks kapok fibers with the alkalizing solution to achieve the surface treatment of kapok fibers and effectively remove the surface wax of kapok fibers. And a traction cable 11 that can move up and down and make the solution wave is arranged in the kapok fiber surface treatment immersion tank 1. The traction cable 11 includes a transparent flexible plastic sleeve 111. The flexible plastic sleeve 111 is mainly the part that can undulate in the solution, which will also be mentioned later. It is generally set to extend in a C shape. And both ends of the flexible plastic sleeve 111 can be connected to lead-out sections. The lead-out sections are relatively rigid, which is convenient for lifting and pulling the ends of the flexible plastic sleeve 111. Similar to the structure of a fitness rope in a gym, the traction cable 11 allows the internal part to form a forward surge along the sine undulation of the traction cable 11, which can better remove the surface wax and has a better surface treatment effect. The undulation of the traction cable 11 can be achieved by the up-and-down swing of one end. One end of the traction cable 11 can be connected to an existing lifting device and then lifted and lowered as long as the up-and-down swing can be achieved. Further, a micro camera 112 is arranged in the kapok fiber surface treatment immersion tank 1. The kapok fiber pretreatment module further includes a processor 113 located outside the kapok fiber surface treatment immersion tank 1 and capable of communicating with the micro camera 112. Both the micro camera 112 and the processor 113 can adopt existing devices and can communicate wirelessly or wired between them. The main purpose is to photograph the distribution and surface morphology of the kapok fibers in the kapok fiber surface treatment immersion tank 1 by the micro camera 112 and feedback it to the processor. Then the processor makes further instructions through effective identification and analysis to optimize the process conditions and continuously optimize the surface treatment process of kapok fibers.

[0029] Preferably, the micro camera 112 is built into the flexible plastic sleeve 111. Ultrasonic transducers 114 are arranged at intervals around the periphery of the kapok fiber surface treatment immersion tank 1. The flexible plastic sleeve 111 can also be understood as the outer structure of some existing cables, with better flexibility as much as possible to facilitate undulation to cause orderly waves in the tank. Of course, when both ends of the flexible plastic sleeve 111 are open, the open ends are not immersed in the tank. If the ends are closed, it can also be put into the tank. The micro camera 112 can be adhered to the flexible plastic sleeve 111, or can be embedded in an existing flexible block material and then snapped into the flexible plastic sleeve 111 together, or introduced into the flexible plastic sleeve 111 through a rope, and implanted into the flexible plastic sleeve 111 by using an existing installation method. Multiple micro cameras 112 can be used and arranged at intervals in the flexible plastic sleeve 111 for shooting at multiple positions. The micro camera 112 can be a wired or wireless camera, both of which are feasible. The flexible plastic sleeve 111 itself has the function of protecting the internal structure. The ultrasonic transducer 114 can further assist in the alkalization cleaning operation. For example, when the kapok fiber in a certain area of the tank is relatively too dense, the ultrasonic transducer 114 needs to be appropriately turned on to strengthen the vibration of the solution, so that the distribution of the kapok fiber in the whole tank is relatively more uniform, which is beneficial to the alkalization effect.

[0030] Furthermore, the kapok fiber surface treatment immersion tank 1 is in a ring shape or a circular shape. This shape is conducive to the circular circulation movement of the solution, and it can maintain the moving state for a long time without stopping. In addition, a wave amplitude limiting structure for limiting the up-and-down undulating movement of the traction cable 11 is provided inside the kapok fiber surface treatment immersion tank 1. Because the amplitude of this surge needs to be controlled, otherwise, an excessive distance may cause damage to the fibers. It is preferably gentle, generally controlled at two up-and-down swings back and forth per second, that is, a wave swing with a frequency within 2 Hz. Of course, it can be adjusted according to the actual situation. Specifically, the wave amplitude limiting structure includes a transparent limiting tube 10 installed and connected to the side wall of the kapok fiber surface treatment immersion tank 1. At least one micro camera 112 is also provided inside at least one of the limiting tubes 10. At least two of the limiting tubes 10 are used as liquid supplement tubes. If the kapok fiber surface treatment immersion tank 1 is made of plastic or glass, the limiting tube 10 can be integrally connected to the side wall of the kapok fiber surface treatment immersion tank 1. If different materials are used, the limiting tube 10 can be installed through existing installation methods. The limiting tube 10 is preferably made of plastic or glass. And if the kapok fiber surface treatment immersion tank 1 is in a ring shape, the limiting tube 10 can be in a straight line type and needs to be arranged at intervals up and down. The axis of the limiting tube 10 is horizontal and in a flat state, and multiple limiting tubes 10 are required on both the upper and lower sides and are arranged in a circular array. In this way, the part of the traction cable 11 in the tank also forms an approximately circular C-shaped structure, so that the wave is a circular circulation pattern, and the solution makes a circular circulating wave movement. If the kapok fiber surface treatment immersion tank 1 is just a circular pool, the limiting tube 10 is preferably two connected pipe segments. One is a circular pipe segment for the traction cable 11 to enter and be limited in all directions of up, down, left, and right, and the other is a straight line segment connected to the circular pipe segment, and this straight line segment is used to be installed on the side wall of the kapok fiber surface treatment immersion tank 1. The limiting tube 10 is stationary. The micro camera 112 in the limiting tube 10 can be mainly used to observe the overall internal situation of the pool and the situation of the traction cable 11, and monitor in real time to ensure the smooth and safe production, etc. And the limiting tube 10 can also be used as a liquid supplement tube. The limiting tube 10 can be connected to the pipeline of the external alkalized solution or the storage container of the alkalized solution such as a storage tank. Of course, in this case, the limiting tube 10 needs to be provided with liquid outlet holes and corresponding electromagnetic valves, that is, inject the alkalized solution for supplementing and optimizing the distribution of the internal kapok fibers when needed. Of course, the alkalized solution can also be injected through the limiting tube 10 at the beginning, but for the injection efficiency, generally a larger liquid inlet pipe placed in the pool is used to inject the alkalized solution.The usage method of the surface treatment immersion tank 1 for kapok fibers is generally as follows: First, a batch of kapok fibers is put in, which can be done manually or by machine. Then, an alkalization solution is added to the required amount, and then the immersion process begins. The immersion can be static, but preferably with waves, that is, the traction cable 11 swings up and down to cause waves for alkalization to remove the wax on the surface of kapok fibers. During this process, a camera observes the internal situation, and an ultrasonic transducer or a liquid supply pipe is used to optimize the distribution of the internal solution and kapok fibers. When the alkalization is completed, the next process is carried out, that is, the alkalized kapok fibers need to be washed.

[0031] Furthermore, the kapok fiber surface treatment soaking pool 1 is provided with a detachable upper filter 21 for preventing the kapok fibers from moving upward and a lower filter 22 for preventing the kapok fibers from moving downward. The upper filter 21 and the lower filter 22 particularly need to be easy to disassemble and assemble. Some step portions and the like for placing and positioning the filter can be fixed or integrally formed on the inner wall of the kapok fiber surface treatment soaking pool 1. The filter can be assembled to these step portions by means of snaps or slots. This detachable structure can adopt the existing detachable filter structure. If it is a heavier ceramic or metal filter, it can be directly placed on the step portion, which is more convenient for taking and placing. Alternatively, some magnetic bodies are fixed on the side walls of the soaking pool, and corresponding magnetic bodies are arranged around the filter, which are attracted and placed by magnetic force. A little force is required when removing it. It is mainly for the convenience of disassembly, replacement and maintenance. Such a structure can make the kapok fibers be located between the upper filter 21 and the lower filter 22. Of course, the upper filter 21 in particular needs to be opened frequently to put in the kapok fibers, and the swinging parts of the limit tube 10 and the traction cable 11 should also be located between the upper filter 21 and the lower filter 22. The upper filter screen 21 allows the wax on the surface of the alkalized kapok fiber to move upward to the upper side of the upper filter screen 21, so that the wax can be filtered out. In this way, the wax at the top can be removed in time by forming an overflow through the replenishing solution, or part of the solution with wax on the surface can be removed manually or mechanically. Since the wax needs to be filtered here, the upper filter screen 21 and the side edges of the inner wall of the kapok fiber surface treatment soaking tank 1 should be sealed as much as possible to prevent the kapok fiber from moving upward, which will affect the setting of the traction cable 11. Here, upper and lower through holes can be opened on the step portion of the inner wall of the soaking tank for the two end pipe sections of the traction cable 11 to pass through and one end to move up and down. Of course, sealing rings should be set as much as possible at such holes to allow one end of the traction cable 11 to move up and down to reduce the outflow of kapok fibers.The main function of the lower filter screen 22 is to reduce the downward movement of kapok fibers. Of course, kapok fibers are very light and will basically stay in the upper part of the pool. Certainly, if the kapok fiber surface treatment immersion tank 1 is only alkalized, the lower filter screen 22 can be set as discrete and small, without completely sealing the downward movement of kapok fibers on the lower side. It can be set without the lower filter screen 22. However, here, mainly when the immersion tank is used for cleaning after alkalization, liquid will be drained to the bottom and cleaning agents will be added, which may carry away kapok fibers. Therefore, the lower filter screen 22 is needed to prevent kapok fibers from being carried away by the discharged solution. In this case, the lower filter screen 22 is required and its size should be such that it is as completely closed as possible with the side wall at the lower side. In this case, the lower filter screen 22 can adopt a flexible filter screen for easy installation. Or the kapok fiber surface treatment immersion tank 1 is of a split type, that is, the side wall and the bottom wall of the immersion tank are separated, and existing mechanical equipment can be used to splice or separate the side wall and the bottom wall. This is convenient for the disassembly and assembly of the lower filter screen 22. Just make a good seal between the side wall and the bottom wall. Such a structure is also convenient for placing and taking kapok fibers on the lower filter screen 22. Of course, kapok fibers can be placed and taken in other ways. Further, a bottom liquid outlet located below the lower filter screen 22 is provided at the bottom of the kapok fiber surface treatment immersion tank 1. The two filter screens ensure that kapok fibers will not go out during cleaning after alkalization. Of course, corresponding valves and output pipes are needed at the bottom liquid outlet, mainly used during cleaning after alkalization. Both the upper filter screen 21 and the lower filter screen 22 are not less than 800 mesh, and generally 800 mesh is sufficient, which can better control kapok fibers in the pool.

[0032] Next is about the cleaning after alkalization. That is, the cotton fiber surface treatment soaking tank 1 can also be used to inject a cleaning solution of ionized water and ethanol. The cleaning solution is used to clean the alkalized cotton fibers to obtain clean solid cotton fibers. After the alkalization is completed, the cleaning solution is injected by directly injecting it from the upper side of the tank or through other connecting pipes. At this time, the bottom of the soaking tank discharges the liquid through the bottom liquid outlet valve to remove the alkalized solution, and the cotton fibers are cleaned with the cleaning solution to prevent the surface of the cotton fibers from carrying alkalizing agent components, such as sodium hypochlorite. By continuously injecting the cleaning solution from the upper side and discharging the liquid from the lower side, the cleaning of the alkalized cotton fibers will be completed, and clean cotton fibers can be obtained. It is possible to detect the pH of the discharged solution or the solution in the tank to determine whether the cleaning is completed, that is, as long as the discharged solution or the solution in the tank is neutral, the cleaning can be ended. The cotton fibers can be taken out as described above through the lower filter screen. If it is through the lower filter screen, then the cleaning solution in the final tank also needs to be completely drained. If it is not through the lower filter screen, a side liquid outlet can be opened on the upper side wall of the cotton fiber surface treatment soaking tank 1. The diameter of the side liquid outlet can be larger. Of course, the side liquid outlet is also equipped with corresponding valves and output pipes. After the cleaning is completed, the side liquid outlet is opened, and the cotton fibers and the cleaning solution are output from the side liquid outlet to other storage tanks. At this time, the cleaning solution still needs to be continuously added until all the cotton fibers are discharged, and then stopped and discharged and collected through the bottom liquid outlet. There will be cotton fibers with cleaning solution in other storage tanks. The cleaning solution can be gradually filtered out through the existing filtration or other existing methods to obtain wet and clean solid cotton fibers.

[0033] Certainly, the cotton fiber pretreatment module also includes a drying device. The drying device is used to dry the clean solid cotton fibers to obtain the final solid cotton fibers with a smooth and dry surface. That is, the aforementioned wet and clean solid cotton fibers can be dried. Of course, if the cotton fibers are taken and placed through the lower filter screen as described above, the wet and clean solid cotton fibers can be obtained after the cleaning solution is drained, which is also convenient for the turnover of the cotton fibers. Generally speaking, large-scale production operations can be carried out.

[0034] Example 2, as Figure 3As shown, a preparation method of a battery hard carbon negative electrode material uses the preparation system of a battery hard carbon negative electrode material in Example 1. It mainly uses the system in Example 1 to alkalize, wash, and dry kapok fibers to obtain very good pre-treated kapok fibers, which is beneficial for subsequent cross-linking modification and carbonization, so as to obtain high-quality hard carbon materials. The method specifically includes Step 1: Pre-treatment of kapok fibers, which specifically includes Step 1.1. Dissolve sodium hypochlorite in ionized water to obtain an alkalization solution, which can be carried out in a conventional existing container; Step 1.2. Immerse the kapok fibers in the alkalization solution for at least 4 hours. This step is preferably carried out in the kapok fiber surface treatment immersion tank 1; Step 1.3. Wash the kapok fibers after immersion alkalization in Step 1.2 with ionized water and ethanol to obtain clean solid kapok fibers. This step is preferably carried out in the kapok fiber surface treatment immersion tank 1; Step 1.4. Dry the clean solid kapok fibers in Step 1.3 to obtain the final solid kapok fibers with a smooth and dry surface. This step can be carried out in an existing drying device, such as an existing oven. Step 2: Preparation of kapok fiber precursor, which specifically includes Step 2.1. Dissolve the pyrolysis auxiliary and nitrogen source in ionized water for a pre-cross-linking reaction to obtain a cross-linking agent solution. This step can be carried out and stored in a conventional container, that is, it needs to be prepared in advance. Step 2.2. Immerse the solid kapok fibers obtained in Step 1.4 in the cross-linking agent solution obtained in Step 2.1 for at least 12 hours to obtain modified kapok fibers after cross-linking agent modification. This step can be carried out in the kapok fiber surface treatment immersion tank 1, but here it is not necessary to generate waves, that is, to modify quietly, or slightly cause fluctuations in the solution. Step 2.3. Wash the modified kapok fibers in Step 2.2 with ionized water and absolute ethanol. This step can be carried out in the kapok fiber surface treatment immersion tank 1 to conveniently obtain the washed kapok fibers. Step 2.4. Dry the modified kapok fibers washed in Step 2.3 to obtain the kapok fiber precursor, and an existing drying device can be used. Step 3: Preparation of hard carbon material, specifically, subject the kapok fiber precursor obtained in Step 2.4 to high-temperature carbonization process to obtain hard carbon materials.

[0035] Preferably, the pyrolysis auxiliary ligand is a zinc-containing compound, including one or more of zinc gluconate, zinc oxide, zinc chloride, zinc nitrate, and zinc carbonate; the nitrogen source is one or more of 2,6-pyridinedicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, 2-methyl-6-pyridinedicarboxylic acid, o-nitrobenzoic acid, m-nitrobenzoic acid, and p-nitrobenzoic acid.

[0036] Preferably, in step 1.2 of step 1, the kapok fiber is immersed in the alkalization solution, and this step is carried out in the kapok fiber surface treatment soaking pool 1. The internal solution of the kapok fiber surface treatment soaking pool 1 and the kapok fiber follow a circulating flow caused by the undulation of the traction cable 11. The part of the traction cable 11 in the kapok fiber surface treatment soaking pool 1 is in a C shape.

[0037] According to the above solution, the following specific preferred embodiments are formed by way of example: The raw materials include kapok fiber, nitrogen source and pyrolysis auxiliary ligand; Pretreatment of kapok fiber: First, 1-100 parts by mass of sodium hypochlorite is fully dissolved in 100-10,000 parts by mass of deionized water to form an alkalization solution. Secondly, 1-100 parts by mass of kapok fiber is immersed in the above solution for 12-48 hours for alkalization to remove wax. After that, it is washed with a cleaning solution of deionized water and ethanol to remove the excess sodium hypochlorite remaining on the surface of the kapok fiber. The judgment standard is that the liquid is neutral after washing. Then, the obtained solid kapok fiber is dried overnight in an oven at 40-80 °C until the solid is in a dry state; Preparation of kapok fiber precursor: 0.1-10 parts by mass of pyrolysis auxiliary ligand and 0.1-10 parts by mass of nitrogen source are dissolved in 50-500 parts by mass of deionized water to form a crosslinking agent solution, and the two are subjected to a pre-crosslinking reaction; Then, 0.1-10 parts by mass of the kapok fiber solid obtained from the pretreatment of kapok fiber is immersed in the above mixed crosslinking agent solution for about 16-48 hours. Subsequently, the crosslinking agent-modified kapok fiber is washed thoroughly with a cleaning solution of deionized water and absolute ethanol and then placed in an oven for thorough drying at 60-100 °C; Preparation of hard carbon material: A high-temperature carbonization process is carried out, that is, the treated modified kapok fiber is heated in a tubular furnace in a nitrogen atmosphere at a heating rate of 3-10 °C / min to 200-350 °C and held for 1.5-3.5 hours, and then heated to 800-1200 °C at the same rate and held for 1-4 hours. After the temperature drops to room temperature, the modified nitrogen-doped hard carbon material can be obtained. Of course, the hard carbon material can be further processed by processes such as ball milling to obtain a higher-quality hard carbon material.

[0038] Under the above-mentioned embodiments, we selected 4 experimental examples of this application and 1 existing comparative example to analyze some properties of the battery made of hard carbon materials: Experimental Example 1, pretreatment of kapok fiber: First, 1 part by mass of sodium hypochlorite was fully dissolved in 100 parts by mass of deionized water to form an alkalization solution. Secondly, 1 part by mass of kapok fiber was immersed in the above solution for 12 hours for alkalization to remove wax. After that, it was washed with a cleaning solution of deionized water and ethanol to remove the excess sodium hypochlorite remaining on the surface of the kapok fiber. The judgment criterion was that the liquid after washing was neutral. All these steps were carried out in the kapok fiber surface treatment immersion tank 1, but the traction cable 11 did not swing up and down. Then, the obtained solid kapok fiber was dried in an oven at 40 °C overnight until the solid was in a dry state; Preparation of kapok fiber precursor: 0.1 part by mass of a pyrolysis auxiliary ligand and 0.1 part by mass of a nitrogen source were dissolved in 50 parts by mass of deionized water to form a cross-linking agent solution, and the two were subjected to a pre-cross-linking reaction; Then, 0.1 part by mass of the kapok fiber solid obtained from the pretreatment of kapok fiber was immersed in the above mixed cross-linking agent solution for about 16 hours. Subsequently, the cross-linking agent-modified kapok fiber was washed thoroughly with a cleaning solution of deionized water and absolute ethanol and then placed in an oven for thorough drying at 60 °C; Preparation of hard carbon material: A high-temperature carbonization process was carried out, that is, the treated modified kapok fiber was heated in a tubular furnace in a nitrogen atmosphere at a heating rate of 3 °C / min to 200 °C and held for 1.5 hours, and then heated to 800 °C at the same rate and held for 1 hour. After the temperature dropped to room temperature, the modified nitrogen-doped hard carbon material could be obtained. Of course, the hard carbon material can be further processed by processes such as ball milling to obtain a higher-quality hard carbon material.

[0039] Experimental Example 2, the difference from Experimental Example 1 is that during the operation in the kapok fiber surface treatment immersion tank 1 in the pretreatment of kapok fiber, the traction cable 11 swings to generate waves.

[0040] Experimental Example 3, Pretreatment of Kapok Fiber: First, 100 parts by mass of sodium hypochlorite was fully dissolved in 10,000 parts by mass of deionized water to form an alkalization solution. Second, 100 parts by mass of kapok fiber was immersed in the above solution for 48 hours for alkalization to remove wax. After that, it was washed with a cleaning solution of deionized water and ethanol to remove the excess sodium hypochlorite remaining on the surface of the kapok fiber. The judgment criterion was that the liquid was neutral after washing. All these steps were carried out in the kapok fiber surface treatment immersion tank 1, but the traction cable 11 did not swing up and down. Then, the obtained solid kapok fiber was dried in an oven at 80 °C overnight until the solid was in a dry state; Preparation of Kapok Fiber Precursor: 10 parts by mass of a pyrolysis auxiliary ligand and 10 parts by mass of a nitrogen source were dissolved in 500 parts by mass of deionized water to form a crosslinking agent solution, and the two were subjected to a pre-crosslinking reaction; Then, 10 parts by mass of the kapok fiber solid obtained from the pretreatment of kapok fiber was immersed in the above mixed crosslinking agent solution for about 48 hours. Subsequently, the crosslinking agent-modified kapok fiber was thoroughly washed with a cleaning solution of deionized water and absolute ethanol and then placed in an oven for thorough drying at 100 °C; Preparation of Hard Carbon Material: A high-temperature carbonization process was carried out, that is, the treated modified kapok fiber was heated in a tubular furnace under a nitrogen atmosphere at a heating rate of 10 °C / min to 350 °C and held for 3.5 hours, and then heated to 1200 °C at the same rate and held for 4 hours. After the temperature dropped to room temperature, the modified nitrogen-doped hard carbon material could be obtained. Of course, the hard carbon material could be further processed by processes such as ball milling to obtain a higher-quality hard carbon material.

[0041] Experimental Example 4, the difference from Experimental Example 3 is that during the operation in the kapok fiber surface treatment immersion tank 1 in the pretreatment of kapok fiber, the traction cable 11 swings to generate waves.

[0042] Comparative Example 1, a hard carbon material processed by an existing phosphoric acid pyrolysis process.

[0043] Preferably, during the process of soaking the inner solution in the kapok fiber surface treatment soaking tank 1 and the kapok fiber undulating, uniform alkalization is carried out through an image analysis feedback process. The image analysis feedback process specifically includes the following steps: a. Kapok fiber image acquisition; b. Kapok fiber image preprocessing; c. Kapok fiber contour extraction; d. Kapok fiber feature extraction and analysis; e. Kapok fiber uniform distribution algorithm; f. Feedback and adjustment. The adjustment step in step f includes adding liquid or adding kapok fiber. Specifically: a. Kapok fiber image acquisition: Use a camera to take images of kapok fibers, ensuring that the images are clear and the lighting is uniform, which helps with subsequent image processing and analysis. b. Kapok fiber image preprocessing: Before image analysis, the images need to be preprocessed, including denoising: Use median filtering or Gaussian filtering to remove noise in the images; enhancing contrast: Use histogram equalization technology to enhance the contrast of the images for better identification of kapok fibers. c. Kapok fiber contour extraction: Use image processing algorithms to extract the contours of kapok fibers; edge detection: Use the Canny edge detection algorithm or the Sobel operator to identify the edges of kapok fibers; morphological operations: Use opening and closing operations to remove small noise points and fill holes in kapok fibers. d. Kapok fiber feature extraction and analysis: Extract the features of kapok fibers, such as area, calculate the area of each fiber region to understand the distribution of kapok fibers. Shape: Analyze the shape features of the fibers to determine if there are overly concentrated or sparse situations. e. Kapok fiber uniform distribution algorithm: Based on the extracted features, use the following algorithms to ensure uniform fiber distribution. Clustering algorithm: Use algorithms such as K-means clustering or DBSCAN to group kapok fibers and analyze the distribution of each group. Uniformity evaluation: Calculate the fiber distribution uniformity index, such as the Gini coefficient or the uniformity index, to quantify the degree of uniformity of the distribution. Optimization algorithm: Genetic algorithms, particle swarm optimization, etc. can be used to adjust the positions of the fibers to make them more evenly distributed. f. Feedback and adjustment: Feed the result of uniform distribution back into the alkalization process, and adjust the parameters of the equipment according to the analysis results, such as adding liquid, ultrasonic vibration, and the vibration frequency and wind force of generating waves. The wind force can be adjusted through existing equipment for air outlet or air blowing.

[0044] Real-time monitoring can also be included. If real-time monitoring is required, the above steps can be integrated into an automated system, and deep learning algorithms, such as convolutional neural networks, can be used to identify and adjust the fiber distribution in real time.

[0045] Through the above steps, the distribution of kapok fibers can be effectively analyzed using image processing and algorithms, and uniform alkalization and cleaning can be achieved.

[0046] As can be seen from the above description, kapok fiber is selected as the precursor material and first treated with an alkalizing agent to remove surface wax and form a smooth surface. Then, a crosslinking reaction occurs between the acid [nitrogen source] with carboxyl groups and the hydroxyl groups in the kapok fiber exposed due to the alkalizing treatment. At the same time, the free zinc ions in the zinc source coordinate with N in the nitrogen source to further fix N into the kapok fiber precursor before carbonization. In addition, the zinc source also serves as an auxiliary pyrolysis agent, which can avoid the direct crosslinking of N and C during the aromatization process, which promotes the retention of the graphite nitrogen content in the kapok fiber precursor and further optimizes the oxygen functional groups in graphite. The kapok pre-precursor forms N-rich hard carbon under the synergistic action of two-step high-temperature carbonization and zinc source treatment. After high-temperature carbonization, more nitrogen exists in the form of pyridine nitrogen, which increases the local electron cloud density and enhances the attraction to Na+ in sodium ion energy storage. The wider carbon layer spacing induced by pyridine nitrogen also plays a role in the insertion of Na+. The unique material treatment method can effectively improve the wetting of the hard carbon material and the electrolyte, thereby reducing the path of Na+ migration and increasing the Na+ transfer rate, which can not only improve the rate performance of the material but also improve the first charge-discharge efficiency of the material.

[0047] In addition, when the proportion of kapok fiber is relatively high, the coordination effect of the zinc source is incomplete and the nitrogen content is limited, so the capacity increase is not obvious. When the proportion of kapok decreases, more zinc sources may interact with the exposed hydroxyl groups, thus affecting the crosslinking of carboxyl groups in the organic nitrogen source, ultimately reducing the nitrogen content and affecting the capacity. At the same time, the zinc ions in the zinc source can promote graphitization, and excessive graphitization of the carbon layer is not conducive to the improvement of capacity. With the addition of an excessive amount of organic nitrogen source, the final morphology of the prepared hard carbon may change. Therefore, when the mass ratio of kapok fiber, organic nitrogen source, and zinc source is preferably 1:1:1, the prepared hard carbon fiber exhibits good rate performance after being made into a battery subsequently.

[0048] Example 3, a sodium ion battery, includes a hard carbon negative electrode material, and the hard carbon negative electrode material is prepared by the preparation method of a battery hard carbon negative electrode material described in Example 2.

[0049] As mentioned above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A system for preparing a hard carbon negative electrode material for a battery, characterized in that: The invention comprises a kapok fiber pretreatment module, a kapok fiber precursor preparation module and a hard carbon material preparation module, wherein the kapok fiber pretreatment module is used to treat the outer surface of the kapok fiber and obtain a solid kapok fiber with a smooth and dry surface, the kapok fiber precursor preparation module is used to crosslink and modify the solid kapok fiber obtained by the kapok fiber pretreatment module and obtain a kapok fiber precursor, the hard carbon material preparation module is used to perform high-temperature carbonization treatment on the kapok fiber precursor to obtain a nitrogen-containing hard carbon material, the kapok fiber pretreatment module comprises an alkalizing agent treatment device, the alkalizing agent treatment device comprises a kapok fiber surface treatment soaking tank (1) for placing the kapok fiber, and the kapok fiber surface treatment soaking tank (1) is also used to inject sodium hypochlorite and ionized water. An alkalizing solution is provided in the kapok fiber surface treatment soaking pool (1), wherein a traction cable (11) is provided which can rise and fall and cause the solution to generate waves, wherein the traction cable (11) comprises a transparent flexible plastic sleeve (111), wherein a micro camera (112) is provided in the kapok fiber surface treatment soaking pool (1), wherein the kapok fiber pre-treatment module further comprises a processor (113) located outside the kapok fiber surface treatment soaking pool (1) and capable of communicating with the micro camera (112), wherein the micro camera (112) is built into the flexible plastic sleeve (111), wherein ultrasonic transducers (114) are provided at intervals on the periphery of the kapok fiber surface treatment soaking pool (1), and wherein the kapok fiber surface treatment soaking pool (1) comprises a plurality of ultrasonic transducers (114) arranged on the periphery of the kapok fiber surface treatment soaking pool (1). A detachable upper filter screen (21) for preventing kapok fibers from moving upward and a lower filter screen (22) for preventing kapok fibers from moving downward are arranged inside the kapok fiber surface treatment soaking pool (1); a bottom liquid outlet located below the lower filter screen (22) is arranged at the bottom of the kapok fiber surface treatment soaking pool (1); the mesh size of the upper filter screen (21) and the lower filter screen (22) are not less than 800; a plurality of miniature cameras (112) are arranged and spaced apart in the flexible plastic sleeve (111); the swing frequency of the traction cable (11) is less than 2 Hz; the portion of the traction cable (11) in the pool is a C-shaped structure; the kapok fiber surface treatment soaking pool (1) is in a ring shape or a circular shape; a device for moving the traction cable (11) upward and downward is arranged inside the kapok fiber surface treatment soaking pool (1) A wave amplitude limiting structure for limiting position by volt-volt action, the wave amplitude limiting structure comprising a transparent limiting tube (10) installed and connected to the side wall of the kapok fiber surface treatment soaking pool (1), at least one of the limiting tubes (10) also being provided with a micro camera (112), wherein at least two of the limiting tubes (10) are used as liquid replenishing tubes, the kapok fiber surface treatment soaking pool (1) can also be used to inject a cleaning solution of ionized water and ethanol, the cleaning solution being used to clean the alkalized kapok fibers to obtain clean solid kapok fibers, the kapok fiber pre-treatment module also comprising a drying device, the drying device being used to dry the clean solid kapok fibers to obtain solid kapok fibers with a smooth and dry surface.

2. A method for preparing a battery hard carbon negative electrode material, using the preparation system for a battery hard carbon negative electrode material as claimed in claim 1, characterized in that: The method comprises step 1: pre-treatment of kapok fibers, specifically comprising step 1.1, dissolving sodium hypochlorite in ionized water to obtain an alkalized solution; step 1.2, soaking the kapok fibers in the alkalized solution for at least 4 hours; step 1.3, washing the alkalized kapok fibers soaked in step 1.2 with ionized water and ethanol to obtain clean solid kapok fibers; step 1.4, drying the clean solid kapok fibers in step 1.3 to obtain solid kapok fibers with smooth surfaces and dryness; step 2: preparing a kapok fiber precursor, specifically comprising step 2.1, dissolving a pyrolysis auxiliary body and a nitrogen source in ionized water to perform a pre-crosslinking reaction and obtain a crosslinking agent solution; step 2.2, soaking the solid kapok fibers obtained in step 1.4 in the crosslinking agent solution obtained in step 2.1 for at least 12 hours; And obtain modified kapok fiber modified by a crosslinking agent, step 2.3, wash the modified kapok fiber in step 2.2 with ionized water and anhydrous ethanol, step 2.4, dry the modified kapok fiber washed in step 2.3 and obtain a kapok fiber precursor, step 3: preparation of hard carbon material, specifically treating the kapok fiber precursor obtained in step 2.4 by a high-temperature carbonization process to obtain a hard carbon material; the pyrolysis auxiliary ligand is a zinc-containing compound, including one or more of zinc gluconate, zinc oxide, zinc chloride, zinc nitrate, and zinc carbonate; the nitrogen source is one or more of 2,6-pyridinedicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, 2-methyl-6-pyridinedicarboxylic acid, o-nitrobenzoic acid, m-nitrobenzoic acid, and p-nitrobenzoic acid.

3. The method for preparing a hard carbon negative electrode material for a battery according to claim 2, characterized in that: In step 1.2 of step 1, the kapok fibers are immersed in the alkalization solution. This step is performed in the kapok fiber surface treatment immersion tank (1). The internal solution and the kapok fibers are subjected to the undulation of the traction cable (11) to cause waves and follow the circulation flow. The portion of the traction cable (11) in the kapok fiber surface treatment immersion tank (1) is in a C shape. During the undulation of the internal solution and the kapok fibers, the kapok fibers are uniformly alkalized by an image analysis feedback process. The image analysis feedback process specifically includes the following steps: a. kapok fiber image acquisition, b. kapok fiber image preprocessing, c. kapok fiber contour extraction, d. kapok fiber feature extraction and analysis, e. kapok fiber uniform distribution algorithm, and f. feedback and adjustment, wherein the adjustment step in step f includes replenishing the solution or adding kapok fibers.

4. A sodium ion battery, characterized in that: It comprises a hard carbon negative electrode material, and the hard carbon negative electrode material is prepared by the preparation method of a battery hard carbon negative electrode material according to claim 2.

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