Preparation system and method of battery hard carbon negative electrode material and sodium ion battery

Abstract

The invention relates to the technical field of sodium-ion batteries, in particular to a system and method for preparing a battery hard carbon negative electrode material and a sodium-ion battery, and the system comprises 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 surfaces of kapok fibers and obtaining solid kapok fibers with smooth and dry surfaces, and the kapok fiber precursor preparation module is used for carrying out crosslinking modification on the solid kapok fibers obtained by the kapok fiber pretreatment module and obtaining a kapok fiber precursor; and the hard carbon material preparation module is used for performing high-temperature carbonization treatment on the kapok fiber precursor to obtain the nitrogen-containing hard carbon material, so that high efficiency is achieved, and high-quality production is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a system and method for preparing a hard carbon negative electrode material for a battery, 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 a focus. Currently, sodium-ion technology has attracted much attention due to its cost-effectiveness and superior performance. Due to the large size of sodium ions, 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 incompatible with sodium-ion batteries. Therefore, non-graphitizable hard carbon materials have unique structural characteristics such as large interlayer spacing and short-range order, making them suitable for adsorbing sodium ions and acting as the main negative electrode material.

[0003] The precursors of hard carbon have oxygen-rich characteristics, and conventional materials are plant-based materials, organic polymers, resins, etc. Among them, resins and organic compounds have better performance than biomaterials, but 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 hard carbon materials prepared by pure carbonization is poor, especially at high current density. In this regard, a lot of work has focused on improving the rate performance by heteroatom doping, such as nitrogen N, sulfur, and phosphorus P doping. Among them, N is the most involved heteroatom, because doping N at the O position will introduce oxygen vacancies, which can increase the "electron-hole" concentration, enhance the conductivity of hard carbon materials, and promote the migration of sodium ions, thereby improving its rate performance. The main problem is that the N element will inevitably escape in a gaseous form during high-temperature pyrolysis, and its functional groups cannot be adjusted during pyrolysis. It is necessary not only to increase the N content after carbonization, but also to optimize the existence form of N after doping to improve the electrochemical performance of biomass-derived hard carbon anode materials at high rates.

[0004] Of course, there are also many existing patent technologies for battery hard carbon materials, such as a method for preparing an in-situ oxidation growth flower-shaped hard carbon sodium ion battery negative electrode disclosed in a Chinese patent with application number 202110612080.6: 1. Heat the popcorn to 230-280°C in an air atmosphere for pre-oxidation treatment; 2. Place the pre-oxidized popcorn in an atmosphere furnace and carbonize at 800-1400°C for 2-3 hours to obtain popcorn hard carbon; 3. Grind and sieve the popcorn hard carbon to obtain a hard carbon powder with a particle size of less than 48μm; 4. Mix the sieved hard carbon powder with multilayer MXene and ball mill with water as solvent. Under the huge energy generated by the collision of ball milling beads, the multilayer MXene is peeled off and reacts with air to generate TiO2 nanorods in situ, thereby forming a flower-like structured TiO2 / MXene / hard carbon composite material.

[0005] As disclosed in the Chinese patent application number 202211223124.7, a reed-derived hard carbon sodium negative electrode material, a preparation method thereof, and an energy storage battery, the present invention realizes the preparation of the reed-derived hard carbon negative electrode material by a phosphoric acid pyrolysis method, and the preparation method mainly includes the following steps: first, the dried reeds are washed with water, and after drying, crushing, and screening, the material is treated with concentrated phosphoric acid acid leaching, and then the material is heated to cause a pyrolysis reaction, and then the P2O5 composite nitrogen-doped porous hard carbon negative electrode material is obtained after crushing and screening.

[0006] For example, a lithium-ion battery composite hard carbon negative electrode material disclosed in Chinese patent application number 201010203768.0 comprises a coating coated on the outside of a hard carbon matrix, a precursor of the hard carbon matrix comprises a thermoplastic resin, which is pyrolyzed to form a hard carbon matrix, a precursor of the coating is an organic matter, and a preparation method thereof comprises: curing, pyrolysis, crushing, and coating.

[0007] For example, a method for preparing a hard carbon material precursor disclosed in a Chinese patent with application number 202111627150.1 includes the following steps: in a halogenated hydrocarbon, a high molecular weight organic matter containing an aromatic hard carbon material raw material is subjected to a Friedel-Crafts alkylation reaction under the action of a Lewis acid catalyst.

[0008] For example, a Chinese patent with application number 202410453573.3 discloses a method for preparing hard carbon using cotton and linen biomass as raw materials and its application, wherein cotton and linen are used as biomass raw materials, and the cotton and linen are carbonized once to obtain a cotton-like carbonized product, which is crushed and ground to obtain a carbonized powder precursor. The carbonized powder precursor is cleaned, and alkali washing can be used to remove impurities such as tar, quinone, and anthracene produced by the first calcination. After cleaning, a high-temperature secondary calcination is performed to obtain hard carbon.

[0009] The aforementioned patented technology is difficult to mass-produce in the production of hard carbon precursors, and the cost is high. The treatment effect on the hard carbon precursor material is not uniform and thorough enough, which will result in the final hard carbon material and battery quality not being superior enough. The battery performance needs to be improved, and there will be some shortcomings in energy conservation and environmental protection, which will not be green and low-carbon enough. Therefore, better improvement plans are needed for battery preparation and the battery itself to better meet the society's green and low-carbon needs. Summary of the invention

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

[0011] The above-mentioned object of the present invention is achieved through the following technical scheme: a preparation system of a battery hard carbon negative electrode material, comprising 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 the kapok fiber and obtain solid kapok fiber with a smooth and dry surface, the kapok fiber precursor preparation module is used to cross-link and modify the solid kapok fiber obtained by the kapok fiber pretreatment module and obtain a kapok fiber precursor, and 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.

[0012] As a preferred embodiment of the present invention, the kapok fiber pre-treatment 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 rise and fall and cause waves in the solution is provided in the cotton fiber surface treatment immersion tank, the traction cable includes a transparent flexible plastic sleeve, a miniature camera is provided in the cotton fiber surface treatment immersion tank, and the kapok fiber pre-treatment module also includes a processor located outside the kapok fiber surface treatment immersion tank and capable of communicating with the miniature camera.

[0013] As a preferred embodiment of the present invention, the micro camera is built into the flexible plastic sleeve, and ultrasonic transducers are distributed at intervals on the periphery of the fiber surface treatment immersion tank.

[0014] As a preferred embodiment of the present invention, the fiber surface treatment immersion tank is in a ring shape or a circle shape, and 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, and the wave amplitude limiting structure includes a transparent limiting tube installed and connected to the side wall of the cotton fiber surface treatment immersion tank, and at least one of the limiting tubes is also provided with a miniature camera, and at least two of the limiting tubes are used as fluid infusion tubes.

[0015] As a preferred embodiment of the present invention, the kapok fiber surface treatment soaking tank is provided with a detachable upper filter screen for preventing the kapok fibers from moving upward and a lower filter screen for preventing the kapok fibers from moving downward, and the bottom of the kapok fiber surface treatment soaking tank is provided with a bottom liquid outlet located below the lower filter screen, and the upper filter screen and the lower filter screen are both not less than 800 meshes.

[0016] As a preferred embodiment 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, and the cleaning solution is used to clean the alkalized kapok fibers to obtain clean solid kapok fibers. The kapok fiber pretreatment module also includes a drying device, and the drying device is used to dry the clean solid kapok fibers to obtain solid kapok fibers with a smooth and dry surface.

[0017] A method for preparing a hard carbon negative electrode material for a battery, using the aforementioned system for preparing a hard carbon negative electrode material for a battery, comprising 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 a smooth surface and dryness, and step 2: preparing a kapok fiber precursor, specifically comprising the steps 2.1, dissolving the pyrolysis auxiliary body and the nitrogen source in ion water for pre-crosslinking reaction and obtaining a crosslinker solution, step 2.2, soaking the solid kapok fiber obtained in step 1.4 in the crosslinker solution obtained in step 2.1 for at least 12 hours, and obtaining modified kapok fiber modified by the crosslinker, step 2.3, washing the modified kapok fiber in step 2.2 with ion water and anhydrous ethanol, step 2.4, drying the modified kapok fiber washed in step 2.3 and obtaining 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.

[0018] As a preferred embodiment 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 preferred embodiment of the present invention, in step 1.2 of step 1, the kapok fiber is immersed in the alkalizing solution, and this step is carried out in a kapok fiber surface treatment immersion tank. The internal solution and the kapok fiber are caused by the undulation of the traction cable and follow the circulation flow. The part of the traction cable in the kapok fiber surface treatment immersion tank is C-shaped, and the internal solution and the kapok fiber are uniformly alkalized during the undulation process 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, and f. feedback and adjustment, wherein the adjustment step in step f includes replenishing liquid or adding kapok fiber.

[0020] A sodium ion battery comprises a hard carbon negative electrode material, wherein the hard carbon negative electrode material is prepared by the aforementioned method for preparing a battery hard carbon negative electrode material.

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

[0024] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0025] 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.

[0026] Embodiment 1, as Figure 1 , 2As shown, a preparation system for a hard carbon negative electrode material for 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 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 design scheme of this embodiment is to achieve the preparation of hard carbon materials by designing the aforementioned three large modules. The main idea is to treat the surface of the kapok fiber, remove the wax, make the surface smooth and the effective ingredients exposed, and allow the kapok fiber to be better crosslinked and modified, so as to obtain a kapok fiber precursor with better quality, and then 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 pre-treatment module includes an alkalizing agent treatment device including a kapok fiber surface treatment soaking pool 1 for placing kapok fibers, and the kapok fiber surface treatment soaking pool 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 soaking pool 1 is to soak the kapok fibers in the alkalizing solution to achieve kapok fiber surface treatment and effectively remove the surface wax of the kapok fibers, and the cotton fiber surface treatment soaking pool 1 is provided with a traction cable 11 that can fluctuate up and down and can make the solution wave, and the traction cable 11 includes a transparent flexible plastic sleeve 111, and the flexible plastic sleeve 111 is mainly a part that can fluctuate in the solution, which will be mentioned later, and is generally set to a C-shaped extension, and the two ends of the flexible plastic sleeve 111 can also be connected to the lead-out section, and the lead-out section is relatively hard to facilitate the lifting and pulling of the end of the flexible plastic sleeve 111, similar to the fitness rope structure in the gym, and the traction cable 11 allows the interior to easily follow the sinusoidal fluctuations of the traction cable 11. The formation of a forward surge can better remove the surface wax and achieve a better surface treatment effect. The ups and downs of the traction cable 11 may be achieved by the up and down swinging of one end. One end of the traction cable 11 can be connected through an existing lifting device and then lifted. As long as the up and down swinging is achieved, it will be fine. Furthermore, a miniature camera 112 is provided in the cotton fiber surface treatment immersion tank 1, and the kapok fiber pre-treatment module also includes a processor 113 located outside the kapok fiber surface treatment immersion tank 1 and capable of communicating with the miniature camera 112. The miniature camera 112 and the processor 113 can both use existing equipment and can communicate wirelessly or wiredly. The main purpose is to use the miniature camera 112 to shoot the distribution and surface morphology of the kapok fiber in the kapok fiber surface treatment immersion tank 1 in the pool, and then feed it back to the processor. Then the processor makes further instructions to optimize the process conditions through effective identification and analysis, so as to continuously optimize the surface treatment process of the kapok fiber.

[0027] As a preferred embodiment, the micro camera 112 is built into the flexible plastic sleeve 111, and the outer periphery of the fiber surface treatment immersion pool 1 is provided with ultrasonic transducers 114 at intervals. The flexible plastic sleeve 111 can also be understood as the outer layer structure of some existing cables, and it is as flexible as possible to facilitate the undulation to cause orderly waves in the pool. Of course, when both ends of the flexible plastic sleeve 111 are open, the open ends are not immersed in the pool. If the ends are closed, it can be placed in the pool. The micro camera 112 can be glued to the flexible plastic sleeve 111, or can be embedded in the existing flexible block material, and then inserted 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 using the existing installation method. The micro camera 112 uses multiple and can be distributed in the flexible plastic sleeve 111 at intervals to shoot at multiple positions. The micro camera 112 uses a wired or wireless camera, which is feasible. The flexible plastic sleeve 111 itself has the function of protecting the internal structure. The ultrasonic transducer 114 can further assist the alkaline cleaning operation. For example, if the kapok fibers in a certain area of ​​the pool are relatively dense, the ultrasonic transducer 114 needs to be properly turned on to enhance the vibration of the solution so that the distribution of the kapok fibers in the entire pool is relatively more uniform, which is conducive to the alkaline effect.

[0028] Furthermore, the fiber surface treatment immersion tank 1 is in a ring shape or a circle shape, which is conducive to the circular circulation of the solution and can maintain the motion state for a long time without stopping. In addition, the kapok fiber surface treatment immersion tank 1 is provided with a wave amplitude limiting structure for limiting the up and down movement of the traction cable 11, because the amplitude of this surge needs to be controlled, otherwise excessive distance may cause damage to the fiber. It should be as gentle as possible, generally controlled to two up and down swings back and forth in one second, that is, the wave swing frequency is within 2 Hz, of course, it can be adjusted according to actual conditions. The specific wave amplitude limiting structure includes a transparent limiting tube 10 installed and connected to the side wall of the cotton fiber surface treatment immersion pool 1, at least one of the limiting tubes 10 is also provided with a miniature camera 112, and at least two of the limiting tubes 10 are used as liquid replenishment tubes. If the kapok fiber surface treatment immersion pool 1 is made of plastic or glass, the limiting tube 10 can be integrally connected to the side wall of the cotton fiber surface treatment immersion pool 1. If different materials are used, the limiting tube 10 can be installed through the existing installation method. The limiting tube 10 is preferably made of plastic or glass, and if it is a ring-shaped fiber surface treatment immersion pool 1, the limiting tube 10 can be linear, and upper and lower intervals need to be set respectively. The axial direction of the limiting tube 10 is horizontal and flat, and the limiting tubes 10 on the upper and lower sides are required to be multiple and in a circular array. In this way, the part of the traction cable 11 in the pool also forms a C-shaped structure that is approximately a circle, so that the wave can be a circular circulation style, and the solution can make a circular circulation wave action. If the fiber surface treatment immersion pool 1 is only a circular pool, the limiting tube 10 preferably needs two connected pipe sections, one of which is a circular pipe section for the traction cable 11 to enter and limit up, down, left and right, and the other is a straight section connected to the circular pipe section, and this straight section can be installed on the side wall of the fiber surface treatment immersion pool 1. The limiting tube 10 is stationary, and the micro camera 112 in the limiting tube 10 can be mainly used to observe the overall internal conditions of the pool and the conditions of the traction cable 11, and monitor in real time to ensure smooth and safe production. The limiting tube 10 can also be used as a liquid replenishment tube. The limiting tube 10 can be connected to the peripheral alkaline solution pipeline or the alkaline solution storage container such as the liquid storage tank. Of course, in this case, the limiting tube 10 needs to have a liquid outlet hole and a corresponding electromagnetic valve, that is, to inject the alkaline solution when needed to supplement and optimize the distribution of the internal kapok fibers. Of course, the alkaline solution can also be injected through the limiting tube 10 at the beginning, but for the efficiency of injection, a larger liquid inlet tube placed in the pool is generally used to inject the alkaline solution.The fiber surface treatment soaking pool 1 is used in a manner that generally a batch of kapok fibers is first placed therein, which can be done manually or by machine, and then an alkalizing solution is placed therein to the required amount, followed by soaking. The soaking can be static, but preferably with waves, i.e. the traction cable 11 swings up and down to cause waves to alkalize and remove wax on the surface of the kapok fibers. During this process, a camera observes the internal situation, and an ultrasonic transducer or a rehydration tube is used to optimize the distribution of the internal solution and kapok fibers. When the alkalization is completed, the next step is carried out, i.e. the alkalized kapok fibers need to be cleaned.

[0029] 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 22 is to reduce the downward movement of kapok fibers. Of course, the kapok fibers themselves are very light and basically remain in the upper part of the pool. Of course, if the kapok fiber surface treatment soaking pool 1 is only alkalized, the lower filter 22 can be set to a discrete small size, and there is no need to seal the entire lower side to prevent the kapok fibers from moving downward. The lower filter 22 can be set. However, here, the main reason is that when the soaking pool is used for cleaning after alkalization, liquid will be discharged to the bottom and put in for easy cleaning, which may carry away the kapok fibers. Therefore, the lower filter 22 is needed to prevent the kapok fibers from being carried away by the discharged solution. In this case, In this case, the lower filter screen 22 is needed and its size should be as completely enclosed as possible with the side wall on the lower side. In this case, the lower filter screen 22 can adopt a flexible filter screen to facilitate installation, or the kapok fiber surface treatment soaking tank 1 adopts a split type, that is, the side wall and the bottom wall of the soaking tank are separate, and the side wall and the bottom wall can be spliced ​​or separated by existing mechanical equipment. This is convenient for the disassembly and assembly of the lower filter screen 22, and the side wall and the bottom wall can be sealed. Such a structure also facilitates the kapok fiber to be placed on the lower filter screen 22 for taking and placing. Of course, the kapok fiber can be taken and placed by other means. Furthermore, a bottom liquid outlet located below the lower filter screen 22 is provided at the bottom of the kapok fiber surface treatment soaking pool 1. The two filter screens prevent the kapok fibers from flowing out during cleaning after alkalization. Of course, the bottom liquid outlet requires corresponding valves and output pipe controls, which are mainly used during cleaning after alkalization. The upper filter screen 21 and the lower filter screen 22 are both not less than 800 meshes, and generally 800 meshes are sufficient, which can better control the kapok fibers in the pool.

[0030] Next is about cleaning after alkalization, that is, 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 is used to clean the alkalized kapok fiber to obtain clean solid kapok fiber, alkalization is completed, and the cleaning solution is injected by directly injecting the upper side of the pool or other connecting pipes. At this time, the bottom of the soaking pool opens the valve to discharge liquid through the bottom liquid outlet, removes the alkalized solution, and cleans the kapok fiber with the cleaning solution to prevent the kapok fiber surface from carrying alkalizing agent components, such as sodium hypochlorite, and continuously injects the cleaning solution on the upper side and discharges the liquid on the lower side, and the cleaning of the alkalized kapok fiber will be completed, and clean kapok fiber can be obtained. The pH of the solution released or the solution in the pool can be detected to determine whether the cleaning is completed, that is, as long as the solution released or the solution in the pool is neutral, the cleaning can be completed. The removal of the kapok fiber can be carried out through the lower filter as mentioned above. If it is through the lower filter, the cleaning solution in the last pool needs to be discharged completely. If it is not through the lower filter screen, a side liquid outlet can be opened on the upper side wall of the kapok fiber surface treatment soaking pool 1. The diameter of the side liquid outlet can be larger, and the side liquid outlet is of course also equipped with a corresponding valve and output pipe. After cleaning, the side liquid outlet is opened, and the kapok fiber and the cleaning solution are output from the side liquid outlet to other storage pools. At this time, the cleaning solution still needs to be continuously added until all the kapok fibers are released and then stopped and collected through the bottom liquid outlet. There will be kapok fibers with cleaning solution in other storage pools. This can be done by gradually filtering out the cleaning solution through existing filtration, or other existing methods can be used to obtain moist and clean solid kapok fibers.

[0031] Of course, the kapok fiber pre-treatment module also includes a drying device, which is used to dry the clean solid kapok fibers to obtain solid kapok fibers with a smooth surface and dryness. That is, the aforementioned wet and clean solid kapok fibers can be dried. Of course, if the kapok fibers are taken and placed using the lower filter net, wet and clean solid kapok fibers can be obtained after the cleaning solution is released, which is also convenient for the turnover of the kapok fibers. Generally speaking, large-scale production operations can be carried out.

[0032] Embodiment 2, as Figure 3As shown, a method for preparing a battery hard carbon negative electrode material uses a battery hard carbon negative electrode material preparation system of Example 1, mainly using the system of Example 1 to alkalize, clean and dry kapok fibers to obtain very good pre-treated kapok fibers, which is beneficial to subsequent cross-linking modification and carbonization, thereby obtaining high-quality hard carbon materials. The method specifically comprises step 1: pre-treatment of kapok fibers, specifically comprising step 1.1, dissolving sodium hypochlorite in ionized water to obtain an alkalized solution, which can be carried out in an existing conventional container; step 1.2, soaking the kapok fibers in the alkalized solution for at least 4 hours, which step is preferably carried out in a kapok fiber surface treatment soaking tank 1; 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, which step is preferably carried out in a kapok fiber surface treatment soaking tank 1; step 1.4, drying the clean solid kapok fibers in step 1.3 to obtain solid kapok fibers with smooth and dry surfaces, which step can be carried out in an existing drying device, such as an existing oven; step 2: preparing a kapok fiber precursor, specifically comprising step 2.1, dissolving a pyrolysis auxiliary body and a nitrogen source in ionized water for a pre-crosslinking reaction to obtain a crosslinking agent solution, which step is carried out in a conventional It can be dissolved and stored in a container, but it needs to be prepared in advance. Step 2.2, soak the solid kapok fiber obtained in step 1.4 in the cross-linking agent solution obtained in step 2.1 for at least 12 hours, and obtain the modified kapok fiber modified by the cross-linking agent. This step can be carried out in the kapok fiber surface treatment immersion tank 1, but there is no need to make waves here, just modify it quietly, or slightly float the solution. Step 2.3, wash the modified kapok fiber in step 2.2 with ionized water and anhydrous ethanol. This step can be carried out in the kapok fiber surface treatment immersion tank 1, which is convenient for obtaining the washed kapok fiber. Step 2.4, dry the modified kapok fiber washed in step 2.3 and obtain a kapok fiber precursor, and use the existing drying device. Step 3: Preparation of hard carbon material, specifically, treating the kapok fiber precursor obtained in step 2.4 through a high-temperature carbonization process to obtain a hard carbon material.

[0033] 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.

[0034] Preferably, in step 1.2 of step 1, the kapok fibers are immersed in the alkaline solution, and this step is carried out in the kapok fiber surface treatment immersion tank 1. The internal solution and kapok fibers of the kapok fiber surface treatment immersion tank 1 are subjected to waves caused by the undulations of the traction cable 11 and follow the circulation flow. The portion of the traction cable 11 in the kapok fiber surface treatment immersion tank 1 is C-shaped.

[0035] According to the above scheme, the following specific preferred implementation is formed by example: the raw materials include kapok fiber, nitrogen source and pyrolysis auxiliary ligand; Kapok fiber pretreatment: first, 1-100 parts by mass of sodium hypochlorite is fully dissolved in 100-10000 parts by mass of deionized water to form an alkaline solution, and then 1-100 parts by mass of kapok fiber is soaked in the above solution for 12-48 hours for alkalization to remove wax, and then washed with a cleaning solution of deionized water and ethanol to remove excess sodium hypochlorite remaining on the surface of the kapok fiber. The judgment standard is that the liquid after washing is neutral, and then the obtained solid kapok fiber is dried in an oven at 40-80° C. overnight until the solid is in a dry state; Preparation of kapok fiber precursor: dissolving 0.1-10 parts by weight of a pyrolysis auxiliary ligand and 0.1-10 parts by weight of a nitrogen source in 50-500 parts by weight of deionized water to form a crosslinker solution, and subjecting the two to a pre-crosslinking reaction; then soaking 0.1-10 parts by weight of kapok fiber solid obtained by pre-treatment of kapok fiber in the mixed crosslinker solution for about 16-48 hours, and then fully washing the crosslinker-modified kapok fiber with a cleaning solution of deionized water and anhydrous ethanol, and then placing it in an oven at 60-100° C. for full drying; Preparation of hard carbon material: high temperature carbonization process, that is, the treated modified kapok fiber is heated to 200-350℃ in a tubular furnace under nitrogen atmosphere at a heating rate of 3-10℃ / min and maintained for 1.5-3.5 hours, and then heated to 800-1200℃ at the same rate and maintained for 1-4 hours, and the modified nitrogen-doped hard carbon material is obtained when the temperature drops to room temperature. Of course, the hard carbon material can be further processed by ball milling and other processes to obtain a higher quality hard carbon material.

[0036] In the above implementation mode, we selected 4 experimental examples of the present application and 1 existing comparative example to analyze some properties of the hard carbon material after being made into a battery: Experimental Example 1, kapok fiber pretreatment: First, 1 part by mass of sodium hypochlorite is fully dissolved in 100 parts by mass of deionized water to form an alkaline solution. Second, 1 part by mass of kapok fiber is soaked in the above solution for 12 hours for alkalinization to remove wax, and then washed with a cleaning solution of deionized water and ethanol to remove excess sodium hypochlorite remaining on the surface of the kapok fiber. The judgment standard is that the liquid after washing is neutral. These steps are all carried out in the kapok fiber surface treatment soaking tank 1, but the traction cable 11 does not swing up and down. Then, the obtained solid kapok fiber is dried in an oven at 40°C overnight until the solid is in a dry state; Preparation of kapok fiber precursor: dissolving 0.1 parts by weight of a pyrolysis auxiliary ligand and 0.1 parts by weight of a nitrogen source in 50 parts by weight of deionized water to form a crosslinker solution, and subjecting the two to a pre-crosslinking reaction; then soaking 0.1 parts by weight of kapok fiber solid obtained by pre-treatment of kapok fiber in the mixed crosslinker solution for about 16 hours, and then fully washing the crosslinker-modified kapok fiber with a cleaning solution of deionized water and anhydrous ethanol, and then placing it in an oven at 60° C. for full drying; Preparation of hard carbon material: high temperature carbonization process, that is, the treated modified kapok fiber is heated to 200°C at a heating rate of 3°C / min in a tubular furnace under nitrogen atmosphere and maintained for 1.5 hours, and then heated to 800°C at the same rate and maintained for 1 hour. When 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 ball milling and other processes to obtain a higher quality hard carbon material.

[0037] Experimental Example 2 is different from Experimental Example 1 in that, during the pre-treatment of kapok fibers, when the kapok fibers are being treated in the kapok fiber surface treatment immersion tank 1 , the traction cable 11 swings and creates waves.

[0038] Experimental Example 3, kapok fiber pretreatment: First, 100 parts by mass of sodium hypochlorite is fully dissolved in 10,000 parts by mass of deionized water to form an alkaline solution. Second, 100 parts by mass of kapok fiber are soaked in the above solution for 48 hours for alkalinization to remove wax, and then washed with a cleaning solution of deionized water and ethanol to remove excess sodium hypochlorite remaining on the surface of the kapok fiber. The judgment standard is that the liquid after washing is neutral. These steps are all carried out in the kapok fiber surface treatment soaking tank 1, but the traction cable 11 does not swing up and down. Then, the obtained solid kapok fiber is dried in an oven at 80°C overnight until the solid is in a dry state; Preparation of kapok fiber precursor: dissolving 10 parts by weight of a pyrolysis auxiliary ligand and 10 parts by weight of a nitrogen source in 500 parts by weight of deionized water to form a crosslinker solution, and subjecting the two to a pre-crosslinking reaction; then soaking 10 parts by weight of kapok fiber solid obtained by pre-treatment of the kapok fiber in the mixed crosslinker solution for about 48 hours, and then fully washing the crosslinker-modified kapok fiber with a cleaning solution of deionized water and anhydrous ethanol, and then placing it in an oven at 100° C. for full drying; Preparation of hard carbon material: high temperature carbonization process, that is, the treated modified kapok fiber is heated to 350°C at a heating rate of 10°C / min in a tubular furnace under nitrogen atmosphere and maintained for 3.5 hours, and then heated to 1200°C at the same rate and maintained for 4 hours. When 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 ball milling and other processes to obtain a higher quality hard carbon material.

[0039] Experimental Example 4 is different from Experimental Example 3 in that, during the pre-treatment of kapok fibers, when the kapok fibers are being treated in the kapok fiber surface treatment immersion tank 1 , the traction cable 11 swings and creates waves.

[0040] Comparative Example 1: A hard carbon material obtained by using the existing phosphoric acid pyrolysis process.

[0041] Preferably, during the undulation of the solution and kapok fibers in the kapok fiber surface treatment soaking pool 1, the image analysis feedback process is uniformly alkalized, and 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, wherein the adjustment step in step f includes replenishing the solution or adding kapok fibers. Specifically: a. Kapok fiber image acquisition: Use a camera to capture the image of the kapok fiber to ensure that the image is clear and the lighting is uniform, which will help with subsequent image processing and analysis.

[0042] b. Kapok fiber image preprocessing. Before image analysis, the image needs to be preprocessed, including denoising: using median filtering or Gaussian filtering to remove noise in the image; contrast enhancement: using histogram equalization technology to enhance the contrast of the image in order to better identify kapok fibers.

[0043] c. Extraction of kapok fiber contour: use image processing algorithm to extract the contour of kapok fiber; edge detection: use Canny edge detection algorithm or Sobel operator to identify the edge of kapok fiber; morphological operation: use opening and closing operations to remove small noise points and fill the holes of kapok fiber.

[0044] d. Extraction and analysis of kapok fiber features: Extract the features of kapok fibers, such as area, and calculate the area of ​​each fiber region to understand the distribution of kapok fibers. Shape: Analyze the shape characteristics of the fibers to determine whether they are too concentrated or sparse.

[0045] 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 the kapok fibers and analyze the distribution of each group. Uniformity evaluation: Calculate the fiber distribution uniformity index, such as the Gini coefficient or uniformity index, to quantify the uniformity of the distribution. Optimization algorithm: Genetic algorithms, particle swarm optimization, and other methods can be used to adjust the position of the fibers to make them more evenly distributed.

[0046] f. Feedback and adjustment: Feedback the uniform distribution results to the alkalization process, and adjust the equipment parameters according to the analysis results, such as liquid replenishment, ultrasonic vibration, wave vibration frequency, wind force, etc., to optimize the fiber distribution. The wind force can be achieved by setting the existing air outlet or wind outlet equipment.

[0047] Real-time monitoring can also be included. If real-time monitoring is required, the above steps can be integrated into an automated system using deep learning algorithms, such as convolutional neural networks, to identify and adjust the distribution of fibers in real time.

[0048] Through the above steps, image processing and algorithms can be effectively used to analyze the distribution of kapok fibers and achieve uniform alkalization and cleaning.

[0049] From the above description, it can be seen that kapok fiber is selected as the precursor material and is first treated with an alkalizing agent to remove the surface wax to form a smooth surface. Then, a cross-linking reaction occurs between the acid [nitrogen source] with a carboxyl group and the hydroxyl groups in the kapok fiber exposed by the alkalization treatment. At the same time, the free zinc ions in the zinc source coordinate with the N in the nitrogen source, further fixing the N to the kapok fiber precursor before carbonization. In addition, the zinc source is also used as an auxiliary pyrolysis agent, which can avoid the direct cross-linking of N and C during the aromatization process, which will promote the retention of the graphite nitrogen content in the kapok fiber precursor and further optimize the functional groups of oxygen in the graphite. The kapok precursor forms N-rich hard carbon under the synergistic effect of two-step high-temperature carbonization and zinc source treatment. After high-temperature carbonization, more nitrogen exists in the form of pyridinic nitrogen to increase the local electron cloud density and enhance the attraction to Na+ in sodium ion energy storage. The wider carbon layer spacing induced by pyridinic nitrogen also plays a role in the insertion of Na+. The unique material treatment method can effectively improve the wetting of hard carbon materials and electrolytes, thereby reducing the migration path of Na+ and increasing the Na+ transfer rate, which can not only improve the material rate performance but also improve the material's first charge and discharge efficiency.

[0050] In addition, when the proportion of kapok fiber is high, the coordination of the zinc source is incomplete, and the nitrogen content is limited, so the capacity increase is not obvious. When the proportion of kapok is reduced, more zinc sources may interact with exposed hydroxyls, thereby affecting the cross-linking of hydroxyls in the organic nitrogen source, ultimately reducing the nitrogen content and affecting the capacity. At the same time, zinc ions in the zinc source can promote graphitization, while excessive graphitization of the carbon layer is not conducive to the improvement of capacity. With the addition of excess organic nitrogen source, the final form 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 obtained hard carbon fiber exhibits good rate performance after subsequent battery manufacturing.

[0051] Embodiment 3, a sodium ion battery, comprising a hard carbon negative electrode material, wherein the hard carbon negative electrode material is prepared by the preparation method of a battery hard carbon negative electrode material described in Embodiment 2.

[0052] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A system for preparing a hard carbon negative electrode material for a battery, characterized in that: It 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 the kapok fiber and obtain solid kapok fiber with a smooth and dry surface. The kapok fiber precursor preparation module is used to cross-link 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.

2. A system for preparing a hard carbon negative electrode material for a battery according to claim 1, characterized in that: The kapok fiber pre-treatment module comprises an alkalizing agent treatment device comprising a kapok fiber surface treatment soaking pool (1) for placing kapok fibers, the kapok fiber surface treatment soaking pool (1) being further used for injecting an alkalizing solution of sodium hypochlorite and ionized water, a traction cable (11) capable of rising and falling and causing the solution to wave is arranged in the kapok fiber surface treatment soaking pool (1), the traction cable (11) comprising a transparent flexible plastic sleeve (111), a miniature camera (112) is arranged in the kapok fiber surface treatment soaking pool (1), and 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 miniature camera (112).

3. A system for preparing a hard carbon negative electrode material for a battery according to claim 2, characterized in that: The micro camera (112) is built into the flexible plastic sleeve (111), and ultrasonic transducers (114) are arranged at intervals on the periphery of the fiber surface treatment immersion tank (1).

4. A system for preparing a hard carbon negative electrode material for a battery according to claim 2, characterized in that: The fiber surface treatment soaking pool (1) 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 (11) is arranged in the kapok fiber surface treatment soaking pool (1). The wave amplitude limiting structure comprises a transparent limiting tube (10) installed and connected to the side wall of the cotton fiber surface treatment soaking pool (1). At least one of the limiting tubes (10) is also provided with a micro camera (112), and at least two of the limiting tubes (10) are used as liquid infusion tubes.

5. A system for preparing a hard carbon negative electrode material for a battery according to claim 2, characterized in that: The kapok fiber surface treatment soaking tank (1) is provided with 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. The bottom of the kapok fiber surface treatment soaking tank (1) is provided with a bottom liquid outlet located below the lower filter screen (22). The mesh size of the upper filter screen (21) and the lower filter screen (22) is not less than 800.

6. A system for preparing a hard carbon negative electrode material for a battery according to claim 2, characterized in that: The kapok 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 kapok fibers to obtain clean solid kapok fibers, and the kapok fiber pretreatment module also includes a drying device, the drying device is used to dry the clean solid kapok fibers to obtain solid kapok fibers with a smooth and dry surface.

7. A method for preparing a battery hard carbon negative electrode material, using a battery hard carbon negative electrode material preparation system as claimed in any one of claims 1 to 6, characterized in that: The method comprises the following steps: 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 ionized water and ethanol in step 1.2 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 and dry surfaces; step 2: preparing a kapok fiber precursor, specifically comprising step 2.1, dissolving a pyrolysis auxiliary body and a nitrogen source in ionized water; water for pre-crosslinking reaction and obtain a crosslinker solution, step 2.2, soaking the solid kapok fiber obtained in step 1.4 in the crosslinker solution obtained in step 2.1 for at least 12 hours, and obtaining modified kapok fiber modified by the crosslinker, step 2.3, washing the modified kapok fiber in step 2.2 with ionized water and anhydrous ethanol, step 2.4, drying the modified kapok fiber washed in step 2.3 to obtain a kapok fiber precursor, step 3: preparation of hard carbon material, specifically, treating the kapok fiber precursor obtained in step 2.4 through a high temperature carbonization process to obtain a hard carbon material.

8. The method for preparing a hard carbon negative electrode material for a battery according to claim 7, characterized in that: 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.

9. The method for preparing a hard carbon negative electrode material for a battery according to claim 8, 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.

10. 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 7.

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