Phosphorus-doped chitin-based hard carbon negative electrode material prepared by sodium pre-treatment method and application

Abstract

The invention discloses a phosphorus-doped chitin-based hard carbon negative electrode material prepared by a pre-sodium modification method and an application of the phosphorus-doped chitin-based hard carbon negative electrode material. Chitin is used as a carbon source, sodium salt is supplemented, then the sodium salt and the carbon source are mixed in a physical ball milling mode, a precursor is obtained, and finally the hard carbon material is obtained after pre-oxidation and carbonization process treatment. The method does not need other additives, and does not need complex chemical reaction, so that the preparation process is simpler, the cost is lower, the preparation is more controllable, the sodium salt and the carbon source are completely mixed and carbonized, and the loss of the sodium salt raw material is less. When the sodium phytate is selected as the sodium salt, the pre-sodium modification is realized, and the phosphorus element is doped by a one-step method, so that the process is simpler, and the cost is lower; and a large number of closed pores can be introduced by utilizing a pre-oxidation process and phytate anion groups, so that storage and diffusion of Na < + > are more facilitated, excessive graphitization of the material is hindered, and performance limitation of the chitin-derived hard carbon material in an application process is solved in a targeted manner.

Description

Technical Field

[0001] The present invention relates to a hard carbon negative electrode material and its preparation and application, in particular to a phosphorus-doped chitin-based hard carbon negative electrode material prepared by a pre-sodiumization method and its application. Background Art

[0002] Bio-derived hard carbon materials are generally made from biomass such as coconut shells, straw, wood, and starch, avoiding dependence on fossil resources and conforming to the concept of sustainable development. Furthermore, the interlayer spacing of hard carbon materials is usually greater than 0.37nm, which is larger than the 0.335nm of graphite materials, making it more conducive to the insertion / deinsertion of sodium ions, and the theoretical capacity can be as high as 300–400mAh / g. At the same time, bio-based hard carbon retains the natural porous or layered structure of biomass, providing abundant sodium storage sites such as pores, defects, and edge sites, which can promote the rapid diffusion of ions. Therefore, bio-derived hard carbon materials have become the anode material of choice for most commercial sodium-ion batteries.

[0003] However, conventional bio-derived hard carbon materials also have drawbacks that cannot be ignored: due to the formation of SEI at the negative electrode interface of sodium-ion batteries and some irreversible sodium adsorption, the first coulombic efficiency of hard carbon negative electrode materials is relatively low, usually 60%-75%. The low first coulombic efficiency leads to excessive consumption of sodium on the positive electrode side of the whole battery, resulting in a reduction in the actual available active sodium, causing a decrease in the battery's discharge capacity and energy density.

[0004] Chitin is a natural high molecular weight polysaccharide that is widely found in the shells of crustaceans, the exoskeletons of insects, and the cell walls of fungi. Its molecular structure contains acetylglucosamine units, which have excellent biocompatibility, degradability, and chemical modifiability. In the field of electrochemistry, chitin can be carbonized to prepare high-performance biomass carbon materials for use in supercapacitors or lithium / sodium ion battery electrodes, exhibiting high specific capacitance and cycle stability; its derivative chitosan can be used as an electrolyte separator or binder to improve battery ion conductivity and electrode structural integrity. In addition, chitin-based flexible conductive films have application potential in wearable energy storage devices, providing new ideas for the development of green electrochemical materials. Therefore, chitin has extremely wide applications in the field of electrochemistry. However, when chitin is directly used as a raw material to prepare sodium ion hard carbon negative electrode materials, there are many defects: mainly including its low ICE, and it is easy to over-graphitize during the carbonization process, resulting in a smaller interlayer spacing, making Na +The difficulty in rapidly shuttling through the material seriously affects the battery's rate performance. Furthermore, the large volume changes caused by the smaller interlayer spacing during charge and discharge also reduce the battery's cycling stability. Furthermore, chitin-based hard carbon materials, like traditional bio-derived hard carbon materials, also suffer from low first coulombic efficiency. Therefore, these defects severely limit the application of chitin in sodium-ion batteries. Improving the ICE and interlayer spacing of chitin-based hard carbon materials will greatly facilitate the application of chitin in the field of sodium-ion batteries.

[0005] For these reasons, the development of advanced sodium-ion batteries has led to higher requirements for hard carbon anode materials, leading to extensive and in-depth research. Numerous strategies for preparing hard carbon anode materials have been explored, including precursor modification and carbonization methods. Pre-sodiumization is considered the most effective approach to addressing the low first-cycle Coulombic efficiency, as it can directly replenish sodium consumption during the first cycle. Phosphorus doping, on the other hand, is considered an effective method for addressing the insufficient interlayer spacing in hard carbon materials.

[0006] Pre-sodiumization refers to the introduction of sodium ions into electrode materials by physical or chemical methods before sodium-ion battery assembly or cycling to compensate for the irreversible sodium loss during the initial charge and discharge process, thereby improving the initial coulombic efficiency and overall battery performance. Phosphorus doping is the introduction of phosphorus into the material to significantly improve the electrochemical performance of hard carbon materials through structural regulation, enhanced electronic conduction, and surface modification, which has important application value in the field of sodium-ion batteries.

[0007] For example, patent publication number CN117466282B discloses a method for pre-sodiumization of hard carbon materials. This method involves mixing a carbon source solution with raw materials such as a surfactant, a weak base, and a soluble sodium salt, reacting and drying the mixture to obtain a precursor, which is then carbonized to obtain the pre-sodiumized hard carbon material. While this patent achieves pre-sodiumization of hard carbon materials, the carbon source is biomass such as glucose, sucrose, and starch, which is relatively costly. Furthermore, the addition of additives such as surfactants and weak bases to the reaction complicates the process, leading to significant raw material loss after filtration and hindering industrial application.

[0008] For example, the patent with publication number CN116666611A discloses a pre-sodiumized hard carbon negative electrode material. The material is composed of soft carbon micropowder as the core, and a pre-sodiumized carbon layer and a carbon deposition layer are coated on the outside of the core to form a core-shell structure, in which the sodium element is located in the pre-sodiumized carbon layer. This patent achieves pre-sodiumization by designing the hard carbon material into a multi-layer structure and adding the sodium element to the outer shell by physical blending. The main problems with this method are: the preparation process of the hard carbon material is complicated, the core-shell structure is unstable, and the sodium element is only present in the shell layer, with poor dispersion.

[0009] In summary, although pre-sodiumization of hard carbon anode materials has been reported, it has more or less suffered from drawbacks such as high pre-sodiumization cost, complex preparation process, high raw material loss, poor stability, and poor sodium dispersion. Furthermore, phosphorus doping and pre-sodiumization of current hard carbon materials are usually performed in different process steps, and the simultaneous pre-sodiumization and phosphorus doping process is even more complex and costly. Therefore, further research on the preparation of hard carbon anode materials to overcome the aforementioned drawbacks remains a key research focus for researchers in this field. Summary of the Invention

[0010] To address the aforementioned technical issues, the present invention provides a phosphorus-doped chitin-based hard carbon anode material prepared by a pre-sodiumization method and its application. This method features low pre-sodiumization cost, a simple preparation process, minimal raw material loss, excellent material stability, and more uniform sodium dispersion. Furthermore, the pre-sodiumization and phosphorus doping processes can be performed in a single step, simplifying the process and reducing costs.

[0011] One of the technical solutions of the present invention:

[0012] Provided is a phosphorus-doped chitin-based hard carbon negative electrode material prepared by a pre-sodiumization method. The material is obtained by using chitin as a raw material, supplemented with sodium salt, followed by ball milling, and finally undergoing pre-oxidation and carbonization processes.

[0013] Preferably, the phosphorus-doped chitin-based hard carbon negative electrode material prepared by the aforementioned pre-sodiumization method specifically comprises the following steps:

[0014] S1. Take chitosan, add sodium salt and place it in a stainless steel ball mill;

[0015] S2, ball milling the chitosan and sodium salt mixture in the ball milling jar to obtain a precursor;

[0016] S3, placing the precursor into a tube furnace for low-temperature pre-oxidation treatment;

[0017] S4. Raising the temperature to carbonize the pre-oxidized precursor, and then grinding it to obtain a pre-sodiumized chitosan-based hard carbon negative electrode material.

[0018] Preferably, in the phosphorus-doped chitin-based hard carbon negative electrode material prepared by the aforementioned pre-sodiumization method, the sodium salt is one or a combination of any multiple of disodium hydrogen phosphate, sodium hydrogen phosphite, sodium hypophosphite, sodium pyrophosphate or sodium phytate in any ratio.

[0019] Preferably, in the phosphorus-doped chitin-based hard carbon negative electrode material prepared by the aforementioned pre-sodiumization method, in S1, the sodium salt accounts for 5-30% of the total mass of the mixture.

[0020] Preferably, for the phosphorus-doped chitin-based hard carbon negative electrode material prepared by the aforementioned pre-sodiumization method, in the S2, the ball milling speed is 400-600 r / min and the time is 2-6 h.

[0021] Preferably, for the phosphorus-doped chitin-based hard carbon negative electrode material prepared by the aforementioned pre-sodiumization method, in S3, the pre-oxidation temperature is 200-500° C. and the time is 1-3 hours.

[0022] Preferably, for the phosphorus-doped chitin-based hard carbon negative electrode material prepared by the aforementioned pre-sodiumization method, in the S4, the carbonization temperature is 1000-1600° C. and the time is 1-3 h.

[0023] Preferably, the phosphorus-doped chitosan-based hard carbon negative electrode material prepared by the aforementioned pre-sodiumization method has a particle size of 3-20 μm.

[0024] The second technical solution of the present invention:

[0025] Provided is a chitosan-based hard carbon negative electrode material, which is prepared according to the aforementioned method.

[0026] The third technical solution of the present invention:

[0027] Provided is an application of a chitosan-based hard carbon negative electrode material in a sodium ion battery. The chitosan-based hard carbon negative electrode material is prepared according to the aforementioned method.

[0028] Beneficial effects of the present invention:

[0029] 1. The present invention uses chitosan as a carbon source, supplemented with sodium salt, and then mixes the sodium salt and the carbon source by physical ball milling to obtain a precursor. This method does not require other additives during the preparation process, and does not require complex chemical reactions. Therefore, the preparation process is simpler, the cost is lower, the preparation is more controllable, and the sodium salt is completely mixed with the carbon source for carbonization, resulting in less loss of sodium salt raw materials.

[0030] 2. In the hard carbon material prepared by the present invention, the sodium salt is fully mixed with the carbon source material, the dispersion of the sodium element in the hard carbon negative electrode is higher, and the material stability is better.

[0031] 3. When sodium phytate is selected as the sodium salt, the present invention not only realizes pre-sodiumization, but also simultaneously incorporates phosphorus in a one-step process, which makes the process simpler and the cost lower.

[0032] 4. When sodium phytate is selected as the sodium salt in the present invention, a large number of closed pores can be introduced by utilizing the pre-oxidation process and the phytate anion group, which is more conducive to Na + It can prevent the storage and diffusion of chitin-derived hard carbon materials and hinder the excessive graphitization of the materials, thus solving the performance limitations of chitin-derived hard carbon materials in their applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The constant current charge-discharge graphs obtained by assembling half-cells of the hard carbon electrode materials obtained in the comparative example, Example 1, and Example 2 of the present invention are shown. After the addition of sodium salt and the pre-oxidation step, the oxygen-containing groups and phytate anion groups introduced during the pre-oxidation process generate volatile gases at high temperatures, creating pores. Furthermore, the residual Na in the carbon layer offsets the irreversible sodium loss during the first down-cycle. This results in Example 2 exhibiting a high first-pass coulombic efficiency of 92.3% and a high specific capacity of 340 mAh / g. Example 1 exhibits a high first-pass coulombic efficiency of 90.4% and a high specific capacity of 316 mAh / g. The comparative example exhibits only a first-pass coulombic efficiency of 72% and a specific capacity of 285 mAh / g.

[0034] Figure 2 Figure 2 shows the capacity contribution of different charge and discharge regions for half-cells assembled from the hard carbon electrode materials obtained in the comparative example, Example 1, and Example 2. The percentage of the plateau region, representing the pore capacity contribution, decreases from Example 2 to Example 1 to the comparative example, demonstrating that the developed pore structure in Example 2 contributes to the increased capacity.

[0035] Figure 3 The figure shows the rate performance of the half-cell assembled with the hard carbon electrode materials obtained in the comparative example, example 1 and example 2 of the present invention. -1 The current density showed 336, 320, 289, 240, 140 mAh g -1 The specific capacity of Example 1 is 0.1-2Ag -1 The current densities of 307, 287, 252, 194, and 107 mAh g -1 The specific capacity of the comparative example is 0.1-2Ag -1 The current density only showed 258, 244, 215, 166, and 90 mAh g -1 Specific capacity.

[0036] Figure 4 Long-term cycling performance at 0.5 A / g for half-cells assembled from the hard carbon electrode materials obtained in the comparative example, Example 1, and Example 2. Example 2 maintained 91% capacity retention after 200 cycles at this current density, while the comparative example exhibited significant capacity decay.

[0037] Figure 5The X-ray diffraction patterns of the hard carbon electrode materials obtained in the comparative example, example 1, and example 2 of the present invention are shown. In the XRD test, the peak at about 25° represents the diffraction peak of the 002 crystal plane. Overall, all three materials show a distinct broad peak representing an undesired structure. However, the width of the diffraction peak representing the 002 crystal plane increases from example 2 to the comparative example, which also indicates an increase in disordered structure. At the same time, the peak position shifts toward a lower angle from example 2 to the comparative example, indicating a widening of the interplanar spacing. The d of example 2 is calculated using the Bragg equation. 002 The spacing is 0.39nm, while that of the comparative example is 0.378nm. The increase in the interlayer spacing of the material is due to the interaction of the introduction of P doping with carbon atoms during the carbonization process.

[0038] Figure 6 This is the transmission electrode spectrum of the hard carbon electrode material obtained in the comparative example, Example 1 and Example 2 of the present invention. In the TEM image, the number of locally ordered microcrystals in the comparative example decreases, and the degree of disorder of the material increases, which is mainly manifested in that the basal plane length of the carbon layer becomes longer and the curvature of the carbon layer becomes greater. Thanks to the fact that the added sodium phytate contains a large amount of O element that escapes in the form of gas during the carbonization process, a large number of pores are found in the image obtained in Example 1 at a lower magnification. The material of Example 2 has undergone a pre-oxidation process, which has a greater increase in pore content. A large number of pores make Na + Diffusion in hard carbon materials becomes easier. At the same time, due to the effect of P element doping on the carbon layer spacing, the d of the carbon layer of Example 2 was calculated by TEM FTT. 002 It is about 0.392nm, which is much larger than the 0.376nm of the comparative example. At the same time, the widened interlayer spacing is more conducive to Na + transmission and storage process.

[0039] Figure 7 These are the low-angle X-ray diffraction patterns of the hard carbon electrode materials obtained in the comparative example, Example 1, and Example 2 of the present invention. The hard carbon material prepared after adding the sodium salt clearly exhibits a plateau in the middle region, indicating a rich closed-pore structure within the material. This closed-pore structure within the hard carbon has been shown to provide a large sodium storage capacity. The comparative example, on the other hand, exhibits only a single inclined straight line, indicating a relatively low level of closed-pore structure. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to the examples, but they are not intended to limit the present invention.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0042] Unless otherwise specified, the reagents and materials used in the following examples can be obtained from commercial sources.

[0043] The battery performance tests in the following embodiments were all conducted using the Chenhua battery testing system. The sodium sheet used as the positive electrode, the prepared hard carbon material as the negative electrode, the glass fiber membrane as the diaphragm, and the electrolyte of the following embodiments were NaFP6 dissolved in diethylene glycol dimethyl ether. The batteries were assembled into CR2032 button batteries in an argon atmosphere, and the electrochemical capacity, rate performance and stability tests were conducted at constant current density and different current densities.

[0044] Comparative Example

[0045] 3 g of chitosan powder was placed in a tube furnace, heated to 1300 °C at a heating rate of 5 °C / min, and carbonized for 2 h to prepare a hard carbon negative electrode material.

[0046] 1MNaFP6 was dissolved in diethylene glycol dimethyl ether electrolyte, sodium sheet was used as positive electrode, the prepared hard carbon material was used as negative electrode, and glass fiber membrane was used as separator. A CR2032 button battery was assembled in an argon atmosphere, and electrochemical capacity, rate performance and stability tests were carried out.

[0047] Example 1

[0048] Add 0.3g of C6H6Na to 3g of chitin 12 O 24 P6, ball milled in a ball mill at a speed of 480 r / min for 4 h to obtain chitosan & sodium phytate precursor powder.

[0049] The chitosan and sodium phytate precursor powders were placed in a tube furnace and heated to a carbonization temperature of 1300°C at a heating rate of 5°C / min for 2 hours to prepare a hard carbon negative electrode material.

[0050] 1MNaFP6 was dissolved in diethylene glycol dimethyl ether electrolyte, sodium sheet was used as positive electrode, the prepared hard carbon material was used as negative electrode, and glass fiber membrane was used as separator. A CR2032 button battery was assembled in an argon atmosphere, and electrochemical capacity, rate performance and stability tests were carried out.

[0051] Example 2

[0052] Add 0.3g of C6H6Na to 3g of chitin 12 O 24 P6, ball milled in a ball mill at a speed of 480 r / min for 4 h to obtain chitosan & sodium phytate precursor powder.

[0053] The chitosan and sodium phytate precursor powders were placed in a tube furnace and pre-oxidized at 350°C in an air atmosphere for 2 hours. The temperature was then raised to a carbonization temperature of 1300°C at a heating rate of 5°C / min in an inert atmosphere for 2 hours to prepare a hard carbon negative electrode material.

[0054] 1MNaFP6 was dissolved in diethylene glycol dimethyl ether electrolyte, sodium sheet was used as positive electrode, the prepared hard carbon material was used as negative electrode, and glass fiber membrane was used as separator. A CR2032 button battery was assembled in an argon atmosphere, and electrochemical capacity, rate performance and stability tests were carried out.

[0055] Example 3

[0056] 0.3 g of disodium hydrogen phosphate was added to 3 g of chitosan, and the mixture was ball milled at a speed of 480 r / min for 4 h to obtain chitosan & disodium hydrogen phosphate precursor powder.

[0057] The chitosan and disodium hydrogen phosphate precursor powders were placed in a tube furnace and pre-oxidized at 350°C in an air atmosphere for 2 hours. The temperature was then raised to a carbonization temperature of 1300°C in an inert atmosphere at a heating rate of 5°C / min for 2 hours to prepare a hard carbon negative electrode material.

[0058] Example 4

[0059] 0.3 g of sodium hydrogen phosphite was added to 3 g of chitosan, and the mixture was ball milled at a speed of 480 r / min for 4 h to obtain chitosan and sodium hydrogen phosphite precursor powder.

[0060] The chitosan and sodium hydrogen phosphite precursor powders were placed in a tube furnace and pre-oxidized at 350°C in an air atmosphere for 2 hours. The temperature was then raised to a carbonization temperature of 1300°C in an inert atmosphere at a heating rate of 5°C / min for 2 hours to prepare a hard carbon negative electrode material.

[0061] Example 5

[0062] 0.3 g of sodium hypophosphite was added to 3 g of chitosan, and the mixture was ball milled at a speed of 480 r / min for 4 h to obtain chitosan and sodium hypophosphite precursor powder.

[0063] The chitosan and sodium hypophosphite precursor powders were placed in a tube furnace and pre-oxidized at 350°C in an air atmosphere for 2 hours. The temperature was then raised to a carbonization temperature of 1300°C at a heating rate of 5°C / min in an inert atmosphere for 2 hours to prepare a hard carbon negative electrode material.

[0064] Example 6

[0065] 0.3 g of sodium pyrophosphate was added to 3 g of chitosan, and the mixture was ball milled at a speed of 480 r / min for 4 h to obtain chitosan and sodium pyrophosphate precursor powder.

[0066] The chitosan and sodium pyrophosphate precursor powders were placed in a tube furnace and pre-oxidized at 350°C in an air atmosphere for 2 hours. The temperature was then raised to a carbonization temperature of 1300°C at a heating rate of 5°C / min in an inert atmosphere for 2 hours to prepare a hard carbon negative electrode material.

[0067] Example 7

[0068] 0.2 g of sodium pyrophosphate and 0.1 g of disodium hydrogen phosphate were added to 3 g of chitosan, and the mixture was ball milled at a speed of 480 r / min for 4 h to obtain chitosan, sodium pyrophosphate, and disodium hydrogen phosphate precursor powder.

[0069] The chitosan & sodium pyrophosphate & disodium hydrogen phosphate precursor powders were placed in a tube furnace and pre-oxidized at 350°C in an air atmosphere for 2 hours. Then, the temperature was increased to a carbonization temperature of 1300°C at a heating rate of 5°C / min in an inert atmosphere for 2 hours to prepare a hard carbon negative electrode material.

[0070] Example 8

[0071] 0.15 g of sodium hydrogen phosphite and 0.15 g of sodium hypophosphite were added to 3 g of chitosan, and the mixture was ball milled at a speed of 480 r / min for 4 h to obtain chitosan, sodium hydrogen phosphite, and sodium hypophosphite precursor powder.

[0072] The chitosan & sodium hydrogen phosphite & sodium hypophosphite precursor powders were placed in a tube furnace and pre-oxidized at 350°C in an air atmosphere for 2 hours. Then, the temperature was increased to a carbonization temperature of 1300°C in an inert atmosphere at a heating rate of 5°C / min for 2 hours to prepare a hard carbon negative electrode material.

[0073] Example 9

[0074] Add 0.5g of C6H6Na to 9.5g of chitin 12 O 24 P6, ball milled in a ball mill at a speed of 400 r / min for 6 h to obtain chitosan & sodium phytate precursor powder.

[0075] The chitosan and sodium phytate precursor powders were placed in a tube furnace and pre-oxidized at 200°C in an air atmosphere for 3 hours. The temperature was then raised to a carbonization temperature of 1000°C at a heating rate of 5°C / min in an inert atmosphere for 3 hours to prepare a hard carbon negative electrode material.

[0076] Example 10

[0077] Add 3g of C6H6Na to 7g of chitin 12 O 24 P6, ball milled in a ball mill at a speed of 600 r / min for 2 h to obtain chitosan & sodium phytate precursor powder.

[0078] The chitosan and sodium phytate precursor powders were placed in a tube furnace and pre-oxidized at 500°C in an air atmosphere for 1 hour. The temperature was then raised to a carbonization temperature of 1600°C in an inert atmosphere at a heating rate of 5°C / min for 1 hour to prepare a hard carbon negative electrode material.

[0079] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, can make equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, which should be covered by the scope of protection of the present invention.

Claims

1. A phosphorus-doped chitin-based hard carbon negative electrode material prepared by a pre-sodiumization method, characterized in that: It is made from chitosan as raw material, supplemented with sodium salt, ball-milled, and finally processed by pre-oxidation and carbonization.

2. The phosphorus-doped chitosan-based hard carbon negative electrode material prepared by the pre-sodiumization method according to claim 1, characterized in that: The specific steps include: S1. Take chitosan, add sodium salt and place it in a stainless steel ball mill; S2, ball milling the chitosan and sodium salt mixture in the ball milling jar to obtain a precursor; S3, placing the precursor into a tube furnace for low-temperature pre-oxidation treatment; S4. Raising the temperature to carbonize the pre-oxidized precursor, and then grinding it to obtain a pre-sodiumized chitosan-based hard carbon negative electrode material.

3. The phosphorus-doped chitosan-based hard carbon negative electrode material prepared by the pre-sodiumization method according to claim 2, characterized in that: The sodium salt is one or a combination of any multiple of disodium hydrogen phosphate, sodium hydrogen phosphite, sodium hypophosphite, sodium pyrophosphate or sodium phytate in any ratio.

4. The phosphorus-doped chitosan-based hard carbon negative electrode material prepared by the pre-sodiumization method according to claim 2, characterized in that: In the S1, the sodium salt accounts for 5-30% of the total mass of the mixture.

5. The phosphorus-doped chitosan-based hard carbon negative electrode material prepared by the pre-sodiumization method according to claim 2, characterized in that: In S2, the ball milling speed is 400-600 r / min and the time is 2-6 h.

6. The phosphorus-doped chitosan-based hard carbon negative electrode material prepared by the pre-sodiumization method according to claim 2, characterized in that: In the step S3, the pre-oxidation temperature is 200-500° C. and the time is 1-3 hours.

7. The phosphorus-doped chitosan-based hard carbon negative electrode material prepared by the pre-sodiumization method according to claim 2, characterized in that: In the step S4, the carbonization temperature is 1000-1600° C. and the carbonization time is 1-3 hours.

8. The phosphorus-doped chitosan-based hard carbon negative electrode material prepared by the pre-sodiumization method according to claim 2, characterized in that: The particle size of the chitosan-based hard carbon negative electrode material is 3-20 μm.

9. A chitosan-based hard carbon negative electrode material, characterized in that: Prepared according to the method according to any one of claims 1 to 8.

10. Application of a chitosan-based hard carbon negative electrode material in a sodium ion battery, characterized in that: The chitosan-based hard carbon negative electrode material is prepared according to the method according to any one of claims 1-8.

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