A nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material and its preparation method and application

Abstract

The invention discloses a preparation method of a nitrogen-phosphorus-sulfur tri-doped hard carbon negative electrode material, comprising the following steps: crushing protein-rich biomass and then sieving and collecting it; soaking the crushed biomass in a phosphorus source solution, separating and drying the solids; introducing an organic small molecule gas into the dried biomass under the protection of an inert gas for high-temperature pyrolysis to obtain a carbon material, and treating it with nitrogen-, phosphorus- and sulfur-containing gases to replace oxygen-containing functional groups; heating and washing the obtained carbon material with a strong alkaline solution to remove excess phosphorus source, washing it with water to neutral separation, and drying it to obtain a nitrogen-phosphorus-sulfur tri-doped hard carbon negative electrode material; cracking and carbonizing the organic small molecule gas in the pores so that the material has an adjustable special pore structure, nitrogen, phosphorus and sulfur doping improves the affinity between sodium ions and the material, and the larger atomic radius of phosphorus and sulfur expands the hard carbon layer spacing, which is beneficial to the insertion and extraction of sodium ions, improves the sodiumization kinetics, and at the same time improves the electrode reversibility, thereby obtaining a higher coulombic efficiency.

Description

Technical Field

[0001] The present invention relates to the fields of biomass utilization and new energy materials, and in particular to a nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material, a preparation method and applications thereof. Background Art

[0002] With the rapid development of electric vehicles, stationary energy storage, and mobile devices, the market has put forward new requirements for high performance and low cost of batteries and battery materials. Lithium-ion batteries and sodium-ion batteries, as important energy storage systems, have the characteristics of high energy density, high charge and discharge efficiency, and high cycle stability. In batteries, the positive electrode material is the main determinant of battery energy. At the same time, the performance of the negative electrode material is also crucial to battery performance. Its capacity and the reversible insertion / deinsertion kinetics of lithium / sodium ions affect the overall performance of the whole battery. In order to meet the requirements of high efficiency, long cycle life, and low cost of batteries, the development of new negative electrode materials is becoming increasingly important. Existing commercial lithium-ion battery negative electrode materials are mainly graphite and silicon carbon, but neither is suitable for sodium-ion batteries and does not have cost advantages. Therefore, finding alternative and sustainable sodium-ion battery negative electrode materials has become a research hotspot.

[0003] Biomass is considered to be the most promising precursor for negative electrode materials of sodium ion batteries due to its low price, abundant resources, and the ability to form hard carbon materials through high-temperature pyrolysis and carbonization. At the same time, the comprehensive utilization of waste biomass resources can also alleviate environmental pressure and increase the added value of waste biomass, especially the residue (oil residue) left after oil extraction from seed crops, which is usually used as animal feed or microbial culture medium with low added value; the main components of oil residue are cellulose and protein, rich in nitrogen and sulfur elements. At the same time, such biomass precursors are treated with the introduction of an external phosphorus source, and the capillary effect brought by their own rich cellulose components can be used to achieve The uniform and sufficient mixing of the precursor and the phosphorus source and the carbonization treatment are beneficial to obtaining nitrogen, phosphorus and sulfur triple-doped carbon materials. In addition, by introducing nitrogen-containing, phosphorus-containing and sulfur-containing atmosphere heat treatment, the oxygen-containing functional groups that are detrimental to the reversibility and coulombic efficiency of the battery can be partially replaced by nitrogen-containing, phosphorus-containing and sulfur-containing functional groups. This nitrogen, phosphorus and sulfur doping treatment of the carbon negative electrode material can adjust and improve the affinity of sodium ions and the negative electrode material. At the same time, phosphorus and sulfur have larger atomic radii, which are also beneficial to expand the interlayer spacing of the hard carbon material and facilitate the insertion and extraction of sodium ions. While improving the kinetics of the sodiumization process, it can also improve the reversibility of the electrode material and obtain higher coulombic efficiency. Summary of the Invention

[0004] The present invention provides a method for preparing a nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material, which solves the problem of low first-cycle coulombic efficiency of existing hard carbon negative electrodes and the problem of high value-added utilization of biomass waste.

[0005] In order to solve this technical problem, the present invention provides the following technical solutions:

[0006] A method for preparing a nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material comprises the following steps:

[0007] S1: crushing the hard carbon negative electrode material biomass precursor and passing it through a 100-500 mesh sieve;

[0008] S2: soaking the sieved hard carbon negative electrode material biomass precursor in a phosphorus source solution for at least 1 hour, then centrifuging or filtering, and vacuum drying;

[0009] S3: placing the dried biomass precursor into a high-temperature atmosphere furnace and introducing inert gas protection, heat treating it at a temperature of 900-1500°C for 1-5 hours. At the end of the heat treatment, additional organic small molecule gas at a certain ratio relative to the inert atmosphere is introduced for 1-10 minutes. The organic small molecule gas undergoes high-temperature vapor deposition, depositing carbon formed by the decomposition of small molecules in the micropores and mesopores of the hard carbon formed by the decomposition of macromolecular components in the biomass precursor, thereby regulating the pore structure of the hard carbon material;

[0010] S4: After the high-temperature heat treatment time in the previous step is completed, the temperature is controlled to be lowered to 250-400°C, and a nitrogen-, phosphorus-, and sulfur-containing gas is additionally introduced in a certain proportion relative to the inert atmosphere, and heat treated for 1-3 hours to partially replace the oxygen-containing functional groups in the carbon material formed by pyrolysis with nitrogen-, phosphorus-, and sulfur-containing functional groups. The tail gas in this process is first introduced into an alkaline solution, then into an acid solution, and finally into water;

[0011] S5: The carbon material obtained by pyrolysis is placed in a strong alkaline solution for washing and heating. The treatment time is not less than 2 hours and the temperature does not exceed 100°C. After the treatment is completed, it is repeatedly washed with water and filtered or centrifuged until it is neutral. After vacuum drying, the nitrogen, phosphorus and sulfur doped hard carbon negative electrode material is obtained.

[0012] The beneficial effects of adopting the above technical solution are as follows: (1) the biomass precursor is crushed and then sieved to obtain a precursor powder with a concentrated particle size distribution, which is beneficial to the uniformity of the precursor absorbing the phosphorus source solution by capillary action during the phosphorus source solution treatment, and the uniform precursor particles are also beneficial to obtaining a hard carbon material with a concentrated particle size distribution after high-temperature carbonization. The concentrated particle size distribution is beneficial to obtaining a negative electrode sheet with uniform quality and thickness after the hard carbon material is subjected to roller treatment in the preparation of the negative electrode sheet;

[0013] (2) The biomass precursor contains a high cellulose content and has a capillary effect. The inorganic or organic phosphorus source solution is easily absorbed into the precursor. After separation, the biomass precursor that absorbs the phosphorus source can be obtained. Since the biomass precursor is pre-crushed and sieved, the uniformity of the phosphorus source absorption in the biomass precursor can be ensured, which is conducive to the uniform doping of phosphorus in the hard carbon material during the further heat treatment and carbonization process.

[0014] (3) The biomass precursor treated with phosphorus source is subjected to high-temperature heat treatment. Since the biomass precursor used is rich in protein components, it is beneficial to the nitrogen and sulfur doping of the carbon material during the high-temperature heat treatment carbonization process. A higher heat treatment temperature is used in this process. At the same time, due to the introduction of phosphorus element, it plays an inducing and promoting role in the crystallization of the carbon material during the high-temperature carbonization process of the biomass precursor. Therefore, the high heat treatment temperature and the introduction of phosphorus source are conducive to obtaining a closed-pore nitrogen-phosphorus-sulfur doped hard carbon material with a low specific surface area. The contact area with the electrolyte is small, and the side reactions on the surface of the material during the battery process are few, resulting in a high first-cycle coulomb efficiency. In addition, phosphorus and sulfur have larger atomic radii. The introduction of the two doping is conducive to expanding the interlayer spacing of the hard carbon material, which is more conducive to the reversible insertion and extraction of sodium ions. When matched with the positive electrode material to form a full battery, the capacity of the positive electrode material can be maximized, and it has a broader practical application prospect.

[0015] (4) During the high-temperature pyrolysis and carbonization of the biomass precursor, organic small molecule gases are introduced. Under high temperature, the organic small molecules enter the void structure of the hard carbon material and undergo cracking and carbonization, filling the micropores and mesopores of the hard carbon material. By controlling the types of different organic small molecules, the proportion of relatively inert atmosphere, and the treatment time, the pore structure and specific surface area of the hard carbon material can be regulated, thereby achieving the adjustable microstructure of the hard carbon material. The adjustable microstructure can also bring about the adjustable performance of the hard carbon negative electrode material.

[0016] (5) The oxygen-containing functional groups in hard carbon materials have too high binding energy with sodium ions, which makes it difficult for sodium ions bound to the active sites of oxygen-containing functional groups during the electrochemical process to be removed, resulting in irreversible sodium storage, which is not conducive to the coulombic efficiency of hard carbon negative electrode materials. By using nitrogen-, phosphorus-, and sulfur-containing gases to treat the carbon materials formed by pyrolysis, some of the oxygen-containing functional groups on the surface of the materials can be replaced with nitrogen-, phosphorus-, and sulfur-containing functional groups. The binding energy of these three functional groups with sodium ions is in a moderate range, which makes it easy to bind to sodium ions without making it difficult to remove sodium ions, and can bring about reversible storage of sodium ions. Therefore, this replacement of oxygen-containing functional groups can effectively improve the reversibility of hard carbon negative electrode materials and obtain higher first-cycle coulombic efficiency.

[0017] (6) The tail gas generated after the carbon material formed by pyrolysis is treated with nitrogen-, phosphorus- and sulfur-containing gases is first passed into an alkaline solution, then into an acid solution, and finally into water. This tail gas treatment method can remove unreacted ammonia, phosphine and hydrogen sulfide gases. Passing the tail gas into the alkaline solution can first remove the two acidic gases phosphine and hydrogen sulfide, then passing the tail gas into the acid solution can remove the remaining ammonia, and finally passing the tail gas into water can remove the remaining trace ammonia, phosphine, hydrogen sulfide, and the solute components in the acid solution that may overflow. In addition, the method of first passing the alkaline solution and then the acid solution can also prevent the large-scale overflow of the solute components of the acid solution that may be caused by the high-temperature tail gas contacting the acid solution.

[0018] (7) Since the energy barrier required for doping phosphorus into carbon materials is high and the reaction kinetics is relatively slow, the phosphorus source introduced in the present invention will not completely bond with the carbon material under high temperature conditions and be doped into the carbon material, and the excess undoped phosphorus source will exist as an impurity, which will inevitably be detrimental to the electrochemical properties of the carbon material. Therefore, the remaining phosphorus source needs to be removed. The remaining phosphorus source may exist in the form of phosphorus element, phosphorus oxide, phosphide, phosphate, etc., and the strong alkaline solution will react with phosphorus element and phosphorus oxide, dissolve the phosphorus element and phosphorus oxide that may be produced, and the phosphide will be hydrolyzed and dissolved when it comes into contact with water. At the same time, phosphate is mainly water-soluble sodium phosphate. Therefore, the carbon material obtained by treating with a strong alkaline solution can completely remove the residual phosphorus element, phosphorus oxide, phosphide, phosphate, etc. that may exist therein, and at the same time, it will not react with the doped phosphorus that has been bonded to the carbon, while maintaining the phosphorus doping amount of the carbon material and removing the unfavorable phosphorus-containing residual impurities, thereby obtaining a high-quality nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material.

[0019] Preferably, the biomass precursor is the residue left after oil is extracted from seed crops, including one or more of cottonseed meal, palm meal, chili seed meal, tung nut meal, litsea cubeba meal and oil-sand soybean meal.

[0020] The beneficial effects of adopting the above technical solution are as follows: (1) The protein content in the residues left after oil extraction from seed crops such as cottonseed meal, palm meal, chili seed meal, tung nut meal, elm seed meal and oil-sand soybean meal is high, and it is easier to form nitrogen- and sulfur-doped hard carbon materials during high-temperature heat treatment and carbonization; (2) The cellulose content in this type of biomass precursor is high, and the overall theoretical carbon content is high, which is conducive to ensuring a high carbon yield; (3) This type of biomass precursor has a large output, narrow existing uses and low added value. It is only used as animal feed or microbial culture medium, and the price is generally 2,000 to 3,000 yuan / ton. The hard carbon negative electrode material prepared from it currently has a market price of 100,000 yuan / ton, which has the advantage of high added value.

[0021] Preferably, the phosphorus source solution is selected from an aqueous solution of phosphoric acid, sodium phosphate, phytic acid, sodium phytate, sodium pyrophosphate, sodium tripolyphosphate, and a carbon tetrachloride solution of triphenyl phosphate, phenylphosphonic acid, phosphorus trichloride, and phosphorus pentachloride, with a concentration of 0.1 mol / L to 5 mol / L.

[0022] The beneficial effects of adopting the above technical solution are as follows: (1) when using this type of inorganic or organic phosphorus source solution to treat a biomass precursor, since the precursor is mainly composed of cellulose, it has a capillary effect and can absorb the phosphorus source into the biological tissue of the precursor, which is beneficial to the incorporation of phosphorus elements during high-temperature heat treatment and obtains phosphorus-doped hard carbon materials; (2) since the biomass precursor must be centrifuged or filtered after treatment with the phosphorus source solution, the amount of phosphorus source solute remaining in the biomass precursor is limited, and the phosphorus source in the phosphorus source solution is extremely excessive, the prepared phosphorus source solution only needs to be supplemented with a very small amount of phosphorus source solute and can be reused.

[0023] Preferably, the heating rate of the heat treatment is 5-10°C / min before 400°C, and 0.5-5°C / min after 400°C.

[0024] The beneficial effects of the above technical solution are as follows: the temperature range of 400-500℃ is the temperature range in which the decomposition and carbonization rate of the biomass precursor is the fastest. Before this temperature, in order to improve the heat treatment efficiency and reduce the time cost, it is necessary to carry out the process at a faster heating rate; after reaching the temperature range of 400-500℃, the biomass will decompose rapidly, producing a large amount of carbon oxide gas and water vapor. After the temperature reaches 400℃, the heating rate should be slowed down to avoid the rapid expansion of the material caused by the large amount of gas generated due to excessive decomposition, which will be ejected from the container and cause pollution to the furnace and materials. Problem: At the same time, after the biomass is carbonized in the temperature range of 400-500℃, further heating it to a higher temperature at a slow heating rate is conducive to the formation of a short-range ordered and long-range disordered characteristic structure of hard carbon materials. If the initial faster heating rate is still maintained during this process, the carbon material will crystallize too quickly, which is not conducive to the formation of a short-range ordered structure. The obtained carbon material cannot fully provide a place for sodium ions to embed when used as the negative electrode of a sodium ion battery, resulting in a decrease in capacity. The above technical solution takes into account the economic efficiency of heat treatment, prevention of pollution of hard carbon materials, and optimization of the performance of hard carbon materials.

[0025] Preferably, the additional organic small molecule gas introduced is selected from one of methane, ethane, acetylene and liquefied petroleum gas, and accounts for 0.5% to 3% of the volume of the inert gas.

[0026] The beneficial effects of adopting the above technical solution are: methane, ethane, acetylene, liquefied petroleum gas and other organic small molecule gases are all cheap and easily available gases. Due to their small molecular weight, they can easily enter the micropores and mesopores, and will undergo cracking at the pyrolysis and carbonization temperature of the hard carbon material used in the present invention. After these organic small molecules entering the micropores and mesopores of the hard carbon are cracked and carbonized, they will fill the micropores and mesopores of the hard carbon material. By controlling the different types of organic small molecules, the proportion of relatively inert atmosphere and the treatment time, the pore structure and specific surface area of the hard carbon material can be regulated, the microstructure of the hard carbon material can be adjusted, and the performance of the hard carbon negative electrode material can be adjusted.

[0027] Preferably, the nitrogen-containing gas is ammonia, the phosphorus-containing gas is phosphine, and the sulfur-containing gas is hydrogen sulfide, wherein ammonia is a finished gas, phosphine is obtained by hydrolysis of aluminum phosphide, or by thermal decomposition of sodium hypophosphite, and hydrogen sulfide is obtained by hydrolysis of sodium sulfide, or by thermal decomposition of dimethyl sulfoxide, and the volume proportion of the ammonia gas relative to the inert gas is 5% to 30%.

[0028] The beneficial effects of the above technical solution are as follows: ammonia, phosphine and hydrogen sulfide gases have high reaction activity at high temperature and can react with some oxygen-containing functional group sites on the surface of hard carbon materials. However, due to the high binding energy of oxygen-containing functional groups with sodium ions, it is difficult for sodium ions bound to the active sites of oxygen-containing functional groups in the electrochemical process to be removed, resulting in irreversible sodium storage, which is not conducive to the coulomb efficiency of hard carbon negative electrode materials. The carbon material formed by pyrolysis is treated with nitrogen-containing, phosphorus-containing and sulfur-containing gases, which can replace some oxygen-containing functional groups on the surface of the material with nitrogen-containing, phosphorus-containing and sulfur-containing functional groups. These three The binding energy between the functional group and the sodium ion is within a moderate range, which makes it easy to bind to the sodium ion but not difficult to remove the sodium ion, thus leading to the reversible storage of the sodium ion. Therefore, this substitution of the oxygen-containing functional group can effectively improve the reversibility of the hard carbon negative electrode material and obtain a higher first-cycle coulombic efficiency. In addition, since phosphine and hydrogen sulfide gases are not easy to store for a long time, the present invention uses sodium sulfide hydrolysis or dimethyl sulfoxide thermal decomposition to prepare fresh hydrogen sulfide gas, and uses aluminum phosphide hydrolysis or sodium hypophosphite thermal decomposition to prepare fresh phosphine gas, which can be prepared and used immediately, solving the storage problem of phosphine and hydrogen sulfide gases.

[0029] Preferably, the strong alkaline solution is selected from one of aqueous solutions of sodium hydroxide and potassium hydroxide, and the concentration is 1 mol / L to 20 mol / L.

[0030] The beneficial effect of adopting the above technical solution is that after introducing a phosphorus source for phosphorus doping, a phosphorus-doped hard carbon negative electrode material can be obtained, but there may be excess phosphorus that is not doped into the carbon material, which may have an adverse effect on battery performance. The use of a strong alkaline solution and heating washing treatment can remove possible residual impurities such as phosphates, phosphides, elemental phosphorus, etc.

[0031] The carbon material obtained by the above-mentioned preparation method of nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material can be applied to the application of sodium ion battery negative electrode material.

[0032] The beneficial effects of adopting the above technical solution are as follows: when using the preparation method of the nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material of the present invention, the protein components rich in the biomass precursors cottonseed meal, palm meal, pepper seed meal, tung seed meal, elm seed meal and oil sand bean meal are helpful for nitrogen and sulfur doping of the carbon material during high temperature carbonization, while the treatment of the phosphorus source is beneficial for phosphorus doping of the carbon material during high temperature carbonization. The two can work together to realize the preparation of nitrogen, phosphorus and sulfur tri-doped hard carbon material. The introduction of organic small molecules can cause their cracking and carbonization in the void structure of the hard carbon material, regulate the pore structure, and nitrogen-, phosphorus- and sulfur-containing gases The high-temperature treatment can partially replace the oxygen-containing functional groups that are detrimental to the reversibility of the hard carbon negative electrode material with nitrogen-containing, phosphorus-containing, and sulfur-containing functional groups, thereby improving the coulombic efficiency of the hard carbon negative electrode. In addition, phosphorus and sulfur have larger atomic radii, which are also beneficial to expand the interlayer spacing of the hard carbon material and facilitate the insertion and extraction of sodium ions. This carbon material has good electrochemical properties when used as the negative electrode of sodium ion batteries. At the same time, the high heat treatment temperature and the induction and promotion effect of phosphorus on the crystallization of carbon materials during the high-temperature carbonization of biomass precursors are conducive to obtaining closed-pore hard carbon materials with low specific surface area (specific surface area ≤10m 2 / g), this hard carbon material has a high specific surface area (specific surface area ≥ 100m 2 / g), its contact area with the electrolyte is small, and fewer side reactions occur on the material surface during the battery process, so the reversibility is greatly improved, and the first-cycle coulombic efficiency is much higher than that of porous hard carbon materials with high specific surface area. The high first-cycle coulombic efficiency is beneficial to the practical application of negative electrode materials. When it is matched with the positive electrode material to form a full battery, the irreversible sodium loss is small, which is conducive to maximizing the capacity of the positive electrode material.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] (1) Resource recycling and added value improvement: The present invention uses the residue left after oil extraction from low-value-added seed crops as a precursor, and utilizes the nitrogen and sulfur elements rich in the residue as well as the additional phosphorus element introduced, to obtain nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode materials through high-temperature pyrolysis and carbonization, turning waste into treasure, achieving effective resource recycling, reducing waste generation and environmental impact, and greatly improving added value;

[0035] (2) Efficient preparation of hard carbon anode materials: Through a unique pyrolysis carbonization process and nitrogen-phosphorus doping process, the present invention successfully prepares nitrogen-phosphorus-sulfur doped hard carbon materials while ensuring a carbon yield greater than 40%. This method can efficiently convert oil-pressing residues of seed crops such as cottonseed meal, palm meal, pepper seed meal, tung seed meal, litsea cubeba meal, and soybean meal into nitrogen-phosphorus-sulfur doped hard carbon materials, providing high-quality anode materials for the preparation of sodium ion batteries.

[0036] (3) Improve battery performance: The prepared hard carbon negative electrode material has a nitrogen, phosphorus and sulfur doped structure, which provides rich active sites, regulates and improves the affinity between sodium ions and negative electrode materials, expands the interlayer spacing of hard carbon materials, and enhances the kinetics of the sodiumization process. At the same time, high heat treatment temperature, the induction and promotion of the crystallization of carbon materials by phosphorus elements during the high-temperature carbonization of biomass precursors, and the cracking and carbonization of organic small molecule gases in the hard carbon pores are conducive to obtaining closed-pore hard carbon materials with low specific surface area, reducing irreversible electrochemical side reactions on the surface of the hard carbon negative electrode. Combined with the substitution of nitrogen-containing, phosphorus-containing and sulfur-containing functional groups for oxygen-containing functional groups, high first-cycle coulomb efficiency can be obtained, which is conducive to maximizing the capacity of the positive electrode material when matched with the full battery.

[0037] (4) The hard carbon negative electrode material obtained by the present invention can be applied to sodium ion batteries to obtain excellent electrochemical performance. -1 The specific capacity reaches 350mAh g at a current density of -1 The above results show that the first-cycle coulombic efficiency reaches more than 80%; by obtaining stable and excellent electrochemical properties, it lays the foundation for the further industrial production of sodium-ion battery negative electrode materials prepared from crop oil extraction residues. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0039] Figure 1 This is a flow chart of the preparation method of the nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material of the present invention;

[0040] Figure 2 The scanning electron micrographs of the nitrogen, phosphorus and sulfur tri-doped hard carbon material prepared in Example 1 at different scales are shown;

[0041] Figure 3 The scanning electron micrographs of the carbon material prepared in Comparative Example 1 at different scales are shown;

[0042] Figure 4 Comparison of the first cycle constant current charge and discharge of the sodium ion battery assembled in Example 8 and Comparative Example 2;

[0043] Figure 5Comparison of the 10th cycle of constant current charge and discharge of the assembled sodium ion batteries of Example 8 and Comparative Example 2. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0045] Example 1

[0046] A method for preparing a nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material, such as Figure 1 As shown, the following steps are included:

[0047] S1: Crush the cottonseed meal using a crusher and collect it after passing it through a 325-mesh sieve;

[0048] S2: soaking the collected crushed cottonseed meal in a 1 mol / L phytic acid solution for 1 hour, filtering and separating the cottonseed meal solids after the treatment, and vacuum drying the treated cottonseed meal solids;

[0049] S3: placing the dried cottonseed meal in a high-temperature atmosphere furnace and introducing an inert gas as protection, heat-treating the mixture at 1300° C. for 2 hours. At the end of the heat treatment, introducing liquefied petroleum gas (1% by volume relative to the inert atmosphere) for an additional 5 minutes to obtain a carbon material;

[0050] S4: After the high-temperature heat treatment time in the previous step is completed, the temperature is controlled to 350°C, and ammonia, phosphine, and hydrogen sulfide gases are additionally introduced at 10% by volume relative to the inert atmosphere. Heat treatment is continued for 2 hours, and the tail gas is first introduced into an alkaline solution, then into an acid solution, and finally into water;

[0051] S5: The carbon material obtained by pyrolysis is placed in a 6 mol / L sodium hydroxide solution for washing and heating for 2 hours at a temperature of 80°C. After the treatment is completed, it is repeatedly washed with water and filtered or centrifuged until neutral. After vacuum drying, a nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material is obtained.

[0052] Example 2

[0053] A method for preparing a nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material comprises the following steps:

[0054] S1: Crush the cottonseed meal using a crusher and collect it after passing it through a 325-mesh sieve;

[0055] S2: soaking the collected crushed cottonseed meal in a 0.5 mol / L phytic acid solution for 1 hour, filtering and separating the cottonseed meal solids after the treatment, and vacuum drying;

[0056] S3: placing the dried cottonseed meal in a high-temperature atmosphere furnace and introducing an inert gas protection, heat-treating the mixture at 900° C. for 2 hours. At the end of the heat treatment, introducing liquefied petroleum gas (1% by volume relative to the inert atmosphere) for an additional 5 minutes to obtain a carbon material;

[0057] S4: After the high-temperature heat treatment time in the previous step is completed, the temperature is controlled to 350°C, and ammonia, phosphine, and hydrogen sulfide gases are additionally introduced at 10% by volume relative to the inert atmosphere. Heat treatment is continued for 2 hours, and the tail gas is first introduced into an alkaline solution, then into an acid solution, and finally into water;

[0058] S5: The carbon material obtained by pyrolysis is placed in a 6 mol / L sodium hydroxide solution for washing and heating for 2 hours at a temperature of 80°C. After the treatment is completed, it is repeatedly washed with water and filtered or centrifuged until neutral. After vacuum drying, a nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material is obtained.

[0059] Example 3

[0060] A method for preparing a nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material comprises the following steps:

[0061] S1: Crush the cottonseed meal using a crusher and collect it after passing it through a 325-mesh sieve;

[0062] S2: soaking the collected crushed cottonseed meal in a 3 mol / L phytic acid solution for 1 hour, filtering and separating the cottonseed meal solids after the treatment, and vacuum drying;

[0063] S3: placing the dried cottonseed meal in a high-temperature atmosphere furnace and introducing an inert gas protection, heat-treating the mixture at 1500° C. for 2 hours. At the end of the heat treatment, introducing liquefied petroleum gas (1% by volume relative to the inert atmosphere) for an additional 5 minutes to obtain a carbon material;

[0064] S4: After the high-temperature heat treatment time in the previous step is completed, the temperature is controlled to 350°C, and ammonia, phosphine, and hydrogen sulfide gases are additionally introduced at 10% by volume relative to the inert atmosphere. Heat treatment is continued for 2 hours, and the tail gas is first introduced into an alkaline solution, then into an acid solution, and finally into water;

[0065] S5: The carbon material obtained by pyrolysis is placed in a 6 mol / L sodium hydroxide solution for washing and heating for 2 hours at a temperature of 80°C. After the treatment is completed, it is repeatedly washed with water and filtered or centrifuged until neutral. After vacuum drying, a nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material is obtained.

[0066] Example 4

[0067] A method for preparing a nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material comprises the following steps:

[0068] S1: crushing the cottonseed meal using a crusher and collecting it after passing it through a 500-mesh sieve;

[0069] S2: soaking the collected crushed cottonseed meal in a 3 mol / L phytic acid solution for 1 hour, filtering and separating the cottonseed meal solids after the treatment, and vacuum drying;

[0070] S3: placing the dried cottonseed meal in a high-temperature atmosphere furnace and introducing an inert gas as protection, heat-treating the mixture at 1300° C. for 2 hours. At the end of the heat treatment, additionally introducing acetylene at 1% by volume relative to the inert atmosphere for 5 minutes to obtain a carbon material;

[0071] S4: After the high-temperature heat treatment time in the previous step is completed, the temperature is controlled to 250°C, and ammonia, phosphine, and hydrogen sulfide gases are additionally introduced at 20% by volume relative to the inert atmosphere. Heat treatment is continued for 2 hours, and the tail gas is first introduced into an alkaline solution, then into an acid solution, and finally into water;

[0072] S5: The carbon material obtained by pyrolysis is placed in a 3 mol / L potassium hydroxide solution for washing and heating for 2 hours at a temperature of 80°C. After the treatment is completed, it is repeatedly washed with water and filtered or centrifuged until neutral. After vacuum drying, a nitrogen, phosphorus and sulfur tri-doped hard carbon negative electrode material is obtained.

[0073] Example 5

[0074] The difference between this embodiment and embodiment 1 is that palm meal, chili seed meal, tung nut meal, litsea cubeba meal or soybean meal is used as the biomass precursor for treatment instead of the cottonseed meal in embodiment 1.

[0075] Example 6

[0076] The difference between this embodiment and embodiment 1 is that an aqueous solution of phosphoric acid, sodium phosphate, phytic acid, sodium phytate, sodium pyrophosphate or sodium tripolyphosphate, or a carbon tetrachloride solution of triphenyl phosphate, phenylphosphonic acid, phosphorus trichloride or phosphorus pentachloride is used instead of the phytic acid solution in embodiment 1 as the phosphorus source for treatment.

[0077] Example 7

[0078] The difference between this embodiment and embodiment 1 is that methane, ethane, and acetylene are used to replace the small organic molecule gas in embodiment 1 for treatment.

[0079] Example 8

[0080] In this embodiment, the carbon material prepared by the method of Example 1 was used as the working electrode, metallic sodium was used as the counter electrode to assemble a sodium ion battery, a glass fiber separator was used as the diaphragm, and a solution of 1M NaClO4 dissolved in ethylene carbonate and diethyl carbonate with a volume ratio of 1:1 and 5wt% fluoroethylene carbonate was added as the electrolyte. The assembled battery was tested at 300mA g -1 Charge and discharge tests were performed at different current densities.

[0081] Comparative Example 1

[0082] The difference between this comparative example and Example 1 is that no phosphorus source is used to treat the biomass precursor.

[0083] Comparative Example 2

[0084] The difference between this comparative example and Example 8 is that the carbon material prepared by the method in Comparative Example 1 is used as the working electrode.

[0085] The materials obtained in Example 1 and Comparative Example 1 were characterized. Figure 2 Scanning electron micrographs of the nitrogen, phosphorus, and sulfur tri-doped hard carbon material prepared in Example 1 at different scales show that the carbon material has a unique pore structure, and the pores exhibit a unique layered structure.

[0086] Attachment Figure 3 The scanning electron micrographs of the carbon material prepared in Comparative Example 1 at different scales show that the carbon material is in the form of loose irregular particles with no obvious pore structure.

[0087] Attachment Figure 4 The first cycle constant current charge and discharge comparison of the sodium ion battery assembled in Example 8 and Comparative Example 2 shows that the first cycle charge capacity of the sodium ion battery assembled in Example 8 is 340 mAh g -1 The first cycle coulombic efficiency reached 83%, which is much higher than that of comparative example 2. The sodium ion battery assembled in comparative example 2 only showed 215 mAh g -1 The first-cycle charging specific capacity and the first-cycle coulomb efficiency are only 61%.

[0088] Since the sodium ion battery assembled in Example 8 uses the nitrogen, phosphorus and sulfur tri-doped hard carbon material prepared in Example 1, and the sodium ion battery assembled in Comparative Example 2 uses the non-phosphorus doped carbon material prepared in Comparative Example 1, combined with the attached Figure 2 and attached Figure 3Comparison of the morphologies of the two carbon materials shows that the nitrogen-phosphorus-sulfur triple-doped hard carbon material obtained by introducing phosphorus source treatment is beneficial to the storage of electrolyte in the material due to its special pore structure and special layered structure in the pores, and can shorten the migration path of sodium ions, making sodium ion migration easier. The nitrogen, sulfur and phosphorus doping treatment can adjust and improve the affinity between sodium ions and the negative electrode material, while improving the kinetics of the sodiumization process, it can also improve the reversibility of the electrode material and obtain a higher coulombic efficiency, thereby obtaining a higher specific capacity and first-cycle coulombic efficiency.

[0089] Attachment Figure 5 This is a comparison of the 10th cycle constant current charge and discharge of the sodium ion batteries assembled in Example 8 and Comparative Example 2. It can be seen from the figure that the nitrogen, phosphorus and sulfur tri-doped hard carbon material prepared in Example 1 used in the sodium ion battery assembled in Example 8 shows a longer low potential platform during the reversible charge and discharge process, indicating that the nitrogen, phosphorus and sulfur tri-doped hard carbon material prepared in Example 1 involves more sodium ion insertion / deinsertion behavior, while the carbon material prepared in Comparative Example 1 used in the sodium ion battery assembled in Comparative Example 2 has a shorter low potential platform during the reversible charge and discharge process, and the capacity contribution is mostly in the inclined platform region, indicating that the carbon material prepared in Comparative Example 1 involves more capacitance contribution; the above results show that phosphorus doping and the special material morphology it brings jointly affect the electrochemical behavior of the material.

[0090] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material, characterized in that: The following steps are involved: S1: crushing the hard carbon negative electrode material biomass precursor and passing it through a 100-500 mesh sieve; S2: soaking the sieved hard carbon negative electrode material biomass precursor in a phosphorus source solution for at least 1 hour, then centrifuging or filtering, and vacuum drying; S3: placing the dried biomass precursor into a high-temperature atmosphere furnace and introducing inert gas protection, heat treating it at a temperature of 900-1500°C for 1-5 hours. At the end of the heat treatment, additional organic small molecule gas at a certain ratio relative to the inert atmosphere is introduced for 1-10 minutes. The organic small molecule gas undergoes high-temperature vapor deposition, depositing the carbon formed by the decomposition of small molecules in the micropores and mesopores of the hard carbon formed by the decomposition of the macromolecular components in the biomass precursor, thereby regulating the pore structure of the hard carbon material; S4: After the high-temperature heat treatment time in the previous step is completed, the temperature is controlled to be lowered to 250-400°C, and nitrogen-, phosphorus-, and sulfur-containing gases are additionally introduced in a certain proportion relative to the inert atmosphere. Heat treatment is performed for 1-3 hours to partially replace the oxygen-containing functional groups in the carbon material formed by pyrolysis with nitrogen-, phosphorus-, and sulfur-containing functional groups. The tail gas in this process is first introduced into an alkaline solution, then into an acid solution, and finally into water; S5: washing the carbon material obtained by pyrolysis in a strong alkaline solution and heating it for at least 2 hours at a temperature not exceeding 100° C. After the treatment, repeatedly washing with water and filtering or centrifuging until neutral, and vacuum drying to obtain a nitrogen-phosphorus-sulfur doped hard carbon negative electrode material; The biomass precursor is the residue left after oil is extracted from seed crops, including one or more of cottonseed meal, palm meal, chili seed meal, tung seed meal, litsea cubeba meal or soybean meal. In step S2, the phosphorus source solution is an aqueous solution of phosphoric acid, sodium phosphate, phytic acid, sodium phytate, sodium pyrophosphate or sodium tripolyphosphate, and a carbon tetrachloride solution of triphenyl phosphate, phenylphosphonic acid, phosphorus trichloride or phosphorus pentachloride, and the concentration of the phosphorus source solution is 0.1 mol / L to 5 mol / L; In step S4, the nitrogen-containing gas is ammonia, the phosphorus-containing gas is phosphine, and the sulfur-containing gas is hydrogen sulfide, wherein the ammonia is a finished gas, the phosphine is obtained by hydrolyzing aluminum phosphide or by thermal decomposition of sodium hypophosphite, and the hydrogen sulfide is obtained by hydrolyzing sodium sulfide or by thermal decomposition of dimethyl sulfoxide, and the volume proportion of the ammonia gas relative to the inert gas is 5% to 30%; In step S3, the heating rate of the heat treatment is 5-10°C / min before 400°C, and 0.5-5°C / min after 400°C.

2. The method for preparing the nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material according to claim 1, characterized in that: The type of the additional organic small molecule gas introduced in step S3 is one of methane, ethane, acetylene, and liquefied petroleum gas, and its volume ratio relative to the inert gas is 0.5% to 3%.

3. The method for preparing the nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material according to claim 1, characterized in that: In step S5, the strong alkaline solution is an aqueous solution of sodium hydroxide or potassium hydroxide, with a concentration of 1 mol / L to 20 mol / L.

4. A nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material obtained by the preparation method of the nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material according to any one of claims 1 to 3.

5. Use of the nitrogen, phosphorus and sulfur triple-doped hard carbon negative electrode material according to claim 4 in a negative electrode material for sodium ion batteries.

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