Nitrogen / phosphorus co-doped honeycomb biomass hard carbon and preparation method thereof and sodium ion battery

Abstract

The application relates to nitrogen / phosphorus co-doped honeycomb biomass hard carbon and a preparation method and a sodium ion battery thereof, and belongs to the technical field of sodium ion batteries. The application discloses nitrogen / phosphorus co-doped honeycomb biomass hard carbon, wherein the nitrogen doping amount of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon is 2-3 wt%, the phosphorus doping amount is 1-1.6 wt%, and the specific surface area is 30-80 m 2 / g. The application further discloses a preparation method of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon, which comprises the following steps: mixing polylactic acid and nitrogenized humus, mixing the mixture with a phosphate solution, drying after ultrasonic treatment, then low-temperature cross-linking and low-temperature carbonization to obtain the nitrogen / phosphorus co-doped honeycomb biomass hard carbon. The application also discloses a sodium ion battery, wherein the negative electrode material of the sodium ion battery comprises the nitrogen / phosphorus co-doped honeycomb biomass hard carbon.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries and relates to a nitrogen / phosphorus co-doped honeycomb biomass hard carbon and a preparation method thereof and a sodium ion battery. Background Art

[0002] Currently, energy storage technology is mainly based on lithium-ion battery energy storage. However, with the rapid growth of global demand for lithium-ion batteries, lithium resources are beginning to face resource constraints. The tight supply and demand of lithium resources has also caused the price of lithium resources to rise sharply since 2021, with the highest price exceeding 520,000 yuan / ton. Compared with lithium resources, sodium resources are very abundant, 440 times that of lithium resources, and are widely distributed and simple to refine. Therefore, sodium-ion batteries are expected to replace lithium-ion batteries. Because the atomic radius of sodium ions is larger than that of lithium ions, sodium ions cannot be efficiently intercalated and deintercalated in graphite negative electrode materials. Therefore, finding a suitable sodium storage negative electrode material is crucial.

[0003] Hard carbon anode materials have a larger interlayer spacing than graphite, which is conducive to the storage and deintercalation of sodium ions and exhibits a high gram capacity. Therefore, hard carbon is an ideal choice for sodium storage anode materials. Biomass hard carbon materials have gained favor among researchers because of their green and pollution-free nature, wide availability, and low price. However, current biomass hard carbon materials have three major disadvantages: (1) low production efficiency, most of which are only 20-30%; (2) low first-cycle coulombic efficiency, which is difficult to reach above 90%; (3) high carbonization temperature of 800°C or even more than 1600°C, resulting in high energy consumption.

[0004] For example, a Chinese patent application document (CN201810859808.3) discloses a method for preparing biomass hard carbon materials for sodium ion battery negative electrodes, using lotus pods as precursors, and obtaining biomass hard carbon materials with large interlayer spacing and a specific surface area of ​​more than 100 m2 through high temperature heat treatment and acid washing. 2 / g of porous biomass hard carbon negative electrode material, the material has a reversible capacity of 328.8mAh / g at a current density of 50mA / g, and maintains a capacity of 295mAh / g after 200 cycles; Chinese patent application document (CN202210815699.1) discloses a rosin-based nitrogen-doped coated hard carbon negative electrode material for sodium ion batteries and a preparation method thereof, wherein a nitrogen source (one or more of urea, melamine, biuret, and aniline) is heat-treated with rosin, and then the powder obtained by carbonizing a precursor material (one or more of cellulose, hemicellulose, and lignin) is mixed, and the mixture is carbonized at a temperature of 900℃~1500℃ to obtain a rosin-based nitrogen-doped coated hard carbon negative electrode material for sodium ion batteries, whose specific surface area is 4.8~11.7m 2 / g, the first reversible capacity at 0.1C is ≥320.9mAh / g, and the first charge-discharge coulombic efficiency at 0.1C is ≥81.9%. Both achieve good performance, but cannot simultaneously meet the requirements of low energy consumption, high yield, and high performance. Summary of the Invention

[0005] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and to propose a nitrogen / phosphorus co-doped honeycomb biomass hard carbon with high specific surface area, high yield, high electrochemical performance and high yield.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A nitrogen / phosphorus co-doped honeycomb biomass hard carbon, wherein the nitrogen doping amount of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon is 2-3wt%, the phosphorus doping amount is 1-1.6wt%, and the specific surface area is 30-80m 2 / g;

[0008] The nitrogen / phosphorus co-doped honeycomb biomass hard carbon is prepared by mixing polylactic acid, nitrogenated humus, and phosphate aqueous solution, and then crosslinking and carbonizing at low temperature.

[0009] The mass ratio of polylactic acid to nitrogenated humus is 1:(0.1-5);

[0010] The mass ratio of the mixture of polylactic acid and nitrogenated humus to the phosphate aqueous solution is 1: (1-100).

[0011] The nitrogen / phosphorus co-doped honeycomb biomass hard carbon of the present invention is realized by cross-linking polylactic acid with nitrogenated humus under the action of phosphate to release small gas molecules, and forming a honeycomb porous structure by self-pore formation at the interface of polylactic acid and nitrogenated humus. The honeycomb porous structure is conducive to electrolyte infiltration, which can reduce the interface impedance between the electrolyte and the nitrogen / phosphorus co-doped honeycomb biomass hard carbon material, and improve the ion transfer rate and the charge and discharge reversible capacity of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon material; and by regulating the amount of raw materials added, the nitrogen doping amount and phosphorus doping amount of the biomass hard carbon material are maintained at a high level, thereby increasing the sodium storage sites and facilitating the occurrence of electrochemical reactions.

[0012] Preferably, the mass ratio of the polylactic acid to the nitrogenated humus is 1:(0.5-1.5).

[0013] The mass ratio of the mixture of polylactic acid and nitrogenated humus to the phosphate aqueous solution is 1: (20-50);

[0014] The concentration of the phosphate aqueous solution is 10 to 1000 g / ml.

[0015] More preferably, the concentration of the phosphate aqueous solution is 80 to 120 g / L.

[0016] More preferably, the phosphate is one or more of potassium phosphate, sodium phosphate, ammonium phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate.

[0017] Preferably, the nitrogenized humus is obtained by stirring, heating, freezing and freeze-drying humus, nitrogen source and water in a mass ratio of 1: (0.5-1): (1-3).

[0018] More preferably, the stirring and heating temperature is 50° C. to 80° C., and the time is 20 to 40 minutes.

[0019] More preferably, the freezing temperature is -10°C and the freezing time is 12 to 48 hours; and the nitrogenized humus after freezing is in a gel-like state.

[0020] More preferably, the freeze-drying temperature is -45°C.

[0021] Preferably, the humus is one or more of fulvic acid, humic acid and humic acid.

[0022] Preferably, the nitrogen source is one or more of urea, ethylenediamine, ammonia water, ammonium bicarbonate, and melamine.

[0023] The present invention also discloses a preparation method of nitrogen / phosphorus co-doped honeycomb biomass hard carbon, which comprises: mixing polylactic acid and nitrogenated humus, then mixing with a phosphate solution, ultrasonically mixing, and drying, and then sequentially performing low-temperature crosslinking and low-temperature carbonization to obtain nitrogen / phosphorus co-doped honeycomb biomass hard carbon.

[0024] Preferably, the low-temperature crosslinking is carried out in an inert gas atmosphere, the heating temperature of the low-temperature crosslinking is 100-170° C., and the holding time is 1-5 hours.

[0025] Preferably, the product obtained by heating during the low-temperature cross-linking is cooled, washed with water until neutral, and then dried.

[0026] Preferably, the low-temperature carbonization is carried out in an inert gas atmosphere, the carbonization temperature is 500-700° C., and the holding time is 1-5 hours.

[0027] More preferably, the heating and holding time of the low-temperature cross-linking is shorter than the carbonization and holding time of the low-temperature carbonization.

[0028] Preferably, the yield of nitrogen / phosphorus co-doped honeycomb biomass hard carbon obtained by the preparation method is ≥62.5%.

[0029] The present invention also discloses a sodium ion battery, wherein the negative electrode material of the sodium ion battery comprises nitrogen / phosphorus co-doped honeycomb biomass hard carbon.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The nitrogen / phosphorus co-doped honeycomb biomass hard carbon of the present invention is formed by self-pore formation at the interface of polylactic acid and nitrogenated humus to form a honeycomb porous structure through cross-linking reaction between polylactic acid and nitrogenated humus under the action of phosphate to release small gas molecules;

[0032] 2. The nitrogen / phosphorus co-doped honeycomb biomass hard carbon material of the present invention has a honeycomb structure, which is conducive to electrolyte infiltration, can reduce the interface impedance between the electrolyte and the hard carbon, and improve the ion transmission rate and the charge and discharge reversible capacity of the hard carbon material;

[0033] 3. During the preparation process of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon material of the present invention, the yield of the biomass hard carbon negative electrode material is improved by low-temperature cross-linking;

[0034] 4. The carbonization temperature during the preparation of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon material of the present invention is relatively low, which reduces the energy consumption and cost of preparing the hard carbon negative electrode material;

[0035] 5. The nitrogen / phosphorus co-doped honeycomb biomass hard carbon material of the present invention is applied to sodium ion batteries to obtain good electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is an SEM image of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon prepared in Example 1 of the present invention.

[0037] Figure 2 This is the nitrogen isothermal adsorption-desorption curve and pore size distribution diagram of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon prepared in Example 1 of the present invention.

[0038] Figure 3 This is a graph showing the capacity change of a sodium ion battery composed of nitrogen / phosphorus co-doped honeycomb biomass hard carbon prepared in Example 1 of the present invention after 200 cycles at 0.1C. DETAILED DESCRIPTION

[0039] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0040] Unless otherwise specified, the raw materials used in the present invention are all commonly used raw materials in the field, and the methods used are all conventional methods in the field.

[0041] Example 1

[0042] Humic acid, urea and water were placed in a reactor in a mass ratio of 1:0.7:1.4, stirred for 20 minutes, and then heated to 70°C. The mixture was stirred and reacted for 30 minutes. The reaction mixture was then placed in a refrigerator and frozen at -10°C for 24 hours to obtain a gel. The gel was placed in a freeze drying oven and freeze-dried at -45°C to obtain nitrogenated humus.

[0043] Polylactic acid and nitrogenated humus were uniformly mixed in a mass ratio of 1:0.5 to obtain a mixed dry powder; the mixed dry powder was prepared into a solution with a 100 g / L potassium phosphate aqueous solution in a mass ratio of 1:30, and after ultrasonication for 30 minutes, the solution was dried in a forced air drying oven at 80°C for 12 hours to obtain a mixture.

[0044] The mixture was placed in a tube furnace and heated to 120°C at a rate of 2°C / min under a nitrogen atmosphere. The mixture was kept at this temperature for 2 hours and then cooled naturally to room temperature. The mixture was then washed with water until neutral and dried at 80°C in a forced air drying oven for 3 hours to obtain cross-linked carbon powder. The cross-linked carbon powder was placed in a tube furnace and heated to 700°C at a rate of 5°C / min under a nitrogen atmosphere. The mixture was kept at this temperature for 3 hours and then cooled naturally to room temperature to obtain nitrogen / phosphorus co-doped honeycomb biomass hard carbon.

[0045] The nitrogen doping amount, phosphorus doping amount, yield and specific surface area of ​​nitrogen / phosphorus co-doped honeycomb biomass hard carbon are shown in Table 1.

[0046] Figure 1 This is the SEM image of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon prepared in this example, showing a distinct honeycomb porous structure. Figure 2 The isothermal adsorption and desorption curve of nitrogen and the pore size distribution diagram are shown. The specific surface area is 75m 2 / g.

[0047] Example 2

[0048] Humic acid, ethylenediamine and water were placed in a reactor in a mass ratio of 1:0.5:3, stirred for 20 minutes, heated to 50°C, and continued to stir and react for 30 minutes. The reaction mixture was then placed in a refrigerator and frozen at -10°C for 24 hours to obtain a gel. The gel was placed in a freeze drying oven and freeze-dried at -45°C to obtain nitrogenated humus.

[0049] Polylactic acid and nitrogenated humus were uniformly mixed in a mass ratio of 1:0.8 to obtain a mixed dry powder; the mixed dry powder was prepared into a solution with a 100 g / L disodium hydrogen phosphate aqueous solution in a mass ratio of 1:50, and after ultrasonication for 30 minutes, the solution was dried at 80° C. in a forced air drying oven for 12 hours to obtain a mixture.

[0050] The mixture was placed in a tube furnace and heated to 170°C at a rate of 5°C / min under a nitrogen atmosphere. The mixture was kept at this temperature for 2 hours and then cooled naturally to room temperature. The mixture was then washed with water until neutral and dried at 80°C in a forced air drying oven for 3 hours to obtain cross-linked carbon powder. The cross-linked carbon powder was placed in a tube furnace and heated to 500°C at a rate of 4°C / min under a nitrogen atmosphere. The mixture was kept at this temperature for 3 hours and then cooled naturally to room temperature to obtain nitrogen / phosphorus co-doped honeycomb biomass hard carbon.

[0051] The nitrogen doping amount, phosphorus doping amount, yield and specific surface area of ​​nitrogen / phosphorus co-doped honeycomb biomass hard carbon are shown in Table 1.

[0052] Example 3

[0053] Fulvic acid, melamine and water were placed in a reactor in a mass ratio of 1:0.5:1, stirred for 20 minutes, heated to 80°C, and stirred for 30 minutes. The reaction mixture was then placed in a refrigerator and frozen at -10°C for 24 hours to obtain a gel. The gel was placed in a freeze drying oven and freeze-dried at -45°C to obtain nitrogenated humus.

[0054] Polylactic acid and nitrogenated humus were uniformly mixed in a mass ratio of 1:1.5 to obtain a mixed dry powder; the mixed dry powder was prepared into a solution with a 100 g / L ammonium phosphate aqueous solution in a mass ratio of 1:20, and after ultrasonication for 30 minutes, the solution was dried at 80°C in a forced air drying oven for 12 hours to obtain a mixture.

[0055] The mixture was placed in a tube furnace and heated to 140°C at a rate of 1°C / min under a nitrogen atmosphere, kept at that temperature for 2 hours, cooled naturally to room temperature, washed with water until neutral, and dried in a forced air drying oven at 80°C for 3 hours to obtain cross-linked carbon powder. The cross-linked carbon powder was placed in a tube furnace and heated to 650°C at a rate of 3°C / min under a nitrogen atmosphere, kept at that temperature for 3 hours, and cooled naturally to room temperature to obtain nitrogen / phosphorus co-doped honeycomb biomass hard carbon.

[0056] The nitrogen doping amount, phosphorus doping amount, yield and specific surface area of ​​nitrogen / phosphorus co-doped honeycomb biomass hard carbon are shown in Table 1.

[0057] Example 4

[0058] Humic acid, ammonia water and water were placed in a reactor in a mass ratio of 1:1:3, stirred for 20 minutes, heated to 65°C, and continued to stir and react for 30 minutes. The reaction mixture was then placed in a refrigerator and frozen at -10°C for 24 hours to obtain a gel. The gel was placed in a freeze drying oven and freeze-dried at -45°C to obtain nitrogenated humus.

[0059] Polylactic acid and nitrogenated humus were uniformly mixed in a mass ratio of 1:1 to obtain a mixed dry powder; the mixed dry powder was prepared into a solution with a 100 g / L sodium phosphate aqueous solution in a mass ratio of 1:40, and after ultrasonication for 30 minutes, the solution was dried at 80°C in a forced air drying oven for 12 hours to obtain a mixture.

[0060] The mixture was placed in a tube furnace, heated to 150°C at a rate of 3°C / min under a nitrogen atmosphere, held for 2 hours, cooled naturally to room temperature, washed with water until neutral, and dried in a forced air drying oven at 80°C for 3 hours to obtain cross-linked carbon powder. The cross-linked carbon powder was placed in a tube furnace, heated to 550°C at a rate of 3°C / min under a nitrogen atmosphere, held for 3 hours, and cooled naturally to room temperature to obtain nitrogen / phosphorus co-doped honeycomb biomass hard carbon.

[0061] The nitrogen doping amount, phosphorus doping amount, yield and specific surface area of ​​nitrogen / phosphorus co-doped honeycomb biomass hard carbon are shown in Table 1.

[0062] Comparative Example 1

[0063] Compared with Example 1, the difference is that no nitrogen source is added.

[0064] Humic acid and water were placed in a reactor at a mass ratio of 1:2.1, stirred for 20 minutes, and then heated to 70°C. The mixture was stirred and reacted for 30 minutes. The reaction mixture was then placed in a refrigerator and frozen at -10°C for 24 hours to obtain a gel. The gel was placed in a freeze drying oven and freeze-dried at -45°C to obtain humus.

[0065] Polylactic acid and humus were uniformly mixed in a mass ratio of 1:0.5 to obtain a mixed dry powder; the mixed dry powder was prepared into a solution with a 100 g / L potassium phosphate aqueous solution in a mass ratio of 1:30, and after ultrasonication for 30 minutes, the solution was dried at 80° C. in a forced air drying oven for 12 hours to obtain a mixture.

[0066] The mixture was placed in a tube furnace, heated at a rate of 2°C / min to 120°C in a nitrogen atmosphere, kept at this temperature for 2 hours, cooled naturally to room temperature, washed with water until neutral, and dried in a forced air drying oven at 80°C for 3 hours to obtain cross-linked carbon powder. The cross-linked carbon powder was placed in a tube furnace, heated at a rate of 5°C / min to 700°C in a nitrogen atmosphere, kept at this temperature for 3 hours, and cooled naturally to room temperature to obtain biomass hard carbon.

[0067] The nitrogen doping amount, phosphorus doping amount, yield and specific surface area of ​​biomass hard carbon are shown in Table 1.

[0068] Comparative Example 2

[0069] Compared with Example 2, the difference is that polylactic acid is not added.

[0070] Put the black humic acid, ethylenediamine, water in the reaction kettle according to the mass ratio of 1:0.5:3, stir for 20 min, then heat to 50℃, continue to stir for 30 min, then put the reaction mixture in the refrigerator, freeze at-10℃ for 24h, obtain the gel; put the gel in the freeze-drying oven, freeze-dry at-45℃ to obtain nitrogenated humus.

[0071] Put the nitrogenated humus and 100g / L aqueous solution of sodium hydrogen phosphate according to the mass ratio of 1:50, ultrasonic for 30 min, then dry in the air drying oven at 80℃ for 12h, obtain the mixture.

[0072] Put the mixture in the tube furnace, under the nitrogen atmosphere, heat to 170℃ at the rate of 5℃ / min, keep for 2h, naturally cool to room temperature, then wash with water until neutral, dry in the air drying oven at 80℃ for 3h, obtain the cross-linked carbon powder. Put the cross-linked carbon powder in the tube furnace, under the nitrogen atmosphere, heat to 500℃ at the rate of 4℃ / min, keep for 3h, naturally cool to room temperature, obtain the biomass hard carbon.

[0073] The nitrogen doping amount, phosphorus doping amount, yield, specific surface area of the biomass hard carbon are shown in Table 1.

[0074] Comparative Example 3

[0075] Compared with Example 3, the difference is that no phosphate is added.

[0076] Put the fulvic acid, melamine, water in the reaction kettle according to the mass ratio of 1:0.5:1, stir for 20 min, then heat to 80℃, continue to stir for 30 min, then put the reaction mixture in the refrigerator, freeze at-10℃ for 24h, obtain the gel; put the gel in the freeze-drying oven, freeze-dry at-45℃ to obtain nitrogenated humus.

[0077] Mix the polylactic acid and nitrogenated humus according to the mass ratio of 1:1.5, obtain the mixed dry powder; mix the dry powder and aqueous solution according to the mass ratio of 1:20, ultrasonic for 30 min, then dry in the air drying oven at 80℃ for 12h, obtain the mixture.

[0078] Put the mixture in the tube furnace, under the nitrogen atmosphere, heat to 140℃ at the rate of 1℃ / min, keep for 2h, naturally cool to room temperature, then wash with water until neutral, dry in the air drying oven at 80℃ for 3h, obtain the cross-linked carbon powder. Put the cross-linked carbon powder in the tube furnace, under the nitrogen atmosphere, heat to 650℃ at the rate of 3℃ / min, keep for 3h, naturally cool to room temperature, obtain the biomass hard carbon.

[0079] The nitrogen doping amount, phosphorus doping amount, yield, specific surface area of the biomass hard carbon are shown in Table 1.

[0080] Comparative Example 4

[0081] Compared with Example 4, the difference is that no nitrogenated humus is added.

[0082] Polylactic acid and 100 g / L sodium phosphate aqueous solution were prepared into a solution at a mass ratio of 1:40, and after ultrasonication for 30 minutes, the solution was dried in a forced air drying oven at 80° C. for 12 hours to obtain a mixture.

[0083] The mixture was placed in a tube furnace, heated at a rate of 3°C / min to 150°C in a nitrogen atmosphere, kept at that temperature for 2 hours, cooled naturally to room temperature, washed with water until neutral, and dried in a forced air drying oven at 80°C for 3 hours to obtain cross-linked carbon powder. The cross-linked carbon powder was placed in a tube furnace, heated at a rate of 3°C / min to 550°C in a nitrogen atmosphere, kept at that temperature for 3 hours, and cooled naturally to room temperature to obtain biomass hard carbon.

[0084] The nitrogen doping amount, phosphorus doping amount, yield and specific surface area of ​​biomass hard carbon are shown in Table 1.

[0085] Application Example 1

[0086] The nitrogen / phosphorus co-doped honeycomb biomass hard carbon prepared in Example 1 was used as the negative electrode material, mixed evenly with a conductive agent and PVDF / NMP, and then coated on a copper foil, vacuum dried, compacted by a roller mill, and punched into a circular negative electrode sheet; metallic sodium was used as the positive electrode, PC as the separator, and NaPF6 / (EC+DMC+DEC) with a concentration of 1 mol / L (volume ratio of 1:1:1) as the electrolyte, and a button-type sodium ion battery was assembled in a vacuum glove box.

[0087] The constant current charge and discharge and rate performance tests were carried out, and the performance results of the battery are shown in Table 1.

[0088] Application Examples 2 to 4

[0089] The nitrogen / phosphorus co-doped honeycomb biomass hard carbon prepared in Examples 2 to 4 was used as the negative electrode material, and a sodium ion battery was prepared according to the method described in Application Example 1.

[0090] The constant current charge and discharge and rate performance tests were carried out, and the performance results of the battery are shown in Table 1.

[0091] Comparative Application Examples 1 to 4

[0092] The biomass hard carbon prepared in Comparative Examples 1 to 4 was used as the negative electrode material, and a sodium ion battery was prepared according to the method described in Application Example 1.

[0093] The constant current charge and discharge and rate performance tests were carried out, and the performance results of the battery are shown in Table 1.

[0094] Table 1. Physical properties of hard carbon materials and sodium ion battery performance data

[0095]

[0096] The apparent morphology of the nitrogen / phosphorus co-doped honeycomb biomass hard carbon prepared by the present invention is shown in FIG. Figure 1 As shown, according to Figure 2 、 Figure 3 From the experimental data in Table 1, it can be seen that the nitrogen / phosphorus co-doped honeycomb biomass hard carbon of the present invention has a honeycomb porous structure, contains high content of nitrogen and phosphorus elements, and has high yield, high specific surface area, high first reversible capacity, high first-cycle coulombic efficiency, and long cycle life.

[0097] However, in Comparative Example 1, no nitrogen source is added, which will result in a low nitrogen content in the humus, resulting in a low nitrogen content in the biomass hard carbon material, reducing the sodium storage site, resulting in a low first reversible capacity, poor first-week coulomb efficiency, and low long-cycle life capacity retention rate; in Comparative Example 2, no polylactic acid is added, resulting in a cross-linking reaction between the nitrogenated humus itself, and the gas generated is insufficient to form a porous structure of honeycomb coal, which is not conducive to electrolyte infiltration, resulting in a reduction in the first-week coulomb efficiency and long-cycle life capacity retention rate of the prepared sodium ion battery; in Comparative Example 3, no phosphate is added, resulting in the inability of polylactic acid and nitrogenated humus to undergo a cross-linking reaction, greatly reducing the yield, and no phosphorus is introduced into the biomass hard carbon material, reducing the sodium storage site, resulting in a low first reversible capacity, poor first-week coulomb efficiency, and low long-cycle life capacity retention rate; in Comparative Example 4, no nitrogenated humus is added, resulting in no nitrogen introduction into the hard carbon material, reducing the sodium storage site, resulting in a low first reversible capacity, poor first-week coulomb efficiency, and low long-cycle life capacity retention rate.

[0098] It can be seen that if the amount of polylactic acid, phosphate, and nitrogenated humus (nitrogen source) added to the raw materials of nitrogen / phosphorus co-doped honeycomb biomass hard carbon decreases, the morphology and element content of the obtained biomass hard carbon will change, affecting the performance of sodium ion batteries; similarly, if excessive amounts of polylactic acid, phosphate, and nitrogenated humus (nitrogen source) are added to the raw materials, the performance of sodium ion batteries will also be affected.

[0099] In summary, the nitrogen / phosphorus co-doped honeycomb biomass hard carbon of the present invention releases small gas molecules by cross-linking polylactic acid and nitrogenated humus under the action of phosphate, and forms a honeycomb porous structure by self-pore formation at the interface between polylactic acid and nitrogenated humus. The honeycomb porous structure is conducive to the infiltration of electrolyte, can reduce the interface impedance between electrolyte and hard carbon, and improve the ion transfer rate and the charge and discharge reversible capacity of the hard carbon material.

[0100] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A nitrogen / phosphorus co-doped honeycomb biomass hard carbon, characterized in that: The nitrogen / phosphorus co-doped honeycomb biomass hard carbon has a nitrogen doping amount of 2-3 wt%, a phosphorus doping amount of 1-1.6 wt%, and a specific surface area of ​​30-80 m 2 / g; The nitrogen / phosphorus co-doped honeycomb biomass hard carbon is prepared by mixing polylactic acid, nitrogenated humus, and phosphate aqueous solution, and then crosslinking and carbonizing at low temperature. The mass ratio of polylactic acid and nitrogenated humus is 1: (0.1~5); The mass ratio of the mixture of polylactic acid and nitrogenated humus to the phosphate aqueous solution is 1: (1-100); The nitrogenized humus is obtained by mixing humus, a nitrogen source, and water in a mass ratio of 1: (0.5-1): (1-3), stirring, heating, freezing, and freeze-drying; The low-temperature crosslinking is carried out in an inert gas atmosphere, the heating temperature of the low-temperature crosslinking is 100-170°C, and the holding time is 1-5 hours; The low-temperature carbonization is carried out in an inert gas atmosphere, the carbonization temperature is 500-700° C., and the holding time is 1-5 hours.

2. The nitrogen / phosphorus co-doped honeycomb biomass hard carbon according to claim 1, characterized in that: The mass ratio of the polylactic acid to the nitrogenated humus is 1: (0.5-1.5); The mass ratio of the mixture of polylactic acid and nitrogenated humus to the phosphate aqueous solution is 1: (20-50); The concentration of the phosphate aqueous solution is 10-1000 g / ml.

3. The nitrogen / phosphorus co-doped honeycomb biomass hard carbon according to claim 1, characterized in that: The stirring and heating temperature is 50-80° C., and the time is 20-40 min.

4. The nitrogen / phosphorus co-doped honeycomb biomass hard carbon according to claim 1, characterized in that: The freezing temperature is -10°C and the freezing time is 12 to 48 hours; the nitrogenized humus after freezing is in a gel state.

5. A method for preparing nitrogen / phosphorus co-doped honeycomb biomass hard carbon as claimed in claim 1, characterized in that: The preparation method comprises: uniformly mixing polylactic acid and nitrogenated humus, then mixing with a phosphate solution, ultrasonically performing the mixing, and drying; and then sequentially performing low-temperature crosslinking and low-temperature carbonization to obtain nitrogen / phosphorus co-doped honeycomb biomass hard carbon.

6. The method for preparing nitrogen / phosphorus co-doped honeycomb biomass hard carbon according to claim 5, characterized in that: The low-temperature crosslinking is carried out in an inert gas atmosphere, the heating temperature of the low-temperature crosslinking is 100-170° C., and the insulation time is 1-5 hours.

7. The method for preparing nitrogen / phosphorus co-doped honeycomb biomass hard carbon according to claim 5, characterized in that: The low-temperature carbonization is carried out in an inert gas atmosphere, the carbonization temperature is 500-700° C., and the holding time is 1-5 hours.

8. The method for preparing nitrogen / phosphorus co-doped honeycomb biomass hard carbon according to claim 5, characterized in that: The holding time of low-temperature cross-linking is shorter than the carbonization time of low-temperature carbonization.

9. A sodium ion battery, characterized in that: The negative electrode material of the sodium ion battery comprises the nitrogen / phosphorus co-doped honeycomb biomass hard carbon according to any one of claims 1 to 4, and / or the nitrogen / phosphorus co-doped honeycomb biomass hard carbon prepared by the preparation method according to any one of claims 5 to 8.

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