Phosphorus-doped porous torreya grandis shell carbon material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion battery preparation, in particular to a phosphorus-doped porous torreya grandis shell carbon material and a preparation method and application thereof. The porous torreya grandis shell carbon material is prepared from torreya grandis shells and sodium dihydrogen phosphate, and the mass ratio of the torreya grandis shells to the sodium dihydrogen phosphate is 0.1: (0.5-2). When the mass ratio of the torreya grandis shell hard carbon to the phosphorus source is 1: 15, when the torreya grandis shell hard carbon / phosphorus source is used as a sodium ion battery negative electrode, excellent electrochemical performance is shown, the highest rate can reach 8Ag <-1 >, and the specific capacity fading rate is as low as 0.075% / circle after 1000 circles of long circulation under 1Ag <-1 >.

Description

Technical Field

[0001] The invention relates to the technical field of sodium ion battery preparation, and in particular to a phosphorus-doped porous Torreya grandis shell carbon material and a preparation method and application thereof. Background Art

[0002] As an emerging energy storage technology, sodium-ion batteries have attracted much attention due to their abundant resources, low cost, and high safety. The content of sodium in the earth's crust is very abundant, accounting for about 2.3%, much higher than lithium and potassium. Therefore, the abundance of sodium resources makes it suitable for large-scale energy storage scenarios such as grid energy storage, household energy storage, and industrial energy storage. It is a candidate that is expected to replace lithium-ion batteries (LIBs).

[0003] Soft carbon in carbon-based materials, such as graphite, is successfully used as anode material in lithium-ion batteries and has a high initial coulombic efficiency. + The mismatch between the larger radius and the relatively narrow interlayer distance (<0.37nm) of soft carbon leads to the poor storage performance of soft carbon in the sodium ion system. However, in comparison, hard carbon materials with rich pores and defect structures perform better in the sodium ion system.

[0004] However, hard carbon still faces the challenge of generally showing low initial coulombic efficiency (ICE) during the first charge and discharge process. This means that a large amount of charge is consumed during the first charge process to form a solid electrolyte interface film (SEI film) and other side reactions, resulting in a decrease in reversible capacity. Low first efficiency will affect the energy density and practical application performance of the battery.

[0005] Therefore, in view of the technical problems existing in the prior art, it is necessary to propose a technical solution to overcome the defects of the prior art. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a phosphorus-doped porous Torreya shell carbon material and a preparation method and application thereof. The porous Torreya shell carbon material provided by the present invention improves the specific capacity.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The invention provides a phosphorus-doped porous Torreya husk carbon material, which is prepared from Torreya husk and a phosphorus source material, wherein the mass ratio of Torreya husk to sodium dihydrogen phosphate is 0.1:0.5-2; and the phosphorus source material comprises sodium dihydrogen phosphate and / or phosphoric acid.

[0009] Preferably, the mass ratio of the Torreya grandis shell to the phosphorus source material is 0.1:1 to 1.5.

[0010] The present invention also provides a method for preparing the porous Torreya grandis shell carbon material described in the above technical solution, comprising the following steps:

[0011] 1) pre-pyrolyzing the Torreya grandis shell to obtain a pre-pyrolyzed material;

[0012] 2) treating the pre-pyrolysis material obtained in step 1) with alkali and acid in sequence, washing it to neutrality and then drying it to obtain a carbon sample;

[0013] 3) The carbon material obtained in step 2) is calcined with a phosphorus source material, and then ground to obtain a porous Torreya grandis shell carbon material.

[0014] Preferably, the pre-pyrolysis conditions in step 1) include: heating to 400° C. at 5° C. / min and keeping the temperature for 2 h.

[0015] Preferably, the conditions of the alkali treatment in step 2) include: dispersing the pre-pyrolysis material in a potassium hydroxide solution for 3 hours;

[0016] The temperature of the potassium hydroxide solution is 60°C;

[0017] The mass percentage of the potassium hydroxide solution is 20%.

[0018] Preferably, the conditions of the acid treatment in step 2) include: the pre-pyrolysis material is dispersed in a hydrochloric acid solution for 5 hours after the alkali treatment;

[0019] The concentration of the hydrochloric acid solution is 3 mol / L;

[0020] The temperature of the hydrochloric acid solution is 60°C.

[0021] Preferably, the drying conditions in step 2) include: a temperature of 120° C. and a drying time of 12 hours.

[0022] Preferably, the calcination conditions in step 3) include: heating to 800° C. at 5° C. / min and keeping the temperature for 2 h.

[0023] Preferably, the step 1) performs a pretreatment before the pre-pyrolysis of Torreya grandis husk, comprising: ultrasonically cleaning the Torreya grandis husk with deionized water and then drying it, wherein the number of ultrasonic cleanings is more than 3 times, each time for 15 minutes.

[0024] The present invention also provides the use of the porous Torreya grandis shell carbon material described in the above technical solution in the preparation of sodium ion batteries.

[0025] Beneficial effects:

[0026] 1. Torreya grandis shell has a high carbon yield and a stable structure after carbonization

[0027] The hard carbon material of the present invention is derived from the shell of Torreya grandis nut, which is a polymer with rich aromatic rings, and its main components include about 30% cellulose and 40% lignin. Usually, a high carbon yield can be guaranteed during the pyrolysis process; and the cellulose surface is enriched with hydroxyl groups, and has good mechanical and thermal stability after carbonization, which is suitable for battery electrode materials to ensure the cycle stability of the electrode structure.

[0028] 2. Phosphorus-doped Torreya grandis shell hard carbon material has a porous structure

[0029] When preparing hard carbon materials, the volatilization of phosphates during high-temperature pyrolysis helps to increase the microporous or mesoporous structure of hard carbon. These pore structures not only increase the specific surface area of ​​the material, but also provide more diffusion paths for sodium ions, thereby improving the electrochemical performance of the material.

[0030] 3. Phosphorus-doped Torreya grandis shell hard carbon material is used for the negative electrode of sodium ion battery, with excellent electrochemical cycle and rate performance.

[0031] When the mass ratio of torreya shell-derived hard carbon (TSHC) to phosphorus source NaH2PO4 is 1:15 (denoted as P-TSHC15), it exhibits excellent electrochemical performance as the negative electrode of sodium ion batteries: the highest rate can reach 8Ag -1 , and at 1A g -1 After 1000 cycles, the specific capacity decay rate is as low as 0.075% / cycle.

[0032] Phosphorus provides excess electrons to the main material, thereby improving its electronic conductivity (reflected in good rate performance); doped phosphorus enhances the adsorption capacity of carbon materials for sodium ions through PO bonds (reflected in good cycle stability); phosphorus atomic radius Larger than the radius of carbon atom After doping, the carbon interlayer spacing is enlarged and the closed pore structure is opened, which enhances the Na + Mesopore filling and intercalation can effectively increase the Na + More storage possibilities and ultimately platform area capacity (reflected in the increase in specific capacity). BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0034] Figure 1 This is the XRD pattern of the phosphorus-doped porous biomass-derived hard carbon material prepared in Example 1;

[0035] Figure 2 This is a SEM image of the phosphorus-doped porous biomass-derived hard carbon material prepared in Example;

[0036] Figure 3 The charge-discharge specific capacity and coulomb efficiency curve of the sodium ion battery using P-TSHC prepared in Example 1 as the negative electrode material after 70 cycles at a current density of 1 A / g;

[0037] Figure 4 The charge-discharge specific capacity and coulombic efficiency curve of the sodium ion battery prepared in Example 2 with the phosphorus-doped porous biomass-derived hard carbon material as the negative electrode material after 70 cycles at a current density of 1 A / g;

[0038] Figure 5 A charge-discharge specific capacity curve of a sodium ion battery prepared in Example 1 using a phosphorus-doped porous biomass-derived hard carbon material as a negative electrode material and charged and discharged 70 times at a current density of 0.5 A / g to 8 A / g;

[0039] Figure 6 The present invention is a flowchart of a phosphorus-doped porous Torreya grandis shell carbon material and a preparation method thereof. DETAILED DESCRIPTION

[0040] The present invention provides a phosphorus-doped porous Torreya grandis shell carbon material, which is prepared from Torreya grandis shell and a phosphorus source material, wherein the mass ratio of the Torreya grandis shell to the phosphorus source material is 0.1:0.5-2; the phosphorus source material includes sodium dihydrogen phosphate and / or phosphoric acid. In the present invention, the mass ratio of the Torreya grandis shell to the phosphorus source material is preferably 0.1:1-1.5.

[0041] The present invention provides a method for preparing the porous Torreya grandis shell carbon material described in the above technical solution, comprising the following steps:

[0042] 1) pre-pyrolyzing the Torreya grandis shell to obtain a pre-pyrolyzed material;

[0043] 2) treating the pre-pyrolysis material obtained in step 1) with alkali and acid in sequence, washing it to neutrality and then drying it to obtain a carbon sample;

[0044] 3) The carbon material obtained in step 2) is calcined with forest raw materials, and then ground to obtain a porous Torreya grandis shell carbon material.

[0045] The present invention pre-pyrolyzes the Torreya grandis shell to obtain a pre-pyrolyzed material. In the present invention, the conditions for the pre-pyrolysis preferably include: heating to 400°C at 5°C / min and keeping warm for 2h. In the present invention, the Torreya grandis shell is preferably pre-treated before pre-pyrolysis, including: ultrasonically cleaning the Torreya grandis shell with deionized water and then drying, and the number of ultrasonic cleanings is more than 3 times, each time for 15min. In the present invention, the role of the pre-pyrolysis is: in a one-step direct pyrolysis, carbon atoms may not have enough time to reorganize, resulting in a pseudographite structure. Two-step carbonization can provide more quasi-balanced hexagonal carbon planes in the amorphous carbon region. The two-step strategy provides the best ICE, reversible capacity and high-rate performance. Therefore, by means of pre-treatment pyrolysis, the reaction conditions can be better controlled, the conversion rate and yield can be improved, and the final product can be purer and have better performance.

[0046] The present invention sequentially treats the obtained pre-pyrolysis material with alkali and acid, washes neutrally and then dries to obtain a carbon sample. In the present invention, the conditions for the alkali treatment preferably include: dispersing the pre-pyrolysis material in a potassium hydroxide solution for 3 hours; the temperature of the potassium hydroxide solution is 60°C; the mass percentage of the potassium hydroxide solution is 20%. In the present invention, the conditions for the acid treatment preferably include: the pre-pyrolysis material is dispersed in a hydrochloric acid solution for 5 hours after the alkali treatment; the concentration of the hydrochloric acid solution is 3 mol / L; the temperature of the hydrochloric acid solution is 60°C. In the present invention, the drying conditions preferably include: the temperature is 120°C and the time is 12 hours. In the present invention, the treatment of hard carbon materials with KOH (potassium hydroxide) solution is a common chemical activation method, which can significantly change the surface properties and pore structure of hard carbon materials. Mesopores and a certain amount of micropores are formed in hard carbon materials by etching and gasification. Changes in the conditions for alkali treatment, such as shortening the activation time, will lead to insufficient activation of the material to a certain extent, and the specific surface area and porosity of the material may be insufficient, resulting in performance degradation. Although KOH is the most common alkaline activator, sodium hydroxide, for example, NaOH, can also be used to activate hard carbon materials. In addition, compared with KOH, the specific surface area of ​​the material after NaOH activation may be lower, and the pore structure may not be as good as the effect of KOH activation.

[0047] The present invention calcines the obtained carbon material with sodium dihydrogen phosphate and grinds it to obtain a porous Torreya grandis shell carbon material. In the present invention, the calcination conditions preferably include: heating to 800° C. at 5° C. / min and keeping the temperature for 2 hours.

[0048] The present invention also provides the use of the porous Torreya grandis shell carbon material described in the above technical solution in the preparation of sodium ion batteries.

[0049] In order to further illustrate the present invention, the present invention is described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] A phosphorus-doped porous biomass-derived hard carbon material, comprising the steps of:

[0052] The Torreya grandis shell was ultrasonically cleaned with deionized water for at least 3 times, each cleaning time was 15 minutes, to remove pollutants on the sample surface and dried overnight to obtain a biomass raw material sample Torreya grandis shell;

[0053] Take 1g of the biomass raw material sample Torreya grandis shell, pre-pyrolyze it at 400℃ for 2h at a heating rate of 5℃ / min in a tube furnace; grind the obtained pre-pyrolysis product into powder in a mortar, disperse the powder in a KOH solution (mass percentage of 20%) at 60℃ for 3h, and place it on a magnetic stirring table for heating and stirring. After filtering, disperse it in a 60℃ 3M HCI solution for 5h and stir it magnetically. After that, rinse the sample with deionized water until neutral, and place it in a drying oven at 120℃ for 12 hours overnight;

[0054] Sodium dihydrogen phosphate (NaH2PO4 1.5g) and 100mg of the dried carbon sample were placed on the upstream and downstream sides of the tube furnace, respectively. The samples were calcined at 800°C at a heating rate of 5°C / min for 2h. The obtained samples were finally ground to obtain the phosphorus-doped porous biomass-derived hard carbon material P-TSHC.

[0055] Mix P-TSHC material, superconducting carbon black and PVDF in a mass ratio of 7:2:1, and adjust the concentration with N-methylpyrrolidone until the required fluidity and uniformity are achieved. The viscosity can be measured by a viscometer, or the state of the slurry can be evaluated by visual inspection and feel. For example, when the stirring container is tilted, the magnetic stirrer can slide naturally, which is the appropriate concentration. Stir for 3 hours to make the slurry. Apply the prepared slurry on the current collector by blade coating and dry it at 60°C for 12 hours under vacuum. Cut into circular electrode sheets with a diameter of 16 mm and assemble them into sodium ion battery tests.

[0056] Figure 2 This is the SEM image of the phosphorus-doped porous biomass-derived hard carbon material prepared in this example, showing an obvious porous structure. Figure 3 The charge-discharge capacity and coulomb efficiency curves of the sodium ion battery with the P-TSHC prepared in this example as the negative electrode material after 70 cycles at a current density of 1A / g. The electrochemical performance test results show that the P-TSHC material prepared in this example is applied to the sodium ion battery with an initial discharge capacity of 342.53mAh / g at a current density of 1A / g, and maintains 190.9mAh / g after 70 cycles.

[0057] Example 2

[0058] A phosphorus-doped porous biomass-derived hard carbon material, comprising the steps of:

[0059] The Torreya grandis shell was ultrasonically cleaned with deionized water for at least 3 times, each cleaning time was 15 minutes, to remove pollutants on the sample surface and dried overnight to obtain a biomass raw material sample Torreya grandis shell;

[0060] Take 1g of the biomass raw material sample Torreya grandis shell, pre-pyrolyze it at 400℃ for 2h at a heating rate of 5℃ / min in a tube furnace; grind the obtained pre-pyrolysis product into powder in a mortar, disperse the powder in a KOH solution (mass percentage of 20%) at 60℃ for 3h, and place it on a magnetic stirring table for heating and stirring. After filtering, disperse it in a 60℃ 3M HCI solution for 5h and stir it magnetically. After that, rinse the sample with deionized water until neutral, and place it in a drying oven at 120℃ for 12 hours overnight;

[0061] Sodium dihydrogen phosphate (NaH2PO4 2g) and 100mg of the dried carbon sample were placed on the upstream and downstream sides of the tube furnace, respectively. The samples were calcined at 800°C at a heating rate of 5°C / min for 2h. The obtained samples were finally ground to obtain the phosphorus-doped porous biomass-derived hard carbon material P-TSHC.

[0062] P-TSHC material, superconducting carbon black and PVDF are mixed evenly in a mass ratio of 7:2:1. The concentration is adjusted with N-methylpyrrolidone until the required fluidity and uniformity are achieved. The viscosity can be measured by a viscometer, or the state of the slurry can be evaluated by visual inspection and touch. For example, when the stirring container is tilted, the magnetic stirrer can slide naturally, which is the appropriate concentration. Stir for 3 hours to make the slurry. Apply the prepared slurry on the current collector by scraping and dry it at 60°C in a vacuum environment for 12 hours. Cut into circular electrode sheets with a diameter of 16 mm and assemble them into sodium ion battery tests.

[0063] Figure 4 The charge-discharge capacity and coulomb efficiency curves of the sodium ion battery with phosphorus-doped porous biomass-derived hard carbon material as the negative electrode material prepared in this example at a current density of 1A / g for 70 cycles. The electrochemical performance test results show that the P-TSHC material prepared in this example is applied to the sodium ion battery with an initial discharge capacity of 398.5mAh / g at a current density of 1A / g, and retains 153.9mAh / g after 70 cycles.

[0064] Example 3

[0065] A phosphorus-doped porous biomass-derived hard carbon material, comprising the steps of:

[0066] The Torreya grandis shell was ultrasonically cleaned with deionized water for at least 3 times, each cleaning time was 15 minutes, to remove pollutants on the sample surface and dried overnight to obtain a biomass raw material sample Torreya grandis shell;

[0067] Take 1g of the biomass raw material sample Torreya grandis shell, pre-pyrolyze it at 400℃ for 2h at a heating rate of 5℃ / min in a tube furnace; grind the obtained pre-pyrolysis product into powder in a mortar, disperse the powder in a KOH solution (mass percentage of 20%) at 60℃ for 3h, and place it on a magnetic stirring table for heating and stirring. After filtering, disperse it in a 60℃ 3M HCI solution for 5h and stir it magnetically. After that, rinse the sample with deionized water until neutral, and place it in a drying oven at 120℃ for 12 hours overnight;

[0068] Sodium dihydrogen phosphate (NaH2PO4 0.5 g) and 100 mg of the dried carbon sample were placed on the upstream and downstream sides of the tube furnace, respectively. The mixture was calcined at 800°C for 2 hours at a heating rate of 5°C / min. The obtained sample was finally ground to obtain a phosphorus-doped porous biomass-derived hard carbon material P-TSHC.

[0069] P-TSHC material, superconducting carbon black and PVDF are mixed evenly in a mass ratio of 7:2:1. The concentration is adjusted with N-methylpyrrolidone until the required fluidity and uniformity are achieved. The viscosity can be measured by a viscometer, or the state of the slurry can be evaluated by visual inspection and touch. For example, when the stirring container is tilted, the magnetic stirrer can slide naturally, which is the appropriate concentration. Stir for 3 hours to make the slurry. Apply the prepared slurry on the current collector by scraping and dry it at 60°C in a vacuum environment for 12 hours. Cut into circular electrode sheets with a diameter of 16 mm and assemble them into sodium ion battery tests.

[0070] The electrochemical performance test results show that the P-TSHC material prepared in this example is applied to sodium ion batteries, and the first discharge specific capacity reaches 316.2 mAh / g at a current density of 1 A / g, and maintains 127.9 mAh / g after 70 cycles.

[0071] Example 4

[0072] A phosphorus-doped porous biomass-derived hard carbon material, comprising the steps of:

[0073] The Torreya grandis shell was ultrasonically cleaned with deionized water for at least 3 times, each cleaning time was 15 minutes, to remove pollutants on the sample surface and dried overnight to obtain a biomass raw material sample Torreya grandis shell;

[0074] Take 1g of the biomass raw material sample Torreya grandis shell, pre-pyrolyze it at 400℃ for 2h at a heating rate of 5℃ / min in a tube furnace; grind the obtained pre-pyrolysis product into powder in a mortar, disperse the powder in a KOH solution (mass percentage of 20%) at 60℃ for 3h, and place it on a magnetic stirring table for heating and stirring. After filtering, disperse it in a 60℃ 3M HCI solution for 5h and stir it magnetically. After that, rinse the sample with deionized water until neutral, and place it in a drying oven at 120℃ for 12 hours overnight;

[0075] Sodium dihydrogen phosphate (NaH2PO4 1g) and 100 mg of the dried carbon sample were placed on the upstream and downstream sides of the tube furnace, respectively. The mixture was calcined at 800°C for 2 hours at a heating rate of 5°C / min. The obtained sample was finally ground to obtain a phosphorus-doped porous biomass-derived hard carbon material P-TSHC.

[0076] P-TSHC material, superconducting carbon black and PVDF are mixed evenly in a mass ratio of 7:2:1. The concentration is adjusted with N-methylpyrrolidone until the required fluidity and uniformity are achieved. The viscosity can be measured by a viscometer, or the state of the slurry can be evaluated by visual inspection and touch. For example, when the stirring container is tilted, the magnetic stirrer can slide naturally, which is the appropriate concentration. Stir for 3 hours to make the slurry. Apply the prepared slurry on the current collector by scraping and dry it at 60°C in a vacuum environment for 12 hours. Cut into circular electrode sheets with a diameter of 16 mm and assemble them into sodium ion battery tests.

[0077] The electrochemical performance test results show that the P-TSHC material prepared in this example is applied to sodium ion batteries, and the first discharge capacity reaches 323.9 mAh / g at a current density of 1 A / g, and maintains 165.6 mAh / g after 70 cycles.

[0078] Example 5

[0079] A phosphorus-doped porous biomass-derived hard carbon material, comprising the steps of:

[0080] The Torreya grandis shell was ultrasonically cleaned with deionized water for at least 3 times, each cleaning time was 15 minutes, to remove pollutants on the sample surface and dried overnight to obtain a biomass raw material sample Torreya grandis shell;

[0081] Take 1g of the biomass raw material sample Torreya grandis shell, pre-pyrolyze it at 400℃ for 2h at a heating rate of 5℃ / min in a tube furnace; grind the obtained pre-pyrolysis product into powder in a mortar, disperse the powder in a KOH solution (mass percentage of 20%) at 60℃ for 3h, and place it on a magnetic stirring table for heating and stirring. After filtering, disperse it in a 60℃ 3M HCI solution for 5h and stir it magnetically. After that, rinse the sample with deionized water until neutral, and place it in a drying oven at 120℃ for 12 hours overnight;

[0082] 16 ml of phosphoric acid (H3PO4) was added to 100 mg of the dried carbon sample and refluxed at 110°C for 4 hours. The acidified sample was washed with deionized water until pH = 3. After drying, the pretreated sample was calcined at 800°C for 2 hours at a heating rate of 5°C / min. The obtained sample was finally ground to obtain a phosphorus-doped porous biomass-derived hard carbon material P-TSHC.

[0083] P-TSHC material, superconducting carbon black and PVDF are mixed evenly in a mass ratio of 7:2:1. The concentration is adjusted with N-methylpyrrolidone until the required fluidity and uniformity are achieved. The viscosity can be measured by a viscometer, or the state of the slurry can be evaluated by visual inspection and touch. For example, when the stirring container is tilted, the magnetic stirrer can slide naturally, which is the appropriate concentration. Stir for 3 hours to make the slurry. Apply the prepared slurry on the current collector by scraping and dry it at 60°C in a vacuum environment for 12 hours. Cut into circular electrode sheets with a diameter of 16 mm and assemble them into sodium ion battery tests.

[0084] The electrochemical performance test results show that the P-TSHC material prepared in this example is applied to sodium ion batteries, and the first discharge capacity reaches 275 mAh / g at a current density of 0.1 A / g, and maintains 120 mAh / g after 70 cycles.

[0085] Comparative Example 1

[0086] A porous Torreya grandis shell carbon material, comprising the following steps:

[0087] The biomass raw material was ultrasonically cleaned with deionized water for at least 3 times, each cleaning time was 15 minutes, to remove pollutants on the sample surface and dried overnight to obtain a biomass raw material sample Torreya grandis shell;

[0088] Take 1g of biomass raw material sample Torreya grandis shell, pre-pyrolyze it at 400℃ for 2h at a heating rate of 5℃ / min in a tubular furnace; grind the obtained pre-pyrolysis product into powder in a mortar, disperse the powder in a KOH solution (mass percentage of 20%) at 60℃ for 3h, and place it on a magnetic stirring table for heating and stirring, filter it, disperse it in a 60℃ 3M HCl solution for 5h and stir it magnetically, then rinse the sample with deionized water until neutral, and place it in a drying oven at 120℃ to dry for 12 hours overnight; finally grind the obtained sample to obtain the biomass-derived hard carbon material TSHC.

[0089] TSHC material, superconducting carbon black and PVDF are mixed evenly in a mass ratio of 7:2:1. The concentration is adjusted with N-methylpyrrolidone until the required fluidity and uniformity are achieved. The viscosity can be measured by a viscometer, or the state of the slurry can be evaluated by visual inspection and touch. For example, when the stirring container is tilted, the magnetic stirrer can slide naturally, which is the appropriate concentration. Stir for 3 hours to make the slurry. Apply the prepared slurry on the current collector by blade coating and dry it at 60°C in a vacuum environment for 12 hours. Cut into circular electrode sheets with a diameter of 16 mm and assemble them into sodium ion battery tests.

[0090] The electrochemical performance test results show that the TSHC material prepared in this control example is applied to sodium ion batteries. The first discharge capacity is 165.3 mAh / g at a current density of 1 A / g, and only 65.7 mAh / g is retained after 300 cycles.

[0091] Comparative Example 2

[0092] A porous Torreya grandis shell carbon material, comprising the following steps:

[0093] The biomass raw material was ultrasonically cleaned with deionized water for at least 3 times, each cleaning time was 15 minutes, to remove pollutants on the sample surface and dried overnight to obtain a biomass raw material sample Torreya grandis shell;

[0094] Take 1g of the biomass raw material sample Torreya grandis shell, pre-pyrolyze it at 400℃ for 2h at a heating rate of 5℃ / min in a tube furnace; grind the obtained pre-pyrolysis product into powder in a mortar, disperse the powder in a KOH solution (mass percentage of 20%) at 60℃ for 1h, and place it on a magnetic stirring table for heating and stirring. After filtering, disperse it in a 60℃ 3M HCI solution for 5h and stir it magnetically. Then rinse the sample with deionized water until it is neutral, and place it in a 120℃ drying oven for 12 hours overnight. Take 100mg of sodium dihydrogen phosphate (NaH2PO41g) and the dried carbon sample, and place them on the upstream and downstream sides of the tube furnace respectively. Calcine at 800℃ at a heating rate of 5℃ / min for 2h. After the obtained sample is finally ground, the phosphorus-doped porous biomass-derived hard carbon material P-TSHC is obtained.

[0095] TSHC material, superconducting carbon black and PVDF are mixed evenly in a mass ratio of 7:2:1. The concentration is adjusted with N-methylpyrrolidone until the required fluidity and uniformity are achieved. The viscosity can be measured by a viscometer, or the state of the slurry can be evaluated by visual inspection and touch. For example, when the stirring container is tilted, the magnetic stirrer can slide naturally, which is the appropriate concentration. Stir for 3 hours to make the slurry. Apply the prepared slurry on the current collector by blade coating and dry it at 60°C in a vacuum environment for 12 hours. Cut into circular electrode sheets with a diameter of 16 mm and assemble them into sodium ion battery tests.

[0096] The electrochemical performance test results show that the TSHC material prepared in this control example is applied to sodium ion batteries. The first discharge capacity is 195.8 mAh / g at a current density of 1 A / g, and only 117.3 mAh / g is retained after 70 cycles.

[0097] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A phosphorus-doped porous Torreya grandis shell carbon material, characterized in that: The invention is prepared from Torreya grandis husk and phosphorus source material, wherein the mass ratio of Torreya grandis husk to phosphorus source material is 0.1:0.5-2; and the phosphorus source material comprises sodium dihydrogen phosphate and / or phosphoric acid.

2. The porous Torreya grandis shell carbon material according to claim 1, characterized in that: The mass ratio of the Torreya grandis shell to the phosphorus source material is 0.1:1-1.

5.

3. A method for preparing the porous Torreya grandis shell carbon material according to claim 1 or 2, characterized in that: The following steps are involved: 1) pre-pyrolyzing the Torreya grandis shell to obtain a pre-pyrolyzed material; 2) treating the pre-pyrolysis material obtained in step 1) with alkali and acid in sequence, washing it to neutrality and then drying it to obtain a carbon sample; 3) The carbon material obtained in step 2) is calcined with a phosphorus source material, and then ground to obtain a porous Torreya grandis shell carbon material.

4. The preparation method according to claim 3, characterized in that: The conditions for pre-pyrolysis in step 1) include: heating to 400° C. at 5° C. / min and keeping the temperature for 2 hours.

5. The preparation method according to claim 3, characterized in that: The conditions of the alkaline treatment in step 2) include: dispersing the pre-pyrolyzed material in a potassium hydroxide solution for 3 hours; The temperature of the potassium hydroxide solution is 60°C; The mass percentage of the potassium hydroxide solution is 20%.

6. The preparation method according to claim 3, characterized in that: The conditions of the acid treatment in step 2) include: the pre-pyrolysis material is then dispersed in a hydrochloric acid solution for 5 hours after the alkali treatment; The concentration of the hydrochloric acid solution is 3 mol / L; The temperature of the hydrochloric acid solution is 60°C.

7. The preparation method according to claim 3, characterized in that: The drying conditions in step 2) include: a temperature of 120° C. and a drying time of 12 hours.

8. The preparation method according to claim 3, characterized in that: The calcination conditions in step 3) include: heating to 800° C. at 5° C. / min and keeping the temperature for 2 hours.

9. The preparation method according to claim 3, characterized in that: The step 1) performs a pretreatment before pre-pyrolysis of Torreya grandis husk, comprising: ultrasonically cleaning the Torreya grandis husk with deionized water and then drying it, wherein the number of ultrasonic cleanings is more than 3 times, each time for 15 minutes.

10. Use of the porous Torreya grandis shell carbon material according to claim 1 or 2 in the preparation of sodium ion batteries.

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