Self-supporting cotton biomass carbon loaded red-phosphorus sodium ion battery negative electrode material and preparation method therefor

Abstract

A self-supporting cotton biomass carbon loaded red-phosphorus sodium ion battery negative electrode material and a preparation method therefor. The self-supporting cotton biomass carbon loaded red-phosphorus sodium ion battery negative electrode material comprises a carbon matrix and nanoscale red phosphorus loaded in pores of the carbon matrix; the carbon matrix is obtained by taking cotton as a biomass carbon precursor and carrying out high-temperature carbonization and etching treatment in argon / ammonia mixed gas. The preparation method comprises: placing cotton in an argon / ammonia mixed gas atmosphere for high-temperature treatment; cooling in an inert gas atmosphere to obtain a carbon matrix; and mixing the carbon matrix with red phosphorus, and carrying out packaging, calcining, cooling, washing and drying to obtain the self-supporting cotton biomass carbon loaded red-phosphorus sodium ion battery negative electrode material. The self-supporting cotton biomass carbon loaded red-phosphorus sodium ion battery negative electrode material has the advantages of high reversible specific capacity and excellent cycling stability.

Description

Self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material and preparation method thereof Technical Field

[0001] The present application relates to the field of secondary batteries, and more specifically, to a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries, as a new type of energy storage device, have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems due to their high energy density and long cycle life. However, the limited, uneven distribution, and high price of lithium resources have limited their development in the future of large-scale energy storage. Next-generation alkali metal ion batteries, such as sodium ion batteries, have a similar "rocking chair" energy storage mechanism as lithium-ion batteries and are abundant and inexpensive, thus showing great potential for application in large-scale energy storage systems.

[0003] At present, sodium-ion battery negative electrode materials are mainly divided into three categories according to their mechanism of storing sodium ions: embedding materials (hard carbon materials), conversion reaction materials (transition metal oxides, sulfides, phosphides, etc.), and alloy reaction materials (bismuth, phosphorus, antimony, etc.). Among them, red phosphorus, based on the alloying reaction mechanism, is a very attractive negative electrode material. Red phosphorus has an ultra-high theoretical specific capacity for sodium storage, which has great application prospects for obtaining high-energy-density sodium-ion full batteries. However, red phosphorus has problems such as poor conductivity and large volume expansion during charging and discharging, resulting in low specific capacity and poor cycle stability of red phosphorus, which limits the further development and application of red phosphorus negative electrodes for sodium-ion batteries.

[0004] In response to the above-mentioned related technologies, the present application provides a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material with high reversible specific capacity and excellent cycle stability, which is conducive to improving the potential of red phosphorus in practical applications.

[0005] Summary of the Invention

[0006] In order to obtain a red phosphorus negative electrode for a sodium ion battery with ultra-high specific capacity, the present application provides a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material and a preparation method thereof.

[0007] In the first aspect, the present application provides a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material, which adopts the following technical solution:

[0008] A self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material, comprising a carbon matrix and nanoscale red phosphorus loaded in the pores of the carbon matrix;

[0009] The carbon matrix is ​​obtained by using cotton as a biomass carbon precursor and undergoing high-temperature carbonization and etching treatment in an Ar / NH3 mixed gas.

[0010] Preferably, the carbon matrix is ​​a nitrogen atom-doped three-dimensional porous hollow carbon nanofiber network structure.

[0011] By adopting the above technical solution, biomass cotton is used as a carbon source, which has the advantages of wide sources, low price, rich heteroatoms and functional groups, and has the structural advantage of natural hollow channels;

[0012] Carbonization and etching of biomass cotton in an Ar / NH3 mixed gas, on the one hand, increases the specific surface area of ​​cotton biomass carbon, and derives a rich microporous structure based on the natural pore structure of cotton, providing abundant loading space for red phosphorus, which can effectively buffer the volume change of red phosphorus during the process of sodium ion insertion and extraction, and significantly improve the cycle stability of red phosphorus as a negative electrode material; on the other hand, the treatment of NH3 atmosphere at high temperature will dope nitrogen atoms into the biomass carbon, thereby improving the electronic conductivity of the carbon matrix. The introduction of nitrogen atoms can promote the adsorption of phosphorus atoms by the carbon matrix, which is beneficial to further improve the electrical contact between red phosphorus and the carbon matrix.

[0013] Preferably, the red phosphorus is loaded onto the carbon substrate by an evaporation-deposition method.

[0014] By adopting the above technical solution, red phosphorus is nanosized and adsorbed and confined in the pores of the carbon matrix, realizing the effective loading of red phosphorus by the carbon matrix, improving the overall conductivity of the electrode negative material, and being conducive to giving full play to the advantage of the ultra-high theoretical specific capacity of the red phosphorus negative electrode, achieving high reversible specific capacity and excellent long-cycle stability.

[0015] Preferably, the volume percentage of NH3 in the Ar / NH3 mixed gas is 5%-10%.

[0016] By adopting the above technical solution, under high temperature conditions, the introduction of NH3 components will have an etching effect on the cotton fibers. By limiting the NH3 content in the mixed gas, the mixed gas can fully and effectively etch the cotton fibers, ensuring that red phosphorus can be fully deposited in the pores of the carbon matrix, so that the carbon matrix can effectively buffer the volume change of red phosphorus during the charge and discharge process; reducing the possibility that when the NH3 content is too low and the etching treatment is insufficient, the micropore volume of the carbon matrix is ​​limited, the pores are loaded with less red phosphorus, and more red phosphorus is deposited on the surface of the carbon matrix, which is easy to fall off during the charge and discharge process and affects the cycle stability of the red phosphorus-carbon battery negative electrode material; at the same time, it reduces the possibility that the micropore volume is too large due to excessive NH3 content, which makes it easy for red phosphorus to fall off from the carbon matrix.

[0017] Preferably, the mass ratio of the carbon matrix to red phosphorus is 1:(1-3).

[0018] By adopting the above technical solution and limiting the mass ratio of the carbon matrix to the red phosphorus, it is possible to ensure that the red phosphorus is effectively deposited in the pores of the carbon matrix, fully exert the buffering effect of the carbon matrix on the volume change of the red phosphorus, and reduce the possibility of red phosphorus being deposited on the surface of the carbon matrix due to excessive red phosphorus loading, and then falling off from the carbon matrix during the charge and discharge process, thereby ensuring that the red phosphorus-carbon battery negative electrode material has better cycle stability; at the same time, it can reduce the possibility of insufficient specific capacity of the red phosphorus-carbon battery negative electrode material due to excessively low red phosphorus loading.

[0019] Preferably, the mass ratio of the carbon matrix to red phosphorus is 1:2.

[0020] By adopting the above technical solution, the carbon matrix can effectively load red phosphorus and effectively buffer the volume change of red phosphorus during the sodium ion insertion and extraction process, so that the red phosphorus-carbon battery negative electrode material has a high reversible specific capacity and excellent cycle stability.

[0021] In a second aspect, the present application provides a method for preparing a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material, using the following technical solution:

[0022] A method for preparing a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material comprises the following steps:

[0023] Clean the cotton;

[0024] The cotton after impurities removal is placed in an Ar / NH3 mixed gas atmosphere and treated at 800-1200°C for 1-3 hours; the temperature is lowered in an inert gas atmosphere to obtain a carbon matrix;

[0025] The carbon matrix is ​​mixed with red phosphorus, encapsulated under vacuum, calcined, and cooled to obtain red phosphorus / carbon mixed powder, which is then washed and dried to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0026] By adopting the above technical solution, carbonization and etching treatment are carried out in an Ar / NH3 mixed gas, thereby increasing the specific surface area of ​​the cotton biomass carbon fiber, thinning the fiber wall of the cotton fiber, and deriving a rich microporous structure based on the natural pore structure of cotton, and doping nitrogen atoms into the carbon matrix. In a one-step operation, a nitrogen-doped three-dimensional porous hollow carbon nanofiber carbon matrix can be obtained, which provides abundant loading sites for the loading of nano red phosphorus. The doping of nitrogen atoms helps to improve the adsorption of red phosphorus by the carbon matrix, and the three-dimensional fiber network structure of the carbon matrix can promote the rapid migration of electrons, has good conductivity, and is conducive to improving the rate performance. At the same time, the one-step etching-doping step simplifies the process, is conducive to improving the preparation efficiency, and reduces the problems of excessive errors and product contamination caused by multiple process steps.

[0027] Loading red phosphorus onto a carbon matrix improves the conductivity of the red phosphorus-carbon battery negative electrode material, which can give full play to the advantages of the ultra-high theoretical specific capacity of the red phosphorus negative electrode, and make the red phosphorus-carbon battery negative electrode material have excellent reversible specific capacity; the three-dimensional porous hollow carbon matrix can effectively buffer the volume change of red phosphorus during the sodium ion insertion and extraction process of charging and discharging, so that the red phosphorus-carbon battery negative electrode material has excellent cycle stability.

[0028] Preferably, the cotton is placed in an Ar / NH 3 mixed gas atmosphere and heated to 800-1200° C. at a rate of 10° C. / min for carbonization and etching.

[0029] Preferably, the calcining and cooling steps specifically include:

[0030] Heat to 800-900℃ at a rate of 4℃ / min, keep warm for 8-10h; then cool to 260℃ at a rate of 1℃ / min, keep warm for more than 24h; then cool naturally to room temperature.

[0031] By adopting the above technical solution, heating causes red phosphorus to evaporate, and then slowly cooling allows the red phosphorus vapor to fully enter and deposit in the pores of the carbon matrix. The particle size of the red phosphorus particles depends on the pore size, thereby achieving nano-sizing of the red phosphorus and making the three-dimensional porous hollow carbon matrix an effective load for the nano-red phosphorus. Uniformly cooling to 260°C and keeping the temperature constant can fully convert white phosphorus into red phosphorus, thereby increasing the yield of red phosphorus.

[0032] Preferably, the washing step comprises: soaking and washing with carbon disulfide 3-4 times.

[0033] By adopting the above technical solution, white phosphorus is dissolved in carbon disulfide and then washed away.

[0034] Preferably, the impurity removal treatment comprises the following steps:

[0035] The cotton is placed in a mixed solution of deionized water and anhydrous ethanol, kept warm at 70-85° C. for 2-6 hours, then washed with anhydrous ethanol for 2-3 times, and dried to obtain the impurity-removed cotton.

[0036] By adopting the above technical solution, impurities in the cotton are reduced, which is beneficial to improving the purity of the carbon matrix.

[0037] In summary, this application has the following beneficial effects:

[0038] 1. This application uses cotton as a biomass carbon source, fully leveraging the advantages of biomass: low price, wide availability, natural hollow pores, and abundant heteroatoms and functional groups. While obtaining a high-performance red phosphorus / carbon sodium-ion battery anode material, it further significantly reduces the cost of sodium-ion batteries, contributing to the rapid development of sodium-ion batteries in the field of large-scale energy storage.

[0039] 2. This application designs and constructs a nitrogen atom-doped three-dimensional porous hollow carbon nanofiber network, which is used as a carbon matrix to achieve effective loading of nano-red phosphorus. The synergistic effects of nano-sizing, N doping, and the three-dimensional porous conductive network are conducive to fully leveraging the advantages of the ultra-high theoretical specific capacity of the red phosphorus negative electrode, so that the red phosphorus-carbon sodium ion battery negative electrode material has a high reversible specific capacity and excellent cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG1 is a SEM (scanning electron microscope) imaging result of the carbon matrix in Example 2 of the present application;

[0041] FIG2 is a TEM (transmission electron microscope) imaging result of the carbon matrix in Example 2 of the present application;

[0042] FIG3 is a SEM (scanning electron microscope) imaging result of the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in Example 2 of the present application;

[0043] FIG4 is a HRTEM (high-resolution transmission electron microscopy) imaging result of the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in Example 2 of the present application;

[0044] Figure 5 is a cyclic voltammetry curve of a button-type sodium ion half-cell assembled based on a self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in Example 2 of the present application at a scan rate of 0.2 mV / s;

[0045] FIG6 is a charge and discharge curve of a button-type sodium ion half-cell assembled based on a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material at a current density of 0.1 A / g in Example 2 of the present application;

[0046] FIG7 is a graph showing the cycling performance of a button-type sodium ion half-cell assembled based on a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material at a current density of 0.1 A / g in Example 2 of the present application;

[0047] Figure 8 is a cycling performance diagram of a button-type sodium ion half-cell assembled based on the self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material at a current density of 2A / g in Example 2 of the present application. DETAILED DESCRIPTION

[0048] The present application is further described in detail below with reference to the accompanying drawings and examples.

[0049] Example

[0050] Example 1

[0051] A self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material is prepared by the following steps:

[0052] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0053] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0054] Step 3: The cotton after impurity removal was placed in a tubular atmosphere furnace, and heated to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 5% NH3 by volume and treated for 1 hour; the temperature was then lowered in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen-doped three-dimensional porous hollow carbon microfiber network structure;

[0055] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:1 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0056] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0057] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0058] Example 2

[0059] A self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material is prepared by the following steps:

[0060] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0061] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0062] Step 3: The cotton after impurity removal was placed in a tubular atmosphere furnace, and heated to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 10% NH3 by volume and treated for 1 hour; the cotton was cooled in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen atom-doped three-dimensional porous hollow carbon microfiber network structure;

[0063] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:2 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0064] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0065] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0066] The carbon matrix obtained in the third step of this embodiment was characterized by SEM (scanning electron microscopy) and TEM (transmission electron microscopy). The imaging results are shown in Figures 1 and 2, respectively. It can be seen that the carbon matrix presents a three-dimensional network structure composed of one-dimensional hollow carbon fibers.

[0067] The self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material finally prepared in this example was characterized by SEM (scanning electron microscopy) and HRTEM (high-resolution transmission electron microscopy), and the results are shown in Figures 3 and 4. The SEM results in Figure 3 show that after loading with red phosphorus, the fiber morphology of the carbon matrix does not change, and there is no obvious aggregation of red phosphorus particles on the fiber surface, indicating that the red phosphorus is successfully embedded in the pores of the porous carbon in a nanoscale form through the evaporation-deposition process; the HRTEM results in Figure 4 show that the red phosphorus-carbon negative electrode material exhibits an amorphous porous structure, indicating that the red phosphorus deposited in the pores of the red phosphorus-carbon negative electrode material is amorphous.

[0068] Example 3

[0069] The only difference between this embodiment and embodiment 2 is that the volume percentage of NH3 in the Ar / NH3 mixed gas is 3%. That is, the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in this embodiment is prepared by the following steps:

[0070] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0071] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0072] The third step is to place the cotton after impurity treatment in a tubular atmosphere furnace, and heat it to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 3% NH3 by volume and treat it for 1 hour; then cool it in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen atom-doped three-dimensional porous hollow carbon micron fiber network structure;

[0073] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:2 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0074] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0075] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0076] Example 4

[0077] The only difference between this embodiment and embodiment 2 is that the NH3 content in the Ar / NH3 mixed gas is 5%. That is, the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in this embodiment is prepared by the following steps:

[0078] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0079] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0080] Step 3: The cotton after impurity removal was placed in a tubular atmosphere furnace, and heated to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 5% NH3 by volume and treated for 1 hour; the temperature was then lowered in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen-doped three-dimensional porous hollow carbon microfiber network structure;

[0081] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:2 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0082] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0083] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0084] Example 5

[0085] The only difference between this embodiment and embodiment 2 is that the NH3 content in the Ar / NH3 mixed gas is 8%. That is, the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in this embodiment is prepared by the following steps:

[0086] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0087] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0088] Step 3: The cotton after impurity removal was placed in a tubular atmosphere furnace, and heated to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 8% NH3 by volume and treated for 1 hour; the cotton was cooled in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen atom-doped three-dimensional porous hollow carbon microfiber network structure;

[0089] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:2 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0090] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0091] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0092] Example 6

[0093] The only difference between this embodiment and embodiment 2 is that the NH3 content in the Ar / NH3 mixed gas is 12%. That is, the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in this embodiment is prepared by the following steps:

[0094] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0095] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0096] The third step is to place the cotton after impurity treatment in a tubular atmosphere furnace, and heat it to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 12% NH3 by volume and treat it for 1 hour; then cool it in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen-doped three-dimensional porous hollow carbon microfiber network structure;

[0097] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:2 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0098] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0099] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0100] Example 7

[0101] The only difference between this embodiment and embodiment 2 is that the mass ratio of carbon matrix to red phosphorus in the fourth step is 1:0.8. That is, the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in this embodiment is prepared by the following steps:

[0102] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0103] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0104] Step 3: The cotton after impurity removal was placed in a tubular atmosphere furnace, and heated to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 10% NH3 by volume and treated for 1 hour; the cotton was cooled in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen atom-doped three-dimensional porous hollow carbon microfiber network structure;

[0105] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:0.8 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0106] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0107] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0108] Example 8

[0109] The only difference between this embodiment and embodiment 2 is that the mass ratio of the carbon matrix to the red phosphorus in the fourth step is 1:1. That is, the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in this embodiment is prepared by the following steps:

[0110] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0111] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0112] Step 3: The cotton after impurity removal was placed in a tubular atmosphere furnace, and heated to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 10% NH3 by volume and treated for 1 hour; the cotton was cooled in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen atom-doped three-dimensional porous hollow carbon microfiber network structure;

[0113] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:1 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0114] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0115] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0116] Example 9

[0117] The only difference between this embodiment and embodiment 2 is that the mass ratio of the carbon matrix to the red phosphorus in the fourth step is 1:3. That is, the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in this embodiment is prepared by the following steps:

[0118] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0119] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0120] Step 3: The cotton after impurity removal was placed in a tubular atmosphere furnace, and heated to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 10% NH3 by volume and treated for 1 hour; the cotton was cooled in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen atom-doped three-dimensional porous hollow carbon microfiber network structure;

[0121] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:3 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0122] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0123] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0124] Example 10

[0125] The only difference between this embodiment and embodiment 2 is that the mass ratio of the carbon matrix to the red phosphorus in the fourth step is 1:5. That is, the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material in this embodiment is prepared by the following steps:

[0126] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0127] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0128] Step 3: The cotton after impurity removal was placed in a tubular atmosphere furnace, and heated to 1000°C at a rate of 10°C / min in an Ar / NH3 mixed gas containing 10% NH3 by volume and treated for 1 hour; the cotton was cooled in an Ar inert atmosphere to prepare a carbon matrix with a nitrogen atom-doped three-dimensional porous hollow carbon microfiber network structure;

[0129] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:5 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0130] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0131] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0132] Comparative Example

[0133] Comparative Example 1

[0134] The only difference between this comparative example and Example 2 is that the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material is prepared by the following steps:

[0135] Step 1: Place the cotton in a mixed solution of deionized water and anhydrous ethanol with a volume ratio of 1:1 and keep it at 80℃ for 6 hours;

[0136] Step 2: After soaking, squeeze out the liquid from the cotton, wash it twice with anhydrous ethanol, and dry it in a forced air drying oven at 100°C for 12 hours;

[0137] Step 3: Place the cotton after impurity removal in a tubular atmosphere furnace, heat it to 1000°C at a rate of 10°C / min in an Ar inert atmosphere and treat it for 1 hour; cool it down in the Ar inert atmosphere to prepare a carbon matrix with a nitrogen atom-doped three-dimensional porous hollow carbon microfiber network structure;

[0138] Step 4: Mix the carbon matrix and commercially available red phosphorus powder in a mass ratio of 1:2 and place them in a quartz tube, and seal the quartz tube under vacuum;

[0139] Step 5: Place the sealed quartz tube in a muffle furnace, heat it to 898°C at a rate of 4°C / min, hold it for 8 hours, then cool it down to 260°C at a rate of 1°C / min and hold it for 24 hours; then cool it naturally to room temperature, open the sealed quartz tube under an Ar inert atmosphere, and obtain a red phosphorus / carbon mixed powder;

[0140] Step 6: Soak the red phosphorus / carbon mixed powder in carbon disulfide and wash it four times, then place it in a vacuum drying oven and dry it for 24 hours to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

[0141] Performance testing

[0142] The self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode materials prepared in each experimental example and each comparative example were applied to a button-type sodium ion half-cell. The preparation method of the button-type sodium ion half-cell is as follows:

[0143] Self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material, acetylene black, and binder polyvinylidene fluoride were ground in a mass ratio of 7:2:1, and the solvent N-methylpyrrolidone was added and ground evenly to obtain a battery slurry. The battery slurry was evenly scraped onto a copper foil by a casting method, dried in a vacuum oven at 60°C for 24 hours, compacted, and punched into a disc with a diameter of 10 mm to serve as the negative electrode material of the sodium ion battery; the sodium sheet was used as the counter electrode and the Waterman glass fiber was used as the separator; the electrolyte included 1M NaClO4 as the electrolyte, ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1 as the electrolyte, and 1% fluoroethylene carbonate was added; the assembly was carried out in an inert atmosphere glove box to obtain a button-type sodium ion half-cell.

[0144] Perform the following test:

[0145] Test 1: Cyclic voltammetry of a button-type sodium ion half-cell was performed in the voltage range of 0.01-2V at a scan rate of 0.2mV / s.

[0146] Test 2: The button-type sodium ion half-cell was subjected to constant current charge and discharge tests at a current density of 0.1 A / g;

[0147] Test 3: The button-type sodium ion half-cell was subjected to charge and discharge cycles at a current density of 0.1 A / g.

[0148] The test results of the button-type sodium ion half-cell assembled based on the self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material of Example 2 are shown in Figures 5 to 8.

[0149] The first charge specific capacity and first coulombic efficiency of button-type sodium ion half-cells assembled from the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode materials of each Example and Comparative Example at a current density of 0.1 A / g were recorded. The capacity retention rate of each button-type sodium ion half-cell after the nth cycle was calculated based on the charge specific capacity after several cycles at a current density of 0.1 A / g: capacity retention rate for the nth cycle = (charge specific capacity after n cycles / initial charge specific capacity) × 100%. The results are summarized in Table 1.

[0150] Table 1

[0151] 5 , it can be seen that the red phosphorus negative electrode of the sodium ion battery has typical sodium ion insertion and extraction characteristics, and the curves show a high degree of overlap, which shows that the button-type sodium ion half-cell has good electrode reaction reversibility.

[0152] 6 , it can be seen that the first charge specific capacity of the button-type sodium ion half-cell assembled based on Example 2 is as high as 896.2 mAh / g, and the corresponding first coulombic efficiency is 79.5%; and the second and third cycle charge and discharge curves have a high degree of overlap, indicating good cycle stability of the electrode material.

[0153] 7 and 8 , it can be seen that the button-type sodium ion half-cell assembled based on Example 2 has a good cycle retention rate. At a current density of 0.1 A / g, after 45 cycles, there is still a charge capacity of 812.6 mAh / g. At a current density of 2 A / g, after 230 cycles, the charge capacity is 452.2 mAh / g, indicating that the self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material of Example 2 has excellent sodium storage performance.

[0154] In combination with Example 2, Figures 5-8 and Table 1, it can be seen that the self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material prepared according to the method disclosed in the present application can give the sodium ion battery extremely high reversible specific capacity and excellent cycle stability, and the first coulomb efficiency is high. This shows that the use of a nitrogen atom-doped three-dimensional porous hollow carbon nanofiber network as a carbon matrix to load nano red phosphorus can give full play to the advantages of the ultra-high theoretical specific capacity of red phosphorus as a negative electrode material, so that the red phosphorus-carbon battery negative electrode material has excellent reversible specific capacity; the porous hollow carbon matrix can effectively buffer the volume change of red phosphorus during the charge and discharge process, so that the negative electrode material has excellent cycle stability, and the three-dimensional fiber network structure of the carbon matrix can promote the rapid migration of electrons, thereby promoting the improvement of the first coulomb efficiency.

[0155] In combination with Example 2 and Comparative Example 1 and Table 1, it can be seen that the treatment of cotton biomass carbon in an Ar / NH3 mixed gas can significantly improve the cycle stability of the button-type sodium ion half-cell, and the first charge specific capacity of the button-type sodium ion half-cell is also significantly improved. This may be because, under high temperature conditions, the introduction of the NH3 component will have an etching effect on the cotton fiber, expand the specific surface area of ​​the carbon matrix, and thin the fiber wall of the cotton fiber, and derive a rich microporous structure based on the natural pore structure of the cotton, so that red phosphorus is deposited and loaded in the micropores of the carbon matrix, so that the carbon matrix can effectively buffer the volume change of red phosphorus during the charge and discharge process; at the same time, nitrogen atoms can be doped into the carbon matrix, which promotes the adsorption of red phosphorus by the carbon matrix, which helps to increase the loading capacity of red phosphorus; the three-dimensional fiber network structure generated by the high-temperature etching treatment of the NH3 component also helps to promote the rapid migration of electrons, improve the conductivity of the red phosphorus-carbon negative electrode material, and promote the improvement of rate performance.

[0156] In combination with Examples 2-6 and Table 1, it can be seen that when the amount of red phosphorus input is constant, as the volume concentration of NH3 in the Ar / NH3 mixed gas increases, the first charge specific capacity of the button-type sodium ion half-cell gradually increases, and the capacity retention rate after the 45th cycle shows a trend of first increasing and then decreasing. This may be because the increase in the volume concentration of NH3 promotes the effect of the high-temperature etching treatment, increases the specific surface area of ​​the carbon matrix, increases the porosity of the micropores generated by the carbon matrix, and increases the nitrogen atom doping on the carbon matrix, which promotes the adsorption and loading of red phosphorus by the carbon matrix, thereby promoting the increase in the first charge specific capacity. The microporous structure can effectively buffer the volume change of red phosphorus during the charge and discharge process, effectively improve the cycle stability, and thus promote the improvement of the capacity retention rate of the button-type sodium ion half-cell.

[0157] When the NH3 volume concentration is too low, the high-temperature etching treatment is insufficient, the carbon matrix has poor adsorption of red phosphorus, and the porosity is low, so that the red phosphorus cannot be fully deposited in the pores of the carbon matrix, resulting in poor first-charge specific capacity and capacity retention of the button-type sodium ion half-cell. When the NH3 volume concentration is too high, the pore diameter of the micropores of the carbon matrix is ​​etched and enlarged, which may cause the red phosphorus loaded in the micropores to easily fall off the carbon matrix, thereby reducing the capacity retention of the button-type sodium ion half-cell. The present application limits the NH3 volume concentration to 5-10%, which can ensure the treatment effect of the Ar / NH3 mixed gas on cotton biomass carbon, and make the red phosphorus-carbon negative electrode material have better cycle stability and higher specific capacity.

[0158] In combination with Example 2, Example 7-10 and Table 1, it can be seen that when the NH3 volume concentration is constant, as the amount of red phosphorus input increases, the mass ratio of the carbon matrix to red phosphorus decreases, the first charge specific capacity of the button-type sodium ion half-cell gradually increases, and the capacity retention rate gradually decreases. This may be due to the increase in the amount of red phosphorus input, the red phosphorus loading of the carbon matrix increases, thereby increasing the specific capacity of the red phosphorus-carbon negative electrode material, and the first charge specific capacity of the button-type sodium ion half-cell gradually increases. After red phosphorus is input, it is deposited in the micropores of the carbon matrix under the adsorption of the carbon matrix, so that the carbon matrix can effectively play a buffering role in the volume change of red phosphorus. As the amount of red phosphorus input increases, due to the limited loading of red phosphorus by the microporous structure of the carbon matrix, part of the red phosphorus is deposited on the surface of the carbon matrix and is easy to fall off during charge and discharge, resulting in a decrease in cycle stability and a decrease in the capacity retention rate of the button-type sodium ion half-cell.

[0159] The present application limits the mass ratio of the carbon matrix to red phosphorus to 1: (1-3), which can ensure that the red phosphorus-carbon negative electrode material has a high specific capacity while making the red phosphorus-carbon negative electrode material have excellent cycle stability. When the mass ratio of the carbon matrix to red phosphorus is too large, the red phosphorus loading of the carbon matrix is ​​too low, so that the specific capacity of the red phosphorus-carbon negative electrode material is low; when the mass ratio of the carbon matrix to red phosphorus is too small, the red phosphorus loaded on the surface of the carbon matrix is ​​too much, and the cycle stability of the red phosphorus-carbon negative electrode material is poor. Moreover, when the mass ratio of the carbon matrix to red phosphorus is 1:2, the specific capacity and cycle stability of the red phosphorus-carbon negative electrode material are relatively balanced, and the red phosphorus-carbon negative electrode material at this time has a high reversible specific capacity and excellent cycle stability.

[0160] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material, characterized in that: It includes a carbon matrix, and nano-scale red phosphorus loaded in the pores of the carbon matrix; The carbon matrix is ​​obtained by using cotton as a biomass carbon precursor through high-temperature carbonization and etching in an Ar / NH3 mixed gas; In the Ar / NH3 mixed gas, the volume percentage of NH3 is 5%-10%; The mass ratio of the carbon matrix to red phosphorus is 1:(1-3).

2. The self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material according to claim 1, characterized in that: The carbon matrix is ​​a three-dimensional porous hollow carbon nanofiber network structure doped with nitrogen atoms.

3. The self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material according to claim 1, characterized in that: The red phosphorus is loaded onto the carbon substrate by an evaporation-deposition method.

4. The self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material according to claim 1, characterized in that: The mass ratio of the carbon matrix to red phosphorus is 1:

2.

5. A method for preparing the self-supporting cotton biomass carbon-supported red phosphorus sodium ion battery negative electrode material according to any one of claims 1 to 4, characterized in that: The following steps are involved: Remove impurities from cotton; The impurity-removed cotton is placed in an Ar / NH3 mixed gas atmosphere and treated at 800-1200°C for 1-3 hours; the temperature is lowered in an inert gas atmosphere to obtain a carbon matrix; The carbon matrix is ​​mixed with red phosphorus, packaged under vacuum, calcined, and cooled to obtain red phosphorus / carbon mixed powder, which is then washed and dried to obtain a self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material.

6. The method for preparing the self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material according to claim 5, characterized in that: The calcination and cooling steps specifically include: Raise the temperature to 800-900℃ at a rate of 4℃ / min, and keep it at that temperature for 8-10h; then cool down to 260℃ at a rate of 1℃ / min, and keep it at that temperature for more than 24h; then cool down naturally to room temperature.

7. The method for preparing the self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material according to claim 5, characterized in that: The washing step comprises: soaking with carbon disulfide and washing 3-4 times.

8. The method for preparing the self-supporting cotton biomass carbon-loaded red phosphorus sodium ion battery negative electrode material according to claim 5, characterized in that: The impurity removal process comprises the following steps: The cotton is placed in a mixed solution of deionized water and anhydrous ethanol, kept warm at 70-85° C. for 2-6 hours, washed with anhydrous ethanol for 2-3 times, and dried to obtain the impurity-removed cotton.

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