A carbon-coated composite material, a preparation method and application thereof

Abstract

The application belongs to the technical field of sodium ion batteries, and particularly relates to a carbon-coated composite material and a preparation method and application thereof. The application provides a carbon-coated composite material, which comprises sodium iron pyrophosphate and a carbon layer coated on the surface of the sodium iron pyrophosphate; the chemical composition of the sodium iron pyrophosphate is Na4Fe 3‑x (PO4)2(P2O7), wherein 0

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a carbon-coated composite material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries boast high energy density and long cycle life, making them widely used in portable electronic devices. However, with the continuous expansion of global demand for large-scale energy storage, the scarcity of lithium resources on Earth will become a bottleneck restricting the future large-scale application of lithium-ion batteries. Sodium belongs to the same group as lithium, has similar chemical properties, and occupies 2.64% of the Earth's crust, far exceeding elemental lithium (0.006%). Therefore, developing abundant and environmentally friendly sodium-ion battery technology is of significant strategic importance and practical value for the development of large-scale energy storage technologies.

[0003] Since sodium ions have a larger radius than lithium ions, the key to current research is finding electrode materials that can stably intercalate and deintercalate sodium ions. Among the many sodium-ion battery cathode materials, polyanionic compounds are considered the most promising class of electrode materials due to their excellent structural stability, safety, and suitable voltage platform.

[0004] Taking phosphates as an example, they mainly consist of Na4Fe3(PO4)P2O7, with tetrahedral PO4 units having strong covalent bonds and a relative separation of valence electrons and polyanions. This special three-dimensional framework structure, accompanied by a multi-electron mechanism, results in smaller energy transitions between the highest and lowest occupied molecular orbitals, which is highly conducive to the rapid extraction and insertion of sodium ions.

[0005] However, the Na4Fe3(PO4)P2O7 electrode material still suffers from poor conductivity and low specific capacity, which limits its application in sodium-ion batteries. Summary of the Invention

[0006] The purpose of this invention is to provide a carbon-coated composite material, its preparation method, and its application. The carbon-coated composite material provided by this invention has good electrical conductivity and high specific capacity.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The present invention provides a carbon-coated composite material, comprising sodium iron phosphate pyrophosphate and a carbon layer coating the surface of the sodium iron phosphate pyrophosphate;

[0009] The chemical composition of the sodium ferric pyrophosphate is Na₄Fe₂O₃. 3-x (PO4)2(P2O7), where 0 <x<0.15。

[0010] Preferably, the thickness of the carbon layer is 50–200 nm.

[0011] This invention also provides a method for preparing the carbon-coated composite material described in the above technical solution, comprising the following steps:

[0012] Sodium source, iron source, phosphorus source and polar organic solvent are first mixed and then wet milled to obtain the precursor;

[0013] The carbon source is acidified to obtain an acidified carbon source;

[0014] The precursor and the second acidified carbon source are mixed and sintered to obtain the carbon-coated composite material.

[0015] Preferably, the sodium source includes one or more of sodium carbonate, sodium hydroxide, and sodium acetate;

[0016] The iron source includes iron phosphate and / or iron oxide;

[0017] The phosphorus source includes ammonium dihydrogen phosphate and / or ammonium monohydrogen phosphate.

[0018] Preferably, in the mixture obtained by the first mixing, the molar ratio of Na, Fe and P is 1:0.6-0.9:0.8-1.5, based on the molar amounts of Na, Fe and P.

[0019] Preferably, the wet sand milling speed is 500-700 rpm and the time is 3-6 hours.

[0020] Preferably, the acidic reagent used in the acidification treatment includes one or more of hydrochloric acid, sulfuric acid, and acetic acid; the concentration of the acidic reagent is 10-50 wt%.

[0021] The carbon source includes one or more of glucose, sucrose, starch, maltose, activated carbon, and carbon nanotubes;

[0022] The ratio of carbon source to acid reagent is 90-100g:500mL;

[0023] The acidification treatment is performed at a temperature of 30–50°C for a time of 0.5–1 hour.

[0024] Preferably, the mass ratio of the precursor to the acidified carbon source is 100:8 to 20.

[0025] Preferably, the sintering temperature is 400–600°C, and the holding time is 12–24 hours.

[0026] The present invention also provides the application of the carbon-coated composite material described in the above technical solution or the carbon-coated composite material prepared by the preparation method described in the above technical solution as a positive electrode material for sodium-ion batteries.

[0027] The present invention provides a carbon-coated composite material, comprising sodium iron pyrophosphate and a carbon layer coated on the surface of the sodium iron pyrophosphate; the chemical composition of the sodium iron pyrophosphate is Na4Fe 3-x (PO4)2(P2O7), where 0 < x < 0.15. In the present invention, by reducing the iron content in the sodium iron pyrophosphate, the heterophase and impurities of the sodium iron pyrophosphate are less. As the Fe content decreases, the NaFePO4 impurity phase in the material can be reduced, and the proportion of the sodium iron pyrophosphate phase can be increased, which is beneficial to the crystallization of the material; on the one hand, the carbon coating layer can undergo a carbothermal reduction reaction, making the iron in the sodium iron pyrophosphate show a +2 valence. At the same time, the carbon coating can further improve the conductivity of the composite material, and thus the obtained composite material has a higher specific capacity and rate performance. Description of the Drawings

[0028] Figure 1 SEM image of the carbon-coated composite material obtained in Example 1;

[0029] Figure 2 Galvanostatic charge-discharge curve of the sodium-ion half-cell prepared from the carbon-coated composite materials obtained in Example 1 and Comparative Example 1;

[0030] Figure 3 Rate performance curve of the sodium-ion half-cell prepared from the carbon-coated composite material obtained in Example 1. Detailed Embodiments

[0031] The present invention provides a carbon-coated composite material, comprising sodium iron pyrophosphate and a carbon layer coated on the surface of the sodium iron pyrophosphate;

[0032] The chemical composition of the sodium iron pyrophosphate is Na4Fe 3-x (PO4)2(P2O7), where 0 < x < 0.15.

[0033] In the present invention, the thickness of the carbon layer is preferably 50 - 200 nm, more preferably 80 - 180 nm, and still more preferably 100 - 150 nm.

[0034] The present invention also provides a preparation method of the sodium-ion cathode material according to the above technical solution, comprising the following steps:

[0035] Mix a sodium source, an iron source, a phosphorus source and a polar organic solvent for the first time, and obtain a precursor through wet sanding;

[0036] Perform acidification treatment on a carbon source to obtain an acidified carbon source;

[0037] Mix the precursor and the acidified carbon source for the second time, and obtain the carbon-coated composite material through sintering.

[0038] In this invention, unless otherwise specified, all raw materials are commercially available products well known to those skilled in the art.

[0039] In this invention, a sodium source, an iron source, a phosphorus source, and a polar organic solvent are first mixed, and then wet-milled to obtain a precursor.

[0040] In this invention, the sodium source preferably includes one or more of sodium carbonate, sodium hydroxide, and sodium acetate; the iron source preferably includes ferric phosphate and / or ferric oxide; and the phosphorus source preferably includes ammonium dihydrogen phosphate and / or ammonium monohydrogen phosphate.

[0041] In this invention, the polar organic solvent preferably includes anhydrous ethanol and / or ethylene glycol.

[0042] In this invention, in the first mixture obtained, the molar ratio of Na, Fe and P is preferably 1:0.6-0.9:0.8-1.5, more preferably 1:0.7-0.8:0.9-1.4, and even more preferably 1:0.7-0.8:1.0-1.3.

[0043] In this invention, the solid content of the mixture obtained by the first mixing is preferably 8-15%.

[0044] The present invention does not limit the mixing process; any process well known to those skilled in the art can be used.

[0045] In this invention, the preferred rotational speed of the wet sand mill is 500–700 rpm, and the preferred time is 3–6 hours. The preferred ball-to-material ratio of the wet sand mill is 5:1–2. The wet sand milling is preferably performed in a sand mill.

[0046] In this invention, the median particle size of the material in the slurry obtained by the wet sand milling is preferably 400-600 nm.

[0047] Following the wet milling process, the present invention preferably further includes drying the resulting slurry. In this invention, the drying method is preferably spray drying. In this invention, the inlet temperature during the spray drying process is preferably 200–250°C, and the outlet temperature is preferably 100–110°C.

[0048] In this invention, the median particle size of the precursor is preferably 5–15 μm; the tap density is preferably 0.9–1.2 m³ / s. 2 / g. In this invention, the precursor is sodium iron pyrophosphate.

[0049] The present invention involves acidifying a carbon source to obtain an acidified carbon source.

[0050] In this invention, the carbon source preferably includes one or more of glucose, sucrose, starch, maltose, activated carbon, and carbon nanotubes.

[0051] In this invention, the acidifying agent used in the acidification treatment preferably includes one or more of hydrochloric acid, sulfuric acid, and acetic acid. In this invention, the concentration of the acidifying agent is preferably 10–50 wt%.

[0052] In this invention, the preferred ratio of carbon source to acidifying reagent is 90-100g:500mL.

[0053] In this invention, the acidification treatment temperature is preferably 30–50°C, and the time is preferably 0.5–1 hour. In this invention, the acidification treatment is preferably carried out under stirring conditions; the stirring speed is preferably 400–500 rpm.

[0054] Following the acidification treatment, the present invention preferably further includes washing and drying the obtained material. The washing process is not particularly limited in the present invention, and can be carried out until the material is neutral. The drying process is not particularly limited in the present invention, and can be any process well known to those skilled in the art.

[0055] In this invention, acidification treatment can improve the surface activity of the carbon source, thereby improving the stability of carbon coating.

[0056] After obtaining the precursor and the acidified carbon source, the present invention mixes the precursor and the acidified carbon source in a second way, and then sintersects them to obtain the carbon-coated composite material.

[0057] In this invention, the mass ratio of the precursor to the acidified carbon source is preferably 100:8 to 20.

[0058] In this invention, the mixing is preferably carried out under stirring conditions; the stirring speed is preferably 400-800 rpm, and the stirring time is preferably 0.5-1 h. In this invention, the mixing is preferably carried out in a high-speed mixer.

[0059] In this invention, the sintering temperature is preferably 400-600℃, more preferably 450-580℃, and even more preferably 500-550℃; the heating rate to the sintering temperature is preferably 3-10℃ / min, more preferably 4-9℃ / min, and even more preferably 5-8℃ / min; the holding time is preferably 12-24h, more preferably 14-20h, and even more preferably 16-18h.

[0060] In this invention, the sintering is preferably carried out in an inert atmosphere; the inert atmosphere is preferably argon or nitrogen.

[0061] After sintering, the present invention preferably further includes sequentially crushing and sieving the obtained material. The present invention does not impose any particular limitation on the crushing and sieving process; any process well known to those skilled in the art can be used.

[0062] The present invention also provides the application of the carbon-coated composite material described in the above technical solution or the carbon-coated composite material prepared by the preparation method described in the above technical solution as a positive electrode material for sodium-ion batteries.

[0063] To further illustrate the present invention, a carbon-coated composite material, its preparation method, and its application are described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0064] Example 1

[0065] 4.06 mol sodium carbonate, 5.74 mol ferric phosphate, 2.54 mol ammonium dihydrogen phosphate, and 10 L anhydrous ethanol were mixed. The resulting mixture was then subjected to wet ball milling at 500 rpm for 4 hours. The resulting slurry (with a median particle size of 0.429 μm) was transferred to a feed tank and spray-dried at an inlet temperature of 230 °C and an outlet temperature of 105 °C to obtain a precursor (particle size of 5.91 μm and tap density of 0.934 m³). 2 / g), the molecular formula of the precursor is Na4Fe 2.91 (PO4)2(P2O7);

[0066] Add 96.6g of glucose to 500mL of 20wt% hydrochloric acid solution and acidify it at 400rpm and 45℃ for 1h. Then wash it with water until neutral and dry it to obtain the acidified carbon source.

[0067] 1000g of precursor and 85g of acidified carbon source were placed in a high-speed mixer and stirred at 700rpm for 0.5h. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 450℃ for 12h. The sintered material was then crushed and sieved to obtain the carbon-coated composite material (where the carbon layer coating thickness was 95nm and the particle size of the composite material was 6.23μm).

[0068] Example 2

[0069] 3.25 mol sodium carbonate, 1.87 mol iron oxide, 6.5 mol ammonium dihydrogen phosphate, and 10 L anhydrous ethanol were mixed. The resulting mixture was then subjected to wet ball milling at 500 rpm for 4 hours. The resulting slurry (with a median particle size of 0.512 μm) was transferred to a feed tank and spray-dried at an inlet temperature of 230 °C and an outlet temperature of 105 °C to obtain a precursor (particle size of 6.24 μm and tap density of 0.873 m³). 2 / g), the molecular formula of the precursor is Na4Fe 2.87 (PO4)2(P2O7);

[0070] Add 98g of activated carbon to 500mL of 20wt% hydrochloric acid solution and acidify it at 400rpm and 45℃ for 1h. Then wash it with water until neutral and dry it to obtain the acidified carbon source.

[0071] 1000g of precursor and 85g of acidified carbon source were placed in a high-speed mixer and stirred at 700rpm for 0.5h. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 500℃ for 10h. The sintered material was then crushed and sieved to obtain the carbon-coated composite material (where the carbon layer coating thickness was 150nm and the particle size of the composite material was 6.98μm).

[0072] Example 3

[0073] 7.95 mol sodium carbonate, 5.68 mol ferric phosphate, 3.62 mol ammonium dihydrogen phosphate, and 10 L anhydrous ethanol were mixed. The resulting mixture was then subjected to wet ball milling at 500 rpm for 4 hours. The resulting slurry (with a median particle size of 0.498 μm) was transferred to a feed tank and spray-dried at an inlet temperature of 230 °C and an outlet temperature of 105 °C to obtain a precursor (particle size of 6.17 μm and tap density of 0.871 m³). 2 / g), the molecular formula of the precursor is Na4Fe 2.91 (PO4)2(P2O7);

[0074] 98g of activated carbon was placed in 500mL of 20wt% hydrochloric acid solution and acidified at 400rpm and 45℃ for 1h. Then it was washed with water until neutral and dried to obtain the acidified carbon source.

[0075] 1000g of precursor and 85g of acidified carbon source were placed in a high-speed mixer and stirred at 700rpm for 0.5h. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 600℃ for 12h. The sintered material was then crushed and sieved to obtain the carbon-coated composite material (where the carbon layer coating thickness was 90nm and the particle size of the composite material was 6.73μm).

[0076] Example 4

[0077] 4.06 mol sodium carbonate, 5.74 mol ferric phosphate, 2.54 mol ammonium dihydrogen phosphate, and 10 L anhydrous ethanol were mixed. The resulting mixture was then subjected to wet ball milling at 500 rpm for 5 hours. The resulting slurry (with a median particle size of 0.354 μm) was transferred to a feed tank and spray-dried at an inlet temperature of 230 °C and an outlet temperature of 105 °C to obtain a precursor (particle size of 6.37 μm and tap density of 0.912 m³ / s). 2 / g), the molecular formula of the precursor is Na4Fe 2.85 (PO4)2(P2O7);

[0078] 100g of activated carbon was placed in 500mL of 30wt% hydrochloric acid solution and acidified at 400rpm and 45℃ for 0.5h. Then it was washed with water until neutral and dried to obtain the acidified carbon source.

[0079] 1000g of precursor and 85g of acidified carbon source were placed in a high-speed mixer and stirred at 700rpm for 0.5h. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 550℃ for 12h. The sintered material was then crushed and sieved to obtain the carbon-coated composite material (where the carbon layer coating thickness was 100nm and the particle size of the composite material was 6.51μm).

[0080] Comparative Example 1

[0081] 4.06 mol sodium carbonate, 5.74 mol ferric phosphate, and 2.54 mol ammonium dihydrogen phosphate were mixed with 10 L of water. The resulting mixture was then subjected to wet ball milling at 500 rpm for 4 hours. The resulting slurry (with a median particle size of 0.537 μm) was transferred to a feed tank and spray-dried at an inlet temperature of 230 °C and an outlet temperature of 105 °C to obtain a precursor (particle size of 6.89 μm and tap density of 0.817 m³). 2 / g), the molecular formula of the precursor is Na4Fe 2.99 (PO4)2(P2O7);

[0082] 96.6g of activated carbon was added to 500mL of 20wt% hydrochloric acid solution and acidified at 400rpm and 45℃ for 1h. Then it was washed with water until neutral and dried to obtain the acidified carbon source.

[0083] 1000g of precursor and 85g of acidified carbon source were placed in a high-speed mixer and stirred at 700rpm for 0.5h. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 450℃ for 12h. The sintered material was then crushed and sieved to obtain the carbon-coated composite material (where the carbon layer coating thickness was 150nm and the particle size of the composite material was 6.99μm).

[0084] Comparative Example 2

[0085] 4.06 mol sodium carbonate, 5.97 mol ferric phosphate, 2.54 mol ammonium dihydrogen phosphate, and 10 L anhydrous ethanol were mixed. The resulting mixture was then subjected to wet ball milling at 500 rpm for 4 hours. The resulting slurry (with a median particle size of 0.524 μm) was transferred to a feed tank and spray-dried at an inlet temperature of 230 °C and an outlet temperature of 105 °C to obtain a precursor (particle size of 6.89 μm and tap density of 0.824 m³). 2 / g), the precursors include Na4Fe3(PO4)2(P2O7) and Na4Fe3PO4;

[0086] 1000g of precursor and 85g of activated carbon were placed in a high-speed mixer and stirred at 700rpm for 0.5h to mix. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 450℃ for 12h. The sintered material was then crushed and sieved to obtain the carbon-coated composite material (where the carbon layer coating thickness was 170nm and the particle size of the composite material was 7.56μm).

[0087] Comparative Example 3

[0088] 4.06 mol sodium carbonate, 5.50 mol ferric phosphate, 2.54 mol ammonium dihydrogen phosphate, and 10 L anhydrous ethanol were mixed. The resulting mixture was then subjected to wet ball milling at 500 rpm for 4 hours. The resulting slurry (with a median particle size of 0.574 μm) was transferred to a feed tank and spray-dried at an inlet temperature of 230 °C and an outlet temperature of 105 °C to obtain a precursor (particle size of 6.57 μm and tap density of 0.789 m³). 2 / g), the molecular formula of the precursor is Na4Fe3(PO4)2(P2O7);

[0089] 96.6g of activated carbon was added to 500mL of 20wt% hydrochloric acid solution and acidified at 400rpm and 45℃ for 1h. Then it was washed with water until neutral and dried to obtain the acidified carbon source.

[0090] 1000g of precursor and 85g of acidified carbon source were placed in a high-speed mixer and stirred at 700rpm for 0.5h. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 450℃ for 12h. The sintered material was then crushed and sieved to obtain the carbon-coated composite material (where the carbon layer coating thickness was 130nm and the particle size of the composite material was 6.87μm).

[0091] Comparative Example 4

[0092] 4.06 mol sodium carbonate, 5.74 mol ferric phosphate, 2.54 mol ammonium dihydrogen phosphate, and 10 L anhydrous ethanol were mixed. The resulting mixture was then subjected to wet ball milling at 500 rpm for 1 hour. The resulting slurry (with a median particle size of 1.031 μm) was transferred to a feed tank and spray-dried at an inlet temperature of 230 °C and an outlet temperature of 105 °C to obtain a precursor (particle size of 7.98 μm and tap density of 0.754 m³). 2 / g), the molecular formula of the precursor is Na4Fe3(PO4)2(P2O7);

[0093] 98g of activated carbon was placed in 500mL of 20wt% hydrochloric acid solution and acidified at 400rpm and 45℃ for 0.5h. Then it was washed with water until neutral and dried to obtain the acidified carbon source.

[0094] 1000g of precursor and 85g of acidified carbon source were placed in a high-speed mixer and stirred at 700rpm for 0.5h. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 800℃ for 12h. The sintered material was then crushed and sieved to obtain the carbon-coated composite material (where the carbon layer coating thickness was 150nm and the particle size of the composite material was 6.97μm).

[0095] Performance testing

[0096] Test Example 1

[0097] The carbon-coated composite material obtained in Example 1 was examined by scanning electron microscopy (SEM), and the resulting SEM images are shown below. Figure 1 As shown;

[0098] from Figure 1 It can be seen that the sodium iron phosphate pyrophosphate material obtained by the present invention has good carbon coating, good particle morphology, and particles of different sizes are well matched with each other, which is beneficial to improving the tap density of the powder.

[0099] Test Example 2

[0100] The carbon-coated materials obtained in Examples 1-4 and Comparative Examples 1-4 were used as positive electrode active materials for electrochemical performance testing.

[0101] In a dry room with a dew point below -40℃ and humidity less than 10%, the active material, binder, and conductive carbon black are mixed in NMP at a mass ratio of 90:5:5, homogenized, and the solid content is controlled at 45%. The mixture is then coated onto an aluminum foil current collector and vacuum baked at 100-110℃ for 4-8 hours. After pressing and forming, the sodium positive electrode sheet is prepared by stamping.

[0102] Sodium-ion half-cells were assembled using sodium metal sheets as the negative electrode and 1 mol / L NaPF6 EC / DMC (Vol 1:1) as the electrolyte. The electrochemical performance of the obtained sodium-ion half-cells was tested using the LAND battery testing system from Wuhan Landian Electronics Co., Ltd.

[0103] (1) The obtained sodium-ion half-cell was subjected to constant current charge-discharge test under the following conditions: 0.1C, voltage range of 2.0–4V; the test results are shown in Table 1. The charge-discharge curves obtained in Example 1 and Comparative Example 1 are shown in Table 1. Figure 2 As shown;

[0104] Table 1. Constant current charge-discharge test results of sodium-ion half-cells

[0105]

[0106] As shown in Table 1, compared with Comparative Example 1, the material synthesized using alcohols as solvents has higher initial charge capacity, initial discharge capacity, and initial efficiency. From Examples 1 and Comparative Examples 2 / 4, it can be seen that when the carbon source is not acidified, or when the iron content is excessive or excessively deficient, the synthesized material has poor capacity and initial efficiency. The iron content affects the impurity phase content in the material, and the impurity phase is inactive. The capacity of the materials synthesized in the examples all reach over 90. In summary, the carbon-coated composite material provided by the present invention has higher charge / discharge specific capacity and initial coulombic efficiency.

[0107] (2) The sodium-ion half-cell prepared from the carbon-coated composite material obtained in Example 1 was subjected to rate performance testing at 1C. The rate performance curve obtained is shown below. Figure 3 As shown; from Figure 3 It can be seen that the capacity of the carbon-coated composite material hardly decreased.

[0108] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-coated composite material, characterized in that, The steps are as follows: 3.25 mol sodium carbonate, 1.87 mol iron oxide, 6.5 mol ammonium dihydrogen phosphate and 10 L anhydrous ethanol were mixed and the resulting mixture was placed in a sand mill for wet ball milling at a speed of 500 rpm for 4 hours. The obtained slurry was transferred to a tank for spray drying. The median particle size of the material in the slurry was 0.512 μm. The inlet temperature was controlled at 230℃ and the outlet temperature at 105℃ to obtain a precursor with the molecular formula Na₄Fe₂O₃. 2.87 (PO4)2(P2O7), the precursor has a particle size of 6.24 μm and a tap density of 0.873 m³ / s. 2 / g; Add 98g of activated carbon to 500mL of 20wt% hydrochloric acid solution and acidify it at 400rpm and 45℃ for 1h. Then wash it with water until neutral and dry it to obtain the acidified carbon source. 1000g of precursor and 85g of acidified carbon source were placed in a high-speed mixer and stirred at 700rpm for 0.5h. The resulting mixture was placed in a box furnace and sintered in a nitrogen atmosphere at a heating rate of 3℃ / min to 500℃ for 10h. The sintered material was then crushed and sieved to obtain a carbon-coated composite material with a carbon layer coating thickness of 150nm and a particle size of 6.98μm.

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