Preparation method of sodium ion battery negative electrode material

Abstract

The invention discloses a preparation method of a sodium-ion battery negative electrode material. The preparation method comprises the following steps: preparing a cross-linked precursor, carrying out pore-forming treatment, pre-carbonizing, and carrying out high-temperature carbonization to obtain the sodium-ion battery hard carbon negative electrode material. According to the preparation method of the biomass-based hard carbon negative electrode material, a crosslinking-pore-forming-carbonization process is adopted, firstly, a carbon precursor is treated through a crosslinking method, a stable carbon-based net structure is obtained, foaming in the pre-carbonization pyrolysis process can be inhibited, and the carbon yield is increased. The pore structure of hard carbon is optimized, regulated and controlled through pore forming-carbonization, and the sodium storage capacity is improved. A large number of nanoscale open pore structures are formed through pore forming, and then the open pore structures are changed into closed pore structures through high-temperature carbonization, so that the platform capacity is remarkably improved, and the specific capacity of the negative electrode is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a method for preparing a negative electrode material for a sodium ion battery. Background Art

[0002] Amidst the global energy transition and the rapid development of energy storage technologies, sodium-ion batteries (Na-ion batteries) have become an important alternative to lithium-ion batteries in large-scale energy storage due to their abundant sodium resources and low cost. The development of low-cost, high-capacity Na-ion battery anode materials is crucial for their commercialization and application.

[0003] Hard carbon is a type of amorphous carbon material that is difficult to graphitize at high temperatures. Its unique structure and abundant pores give it excellent sodium storage properties, making it an ideal choice for sodium-ion battery anode materials. The precursor raw materials for preparing hard carbon come from a wide range of sources, including biomass, resins, and polysaccharides. However, the development and application of hard carbon anodes still face key challenges. The first is the high cost of hard carbon, and the second is that the electrochemical performance needs to be further improved to meet the practical application of sodium-ion batteries in multiple scenarios.

[0004] Starch is widely available, has high yield, and is inexpensive, making it one of the ideal precursors for preparing hard carbon. However, the sodium storage capacity of hard carbon prepared by direct starch carbonization is still unsatisfactory and needs to be further improved. In addition, direct starch carbonization is prone to foaming, has a low carbon yield, and increases costs. Therefore, further improving the structural order and surface chemical properties of hard carbon by regulating the composition of starch precursors, optimizing the carbonization process, or introducing heteroatom doping has become an important research direction for breaking through the practical application of starch-based hard carbon in the field of sodium ion batteries.

[0005] Patent application CN118908183A discloses a starch-doped hard carbon material, its preparation method, and applications. The preparation method comprises the following steps: mixing starch with an esterifying agent, performing an esterification reaction to produce esterified starch, then pre-carbonizing the starch to produce a pre-carbonized material, and then carbonizing the starch-doped hard carbon material. The esterifying agent includes a phosphate and an acid anhydride. This method requires a coating process, but lacks the pre-carbonization and pore-forming steps, which hinders the improvement of the sodium storage capacity of the hard carbon material. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a negative electrode material for a sodium ion battery.

[0007] The present invention is achieved through the following technical solutions.

[0008] The present invention provides a method for preparing a negative electrode material for a sodium ion battery, comprising the following steps:

[0009] Step 1: preparing a cross-linked precursor, mixing a polysaccharide biomass precursor with a phosphorus-containing cross-linking agent and heating to obtain a cross-linked precursor;

[0010] Step 2: Pore-forming treatment, mixing and drying the cross-linking precursor and the pore-forming agent in step 1 to obtain a mixed sample;

[0011] Step 3: Pre-carbonization, pre-carbonizing the mixed sample and forming pores to obtain a porous mixed sample;

[0012] Step 4: high-temperature carbonization, subjecting the pore-forming mixed sample obtained in step 3 to high-temperature carbonization to obtain a hard carbon negative electrode material for sodium ion batteries.

[0013] Preferably, the mixing method in step 1 is ball milling, the heating temperature is greater than 30° C., and the drying time is greater than 1 hour.

[0014] Preferably, the polysaccharide biomass precursor includes one or more of cellulose, chitosan, and starch, and the cross-linking agent includes one or more of the phosphates sodium trimetaphosphate, sodium dihydrogen phosphate, sodium pyrophosphate, and ammonium dihydrogen phosphate.

[0015] Preferably, in step 2, the cross-linking precursor and the aqueous solution of the pore-forming agent are mixed, and then dried under thermal evaporation conditions to obtain a mixed sample, with a drying temperature of 60 to 80° C. and a drying time of 8 to 12 hours.

[0016] Preferably, the pore-forming agent is one or more of zinc chloride, potassium hydroxide, sodium hydroxide, and phosphoric acid.

[0017] Preferably, in step 3, the pre-carbonization temperature is 400-800° C., and the carbonization pore-forming time is 0.5-10 h.

[0018] Preferably, in step 4, the high-temperature carbonization temperature is 1200-1800° C., the heating rate is 0.5-20° C. / min, and the insulation time is 0.5-8 h.

[0019] Preferably, both step 3 and step 4 are carried out under gas protection, and the gas is one or both of argon and nitrogen.

[0020] Preferably, the mixing mass ratio of the polysaccharide biomass to the cross-linking agent is 1 to 4:1.

[0021] Preferably, the cross-linking precursor and the pore-forming agent are mixed in a mass ratio of 1:1 to 4.

[0022] The beneficial effects of the present invention are:

[0023] The method of the present invention is a method for preparing a biomass-based hard carbon negative electrode material. It adopts a crosslinking-pore formation-carbonization process. First, a carbon precursor is treated by a crosslinking method to obtain a relatively stable carbon-based network structure, which can suppress foaming during the pre-carbonization pyrolysis process and improve the carbon yield. The pore structure of the hard carbon is optimized and regulated by pore formation-carbonization to increase the sodium storage capacity. A large number of nano-scale open pore structures are formed by pore formation. The subsequent high-temperature carbonization converts the open pore structure into a closed pore structure, significantly improving the platform capacity, thereby further improving the specific capacity of the negative electrode.

[0024] The material of the present invention has a simple preparation process, low cost, and significant performance improvements. The hard carbon material prepared by the present invention, used as a negative electrode for sodium-ion batteries, has a reversible capacity of over 380 mAh / g at 0.1C and an initial coulombic efficiency of over 90%. It has great potential commercial value and is suitable for commercial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a SEM image of the negative electrode material obtained in Example 1;

[0026] Figure 2 This is a SEM image of the negative electrode material obtained in Example 3;

[0027] Figure 3 This is a SEM image of the negative electrode material obtained in Example 5;

[0028] Figure 4 This is the SEM image of the negative electrode material obtained in Comparative Example 1;

[0029] Figure 5 This is the SEM image of the negative electrode material obtained in Comparative Example 3;

[0030] Figure 6 This is a performance test result diagram of the negative electrode material obtained in Example 3 as a negative electrode material for sodium ion batteries. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the above. Figures 1 to 6 shown.

[0032] Example 1

[0033] A method for preparing a negative electrode material for a sodium ion battery comprises the following steps:

[0034] Step 1: Preparation of a cross-linked precursor: starch and sodium dihydrogen phosphate were mixed in water at a mass ratio of 1:0.05, wherein the solid-liquid ratio was 20%, and then heated and dried to obtain a cross-linked precursor at a drying temperature of 60° C. and a drying time of 12 h;

[0035] Step 2: Pore formation treatment, the cross-linking precursor in step 1 and potassium hydroxide are mixed in water at a mass ratio of 1:1, wherein the solid-liquid ratio is 20%, and then dried to obtain a mixed sample, the drying temperature is 60° C., and the drying time is 8 hours;

[0036] Step 3: Pre-carbonization: pre-carbonize the mixed sample and form pores under nitrogen atmosphere, heating at a rate of 5°C / min to 400°C, and keep warm for 0.5h to obtain a porous mixed sample;

[0037] Step 4: high-temperature carbonization. The pore-forming mixed sample obtained in step 3 is subjected to high-temperature carbonization under the protection of an argon atmosphere, with a heating rate of 0.5°C / min, a carbonization temperature of 1500°C, and a holding time of 0.5h to obtain a hard carbon negative electrode material for sodium ion batteries.

[0038] Example 2

[0039] A method for preparing a negative electrode material for a sodium ion battery comprises the following steps:

[0040] Step 1: Preparation of a cross-linked precursor: chitosan and sodium pyrophosphate were mixed in water at a mass ratio of 1:0.02 with a solid-liquid ratio of 20%, and then heated and dried to obtain a cross-linked precursor at a drying temperature of 60° C. and a drying time of 12 h.

[0041] Step 2: Pore formation treatment, the cross-linking precursor in step 1 and zinc chloride are mixed in water at a mass ratio of 1:3, wherein the solid-liquid ratio is 20%, and then dried to obtain a mixed sample, the drying temperature is 80°C, and the drying time is 12 hours;

[0042] Step 3: Pre-carbonization: pre-carbonize the mixed sample and form pores under nitrogen atmosphere, heating at a rate of 10°C / min to 800°C, and keep the temperature for 10 hours to obtain a porous mixed sample;

[0043] Step 4: high-temperature carbonization. The pore-forming mixed sample obtained in step 3 is subjected to high-temperature carbonization under the protection of an argon atmosphere, with a heating rate of 20°C / min, a carbonization temperature of 1800°C, and a holding time of 8 hours to obtain a hard carbon negative electrode material for sodium ion batteries.

[0044] Example 3

[0045] A method for preparing a negative electrode material for a sodium ion battery comprises the following steps:

[0046] Step 1: Preparation of a cross-linked precursor: starch and sodium trimetaphosphate were mixed in water at a mass ratio of 1:0.05, wherein the solid-liquid ratio was 20%, and then heated and dried to obtain a cross-linked precursor at a drying temperature of 60° C. and a drying time of 12 h;

[0047] Step 2: Pore formation treatment, the cross-linking precursor in step 1 and zinc chloride are mixed in water at a mass ratio of 2:1, wherein the solid-liquid ratio is 20%, and then dried to obtain a mixed sample, the drying temperature is 70° C., and the drying time is 10 h;

[0048] Step 3: Pre-carbonization: pre-carbonize the mixed sample and form pores under nitrogen atmosphere, heating at a rate of 2°C / min to 600°C, and keep the temperature for 6 hours to obtain a porous mixed sample;

[0049] Step 4: high-temperature carbonization. The pore-forming mixed sample obtained in step 3 is subjected to high-temperature carbonization under the protection of an argon atmosphere, with a heating rate of 11°C / min, a carbonization temperature of 1400°C, and a holding time of 5 hours to obtain a hard carbon negative electrode material for sodium ion batteries.

[0050] Example 4

[0051] A method for preparing a negative electrode material for a sodium ion battery comprises the following steps:

[0052] Step 1: Preparation of a cross-linked precursor: cellulose and sodium trimetaphosphate were mixed in water at a mass ratio of 1:0.1, wherein the solid-liquid ratio was 20%, and then heated and dried to obtain a cross-linked precursor at a drying temperature of 60° C. and a drying time of 12 hours;

[0053] Step 2: Pore formation treatment, the cross-linking precursor in step 1 and phosphoric acid are mixed in water at a mass ratio of 1:1, wherein the solid-liquid ratio is 20%, and then dried to obtain a mixed sample, the drying temperature is 80° C., and the drying time is 8 hours;

[0054] Step 3: Pre-carbonization: pre-carbonize the mixed sample and form pores under nitrogen atmosphere, heating at a rate of 5°C / min to 600°C, and keep warm for 2h to obtain a porous mixed sample;

[0055] Step 4: high-temperature carbonization. The pore-forming mixed sample obtained in step 3 is subjected to high-temperature carbonization under the protection of an argon atmosphere, with a heating rate of 5°C / min, a carbonization temperature of 1200°C, and a holding time of 3 hours to obtain a hard carbon negative electrode material for sodium ion batteries.

[0056] Example 5

[0057] Step 1: Preparation of a cross-linked precursor: starch and sodium pyrophosphate at a mass ratio of 1:0.1, sodium dihydrogen phosphate accounting for 10% of the total mass of the solid mixture, are mixed in water, wherein the solid-liquid ratio is 20%, and then heated and dried to obtain a cross-linked precursor, the drying temperature being 60° C. and the drying time being 12 hours;

[0058] Step 2: Pore formation treatment, the cross-linking precursor in step 1 and phosphoric acid are mixed in water at a mass ratio of 3:1, wherein the solid-liquid ratio is 20%, and then dried to obtain a mixed sample, the drying temperature is 80° C., and the drying time is 8 hours;

[0059] Step 3: Pre-carbonization: pre-carbonize the mixed sample and form pores under nitrogen atmosphere, heating at a rate of 5°C / min to 800°C, and keep the temperature for 4 hours to obtain a porous mixed sample;

[0060] Step 4: high-temperature carbonization. The pore-forming mixed sample obtained in step 3 is subjected to high-temperature carbonization under the protection of an argon atmosphere, with a heating rate of 6°C / min, a carbonization temperature of 1400°C, and a holding time of 6 hours to obtain a hard carbon negative electrode material for sodium ion batteries.

[0061] Comparative Example 1

[0062] A method for preparing a negative electrode material for a sodium ion battery comprises the following steps:

[0063] Step 1: Preparation of a cross-linked precursor: starch and sodium dihydrogen phosphate were mixed in water at a mass ratio of 1:0.05, wherein the solid-liquid ratio was 20%, and then heated and dried to obtain a cross-linked precursor at a drying temperature of 60° C. and a drying time of 12 h;

[0064] Step 2: Pre-carbonization: pre-carbonize the cross-linked precursor under nitrogen atmosphere, heating at a rate of 5°C / min to 800°C, and keep warm for 2 hours to obtain a pore-forming mixed sample;

[0065] Step 3: High-temperature carbonization: The pore-forming mixed sample product obtained in step 2 is subjected to high-temperature carbonization under the protection of an argon atmosphere, with a heating rate of 2°C / min, a carbonization temperature of 1500°C, and a holding time of 2h to obtain a hard carbon negative electrode material for sodium ion batteries.

[0066] Comparative Example 2

[0067] A method for preparing a negative electrode material for a sodium ion battery comprises the following steps:

[0068] Step 1: Starch and zinc chloride are mixed in water at a mass ratio of 2:1, wherein the solid-liquid ratio is 20%, and then dried at a drying temperature of 60° C. and a drying time of 12 h to obtain a precursor sample;

[0069] Step 2: Pre-carbonization: Pre-carbonize the precursor sample under nitrogen atmosphere, heating at a rate of 5°C / min to 800°C, and keep the temperature for 2 hours to obtain a pore-forming mixed sample;

[0070] Step 3: High-temperature carbonization: The pore-forming mixed sample obtained in step 2 is subjected to high-temperature carbonization under the protection of an argon atmosphere, with a heating rate of 2°C / min, a carbonization temperature of 1400°C, and a holding time of 2h to obtain a hard carbon negative electrode material for sodium ion batteries.

[0071] Comparative Example 3

[0072] A method for preparing a negative electrode material for a sodium ion battery comprises the following steps:

[0073] Step 1: Pre-carbonize the starch under nitrogen atmosphere, heating at a rate of 5°C / min to 800°C, and keep warm for 2 hours;

[0074] Step 2: high-temperature carbonization: the product obtained in step 1 is subjected to high-temperature carbonization under the protection of argon atmosphere, with a heating rate of 2°C / min, a carbonization temperature of 1400°C, and a holding time of 2h to obtain a hard carbon negative electrode material for sodium ion batteries.

[0075] Performance Testing

[0076] The hard carbon materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were assembled into sodium ion batteries, and their electrochemical performance was tested. The hard carbon material, sodium carboxymethyl cellulose (CMC), and conductive agent (SuperP) were mixed in a ratio of 85:5:10 by mass, coated on aluminum foil, and dried to serve as the positive electrode of the battery. Metallic sodium was used as the negative electrode of the battery, glass fiber was used as the battery separator, and a dimethyl ether (DME) solution of NaPF6 was used as the electrolyte.

[0077] After the battery was assembled, it was left to stand for 8 hours and then subjected to charge and discharge tests. The voltage window was 0.005-3.0V and the charge and discharge tests were completed at a current density of 25mA / g. The results are shown in the table below.

[0078] Material name Reversible capacity (mAh / g) First effect (%) Example 1 381.5 86.2 Example 2 372.0 83.2 Example 3 397.6 85.1 Example 4 366.5 86.3 Example 5 369.3 85.5 Comparative Example 1 338.5 88.5 Comparative Example 2 342.2 87.9 Comparative Example 3 328.1 88.6

[0079] Through the test results of Example 3 and Comparative Example 3, it can be found that the hard carbon negative electrode material of Example 3 can reach a reversible capacity of 397.6 mAh / g in the first charge and discharge, and the coulombic efficiency reaches 85.1%. The hard carbon negative electrode obtained in Comparative Example 3 can reach a first discharge capacity of 328.1 mAh / g and a coulombic efficiency of 88.6%. This shows that the addition of pore-forming agents can increase the number of closed pores in hard carbon, thereby improving the sodium storage capacity. During the pyrolysis process, the carbon material is activated and pore-formed to generate a large number of open-pore structures. After high-temperature carbonization, the open pores are transformed into closed-pore structures, which increase the sodium storage sites and thus improve the sodium storage capacity.

[0080] Through Comparative Examples 1 and 3, it was found that the starch had not undergone cross-linking and could not maintain the original spherical structure of the precursor in terms of morphology, and the structure was broken. This was caused by foaming during the thermal decomposition process of the precursor.

[0081] Comparative Examples 2 and 3 show that pore-forming treatment can enhance the sodium storage capacity of hard carbon. The cross-linked precursor increases the carbon yield of starch, regulates the internal pore structure of starch-based hard carbon, promotes the retention of carbon structure during pyrolysis, increases carbon yield, rearranges and fixes at high temperatures, and retains a large interlayer spacing. Pre-carbonization pore-forming treatment imparts a more microporous and closed-pore structure to the hard carbon with smaller surface defects, while also improving its sodium storage capacity and initial efficiency.

Claims

1. A method for preparing a negative electrode material for a sodium ion battery, characterized in that: The following steps are involved: Step 1: preparing a cross-linked precursor, mixing a polysaccharide biomass precursor with a cross-linking agent and heating to obtain a cross-linked precursor; Step 2: Pore-forming treatment, mixing and drying the cross-linking precursor and the pore-forming agent in step 1 to obtain a mixed sample; Step 3: Pre-carbonization, pre-carbonizing the mixed sample and forming pores to obtain a porous mixed sample; Step 4: high-temperature carbonization, subjecting the pore-forming mixed sample obtained in step 3 to high-temperature carbonization to obtain a hard carbon negative electrode material for sodium ion batteries.

2. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: The mixing method in step 1 is ball milling, the heating temperature is greater than 30° C., and the drying time is greater than 1 hour.

3. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: The polysaccharide biomass precursor includes one or more of cellulose, chitosan, and starch, and the cross-linking agent includes one or more of sodium trimetaphosphate, sodium dihydrogen phosphate, sodium pyrophosphate, and ammonium dihydrogen phosphate.

4. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: In step 2, the cross-linking precursor and the aqueous solution of the pore-forming agent are mixed, and then dried under thermal evaporation conditions to obtain a mixed sample at a drying temperature of 60 to 80° C. and a drying time of 8 to 12 hours.

5. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: The pore-forming agent is one or more of zinc chloride, potassium hydroxide, sodium hydroxide and phosphoric acid.

6. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: In step 3, the pre-carbonization temperature is 400-800° C., and the carbonization pore-forming time is 0.5-10 h.

7. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: In step 4, the high-temperature carbonization temperature is 1200-1800° C., the heating rate is 0.5-20° C. / min, and the insulation time is 0.5-8 hours.

8. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: Both step 3 and step 4 are carried out under gas protection, and the gas is one or both of argon and nitrogen.

9. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: The mixing mass ratio of the polysaccharide biomass to the cross-linking agent is 1 to 4:

1.

10. The method for preparing a negative electrode material for a sodium ion battery according to claim 1, wherein: The cross-linking precursor and the pore-forming agent are mixed in a mass ratio of 1:1 to 4.

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