CN115939378B - A method for improving the performance of battery starch-based hard carbon negative electrode and prepared negative electrode material and application - Google Patents

Abstract

The present invention discloses a method for improving the performance of a battery starch-based hard carbon negative electrode, a prepared negative electrode material and an application, comprising the following steps: step 1, drying, drying the starch to remove moisture; step 2, pre-oxidation, heating the starch obtained after step 1 in a muffle furnace for pre-oxidation; step 3, organic acid treatment, placing the starch obtained after step 2 in an organic acid solution, stirring and heating, filtering and washing, and placing the sample in a blast oven for drying; step 4, carbonization, high-temperature carbonization of the starch sample obtained after step 3 under the protection of an inert gas, cooling to room temperature to obtain a starch-based hard carbon material for a sodium ion battery negative electrode. The raw materials used in the present invention are widely available, cheap, and the preparation process is simple and environmentally friendly. The final product is a sphere with a small specific surface area, and the prepared battery has a reversible capacity of 325mAh/g and a first-cycle coulomb efficiency of 90.77%.

Description

A method for improving the performance of battery starch-based hard carbon negative electrode and the prepared negative electrode material and application

Technical Field

The present invention belongs to the technical field of electrode materials, and specifically relates to a method for improving the performance of a starch-based hard carbon negative electrode of a battery, a prepared negative electrode material and an application thereof.

Background technique

In recent years, the rapid development of social economy has led to a great consumption of traditional energy, resulting in severe ecological environmental deterioration and energy depletion. Various green and clean energy sources such as tidal energy and solar lamps have attracted people's attention. However, due to the characteristics of inability to work continuously and unstable production capacity, large-scale energy storage equipment must be configured. Therefore, it is very important to develop an effective and cheap energy storage system. Electrochemical energy storage devices such as lithium-ion batteries and sodium-ion batteries have received great attention and have great commercial potential. However, due to the limited lithium resources and the urgent need for large-scale energy storage equipment, the future demand for energy development cannot be met by lithium-ion batteries alone. The development of new energy storage systems is imminent. Sodium is one of the ubiquitous elements in nature. It is more abundant in the earth's crust than lithium and is easier to obtain. In addition, sodium and lithium have similar physical and chemical properties. In large-scale energy storage systems, sodium-ion batteries can become an ideal substitute and have good application prospects.

Among the many materials used as negative electrodes for sodium-ion batteries, hard carbon is considered to be the most likely negative electrode material for sodium-ion batteries to be industrialized first due to its abundant reserves, low cost, good conductivity, high sodium storage capacity, environmental friendliness, and low redox potential. Biomass, as a low-cost, environmentally friendly, and sustainable resource, has attracted widespread attention in recent years. A large number of biomass precursors have been used to prepare carbon materials due to their diverse morphology and structure, and have been widely used in the field of sodium-ion batteries. Starch, as one of the most widely available biomass, has abundant production and a reasonable price. The spherical structure of starch itself is retained when it is later prepared into hard carbon. This spherical structure creates a large number of active sites for the embedding and extraction of sodium ions, which is beneficial to improving the reversible capacity and first-cycle coulombic efficiency of the battery.

After the starch is pre-oxidized, some ash remains. During the later high-temperature carbonization, some of this ash will escape due to the heat, and the spherical structure of the starch-based hard carbon will be destroyed during the escape process. Therefore, after pre-oxidation, acid treatment of the pre-oxidized material can effectively reduce the ash content and improve the spherical retention rate of the final starch-based hard carbon. Compared with strong acids such as hydrochloric acid and sulfuric acid, organic acids are weaker in acidity, which can effectively reduce the hydrolysis of starch particles during the treatment process, have less impact on the environment, and are more cost-effective.

Summary of the invention

The primary purpose of the present invention is to provide a method for improving the performance of starch-based hard carbon negative electrodes for batteries, which mainly overcomes the shortcomings of the prior art, such as low capacity of hard carbon negative electrode materials for sodium ion batteries, high cost of developing other electrode materials, and low first-cycle coulombic efficiency of other electrode materials.

The method of improving the performance of starch-based hard carbon negative electrode of battery in the present invention is as follows:

The pre-oxidized starch is treated with organic acid and then carbonized to obtain a starch-based hard carbon negative electrode material treated with organic acid.

The method described,

The organic acid is a C1-C10 carboxylic acid compound, preferably at least one of acetic acid, propionic acid, citric acid and oxalic acid.

The starch is a high molecular carbohydrate formed by the polymerization of glucose molecules, including cassava starch, corn starch, guava starch, potato starch, pea starch and the like.

The method comprises placing the pre-oxidized starch in an organic acid solution with a concentration of 5% to 20% (w/v) at a material-liquid ratio of 1:5 to 1:20, and stirring and heating for reaction.

The method comprises adding an organic acid solution, heating to 30-50° C. and treating for 0.5-2.0 h, and then separating the solid from the liquid, washing, and drying.

According to the method, after the organic acid treatment, the sample is placed in a forced air oven for drying at a drying temperature of 70 to 80°C.

In the method, the starch is dried to remove moisture before pre-oxidation, preferably at a drying temperature of 70 to 80° C. and a drying time of 2 to 3 hours.

The method comprises heating the dried starch to 100-300° C. for pre-oxidation for 10-35 hours, and then cooling the starch to room temperature to obtain a pre-oxidized material.

Furthermore, the pre-oxidation heating rate is 2-5°C/min; the pre-oxidation is completed in a muffle furnace; and the sample after the pre-oxidation needs to be dispersed.

The method comprises the following steps: carbonizing the starch treated with organic acid under the protection of inert gas, treating the starch at 100-200° C., 300-600° C., and 1000-1700° C. for 3-9 h, 1-4 h, and 2-5 h, respectively, and cooling the carbonized starch to room temperature to obtain the starch-based hard carbon negative electrode material treated with organic acid.

Furthermore, the carbonization is completed in a tubular furnace; the heating rate is 2-5°C/min; and the process also includes grinding and crushing the carbonized material.

The second object of the present invention is to provide a starch-based hard carbon negative electrode material prepared by the method described.

The third object of the present invention is to provide the use of the starch-based hard carbon negative electrode material in the preparation of battery negative electrodes, especially in the negative electrodes of sodium ion batteries.

The present invention preferably provides a method for improving the performance of a starch-based hard carbon negative electrode for a sodium ion battery, comprising the following steps:

Step 1, drying, placing food-grade cassava starch in a blast drying oven, drying at 70-80° C., drying time 2-3 h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained in step 1 in a muffle furnace, pre-oxidizing at 100-300° C. for 10-35 hours, with a heating rate of 2-5° C./min, and cooling to room temperature after the pre-oxidation to obtain a pre-oxidized material;

Step 3, organic acid treatment, placing the pre-oxidized material after step 2 in an organic acid solution with a concentration of 5% to 20% (w/v) at a material-liquid ratio of 1:5 to 1:20, stirring and heating to 30 to 50° C. for 0.5 to 2.0 hours, then filtering and washing, and placing the sample in a blast oven to dry at a drying temperature of 70 to 80° C.;

Step 4, carbonization, placing the sample obtained after step 3 in a tubular furnace, passing inert gas protection, heating to 100-200°C, 300-600°C, and 1000-1700°C at 2-5°C/min, treating for 3-9h, 1-4h, and 2-5h, respectively, cooling to room temperature, grinding, and obtaining the product.

The advantages and beneficial effects of the present invention are:

The present invention uses starch as a carbon source, first undergoes pre-oxidation and organic acid treatment, and then undergoes high-temperature pyrolysis in an inert gas atmosphere to obtain spherical hard carbon with an appropriate degree of graphitization. The raw materials used in the present invention are widely available, cheap, and the preparation process is simple and suitable for mass production. The final product is spherical, has a smooth surface, and a small specific surface area. This special spherical structure creates a large number of active sites for the insertion and extraction of sodium ions. The obtained battery has a reversible capacity of 325mAh/g and a first-cycle coulomb efficiency of 90.77%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM comparison diagram of starch raw material, Example 1 of the present invention and Comparative Example 1:

a and b are starch raw materials; c and d are hard carbon materials prepared in Example 1; e and f are hard carbon materials prepared in Comparative Example 1.

FIG. 2 is a first cycle charge and discharge curve of an electrode prepared from the material of Comparative Example 1 of the present invention.

FIG. 3 is a first cycle charge and discharge curve of an electrode prepared from the material of Example 1 of the present invention.

FIG. 4 is a first cycle charge and discharge curve of an electrode prepared from the material of Example 2 of the present invention.

FIG. 5 is a N ₂ adsorption-desorption curve of the hard carbon material prepared in Example 1 of the present invention.

For ordinary technicians in this field, without any creative work, other related drawings can be obtained based on the above drawings.

Detailed ways

The present invention is further explained below with reference to the embodiments, but is not limited thereto.

Comparative Example 1

The embodiment of the present invention provides a method for preparing a starch-based sodium ion battery hard carbon negative electrode material, the steps of which include:

Step 1, drying, taking 10g of food-grade cassava starch and placing it in a blast drying oven, drying temperature 80°C, drying time 2h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained after step 1 in a muffle furnace, heating it to 200°C at a heating rate of 2°C/min, pre-oxidizing it for 24 hours, and cooling it to room temperature to obtain a pre-oxidized material;

Step 3, carbonization, placing the pre-oxidized material obtained after step 2 in a tube furnace, heating to 200°C, 400°C, and 1500°C at a rate of 2°C/min in an argon atmosphere for 6h, 3h, and 3h, respectively, cooling to room temperature, grinding, and obtaining a starch pyrolysis hard carbon electrode material;

Step 4: Use the carbon material prepared above as the active material of the battery negative electrode material for the preparation of a sodium ion battery.

According to the mass ratio of 92%:3%:1.5%:3.5%, 184 mg of carbon material powder, 6 mg of conductive carbon black, 6 mg of 2% (w/w) carboxymethyl cellulose solution, and 17.5 mg of 40% (w/w) styrene-butadiene rubber were weighed, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. The mixture was evenly coated on the surface of a copper (Cu) foil using a 100 μm scraper and dried in a 105°C forced air drying oven for 2 hours. The Cu foil with active materials was cut into disc-shaped negative electrode sheets, which were then transferred to a glove box for use.

The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere, using the prepared carbon material electrode as the negative electrode, commercial electrolyte 1.0 mol/L NaPF ₆ /EC:DMC (1:1) (V:V) as the electrolyte, and Na metal sheet as the counter electrode to assemble a 2016 button cell.

After the assembled button cell was left for 6 hours, it was placed in a 30°C constant temperature test system and subjected to charge and discharge tests in the voltage range of 0.01-2.0V (vs. Na+/Na, the same below). The electrochemical test results are shown in FIG2 . From the first charge and discharge curve in FIG2 , it can be seen that the first coulombic efficiency of the half-cell with 1.0 mol/L NaPF ₆ /EC:DMC as the electrolyte is 69.97% at a current density of 20 mA/g, the first cycle discharge specific capacity is 412.63 mAh/g, and the first cycle charge specific capacity is 288.73 mAh/g.

Comparative Example 2

The embodiment of the present invention provides a method for preparing a starch-based sodium ion battery hard carbon negative electrode material, the steps of which include:

Step 1, drying, taking 10g of food-grade cassava starch and placing it in a blast drying oven, drying temperature 80°C, drying time 2h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained after step 1 in a muffle furnace, heating it to 200°C at a heating rate of 2°C/min, pre-oxidizing it for 24 hours, and cooling it to room temperature to obtain a pre-oxidized material;

Step 3, inorganic acid treatment, the pre-oxidized material after step 2 is placed in a 5% (w/v) hydrochloric acid solution at a material-liquid ratio of 1:20, stirred and heated to 50°C for 1h, then filtered and washed, and the sample is placed in a blast oven to dry at a drying temperature of 80°C;

Step 4, carbonization, placing the pre-oxidized material obtained after step 3 in a tube furnace, heating to 200°C, 400°C, and 1500°C at a rate of 2°C/min in an argon atmosphere for 6h, 3h, and 3h, respectively, cooling to room temperature, grinding, and obtaining a starch pyrolysis hard carbon electrode material;

Step 5, using the carbon material prepared above as an active substance for a negative electrode material of a battery for preparing a sodium ion battery.

According to the mass ratio of 92%:3%:1.5%:3.5%, 184 mg of carbon material powder, 6 mg of conductive carbon black, 6 mg of 2% (w/w) carboxymethyl cellulose solution, and 17.5 mg of 40% (w/w) styrene-butadiene rubber were weighed, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. The mixture was evenly coated on the surface of a copper (Cu) foil using a 100 μm scraper and dried in a 105°C forced air drying oven for 2 hours. The Cu foil with active materials was cut into disc-shaped negative electrode sheets, which were then transferred to a glove box for use.

The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere, using the prepared carbon material electrode as the negative electrode, commercial electrolyte 1.0 mol/L NaPF ₆ /EC:DMC (1:1) (V:V) as the electrolyte, and Na metal sheet as the counter electrode to assemble a 2016 button cell.

Example 1

The embodiment of the present invention provides a method for improving the performance of a starch-based hard carbon negative electrode for a sodium ion battery, the steps of which include:

Step 1, drying, taking 10g of food-grade cassava starch and placing it in a blast drying oven, drying temperature 80°C, drying time 2h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained after step 1 in a muffle furnace, heating it to 200°C at a heating rate of 2°C/min, pre-oxidizing it for 24 hours, and cooling it to room temperature to obtain a pre-oxidized material;

Step 3, organic acid treatment, the pre-oxidized material after step 2 is placed in a 5% (w/v) oxalic acid solution at a material-liquid ratio of 1:20, stirred and heated to 50°C for 1h, then filtered and washed, and the sample is placed in a blast oven to dry at a drying temperature of 80°C;

Step 4, carbonization, placing the pre-oxidized material obtained after step 2 in a tube furnace, heating to 200°C, 400°C, and 1500°C at a rate of 2°C/min in an argon atmosphere for 6h, 3h, and 3h, respectively, cooling to room temperature, grinding, and obtaining a starch pyrolysis hard carbon electrode material;

Step 5, using the carbon material prepared above as an active substance for a negative electrode material of a battery for preparing a sodium ion battery.

According to the mass ratio of 92%:3%:1.5%:3.5%, 184 mg of carbon material powder, 6 mg of conductive carbon black, 6 mg of 2% (w/w) carboxymethyl cellulose solution, and 17.5 mg of 40% (w/w) styrene-butadiene rubber were weighed, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. The mixture was evenly coated on the surface of a copper (Cu) foil using a 100 μm scraper and dried in a 105°C forced air drying oven for 2 hours. The Cu foil with active materials was cut into disc-shaped negative electrode sheets, which were then transferred to a glove box for use.

The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere, using the prepared carbon material electrode as the negative electrode, commercial electrolyte 1.0 mol/L NaPF ₆ /EC:DMC (1:1) (V:V) as the electrolyte, and Na metal sheet as the counter electrode to assemble a 2016 button cell.

After the assembled button cell was set aside for 6 hours, it was placed in a 30°C constant temperature test system and subjected to charge and discharge tests in the voltage range of 0.01-2.5V (vs. Na+/Na, the same below). The electrochemical test results are shown in FIG3 . From the first charge and discharge curves in FIG3 , it can be seen that the first coulombic efficiency of the half-cell with 1.0 mol/L NaPF ₆ /EC:DMC as the electrolyte was increased to 90.77% at a current density of 20 mA/g, the first cycle discharge specific capacity was 358.48 mAh/g, and the first cycle charge specific capacity was 325.38 mAh/g.

As can be seen from Figure 1, before and after pyrolysis, starch can maintain a spherical shape well. Due to the high-temperature release of other elements except carbon, the volume of the sphere is reduced, and the specific surface area of the sphere is further reduced. This spherical structure with a small specific surface area creates a large number of active sites for the embedding and release of sodium ions, which is beneficial to improving the reversible capacity and first-cycle coulomb efficiency of the battery. After the starch is pre-oxidized, some ash remains. During the high-temperature carbonization in the later stage, some of this ash will escape due to heat, and the spherical structure of the starch-based hard carbon will be destroyed during the escape process. It can be seen from Figure 1 that the spherical structure of the starch sample that is directly carbonized without organic acid treatment is severely damaged. Therefore, after pre-oxidation, acid treatment of the pre-oxidized material can effectively reduce the ash content therein and improve the spherical retention rate of the final starch-based hard carbon. Compared with strong acids such as hydrochloric acid and sulfuric acid, organic acids are weaker in acidity, which can effectively reduce the hydrolysis of starch particles during the treatment process, and have less impact on the environment and lower costs.

FIG5 confirms that the hard carbon material prepared after pyrolysis has a small specific surface area, and the BET surface area is 1.693 m ² /g.

Example 2

The embodiment of the present invention provides a method for improving the performance of a starch-based hard carbon negative electrode for a sodium ion battery, the steps of which include:

Step 1, drying, taking 10g of food-grade cassava starch and placing it in a blast drying oven, drying temperature 80°C, drying time 2h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained after step 1 in a muffle furnace, heating it to 200°C at a heating rate of 2°C/min, pre-oxidizing it for 24 hours, and cooling it to room temperature to obtain a pre-oxidized material;

Step 3, organic acid treatment, the pre-oxidized material after step 2 is placed in a 5% (w/v) citric acid solution at a material-liquid ratio of 1:20, stirred and heated to 50°C for 1h, then filtered and washed, and the sample is placed in a blast oven to dry at a drying temperature of 80°C;

Step 4, carbonization, placing the pre-oxidized material obtained after step 2 in a tube furnace, heating to 200°C, 400°C, and 1500°C at a rate of 2°C/min in an argon atmosphere for 6h, 3h, and 3h, respectively, cooling to room temperature, grinding, and obtaining a starch pyrolysis hard carbon electrode material;

Step 5, using the carbon material prepared above as an active substance for a negative electrode material of a battery for preparing a sodium ion battery.

According to the mass ratio of 92%:3%:1.5%:3.5%, 184 mg of carbon material powder, 6 mg of conductive carbon black, 6 mg of 2% (w/w) carboxymethyl cellulose solution, and 17.5 mg of 40% (w/w) styrene-butadiene rubber were weighed, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. The mixture was evenly coated on the surface of a copper (Cu) foil using a 100 μm scraper and dried in a 105°C forced air drying oven for 2 hours. The Cu foil with active materials was cut into disc-shaped negative electrode sheets, which were then transferred to a glove box for use.

The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere, using the prepared carbon material electrode as the negative electrode, commercial electrolyte 1.0 mol/L NaPF ₆ /EC:DMC (1:1) (V:V) as the electrolyte, and Na metal sheet as the counter electrode to assemble a 2016 button cell.

The assembled button cell was placed in a 30°C constant temperature test system after being set aside for 6 hours, and was subjected to charge and discharge tests in the voltage range of 0.01-2.0V (vs. Na+/Na, the same below). The electrochemical test results are shown in FIG4 . From the first charge and discharge curve in FIG4 , it can be seen that the first coulombic efficiency of the half-cell with 1.0 mol/L NaPF ₆ /EC:DMC as the electrolyte is 78.71% at a current density of 20 mA/g, the first cycle discharge specific capacity is 402.13 mAh/g, and the first cycle charge specific capacity is 318.50 mAh/g.

Example 3

The embodiment of the present invention provides a method for improving the performance of a starch-based hard carbon negative electrode for a sodium ion battery, the steps of which include:

Step 1, drying, taking 10g of food-grade cassava starch and placing it in a blast drying oven, drying temperature 80°C, drying time 2h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained after step 1 in a muffle furnace, heating it to 200°C at a heating rate of 2°C/min, pre-oxidizing it for 24 hours, and cooling it to room temperature to obtain a pre-oxidized material;

Step 3, organic acid treatment, the pre-oxidized material after step 2 is placed in a 10% (w/v) oxalic acid solution at a material-liquid ratio of 1:20, stirred and heated to 50°C for 1h, then filtered and washed, and the sample is placed in a blast oven to dry at a drying temperature of 80°C;

Step 4, carbonization, placing the pre-oxidized material obtained after step 2 in a tube furnace, heating to 200°C, 400°C, and 1500°C at a rate of 2°C/min in an argon atmosphere for 6h, 3h, and 3h, respectively, cooling to room temperature, grinding, and obtaining a starch pyrolysis hard carbon electrode material;

Step 5, using the carbon material prepared above as an active substance for a negative electrode material of a battery for preparing a sodium ion battery.

According to the mass ratio of 92%:3%:1.5%:3.5%, 184 mg of carbon material powder, 6 mg of conductive carbon black, 6 mg of 2% (w/w) carboxymethyl cellulose solution, and 17.5 mg of 40% (w/w) styrene-butadiene rubber were weighed, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. The mixture was evenly coated on the surface of a copper (Cu) foil using a 100 μm scraper and dried in a 105°C forced air drying oven for 2 hours. The Cu foil with active materials was cut into disc-shaped negative electrode sheets, which were then transferred to a glove box for use.

The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere, using the prepared carbon material electrode as the negative electrode, commercial electrolyte 1.0 mol/L NaPF ₆ /EC:DMC (1:1) (V:V) as the electrolyte, and Na metal sheet as the counter electrode to assemble a 2016 button cell.

Example 4

The embodiment of the present invention provides a method for improving the performance of a starch-based hard carbon negative electrode for a sodium ion battery, the steps of which include:

Step 1, drying, taking 10g of food-grade cassava starch and placing it in a blast drying oven, drying temperature 80°C, drying time 2h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained after step 1 in a muffle furnace, heating it to 200°C at a heating rate of 2°C/min, pre-oxidizing it for 24 hours, and cooling it to room temperature to obtain a pre-oxidized material;

Step 3, organic acid treatment, the pre-oxidized material after step 2 is placed in a 5% (w/v) oxalic acid solution at a material-liquid ratio of 1:10, stirred and heated to 50°C for 1h, then filtered and washed, and the sample is placed in a blast oven to dry at a drying temperature of 80°C;

Step 4, carbonization, placing the pre-oxidized material obtained after step 2 in a tube furnace, heating to 200°C, 400°C, and 1500°C at a rate of 2°C/min in an argon atmosphere for 6h, 3h, and 3h, respectively, cooling to room temperature, grinding, and obtaining a starch pyrolysis hard carbon electrode material;

Step 5, using the carbon material prepared above as an active substance for a negative electrode material of a battery for preparing a sodium ion battery.

According to the mass ratio of 92%:3%:1.5%:3.5%, 184 mg of carbon material powder, 6 mg of conductive carbon black, 6 mg of 2% (w/w) carboxymethyl cellulose solution, and 17.5 mg of 40% (w/w) styrene-butadiene rubber were weighed, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. The mixture was evenly coated on the surface of a copper (Cu) foil using a 100 μm scraper and dried in a 105°C forced air drying oven for 2 hours. The Cu foil with active materials was cut into disc-shaped negative electrode sheets, which were then transferred to a glove box for use.

The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere, using the prepared carbon material electrode as the negative electrode, commercial electrolyte 1.0 mol/L NaPF ₆ /EC:DMC (1:1) (V:V) as the electrolyte, and Na metal sheet as the counter electrode to assemble a 2016 button cell.

Example 5

The embodiment of the present invention provides a method for improving the performance of a starch-based hard carbon negative electrode for a sodium ion battery, the steps of which include:

Step 1, drying, taking 10g of food-grade cassava starch and placing it in a blast drying oven, drying temperature 80°C, drying time 2h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained after step 1 in a muffle furnace, heating it to 200°C at a heating rate of 2°C/min, pre-oxidizing it for 24 hours, and cooling it to room temperature to obtain a pre-oxidized material;

Step 3, organic acid treatment, the pre-oxidized material after step 2 is placed in a 5% (w/v) oxalic acid solution at a material-liquid ratio of 1:20, stirred and heated to 50°C for 2h, filtered and washed, and the sample is placed in a blast oven to dry at a drying temperature of 80°C;

Step 4, carbonization, placing the pre-oxidized material obtained after step 2 in a tube furnace, heating to 200°C, 400°C, and 1500°C at a rate of 2°C/min in an argon atmosphere for 6h, 3h, and 3h, respectively, cooling to room temperature, grinding, and obtaining a starch pyrolysis hard carbon electrode material;

Step 5, using the carbon material prepared above as an active substance for a negative electrode material of a battery for preparing a sodium ion battery.

According to the mass ratio of 92%:3%:1.5%:3.5%, 184 mg of carbon material powder, 6 mg of conductive carbon black, 6 mg of 2% (w/w) carboxymethyl cellulose solution, and 17.5 mg of 40% (w/w) styrene-butadiene rubber were weighed, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. The mixture was evenly coated on the surface of a copper (Cu) foil using a 100 μm scraper and dried in a 105°C forced air drying oven for 2 hours. The Cu foil with active materials was cut into disc-shaped negative electrode sheets, which were then transferred to a glove box for use.

The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere, using the prepared carbon material electrode as the negative electrode, commercial electrolyte 1.0 mol/L NaPF ₆ /EC:DMC (1:1) (V:V) as the electrolyte, and Na metal sheet as the counter electrode to assemble a 2016 button cell.

Example 6

The embodiment of the present invention provides a method for improving the performance of a starch-based hard carbon negative electrode for a sodium ion battery, the steps of which include:

Step 1, drying, taking 10g of food-grade cassava starch and placing it in a blast drying oven, drying temperature 80°C, drying time 2h, drying to remove moisture;

Step 2, pre-oxidation, placing the starch obtained after step 1 in a muffle furnace, heating it to 200°C at a heating rate of 2°C/min, pre-oxidizing it for 24 hours, and cooling it to room temperature to obtain a pre-oxidized material;

Step 3, organic acid treatment, the pre-oxidized material after step 2 is placed in a 5% (w/v) oxalic acid solution at a material-liquid ratio of 1:20, stirred and heated to 60°C for 1h, then filtered and washed, and the sample is placed in a blast oven to dry at a drying temperature of 80°C;

Step 4, carbonization, placing the pre-oxidized material obtained after step 2 in a tube furnace, heating to 200°C, 400°C, and 1500°C at a rate of 2°C/min in an argon atmosphere for 6h, 3h, and 3h, respectively, cooling to room temperature, grinding, and obtaining a starch pyrolysis hard carbon electrode material;

Step 5, using the carbon material prepared above as an active substance for a negative electrode material of a battery for preparing a sodium ion battery.

According to the mass ratio of 92%:3%:1.5%:3.5%, 184 mg of carbon material powder, 6 mg of conductive carbon black, 6 mg of 2% (w/w) carboxymethyl cellulose solution, and 17.5 mg of 40% (w/w) styrene-butadiene rubber were weighed, and an appropriate amount of deionized water was added. The mixture was stirred for 20 minutes until a uniform slurry was formed. The mixture was evenly coated on the surface of a copper (Cu) foil using a 100 μm scraper and dried in a 105°C forced air drying oven for 2 hours. The Cu foil with active materials was cut into disc-shaped negative electrode sheets, which were then transferred to a glove box for use.

The assembly of the simulated battery was carried out in a MIKROUNA glove box filled with Ar atmosphere, using the prepared carbon material electrode as the negative electrode, commercial electrolyte 1.0 mol/L NaPF ₆ /EC:DMC (1:1) (V:V) as the electrolyte, and Na metal sheet as the counter electrode to assemble a 2016 button cell.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Table 1 The following are the relevant parameters of the half-cells assembled in Comparative Examples 1-2 and Examples 1-6

Claims (8)

1. A method for improving the performance of a starch-based hard carbon negative electrode of a battery, characterized in that the pre-oxidized starch is treated with an organic acid and then carbonized to obtain a starch-based hard carbon negative electrode material treated with an organic acid; The step of pre-oxidizing the starch is as follows: drying the starch, heating the dried starch to 100-300° C. for pre-oxidation for 10-35 hours, and cooling to room temperature to obtain a pre-oxidized material; The steps of organic acid treatment are: placing the pre-oxidized starch in an organic acid solution with a concentration of 5% to 20% (w/v) at a solid-liquid ratio of 1:5 to 1:20, stirring and heating for reaction; heating to 30 to 50° C. after adding the organic acid solution for treatment for 0.5 to 2.0 hours, and then separating the solid from the liquid, washing, and drying. 2 . The method according to claim 1 , wherein the organic acid is a C1 to C10 carboxylic acid compound. 3. The method according to claim 2, characterized in that the organic acid is at least one of acetic acid, propionic acid, citric acid and oxalic acid. 4. The method according to claim 1, characterized in that after the organic acid treatment, the sample is placed in a forced air oven for drying at a drying temperature of 70 to 80°C. 5. The method according to claim 1, characterized in that the starch is dried to remove moisture before pre-oxidation, the drying temperature is 70-80°C, and the drying time is 2-3h. 6. The method according to claim 1 is characterized in that the starch treated with organic acid is carbonized under the protection of inert gas, and is treated at 100-200°C, 300-600°C, and 1000-1700°C for 3-9h, 1-4h, and 2-5h, respectively, and cooled to room temperature to obtain the starch-based hard carbon negative electrode material treated with organic acid. 7. A starch-based hard carbon negative electrode material prepared by the method according to any one of claims 1 to 6. 8. The use of the starch-based hard carbon negative electrode material according to claim 7 in preparing a negative electrode for a battery, characterized in that it is used in preparing a negative electrode for a sodium ion battery.