Preparation method and application of a starch-based hard carbon material for sodium ion battery negative electrode

Abstract

The application discloses a preparation method and application of a starch-based hard carbon material for a sodium ion battery negative electrode. The method modifies starch into a starch-based precursor with a rich carbonyl structure and without fluidity by regulating the hydrogen bond environment of the starch in a weak alkali environment, and synthesizes the starch-based hard carbon material for the sodium ion battery negative electrode with good performance. The method can reduce the time and temperature of low-temperature heating, solve the problem of starch melting and foaming, completely retain the spherical structure of the starch in the process of being converted into the hard carbon, overcome the defects of a crosslinking agent and long-time high-energy consumption heating, is simple in operation, has a wide source of raw materials, and has excellent performance, and is suitable for large-scale production. The method has important significance for exploring the sodium storage mechanism of the hard carbon material, breaking through the bottleneck of the practical application of the material, and accelerating the commercial application of the hard carbon negative electrode material of the sodium ion battery.

Description

Technical Field

[0001] This invention relates to electrochemistry and battery technology, specifically a method for preparing and applying a starch-based hard carbon material for the negative electrode of a sodium-ion battery. Background Technology

[0002] In recent years, lithium, sodium, and potassium-ion batteries have attracted much attention due to their advantages such as abundant resources, low cost, and high safety, which are significant compared to lead-acid batteries. In the sodium-ion battery system, the performance bottleneck of the anode material is the key to limiting overall performance. High-performance and low-cost anode materials are crucial for the industrialization of sodium-ion batteries. Starch, as a raw material for preparing anode materials for sodium-ion batteries, has advantages such as wide availability, low cost, and renewability. Furthermore, the hard carbon derived from starch possesses an abundant sodium storage environment, high sodium storage specific capacity, and a stable structure during charge-discharge cycles. These advantages make starch-derived hard carbon an ideal commercial anode material for sodium-ion batteries.

[0003] However, direct high-temperature sintering of starch granules causes the decomposition of non-aromatic polysaccharide structures, resulting in granule melting and bubbling. This leads to structural collapse, low carbon yield, and uncontrollable pore structure, which has a fatal impact on the sodium storage performance of hard carbon materials. Therefore, it is urgent to develop effective strategies to maintain the original structure of starch during pyrolysis and enable hard carbon materials to exhibit high sodium storage performance. To address this issue, some patented technologies or literature propose long-term low-temperature stabilization treatment of starch in an air or inert gas atmosphere, followed by high-temperature carbonization. This method can effectively solve the problem of starch puffing during heating, but it also has drawbacks such as excessively long stabilization time, low production efficiency, and unfavorable conditions for large-scale production. Another approach is to crosslink ordinary starch with different additives before high-temperature carbonization, such as crosslinking starch with a crosslinking agent. However, the presence of such reagents leads to a decrease in the initial coulombic efficiency due to heteroatom doping, making them unsuitable for large-scale production and application. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing starch-based hard carbon materials for sodium-ion battery anodes and their applications. This method reduces the time and temperature required for low-temperature heating, solves the problem of starch melting and foaming, fully preserves the spherical structure of starch during its conversion into hard carbon, overcomes the defects of crosslinking agents and prolonged high-energy-consumption heating, and is simple to operate, has a wide range of raw material sources, and excellent performance, making it suitable for large-scale production. This method is of great significance for exploring the sodium storage mechanism of hard carbon materials, overcoming practical application bottlenecks, and accelerating the commercial application of hard carbon anode materials for sodium-ion batteries.

[0005] The technical solution to achieve the objective of this invention is:

[0006] A method for preparing a starch-based hard carbon material for the negative electrode of a sodium-ion battery includes the following steps:

[0007] 1) The starch material was soaked in a 10-50 wt.% (NH4)2HPO4 solution with weak alkalinity and stirred for 2 h. The mixture was filtered using a Buchner funnel. The mass ratio of the 10-50 wt.% (NH4)2HPO4 solution to the starch was 3-5:1. The starch was then washed three times with deionized water and filtered again. The filtered starch sample was collected and dried in an 80℃ oven to remove moisture. The dried starch was then ground through a 400-mesh sieve. The sieved sample was then dehydrated and oxidized in an electric blast oven at 190℃-230℃ for 0-60 h to obtain a brown powder, which is the precursor of starch-based hard carbon.

[0008] 2) The dehydrated precursor obtained in step 1) is ground through a 400-mesh sieve, and the resulting powder is subjected to segmented high-temperature carbonization treatment: The segmented high-temperature carbonization treatment is as follows: first, the temperature is increased to 200 ℃ at a heating rate of 3 ℃·min-1, then increased to 320 ℃ at a heating rate of 0.2 ℃·min-1, then increased to 500 ℃ at a heating rate of 1 ℃·min-1, and finally increased to 1000-1800 ℃ at a heating rate of 3 ℃·min-1, and held at this temperature for 2-10 hours. The entire process is carried out under the protection of an inert atmosphere to obtain powder, namely starch-based hard carbon, which is a high-performance sodium-ion battery anode material.

[0009] The starch mentioned in step 1) is taro starch, tapioca starch, corn starch, wheat starch, etc., as well as modified starch. The modification treatment of starch includes one or more of physical modification treatment, chemical modification treatment, and biological modification treatment.

[0010] The (NH4)2HPO4 solution mentioned in step 1) is one or more alkaline solutions such as diammonium hydrogen phosphate, ammonium dihydrogen phosphate, potassium bicarbonate, and sodium bicarbonate.

[0011] The inert atmosphere mentioned in step 2) is one of pure nitrogen, helium, neon, argon, and xenon.

[0012] The above-mentioned preparation method produces a starch-based hard carbon material for sodium-ion battery anodes.

[0013] The application of starch-based hard carbon materials for sodium-ion battery anodes prepared by the above method in sodium-ion batteries, lithium-ion batteries, potassium-ion batteries, and alkali metal-ion batteries.

[0014] This method utilizes a weakly alkaline environment to regulate the hydrogen bonding environment of starch, reducing the time and temperature required for low-temperature heating. It modifies starch into a non-flowing, carbonyl-rich starch-based precursor, synthesizing high-performance starch-based hard carbon materials for sodium-ion battery anodes. This method solves the problem of starch melting and foaming, fully preserves the spherical structure of starch during its conversion to hard carbon, and overcomes the shortcomings of crosslinking agents and prolonged high-energy-consumption heating. Furthermore, it is simple to operate, has a wide range of raw material sources, and offers superior performance, making it suitable for large-scale production. This method is of great significance for exploring the sodium storage mechanism of hard carbon materials, overcoming practical application bottlenecks, and accelerating the commercial application of hard carbon anode materials for sodium-ion batteries. Attached Figure Description

[0015] Figure 1 This is a scanning electron microscope image of the hard carbon anode material in Example 1;

[0016] Figure 2 The images show the 1H NMR spectra of the starch precursor before and after soaking in Example 1.

[0017] Figure 3 The image shows the XRD pattern of the hard carbon anode material in Example 1.

[0018] Figure 4 The cycle performance test curve of the 18650 battery in Example 1;

[0019] Figure 5 The rate performance test curve of the 18650 battery in Example 1;

[0020] Figure 6 This is a charge-discharge curve of the hard carbon anode material in Example 2;

[0021] Figure 7 This is the Raman curve of the hard carbon anode material in Example 2;

[0022] Figure 8 The image shows the XRD pattern of the hard carbon anode material in Example 3. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this is not intended to limit the scope of the invention.

[0024] Example 1:

[0025] A method for preparing a starch-based hard carbon material for a sodium-ion battery negative electrode includes the following steps:

[0026] Weigh 3g of taro starch, immerse it in a 20 wt.% (NH4)2HPO4 solution (which is weakly alkaline) and stir for 2 h. Filter the mixture using a Buchner funnel. The mass ratio of the 20 wt.% (NH4)2HPO4 solution to the mass of starch used is 3:1. Filter the mixture using a Buchner funnel, wash it three times with deionized water and filter again. Collect the filtered starch sample and dry it in an oven (80℃) to remove moisture. Then grind the freeze-dried starch through a 400-mesh sieve. The sieved sample is then decomposed in an electric blast oven at 200℃ for 6 h to obtain a brown powder, which is the precursor of starch-based hard carbon.

[0027] The taro starch-based hard carbon precursor was placed in an atmosphere tube furnace under an argon atmosphere, initially at 5°C·min. -1 The temperature was increased to 200℃ at a rate of 0.2℃·min. -1 The heating rate was increased from 200℃ to 320℃ at a rate of 1℃·min. -1 The heating rate increased from 320℃ to 500℃, and the final high-temperature carbonization temperature was 1400℃, with a heating rate of 5℃·min. -1 The high-temperature carbonization process was maintained at a constant temperature for 6 hours, resulting in powder, namely starch-based hard carbon. The scanning electron microscope (SEM) image of the hard carbon anode material is shown below. Figure 1 As shown in the figure, the starch-based hard carbon used as the negative electrode material in this example exhibits uniform spherical nanoparticles ranging from 1 to 10 micrometers in size, with a smooth surface. The 1H NMR spectrum of the starch precursor material is shown in the figure. Figure 2 As shown, the results indicate that the hydrogen bonding environment changes before and after starch precursor treatment. The XRD pattern of the hard carbon anode material is shown in the figure. Figure 3 As shown, the carbon layer spacing d of the hard carbon anode material 002 The wavelength is 0.36-0.41 nm, and related density tests show that the true density of the hard carbon anode material is 1.5-2.1 g / cm³. 3 The tap density is 0.7-1 g / cm³. 3 The compacted density of the powder is 0.9-1.2 g / cm³. 3 The hard carbon material was tested in an 18650 battery, and the results are as follows: Figure 4 , Figure 5 As shown, the battery cycle and rate performance both exhibit excellent results.

[0028] Example 2:

[0029] A method for preparing a starch-based hard carbon material for a sodium-ion battery negative electrode includes the following steps:

[0030] Weigh 3g of taro starch, soak it in a 30 wt.% KHCO3 solution that shows weak alkalinity and stir for 2 h. Filter the mixture using a Buchner funnel. The mass ratio of KHCO3 solution to starch is 3:1. Filter the mixture using a Buchner funnel, wash it three times with deionized water and filter again. Collect the filtered starch sample and dry it in an oven (80℃) to remove moisture. Then grind the freeze-dried starch through a 400-mesh sieve. The sieved sample is then decomposed in an electric blast oven at 210℃ for 3 h to obtain a brown powder, which is the precursor of starch-based hard carbon.

[0031] The taro starch-based hard carbon precursor was placed in an atmosphere tube furnace under an argon atmosphere, initially at 5°C·min. -1 The temperature was increased to 200℃ at a rate of 0.2℃·min. -1 The heating rate was increased from 200℃ to 320℃ at a rate of 1℃·min. -1 The heating rate increased from 320℃ to 500℃, and the final high-temperature carbonization temperature was 1300℃, with a heating rate of 5℃·min. -1 The high-temperature carbonization process was maintained at a constant temperature for 2 hours to obtain powder, namely starch-based hard carbon anode material. The Raman spectroscopy of the hard carbon material was performed as follows: Figure 7 As shown, the hard carbon material has two diffraction peaks at 1350 cm⁻¹ and 1590 cm⁻¹, namely the D peak and the G peak, respectively. The ID / IG ratio is used to determine the degree of defects or graphitization of the material. The calculated ID / IG ratio is 2, which indicates that the material has a certain sp² aromatic carbon structure and a defect structure of disordered carbon.

[0032] Example 3:

[0033] A method for preparing a starch-based hard carbon material for a sodium-ion battery negative electrode includes the following steps:

[0034] Weigh 3g of taro starch, soak it in a 20 wt.% ammonium dihydrogen phosphate solution that shows weak alkalinity and stir for 2 h. Filter the mixture using a Buchner funnel. The mass ratio of the ammonium dihydrogen phosphate solution to the mass of the starch is 5:1. Filter the mixture using a Buchner funnel, wash it three times with deionized water and filter it again. Collect the filtered starch sample and dry it in an oven (80℃) to remove moisture. Then grind the freeze-dried starch through a 400-mesh sieve. The sieved sample is then subjected to a decomposition treatment at 210℃ for 6 h in an electric blast oven to obtain a brown powder, which is the precursor of starch-based hard carbon.

[0035] The taro starch-based hard carbon precursor was placed in an atmosphere tube furnace under an argon atmosphere, initially at 3°C·min. -1 The temperature was increased to 200℃ at a rate of 0.2℃·min. -1The heating rate was increased from 200℃ to 320℃ at a rate of 1℃·min. -1 The heating rate increased from 320℃ to 500℃, and the final high-temperature carbonization temperature was 1500℃, with a heating rate of 5℃·min. -1 The high-temperature carbonization process was maintained at a constant temperature for 10 hours, resulting in powder, i.e., starch-based hard carbon anode material. The XRD pattern of the hard carbon anode material is shown below. Figure 8 As shown, the carbon layer spacing d of the hard carbon anode material 002 The wavelength is 0.36-0.41 nm, indicating that it has an amorphous carbon structure.

[0036] Application Experiment Example: The hard carbon anode material, super carbon black conductive agent, and carboxymethyl cellulose prepared in Examples 1-3 were mixed in a mass ratio of 8:1:1 to form a slurry, which was then coated onto copper foil to obtain an electrode sheet. The electrode sheet was then dried in an 80°C drying oven for 4 hours. Finally, a coin cell was assembled in a glove box filled with argon atmosphere. The electrolyte used was dimethyl ethylene glycol dimethyl ether, and sodium metal was used as the counter electrode and reference electrode. The material prepared in Example 2 showed excellent performance when applied to the coin cell. The initial discharge specific capacity of the battery was 550 mAh / g, the charge specific capacity was 490 mAh / g, and the initial coulombic efficiency was 88.9%. The cycle performance of the coin cell is shown in the figure below. Figure 6 As shown, after 40 cycles at a current density of 100 mA / g at 25 °C, its reversible specific capacity is 430 mAh / g.

Claims

1. A method for preparing a starch-based hard carbon material for the negative electrode of a sodium-ion battery, characterized in that, Includes the following steps: 1) The starch material was soaked in a 10-50 wt.% (NH4)2HPO4 solution with weak alkalinity and stirred for 2 h. The mixture was filtered using a Buchner funnel. The mass ratio of the 10-50 wt.% (NH4)2HPO4 solution to the starch was 3-5:

1. The starch was then washed three times with deionized water and filtered again. The filtered starch sample was collected and dried in an 80℃ oven to remove moisture. The dried starch was then ground through a 400-mesh sieve. The sieved sample was then dehydrated and oxidized in an electric blast oven at 190℃-230℃ for 0-60 h to obtain a brown powder, which is the precursor of starch-based hard carbon. 2) The dehydrated precursor obtained in step 1) is ground through a 400-mesh sieve, and the resulting powder is subjected to segmented high-temperature carbonization treatment: The segmented high-temperature carbonization treatment is as follows: first, the temperature is increased to 200 ℃ at a heating rate of 3 ℃·min-1, then increased to 320 ℃ at a heating rate of 0.2 ℃·min-1, then increased to 500 ℃ at a heating rate of 1 ℃·min-1, and finally increased to 1000-1800 ℃ at a heating rate of 3 ℃·min-1, and held at this temperature for 2-10 hours. The entire process is carried out under the protection of an inert atmosphere to obtain powder, namely starch-based hard carbon, which is a high-performance sodium-ion battery anode material.

2. The method for preparing starch-based hard carbon material for sodium-ion battery negative electrode according to claim 1, characterized in that, The starch mentioned in step 1) is taro starch, tapioca starch, corn starch, wheat starch, etc., as well as modified starch. The modification treatment of starch includes one or more of physical modification treatment, chemical modification treatment, and biological modification treatment.

3. The method for preparing starch-based hard carbon material for sodium-ion battery negative electrode according to claim 1, characterized in that, The (NH4)2HPO4 solution mentioned in step 1) is one or more alkaline solutions such as diammonium hydrogen phosphate, ammonium dihydrogen phosphate, potassium bicarbonate, and sodium bicarbonate.

4. The method for preparing starch-based hard carbon material for sodium-ion battery negative electrode according to claim 1, characterized in that, The inert atmosphere mentioned in step 2) is one of pure nitrogen, helium, neon, argon, and xenon.

5. A starch-based hard carbon material for sodium-ion battery anodes prepared by any one of claims 1-4.

6. The application of starch-based hard carbon material for sodium-ion battery negative electrodes prepared by any one of claims 1-4 in sodium-ion batteries, lithium-ion batteries, potassium-ion batteries, and alkali metal-ion batteries.

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