A hard carbon anode material prepared using rice husks, its preparation method and application

Abstract

This invention belongs to the field of battery materials technology, specifically relating to a hard carbon anode material prepared from rice husks, its preparation method, and its application. Using rice husks as raw material, the hard carbon anode material is prepared through processes such as washing, drying, crushing, acid cooking, pre-carbonization, and high-temperature carbonization. This invention utilizes inexpensive raw materials, employs a simple and environmentally friendly preparation method, aligns with the concept of green and sustainable development, and produces a hard carbon anode with good structural stability, low cost, and excellent electrochemical performance. It also provides an effective pathway for the recycling and reuse of rice husks.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a hard carbon anode material prepared using rice husks, its preparation method, and its application. Background Technology

[0002] Among numerous emerging energy storage technologies, lithium-ion batteries hold a dominant position. Lithium-ion batteries offer significant advantages in cycle life, energy density, and response speed. However, due to the scarcity and uneven geographical distribution of lithium resources, the cost of lithium-ion batteries continues to rise, limiting their large-scale application. Sodium-ion batteries, on the other hand, are expected to accelerate their penetration in power storage due to their inherent advantages. Sodium resources are abundant (the sodium content in the Earth's crust reaches 2.75%, far exceeding the 0.065‰ of lithium), evenly distributed, and inexpensive, possessing strong sustainability and broad application prospects. Developing sodium-ion batteries is of significant strategic importance for reducing my country's dependence on imported lithium resources. However, sodium ions have a large atomic radius, and the interlayer compounds they form are thermodynamically unstable. Conventional materials suitable for lithium-ion intercalation and deintercalation are insufficient to meet the requirements of sodium ions. This is one of the main reasons why lithium-ion batteries are widely commercialized, while sodium-ion batteries remain in the laboratory stage.

[0003] Choosing the right anode material is crucial for the commercialization of sodium-ion batteries. Compared to metal alloys and metal oxides, which suffer from high volume expansion and low conductivity, hard carbon is the most promising industrial-grade anode material for sodium-ion batteries. Among these, biomass-based hard carbon materials, with their wide availability and unique sodium-storage microstructure, have become a current research hotspot. Biomass, such as agricultural and forestry waste, fruit shells, and straw, are considered ideal precursors due to their abundant sources and low cost. However, hard carbon materials prepared from different biomass materials differ in composition and structure, resulting in inconsistent sodium storage performance. Furthermore, lignin in the precursors can cause severe graphitization in the prepared hard carbon, which is detrimental to sodium ion storage. Therefore, removing some lignin before preparing hard carbon can improve the electrochemical performance and stability of the hard carbon material.

[0004] Chinese patent document CN118183695A discloses a hard carbon anode material prepared from waste poplar bark and its preparation method. The method involves crushing the waste poplar bark, mixing it evenly with water, adding an alkali and anthraquinone compounds, reacting the mixture at a certain temperature, washing and drying the reacted material, and then ball-milling it to obtain a precursor. The precursor is then pre-carbonized and then carbonized in an inert atmosphere to obtain the hard carbon material. However, this patent's precursor preparation process suffers from low delignification selectivity, resulting in low delignification efficiency. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a hard carbon anode material prepared using rice husks, its preparation method, and its application.

[0006] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0007] A method for preparing hard carbon anodes using rice husks involves efficiently controlling the lignin content in biomass precursors through acid pretreatment of the rice husks, resulting in high-performance hard carbon anode materials. The acid used is formic acid, and hydrogen peroxide is used as a cooking aid. By controlling the amounts of acid and aid added, hard carbon materials with excellent performance are obtained.

[0008] A method for preparing hard carbon anodes using rice husks includes the following steps:

[0009] (1) Dry the rice husks and make them into rice husk powder;

[0010] (2) Mix rice husk powder with water to obtain a mixture;

[0011] (3) Add formic acid to the mixture in step (2), then add hydrogen peroxide, and heat the rice husk powder at a rate of 1-3℃ / min to cook it. After the cooking process, let it cool naturally to room temperature.

[0012] (4) Wash the cooked rice husk powder with deionized water until neutral, dry it in an oven, and then ball mill it into precursor powder.

[0013] (5) Under an inert atmosphere, the precursor powder is first heated to the pre-carbonization temperature at a rate of 3 to 8 °C / min for pre-carbonization, and then heated to the carbonization temperature for carbonization to obtain hard carbon material.

[0014] This invention first involves acid cooking of rice husk powder with the addition of cooking aids to remove a certain amount of lignin from the rice husk and protect cellulose and hemicellulose. Then, the cooked rice husk is washed and dried to remove excess acid and soften the rice husk powder, so that it can be ball-milled to obtain rice husk powder with richer pores. Finally, carbonization is performed to obtain a high-performance rice husk-based hard carbon anode material.

[0015] Preferably, the solid-liquid weight ratio of rice husk powder to water in step (2) is 1:3 to 7.

[0016] Preferably, the mass ratio of formic acid to rice husk powder in step (3) is 5-25%, more preferably 5-20%, further preferably 15-20%, and even more preferably 20%.

[0017] Preferably, the mass ratio of hydrogen peroxide to rice husk powder in step (3) is 0.3-0.8%. Adding too much hydrogen peroxide will increase the delignification rate during cooking, resulting in a significant reduction in the lignin content of the rice husk. Adding too little hydrogen peroxide will decrease the delignification rate, resulting in a reduction in the amount of lignin removed from the rice husk during cooking. Both of these factors will affect the performance of the final hard carbon material.

[0018] Preferably, the temperature of the cooking process in step (3) is 120℃-160℃ and the cooking time is 3-8h.

[0019] Preferably, the inert atmosphere in step (5) is nitrogen, argon, or similar atmosphere. The pre-carbonization temperature is 350-500℃, and the pre-carbonization time is 2-4 hours. The carbonization temperature is 1200℃-1400℃, and the carbonization time is 4-6 hours. Pre-carbonization and carbonization are carried out in a tube furnace.

[0020] The present invention also provides a method for preparing hard carbon anodes using rice husks to obtain rice husk-based hard carbon anode materials.

[0021] The present invention also provides the application of the above-mentioned rice husk-based hard carbon anode material in the preparation of battery anode electrode sheets for ion-type batteries.

[0022] Preferably, the preparation steps of the battery negative electrode sheet include: mixing the rice husk-based hard carbon negative electrode material with conductive carbon black and a binder, stirring evenly to obtain an electrode slurry; coating the electrode slurry onto a current collector, drying it, and then stamping it to obtain the battery negative electrode sheet.

[0023] In the electrode slurry, the mass percentage of rice husk-based hard carbon anode material is 75-85%, the mass percentage of conductive carbon black is 5-15%, the mass percentage of binder is 5-15%, and the remainder is solvent. The solvent in the electrode slurry is water. The binder is specifically carboxymethyl cellulose and styrene-butadiene rubber.

[0024] Preferably, the mass ratio of rice husk-based hard carbon anode material to conductive carbon black and binder is 8:1:1.

[0025] Preferably, the amount applied to the current collector is 3.0 mg / cm³. 2 .

[0026] The beneficial technical effects of the present invention are as follows:

[0027] (1) This invention is the first to use formic acid and hydrogen peroxide to regulate the lignin content of rice husks, thereby preparing precursors with different lignin contents, and further obtaining precursors with different crystallinity and closed-cell structures. These precursors are then carbonized at high temperatures to prepare hard carbon materials, effectively improving the electrochemical performance of batteries. This will expand the application of biomass materials in the field of sodium-ion anode materials. In this invention, when the lignin content of the rice husk precursors is 5% to 10 wt%, the crystallinity is high and the closed-cell structure is abundant, resulting in higher electrochemical performance of the prepared hard carbon.

[0028] (2) The formic acid cooking pretreatment of this invention has high delignification selectivity and high delignification efficiency. The formic acid in the waste liquid can be recycled and reused. It has great advantages in energy saving, COD emission reduction, environmental protection and improving the quality of biomass products. Moreover, the rice husk-based hard carbon anode material and battery anode electrode sheet provided by this invention have simple preparation process, which is conducive to large-scale promotion and application. Attached Figure Description

[0029] Figure 1 This is the X-ray diffraction pattern of the precursor obtained in this invention. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments.

[0031] Examples 1-16

[0032] A method for preparing hard carbon anodes using rice husks includes the following steps:

[0033] (1) Wash the rice husks discarded by the food processing plant with clean water, dry them, grind them into powder and sieve them.

[0034] (2) Add the dried rice husk powder from step (1) and water to the reactor at a solid-liquid weight ratio of 1:5;

[0035] (3) Add a certain amount of formic acid to the reactor; then add hydrogen peroxide, the amount of which is 0.5% of the weight of rice husk powder. Set the reactor to heat up to 120℃-160℃ at a rate of 2℃ / min, keep it at that temperature for 5 hours, and then let it cool naturally to room temperature.

[0036] (4) Wash the cooked rice husk powder with water until pH=7, dry it in an oven at 60℃ for 12h, and then ball mill it into precursor powder;

[0037] (5) Inert gas is introduced into a tube furnace, and the precursor powder is placed into the tube furnace at a heating rate of 5℃ / min. It is pre-carbonized at 350℃-500℃ for 3h, and then carbonized at 1200℃-1400℃ to obtain hard carbon material for 5h.

[0038] Comparative Example 1 is the rice husk powder obtained in step (1).

[0039] Comparative Example 2

[0040] The difference from Example 12 is that formic acid is not added.

[0041] Comparative Example 3

[0042] The difference from Example 12 is that hydrogen peroxide is not added.

[0043] Comparative Example 4

[0044] The difference from Example 12 is that hydrogen peroxide is replaced with an equal amount of anthraquinone.

[0045] Comparative Example 5

[0046] The difference from Example 12 is that hydrogen peroxide is replaced with an equal amount of sodium hydroxide.

[0047] Comparative Example 6

[0048] The difference from Example 12 is that sulfuric acid is replaced with an equal amount of formic acid.

[0049] Comparative Example 7

[0050] The difference from Example 12 is that the cooking conditions are set to formic acid: rice husk at a ratio of 25:100.

[0051] Table 1 shows the powder precursors prepared according to steps (1) to (5) above. The specific conditions are shown in the table below.

[0052]

[0053]

[0054] Hard carbon anode materials were prepared using the precursors obtained from the examples and comparative examples.

[0055] Test method for the electrochemical performance of hard carbon anode materials: Using a charge-discharge tester, following the sodium-ion battery test procedure in the national standard GB / T 43114-2023 for hard carbon anodes, at 30 mA·g -1 The material was subjected to charge-discharge tests at a current density of [value missing].

[0056] Table 2 Electrochemical properties of the hard carbon materials obtained in this invention

[0057]

[0058]

[0059]

[0060] The results show that when the mass ratio of formic acid to rice husk is between 15 and 20:100, the lignin content is approximately 7% to 10%. Within this range, the crystallinity of the precursor is 35% to 45%, and the pore structure is mainly mesoporous. Pretreatment with formic acid cooking at 140°C further improves the crystallinity and pore structure of the precursor, which is more conducive to battery performance. The crystallinity of the precursor obtained in Example 1 was 37.3%, in Example 6 it was 39.4%, in Example 12 it was 43.2%, and in Comparative Example 1 it was 32.1%. XRD patterns are shown in Table 1. Carbonization of the precursor yields hard carbon, and the number of closed micropores is negatively correlated with the lignin content. For precursors with a lignin content of 7% to 10%, lower lignin content results in more abundant closed pores, which is more conducive to sodium ion storage in hard carbon.

Claims

1. A method for preparing a hard carbon negative electrode using rice husks, characterized by, The method comprises the following steps: (1) drying and making rice husk powder; (2) mixing the rice husk powder with water to obtain a mixture; (3) adding formic acid to the mixture of step (2), the mass ratio of formic acid to rice husk powder being 20%, and then adding hydrogen peroxide, the mass ratio of hydrogen peroxide to rice husk powder being 0.3-0.8%, and then performing steaming treatment on the rice husk powder at a rate of 1-3 ℃ / min, and then naturally cooling to room temperature after the steaming treatment is completed; (4) washing the steamed rice husk powder with deionized water to neutral, placing it in an oven for drying, and then ball-milling and crushing it into a precursor powder, the content of lignin in the precursor powder being 5-10 wt%; (5) under an inert atmosphere, first heating the precursor powder to a pre-carbonization temperature at a rate of 3-8 ℃ / min for pre-carbonization, and then heating it to a carbonization temperature for carbonization to obtain a hard carbon material.

2. The method for preparing a hard carbon negative electrode using rice husks according to claim 1, characterized by, The solid-liquid weight ratio of the rice husk powder to water in step (2) is 1:3-7.

3. The method for preparing a hard carbon negative electrode using rice husks according to claim 1, characterized by, The temperature of the steaming treatment in step (3) is 120-160 ℃, and the steaming treatment time is 3-8 h.

4. The method for preparing a hard carbon negative electrode using rice husks according to claim 1, characterized by, The pre-carbonization temperature in step (5) is 350-500 ℃, and the pre-carbonization time is 2-4 h; the carbonization temperature is 1200-1400 ℃, and the carbonization time is 4-6 h.

5. The method for preparing a hard carbon negative electrode using rice husks according to claim 1, characterized by, The inert atmosphere in step (5) is a nitrogen or argon atmosphere.

6. A rice husk-based hard carbon negative electrode material prepared by the method of any one of claims 1-5.

7. Use of the rice husk-based hard carbon negative electrode material prepared by the method of any one of claims 1-5 in the preparation of a battery negative electrode sheet of an ionic battery.

8. Use according to claim 7, characterized in that, The preparation steps of the battery negative electrode sheet comprise: mixing the rice husk-based hard carbon negative electrode material with conductive carbon black and a binder, stirring uniformly to obtain an electrode slurry; applying the electrode slurry on a current collector, drying, and then punching to obtain the battery negative electrode sheet.

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