Biomass hard carbon negative electrode material and preparation method and application thereof

Abstract

The application discloses a biomass hard carbon negative material and a preparation method and application thereof. The application comprises the following steps: S1: crushing three agricultural wastes, and performing low-oxygen pre-carbonization on the crushed three agricultural wastes in an inert atmosphere to obtain first intermediate carbon; S2: blending the first intermediate carbon with a modifier, and performing ball milling modification to obtain second intermediate carbon; S3: performing alkali leaching purification or sequentially performing alkali leaching and acid leaching purification on the second intermediate carbon; and S4: performing high-temperature carbonization on the second intermediate carbon after purification to obtain the hard carbon negative material, and the carbonization atmosphere is an inert gas atmosphere. The biomass active oxygen-containing groups are reserved through the low-oxygen pre-carbonization, and the carbon material particle size is micronized and the material is compounded through high-energy ball milling modification, so that the capacity and the first effect index of the final product are significantly improved, the sodium intercalation capacity of the biomass hard carbon negative electrode is greater than 320 mgh / g, and the first effect is greater than 85%.

Description

Technical Field

[0001] This invention belongs to the field of anode materials, specifically relating to a biomass hard carbon anode material, its preparation method, and its application. Background Technology

[0002] Graphite anodes are unsuitable for sodium-ion batteries, necessitating a re-selection of anode materials. Anode materials play a crucial role in loading sodium ions and are the core components of sodium-ion batteries, directly impacting energy density, cycle performance, and initial efficiency. Carbon-based materials, with their wide availability and strong sodium storage capacity, have become the mainstream choice. Carbon-based materials can be categorized into hard carbon and soft carbon based on whether they graphitize after high-temperature treatment. Hard carbon is carbon that does not graphitize after treatment at 2800℃, while soft carbon is carbon that can graphitize after high-temperature treatment. Hard carbon materials possess numerous active sites for sodium storage and have a high specific capacity, offering significant advantages. Compared to soft carbon, hard carbon has a more porous and disordered internal crystal structure, exhibiting various types of reversible sodium storage sites and resulting in a higher sodium storage capacity. The sodium ion storage sites of hard carbon mainly include: 1) sodium storage through intercalation reaction; 2) sodium storage through the formation of atomic clusters within closed pores; 3) sodium storage through capacitive adsorption on the electrolyte surface; and 4) sodium storage through pseudocapacitive methods at defect sites. Hard carbon also boasts advantages such as minimal volume expansion after sodium intercalation, high safety, structural stability, excellent conductivity, and environmental friendliness. Furthermore, it exhibits good performance in fast charging and low-temperature operation. Currently, mainstream companies in the industry utilize the hard carbon anode route, demonstrating its strong commercial potential.

[0003] In sodium-ion batteries, the anode material accounts for approximately 16% of the cost structure, higher than that of lithium-ion batteries. With the current rising price of lithium carbonate, the cathode accounts for about 50% of the cost structure of lithium-ion batteries, while graphite anodes account for 5%-8%. According to calculations by Zhongke Haina, the anode material accounts for approximately 16% of the cost of sodium-ion batteries. Since the choice of anode material directly affects the battery's energy density, initial efficiency, and cycle performance, its importance is increased compared to lithium-ion batteries. For hard carbon, the yield of raw materials is relatively low; for example, the yield from biomass to hard carbon is only about 30%, while the yield of graphite anodes is about 80%. Therefore, the selection of raw materials for sodium-ion batteries is currently a bottleneck in research and development. Choosing suitable precursor materials for large-scale production is a pressing issue for the development of sodium-ion batteries. Currently, the precursor raw materials used for hard carbon mainly include biomass, resin-based, and petroleum-based materials. Biomass precursor raw materials mainly include coconut shells, straw, bamboo, walnut shells, sugar, and starch. Hard carbon materials prepared from different precursors exhibit similar charge-discharge curves, but their electrochemical performance varies considerably.

[0004] Existing biomass-based hard carbon production processes suffer from high raw material costs, low product performance, sodium intercalation capacity generally below 300 mA / g, and initial efficiency less than 80%. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned shortcomings of the prior art by providing a biomass hard carbon anode material, its preparation method, and its application.

[0006] The present invention provides a method for preparing a biomass hard carbon anode material, comprising the following steps:

[0007] S1: The agricultural waste is crushed and then pre-carbonized in an inert atmosphere to obtain the first intermediate carbon.

[0008] S2: The first intermediate carbon is blended with a modifier and ball-milled to obtain the second intermediate carbon;

[0009] S3: The second intermediate carbon is purified and impurities are removed by alkaline leaching or by a combination of alkaline leaching and acid leaching.

[0010] S4: The purified second intermediate carbon is carbonized at high temperature to obtain hard carbon anode material, and the carbonization atmosphere is an inert gas atmosphere.

[0011] Furthermore, in step S1, the carbonization temperature is 400℃-600℃, the oxygen content is no more than 0.5%, and the carbonization time is 30min-180min.

[0012] Furthermore, in step S2, the modification time is no more than 60 minutes.

[0013] Furthermore, in step S3, the alkali leaching is carried out at room temperature with an alkali concentration of 1%-20%; the acid leaching uses an acid concentration of 0-15%; the alkali used for alkali leaching is sodium hydroxide or potassium hydroxide; the acid used for acid leaching is one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0014] Furthermore, in step S4, the carbonization temperature is 1000℃-1500℃, and the carbonization time is 30min-180min.

[0015] Furthermore, the agricultural waste mentioned in step S1 is one of sawdust, straw, waste bamboo, and bagasse; the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0016] Furthermore, the modifier is one or more of potassium permanganate, perchloric acid, sodium hypochlorite, sodium ferrate, maghemite, metallic tin, and tin-phosphorus alloy.

[0017] Furthermore, in step S2, the modification is carried out in a high-energy ball mill, which is one of a planetary ball mill, a stirred mill, or a vibratory mill; the high-temperature carbonization atmosphere of the second intermediate carbon is a nitrogen atmosphere or an argon atmosphere.

[0018] A hard carbon anode material prepared by the preparation method described above.

[0019] A biomass hard carbon anode material, as described above, is used in sodium battery anodes.

[0020] This scheme preserves the oxygen-containing active groups of biomass through low-oxygen pre-carbonization and achieves micro-nano particle size reduction and material composites of carbon materials through high-energy ball milling modification. Specifically, this invention employs mechanochemical technology to treat intermediate carbon, causing it to undergo a solid-phase reaction with a modifier, achieving solid-phase oxidation modification of the intermediate carbon molecular chain, while simultaneously realizing micro-nano composites between the modifier and the carbon chain. Mechanochemical modification alters the material properties as follows: 1. Under the action of mechanical force, the crystal structure of the intermediate carbon changes, tending towards disorder, resulting in a relatively loose mineral structure and reduced density; 2. Mechanochemical changes alter the conductivity and surface electrokinetic behavior of the intermediate carbon; 3. During the mechanochemical modification process, unsaturated bonds and charged structural units appear on the fracture surface, placing the particles in an unstable high-energy state, thereby improving their surface adsorption capacity. The surface of the intermediate carbon is rich in unsaturated bonds and activation sites with residual charges, which promotes the improvement of ion exchange or displacement capacity; 4. The crystal structure is also destroyed, forming amorphous substances, which changes its properties, lowers the activation energy of the reaction, and allows the solid-phase oxidation reaction to proceed, and enables the modifier to form a heterostructure with the intermediate carbon. The above-mentioned changes in properties promote a significant improvement in the final product capacity and first-efficiency index, with a sodium intercalation capacity of >320 mgh / g and a first-efficiency of >85% for the biomass hard carbon anode. Attached Figure Description

[0021] Figure 1 This is a flowchart of a method for preparing a biomass hard carbon anode material according to the present invention. Detailed Implementation

[0022] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0023] like Figure 1 As shown, a method for preparing a biomass hard carbon anode material includes:

[0024] Agricultural waste is crushed and then pre-carbonized in an inert atmosphere to obtain the first intermediate carbon. The carbonization temperature is 400℃-600℃, the oxygen content is 0%-0.5%, and the carbonization time is 30min-180min.

[0025] The first intermediate carbon was blended with a modifier and modified in a high-energy ball mill for 0-60 minutes to obtain the second intermediate carbon. The second intermediate carbon was then purified by alkali leaching and acid leaching, both carried out at room temperature, with an alkali concentration of 1%-20% and an acid concentration of 0%-15%.

[0026] The purified second intermediate carbon is carbonized at high temperature to obtain hard carbon anode material. The carbonization atmosphere is an inert gas atmosphere, the carbonization temperature is 1000℃-1500℃, and the carbonization time is 30min-180min.

[0027] Example 1

[0028] Wood chip hard carbon anode material, using Figure 1 The process flow parameters are as follows:

[0029]

[0030] The product test results are as follows:

[0031] Hard carbon product name Wood Chip Hard Charcoal #1 Wood Chip Hard Charcoal #2 Wood Chip Hard Charcoal 3# Sodium intercalation capacity 276 mah / g 305mah / g 335mah / g First effect 77％ 80％ 86％

[0032] The product capacity and initial efficiency are low due to the absence of oxygen carbonization and high-energy ball milling modification. However, the product performance is significantly improved after increasing the oxygen content of the carbonization and high-energy ball milling modification.

[0033] Example 2

[0034] Straw hard carbon anode material, using Figure 1 The process flow parameters are as follows:

[0035] The product test results are as follows:

[0036] raw materials straw Low-temperature carbonization temperature and atmosphere 600℃ Argon Oxygen content 0.25％ Low temperature carbonization time 180min Types of high-energy mills Stirred ball mill Types of modifiers and modification time Maghematite, 60 min Types and concentrations of alkaline solutions 20% sodium hydroxide Acid type and concentration 0% sulfuric acid High-temperature carbonization temperature and atmosphere 1500℃ nitrogen

[0037] Example 3

[0038] Waste bamboo hard carbon anode material, using Figure 1 The process flow parameters are as follows:

[0039] Sodium intercalation capacity 325mah / g First effect 87％

[0040]

[0041]

[0042] The product test results are as follows:

[0043] Sodium intercalation capacity 351mah / g First effect 87％

[0044] Example 4

[0045] Sugarcane bagasse hard carbon anode material, using Figure 1The process flow parameters are as follows:

[0046] raw materials sugarcane bagasse Low-temperature carbonization temperature and atmosphere 400℃ nitrogen Oxygen content 0.35％ Low temperature carbonization time 600min Types of high-energy mills Stirred ball mill Types of modifiers and modification time Phosphorus-tin alloy, 15 min Types and concentrations of alkaline solutions 10% sodium hydroxide Acid type and concentration 5% sulfuric acid High-temperature carbonization temperature and atmosphere 1300℃ Argon

[0047] The product test results are as follows:

[0048] Sodium intercalation capacity 345mah / g First effect 86％

[0049] The preparation method of a biomass hard carbon anode material of the present invention is used to treat agricultural waste. The biomass hard carbon anode has a sodium intercalation capacity of >320mgh / g and an initial efficiency of >85%, which can be effectively applied to sodium electrode anode materials.

[0050] For any points not covered above, existing technologies shall apply.

[0051] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a biomass hard carbon anode material, characterized in that, Includes the following steps: S1: The agricultural waste is crushed and then pre-carbonized in an inert atmosphere to obtain the first intermediate carbon. S2: The first intermediate carbon is blended with a modifier and ball-milled to obtain the second intermediate carbon; S3: The second intermediate carbon is purified and impurities are removed by alkaline leaching or by a combination of alkaline leaching and acid leaching. S4: The purified second intermediate carbon is carbonized at high temperature to obtain biomass hard carbon anode material. The carbonization atmosphere is an inert gas atmosphere. In step S1, the carbonization temperature is 400℃-600℃, the oxygen content is no more than 0.5%, and the carbonization time is 30min-180min; In step S2, the modification time shall not exceed 60 min; The modifier is one or more of potassium permanganate, magnetite, metallic tin, and tin phosphate alloy; In step S3, the alkaline leaching is carried out at room temperature with an alkaline solution concentration of 1%-20%; the acid leaching uses an acid solution concentration greater than 0 and not greater than 15%; the alkaline solution used for alkaline leaching is sodium hydroxide or potassium hydroxide; the acid solution used for acid leaching is one or more of hydrochloric acid, sulfuric acid, and nitric acid. In step S4, the carbonization temperature is 1000℃-1500℃ and the carbonization time is 30min-180min.

2. The method for preparing a biomass hard carbon anode material as described in claim 1, characterized in that, The agricultural waste mentioned in step S1 is one of sawdust, straw, waste bamboo, and bagasse; the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

3. The method for preparing a biomass hard carbon anode material as described in claim 1, characterized in that, In step S2, the modification is carried out in a high-energy ball mill, which is one of a planetary ball mill, a stirred mill, or a vibratory mill; the high-temperature carbonization atmosphere of the second intermediate carbon is a nitrogen atmosphere or an argon atmosphere.

4. A biomass hard carbon anode material prepared by the preparation method according to any one of claims 1-3.

5. A biomass hard carbon anode material as described in claim 4, applied to the anode of a sodium battery.

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