A method for preparing energy storage material by using straw waste
Patent Information
- Application Number
- CN202611020615.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-09
- Publication Date
- 2026-09-04
AI Technical Summary
[0003]当前，秸秆基储能材料的制备多以物理改性或简单化学修饰为核心，技术路线存在明显局限，难以兼顾材料的储能性能、结构稳定性与工艺绿色性；原料预处理深度不足，现有技术多依赖粉碎、球磨、等离子体刻蚀等物理手段，仅能改变秸秆的外观形态，无法从分子层面断裂纤维素、木质素的致密大分子链，难以定向引入高密度活性官能团，导致后续掺杂、交联等改性效率低下，碳材料的结构与电子特性优化受限；多步改性工艺缺乏化学协同性，杂原子掺杂、孔道活化、金属化合物复合等环节多为独立操作或物理叠加，未形成深度化学衔接，使得N、S等杂原子难以通过化学键稳定锚定在碳骨架上，孔道结构与活性位点的匹配度差，材料在充放电过程中易出现活性位点流失、结构坍塌等问题；金属化合物复合效果不佳，现有技术中Fe3O4等金属化合物与秸秆基碳材料的复合多采用物理混合或简单化学沉淀法，二者仅依靠范德华力结合，界面结合力弱，金属颗粒易团聚、脱落，不仅无法充分发挥赝电容贡献，还会导致材料循环性能快速衰减
[0025] This application utilizes the ·OH radicals generated by Fenton oxidation to break the macromolecular chains of straw cellulose and lignin, directionally introducing active functional groups such as hydroxyl and carboxyl groups. Then, chemical crosslinking is formed through esterification of the active functional groups with a polycarboxylic acid crosslinking agent, constructing a stable three-dimensional molecular framework. Based on the active functional groups of the modified straw, pre-adsorption and chemical bonding of dopants are achieved. During pyrolysis, N and S atoms are stably doped into the carbon framework through CN and CS chemical bonds. Simultaneously, the chemical etching reaction between KOH and the carbon framework precisely constructs microporous-mesoporous hierarchical channels, improving the material's specific surface area and ion transport efficiency. Finally, using the N and O atoms on the nitrogen-sulfur co-doped carbon surface as coordination sites, Fe... 3+ In-situ hydrolysis-precipitation reaction generates Fe3O4 nanoparticles, forming Fe-N and Fe-O chemical bonded loads, avoiding the particle agglomeration and shedding problems caused by traditional physical composites. Ultimately, it achieves a triple synergistic improvement in carbon framework double-layer capacitance, heteroatom N/S pseudocapacitance, and Fe3O4 redox pseudocapacitance, while ensuring the structural stability of the material during long-cycle, high-rate charge-discharge processes.
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Figure CN122685074A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of energy storage material preparation technology, specifically relating to a method for preparing energy storage materials using straw waste. Background Technology
[0002] With the global energy crisis and environmental problems becoming increasingly prominent, the development of low-cost, high-performance, and environmentally friendly energy storage materials has become a research hotspot in the energy storage field. Straw, as a huge renewable waste in agricultural production, has a global annual emission of hundreds of millions of tons. Its main components are cellulose, lignin, and hemicellulose, and it has advantages such as high carbon content, wide availability, and low price. Converting it into energy storage materials can realize the high-value utilization of agricultural waste.
[0003] Currently, the preparation of straw-based energy storage materials mainly focuses on physical modification or simple chemical modification, which has significant limitations in terms of technical routes. It is difficult to simultaneously achieve the energy storage performance, structural stability, and green process of the materials. The depth of raw material pretreatment is insufficient. Existing technologies mostly rely on physical methods such as crushing, ball milling, and plasma etching, which can only change the appearance of straw and cannot break the dense macromolecular chains of cellulose and lignin at the molecular level. It is difficult to directionally introduce high-density active functional groups, resulting in low efficiency of subsequent doping, cross-linking, and other modifications, and limiting the optimization of the structure and electronic properties of carbon materials. Multi-step modification processes lack chemical synergy, and heteroatom doping, channel activation, and metal... Compound composite processes are mostly independent operations or physical superpositions, without forming deep chemical connections. This makes it difficult for heteroatoms such as N and S to be stably anchored to the carbon framework through chemical bonds. The matching degree between the pore structure and active sites is poor, and the material is prone to problems such as loss of active sites and structural collapse during charging and discharging. The composite effect of metal compounds is not good. In the existing technology, the composite of metal compounds such as Fe3O4 with straw-based carbon materials mostly adopts physical mixing or simple chemical precipitation methods. The two rely solely on van der Waals forces for bonding, resulting in weak interfacial bonding. Metal particles are prone to agglomeration and detachment, which not only fails to fully utilize the pseudocapacitive contribution, but also leads to rapid degradation of the material's cycling performance.
[0004] Therefore, there is an urgent need to develop a method for preparing energy storage materials using straw waste, so as to simultaneously improve the energy storage performance and structural stability of the materials. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this application provides a method for preparing energy storage materials using straw waste, comprising the following steps:
[0006] S1: Take dry straw, put it into a crusher to crush it to obtain straw powder, add it to an acid solution, stir to remove ash, filter and wash, and then dry to obtain pretreated straw powder;
[0007] S2: Take the pretreated straw powder, add deionized water, ultrasonically disperse, add ferrous salt and oxidant in sequence, stir, filter and wash, and dry to obtain oxidized straw powder;
[0008] S3: Take oxidized straw powder, add deionized water and polycarboxylic acid crosslinking agent, stir, filter, wash and dry to obtain modified straw powder;
[0009] S4: Take modified straw powder, add nitrogen source, sulfur source and deionized water, stir, filter and wash, and then dry to obtain nitrogen-sulfur doped precursor;
[0010] S5: Grind the nitrogen-sulfur doped precursor and KOH evenly, put them into a reaction vessel, introduce an inert gas as a protective atmosphere, heat up to react, and then cool naturally to room temperature to obtain nitrogen-sulfur co-doped porous carbon.
[0011] S6: Take nitrogen-sulfur co-doped porous carbon, add deionized water for ultrasonic dispersion, add iron salt to dissolve, adjust the pH of the mixture with alkali solution, stir, keep warm in water bath, filter and wash, and dry to obtain straw-based energy storage material.
[0012] Preferably, the ferrous salt includes any one of ferrous sulfate heptahydrate, anhydrous ferrous sulfate, and ferrous chloride; the oxidant includes any one of hydrogen peroxide and ammonium persulfate; and the polycarboxylic acid crosslinking agent includes any one of citric acid, malic acid, and succinic acid.
[0013] In this case, ferrous salts such as ferrous sulfate heptahydrate, anhydrous ferrous sulfate, and ferrous chloride readily dissociate into Fe in aqueous solution. 2+ It can efficiently trigger the Fenton reaction to generate ·OH free radicals, and the by-products (sulfates, chlorides) are easily removed by washing, leaving no harmful residues; citric acid, malic acid, succinic acid and other carboxylic acids contain two or more carboxyl groups, which can undergo multi-site esterification reactions with the hydroxyl groups on the straw surface to build a dense and stable three-dimensional framework. Moreover, the carboxylic acid molecular chains are relatively short and will not block the pores formed later, thus balancing the cross-linking effect and the permeability of the pores.
[0014] Preferably, the nitrogen source is any one of urea, melamine, and ammonium chloride; and the sulfur source is any one of thiourea and sodium sulfate.
[0015] In this context, nitrogen sources such as urea, melamine, and ammonium chloride are selected. Urea generates amino free radicals after pyrolysis, which easily combine with the carbon skeleton to form active sites such as pyrrole N and pyridine N. Sulfur sources such as thiourea and sodium sulfate are selected. Thiourea generates sulfur-containing active species after pyrolysis, which can form CS bonds with the carbon skeleton and also have a certain dispersing effect. Both can work synergistically with nitrogen sources to regulate the electronegativity and conductivity of carbon materials and enhance pseudocapacitance contribution.
[0016] Preferably, the iron salt includes any one of ferric chloride hexahydrate, ferrous chloride, and ferric sulfate.
[0017] In this case, ferric chloride hexahydrate, ferrous chloride, and ferric sulfate are all water-soluble iron salts. Under alkaline conditions, Fe... 3+ (Ferrous chloride is easily oxidized to Fe) 3+ It can rapidly hydrolyze to generate Fe(OH)3, which is then dehydrated to form Fe3O4 nanoparticles. At the same time, this type of iron salt has a high degree of dissociation and can efficiently coordinate with N and O atoms on the surface of carbon materials to achieve in-situ bonding and loading. Moreover, the by-products are easy to wash away and will not have a negative impact on the energy storage performance of the material, making it suitable for overall aqueous phase green processes.
[0018] Preferably, in step S1, the mass ratio of straw powder to acid solution is 1:(3-8); the concentration of the acid solution is 0.8-2 mol / L; the acid solution includes any one of hydrochloric acid solution, sulfuric acid solution, and nitric acid solution; the conditions for stirring and deashing are: stirring speed 400-450 r / min, temperature 70-90℃, time 1-3 h; the conditions for drying are: temperature 100-110℃, time 4-8 h.
[0019] Preferably, in step S2, the mass ratio of pretreated straw powder, deionized water, ferrous salt, and oxidant is 1:(5-8):(0.1-0.15):(0.25-0.3); the stirring conditions are: stirring speed 400-450 r / min, temperature 20-40℃, time 0.5-2 h; the drying conditions are: temperature 100-110℃, time 4-8 h.
[0020] Preferably, in step S3, the mass ratio of oxidized straw powder, deionized water, and polycarboxylic acid crosslinking agent is 1:(3-5):(0.2-0.3); the stirring conditions are: stirring speed 400-450 r / min, temperature 70-90℃, time 1-3 h; the drying conditions are: temperature 100-110℃, time 4-8 h.
[0021] Preferably, in step S4, the mass ratio of modified straw powder, nitrogen source, sulfur source and deionized water is 1:(0.8-1.2):(0.8-1.2):(5-6); the stirring conditions are: stirring speed 400-450 r / min, temperature 80-85℃, time 1-3 h; the drying conditions are: temperature 100-110℃, time 2-5 h.
[0022] Preferably, in step S5, the mass ratio of nitrogen-sulfur doped precursor to KOH is 1:(1-3); the inert gas includes either nitrogen or argon, with a gas flow rate of 30-80 mL / min; and the reaction temperature is 750-900 °C.
[0023] Preferably, in step S6, the mass ratio of nitrogen-sulfur co-doped porous carbon, deionized water, and iron salt is 1:(5-8):(1.2-1.5); the alkaline solution is a 0.5-1.5 mol / L sodium hydroxide solution or potassium hydroxide solution; the pH of the mixture is adjusted to 9-11; the stirring conditions are: stirring speed 400-450 r / min, stirring time 0.5-2 h; the water bath temperature is 70-90℃, time 1-3 h; the drying conditions are: temperature 100-110℃, time 4-8 h.
[0024] Beneficial technical effects:
[0025] This application utilizes the ·OH radicals generated by Fenton oxidation to break the macromolecular chains of straw cellulose and lignin, directionally introducing active functional groups such as hydroxyl and carboxyl groups. Then, chemical crosslinking is formed through esterification of the active functional groups with a polycarboxylic acid crosslinking agent, constructing a stable three-dimensional molecular framework. Based on the active functional groups of the modified straw, pre-adsorption and chemical bonding of dopants are achieved. During pyrolysis, N and S atoms are stably doped into the carbon framework through CN and CS chemical bonds. Simultaneously, the chemical etching reaction between KOH and the carbon framework precisely constructs microporous-mesoporous hierarchical channels, improving the material's specific surface area and ion transport efficiency. Finally, using the N and O atoms on the nitrogen-sulfur co-doped carbon surface as coordination sites, Fe... 3+ In-situ hydrolysis-precipitation reaction generates Fe3O4 nanoparticles, forming Fe-N and Fe-O chemical bonded loads, avoiding the particle agglomeration and shedding problems caused by traditional physical composites. Ultimately, it achieves a triple synergistic improvement in carbon framework double-layer capacitance, heteroatom N / S pseudocapacitance, and Fe3O4 redox pseudocapacitance, while ensuring the structural stability of the material during long-cycle, high-rate charge-discharge processes. Attached Figure Description
[0026] Figure 1 This is a flowchart illustrating the preparation process of energy storage materials using straw waste, as described in this application. Detailed Implementation
[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.
[0028] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.
[0029] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0030] The present invention will be further described below with reference to embodiments, but is not limited thereto.
[0031] Example 1
[0032] This embodiment provides a method for preparing energy storage materials using straw waste, including the following steps:
[0033] S1: Take dry straw, put it into a pulverizer to crush it to obtain straw powder, add it to a 1 mol / L hydrochloric acid solution, stir for 2 h at 80℃ and 400 r / min to remove ash, filter and wash, and dry at 105℃ for 6 h to obtain pretreated straw powder; wherein the mass ratio of straw powder to acid solution is 1:5;
[0034] S2: Take the pretreated straw powder, add it to deionized water, disperse it ultrasonically, add ferrous sulfate heptahydrate and hydrogen peroxide in sequence, stir for 1 hour at 25℃ and 400 r / min, filter and wash, and dry at 105℃ for 6 hours to obtain oxidized straw powder; wherein the mass ratio of pretreated straw powder, deionized water, ferrous sulfate heptahydrate and hydrogen peroxide is 1:5:0.1:0.275;
[0035] S3: Take oxidized straw powder, add deionized water and citric acid, stir for 2 hours at 80℃ and 400r / min, filter and wash, and dry at 105℃ for 6 hours to obtain modified straw powder; wherein the mass ratio of oxidized straw powder, deionized water and citric acid is 1:4:0.25.
[0036] S4: Take modified straw powder, add urea, thiourea and deionized water, stir at 82℃ and 400r / min for 1.5h, filter and wash, and dry at 110℃ for 3h to obtain nitrogen-sulfur doped precursor; wherein the mass ratio of modified straw powder, urea, thiourea and deionized water is 1:1:1:6.
[0037] S5: Grind the nitrogen-sulfur doped precursor and KOH at a mass ratio of 1:2 until uniform, and load them into a ceramic boat; introduce nitrogen gas at 50 mL / min as a protective atmosphere, raise the temperature to 800℃ at a rate of 5℃ / min, hold the reaction at this temperature for 2 hours, and cool naturally to room temperature to obtain nitrogen-sulfur co-doped porous carbon.
[0038] S6: Take nitrogen-sulfur co-doped porous carbon, add deionized water for ultrasonic dispersion, then add ferric chloride hexahydrate to dissolve it, adjust the pH of the mixture to 10 with 1 mol / L sodium hydroxide solution, stir at 400 r / min for 1 h, keep warm at 80℃ for 2 h, filter and wash, and dry at 105℃ for 6 h to obtain straw-based energy storage material; wherein the mass ratio of nitrogen-sulfur co-doped porous carbon, deionized water and ferric chloride hexahydrate is 1:7:1.5.
[0039] Example 2
[0040] This embodiment provides a method for preparing energy storage materials using straw waste, including the following steps:
[0041] S1: Take dry straw, put it into a pulverizer to crush it to obtain straw powder, add it to a 0.8 mol / L sulfuric acid solution, stir for 1.5 h at 90℃ and 450 r / min to remove ash, filter and wash, and dry at 110℃ for 4 h to obtain pretreated straw powder; wherein the mass ratio of straw powder to acid solution is 1:6.
[0042] S2: Take the pretreated straw powder, add it to deionized water, disperse it ultrasonically, add anhydrous ferrous sulfate and ammonium persulfate in sequence, stir for 0.8 h at 30℃ and 450 r / min, filter and wash, and dry at 110℃ for 6 h to obtain oxidized straw powder; wherein the mass ratio of pretreated straw powder, deionized water, anhydrous ferrous sulfate and ammonium persulfate is 1:7:0.11:0.28;
[0043] S3: Take oxidized straw powder, add deionized water and malic acid, stir at 75℃ and 450r / min for 2.5h, filter and wash, and dry at 110℃ for 4h to obtain modified straw powder; wherein the mass ratio of oxidized straw powder, deionized water and malic acid is 1:3:0.2.
[0044] S4: Take modified straw powder, add melamine, thiourea and deionized water, stir for 1 h at 85℃ and 450 r / min, filter and wash, and dry at 110℃ for 2 h to obtain nitrogen-sulfur doped precursor; wherein the mass ratio of modified straw powder, melamine, thiourea and deionized water is 1:0.9:0.9:5;
[0045] S5: Grind the nitrogen-sulfur doped precursor and KOH at a mass ratio of 1:1.5 until homogeneous, and load them into a ceramic boat; introduce argon gas at 60 mL / min as a protective atmosphere, raise the temperature to 850℃ at a heating rate of 6℃ / min, hold the reaction at this temperature for 1.5 h, and allow it to cool naturally to room temperature to obtain nitrogen-sulfur co-doped porous carbon.
[0046] S6: Take nitrogen-sulfur co-doped porous carbon, add deionized water for ultrasonic dispersion, then add ferrous chloride to dissolve it, adjust the pH of the mixture to 9.5 with 1.5 mol / L potassium hydroxide solution, stir at 450 r / min for 1.5 h, keep warm at 85℃ for 1.5 h, filter and wash, and dry at 110℃ for 4 h to obtain straw-based energy storage material; wherein the mass ratio of nitrogen-sulfur co-doped porous carbon, deionized water and ferrous chloride is 1:8:1.3.
[0047] Example 3
[0048] This embodiment provides a method for preparing energy storage materials using straw waste, including the following steps:
[0049] S1: Take dry straw, put it into a pulverizer to crush it to obtain straw powder, add it to a 2 mol / L nitric acid solution, stir for 3 h at 70℃ and 420 r / min to remove ash, filter and wash, and dry at 100℃ for 8 h to obtain pretreated straw powder; wherein the mass ratio of straw powder to acid solution is 1:3;
[0050] S2: Take the pretreated straw powder, add it to deionized water, disperse it ultrasonically, add ferrous chloride and hydrogen peroxide in sequence, stir for 2 hours at 40℃ and 420r / min, filter and wash, and dry at 100℃ for 8 hours to obtain oxidized straw powder; wherein the mass ratio of pretreated straw powder, deionized water, ferrous chloride and hydrogen peroxide is 1:6:0.1:0.3;
[0051] S3: Take oxidized straw powder, add deionized water and succinic acid, stir for 1 hour at 90℃ and 420r / min, filter and wash, and dry at 100℃ for 8 hours to obtain modified straw powder; wherein the mass ratio of oxidized straw powder, deionized water and succinic acid is 1:5:0.3.
[0052] S4: Take modified straw powder, add ammonium chloride, sodium sulfate and deionized water, stir for 2 hours at 80℃ and 420r / min, filter and wash, and dry at 100℃ for 5 hours to obtain nitrogen-sulfur doped precursor; wherein the mass ratio of modified straw powder, ammonium chloride, sodium sulfate and deionized water is 1:1.2:1.2:7.
[0053] S5: Grind the nitrogen-sulfur doped precursor and KOH at a mass ratio of 1:3 until uniform, and load them into a ceramic boat; introduce nitrogen gas at 30 mL / min as a protective atmosphere, raise the temperature to 900℃ at a heating rate of 3℃ / min, hold the reaction at this temperature for 1 h, and cool naturally to room temperature to obtain nitrogen-sulfur co-doped porous carbon.
[0054] S6: Take nitrogen-sulfur co-doped porous carbon, add deionized water for ultrasonic dispersion, then add ferric chloride hexahydrate to dissolve it, adjust the pH of the mixture to 11 with 0.5 mol / L sodium hydroxide solution, stir at 420 r / min for 0.5 h, keep warm at 70℃ for 3 h, filter and wash, and dry at 100℃ for 8 h to obtain straw-based energy storage material; wherein the mass ratio of nitrogen-sulfur co-doped porous carbon, deionized water and ferric chloride hexahydrate is 1:5:1.2.
[0055] Example 4
[0056] This embodiment provides a method for preparing energy storage materials using straw waste, including the following steps:
[0057] S1: Take dry straw, put it into a pulverizer to crush it to obtain straw powder, add it to a 1.5 mol / L hydrochloric acid solution, stir for 1.2 h at 85℃ and 400 r / min to remove ash, filter and wash, and dry at 108℃ for 5 h to obtain pretreated straw powder; wherein the mass ratio of straw powder to acid solution is 1:8.
[0058] S2: Take the pretreated straw powder, add it to deionized water, ultrasonically disperse it, add ferrous sulfate heptahydrate and ammonium persulfate in sequence, stir for 1.2 h at 35℃ and 400 r / min, filter and wash, and dry at 108℃ for 5 h to obtain oxidized straw powder; wherein the mass ratio of pretreated straw powder, deionized water, ferrous sulfate heptahydrate and ammonium persulfate is 1:7:0.13:0.28;
[0059] S3: Take oxidized straw powder, add deionized water and citric acid, stir for 1.8 h at 85℃ and 400 r / min, filter and wash, and dry at 108℃ for 5 h to obtain modified straw powder; wherein the mass ratio of oxidized straw powder, deionized water and citric acid is 1:4.5:0.25.
[0060] S4: Take modified straw powder, add urea, thiourea and deionized water, stir at 83℃ and 400r / min for 1.8h, filter and wash, and dry at 108℃ for 3h to obtain nitrogen-sulfur doped precursor; wherein the mass ratio of modified straw powder, urea, thiourea and deionized water is 1:1.1:0.96:6;
[0061] S5: Grind the nitrogen-sulfur doped precursor and KOH at a mass ratio of 1:1 until homogeneous, and load them into a ceramic boat; introduce argon gas at 80 mL / min as a protective atmosphere, raise the temperature to 750℃ at a heating rate of 3℃ / min, hold the reaction at this temperature for 2.5 h, and allow it to cool naturally to room temperature to obtain nitrogen-sulfur co-doped porous carbon.
[0062] S6: Take nitrogen-sulfur co-doped porous carbon, add deionized water for ultrasonic dispersion, then add ferric chloride hexahydrate to dissolve it, adjust the pH of the mixture to 10.5 with 1 mol / L potassium hydroxide solution, stir at 400 r / min for 1.2 h, keep warm at 82℃ for 2 h, filter and wash, and dry at 105℃ for 6 h to obtain straw-based energy storage material; wherein the mass ratio of nitrogen-sulfur co-doped porous carbon, deionized water and ferric chloride hexahydrate is 1:6:1.4.
[0063] Comparative Example 1
[0064] This comparative example provides a method for preparing energy storage materials using straw waste. The difference from Example 1 is that the S2 Fenton oxidation step is deleted, and the S3 citric acid crosslinking is carried out directly after the S1 pretreatment. The remaining steps, reagents and parameters are the same as in Example 1.
[0065] Comparative Example 2
[0066] This comparative example provides a method for preparing energy storage materials using straw waste. The difference from Example 1 is that S6 is changed to "mechanically grinding 2g of nitrogen-sulfur co-doped porous carbon and 3g of Fe3O4 powder for 30min, mixing evenly and drying at 105℃". The remaining steps and parameters are the same as in Example 1.
[0067] Comparative Example 3
[0068] This comparative example provides a method for preparing energy storage materials using straw waste. The difference from Example 1 is that the S3 polycarboxylic acid crosslinking step is deleted, and the S4 dopant pre-adsorption is performed directly after S2 Fenton oxidation. The remaining steps, reagents and parameters are the same as in Example 1.
[0069] The energy storage materials prepared from straw waste in Examples 1-4 and Comparative Examples 1-3 of this application were tested for specific capacitance (F / g) of 1A / g, retention rate (%) of 3A / g after 10,000 cycles, retention rate (%) of 10A / g at high rate, and agglomeration rate (%) of Fe3O4.
[0070] Test method:
[0071] 1A / g specific capacitance (F / g): The working electrode is made of active material, acetylene black and polytetrafluoroethylene in a ratio of 8:1:1. With Hg / HgO as reference, platinum sheet as counter electrode and 6mol / L KOH as electrolyte, the current density of 1A / g is used for charging and discharging in the voltage range of -1.0~0V. The specific capacitance is calculated according to the formula C=(I×Δt) / (m×ΔV).
[0072] 3A / g 10000-cycle capacity retention (%): 10000 constant current charge-discharge cycles were performed at a current density of 3A / g. The discharge capacity of each cycle was recorded, and the capacity retention rate after the cycle was calculated as (capacity after cycle / initial capacity × 100%).
[0073] 10A / g high rate retention rate (%): The specific capacitance was tested at 1A / g and 10A / g respectively and the average value was taken. The result was calculated as the ratio of the average value at 10A / g to the average value at 1A / g.
[0074] Table 1. Test results of energy storage materials prepared from straw waste in the examples and comparative examples.
[0075]
[0076] Examples 1-4 of this application utilize the ·OH free radicals generated by Fenton oxidation to break the macromolecular chains of straw cellulose and lignin, directionally introducing active functional groups such as hydroxyl and carboxyl groups. Then, chemical crosslinking is formed through the esterification reaction of polycarboxylic acid crosslinking agents with the active functional groups, constructing a stable three-dimensional molecular framework. Based on the active sites of the modified straw, pre-adsorption and chemical bonding of dopants are achieved. During pyrolysis, N and S atoms are stably doped into the carbon framework through CN and CS chemical bonds. Simultaneously, microporous-mesoporous hierarchical channels are precisely constructed using the chemical etching reaction of KOH with the carbon framework, improving the specific surface area and ion transport efficiency of the material. Finally, using the N and O atoms on the nitrogen-sulfur co-doped carbon surface as coordination sites, Fe... 3+ In-situ hydrolysis-precipitation reaction generates Fe3O4 nanoparticles, forming Fe-N and Fe-O chemical bonded loads, avoiding the particle agglomeration and shedding problems caused by traditional physical composites. Ultimately, it achieves a triple synergistic improvement in carbon framework double-layer capacitance, heteroatom N / S pseudocapacitance, and Fe3O4 redox pseudocapacitance, while ensuring the structural stability of the material during long-cycle, high-rate charge-discharge processes.
[0077] Comparative Example 1, due to the removal of the Fenton oxidation step, cannot break the straw macromolecular chain at the molecular level by relying solely on physical pretreatment. The introduction of active functional groups is severely insufficient, resulting in low efficiency of subsequent crosslinking and doping, disordered pore structure, lack of energy storage active sites, and a significant decrease in specific capacitance and rate performance.
[0078] Comparative Example 2 replaced the in-situ bonding composite of Fe3O4 with physical grinding and mixing. The particles and carbon-based materials were only bonded by van der Waals forces, resulting in extremely weak interfacial bonding. This not only led to severe agglomeration with an agglomeration rate of 42.6%, but also caused particle shedding during charge and discharge, resulting in extremely poor cycle stability.
[0079] Comparative Example 3 omits the polycarboxylic acid crosslinking step, lacks a stable three-dimensional framework support, and the carbon framework is prone to collapse and the pore structure is damaged during pyrolysis. The active sites are easily lost and cannot withstand high-rate charge and discharge shocks. Ultimately, the performance of all three is far lower than that of the embodiments of the present invention.
[0080] It should be understood that the above are only some embodiments of the present invention. It should be pointed out that for those skilled in the art, other modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.
Claims
1. A method for preparing energy storage materials using straw waste, characterized in that, Includes the following steps: S1: Take dry straw, put it into a crusher to crush it to obtain straw powder, add it to an acid solution, stir to remove ash, filter and wash, and then dry to obtain pretreated straw powder; S2: Take the pretreated straw powder, add deionized water, ultrasonically disperse, add ferrous salt and oxidant in sequence, stir, filter and wash, and dry to obtain oxidized straw powder; S3: Take oxidized straw powder, add deionized water and polycarboxylic acid crosslinking agent, stir, filter, wash and dry to obtain modified straw powder; S4: Take modified straw powder, add nitrogen source, sulfur source and deionized water, stir, filter and wash, and then dry to obtain nitrogen-sulfur doped precursor; S5: Grind the nitrogen-sulfur doped precursor and KOH evenly, put them into a reaction vessel, introduce an inert gas as a protective atmosphere, heat up to react, and then cool naturally to room temperature to obtain nitrogen-sulfur co-doped porous carbon. S6: Take nitrogen-sulfur co-doped porous carbon, add deionized water for ultrasonic dispersion, add iron salt to dissolve, adjust the pH of the mixture with alkali solution, stir, keep warm in water bath, filter and wash, and dry to obtain straw-based energy storage material.
2. The method for preparing energy storage materials using straw waste according to claim 1, characterized in that, The ferrous salt includes any one of ferrous sulfate heptahydrate, anhydrous ferrous sulfate, and ferrous chloride; the oxidant includes any one of hydrogen peroxide and ammonium persulfate; and the polycarboxylic acid crosslinking agent includes any one of citric acid, malic acid, and succinic acid.
3. The method for preparing energy storage materials using straw waste according to claim 1, characterized in that, The nitrogen source is any one of urea, melamine, and ammonium chloride; the sulfur source is any one of thiourea and sodium sulfate.
4. The method for preparing energy storage materials using straw waste according to claim 1, characterized in that, The iron salt includes any one of ferric chloride hexahydrate, ferrous chloride, and ferric sulfate.
5. The method for preparing energy storage materials using straw waste according to claim 1, characterized in that, In step S1, the mass ratio of straw powder to acid solution is 1:(3-8); the concentration of the acid solution is 0.8-2 mol / L; the acid solution includes any one of hydrochloric acid solution, sulfuric acid solution, and nitric acid solution; the conditions for stirring and deashing are: stirring speed 400-450 r / min, temperature 70-90℃, time 1-3 h; the pH of the filtrate obtained by vacuum filtration and washing is 6.5-7.5; the conditions for drying are: temperature 100-110℃, time 4-8 h.
6. The method for preparing energy storage materials using straw waste according to claim 1, characterized in that, In step S2, the mass ratio of pretreated straw powder, deionized water, ferrous salt, and oxidant is 1:(5-8):(0.1-0.15):(0.25-0.3); the stirring conditions are: stirring speed 400-450 r / min, temperature 20-40℃, time 0.5-2 h; the drying conditions are: temperature 100-110℃, time 4-8 h.
7. The method for preparing energy storage materials using straw waste according to claim 1, characterized in that, In step S3, the mass ratio of oxidized straw powder, deionized water, and polycarboxylic acid crosslinking agent is 1:(3-5):(0.2-0.3); the stirring conditions are: stirring speed 400-450 r / min, temperature 70-90℃, time 1-3 h; the drying conditions are: temperature 100-110℃, time 4-8 h.
8. A method for preparing energy storage materials using straw waste according to claim 1, characterized in that, In step S4, the mass ratio of modified straw powder, nitrogen source, sulfur source and deionized water is 1:(0.8-1.2):(0.8-1.2):(5-6); the stirring conditions are: stirring speed 400-450 r / min, temperature 80-85℃, time 1-3 h; the drying conditions are: temperature 100-110℃, time 2-5 h.
9. A method for preparing energy storage materials using straw waste according to claim 1, characterized in that, In step S5, the mass ratio of nitrogen-sulfur doped precursor to KOH is 1:(1-3); the inert gas includes either nitrogen or argon, and the gas flow rate is 30-80 mL / min; the reaction temperature is 750-900℃.
10. A method for preparing energy storage materials using straw waste according to claim 1, characterized in that, In step S6, the mass ratio of nitrogen-sulfur co-doped porous carbon, deionized water, and iron salt is 1:(5-8):(1.2-1.5); the alkaline solution is a 0.5-1.5 mol / L sodium hydroxide solution or potassium hydroxide solution; the pH of the mixture is adjusted to 9-11; the stirring conditions are: stirring speed 400-450 r / min, stirring time 0.5-2 h; the water bath temperature is 70-90℃, time 1-3 h; the pH of the filtrate obtained by vacuum filtration and washing is 6.5-7.5; the drying conditions are: temperature 100-110℃, time 4-8 h.