Preparation method and application of long-circulation high-compaction biomass hard carbon negative electrode material

Abstract

The invention provides a preparation method and application of a long-circulation high-compaction biomass hard carbon negative electrode material, and the preparation method comprises the following steps: adding a pretreated biomass raw material into a mixed solution of Zn (NO3) 2 and NaOH for treatment, pre-carbonizing, crushing and purifying after treatment, uniformly mixing the purified material and an impregnant, and circularly mechanically forging and pressing to obtain a densified body, thereby obtaining the long-circulation high-compaction biomass hard carbon negative electrode material. And then carrying out high-temperature heat treatment, depolymerization and surface modification to obtain the long-circulation high-compaction biomass hard carbon negative electrode material. According to the invention, the material is subjected to combined treatment of alkali liquor and zinc nitrate before pre-carbonization, so that the material can form a microporous and mesoporous graded porous structure in the carbonization process, the structural stability of the material is improved, the sodium storage performance is optimized, and the cycle performance is improved; and then the gas production of the battery is controlled and the cycle performance is improved through pickling purification, and a densified body fully permeated by the impregnant is obtained through circulating mechanical forging and pressing, so that the energy density of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass hard carbon, and particularly to a preparation method and application of a long-cycle and high-compaction biomass hard carbon anode material. Background Art

[0002] The popularization and application of battery products are advancing rapidly. Considering safety performance and low cost, sodium-ion batteries with abundant sodium resources and similar structures have become the top candidates for lithium-ion batteries. Their industrial chains are generally the same. In terms of anode materials, due to the very poor sodium storage performance of traditional graphite anodes and the thermodynamic instability of sodium-graphite compounds, non-graphite disordered carbon materials have emerged. Non-graphite carbon materials mainly include two categories: hard carbon (biomass hard carbon, resin hard carbon, fossil hard carbon, plastic hard carbon, etc.) and soft carbon (coke, mesophase carbon microspheres, carbon fibers, etc.).

[0003] Currently, biomass raw materials are usually used as carbon sources to prepare hard carbon anode materials for sodium-ion batteries. The biomass raw materials are processed through pre-carbonization, high-temperature carbonization, pulverization and other processes to obtain the final hard carbon anode materials. However, the prepared biomass hard carbon materials still show poor performance in terms of compaction density, cycle stability, Coulomb efficiency, etc., resulting in bottlenecks in the development of sodium-ion batteries and having a greater impact on promoting the application of sodium-ion batteries. Therefore, developing a biomass hard carbon anode material with excellent cycle performance and high compaction and its preparation method is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a preparation method of a long-cycle and high-compaction biomass hard carbon anode material to solve the problems of poor cycle performance and insufficient compaction density of the biomass hard carbon anode materials prepared in the prior art. At the same time, the present invention also provides a long-cycle and high-compaction biomass hard carbon anode material and its application.

[0005] To achieve the above purpose and other related purposes, the present invention provides the following technical solutions: In the first aspect of the present invention, a preparation method of a long-cycle and high-compaction biomass hard carbon anode material is provided, including the following steps: (1) Cleaning and drying the biomass raw material to obtain a pretreated material; (2) Adding the pretreated material obtained in step (1) to a mixed solution of Zn(NO3)2 and NaOH, stirring evenly by ultrasonic, standing at room temperature for a period of time, and obtaining a dried material after filtration, suction filtration and drying; (3) Under an inert atmosphere, performing pre-carbonization treatment on the dried material obtained in step (2) to obtain a pre-carbonized material; (4) Pulverizing the pre-carbonized material obtained in step (3) to obtain a pulverized material; (5) The crushed material obtained in step (4) is first subjected to acid washing for impurity removal and then water washing, and then filtered and dried to obtain a purified material; (6) The purified material obtained in step (5) is mixed evenly with an impregnating agent, and then subjected to cyclic mechanical forging to obtain a densified body; (7) Under an inert atmosphere, the densified body obtained in step (6) is subjected to high-temperature heat treatment, and after cooling, depolymerization is carried out to obtain a depolymerized material; (8) The depolymerized material obtained in step (7) is mixed evenly with a modifier, and then surface modification is carried out under an inert atmosphere. After cooling, a long-cycle high-compaction biomass hard carbon negative electrode material is obtained.

[0006] On the one hand, before the pyrolysis of the material, the present invention first performs a combined treatment of zinc nitrate and alkali solution on it to make it reverse crystallize, increase entropy, improve the material disorder degree, and enable the material to form a hierarchical porous structure of micropores + mesopores during the carbonization process, maintain the stability of the amorphous state of hard carbon, and optimize the sodium storage performance. On the other hand, the present invention performs cyclic mechanical forging on the purified material, and cooperates with the impregnating agent to fill the pores, improving the bulk density of the material, thereby improving the energy density of the battery. On the further hand, high-temperature heat treatment and surface modification can reduce the content of oxygen-containing functional groups (such as carboxyl groups and hydroxyl groups) on the material surface, reduce the interfacial resistance. After the stable SEI film is formed during the first charge and discharge, it can effectively prevent the co-insertion of solvent molecules, avoid the damage to the battery system caused by the co-insertion of solvent molecules, and thus significantly improve the cycle performance and service life of the sodium-ion battery. Therefore, the present invention can effectively reduce the capacity attenuation during the charge and discharge process of the battery and improve the service life of the battery by improving the stability of the internal structure of the material and optimizing the surface functional groups.

[0007] In an embodiment of the present invention, the biomass raw material in step (1) is selected from any one of hazelnut shells, coconut shells, and almond shells.

[0008] In an embodiment of the present invention, in step (1), the biomass raw material is first rinsed clean with pure water, the surface moisture is filtered off, and then dried in a drying oven to obtain a pretreated material.

[0009] Further, the drying temperature of the drying oven is 50-150 °C, and the drying time is 8-48 h.

[0010] In an embodiment of the present invention, in step (2), the concentration of the Zn(NO3)2 solution is 0.01-0.5 mol / L, and the concentration of the NaOH solution is 0.01-0.5 mol / L.

[0011] Compared with the treatment of biomass materials with a single alkali solution, the alkali solution will corrode the natural fiber structure in the materials, which is prone to collapse during the subsequent high-temperature carbonization process, resulting in an unstable SEI film formed during the first charge and discharge, leading to poor cycle stability; moreover, mainly micropores are formed in the materials after alkali treatment, and too high a proportion of micropores will lead to poor electrolyte wettability and large ion transport resistance.

[0012] In the present invention, however, Zn(NO3)2 will generate Zn(OH)2 or ZnO nanoparticles under alkaline conditions. These particles can serve as "hard templates" to form mesoporous structures during the biomass carbonization process, cooperate with the alkali solution to form a hierarchical porous structure of micropores + mesopores in the materials, improve the electrolyte wettability, and optimize the sodium storage performance; during the subsequent carbonization process, Zn(OH)2 / ZnO is partially reduced to metallic Zn and volatilized (or remains as a ZnO doping phase), leaving conductive channels, reducing the material resistance, and improving the rate performance; and the remaining Zn or ZnO is evenly distributed in the carbon matrix, which helps to form a more stable SEI film and improve the long-cycle performance.

[0013] Furthermore, the mass ratio of the Zn(NO3)2 solution to the NaOH solution is 1:0.5~3, and this mixing ratio can obtain a more optimal mesopore / micropore ratio.

[0014] In an embodiment of the present invention, in step (2), the mass ratio of the pretreated material to the mixed solution of Zn(NO3)2 and NaOH is 1:0.5~3.

[0015] In an embodiment of the present invention, in step (2), the room temperature standing time is 8~48 hours.

[0016] In an embodiment of the present invention, in step (2), the drying temperature is 50~100 °C, and the drying time is 6~24 h.

[0017] In an embodiment of the present invention, in steps (3) and (7), the inert atmosphere is selected from at least one of nitrogen, helium, and argon.

[0018] In an embodiment of the present invention, in step (3), the conditions for the pre-carbonization treatment are: the heating rate is 1~10 °C / min, the pre-carbonization temperature is 200~800 °C, the holding time is 1~8 h, and the pre-carbonization treatment is carried out in an electric furnace.

[0019] In an embodiment of the present invention, in step (4), the equipment used for pulverization is selected from at least one of a classification impact mill, a roller press mill, an ultrafine mill, and a jet pulverizer classifier.

[0020] In an embodiment of the present invention, in step (4), the particle size D 50 is controlled at 4~10 um.

[0021] In one embodiment of the present invention, in step (5), the acid used for pickling is selected from at least one of hydrofluoric acid, hydrochloric acid, and nitric acid; Furthermore, the concentration of the acid is 0.5 - 8 mol / L; Furthermore, the reaction temperature for pickling is 60 - 100 °C; Furthermore, the solid - liquid mass ratio for pickling is 1:1 - 6; Furthermore, the pickling time is 8 - 24 h.

[0022] In one embodiment of the present invention, in step (5), the drying temperature is 80 - 150 °C and the drying time is 12 - 48 h.

[0023] In one embodiment of the present invention, in step (6), the impregnating agent is selected from at least one of petroleum - based pitch and coal - based pitch, and its softening point is 100 - 260 °C.

[0024] In one embodiment of the present invention, in step (6), the mass ratio of the purified material to the impregnating agent is 100:1 - 10.

[0025] In one embodiment of the present invention, in step (6), the compacting density of the densified body is pressed to 1 - 1.6 g / cm through cyclic mechanical forging 3 .

[0026] In one embodiment of the present invention, in step (7), the conditions for high - temperature heat treatment are: the heating rate is 1 - 10 °C / min, the high - temperature holding temperature is 1100 - 1500 °C, the holding time is 3 - 6 h, and the high - temperature heat treatment is carried out in an atmosphere high - temperature furnace.

[0027] In one embodiment of the present invention, in step (7), the equipment used for depolymerization is selected from at least one of a depolymerizer and a turbo - crusher.

[0028] In one embodiment of the present invention, in step (7), the particle size D of the depolymerized material 50 is controlled to be 4 - 10 μm.

[0029] In one embodiment of the present invention, in step (8), the modifier is selected from at least one of phenolic resin, epoxy resin, and asphalt composite β - resin, and the coking value of the modifier is 40 - 70%.

[0030] In one embodiment of the present invention, in step (8), the mass ratio of the modifier to the depolymerized material is 1 - 10:100.

[0031] In one embodiment of the present invention, in step (8), the conditions for surface modification are: the heating rate is 1 - 10 °C / min, the high - temperature holding temperature is 800 - 1500 °C, and the holding time is 3 - 6 h.

[0032] In a second aspect of the present invention, there is provided a long-cycle and high-compaction biomass hard carbon anode material obtained by the above preparation method.

[0033] In a third aspect of the present invention, there is provided an application of the above long-cycle and high-compaction biomass hard carbon anode material in a sodium-ion battery.

[0034] As described above, a preparation method and an application of a long-cycle and high-compaction biomass hard carbon anode material of the present invention have the following beneficial effects: 1. Before pre-carbonizing the biomass raw material, the present invention first performs a combined treatment of an alkali solution and zinc nitrate on it, enabling the material to form a hierarchical porous structure of micropores + mesopores during the carbonization process, and controlling the micropore / mesopore ratio by concentration and proportion, thereby improving the structural stability of the material and optimizing the sodium storage performance.

[0035] 2. After pre-carbonization, the present invention performs pickling to remove impurities, reducing the content of impurity elements in the pre-carbonized material, reducing the influence of side reactions during battery cycling, effectively controlling battery gas generation and improving cycling performance; and after mixing the purified material with an impregnating agent, cyclic mechanical forging is carried out. The impregnating agent can fill the pores, and multiple cycles of pressurization - depressurization can gradually compress the gaps between hard carbon particles and the internal macropores, and enable the impregnating agent to fully penetrate into microcracks and pores under cyclic pressure to form a denser composite body, improving the battery energy density; and this densified structure can limit the excessive penetration of the electrolyte, form a thinner SEI film, and improve the initial efficiency.

[0036] 3. The present invention performs high-temperature heat treatment and surface modification on the densified body, reducing the specific surface area of the material, improving defects, enhancing the initial efficiency, and extending the battery service life; and surface modification can optimize the surface functional groups of hard carbon, reduce the interfacial resistance, and reduce the loss of reversible capacity. Description of the Drawings

[0037] Figure 1 It is a charge-discharge test chart of Example 1 and Comparative Example 1 at a current density of 0.1C.

[0038] Figure 2 It is an SEM chart of the long-cycle and high-compaction biomass hard carbon anode material prepared in Example 1.

[0039] Figure 3 It is a 1C / 1C cycle chart of a full electric soft-pack battery made of the long-cycle and high-compaction biomass hard carbon anode material of Example 1. Detailed Embodiments

[0040] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0041] Example 1 A long-cycle high-compaction biomass hard carbon anode material, and its preparation method is as follows: (1) Rinse the hazelnut shells with pure water, filter to remove surface moisture, and dry them in an oven at 105 °C for 41 h to obtain a pretreated material after drying the moisture; (2) Add the pretreated material obtained in step (1) to a mixed solution of Zn(NO3)2 solution and NaOH solution. After ultrasonic stirring evenly, let it stand at room temperature for 10 h, filter and then perform suction filtration, and then put it into an oven and dry it at 65 °C for 18 h to obtain a dried material; among them, the concentration of the Zn(NO3)2 solution is 0.05 mol / L, the concentration of the NaOH solution is 0.1 mol / L, the mass ratio of the Zn(NO3)2 solution to the NaOH solution is 1:1.2, and the mass ratio of the pretreated material to the mixed solution is 1:1.6; (3) Put the dried material into an electric furnace, and under a nitrogen atmosphere, heat it up to 520 °C at a heating rate of 3 °C / min and pyrolyze and regulate it for 3 h to obtain a pre-carbonized material; (4) Crush the pre-carbonized material with an air-flow crushing and grading machine to obtain a crushed material, and the particle size D 50 is controlled to be about 7 μm; (5) Add the crushed material to a HCl solution with a concentration of 5 mol / L, with a solid-liquid mass ratio of 1:2.8, and carry out acid washing and impurity removal at a temperature of 85 °C and a holding time of 10 h. After acid washing, wash it with pure water multiple times until the filtrate is close to neutral, then perform suction filtration to remove part of the water, and put it into an oven and dry it at 85 °C for 32 h to obtain a purified material; (6) Mix the purified material obtained in step (5) with petroleum-based asphalt with a softening point of 130 °C evenly at a ratio of 100:6, and then carry out cyclic mechanical forging and pressing until the compaction density reaches 1.6 g / cm 3 to obtain a densified body; (7) Put the densified body into an atmosphere high-temperature furnace, and under a nitrogen atmosphere, heat it up to 1400 °C at a heating rate of 3 °C / min, hold it at high temperature for 4 h, cool it, and then use a depolymerizer for depolymerization. The particle size D of the depolymerized material after depolymerization 50 is controlled to be about 7 μm; (8) Mix the depolymerized material obtained in step (7) with asphalt composite β-resin with a coking value of 65% evenly at a mass ratio of 100:2, put it into an atmosphere high-temperature furnace, and then under a nitrogen atmosphere, heat it up to 900 °C at a heating rate of 3 °C / min, hold it at high temperature for 5 h, and cool it to obtain a long-cycle high-compaction biomass hard carbon anode material.

[0042] Example 2 A long-cycle high-compaction biomass hard carbon anode material, and its preparation method is as follows: (1) Rinse the almond shells thoroughly with pure water, filter to remove surface moisture, and dry them in an oven at 105 °C for 41 h to obtain a pretreated material after drying the moisture. (2) Add the pretreated material obtained in step (1) to a mixed solution of Zn(NO3)2 solution and NaOH solution. After ultrasonic stirring to uniformity, let it stand at room temperature for 10 h, filter and then perform suction filtration, and then put it into an oven to dry at 65 °C for 18 h to obtain a dried material; among them, the concentration of the Zn(NO3)2 solution is 0.05 mol / L, the concentration of the NaOH solution is 0.1 mol / L, the mass ratio of the Zn(NO3)2 solution to the NaOH solution is 1:1.2, and the mass ratio of the pretreated material to the mixed solution is 1:1.6. (3) Put the dried material into an electric furnace, under a nitrogen atmosphere, heat it up to 520 °C at a heating rate of 3 °C / min, and pyrolyze and control for 3 h to obtain a pre-carbonized material. (4) Crush the pre-carbonized material with an air flow crushing and grading machine to obtain a crushed material, and the particle size D 50 is controlled at about 7 μm. (5) Add the crushed material to an HF solution with a concentration of 4 mol / L, with a solid-liquid mass ratio of 1:2.8, carry out acid washing and impurity removal under the conditions of a temperature of 85 °C and a heat preservation time of 10 h. After acid washing, wash it with pure water multiple times until the filtrate is close to neutral, then perform suction filtration to remove part of the water, and put it into an oven to dry at 85 °C for 32 h to obtain a purified material. (6) Mix the purified material obtained in step (5) with a petroleum-based asphalt with a softening point of 130 °C evenly at a ratio of 100:6, and then carry out cyclic mechanical forging and pressing until the compaction density is pressed to 1.6 g / cm 3 to obtain a densified body. (7) Put the densified body into an atmosphere high-temperature furnace, under a nitrogen atmosphere, heat it up to 1400 °C at a heating rate of 3 °C / min, keep it at high temperature for 4 h, cool it, and then use a depolymerizer for depolymerization. The particle size D of the depolymerized material after depolymerization 50 is controlled at about 7 μm. (8) Mix the depolymerized material obtained in step (7) with an asphalt composite β-resin with a coking value of 65% evenly at a mass ratio of 100:2, put it into an atmosphere high-temperature furnace, and then under a nitrogen atmosphere, heat it up to 900 °C at a heating rate of 3 °C / min, keep it at high temperature for 5 h, and cool it to obtain a long-cycle high-compaction biomass hard carbon negative electrode material.

[0043] Example 3 A long-cycle high-compaction biomass hard carbon negative electrode material, and its preparation method is as follows: (1) Rinse the coconut shells thoroughly with pure water, filter to remove surface moisture, and dry them in an oven at 105 °C for 41 h to obtain a pretreated material after drying the moisture. (2) Add the pretreated material obtained in step (1) into the mixed solution of Zn(NO3)2 solution and NaOH solution. After ultrasonic stirring evenly, let it stand at room temperature for 10 h, filter and then perform suction filtration, and then put it into a drying oven and dry at 65 °C for 18 h to obtain a dried material; wherein, the concentration of the Zn(NO3)2 solution is 0.05 mol / L, the concentration of the NaOH solution is 0.1 mol / L, the mass ratio of the Zn(NO3)2 solution to the NaOH solution is 1:1.2, and the mass ratio of the pretreated material to the mixed solution is 1:1.6; (3) Put the dried material into an electric furnace, under a nitrogen atmosphere, heat it up to 520 °C at a heating rate of 3 °C / min, and pyrolyze and regulate for 3 h to obtain a pre-carbonized material; (4) Crush the pre-carbonized material with a pneumatic crushing and classification machine to obtain a crushed material, and the particle size D of the crushed material 50 is controlled at about 7 μm; (5) Add the crushed material into a HNO3 solution with a concentration of 3 mol / L, with a solid-liquid mass ratio of 1:2.8, and perform acid washing and impurity removal at a temperature of 85 °C and a holding time of 10 h. After acid washing, wash it with pure water multiple times until the filtrate is close to neutral, then perform suction filtration to remove part of the water, and put it into a drying oven and dry at 85 °C for 32 h to obtain a purified material; (6) Mix the purified material obtained in step (5) with petroleum-based asphalt with a softening point of 130 °C in a ratio of 100:6 evenly, and then perform cyclic mechanical forging and pressing, and press the compaction density to 1.6 g / cm 3 to obtain a densified body; (7) Put the densified body into an atmosphere high-temperature furnace, under a nitrogen atmosphere, heat it up to 1400 °C at a heating rate of 3 °C / min, hold at high temperature for 4 h, cool and then use a depolymerizer for depolymerization. The particle size D of the depolymerized material 50 is controlled at about 7 μm; (8) Mix the depolymerized material obtained in step (7) with asphalt composite β-resin with a coking value of 65% in a mass ratio of 100:2 evenly, put it into an atmosphere high-temperature furnace, and then under a nitrogen atmosphere, heat it up to 900 °C at a heating rate of 3 °C / min, hold at high temperature for 5 h, and cool to obtain a long-cycle high-compaction biomass hard carbon anode material.

[0044] Example 4 A long-cycle high-compaction biomass hard carbon anode material, and its preparation method is as follows: (1) Rinse the hazelnut shell with pure water, filter to remove the surface moisture, and dry it in a drying oven at 120 °C for 8 h to obtain a pretreated material after drying the moisture; (2) Add the pretreated material obtained in step (1) to the mixed solution of Zn(NO3)2 solution and NaOH solution. After ultrasonic stirring evenly, let it stand at room temperature for 10 h, filter and then perform suction filtration, and then put it into a drying oven and dry at 65 °C for 18 h to obtain a dried material; among them, the concentration of Zn(NO3)2 solution is 0.03 mol / L, the concentration of NaOH solution is 0.05 mol / L, the mass ratio of Zn(NO3)2 solution to NaOH solution is 1:1.2, and the mass ratio of the pretreated material to the mixed solution is 1:1.6; (3) Put the dried material into an electric furnace, and under a nitrogen atmosphere, heat it up to 400 °C at a heating rate of 1 °C / min and pyrolyze and control for 2 h to obtain a pre-carbonized material; (4) Crush the pre-carbonized material with a pneumatic crushing and classification machine to obtain a crushed material, and the particle size D of the crushed material 50 is controlled at about 7 μm; (5) Add the crushed material to a HCl solution with a concentration of 2 mol / L, with a solid-liquid mass ratio of 1:1. Perform acid washing and impurity removal at a temperature of 60 °C and a heat preservation time of 8 h. After acid washing, wash it with pure water several times until the filtrate is close to neutral, then perform suction filtration to remove part of the water, and put it into a drying oven and dry at 85 °C for 12 h to obtain a purified material; (6) Mix the purified material obtained in step (5) with petroleum-based asphalt with a softening point of 130 °C in a ratio of 100:6 evenly, and then perform cyclic mechanical forging and pressing to compress the compaction density to 1.0 g / cm 3 to obtain a densified body; (7) Put the densified body into an atmosphere high-temperature furnace, and under a nitrogen atmosphere, heat it up to 1100 °C at a heating rate of 3 °C / min, keep it at high temperature for 3 h, cool it, and then use a depolymerizer for depolymerization. The particle size D of the depolymerized material 50 is controlled at about 7 μm; (8) Mix the depolymerized material obtained in step (7) with phenolic resin with a coking value of 50% in a mass ratio of 100:5 evenly, put it into an atmosphere high-temperature furnace, and then under a nitrogen atmosphere, heat it up to 800 °C at a heating rate of 4 °C / min, keep it at high temperature for 3 h, and cool it to obtain a long-cycle high-compaction biomass hard carbon anode material.

[0045] Example 5 A long-cycle high-compaction biomass hard carbon anode material, and its preparation method is as follows: (1) Rinse the hazelnut shells with pure water, filter to remove the surface moisture, and dry them in a drying oven at 105 °C for 41 h to obtain a pretreated material after drying the moisture; (2) Add the pre-treated material obtained in step (1) to the mixed solution of Zn(NO3)2 solution and NaOH solution. After ultrasonic stirring evenly, let it stand at room temperature for 10 h, filter and then perform suction filtration, and then put it into a drying oven and dry at 65 °C for 18 h to obtain a dried material; wherein, the concentration of the Zn(NO3)2 solution is 0.1 mol / L, the concentration of the NaOH solution is 0.1 mol / L, the mass ratio of the Zn(NO3)2 solution to the NaOH solution is 1:3, and the mass ratio of the pre-treated material to the mixed solution is 1:1.6; (3) Put the dried material into an electric furnace, and under a nitrogen atmosphere, heat it up to 520 °C at a heating rate of 3 °C / min and pyrolyze and control for 3 h to obtain a pre-carbonized material; (4) Crush the pre-carbonized material with a pneumatic crushing and classification machine to obtain a crushed material, and the particle size D of the crushed material 50 is controlled at about 7 μm; (5) Add the crushed material to a HCl solution with a concentration of 5 mol / L, with a solid-liquid mass ratio of 1:2.8, and carry out acid washing and impurity removal at a temperature of 85 °C and a holding time of 10 h. After acid washing, wash it with pure water several times until the filtrate is close to neutral, then perform suction filtration to remove part of the water, and put it into a drying oven and dry at 85 °C for 32 h to obtain a purified material; (6) Mix the purified material obtained in step (5) with a petroleum-based pitch with a softening point of 130 °C in a ratio of 100:6 evenly, and then carry out cyclic mechanical forging and pressing to compress the compaction density to 1.6 g / cm 3 to obtain a densified body; (7) Put the densified body into an atmosphere high-temperature furnace, and under a nitrogen atmosphere, heat it up to 1400 °C at a heating rate of 3 °C / min, hold it at high temperature for 4 h, cool it, and then use a depolymerizer to depolymerize it. The particle size D of the depolymerized material 50 is controlled at about 7 μm; (8) Mix the depolymerized material obtained in step (7) with a pitch composite β-resin with a coking value of 65% in a mass ratio of 100:2 evenly, put it into an atmosphere high-temperature furnace, and then under a nitrogen atmosphere, heat it up to 900 °C at a heating rate of 3 °C / min, hold it at high temperature for 5 h, and cool it to obtain a long-cycle high-compaction biomass hard carbon negative electrode material.

[0046] Comparative Example 1 A biomass hard carbon negative electrode material, and its preparation method is as follows: (1) Rinse the hazelnut shells with pure water, filter to remove the surface moisture, and dry them in a drying oven at 105 °C for 41 h to obtain a pre-treated material after drying the moisture; (2) Add the pretreated material obtained in step (1) into the NaOH solution. After ultrasonic stirring to make it uniform, let it stand at room temperature for 10 h. After filtration, perform suction filtration, and then put it into a drying oven and dry at 65 °C for 18 h to obtain a dried material. Among them, the concentration of the NaOH solution is 0.1 mol / L, and the mass ratio of the pretreated material to the NaOH solution is 1:1.6; (3) Put the dried material into an electric furnace. Under a nitrogen atmosphere, heat it up to 520 °C at a heating rate of 3 °C / min and pyrolyze and control for 3 h to obtain a pre-carbonized material; (4) Crush the pre-carbonized material with a pneumatic grinding and classification machine to obtain a crushed material, and the particle size D of the crushed material 50 is controlled at about 7 μm; (5) Add the crushed material into a HCl solution with a concentration of 5 mol / L, with a solid-liquid mass ratio of 1:2.8. Perform acid washing for impurity removal under the conditions of a temperature of 85 °C and a heat preservation time of 10 h. After acid washing, wash it with pure water multiple times until the filtrate is close to neutral, then perform suction filtration to remove part of the moisture, and put it into a drying oven and dry at 85 °C for 32 h to obtain a purified material; (6) Mix the purified material obtained in step (5) with a petroleum-based asphalt with a softening point of 130 °C in a ratio of 100:6 and mix evenly, and then perform cyclic mechanical forging and pressing until the compaction density reaches 1.6 g / cm 3 to obtain a densified body; (7) Put the densified body into an atmosphere high-temperature furnace. Under a nitrogen atmosphere, heat it up to 1400 °C at a heating rate of 3 °C / min, keep it at a high temperature for 4 h, and after cooling, use a depolymerizer for depolymerization. The particle size D of the depolymerized material after depolymerization 50 is controlled at about 7 μm; (8) Mix the depolymerized material obtained in step (7) with an asphalt composite β-resin with a coking value of 65% in a mass ratio of 100:2 and mix evenly. Put it into an atmosphere high-temperature furnace, and then under a nitrogen atmosphere, heat it up to 900 °C at a heating rate of 3 °C / min, keep it at a high temperature for 5 h, and after cooling, obtain a biomass hard carbon negative electrode material.

[0047] Comparative Example 2 A biomass hard carbon negative electrode material, and its preparation method is as follows: (1) Rinse the hazelnut shells with pure water, filter to remove the surface moisture, and dry them in a drying oven at 105 °C for 41 h to obtain a pretreated material after drying the moisture; (2) Add the pretreated material obtained in step (1) to the mixed solution of Zn(NO3)2 solution and NaOH solution. After ultrasonic stirring evenly, let it stand at room temperature for 10 h, filter and then perform suction filtration, and then put it into a drying oven to dry at 65 °C for 18 h to obtain a dried material; wherein, the concentration of the Zn(NO3)2 solution is 0.05 mol / L, the concentration of the NaOH solution is 0.1 mol / L, the mass ratio of the Zn(NO3)2 solution to the NaOH solution is 1:1.2, and the mass ratio of the pretreated material to the mixed solution is 1:1.6; (3) Put the dried material into an electric furnace, and under a nitrogen atmosphere, heat it up to 520 °C at a heating rate of 3 °C / min and pyrolyze and control for 3 h to obtain a pre-carbonized material; (4) Crush the pre-carbonized material with a pneumatic crushing and classifying machine to obtain a crushed material, and the particle size D of the crushed material 50 is controlled at about 7 μm; (5) Add the crushed material to a HCl solution with a concentration of 5 mol / L, with a solid-liquid mass ratio of 1:2.8, carry out acid washing and impurity removal at a temperature of 85 °C and a heat preservation time of 10 h. After acid washing, wash it with pure water several times until the filtrate is close to neutral, then perform suction filtration to remove part of the water, and put it into a drying oven to dry at 85 °C for 32 h to obtain a purified material; (6) Put the purified material into an atmosphere high-temperature furnace, and under a nitrogen atmosphere, heat it up to 1400 °C at a heating rate of 3 °C / min, keep it at high temperature for 4 h, cool it, and then use a depolymerizer for depolymerization. The particle size D of the depolymerized material 50 is controlled at about 7 μm; (7) Mix the depolymerized material obtained in step (6) with pitch composite β-resin with a coking value of 65% evenly at a mass ratio of 100:2, put it into an atmosphere high-temperature furnace, and then under a nitrogen atmosphere, heat it up to 900 °C at a heating rate of 3 °C / min, keep it at high temperature for 5 h, and cool it to obtain a biomass hard carbon anode material.

[0048] Comparative Example 3 A biomass hard carbon anode material, and its preparation method is as follows: (1) Rinse the hazelnut shells clean with pure water, filter to remove the surface moisture, and dry them in a drying oven at 105 °C for 41 h to obtain a pretreated material after drying the moisture; (2) Add the pretreated material obtained in step (1) to the mixed solution of Zn(NO3)2 solution and NaOH solution. After ultrasonic stirring evenly, let it stand at room temperature for 10 h, filter and then perform suction filtration, and then put it into a drying oven to dry at 65 °C for 18 h to obtain a dried material; wherein, the concentration of the Zn(NO3)2 solution is 0.05 mol / L, the concentration of the NaOH solution is 0.1 mol / L, the mass ratio of the Zn(NO3)2 solution to the NaOH solution is 1:1.2, and the mass ratio of the pretreated material to the mixed solution is 1:1.6; (3) Put the dried material into an electric furnace and heat it to 520 °C at a heating rate of 3 °C / min under a nitrogen atmosphere, and pyrolyze and regulate for 3 h to obtain a pre-carbonized material; (4) Crush the pre-carbonized material with a pneumatic crushing and classifying machine to obtain a crushed material, and control the particle size D of the crushed material 50 to be about 7 μm; (5) Add the crushed material into a HCl solution with a concentration of 5 mol / L, with a solid-liquid mass ratio of 1:2.8, carry out acid washing and impurity removal at a temperature of 85 °C and a holding time of 10 h. After acid washing, wash it with pure water several times until the filtrate is close to neutral, then filter to remove part of the water, put it into a drying oven and dry it at 85 °C for 32 h to obtain a purified material; (6) Mix the purified material obtained in step (5) with petroleum-based asphalt with a softening point of 130 °C evenly at a ratio of 100:6, and then carry out cyclic mechanical forging and pressing to compress the compaction density to 1.6 g / cm 3 to obtain a densified body; (7) Put the densified body into an atmosphere high-temperature furnace, heat it to 1400 °C at a heating rate of 3 °C / min under a nitrogen atmosphere, hold it at high temperature for 4 h, cool it, and then carry out depolymerization with a depolymerizer. Control the particle size D of the depolymerized material 50 to be about 7 μm, and a biomass hard carbon anode material is obtained after depolymerization.

[0049] Performance test Use the biomass hard carbon anode materials prepared in Examples 1-5 and Comparative Examples 1-3 above as anode materials to fabricate sodium-ion batteries. The fabrication method is as follows: Weigh 0.2 g of CMC, 0.3 g of Super P, 9.3 g of the above-prepared biomass hard carbon anode material, and 0.4 g of SBR respectively according to the mass ratio of 2%:3%:93%:2%, add an appropriate amount of deionized water, and mechanically stir for 30 min until it becomes a uniform slurry. Use a coater to evenly coat it on the surface of the copper foil, dry it in a blast drying oven at 105 °C for 3 h, and then use a slicing machine to slice the coated electrode sheet to obtain a negative electrode sheet; inside a glove box with an Ar atmosphere, use a commercial electrolyte 1.0 mol / L NaPF6 / EC:DMC(1:1)(V:V) as the electrolyte, a metal sodium sheet as the counter electrode, and a glass fiber as the separator to fabricate a CR2032 coin cell with the obtained negative electrode sheet, and then use a constant current charge-discharge mode to carry out charge-discharge tests at a current density of 0.1C.

[0050] For the full cell, according to the mass ratio of hard carbon material:CMC:SP:SBR = 92%:2%:3%:3%, a polyanion system, fabricate a soft-pack battery, carry out 1C constant current and constant voltage charging and 1C constant current discharging to test the cycle performance.

[0051] The 8 kinds of biomass hard carbon anode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were made into sodium-ion batteries and then tested for battery performance. The test results are shown in Table 1.

[0052] Table 1. Performance test results of sodium-ion batteries

[0053] It can be seen from the test results in Table 1 that the biomass hard carbon anode materials obtained by the preparation method of the present invention have a high specific capacity and a high cycle retention rate. The capacity retention rate of Examples 1-5 at 1C / 1C for 300 cycles is significantly better than that of Comparative Examples 1-3. This is mainly because the biomass materials in Examples 1-5 are first subjected to a combined treatment of alkali solution and zinc nitrate before pyrolysis to regulate the pore structure of the materials, control the micropore / mesopore ratio, and improve the structural stability of the materials; after pre-carbonization, acid washing is carried out to remove impurities, reduce the content of impurity elements in the pre-carbonized material, reduce the influence of side reactions during the battery cycle, effectively control battery gas production and improve the cycle performance; high-temperature heat treatment and surface modification can reduce the specific surface area of the material, improve defects, improve the first efficiency, and extend the battery life; at the same time, optimize its surface functional groups, reduce the interfacial resistance, and reduce the loss of reversible capacity.

[0054] Among them, through the comparison of Example 1, Example 5 and Comparative Example 1, it can be seen that the effect of the combined treatment of Zn(NO3)2 and alkali solution on biomass raw materials is better than that of single alkali solution treatment. This is because the alkali solution can only form most of the microporous structure, while the combination of Zn(NO3)2 and alkali solution can form a hierarchical porous structure of micropores + mesopores, improve the wettability of the electrolyte, and optimize the sodium storage performance; and by optimizing the ratio of Zn(NO3)2 and NaOH, the micropore / mesopore ratio can be optimized to make the performance of the material reach the best. At the same time, during the subsequent carbonization process, Zn(OH)2 / ZnO is partially reduced to metallic Zn and volatilized (or remains as a ZnO doping phase), leaving a conductive channel, reducing the material resistance, and improving the rate performance; while the remaining Zn or ZnO is evenly distributed in the carbon matrix, which helps to form a more stable SEI film and improve the long-cycle performance.

[0055] Among them, through the comparison of Example 1 and Comparative Example 2, it can be seen that Comparative Example 2 only lacks the operation of mixing the purified material and the impregnating agent and cyclic mechanical forging compared with Example 1, but the performance of the material prepared by it has decreased significantly. This is because the multiple cycles of pressurization - depressurization of the purified material and the impregnating agent can gradually compress the gaps between hard carbon particles and the macropores inside, and make the impregnating agent fully penetrate into the microcracks and pores under the cyclic pressure to form a denser composite. And this densified structure can limit the excessive penetration of the electrolyte, form a thinner SEI film, and improve the first efficiency. And single high pressure is likely to cause elastic rebound of the material, while cyclic forging accumulates plastic deformation, resulting in a stable increase in density and a more stable structure.

[0056] In summary, before the pre-carbonization of the biomass raw material, the present invention first performs a combined treatment of alkali solution and zinc nitrate on it, enabling the material to form a hierarchical porous structure of micropores + mesopores during the carbonization process, and controlling the micropore / mesopore ratio through concentration and proportion, thereby enhancing the structural stability of the material and optimizing the sodium storage performance. Then, after pre-carbonization, the present invention performs pickling to remove impurities, reducing the content of impurity elements in the pre-carbonized material, reducing the influence of side reactions during battery cycling, effectively controlling battery gas generation and improving cycling performance, and obtaining a densified body with sufficient penetration of the impregnating agent through cyclic mechanical forging, thereby enhancing the battery energy density. Moreover, the present invention reduces the specific surface area of the material, improves defects, enhances the initial efficiency, and prolongs the battery service life through high-temperature heat treatment and surface modification. At the same time, the optimization of surface functional groups can reduce the interfacial resistance and reduce the loss of reversible capacity. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0057] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A preparation method of a long-cycle and high-compaction biomass hard carbon anode material, characterized in that, It includes the following steps: (1) Clean and dry the biomass raw material to obtain a pretreated material; (2) Add the pretreated material obtained in step (1) into a mixed solution of Zn(NO3)2 and NaOH, stir evenly by ultrasonic wave, stand for a period of time at room temperature, and obtain a dried material after filtration, suction filtration and drying; (3) Under an inert atmosphere, perform pre-carbonization treatment on the dried material obtained in step (2) to obtain a pre-carbonized material; (4) Crush the pre-carbonized material obtained in step (3) to obtain a crushed material; (5) First, wash the crushed material obtained in step (4) with acid to remove impurities and then with water, and then perform suction filtration and drying to obtain a purified material; (6) Mix the purified material obtained in step (5) with an impregnating agent evenly, and then perform cyclic mechanical forging to obtain a densified body; (7) Under an inert atmosphere, perform high-temperature heat treatment on the densified body obtained in step (6), and perform depolymerization after cooling to obtain a depolymerized material; (8) Mix the depolymerized material obtained in step (7) with a modifier evenly, and then perform surface modification under an inert atmosphere, and obtain a long-cycle high-compaction biomass hard carbon anode material after cooling.

2. The preparation method of the long-cycle and high-compaction biomass hard carbon anode material according to claim 1, wherein The biomass raw material in step (1) is selected from any one of hazelnut shells, coconut shells and almond shells.

3. The preparation method of the long-cycle high-compaction biomass hard carbon negative electrode material according to claim 1, characterized in that, In the mixed solution of Zn(NO3)2 and NaOH in step (2), the concentration of the Zn(NO3)2 solution is 0.01 - 0.5 mol / L, and the concentration of the NaOH solution is 0.01 - 0.5 mol / L; the mass ratio of the Zn(NO3)2 solution to the NaOH solution is 1:0.5 - 3.

4. The preparation method of the long-cycle and high-compaction biomass hard carbon anode material according to claim 1, wherein In step (2), the mass ratio of the pretreated material to the mixed solution of Zn(NO3)2 and NaOH is 1:0.5 - 3.

5. The preparation method of the long-cycle and high-compaction biomass hard carbon anode material according to claim 1, characterized in that, In step (3), the conditions for the pre-carbonization treatment are: the heating rate is 1 - 10 °C / min, the pre-carbonization temperature is 200 - 800 °C, and the heat preservation time is 1 - 8 h.

6. The preparation method of the long-cycle and high-compaction biomass hard carbon anode material according to claim 1, characterized in that, In step (5), the acid used for acid washing is selected from at least one of hydrofluoric acid, hydrochloric acid and nitric acid; the concentration of the acid is 0.5 - 8 mol / L; the reaction temperature for acid washing is 60 - 100 °C; the solid-liquid mass ratio for acid washing is 1:1 - 6; the time for acid washing is 8 - 24 h.

7. The preparation method of the long-cycle and high-compaction biomass hard carbon negative electrode material according to claim 1, wherein, The impregnating agent in step (6) is selected from at least one of petroleum-based asphalt and coal-based asphalt, and its softening point is 100-260 °C; the mass ratio of the purified material to the impregnating agent is 100:1-10; the compacting density of the densified body is pressed to 1-1.6 g / cm 3 .

8. The preparation method of the long-cycle and high-compaction biomass hard carbon anode material according to claim 1, characterized in that, In step (8), the modifier is selected from at least one of phenolic resin, epoxy resin and asphalt composite β resin, and the coking value of the modifier is 40 - 70%; the mass ratio of the modifier to the depolymerized material is 1 - 10:100; the conditions for surface modification are: the heating rate is 1 - 10 °C / min, the high-temperature heat preservation temperature is 800 - 1500 °C, and the heat preservation time is 3 - 6 h.

9. A long-cycle and high-compaction biological hard carbon anode material, characterized in that It is made by the preparation method of the long-cycle high-compaction biomass hard carbon anode material according to any one of claims 1 - 8.

10. Application of a long-cycle high-compaction biomass hard carbon anode material as described in claim 9 in a sodium-ion battery.

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