Hard carbon negative electrode material and preparation method and application thereof

Abstract

The invention provides a hard carbon negative electrode material and a preparation method and application thereof, and belongs to the technical field of negative electrode materials, and the preparation method of the hard carbon negative electrode material comprises the following steps: mixing bamboo powder, a reducing agent and a solvent, and performing dispersion treatment to obtain mixed slurry; carrying out solid-liquid separation on the mixed slurry to obtain a wet material; mixing the wet material with a phosphorus source and a sodium source to obtain a mixed material; and drying and calcining the mixed material to obtain the hard carbon negative electrode material. Lignin in the bamboo powder is removed through the reduction reaction, cellulose obtained after lignin removal is mixed with the phosphorus source and the sodium source, and the mixture is dried and calcined, so that the hard carbon negative electrode material with relatively good electrochemical performance can be obtained; therefore, the first coulombic efficiency and the charge / discharge specific capacity of the sodium ion battery prepared from the hard carbon negative electrode material can be improved.

Description

Technical Field

[0001] This application relates to the technical field of anode materials, and particularly relates to a hard carbon anode material, a preparation method thereof, and an application thereof. Background Art

[0002] Rechargeable batteries are indispensable in modern society and can provide power for various fields as needed, such as being applied in the field of new energy vehicles. Lithium-ion batteries are currently the most widely used battery energy storage devices, but the lack of lithium resources and the rising costs will become key factors restricting the development of lithium-ion batteries. Compared with lithium-ion batteries, sodium has rich reserves and reasonable prices, and sodium-ion batteries have a similar working principle to lithium-ion batteries, so they have become the first choice for a new generation of energy storage batteries.

[0003] Currently, the anode materials for sodium-ion batteries mainly include carbon-based materials, alloy materials, conversion materials, organic materials, and metal oxide materials. Carbon-based materials have become the mainstream choice for sodium-ion battery anodes due to their wide sources and strong sodium storage capacity. Carbon-based materials can be further divided into hard carbon and soft carbon according to whether they are graphitized after high-temperature carbonization. Among them, hard carbon has a disordered internal crystal arrangement, a large interlayer spacing, rich pores, and a high theoretical capacity, making it the first choice for sodium-ion battery anode materials.

[0004] Bamboo, as a plant of the subfamily Bambusoideae, has an extremely fast growth rate and a high cellulose content, making it an excellent precursor for synthesizing hard carbon materials. However, bamboo also has a high content of lignin, which will lead to poor electrochemical performance of the prepared hard carbon anode material and is difficult to meet the preparation requirements of sodium-ion batteries.

[0005] Therefore, there is an urgent need to provide a new method for preparing hard carbon materials using bamboo to improve the technical problem that the electrochemical performance of existing bamboo-based hard carbon materials is difficult to meet the requirements of sodium-ion batteries. Summary of the Invention

[0006] In view of the technical problems existing in the background art, this application provides a hard carbon anode material, a preparation method thereof, and an application thereof, aiming to solve the technical problem of poor electrochemical performance of existing hard carbon anode materials.

[0007] In a first aspect, an embodiment of this application provides a preparation method for a hard carbon anode material, including the following steps: Mix bamboo powder, a reducing agent, and a solvent phase, and perform dispersion treatment to obtain a mixed slurry; Perform solid-liquid separation on the mixed slurry to obtain a wet material; Mix the wet material with a phosphorus source and a sodium source to obtain a mixed material; Subject the mixed material to drying and calcination treatments to obtain the hard carbon anode material.

[0008] In the technical solution of the embodiment of the present application, bamboo powder is first mixed with a reducing agent, and lignin in the bamboo powder is removed through a reduction reaction to obtain cellulose with a relatively high purity. Among them, the removal of lignin can improve the purity of cellulose and avoid the decrease in the Coulomb efficiency of the hard carbon negative electrode material due to the high content of lignin in the cellulose. Subsequently, the cellulose obtained after removing lignin is mixed with a phosphorus source and a sodium source, and then subjected to drying and calcination treatments to obtain a hard carbon negative electrode material with better electrochemical performance. Furthermore, when the hard carbon negative electrode material is used to prepare a sodium-ion battery, the initial Coulomb efficiency and the charge / discharge specific capacity of the obtained sodium-ion battery are both improved.

[0009] In some embodiments, the mass ratio of the reducing agent to the bamboo powder is (0.06~0.12):1; and / or, the reducing agent is one or more of sodium hypochlorite and hydrogen peroxide.

[0010] In this embodiment, reducing agents such as sodium hypochlorite and hydrogen peroxide can react with lignin in the bamboo powder through a reduction reaction, thereby removing the lignin in the bamboo powder and improving the purity of cellulose. Among them, if the dosage of the reducing agent is too low, the lignin in the bamboo powder will not be completely removed, resulting in an impact on the electrochemical performance of the prepared hard carbon negative electrode material, and further resulting in poor electrochemical performance of the sodium-ion battery prepared using this hard carbon negative electrode material. If the dosage of the reducing agent is too high, it will cause waste of the agent and increase the cost.

[0011] In some embodiments, the solid content of the mixed slurry is 10~20%; and / or, the D50 particle size of the mixed slurry is 4~6 μm, and the D100 particle size < 35 μm.

[0012] In this embodiment, by controlling the solid content of the mixed slurry within a suitable range, it is beneficial for the reducing agent and the bamboo powder to come into full contact and undergo a reduction reaction. If the solid content of the mixed slurry is too large, the bamboo powder and the reducing agent will not be evenly dispersed, which is not conducive to their full contact, resulting in incomplete removal of lignin in the bamboo powder. If the solid content of the mixed slurry is too small, the time for solid-liquid separation will increase due to the too high solvent content in the mixed slurry, reducing the production efficiency. Controlling the particle size of the mixed slurry within a suitable range facilitates the full mixing of the wet material obtained after solid-liquid separation with the phosphorus source and the sodium source, and at the same time, improves the drying efficiency of the mixed material.

[0013] In some embodiments, the solid-liquid separation step includes: subjecting the mixed slurry to pressure filtration and washing until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0014] In this embodiment, by subjecting the mixed slurry to pressure filtration and washing, impurities such as acids and salts generated by the reduction reaction of lignin and the reducing agent can be removed to obtain cellulose with a relatively high purity. If the pH of the filtrate < 6 or the conductivity > 20 μS / cm, it indicates that the acids and salts generated by the reduction reaction have not been completely washed away.

[0015] In some embodiments, the mass ratio of the total mass of the phosphorus source and the sodium source to the mass of the bamboo powder is (0.08 - 0.12):1; and / or, the phosphorus source is one or more of phosphoric acid, sodium dihydrogen phosphate, sodium hydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate; and / or, the sodium source is one or more of sodium hydroxide, sodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, and disodium hydrogen phosphate.

[0016] In this embodiment, by controlling the mass ratio of the total mass of the phosphorus source and the sodium source to the mass of the bamboo powder to be (0.08 - 0.12):1, it is convenient to obtain a hard carbon negative electrode material with appropriate phosphorus doping content and appropriate sodium doping content. If the dosage of the phosphorus source and the sodium source is too much, sp 3 defects are easily formed in the carbon lattice, distorting the π-conjugated system, thereby reducing the electronic conductivity of the hard carbon negative electrode material; while if the dosage of the phosphorus source and the sodium source is too little, the interaction between the doping element and the hard carbon negative electrode material cannot be exerted, thus the specific capacity of the hard carbon negative electrode material cannot be effectively improved, and further affecting the electrochemical performance of the sodium ion battery prepared using this hard carbon negative electrode material.

[0017] In some embodiments, the drying method is spray drying. Among them, the inlet air temperature of the spray drying is 230 - 270 °C, the outlet temperature of the spray drying is 80 - 100 °C, and the particle size of the obtained dried material is 10 - 20 μm.

[0018] In this embodiment, granular materials with uniform particle size can be obtained through spray drying, and then a hard carbon negative electrode material with spherical primary particles and good processing dispersibility can be obtained. Among them, controlling the particle size of the dried material to be 10 - 20 μm can promote the doping degree of the phosphorus source and the sodium source during the calcination process and improve the sintering rate.

[0019] In some embodiments, the process of calcining the dried material includes: first-stage calcination, second-stage calcination, and third-stage calcination; the process conditions of the first-stage calcination include: heating rate 1 - 3 °C / min, temperature 90 - 110 °C, and holding time 2 - 3 h; the process conditions of the second-stage calcination include: heating rate 1 - 3 °C / min, temperature 110 - 1000 °C, and holding time 2 - 3 h; the process conditions of the third-stage calcination include: heating rate 1 - 2 °C / min, temperature 1000 - 1400 °C, and holding time 2 - 3 h.

[0020] In this embodiment, by subjecting the dried material to first-stage calcination, second-stage calcination, and third-stage calcination, the charge-discharge specific capacity and first Coulombic efficiency of the hard carbon anode material can be significantly improved. Among them, during the low-temperature calcination in the first stage, the moisture contained in the dried material can be fully removed, avoiding the reaction between the water in the dried material and the carbon generated after the cellulose is carbonized during the subsequent calcination process, which would change the graphitization degree of the hard carbon anode material; during the medium-temperature calcination in the second stage, the completely dehydrated material can decompose, promoting preliminary carbonization; during the high-temperature calcination in the third stage, the decomposed material can be carbonized. At the same time, setting a lower heating rate can improve the degree of carbonization and facilitate the acquisition of a hard carbon anode material with a suitable layer spacing. Among them, if the heating rate is too fast, the carbonization rate will be too fast, resulting in incomplete carbonization, while if the heating rate is too slow, the graphitization degree of the hard carbon anode material will be too high, thereby reducing the layer spacing of the hard carbon anode material and being unfavorable for the insertion and extraction of sodium ions in the hard carbon anode material.

[0021] In a second aspect, an embodiment of the present application provides a hard carbon anode material, which is prepared by the preparation method described in the first aspect.

[0022] In the technical solution of the embodiment of the present application, the hard carbon anode material is prepared by the preparation method described in the first aspect, and thus has better electrochemical performance.

[0023] In a third aspect, an embodiment of the present application provides a negative electrode sheet, which includes the hard carbon anode material described in the second aspect.

[0024] In the technical solution of the embodiment of the present application, the negative electrode sheet includes the hard carbon anode material described in the second aspect, and thus has better electrochemical performance.

[0025] In a fourth aspect, an embodiment of the present application provides a sodium-ion battery, which includes the negative electrode sheet described in the third aspect.

[0026] In the technical solution of the embodiment of the present application, the sodium-ion battery includes the negative electrode sheet described in the third aspect, and thus has a high charge-discharge specific capacity and first Coulombic efficiency.

[0027] The above description is only an overview of the technical solution of the present application. In order to be able to understand the technical means of the present application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features, and advantages of the present application more obvious and understandable, the following specifically illustrates the specific embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0029] Figure 1 SEM image of the hard carbon negative electrode material prepared in Example 1 of this application; Figure 2 Raman spectrum of the hard carbon negative electrode material prepared in Example 1 of this application; Figure 3 Charge-discharge curve of the hard carbon negative electrode material prepared in Example 1 of this application at a current density of 0.1 C. Detailed implementation manners

[0030] The embodiments of the technical solutions of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of this application, so they are only examples and cannot be used to limit the protection scope of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above accompanying drawing descriptions are intended to cover non-exclusive inclusion.

[0032] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality" means two or more, unless otherwise specifically defined.

[0033] Referring to "embodiments" herein means that the specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appears in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0034] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the preceding and following associated objects.

[0035] In the description of the embodiments of the present application, the term "plurality" refers to two or more (including two). Similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces).

[0036] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the embodiments of the present application.

[0037] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0038] In the prior art, when preparing a hard carbon negative electrode material using bamboo powder, due to the relatively high lignin content in the bamboo powder, the initial Coulombic efficiency of the prepared hard carbon negative electrode material is relatively low. At the same time, the specific capacity and rate performance of the bamboo-based hard carbon negative electrode material prepared by the existing process are limited, which restricts its wide application in rechargeable batteries.

[0039] In order to solve the technical problems of the relatively low specific capacity and initial Coulombic efficiency of the hard carbon negative electrode material prepared by the prior art, the present application provides a hard carbon negative electrode material, its preparation method and application. Among them, by removing the lignin in the bamboo powder through a reduction reaction, and mixing the cellulose obtained after removing the lignin with a phosphorus source and a sodium source, and then performing drying and calcination treatments, a hard carbon negative electrode material with better electrochemical performance can be obtained, thereby obtaining a sodium ion battery with a higher specific capacity and initial Coulombic efficiency.

[0040] In a first aspect, an embodiment of the present application provides a method for preparing a hard carbon anode material, comprising the following steps: Mix bamboo powder, a reducing agent and a solvent phase, and perform a dispersion treatment to obtain a mixed slurry; Perform solid-liquid separation on the mixed slurry to obtain a wet material; Mix the wet material with a phosphorus source and a sodium source to obtain a mixed material; Subject the mixed material to drying and calcination treatments to obtain a hard carbon anode material.

[0041] In the technical solution of the embodiment of the present application, first mix bamboo powder with a reducing agent, and remove lignin in the bamboo powder through a reduction reaction to obtain cellulose with a relatively high purity; subsequently, mix the cellulose obtained after removing lignin with a phosphorus source and a sodium source and perform drying and calcination treatments to obtain a hard carbon anode material with better electrochemical performance. Among them, the removal of lignin can improve the purity of cellulose and prevent the electrochemical performance of the hard carbon anode material from being damaged due to a relatively high lignin content in the cellulose; the phosphorus source can increase the charge specific capacity of the hard carbon anode material, and the sodium source can increase the first Coulombic efficiency of the hard carbon anode material.

[0042] Further, in some embodiments, the mass ratio of the reducing agent to the bamboo powder is (0.06~0.12):1; and / or, the reducing agent is one or more of sodium hypochlorite and hydrogen peroxide.

[0043] Specifically, the mass ratio of the reducing agent to the bamboo powder can be 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, or any ratio within the above range.

[0044] Among them, preferably, the mass ratio of the reducing agent to the bamboo powder is (0.08~0.11):1.

[0045] In the technical solution of the embodiment of the present application, reducing agents such as sodium hypochlorite and hydrogen peroxide can react with lignin in the bamboo powder through a reduction reaction, thereby removing the lignin in the bamboo powder and improving the purity of cellulose. Among them, if the dosage of the reducing agent is too low, the lignin in the bamboo powder cannot be completely removed, resulting in an impact on the electrochemical performance of the hard carbon anode material, and further resulting in poor electrochemical performance of the sodium ion battery prepared using this hard carbon anode material. If the dosage of the reducing agent is too high, it will cause waste of the reagent and increase the cost.

[0046] Further, in some embodiments, the solid content of the mixed slurry is 10~20%; and / or, the D50 particle size of the mixed slurry is 4~6μm, and the D100 particle size < 35μm.

[0047] In the technical solution of the embodiment of the present application, by controlling the solid content of the mixed slurry within a suitable range, it is beneficial for the reducing agent and bamboo powder to come into full contact and undergo a reduction reaction. If the solid content of the mixed slurry is too high, the bamboo powder and the reducing agent are not evenly dispersed, which is not conducive to their full contact, resulting in incomplete removal of lignin in the bamboo powder; while if the solid content of the mixed slurry is too low, the time for solid-liquid separation will increase due to the too high solvent content of the mixed slurry, reducing the production efficiency. Controlling the particle size of the mixed slurry within a suitable range facilitates the full mixing of the wet material obtained after solid-liquid separation with the phosphorus source and the sodium source, and at the same time, improves the drying efficiency of the mixed material.

[0048] Further, in some embodiments, the solid-liquid separation step includes: pressure filtering and washing the mixed slurry until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0049] In the technical solution of the embodiment of the present application, by pressure filtering and washing the mixed slurry, impurities such as acids and salts generated by the reduction reaction of lignin with the reducing agent can be removed to obtain cellulose with higher purity. If the pH of the filtrate < 6 or the conductivity > 20 μS / cm, it indicates that the acids and salts generated by the reduction reaction have not been completely washed away.

[0050] Further, in some embodiments, the mass ratio of the total mass of the phosphorus source and the sodium source to the mass of the bamboo powder is (0.08 - 0.12):1; and / or, the phosphorus source is one or more of phosphoric acid, sodium dihydrogen phosphate, sodium hydrogen phosphate, disodium hydrogen phosphate, sodium phosphate; and / or, the sodium source is one or more of sodium hydroxide, sodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, disodium hydrogen phosphate.

[0051] Specifically, the mass ratio of the total mass of the phosphorus source and the sodium source to the mass of the bamboo powder can be 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, or any ratio within the above range.

[0052] In the technical solution of the embodiment of the present application, by controlling the mass ratio of the total mass of the phosphorus source and the sodium source to the mass of the bamboo powder to be (0.08 - 0.12):1, it is convenient to obtain a hard carbon anode material with a suitable phosphorus doping amount and a suitable sodium doping amount. If the amounts of the phosphorus source and the sodium source are too large, sp 3 defects are easily formed in the carbon lattice of the hard carbon anode material, distorting the π-conjugated system, thereby reducing the electronic conductivity of the hard carbon anode material; while if the amounts of the phosphorus source and the sodium source are too small, the interaction between the doping elements and the hard carbon material cannot be exerted, thus unable to effectively improve the electrochemical performance of the hard carbon anode material.

[0053] Among them, preferably, the mass ratio of the total mass of the phosphorus source and the sodium source to the mass of the bamboo powder is (0.09 - 0.11):1.

[0054] Further, in some embodiments, the drying method is spray drying. Among them, the inlet air temperature of the spray drying is 230-270°C, the outlet temperature of the spray drying is 80-100°C, and the particle size of the obtained dried material is 10-20 μm.

[0055] In the technical solution of the embodiment of the present application, through spray drying, particulate materials with uniform particle size can be obtained, and then a hard carbon negative electrode material with spherical primary particles and good processing dispersibility can be obtained. Among them, controlling the particle size of the dried material to be 10-20 μm can promote the doping degree of the phosphorus source and the sodium source during the calcination process and improve the sintering rate.

[0056] Further, in some embodiments, the process of calcining the dried material includes: first-stage calcination, second-stage calcination, and third-stage calcination; the process conditions of the first-stage calcination include: a heating rate of 1-3°C / min, a temperature of 90-110°C, and a heat preservation time of 2-3 h; the process conditions of the second-stage calcination include: a heating rate of 1-3°C / min, a temperature of 110-1000°C, and a heat preservation time of 2-3 h; the process conditions of the third-stage calcination include: a heating rate of 1-2°C / min, a temperature of 1000-1400°C, and a heat preservation time of 2-3 h.

[0057] In the technical solution of the embodiment of the present application, by performing first-stage calcination, second-stage calcination, and third-stage calcination on the dried material, the charge specific capacity and the first Coulomb efficiency of the hard carbon negative electrode material can be significantly improved. Among them, during the low-temperature calcination process of the first stage, the moisture contained in the dried material can be fully removed, avoiding the reaction between the water present in the dried material and the carbon generated after the cellulose is carbonized during the subsequent calcination process, which may change the graphitization degree of the hard carbon negative electrode material; during the medium-temperature calcination process of the second stage, the completely dehydrated material can be decomposed to promote preliminary carbonization; during the high-temperature calcination process of the third stage, the decomposed material can be carbonized. At the same time, setting a lower heating rate can improve the degree of carbonization and facilitate obtaining a hard carbon negative electrode material with a suitable layer spacing. If the heating rate is too fast, the carbonization rate will be too fast, resulting in incomplete carbonization. If the heating rate is too slow, the graphitization degree of the hard carbon negative electrode material will be too high, thereby reducing the layer spacing of the hard carbon negative electrode material, which is not conducive to the insertion and extraction of sodium ions in the hard carbon negative electrode material.

[0058] Among them, preferably, the temperature of the first-stage calcination is 90-110°C, and the heat preservation time is 2-3 h; the temperature of the second-stage calcination is 900-1000°C, and the heat preservation time is 2-3 h; the temperature of the third-stage calcination is 1200-1400°C, and the heat preservation time is 2-3 h.

[0059] In a second aspect, the embodiment of the present application provides a hard carbon negative electrode material, which is prepared by the preparation method described in the first aspect.

[0060] In the technical solution of the embodiment of the present application, the hard carbon negative electrode material is prepared by the preparation method described in the first aspect, and thus has better electrochemical performance.

[0061] In the third aspect, the embodiment of the present application provides a negative electrode sheet, which includes the hard carbon negative electrode material described in the second aspect.

[0062] In the technical solution of the embodiment of the present application, the negative electrode sheet includes the hard carbon negative electrode material described in the second aspect, and thus has better electrochemical performance.

[0063] In the fourth aspect, the embodiment of the present application provides a sodium ion battery, which includes the negative electrode sheet described in the third aspect.

[0064] In the technical solution of the embodiment of the present application, the sodium ion battery includes the negative electrode sheet described in the third aspect, and thus has a high charge-discharge specific capacity and a first Coulomb efficiency.

[0065] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those without specific techniques or conditions noted in the embodiments, the techniques or conditions described in the literature in this field or according to the product specifications are followed. Those reagents or instruments without the manufacturer noted are all conventional products that can be obtained through commercial purchases.

[0066] I. Preparation Method Example 1 (1) Add bamboo powder, sodium hypochlorite and pure water to a ball mill, and obtain a mixed slurry after ball milling for 4 h; wherein, the mass ratio of sodium hypochlorite to bamboo powder is 0.08:1, the solid content of the obtained mixed slurry is 15%, the particle size D50 of the mixed slurry is 5 μm, and D100 is 20 μm.

[0067] (2) Press-filter and wash the mixed slurry in a plate and frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0068] (3) Mix the wet material, sodium dihydrogen phosphate and pure water to obtain a mixed material with a solid content of 10%; wherein, the mass ratio of sodium dihydrogen phosphate to bamboo powder is 0.1:1. Then, spray-dry the mixed material. The inlet air temperature for spray drying is 230 °C, and the outlet temperature for spray drying is 90 °C to obtain a dried material with a particle size of 10 μm.

[0069] (4) Put the dried material into a box-type furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it at a heating rate of 2 °C / min to 100 °C and hold for 2 h; then heat it at a heating rate of 2 °C / min to 1000 °C and hold for 1 h; then heat it at a heating rate of 1.33 °C / min to 1400 °C and hold for 2 h; finally, cool it naturally to room temperature to obtain the hard carbon anode material.

[0070] Example 2 (1) Add bamboo powder, sodium hypochlorite and pure water to a ball mill, and obtain a mixed slurry after ball milling for 4 h; among them, the mass ratio of sodium hypochlorite to bamboo powder is 0.08:1, the solid content of the obtained mixed slurry is 15%, the particle size D50 of the mixed slurry is 5 μm, and D100 is 20 μm.

[0071] (2) Carry out pressure filtration and washing of the mixed slurry in a plate and frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0072] (3) Mix the wet material, sodium dihydrogen phosphate and pure water to obtain a mixed material with a solid content of 10%; among them, the mass ratio of sodium dihydrogen phosphate to bamboo powder is 0.08:1. Then, carry out spray drying on the mixed material, the inlet air temperature of the spray drying is 230 °C, the outlet temperature of the spray drying is 90 °C, and obtain a dried material with a particle size of 10 μm.

[0073] (4) Put the dried material into a box-type furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it at a heating rate of 2 °C / min to 100 °C and hold for 2 h; then heat it at a heating rate of 2 °C / min to 1000 °C and hold for 1 h; then heat it at a heating rate of 1.33 °C / min to 1400 °C and hold for 2 h; finally, cool it naturally to room temperature to obtain the hard carbon anode material.

[0074] Example 3 (1) Add bamboo powder, sodium hypochlorite and pure water to a ball mill, and obtain a mixed slurry after ball milling for 4 h; among them, the mass ratio of sodium hypochlorite to bamboo powder is 0.08:1, the solid content of the obtained mixed slurry is 15%, the particle size D50 of the mixed slurry is 5 μm, and D100 is 20 μm.

[0075] (2) Carry out pressure filtration and washing of the mixed slurry in a plate and frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0076] (3) Mix the wet material, sodium dihydrogen phosphate, and pure water to obtain a mixed material with a solid content of 10%; wherein, the mass ratio of sodium dihydrogen phosphate to bamboo powder is 0.09:1. Subsequently, spray-dry the mixed material. The inlet air temperature for spray drying is 230 °C, and the outlet temperature for spray drying is 90 °C to obtain a dried material with a particle size of 10 μm.

[0077] (4) Place the dried material in a box furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it to 100 °C at a heating rate of 2 °C / min and hold for 2 h; then heat it to 1000 °C at a heating rate of 2 °C / min and hold for 1 h; then heat it to 1400 °C at a heating rate of 1.33 °C / min and hold for 2 h; finally, cool it naturally to room temperature to obtain a hard carbon negative electrode material.

[0078] Example 4 (1) Add bamboo powder, sodium hypochlorite, and pure water to a ball mill and obtain a mixed slurry after ball milling for 4 h; wherein, the mass ratio of sodium hypochlorite to bamboo powder is 0.08:1, the solid content of the obtained mixed slurry is 15%, the particle size D50 of the mixed slurry is 5 μm, and D100 is 20 μm.

[0079] (2) Press-filter and wash the mixed slurry in a plate and frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0080] (3) Mix the wet material, sodium dihydrogen phosphate, and pure water to obtain a mixed material with a solid content of 10%; wherein, the mass ratio of sodium dihydrogen phosphate to bamboo powder is 0.11:1. Subsequently, spray-dry the mixed material. The inlet air temperature for spray drying is 230 °C, and the outlet temperature for spray drying is 90 °C to obtain a dried material with a particle size of 10 - 20 μm.

[0081] (4) Place the dried material in a box furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it to 100 °C at a heating rate of 2 °C / min and hold for 2 h; then heat it to 1000 °C at a heating rate of 2 °C / min and hold for 1 h; then heat it to 1400 °C at a heating rate of 1.33 °C / min and hold for 2 h; finally, cool it naturally to room temperature to obtain a hard carbon negative electrode material.

[0082] Example 5 (1) Add bamboo powder, sodium hypochlorite, and pure water to a ball mill and obtain a mixed slurry after ball milling for 4 h; wherein, the mass ratio of sodium hypochlorite to bamboo powder is 0.08:1, the solid content of the obtained mixed slurry is 15%, the particle size D50 of the mixed slurry is 5 μm, and D100 is 20 μm.

[0083] (2) Press-filter and wash the mixed slurry in a plate-and-frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0084] (3) Mix the wet material, sodium dihydrogen phosphate, and pure water to obtain a mixed material with a solid content of 10%; wherein, the mass ratio of sodium dihydrogen phosphate to bamboo powder is 0.12:1. Subsequently, spray-dry the mixed material. The inlet air temperature for spray drying is 230 °C, and the outlet temperature for spray drying is 90 °C to obtain a dried material with a particle size of 10 μm.

[0085] (4) Place the dried material in a box furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it from room temperature to 100 °C at a heating rate of 2 °C / min and hold for 2 h; then heat it from 100 °C to 1000 °C at a heating rate of 2 °C / min and hold for 1 h; then heat it from 1000 °C to 1400 °C at a heating rate of 1.33 °C / min and hold for 2 h; finally, cool it naturally to room temperature to obtain a hard carbon negative electrode material.

[0086] Example 6 (1) Add bamboo powder, sodium hypochlorite, and pure water to a ball mill and ball mill for 4 h to obtain a mixed slurry; wherein, the mass ratio of sodium hypochlorite to bamboo powder is 0.06:1, the solid content of the obtained mixed slurry is 15%, the D50 of the mixed slurry is 5 μm, and the D100 is 20 μm.

[0087] (2) Press-filter and wash the mixed slurry in a plate-and-frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0088] (3) Mix the wet material, sodium dihydrogen phosphate, and pure water to obtain a mixed material with a solid content of 10%; wherein, the mass ratio of sodium dihydrogen phosphate to bamboo powder is 0.1:1. Subsequently, spray-dry the mixed material. The inlet air temperature for spray drying is 230 °C, and the outlet temperature for spray drying is 90 °C to obtain a dried material with a particle size of 10 μm.

[0089] (4) Place the dried material in a box furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it from room temperature to 100 °C at a heating rate of 2 °C / min and hold for 2 h; then heat it from 100 °C to 1000 °C at a heating rate of 2 °C / min and hold for 1 h; then heat it from 1000 °C to 1400 °C at a heating rate of 1.33 °C / min and hold for 2 h; finally, cool it naturally to room temperature to obtain a hard carbon negative electrode material.

[0090] Example 7 (1) Add bamboo powder, sodium hypochlorite, and pure water to a ball mill. After ball milling for 4 h, a mixed slurry is obtained. Among them, the mass ratio of sodium hypochlorite to bamboo powder is 0.1:1. The solid content of the obtained mixed slurry is 15%, the particle size D50 of the mixed slurry is 5 μm, and D100 is 20 μm.

[0091] (2) Press-filter and wash the mixed slurry in a plate-and-frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0092] (3) Mix the wet material, sodium dihydrogen phosphate, and pure water to obtain a mixed material with a solid content of 10%. Among them, the mass ratio of sodium dihydrogen phosphate to bamboo powder is 0.1:1. Subsequently, spray-dry the mixed material. The inlet air temperature for spray drying is 230 °C, and the outlet temperature for spray drying is 90 °C to obtain a dried material with a particle size of 10 μm.

[0093] (4) Put the dried material into a box furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it at a heating rate of 2 °C / min to 100 °C and hold for 2 h; then heat it at a heating rate of 2 °C / min to 1000 °C and hold for 1 h; then heat it at a heating rate of 1.33 °C / min to 1400 °C and hold for 2 h; finally, cool it naturally to room temperature to obtain a hard carbon negative electrode material.

[0094] Example 8 (1) Add bamboo powder, sodium hypochlorite, and pure water to a ball mill. After ball milling for 4 h, a mixed slurry is obtained. Among them, the mass ratio of sodium hypochlorite to bamboo powder is 0.11:1. The solid content of the obtained mixed slurry is 15%, the particle size D50 of the mixed slurry is 5 μm, and D100 is 20 μm.

[0095] (2) Press-filter and wash the mixed slurry in a plate-and-frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0096] (3) Mix the wet material, sodium dihydrogen phosphate, and pure water to obtain a mixed material with a solid content of 10%. Among them, the mass ratio of sodium dihydrogen phosphate to bamboo powder is 0.1:1. Subsequently, spray-dry the mixed material. The inlet air temperature for spray drying is 230 °C, and the outlet temperature for spray drying is 90 °C to obtain a dried material with a particle size of 10 μm.

[0097] (4) Put the dried material into a box furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it at a heating rate of 2 °C / min to 100 °C and hold for 2 h; then heat it at a heating rate of 2 °C / min to 1000 °C and hold for 1 h; then heat it at a heating rate of 1.33 °C / min to 1400 °C and hold for 2 h; finally, cool it naturally to room temperature to obtain a hard carbon negative electrode material.

[0098] Example 9 (1)Bamboo powder, sodium hypochlorite and pure water were added to a ball mill, and a mixed slurry was obtained after ball milling for 4 h. Among them, the mass ratio of sodium hypochlorite to bamboo powder was 0.12:1, the solid content of the obtained mixed slurry was 15%, the particle size D50 of the mixed slurry was 5 μm, and D100 was 20 μm.

[0099] (2)The mixed slurry was pressure-filtered and washed in a plate-and-frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm, and then a wet material was obtained.

[0100] (3)The wet material, sodium dihydrogen phosphate and pure water were mixed to obtain a mixed material with a solid content of 10%. Among them, the mass ratio of sodium dihydrogen phosphate to bamboo powder was 0.1:1. Then, the mixed material was spray-dried. The inlet air temperature of the spray drying was 230 °C, and the outlet temperature of the spray drying was 90 °C, and a dried material with a particle size of 10 μm was obtained.

[0101] (4)The dried material was placed in a box furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first it was heated to 100 °C at a heating rate of 2 °C / min and held for 2 h; then it was heated to 1000 °C at a heating rate of 2 °C / min and held for 1 h; then it was heated to 1400 °C at a heating rate of 1.33 °C / min and held for 2 h; finally, it was naturally cooled to room temperature to obtain a hard carbon negative electrode material.

[0102] Comparative Example 1 (1)Bamboo powder and pure water were added to a ball mill, and a mixed slurry was obtained after ball milling for 4 h. The solid content of the obtained mixed slurry was 15%, the particle size D50 of the mixed slurry was 4 - 6 μm, and D100 < 35 μm.

[0103] (2)The mixed slurry was pressure-filtered and washed in a plate-and-frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm, and then a wet material was obtained.

[0104] (3)The wet material, sodium dihydrogen phosphate and pure water were mixed to obtain a mixed material with a solid content < 15%. Among them, the mass ratio of sodium dihydrogen phosphate to bamboo powder was 0.1:1. Then, the mixed material was spray-dried. The inlet air temperature of the spray drying was 230 °C, and the outlet temperature of the spray drying was 90 °C, and a dried material with a particle size of 10 - 20 μm was obtained.

[0105] (4) Put the dried material into a box-type furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it to 100°C at a heating rate of 2°C / min and hold for 2 h; then heat it to 1000°C at a heating rate of 2°C / min and hold for 1 h; then heat it to 1400°C at a heating rate of 1.33°C / min and hold for 2 h; finally, cool it naturally to room temperature to obtain the hard carbon negative electrode material.

[0106] Comparative Example 2 (1) Add bamboo powder, sodium hypochlorite, and pure water to a ball mill and obtain a mixed slurry after ball milling for 4 h. Among them, the mass ratio of sodium hypochlorite to bamboo powder is 0.08:1, the solid content of the obtained mixed slurry is 15%, the particle size D50 of the mixed slurry is 4 - 6 μm, and D100 < 35 μm.

[0107] (2) Press-filter and wash the mixed slurry in a plate-and-frame filter press until the pH of the filtrate > 6 and the conductivity < 20 μS / cm to obtain a wet material.

[0108] (3) Mix the wet material with pure water to obtain a mixed material with a solid content < 15%. Then, spray-dry the mixed material. The inlet air temperature for spray drying is 230°C, and the outlet temperature for spray drying is 90°C to obtain a dried material with a particle size of 10 - 20 μm.

[0109] (4) Put the dried material into a box-type furnace for high-temperature staged calcination. Under a nitrogen atmosphere, first heat it to 100°C at a heating rate of 2°C / min and hold for 2 h; then heat it to 1000°C at a heating rate of 2°C / min and hold for 1 h; then heat it to 1400°C at a heating rate of 1.33°C / min and hold for 2 h; finally, cool it naturally to room temperature to obtain the hard carbon negative electrode material.

[0110] II. Test Methods Use the hard carbon negative electrode materials prepared in Examples 1 - 9 and Comparative Examples 1 - 2 to prepare sodium-ion batteries. Specifically: (1) Prepare the negative electrode plate: Weigh 100 mg of CMC, 100 mg of SP, and 800 mg of the bamboo-based hard carbon negative electrode material according to the mass ratio of 10.0%:10.0%:80.0%, add an appropriate amount of deionized water, stir for 8 h until it becomes a uniform paste, and use a four-sided preparation scraper to evenly coat it on the surface of the copper foil. Dry it in a forced-air drying oven at 110°C for 12 h, and cut the Cu foil loaded with the active material in a glove box into round sheet electrodes to obtain the negative electrode plate.

[0111] (2)Preparation of sodium-ion battery: The assembly of the simulated battery was carried out in a glove box under an Ar atmosphere. The bamboo-based hard carbon electrode sheet prepared above was used as the negative electrode, a 1.0 mol / L commercial electrolyte, and the commercial electrolyte was prepared as follows: NaPF6 was added to a volume ratio of EC:DMC = 1:1, and a Na metal sheet was used as the counter electrode to assemble a CR2032 coin cell.

[0112] The sodium-ion batteries prepared in Examples 1-9 and Comparative Examples 1-2 were subjected to charge and discharge tests at a current density of 0.1C and different rates. The test results are shown in Table 1, where Figure 3 is the charge-discharge curve of the hard carbon negative electrode material prepared in Example 1 at a current density of 0.1C.

[0113] III. Analysis of Test Results of Each Example and Comparative Example Table 1 Electrochemical Performance of Sodium-Ion Batteries in Examples and Comparative Examples

[0114] From the data of Examples 1-5, it can be seen that the initial charge specific capacity, initial discharge specific capacity, and initial Coulomb efficiency of the sodium-ion battery first increase and then decrease with the increase of the doping amounts of sodium source and phosphorus source in the hard carbon negative electrode material. Among them, when the total mass ratio of phosphorus source and sodium source to the mass of bamboo powder is 0.1:1, the electrical performance of the obtained hard carbon negative electrode material is the best, that is, the initial charge specific capacity, initial discharge specific capacity, and initial Coulomb efficiency of the obtained sodium-ion battery are all the best. From the data of Examples 1 and 6-9, it can be seen that the initial discharge specific capacity of the sodium-ion battery decreases with the increase of the amount of reducing agent in the hard carbon negative electrode material. And with the increase of the amount of reducing agent, the initial charge specific capacity and capacity retention rate of the sodium-ion battery first increase and then decrease, while the initial Coulomb efficiency gradually increases, indicating that using a reducing agent to remove lignin from bamboo powder can improve the electrochemical performance of the prepared hard carbon negative electrode material, which is conducive to improving the initial Coulomb efficiency of the prepared sodium-ion battery. Among them, when the mass ratio of the reducing agent to bamboo powder is 0.08:1, applying the prepared hard carbon negative electrode material to the sodium-ion battery, the initial charge specific capacity, initial discharge specific capacity, initial Coulomb efficiency, and 1C / 0.1C capacity retention rate of the prepared sodium-ion battery are all good.

[0115] Furthermore, compared with Example 1, in Comparative Example 1, the bamboo powder was not subjected to reduction treatment, that is, lignin was not removed. Due to the relatively high content of oxygen-containing functional groups in lignin, the oxygen defect concentration of the hard carbon negative electrode material after sintering is relatively high, and there are more reactive sites. Therefore, the initial discharge capacity of the sodium-ion battery prepared with this hard carbon negative electrode material is relatively high, but at the same time, there is a significant decrease in the initial Coulomb efficiency and rate performance.

[0116] Furthermore, compared with Example 1, in Comparative Example 2, sodium dihydrogen phosphate was not added, that is, P and Na elements were not introduced. Therefore, the first charge specific capacity, the first discharge specific capacity, the first Coulombic efficiency, and the rate performance of the sodium-ion battery prepared with this hard carbon negative electrode material are all poor.

[0117] Furthermore, Figure 1 FIG. is the SEM image of the hard carbon negative electrode material prepared in Example 1. It can be seen that the hard carbon negative electrode material prepared in this application presents a hollow fibrous structure. The hollow fiber structure is beneficial to the infiltration of the electrolyte, thereby improving the rate performance of the sodium-ion battery.

[0118] Furthermore, Figure 2 FIG. is the Raman spectrum of the hard carbon negative electrode material prepared in Example 1. It can be seen that I D / I G = 1.121. The larger the value of I D / I G , the more carbon defects in the material, indicating that the preparation method provided by the present invention causes partial graphitization of the material during the calcination process, and the prepared hard carbon negative electrode material is an amorphous structure.

[0119] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples. Embodiments having the same composition and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be thought of by those skilled in the art to the embodiments, and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A method for preparing a hard carbon negative electrode material, characterized in that, It includes the following steps: Mix bamboo powder, a reducing agent and a solvent, and perform dispersion treatment to obtain a mixed slurry; Perform solid-liquid separation on the mixed slurry to obtain a wet material; Mix the wet material with a phosphorus source and a sodium source to obtain a mixed material; Perform drying and calcination treatment on the mixed material to obtain a hard carbon negative electrode material.

2. The preparation method of the hard carbon negative electrode material according to claim 1, wherein, The mass ratio of the reducing agent to the bamboo powder is (0.06~0.12):1; and / or The reducing agent is one or more of sodium hypochlorite and hydrogen peroxide.

3. The preparation method of the hard carbon negative electrode material according to claim 1, wherein, The solid content of the mixed slurry is 10~20%; and / or The D50 particle size of the mixed slurry is 4~6μm, and the D100 particle size < 35μm.

4. The preparation method of the hard carbon negative electrode material according to claim 1, wherein, The solid-liquid separation step includes: performing pressure filtration and washing on the mixed slurry until the pH of the obtained filtrate > 6 and the conductivity < 20 μS / cm to obtain the wet material.

5. The preparation method of the hard carbon negative electrode material according to claim 1, characterized in that, The mass ratio of the total mass of the phosphorus source and the sodium source to the mass of the bamboo powder is (0.08~0.12):1; and / or The phosphorus source is one or more of phosphoric acid, sodium dihydrogen phosphate, sodium hydrogen phosphate, disodium hydrogen phosphate, and sodium phosphate; and / or The sodium source is one or more of sodium hydroxide, sodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, and disodium hydrogen phosphate.

6. The preparation method of the hard carbon negative electrode material according to claim 1, characterized in that, The drying method is spray drying. Among them, the inlet air temperature of the spray drying is 230 - 270°C, the outlet temperature of the spray drying is 80 - 100°C, and the particle size of the obtained dried material is 10 - 20μm.

7. The preparation method of the hard carbon negative electrode material according to claim 1, characterized in that, The process of calcining the dried material includes: first-stage calcination, second-stage calcination, and third-stage calcination; The process conditions of the first-stage calcination include: heating rate 1 - 3°C / min, temperature 90 - 110°C, and heat preservation time 2 - 3h; The process conditions of the second-stage calcination include: heating rate 1 - 3°C / min, temperature 110 - 1000°C, and heat preservation time 2 - 3h; The process conditions of the third-stage calcination include: heating rate 1 - 2°C / min, temperature 1000 - 1400°C, and heat preservation time 2 - 3h.

8. A hard carbon negative electrode material, characterized in that, Prepared by the preparation method according to any one of claims 1~7.

9. A negative electrode sheet, characterized in that, It includes the hard carbon negative electrode material according to claim 8.

10. A sodium-ion battery, characterized in that, It includes the negative electrode sheet according to claim 9.

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