Preparation and application of sodium-ion battery and its bamboo-based composite hard carbon negative electrode active material

Abstract

The application belongs to the technical field of sodium ion batteries, and particularly relates to a preparation method of a bamboo-based composite hard carbon negative electrode active material of a sodium ion battery. Bamboo powder is pretreated by alkali treatment and then by acid treatment to obtain pretreated bamboo powder. The pretreated bamboo powder is pre-carbonized and then dispersed in an alcohol aqueous solution together with starch for heat treatment, followed by cross-linking and carbonization treatment to obtain the bamboo-based composite hard carbon negative electrode active material. The application also includes the negative electrode material prepared by the method and the application of the negative electrode material in sodium ion batteries. The method can be used for preparing hard carbon negative electrode materials suitable for sodium ions, and is helpful to improve the electrochemical performance of sodium ion batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to the field of hard carbon negative electrode materials of sodium ion batteries. BACKGROUND

[0002] Among various new energy storage technologies, lithium ion batteries have an absolute dominant position, and have great advantages in cycle times, energy density and response speed. However, due to the scarcity and uneven distribution of lithium resources, the cost of lithium ion batteries is rising, and its further large-scale application is limited. Sodium ion batteries are expected to accelerate penetration in power storage with their own advantages.

[0003] Sodium resources are abundant (the content of sodium in the earth's crust is 2.75%, higher than the content of lithium 0.065‰), evenly distributed and low in cost, so they have strong sustainability and broad application prospects. However, the atomic radius of sodium ions is larger than that of lithium ions, and the interlayer compounds formed are unstable in thermodynamic properties. Conventional materials suitable for lithium ion intercalation and deintercalation are difficult to meet the effective intercalation and deintercalation requirements of sodium ions. This is one of the main reasons why lithium ion batteries have been widely used in commercial applications, while sodium ion batteries similar in theory are still in the laboratory stage.

[0004] Therefore, to commercialize sodium ion batteries, it is crucial to select the appropriate negative electrode material. Compared with metal alloys and metal oxides, which have fatal defects such as high volume expansion rate and low conductivity, hard carbon is the most promising industrial-grade negative electrode for sodium ion batteries. Among them, biomass with a wide range of sources and unique sodium storage microstructure is currently a popular application. However, the composition and structure of hard carbon materials prepared from different biomass materials differ greatly, and their sodium storage performance varies greatly. The existing biomass hard carbon preparation process is complex and unstable in performance, so there is an urgent need to develop a simple, excellent and stable biomass hard carbon material. SUMMARY

[0005] In view of the problem that the adaptability of biomass carbon to sodium ions is not ideal, and the sodium storage capacity, rate and other performances are not ideal, the application provides a preparation method of a bamboo-based composite hard carbon negative electrode active material for a sodium ion battery, aiming to prepare a hard carbon negative electrode active material with excellent capacity, rate and other performances suitable for sodium ion batteries.

[0006] The second object of the application is to provide a bamboo-based composite negative electrode hard carbon active material prepared by the preparation method.

[0007] The third object of the application is to provide the application of the bamboo-based composite hard carbon negative electrode active material in a sodium ion battery.

[0008] The fourth object of the present application is to provide a sodium ion battery comprising the bamboo-based composite hard carbon negative electrode active material.

[0009] Different biomasses have different material compositions and microstructure characteristics, and the schemes and effects of preparing electrode materials are different. Therefore, the present application attempts to use bamboo as a raw material to prepare a negative electrode material suitable for a sodium ion battery. However, it is found that when bamboo is used to prepare a sodium battery suitable material, many technical problems caused by the bamboo raw material need to be faced, for example: first, a large amount of small gas molecules is discharged during the carbonization of bamboo, which easily leads to the formation of open pores and the increase of specific surface area, promotes the excessive decomposition of electrolyte to form a thick SEI film, and inhibits the diffusion and migration of sodium ions. Second, the inherent high defect content of the short-range disordered carbon layer edge or interlayer will inevitably cause irreversible sodium ion adsorption, resulting in poor specific capacity and first cycle coulombic efficiency. Third: due to the fiber structure characteristics of bamboo, it is difficult to form a suitable pore and path for sodium ion intercalation and deintercalation; Fourth: bamboo contains a large amount of trace elements, including electrochemical beneficial components and a large number of electrochemical non-beneficial components. How to selectively use beneficial components and minimize the interference of non-beneficial components is another major problem affecting the preparation effect. Fifth, the carbonized material of bamboo and other biomasses often has a disordered and fragmented morphology, and the electrode compact density is low, which is not conducive to future uniform industrial production.

[0010] In view of the above-mentioned problems in preparing a sodium ion suitable negative electrode active material from bamboo raw material, the present application provides the following solutions:

[0011] A preparation method of a bamboo-based composite hard carbon negative electrode active material for a sodium ion battery, comprising the following steps:

[0012] Step (1):

[0013] The bamboo powder is pretreated by alkali treatment and then by acid treatment to obtain pretreated bamboo powder;

[0014] Step (2):

[0015] The pretreated bamboo powder is pre-carbonized and then dispersed in an alcohol-water solution with starch for heat treatment, followed by carbonization treatment to obtain the bamboo-based composite hard carbon negative electrode active material.

[0016] In view of the problem that bamboo is difficult to meet the requirements of a sodium ion battery due to its own physicochemical characteristics, the present application innovatively pretreats it by alkali and then by acid, and then performs pre-carbonization, alcohol-water solvent heat treatment with starch, and carbonization treatment. In this way, the electrochemical beneficial components in the bamboo raw material can be selectively used, and the microstructure and surface activity can be improved, so that the requirements of a sodium ion battery can be met, the intercalation and deintercalation behavior of the sodium ion battery can be improved, the transmission network and path can be optimized, and the capacity, coulombic efficiency, and rate performance of the hard carbon negative electrode of the sodium ion battery can be improved.

[0017] In the present application, the bamboo is the raw material, and the combination of subsequent processes can achieve synergy, not only solving the problem of inadaptability of sodium-ion batteries caused by the physical and chemical characteristics of bamboo raw materials, but also helping to improve the capacity, coulomb efficiency and rate performance of sodium batteries.

[0018] In the present application, the bamboo powder is the powder of bamboo stems.

[0019] Preferably, the bamboo stems are dried and then crushed to obtain the bamboo powder; the particle size thereof is, for example, 10-30um.

[0020] In the present application, in view of the problems faced in the preparation of sodium-ion battery negative electrodes from bamboo raw materials, the present application innovatively adopts a pretreatment process of alkali followed by acid, which can solve the problem of selective use of components and is beneficial to improve the performance of the prepared material in sodium batteries.

[0021] In the present application, the alkaline solute in the alkali solution used in the alkali treatment stage includes at least one of alkali metal hydroxide, alkali metal carbonate and ammonia water.

[0022] Preferably, the alkaline solute is NaOH.

[0023] Preferably, in the alkali solution, the concentration of the alkaline solute is 0.1-1.5M, further preferably 0.9-1.1M.

[0024] The present application has found that the temperature of the alkali treatment stage is preferably controlled, which is helpful to further improve the synergistic effect of the combination of the process and the subsequent process. Preferably, the temperature of the alkali treatment stage is 20-100℃, further preferably 50-90℃, more preferably 60-80℃, and most preferably 75-85℃.

[0025] In the present application, the time of alkali treatment is 5-10h, and considering the processing cost and efficiency, it is further preferably 7-9h.

[0026] In the present application, the acid solute of the acid solution used in the acid treatment stage is at least one of HCl, sulfuric acid, nitric acid, citric acid, EDTA and gluconic acid. It has been found that the use of HCl compared to other single acids can unexpectedly further improve the adaptability of bamboo-based materials and sodium ions, which is helpful to further improve the performance of the prepared material.

[0027] Further preferably, the acidic solute comprises a combination of HCl and an auxiliary acid, the auxiliary acid being at least one of citric acid, EDTA, gluconic acid. The molar ratio of HCl and the auxiliary acid is for example 0.5-1.5:1. The present application finds that the preferred ingredients help to further selectively regulate the beneficial ingredients in the bamboo raw material, and facilitate the control of the sodium ion adaptation structure thereof, and help to make the prepared material exhibit more optimal electrochemical performance.

[0028] Preferably, in the acid solution, the concentration of the acidic solute is 0.5-3M, and further preferably 0.7-1.2M, considering the processing cost;

[0029] In the present application, the acid treatment stage can be carried out at room temperature, for example, at a temperature of 10-40℃.

[0030] In the present application, the acid treatment time is 8-15h, and further 10-14h, considering the processing efficiency;

[0031] In the present application, after acid treatment, water washing treatment is carried out, such as washing to neutral filtrate.

[0032] In the present application, the pre-treated material is pre-carbonized again, which helps to solve the problem of inadaptation of the prepared sodium battery negative electrode caused by the composition of the bamboo raw material, compared to pre-carbonization followed by alkali and then acid treatment.

[0033] In the present application, the atmosphere in the pre-carbonization stage is a protective atmosphere; for example, it can be at least one of nitrogen and argon.

[0034] In the present application, the pre-carbonization temperature is not particularly limited, for example, it can be 500-700℃.

[0035] In the present application, the pre-carbonization time can be adjusted as needed, for example, the processing time can be shortened when the temperature is higher, and the processing time can be prolonged when the temperature is relatively lower, and further 1-3h, considering the processing efficiency.

[0036] In the present application, starch is innovatively used to repair the pore structure and surface of pre-carbonization, and further combined with the joint control of alcohol-water solvent and heat treatment conditions, which can further improve the structure repair effect and help to further improve the electrochemical performance of the prepared material in sodium battery.

[0037] As preferred, the weight ratio of the pre-carbonized bamboo powder and starch is 1-10:1, and further 2-4:1; the preferred ratio can further improve the performance.

[0038] Preferably, the alcohol-water solution is a mixed solution of C1-C4 alcohol and water.

[0039] Preferably, the volume percentage of alcohol in the alcohol aqueous solution is 80-90V%;

[0040] Preferably, the volume ratio of the total weight of the pre-carbonized material and starch to the alcohol aqueous solution is 30-80mL / g.

[0041] Preferably, the temperature of the heat treatment is 60-80℃.

[0042] The time of the heat treatment is not particularly required, for example, it can be 1-8h, and further can be 3-5h.

[0043] In the present application, the carbonization process includes a first-stage carbonization at T1 and a second-stage carbonization at T2.

[0044] Preferably, the temperature of T1 is 400-600℃, and further can be 450-550℃.

[0045] Preferably, the temperature of T2 is 1000-1600℃, and further can be 1200-1400℃.

[0046] Preferably, the holding time t1 at T1 is 1-3h.

[0047] Preferably, the holding time t2 at T2 is 1-3h.

[0048] The present application also provides a bamboo-based composite hard carbon negative electrode active material prepared by the preparation method.

[0049] The preparation method of the present application can endow the prepared material with special physicochemical characteristics, and the material with the characteristics can unexpectedly exhibit excellent sodium ion adaptation effect and better electrochemical performance in sodium batteries.

[0050] The present application also provides the application of the bamboo-based composite hard carbon negative electrode active material prepared by the preparation method, which is used as a negative electrode active material to prepare a sodium ion battery.

[0051] In the present application, the sodium ion battery and its components required for the preparation of the negative electrode active material can be prepared based on known processes and equipment. For example, the negative electrode active material can be compounded and coated on a current collector together with a binder to form a negative electrode sheet for a sodium ion battery.

[0052] The present application also provides a sodium ion button-type half-cell, which comprises a hard carbon material electrode sheet as a positive electrode, a glass fiber separator and a sodium negative electrode, which are sequentially compounded, characterized in that the positive electrode sheet is a bamboo-based composite hard carbon negative electrode active material prepared by the preparation method.

[0053] A sodium ion battery (full battery) comprising a negative electrode, a separator and a positive electrode which are sequentially compounded, wherein the negative electrode comprises a bamboo-based composite hard carbon negative electrode active material prepared by the preparation method.

[0054] In the present application, in addition to the negative electrode comprising the bamboo-based composite hard carbon negative electrode active material, other materials and structures can be known in the industry.

[0055] The present application has the following advantages:

[0056] In view of the problem that the physical and chemical characteristics of bamboo itself make it difficult to adapt to the application requirements of sodium ion batteries, the present application innovatively performs pretreatment of alkali followed by acid on the bamboo, and then performs pre-carbonization, alcohol-water solvothermal treatment of starch, and carbonization treatment. This can selectively utilize the electrochemical beneficial components in the bamboo raw material, improve the microstructure and surface activity thereof, adapt to the application requirements of sodium ion batteries, improve the transmission network and path, optimize the embedding and de-embedding behavior of sodium ion batteries, and further improve the capacity, coulombic efficiency and rate performance of sodium ion batteries. The present application further optimizes the conditions of alkali treatment, acid treatment and material compounding, which is helpful to further improve the performance of the prepared material. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 SEM image of the negative electrode active material prepared in Example 1;

[0058] Figure 2 Test chart of Example 1; DETAILED DESCRIPTION

[0059] In order to further understand the present application, the following embodiments are used to further explain the features and advantages of the present application, but the present application is not limited to the following several embodiments.

[0060] In the present application, unless otherwise stated, the bamboo used refers to the stem part. After conventional crushing treatment, the particle size of the bamboo powder is not particularly required. In the following cases, unless otherwise stated, the D50 particle size of the bamboo powder is 10-30 um.

[0061] In the following cases, unless otherwise stated, the room temperature refers to a temperature between 20-35℃.

[0062] Example 1

[0063] Step (1): Preparation of bamboo powder

[0064] Bamboo is selected as the precursor, residual water is removed in a 100℃ oven, and a granular (bamboo powder) is coarsely crushed by an impact crusher.

[0065] Step (2): Pretreatment

[0066] In step (1), the dry bamboo chips (bamboo powder) were added with alkali solution (1M NaOH solution, liquid-solid ratio of 20 mL / g) and treated at 80°C for 8h, followed by centrifugal separation and then treated with acid solution (1M hydrochloric acid, liquid-solid ratio of 20 mL / g) for 12h (the temperature of the acid treatment stage was room temperature); finally washed with pure water until the filtrate was neutral, and dried in an 80°C oven to obtain the pretreated material;

[0067] Step (3): starch repair

[0068] The pretreated material was pre-carbonized at a temperature of 600°C under nitrogen for 2h to obtain a pre-carbonized material, which was then mixed with starch at a weight ratio of 7:3 and dispersed in 80% ethanol aqueous solution (liquid-solid ratio of 80 mL / g) and treated at a temperature of 70°C for 4h, followed by continued evaporation and drying to obtain a precursor;

[0069] Step (4): two-stage carbonization

[0070] The precursor was pre-carbonized at 500°C (marked as T1) for 2h (marked as t1) under a nitrogen atmosphere, and then ball-milled in a planetary ball mill at a speed of 400 rpm for 30 min, and sieved to a powder with a particle size D 50 of 20um, and finally transferred to a vacuum tube furnace and carbonized at a temperature of 1300°C (marked as T2) for 2h (marked as t2), with a heating rate of 5°C / min in the T1 / T2 stage. The negative electrode active material was prepared.

[0071] The hard carbon composite material obtained in Example 1 and sodium alginate were uniformly mixed at a mass ratio of 9:1, mixed and ground with the solvent N-methyl pyrrolidone (NMP), coated on a copper foil current collector, and vacuum dried at 80°C to obtain a negative electrode sheet. The battery assembly and testing were as follows: the negative electrode sheet was punched into an electrode sheet with a diameter of 10 mm, a metal sodium was used as the counter electrode, a glass fiber was used as the separator, and a 1M NaPF6 / EC:DEC (1:1) electrolyte was used to assemble a CR2032 button cell in a glove box. Constant current charge and discharge tests were carried out at 25°C and a current density of 30 mA / g. The electrochemical performance test results were as follows: the initial discharge specific capacity was 368 mAh / g, the first cycle coulombic efficiency was 90.96%, and the reversible capacity was 248 mAh / g after 100 cycles at 1C.

[0072] Example 2

[0073] Compared with Example 1, the only difference is that the conditions of the alkali treatment in step 2 are changed, and the experimental groups are as follows:

[0074] Group A: the temperature of alkali treatment stage is 60℃. Other process parameters, experimental steps remain consistent with Example 1. The electrochemical performance test results: the first discharge specific capacity is 363 mAh / g, the first cycle coulombic efficiency is 90.08%. The reversible capacity is 239 mAh / g after 100 cycles at 1C.

[0075] Group B: the temperature of alkali treatment stage is 100℃. Other process parameters, experimental steps remain consistent with Example 1. The electrochemical performance test results: the first discharge specific capacity is 331 mAh / g, the first cycle coulombic efficiency is 83.78%. The reversible capacity is 232 mAh / g after 100 cycles at 1C.

[0076] Group C: the temperature of alkali treatment stage is room temperature (20-25℃). Other process parameters, experimental steps remain consistent with Example 1. The electrochemical performance test results: the first discharge specific capacity is 344 mAh / g, the first cycle coulombic efficiency is 88.78%. The reversible capacity is 229 mAh / g after 100 cycles at 1C.

[0077] Example 3

[0078] Compared with Example 1, the only difference is that the conditions of acid treatment are changed, and the experimental groups are as follows:

[0079] Group A: the acid is nitric acid. Other process parameters, experimental steps remain consistent with Example 1. The electrochemical performance test results: the first discharge specific capacity is 347 mAh / g, the first cycle coulombic efficiency is 89.09%. The reversible capacity is 233 mAh / g after 100 cycles at 1C.

[0080] Group B: the acid is sulfuric acid. Other process parameters, experimental steps remain consistent with Example 1. The electrochemical performance test results: the first discharge specific capacity is 352 mAh / g, the first cycle coulombic efficiency is 90.27%. The reversible capacity is 238 mAh / g after 100 cycles at 1C.

[0081] Group C: the acid is a mixed acid of 0.5M hydrochloric acid and 0.5M EDTA. Other process parameters, experimental steps remain consistent with Example 1. The electrochemical performance test results: the first discharge specific capacity is 375 mAh / g, the first cycle coulombic efficiency is 91.87%. The reversible capacity is 251 mAh / g after 100 cycles at 1C.

[0082] From Example 1 and 3, it can be seen that using HCl can be combined with other processes to improve performance synergistically, and innovatively combining HCl and auxiliary acid can unexpectedly further improve the synergistic effect.

[0083] Example 4

[0084] Compared with Example 1, the only difference is that the conditions of step 3 are changed, and the experimental groups are as follows:

[0085] Group A: the mass ratio of pre-carbonized material to starch is 5:5. Other process parameters and experimental steps remain the same as those of Example 1. The electrochemical performance test results are as follows: the initial specific discharge capacity is 364 mAh / g, the first cycle coulombic efficiency is 87.73%, and the reversible capacity is 227 mAh / g after 100 cycles at 1C.

[0086] Group B: the mass ratio of pre-carbonized material to starch is 9:1. Other process parameters and experimental steps remain the same as those of Example 1. The electrochemical performance test results are as follows: the initial specific discharge capacity is 352 mAh / g, the first cycle coulombic efficiency is 88.97%, and the reversible capacity is 239 mAh / g after 100 cycles at 1C.

[0087] Group C: the volume of ethanol in the ethanol aqueous solution is changed to 90%. Other process parameters and experimental steps remain the same as those of Example 1. The electrochemical performance test results are as follows: the initial specific discharge capacity is 352 mAh / g, the first cycle coulombic efficiency is 89.71%, and the reversible capacity is 237 mAh / g after 100 cycles at 1C.

[0088] Group D: the pre-carbonization temperature is 500°C. Other process parameters and experimental steps remain the same as those of Example 1. The electrochemical performance test results are as follows: the initial specific discharge capacity is 356 mAh / g, the first cycle coulombic efficiency is 88.53%, and the reversible capacity is 241 mAh / g after 100 cycles at 1C.

[0089] From Examples 1 and 4A, 4B, it can be seen that under the preferred mass ratio of pre-carbonized material to starch of 2-4:1, a better synergistic effect can be obtained.

[0090] Example 5

[0091] Compared with Example 1, the only difference is that the conditions of step 4 are changed, and the specific changes are as follows:

[0092] Group A: T1 is 400°C, t1 is 3h; T2 is 1100°C, t2 is 3h. Other process parameters and experimental steps remain the same as those of Example 1. The electrochemical performance test results are as follows: the initial specific discharge capacity is 361 mAh / g, the first cycle coulombic efficiency is 87.28%, and the reversible capacity is 238 mAh / g after 100 cycles at 1C.

[0093] Group B: T1 is 600°C, t1 is 1h; T2 is 1500°C, t2 is 1.5h. Other process parameters and experimental steps remain the same as those of Example 1. The electrochemical performance test results are as follows: the initial specific discharge capacity is 349 mAh / g, the first cycle coulombic efficiency is 89.17%, and the reversible capacity is 227 mAh / g after 100 cycles at 1C.

[0094] Comparative Example 1

[0095] Compared with Example 1, the only difference is that cotton is used to replace the bamboo in the same amount, and other operations and parameters are the same as those in Example 1. The electrochemical performance test results are as follows: the first discharge specific capacity is 322 mAh / g, the first cycle coulombic efficiency is 85.17%, and the reversible capacity is 202 mAh / g after 100 cycles at 1C.

[0096] Comparative Example 2

[0097] Compared with Example 1, the only difference is that the step 2 treatment is not performed, and the bamboo powder of step 1 is directly subjected to step 3 and subsequent steps, and other parameter conditions are the same as those in Example 1. The electrochemical performance test results are as follows: the first discharge specific capacity is 289 mAh / g, the first cycle coulombic efficiency is 79.37%, and the reversible capacity is 186 mAh / g after 100 cycles at 1C.

[0098] Comparative Example 3

[0099] Compared with Example 1, the only difference is that in step 2, only alkali treatment is performed, and no acid treatment is performed, and the alkali treatment conditions are the same as those in Example 1. The electrochemical performance test results are as follows: the first discharge specific capacity is 314 mAh / g, the first cycle coulombic efficiency is 82.17%, and the reversible capacity is 208 mAh / g after 100 cycles at 1C.

[0100] Comparative Example 4

[0101] Compared with Example 1, the only difference is that in step 2, only acid treatment is performed, and no alkali treatment is performed, and the acid treatment conditions are the same as those in Example 1. The electrochemical performance test results are as follows: the first discharge specific capacity is 309 mAh / g, the first cycle coulombic efficiency is 84.17%, and the reversible capacity is 198 mAh / g after 100 cycles at 1C.

[0102] Comparative Example 5

[0103] Compared with Example 1, the only difference is that in step 2, acid treatment is performed first, and then alkali treatment is performed, and the acid treatment and alkali treatment parameter conditions are the same as those in Example 1. The electrochemical performance test results are as follows: the first discharge specific capacity is 349 mAh / g, the first cycle coulombic efficiency is 86.93%, and the reversible capacity is 227 mAh / g after 100 cycles at 1C.

[0104] From Example 1 and Comparative Example 5, it can be seen that the process for treatment according to the application can unexpectedly solve the problem that bamboo is not suitable for sodium-ion batteries, and can unexpectedly obtain better electrochemical performance.

[0105] Comparative Example 6

[0106] Compared with Example 1, the only difference is that the starch is replaced by the same weight of glucose, and other operations and parameters are the same as those in Example 1. The electrochemical performance test results are as follows: the initial specific discharge capacity is 338 mAh / g, the first cycle coulombic efficiency is 86.27%, and the reversible capacity is 216 mAh / g after 100 cycles at 1C.

[0107] Comparative Example 7

[0108] Compared with Example 1, the only difference is that the starch is replaced by the same weight of pitch, and other operations and parameters are the same as those in Example 1. The electrochemical performance test results are as follows: the initial specific discharge capacity is 302 mAh / g, the first cycle coulombic efficiency is 84.66%, and the reversible capacity is 223 mAh / g after 100 cycles at 1C.

[0109] Comparative Example 8

[0110] Compared with Example 1, the only difference is that the aqueous ethanol solution in step 3 is replaced by pure water, and the amount of pure water is the same as that of the aqueous ethanol solution. The electrochemical performance test results are as follows: the initial specific discharge capacity is 342 mAh / g, the first cycle coulombic efficiency is 86.94%, and the reversible capacity is 211 mAh / g after 100 cycles at 1C.

[0111] Comparative Example 9

[0112] Compared with Example 1, the only difference is that the pre-carbonized material and the starch are dry ball milled in step 3 for 30 min at a speed of 300 r / min. The electrochemical performance test results are as follows: the initial specific discharge capacity is 329 mAh / g, the first cycle coulombic efficiency is 83.07%, and the reversible capacity is 203 mAh / g after 100 cycles at 1C.

[0113] In summary, in view of the problem that the bamboo base is difficult to adapt to the application requirements of sodium ion batteries due to its own physicochemical characteristics, the present application innovatively performs a pre-alkali and post-acid pretreatment on the bamboo base, and then performs a pre-carbonization, an alcohol-water solvent heat treatment with starch, and a carbonization treatment. In this way, the electrochemically beneficial components in the bamboo raw material can be selectively utilized, and the microstructure and surface activity of the bamboo raw material can be improved, so that the bamboo raw material can adapt to the application requirements of sodium ion batteries, the transmission network and pathway can be improved, the embedding and de-embedding behavior of the sodium ion battery can be optimized, and the capacity, coulombic efficiency, and rate performance of the sodium ion battery can be improved. The present application further optimizes the conditions of alkali treatment, acid treatment, and material compounding, which is helpful to further synergistically improve the performance of the prepared material.

[0114] The above merely provides the preferred embodiment of the present application, and should not be used to limit the implementation of the present application. Those skilled in the art can make various modifications and variations without departing from the spirit of the present application. Therefore, the scope of the present application shall be determined only by the scope of the claims.

Claims

1. A method for preparing a bamboo-based composite hard carbon negative electrode active material of a sodium-ion battery, characterized by the steps of The application relates to a preparation method of a bamboo-based composite hard carbon negative electrode active material. Step (1): The bamboo powder is pretreated by alkali treatment and then by acid treatment to obtain pretreated bamboo powder; Step (2): The pretreated bamboo powder is pre-carbonized, and then the pre-carbonized material and starch are dispersed in an alcohol aqueous solution for heat treatment, and then carbonization treatment is carried out to obtain the bamboo-based composite hard carbon negative electrode active material; The mass ratio of the pre-carbonized material to the starch is 1-10:1; In the alcohol aqueous solution, the volume percentage of alcohol is 80-90%; The heat treatment temperature is 60-80 DEG C.

2. The method of claim 1, wherein the sodium-ion battery bamboo-based composite hard carbon negative electrode active material is prepared by the following steps: 1) preparing a bamboo-based carbon precursor; 2) mixing the bamboo-based carbon precursor with a sodium source to obtain a mixture; 3) heating the mixture to obtain a sodium-ion battery bamboo-based composite hard carbon negative electrode active material. The bamboo powder is bamboo stem powder.

3. The preparation method of the bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as described in claim 2, characterized in that, The bamboo stem is dried and then crushed to obtain the bamboo powder.

4. The preparation method of the bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as described in claim 3, characterized in that, The particle size of the bamboo powder is 10-30 um.

5. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The alkali solution in the alkali treatment stage adopts at least one of alkali metal hydroxide, alkali metal carbonate and ammonia water as an alkali solute.

6. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 5, wherein, The alkali solute is NaOH.

7. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 5, wherein, In the alkali solution, the concentration of the alkali solute is 0.1-1.5 M.

8. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 5, wherein, The temperature in the alkali treatment stage is 20-100 DEG C.

9. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 8, wherein, The temperature in the alkali treatment stage is 50-90 DEG C.

10. The method for preparing the bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as described in claim 9, characterized in that, The temperature in the alkali treatment stage is 60-80 DEG C.

11. The method of making a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries according to claim 9, wherein, The temperature in the alkali treatment stage is 75-85 DEG C.

12. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The alkali treatment time is 5-10 h.

13. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The acid solution in the acid treatment stage adopts at least one of HCl, sulfuric acid, nitric acid, citric acid, EDTA and gluconic acid as an acid solute.

14. The method for preparing the bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as described in claim 13, characterized in that, The acid solute is a combined acid of HCl and auxiliary acid, and the auxiliary acid is at least one of citric acid, EDTA and gluconic acid.

15. The method of making a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries according to claim 14, wherein, The molar ratio of HCl to auxiliary acid is 0.5-1.5:

1.

16. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 13, wherein, In the acid solution, the concentration of the acid solute is 0.5-3 M.

17. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The acid treatment time is 8-15 h.

18. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, After the acid treatment, water washing treatment is carried out until neutralization.

19. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The atmosphere in the pre-carbonization stage is a protective atmosphere.

20. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The pre-carbonization temperature is 500-700 DEG C.

21. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The pre-carbonization time is 1-3 h.

22. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The alcohol aqueous solution is a mixed solution of C1-C4 alcohol and water.

23. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The total weight of the pre-carbonized material and starch and the volume of the alcohol aqueous solution are in a ratio of 30-80 mL / g.

24. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, After the heat treatment, evaporation desolventization and drying are carried out, and then subsequent carbonization treatment is carried out.

25. The process for the preparation of a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries as claimed in claim 1, wherein, The carbonization process comprises a first-stage carbonization at T1 and a second-stage carbonization at T2. The temperature T1 is 400-600 DEG C. The temperature T2 is 1000-1600 DEG C.

26. The method of producing a bamboo-based composite hard carbon negative electrode active material for sodium-ion batteries according to claim 25, wherein The holding time t1 at the temperature T1 is 1-3 h. The holding time t2 at the temperature T2 is 1-3 h.

27. A bamboo-based composite hard carbon negative electrode active material prepared by the preparation method in any one of claims 1-26.

28. The use of a bamboo-based composite hard carbon negative electrode active material prepared by the method of any one of claims 1-26, characterized in that, The bamboo-based composite hard carbon negative electrode active material is used as a negative electrode active material to prepare a sodium ion battery.

29. A sodium-ion battery comprising a negative electrode, a separator, and a positive electrode, which are sequentially compounded, characterized in that, The negative electrode of the sodium ion battery comprises the bamboo-based composite hard carbon negative electrode active material prepared by the preparation method in any one of claims 1-26.

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