Preparation method and application of biomass hard carbon negative electrode material with reduced pH value

Abstract

The present application belongs to the technical field of biomass hard carbon, and particularly relates to a preparation method and application of a biomass hard carbon negative material with reduced pH value. The preparation method comprises the following steps: after the biomass raw material is cleaned and filtered dry, the water is removed by drying, the pretreated material is pre-carbonized under a protective atmosphere to obtain pre-carbonized material; the pre-carbonized material is crushed to obtain crushed material; the crushed material is first subjected to acid pickling and then water washing and ash removal, and then is subjected to suction filtration and drying to obtain purified material; the purified material is subjected to high-temperature carbonization under a protective atmosphere to obtain high-temperature carbonized material; the high-temperature carbonized material is again subjected to acid pickling, and then is subjected to water washing, suction filtration and drying to obtain acid-pickling carbonized material; the acid-pickling carbonized material is uniformly mixed with a modifier, and then is subjected to high-temperature coating carbonization under a protective atmosphere, and after iron is removed by sieving, the biomass hard carbon negative material with reduced pH value is obtained. The application comprises a negative electrode sheet and a battery. By reducing the pH value of the biomass hard carbon negative material, the first coulomb efficiency of the biomass hard carbon negative material is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biomass hard carbon and specifically relates to a preparation method and application of a biomass hard carbon negative material with reduced pH value. BACKGROUND

[0002] Due to the rich resource of sodium, the similar physical and chemical properties of sodium ion batteries and lithium ion batteries and the same principle, both of which belong to "rocking chair batteries", sodium ion batteries have been paid attention again. The sodium ion battery is mainly composed of a positive material, a negative material, an electrolyte and a separator, wherein the positive and negative materials of the sodium ion battery are decisive factors and play a key role in the performance of the whole battery. The negative material is mainly carbon-based material (soft carbon / hard carbon, etc.), alloy material, transition metal compound and organic compound. Due to the advantages of rich resource, good conductivity, stable cycle performance and non-toxicity of the hard carbon material, the industrialization thereof is fast, so that it becomes the preferred negative material of the sodium ion battery.

[0003] However, the existing hard carbon negative material has problems of low initial efficiency, poor cycle stability and rate performance, which seriously hinders the application of the hard carbon negative material in the industrialization of the sodium ion battery. At present, the sodium storage performance of the hard carbon negative material is improved mainly through the following aspects: (1) controlling the synthesis and pyrolysis process of the precursor to regulate the pore structure and interlayer spacing of the hard carbon; (2) coating and compounding with other materials, doping of heteroatoms and the like to regulate the defect degree and interlayer spacing of the material, but few studies focus on the influence of pH value on the energy storage performance. In fact, controlling the pH value of the hard carbon negative material to reduce defects and maintain the structure stability is very crucial to the improvement of the battery performance. Therefore, it is of great significance to study the effect of pH value on the biomass hard carbon negative material. SUMMARY

[0004] The first object of the present application is to provide a preparation method of a biomass hard carbon negative material with reduced pH value, the second object of the present application is to provide a biomass hard carbon negative material with reduced pH value, the third object of the present application is to provide a negative electrode sheet, and the fourth object of the present application is to provide a battery.

[0005] The present application reduces the pH value of the biomass hard carbon negative material, improves the initial coulombic efficiency and cycle stability of the biomass hard carbon negative material.

[0006] To achieve the above objects and other related objects, the present application provides the following technical solutions.

[0007] In a first aspect, the present application provides a preparation method of a biomass hard carbon negative material with reduced pH value, comprising the following steps,

[0008] Preprocessing: after the biomass raw material is washed and filtered dry, water is removed by drying to obtain the pretreated material;

[0009] Low-temperature pre-carbonization: the pretreated material is pre-carbonized under a protective atmosphere to obtain a pre-carbonized material;

[0010] Crushing: the pre-carbonized material is crushed to obtain a crushed material;

[0011] Purification: the crushed material is first pickled and then washed with water to remove ash, and then filtered and dried to obtain a purified material;

[0012] High-temperature carbonization: the purified material is high-temperature carbonized under a protective atmosphere to obtain a high-temperature carbonized material;

[0013] It should be noted that the high-temperature carbonized material is pickled again in the present application, which not only reduces the amino functional groups attached to the surface and further reduces the pH, but also removes the residual metal on the surface to reduce the ash content, thereby improving the capacity of the battery.

[0014] Pickling: the high-temperature carbonized material is pickled again, then washed with water, filtered and dried to obtain a pickled carbonized material;

[0015] Coated carbonization: the pickled carbonized material is mixed with a modifier, then high-temperature coated carbonization is performed under a protective atmosphere, and iron is removed by sieving to obtain a biomass hard carbon negative material with reduced pH.

[0016] With the above technical solution, in the prior art, because the oxygen content of phenolic resin is relatively high, phenolic resin is often used to prepare porous carbon. Foaming method and other methods are usually used to prepare phenolic resin carbon precursor, but in the present application, it is found that phenolic resin has other effects. Specifically: because of the objective defects of pickling, such as: although the high-temperature carbonized material is pickled again to reduce the pH of the high-temperature carbonized material and remove part of the impurities, pickling can destroy the oxygen-containing functional groups and form pore structures on the surface, increase the pore collapse rate and defect degree, cause the specific surface area to be too large, and affect the battery performance. Therefore, after the carbonized material is pickled, the present application finds that the structure can be repaired by high-temperature coated carbonization of phenolic resin, the closed porosity and porosity are reduced, and the first coulombic efficiency and cycle stability of the biomass hard carbon negative material are improved.

[0017] In an embodiment of the present application, in the preprocessing, the biomass raw material is washed clean with deionized water, filtered dry, and then placed in a forced air drying oven, the drying temperature is 60-200℃, the drying time is 6-48h, and the water is removed by drying to obtain the pretreated material; the biomass raw material includes at least one of bamboo, coconut shell and wood.

[0018] In an embodiment of the present application, in the low-temperature pre-carbonization, the protective atmosphere comprises at least one of nitrogen, argon and helium; the pre-carbonization conditions comprise a heating rate of 2-10°C / min, a pre-carbonization temperature of 200-800°C, a holding time of 1-3h, and the pre-carbonization is performed in an atmosphere carbonization furnace.

[0019] In an embodiment of the present application, in the pulverization, the pulverization equipment comprises at least one of a mechanical pulverizer, a roller mill pulverizer and an air flow pulverizer, and the particle size of the pulverized material is controlled to be 3-17um.

[0020] In an embodiment of the present application, in the acid washing, the acid comprises at least one of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid and sulfuric acid; the acid concentration is 0.5-5mol / L, the reaction temperature is 60-100°C, the solid-liquid mass ratio is 1:0.7-5.5, and the acid washing time is 6-24h; the water washing and ash removal comprises multiple deionized water washing until the filtrate is close to neutral, followed by suction filtration, a drying temperature of 80-150°C and a drying time of 6-48h.

[0021] In an embodiment of the present application, in the high-temperature carbonization, the high-temperature carbonization conditions comprise a heating rate of 2-10°C / min, a high-temperature carbonization temperature of 1200-1800°C, a holding time of 2-6h, and the high-temperature carbonization is performed in an atmosphere carbonization furnace; the protective atmosphere comprises at least one of nitrogen, argon and helium.

[0022] In an embodiment of the present application, in the acid washing, the acid comprises at least one of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid and sulfuric acid; the acid concentration is 0.5-3mol / L, the reaction temperature is 60-100°C, the solid-liquid mass ratio is 1:0.8-2, and the acid washing time is 6-12h; the water washing comprises multiple deionized water washing until the filtrate is close to neutral, followed by suction filtration, a drying temperature of 80-150°C and a drying time of 6-48h.

[0023] In an embodiment of the present application, in the high-temperature carbonization, the high-temperature carbonization conditions comprise a heating rate of 2-10°C / min, a high-temperature carbonization temperature of 1200-1800°C, a holding time of 2-6h, and the high-temperature carbonization is performed in an atmosphere carbonization furnace; the protective atmosphere comprises at least one of nitrogen, argon and helium.

[0024] In a second aspect, the present application provides a biomass hard carbon negative electrode material with reduced pH value, which is prepared by the above-mentioned method for preparing a biomass hard carbon negative electrode material with reduced pH value.

[0025] In a third aspect, the present application provides a negative electrode sheet, which uses the biomass hard carbon negative material with reduced pH value as an active material of a battery negative electrode material.

[0026] The preparation method of the negative electrode sheet comprises the following steps:

[0027] The binder, the additive, the biomass hard carbon negative material with reduced pH value, and the polymer are mixed in proportion to a uniform slurry, which is uniformly coated on a carrier, dried, and a negative electrode sheet is prepared.

[0028] In an embodiment of the present application, the binder comprises CMC (sodium carboxymethyl cellulose), the additive comprises conductive carbon black, and the polymer comprises SBR (styrene butadiene rubber).

[0029] In an embodiment of the present application, the mass ratio of the binder, the additive, the biomass hard carbon negative material with reduced pH value, and the polymer is 1-2.0%:2-4.0%:90.0-95%:1-2.0%.

[0030] In an embodiment of the present application, the carrier comprises a copper foil.

[0031] In an embodiment of the present application, the drying conditions comprise a drying temperature of 100-120°C and a drying time of 10-25 min.

[0032] In an embodiment of the present application, the specific preparation steps of the negative electrode sheet comprise:

[0033] CMC (sodium carboxymethyl cellulose) 0.2 g, conductive carbon black 0.4 g, hard carbon material 9.2 g, and SBR (styrene butadiene rubber, solid content 40%) 0.5 g are weighed according to the mass ratio of 2.0%:4.0%:92.0%:2.0%, and a proper amount of deionized water is added dropwise, stirred for 20 min to a uniform slurry, which is uniformly coated on the surface of a copper foil using a 100 μm scraper, dried in a 105°C air drying oven for 2 h, and the copper foil with active material is cut into a circular sheet negative electrode sheet, which is immediately transferred to a glove box for standby.

[0034] In a fourth aspect, the present application provides a battery, which is a sodium ion battery, the sodium ion battery comprising a negative electrode, a positive electrode, a separator, an electrolyte, a counter electrode, the negative electrode comprising the negative electrode sheet of claim 9, the sodium ion battery having a pH value of 6-8, a first charge specific capacity of 300-340 mAh / g, a first discharge specific capacity of 330-360 mAh / g, and a first efficiency of 90-95%, when subjected to charge-discharge test at a current density of 0.1C.

[0035] In an embodiment of the present application, the protective atmosphere comprises Ar.

[0036] In an embodiment of the present application, the electrolyte comprises at least one of NaPF6, EC, and DMC.

[0037] In an embodiment of the present application, the counter electrode comprises a Na metal sheet.

[0038] In an embodiment of the present application, the specific preparation steps of the sodium ion battery comprise: performing the assembly of the battery in a glove box in an Ar atmosphere, using the prepared biomass hard carbon negative electrode material negative electrode sheet with reduced pH value as the negative electrode, 1.0 mol / L commercial electrolyte, the commercial electrolyte being prepared as follows: the V:V of NaPF6 / EC:DMC is 1:1, and a Na metal sheet is used as the counter electrode, assembling a CR2032 button cell, and then using a constant current charge-discharge mode to perform charge-discharge test at a current density of 0.1C.

[0039] The negative electrode sheet and the battery described above are applications of the biomass hard carbon negative electrode material with reduced pH value.

[0040] The present application has the following beneficial effects:

[0041] During the high-temperature pyrolysis process of the biomass hard carbon, as the temperature increases, hydrogen atoms and nitrogen atoms escape, forming amino functional groups on the surface of the biomass hard carbon, causing the pH to be high, and in the subsequent process of forming a mixed slurry of the active material as the negative electrode material of the sodium battery, the binder, and the conductive carbon black, there is a phenomenon of colloidal agglomeration and corrosion of the aluminum foil during coating, resulting in uneven coating, and ultimately causing the specific capacity and the first efficiency of the battery to be low.

[0042] The present application re-acid pickles the high-temperature carbonized material, which can not only reduce the amino functional groups attached to the surface and further reduce the pH, but also remove the residual metal on the surface to reduce the ash content and improve the capacity of the battery. Although re-acid pickling can reduce the pH of the high-temperature carbonized material and remove part of the impurities, the acid pickling will destroy the oxygen-containing functional groups, form a pore structure on the surface by corrosion, increase the pore collapse rate and defect degree, cause the specific surface area to be too large, and affect the battery performance. Therefore, after acid pickling of the carbonized material, structure repair is needed by phenolic resin high-temperature coating carbonization to reduce the closed pores and porosity, so as to improve the first coulombic efficiency and cycle stability of the biomass hard carbon negative material. BRIEF DESCRIPTION OF DRAWINGS

[0043] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, illustrate embodiments of the present application and are used to explain the present application, and do not constitute a limitation on the present application. In the drawings:

[0044] Figure 1 is the XRD comparison diagram of the biomass hard carbon negative material of Example 1 and Comparative Example 1-3 of the present application;

[0045] Figure 2 is the SEM diagram of the biomass hard carbon negative material of Example 1 of the present application;

[0046] Figure 3 is the SEM diagram of the biomass hard carbon negative material of Comparative Example 1 of the present application;

[0047] Figure 4 is the IR comparison diagram of the biomass hard carbon negative material of Example 1 and Comparative Example 1 of the present application;

[0048] Figure 5 is the charge-discharge curve comparison diagram of the biomass hard carbon negative material of Example 1 and Comparative Example 1 of the present application under the condition of 0.1C.

[0049] Figure 6 is the cycle diagram of 700 cycles of the full battery of Example 1 of the present application under the condition of 1C. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0051] The equipment and materials used in the embodiments can be easily obtained from commercial companies if not specifically stated.

[0052] Phenol formaldehyde resin (AR, aladdin reagent)

[0053] A preparation method of a biomass hard carbon negative electrode material with reduced pH value, comprising the following steps:

[0054] Pre-treatment: the biomass raw material is cleaned with deionized water, filtered and dried, and then placed in a blast drying oven, with a drying temperature of 60-200 DEG C and a drying time of 6-48 h to remove water and obtain a pre-treated material; wherein the biomass raw material is at least one of bamboo, coconut shell and wood.

[0055] Low-temperature pre-carbonization: the pre-treated material is pre-carbonized under a protective atmosphere to obtain a pre-carbonized material, wherein the protective atmosphere is at least one of nitrogen, argon and helium; the pre-carbonization conditions are: a heating rate of 2-10 DEG C / min, a pre-carbonization temperature of 200-800 DEG C, and a holding time of 1-3 h, and the pre-carbonization is carried out in an atmosphere carbonization furnace.

[0056] Crushing: the pre-carbonized material is crushed to obtain a crushed material; the crushing equipment is at least one of a mechanical crusher, a roller mill crusher and an air flow crusher, and the particle size is controlled to be 3-17 um.

[0057] Purification: the crushed material is first subjected to acid washing, then water washing and ash removal, and then suction filtration and drying to obtain a purified material; wherein the acid for acid washing is at least one of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid and sulfuric acid, the acid concentration is 0.5-5 mol / L, the acid washing reaction temperature is 60-100 DEG C, the acid washing solid-liquid mass ratio is 1:0.7-5.5, and the acid washing time is 6-24 h; the specific process of water washing and ash removal is: multiple deionized water washing until the filtrate is close to neutral, and then suction filtration; the drying temperature is 80-150 DEG C, and the drying time is 6-48 h.

[0058] High-temperature carbonization: the purified material is subjected to high-temperature carbonization under a protective atmosphere to obtain a high-temperature carbonized material, and the high-temperature carbonization conditions are: a heating rate of 2-10 DEG C / min, a high-temperature carbonization temperature of 1200-1800 DEG C, and a holding time of 2-6 h, and the high-temperature carbonization is carried out in an atmosphere carbonization furnace; the protective atmosphere is at least one of nitrogen, argon and helium.

[0059] Acid washing: the high-temperature carbonized material is again subjected to acid washing, then water washing, suction filtration and drying to obtain an acid-washed carbonized material. The acid for the second acid washing is at least one of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid and sulfuric acid; the acid concentration is 0.5-3 mol / L, the acid washing reaction temperature is 60-100 DEG C, the acid washing solid-liquid mass ratio is 1:0.8-2, and the acid washing time is 6-12 h. The specific process of water washing is: multiple deionized water washing until the filtrate is close to neutral, and then suction filtration. The drying temperature is 80-150 DEG C, and the drying time is 6-48 h.

[0060] Coated carbonization: the pickling carbonized material is mixed with a modifier in a VC machine first, then high-temperature coated carbonization is carried out under a protective atmosphere, and a pH-reduced biomass hard carbon negative electrode material is obtained after screening out iron. The modifier is at least one of pitch and resin. The mass of the modifier accounts for 1-10%wt of the mass of the pickling carbonized material. The mixing time is 0.5-3h. The high-temperature coated carbonization conditions are: the heating rate is 2-10℃ / min, the high-temperature coated carbonization temperature is 1200-1800℃, and the holding time is 2-6h. The protective atmosphere is at least one of nitrogen, argon and helium. The mesh number of the vibrating screen machine used for screening is 200-400 mesh.

[0061] Application: the biomass hard carbon negative electrode material prepared above is used as an active substance of a battery negative electrode material for a sodium ion battery, and the preparation method is:

[0062] According to a mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2g, conductive carbon black 0.4g, hard carbon material 9.2g, and SBR 0.5g (styrene-butadiene rubber, solid content 40%) are weighed, and a proper amount of deionized water is added dropwise, stirred for 20min to form a uniform slurry, and then a 100μm doctor blade is used to uniformly coat the slurry on the surface of a copper foil. The copper foil with the active material is dried in a 105℃ air drying oven for 2h, cut into a circular negative electrode sheet, and then transferred to a glove box for standby.

[0063] The assembly of the simulated battery is carried out in an Ar atmosphere glove box, the prepared biomass hard carbon negative electrode sheet is used as the negative electrode, 1.0mol / L commercial electrolyte, the commercial electrolyte is prepared as follows: NaPF6 / EC:DMC V:V is 1:1, Na metal sheet is used as the counter electrode, CR2032 button cell is assembled, and then the constant current charge and discharge mode is used to carry out the charge and discharge test at a current density of 0.1C.

[0064] Example 1

[0065] A preparation method of a pH-reduced biomass hard carbon negative electrode material, comprising the following steps:

[0066] Step 1: pretreatment, the raw material of bamboo is cleaned with deionized water, filtered and dried, and then placed in a blast drying oven, the drying temperature is 120℃, the drying time is 24h, and the water is removed by drying to obtain pretreated material;

[0067] Step 2: low-temperature pre-carbonization, the pretreated material is placed in a nitrogen atmosphere carbonization furnace, heated to 500℃ at a heating rate of 5℃ / min, and held for 2h to obtain a bamboo precursor, i.e. pre-carbonized material;

[0068] Step 3: crushing, after the pre-carbonized material is cooled to room temperature, the bamboo precursor is taken out and crushed by roller grinding. The particle size D50 in the crushed particles is controlled at about 10 um, and a crushed material is obtained;

[0069] Step 4: purification, after crushing, the crushed material is placed in a 3 mol / L HCl aqueous solution, and acid washing is performed under the conditions of a solid-liquid mass ratio of 1:3, a temperature of 80°C, and a holding time of 12h. The filtrate is washed with deionized water until it is nearly neutral, and then filtered and placed in a forced air drying oven at a drying temperature of 120°C for 24h to obtain a purified material;

[0070] Step 5: high-temperature carbonization, the purified material is placed in a high-temperature atmosphere carbonization furnace and subjected to high-temperature carbonization at 5°C / min from room temperature to 1400°C under a nitrogen atmosphere for 4h to obtain a high-temperature carbonized material;

[0071] Step 6: acid washing, the high-temperature carbonized material is placed in a 2 mol / L HCl aqueous solution and subjected to acid washing under the conditions of a solid-liquid mass ratio of 1:1.4, a temperature of 80°C, and a holding time of 10h. The filtrate is washed with deionized water until it is nearly neutral, and then filtered and placed in a forced air drying oven at a drying temperature of 120°C for 24h to obtain an acid-washed carbonized material;

[0072] Step 7: coated carbonization, the obtained acid-washed carbonized material is mixed with phenolic resin at room temperature using a VC machine, and the mass of the phenolic resin is controlled to be 5wt% of the total mass of the acid-washed carbonized material. After mixing for 2h, the mixture is placed in a carbonization furnace for high-temperature coated carbonization. The temperature is raised to 1400°C at a rate of 5°C / min under a nitrogen atmosphere, and the carbonization time is 4h. After completion, the coated carbonized material is sieved in a vibrating screen machine with a mesh size of 325 mesh to obtain a biomass hard carbon negative material with reduced pH value. The structure analysis is referred to Figure 1 .

[0073] Step 8: the biomass hard carbon material prepared above is used as an active material for a battery negative material for a sodium ion battery. The preparation method is as follows:

[0074] According to a mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2g, conductive carbon black 0.4g, biomass hard carbon material 9.2g, SBR (styrene-butadiene rubber, solid content 40%) 0.5g, and an appropriate amount of deionized water are weighed and added. Stir for 20min until a uniform slurry is obtained. Use a 100um doctor blade to uniformly coat the surface of the copper foil. Dry in a 105°C air drying oven for 2h. Cut the Cu foil with active material into a circular negative electrode sheet and immediately transfer it to a glove box for standby.

[0075] The assembly of the simulation battery was carried out in an Ar atmosphere glove box, using the prepared biomass hard carbon negative electrode sheet as the negative electrode, 1.0 mol / L commercial electrolyte, the commercial electrolyte was prepared as follows: the V:V of NaPF6 / EC:DMC was 1:1, a Na metal sheet was used as the counter electrode, a CR2032 button cell was assembled, and then a constant current charge-discharge mode was used to carry out charge-discharge test at a current density of 0.1C, the first charge capacity was 334.6 mAh / g, the discharge capacity was 356.5 mAh / g, and the first coulombic efficiency was 93.9%.

[0076] Example 2

[0077] A preparation method of a biomass hard carbon negative electrode material with reduced pH value, comprising the following steps:

[0078] Step 1: pretreatment, the coconut shell raw material was cleaned with deionized water, dried, then placed in a forced air drying oven, the drying temperature was 120℃, the drying time was 24h, the water was removed by drying, and the pretreated material was obtained;

[0079] Step 2: low-temperature pre-carbonization, the pretreated material was placed in an atmosphere carbonization furnace, heated to 500℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and kept for 2h, and a coconut shell precursor was obtained, i.e. the pre-carbonized material;

[0080] Step 3: crushing, after the pre-carbonized material was cooled to room temperature, the coconut shell precursor was taken out and crushed by roller grinding, the particle size D50 in the crushed particles was controlled at about 10um, and the crushed material was obtained;

[0081] Step 4: purification, after crushing, the crushed material was placed in a 3mol / L HCL aqueous solution, acid washing and impurity removal were carried out under the conditions of a solid-liquid mass ratio of 1:3, a temperature of 80℃ and a holding time of 12h, deionized water was washed multiple times until the filtrate was close to neutral, then filtered and placed in a forced air drying oven, the drying temperature was 120℃, the drying time was 24h, and the purified material was obtained;

[0082] Step 5: high-temperature carbonization, the purified material was placed in a high-temperature atmosphere carbonization furnace, high-temperature carbonization was carried out at 5℃ / min from room temperature to 1400℃ under a nitrogen atmosphere for 4h, and a high-temperature carbonized material was obtained;

[0083] Step 6: acid washing, the high-temperature carbonized material was placed in a 2mol / L HCL aqueous solution, acid washing was carried out under the conditions of a solid-liquid mass ratio of 1:1.4, a temperature of 80℃ and a holding time of 10h, deionized water was washed multiple times until the filtrate was close to neutral, then filtered and placed in a forced air drying oven, the drying temperature was 120℃, the drying time was 24h, and the acid-washed carbonized material was obtained;

[0084] Step 7: carbonization, the obtained pickling carbonization material is mixed with phenolic resin at room temperature by a VC machine, the mass of the phenolic resin is controlled to be 5wt% of the total mass of the pickling carbonization material, after mixing for 2h, the mixture is placed in a carbonization furnace for high-temperature carbonization, the temperature is raised to 1400℃ at a rate of 5℃ / min under a nitrogen atmosphere, the carbonization time is 4h, after completion, the carbonized material is placed in a vibrating screen machine for screening, the mesh size of the vibrating screen machine is 325 mesh, after removing iron, a biomass hard carbon negative electrode material with reduced pH value is obtained.

[0085] Step 8: the biomass hard carbon material prepared above is used as an active material of a battery negative electrode for a sodium ion battery. The preparation method is as follows:

[0086] According to a mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2g, conductive carbon black 0.4g, biomass hard carbon material 9.2g, SBR (styrene-butadiene rubber solid content 40%) 0.5g are weighed, and an appropriate amount of deionized water is added dropwise, stirred for 20min to form a uniform slurry, and then a 100μm doctor blade is used to uniformly coat the slurry on the surface of a copper foil, and the copper foil is dried in a 105℃ air drying oven for 2h. The Cu foil with active material is cut into a circular negative electrode sheet, which is then transferred to a glove box for standby.

[0087] The assembly of the simulation battery is carried out in an Ar atmosphere glove box, the prepared biomass hard carbon negative electrode sheet is used as the negative electrode, 1.0mol / L commercial electrolyte, the commercial electrolyte is prepared as follows: NaPF6 / EC:DMC V:V is 1:1, Na metal sheet is used as the counter electrode, CR2032 button cell is assembled, and then the constant current charge and discharge mode is used for charge and discharge test at a current density of 0.1C.

[0088] Example 3

[0089] A preparation method of a biomass hard carbon negative electrode material with reduced pH value, comprising the following steps:

[0090] Step 1: pretreatment, the wood raw material is cleaned with deionized water, filtered and dried, and then placed in a forced air drying oven, the drying temperature is 120℃, the drying time is 24h, and the water is removed by drying to obtain a pretreated material;

[0091] Step 2: low-temperature pre-carbonization, the pretreated material is placed in a gas atmosphere carbonization furnace, the temperature is raised to 500℃ at a rate of 5℃ / min under a nitrogen atmosphere, and the temperature is maintained for 2h to obtain a wood precursor, i.e. a pre-carbonized material;

[0092] Step 3: crushing, after the pre-carbonized material is cooled to room temperature, the wood precursor is taken out and crushed by roller grinding, the particle size D50 in the crushed particles is controlled to be about 10um, and a crushed material is obtained;

[0093] Step 4: purification, after the crushing is completed, the crushed material is placed in a 3 mol / L HCL aqueous solution, the solid-liquid mass ratio is 1:3, the temperature is 80℃, and the incubation time is 12h. The impurities are removed by acid washing, and the filtrate is washed with deionized water until it is nearly neutral. Then it is filtered and placed in a forced air drying oven, the drying temperature is 120℃, and the drying time is 24h. The purified material is obtained;

[0094] Step 5: high-temperature carbonization, the purified material is placed in a high-temperature atmosphere carbonization furnace, and the temperature is raised from room temperature to 1400℃ at a rate of 5℃ / min under a nitrogen atmosphere for 4h. The high-temperature carbonized material is obtained;

[0095] Step 6: acid washing, the high-temperature carbonized material is placed in a 2 mol / L HCL aqueous solution, the solid-liquid mass ratio is 1:1.4, the temperature is 80℃, and the incubation time is 10h. The impurities are removed by acid washing, and the filtrate is washed with deionized water until it is nearly neutral. Then it is filtered and placed in a forced air drying oven, the drying temperature is 120℃, and the drying time is 24h. The acid-washed carbonized material is obtained;

[0096] Step 7: coated carbonization, the obtained acid-washed carbonized material is mixed with phenolic resin at room temperature using a VC machine, and the mass of phenolic resin is controlled to be 5wt% of the total mass of acid-washed carbonized material. After mixing for 2h, it is placed in a carbonization furnace for high-temperature coated carbonization. The temperature is raised to 1400℃ at a rate of 5℃ / min under a nitrogen atmosphere. The carbonization time is 4h. After completion, the coated carbonized material is placed in a vibrating screen machine for screening. The vibrating screen machine has a mesh size of 325 mesh. After removing iron, a biomass hard carbon negative material with reduced pH value is obtained.

[0097] Step 8: the biomass hard carbon material prepared above is used as an active material for battery negative material for sodium ion battery. The preparation method is as follows:

[0098] According to the mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2g, conductive carbon black 0.4g, biomass hard carbon material 9.2g, SBR (styrene-butadiene rubber, solid content 40%) 0.5g are weighed, and an appropriate amount of deionized water is added. Stir for 20min until uniform slurry. Use a 100μm spatula to evenly coat the surface of the copper foil. Dry in a 105℃ forced air drying oven for 2h. Cut the Cu foil with active material into round negative electrode sheets, and immediately transfer to a glove box for standby.

[0099] The assembly of the simulation battery was carried out in a glove box in an argon atmosphere, using the prepared biomass hard carbon negative electrode sheet as the negative electrode, 1.0 mol / L commercial electrolyte, the commercial electrolyte was prepared as follows: the V:V of NaPF6 / EC:DMC was 1:1, a Na metal sheet was used as the counter electrode, a CR2032 button cell was assembled, and then a constant current charge-discharge mode was used to carry out charge-discharge test at a current density of 0.1C.

[0100] Result analysis: according to the above examples 1-3, the raw material of the preparation method can be at least one of the bamboo raw material, the coconut shell raw material and the wood raw material.

[0101] Example 4

[0102] A preparation method of a biomass hard carbon negative electrode material with reduced pH value, comprising the following steps:

[0103] Step 1: pretreatment, the bamboo raw material is cleaned with deionized water, dried by filtration, and then placed in a forced air drying oven, the drying temperature is 60℃, the drying time is 6h, the water is removed by drying, and the pretreated material is obtained;

[0104] Step 2: low-temperature pre-carbonization, the pretreated material is placed in an atmosphere carbonization furnace, heated to 200℃ at a heating rate of 2℃ / min under argon atmosphere, and kept for 1h, to obtain bamboo precursor, i.e. pre-carbonized material;

[0105] Step 3: crushing, after the pre-carbonized material is cooled to room temperature, the bamboo precursor is taken out and crushed by roller grinding, the particle size D50 in the crushed particles is controlled at about 3um, and the crushed material is obtained;

[0106] Step 4: purification, after crushing, the crushed material is placed in a 0.5mol / L HF aqueous solution, acid washing is carried out under the conditions of solid-liquid mass ratio 1:0.7, temperature 60℃ and holding time 6h, deionized water is washed for multiple times until the filtrate approaches neutral, then filtered and placed in a forced air drying oven, the drying temperature is 80℃, and the drying time is 6h, to obtain the purified material;

[0107] Step 5: high-temperature carbonization, the purified material is placed in a high-temperature atmosphere carbonization furnace, and high-temperature carbonization is carried out at 2℃ / min from room temperature to 1200℃ under argon atmosphere for 2h, to obtain high-temperature carbonized material;

[0108] Step 6: acid washing, the high-temperature carbonized material is placed in a 0.5mol / L HF aqueous solution, acid washing is carried out under the conditions of solid-liquid mass ratio 1:0.8, temperature 60℃ and holding time 6h, deionized water is washed for multiple times until the filtrate approaches neutral, then filtered and placed in a forced air drying oven, the drying temperature is 80℃, and the drying time is 6h, to obtain the acid-washed carbonized material;

[0109] Step 7: carbonization, the obtained pickling carbonization material is mixed with phenolic resin at room temperature by a VC machine, the mass of the phenolic resin is controlled to be 1wt% of the total mass of the pickling carbonization material, after mixing for 0.5h, the mixture is placed in a carbonization furnace for high-temperature carbonization, the temperature is raised to 1200℃ at a rate of 2℃ / min under an argon atmosphere, the carbonization time is 2h, after completion, the carbonized material is placed in a vibrating screen machine for screening, the mesh size of the vibrating screen machine is 200 mesh, and an iron-removed biomass hard carbon negative electrode material with reduced pH value is obtained.

[0110] Step 8: the biomass hard carbon material prepared above is used as an active material of a battery negative electrode for a sodium ion battery. The preparation method is as follows:

[0111] According to a mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2g, conductive carbon black 0.4g, biomass hard carbon material 9.2g, SBR (styrene-butadiene rubber, solid content 40%) 0.5g, and an appropriate amount of deionized water are weighed and added dropwise, stirred for 20min to form a uniform slurry, and then the slurry is uniformly coated on the surface of a copper foil using a 100μm doctor blade. The coated copper foil is dried in a 105℃ air drying oven for 2h, and then the copper foil with active material is cut into a circular negative electrode sheet, which is then transferred to a glove box for standby.

[0112] The assembly of the simulation battery is carried out in an Ar atmosphere glove box, the prepared biomass hard carbon negative electrode sheet is used as the negative electrode, 1.0mol / L commercial electrolyte, the commercial electrolyte is prepared as follows: NaPF6 / EC:DMC V:V is 1:1, Na metal sheet is used as the counter electrode, CR2032 button cell is assembled, and then the constant current charge and discharge mode is used for charge and discharge test at a current density of 0.1C.

[0113] Example 5

[0114] A preparation method of a biomass hard carbon negative electrode material with reduced pH value, comprising the following steps:

[0115] Step 1: pretreatment, the raw material of moso bamboo is cleaned with deionized water, filtered and dried, and then placed in a forced air drying oven, the drying temperature is 200℃, the drying time is 48h, and the water is removed by drying to obtain pretreated material;

[0116] Step 2: low-temperature pre-carbonization, the pretreated material is placed in a gas atmosphere carbonization furnace, the temperature is raised to 800℃ at a rate of 10℃ / min under a helium atmosphere, and the temperature is kept for 3h to obtain a bamboo precursor, i.e. pre-carbonized material;

[0117] Step 3: crushing, after the pre-carbonized material is cooled to room temperature, the bamboo precursor is taken out and crushed by roller grinding, the particle size D50 in the crushed particles is controlled to be about 17um, and a crushed material is obtained.

[0118] Step 4: purification, after the crushing is completed, the crushed material is placed in a 5 mol / L HNO3 aqueous solution, the solid-liquid mass ratio is 1:5.5, the temperature is 100℃, and the holding time is 24h for acid pickling to remove impurities, and then washed with deionized water for multiple times until the filtrate is close to neutral, then filtered and placed in a blast drying oven, the drying temperature is 150℃, and the drying time is 48h to obtain purified material;

[0119] Step 5: high-temperature carbonization, the purified material is placed in a high-temperature atmosphere carbonization furnace, and heated from room temperature to 1800℃ at a rate of 10℃ / min under a helium atmosphere for 6h to obtain high-temperature carbonized material;

[0120] Step 6: acid pickling, the high-temperature carbonized material is placed in a 3 mol / L HNO3 aqueous solution, the solid-liquid mass ratio is 1:2, the temperature is 100℃, and the holding time is 12h for acid pickling, and then washed with deionized water for multiple times until the filtrate is close to neutral, then filtered and placed in a blast drying oven, the drying temperature is 150℃, and the drying time is 48h to obtain acid-washed carbonized material;

[0121] Step 7: coated carbonization, the obtained acid-washed carbonized material is mixed with phenolic resin at room temperature using a VC machine, the mass of phenolic resin is controlled to be 10wt% of the total mass of acid-washed carbonized material, and mixed for 3h, then placed in a carbonization furnace for high-temperature coated carbonization, heated to 1800℃ at a rate of 10℃ / min under a helium atmosphere, and the carbonization time is 6h, after completion, the coated carbonized material is placed in a vibrating screen machine for screening, the vibrating screen machine has a mesh size of 400 meshes, and after removing iron, a biomass hard carbon negative material with reduced pH value is obtained.

[0122] Step 8: the biomass hard carbon material prepared above is used as an active material of a battery negative material for a sodium ion battery. The preparation method is as follows:

[0123] According to the mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2g, conductive carbon black 0.4g, biomass hard carbon material 9.2g, SBR (styrene-butadiene rubber, solid content 40%) 0.5g, and appropriate amount of deionized water are weighed, stirred for 20min to form a uniform slurry, and then coated on the surface of a copper foil using a 100μm doctor blade, dried in a 105℃ blast drying oven for 2h, and then the Cu foil with active material is cut into a circular negative electrode sheet, and then transferred to a glove box for standby.

[0124] The assembly of the simulation battery was carried out in an Ar atmosphere glove box, using the prepared biomass hard carbon negative electrode sheet as the negative electrode, 1.0 mol / L commercial electrolyte, the commercial electrolyte was prepared as follows: the V:V of NaPF6 / EC:DMC was 1:1, a Na metal sheet was used as the counter electrode, a CR2032 button cell was assembled, and then a constant current charge and discharge mode was used to carry out charge and discharge test at a current density of 0.1C.

[0125] Comparative Example 1

[0126] A biomass hard carbon negative electrode material, comprising the following steps:

[0127] Step 1: Pretreatment, the raw material of the bamboo was cleaned with deionized water, dried by filtration, and then placed in a forced air drying oven, the drying temperature was 120℃, the drying time was 24h, the water was removed by drying, and the pretreated material was obtained;

[0128] Step 2: Low-temperature pre-carbonization, the pretreated material was placed in a gas atmosphere carbonization furnace, and heated to 500℃ at a heating rate of 5℃ / min under a nitrogen atmosphere, and kept for 2h, to obtain a bamboo precursor, i.e. the pre-carbonized material;

[0129] Step 3: Pulverization, after the pre-carbonized material was cooled to room temperature, the bamboo precursor was taken out and pulverized by a roller grinding mill, the particle size D50 in the pulverized particles was controlled at about 10um, and the pulverized material was obtained;

[0130] Step 4: Purification, after the pulverization, the pulverized material was placed in a 3mol / L HCl aqueous solution, and acid washing was carried out under the conditions of a solid-liquid mass ratio of 1:3, a temperature of 80℃, and a holding time of 12h, and then washed with deionized water for multiple times until the filtrate was close to neutral, and then filtered and placed in a forced air drying oven, the drying temperature was 120℃, and the drying time was 24h, to obtain the purified material;

[0131] Step 5: High-temperature carbonization, the purified material was placed in a high-temperature atmosphere carbonization furnace, and high-temperature carbonization was carried out at 5℃ / min from room temperature to 1400℃ under a nitrogen atmosphere for 4h, to obtain a high-temperature carbonized material; the high-temperature carbonized material was placed in a vibrating screen machine for screening, the mesh number of the vibrating screen machine was 325 mesh, and a biomass hard carbon negative electrode material was obtained after iron removal. The structure analysis is referred to Figure 1 .

[0132] Step 6: The biomass hard carbon material prepared above was used as an active substance of a battery negative electrode material for a sodium ion battery. The preparation method was as follows:

[0133] According to the mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2 g, conductive carbon black 0.4 g, biomass hard carbon material 9.2 g, SBR (styrene-butadiene rubber, solid content 40%) 0.5 g are weighed, and a proper amount of deionized water is added dropwise, stirred for 20 min to form a uniform slurry, and then the slurry is uniformly coated on the surface of a copper foil using a 100 μm doctor blade. The coated copper foil is dried in a 105°C air drying oven for 2 h, and then the Cu foil with active material is cut into a circular negative electrode sheet, which is then transferred to a glove box for standby.

[0134] The assembly of the simulated battery is carried out in an Ar atmosphere glove box, using the prepared biomass hard carbon negative electrode sheet as the negative electrode, 1.0 mol / L commercial electrolyte, the commercial electrolyte is prepared as follows: NaPF6 / EC:DMC V:V is 1:1, Na metal sheet as the counter electrode, assemble CR2032 button cell, and then use constant current charge and discharge mode, and carry out charge and discharge test at 0.1C current density.

[0135] Result analysis: compared with example 1, in comparative example 1, after high-temperature carbonization, the material is not subjected to acid washing and carbon coating, and the high-temperature carbonized material is directly screened to remove iron to obtain a biomass hard carbon negative electrode material.

[0136] Comparative example 2

[0137] A biomass hard carbon negative electrode material, comprising the following steps:

[0138] Step 1: pretreatment, the raw material of moso bamboo is cleaned with deionized water, filtered and dried, and then placed in a forced air drying oven, with a drying temperature of 120°C and a drying time of 24 h to remove water, obtaining a pretreated material;

[0139] Step 2: low-temperature pre-carbonization, the pretreated material is placed in a nitrogen atmosphere carbonization furnace and heated to 500°C at a heating rate of 5°C / min under nitrogen atmosphere, and then kept for 2 h to obtain a bamboo precursor, i.e. a pre-carbonized material;

[0140] Step 3: crushing, after the pre-carbonized material is cooled to room temperature, the bamboo precursor is taken out and crushed by a ring roller press grinder, and the particle size D50 in the crushed particles is controlled at about 10 um, obtaining a crushed material;

[0141] Step 4: purification, after crushing, the crushed material is placed in a 3 mol / L HCl aqueous solution, and acid washing is carried out under the conditions of a solid-liquid mass ratio of 1:3, a temperature of 80°C and a holding time of 12 h. The liquid is washed with deionized water until it is nearly neutral, and then filtered and placed in a forced air drying oven, with a drying temperature of 120°C and a drying time of 24 h, obtaining a purified material;

[0142] Step 5: high-temperature carbonization, the purified material is placed in a high-temperature atmosphere carbonization furnace, and high-temperature carbonization is carried out at 5 ℃ / min from room temperature to 1400 ℃ under an argon atmosphere for 4 h to obtain a high-temperature carbonized material;

[0143] Step 6: acid washing, the high-temperature carbonized material is placed in a 2 mol / L HCl aqueous solution, and acid washing is carried out under the conditions of a solid-liquid mass ratio of 1:1.4, a temperature of 80 ℃, and a holding time of 10 h to reduce the pH. The solution is washed with deionized water multiple times until the liquid is nearly neutral, and then filtered and placed in a forced air drying oven. The drying temperature is 120 ℃, and the drying time is 24 h to obtain an acid-washed carbonized material, which is a biomass hard carbon negative electrode material. Structural analysis is referred to Figure 1 .

[0144] Step 7: the biomass hard carbon material prepared above is used as an active material for a battery negative electrode material for a sodium ion battery. The preparation method is as follows:

[0145] According to a mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2 g, conductive carbon black 0.4 g, biomass hard carbon material 9.2 g, and SBR (styrene-butadiene rubber, solid content 40%) 0.5 g are weighed, and an appropriate amount of deionized water is added. Stirring is carried out for 20 min until a uniform slurry is obtained. A 100 μm doctor blade is used to uniformly coat the slurry on the surface of a copper foil. The copper foil is dried in a 105 ℃ forced air drying oven for 2 h. The Cu foil with the active material is cut into a circular negative electrode sheet, which is then transferred to a glove box for standby.

[0146] The assembly of the simulation battery is carried out in an Ar atmosphere glove box. The prepared biomass hard carbon negative electrode sheet is used as the negative electrode, 1.0 mol / L commercial electrolyte, and the commercial electrolyte is prepared as follows: NaPF6 / EC:DMC V:V is 1:1, and Na metal sheet is used as the counter electrode. A CR2032 button cell is assembled, and then a constant current charge and discharge mode is used for charge and discharge test at a current density of 0.1 C.

[0147] Result analysis: compared with Example 1, in Comparative Example 2, the acid-washed carbonized material is obtained without carbon coating, and the biomass hard carbon negative electrode material is directly obtained.

[0148] Comparative Example 3

[0149] A biomass hard carbon negative electrode material includes the following steps:

[0150] Step 1: pretreatment, the raw bamboo material is cleaned with deionized water, filtered and dried, and then placed in a forced air drying oven. The drying temperature is 120 ℃, and the drying time is 24 h to remove water and obtain a pretreated material;

[0151] Step 2: low-temperature pre-carbonization, the pretreated material is placed in an atmosphere carbonization furnace, heated to 500℃ at a heating rate of 5℃ / min under nitrogen atmosphere, and kept for 2h to obtain the bamboo precursor, i.e. pre-carbonized material;

[0152] Step 3: crushing, after the pre-carbonized material is cooled to room temperature, the bamboo precursor is taken out and crushed by a roll pressure grinder, the particle size D50 in the crushed particles is controlled at about 10um, and the crushed material is obtained;

[0153] Step 4: purification, after crushing, the crushed material is placed in a 3mol / L HCl aqueous solution, acid washing is carried out under the conditions of solid-liquid mass ratio 1:3, temperature 80℃ and holding time 12h, and then washed with deionized water for multiple times until the liquid is nearly neutral, then filtered and placed in a blast drying oven, dried at 120℃ for 24h to obtain the purified material;

[0154] Step 5: high-temperature carbonization, the purified material is placed in a high-temperature atmosphere carbonization furnace, and high-temperature carbonization is carried out at 1400℃ under argon atmosphere at a heating rate of 5℃ / min from room temperature for 4h to obtain high-temperature carbonized material;

[0155] Step 6: acid washing, the carbonized material is placed in a 2mol / L HCl aqueous solution, and acid washing is carried out under the conditions of solid-liquid mass ratio 1:1.4, temperature 80℃ and holding time 10h, and then washed with deionized water for multiple times until the liquid is nearly neutral, then filtered and placed in a blast drying oven, dried at 120℃ for 24h to obtain the acid-washed carbonized material;

[0156] Step 7: second high-temperature carbonization, the obtained acid-washed carbonized material is placed in a carbonization furnace, and second high-temperature carbonization is carried out at 1400℃ under nitrogen atmosphere at a heating rate of 5℃ / min for 4h, and the second high-temperature carbonized material is screened in a vibrating screen with a mesh size of 325 mesh to obtain the biomass hard carbon negative material after iron removal. The structure analysis is referred to Figure 1 .

[0157] Step 8: the biomass hard carbon material prepared above is used as the active material of the battery negative electrode material for sodium ion battery. The preparation method is as follows:

[0158] According to the mass ratio of 2.0%:4.0%:92.0%:2.0%, CMC (sodium carboxymethyl cellulose) 0.2g, conductive carbon black 0.4g, biomass hard carbon material 9.2g, SBR (styrene-butadiene rubber, solid content 40%) 0.5g, and appropriate amount of deionized water are weighed, stirred for 20min to form a uniform slurry, and then uniformly coated on the surface of a copper foil using a 100um doctor blade, dried in a 105℃ blast drying oven for 2h, and the Cu foil with active material is cut into a circular negative electrode sheet, which is then transferred to a glove box for standby.

[0159] The assembly of the simulated battery was carried out in an Ar atmosphere glove box, using the prepared biomass hard carbon negative electrode sheet as the negative electrode, 1.0 mol / L commercial electrolyte, the commercial electrolyte was prepared as follows: the V:V of NaPF6 / EC:DMC was 1:1, a Na metal sheet was used as the counter electrode, a CR2032 button cell was assembled, and then a charge-discharge test was carried out at a current density of 0.1 C using a constant current charge-discharge mode.

[0160] Result analysis: compared with Example 1, in Comparative Example 3, the carbonized material after acid washing was not coated and carbonized, but was subjected to secondary high-temperature carbonization to obtain the biomass hard carbon negative electrode material.

[0161] The eight biomass hard carbon negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to pH testing and assembled into sodium ion button cells for electrochemical performance testing, and the test results are shown in Table 1 and Figure 4

[0162] Table 1 pH value and electrochemical performance of sodium ion batteries

[0163]

[0164] As can be seen from Table 1, the biomass hard carbon negative electrode material prepared by the present application has a neutral pH value, a high initial discharge specific capacity, a high initial charge specific capacity and a high initial efficiency; the pH value of the material of Comparative Example 1 is higher than that of Examples 1-5, the pH value of Comparative Example 1 is 1.5 times that of Examples 1-5, and the difference is 3.27; the pH value of the material of Comparative Example 2 is lower than that of Examples 1-5, and the pH value of the material of Comparative Example 3 is equivalent to that of Examples 1-5; the initial charge-discharge specific capacity and the initial efficiency of the materials of Comparative Examples 1-3 are lower than those of Example 1. The initial efficiency of Comparative Example 1 and Example 1 can differ by 3.9%, the initial efficiency of Comparative Example 2 and Example 2 can differ by 20.6%, and the initial efficiency of Comparative Example 3 and Example 2 can differ by 2%. This is mainly because the carbonized material of Comparative Example 1 is not subjected to acid washing and coating carbonization, so that the pH value of the material is high, and in the process of forming a mixed slurry of the active material, the binder and the conductive carbon black as the negative electrode material of the sodium battery, there is colloid agglomeration and corrosion of the aluminum foil during coating, which also increases the pore collapse rate and the specific surface, ultimately resulting in low capacity and low initial efficiency of the battery; the carbonized material of Comparative Example 2 is only subjected to acid washing without coating carbonization, so that the pH value of the material is acidic, and the residual acid corrodes to form a pore structure on the surface of the carbonized material, resulting in an excessively large specific surface and affecting the battery performance; the carbonized material of Comparative Example 3 is subjected to acid washing and high-temperature carbonization, but not to coating carbonization, so that the hard carbon has a serious side reaction with the electrolyte, the surface defects increase, the irreversible capacity increases, and the initial charge capacity and the initial efficiency decrease.

[0165] Reference Figure 1 ​The XRD patterns of the biomass hard carbon negative electrode material of example 1 and comparative examples 1-3 are compared, the peak positions of comparative examples 1-3 are the same as that of example 1, the intensities are different, the intensity of example 1 is higher, and the crystal form is better.

[0166] With reference to Figure 2 and Figure 3 The pickling carbonized material of example 1 is coated and carbonized, and a biomass hard carbon negative electrode material with reduced pH value is successfully obtained compared with comparative example 1.

[0167] With reference to Figure 4 The IR patterns of the biomass hard carbon negative electrode material of example 1 and comparative example 1 are compared, the amino group of example 1 is obviously reduced, thereby resulting in a reduced pH value.

[0168] With reference to Figure 5 The charge-discharge curves of the biomass hard carbon negative electrode material of example 1 and comparative example 1 under the condition of 0.1C are compared, and it can be directly seen that the charge-discharge capacity of example 1 is better.

[0169] With reference to Figure 6 The full battery of example 1 is cycled for 700 cycles under the condition of 1C, and the capacity retention is still higher than 80%.

[0170] Example 1, example 4 and example 5 are compared, the initial specific discharge capacity, the initial specific charge capacity and the initial efficiency of example 1 are higher than those of example 4 and example 5, and in the case that the raw material of moso bamboo is used as the raw material, the parameter conditions of example 1 are preferred.

[0171] Example 1-3 are compared, the initial specific discharge capacity, the initial specific charge capacity and the initial efficiency of example 1 are higher than those of example 2 and example 3, and in the case that the parameter conditions are the same, the raw material of moso bamboo is more suitable for the preparation method of the application, and the biomass hard carbon negative electrode material prepared is more suitable for being used as the active material of the battery negative electrode material for sodium ion battery.

[0172] The above only describes the preferred embodiments of the application, and is not used to limit the application, although the application is described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a biomass hard carbon negative electrode material with reduced pH, characterized in that, The method comprises the following steps: Preprocessing: cleaning and drying the biomass raw material to obtain the pretreated material; Low-temperature pre-carbonization: pre-carbonizing the pretreated material in a protective atmosphere to obtain pre-carbonized material; Crushing: crushing the pre-carbonized material to obtain crushed material; Purification: acid washing and water washing the crushed material, then drying by suction filtration to obtain purified material; High-temperature carbonization: high-temperature carbonizing the purified material in a protective atmosphere to obtain high-temperature carbonized material; Acid washing: acid washing the high-temperature carbonized material again, then water washing, suction filtration and drying to obtain acid-washed carbonized material; the acid used for the second acid washing comprises at least one of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid and sulfuric acid; the concentration of the acid is 0.5-3 mol / L, the reaction temperature of the second acid washing is 60-100°C, and the solid-liquid mass ratio of the second acid washing is 1:0.8-2; Coated carbonization: uniformly mixing the acid-washed carbonized material with a modifier, then high-temperature coated carbonization in a protective atmosphere, and obtaining a pH-reduced biomass hard carbon negative electrode material after removing iron by sieving; the mass of the modifier accounts for 1-10%wt of the mass of the acid-washed carbonized material; The conditions of the high-temperature coated carbonization include that the high-temperature coated carbonization temperature is 1200-1800°C.

2. The method of producing a pH-reduced biomass hard carbon negative material according to claim 1, wherein In the preprocessing, the biomass raw material is cleaned with deionized water, dried by filtration, and then placed in a forced air drying oven, with a drying temperature of 60-200°C, a drying time of 6-48h, and a drying time of 6-48h, to remove water and obtain the pretreated material; the biomass raw material comprises at least one of bamboo, coconut shell and wood.

3. The method of producing a pH-reduced biomass hard carbon anode material according to claim 1, wherein In the low-temperature pre-carbonization, the protective atmosphere comprises at least one of nitrogen, argon and helium; the pre-carbonization conditions include a heating rate of 2-10°C / min, a pre-carbonization temperature of 200-800°C, a holding time of 1-3h, and pre-carbonization in an atmosphere carbonization furnace.

4. The method of producing a pH-reduced biomass hard carbon anode material according to claim 1, characterized by, In the crushing, the crushing equipment includes at least one of a mechanical crusher, a roller mill crusher and an air jet crusher, and the particle size of the crushed material is controlled to be 3-17um.

5. The method of producing a pH-reduced biomass hard carbon anode material according to claim 1, wherein In the purification, the acid used for the acid washing comprises at least one of hydrochloric acid, nitric acid, hydrofluoric acid, phosphoric acid and sulfuric acid; the concentration of the acid in the acid washing is 0.5-5 mol / L, the reaction temperature of the acid washing is 60-100°C, the solid-liquid mass ratio of the acid washing is 1:0.7-5.5, and the acid washing time is 6-24h; the water washing and deashing comprises multiple deionized water washing until the filtrate is close to neutral, followed by suction filtration, a drying temperature of 80-150°C and a drying time of 6-48h.

6. The method of producing a pH-reduced biomass hard carbon anode material according to claim 1, wherein In the high-temperature carbonization, the high-temperature carbonization conditions include a heating rate of 2-10°C / min, a high-temperature carbonization temperature of 1200-1800°C, a holding time of 2-6h, and high-temperature carbonization in an atmosphere carbonization furnace; the protective atmosphere comprises at least one of nitrogen, argon and helium.

7. The method of producing a pH-reduced biomass hard carbon anode material according to claim 1, wherein In the acid washing, the acid washing time is 6-12h; the water washing includes multiple deionized water washing until the filtrate is close to neutral, followed by suction filtration, a drying temperature of 80-150°C and a drying time of 6-48h.

8. The method of producing a pH-reduced biomass hard carbon anode material according to claim 1, wherein In the carbon coating, the modifier comprises at least one of pitch and resin, the mixing time is 0.5-3 h; the conditions of high-temperature carbon coating comprise a heating rate of 2-10 ℃ / min, a holding time of 2-6 h, and a protective atmosphere comprising at least one of nitrogen, argon and helium; and the mesh number of a vibrating screening machine used for sieving is 200-400 mesh.

9. A negative electrode sheet characterized by comprising: The negative pole piece uses the biomass hard carbon negative material with reduced pH value as the active substance of the battery negative material, and the biomass hard carbon negative material with reduced pH value is prepared by the preparation method of the biomass hard carbon negative material with reduced pH value in any one of claims 1-8.

10. A battery, characterized by The battery is a sodium ion battery, which comprises a negative pole, a positive pole, a diaphragm and an electrolyte, the negative pole comprises the negative pole piece in claim 9, the sodium ion battery has a pH value of 6-8, a first charge specific capacity of 300-340 mAh / g, a first discharge specific capacity of 330-360 mAh / g and a first efficiency of 90-95% in a charge-discharge test at a current density of 0.1 C.

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