Biomass asphalt composite derived hard carbon material as well as preparation method and application thereof

Abstract

The invention discloses a biomass asphalt composite derivative hard carbon material and a preparation method and application thereof, and the preparation method comprises the following steps: step (1), placing biomass raw material powder in an acid pickling solvent for acid pickling, washing to be neutral after acid pickling, and drying to obtain a biomass precursor; (2) mixing the biomass precursor with asphalt to obtain a precursor mixture; and (3) carrying out low-temperature pre-oxidation on the precursor mixture, and then carrying out high-temperature carbonization, so as to obtain the biomass asphalt composite derivative hard carbon material after the high-temperature carbonization is finished. The prepared biomass asphalt composite derivative hard carbon material is used for preparing a sodium ion battery negative electrode. The technical problems that an existing biomass hard carbon material is low in capacity and tap density, difficult in impurity removal and the like can be solved, the biomass hard carbon material can be used for a sodium-ion battery negative electrode, and the sodium storage performance of a sodium-ion battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of hard carbon materials, in particular to a biomass pitch composite derived hard carbon material and a preparation method and application thereof. Background Art

[0002] Sodium-ion batteries have the advantages of low cost, unlimited resources and high safety, and have important application prospects in the field of large-scale energy storage. The quality of battery performance depends on the electrode material. Among them, cost-effective hard carbon materials are the first choice for the negative electrode of sodium-ion batteries. Plant-derived carbon materials have unique characteristics such as diverse types, good physical and chemical properties, environmental friendliness and considerable economic value, and have very great prospects. However, the internal components of plants are diverse, the microstructure is complex, and the sodium storage performance varies. How to prepare high-performance hard carbon is a difficult problem. In addition, the tap density of most biomass hard carbon materials is not high, and the surface density of the electrode prepared from this is difficult to meet the national standard. Even if the standard is met, the electrode may be too thick, making it difficult for the electrolyte to infiltrate or the active material to fall off during the cycle, resulting in a series of problems such as low capacity or poor cycle stability. Summary of the Invention

[0003] To this end, the technical problem to be solved by the present invention is to provide a biomass asphalt composite-derived hard carbon material and its preparation method and use, so as to solve the technical problems of low capacity, low tap density and difficulty in removing impurities of existing biomass hard carbon materials, so that it can be used for the negative electrode of sodium ion batteries and improve the sodium storage performance of sodium ion batteries.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A method for preparing a biomass pitch composite-derived hard carbon material comprises the following steps:

[0006] Step (1), placing the biomass raw material powder in an acid washing solvent for acid washing, washing to neutrality and drying after the acid washing is completed to obtain a biomass precursor;

[0007] Step (2), mixing the biomass precursor with asphalt to obtain a precursor mixture;

[0008] In step (3), the precursor mixture is first subjected to low-temperature pre-oxidation and then to high-temperature carbonization. After the high-temperature carbonization is completed, a biomass pitch composite-derived hard carbon material is obtained.

[0009] In the preparation method of the above-mentioned biomass asphalt composite-derived hard carbon material, in step (1), the biomass raw material is one or two or a mixture of more than one of bagasse, straw, peanut shell, hemp stalk, starch, eucalyptus, glucose, straw, reed, palm shell and macadamia shell, among which the precursor prepared using hard shells such as palm shell and macadamia shell as raw materials has better performance, and the hard carbon material formed by adding asphalt composite to the hard shell biomass raw material has a higher tap density, improved first effect and increased porosity; the pickling solvent is one or two or a mixture of more than two of hydrochloric acid solution, sulfuric acid solution and nitric acid solution.

[0010] The preparation method of the above-mentioned biomass asphalt composite-derived hard carbon material, in step (1), the biomass raw material powder is the undersize material passing through a 300-mesh sieve; the total molar concentration of the inorganic acid in the pickling solvent is 0.05-0.20 mol / L, and different acidic solvents have different pickling and impurity removal effects on the biomass raw material powder. Among them, dilute sulfuric acid with a concentration of 0.05-0.20 mol / L has a relatively good pickling treatment effect on the biomass raw material powder, which not only removes impurities thoroughly, but also can introduce more CC bonds and C=O groups; the mass volume ratio of the biomass raw material powder to the pickling solvent is (30-50) g / L; the pickling conditions are: stirring at 300-500 rpm for 10-15 hours; the drying conditions are: drying at 70-90°C for 10-16 hours.

[0011] The silicate layer on the surface of biomass raw material powder is similar to metal oxide scale. If the particle size of the biomass raw material powder is too large, the pickling reaction will be incomplete, and the residue will form insulating particles during carbonization, reducing the conductivity of hard carbon and increasing irreversible capacity loss; and the internal pore structure of large particles is complex, and it is difficult for the acid to fully infiltrate the core area. The undissolved ash inside the large particles will block the nano-scale pores during carbonization, reducing the closed-pore volume and resulting in a decrease in the sodium storage platform capacity.

[0012] If the concentration of the dilute sulfuric acid used is too high, the biomass skeleton of the biomass raw material powder will collapse, and the acid washing cost will increase, which is not environmentally friendly; if the concentration of the dilute sulfuric acid is too low, the biomass acid hydrolysis will be unsatisfactory, affecting the structure of the subsequent hard carbon.

[0013] If the amount of pickling solvent used during pickling is too small, the ash removal rate in the biomass raw material powder will decrease, which will affect the initial efficiency and specific capacity of the hard carbon material finally prepared; if the amount of pickling solvent used is too large, the acid will penetrate the pores of the biomass and destroy its organic skeleton, causing the closed-pore volume after carbonization to decrease by 20-30%, and the sodium storage capacity in the high-pressure zone to be seriously lost.

[0014] In addition, the stirring rate and stirring time during pickling will also affect the pickling effect: if the stirring is too fast or the stirring time is too long, the fiber structure of the biomass raw material will be damaged, the subsequent carbonization closed-pore development will be hindered, and the reaction system will be out of control; furthermore, frictional heat will increase the temperature of the acid solution, and heat accumulation will accelerate acid volatilization, requiring additional acid replenishment and increasing costs; high-speed eddy currents will also cause the removed ash to re-adsorb on the fiber surface, resulting in secondary ash deposition, leading to an increase in the residual ash concentration; if the stirring speed and time are too low, the ash removal efficiency is insufficient, ash residue will remain, and the subsequent carbonization micropores will be blocked; the reaction kinetics will deteriorate, the mass transfer resistance will increase, and the increase in boundary layer thickness will cause H + The diffusion rate decreases and the pickling time needs to be extended.

[0015] The present invention controls the particle size of the biomass raw material powder, the usage ratio of the biomass raw material powder to the pickling solvent, the type and concentration of the pickling solvent, the pickling stirring rate, the pickling time, etc. during pickling, thereby not only effectively removing impurities in the biomass raw material, but also introducing more C—C bonds and C═O groups into the biomass raw material after pickling, thereby increasing the interlayer distance and enhancing the electrochemical reaction activity, thereby improving its electrical cycling performance.

[0016] In the above-mentioned method for preparing a biomass-asphalt composite-derived hard carbon material, in step (2), the specific process of mixing the biomass precursor and asphalt is as follows: adding the biomass precursor and asphalt to anhydrous ethanol and stirring and mixing them uniformly to obtain a mixed dispersion; drying the mixed dispersion, and after drying, grinding the solid mixture into powder to obtain a precursor mixture. Compared with directly mixing and grinding the biomass precursor and asphalt, the present invention adopts a method of first adding the biomass precursor and asphalt to anhydrous ethanol for dispersion and mixing, and then volatilizing and grinding. This not only allows the biomass precursor and asphalt to be mixed more thoroughly, but also allows the biomass precursor and asphalt to be tightly bonded during the process. After mixing and grinding, biomass precursor-asphalt tightly bonded composite particles with a particle size of less than or equal to 300 mesh are formed, providing favorable conditions for cross-linking the biomass precursor and asphalt during the subsequent low-temperature pre-oxidation and high-temperature carbonization processes.

[0017] The preparation method of the above-mentioned biomass asphalt composite-derived hard carbon material is as follows: the biomass precursor and asphalt are added to anhydrous ethanol at a stirring rate of 300-500rpm and a stirring time of 2-4h; the mass fraction of the biomass precursor in the mixed dispersion is 5-10wt%; the drying treatment conditions are 70-85℃ drying for 18-24h; the mass fraction of the biomass precursor in the precursor mixture is 70-95wt%; the precursor mixture is the undersize after grinding and passing through a 300-mesh sieve; the asphalt is an asphalt powder with a particle size less than or equal to 3μm and a softening point greater than or equal to 85℃.

[0018] If too little asphalt is added to the precursor mixture, that is, the content of biomass precursor exceeds 95wt%, the closed-pore structure of the hard carbon material finally prepared will be underdeveloped, the ash residue will increase, the pore blockage will be aggravated, the closed-pore volume will decrease, and the sodium ion embedding sites will decrease; the degree of graphitization will be uneven, the first effect will decrease, and the material cycle life will be shortened; if the asphalt proportion is too high, it will lead to problems such as excessive densification of closed-pores and rigidity of the conductive network.

[0019] In the process of drying the mixed dispersion to evaporate the solvent, if the temperature is too high, the effective ingredients in the biomass raw material will be destroyed, thereby reducing the mechanical strength of the hard carbon material; if the temperature is too low, the precursor mixture will not be dried thoroughly, and in the subsequent low-temperature pre-oxidation and high-temperature carbonization process, the water will vaporize and expand, resulting in an increase in the microcracks of the formed hard carbon material, thereby affecting the electrical cycle performance and cycle life of the material.

[0020] In addition, the prepared mixture of biomass precursor and asphalt is passed through a 300-mesh sieve and the material under the sieve is taken as the precursor mixture. This is because the escape path of the gas generated by pyrolysis inside the large particles is prolonged, forming millimeter-scale voids in the carbon layer instead of nano-closed pores for ideal sodium storage, which will lead to a decrease in specific capacity and first efficiency; and the diffusion path of sodium ions inside the large particles is prolonged, resulting in poor rate performance.

[0021] In the preparation method of the biomass pitch composite-derived hard carbon material, in step (3), the low-temperature pre-oxidation method is: in an air atmosphere, heating from room temperature to 200-400°C at a heating rate of 3-5°C / min, keeping the temperature at 200-400°C for 4-8 hours, and then naturally cooling to room temperature;

[0022] During low-temperature pre-oxidation, if the treatment temperature is too high, the carbon layer arrangement will become excessively disordered, destroying the micropore-closed-pore equilibrium structure required for sodium storage. In addition, high temperature promotes the excessive release of small molecular gases, increasing the decomposition rate of the carbon source, resulting in a significant decrease in carbon yield. If the treatment temperature is too low, the oxygen molecules and asphalt molecules are not sufficiently active, making it difficult to trigger effective cross-linking, resulting in low oxygen content and poor development of the closed-pore structure after carbonization. In addition, the softening point is limited, and the asphalt skeleton is prone to melting and collapse during subsequent carbonization, resulting in a decrease in material performance.

[0023] By controlling the heating rate, oxidation temperature, and oxidation time during the low-temperature pre-oxidation process within the above-mentioned ranges, the present invention can introduce an appropriate amount of oxygen-containing functional groups into the precursor mixture, increase the number of micropores, expand the carbon layer spacing, and effectively inhibit the degree of graphitization of the precursor mixture during the carbonization process, forming a more disordered carbon layer structure, thereby improving the capacity and initial coulombic efficiency of the material. If carbonization is directly performed without low-temperature pre-oxidation, the degree of graphitization of the pitch hard carbon will be aggravated, resulting in a serious decline in its electrochemical performance.

[0024] In step (3), the high-temperature carbonization method is: in an inert atmosphere, heating from room temperature to 900-1400°C at a heating rate of 5-8°C / min, keeping the temperature at 900-1400°C for 4-8h, and then naturally cooling to room temperature. During the carbonization process, if the carbonization temperature is too high, the following defects will occur: the carbon yield decreases, the closed-pore structure is destroyed, the sodium storage active site is lost, the biomass carbon skeleton is over-graphitized, and the asphalt structure collapses; if the carbonization temperature is too low, the following defects will occur: the carbon yield of the material fluctuates, the pore structure is underdeveloped, the cross-linking density is insufficient, the conductivity decreases; the asphalt closed-pore structure is missing, and the sodium storage capacity is lost. The present invention can make the prepared hard carbon material have a higher tap density and capacitance by controlling the heating rate, oxidation temperature and oxidation time in the carbonization process within the above range.

[0025] The preparation method of the above-mentioned biomass pitch composite-derived hard carbon material, in step (1), the biomass raw material powder is the sieve undersize of sugarcane bagasse after crushing and passing through a 300-mesh sieve; the pickling solvent is a sulfuric acid solution with a concentration of 0.10 mol / L; the mass volume ratio of the biomass raw material powder to the pickling solvent is 40 g / L; the pickling conditions are: stirring at 500 rpm for 12 hours; the drying conditions are: drying at 80°C for 12 hours;

[0026] In step (2), the specific process of mixing the biomass precursor and the asphalt is as follows: adding the biomass precursor and the asphalt in a mass ratio of 7:3 to anhydrous ethanol and stirring at 500 rpm for 3 hours to obtain a mixed dispersion; the mass fraction of the biomass precursor in the mixed dispersion is 9 wt%; drying the mixed dispersion at 80°C for 24 hours to obtain a solid mixture; grinding the solid mixture into powder and sieving it through a 300-mesh sieve to obtain the precursor mixture; the asphalt is an asphalt powder with a particle size of less than or equal to 3 μm and a softening point greater than or equal to 85°C;

[0027] In step (3), the low-temperature pre-oxidation method is: in an air atmosphere, heating the temperature to 300°C at a heating rate of 3°C / min, and keeping it at 300°C for 4 hours; the high-temperature carbonization method is: in an inert atmosphere, heating the temperature to 1300°C at a heating rate of 8°C / min, and keeping it at 1300°C for 2 hours.

[0028] A biomass pitch composite derived hard carbon material is a biomass pitch composite derived hard carbon material prepared by the above-mentioned preparation method of the biomass pitch composite derived hard carbon material.

[0029] A use of a biomass pitch composite-derived hard carbon material, wherein the biomass pitch composite-derived hard carbon material is used to prepare a negative electrode for a sodium ion battery.

[0030] The use of the above-mentioned biomass asphalt composite derived hard carbon material is as follows: 4 parts by weight of the biomass asphalt composite derived hard carbon material, 0.5 parts by weight of sodium alginate and 0.5 parts by weight of conductive carbon black are mixed to obtain an electrode material; deionized water is added to the electrode material and mixed evenly to obtain an electrode slurry; the amount of deionized water added is controlled so that the viscosity of the electrode slurry is 4000-6000cps; the electrode slurry is evenly coated on a copper foil, vacuum dried at 80°C for 12 hours, and then cut into shape to obtain a negative electrode sheet for a sodium ion battery.

[0031] The technical solution of the present invention achieves the following beneficial technical effects:

[0032] 1. The present invention addresses the problems of low capacity and low tap density of existing biomass hard carbon materials. By acid-washing the biomass precursor and combining the regulation of morphology and structure, the hard carbon is modified and optimized, and an electrode material with excellent stability - a biomass pitch composite-derived hard carbon material is prepared. The electrode material is used to prepare electrode slurry and used for the negative electrode of sodium ion battery, which can exhibit better sodium storage performance.

[0033] 2. In the method of the present invention for composite derivation of hard carbon materials from biomass asphalt, acid washing of the biomass is beneficial to removing impurities, adjusting the components of the biomass, and achieving close bonding between the biomass and asphalt, thereby increasing the tap density of the material; the introduction of a biomass template skeleton during the pre-oxidation process of the present invention is beneficial to the entry of air into the interior of the precursor mixture, thereby enhancing the pre-oxidation effect; biomass is rich in oxygen functional groups that can promote asphalt cross-linking, and biomass can serve as a skeleton to inhibit the softening and rearrangement of asphalt, and provide a rich microporous structure.

[0034] 3. The biomass asphalt composite-derived hard carbon material prepared by the method of the present invention is a hard carbon / hard carbon composite material (biomass hard carbon / asphalt hard carbon). This structure has rich heterogeneous interfaces, which is conducive to the rapid transport of sodium ions during the charging and discharging process and improves the electrode stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Scanning electron microscope image of the biomass pitch composite-derived hard carbon material prepared in Example 1 of the present invention;

[0036] Figure 2 Scanning electron microscope image of the biomass pitch composite-derived hard carbon material prepared in Comparative Example 1 of the present invention;

[0037] Figure 3 Scanning electron microscope image of the biomass pitch composite-derived hard carbon material prepared in Comparative Example 2 of the present invention;

[0038] Figure 4 Scanning electron microscope image of the biomass pitch composite-derived hard carbon material prepared in Comparative Example 3 of the present invention;

[0039] Figure 5 XRD comparison charts of biomass hard carbon materials prepared in Example 1 and Comparative Examples 1-3 of the present invention;

[0040] Figure 6 Raman comparison charts of biomass hard carbon materials prepared in Example 1 and Comparative Examples 1-3 of the present invention;

[0041] Figure 7 Pore ​​size distribution ratio of biomass hard carbon materials prepared in Example 1 and Comparative Examples 1-3 of the present invention;

[0042] Figure 8 The first charge and discharge performance diagram of the biomass pitch composite-derived hard carbon material in Example 1 of the present invention;

[0043] Figure 9 The first charge and discharge performance diagram of the biomass pitch composite-derived hard carbon material of Comparative Example 1 of the present invention;

[0044] Figure 10 The first charge and discharge performance diagram of the biomass pitch composite derived hard carbon material of Comparative Example 2 of the present invention;

[0045] Figure 11 The first charge and discharge performance diagram of the biomass pitch composite-derived hard carbon material of Comparative Example 3 of the present invention;

[0046] Figure 12 Comparison of the rate performance of the biomass hard carbon materials of Example 1 and Comparative Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0047] Example 1

[0048] The preparation method of the biomass pitch composite derived hard carbon material in this embodiment includes the following steps:

[0049] Step (1), beating the bagasse into powder with a powder machine, passing it through a 300-mesh sieve, leaving the 300-mesh sieve under the sieve as a biomass raw material powder, placing 20 g of the biomass raw material powder in 500 mL of a 0.1 mol / L dilute sulfuric acid solution for acid washing, stirring at 500 rpm for 12 h, filtering after the acid washing, washing with deionized water until the washing liquid is neutral, and placing the washed biomass raw material powder in a blast drying oven at 80° C. for 12 h. After drying, a biomass precursor is obtained;

[0050] Step (2), adding 14 g of biomass precursor and 6 g of asphalt to 200 mL of anhydrous ethanol and stirring at 500 rpm for 3 h to obtain a mixed dispersion; drying the mixed dispersion at 80° C. for 24 h to obtain a solid mixture; grinding the solid mixture into a powder and sieving the undersize through a 300-mesh sieve to obtain a precursor mixture;

[0051] In step (3), the precursor mixture is first subjected to low-temperature pre-oxidation and then to high-temperature carbonization. The method of low-temperature pre-oxidation is: in an air atmosphere, the temperature is increased to 300°C at a heating rate of 3°C / min, and the temperature is kept at 300°C for 4 hours; the method of high-temperature carbonization is: in a nitrogen atmosphere, the temperature is increased to 1300°C at a heating rate of 8°C / min, and the temperature is kept at 1300°C for 2 hours; after the high-temperature carbonization is completed, a biomass asphalt composite-derived hard carbon material is obtained.

[0052] The biomass pitch composite-derived hard carbon material prepared in this example was used to prepare a sodium ion battery negative electrode, and its charge and discharge performance was tested; the specific method is as follows:

[0053] (1) Take 4g of biomass asphalt composite derived hard carbon material, 0.5g of sodium alginate, 0.5g of Super-P and an appropriate amount of deionized water, place them in a high-speed blender and disperse them evenly, adjust the viscosity of the rubber compound to within the range of 4000-6000cps, and vacuum seal it for later use.

[0054] (2) The obtained electrode slurry was evenly coated on copper foil and vacuum dried at 80°C for 12 hours to obtain a negative electrode sheet. The sheet was then pressed and shaped using a sheet press and cut to obtain a battery negative electrode sheet. The prepared materials were assembled in a vacuum glove box in the order of positive electrode shell - active material - glass fiber membrane - electrolyte - sodium sheet - gasket - spring sheet - negative electrode shell, and then placed in a button cell packaging machine for sheet pressing. The pressed battery was left horizontally for 24 hours before testing.

[0055] (3) Using the LAND blue battery charge and discharge tester, the charge and discharge performance test was carried out at a current density of 50mAg-1 and a voltage range of 0.01-2V. The test temperature was kept constant at 25℃.

[0056] Example 2

[0057] The preparation method of biomass asphalt composite-derived hard carbon material in this embodiment differs from that in Example 1 only in that: in step (1), the biomass raw material used is straw; in step (2), 16g of biomass raw material and 4g of asphalt are used; the other process steps, raw material specifications and parameters are the same as those in Example 1.

[0058] The biomass pitch composite-derived hard carbon material prepared in this example was used to prepare a sodium ion battery negative electrode, and its charge and discharge performance was tested; the specific method was exactly the same as in Example 1.

[0059] Example 3

[0060] The preparation method of biomass asphalt composite-derived hard carbon material in this embodiment differs from that in Example 1 only in that: in step (1), the biomass raw material used is palm fruit shell; in step (2), 18g of biomass raw material and 2g of asphalt are used; the other process steps, raw material specifications and parameters are the same as those in Example 1.

[0061] The biomass pitch composite-derived hard carbon material prepared in this example was used to prepare a sodium ion battery negative electrode, and its charge and discharge performance was tested; the specific method was exactly the same as in Example 1.

[0062] Comparative Example 1

[0063] The preparation method of the biomass pitch composite derived hard carbon material in this comparative example comprises the following steps:

[0064] Step (1), beating the bagasse into powder with a powder machine, passing it through a 300-mesh sieve, leaving the 300-mesh sieve under the sieve as a biomass raw material powder, placing 20 g of the biomass raw material powder in 500 mL of a 0.1 mol / L dilute sulfuric acid solution for acid washing, stirring at 500 rpm for 12 h, filtering after the acid washing, washing with deionized water until the washing liquid is neutral, and placing the washed biomass raw material powder in a blast drying oven at 80° C. for 12 h. After drying, a biomass precursor is obtained;

[0065] Step (2): 14 g of biomass precursor and 6 g of asphalt are subjected to low-temperature pre-oxidation and then to high-temperature carbonization to obtain carbonized biomass and carbonized asphalt, respectively; the low-temperature pre-oxidation method is: in an air atmosphere, the temperature is increased to 300° C. at a heating rate of 3° C. / min, and the temperature is kept at 300° C. for 4 h; the high-temperature carbonization method is: in a nitrogen atmosphere, the temperature is increased to 1300° C. at a heating rate of 8° C. / min, and the temperature is kept at 1300° C. for 2 h;

[0066] Step (3): Grind and mix the carbonized biomass and carbonized asphalt obtained after carbonization, and pass them through a 300-mesh sieve to obtain a biomass asphalt composite-derived hard carbon material.

[0067] The biomass pitch composite-derived hard carbon material prepared in this comparative example was used to prepare a sodium ion battery negative electrode, and its charge and discharge performance was tested; the specific method was exactly the same as in Example 1.

[0068] Comparative Example 2

[0069] The preparation method of the biomass pitch composite derived hard carbon material in this comparative example comprises the following steps:

[0070] Step (1), pulverizing the bagasse with a pulverizer, passing the powder through a 300-mesh sieve, and retaining the 300-mesh sieve undersize as a biomass precursor;

[0071] Step (2), 14 g of the biomass precursor and 6 g of asphalt were mixed and stirred uniformly, and then passed through a 300-mesh sieve to obtain a precursor mixture;

[0072] In step (3), the precursor mixture is first subjected to low-temperature pre-oxidation and then to high-temperature carbonization; the method for low-temperature pre-oxidation is: in an air atmosphere, the temperature is increased to 300°C at a heating rate of 3°C / min, and the temperature is kept at 300°C for 4 hours; the method for high-temperature carbonization is: in a nitrogen atmosphere, the temperature is increased to 1300°C at a heating rate of 8°C / min, and the temperature is kept at 1300°C for 2 hours; after the high-temperature carbonization is completed, a biomass asphalt composite-derived hard carbon material is obtained.

[0073] The biomass pitch composite-derived hard carbon material prepared in this comparative example was used to prepare a sodium ion battery negative electrode, and its charge and discharge performance was tested; the specific method was exactly the same as in Example 1.

[0074] Comparative Example 3

[0075] The preparation method of the biomass hard carbon material in this comparative example comprises the following steps:

[0076] Step (1), beating the bagasse into powder with a powder machine, passing it through a 300-mesh sieve, leaving the 300-mesh sieve under the sieve as a biomass raw material powder, placing 20 g of the biomass raw material powder in 500 mL of a 0.1 mol / L dilute sulfuric acid solution for acid washing, stirring at 500 rpm for 12 h, filtering after the acid washing, washing with deionized water until the washing liquid is neutral, and placing the washed biomass raw material powder in a blast drying oven at 80° C. for 12 h. After drying, a biomass precursor is obtained;

[0077] In step (2), the biomass precursor is first subjected to low-temperature pre-oxidation and then to high-temperature carbonization. The method of low-temperature pre-oxidation is: in an air atmosphere, the temperature is increased to 300°C at a heating rate of 3°C / min, and the temperature is kept at 300°C for 4 hours; the method of high-temperature carbonization is: in a nitrogen atmosphere, the temperature is increased to 1300°C at a heating rate of 8°C / min, and the temperature is kept at 1300°C for 2 hours; after the high-temperature carbonization is completed, a biomass hard carbon material is obtained.

[0078] The biomass hard carbon material prepared in this comparative example was used to prepare a negative electrode for a sodium ion battery, and its charge and discharge performance was tested; the specific method was exactly the same as that in Example 1.

[0079] The relevant performance test results of the hard carbon materials prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are shown in the accompanying drawings of the specification.

[0080] contrast Figures 1 to 4It can be seen that the surface of the hard carbon material prepared in Example 1 has obvious bubbles, while the surfaces of the hard carbon materials prepared in Comparative Examples 1 to 3 have no obvious bubbles, indicating that after the biomass raw material is acid-washed, the biomass components have changed, and the asphalt is induced to form a spherical morphology during the process of low-temperature pre-oxidation and high-temperature carbonization with asphalt, and then closely combined with sugarcane bagasse, thereby improving the tap density and electrochemical properties of the hard carbon material.

[0081] By XRD ( Figure 5 ) diffraction peaks, no impurity peaks appeared in the XRD of Example 1, and the interlayer spacing was 0.409 nm, which was better than that of the comparative examples, indicating that acid washing can optimize the components of the precursor, and the mixed pre-oxidation and carbonization of the precursor can improve the tap density and consistency of the material. The tap density of the hard carbon material prepared in Example 1 is 0.62 g / cm 3 , while the tap densities of the hard carbon materials prepared in Comparative Examples 1 to 3 were 0.47 g / cm 3 , 0.42g / cm 3 , 0.31g / cm 3 All less than 0.5g / cm 3 .

[0082] Raman spectrum ( Figure 6 ) is used to characterize the degree of defects in the material. According to the ratio of ID / IG, the ID / IG of Example 1 is 1.05, which is higher than that of other comparative examples, indicating that Example 1 has the highest degree of disorder and the most defects.

[0083] By comparing the pore size distribution diagram ( Figure 7 ), the pore size distribution of Example 1 is mainly concentrated in the micropores, which is more uniform than that of other comparative examples. The uniform porous structure is conducive to increasing the contact area between the electrode and the electrolyte, which is Na + It provides more active sites for Na + Ion diffusion and Na-filled pores provide more favorable ion pathways.

[0084] At a current density of 50 mA / g ( Figures 8 to 11 ), the first cycle capacity of Example 1 is 325.5 mAh g -1 The first cycle capacity of Comparative Examples 1 to 3 is 284.7 mAh g -1 , 267.7mAh g -1 、235.3mAh g -1 The first efficacy rates were 86.69%, 87.94% and 80.45% respectively.

[0085] In addition, at different current densities ( Figure 12), the rate performance of Example 1 is better than that of the comparative example, wherein the performance of Example 1 at a current density of 3A / g is 202mAh g -1 .

[0086] The microscopic morphology and internal structural characteristics of the biomass pitch composite-derived hard carbon materials prepared in Example 2 and Example 3 are similar to those in Example 1 and will not be characterized here.

[0087] The tap density of the hard carbon materials prepared in Example 2 and Example 3 is 0.59 g / cm 3 , 0.65g / cm 3 The ID / IG values ​​of the hard carbon materials prepared in Example 2 and Example 3 were 1.03 and 1.10, respectively; the first cycle capacities of Example 2 and Example 3 were 319.3 mAh g -1 、331.7mAh g -1 The first efficiency is 88.01% and 89.27% ​​respectively; the performance of Example 2 and Example 3 at a current density of 3A / g is 199mAh g -1 , 207mAh g -1 .

[0088] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing a biomass pitch composite-derived hard carbon material, characterized in that: The steps include: Step (1), placing the biomass raw material powder in an acid washing solvent for acid washing, washing to neutrality and drying after the acid washing is completed to obtain a biomass precursor; Step (2), mixing the biomass precursor with asphalt to obtain a precursor mixture; In step (3), the precursor mixture is first subjected to low-temperature pre-oxidation and then to high-temperature carbonization. After the high-temperature carbonization is completed, a biomass pitch composite-derived hard carbon material is obtained.

2. The method for preparing a biomass pitch composite-derived hard carbon material according to claim 1, characterized in that: In step (1), the biomass raw material is one or two or more of bagasse, straw, peanut shell, hemp stalk, starch, eucalyptus, glucose, straw, reed, palm shell and macadamia shell; the pickling solvent is one or two or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution.

3. The method for preparing a biomass pitch composite-derived hard carbon material according to claim 1, characterized in that: In step (1), the biomass raw material powder is the undersize of a 300-mesh sieve; the total molar concentration of the inorganic acid in the pickling solvent is 0.05-0.20 mol / L; the mass volume ratio of the biomass raw material powder to the pickling solvent is (30-50) g / L; the pickling conditions are: stirring at 300-500 rpm for 10-15 hours; and the drying conditions are: drying at 70-90° C. for 10-16 hours.

4. The method for preparing a biomass pitch composite-derived hard carbon material according to claim 1, characterized in that: In step (2), the specific process of mixing the biomass precursor and the asphalt is as follows: adding the biomass precursor and the asphalt to anhydrous ethanol and stirring and mixing them uniformly to obtain a mixed dispersion; drying the mixed dispersion, and after drying, grinding the solid mixture into powder to obtain a precursor mixture.

5. The method for preparing a biomass pitch composite-derived hard carbon material according to claim 4, characterized in that: The biomass precursor and asphalt are added to anhydrous ethanol at a stirring rate of 300-500 rpm and a stirring time of 2-4 hours; the mass fraction of the biomass precursor in the mixed dispersion is 5-10wt%; the drying treatment conditions are 70-85°C and drying for 18-24 hours; the mass fraction of the biomass precursor in the precursor mixture is 70-95wt%; the precursor mixture is the undersize after grinding and passing through a 300-mesh sieve; the asphalt is an asphalt powder with a particle size less than or equal to 3μm and a softening point greater than or equal to 85°C.

6. The method for preparing a biomass pitch composite-derived hard carbon material according to claim 1, characterized in that: In step (3), the low-temperature pre-oxidation method is: in an air atmosphere, heating from room temperature to 200-400°C at a heating rate of 3-5°C / min, keeping the temperature at 200-400°C for 4-8 hours, and then naturally cooling to room temperature; In step (3), the high-temperature carbonization method is: in an inert atmosphere, heating from room temperature to 900-1400°C at a heating rate of 5-8°C / min, keeping at 900-1400°C for 4-8h, and then naturally cooling to room temperature.

7. The method for preparing a biomass pitch composite-derived hard carbon material according to claim 1, characterized in that: In step (1), the biomass raw material powder is the undersize of 300-mesh sieve after crushing sugarcane bagasse; the pickling solvent is a sulfuric acid solution with a concentration of 0.10 mol / L; the mass volume ratio of the biomass raw material powder to the pickling solvent is 40 g / L; the pickling conditions are: stirring at 500 rpm for 12 hours; and the drying conditions are: drying at 80° C. for 12 hours. In step (2), the specific process of mixing the biomass precursor and the asphalt is as follows: adding the biomass precursor and the asphalt in a mass ratio of 7:3 to anhydrous ethanol and stirring at 500 rpm for 3 hours to obtain a mixed dispersion; the mass fraction of the biomass precursor in the mixed dispersion is 9 wt%; drying the mixed dispersion at 80°C for 24 hours to obtain a solid mixture; grinding the solid mixture into powder and sieving it through a 300-mesh sieve to obtain the precursor mixture; the asphalt is an asphalt powder with a particle size of less than or equal to 3 μm and a softening point greater than or equal to 85°C; In step (3), the method of low-temperature pre-oxidation is: in an air atmosphere, heating to 300°C at a heating rate of 3°C / min, and keeping at 300°C for 4 hours; The high-temperature carbonization method is as follows: in an inert atmosphere, heating to 1300°C at a heating rate of 8°C / min, and keeping at 1300°C for 2h.

8. A biomass pitch composite derived hard carbon material, characterized in that: The biomass pitch composite derived hard carbon material is prepared by the preparation method of the biomass pitch composite derived hard carbon material as described in any one of claims 1-7.

9. A use of a biomass pitch composite derived hard carbon material, characterized in that: The biomass pitch composite-derived hard carbon material as claimed in claim 8 is used to prepare the negative electrode of a sodium ion battery.

10. The use of the biomass pitch composite derived hard carbon material according to claim 9, characterized in that: An electrode material is obtained by mixing 4 parts by weight of a biomass asphalt composite-derived hard carbon material, 0.5 parts by weight of sodium alginate, and 0.5 parts by weight of conductive carbon black; deionized water is added to the electrode material and mixed evenly to obtain an electrode slurry; the amount of deionized water added is controlled so that the viscosity of the electrode slurry is 4000-6000 cps; the electrode slurry is evenly coated on a copper foil, vacuum-dried at 80°C for 12 hours, and then cut into pieces to obtain a negative electrode sheet for a sodium ion battery.

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