A method for preparing sodium-ion battery hard carbon negative electrode material by treating biomass with xylanase

Abstract

The application discloses a method for preparing a hard carbon negative material for a sodium ion battery by treating biomass by using a xylanase. The method uses biomass as a precursor, removes part of hemicellulose by using a xylanase, and then carbonizes to obtain a biomass-based hard carbon for a negative electrode of a sodium ion battery. The preparation method is simple, environment-friendly, non-toxic and harmless, and conforms to the green and sustainable development concept. The prepared hard carbon negative material exhibits excellent performance in the sodium ion battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion batteries, and particularly relates to a method for preparing a sodium ion battery hard carbon negative electrode material by treating biomass with xylanase. BACKGROUND

[0002] With the progress of science and technology, the demand for energy storage devices such as batteries is gradually increasing. However, the widespread use of lithium ion batteries hinders their commercial application due to high cost and poor safety. Researchers are committed to finding products with comparable capacity and service life to lithium ion batteries, lower cost and better safety performance to meet people's daily needs. Through investigation, it is found that sodium ion batteries are the most potential alternative to lithium ion batteries. Biomass-based hard carbon is attracting attention due to its abundant raw material sources, low cost, easy availability, high carbon yield, environmental friendliness and the presence of multiple elements. Its unique microstructure exhibits obvious advantages and great commercial potential among many sodium ion battery negative electrode materials. Biomass is widely available, but its consistency is poor, so it needs to be simply regulated through pretreatment to find hard carbon precursors with good performance.

[0003] However, due to the limitations of the composition and structural characteristics of the biomass precursor, the electrical performance of the biomass-based hard carbon material prepared by direct carbonization cannot meet the demand. The existing hard carbon material prepared from biomass has the problem of poor sodium storage capacity. Therefore, by pretreating the biomass precursor under specific conditions, the composition and structure of the biomass precursor are adjusted and optimized to enhance its electrochemical performance. However, the existing hard carbon negative electrode material prepared by the existing method has the disadvantage of poor reversible capacity and rate performance. Moreover, the existing chemical pretreatment method requires the use of a large amount of chemical reagents, which has the problem of difficult post-treatment, and the physical method has the problem of high energy consumption. SUMMARY

[0004] The application provides a method for preparing a sodium ion battery hard carbon negative electrode material by treating biomass with xylanase.

[0005] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0006] A method for preparing a sodium ion battery hard carbon negative electrode material by treating biomass with xylanase, which uses xylanase to pretreat the biomass, and then high-temperature carbonizes to obtain a hard carbon material.

[0007] The xylanase pretreatment refers to reducing the content of xylan in the biomass by using xylanase. After pretreatment with xylanase, the content of hemicellulose in the hard carbon precursor is 10-35wt%. Preferably, when the biomass is walnut shell, the content of hemicellulose in the precursor is 18wt%, and the battery performance is the best. When the biomass is corn straw, the content of hemicellulose in the precursor is 20%, and the battery performance is the best.

[0008] The present application adjusts the content of xylan in the biomass by xylanase enzymatic pretreatment, and prepares biomass with different xylan contents; the biomass after enzymatic treatment is carbonized at high temperature into hard carbon, which can be used as the negative electrode of sodium ion battery, is green and environmentally friendly, and has excellent performance.

[0009] Preferably, the xylanase is selected from xylanase powder or xylanase liquid.

[0010] Preferably, the pretreatment time is 1-48h.

[0011] Preferably, the biomass includes walnut shell, corn straw, etc.

[0012] Preferably, the high-temperature carbonization is step-by-step carbonization, the first-step carbonization temperature is 500℃, the holding time is 1-5h, and the heating rate is 3-8℃ / min; the second-step carbonization temperature is 1300℃, the holding time is 1-5h, and the heating rate is 3-10℃ / min. Too high carbonization temperature will cause serious graphitization and decrease the sodium storage capacity.

[0013] Preferably, the specific steps of the above method are as follows:

[0014] (1) crushing the biomass raw material into small pieces and then grinding into powder, washing and drying for standby use;

[0015] (2) adding xylanase into buffer solution to obtain xylanase enzyme liquid;

[0016] (3) mixing the dried biomass raw material with the xylanase enzyme liquid at an enzyme dosage of 20-60u / g;

[0017] (4) placing the mixed xylanase enzyme liquid and biomass raw material into a shaker for enzymatic hydrolysis at 40-60℃ for 1-48h;

[0018] (5) adding hot water at 60-100℃ to the biomass after enzymatic hydrolysis for enzyme inactivation treatment, then washing, filtering and drying to obtain hard carbon precursor;

[0019] (6) high-temperature carbonizing the hard carbon precursor by a high-temperature tube furnace to obtain hard carbon material.

[0020] Preferably, the mechanical method in step (1) includes one or more of cell wall breaker, ball mill and vibration mill.

[0021] Preferably, the biomass is crushed to 1-10mm in step (1). The oven temperature is 70-100℃, and the time is 18-36h.

[0022] Preferably, the xylanase in step (3) is selected from microorganisms such as fungi or bacteria and is produced by fermentation.

[0023] The enzyme solution is obtained by dissolving xylanase in a citric acid / sodium citrate buffer solution, and the pH of the buffer solution is 5. The enzyme activity in the xylanase enzyme solution is 4-12 u / ml.

[0024] The application also provides application of the biomass-based hard carbon prepared by the method in preparation of a negative electrode material of a sodium ion battery.

[0025] The application also provides a negative electrode sheet of a sodium ion battery, which comprises a current collector and an electrode paste coated on the current collector, and the electrode paste comprises a binder, a conductive agent and the biomass-based hard carbon prepared by the method.

[0026] Preferably, the conductive agent is conductive carbon black, and the binder is sodium carboxymethyl cellulose. Preferably, the electrode paste is prepared by mixing the hard carbon, the conductive agent and the binder according to a mass ratio of 95:3:2. The coating thickness of the electrode paste on the current collector is 110 um, and the coating amount is 2-3 mg / cm 2 .

[0027] The application also provides a sodium ion secondary battery comprising the negative electrode sheet of the sodium ion battery.

[0028] The application has the following beneficial effects:

[0029] The application is beneficial to the formation of hard carbon closed pores by removing xylan, and a sodium ion battery hard carbon negative electrode material with excellent performance is prepared.

[0030] The application first controls the xylan content in biomass, and biomass-based hard carbon precursors with different xylan contents are prepared. By controlling the xylan content, hard carbon materials with different porosities and interlayer spacings are obtained, which effectively improve the sodium storage capacity of the battery, and this will expand the application of biomass materials in the field of sodium ion negative electrode materials.

[0031] The material provided by the application has a wide source, low cost and simple process. The sodium ion secondary battery using the material as a negative active material has a high working voltage and energy density, a high sodium storage capacity, a long cycle life and good safety performance.

[0032] The xylanase treatment of biomass can partially remove hemicellulose, and the lower the hemicellulose content in biomass, the higher the graphitization degree of the hard carbon produced. The removal of hemicellulose affects the crosslinking degree among lignin, hemicellulose and cellulose, and further affects the structure of the hard carbon produced. Moderate removal of hemicellulose can expand the interlayer spacing and is beneficial to the insertion of sodium ions, but the treatment has an optimal range, and the performance of the hard carbon obtained by excessive removal is worse.

[0033] The application not only has a simpler and more convenient operation, lower process difficulty, and is green, environmentally friendly, and pollution-free, and no chemical reagent is used. The battery performance of the obtained hard carbon material is significantly improved, and the reversible capacity and rate performance are greatly improved, and the capacity can be increased to 60 mAh / g at a current of 30 mA / g. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 SEM image of walnut shell powder without enzyme treatment;

[0035] Figure 2 SEM image of hard carbon precursor obtained in Example 7;

[0036] Figure 3 TEM image of walnut shell powder without enzyme treatment;

[0037] Figure 4 TEM image of hard carbon precursor obtained in Example 7;

[0038] Figure 5 Cycle performance test effect of hard carbon negative material H1 obtained in Example 7;

[0039] Figure 6 Battery cycle performance test effect of Japan Kurari cycle performance.

[0040] Figure 7 Reversible capacity of Japan Kurari, hard carbon material H0, and hard carbon material H1 at a current of 1 A / g. DETAILED DESCRIPTION

[0041] The technical solutions of the application will be further described below in combination with specific examples. The xylanase used in the examples or comparative examples has an enzyme activity of 50000 u / ml and is purchased from Shandong Longkete Enzyme Preparation Co., Ltd.

[0042] Examples 1-26

[0043] The method for preparing a hard carbon precursor for a sodium-ion battery by treating biomass with xylanase comprises the following steps:

[0044] (1) The biomass raw material is crushed into small pieces and then ground into powder, washed and dried, and then placed in an oven at 90℃ overnight for drying;

[0045] (2) The xylanase is added to the prepared citric acid / sodium citrate buffer solution, the pH of the buffer solution is 5, the xylanase enzyme solution is prepared, and the enzyme activity in the xylanase enzyme solution is 4 u / ml, 8 u / ml or 12 u / ml;

[0046] (3) Dry biomass raw material and xylanase enzyme solution were mixed at a solid-liquid ratio of 1 g:5 ml;

[0047] (4) The mixed xylanase enzyme solution and biomass raw material were placed in a shaker for enzymatic hydrolysis at 40-60°C for 1-48h.

[0048] (5) The enzymatically hydrolyzed biomass sample was added with hot water at 100°C for enzyme inactivation treatment, then washed, filtered and dried to obtain a hard carbon precursor. The specific enzymatic hydrolysis conditions are shown in Table 1.

[0049] Comparative Example 1

[0050] The preparation method of the hard carbon negative electrode material was the same as that of Example 7, except that mannanase was used for pretreatment.

[0051] Table 1 Enzyme treatment conditions and effects

[0052]

[0053]

[0054] The unenzymatically treated walnut shell powder, unenzymatically treated straw powder, and hard carbon precursors of some examples and comparative examples were subjected to high-temperature carbonization to prepare hard carbon negative electrode materials, and their application performance in sodium ion batteries was tested.

[0055] Preparation of hard carbon negative electrode material: The unenzymatically treated walnut shell powder, unenzymatically treated straw powder, and the obtained hard carbon precursors were subjected to high-temperature carbonization of the enzymatically hydrolyzed biomass sample by a high-temperature tube furnace to obtain a hard carbon material. The first step of carbonization was at a carbonization temperature of 400-500°C for 2h, and the heating rate was 5°C / min. The second step of carbonization was at a carbonization temperature of 1100-1300°C for 2h, and the heating rate of the high-temperature tube furnace was 5°C / min. The specific conditions are shown in Table 2.

[0056] The battery performance test method was as follows:

[0057] (1) The hard carbon negative electrode materials prepared in the examples and comparative examples, conductive carbon black, and sodium carboxymethyl cellulose were mixed uniformly at a mass ratio of 95:3:2, then dispersed into an aqueous solution to form a uniform slurry. Then the slurry was coated on a copper foil (the coating thickness of the slurry on the current collector was 110um) and vacuum dried at 90°C to obtain a hard carbon electrode sheet.

[0058] (2) The hard carbon electrode sheet in step (1) is paired with a metal sodium negative electrode, and a CR2032 type button cell is assembled in an inert atmosphere to test the electrochemical performance of the hard carbon electrode. The electrolyte is 1M NaPF6-EC / EDC (volume ratio 1:1) + 5% FEC. The button cell structure includes a positive electrode shell (stainless steel), a negative electrode shell (stainless steel), a gasket (stainless steel), a hard carbon electrode, a sodium sheet, an electrolyte, and a separator (glass fiber). The test results are shown in Table 2.

[0059] Table 2 Carbonization conditions of hard carbon material and performance of hard carbon negative electrode material

[0060]

[0061]

[0062] From the above results, it can be seen that for walnut shells, the battery performance is optimal when the hemicellulose content is about 18wt% after pretreatment with xylanase, and for corn stalks, the battery performance is optimal when the hemicellulose content is about 20wt% after pretreatment with xylanase. Too much xylanase will cause waste and not fully utilize the effect of hemicellulose removal, while too little xylanase will result in insufficient hemicellulose removal and thus not significantly improve battery performance. Compared with the prior art, the first coulombic efficiency is higher, and the pretreatment method is more environmentally friendly, environmentally friendly, and pollution-free.

[0063] Figure 1 Figure 2 is a SEM image of walnut shell powder without enzyme treatment, Figure 2 Figure 3 is a SEM image of the hard carbon precursor obtained in Example 7; from Figure 1 and Figure 2 As can be seen by comparison, after removing part of the hemicellulose with xylanase, the walnut shell has more pores, which is beneficial to the formation of closed pores during carbonization and increases its sodium storage capacity. Figure 3 Figure 4 is a TEM image of walnut shell powder without enzyme treatment, Figure 4 Figure 5 is a TEM image of the hard carbon precursor obtained in Example 7; from the TEM image, it can be observed that moderate removal of hemicellulose can expand the interlayer spacing, which is beneficial to the insertion of sodium ions and increases its rate performance, and the removal of hemicellulose is beneficial to the formation of carbon layers and the increase of closed pores, which increases its sodium storage capacity. Figure 5 Figure 6 is the cycle performance test results of the hard carbon negative electrode material H1 obtained in Example 7, Figure 6 Figure 7 is the cycle performance test results of the battery cycle performance of Japan Kureha. From Figure 5 and Figure 6 As can be seen, the capacity of the sample of Example 7 is much higher than that of Japan Kureha, and after 100 cycles, it can still reach more than 90%, and the sodium storage performance and cycle performance under high current are better than those of Japan Kureha products. Figure 7Reversible capacity of Asahi Kogyo, hard carbon material H0, hard carbon material H1 at 1 A / g current.

Claims

1. A method for preparing sodium-ion battery hard carbon anode material by treating biomass with xylanase, characterized in that, The method comprises the following steps: (1) crushing walnut shell into small pieces and then grinding into powder, washing and drying, and then placing in an oven for drying for standby; (2) adding xylanase into a prepared buffer solution to prepare xylanase solution; (3) preparing the dry biomass raw material and the xylanase solution according to a dosage of 40 u / g of enzyme; (4) placing the mixed xylanase and biomass raw material into a shaker for enzymolysis at 50 DEG C for 24 h; (5) adding 60-100 DEG C hot water to the enzymolysed biomass sample for enzyme inactivation treatment, and then washing, filtering and drying to obtain hard carbon precursor, wherein the obtained hard carbon precursor has a hemicellulose content of 18 wt%; (6) obtaining hard carbon material by high-temperature carbonization of the obtained hard carbon precursor through a high-temperature tube furnace, wherein the high-temperature carbonization is stepwise carbonization, the first step carbonization temperature is 500 DEG C, and the second step carbonization temperature is 1300 DEG C.

2. The method of claim 1, wherein, The xylanase is selected from xylanase powder or xylanase solution.

3. The method of claim 1, wherein, In step (1), the biomass is crushed to 1-10 mm; the oven temperature is 70-100 DEG C, and the time is 18-36 h; and in step (3), the xylanase is selected from fungi or bacteria for fermentation production.

4. Application of the biomass-based hard carbon prepared by the method of any one of claims 1-3 in preparation of anode material of sodium ion battery.

5. A negative electrode sheet of a sodium-ion battery, characterized by, It comprises: a current collector, a binder coated on the current collector, a conductive agent and the biomass-based hard carbon prepared by the method of any one of claims 1-3.

6. A sodium-ion secondary battery, characterized by, The anode sheet of the sodium ion battery comprises the anode sheet of the sodium ion battery.

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