Preparation method of modified pagodatree flower-based hard carbon by combining acid treatment and two-step carbonization

Abstract

The invention discloses a preparation method of modified pagodatree flower-based hard carbon by combining acid treatment and two-step carbonization, which comprises the following steps: (1) cleaning collected pagodatree flowers, respectively carrying out ultrasonic treatment for 30 minutes by using ethanol, acetone and water, then putting the pagodatree flowers into an air dry oven, drying for 12 hours, and smashing the dried pagodatree flowers into powder to obtain a precursor; (2) putting the sophora flower powder obtained in the step (1) into a tubular furnace, heating to 600 DEG C at a heating rate of 2 DEG C / min in an N2 atmosphere, carbonizing for 2 hours, and cooling to room temperature; (3) soaking the powder obtained in the step (2) in a beaker with 100ml of 5mol / l H2SO4 solution, and stirring at room temperature for 6 hours; and (4) performing heat treatment on the powder obtained in the step (3) to obtain the sophora flower-based hard carbon negative electrode material. According to the preparation method of the modified pagodatree flower-based hard carbon by combining the acid treatment and the two-step carbonization, the precursor has a natural and unique microstructure, the price is low, natural resources are rich, and the obtained pagodatree flower-based hard carbon material can be applied to a sodium ion battery negative electrode and can provide relatively high specific capacity and excellent cycling stability.

Description

TECHNICAL FIELD

[0001] The application discloses a preparation method for modifying sophora flower base hard carbon by combining acid treatment and two-step carbonization, and more particularly relates to a preparation method for a sodium ion battery negative electrode hard carbon material, namely SJO-1300, applied to improve sodium storage performance BACKGROUND

[0002] The growing energy crisis and environmental pollution seriously restrict the sustainable development of the world. Therefore, the research on sustainable, low-cost, high-power and clean energy storage and energy conversion components is of great significance to science and technology. Metal sodium has similar chemical properties with metal lithium, and attracts more and more attention due to its low price and rich resources. In large-scale energy storage applications, sodium ion batteries are considered to be the first choice for future commercialization.

[0003] It is an urgent problem to develop sodium ion batteries with high power density, large energy density and high energy conversion efficiency. The electrochemical properties of sodium ion batteries are related to the battery structure and other components such as positive electrode / negative electrode, electrolyte and separator. Among them, the performance of NIBs mainly depends on their active electrode materials, which is controlled by the electrochemical activity and kinetic characteristics of the electrode

[0004] In view of these problems, researchers must properly design and synthesize electrode materials to improve the kinetics of ion and electron transport in order to achieve high-performance sodium ion batteries.

[0005] Carbon materials have obvious advantages such as rich resources, low cost and chemical inertness, and are an important branch of research on sodium ion battery negative electrode materials. According to the structural characteristics, carbon negative electrode materials can be divided into three categories: hard carbon, soft carbon and graphite. Graphite-based carbon has been widely used in lithium ion batteries. However, due to the large atomic radius of sodium ions, graphite-based carbon has been greatly limited in sodium ion batteries. Compared with soft carbon, hard carbon has more functional groups, larger interlayer spacing and more closed pores, thereby providing more sodium storage sites and diffusion paths.

[0006] Biomass, natural polymer macromolecules (sucrose, cellulose, lignin, etc.) and synthetic polymer macromolecules (polyacrylonitrile, phenolic resin, etc.) can be used as hard carbon precursors. Because biomass itself has low cost and rich natural resources, we use sophora flower with a unique microstructure as a precursor to prepare hard carbon as a negative electrode material for sodium ion batteries.

[0007] In order to solve the problems of large specific surface area, large first irreversible reaction capacity and complex structure, methods such as modifying microstructure, doping heteroatoms, introducing functional groups and increasing active sites are proposed to improve the sodium storage performance of sodium ion batteries. Therefore, we use the preparation method of combining acid treatment and two-step carbonization to increase the content of carbonyl functional groups and the number of closed micropores, thereby improving the sodium storage performance of sodium ion batteries. SUMMARY

[0008] The present application aims to improve the sodium storage performance of sodium ion battery negative electrode materials, so that sodium ion batteries can be truly commercialized.

[0009] To achieve the above purpose, the present application adopts the following technical scheme: a preparation method for modifying sophora flower-based hard carbon by combining acid treatment and two-step carbonization, specifically including the following steps:

[0010] (1) Preparation of precursor. The collected sophora flower is washed clean, ultrasonic treated with ethanol, acetone and water for 30 min respectively, and then placed in a forced air drying oven for drying for 12 h. The dried sophora flower is crushed into powder;

[0011] (2) One-step carbonization. The sophora flower powder is placed in a tube furnace and carbonized at 600℃ under N2 atmosphere at a heating rate of 2℃ / min for 2h, and then cooled to room temperature;

[0012] (3) Acid treatment. A 100ml 5mol / l H2SO4 solution is prepared, and the powder obtained by one-step carbonization is placed in a beaker containing the H2SO4 solution and soaked at room temperature (stirring) for 6h; -1

[0013] (4) The soaked solution is washed with distilled water for 3-4 times, and the precursor is obtained by suction filtration and placed in a forced air drying oven for drying for 12h;

[0014] (5) Two-step carbonization. The dried precursor is placed in a tube furnace and carbonized at 1300℃ under N2 atmosphere at a heating rate of 2℃ / min for 2h, and then cooled to room temperature;

[0015] The sophora flower-based carbon hard carbon material prepared according to the preparation method is applied to the negative electrode of a sodium ion battery.

[0016] Compared with the prior art, the preparation method for modifying sophora flower-based hard carbon by combining acid treatment and two-step carbonization has the following advantages:

[0017] 1) The preparation method for modifying sophora flower-based hard carbon by combining acid treatment and two-step carbonization is simple in process, in line with the concept of sustainable development, and low in cost.

[0018] ​2) The present application adopts an acid treatment and a two-step carbonization combined preparation method, on the one hand, the acid treatment increases the carbonyl content in the hard carbon, and reversibly reacts with sodium ions, thereby improving the slope capacity in the sodium storage process, on the other hand, the two-step carbonization forms more closed micropores in the hard carbon, and the graphitization degree is higher to adsorb more sodium ions, further increasing the platform capacity. The synergistic effect of the two aspects improves the sodium storage performance and electrochemical performance of the sodium ion battery negative electrode material.

[0019] 3) The prepared sophorose-based hard carbon negative electrode material has abundant raw materials and a natural microstructure, the production conditions are controllable, and a series of problems such as low reversible capacity and low first coulomb efficiency can be greatly improved, and it is a developable sodium ion battery negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The SEM image of the precursor biomass of the sophorose-based hard carbon material in Example 1 is the petal part of sophora japonica.

[0021] Figure 2 The SEM image of the precursor biomass of the sophorose-based hard carbon material in Example 1 is the petal part of sophora japonica.

[0022] Figure 3 The SEM image of the sophorose-based hard carbon material in Example 1 is the petal part of sophora japonica.

[0023] Figure 4 The SEM image of the sophorose-based hard carbon material in Example 1 is the petal part of sophora japonica.

[0024] Figure 5 The XRD image of the sophorose-based hard carbon material in Example 1 is the petal part of sophora japonica.

[0025] Figure 6 The XPS total spectrum of the sophorose-based hard carbon material in Example 1 is the petal part of sophora japonica.

[0026] Figure 7 The O1s XPS high-resolution spectrum of the sophorose-based hard carbon material in Example 1 is the petal part of sophora japonica.

[0027] Figure 8 The pore size distribution graph of the N2 adsorption-desorption curve of the sophorose-based hard carbon material in Example 1 is the petal part of sophora japonica.

[0028] Figure 9 The rate performance graph of the half-cell of the SJO-1300 hard carbon material in Example 2 is the petal part of sophora japonica.

[0029] Figure 10 The cycle efficiency graph of the half-cell of the SJO-1300 hard carbon material in Example 2 is the petal part of sophora japonica.

[0030] Figure 11Electrochemical impedance plots of SJO-1300 hard carbon material in half-cell of Example 2. DETAILED DESCRIPTION

[0031] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which the present application belongs. The test reagents used in the following examples are all conventional biochemical reagents unless otherwise specified; and the experimental methods are all conventional methods unless otherwise specified.

[0032] The application will be described in detail below with reference to the examples and the accompanying drawings.

[0033] The model and manufacturer information of the equipment used in each embodiment of the present application are as follows:

[0034] Electronic balance, model FA2004, Shanghai Hengping Scientific Instrument Co., Ltd.; constant temperature magnetic stirrer, model 85-2, Henan Gugyi Ruihua Liability Co., Ltd.; numerical control ultrasonic cleaner, model Ka2200DB, Kunshan Ultrasonic Instrument Co., Ltd.; electric heating air drying oven, model WG-136, Shanghai Yiheng Scientific Instrument Co., Ltd.; vacuum drying oven, model DFZ, Beijing Keye Yongxing Instrument Co., Ltd.; tubular high-temperature furnace, model BTF-1700C, Anhui Beiyeike Equipment Technology Co., Ltd.; coating machine, model MSK-AFA-ES200, Hefei Kejing Co., Ltd.; punching machine, model MRXCP60, Hefei Kejing Co., Ltd.; glove box, model 168P12508A1NB, Shenzhen Yongxingye Precision Mould Co., Ltd.; button cell sealing machine, model SY160, Shenzhen Yongxingye Precision Mould Co., Ltd.; LAND battery tester, model LANDCT2001A, Wuhan Jinuo Electronics Co., Ltd.; Autolab electrochemical workstation, model PGSTAT 128N, Switzerland Wintone; electrochemical analyzer, model CHI604E, Shanghai Chenhua Instrument Co., Ltd.; scanning electron microscope, model Hitachi S4800, Japan Hitachi Co., Ltd.; small-angle X-ray scattering instrument, model Nano-inXide, France Xenocs Co., Ltd.; X-ray photoelectron spectrometer, model K-Aepna, Germany Thermo Fisher Scientific Co., Ltd.; X-ray diffractometer, model D8 ADVANCE, Germany BRUKER Co., Ltd.

[0035] The raw material information used in each embodiment of the present application is as follows:

[0036] Sophora japonica flowers, collected on campus; sulfuric acid (H2SO4), analytical grade, purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium carboxymethyl cellulose (CMC-Na), analytical grade, purchased from Tianjin Kemei Chemical Reagent Co., Ltd.; styrene-butadiene rubber latex (SBR), ~50wt%, purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd.; conductive carbon black (VXC72R), industrial grade, purchased from Shanghai Auman Chemical Co., Ltd.; metallic sodium, 99.99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; sodium-ion battery separator. The following materials were purchased: glass fiber (UK: Whatman); battery-grade copper foil (Hefei: Kejing Materials Technology Co., Ltd.); 99.99% nitrogen (N2) (Tianjin: Huanyu Gas Co., Ltd.); analytical grade acetone (C3H6O) (Fengchuan Chemical Reagent Technology Co., Ltd.); analytical grade anhydrous ethanol (C2H6O) (Tianjin: Fengchuan Chemical Reagent Technology Co., Ltd.); CR2432 battery casing (Shenzhen: Yongxingye Precision Abrasives Co., Ltd.); and 1 mol / L NaPF6-DEGDME. -1 Battery grade, purchased from Kelude New Energy Technology Co., Ltd.; graphite plate, 99.99% grade, purchased from Tianjin Zhongnuo Co., Ltd.

[0037] Example 1

[0038] A method for preparing SJO-1300, a modified sophora japonica-based hard carbon, by combining acid treatment and two-step carbonization, includes the following steps:

[0039] (1) Clean the collected Sophora japonica flowers, sonicate them with ethanol, acetone and water for 30 minutes each, then dry them in a forced-air drying oven for 12 hours, and crush the dried Sophora japonica flowers into powder.

[0040] (2) Place the Sophora japonica powder in a tube furnace and heat it to 600℃ for 2 hours under N2 atmosphere at a heating rate of 2℃ / min. Then cool it to room temperature.

[0041] (3) Prepare 100 ml of 5 mol / L solution -1 The powder obtained from one-step carbonization was placed in a beaker containing H2SO4 solution and soaked at room temperature (with stirring) for 6 hours.

[0042] (4) Wash the soaked solution with distilled water 3-4 times, filter to obtain the precursor, and dry it in a forced-air drying oven for 12 hours.

[0043] (5) The dried precursor was placed in a tube furnace and carbonized at 1300℃ for 2 hours under N2 atmosphere at a heating rate of 2℃ / min, and then cooled to room temperature to obtain hard carbon material SJO-1300.

[0044] The electrode materials prepared by the above method were subjected to various tests, and the test results are shown in Table 1. Figures 1-8 .

[0045] Sophora japonica as a herb has petals and stamens, Figure 1 is a SEM image of the precursor stamen structure in Example 1, Figure 2 is a SEM image of the precursor stamen structure in Example 1, Figure 3 is a SEM image of the stamen structure of the hard carbon material SJO-1300 in Example 1, Figure 4 is a SEM image of the petal structure of the hard carbon material SJO-1300 in Example 1. From Figure 1 and Figure 3 , the microstructure of the stamen can be seen, which is a multi-channel structure stacked together. From Figure 2 and Figure 4 , the microstructure of the petal can be seen, which is a surface with interlaced ravines and intersecting meridians. After carbonization, it can be seen that the hard carbon still retains the microstructure, and through the cross section it can be seen that the stamen part of the hard carbon after carbonization forms a multi-channel tubular carbon structure, which helps the penetration of the electrolyte and reduces the diffusion distance of Na+. While the petal still retains its microstructure after carbonization and generates micropores on the surface, providing more active sites for sodium ions. It is proved that the natural microstructure of Sophora japonica is still retained after carbonization and has a positive effect on improving the sodium storage performance of sodium ion batteries.

[0046] Figure 5 is the XRD pattern of the hard carbon material SJO-1300 in Example 1, and the sample in the spectrum shows two broad diffraction peaks at 2θ≈23° and 2θ≈43°, respectively, corresponding to the (002) and (100) crystal planes of graphite-like microcrystals, which is a typical hard carbon diffraction pattern. The wide diffraction peak at 23° in the spectrum corresponds to the typical peak structure of amorphous carbon material, which proves that after high-temperature annealing of Sophora japonica-based carbon, the carbon in the three-dimensional carbon skeleton material is converted into amorphous carbon.

[0047] Figure 6 is the XPS total spectrum of the hard carbon material SJO-1300 in Example 1, which shows that the hard carbon material is mainly composed of carbon and oxygen.

[0048] Figure 7 is the O1s XPS high-resolution spectrum of the hard carbon material SJO-1300 in Example 1, and the Ols spectrum can be convoluted into two peaks, representing carbonyl at 532.3ev and ether group at 533.2eV, respectively. C-O functional groups will undergo irreversible reactions with Na + , resulting in irreversible capacity and affecting the initial coulombic efficiency (ICE). In contrast, C=O functional groups are believed to undergo reversible reactions with Na + , increasing the reversible capacity of the electrode.

[0049] Figure 8 The pore size distribution curve of N2sorption / desorption curve of hard carbon material SJO-1300 in Example 1 was obtained using DFT model, which shows that SJO-1300 has less micropore content and more mesopore content. It may be because the two-step carbonization makes the open pores gradually disappear or form closed pores. Unlike micropores, which increase the irreversible capacity, mesopores help to infiltrate the electrolyte and rapidly transport ions, which is beneficial to the rate performance of the electrode.

[0050] Example 2

[0051] The hard carbon, conductive carbon black (Super-P), binder 50wt% styrene-butadiene rubber (SBR) and 2wt% sodium cellulose acetate (CMC-Na) were mixed with distilled water in a mass ratio of 85:10:3:2 to form a slurry, which was coated on a copper foil, dried at 70°C for 12h, and then punched to obtain a φ=13mm working electrode.

[0052] The electrode material prepared by the above steps was assembled into a half-cell for electrochemical performance test; the dried electrode was used as the working electrode, sodium metal was used as the counter electrode, glass fiber separator was used, and 1mol / L NaFP6 dissolved in diethylene glycol dimethyl ether (DEGDME) was used as the ether-based electrolyte. The CR-2032 type button cell was assembled in an argon glove box (H2O<1ppm, O2<1ppm).

[0053] Figure 9 The rate performance graph of SJO-1300 half-cell in Example 2, as the current density increased from 20mA g -1 to 2000mA g -1 , SJO-1300 showed excellent rate performance, and when the current returned to a small current from a large current, the reversible capacity of the electrode basically returned to the initial level, which proved that the electrode material had a stable structure.

[0054] Figure 10 The cycle performance graph of SJO-1300 half-cell in Example 2, which shows the discharge / charge curves of SJO-1300 in the voltage range of 100mA g -1 , 0-2.8V after 200 cycles. It can be seen that the electrode shows satisfactory stability. After 200 cycles, the capacity retention rate of SJO-1300 is 86.1%.

[0055] Figure 11 The electrochemical impedance graph of SJO-1300 half-cell in Example 2, from which it can be seen that the graph of SJO-1300 is composed of high-frequency region corresponding to the interface impedance (R SEI) and charge transfer resistance (R ct ) and the low frequency region corresponds to the diffusion impedance related to the sloped line in the ion electrode. From the semicircle in the high frequency region, it can be seen that SJO-1300 exhibits a smaller interfacial impedance and charge transfer resistance, which can be attributed to less irreversible reactions and a low specific surface area. For the sloped line in the low frequency region, the slope of SJO-1300 is significantly higher, proving that it has a higher Na + diffusion coefficient.

[0056] The application selects an acid treatment and a two-step carbonization combined preparation process to generate hard carbon material, and on this basis, selects a sophora flower with a natural microstructure and abundant natural resources as a precursor to prepare hard carbon material for a sodium ion battery negative electrode. The material has a high reversible capacity, and the raw material is simple, environmentally friendly, and low in cost, and is considered to be a very potential sodium ion battery negative electrode material.

[0057] The above only describes the preferred examples of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing modified sophora japonica-based hard carbon by a combination of acid treatment and two-step carbonization, characterized in that: Specifically, the following steps are included: (1) The collected Sophora japonica flowers were cleaned and ultrasonicated with ethanol, acetone and water for 30 min respectively. Then they were dried in a forced-air drying oven for 12 h. The dried Sophora japonica flowers were crushed into powder to obtain the precursor. (2) Place the Sophora japonica powder obtained in step (1) into a tube furnace and heat it to 600℃ for 2 hours under N2 atmosphere at a heating rate of 2℃ / min. Then cool it to room temperature. (3) Place the powder obtained in step (2) into a container containing 100 ml of 5 mol / L water. -1 Soak in a beaker of H2SO4 solution at room temperature (with stirring) for 6 hours; (4) After filtering, washing and drying the powder obtained in step (3), put it into a tube furnace and heat it to 1300℃ for 2 hours under N2 atmosphere at a heating rate of 2℃ / min. Then cool it to room temperature.

2. The method for preparing modified sophora japonica-based hard carbon by combining acid treatment and two-step carbonization according to claim 1, characterized in that: The precursor used in step 1 is biomass locust flower, which has a unique natural microstructure that is retained after carbonization. It is a natural resource that is abundant and low in cost.

3. The method for preparing modified sophora japonica-based hard carbon by combining acid treatment and two-step carbonization according to claim 1, characterized in that: The heat treatment process in step 2 includes the following steps: placing the Sophora japonica powder into a tube furnace and heating it to 600°C for 2 hours at a heating rate of 2°C / min under a N2 atmosphere, and then cooling it to room temperature.

4. The method for preparing modified sophora japonica-based hard carbon by combining acid treatment and two-step carbonization according to claim 1, characterized in that: The acid treatment process in step 3 includes the following steps: preparing 100 ml of 5 mol / L solution. -1 The powder obtained from the one-step carbonization was placed in a beaker containing H2SO4 solution and soaked at room temperature (with stirring) for 6 hours.

5. The method for preparing modified sophora japonica-based hard carbon by combining acid treatment and two-step carbonization according to claim 1, characterized in that: The heat treatment process in step 4 includes the following steps: after acid treatment, the powder is filtered, washed with water, dried, and then placed in a tube furnace. Under N2 atmosphere, the temperature is increased to 1300℃ for 2 hours at a heating rate of 2℃ / min, and then cooled to room temperature.

6. The SJO-1300 anode material is prepared by the preparation method according to any one of claims 1-5.

7. The application of the SJO-1300 negative electrode material prepared by the preparation method according to any one of claims 1-5 in sodium-ion batteries.

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