Rice husk-based graphene-like zinc silicate composite block and preparation method and application thereof

Abstract

The invention discloses a method for preparing a rice husk-based graphene-loaded zinc silicate composite material block and the application of the material as a negative electrode material for a sodium ion battery. The raw material required for the invention is rice husk, a byproduct in agricultural production. First, the crushed rice husk is acid-washed to remove metal ions in the rice husk; then the obtained rice husk powder is evenly mixed with zinc powder and pressed into a block by a tablet press. At high temperature, the zinc powder acts as a hard template and can react with silicon dioxide in the rice husk to generate zinc silicate, and finally a graphene-loaded zinc silicate composite material is obtained. The synthesis method not only has a wide source of raw rice husks, is environmentally friendly and sustainable, but also the zinc powder used as a hard template can be continuously recycled, and the prepared composite material does not require subsequent treatment. When the rice husk-based graphene-loaded zinc silicate composite material is applied to the negative electrode of a sodium ion battery, it has good electron and ion transmission capabilities, and the prepared sodium ion battery has good electrochemical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of composite materials, and specifically relates to a method for preparing a graphene-like loaded zinc silicate composite material block using rice husk as a raw material, and application of the material as a negative electrode material for a sodium ion battery. Background Art

[0002] With the rapid development of modern economy, the global population has increased dramatically, and the demand for energy has also increased. However, traditional energy sources such as coal, oil, and natural gas are primary energy sources, non-renewable, and there are environmental pollution problems when they are used. Therefore, it is very important to explore and study renewable clean energy. Clean energy such as solar energy cannot be used directly, but needs to be used in energy storage devices.

[0003] Environmentally friendly electrochemical energy storage methods have received widespread attention. With the development of new energy vehicles and portable electronic products, lithium-ion batteries have been widely used due to their advantages such as high energy density and power, long cycle life, and safe use. However, lithium resources as electrode materials are relatively scarce, so it is necessary to find substitutes for lithium to meet the needs of future energy materials. Metallic sodium has similar physical and chemical properties to metallic lithium, and sodium resources are widely distributed and cheap, so it is considered to be a substitute for metallic lithium. However, due to the large radius of sodium ions and high ionization potential, the carbon-based negative electrode materials of lithium-ion batteries, represented by graphite, have poor sodium storage performance. Therefore, finding negative electrode materials suitable for sodium-ion batteries still faces many challenges.

[0004] Biomass materials are abundant in nature, are sustainably renewable, non-toxic and harmless, and are a source of battery electrode materials with great prospects for use. China is a large agricultural country. The straw, bracts, etc. produced during corn production in the north and the rice husks produced during rice production in the south have not been reasonably utilized. Carbon derived from biomass materials has become a current research hotspot due to its easy source and simple processing method. However, due to the limitations of its own structure and composition, the direct carbonization of agricultural waste and the resulting materials do not meet the performance requirements for direct use in secondary batteries. The present invention selects agricultural waste rice husks, and then transforms the rice husks into graphene-loaded zinc silicate composite materials suitable for sodium ion batteries through specific experimental methods. Summary of the invention

[0005] In view of the above problems, the present invention is based on the selection of cheap raw materials and environmentally friendly preparation methods, using rice husk as raw material and adopting a method in which the metal zinc template can be recycled, and proposes a preparation method for a graphene-like loaded zinc silicate composite material block. To achieve the above purpose, the technical solution of the present invention is:

[0006] 1. Wash the rice husk powder with ultrapure water and dry it, soak it in a 1-5 mol / L hydrochloric acid solution, stir it at 60-90°C for 6-8 hours, then filter it, wash it with water, and dry it to obtain product A;

[0007] 2. Mix product A and zinc powder in a certain proportion, grind and mix evenly in a mortar to obtain product B;

[0008] 3. Add product B into the tablet press mold and press it into blocks to obtain product C;

[0009] 4. Place product C in a quartz boat in the center of a tube furnace. Under the protection of argon, nitrogen or argon-nitrogen mixed gas, heat it to 400°C at 5-10°C / min, then quickly heat it to 1000°C at 20-30°C / min and keep it warm for 20-60min. Finally, cool it naturally to room temperature to obtain a block of graphene-like zinc silicate composite material.

[0010] The principle of the preparation method of the present invention can be summarized as follows:

[0011] Zinc powder is mixed with rice husk powder, pressed into blocks and then carbonized. The melting point of zinc is 419.5°C and the boiling point is 907°C. The metallic zinc melts at high temperatures and penetrates and extrude the gradually carbonized rice husks, eventually inducing the rice husk carbon to form a graphene-like structure. Part of the zinc is oxidized to zinc oxide at high temperatures and reacts with silicon dioxide in the rice husk to form zinc silicate. In addition, due to the low boiling point of zinc, it will completely volatilize at 1000°C, and no subsequent treatment steps are required. At the same time, the volatilized zinc powder is deposited on both sides of the furnace tube and can be recycled.

[0012] In addition, the present invention also provides the use of the rice husk-based graphene-like loaded zinc silicate composite material as a negative electrode material for a sodium ion battery.

[0013] The beneficial effects of the present invention are:

[0014] 1. The present invention uses zinc powder as a hard template to convert rice husk carbon, which originally has few pores and is not suitable for sodium ion battery energy storage, into a graphene-like structure with good electrochemical performance. At the same time, zinc as a reactant reacts with silicon dioxide to form zinc silicate, so that the silicon dioxide in the rice husk, which is inert to the sodium ion battery, is converted into the active substance zinc silicate.

[0015] 2. The rice husk-based graphene-loaded zinc silicate composite material prepared by the present invention, as a negative electrode material for sodium ion batteries, has good charge transfer capacity and ion transfer capacity, and exhibits good rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 These are optical photographs of the rice husk-based graphene-loaded zinc silicate composite material obtained in Example 1 of the present invention before and after carbonization.

[0017] Figure 2 This is a scanning electron microscope image of the rice husk-based graphene-loaded zinc silicate composite material obtained in Example 1 of the present invention.

[0018] Figure 3 This is a scanning electron microscope image of the rice husk-based silica / carbon composite material obtained in Comparative Example 1 of the present invention.

[0019] Figure 4 XRD spectra of the graphene-like zinc silicate composite material obtained in Example 1 of the present invention and the rice husk-based silicon dioxide / carbon composite material obtained in Comparative Example 1.

[0020] Figure 5 The cycle curves of the sodium ion batteries obtained in Example 1 of the present invention and Comparative Example 1 at a current density of 500 mA / g.

[0021] Figure 6 This is the sodium ion battery rate curve obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] Comparative Example 1

[0023] Step 1: Wash the rice husk powder with ultrapure water and dry it, soak it in a 2 mol / L hydrochloric acid solution, stir it at 80°C for 6 hours, and then filter it, wash it with water, and dry it to obtain acid-washed rice husk powder;

[0024] Step 2: Take 5 g of rice husk powder and place it in a quartz boat in the center of a tube furnace. In an argon atmosphere, heat it to 400°C at 5-10°C / min, then quickly heat it to 1000°C at 20-30°C / min and keep it warm for 20-60 minutes, then naturally cool it to room temperature to obtain a rice husk-based silica / carbon composite material.

[0025] Assembly of sodium ion battery: The rice husk-based silica / carbon composite material is used as the electrode active material, the conductive carbon black is used as the conductive agent, and the sodium carboxymethyl cellulose is used as the binder to prepare the slurry, and the composition ratio is 8:1:1. Copper foil is used as the current collector, the electrode thickness is 200μm, and it is dried at 80℃. At this time, the electrode loading is about 1mg / cm 2 . Use 1 mol / L NaClO 4 Ethylene carbonate (EC) / diethyl carbonate (DEC) (volume ratio of 1:1) solution was used as the electrolyte of the sodium ion battery, glass fiber filter paper and pure sodium metal foil were used as the sodium ion battery separator and counter electrode, respectively, and the sodium ion button cells were assembled in an argon atmosphere glove box.

[0026] Example 1

[0027] Step 1: Wash the rice husk with ultrapure water and dry it, soak it in a 2 mol / L hydrochloric acid solution, stir it at 80°C for 6 hours, and then filter it, wash it with water, and dry it to obtain acid-washed rice husk powder;

[0028] Step 2: Mix rice husk powder and zinc powder in a mass ratio of 7:93, add the mixture into a mortar and grind and mix evenly to obtain a mixed powder of rice husk powder and zinc powder;

[0029] Step 3: Weigh 2 g of the mixed powder of rice husk powder and zinc powder and add it into a tablet press mold, and press it into a round block with a diameter of 20 mm and a thickness of 2 mm;

[0030] Step 4: Place the rice husk powder and zinc powder block in a quartz boat in the center of a tube furnace, and under argon protection, heat the boat to 400°C at 10°C / min, then quickly heat the boat to 1000°C at 30°C / min and keep the temperature for 30 minutes to obtain a graphene-like zinc silicate composite material.

[0031] Assembly of sodium ion battery: The rice husk-based graphene-loaded zinc silicate composite material is used as the electrode active material, conductive carbon black is used as the conductive agent, and sodium carboxymethyl cellulose is used as the binder to prepare the slurry, and the composition ratio is 8:1:1. Copper foil is used as the current collector, the electrode thickness is 200μm, and it is dried at 80℃. At this time, the electrode loading is about 1mg / cm 2 . A 1 mol / L NaClO4 solution of ethylene carbonate (EC) / diethyl carbonate (DEC) (volume ratio of 1:1) was used as the sodium ion battery electrolyte, and glass fiber filter paper and pure sodium metal foil were used as the sodium ion battery separator and counter electrode, respectively, to assemble sodium ion button cells in an argon atmosphere glove box.

[0032] Example 2

[0033] The difference between Example 2 and Example 1 is that the mass ratio of rice husk powder to zinc powder is 10:90 in step 2. Since the zinc powder content is lower than that in Example 1, the zinc template effect is relatively low, so the layer thickness of the obtained rice husk graphene is larger.

[0034] Example 3

[0035] The difference between Example 3 and Example 1 is that the mass ratio of rice husk powder to zinc powder in step 2 is 5:95. Since the zinc powder content is higher than that in Example 1, the zinc template function is more sufficient, so the thickness of the obtained rice husk graphene layer is smaller. However, the interconnected structure is more messy, which is relatively not conducive to the transport of ions and electrons.

[0036] Example 4

[0037] The difference between Example 4 and Example 1 is that the temperature rise program in step 4 is to rise to 1000°C at 10°C / min and keep the temperature for 30 minutes. Since the heating rate is slower than that in Example 1, the oxygen atoms in the rice husk volatilize as carbon monoxide or carbon dioxide, the oxygen supply for the reaction between zinc and silicon dioxide is insufficient, and silicon dioxide is not completely converted into zinc silicate.

[0038] Figure 1 The macroscopic morphology of the rice husk-based graphene-loaded zinc silicate composite material prepared in Example 1 is shown. The morphology before and after carbonization remains consistent without obvious deformation.

[0039] Figure 2 The microscopic morphology of the rice husk-based graphene-like loaded zinc silicate composite material in Example 1 is shown. The rice husk is infiltrated and squeezed by zinc as a template to present a wrinkled carbon film. The interconnection of the carbon film constitutes a good channel for transmitting electrons, phonons and mechanical forces. Similarly, the interconnected carbon film cavities provide sufficient space for the mass transfer process. Zinc silicate appears certain aggregates at high temperature and is evenly dispersed in the graphene-like carbon film in the form of particles, thereby improving the conductivity of zinc silicate.

[0040] Figure 3 This is a scanning electron microscope image of the rice husk-based silica / carbon composite material obtained in Comparative Example 1 of the present invention. The rice husk carbon is in a block-like shape, and the relatively dense structure is not conducive to electrochemical energy storage.

[0041] Figure 4 The XRD spectra of the graphene-like zinc silicate composite material obtained in Example 1 of the present invention and the rice husk-based silicon dioxide / carbon composite material obtained in Comparative Example 1 are shown to determine the composition of the final product.

[0042] The graphene-like carbon component of the graphene-like loaded zinc silicate composite material obtained in Example 1 was removed in a muffle furnace at high temperature to obtain a zinc silicate component. According to the mass ratio before and after, it was found that the zinc silicate content in the composite material was 77.5 wt.%.

[0043] Figure 5 The cyclic stability curves of the sodium ion batteries obtained in Example 1 and Comparative Example 1 of the present invention at a current density of 500 mA / g are shown. After 50 cycles at 500 mA / g, Comparative Example 1 has a capacity of only 36.8 mAh / g, while Example 1 has a reversible capacity of 126.4 mAh / g after 50 cycles at 500 mA / g.

[0044] Figure 6This is the rate performance curve of the sodium ion battery obtained in Example 1 of the present invention. The charge and discharge tests were carried out at a current of 50 to 5000 mA / g, showing good rate performance. At a current of 5000 mA / g, there was still a reversible capacity of 50 mAh / g, and when the current was restored to 50 mA / g, the battery capacity also returned to 173 mAh / g.

[0045] The present specification selects and specifically describes these embodiments in order to better explain the principles and effects of the present invention, so that those skilled in the art can better understand and utilize the present invention. The protection scope of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing a block of a rice husk-based graphene-loaded zinc silicate composite material. It is characterized in that The method comprises the following steps: (1) washing the rice husk powder with ultrapure water and drying it, soaking it in a 1-5 mol / L hydrochloric acid solution, stirring it at 60-90° C. for 6-8 hours, and then filtering it, washing it with water, and drying it to obtain acid-washed rice husk powder; (2) mixing the pickled rice husk powder and zinc powder in a certain proportion, grinding and mixing in a mortar to obtain a mixed powder of rice husk powder and zinc powder; (3) Take 2 g of the mixed powder of rice husk powder and zinc powder and add it into the tablet press mold, and press it into a round block with a diameter of 20 mm and a thickness of 2 mm; (4) The rice husk powder and the zinc powder block are placed in a quartz boat and placed in the center of a tube furnace. Under the protection of argon, nitrogen or argon-nitrogen mixed gas, they are heated according to a certain temperature rising program, and finally cooled naturally to room temperature to obtain a graphene-like loaded zinc silicate composite material block.

2. The method for preparing the rice husk-based graphene-like zinc silicate composite block according to claim 1, It is characterized in that In step (2), the zinc powder particle size is 1 to 20 μm.

3. The method for preparing the rice husk-based graphene-like zinc silicate composite block according to claim 1, It is characterized in that In step (2), the mass ratio of rice husk powder to zinc powder is 10:(90-190).

4. The method for preparing the rice husk-based graphene-like zinc silicate composite block according to claim 1, It is characterized in that In step (3), the compression pressure of the tablet press is 15 to 25 MPa.

5. The method for preparing the rice husk-based graphene-like zinc silicate composite block according to claim 1, It is characterized in that In step (4), the temperature raising procedure is to heat to 400°C at 5-10°C / min, then rapidly heat to 1000°C at 20-30°C / min and keep warm for 20-60 min.

6. A graphene-like zinc silicate composite negative electrode sheet, It is characterized in that The negative electrode sheet is prepared by the following steps: The graphene-like zinc silicate composite material block described in claim 1 is evenly ground with conductive carbon black and sodium carboxymethyl cellulose in a ratio of 8:1:1, and after adding deionized water, magnetic stirring is performed to obtain a uniformly mixed electrode slurry, and the battery slurry is evenly coated on a copper foil with a coating machine, placed in a vacuum drying oven at 80°C for 12 hours, and then cut into disc electrodes with a punching machine to obtain a negative electrode sheet of the graphene-like zinc silicate composite material.

7. A sodium ion battery, wherein the sodium ion battery is obtained by assembling a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte under the protection of an inert atmosphere, It is characterized in that The negative electrode sheet of the sodium ion battery is the negative electrode sheet as claimed in claim 6.

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