Method for preparing'spring pad '-like porous carbon material by biomimetic mineralization pyrolysis method and sodium storage application of'spring pad'-like porous carbon material

Abstract

The invention provides a method for preparing a'spring cushion '-like porous carbon nanomaterial by a biomimetic mineralization pyrolysis method. The method comprises the following steps: preparing a mixed aqueous solution from sodium alginate as a precursor and sodium bicarbonate according to a certain proportion; and then freeze-drying the solution to obtain a flaky mixture with a biomineralization-like structure. Placing the mixture in a tubular furnace, and carbonizing at 500 DEG C; and cleaning the carbonized material with a large amount of deionized water to obtain the rigid and soft porous carbon nanomaterial similar to a spring pad. The nanostructure of the material is similar to that of a common spring cushion in life, and the material has good structural stability. And due to the relatively high specific surface area, the developed pore structure and abundant surface functional groups, the material shows excellent electrochemical performance when being used as a sodium ion capacitor electrode material.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical energy storage materials, and provides a method for preparing a "spring pad"-like porous carbon material by biomimetic mineralization pyrolysis, and its application in sodium-ion supercapacitor electrode materials. Background Art

[0002] Large-scale electrochemical energy storage devices have always been one of the focuses of modern social development. Among many electrochemical energy storage devices, lithium-ion energy storage systems are considered to be one of the main devices for large-scale energy storage due to their excellent energy storage mechanism and high electrochemical performance. However, due to the scarcity and severe uneven distribution of global lithium resources, the wide application of lithium-ion energy storage systems in large-scale energy storage is restricted. Sodium resources have attracted extensive attention because of their high content in the earth's crust, low price, wide resource distribution, and similar chemical properties to lithium. Sodium-ion energy storage systems (including energy storage devices such as sodium-ion batteries and sodium-ion capacitors) have a similar energy storage mechanism to lithium ions, and have a redox potential (Na / Na + , -3.04V) similar to that of lithium ions (Li / Li + , -2.73V). Therefore, from the perspective of large-scale energy storage, sodium-ion energy storage systems have broad development prospects.

[0003] However, compared with the well-developed lithium-ion energy storage system, sodium-ion energy storage is still in its infancy. High-performance sodium storage materials are still the key to the development of sodium-ion energy storage. Porous carbon nanomaterials are one of the dominant materials in the current lithium-ion energy storage system. Therefore, constructing porous carbon nanomaterials with a high specific surface area and a rich pore structure can accommodate more sodium ions. However, the problem still remains that due to the relatively large radius of sodium ions, when sodium ions are embedded in the carbon material, it often causes serious volume expansion and structural collapse of the electrode material. As a result, the rate performance and cycle life of the electrode material are poor. It can be considered that for porous carbon electrode materials, serious volume expansion is still a great challenge for high-performance sodium-ion energy storage devices. To solve this problem, this patent designs a porous carbon nanomaterial with a rigid-flexible "spring pad"-like structure, which has a certain rigidity to ensure the structural stability of the electrode and sufficient elasticity to buffer the volume change of the electrode.

[0004] This kind of "spring"-shaped porous carbon material is prepared by using sodium alginate molecules to induce the biomimetic mineralization arrangement of inorganic nanoparticles and then through high-temperature pyrolysis carbonization. During the freeze-drying process of the prepared mixed solution of sodium alginate and sodium bicarbonate, water is gradually frozen into ice crystals; when the solution concentration reaches the saturation concentration of sodium bicarbonate, sodium bicarbonate begins to nucleate and grow; the sodium alginate molecules contained in the solution induce the orderly arrangement of sodium bicarbonate nanoparticles to form an organic-inorganic composite precursor with a biomimetic mineralization structure. In this precursor, sodium bicarbonate acts as a "foaming agent" and decomposes to produce a large amount of gas during the carbonization process, playing a role in chemical foaming, thus obtaining a "spring pad"-shaped porous carbon. The prepared carbon material is a micron sheet similar to a spring pad, containing a large number of through pores, which not only provides an effective diffusion channel for Na+ ions and electrolytes, but also effectively buffers the volume expansion generated by the insertion of Na+ ions. When this carbon nanomaterial is used as the electrode material of a sodium-ion capacitor for electrochemical performance testing, it all shows excellent sodium storage performance. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a "spring pad"-shaped carbon nanomaterial. This method is based on the nucleation and precipitation of sodium bicarbonate induced by sodium alginate during the freeze-drying process, thereby forming an organic-inorganic precursor with a biomimetic mineralization structure. A large number of bubbles are generated by the decomposition of salt crystals in this precursor during the carbonization process, thus obtaining a carbon nanomaterial with a "spring pad" structure. This kind of "spring pad"-shaped carbon nanomaterial has good electrochemical performance when used as the electrode material of a sodium-ion energy storage system.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is:

[0007] Take a certain amount of sodium alginate and dissolve it in an aqueous solution, and add sodium bicarbonate according to a certain ratio. After fully dissolving, dry the mixture in a freeze-drying device. The dried mixture undergoes procedures such as pre-carbonization, carbonization, washing, and drying to obtain a "spring pad"-shaped carbon nanomaterial.

[0008] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0009] (1) The biomimetic mineralization pyrolysis synthesis route can achieve the green and low-cost synthesis of carbon nanomaterials. From the perspective of application prospects, it greatly reduces the process for preparing carbon nanomaterials, having the advantages of low cost, simple method, and large-scale production.

[0010] (2) The prepared porous carbon material has a high specific surface area, developed porosity, and a nano-structure that combines rigidity and flexibility, and can achieve high and stable sodium storage performance. Description of the Drawings

[0011] Figure 1 Scanning electron microscope (SEM) photograph of the biomimetic mineralized organic-inorganic precursor obtained in Example 1.

[0012] Figure 2 Scanning electron microscope (SEM) photograph of the porous carbon nanomaterial obtained in Example 2.

[0013] Figure 3 When the porous carbon nanomaterials prepared in Examples 1-3 of the present invention are used as the negative electrode material of a sodium ion supercapacitor, the rate performance at a current density of 0.1-10 A g -1 Current density. Detailed implementation manners

[0014] The present invention will now be described with reference to the following specific examples, but is not limited to the examples.

[0015] Example 1

[0016] Weigh 1 g of sodium alginate and dissolve it in 200 mL of deionized water, then add 3 g of NaHCO3 salt crystal templating agent to the solution and dissolve it fully. The mixed solution is freeze-dried to obtain a dried white solid mixture. As shown Figure 1 by the SEM picture, the NaHCO3 salt crystals precipitated under the induction of sodium alginate molecules form a unique organic-inorganic composite rod-like structure, which has the characteristics of a biomimetic mineralized structure.

[0017] Example 2

[0018] The method of this example is basically the same as that of Example 1, the difference is: the prepared organic-inorganic precursor is heated to 500 °C at a rate of 5 °C / min in an N2 atmosphere and kept at this temperature for 1 h for carbonization to prepare a porous carbon material with a spring pad structure. As shown Figure 2 by the SEM picture, the porous carbon nanomaterial prepared by biomimetic mineralized pyrolysis has a flaky structure and many pores on its surface.

[0019] Example 3

[0020] The method of this example is basically the same as that of Example 1, the difference is: the prepared porous carbon material, conductive acetylene black, and PVDF are prepared into an electrode sheet according to a mass ratio of 7:2:1. It is assembled with a sodium metal sheet and a glass fiber separator into a button battery, and its electrochemical performance is tested. As shown Figure 3As shown, the prepared porous carbon materials have discharge capacities of 374, 290, 239, 208, 186, and 166 mAh g-1 at current densities of 0.1, 0.2, 0.5, 1, 2, and 5 A g-1, respectively. Even at a high current density of 10 A g-1, the discharge capacity is still 146 mAh g-1. When the current density is restored to 0.1 A g-1, the capacity can reach 265 mAh g-1.

Claims

1. A method for preparing a "spring pad"-like porous carbon material by biomimetic mineralization pyrolysis and its application in sodium storage, characterized in that It includes the following steps: (a) Mixing: Sodium alginate and sodium bicarbonate are formulated into a mixed aqueous solution according to a certain ratio, and then the aqueous solution is freeze-dried to obtain a flaky solid mixture with a biomimetic mineralized structure; (b) Carbonization: The flaky solid mixture is placed in a tubular furnace and heated to a suitable temperature at a certain heating rate in an inert atmosphere for pre-carbonization, and then continuously heated to a suitable temperature and kept for a certain time for carbonization; (c) Cleaning: The calcined sample is washed with a large amount of deionized water and dried in an oven to obtain a "spring pad"-like porous carbon nanomaterial; 2. The method for preparing a "spring pad"-like porous carbon material by biomimetic mineralization pyrolysis according to claim 1, characterized in that: In step a, the ratio of sodium alginate to sodium bicarbonate can be controlled at 1:1 to 1:6; 3. The method for preparing a "spring pad"-like porous carbon material by biomimetic mineralization pyrolysis according to claim 1, characterized in that: In step b, the carbonization temperature is 500 - 900 °C, and the heating rate is 1 - 10 °C / min -1 , and the heat preservation time is 1 - 6 h.

4. The method for preparing a "spring pad"-like porous carbon material by biomimetic mineralization pyrolysis according to claims 1-3, wherein: When the sodium alginate and sodium bicarbonate mixture is used as a template to prepare a solution, the prepared porous carbon nanomaterial has a structure similar to the commonly used "spring pad" in life, and the bubble size is in the range of 500-1000 nm; 5. The method for preparing a "spring pad"-like porous carbon material by biomimetic mineralization pyrolysis according to claims 1-4, characterized in that: This "spring pad"-like porous carbon nanomaterial can be used as an electrode material for sodium-ion hybrid capacitors and exhibits excellent sodium storage performance.

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