Structural Design And Sodium Storage Mechanism Of Amorphous Carbon-based Materials: Research And Application

Amorphous carbon anodes are one of the most commercially promising anode materials for sodium-ion batteries due to their wide availability,mature preparation process and obvious price advantage.In terms of sodium storage performance,due to its low sodium storage potential,it can achieve high energy density and has better rate and low temperature performance compared to graphite materials.Overall,amorphous carbon anodes meet the pain point needs of sodium-ion battery development in all aspects.However,amorphous carbon anodes also face many shackles that hinder their practical application.First of all,the sodium storage mechanism of amorphous carbon anodes is not clear and academia is still arguing about it.Therefore,there is no conclusion on the structural design of amorphous carbon anodes.Secondly,amorphous carbon anodes themselves are amorphous materials with a microstructure belonging to stacking fault type defects.Therefore,there are considerable difficulties in regulating their microstructure and they can only be simply adjusted by adding exogenous reactants instead of growing according to people’s ideas.Finally,the capacity of amorphous carbon anodes still has shortcomings compared to alloy anodes and metal anodes etc.,so it is very important for future development of sodium-ion batteries how to better develop application scenarios for amorphous carbon anodes.Based on the microstructure regulation of amorphous carbon anode this paper focuses on exploring its sodium storage mechanism and promoting structural design through its sodium storage mechanism.The main research contents and results are as follows:(1)By adjusting the microstructure composition of amorphous carbon materials,different electrochemical behaviors were achieved in the sodium storage process.Using a variety of characterization methods to analyze the structure of the material,combined with electrochemical characteristics and in-situ electrochemical test results,the optimized amorphous carbon sodium storage mechanism was obtained,namely “multi-stage adsorption-pore filling”.Constructive suggestions were put forward for the structure of high-performance amorphous carbon anode materials.Building more closed pore volume can help improve platform sodium storage capacity and good cycle stability.(2)According to the sodium storage mechanism proposed in(1),the generation environment of amorphous carbon was regulated to prepare an amorphous carbon anode with less defects and high closed pore volume.Physical characterization and electrochemical testing verified the positive guiding role of the above mechanism and verified and supplemented the “pore filling” mechanism.Combined with electrochemical test results and non-in-situ characterization,it was found that a larger average pore size of closed pores may be beneficial to depolarization during charging and discharging to achieve better rate performance and sodium storage capacity.(3)An amorphous carbon-based host material with a gradient disordered structure was prepared by regulating it and applied to a sodium metal anode.Through a series of physical characterizations and ex-situ tests,we explored the deposition process of sodium metal on host materials and proposed that “gradient affinity for sodium” structure is closely related to disorderliness in carbon matrixes.That is,highly disordered carbon matrixes may have better affinity for sodium.The “gradient affinity for sodium” structure we constructed as a host carrying sodium metal achieved highly reversible uniform deposition/stripping without dendrites or “dead sodium” excellent deposition morphology.It provides a referenceable idea for designing and preparing efficient host structures for sodium metal anodes.In summary,this paper systematically investigates the microstructural composition of amorphous carbon materials,and points out the unique roles played by different structural forms in sodium storage.The "multi-stage adsorption pore filling" mechanism of sodium storage in amorphous carbon is developed,and the diffusion path of sodium ions in amorphous carbon matrix is summarized,which provides a constructive reference for the structural design of amorphous carbon as the sodium-ion batteries anode.Finally,based on the study of the sodium storage mechanism of amorphous carbon materials,the microstructure of amorphous carbon materials is improved and its application scenarios are expanded,and its excellent performance as a sodium-metal anode host material is achieved.