Preparation And Electrochemical Properties Of Hard Carbon-coated Alloy Sodium Ion Anode Materials

Due to the high theoretical capacity and typical self-healing mechanism at lower working potential,Sn-P(Sn₄P₃,SnP₃)alloy stands out among the four major anode materials and has become potential large-scale energy storage in sodium-ion battery(SIBs)candidate materials for the system.This mechanism is attributed to the combination of the reversible conversion reaction and the alloy reaction,which effectively controls the electrochemical microenvironment around the negative electrode to be stabilized.However,due to the problem of volume expansion,alloy materials inevitably shorten the service life of SIBs.Although a large number of non-hard carbon materials have been reported to suppress volume expansion and increase electrical conductivity,they have reduced the weight and energy density of composite materials.Based on the above background,this project comprehensively considers that the hard carbon(HC)in the embedded negative electrode has a more suitable sodium-intercalation layer spacing,and a large number of micropores or defects can provide a wealth of sodium storage sites and other advantages.By constructing an adsorption-intercalation-alloying hybrid sodium storage mechanism,we innovatively designed HC-coated alloy nanostructures to achieve synergistic and efficient sodium storage.And we also combined with the research status,further explore the influence of ⁶⁰Co?-ray irradiation technology on the overall structure and electrochemical performance of composite materials.This research lays the foundation for the reasonable selection of high-efficiency active materials for wearable electronic devices and smart textiles to achieve excellent electrochemical storage.The main research contents of this paper are as follows:(1)Through a simple ball milling process,the HC-coated alloy(Sn₄P₃@HC)electrode structure with high capacity and electrochemical stability was designed and prepared.The pyrolysis temperature(800?-1400?)of puffed popcorn HC was further adjusted,and the influence of temperature gradient on the overall electrochemical performance of Sn₄P₃@HC composite was systematically explored.Due to the synergistic structural characteristics,the prepared Sn₄P₃@HC-1000nanocomposite shows an extremely high capacity of 550 mAh g^-1 when the current density is 0.1 A g^-1,and still shows 430 mAh g^-1 after 100 cycles.This study described the self-healing characteristics of Sn₄P₃ and the mechanism of HC synergistic sodium storage using the energy law.The results show that the capacity contribution of pseudocapacitance in the electrode increases from 49.5%to 80.8%with the increase of the scan rate,which proves that the excellent design of HC and Sn₄P₃ can synergistically improve the electrochemical performance of SIBs.(2)By introducing ⁶⁰Co?-ray irradiation technology to adjust the defect modification of HC at 1000?,a defect-rich HC-coated alloy structure(SnP₃@HC-?)was designed to further improve the efficiency of sodium insertion in the negative electrode.And we discussed the advantages of irradiation technology over traditional defect methods(wet chemical N doping and plasma F doping).Due to the high energy of?-ray,strong permeability,the constructed defect engineering effectively changes the interlayer structure and performance of the expanded popcorn HC,and exposes a large number of coordination unsaturated sites,further accelerating the reaction kinetics on the surface.Based on the synergistic effect of defect-rich HC and alloy,SnP₃@HC-?composite material has a good reversible capacity of 668 mAh g^-1 at a current density of 0.1 A g^-1.Even under the condition of a current density of 1.0 A g^-1,it still maintains a capacity retention rate of 88%(430 mAh g^-1)after 400 cycles and has excellent long-cycle stability.