Design And Optimization Of High Performance Anode Materials For Sodium-ion Batteries

Na-ion batteries are one of the most promising secondary battery technologies after lithium-ion batteries.Throughout the development of lithium-ion batteries,the research on anode materials plays a crucial role in promoting the commercialization of lithium-ion batteries.As the most commercially successful anode material for lithium-ion batteries,graphite is not suitable for use in sodium-ion battery systems.The commonly used hard carbon anode material in sodium-ion batteries typically displays a specific capacity of<300 mAh/g.Therefore,the search of anode materials with high energy density and high stability has become a key research topic in the development of Na-ion batteries.Based on the current research trends,two kinds of anode materials for sodium-ion batteries with certain advantages are studied in this paper,mainly for structural design and performance optimization.The details are as follows:Taking the molybdenum disulfide anode material with high theoretical specific capacity as the research object,based on morphology control and performance optimization,carbon nanotubes are incorporated in the process of hydrothermal synthesis to improve the inherent low electronic conductivity of molybdenum disulfide,MoS2@CNTs composites with molybdenum disulfide/carbon nanotube coaxial structure were rationally designed.The final synthesized MoS2@CNTs composite exhibits outstanding high-rate performance and excellent cycling stability.The MoS2@CNTs anode exhibited almost no degradation in capacity(356 mAh/g)for 400 cycles at a current density of 0.5 A/g,and it maintained a high capacity of 185 mAh/g at a current density of 5 A/g.The results show that the carbon nanotube substrate improves the electrical conductivity of the bulk material,and the stable structural scaffold effectively suppresses the volume expansion of the material during the electrochemical process,thereby improving the rate capability of the electrode material and cycle stability.Taking the tin-based alloy material with high sodium storage capacity as the base point,the active metal antimony with a different sodium-ion intercalation potential is introduced,and the two act as buffer substrates for each other to relieve the huge internal stress of the alloy anode material in the process of sodiumization.The synergistic effect between the bimetals in the alloy effectively improves the sodium storage performance.The SnSb@CNFs composite was prepared by a hydrothermal method combined with high-temperature solid-phase reduction,and the SnSb@CNFs anode exhibited excellent cycling stability in electrochemical tests(150 cycles at 0.5 A/g,350 mAh/g)and excellent high rate performance(5 A/g,278 mAh/g).Then,the sodium-ion intercalation process in SnSb@CNFs was further characterized by in-situ XRD and Raman spectroscopy,and it was found that the micron-sized SnSb alloy material is not enough to cope with the extreme stress generated inside the material during the sodiumization/de-sodiumization processes.Pulverization,amorphization and other structural instability problems in the electrode material can still occur.A micro-nano structured tin-antimony bimetals alloy was rationally designed.The alloy anode displays synergistical effect on improving sodium storage properties.Compositing with carbon material,the SnSb@C composite nanosheets were synthesized by freeze-drying and pyrolysis methods.The SnSb alloy nanoparticles were directly anchored on carbon nanosheets.Nano-sized SnSb alloy particles are conducive to more uniform sodiumization,resulting in higher specific capacity of 429.8 mAh/g at 0.5 A/g,and the nano-size particles can significantly reduce the absolute volume change of SnSb alloy,which is more effective in alleviating volume expansion issues,thereby improving cycle stability.