Research On Carbon-assisted Systhesis And Fast Lithium Storage Of High-performance Composite

In recent years,researchers have devoted a great amount of time to the study of fast-storing lithium electrode materials due to the increasing demand for fast charge/discharge lithium-ion batteries.In order to improve the rapid lithium-storage performance of lithium-ion battery materials,carbon-assisted synthesis of carbon-coated electrode materials for improving the battery's rate performance and cycle stability is designed and proved in this dissertation.First of all,by using the glucose as a carbon source and DMEA as a surfactant,as well as a bimolecular structure inducer,a layer of nanoporous LiTi₂?PO₄?₃ electrode material was obtained.In the high-temperature calcination process,a large amount of Ti³⁺and oxygen defects were produced,which increased the electronic conductivity of the LiTi₂?PO₄?₃.Under the coating of the ultra-thin graphitized carbon layer,the electronic conductivity of the LiTi₂?PO₄?₃ was further improved,and the cycling performance was enhanced,owing to that it can prevent direct contact between the electrode material and the electrolyte.In addition,the coated carbon material can prevent the growth of LiTi₂?PO₄?₃ grain and agglomeration during hydrothermal and high temperature calcination processes.Secondly,commercial iron oxalate was used as the iron source,the graphene binder as the carbon source and the binder.The iron oxalate and the graphene binder were mixed through simply ball milling,and then kept at 200°C for 5 hours to decompose it,obtaining the graphene-coated amorphous Fe₂O₃ simultaneously.Its particle size ranged from 10 to 30 nm and dispersed between graphene sheets.The high electrical conductivity of coated graphene and the three-dimensional space structure can prevent the capacity decrease that caused by volume expansion during charging and discharging.The electrochemical performance of Fe₂O₃/G is superior to that of commercial graphite electrode materials even at a high current density of 2 A g^-1.Finally,the commercial V₂O₅ was used as a vanadium source.The H₂O₂ was used to assist the dissolution of V₂O₅,and then LiOH and graphene binder were mixed and dried.After keeping at 200°C for 10 hours,the graphene-coated Li₃VO₄ was obtained.The particle size was about 300 nm and distributed uniformly without agglomeration.The high conductivity and three-dimensional structure of graphene can increase the initial capacity and rate performance.At 10 A g^-1 rate,the capacity of graphene-coated Li₃VO₄ can be maintained 150 mAh g^-1 after 3000 cycles,indicating its excellent stability.Comparing with commercial Li₄Ti₅O₁₂ electrode materials,it has many advantages such as high capacity and low voltage platform.