Synthesis And Performance Of WS₂ Anode Material For Sodium Ion Batteries

In order to alleviate the shortage of lithium,sodium ion batteries become the replacement of lithium ion battery.Because tungsten sulfide（WS₂）has unique graphene layered structure and is beneficial to the electrochemical reaction,so it is widely concerned by researchers.Due to unstable structure,volume expansion during the charge and discharge process limited WS₂ application.Therefore,how to effectively improve the electrochemical performance has become a research hot issue.In this paper,in order to improve the electrochemical performance of WS₂ material,we innovative composite Super P with WS₂,and explore the conditions and regulation of nitrogen doped Super P and WS₂ on the structure of the product,the effects of sodium storage performance and mechanism was researched.（1）WO₃/Super P as the precursor by sulfide reduction can made nanosheet WS₂/Super P composites at low temperature,this method is simple and easy to operate.Through composite conductive carbon Super P,WS₂/Super P composites exhibited high reversible capacity: 389 mA h g-1,high coulombic efficiency:81%,which has excellent cycle stability and rate performance as anode materials for lithium ion batteries.After 200 cycles of charge transfer resistance is still low:53 Ω.Through the analysis of the mechanism,adding Super P in the product can achieve the small particle size and uniform structure products,the electrical conductivity is improved,the insertion/extraction process will be accelerate of Li between the electrode and the electrolyte,improved the electrochemical stability.（2）As-synthesis WO₃ and CH3CSNH2 are the main original materials,vacuum vulcanization method has been used to control WS₂ crystal structure by controlling exposure crystal surface and the crystallinity,the electrochemicalperformance as sodium ion batteries can be improved.Under the experimental conditions: sulfide 2 hours of WS₂ sample electrode at the current density of 100 mA g-1,after 100 cycles the capacity retention rate was 85%,at the current density of 100 mA g-1,in the case of high current density of 2000 mA g-1,its capacity can reach 148 mA h g-1.By mechanism analysis shows that:（002）crystal surface with large interlayer spacing,can accelerate the Na+ between the electrode and the electrolyte of the insertion/extraction the electrochemical reaction,improving the cycling stability.（3）The reversion rate can be tailored by using the different sulfides as sulfur source.Thioacetamide（TAA）as sulfur source,the reduction reaction is fast,the sample has small size and few layer structure.The electrode at a current density of 100 mA g-1,its capacity can reach 261 mA h g-1,the current density of700 mA g-1,its capacity can reach 226 mA h g-1.By mechanism analysis: few layer structure and small size nanosheet has more Na+ storage sites and faster Na diffusion rate,the electrochemical performance can be improved.（4）CH3CSNH2 as sulfur source,（CO（NH2）2）as nitrogen source,under the condition of 900℃,2 h,the nitrogen doped conductive carbon Super P and WS₂ composite is produced.At the current density of 100 mA g-1,the capacity of the electrode is ³60 mA h g-1 after 100 cycles;at current density of 1000 mA g-1,after 100 cycles the capacity is ²00 mA h g-1.The mechanism research indicated that WS₂-NC nanocomposite materials as sodium ion battery electrode own capacity stability and good rate capability.This superior electrochemical performance is due to the interfacial reaction.By nitrogen doped Super P,surface defect can promote the electron/ion transformation in convertion reaction stage,largely Na+ can be adsorbed in interface reaction by fast electron/ion transfer rate.