Study On The Electrochemical Properties Of WSe₂ Nanoparticles Prepared By Chemical Vapor Deposition

Hybrid supercapacitor is a new type of energy storage device.Its energy density is between battery and supercapacitor,but in theory it possesses power output and cycle life similar to supercapacitors.Hence,hybrid supercapacitors are considered as the direction of development of new generation supercapacitors,which has attracted extensive attention of researchers.Graphene-like two-dimensional transition metal disulfides play an important role in the field of energy storage devices because of their unique structure and properties.Therefore,it is a meaningful and challenging work to study hybrid capacitors based on transition metal disulfide anodes to improve their electrochemical performance.In this work,WSe₂ nanoparticles were prepared by chemical vapor deposition(CVD)method.The resultant material has an unique onion-like structure and an average particle size of 70 nm.For lithium ion storage performance,WSe₂ anodes under current densities of 1.6and 10 A g^-1 express specific capacities of 277.6 and 116 mA h g^-1,respectively.For sodium ion storage performence,WSe₂ anodes at current densities of 1.6 and 10 A g^-1 exhibit specific capacities of 323.2 and 214 mA h g^-1,respectively.More importantly,WSe₂ exhibits a very high ratio of capacitive contribution,indicating a fast insertion/extraction reaction for both lithium and sodium ion reactions.The mechanism of lithium and sodium storage in WSe₂was also analyzed by ex-situ XRD,ex-situ Raman and ex-situ TEM methods.The lithium storage mechanism of WSe₂ is reversible intercalation reaction,while the sodium storage mechanism is divided into two steps:the first irreversible intercalation reaction and the subsequent reversible conversion reaction.Different intercalation mechanisms lead to faster storage of sodium ions than that of lithium ions in WSe₂.The lithium ion capacitors(LICs)using the WSe₂ anodes and active carbon cathodes were measured.The maximum energy and power density of 80.1 Wh kg^-1 and 14.4 k W kg^-1 was obtained,and the LICs maintained91.5%capacity retention after 10000 cycles at current density of 1 A g^-1.The sodium ion capacitors(SICs)consisting of WSe₂ anodes and activated carbon cathodes provided the maximum energy and power density of 123.1 Wh kg^-1 and 14.4 k W kg^-1.Capacity retention rate of the SICs is 72%after 2000 cycles under current density of 1 A g^-1,demonstrating that the SIC based on the WSe₂ anode can compete with the LIC.Subsequently,WSe₂/reduced graphene oxide(rGO)nanocomposite was synthesized by the CVD method.WSe₂ nanoparticle is deposited uniformly at the surface of rGO nanosheets.The unique structure endows the composite with outstanding electrochemical properties.The specific capacity of 133.3 mA h g^-1 at an ultrahigh current density of 60 A g^-1 can be delivered.At the same time,the WSe₂/rGO delivered very high ratio of capacitive contribution during the sodium ion reaction.The SICs assembled with the WSe₂/rGO nanocomposite as anodes and active carbon as cathodes showed the superior cyclic stability and a maximum energy density of 118.8 W h kg^-1 and a maximum power density of 13.76 k W kg^-1 as well as the superior cyclic stability,indicatiing that WSe₂/rGO anode has good application prospects in SICs.