Synthesis Of Transitional Metal Sulfides-carbon Composites And Their Electrochemical Performances For Lithium/Sodium Ion Batteries

With the progress of technology and the development of society,various portable devices and new energy vehicles have become more and more popular,leading to the increasing of people's demand for green and efficient energy storage devices.Because of its advantages,lithium ion battery has aroused widespread concerns in the academic and industrial fields.However,the limited resource of lithium in the earth to some extent severely impedes its large-scale application of lithium ion battery.In recent years,due to the natural abundance of sodium resource in comparison to lithium on earth,sodium ion battery as a new energy storage device has received wide attentions.However,whether lithium ion batteries or sodium ion batteries,during their more large-scale application in the future,there are still many problems should be solved,such as the generally poor conductivity,the serious volume expansion,and inferior specific capacity.Therefore,developing high performance lithium/sodium ion battery anode materials has been regarded as the top priority of the present research work.However,among many new type anode materials,because of rich reserves,high safety,simple preparation process and high theoretical specific capacity,the transition metal sulfide has been regarded as a protential in energy storage.Therefore,in this paper,the different carbon based transition metal sulfide composite materials have been prepared through a series of physical and chemical methods.The morphology,microstructure,and composition investigations of the materials are tested and analyzed.Afterwards,the as-prepared composites also have been tasted as anode materials of lithium/sodium ion battery to study their electrochemical properties.The main contents of this paper are as follows:1.The three-dimensional CoS₂ nanoparticles/graphene/carbon nanotube aerogels?CoS₂/GCAs?are successfully synthesized by one-step hydrothermal method,in which the CoCl₂.6H₂O,Na₂S₂O₃.5H₂O,graphite oxide and commercial carbon nanotubes are served as precursors.SEM and TEM results suggest that in CoS₂/GCAs composite,the CoS₂nanoparticles,with the diameter of 250 nm,are evenly wrapped in the graphene/carbon nanotube substrate which has good conductivity.Thus,the CoS₂/GCAs composite material exhibits superior electrochemical performance compared with the pure CoS₂ and CoS₂/GNs when used as anodes of lithium/sodium ion batteies.When used as an anode for LIBs,CoS₂/GCAs possesses a high reversible capacity of 975 mAh g^-1after 100 cycles at0.25 A g^-1.Apart from that,it also shows an outstanding cycling stability with the capacity of 258 mAh g^-1in 100 th at 0.05 A g^-11 for SIBs.2.Co₉S₈ nanoparticles anchored in three-dimensional carbon nanosheet networks?3D Co₉S₈@CNNs?composites are fabricated by a simple strategy with the assistance of NaCl,in which the C₆H₈O₇,CoCl₂.6H₂O,?NH₂?₂CS are served as carbon,cobalt and sulfur sources,respectively.In this architecture,Co₉S₈ nanoparticles?with the diameter of 25 nm?are uniformly embedded in the three-dimensional carbon nanosheet networks,which not only can effectively alleviate the volume effect of active material in the processes of charge and discharge,but also can effectively enhance the conductivity of the active material,increase the contact area between the active material and the electrolyte,and effectively provide abundant electrochemical active sites.Therefore,when evaluated as an anode for LIBs,the 3D Co₉S₈@CNNs electrode exhibits outstanding electrochemical performance with the capacity of 935 mAh g^-1after 200 cycles at 0.25 A g^-1.As for SIBs,it also delivers a superior cycling stability with the capacity of 250 mAh g^-1after 50 cycles at 0.1 A g^-1.3.A series of metal sulfide/graphene/carbon nanotube?M_xS_y/GC?composite materials with a unique sandwich architecture assembled by uniform M_xS_y nanoparticles anchored in the GC matrix are fabricated by a simple calcination method,and electrochemical properties when used as the anode materials of LIBs/SIBs are discussed.M_xS_y/GC composites fabricated by this convenient,fast,green and scalable approach have the advantages of high theoretical capacity,good conductivity and flexibility,leading to excellent cycle and rate performance.Using the FeS/GC composite as an example,it demonstrates excellent electrochemical performances in LIBs with favorable cycling stability,high specific capacity(⁸70 mAh g^-1at a current density of 0.25 A g^-1)and remarkable rate performance.When applied as an anode material for SIBs,the FeS/GC composite still exhibits a superior reversible capacity of 300 mAh g^-1at acurrent density of0.1 A g^-1after 100 cycles.