Preparation And Electrochemical Performance Of 1D Cobalt Sulfides Composites

Transition metal sulfides have attracted extensive attention in the field of electrochemistry due to their high conductivity,good thermal stability and abundant resources,as well as good energy storage and energy conversion capacity.Among them,the cobalt sulfides as anode electrodes for LIBs/SIBs show high theoretical capacity,which is higher than that of the traditional inserted type materials（for example:carbon-based materials,titanium dioxide and lithium titanate）.In addition,the cobalt sulfides combined with sulfur as the cathode for lithium-sulfur batteries also show excellent electrochemical performance,due to the cobalt sulfides have strong binding effects with polysulfides and can inhibit the shuttle effects.However,there are many problems that restrict the commercial application of cobalt sulfides.For example,there is a obvious volume change during the process of lithium/sodium ion embedding in cobalt sulfides,and the host of the active materials cannot withstand the stress,even leading to the fracture or pulverization of cobalt sulfides.Besides,the intermediate product Li₂S/Na₂S could easily dissolve in electrolyte and deposit on the surface of lithium in the charging/discharging process,resulting in the amount loss of the active materials.To date,cobalt sulfides combined with conductive materials can significantly improve the conductivity of electrodes,and thus enhance the electrochemical properties of lithium ion batteries.Here in,the cobalt sulfides nanomaterials are studied,using the electrospinning technology,hydrothermal method and high temperature annealing to prepare the one-dimensional sulfide cobalts nanocomposite materials used in LIBs and SIBs,demonstrating the versatility of sulfide cobalts.The research content has the following three parts:1.The preparation of one-dimensional CNT/PAN@Co₉S₈@C and its application in LIBs.CNT/PAN nanofibers were prepared by electrospinning method firstly,and then the one-dimensional CNT/PAN@Co₉S₈@C composites were successfully prepared by hydrothermal and annealing processes.The electrochemical properties of CNT/PAN@Co₉S₈@C are better than those of CNT@Co₉S₈@C with non-electrospinning process.The former exhibits specific capacity of 455 mAh g^-1after 100 cycles under the current density of 2 A g^-1,and the capacity retention rate is86%（except the first three cycles）.2.The preparation of one-dimensional CoS/TiO₂ nanomaterials and their applications in lithium-sulfur batteries.One-dimensional hollow coaxial nanowire CoS/TiO₂ composites were prepared by electrospinning,hydrothermal method and annealing process.Both CoS and TiO₂have strong adsorption for polysulfides.After a series of phase characterization and electrochemical tests,the CoS/TiO₂ electrode shows superior electrochemical properties in lithium-sulfur batteries.The first cycle discharge capacity at the current density of 0.1 C is 1198.6 mAh g^-1,and after 200 cycles,it is still 611.1 mAh g^-1.3.The preparation and sodium storage properties of CoS/MWCNT composite.In recent years,cobalt sulfide with high theoretical capacity as sodium ion batteries cathode materials have been widely concerned.In this chapter,one step hydrothermal method was used to prepare one-dimensional CoS/MWCNT composite,then the target product was obtained by high temperature calcination process.The electrochemical properties as a anode electrode of sodium ion batteries were tested in different electrolytes.The CoS/MWCNT shows better electrochemical properties in 1mol/L NaClO₄-EC/DEC（1:1,V/V）-5%FEC electrolyte than those in 1 mol/L NaClO₄-EC/PC（1:1,V/V）-5%FEC electrolyte.The initial specific capacity is 390.8mAh g^-1,and remains 280 mAh g^-1 after 100 cycles.