Design Of Metal Inorganic/Carbon Nanocomposites With The Improved Cathode Performance For Lithium-Sulfur Batteries

Lithium-sulfur battery utilizes the electrochemical conversion reaction of cathode material sulfur and anode material metal lithium,which has extremely high theoretical specific energy of 2600 Wh kg-1.Moreover,the elemental sulfur is abundant,cheap,and environmentally friendly.It is therefor regarded as one of the ideal choices for the new generation of battery system.However,sulfur cathodes have some problems such as poor conductivity,shuttle effect of polysulfides,and large volume changes during charging and discharging processes,which severely restrict their commercial application.In this paper,aiming at the above problems of sulfur cathodes,metal inorganic/carbon nanocomposite materials haven been designed for improving the performance of sulfur cathode in lithium-sulfur batteries.Through comprehensive studies including material structure characterization,theoretical calculations,electrochemical tests,the role of metal inorganics/carbon nanocomposites on the performance of sulfur cathode was discussed.The specific research content is summarized as follows:(1)In the construction of multifunctional adsorption-catalytic separators,ZnO-rGO nanocomposites are used to lock soluble polysulfides on the cathode side to mitigate the shuttle effect.As a conductive material,graphene improves the overall conductivity of the battery and the utilization of active material,as well as playing a physical confinement role via physical adsorption.Polar ZnO has strong chemical adsorption and high-efficiency catalytic effects on polysulfides,which can alleviate polysulfide shuttle.The introduction of the ZnO-rGO modified layer not only improves the mechanical properties of the separator and the wettability of the electrolyte,but also effectively restrains the soluble polysulfide on the cathode side,thereby improving the discharge capacity and cycle stability of the battery.The sulfur cathode with ZnO-rGO/PP retains a reversible capacity of 643 mAh g-1 at 0.2 C after 300 cycles with a coulombic efficiency close to 100%,and the capacity decay rate per cycle is only 0.19%.(2)Two kinds of niobium-based inorganic nanoparticles(NbC,Nb2O5)/hollow carbon nanospheres(HCN)complex hosts with different electrical conductivity were prepared as the sulfur host.HCN has a large hollow space to achieve high sulfur loading with well-developed mesoporous channels imposing physical confinement on polysulfides.Combinging the physic confiments of nanoporous carbon materials and the catalytic effect of Nb-based inorganics,the shuttle effect of polysulfides could be effectively inhibited.Furthermore,it is revealed that the highly conductive NbC has better electrochemical catalytic performance than the semiconductor Nb2O5.The resulting HCN@NbC/S composite has excellent cycle stability and rate performance,which maintains a reversible capacity of 500 mAh g-1 after 800 cycles at and 3 C.