The Synthesis Of Co Based Composite Materialand Its Application In Electrochemical Energy Storage

Li-S and Na-S batteries have attracted much attention due to their high energy density,low cost and excellent cycle performance.However,due to the slow reaction kinetics of the intermediate products(Li PSs/Na PSs),they can dissolve in the electrolyte,leading to the"shuttle"effect.The"shuttle"effect and the electronic insulation of S cause serious capacity loss,low S utilization and poor structural cycle stability.To suppress the"shuttle"effect,fabricating hollow or porous polar composite material can is effective to realize physical confinement adsorption,chemical adsorption and chemical catalysis to enhance the conversion efficiency of intermediate products.The hollow/porous structure can effectively buffer the caused volume expansion during Li⁺/Na⁺depositing/peeling,and greatly improve the cycling and rate performance of electrodes.Compared with Li⁺,The more sluggish(de)insertion kinetics of Na⁺with a large size prevent the normal operation of Na-S battery at room temperature.By optimizing the structure/composition,reducing the size and the compositing with high conductive matrix,the abundant electrochemical active sites,rapid charge transfer and ion diffusion kinetics and optimized interface engineering were obtained,which significantly reduce the operation temperature of Na-S battery.In this paper,building the polar TiO₂@CN@Co₃O₄/Sand FCNT@Co₃C-Co composites was performed and they were applied in Li-S and Na-S batteries,respectively.This paper is mainly focused on the following two aspects:First,the preparation of porous TiO₂@CN@Co₃O₄/S composite and its application in Li-S battery were carried out,in which the structure/component optimization was involved.The"shuttle effect"of Li PSs can be inhibited by strong physical confinement adsorption,strong chemical adsorption and the step multi-electrocatalysis of various Li PSs intermediates.The hollow structure can effectively resist the volume expansion,and improve the cycle stability of the electrode.Polar CN and Co₃O₄/TiO₂can promote long chain to short chain and long chain to short chain conversion efficiencies.The"shuttle effect"of Li PSs was seriously inhibited by the transformation of Li₂S₄intermediate.CN can increase the conductivity of electrode,the capacity and rate performance of Li-S battery.TiO₂@CN@Co₃O₄/S delivered a high specific capacity of 1196 m Ah g^-1at 0.2C.,it still displayed a capacity of 711 m Ah g^-1at 5C.After 1000 loops at 2c,it presents a weak decay with only 0.037%for each cycle.Even under the condition of poor electrolyte(E/S=5 m Lg^-1)and a high sulfur load(10 mg cm^-2),the Na-S battery can still operate normally.Second,the preparation of FCNT@Co₃C-Co and its application in Na-S energy storage at room temperature was investigated.The Na PSs can physically confined within the three-dimensional(3CD)porous FCNT@Co₃C-Co,accompanied by the strong chemical bonding among strong polar CN,Co₃C,Co and Na PSs,which can effectively catalyze the conversion of Na PSs intermediates.The flexible 3D porous frame can effectively buffer the volume expansion,improve the Na⁺diffusion kinetics,and endow FCNT@Co₃C-Co/S excellent structure robustness during repeated cycling.FCNT@Co₃C-Co/S exhibited a high discharge capacity of 1364 m Ahg^-1at 0.1C,and the Coulomb efficiency is still higher than 75%after 500 cycles at 2 C,even under a lean electrolyte(E/S=5 m Lg^-1)and a high sulfur loading of 8.6 mg cm^–2conditions.This work provides effective technical and theoretical guidance for the design of high performance Na-S battery at room temperature.