Preparation Of Transition Metal Sulfide And Carbon Composites And Their Electrochemical Energy Storage Studies

In order to reduce the cost and alleviate the pressure of resource shortage,it is urgent to find alternatives to lithium-ion batteries.Potassium ion batteries have attracted a lot of attention from researchers because of the abundant potassium reserves,low cost and similar physical and chemical properties of potassium and lithium.However,the radius of potassium ions is much larger than that of lithium ions,and it is especially important to find anode materials that can accommodate potassium ions.Among many anode materials,transition metal sulfides stand out from other anode materials as their high theoretical capacity and large layer spacing.However,transition metal sulfide anode materials are confined by poor electronic conductivity,large volume changes and sluggish chemical kinetics,resulting in poor structural stability,dendrite potassium growth,poor battery cycling performance.Therefore,this paper will improve the potassium storage performance of transition metal sulfide materials in terms of optimizing structure/component design and reducting size.The details of the study are listed as follows:Firstly,the MoS₂@MoO₂@Fe@CN heterojunction composite was designed via encapsulating MoS₂@MoO₂into the Fe doped nitrogen-doped porous carbon(CN)derived from biomass Magnolia fruits prepared by hydrothermal method,and was applied in potassium ion batteries.CN can provide abundant active sites,improve the electrical conductivity of the electrode,buffer the volume expansion/contraction during repeated cycling,and improve the stability of the electrode;the combining of MoO₂with MoS₂can promote the charge transfer and ion diffusion ability of the electrode material,homogenize the electrode electric field distribution,substantially improve the reaction kinetics and effectively inhibit the growth of dendrite potassium.Thus,the MoS₂@MoO₂@Fe@CN composite exhibited good electrochemical performance for K⁺storage.After 100 repetitive loops,a high capacity of 312 m Ah g^-1can still be maintained at 0.1 A g^-1,even after 500 cycles at 0.5 A g^-1,a capacity of 271m Ah g^-1can be left.SnS₂posesses a larger theoretical capacity than that of MoS₂,and hence the higher energy density in KIBs,satisfying the progressively increasing requirements for energy demands.The K⁺storage performance of modified SnS₂was also investigated.A monodisperse three-dimensional SnS₂spheres with a core-shell structure was designed,consisted of oriented defective two-dimensional nanosheets with abundant sites and large layer spacing,in which the tightly contacted core-shell structure can improve the K⁺diffusion ability and expedite the charge transfer kinetics.SnS₂@Fe₃C@CN composite with a core-shell structure were prepared by combining nitrogen-doped carbon layers with Fe₃C.The elastic carbon matrix and core-shell structure can effectively buffer the volume change during potassium storage;abundant active sites were achieved,benefited from the high specific surface area because of the mesoporous-macroporous texture.CN and Fe₃C can greatly enhance the electrode conductivity and improve the potassiphilicity,resulting in excellent rate and cycling performance.The charge capacity up to 178 m Ah g^-1at 2.0 A g^-1supports its prominent rate behaviors.After 100 cycles at 0.2 A g^-1,a high charge capacity as high as 325 m Ah g^-1was still delivered and even under repeated 500 cycles at 1.0 A g^-1,a high reversible charge capacity of 183 m Ah g^-1was still displayed.