Fabrication And Electrochemical Performance Of ZnS-MWCNTs Composites As Anode For Lithium/Sodium Ion Batteries

As an important component of the battery,electrode material determines the electrochemical performance of LIBs/SIBs to a large extent,such as specific capacity,cycle stability and rate performance.Reasonable structure design can greatly improve the comprehensive electrochemical performance of electrode materials.ZnS electrode material has the advantages of high theoretical capacity,low cost and no pollution,which is considered to be a very competitive anode material for LIBs/SIBs.However,it can not be ignored that ZnS also has some disadvantages:(1)serious volume expansion and structural changes in the process of repeated charging/discharging lead to poor cycle stability;(2)low electron conductivity and ion mobility lead to poor rate performance.In this paper,the microstructure and composition of ZnS electrode materials are designed:(1)bimetal nitrogen-doped carbon polyhedron structure;(2)3D conductive network structure.These strategies effectively improve the electrochemical performance of ZnS as anode materials for LIBs/SIBs.Details are as following:In the first part,the bimetal nitrogen-doped carbon polyhedron ZnS-Co₉S₈/MWCNTs(ZCS/MWCNTs)composite was prepared by ZIF template method combined with carbonization and vulcanization.Based on ZnS,the second active component(Co₉S₈)was introduced into the composite,which combined with the nitrogen doped carbon polyhedron structure with high specific surface area and porous structure derived from ZIF,and a small amount of MWCNTs was synthesized.Compared with single metal sulfide(pure ZnS),bimetallic sulfide(ZCS/MWCNTs)can enhance the charge transfer between the heterogeneous metal ions and provide more redox reactions,significantly improving the cycle performance and rate performance of electrode materials.As the anode material of LIB,ZCS/MWCNTs composite delivers 751 m A h g^-1specific capacities at 100 m A g^-1after 50 cycles and remains a reversible specific capacity of 453 m A h g^-1at 1 Ag^-1after 300 cycles.In the second part,the ZnS/MWCNTs composite was synthesized via a simple one-pot hydrothermal method as anodes for sodium-ion batteries,and the effects of different thiourea concentration and MWCNTs addition on the microstructure and morphology of ZnS/MWCNTs composite were investigated.The electrochemical reaction mechanism was analyzed by ex-situ XRD.The optimized ZnS/MWCNTs composite(ZnS/MWCNTs-B)has the best three-dimensional(3D)conductive network structure.The MWCNTs backbone can form an interconnected network and nano-sized ZnS spheres are uniformly and closely anchored on the 3D network of MWCNTs.Benefiting from the rational structural design,ZnS/MWCNTs-B delivers a high specific capacity and excellent rate performance for sodium storage at room temperature with a reversible capacities of 320 m A h g^-1even at high current densities of 4 A g^-1after 300 cycles.The reversible capacity of ZnS/MWCNT-B at high rate surpasses most of the ZnS-based anode materials,verifying its great potential application in high-performance SIBs anodes.Moreover,the optimal ZnS/MWCNTs shows superior electrochemical performance even at low temperatures(-10°C),delivering high reversible capacities of 230 m A h g^-1at 1 A g^-1after 400 cycles.