Construction And Lithium Storage Properties Of MOFs-derived Metal Selenide/Carbon-based Anodes

Currently,Lithium-ion batteries（LIBs）are emerging in endless applications in consumer electronics,grid energy industry,and transportation.However,the theoretical capacity(372 m Ah g^-1)of commercial graphite is stretched for the goal of high specific energy LIBs,and the rate performance is not satisfactory,which is difficult to meet the increasing energy demand.The search for new anode materials with high specific energy is urgent.Metal selenides（MSs）with high theoretical capacity as well as low cost are promising anode materials for LIBs.Relatively low electrical conductivity and severe volume expansion are urgent problems for MSs.Combining MSs with carbon materials can solve both problems simultaneously.In this paper,based on MOFs with regular structure and large specific surface area as precursors,the composite materials of MSs and carbon materials were constructed by the one-step annealing method,aiming at realizing high capacity and high-loading LIBs anode.The main research work includes:（1）MSs with high theoretical capacity can solve the drawbacks of limited capacity of commercial graphite.We successfully constructed the In₂Se₃/PNC composites with In₂Se₃nanocrystals encapsulated in MOFs derived porous nitrogen-doped carbon matrix by solvothermal and selenization annealing method.The In₂Se₃/PNC with hierarchically porous structure and rich N-doping affords highly efficient channels for fast transportion of Li⁺and electrons,as well as provides sufficient void space to withstand the mechanical stress during the repeated electrochemical cycles.The optimized In₂Se₃/PNC-800（annealed at 800°C）electrode exhibited high revestible capacity up to1 038 m Ah g^-1 at 200 m A g^-1,excellent cycling stability over 2 000 cycles under1 A g^-1.In situ XRD explored the lithium storage mechanism of the irreversible transformation reaction between In₂Se₃/PNC-800 electrode and Li⁺,followed by the reversible alloying reaction.DFT density functional theory calculations reveal the electrochemical mechanism that the In₂Se₃/PNC-800 electrode has the largest binding energy and the easiest reaction with Li⁺.This study may present broad opportunities for high-performance LIBs anode.（2）Using high-precision and easy-to-operate ink direct writing to print a high-loading,self-supporting cellular electrode structure that cannot be achieved by traditional blade coating methods,maximizing Li⁺transmission efficiency and the utilization of surface-active materials.The ion transmission paths are more abundant,and the use of current collectors is avoided,which effectively improves the energy density of the device.The Zn Se/NC composite with Zn Se nanoparticles encapsulated in MOFs derived porous nitrogen-doped carbon material was successfully constructed by co-precipitation and selenization annealing method.N-doped carbon acts as a buffer layer for Zn Se nanoparticles while improving conductivity,accelerating electron migration and Li⁺transport.As the anode for LIBs,the discharge specific capacity of Zn Se/NC charged and discharged at 100 m A g^-1 was 1 170 m Ah g^-1.The cellular electrode by direct ink writing was stably charged and discharged for 200 cycles at 100 m A g^-1.This research provides some reference for the application of 3D ink direct writing in high-loading LIBs electrodes.