In Situ Pyrolysis Preparation And Li/Na-ion Storage Performance Of Carbon-coated Transition Metal Fluoride/phosphide

Transition metal compounds such as oxides,sulfides,selenide,fluorides and phosphides have received increasing attention as promising electrode materials for lithium-ion batteries(LIBs)and sodium-ion batteries(SIBs)due to their higher specific capacities.Among them,the preparation methods of transition metal oxides(TMOs)are simple because of the source of oxygen is wide and safe.However,the raw materials of transition metal sulfides(TMSs),selenides(TMSes),fluorides(TMFs)and phosphides(TMPs)are dangerous,which limited their synthesis methods.At present,scientists have mainly tried to prepare TMFs and TMPs are mostly by ball-milling and fluorine/phosphating.These methods have some disadvantages,such as the obtained samples by ball-milling are normally consisted of irregular particles with dimensions ranging from several hundreds of nanometres to tens of micrometres and a large amount of fluorine/phosphorus resources during the fluorination/phosphorization process,which results in the waste of raw materials and release toxic gases.Therefore,developing an environmental friend strategy to synthesize Transition metal compounds with nanostructures remains a challenge.In this work,we prepared carbon coated NH4Fe3 nanosheet(NH4FeF3/CNS)composites and carbon coated Cu3P nanosheet(Cu3P/CNS)composites by in situ pyrolysis method.We first prepared NH4FeF3/CNS with a size of ca.500 nm via in situ pyrolysis of ferric acetylacetonate and NH4F.The average diameter of NH4FeF3 nanoparticles in the carbon matrixs is ca.30-100 nm,and NH4FeF3 has an open framework structure with a perovskite topology.The 3D open-framework structure constructs kinetically favourable Li/Na ion channels and benefits the alleviation of volume expansion.When used as an anode for LIBs,the NH4FeF3/CNS composite delivered a specific capacity of 800 mA h g-1 at 500 mA g-1 after 300 cycles.When used as an anode for SIBs,the NH4FeF3/CNS also exhibited a high specific capacity of 504 mA h g-1.In addition,we also prepared Cu3P/CNS by in situ pyrolysis method.We Cu(NO3)2 as metal centres and 1,3,5-triaza-7-phosphaadamantane(PTA)as an organophosphine ligand are employed to construct Cu/PTA coordination frameworks(Cu/PTA-MOFs)with a two-dimensional nanosheet structure.Cu/PTA-MOFs can be converted to P/N codoping carbon coated Cu3P composite nanosheets(Cu3P/CNS)after a simple annealing process.The average diameter of Cu3P nanoparticles in the carbon matrixs is ca.50 nm.When used as an anode for SIBs,the Cu3P/CNS composites exhibit a better rate performance and cycling stability.At current densities of 50 mA g-1,the reversible capacities of Cu3P/CNS can reach 332 mA h g-1,and exhibited a much better cyclic stability compared with TMPs prepared using other approaches.The carbon-coated transition metal compounds were prepared by in situ pyrolysis of organic matter and metal compounds,which offer the carbon source and the metal source to form catalyst.In addition,the materials containing F and P heteroatoms are added to provide heteroatoms for the preparation of carbon coated transition metal fluorine/phosphating nanosheets.Therefore,in situ pyrolysis method provides a new idea for preparing other carbon-based transition metal compounds with new-structure and high-performance.