Research For Preparation And Electrochemical Performance Of Transition Metal Phosphides

Lithium-ion batterirs(LIBS)have attracted wide attention in the energy-intensive fieds such as portable electronic devices and electric vehicles thanks to their high energy density,memory-free effect and long cycle life.So far,the commercial anode is still using graphite.Although they have high electrochemical performance and rich in raw materials,which can't meet the increasing energy demand due to their poor rate capability and low theoretical capacity.Accordingly,the development of new lithium ion battery anode material with excellent performance and high safety is one of the current hot research topics in the field of new energy.Transition metal phosphides(TMPs)anode materials are widely favored by researchers with larger specific capacity and smaller polarization and abundant resources.However,the main drawbacks of TMPs such as low electronic conductivity and large volume expansion restrict its further development.In this thesis,research work is mianly tend to regulate the TMPs microstructure and electrochemical properties by means of metal element doping and graphene oxide.The main research is as follows:1.The GO supports CoP nanoparticles coated with nitrogen doped carbon(CoP@NC/GO)was obtained through low-temperature phosphating of MOF-Co/GO,which synthesized via coordination reaction of Co-based metal organic frameworks(MOF-Co)and graphene oxide(GO).The prepared materials show excellent multiplier performance and cyclic stabillty with the double carbon composite microstructure.A remarkable reversible capacity of 506 mAh g-1 is still sustained after 500 cycles at a current density of 600 mA g-1,higher than the theoretical capacity of graphite(372 mAh g-1).2.The sphericity-like Mo-CoP@NC nanosheets were prepared via low-temperature phosphating of Mo-doped MOF-Co composite as precursor,which synthesized by hydrothermal method.The systematic study on the electrochemical properties of Mo-doped CoP was conducted,and it was proved that can regulate the electronic structure of cobalt phosphide during the phase change process.The issues of poor conductivity and volume expansion during the reaction process were improved by using combination of designing different nanostructures and doped metal elements.Excellent electrochemical properties of lithium and sodium storage were demonstrated.The high specific capacity of 451 mAh g-1 can be obtained at 5 A g-1,which is 121%higher than that of graphite anode.3.The rGO-coated hexahedral structure Cu2O/rGO was synthesized by solvothermal method as precursor,Cu3P@C/rGO with two-dimensional layered was obtained through phosphating way.This particular structure provides more active sites for ion embedding,and the reduced graphene oxide serves as high speed conducting network and buffer the volume change of the electrode material.Therefore,the Cu3P@C/rGO exhibits superior elecctrochemical performance as an anode material for lithium-ion batteries.When cycled at 1 A g-1,the electrode exhibits a discharge capacity of around 410 mAh g-1 after 800 cycles.Compared with graphite anode,the capacity is increased by 110%.