Preparation And Electrochemical Performance Of Nanostructured Transition-metal Phosphide/Carbon Composites

The rechargeable lithium-ion battery is a linchpin to drive the development of such fields like portable electronics,electrical vehicles,and large-scale energy storage network because it has advantages like high energy density and long cycling life,etc.Developing electrode materials used for advanced energy storage devices such as lithium-ion batteries is of great importance to sustainable social development.The transition-metal phosphide has been an ideal choice to be used as advanced energy storage devices owing to its low-cost and high theoretical specific capacity,however,the rapidly decrease of specific capacity and cycle life from the structure change,which usually leads to the irreversible collapse and mechanical damage during charge and discharge processes.In addition,the nanomaterial has been studied extensively in energy storage field due to its merits like high transport rates of Li⁺and electrons,short charge diffusion paths and high surface areas,etc.Therefore,in this paper,we design nanostructured transition metal phosphides and compound them with carbon to enhance the electrochemical performance.The rich-metal-phase Ni₂P@C nano-hollow-tubular self-supporting fiber membrane was obtained by using the coaxial electrospinning technology combined with pyrolysis carbonization and low-temperature gas-solid phosphating reaction.The results of TEM characterization show that Ni₂P particles with the diameter of?20 nm are uniformly embedded in N-doped carbon nanotubes with the wall thickness of?100 nm.The self-supporting film has certain mechanical stability and flexibility.By changing the content of nickel acetate in the spinning solution,the composite materials with different content of Ni₂P were obtained.The Ni₂P@CNHF-1.2 material prepared by adding 1.2 g of nickel acetate to the 10 m L spinning solution showed the best high-rate discharge performance and cycle stability.After the discharge test with different rate,the current density returns to 100 m A g^-1,the capacity of Ni₂P@CNHF-1.2 remains 446.1 m Ah g^-1.Co-MOF-74,a metal organic framework compound,was carbonized as the precursor,and Co P/C materials were obtained by phosphorization in low-temperature molten salt and gas-solid phase phosphating,respectively.The characterization of the materials by SEM indicates that the MS-Co P/C materials from phosphorization in low-temperature molten salt have nano-flower structure,and the construction of the three-dimensional nanostructure can effectively increase the reversibility of charge and discharge.MS-Co P/C nano-flower material has better rate discharge performance in the performance test of lithium-ion battery,delivering a superiorly stable capacity of 269.2 m Ah g^-1 after 400 cycles at high current of 500 m A g^-1,the capacity retention is 86.6%.The FeP₂/rGO material was obtained by using sodium borohydride to reduce and load nanoscale zero-valent iron particles on the graphene sheet,and directly phosphorizing the Fe/rGO using red phosphorus.The discharge capacity of the FeP₂/rGO-1:1 material(iron/graphene load ratios=1:1)is 562.9 m Ah g^-1 under the current density of 100 m A g^-1.