Synthesis Of Cu₃P@C And Ni₂P@NC And Study On Their Sodium Storage Properties

Due to the depletion and pollution of fossil fuels,various green energy sources such as wind,solar,water and tidal energy have been used to replace fossil fuels.However,because of its instability and discontinuity,this power cannot be fed directly into the current grid system.Therefore,how to regulate unstable voltage and intermittent power generation is the key problem to solve the above challenges.The integration of large-scale energy storage system in smart grid is a way to improve power supply security.Among the current energy storage technologies,lithium ion batteries（LIBs）are considered as one of the most promising energy storage system components because of their high energy density and long life.However,in the future,the development of lithium ion batteries in large-scale storage may be hindered by the high price of lithium resources.Because the earth’s crust of lithium content is very low（only0.0017%?quality content）.Non-aqueous sodium ion battery is a new type of organic electrolyte"rocking chair"battery with similar chemical properties to lithium ion batteries.The difference is that sodium ion batteries use sodium ions as carriers.Due to the abundant sodium resources in the earth’s crust,sodium ion battery is expected to replace lithium ion battery as the preferred energy storage device of the next generation.However,the development of sodium ion batteries is still at an early stage,and many problems remain to be solved,compared with lithium ion,sodium ion has larger ion radius（Li⁺（0.076nm）Na⁺（0.102nm））,this leads to poor cycle life,low power density and slow ion dynamics.This puts forward different requirements for the anode and cathode materials of sodium ion batteries.Among them,the metal phosphide negative electrode has a safe operating voltage,excellent thermal stability,high specific capacity,abundant phosphorus reserves and low price.This paper takes metal phosphide as the research object,designs the metal phosphide anode material with excellent performance through the simple and clean experiment method,and carries on the detailed analysis and the demonstration to it.The main research contents of this paper are as follows:（1）With the help of"epitaxial growth"method,a novel three-dimensional shape of nitrogen-doped Cu₃P@C nanosheet heterostructure was successfully synthesized by a one-step reaction in the inert gas at high temperature.Nanocrystals are well dispersed and spontaneously assembled into flower-like structures,which is beneficial to inhibit the agglomeration effect of materials during the cycling process of sodium ion batteries.At the same time,Cu₃P@C is a carbon coated Cu₃P nanosheet material.The nitrogen-doped carbon layer growing evenly on the surface of Cu₃P is conducive to increasing the conductivity of the material,inhibiting Cu₃P’s fragmentation in the battery cycle reaction,and thus improving the multiplicative performance and cycling stability of the anode material of sodium ion battery.As an anode material for sodium ion batteries,Cu₃P@C has a reversible capacity of 340.7 m Ah g^-1at the current density of 0.1 A g^-1,and the coulomb efficiency of first cycle is as high as 89%.Under the high current density 5 A g^-1,the cycle can still maintain 118m Ah g^-1for 2000 cycles,and the average capacity attenuation rate of each cycle is 0.013%.（2）The carbon-coated nickel-phosphide nanorods core-shell structures were formed by C-P pyrolysis gas released from high temperature pyrolysis using phosphorous resin and nickel foam as precursors.The two-dimensional structure of nickel phosphide rod has a large specific surface area,which enables a large number of sodium ions to participate in the reaction,which is beneficial to the shuttle of sodium ions in the process of charge and discharge.The nitrogen-doped carbon layer growing evenly on the surface of nickel phosphide is beneficial to restrain the volume expansion and crushing of nickel phosphide in the cycling process and increase the conductivity of the material.At the same time,there is a channel between the carbon layer and nickel phosphide nanorods,which is conducive to the infiltration of electrolyte and improve the electrochemical performance of Ni₂P@NC.At the current density of 0.1 A g^-1,the reversible capacity of Ni₂P@NC reach to 343.2 m Ah g^-1.At a high current density of 2 A g^-1,the specific capacity of 151 m Ah g^-1is still available for 2000cycles of charge-discharge.