Mass Production Of Cobalt (Nickel) Phosphides/Carbon Nanosheets Composites And Their Lituium Storage Properties Study

Lithium ion batteries dominate the portable electronic battery technology due to their advantages of high energy density,long life,and low cost,and are gradually applied to large energy storage devices.With the increase in energy consumption and the development of large-scale equipment such as electric vehicles and energy storage grids,the growing demand for advanced energy storage technologies has attracted extensive research on lithium-ion batteries.The theoretical capacity of traditional commercial anode graphite materials is only 372m Ah g^-1,which makes it difficult to meet the energy density requirements of existing power electronic equipment.Therefore,it is of great significance to develop new anode materials with high energy density.To date,various anode materials with higher specific capacities have been proposed to replace the most widely used graphite.Among them,transition metal phosphides have received widespread attention because of their high energy density,good thermal stability,and wide sources.In this thesis,the composite material of transition metal phosphide and carbon nanosheet is used as the negative electrode of lithium ion battery.The main research contents are as follows:（1）The composite material of cobalt phosphide/nickel phosphide and carbon nanosheets is prepared by chemical foaming method.This method is simple in process and low in cost.A small amount of precursor can be foamed and expanded into a large amount of foam-like material,which can achieve macro preparation.（2）Cobalt acetate,phytic acid,and L-cysteine are ground evenly with the help of a mortar,and a chemical foaming method is used to successfully prepare a three-dimensional cellular Co P/C composite material,in which cobalt acetate is both a metal source and a foam Agent,phytic acid is the source of phosphorus,L-cysteine plays the role of carbon source and N,S element doping.The resulting product exhibits the shape of carbon foam under the macroscopic view,and the microstructure observed under the electron microscope is that the Co P particles coated with the carbon layer are embedded in the two-dimensional carbon nanosheets,and the two-dimensional carbon nanosheets are connected to form a three-dimensional cellular structure.The experimental results show that the Co P/C composite has the most excellent electrochemical performance at a heat treatment temperature of 900°C,when the nitrogen element doping content is3.71 at%and the sulfur element atom doping content is 0.25 at%Under the current density of m A g^-1,the specific discharge capacity was 2084.6 m Ah g^-1 for the first time and the specific charge capacity was 1022.7 m Ah g^-1.After 180 cycles,the specific discharge capacity was still 595.3 m Ah g^-1.It is worth mentioning that at a high current density of 1000 m A g^-1,after 1000 cycles,its capacity can be maintained at 334.6 m Ah g^-1,and the Co P/C electrode material has a high Stability and good lithium storage capacity.（3）Add ethylenediaminetetraacetic acid,ethylene glycol,ammonia water,ammonium dihydrogen phosphate,nickel chloride hexahydrate to the beaker and stir it magnetically until a homogeneous solution,and then add it to an oil bath and heat it at a constant temperature to prepare Ni₁₂P₅/C foam precursor,then heat-treated foam in tube furnace,stabilized and solidified into Ni₁₂P₅/C foam,successfully synthesized two-dimensional Ni₁₂P₅/C sheet structure,in which Ni₁₂P₅ nanoparticles were evenly embedded in two-dimensional carbon nanosheets.In this system,ethylenediaminetetraacetic acid reacts with ethylene glycol to form an organic system to be used as a carbon source.The ammonium salt is a chemical blowing agent that releases NH₃ during heating and blows the heated viscous liquid into foam.Ammonium dihydrogen phosphate is the source of phosphorus,and nickel chloride hexahydrate is both a metal source and a catalyst for carbon graphitization in the foaming process.When the Ni₁₂P₅/C composite material is used as a negative electrode of a lithium-ion battery,at a current density of 100 m A g^-1,the specific capacity for the first discharge is 1216.3 m Ah g^-1,and the specific capacity for the first charge is 552.0 m Ah g^-1,from the 17th At the beginning of the cycle,the capacity of the battery began to rise.After400 cycles,the capacity of the material basically recovered to the second reversible discharge capacity,reaching 607 m Ah g^-1.And from the second cycle,its Coulomb efficiency is basically maintained at about 100%.The stable cycle performance can be attributed to the porous sheet structure that is beneficial to buffer the volume expansion of the lithium ion insertion and extraction process,and the later capacity recovery is the material activation The reason is that the polarization degree of the electrode is reduced and the charge transfer resistance is reduced.