Regulation Of Phosphorus Containing Composite Anode Materials Through Polymer Assistance For Sodium-Ion Batteries

In the era of“carbon neutral”,it is the general trend to ban the sale of fuel vehicles,and the development of large-scale energy storage is also changing with each passing day.Therefore,it is urgent to research and develop efficient energy storage equipments with industrial economic benefits.Lithium-ion batteries（LIBs）are widely used in 3C products,electric vehicles,military unmanned aerial vehicles and other fields due to their advantages of high energy density,lightness,and no pollution.However,due to the increasing shortage of lithium resources,people have to search for new substitutes.Sodium and lithium share many similarities,which make sodium-ion batteries（SIBs）a promising candidate.However,due to the larger radius of sodium ions,the material experienced a larger volume change during the electrode insertion/extraction process,leading to structural collapse and a shorter cycling life.The sluggish diffusion of sodium ions between cathode and anode leads to poor rate performance.Therefore,in order to realize the large-scale application of sodium ion batteries,it is one of the most important difficulties to find the anode material with long cycle life and good rate performance.The main research contents of this thesis are as follows:Firstly,a simple method to synthesize niobium pyrophosphate(Nb P_1.8O₇)through polymer assistance is presented for the first time,which avoids the use of hydrofluoric acid and other reagents which are corrosive.The crystallinity of niobium pyrophosphate can be controlled by changing the heating rate during the calcination process.The material with low crystallinity can be obtained at a higher heating rate.The effect of the crystallinity of the material on the sodium storage properties of the material were studied.The test results show that the lower crystallinity is beneficial to the rapid diffusion of sodium ions,showing excellent long-term cycle stability and rate performance.Under the current density of 1000m A g^-1,the reversible discharge specific capacity can reach 164.6 m Ah g^-1 after 5000 cycles.Secondly,a novel polyanion compound niobium phosphate oxide Nb（PO₄）O was synthesized through a supramolecular polymerization assisted by phytate-melamine.When the material is used as SIBs anode,the reversible discharge specific capacity can reach 133.7m Ah g^-1 after 3000 cycles at the current density of 1000 m A g^-1,and 117.9 m Ah g^-1 at the current density of 4000 m A g^-1.Kinetic analysis shows that diffusion controlled manner is the main energy storage mechanism of the material.Owning to the large frame structure,it holds a rapid sodium diffusion coefficient.Lastly,nitrogen and phosphorus hybrid carbon materials were prepared by co-carbonization of chitosan and polymer containing heteroatoms of nitrogen and phosphorus.By adjusting and fixing the content of nitrogen hybridization and other variables,the specific effects of phosphorus hybridization in the nitrogen-phosphorus hybrid carbon materials were studied,such as enlarging the carbon layer spacing,increasing the contribution of pseudocapacitance and increasing the diffusion coefficient of sodium ions.The nitrogen and phosphorus hybrid carbon material shows excellent long-term cycling stability and rate performance of sodium storage.