Preparation Of Titanium Phosphate / C Composites And The Study Of Their Electro Chemical Properties

In this thesis,through the carbon doping,nitrogen substitution,tin substitution and other modification measures of sodium titanium phosphate,sodium titanium phosphate/carbon composite materials were synthesized,and the synthesis mechanism of titanium titanium phosphate/carbon composite materials was studied.The influence of the electrochemical performance of the material,and by exploring the matching technology of sodium ion full battery,the electrochemical performance of the sodium titanium phosphate full battery has been improved.The specific research contents are as follows:A carbon-coated sodium titanium phosphate/carbon composite was synthesized by the sol-gel method.The effects of carbon content and sintering temperature on the composition,structure and electrochemical performance of the material were explored,and the best synthesis conditions were obtained.The research results show that the sintering temperature will affect the crystalline properties of the material,resulting in differences in the crystal structure of the material;the carbon content of the material will have a certain effect on the electrochemical performance of the material,the amount of carbon content is whether it can form continuous carbon The key to the network and improve the conductivity of the material;by carbon coating the surface of the sodium titanium phosphate/carbon anode material,the electrolyte can enter the interior of the sodium titanium phosphate and promote the ion transport of the material,thereby improving the ion conductivity.At 800?,Ti:citric acid=2:3,p H<4,the electrochemical performance of the sample is the best,the specific capacity of the first discharge at 0.5C is 213 m Ah g^-1,the specific capacity of the first discharge at 20C is 152 m Ah g^-1.Using chitosan as a biological template,using its special structure and properties,a sol-gel method was used to synthesize sodium titanium phosphate/nitrogen-doped mesoporous hard carbon?NTP/N-MHC?composite materials.Influence of material composition,structure and electrochemical performance.The results show that the material has a unique sandwich structure,which greatly improves the rate performance and cyclic stability of the NTP/N-MHC composite.At the same time,the nitrogen doping in the material can enhance the conductivity by adjusting the surface functional groups,which is beneficial to the charge Transfer and electrode-electrolyte interaction to improve its electrochemical performance.As a negative electrode material for sodium ion batteries,NTP/N-MHC composite materials have excellent electrochemical performance,with a wide voltage range of 0.01-3.0V,a reversible capacity of up to 247 m Ah g^-1 at 0.5 C and a reversible capacity of 113.2 m Ah g^-1.After 1000 cycles,the capacity retention rate was 73.6%,and its energy density and power density reached 76.56 Wh kg^-1 and 5104 W kg^-1,respectively.The discharge specific capacity of NTP/N-MHC//PNVP full battery at 0.1C is 91.3m Ah g^-1,the reversible capacity of 10 C is 69 m Ah g^-1,and the capacity retention rate after 1000 cycles is 81.6%.The power density reached 104 Wh kg^-1 and 5256 W kg^-1,respectively.It can be seen that the design of composite materials with unique microstructure and nitrogen doping can greatly improve the electrochemical stability and energy/power density of sodium titanium phosphate,which provides a new way of thinking for the development of high-performance sodium ion full batteries.Using oxalic acid as the carbon source,a tin-doped sodium titanium phosphate/carbon?NTSP/C?composite material was prepared by solvothermal method.The effect of tin doping on the composition,structure and electrochemical properties of the material was studied.The research results show that the alloying reaction of tin element will cause the volume change of the active material,and the NTSP/C material with a porous and conductive thin carbon layer coating is obtained by a small amount of tin doping,and the tin element has high electronic conductivity,Can increase the electronic conductivity of the active material,can significantly improve the electrochemical performance.The specific discharge capacity of the NTSP/C composite material for the first discharge at 0.2C is 111.3 m Ah g^-1;the specific discharge capacity for the first discharge at 10C is 109.1 m A h g^-1,and the reversible capacity after 1000 cycles is 98.9 m Ah g^-1,Its retention rate is 90.6%;the specific discharge capacity is 102.5 m Ah g^-1 for the first time at 20C.When it is restored to 0.2C,it can still retain 96.1%of the original capacity.