Synthesis And Modification Research Of Sodium Vanadium Phosphate Cathode Materials

In this paper,Na₃V₂?PO₄?₃?NVP?served as the basic material.This work selected cheap carbon sources with special structural properties and chemical synthesis method to synthetise composite cathode materials.And improved materials'electrochemical performance through carbon coating,grain refinement,special structure construction,nitrogen doping.The synthesis mechanism,composition,structure,pseudocapacitance transmission mechanism and electrochemical performance of the composite materials were studied through test characterization.Using Purong as the carbon source,a high-capacity sodium vanadium phosphate/carbon?NVP/C?composite material was prepared by hydrothermally assisted carbothermal reduction method.The research results show that NVP/C in the synthetic material is a pure crystalline phase and there is no impurity peak and heterophase.The Purong is calcined to form a unique porous rod-like structure to provide a strong frame for the NVP/C composite material,and the composite material exhibits multi-level morphological structures through hydrothermal processes,including solid balls,hollow balls and stacked grains.Effectively improve the electrochemical performance of sodium vanadium phosphate.The sample added with1.5 g of velvet was calcined at 800?for 8 h,and it exhibited the best electrochemical performance.The specific discharge capacity at the first cycle reached 112.0 m Ah g^-1at 0.1 C and 52.1 m Ah g^-1 at 10 C.After 1000 cycles at 10 C,the capacity retention rate is as high as 70.6%,and its coulomb efficiency is maintained at about 100%.Using a mixed solution of ethylene glycol,ethylenediamine and water as a solvent,a nitrogen-doped hard carbon-soft carbon double coated sodium vanadium phosphate mixed pore microsphere composite material?NVP/DC?was obtained by solvothermally assisted carbothermal reduction method,which has a surface-folded and porous microsphere structure with a specific surface area of up to 40.5 m²g^-1 and an average particle size of 4.71?m;the doped N element in carbon is mainly pyridine nitrogen and pyrrole nitrogen and forms Holes and lone electrons,these factors are conducive to the transmission of sodium ions and electrons.The sample prepared according to the ratio of 1:1:10 of the mixed solvent is calcined at 800?for 8 hours.The composite material has excellent electrochemical performance.The specific discharge capacity of the first cycle at 0.1 C is 106.90 m Ah g^-1.And the first discharge specific capacity is 91.52 m Ah g^-1 at 20 C,and the capacity remains 46.4%after 600cycles,and its coulomb efficiency has been maintained at about 100%.The composite material can reach a power density of up to 12600 W kg^-1 while maintaining the energy density of 73.5 Wh kg^-1 demonstrates excellent energy density and power density performance.Ion doping of phosphate sites by Cl ions,Na₃V₂?PO₄?_3-1/3xCl_x/C composites were prepared by solid-phase assisted carbothermal reduction method,and its structure was formed by stacking plate-like particles of about 50 nm.Cl ion doping can significantly improve the electrochemical performance of the composite material.With the increase of the content of doped chlorine element and the decrease of the phosphate content,the specific discharge capacity of the composite material at 0.1 C first increased first and then decreased.The sample Na₃V₂?PO₄?_2.7Cl_0.9/C prepared with a molar ratio offirst cycle,which is much higher than the theoretical specific capacity of sodium vanadium phosphate(117 m Ah g^-1).And the initial discharge specific capacity at 10C can reach 84.8 m Ah g^-1,the specific discharge capacity after 100 cycles is 68.3 m Ah g^-1,and the capacity retention rate is 80.5%.The energy density of sample is up to384.3 Wh kg^-1 at 0.1 C,and the power density is up to 5208.08 W kg^-1 at 10 C with an energy density of 260.4 Wh kg^-1.