Investigation On Electrochemical Performance Of Sodium Vanadium Phosphate Cathode In Aqueous Rechargeable Batteries

NASICON?Na-super-ionic-conductors?-structured materials is a family of compelling electrode and solid-state electrolyte materials in electrochemical energy storage areas.The Na₃V₂?PO₄?₃ belongs to the NASICON-structured materials and it applied widely in lithium ion batteries and sodium ion batteries.Zinc-ion batteries have become a research hotspot because of their high power density and energy density,excellent rate performance,low cost,high safety,and environmental friendliness.Therefore,we choosed Na₃V₂?PO₄?₃ as cathode material to design a novel Na⁺/Zn²⁺hybrid aqueous electrolyte battery and zinc-ion battery and investigated the degradation mechanism of the battery.A capacity fading mechanism for Na-Zn hybrid aqueous rechargeable batteries was proposed for the first time.The main work is as follows:?1?The Na3V2?PO4?3/C composites were synthesized by sol-gel method and characterized by X-ray diffraction,fourier transform infrared spectroscopy,raman spectroscopy,scanning electron microscopy and thermogravimetric analysis,etc.It was proved that the Na₃V₂?PO₄?₃/C composite is similar to spherical structure,the particle size is nano-scale and has a pure phase structure with the uniform carbon coating.?2?A novel Na⁺/Zn²⁺hybrid aqueous battery based on Na₃V₂?PO₄?₃ cathode and Zn metal anode was constructed.The effects of sulfate,nitrate,and acetic acid-based electrolytes on the electrochemical performance of the battery were explored,and the optimal electrolyte system was optimized.By measuring the electrochemical performance of Na₃V₂?PO₄?₃//Zn batteries and investigating the structure,composition,and morphology changes of Na₃V₂?PO₄?₃ through comprehensive characterization technologies?scanning electron microscope,transmission electron microscope and X-ray diffraction,ect.?,a capacity fading mechanism for Na-Zn hybrid aqueous rechargeable batteries was proposed for the first time.This work will shed light on improving the cycling life of NASICON-structured materials in rechargeable batteries.?3?By adjusting the ratio of Na⁺/Zn²⁺in different electrolytes,it was found that the Na₃V₂?PO₄?₃ cathode material also has the ability to deintercalate Zn²⁺.A zinc-ion battery with NaV₂?PO₄?₃ as cathode,mental Zn as anode was designed.The initial discharge capacity is 81 mAh g^-1,and after 100 cycles the capacity is 68.1 mAh g^-1,the capacity retention is 84%.The ex-situ XRD technique is used to thoroughly investigate the reaction mechanisms and structural changes of materials under different charge and discharge states.