Sodium Storage Performance Of NASICON Materials In Aqueous Sodium Ion Battery

Energy and environment crisis are the two major obstacles to the development of modern society, and the fundamental solution to these two crises lies in large-scale use of clean energy. During the use of clean energy, energy storage battery is one of the key technologies. However, the commercial battery such experience lithium ion battery and low performance lead-acid battery cannot meet the need of large-scale energy storage, and a low cost, high performance, long cycle life, high security energy storage battery is urgently needed by current society. Sodium ion battery?SIB? is the next generation energy storage battery that can meet the need above and get more and more attention from researchers.Sodium superionic conductor?NASICON? material has been favored by researchers because of its open and stable 3D framework structure, facile sodium ion conductivity. Unfortunately, this kind of material has a serious defect that is low electronic conductivity, which makes the electrochemical performance unsatisfied. This paper focus on phosphate NASICON material, cathode material Na₃V₂?PO₄?₃ and anode material NaTi₂?PO₄?₃ are synthesized through mechanical milling and subsequent calcinations. And different routes of coating are employed to enhance the electronic conductivity. The sodium storage performance and mechanism of capacity decay in aqueous sodium ion battery?ARSB? are also explored.Firstly, the decomposition of acetylene gas led to carbon deposition on the surface of NaTi₂?PO₄?₃ particles and growth of carbon nanofibers between the NaTi₂?PO₄?₃ particles forming a conductive network. The electrical conductivity of NaTi₂?PO₄?₃ is rapidly improved after acetylene decomposition, at a current density of 1C the NaTi₂?PO₄?₃ electrode is still capable of delivering a specific capacity up to 110 mA h g-1after 1000 cycle, and the capacity retention is up to 96%. Na₃V₂?PO₄?₃ was coated by incorporating with conducting polymer polyaniline?PANI? through polymerization proceeding. Na₃V₂?PO₄?₃ with coating deliver capacity of 100.1 mA h g-1 after 500 cycle at a current density of 1C.Secondly, Na₃V₂?PO₄?₃ and NaTi₂?PO₄?₃ sodium storage performance and mechanism of capacity decay in ARSB are also explored. We find that Na₃V₂?PO₄?₃ capacity decay dramatically in ARSB with the reason of material dissolution in aqueous electrolyte. And the main reason of anode material capacity decay is that H₂O and O₂ may react with discharged state of sodium-ion intercalated compounds of all negative electrode materials suitable for ARSB. Through theory calculation, we find how to inhibit the occurrence of this side reaction, that is, regulation the test atmosphere and pH of electrolyte. In the absence of O₂, the side reaction of NaTi₂?PO₄?₃ is avoided at the electrolyte pH above 10. In this end, Ni Fe-PBA/NaTi₂?PO₄?₃ full cell assembled deliver a specific capacity 42 mA h g-1 at the current density of 4C in the electrolyte of pH=13.This paper indicates that the reason of ARSB capacity decay may come from the dissolution and side reaction between electrode material and electrolyte. The low cost and long cycle life ARSB can be constructed through picking structural stable electrode material, regulation the pH and O2 content of aqueous electrolyte.