A Polymer-Assisted Spinodal Decomposition Strategy toward Interconnected Porous Sodium Super Ionic Conductor-Structured Polyanion-Type Materials and Their Application as a High-Power Sodium-Ion Battery Cathode

Abstract

A general polymer-assisted spinodal decomposition strategy is used to prepare hierarchically porous sodium super ionic conductor (NASICON)-structured polyanion-type materials (e.g., Na3V2(PO4)3, Li3V2(PO4)3, K3V2(PO4)3, Na4MnV(PO4)3, and Na2TiV(PO4)3) in a tetrahydrofuran/ethanol/H2O synthesis system. Depending on the boiling point of solvents, the selective evaporation of the solvents induces both macrophase separation via spinodal decomposition and mesophase separation via self-assembly of inorganic precursors and amphiphilic block copolymers, leading to the formation of hierarchically porous structures. The resulting hierarchically porous Na3V2(PO4)3 possessing large specific surface area (≈77 m2 g−1) and pore volume (≈0.272 cm3 g−1) shows a high specific capacity of 117.6 mAh g−1 at 0.1 C achieving the theoretical value and a long cycling life with 77% capacity retention over 1000 cycles at 5 C. This method presented here can open a facile avenue to synthesize other hierarchically porous polyanion-type materials.