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., Na₃ V₂ (PO₄ )₃ , Li₃ V₂ (PO₄ )₃ , K₃ V₂ (PO₄ )₃ , Na₄ MnV(PO₄ )₃ , and Na₂ TiV(PO₄ )₃ ) in a tetrahydrofuran/ethanol/H₂ O 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 Na₃ V₂ (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.