Phosphate Bonded Perchloric Superstructure Enables Energy-Dense and Ultra-Stable Aqueous Sodium-Ion Batteries.

Abstract

Aqueous sodium-ion batteries (ASIBs) offer a cost-effective and safe platform for grid-scale energy storage, but their practical application is impeded by poor energy density and limited operating time, primarily due to the sluggish Na⁺ intercalation kinetics and severe parasitic side reactions. Here, through multiple characterizations and molecular dynamics simulations, an unexpected phase transition of the NaMnO₂ cathode and incomplete formation of phosphorus oxide interphase on the anode is observed, which causes the failure of ASIBs. To circumvent these issues, an electrolyte with phosphate bonded perchloric (PBP) superstructure is proposed to simultaneously boost cathodic Na⁺ transport and promote the formation of a robust Na₄P₂O₆/Na₄P₂O₇ interphase on the anode surface. This electrolyte design enables batteries to deliver a cathodic specific capacity of 198.21 mAh g^-1 at 50 mA g^-1, with prolonged operating time exceeding 1440 h and an energy density of 82.31 Wh kg^-1 (based on the mass of electrode materials). Even under practical application conditions (-20 °C and a mass loading of 10 mg cm^-2), the batteries remain functional and exhibit exceptional electrochemical performance. The study underscores the potential of PBP superstructure as an alternative electrolyte engineering pathway toward energy-dense and long lifespan ASIBs.