Selective asymmetric polarization of PAANa “diapers”: Solving the water challenge of prussian blue cathode in organic sodium ion battery

Significant research attention has been directed towards the prussian blue analogues (PBAs) cathode for sodium-ion batteries, yet the major obstacle of inferior cycling stability persists. This issue is fundamentally associated with the liberation of their structural and coordinated water into the electrolyte during charge–discharge. In this work, a sodium polyacrylate “diaper” with selective asymmetric polarization is proposed. It’s designed to adsorb water from PBAs during charge–discharge. It ionizes ions to form an asymmetric layer on PBAs, enhancing interfacial kinetics. Density Functional Theory computations validate that PAANa exhibits a more pronounced binding energy with water, efficiently confining moisture within the interface layer and consequently elevating the ionic conductivity of PAANa. Moreover, upon interaction with water, PAANa promptly polarizes, inducing sodium ions to migrate towards the electrolyte side and form a stable charging electrolyte interface. Simultaneously, carboxylate anions engage in robust ion–dipole interactions with the PBA cathode surface, creating a compact coating layer that facilitates sodium ion solvation and desolvation processes, thereby enhancing structural stability. Consequently, PAANa contributes to enhanced rate performance, improve cycle performance (97.9% capacity at 0.15 A g −1 after 300 cycles) and suppresses side reactions at the anode, thereby prolonging the cycling life of the battery.