Sodium-Coordinated Polymeric Phthalocyanines as Stable High-Capacity Organic Anodes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have attracted considerable interest as an alternative to lithium-ion batteries owing to their similar electrochemical performance and superior long-term cycle stability. Organic materials are regarded as promising anode materials for constructing SIBs with high capacity and good retention. However, utilization of organic materials is rather limited by their low energy density and poor stability at high current densities. To overcome these limitations, we utilized a novel polymeric disodium phthalocyanines (pNaPc) as SIB anodes to provide stable coordination sites for Na ions as well as to enhance the stability at high current density. By varying the linker type during a one-pot cyclization and polymerization process, two pNaPc anodes with O- (O-pNaPc) and S-linkers (S-pNaPc) were prepared, and their structural and electrochemical properties were investigated. The O-pNaPc binds Na ions with a lower binding energy compared with S-pNaPc, which leads to more facile Na-ion coordination/dissociation when engaged as SIB anode. The use of O-pNaPc significantly improves the redox kinetics and cycle stability and allows the fabrication of a full cell against Na₃V₂(PO₄)₂F₃/C cathode, which demonstrates its practical application with high energy density (288 Wh kg⁻¹) and high power density (149 W kg⁻¹).