Non-Substituted Aromatic Pyridine N-Oxide Additives with an Intrinsic N→O Acceptor for Ultra-Long-Life Zn||MnO2 Batteries

Various organic and inorganic reagents containing N/O functional groups have been developed as additives to aqueous electrolytes (e.g., ZnSO₄, ZS) of zinc-ion batteries (ZIBs). However, finding an additive that can significantly enhance the durability of Zn anodes by inhibiting Zn dendrites and side reactions remains a considerable challenge. Herein, pyridine N-oxide (PNO), a non-substituted aromatic compound with a nitrogen positive charge-induced N→O bond, is explored as ZS additives for highly durable Zn plating/stripping electrolytes (i.e., PNO/ZS). The optimized PNO_0.03/ZS mixture demonstrates exceptional stability for Zn anodes, achieving a cycle life exceeding 4200 h and a Coulombic efficiency of 99.9 % at 1 mA cm⁻² and 1 mAh cm⁻². It maintains over 1000 h of life and a cumulative capacity of 2.5 Ah cm⁻², even when subjected to plating/stripping conditions intensified by a factor of 5. Importantly, it enables Zn||α-MnO₂ cells to sustain high-current charge/discharge cycles for over 5000 cycles, retaining 80 % (125 mAh g⁻¹) of the initial capacity, which is the best performance reported for similar additive systems. This exceptional stability is ascribed to the highly reversible Zn anode plating/stripping, facilitated by the suitable coordination interactions between the N→O acceptor of PNO and the Zn²⁺/H₂O donor, effectively inhibiting side reactions.