Atomic High-Spin Cobalt Unlocks Reversible Multi-Electron Transfer Chemistry for Superb Aqueous Zn-Mn Batteries

Abstract

Abstract To settle inherent irreversible phase transition and motivate re-dissolution of deposited “dead” MnO 2 without acid and redox mediator addition, we introduced atomic-dispersed Co atoms with high-spin state into layered MnO 2 , denoted as Co–MnO 2 , via an in situ topological phase transformation strategy, thereby unlocking reversible multi-electron transfer chemistry for superb Zn–Mn batteries. Specifically, atomic-distributed Co atoms within Co–MnO 2 effectively modulate [MnO 6 ] octahedral symmetry and reduce Co–O bond covalency along with enhanced lattice oxygen activity. Based on this, high-spin Co (t 2g 4 e g 2 ) greatly mitigates the Jahn–Teller distortion as well as promotes electrolytic MnO 2 deposited onto the cathode surface completely converted from adsorbed Mn 2+ for inhibited “Mn dendrites”, achieving reversible MnO 2 /Mn 3+ and electrolytic MnO 2 /Mn 2+ reactions with highly thermodynamical favorability. Benefiting from the “two-step, three-electron” mechanism triggered by high-spin Co, Zn//Co–MnO 2 battery delivers an outstanding capacity of 658 mAh g –1 and ultra-long lifespan over 15,000 cycles. This work reveals the critical role of transition-metal spin state modulation for energy-dense and durable Zn-MnO 2 batteries with reversible multi-electron storage mechanisms.