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

To settle inherent irreversible phase transition and motivate re-dissolution of deposited "dead" MnO2 without acid and redox mediator addition, we introduced atomic-dispersed Co atoms with high-spin state into layered MnO2, denoted as Co-MnO2, 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-MnO2 effectively modulate [MnO6] octahedral symmetry and reduce Co-O bond covalency along with enhanced lattice oxygen activity. Based on this, high-spin Co (t2g4eg2) greatly mitigates the Jahn-Teller distortion as well as promotes electrolytic MnO2 deposited onto the cathode surface completely converted from adsorbed Mn2+ for inhibited "Mn dendrites", achieving reversible MnO2/Mn3+ and electrolytic MnO2/Mn2+ reactions with highly thermodynamical favorability. Benefiting from the "two-step, three-electron" mechanism triggered by high-spin Co, Zn//Co-MnO2 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-MnO2 batteries with reversible multi-electron storage mechanisms.