Understanding the Dual-Phase Synergy Mechanism in Mn₂O₃–Mn₃O₄ Catalyst for Efficient Li–CO₂ Batteries

Rechargeable Li–CO₂ batteries have been receiving intense interest because of their high theoretical energy density and environmentally friendly CO₂ fixation ability. However, due to the sluggish CO₂ reduction/evolution reaction (CRR/CER) kinetics, the current Li–CO₂ batteries still suffer from severe polarization and poor cycling stability. Herein, we designed and in situ synthesized sea urchinlike Mn₂O₃–Mn₃O₄ nanocomposite and explored the synergistic effect between Mn₂O₃ and Mn₃O₄ during charge–discharge process in Li–CO₂ batteries. It is found that Mn₃O₄ can effectively promote the kinetics of CRR process, and Mn₂O₃ can induce the nucleation of Li₂CO₃ and promote its decomposition (CER). Benefiting from the dual-phase synergy, the Mn₂O₃–Mn₃O₄ cathode combines the respective catalytic advantages of the both and delivers a high full discharge capacity of 19 024 mAh g^–1, a low potential gap of 1.24 V, and durable cycling stability (1380 h) at a current density of 100 mA g^–1. Moreover, based on experimental results and density functional theory (DFT) calculations, a charge–discharge process model of the Mn₂O₃–Mn₃O₄ cathode was established to display the electrochemical reaction mechanism. We hope that this design strategy can encourage further studies for efficient cathode catalysts to accelerate the practical application of Li–CO₂ batteries and even the metal–air batteries.