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.