Revealing the Indispensable Role of In Situ Electrochemically Reconstructed Mn(II)/Mn(III) in Improving the Performance of Lithium-Carbon Dioxide Batteries.

Li-CO2 batteries are regarded as promising high-energy-density energy conversion and storage devices, but their practicability is severely hindered by the sluggish CO2 reduction/evolution reaction (CORR/COER) kinetics. Due to the various crystal structures and unique electronic configuration, Mn-based cathode catalysts have shown considerable competition to facilitate CORR/COER. However, the specific active sites and regulation principle of Mn-based catalysts remain ambiguous and limited. Herein, this work designs novel Mn dual-active sites (MOC) supported on N-doped carbon nanofibers and conduct a comprehensive investigation into the underlying relationship between different Mn active sites and their electrochemical performance in Li-CO2 batteries. Impressively, this work finds that owing to the in situ generation and stable existence of Mn(III), MOC undergoes obvious electrochemical reconstruction during battery cycling. Moreover, a series of characterizations and theoretical calculations demonstrate that the different electronic configurations and coordination environments of Mn(II) and Mn(III) are conducive to promoting CORR and COER, respectively. Benefiting from such a modulating behavior, the Li-CO2 batteries deliver a high full discharge capacity of 10.31 mAh cm-2 , and ultra-long cycle life (327 cycles/1308 h). This fundamental understanding of MOC reconstruction and the electrocatalytic mechanisms provides a new perspective for designing high-performance multivalent Mn-integrated hybrid catalysts for Li-CO2 batteries.