Unraveling the Mechanism of Field-Induced Li+ Concentration for Improved Kinetics in Rechargeable Li−Co2 Batteries

The design of highly efficient electrocatalysts is a promising strategy to improve the electrochemical kinetics of Li−CO2 batteries. However, electrocatalysts usually aim to reduce the energetic barrier for the corresponding electrochemical reactions; little attention has been given to modulating the kinetics that directly determine the local concentration of reaction molecules surrounding catalysts. Herein, we present a systematic study on the role of Li+ reunion on the improvement of reaction kinetics in Li−CO2 batteries. Specifically, this local, geometry-driven tip effect can enrich the local electron concentration to facilitate Li+-ion diffusion from the bulk electrolyte to the surface of catalyst, leading to boosted catalytic performance. Further studies demonstrate that Cu(II/I) as a solid redox mediator dominates the reversible bulk redox reactions in Cu cone-cathode, which acts as an electron-hole transfer agent and permits the efficient reduction and oxidation of solid Li2CO3, contributing to an accessible theoretical discharge voltage, low charge potential below 3.2 V, impressive rate capability and a long cycling stability (333 days) for Li−CO2 batteries. The exploitation of the sharp-tip enhancement effect and dynamic creation of catalytic active sites is expected to become routine practice in future mechanistic studies for metal-air batteries.