Synergetic Effect of Liquid and Solid Catalysts on the Energy Efficiency of Li-O<sub>2</sub> Batteries: Cell Performances and Operando STEM Observations.

Hou, Chen; Han, Jiuhui; Liu, Pan; Huang, Gang; Chen, Mingwei · Nano Lett · 2020

basic_science · Level V

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Abstract

The sluggish cathodic kinetics and lower energy efficiency, associated with solid and insulating discharge products of Li<sub>2</sub>O<sub>2</sub>, are the key factors that prevent the practical implementation of Li-O<sub>2</sub> batteries (LOBs). Here we demonstrate that the combination of the solid catalyst (RuO<sub>2</sub>) and soluble redox mediator tetrathiafulvalene (TTF) exhibits a synergetic effect in improving the cathodic kinetics and energy efficiency of LOBs by reducing both charge and discharge overpotentials. Operando electron microscopy observations and electrochemical measurements reveal that RuO<sub>2</sub> not only exhibits bifunctional catalysis for Li-O<sub>2</sub> reactions but also benefits the catalytic efficiency of TTF. Meanwhile, TTF plays an important role in activating the Li<sub>2</sub>O<sub>2</sub> passivated RuO<sub>2</sub> catalysts and in helping RuO<sub>2</sub> effectively oxidize the discharge products during charging. The synergetic effect of solid and liquid catalysts, beyond traditional bifunctional catalysis, obviously increases the cathodic kinetics and round-trip energy efficiency of LOBs.