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An all redox flow lithium battery with strikingly high energy density is successfully demonstrated.

Water contamination is generally considered to be detrimental to the performance of aprotic lithium-air batteries, whereas this view is challenged by recent contrasting observations. This has provoked a range of discussions on the role of water and its impact on batteries. In this work, a distinct battery chemistry that prevails in water-contaminated aprotic lithium-oxygen batteries is revealed. Both lithium ions and protons are found to be involved in the oxygen reduction and evolution reactions, and lithium hydroperoxide and lithium hydroxide are identified as predominant discharge products. The crystallographic and spectroscopic characteristics of lithium hydroperoxide monohydrate are scrutinized both experimentally and theoretically. Intriguingly, the reaction of lithium hydroperoxide with triiodide exhibits a faster kinetics, which enables a considerably lower overpotential during the charging process. The battery chemistry unveiled in this mechanistic study could provide important insights into the understanding of nominally aprotic lithium-oxygen batteries and help to tackle the critical issues confronted.

The redox-targeting reactions can disruptively boost the energy density but introduce additional free-energy loss. Here, the Nernstian-potential-driven redoxtargeting reaction considerably eliminates the voltage loss of the system while maintaining a high energy density. Driven by the Nernstian potential difference, the redox molecule, a ferrocene-grafted ionic liquid with standard potential identical to that of LiFePO 4 , reacts with the solid material both anodically and cathodically and exhibits near-unity solid material utilization, 95% voltage efficiency, and energy density.

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A redox flow lithium-oxygen battery (RFLOB) by using soluble redox catalysts with good performance was demonstrated for large-scale energy storage. The new device enables the reversible formation and decomposition of Li2O2 via redox targeting reactions in a gas diffusion tank, spatially separated from the electrode, which obviates the passivation and pore clogging of the cathode.

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