Designing strategies for high-redox-potential conjugated carbonyl organic cathodes in lithium- and sodium-ion batteries

Abstract

Conjugated carbonyl compounds are promising cathode materials in lithium- and sodium-ion batteries due to their high structural diversity, specific capacity and fast reaction kinetics. However, these materials are plagued by low discharge potentials and high solubility, which hinder their practical application in battery systems. To address these challenges, molecular design strategies have been proposed, including the introduction of fully unsaturated five-membered rings, the adjustment of carbonyl group position and the substitution of functional groups. The results show that placing carbonyls on the rings with stronger aromaticity of the conjugated skeleton and incorporating fully unsaturated five-membered rings into the conjugated skeleton of carbonyl compounds are favorable approaches for generating molecules with higher redox potentials. Six-designed carbonyl electrodes, CAT, CAT-CN, AST, BST, BST-CN and PST, exhibit outstanding adiabatic redox potential in the range of 3.18–4.61 V vs. Li/Li⁺ and 2.84–4.44 V vs. Na/Na⁺. We have conducted in-depth investigations to uncover the intrinsic factors that enhance their redox potentials, as well as the underlying mechanism of lithium/sodium storage during the discharging process. Furthermore, our predictions indicate that CAT-CN and CAT possess higher theoretical specific capacity and energy density compared to conventional inorganic and organic materials. The solubility analysis suggests that anchoring these carbonyl compounds onto conductive carbon materials, such as graphene, can effectively mitigate their solubility in electrolytes. This work provides valuable insights into designing high-performance organic cathodes for lithium- and sodium-ion batteries.