Conjugacy of organic cathode materials for high-potential lithium-ion batteries: Carbonitriles versus quinones

Identification of redox-active moieties other than well-known carbonyl is essential to design the best candidates for organic cathodes in lithium-ion batteries among a broad-array of organic materials. In this study, an advanced computational modeling approach is employed to comprehensively investigate the redox properties for two representative organic classes, namely carbonitriles and quinones. It is highlighted that organic molecules with conjugating (non-conjugating) backbones would show higher redox potential for longer (shorter) backbone, owing to the strengthened inductive effect. Further examination verifies the importance of the relative electron-withdrawing strength of functionality over hydrogen on the redox potential and battery performance, suggesting a molecular design direction toward a carbonitrile with a longer conjugating backbone functionalized by an acyl chloride for highly-durable, high-performance cathodes. All these findings are comprehensively understood by the established universal correlations on redox property-electron affinity-solvation energy, highlighting two-stage transition behaviors of carbonitriles during the discharging process.