Constructing Extended π-Conjugated Molecules with o-Quinone Groups as High-Energy Organic Cathode Materials

Although organic cathode materials with sustainability and structural designability have great potential for rechargeable lithium batteries, the dissolution issue presents a huge challenge to meet the demands of cycling stability and energy density simultaneously. Herein, we have designed and successfully synthesized two novel small-molecule organic cathode materials (SMOCMs) by the same innovative route, namely 7,14-diazabenzo[a]tetracene-5,6,8,13-tetraone (DABTTO) and 7,9,16,18-tetraazadibenzo[a,l]pentacene-5,6,8,14,15,17-hexaone (TADBPHO). The integrated p-quinone, o-quinone, and pyrazine groups provide these SMOCMs with attractive theoretical capacities of 473 and 568 mAh g–1 based on 6- and 10-electron reactions, respectively, which were almost fully utilized within 0.8–3.8 V vs Li+/Li. The extended aromatic nucleus of TADBPHO makes it much less soluble than DABTTO and thus able to achieve the highest level of cycling stability (66% @ 500th cycle) for SMOCMs in addition to the exceptional energy density (364 mAh g–1 × 2.56 V = 932 Wh kg–1) within 1.5–3.8 V. In addition to the excellent electrochemical performance, the redox reaction and capacity fading mechanisms have been also investigated in detail. The novel approach to construct extended π-conjugated molecules with o-quinone groups is enlightening for the development of high-energy and stable OCMs for future efficient and sustainable energy storage devices.