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

Abstract

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[<i>a</i>]tetracene-5,6,8,13-tetraone (DABTTO) and 7,9,16,18-tetraazadibenzo[<i>a</i>,<i>l</i>]pentacene-5,6,8,14,15,17-hexaone (TADBPHO). The integrated <i>p</i>-quinone, <i>o</i>-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 <i>o</i>-quinone groups is enlightening for the development of high-energy and stable OCMs for future efficient and sustainable energy storage devices.