Stable cycling of small molecular organic electrode materials enabled by high concentration electrolytes

Abstract

Small molecular organic electrode materials (SMOEMs) enjoy favorable high capacity and low cost, but suffer from poor cycling stability and low Coulombic efficiency due to the unavoidable dissolution in aprotic electrolytes. Previous studies of the dissolution inhibition strategy mainly focused on the molecular designing or electrode engineering, but neglected the important or crucial influence of the electrolyte. Herein, a facial “high concentration electrolyte” strategy is employed to study two typical dianhydride molecules, namely 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), achieving dramatically improved cycling stability for both. Remarkably, in 3 ​M LiTFSI/DOL ​+ ​DME electrolyte (lithium bis(trifluoromethanesulphonyl)imide/1,3-dioxolane ​+ ​1,2-dimethoxyethane), PTCDA shows a high capacity retention of 87% (relative to the maximum capacity of 147 mAh g−1) after 1000 cycles at a current rate of 100 ​mA ​g−1, along with an exceptional average Coulombic efficiency of 99.99%, setting one of the best cycling performance records for SMOEMs. The comparative study of NTCDA and PTCDA in LiTFSI/DOL ​+ ​DME electrolytes with different concentrations (1, 2, 3, and 4 ​M) indicates that both intrinsic crystalline structure stability of the active material and appropriate electrolyte are key origins of good cycling stability. According to ex-situ characterization results, a “dissolution–redeposition” mechanism of SMOEMs is proposed to update researchers’ obscure understanding of the dissolution behavior. We believe this work provides not only confidence on the performance potential but also insightful mechanism understanding of SMOEMs, which are important for their further development towards practical application.