Abnormal extra capacity of conjugated dicarboxylate in lithium ion batteries

Abstract

Lithium-ion batteries (LIBs) are believed to be main energy storage systems needed to secure reliable, sustainable, and eco-friendly energy sources. Redox-active organic compounds have been proposed as attractive candidates for electrode materials for the next-generation LIBs due to their flexible molecular design, low production price and recyclability. Despite wide attraction, a molecular-level understanding of the electrochemical lithiations/delithiations of organic electrode materials remains rudimentary. We synthesized a set of π-conjugated dicarboxylates and discovered extra capacities for inverse-Wurster–type nonfused aromatic compounds (dilithium terephthalate and dilithium thiophene-2,5-dicarboxylate) for the first time. Investigations for molecular structure based on solid-state CP/MAS 13C NMR combined with the stable isotope labeling technique and ex situ X-ray diffraction were prepared to describe the origin of the excess reversible capacity. Intriguingly, an analogous behavior was not observed from an open-chain–type dilithium muconate, which means the cyclic moiety is played by key role in the electrochemical reaction.