Poorly Soluble 2,6-Dimethoxy-9,10-anthraquinone Cathode for Lithium-Ion Batteries: The Role of Electrolyte Concentration.

In this work, a 9,10-anthraquinone (AQ) derivative functionalized by two methoxy groups, 2,6-dimethoxy-9,10-anthraquinone (DMAQ), was synthesized and its electrochemical performance was comprehensively studied with different electrolyte concentrations. Density functional theory (DFT) calculations demonstrate that there exists a conjugation effect between oxygen atoms of methoxy groups and the AQ skeleton, which could extend the conjugate plane and increase intermolecular interaction. As a result, DMAQ shows considerably reduced solubility in ether solvent/electrolyte and greatly enhanced cycling performance compared with those of AQ. Interestingly, it is found that the electrolyte concentration plays an important role in determining the electrochemical performance. Cycling under a relatively low (2 M) or high (6 M) concentration electrolyte of lithium bis(trifluoromethanesulfonyl)imide in a mixture solvent of 1,3-dioxolane and 1,2-dimethoxyethane (1/1, v/v) displays unsatisfied cell performance. While a moderate electrolyte concentration of 4 M delivers the highest initial capacity and the best cycling stability. The work would shed light on the rational molecular structure design and electrolyte concentration optimization for achieving the high electrochemical performance of organic electrode materials.