Approaches to Electrolyte Solvent Selection for Poly-Anthraquinone Sulfide Organic Electrode Material

Organic materials such as polyanthraquinone sulfide (PAQS) are receiving increased attention as electrodes for energy storage systems owing to their good environmental compatibility, high rate capability, and large charge-storage capacity. However, one of their limitations is the solubility in organic solvents typically composing the electrolytes. Here, the solubility of PAQS was tested in 17 different solvents using UV/Vis spectroscopy. The results show that PAQS exhibits a very wide range of solubility according to the nature of the solvent and the obtained trend agrees well with the predictions from Hansen solubility analysis. Furthermore, the transport properties (conductivity, σ, and viscosity, η) of selected electrolytes composed of non-solubilising solvents with 1 m LiTFSI are compared and discussed in the temperature range from -40 °C to 80 °C. In the second part of this study, the electrochemical characterization of PAQS as electrode material in selected pure or mixture of solvents with 1 m LiTFSI as salt was made in half-cells by a galvanostatic method. In a methylglutaronitrile (2MeGLN)-based electrolyte that exhibits low solubility of PAQS, it appears that the capacity fade is intricately linked to the large irreversibility of the second step of the redox process. Although the standard cyclic carbonate solvents mixture (ethylene carbonate and propylene carbonate) led to rapid capacity fade in the initial 10-15 cycles owing to their high solubilising ability. Finally, it is shown that a pure linear alkylcarbonate (dimethyl carbonate) or binary mixture of ether-based (dioxolane/dimethoxy ethane) electrolyte is much more compatible for enhanced capacity retention in PAQS with more than 120 mAh g^-1 for 1000 cycles at 4 C.