A two-compartment cell for using soluble benzoquinone derivatives as active materials in lithium secondary batteries

In this study, soluble redox couples were used as active materials for an electrode using a newly designed two-compartment cell. In this cell, liquid electrolyte was separated by a solid electrolyte diaphragm, which prevents dissolved active materials from reaching the counter electrode. To balance the apparent current density and the apparent energy density, a porous sheet made of carbon paper as a current collector was set on the side of the positive electrode with an active material impregnated into it, and Li foil was set on the side of the negative electrode. Some soluble benzoquinone derivatives were examined by charge/discharge cycling for use as active materials of the positive electrode in lithium secondary batteries. Some of them showed specific capacities close to the theoretical values, assuming two-electron reduction. Among them, 2,5-dipropoxy-1,4-benzoquinone (DPBQ) could be cycled regardless of whether the amount used exceeded the solubility (with precipitate in the electrolyte) or not (all is dissolved). This implies that the active material reacts at the surface of the current collector in the dissolved state, and the precipitated fraction also participates by dissolution into the electrolyte. The results also suggest that a good cycle performance using our two-compartment cell requires an active material with relatively high solubility.