Combined mediator and electrochemical charging and discharging of redox targeting lithium-sulfur flow batteries

Li-S batteries have drawn increasing interest as the battery technology likely to succeed the Li-ion batteries. Current development is however hindered by some tenacious issues of the sulfur cathode; resulting in the use of excess conducting additive or operations in a smaller voltage window (where the active sulfur species are soluble). The battery energy density is significantly reduced by these compromises. We have previously demonstrated a viable flow battery alternative based on the principle of redox-targeting by using two redox mediators in tandem. This paper reports an improved design using only one redox mediator (ethyl viologen diperchlorate); and the combined chemical and electrochemical charging and discharging of the sulfur cathode to enable the flow battery to operate closer to the full potential of the Li-S chemistry without additive or a soluble cathode. This new solution strategy is generic and may be applied to other high energy density flow batteries.