Development of high-voltage and high-energy membrane-free nonaqueous lithium-based organic redox flow batteries

Lithium-based nonaqueous redox flow batteries (LRFBs) are alternative systems to conventional aqueous redox flow batteries because of their higher operating voltage and theoretical energy density. However, the use of ion-selective membranes limits the large-scale applicability of LRFBs. Here, we report high-voltage membrane-free LRFBs based on an all-organic biphasic system that uses Li metal anode and 2,4,6-tri-(1-cyclohexyloxy-4-imino-2,2,6,6-tetramethylpiperidine)-1,3,5-triazine (Tri-TEMPO), N-propyl phenothiazine (C3-PTZ), and tris(dialkylamino)cyclopropenium (CP) cathodes. Under static conditions, the Li parallel to Tri-TEMPO, Li parallel to C3-PTZ, and Li parallel to CP batteries with 0.5M redox-active material deliver capacity retentions of 98%, 98%, and 92%, respectively, for 100 cycles over similar to 55 days at the current density of 1 mA/cm(2) and a temperature of 27 degrees C. Moreover, the Li parallel to Tri-TEMPO (0.5 M) flow battery delivers an initial average cell discharge voltage of 3.45 V and an energy density of similar to 33Wh/L. This flow battery also demonstrates 81% of capacity for 100 cycles over similar to 45 days with average Coulombic efficiency of 96% and energy efficiency of 82% at the current density of 1.5mA/cm(2) and at a temperature of 27 degrees C.