A fundamental study on clarifying the potential performance of a new rechargeable battery using uranium as an active material

Depleted uranium is a byproduct of the production of nuclear fuel, and various efforts have been made to develop new applications of it. The utilization of depleted uranium as an active material in redox-flow batteries is one of the promising applications. Quite recently we demonstrated a new static battery system using uranium and iron as active materials (UFe battery), but the potential performance is poorly understood. It is because the focus was on whether uranium works as an active material. Besides, there was limited information about the electrode reactions and the electrical conductivity of the electrolytic solutions. To clarify the ideal performance of the UFe battery, we investigated redox behaviors of uranium (IV) chloride and iron (II) chloride in chloride-containing non-aqueous solution by cyclic voltammetry and chronoamperometry techniques. In addition, the electrical conductivity of the solution was estimated by electrochemical impedance spectroscopy. As a result, the standard rate constants of both U(IV)/U(III) and Fe(III)/Fe(II) redox reactions were comparable to those in all-vanadium redox flow batteries (VRFBs), whereas the conductivity of the electrolytic solution was about 10 times lower than that of conventional aqueous batteries. The simulation using these electrochemical parameters suggested that the ideal performance of the UFe battery may be comparable to that of VRFBs when the distance between electrodes is sufficiently reduced. While there are many challenges for the application to the flow battery system, the UFe battery has the potential to be a new energy storage system and to utilize large amounts of depleted uranium.