On the Stability and Reactivity of Phenothiazine-Based Redox Shuttles for Overcharge Protection

The performance of aromatic compounds as redox shuttles for overcharge protection in lithium-ion batteries is variable and difficult to predict. Redox shuttles can decompose in battery electrolyte in their neutral and oxidized forms, both of which are present during overcharge protection. The reasons for differing stability in compounds with only slight structural differences is often unclear, and the exploration of decomposition of redox shuttles has been severely limited, restricting our ability to design improved versions of redox shuttles. To better understand the stability and reactivity of redox shuttles (also relevant to the improvement of positive electrode materials in non-aqueous redox flow batteries) our research has focused on measuring the stability of neutral and oxidized forms of redox shuttle candidates as well as using a variety of spectroscopic methods to analyze the byproducts of decomposition, both from radical cations generated in model solvents and electrolytes from postmortem analysis of failed batteries. Figure 1