Asymmetric Form of Redox Shuttle Based on 1,4-Di-tert-butyl-2,5-dimethoxybenzene

The concept of redox shuttles (RS) has been applied in lithium ion batteries for overcharge protection as well as catholytes for non-aqueous flow batteries. Stable RS compounds typically have a symmetric molecular structure with C2 v symmetry incorporating two identical alkoxy groups. We have successfully broken this symmetry by incorporating two non-identical alkoxy groups (-OMe and –OCH2CF3) on the parent 2,5-di-tert-butylbenzene structure. This asymmetric form of RS compound can survive more than 70 overcharge cycles for more than 1000 hours (100% overcharge, C/5 rate) at relatively low concentration of 0.1 M RS in 1.2M LiPF6 EC/EMC electrolyte for LiFePO4 /Li4Ti5O12 cell.