Tetraphenylbiphenyldiamine: insight into anion storage mechanism as a cathode in dual ion batteries

Abstract Dual ion batteries (DIBs) that involve the intercalation/de-intercalation behavior of cations and anions present considerable application prospect in large-scale energy storage applications. However, the large size of anions has restricted the reversible intercalation in the cathode of DIBs efficiently. Here we propose N,N,N’,N’- tetraphenyl-1,1’-biphenyl-4,4’-diamine (TPB) with large π-electron conjugate system and amino redox groups as the cathode material of DIBs for the first time. TPB displays the reversible capacity of 77.4 and 52 mAh g-1 at the current densities of 50 and 1000 mA g-1 respectively, and the capacity retention of 61% after 450 cycles at 50 mA g-1. The PF6- storage mechanism of TPB has been studied by molecular structure evolution, quantitative kinetics and theoretical calculations, which indicate TPB presents the redox activity to form/break the C=N+ bond for storing PF6- around the N atoms and the C atoms of biphenyl groups reversibly. This work provides insight into designing and understanding the high anion storage cathodes of DIBs.