Biphenylite with an Ultrahigh Capacity of Hexafluorophosphate Anions as a Promising Electrode Material in Dual-Ion Batteries

Dual-ion batteries (such as alkali metal ion-hexafluorophosphate anion systems) have demonstrated an excellent performance; however, identifying suitable cathode materials with superior electrochemical properties remains a major challenge impeding their advancement. In this work, the feasibility of biphenylite as a dual-ion battery cathode material is investigated systematically by first-principles calculations. The calculated result indicates that biphenylite has an ultrahigh cathode specific capacity for PF₆^- anions (107.3 mAh·g^-1, much higher than that of graphite), a lower diffusion barrier energy (0.03-0.09 eV), and high voltage ranges (3.87-5.01 V for the ion paired with Li metal in a Li⁺-PF₆^- dual-ion system, 3.90-5.04 V for Na metal, and 4.49-5.63 V for K metal). Notably, the all-carbon-based electrode system of M-biphenylite|PF₆-biphenylite (M = Li/Na/K) demonstrates a higher energy density than its M-graphite|PF₆-graphite counterparts. Therefore, biphenylite can be regarded as a promising electrode material for alkali metal ion-PF₆ dual-ion batteries, boosting a new stage for the dual-ion batteries.