Ferrocene-Based Mixed-Valence Metal-Organic Framework as an Efficient and Stable Cathode for Lithium-Ion-Based Dual-Ion Battery

Organic anion-hosting cathodes are remarkably attractive platform candidates for lithium-ion-based dual-ion batteries (LDIBs) due to their various advantages such as variety, designable, and adjustable. Here, a new organic anion-hosting mixed-valence metal-organic framework cathode (Co₂^IICo^III(DFc)₂(OH)₃·H₂O, abbreviated as Co(DFc)x) is first employed in LDIBs. With the redox reactions happening in the couples of Fe²⁺/Fe³⁺ and Co²⁺/Co³⁺, PF₆^- anions can be incorporated into the cathode and reversibly released into the LiPF₆-based electrolyte. Meanwhile, benefiting from its unique structure and insolubility, Co(DFc)x shows a high energy density of 632 Wh kg^-1 (vs lithium anode), a high operating potential of 3.63 V (vs Li⁺/Li), a high reversible (discharge) capacity of 170 mAh g^-1 at 50 mA g^-1 (the third cycle), an excellent rate performance (up to 2000 mA g^-1, 5 min for one cycle), and extraordinary cycling stability (an average capacity of 74.9 mAh g^-1 for 8000 cycles at 2000 mA g^-1).