Conversion/insertion pseudocapacitance-driven vacancy defective perovskite fluorides K0.82Co0.43Mn0.57F2.66@reduced graphene oxide anode for powerful Na-based dual-ion batteries and capacitors

Abstract Na-based dual-ion batteries (Na-DIBs) and capacitors (NICs) have received particular attention in the recent years because of the advantages of simple design, environmentally friendly, feasibility, and low cost, etc. Herein, we report a new vacancy defective perovskite fluorides K0.82Co0.43Mn0.57F2.66@reduced graphene oxide (KCMF(1-1)@rGO) nanocrystal as a promising anode material for Na-DIBs and NICs, showing the pseudocapacitance-dominated conversion-insertion hybrid mechanisms. Thanks for the synergistic effect of Co/Mn active species, the fast kinetics of pseudocapacitive behavior, the improved ion storage ability of K-ion vacancy, and the unique K0.82Co0.43Mn0.57F2.66@rGO nano-heterostructures, the KCMF(1-1)@rGO anode exhibits superior specific capacity, rate and cycling behavior (176-84 mAh g−1 at 0.05-1 A g−1, 67 % retention/500 cycles/0.3 A g−1). Furthermore, the designed Na-DIBs and NICs with the KCMF(1-1)@rGO anode and graphite (KS6)/activated carbon (AC) as cathodes demonstrate remarkable performance, showing the 145.9 Wh kg−1/0.83 kW kg−1/60%/1000 cycles/5 A g−1 and 66.51~29 Wh kg−1/0.53~16.84 kW kg−1/81%/1000 cycles/5 A g−1 for the KCMF(1-1)@rGO//KS6 Na-DIBs and KCMF(1-1)@rGO//AC NICs respectively, indicating a promising application for Na-ion energy storage.