rGO–Encapsulated Co/Ni dual–doped FeF3·0.33H2O nanoparticles enabling a high-rate and long-life iron (III) fluoride–lithium battery

Conversion-type iron fluoride promises a high energy density and redox potential, which is considered an extremely promising candidate for next-generation high-specific-energy and low-cost Li-ion battery. Unfortunately, its commercialization is plagued by the poor rate capability and fast capacity degradation resulting from its inferior electronic conductivity and large volumetric expansion. Herein, a three-dimensional sandwich architecture of rGO-encapsulated Ni/Co dual‐doped FeF3·0.33H2O nanoparticles (NC-FF) is fabricated by co-precipitation and subsequent calcination. The results show that the flower-like Ni/Co dual‐doped FeF3·0.33H2O nanoparticles are firmly encapsulated within highly conductive rGO sheets through MOC bonding interaction, which constructs a robust electronic/ionic network and a buffer layer against the severe volume variation. The Ni-doping can facilitate to the capacity improvement by expanding the cell volume, and the Co-doping can promote the rate capability and cycling stability enhancement by accelerating Li+ migration. Benefiting from the synergies of Ni/Co dual-doping and encapsulation of rGO, the NC-FF exhibits a high-rate capability of 200.1 mAh g−1 at 5.0 C and good cycle stability of 177.8 mAh g−1 after 400cycles. Moreover, the NC-FF|Graphite symmetric-cell still shows a high reversible capacity of 396.2 mAh g−1 at 1.0C and good cycle stability of 247.5 mAh g−1 after 100cycles.