Band-Gap Engineering of FeF3·0.33H2O Nanosphere via Ni Doping as a High-Performance Lithium-Ion Battery Cathode

Iron-based fluorides, a kind of intercalation–conversion cathode material, are considered as one of the most promising candidate cathode materials for lithium-ion batteries due to their high capacity and cheap cost. Nevertheless, poor electrical conductivity and sluggish reaction kinetics upon cycling impede their practical application. Herein, Ni-doped FeF3·0.33H2O has been put forward and fabricated by a simple solvothermal method to overcome the above deficiency. The impact of Ni doping on the physical and electrochemical performances has been studied by first-principles calculations combined with comprehensive physicochemical characterizations. The results reveal that appropriate substitution of Fe sites by Ni can result in F vacancies without changing the intrinsic crystal structure, but it not only reduces the band gap and improves its intrinsic conductivity but also broadens the ion channel, thus facilitating the rapid transport of ions and electrons to acquire excellent electrochemical properties. Compared with the bare FeF3·0.33H2O, the appropriate amount (8%) of Ni2+ doping exhibits higher reversible capacity, longer cyclic stability, and better rate capability. It presents a 412 mAh g–1 initial discharge capacity and remains 264 mAh g–1 after 100 cycles at 0.25 C (1 C = 200 mA g–1) within a range of 1.5–4.5 V. Additionally, at 2.0 C, it still delivers a high discharge capacity of 248 mAh g–1. The excellent electrochemical performance is ascribed to the improvement of electronic conductivity and reaction kinetics caused by the moderate Ni doping.