Double-Layered Perovskite Oxyfluoride Cathodes with High Capacity Involving O–O Bond Formation for Fluoride-Ion Batteries
Hidenori Miki, Kentaro Yamamoto, Hiroyuki Nakaki, Takahiro Yoshinari, Koji Nakanishi, Shinji Nakanishi, Hideki Iba, Jun Miyawaki, Yoshihisa Harada, Akihide Kuwabara, Yanchang Wang, Toshiki Watanabe, Toshiyuki Matsunaga, Kazuhiko Maeda, Hiroshi Kageyama, Yoshiharu Uchimoto
Abstract
Developing electrochemical high-energy storage systems is of crucial importance toward a green and sustainable energy supply. A promising candidate is fluoride-ion batteries (FIBs), which can deliver a much higher volumetric energy density than lithium-ion batteries. However, typical metal fluoride cathodes with conversion-type reactions cause a low-rate capability. Recently, layered perovskite oxides and oxyfluorides, such as LaSrMnO 4 and Sr 3 Fe 2 O 5 F 2, have been reported to exhibit relatively high rate performance and cycle stability compared to typical metal fluoride cathodes with conversion-type reactions, but their discharge capacities (∼118 mA h/g) are lower than those of typical cathodes used in lithium-ion batteries. Here, we show that double-layered perovskite oxyfluoride La 1.2 Sr 1.8 Mn 2 O 7−δ F 2 exhibits (de) intercalation of two fluoride ions to rock-salt slabs and further (de) intercalation of excess fluoride ions to the perovskite layer, leading to a reversible capacity of 200 mA h/g. The additional fluoride-ion intercalation leads to the formation of O–O bond in the structure for charge compensation (i.e., anion redox). These results highlight the layered perovskite oxyfluorides as a new class of active materials for the construction of high-performance FIBs.