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 LaSrMnO4 and Sr3Fe2O5F2, 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 La1.2Sr1.8Mn2O7−δF2 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.