Manganese-cobalt oxide as an effective bifunctional cathode for rechargeable Zn-air batteries with a compact quad-cell battery design

Metal-air batteries, which are economical and ecological alternatives to Li-ion batteries, have become an important energy storage system. In this study, bimetallic oxides of widely accepted transition metal oxides like MnCo2O4 and NiFe2O4 have been explored to fabricate an efficient rechargeable Zn-air battery. The synthesis of these materials involves a single step direct decomposition of constituent metallic salts using polyvinyl pyrrolidone as a stabilizer cum nanostructure growth modifier by a simple open-air spray pyrolysis. The well characterized materials are used as cathodes in the assembly of a Zn-air battery that delivers a decent specific capacity of 780.1 mA h g(-1). It also offers long term charge-discharge for more than 900 cycles with a week-long break-free operational stability under a small voltage gap (0.65-0.73 V). Finally, a unique and compact quad-cell solid state battery design has been introduced using these cathodes and chemically modified anodes resembling the commercial lithium-ion mobile phone battery. This tiny portable Zn-air battery displays an open circuit potential (OCP) of 4.46 V.