Nanostructured coating strategies of cathode for improved sodium ion battery performance

Owing to scarce and expensive lithium based energy storage system, sodium ion batteries have gained attention as a potential alternative, leveraging their low cost components including abundant sodium as anode over competing energy storage technologies. However, structural instability, low electronic and ionic conductivity, severe polarization and low operating potential have significantly limited their practical application. The highly oxidative nature, low tap density and temperature instability of prussian blue, poor electronic conductivity of polyanions and iron-based fluoride based cathode materials have severe capacity fading and need to be optimized for better electrochemical performance. To overcome these challenges, surface engineering of cathode materials through nanostructured organic and inorganic coating have been explored as a means to improve their performance which provide uniform state of charge distribution and strength to cathode, which facilitates fast transport of electrons and ions and also prevents the transition metals dissolution and undesirable side reactions at the interface of cathode and electrolyte. These nanostructured coatings, made of compounds such as oxides, polyanions, conducting polymers and carbon materials have been widely exploited on various cathodes by using solution-phase mixing, Atomic layer deposition (ALD), Physical vapor deposition (PVD) techniques, etc. This review concludes a systematic comparison of different types of nanostructured coating on cathodes and their impact on electrochemical performance with the aim of exploring the potential for practical application of sodium ion batteries.