Nanoarchitectured 3D cathodes for Li-ion microbatteries.

Rechargeable lithium ion batteries, due to their high energy density and design fl exibility, are the vital power sources for a variety of modern portable electronic devices and are the prime candidates to power next generation of electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs). [ 1 ] With a rich and versatile chemistry leading to a wide range of electrode materials, several efforts have been devoted to the development of Li-ion technology. [ 2–5 ] Apart from the hunt for novel electrode materials to meet high volume applications, newer electrode designs with the existing materials could effectively provide the power necessary to several specifi c applications. The recent advancements in microor nanoelectromechanical systems (MEMS/NEMS) technology have led to a variety of small-scale devices in microelectronics and biomedical area including microsensors, micromachines, and drug delivery systems. Hence the need to develop small-scale electrical power sources that enable on-board microbattery power delivery in these microscale devices. Insuffi cient power from 2D microbattery confi gurations leads to the search for development of 3D microor nanobattery using cheap and light micro/nano fabrication materials. [ 6 ] Such battery designs are expected to offer marked improvements in power while maintaining comparable energy density as compared to 2D. Several confi gurations have been recently proposed for 3D Li-ion microbatteries to meet the required energy and power densities. [ 6 ] Standard depositions of electrode and electrolyte layers onto nanostructured current collectors are seen as an effi cient and feasible route for the fabrication of 3D microbatteries. We have previously shown that free standing arrays of copper and aluminium nanorods can be directly grown on the respective base substrates using template approach. [ 4 , 7 ] However, there are only a few reports on 3D microbatteries and most of them have been largely devoted to 3D negative electrodes. [ 8–11 ] Nanostructured 3D negative electrodes show improved capacities and rate capabilities compared to their planar counterparts. [ 8 ] It is now important to develop 3D positive electrodes to facilitate the 3D microbattery cell