Influence of nanosize and thermodynamics on lithium storage in insertion and conversion reactions

Size reduction in nanocrystals leads to a variety of unexpected exciting phenomena due to enhanced surface-to-volume ratio and reduced length for the transport [1, 2]. Here, we consider the effects of nano-size on the kinetics and thermodynamics and study its bearing on the lithium storage performance in insertion and conversion based Li storage mechanism. Firstly, we investigate the storage performance of nanocrystalline LiMnPO4 by insertion reaction. Ball milling of LiMnPO4 synthesized by soft-template method with carbonaceous materials helps to reduce the grain size as well as formation of a thin layer of carbon coating. Nanostructuring by ball milling process promotes high surface area of the active electrode material for improved electrolyte wetting, short transport length for Li diffusion while the carbon coatings facilitates electronic wiring all of which contribute to the enhanced storage performance. Additionally, we show that combining nanostructuring with divalent cation doping further improves the storage performance of the system which make them potential high voltage cathodes for real applications. Secondly, we discuss the size effect on thermodynamics during the conversion reaction, considering Fe2O3 as an example. The process of Li storage by conversion induces drastic size reduction, leading to stabilization of metastable phase of g-Fe2O3. We show here that apart from kinetics, thermodynamics at nanosize also limit the rate of conversion reaction. Finally, we show that Fe2O3 can be a potential anode material for practical applications as they demonstrate a high degree of reversibility ~ 90% and excellent high rate performance.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.