Nanostructured Li ion insertion electrodes. 1. Discussion on fast transport and short path for ion diffusion

This paper describes the mechanisms of ion and electron transport in nanostructured insertion electrode materials such as metal oxide electrochromics and/or Li ion batteries. A general description is given of cases of insertion into a short path region predicted by the geometric disposition of insertion materials in nanostructural electrodes, designed mainly by connected spherical-like particles and nanofibers, both protruding from the cur-rent collector substrate. The short path scheme for ion diffusion (nanometer length) permits an ion storage mechanism to be treated as a capacitance charge rather than a diffusion process, an effect that is dubbed the nanoscale effect. As a result of heterogeneous charge-transfer resistance, the intercalation sites may be seen as the occupation of an ion immobilized-like state. A scheme of an ion trapping-like state represents, in the present case, an ion-binding process occurring during the intercalation reaction, like Li+ forming a bond to a bridging-type oxygen in metal oxide based insertion materials. The model predicts a relaxation process for the intercalation reaction which is more clearly visible in cases of fast transport (occurring throughout the solid and liquid/electrolyte phases of a nanosized macrohomogeneous medium) and/or high state-of-charge. The characteristic frequency of this relaxation process can be used to predict the rate of Li ion intercalation reaction in different nanosized host materials.