Nanostructured Li ion insertion electrodes. 2. Tin dioxide nanocrystalline layers and discussion on nanoscale effect

Relaxation processes occurring during electroinsertion into pure SnO2 and electrochromic SnO2/Sb were interpreted on the basis of frequency-dependent response models. Within the framework of the classic theory of porous electrodes, the results indicated that, in the case of nanosized particle-based electrodes, the overall kinetic aspects of the insertion process can be controlled by the transport of ionic and electronic species in the liquid and solid phases, respectively. Therefore, if both the electronic and ionic transport are fast in both the solid and liquid phases, or if the state-of-charge is high, a relaxation process corresponding to the insertion of Li+ in specific sites inside the nanosized particles is clearly identifiable, as foreseen by the model discussed in part 1. As a result, in the SnO2/Sb samples, we have successfully separated the frequency of slow charging of transport effects due to the nonfaradaic capacitance-related process from that of faradaic related capacitances, because these two processes do not overlap and can, in such specific situations, be separated in complex capacitance diagrams. Moreover, our interpretation of the results indicates that the participation of a large amount of inserted charge in the Sb-doped sample is possible due to the nanoscale factor, which, allied to the high electronic conductivity in the solid phase, causes rapid charging of the faradaic capacitance-related process. In our interpretation, the faradaic capacitance related process is linked to the insertion of Li+ into the solid-state phase of nanosized particles and can be interpreted as an ion immobilization or trapping process, as discussed earlier in part 1.