Fast Li-ion Storage and Dynamics in TiO2 Nanoparticle Clusters Probed by Smart Scanning Electrochemical Cell Microscopy.

Anatase TiO2 is a promising material for Li-ion (Li+) batteries with fast charging capability. However, Li+ (de)intercalation dynamics in TiO2 remain elusive and reported diffusivities span many orders of magnitude. Here, we develop a smart protocol for scanning electroche-mical cell microscopy (SECCM) with in situ optical microscopy (OM) to enable the high-throughput charge/discharge analysis of single TiO2 nanoparticle clusters. Directly probing active nanoparticles revealed that TiO2 with a size of ~50 nm can store over 30% of the theoretical capacity at an extremely fast charge/discharge rate of ~100 C. This finding of fast Li+ storage in TiO2 particles strengthens its potential for fast-charging batteries. More generally, smart SECCM-OM should find wide applications for high-throughput electrochemical screening of nanostructured materials.