Dynamics of Lithium Insertion in Electrochromic Titanium Dioxide Nanocrystal Ensembles

Nanocrystalline anatase TiO2 is a robust model anode for Li insertion in batteries. The influence of nanocrystal size on the equilibrium potential and kinetics investigated with operando spectroelectrochemistry thin film electrodes. Distinct visible infrared responses correlate electron accumulation, respectively, these optical signals are used to deconvolute bulk from other electrochemical responses, such as double-layer capacitance, pseudocapacitance, electrolyte leakage. Electrochemical titration phase-field simulations reveal that difference surface energies between lithiated phases systematically tunes Li-insertion potentials particle size. However, does not affect ensemble Rather, rates depend applied overpotential, concentration, initial state charge. We conclude diffusivity phase propagation rate limiting during nanocrystals. Both processes occur rapidly once transformation low-Li high-Li orthorhombic begins particle. Instead, discontinuous accumulation particles prior transformations limits (dis)charging rates. demonstrate practical means nonequilibrium charging behavior nanocrystalline electrodes through combination colloidal synthesis, field simulations, spectroelectrochemistry.