Electrochemically Induced Deformation Determines the Rate of Lithium Intercalation in Bulk TiS2

Abstract

Understanding the kinetic limitations of intercalation reactions is essential to create high-power intercalation host materials. In this Letter, we show the existence of both diffusion-limited and non-diffusion-limited lithiation regimes in the model material bulk TiS2. The regions can be clearly identified by electrochemical impedance spectroscopy. A decreasing charge-transfer resistance is observed with increasing electrode polarization in the diffusion-limited region, whereas it remains constant when the electrochemical process is non-diffusion-limited. We highlight how TiS2 interlayer deformation is closely tied to the intercalation kinetics. While regions of TiS2 interlayer expansion/contraction are correlated with diffusion limitations, lithiation occurring under constant interlayer spacing is non-diffusion-limited: the material exhibits pseudocapacitive behavior. Larger TiS2 interlayer spacing results in faster ionic transport. The study sheds light on the close ties between deformation, interlayer distance, and intercalation kinetics in a model layered host material.