Lithium diffusion through the TiN coating layer and formation of Li-Si alloy over Si@TiN anode

•In-situ X-ray diffraction is used to detect the diffusion of lithium in TiN layer and the formation of Li-Si alloy over Si@TiN anode.•The alloying reaction is controlled by diffusion, and the Li-Si alloy formation corresponds with the shrinking core model in Si@TiN system.•The use of the non-Faradaic process prevents the formation of an unstable solid electrolyte interphase (SEI), and this avoids the interference from the SEI.•Empirical equation is established to quantify the lithium diffusion across the TiN layer.