Tracking the capacitive energy storage process in layered MXene across length scales

Intercalation of ions in layered materials forms the basis of electrochemical energy storage and conversion and is especially attractive due to the typically ultra-fast intercalation kinetics. Enhancing the energy stored and power delivered by these materials relies strongly on improved understanding of the intercalation chemistry of cations including the intricate interplay of cations, water, and electrode interactions as well as the role of confinement. Here we report a highly integrated study between experimental and modeling approaches to investigate the intercalation processes for aqueous Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺ into Ti₃C₂ MXenes. Experiments include microcalorimetry, atomic force microscopy and cyclic voltammetry whose results are directly linked to the results of ab initio modeling. Our integrated analysis allows for a complete understanding of energy storage processes highlighting the importance of the dynamics of cations and positionings and their role in capacitive energy storage properties. Our findings will expedite the evolutions of various energy related functional devices driven by the design of higher-performing membranes and two-dimensional materials.