MXenes, firstly described in 2011, are a relatively new class of layered materials, each layer consisting of a few atoms of transition metal carbides and/or nitrides, e.g. Ti3
. MXenes have attracted considerable research attention for electronics and electrochemical applications, benefiting from their outstanding electrical and ionic transport properties. However, the nature of charges which can move freely in the material – so-called “free electrons” - and their transport mechanism in MXenes have remained elusive. In the past, strongly conflicting charge transport mechanisms have been proposed. New research shows that a free electron in MXenes displaces the atoms in the material's lattice: the electron is “dressed” by a local lattice deformation, extending over several lattice constants. This transforms the electron into a polaron, a quasi-particle, which plays a crucial role in determining the electrical conductivity of MXenes.