  Ionic liquids (ILs) gain much interest as possible electrolytes in the next
generation of mixed-solid Li-ion batteries. However, such properties of ionic
liquids as melting transition, diffusion, strength and structure of hydrogen
bond network remain poorly investigated. Here 2H NMR study of a prototypical
ionic liquid [TEA][NTf2] has been performed. We show that the dynamical melting
occurs through a dynamically heterogeneous phase stable between 223-277 K and
the transition process is characterized by two standard molar enthalpy changes
indicating to the multistage nature of the melting. The spin relaxation
analysis allowed determining geometry, rates and energetics of IL mobility in
both solid and liquid state. We compare these properties with previously
reported data on [TEA][OTf] and [TEA][OMs] ILs that share cation but have
anions of varying strength. Our results prove that the stronger hydrogen bonds
between cation and anion lead to the lower enthalpy change between solid and
liquid state, higher activation barrier of tumbling motion and lower amplitude
of libration motion.
