Abstract
Interfacial phenomena are inherent to numerous applied systems including active sites in heterogeneous catalysts and p-n junctions in integrated circuits. In energy storage and conversion materials/devices, they play critical roles in determining their performance and life time. Here, we present an in situ scanning transmission electron microscopy (STEM), coupled with electron energy loss spectroscopy (EELS), study of the interfacial phenomena related to lithium ion transport and its corresponding charge transfer in all-solid-state batteries. The high spatial and energy resolution of this coupled technique enabled observation of dynamic compositional and electronic bonding changes at the interface between solid electrolyte and solid electrode. An unexpected structurally disordered interphase layer was discovered between LiCoO2 cathode and LiPON electrolyte. During in situ charging, this interfacial layer evolved to form highly oxidized Co ions and lithium oxide species. Furthermore, insights gained from our technique will facilitate the improved engineering of various interfaces far from equilibrium.
