Resolving local dynamics of dual ions at the nanoscale in electrochemically active materials

Electrochemical conversion is typically studied at macroscopic scale, and it is quite challenging to probe local electrochemistry at the nanoscale, especially those involving multiple ions. Through a series of atomic force microscopy experiments, we demonstrate that two competing ionic strains arising from molar volume changes and electrochemical dipoles in a dual-ion system can reveal themselves in distinct relaxation behavior, enabling us to decouple their respective contributions and thus measure local diffusivity along with activation energy. Using soda-lime float glass as a model system, we observe a fast relaxation corresponding to diffusion of Na+ and a slow relaxation associated with electrochemical dipoles formed between Na+ and non-bridging oxygen. Assisted by simulations, we determine the local diffusivity of 5.64 x 107 16 m(2)/s and activation energy of 0.55eV for Na+ at 100 degrees C. The study provides a powerful tool to resolve local dynamics of dual ions, which can be applied to study a variety of complex energy conversion and storage systems.