Scientific Achievement
We compared the molecular dynamics of two different but structurally-related electrolytes in highly concentrated solutions. One catholyte is compact and symmetrical; the other is bulkier and less symmetrical. Incoherent elastic and quasi-elastic neutron scattering measurements showed significant differences in crystallization, supercooling, and sudden microheterogeneity.
Significance and Impact
Catholytes of high solubility also disfavor crystallization; this intuitive behavior needs better understanding to realize improved molecular design of high energy-dense flow battery materials. The need is being addressed by structure and dynamics studies of supercooled, highly-concentrated nonaqueous electrolyte solutions. Our findings suggest that solvation inhomogeneities and molecular crowding are important.
Research Detail
- Synthesis of deuterated redox-active organic molecules to visualize only protiated (hydrogen-containing) electrolyte components.
- Variable-temperature neutron scattering of two catholyte solutions show that the symmetrical catholyte prefers crystallization while the bulky one exhibits supercooling behavior.
- Isothermal quasi-elastic neutron scattering from solutions of the supercooled bulky catholyte reveal thermal history-dependent dynamics. The data were fit to models of molecular dynamics and provide details of solution metastability.
