Speaker: Tim Fister, ANL
Program Description:
Lithium batteries are a central component for many growing technologies, but are still predicated on intercalation hosts similar to the original rocking chair battery released nearly 30 years ago. Rather than relying on the number and type of open crystallographic sites, metal oxides can also undergo conversion reactions that break down the original crystal structure to form nanoscale lithia and metal products. While such a process should have a much higher energy density than typical cathode materials, the destructive nature of oxide conversion reactions typically have severe overpotentials and reversibility issues that are attributed to the interfaces that form between the resulting oxide and metal species. To better understand the role of these interfaces, we have grown model oxide electrodes as thin films, multilayers, and patterned nanostructures ranging from 1-100 nm that are amenable to x-ray reflectivity and small angle x-ray scattering during lithiation. For ultrathin NiO films, we find a new lithiation mechanism at higher potentials that occur at the buried interface with its current collector, followed by wholesale conversion at previously observed potentials. By comparing reflectivity data with DFT-calculated interfacial energies, we find an accumulation of lithium ions at the solid/solid interface help bypass the strong overpotentials normally found with lithiation in bulk electrodes. By initiating and confining the reaction between metal and oxide interfaces, we are also able to control the substantial volume change using multilayer structures. Similar strategies were also explored for in-plane oxide structures grown by polymer-templated atomic layer deposition. These studies help establish that tailored interfaces can actually have a beneficial role during conversion.
