Invited: Interfacial Lithiation of Layered Heterostructures Measured by Real-Time X-ray Reflectivity

Intermetallics, such as silicon or tin, tend to have limited reversibility in batteries due to their substantial volume change during lithiation that amorphizes the electrode and leads to delamination. Numerous methods have been proposed to direct the volume change using nanofabrication, but many of these routes require partial lithiation and can suffer from reduced Coulombic efficiency related to the electrode’s resulting high surface area. In the spirit of layered crystal structures that support intercalation, we fabricated superlattices consisting of alternating layers of amorphous silicon and chromium silicide that maintain their 1D ‘crystal structure,’ despite 300% vertical expansion of the silicon layers. Diffraction peaks from the repeated bilayer structure confirm the reversibility of the overall reaction despite four-fold vertical expansion from each silicon layer. X-ray reflectivity also shows that the metallic layers remain intact during the entire process and that structural changes can be influenced by using potentiostatic or galvanostatic boundary conditions. Similar results were found in germanium/titanium multilayers, where intermixed GeTi_x regions were found to also participate in the lithiation. In each case, the long term cycling and Coulombic efficiency of the multilayers far outperform pure-phase thin films and show similar rate capabilities. We discuss the universality of this approach and prospects for using the layered structure to tailor phase separation in multicomponent conversion reactions.