Understanding the Mechanisms Governing Anode-Free and Alloy-Anode Solid-State Batteries

Solid-state batteries offer the promise of improved energy density and safety compared to lithium-ion batteries, but electro-chemo-mechanical evolution and degradation of materials and interfaces can play an outsized role in limiting their performance. Here, I will discuss our work on solid-state batteries with both lithium metal and alloy-based anodes. Lithium metal batteries are especially beneficial if used in an “anode-free” configuration in which there is no lithium initially present at the anode current collector. Using X-ray tomography, cryo-FIB, and finite-element modeling, we show that lithium metal anode-free solid-state batteries are intrinsically limited by current concentrations at the end of stripping due to localized lithium depletion, which accelerates short circuiting compared to lithium-excess cells. The beneficial influence of metal alloy interfacial layers on controlling lithium evolution and mitigating contact loss from localized lithium depletion will be introduced and discussed. Furthermore, the growth of lithium filaments in anode-free cells is visualized and quantified with X-ray tomography. Next, we investigate alloy anode materials for solid-state batteries. We show that local chemo-mechanical interactions between neighboring particle domains in silicon electrodes can cause interfacial delamination from the solid-state electrolyte during delithiation. Increasing the uniformity of the electrode thickness can mitigate this issue. Additionally, the influence of stack pressure on alloy anode evolution is investigated, and we show that anode morphology changes during charge/discharge are highly pressure-dependent. Taken together, these findings show the promise of both lithium metal and alloy anodes for solid-state batteries, with divergent reaction mechanisms giving rise to different operating conditions necessary for each class of materials.