SUMMARY

Solid-state batteries (SSBs) can offer increased energy density and improved safety compared to conventional liquid-based Li-ion batteries by potentially allowing the use of Li metal as an anode. SSBs are ideal for applications within high capacity electric vehicles as well as in enabling battery-powered aircraft. However, the significant challenge exists of premature degradation driven by the unstable interface between the solid-state electrolyte (SSE) and Li metal. Ceramics are the most promising of SSE materials, but they can react with Li, causing the formation of an amorphous interphase at the Li/SSE interface. This generates stresses that eventually drive fracture in brittle ceramic SSEs, a process that impedes Li-ion flow and renders the battery useless.

Discerning where this fracture initiates and how crack propagation negatively impacts electrochemical performance is critical in furthering the lacking knowledge surrounding stabilizing SSE/Li interfaces. This work uses computed X-ray tomography to image global fracture of an SSE in contact with Li metal, tracking the growth of the crack network by obtaining a 3D volume with a voxel size of ~20 μm. X-ray tomography is done in-operando, allowing the morphology change of the SSE to be studied as a function of electrochemical cycling. Impedance of the cell is also tracked, showing that mechanical degradation plays a direct role in obstructing Li ion transfer. Experimental findings are supported by FEA studies, and for the first time, the electrochemical degradation of a SSB electrolyte is found to directly increase due to crack formation.