Solid-state batteries promise to revolutionise battery safety and energy density. However, there remain significant challenges to be overcome before their potential can be realised. This thesis focuses on the difficulties of interfacing a metal anode with a solid electrolyte. Perhaps the most limiting problem is that the metal anode/solid electrolyte interface is morphologically unstable at high rates of charge/discharge, with dendrites penetrating through the solid electrolyte on plating, and voids forming at the interface during stripping.
In Chapter 3, the formation of interfacial voids during stripping is investigated for a Na metal anode. The Na anode enables the use of X-ray computed micro-tomography to follow the dynamics of voiding at the interface during cycling, revealing how voiding worsens with each successive stripping until failure of the cell. The Na anode also offers an interesting contrast to previous work on Li anodes, with lower stack-pressures required to suppress voiding, due to its greater propensity to creep under pressure.
Chapter 4 describes investigation of the temperature dependence of voiding at the Li anode/solid electrolyte interface, finding that moderately elevated temperatures enable higher rates of morphologically stable stripping by increasing self-diffusion and creep in the Li metal. Stable cycling at a high current density of 2.5 mA/cm2 is demonstrated under 5 MPa stack-pressure at a moderately elevated temperature of 80 °C.
Finally, Chapter 5 investigates the use of carbon-based interlayers to protect the solid electrolyte from dendrite penetration. A number of interlayers are investigated, with their effectiveness determined to be dependent on the Li diffusivity. Addition of silver to graphite interlayers is also studied, finding that formation of a Ag-Li alloy significantly improves the homogeneity of Li deposition during charging
