Characterizing Solid State Battery Degradation Using Optical Microscopy and Operando X-Ray Tomography

Abstract

The implementation of solid-state electrolytes (SSEs) into lithium-ion batteries shows much promise in enabling the use of higher energy density anodes, such as pure lithium metal. However, the implementation of SSEs and lithium metal anodes in lithium-ion batteries is currently not possible due to degradation mechanisms that lead to premature failure of the battery. These mechanisms, such as the formation of a new phase known as the interphase and the growth of lithium metal dendrites, are initiated at the interface between the anode and electrolyte and are linked to the current density at which the battery is cycled. Reported are two methods of characterizing the interfacial degradation phenomena that occur between lithium metal anodes and the SSE Li10SnP2S12 (LSPS). A novel symmetric battery setup was developed to allow an operando optical microscopy study of the lithium metal and SSE interface as charge was passed through the battery. Though this characterization method presented challenges, interphase formation and dendrite growth were both observed. Further, operando x-ray computed tomography of a novel cell geometry provided detailed three dimensional scans that also showed evidence of interphase growth and dendrite formation. Additionally, interfacial void formation was identified, indicating a loss of contact that increases current density. These results provide insight into the failure of solid-state batteries and show how operando optical microscopy and x-ray tomography can be used to gain a more complete understanding of the degradation of higher energy density lithium-ion batteries.