Visualizing the Li distribution in an all-solid-state battery composite electrode using combined plasma focused-ion beam microscopy and secondary-ion mass spectroscopy

Using a Li metal anode, the all-solid-state battery (ASSB) promises a step change in specific energy over Li-ion batteries and the potential for increased battery safety. ASSBs rely critically on the efficient movement of Li charge carriers through a Li-conducting solid electrolyte (SE) separator and throughout a composite cathode (CC) comprising active particles, particulate SE, polymeric binder, and carbon. Unfortunately, there is no readily accessible laboratory method to visualise Li distributions at both particle and electrode scales to help understand and optimise Li electrode dynamics in ASSBs. We report a method to map all electrode elements in a 3D volume, including Li, within a typical ASSB composite cathode. The method combines a xenon plasma focused-ion beam (PFIB) for 3D milling, energy dispersive X-ray spectroscopy (EDS) to map non-Li elements, and secondary ion mass spectrometry (SIMS) to map Li. We manipulate 3D EDS and SIMS datasets into a common format and then recombine them in 3D to differentiate the different materials at high resolution. This new approach can be applied to understand and optimise the role of microstructure in controlling ASSB performance.