Void growth in the lithium anode of a solid state battery

It has been conjectured that the growth of voids within the Li anode of a solid state battery promotes dendrites within the ceramic electrolyte and resists Li transport into the electrolyte. We explore experimentally the evolution of a pre-existing void within the Li anode of a solid state battery resulting from its stack pressure and/or a superposed electrical current. The battery comprises Li electrodes and an electrolyte made from Ta-doped lithium lanthanum zirconate (Li/LLZO/Li). A circular cylindrical void was generated within the Li layer and adjacent to the LLZO interface by withdrawing a niobium wire of diameter 200 μm from the Li layer prior to testing. The sensitivity of void collapse to applied pressure was determined by varying the radius to height of the Li pancake-layer and by varying the applied load. The evolution of specimen height with time and the closure rate of the voids are consistent with power law creep of the Li. An additional set of experiments was performed whereby the Li migrated into the LLZO substrate by imposition of a constant electrical current. It was found that the void shrinks at a rate consistent with migration of the Li layer into the LLZO, with negligible flux focussing in the vicinity of the void. The study has direct relevance to the effect of stack pressure and battery operation upon void evolution in a solid state Li battery.