Lawrence Berkeley National Laboratory

A challenge for lithium lanthanum zirconate (LLZO)-based solid-state batteries is to increase the critical current density (CCD) to enable high current cycling. A promising strategy is to modify the LLZO surface morphology to provide a larger contact area with Li metal. Examples of such modifying surface morphology include surface patterning through laser cutting [1] and roughening by shot peening [2]. However, these techniques still have challenges in scale-up and application to thin electrolyte layers. Surface patterning using a laser cutter leads to surface contamination requiring post-heat treatment in an inert atmosphere, and shot-peening has a potential risk of mechanical failure caused by impact stress, making it especially difficult to use for thin electrolytes. Here, we present an easily scalable process to prepare surface-textured thin LLZO electrolytes. The texturing process is a simple pressing of green LLZO tapes between micro-textured substrates. A variety of textures can be produced depending on the type of substrate, and texturing can be on either one side or both sides. For this work, after pressing and sintering, several micro-patterns are formed on thin LLZO (~118 μm thick). The properties of the various samples were characterized to investigate the impact of the surface texturing, and the most promising ones were selected for electrochemical testing in symmetrical lithium cells and full cells. Li symmetric cells using a coarse ridge-textured LLZO exhibit ~2.5 times increased CCD compared to planar non-textured LLZO, and a solid-state full cell shows stable cycling and improved rate performance. We believe this process offers a favorable tradeoff of processing complexity vs. structural optimization to maximize CCD. [1] Xu R, et al Adv. Mater., e2104009, 33(49), (2021) [2] Kodama M, et al J. Power Sources, 231556, 537 (2022)