Revealing the mechanisms of lithium-ion transport and conduction in composite solid polymer electrolytes

Conductive filler-based solid polymer electrolytes are excellent candidates for the large-scale production of solid-state lithium-ion batteries. However, the transport and conduction mechanisms of lithium ions in such solid polymer electrolyte systems remain largely unrevealed. In this work, the results of in situ conductive atomic force microscopy demonstrate that lithium ions travel mainly through the Li6.4La3Zr1.4Ta0.6O12 (LLZO) filler in polyethylene oxide (PEO)-based SPEs. The transport routes from LLZO into the polymer matrix can be greatly altered by adding succinonitrile (SCN). Combining experiment with ab initio simulations, we find that the adsorption affinity order for lithium ions is SCN > LLZO > PEO. Diffusion barriers are calculated for various composites, showing higher barriers for migration of lithium on the surface compared with in bulk. This work provides understanding of lithium affinity, diffusion barriers, and conductive mechanisms in solid polymer electrolytes, enhancing our understanding of mechanisms to guide future designs.