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 Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (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.
Lithium-conducting fillers play crucial roles in enhancing the ionic conductivity of solid polymer electrolytes (SPEs). By providing supplementary rapid Li+ transport channels, they substantially boost the practical viability of solid-state batteries. Nevertheless, the inherent incompatibility between polymers and inorganic fillers invariably leads to phase separation, which exacerbates the transport barrier for lithium through interfaces and impedes the full utilization of these swift channels. Herein, a novel “Rotaxane chemistry” has been employed to engineer stable lithium transport pathways at the Li7La3Zr2O12(LLZO)/PEO interface. This strategy confines PEO chains within molecular semicircles on the surface of modified filler, namely LLZO@Rotaxane, which loosens chain entanglement and breaks tight coordination of (EO)n–Li. This promotes Li spontaneous diffusion to and transport through the nano-confinement space in the interface as well as through the LLZO. Consequently, the proportion of lithium transported by LLZO and interface has surged from 28.4 % to 56.0 %, endowing the PEO-LLZO@Rotaxane with an outstanding ionic conductivity of 1.90 mS cm−1 at 60 °C and Li+ transference number of 0.74. Correspondingly, the batteries fabricated with PEO-LLZO@Rotaxane also manifest excellent cyclic and rate performance. Thus, this work offers novel insights into increasing the ionic conductivity by interface engineering.
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