Rotaxane chemistry tailoring interfacial lithium transport channels for composite solid electrolytes

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.