Realization of the Li+ domain diffusion effect via constructing molecular brushes on the LLZTO surface and its application in all-solid-state lithium batteries

Abstract

All-solid-state lithium metal batteries based on polymer electrolytes provide great promise for solving safety and specific energy issues. However, poor ionic conductivity and large interfacial impedance still hold back their development. A strategy of introduction of inorganic nanoparticles was used to improve ionic conductivity and enhance mechanical properties but the current migration mechanism in composite polymer electrolytes (CPEs) is ambiguous. In this work, Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) nanoparticles with molecular brushes (MB-LLZTO) were designed and introduced into poly(ethylene oxide) (PEO) to form a high ionic conductivity composite electrolyte. MB-LLZTO in the polymer matrix plays an ideal role in increasing the ionic conductivity by the Li⁺ domain-diffusion effect. The CPE with 15 wt% MB-LLZTO exhibits the highest ionic conductivity of 3.11 M10⁻⁴ S cm⁻¹ at 45 °C (the corresponding value of the pristine LLZTO-CPE is 9.16 × 10⁻⁵ S cm⁻¹). High-resolution solid-state Li NMR provides experimental evidence for the proposed mechanism in the composite electrolyte that Li⁺ tends to diffuse in the fast-conduction domains introduced by the brushes of the MB-LLZTO surface. Consequently, the all-solid-state lithium–sulfur battery with the MB-LLZTO-CPE shows a discharge capacity of approximately 1280 mA h g⁻¹ at low temperature and stable cycling performance (752 mA h g⁻¹ after 220 cycles). Construction of molecular brushes on the LLZTO surface may be an effective way to unlock more potential solid polymer electrolytes.