Investigation of ion diffusion in polyethylene oxide-based solid electrolyte with functionalized La(OH)₃ nanofibers for high-rate all-solid-state lithium-metal batteries

Solid polymer electrolytes have emerged as promising materials for next-generation lithium metal batteries due to their enhanced safety and high energy density potential. However, their widespread adoption is hindered by slow ion transport and inefficient lithium-ion (Li⁺) selectivity. To overcome these limitations, this study introduces a composite electrolyte by incorporating functionalized La(OH)₃ nanofibers with oxygen vacancies into a Poly(ethylene oxide) (PEO) matrix. These nanofibers, synthesized via a simple method, are designed to improve Li⁺ mobility by leveraging their oxygen vacancies to immobilize TFSI⁻ anions from the bis(trifluoromethanesulfonyl)imide (LiTFSI). Simultaneously, amino groups on the nanofiber surface act as binding sites, facilitating lithium salt dissociation and creating supplementary ion transport pathways. Density functional theory (DFT) and molecular dynamics (MD) simulations reveal that the functionalized La(OH)₃ nanofibers effectively suppress TFSI⁻ anion movement while reducing the energy barrier for Li⁺ migration. This mechanism elevates the Li⁺ transference number to 0.51, a significant improvement over the conventional PEO-based electrolytes. The composite electrolyte exhibits excellent performance in Li||Li cells, maintaining stable cycling for over 600 h at a current density of 0.38 mA cm⁻². Furthermore, a solid-state LiFePO₄||Li battery demonstrates highly reversible capacities of 100.2 mAh g⁻¹ after 600 cycles at 8C. By combining anion confinement strategies with tailored electronic interactions, this work provides a practical approach to advancing solid-state battery performance. The findings not only highlight the potential of La(OH)₃-PEO composite electrolytes but also establish a new framework for optimizing ionic conductivity through targeted molecular design.