Low-Cost GeO₂-Derived LAGP Nanofiber Enhanced Composite Solid Electrolytes Enabling High-Performance Solid-State Lithium Metal Batteries

Composite solid electrolytes (CSEs) have garnered significant interest due to their synergistic combination of the high ionic conductivity inherent in ceramic electrolytes and the superior mechanical flexibility of polymer matrices. Incorporating active ceramic nanofibers (NFs) into polymer matrices offers a promising strategy for constructing 3D continuous ion-conduction pathways, thereby maximizing the ionic conductivity. Herein, Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) ceramic NFs are synthesized for the first time via a cost-effective electrospinning method using GeO 2 as the precursor, and the cost of raw materials can be reduced by approximately 80%. Systematic optimization of calcination temperatures (700–800 °C) and NFs loading (5–20 wt %) in PVDF-HFP matrices reveals that the CSE containing 15 wt % LAGP NFs (CSE(15NFs)) achieves outstanding properties at 20 °C: a high ionic conductivity of 2.22 × 10 –4 S·cm –1, a broad electrochemical stability window (ESW) exceeding 4.8 V, a low activation energy ( E a ) of 0.32 eV, and a high lithium-ion transference number (t Li+ ) of 0.52. Notably, the implementation of an integrated LiFePO 4 (LFP)/CSE(15NFs) interfacial architecture in solid state lithium metal batteries (LMBs) demonstrates enhanced rate capability and superior capacity cycling stability, retaining 83.7% of its capacity after 200 cycles at 0.2 C. This study highlights the considerable application potential of low-cost GeO 2 -derived LAGP NFs in high-performance CSEs and solid-state lithium batteries.