<p>High ionic conductivity, excellent interfacial stability, and low interfacial resistance in quasi-solid-state electrolytes are essential for the practical implementation of semi-solid-state batteries. In order to improve safety and performance, composite polymer electrolytes (CPEs) were developed by integrating garnet-type Li_6.25Ga_0.25La₃Zr₂O₁₂ (LLZO-Ga) powder into a polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) matrix, in conjunction with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The CPEs containing 10% wt. LLZO-Ga demonstrated an ionic conductivity of 7.29 × 10⁻⁴ S cm⁻¹ and an expanded electrochemical window reaching up to 4.90 V vs Li/Li⁺. Additionally, the formation and composition of the solid electrolyte interphase (SEI) layer were examined using X-ray photoelectron spectroscopy (XPS). When coupled with LFP and NMC111 cathodes and using a high-concentration electrolyte (4MLiFSI: DEE), the quasi-solid composite polymer electrolyte cells (QCPEs) exhibited promising cycling performance at different rates, maintaining discharge capacities of 108.7 mAh g⁻¹ (LFP) and 115.6 mAh g⁻¹ (NMC111) at 1C, respectively. The mechanical tests with pouch cell of bending, cutting, and burning further highlighted the superior safety and potential applications of the PVDF-HFP-based quasi-solid batteries with Li metal at room temperature.</p> Graphical Abstract <p></p>