Solution-processed poly(vinylidene difluoride)/cellulose acetate/Li_1+xAl_xTi_2-x(PO₄)₃ composite solid electrolyte for improving electrochemical performance of solid-state lithium-ion batteries at room temperature

To enhance energy density and secure the safety of lithium-ion batteries, developing solid-state electrolytes is a promising strategy. In this study, a composite solid-state electrolyte (CSE) composed of poly(vinylidene difluoride) (PVDF)/cellulose acetate (CA) matrix, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) fillers is developed via a facile solution-casting method. The PVDF/CA ratio, LiTFSI, and LATP fractions affect the crystallinity, structural porosity, and thermal and electrochemical stability of the PVDF/CA/LATP CSE. The optimized CSE (4P1C-40LT/20F) presents a high ionic conductivity of 4.9 × 10^-4 S cm⁻¹ and a wide electrochemical window up to 5.0 V vs. Li/Li⁺. A lithium iron phosphate-based cell containing the CSE delivers a high discharge capacity of over 160 mAh g⁻¹ at 25 °C, outperforming its counterpart containing PVDF/CA polymer electrolyte. It also exhibits satisfactory cycling stability at 1C with approximately 90 % capacity retention at the 200th cycle. Additionally, its rate performance is promising, demonstrating a capacity retention of approximately 80 % under varied rates (2C/0.1C). The increased amorphous region, Li⁺ transportation pathways, and Li⁺ concentration of the 4P1C-40LT/20F CSE membrane facilitate Li⁺ migration within the CSE, thus improving the battery performance.