Preparation and Characterization of a LiFePO4- Lithium Salt Composite Cathode for All-Solid-State Li-Metal Batteries

This study develops a composite cathode material suitable for solid-state Li-ion batteries (SSLIB). The composite cathode consists of LiFePO4 as the active material, Super P and KS-4 carbon materials as the conductive agents, and LiTFSI as the lithium salt. An LiFePO4/LATP-PVDF-HFP/Li all-solid-state LIB was assembled using Li1.3Al0.3Ti1.7(PO4)3 (LATP)/ poly(vinylidenefluoride-co-hexafluoropropylene (PVDF-HFP) as the solid-state electrolyte and lithium metal as the anode. The structure of the synthesized LATP was analyzed using X-ray diffraction, and the microstructure of the composite cathode and solid electrolyte layer was observed using a field emission scanning electron microscope. The electrochemical properties of the all-solid-state LIB were analyzed using electrochemical impedance spectroscopy (EIS) and a charge–discharge test. The effect of the composition ratio of the fabricated cathode on SSLIB performance is discussed. The results reveal that the SSLIB fabricated using the cathode containing LiFePO4, Super P, KS-4, PVDF, and LiTFSI at a weight ratio of 70:10:10:7:3 (wt.%) and a LATP/PVDF-HFP solid electrolyte layer containing PVDF-HFP, LiTFSI, and LATP at a weight ratio of 22:33:45 (wt.%) exhibited the optimal performance. Particularly, the SSLIB fabricated using the cathode containing 3% LiTFSI exhibited a discharge capacity of 168.9 mAhg−1 at 0.1 C, which is close to the theoretical capacity (170 mAhg−1), and had very good stability. The findings of this study suggests that the incorporation of an appropriate amount of LiTFSI can significantly enhance the electrochemical performance of SSLIB batteries.