Fabrication and electrochemical behavior of thin composite solid electrolyte for all-solid lithium batteries

Loading level, active material content of the cathode, and the thickness of composite solid electrolyte (CSE) sheets were optimized as 13 mg cm −2 , 88 wt%, and 60 μm, respectively, for the development of all-solid lithium batteries (ASLBs) with high energy density. Thin CSE sheets were fabricated by adding PVDF binder with Al-LLZO powder and PEO-Li salt solution. PVDF had effects on the ionic conductivity, strength, and electrochemical stability of the CSE sheet. When the PVDF content was increased to 7 wt%, CSE sheet strength increased from 1.4 to 2.83 MPa, while the electrochemical stability has significantly improved at the range of oxidation and reduction potential. However, the ionic conductivity decreased from 3.7 × 10 −4 to 1.73 × 10 −4 S cm −1 at 70 °C. Moreover, the surface layer of the composite cathode was smoother than that of normal composition, and the interfacial resistance between the cathode compound layer and Al current collector has also decreased by adding PVDF. As a result of the test, the initial discharge capacity of the coin cell showed 207 mAh g −1 and 2.3 mAh cm −2 at 70 °C.