Solvent-Free Processed Polymer Electrolyte for Li-Metal Batteries

In this work, PVdF-HFP-based solid polymer electrolytes with LiTFSI as a lithium salt and an ionic liquid as a plasticizer were prepared through solvent-free processing. The processing conditions used for the membrane preparation are described. Moreover, the study shows full characterization of the resulting membranes, including structural (X-ray diffraction and Fourier Transform Infrared spectroscopy), thermal (Thermogravimetric analysis, differential scanning calorimetry), mechanical, and electrochemical (ionic conductivity, transference number, stripping plating ability, and critical current density) characterization. Due to the limited conductivity of the pure PVdF-HFP containing polymer electrolyte membranes, blends with poly(ethylene oxide) (PEO) and different EO/Li+ ratios were also prepared and characterized. Driven by the good electrochemical characteristics of the blend polymer membranes, full cells with NMC-811 and metallic Li as the cathode and anode, respectively, were assembled and subjected to cycling stability tests. Expected initial capacity values for NMC-811 were obtained with 41% capacity retention after 100 cycles at C/10. Interestingly, no evidence of PEO-containing electrolyte degradation was observed, indicating that the blending strategy, in addition to increasing the conductivity values of PVdF-HFP-based electrolytes, resulted in the electrochemical stabilization of the PEO-containing electrolyte.