Cross-Linked Composite Solid Polymer Electrolyte Doped with Li_6.4La₃Zr_1.4Ta_0.6O₁₂ for High Voltage Lithium Metal Batteries

Composite solid polymer electrolytes (CSPEs) are safer alternatives to liquid electrolytes and excellent candidates for high-voltage solid-state batteries. However, interfacial instabilities between the electrodes and CSPEs are one of the bottlenecks in pursuing these systems. In this study, a cross-linked CSPE was synthesized based on polypropylene carbonate, polyethylene glycol methyl ether acrylate, polyethylene glycol diacrylate with additives including lithium bis(trifluoromethane)sulfonimide salt, and tantalum-doped lithium lanthanum zirconium oxide (LLZTO). Mass fractions of 10, 20, and 40% LLZTO were added to the CSPE matrix. In a symmetric cell, lithium plating and stripping revealed that the interface between the lithium metal anode and CSPE with 10% of the LLZTO (CSPE-10LLZTO) shows the most stable interface. The CSPE-10LLZTO sample demonstrated high flexibility and showed no degradation over 800 h of cycling at varying current densities. The ionic conductivity for the CSPE-10LLZTO sample at 40 °C was 6.4 × 10^-4 S/cm. An all-solid-state full cell was fabricated with LiNi_0.5Mn_0.3Co_0.2O₂ as the cathode, CSPE-10LLZTO as the electrolyte and separator, and Li metal as the anode, delivering approximately 140 mAh/g of capacity. Differential scanning calorimetry measurements on CSPE-<i>x</i>LLZTO showed high miscibility and the elimination of crystallinity. Raman spectroscopy revealed uniformity in the structure. These findings demonstrate the capability of the CSPEs to develop high-voltage solid-state lithium metal batteries.