Cross-Linked\nComposite Solid Polymer Electrolyte Doped\nwith Li<sub>6.4</sub>La<sub>3</sub>Zr<sub>1.4</sub>Ta<sub>0.6</sub>O<sub>12</sub> for High Voltage Lithium Metal Batteries

Composite solid polymer\nelectrolytes (CSPEs) are safer alternatives\nto liquid electrolytes and excellent candidates for high-voltage solid-state\nbatteries. However, interfacial instabilities between the electrodes\nand CSPEs are one of the bottlenecks in pursuing these systems. In\nthis study, a cross-linked CSPE was synthesized based on polypropylene\ncarbonate, polyethylene glycol methyl ether acrylate, polyethylene\nglycol diacrylate with additives including lithium bis(trifluoromethane)sulfonimide\nsalt, and tantalum-doped lithium lanthanum zirconium oxide (LLZTO).\nMass fractions of 10, 20, and 40% LLZTO were added to the CSPE matrix.\nIn a symmetric cell, lithium plating and stripping revealed that the\ninterface between the lithium metal anode and CSPE with 10% of the\nLLZTO (CSPE-10LLZTO) shows the most stable interface. The CSPE-10LLZTO\nsample demonstrated high flexibility and showed no degradation over\n800 h of cycling at varying current densities. The ionic conductivity\nfor the CSPE-10LLZTO sample at 40 °C was 6.4 × 10<sup>–4</sup> S/cm. An all-solid-state full cell was fabricated with LiNi<sub>0.5</sub>Mn<sub>0.3</sub>Co<sub>0.2</sub>O<sub>2</sub> as the cathode,\nCSPE-10LLZTO as the electrolyte and separator, and Li metal as the\nanode, delivering approximately 140 mAh/g of capacity. Differential\nscanning calorimetry measurements on CSPE-<i>x</i>LLZTO\nshowed high miscibility and the elimination of crystallinity. Raman\nspectroscopy revealed uniformity in the structure. These findings\ndemonstrate the capability of the CSPEs to develop high-voltage solid-state\nlithium metal batteries.