Solid Polymer Electrolyte with 4.8 V Stability for High-Voltage Lithium Metal Batteries with a 523 Wh kg –¹ Prototype Demonstration

Solid polymer electrolytes offer a promising pathway toward safe, high-energy solid-state lithium metal batteries. However, their practical deployment remains limited by insufficient ionic conductivity, narrow oxidative stability windows, and poor interfacial compatibility with metal anodes. In particular, conventional polymer systems such as PEO typically operate below ∼3.8 V and cannot sustain high-voltage cathode chemistry. In this work, a solid polymer electrolyte based on a proprietary carbonate–fluorinated methacrylate copolymer PIRION-F (denoted as PCFMA) is developed and systematically evaluated. Comprehensive FTIR, X-ray diffraction, differential scanning calorimetry, TGA, and scanning electron microscopy analyses confirm the amorphous nature of the polymer, its robust thermal stability, and the dense microstructure of the solid electrolyte membrane. The PCFMA exhibits outstanding LiTFSI solubility, high ionic conductivity (0.1 mS cm–1 at room temperature and 1.2 mS cm–1 at 70 °C), and a wide oxidative stability window up to ∼4.8 V vs Li+/Li, enabling operation with high-voltage cathodes. Li symmetric cells display ultrastable cycling for over 4500 h with low polarization. All-solid-state Li//NCM622 and high-voltage Ni-rich cells further show reversible charge/discharge behavior and strong capacity retention during extended cycling at room temperature. To contextualize broader manufacturability, an independent multilayer pouch-cell prototype fabricated by a technology startup collaborator delivers a cell-level energy density of 523 Wh kg–1. Collectively, these results demonstrate the strong potential of PCFMA-based solid electrolytes for next-generation high-voltage solid-state lithium metal batteries.