Influence of the operating temperature on the ageing and interfaces of double layer polymer electrolyte solid state Li metal batteries

Solid-state lithium metal batteries (SSLMBs) are considered an auspicious technology to develop high energy density and safe energy storage devices. The double layer polymer electrolyte (DLPE) is a rational approach for engineering high-performance SSLMBs addressing electrolyte requirements with specifically designed polymers at the positive electrode and as separator. In this work, SSLMBs were assembled with poly(propylene carbonate) (PPC), offering stability toward oxidation at the positive electrode, and a gel polymer electrolyte with polyethyleneglycol dimethylether (PEGDME) as separator, offering high ionic conductivity at low temperature and sufficient interfacial stability with Li metal. The electrochemical properties and performance of cells with LiFePO4 and Li[Ni0.6Mn0.2Co0.2]O2 positive electrodes are thoroughly investigated as function of the operating temperature by using a host of characterization techniques. High-voltage cells with an areal capacity of 0.7 mAh·cm−2 cycled at 40 °C exhibit a higher capacity retention than the cells cycled at 70 °C. To understand such differences, a three-electrode setup is applied to discriminate anodic processes from cathodic as function of the temperature. We elucidate the ageing and interfacial evolution for DLPE cells with gel polymer electrolytes paving the way for building performance solid state batteries.