 Solid-state lithium batteries, SSLBs, with composite polymer electrolytes, CPEs offer excellent energy density and safety compared to conventional liquid electrolytes. The key components of CPEs include polymer matrices and fillers, which can be tailored to optimize ionic conductivity and reduce interfacial impedance. Ionic conductivity is influenced by both macroscopic and microscopic factors, including the polymer structure, ion mobility, and carrier concentration. Additionally, the electrode-electrolyte interface must be optimized to ensure efficient ion transport. By understanding these factors, it is possible to develop CPEs with improved performance. This article was authored by Shwaying Yang, Jiaxian Lu, Nan Biao Pei, and others.