Recent advances in solid-state composite polymer electrolytes with active and inactive additives

Composite polymer electrolytes (CPEs), composed of a polymer matrix with organic or inorganic fillers, have demonstrated significant potential for practical applications. However, the exact mechanisms through which various fillers enhance ion transport remain unclear. This review provides a comprehensive overview of the current state-of-the-art in CPEs, emphasizing design strategies and synthesis methods that utilize active and inactive fillers such as NASICON-type, garnet-type, and oxides. We explore their contributions to enhancing ionic conductivity and forming stable interfaces with electrodes. Additionally, we discuss future strategies and perspectives that could guide the advancement of CPE technology, outlining potential directions for accelerating the development of composite solid polymer electrolytes (CSPEs). By classifying fillers according to their Li+ transport mechanisms, this work offers fresh insights and guidelines for optimizing solid composite electrolytes. © 2026 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license. http://creativecommons.org/licenses/by/4.0/