Nanofiber-Based Composite Solid Electrolytes for Solid-State Batteries: from Fundamentals to Applications

Recent advancements in next-generation rechargeable batteries have focused on solid-state batteries (SSBs) due to their promising potential for improved energy density and safety. Among the various types of solid electrolytes, composite solid electrolytes (CSEs), composed of fillers and salts dispersed within a polymer matrix, have gained significant attention for their balanced properties of ionic conductivity and stability toward both electrodes, making them more suitable for practical SSB applications. In CSEs, the relationship between structure, properties, and performance is crucial. Unfortunately, conventional CSEs are still limited by randomly distributed fillers and agglomeration phenomena, which may impede ion transportation. Nanofiber fillers, characterized by their long-range structure, high surface area-to-volume ratios, and high aspect ratios, have the potential to significantly enhance CSE properties. Furthermore, they can shorten the ion-migration pathway and be aligned in a single direction. In this review, current technologies related to nanofiber-based CSEs are summarized. Typically, recent strategies for nanofiber structural design and synthesis, from principles to practical applications, are systematically reviewed. Subsequently, promising approaches to implementing nanofiber-based CSEs in SSBs with superior electrochemical performance and cyclability are discussed. Thus, this review provides a comprehensive overview of the state-of-the-art nanofiber-based CSEs for high-performance SSBs, which have the potential to safely accelerate the development of next-generation rechargeable batteries.