Recent advances and future perspectives of Ruddlesden–Popper perovskite oxides electrolytes for all-solid-state batteries

All-solid-state batteries equipped with solid-state electrolytes (SSEs) have gained significant interest due to their enhanced safety, energy density, and longevity in comparison to traditional liquid organic electrolyte-based batteries. However, many SSEs, such as sulfides and hydrides, are highly sensitive to water, limiting their practical use. As one class of important perovskites, the Ruddlesden–Popper perovskite oxides (RPPOs), show great promise as SSEs due to their exceptional stability, particularly in terms of water resistance. In this review, the crystal structure and synthesis methods of RPPOs SSEs are first introduced in brief. Subsequently, the mechanisms of ion transportation, including oxygen anions and lithium-ions, and the relevant strategies for enhancing their ionic conductivity are described in detail. Additionally, the progress made in developing flexible RPPOs SSEs, which are critical for flexible and wearable electronic devices, has also been summarized. Furthermore, the key challenges and prospects for exploring and developing RPPOs SSEs in all-solid-state batteries are suggested. This review presents in detail the synthesis methods, the ion transportation mechanism, and strategies to enhance the room temperature ionic conductivity of RPPOs SSEs, providing valuable insights on enhancing their ionic conductivity and thus for their practical application in solid-state batteries.