Hybrid electrolytes for solid-state lithium batteries: Challenges, progress, and prospects

Solid-state lithium batteries (SSLBs) based on solid-state electrolytes (SSEs) are considered ideal candidates to overcome the energy density limitations and safety hazards of traditional Li-ion batteries. However, few individual SSEs fulfill the standard requirements for practical applications owing to their poor performance. Hybrid electrolytes, which rationally integrate the benefits of single inorganic solid electrolytes (ISEs) and solid polymer electrolytes (SPEs) as well as achieve sufficiently high ionic conductivity, low interfacial impedance, and high electrode stability, have attracted significant interest for use in SSLBs. In this review, we describe the chronological progress of solid electrolytes as well as the properties of and challenges associated with single ISEs, SPEs, and hybrid electrolytes. State-of-the-art strategies for overcoming the inherent challenges of hybrid electrolytes, including insufficient ionic conductivity; undesirable electrochemical, thermal, and mechanical properties; and large electrolyte-electrode interfacial impedances, are also summarized. Finally, advanced computational techniques, including density functional theory calculations, ab initio molecular dynamics simulations, and machine-learning-assisted simulation strategies, which complement experimental systems, are discussed. The challenges and future technological perspectives associated with hybrid electrolytes for practical energy-storage systems are also highlighted.