A critical review on composite solid electrolytes for lithium batteries: Design strategies and interface engineering

The rapid development of new energy vehicles and 5G communication technologies has led to higher demands for the safety, energy density, and cycle performance of lithium-ion batteries as power sources. However, the currently used liquid carbonate compounds in commercial lithium-ion battery electrolytes pose potential safety hazards such as leakage, swelling, corrosion, and flammability. Solid electrolytes can be used to mitigate these risks and create a safer lithium battery. Furthermore, high-energy density can be achieved by using solid electrolytes along with high-voltage cathode and metal lithium anode. Two types of solid electrolytes are generally used: inorganic solid electrolytes and polymer solid electrolytes. Inorganic solid electrolytes have high ionic conductivity, electrochemical stability window, and mechanical strength, but suffer from large solid/solid contact resistance between the electrode and electrolyte. Polymer solid electrolytes have good flexibility, processability, and contact interface properties, but low room temperature ionic conductivity, necessitating operation at elevated temperatures. Composite solid electrolytes (CSEs) are a promising alternative because they offer light weight and flexibility, like polymers, as well as the strength and stability of inorganic electrolytes. This paper presents a comprehensive review of recent advances in CSEs to help researchers optimize CSE composition and interactions for practical applications. It covers the development history of solid-state electrolytes, CSE properties with respect to nanofillers, morphology, and polymer types, and also discusses the lithium-ion transport mechanism of the composite electrolyte, and the methods of engineering interfaces with the positive and negative electrodes. Overall, the paper aims to provide an outlook on the potential applications of CSEs in solid-state lithium batteries, and to inspire further research aimed at the development of more systematic optimization strategies for CSEs.