Recent advances of composite electrolytes for solid-state Li batteries

All-solid-state lithium batteries (ASSLBs) are recognized as high energy density batteries system without safety issues within the next generation of batteries. The development of solid electrolytes is the crucial step of ASSLBs. The composite electrolyte has stable physical and electrochemical characteristics, and its comprehensive performance surpasses the individual solid electrolyte, bringing unique vitality to the solid electrolyte. However, their intrinsic weakness limits the development of composite electrolytes. In this review, we provide a comprehensive and in-depth understanding of the challenges and opportunities of composite electrolytes, with special focus on mechanisms of ion transport, nanostructure design towards high ionic conductivity, interfacial issues within electrolytes and electrodes. Furthermore, future development is prospected, which can shed light on researchers in this field and accelerate the industrial production of composite electrolytes.