Recent progress on solid-state hybrid electrolytes for solid-state lithium batteries

Lithium batteries are promising energy storage systems for applications in electric vehicles. However, conventional liquid electrolytes inherit serious safety hazards including leakage, ignition and even explosion upon overheating. Solid-state electrolytes (SSEs) are considered as the ultimate solution to these safety concerns because of their excellent thermal and electrochemical stabilities. Nevertheless, few individual SSE has reached practical application standards due to incomprehensive performance. High ionic conductivity, low interfacial resistance, and high stability towards electrodes are difficult to achieve simultaneously with an individual SSE. Hybrid electrolytes rationally combining two or more types of SSEs with complementary advantages are promising for building feasible solid-state lithium batteries (SSLBs). Coupling desired soft electrolyte and stiff inorganic SSEs can ensure good electrode wettability, high ionic conductivity, and high mechanical strength to prevent lithium dendrite formation at the same time. In this review, comprehensive perspectives from the broad context of the importance of hybrid electrolytes to subtle design concepts are summarized. This review not only covers the introductory of classifications, synthesis methods, and ionic conductivity mechanism, but also crystallizes the strategies for enhancing the ionic conductivity of hybrid electrolyte, the understandings on the interfacial challenges of the electrolyte/electrolyte and electrolyte/electrode interfaces, and the strategies for building feasible SSLBs with different hybrid electrolyte combinations.