High-Safety Composite Solid Electrolyte Based on Inorganic Matrix for Solid-State Lithium-Metal Batteries

Composite solid electrolytes (CSEs) combine the advantages of polymer electrolytes and inorganic ceramic electrolytes, which have attracted increasing attention for solid-state lithium-metal batteries. However, the most studied polymer-based CSEs are easily ignited and can be penetrated by lithium (Li) dendrite, leading to safety issue. Herein, we report CSEs with very high inorganic ceramic loadings of >90% by a cold sintering method at a low temperature of 200°C. The ceramic-based CSEs show better safety and mechanical properties than polymer-based CSEs. The Li symmetric cell–symmetric Li-ion cells have the same material as the positive and negative electrode [when cells are assembled one would already contain lithium and the other would not]–using the ceramic-based CSE delivers a stable cycling performance of over 550 h at the current density of 0.3 mA/cm2. More importantly, according to the electrochemical impedance spectroscopy (EIS), Debye diagram, and power law equation, the Li-ion conduction mechanism in CSEs is systematically investigated. Using a modified brick layer model, the conductivities for Li-ions transport parallel with ceramic/polymer interfaces are calculated to be five orders of magnitudes higher than that perpendicular to the interfaces. This work provides a new analytical method for inorganic matrix based CSEs for high-safety batteries and conducts an in-depth research on the ion conduction mechanism.