A brief review of engineering “balance” challenges for electrolytes of all-solid-state lithium-metal battery

Solid-state electrolytes are promising in enhancing safety and energy density of lithium-metal batteries. Significant progress made in recent years calls for a fresh perspective on the electrolyte development to guide future research. After thorough investigation and analysis, we propose that the current bottleneck lies in property “balance” to achieve practical applications of solid electrolytes. In this review, we present the state art of inorganic solid electrolytes, polymer electrolytes, and hybrid solid electrolytes, and discuss the strategies to “balance” the properties of those electrolytes especially the advanced preparation methods and sophisticated structural designs. Firstly, we provide an overview of different types of solid-state electrolytes, highlighting their potential benefits. Then we delve into their separated challenges faced by the proposed paired properties with correlation. For inorganics, we explore the balance between cost and conductivity, interphase e^- and Li⁺ transportation, thickness and mechanical property. As for polymers, we examine the balance between Li⁺ transference number and conductivity, mechanical property and conductivity, anodic and cathodic stability. Furthermore, we summarize effective strategies for constructing hybrid solid electrolytes with low interfacial resistance and high Li⁺ conductivity. Lastly, we offer comments and expectations on the future development of solid electrolytes based on “balance” strategy.