All solid-state lithium batteries (ASSLBs) overcome the safety concerns associated with traditional lithium-ion batteries and ensure the safe utilization of high-energy-density electrodes, particularly Li metal anodes with ultrahigh specific capacities. However, the practical implementation of ASSLBs is limited by the instability of the interface between the anode and solid-state electrolyte (SSE). To mitigate this, considerable research has been dedicated to achieving enhanced stability at the anode/SSE interface. Among the current strategies for enhancing interface performance, the concept of Li-alloy materials is extensively used and well functionalized in various scenarios, including Li alloys as anodes, Li-alloy interlayers and Li alloys in the anode. Despite the notable achievements of Li-alloy materials in ASSLBs, the functionality, practicality and working mechanism of Li-alloys have not been fully elucidated. This review commences by providing an exhaustive and in-depth examination of the fundamental kinetics, thermodynamics, and mechanics, highlighting Li-alloy materials. Subsequently, through a systematic interconnection of material properties and their practical applications, we undertake a comprehensive analysis of the operative principles governing Li alloys. This analytical approach allows a thorough evaluation of the viability and utility of Li alloys within the context of ASSLBs. Finally, this review concludes by succinctly summarizing the future prospects and inherent potential of Li-alloy materials for further advancing the field of ASSLBs.