Li alloys in all-solid-state lithium batteries (ASSLBs) are crucial for enhancing the stability and performance of the anode/solid-state electrolyte (SSE) interface. ASSLBs offer higher energy density and improved safety compared to traditional lithium-ion batteries (LIBs), but their practical implementation is hindered by the instability of the anode/SSE interface. Li alloys are used in three main applications: as anodes, as interlayers, and as components within the anode. These materials help suppress side reactions, reduce Li metal intrusion, and improve interfacial contact. However, the fundamental mechanisms, practical applications, and physicochemical properties of Li alloys remain poorly understood. This review provides an in-depth analysis of the kinetics, thermodynamics, and mechanics of Li alloys, highlighting their role in ASSLBs. It also discusses the current strategies for improving interface stability and performance, emphasizing the importance of Li alloys in advancing ASSLB technology. The review concludes by summarizing the future potential of Li alloys in further developing ASSLBs. The key challenges include the instability of the anode/SSE interface, which leads to side reactions, Li metal intrusion, and high interfacial resistance. To address these issues, research focuses on improving the interfacial behavior and stability of ASSLBs. Li alloys are extensively used in various scenarios to enhance the performance and stability of ASSLBs. Despite their promising applications, the full understanding of Li alloys' functionality and working mechanisms is still lacking. This review aims to fill this gap by combining fundamental concepts with practical applications, providing insights for future research in ASSLBs.Li alloys in all-solid-state lithium batteries (ASSLBs) are crucial for enhancing the stability and performance of the anode/solid-state electrolyte (SSE) interface. ASSLBs offer higher energy density and improved safety compared to traditional lithium-ion batteries (LIBs), but their practical implementation is hindered by the instability of the anode/SSE interface. Li alloys are used in three main applications: as anodes, as interlayers, and as components within the anode. These materials help suppress side reactions, reduce Li metal intrusion, and improve interfacial contact. However, the fundamental mechanisms, practical applications, and physicochemical properties of Li alloys remain poorly understood. This review provides an in-depth analysis of the kinetics, thermodynamics, and mechanics of Li alloys, highlighting their role in ASSLBs. It also discusses the current strategies for improving interface stability and performance, emphasizing the importance of Li alloys in advancing ASSLB technology. The review concludes by summarizing the future potential of Li alloys in further developing ASSLBs. The key challenges include the instability of the anode/SSE interface, which leads to side reactions, Li metal intrusion, and high interfacial resistance. To address these issues, research focuses on improving the interfacial behavior and stability of ASSLBs. Li alloys are extensively used in various scenarios to enhance the performance and stability of ASSLBs. Despite their promising applications, the full understanding of Li alloys' functionality and working mechanisms is still lacking. This review aims to fill this gap by combining fundamental concepts with practical applications, providing insights for future research in ASSLBs.