Sulfide solid-state electrolytes (SSEs) emerge as a promising candidate for replacing conventional liquid electrolytes in all-solid-state lithium batteries (ASSLBs). With their inherent advantages of high ionic conductivity, low activation energy, and good mechanical properties, sulfide SSEs hold a great potential for achieving high safety and energy density in next-generation energy storage devices. Unfortunately, the electrolyte layers or solid-state films of sulfide-based ASSLBs typically require a thickness of greater than 100 μm to prevent lithium dendrite penetration and SSEs layer fracture, leading to short circuits during battery cycling. Ultra-thin sulfide SSEs films have attracted recent attention. Compared to conventional thick films, ultra-thin sulfide SSEs films can significantly reduce the non-active material content in batteries, thereby improving energy density. They can also enhance Li⁺ transport efficiency, lower electrolyte surface resistance and battery internal resistance, and improve battery cycling performance and rate performance.Some binders need to be added when the thickness of the sulfide SSEs layer is less than 100 μm, resulting in a conductivity of less than 1.0 mS/cm. Therefore, the development of ultra-thin SSEs films with high ionic conductivity, high strength, high toughness, and based on sulfide electrolytes is a key direction for high-energy-density sulfide ASSLBs. This review represents recent development on sulfide SSEs, focusing on material development, synthesis methods, film preparation, binder selection, densification strategies, and interface stability.This review introduces the significant advancements of sulfide SSEs in recent years. Various types of sulfide SSEs with superior properties are developed, including glass, glass-ceramics, thio-LISICON, LGPS, and argyrodite-type materials. These materials exhibit diverse structures and properties, and the ion conductivity and stability of sulfide SSEs are continuously improved through various strategies, such as component optimization, element substitution, and crystal structure engineering. Several methods exist for synthesizing sulfide SSEs, each with its advantages and disadvantages. Solid-state synthesis, mechanochemical synthesis, and liquid-phase synthesis are the most commonly used methods.Developing thin and flexible sulfide SSEs films is crucial for achieving high energy density in ASSLBs. Wet processes such as slurry casting, spin coating, and dip coating are commonly used, but can be limited by solvent compatibility and film uniformity. Dry processes like powder pressing, powder spraying, and binder fiberization offer advantages in terms of film quality and process efficiency, but require further development for large-scale production. These dry methods offer a potential for minimizing solvent effects and improving film performance via directly depositing the SSEs powder onto the substrate without solvents. The choice of binder plays a vital role in film properties. Inert binders like ethylcellulose and SBR provide good mechanical strength, but can hinder Li⁺ transport. Li⁺ conducting binders like LiTFSI and PVDF offer an improved ion conductivity, but require careful optimization of processing conditions. PTFE is a popular option for dry film fabrication due to its low percolation threshold and good mechanical properties. The selection of binder depends on the specific application requirements and the desired trade-off among ion conductivity, mechanical strength, and interface stability.Densification techniques like hot pressing and cold pressing are essential for achieving high ion conductivity and mechanical strength in sulfide SSEs films. These techniques improve the packing density and reduce the porosity of the films, leading to enhanced ion transport and mechanical properties. Also, innovative approaches like solvent-free synthesis and the use of reinforcing structures like fibers are explored to further enhance film properties and address the challenges associated with conventional wet processes. Ensuring interface stability between sulfide SSEs films and electrode materials is crucial for the battery performance. Sulfide SSEs can react with both cathode materials and lithium metal, leading to interface issues such as decreased ion conductivity, increased interface resistance, and battery capacity degradation. Strategies to address these challenges include surface modification of electrode materials, component optimization, and the use of interlayer materials like precursors of solid electrolyte interface (SEI). These approaches can improve the compatibility between sulfide SSEs and electrode materials and reduce the occurrence of interface reactions.Summary and ProspectsWhile significant progress is made in sulfide SSEs research, some challenges are related to film properties, interface stability, and large-scale production remain. Future efforts should focus on several key areas, i.e., developing new sulfide SSEs materials with higher ionic conductivity, lower activation energy, and better chemical stability through material engineering and structure optimization; optimizing particle size and morphology to achieve optimal film properties and Li⁺ transport efficiency, which can be achieved through controlled synthesis and particle size engineering techniques; exploring new techniques like solvent-free synthesis, solution processing, and additive manufacturing to improve film performance, uniformity, and scalability; developing strategies to improve interface stability between sulfide SSEs films and electrode materials, including the use of interlayer materials, surface modification, and SEI engineering techniques; and implementing efficient and cost-effective production processes to enable commercialization of sulfide SSEs for ASSLBs, which requires the development of automation, high-throughput equipment, and optimization of production parameters. ASSLBs have a potential to revolutionize the energy storage landscape via addressing these challenges and continuously advancing sulfide SSEs technology, paving a way for a sustainable future with cleaner and more efficient energy storage solutions. The development of high-performance sulfide SSEs films is crucial for achieving this vision and unlocking the full potential of ASSLBs in various applications, including electric vehicles, grid-scale energy storage and portable electronics.