1 Department of Chemical and Materials Engineering, Concordia University, Montreal, QC, H3G 1M8, Canada.
2 Research Center for All-Solid-State Battery, Institute of Integrated Research, Institute of Science Tokyo, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8502, Japan.

All-solid-state lithium batteries (ASSBs) outperform lithium-ion batteries (LIBs) in safety, energy density, and thermal stability. Their performance depends on high ionic conductivity, chemical/physical stability, and scalable manufacture of solid electrolytes (SEs). This study compares sulfide- and halide-based SEs, two promising next-generation energy storage options. Soft mechanics permit sulfides with high room-temperature conductivity, low activation energies, and processability, but high-voltage cathode instability, moisture sensitivity, and probable hydrogen sulfide (H₂S) release. Market prospects are favorable as the industry improves crystallinity and elemental substitution, especially for automotive cells. Chloride-based halides are more environmentally friendly, have adequate voltage stability, and can be used with oxide cathodes without coatings. Despite traditionally low conductivity, high-entropy, and oxyhalide chemistries currently reach 10 mS cm^-1, and scalable solvent syntheses and dry processing are driving adoption. Mechanical compliance and the use of rare elements (In, Sc) continue to cause integration and cost issues. Composition, microstructure, synthesis techniques, interfacial behavior, mechanical characteristics, and scalability are evaluated. The findings show sulfides have better conductivity and Li-metal compatibility, but halides are more stable and manufacturable, recommending hybrid or tailored material selection based on application. Optimizing ASSB systems requires complementary sulfide/chloride utilization due to halides' mechanical constraints.