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• Roasting tests of all-solid-state lithium-ion batteries (ASS-LIBs) were performed. • The chemical speciation changes of the ASS-LIBs caused by roasting were determined. • The metals showed complicated reaction paths owing to O 2 , S, P, and C coexistence. • The roasting parameters need to be accurately controlled for high metal recovery. All-solid-state lithium-ion batteries (ASS-LIBs) are expected to replace current liquid-based LIBs in the near future owing to their high energy density and improved safety. It would be preferable if ASS-LIBs could be recycled by the current recycling processes used for liquid-based LIBs, but this possibility remains to be determined. Here, we subjected an ASS-LIB test cell containing an argyrodite-type solid electrolyte (Li 6 PS 5 Cl) and nickel–manganese–cobalt-type active material (Li(Ni 0.5 Mn 0.3 Co 0.2)O 2) to roasting, a treatment process commonly used for recycling of the valuable metals from liquid-based LIBs, and investigated the changes in chemical speciation. Roasting was performed at various temperatures (350–900 °C), for various times (60–360 min), and under various oxygen fugacity (air or O 2) conditions. The chemical speciation of each metal element after roasting was determined by sequential elemental leaching tests and X-ray diffraction analysis. Li formed sulfates or phosphates over a wide temperature range. Ni and Co followed very complicated reaction paths owing to coexistence of S, P, and C, and they formed sulfides, phosphates, and complex oxides. The optimum conditions for minimizing formation of insoluble compounds, such as complex oxides, were a roasting temperature of 450–500 °C and a roasting time of 120 min. The results indicated that although ASS-LIBs can be treated by the same roasting processes as those used for current liquid-based LIBs, the optimal roasting conditions have narrow ranges. Thus, careful process control will be needed to achieve high extraction percentages of the valuable metals from ASS-LIBs. [ABSTRACT FROM AUTHOR]