<p>Mechanical stability is critically essential in the design of thermoelectric devices. In this study, we employed first-principles calculations based on density functional theory to investigate the failure mechanisms at the CoSb₃/Ni interface. Our findings reveal that the CoSb₃(100)/Ni(100) and CoSb₃(100)/Ni(111)_1 configurations are favorable interface structures. The ideal tensile strength of the CoSb₃/Ni interface is markedly lower than that of bulk CoSb₃, which can be attributed to structural rearrangements near the interface that weaken the strength of the Co–Sb bonds. Interface failure occurs in CoSb₃, where covalent Sb–Sb bonds exhibit a tendency to soften prior to the ionic Co–Sb bonds due to their comparatively lower rigidity. Consequently, the breakage of the Co–Sb bonds leads to interface failure. Structural failure at both single-layer Sb_CoSb₃(100)/Ni(100) and single-layer Sb_CoSb₃(100)/Ni(111)_1 interfaces results from ruptures in intermediate Co–Sb bonds in CoSb₃, whereas failures at double-layer Sb_CoSb₃(100)/Ni(100) and double-layer Sb_CoSb₃(100)/Ni(111)_1 interfaces stem from fractures in the uppermost Co–Sb bonds. This behavior is primarily driven by atomic rearrangements near the single-layer Sb_CoSb₃ interface, which promote bond formation between Sb–Ni and Co–Ni, thereby enhancing stability within the superstructure of CoSb₃. This study will provide a theoretical basis for the interface design of thermoelectric devices.</p>