Confined Reconstruction of Thiospinels Toward Stable Li-CO₂ Batteries

Oxidative reconstruction of thiospinel catalysts is well recognized as a common phenomenon in Li-CO₂ batteries, and the oxidation state of catalysts after reconstruction is known to be decisive for battery performance. However, the underlying mechanism of this correlation remains unclear, making it challenging to achieve a thiospinel catalysts that are active and invulnerable to restructuring in Li-CO₂ batteries. Here, the confined reconstruction of NiCo₂S₄ during battery operation is achieved via a mild oxidation strategy and the mechanism for the improved durability is revealed. Operando X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations reveal that the oxygen substitution creates a mixed O/S coordination environment for metal atoms (Co and Ni) in NiCo₂S₄ and larger metal-sulfur bond energy. The resulting strong metal-sulfur interaction can stabilize the sulfur atoms and thereby enhance the structural durability against the oxidative reconstruction. Thus, the mild oxidation affords NiCo₂S₄ cathode possessing excellent catalytic activities (high discharge capacity of 6906.8 µA h cm^-2) and activity retention for over 2000 h. The mild oxidation principles proposed here provide a generalizable strategy for the design of stable electrocatalyst materials.