Crystal Void Fraction‐Engineered Fe‐S Catalysts for Self‐Sustaining Li‐CO 2 Mars Batteries

ABSTRACT Efficient energy storage is vital for self‐sustaining Martian exploration. Li‐CO 2 batteries are promising by utilizing the Martian atmosphere (∼95% CO 2 ) as active materials. Fe‐S minerals, abundant on Mars, offer a viable candidate for cathode catalysts, yet their structural diversity necessitates a rational selection criterion. Here, we propose crystal void fraction as a governing descriptor correlating with affinity toward critical oxygen‐containing species, Li 2 CO 3 and singlet oxygen ( 1 O 2 ). Higher void fraction with decreased Fe‐S 6 octahedra packing density upshifts the d‐band center and brings the z‐containing orbitals closer to the Fermi level. Given the pronounced O‐2p z character of Li 2 CO 3 band‐edge states and the π* orbital of 1 O 2 frontier orbital, symmetry matching along surface orbitals with z‐directional components strengthens orbital coupling, correlating higher crystal void fractions with increased affinity for oxygen‐containing species. Crucially, this affinity exhibits a dual role. High void fraction promotes Li 2 CO 3 decomposition but 1 O 2 ‐induced catalyst degradation, while low void fraction exhibits the opposite tendency. Marcasite with moderate void fraction achieves an optimal balance, achieving 88% energy efficiency and 1000 h cycle life. This work establishes crystal void fraction as a predictive metric for screening suitable catalysts for achieving activity‐stability trade‐off, and provides a promising landscape for in‐situ resource utilization on Mars.