Shielding Mn³⁺ Disproportionation with Graphitic Carbon-Interlayered Manganese Oxide Cathodes for Enhanced Aqueous...

Manganese dioxide (MnO₂) materials have recently garnered attention as prospective high-capacity cathodes, owing to their theoretical two-electron redox reaction in charge storage processes. However, their practical application in aqueous energy storage systems faces a formidable challenge: the disproportionation of Mn³⁺ ions, leading to a significant reduction in their capacity. To address this limitation, the study presents a novel graphitic carbon interlayer-engineered manganese oxide (CI-MnO_x) characterized by an open structure and abundant defects. This innovative material serves several essential functions for efficient aqueous energy storage. First, a graphitic carbon layer coats the MnO_x molecular interlayer, effectively inhibiting Mn³⁺ disproportionation and substantially enhancing electrode conductivity. Second, the phase variation within MnO_x generates numerous crystal defects, vacancies, and active sites, optimizing electron-transfer capability. Third, the flexible carbon layer acts as a buffer, mitigating the volume expansion of MnO_x during extended cycling. The synergistic effects of these features result in the CI-MnO_x exhibiting an impressive high capacity of 272 mAh g^-1 (1224 F g^-1) at 0.25 A g^-1. Notably, the CI-MnO_x demonstrates zero capacity loss after 90 000 cycles (≈3011 h), an uncommon longevity for manganese oxide materials. Spectral characterizations reveal reversible cation intercalation and conversion reactions with multielectron transfer in a LiCl electrolyte.