A Robust Mn-Based Metal–Organic Framework Cathode with Long-Cycle-Life Enabled by Metal Valence Stability and Hydrogen Bond Networks for High-Performance Sodium-Ion Batteries

Abstract

Sodium-ion batteries (SIBs) hold significant potential for sustainable energy storage but face challenges in cathode material stability and capacity. Metal–organic frameworks (MOFs) are promising owing to their tunable structures and redox-active sites but often suffer structural degradation from metal ion valence changes during cycling. Here, a novel manganese-based MOF (Mn-PTO) is introduced, representing a new class of MOFs specifically engineered for enhanced stability and performance in SIBs. Mn-PTO addresses valence changes and structural degradation through two synergistic mechanisms. First, it ensures valence stability by confining redox activity to the ligand's carbonyl groups, stabilizing Mn ions in the divalent state, and preventing structural collapse. Second, its hydrogen bond network reinforces structural integrity and mitigates stresses from repeated ion insertion and extraction. These innovations enable Mn-PTO to deliver exceptional electrochemical performance, including remarkable cycling stability, maintaining a capacity of 118 mAh g⁻¹ over 7,000 cycles at 5 A g⁻¹. This performance surpasses most reported organic electrode materials. Additionally, Mn-PTO exhibits an impressive rate capability of 124 mAh g⁻¹ at 20 A g⁻¹. These results firmly establish Mn-PTO as a groundbreaking cathode material, offering a robust and durable solution to the limitations of traditional MOF-based systems.