Melt-carbonization of liquid metal organic frameworks reconfigured hard carbon surface with boosted sodium storage

Hard carbon (HC) is the most widely used sodium battery anode material for commercialization. However, the exposed unsaturated carbon structure triggers irreversible electrolyte decomposition in initial cycles and causes low initial coulombic efficiency (ICE). Moreover, the solvated sodium ions occupy extra active sites and lead to low specific capacity. Herein, we developed a melt-carbonization coating strategy via the solid-liquid conversion of ZIF-62 to construct a liquid MOF-derived carbon/HC composite. The liquid ZIF-62-derived carbon layer on HC reduces side reactions and desolvates sodium ions by sealing exposed open pores, resulting in higher ICE and boosted Na⁺ storage. Consequently, the designed anode delivers an enhanced reversible capacity from 228.8 to 302.1 mAh g⁻¹ and ICE from 67.1% to 81.0%. At a higher current density of 2 C, the capacity was improved from 31.2 to 89.8 mAh g⁻¹. When coupled with Na₃V₂(PO₄)₃ cathode, the full cell delivered a capacity retention of 77.1% after 600 cycles at 0.5 C and a high capacity of 67.5 mAh g⁻¹ even at a high rate of 6.0 C.