Metal–organic framework glass enables durable sodium-ion storage for hard carbon negative electrodes

Hard carbon negative electrodes, owing to their abundant precursors and low operating potential, are promising candidates for sodium-ion batteries. However, sluggish desolvation kinetics and unstable electrode–electrolyte interfaces hinder their practical deployment. Here we report a melt-coating strategy to encapsulate hard carbon particles with a metal–organic framework glass. The resulting glass coating contains sub-nanometer channels that lower the desolvation activation energy, accelerate sodium-ion transport, and induce a thin, anion-derived solid electrolyte interphase rich in NaF during cycling. The optimized interface promotes the formation of quasi-metallic sodium clusters within the closed pores of hard carbon, activating a high-capacity sodium storage mechanism. Consequently, the glass-coated hard carbon delivers a reversible capacity of 462.2 mAh g−1, cycling stability of 89.1% capacity retention after 4000 cycles at 1 A g−1 and 95.3% capacity retention after 8000 cycles at 2 A g−1, and high-rate capability. This work offers insights into interfacial design strategies for durable sodium-ion storage in hard carbon negative electrodes. Slow ion transport and unstable interfaces limit the performance of hard carbon negative electrodes for Na-ion batteries. Here, authors develop a melt-coated metal-organic framework glass layer on hard carbon to accelerate Na+ transport and enable high-capacity storage via quasi-metallic sodium clusters.