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.