Pore Mouth Engineering: An Insulating Strategy to Dictate Interfacial Chemistry in Hard Carbon Anodes

While the pore mouth (PM) of hard carbon (HC) is known to be critical for performance, the specific impact of its properties (e.g., size, conductivity, and role in electrolyte decomposition) on key metrics like initial Coulombic efficiency (ICE), capacity, and rate capability remains poorly understood. Herein, we originally clarified this critical but poorly understood issue. By sealing the conductive 5.23 Å PM of commercial HC with an insulating microporous glassy metal-organic framework (MOF glass), we engineered a 2.98 Å, nonconductive MOF PM that fundamentally alters ion transport and interfacial chemistry. This tailored structure promotes Na⁺ pre‑desolvation, facilitates a highly aggregated electrolyte configuration, and suppresses parasitic decomposition-collectively fostering a superior inorganic‑rich solid-electrolyte interphase (SEI). As a result, the modified HC (1G-HC) exhibits a largely enhanced ICE of 87.8% and a capacity of ∼400 mAh/g, alongside excellent cycling stability at high rate (∼12 C, 80% capacity retention after 3000 cycles) and good low-temperature performance of -25°C (∼5 C, 79.3% capacity retention over 500 cycles). In a practical 3.19 Ah-level 1G-HC||Na₃V₂(PO₄)₃ pouch cell, it achieves 108 mAh/g with 92.0% retention over 160 cycles. This work establishes PM design as a pivotal strategy for advancing sodium-ion battery anodes.