Molecular-Level Precursor Engineering Enables High Utilization of Closed Nanopores in Hard Carbon for Sodium-Ion Batteries

Abstract

Closed nanopores in hard carbon (HC) are widely regarded as the primary host for low-voltage plateau capacity in sodium-ion batteries, yet their electrochemical inactivity due to poor accessibility remains a critical bottleneck. Here we report a molecular-templating liquid-phase carbonization strategy that engineers biomass precursors with sodium acetate to unlock closed-pore utilization. Sodium acetate simultaneously enriches oxygen-containing functionalities and generates molecular-scale pre-pores during liquid-phase carbonization, enabling controllable closed-pore density and size in bamboo-derived HC. Upon high-temperature treatment, these pre-pores evolve into percolating mesoporous channels that bridge otherwise isolated closed nanopores, thereby constructing an efficient ion-transport network and markedly shortening the solid-state diffusion distance. As a result, the closed-pore utilization reaches 86%, delivering a substantially enhanced plateau contribution together with an expanded interlayer spacing (d₀₀₂ = 0.391 nm). The optimized HC exhibits a high reversible capacity of 369 mAh g^-1 at 0.1C with 88.9% initial Coulombic efficiency, retains ~85% capacity after 500 cycles at 2 C, and maintains 257 mAh g^-1 at -20 °C. This work establishes a molecular-level precursor-engineering route to transform closed pores from “present” to “accessible”, providing a general design principle for high-energy HC anodes.