Engineering the pore structure in phenolic resin-derived hard carbon via CO2-assisted carbonization for enhanced sodium storage

Abstract

Hard carbon (HC) is an attractive anode for sodium-ion batteries (SIBs), but its practical application has been hindered by low reversible capacity and initial coulombic efficiency (ICE). In this study, we propose a CO₂-assisted carbonization strategy based on a tunable phenolic resin as the precursor. The carbonization process can be governed by a two-step process, CO₂-induced pore opening followed by carbon skeletal reorganization, promoting the formation of well-controlled closed micropores and improved surface chemistry. Structural and electrochemical characterization studies further demonstrate that such modification greatly enhances sodium storage performance. The optimized HC anode exhibited a high initial capacity of 305.8 mAh g⁻¹ and an ICE of 95.6% at 30 mA g⁻¹. These values are much higher than those for the traditional control (230.9 mAh g⁻¹, 86.16%). After 500 cycles at 1 A g⁻¹, it also retained 90.02% of its capacity. This work provides an efficient and controllable route for designing high-performance SIB anodes and offering new application potential of phenolic resin-based carbons in sustainable electrochemical energy storage.