Electrochemical Activation–Driven Micropore Expansion Toward High–Capacity Hard Carbon Anodes for Advanced Li–Ion Batteries

ABSTRACT Hard carbon (HC) is gaining renewed attention as an anode material for lithium‐ion batteries (LIBs) due to its unique structural characteristics, despite the current market dominance of graphite. This study demonstrates an electrochemical approach to modify the internal structure of HC through electrochemical Na‐treatment, which enhances its Li storage capability. While conventional modification methods require high energy input or complex processing steps, our approach enables structural regulation directly at the electrode level. Through Raman and XRD analyses, we confirm that the HC framework remains structurally stable during Li‐treatment, while Na‐treatment induces irreversible amorphization associated with Na storage in internal pores. Electrochemical evaluation in Li‐ion half cells reveals that Na‐treated HC electrodes exhibit significantly improved performance, delivering approximately 37% higher charging capacity and 24% higher discharge capacity compared to Li‐treated HC electrodes. SAXS analysis clarifies that decreasing the Na‐treatment charged cut‐off voltage promotes increased Na filling of internal pores, resulting in pronounced pore expansion. The Na‐treated HC electrodes maintain a discharge capacity approximately 50 mAh g − 1 higher than Li–treated HC electrode even after 100 cycles at 0.05 C, demonstrating the effectiveness of electrochemical structural modification strategy for next‐generation LIB anodes.