Constructing ultramicropore structures in hard carbon via low-temperature force-field-induced esterification reactions for enhancing sodium storage

Abstract

Hard carbon (HC) with an ultramicropore structure has emerged as a promising material for sodium-ion batteries. However, it is still a challenge to fabricate high-performance ultramicropore structures at low temperatures. Herein, low-temperature (900 °C) force-field (20 MPa) induced esterification reactions were proposed to prepare HC rich in ultramicropores (0.4–0.7 nm). The force field promotes the esterification reaction between carboxyl and hydroxyl groups to form OC–O bonds, inducing carbon layer bending. Simultaneously, the force field accelerates the growth and stacking of carbon layers to construct abundant ultramicropores. HC-20 exhibits a large pore volume and a small entrance diameter, which not only increases reversible capacity but also limits the contact between solvated sodium ions and pores. The optimized HC showed an excellent ICE of 82.2% and a high reversible capacity of 316.2 mA h g⁻¹, as well as 98.0% capacity retention at 25 mA g⁻¹ after 100 cycles. Besides, the HC-20//NFM full cell exhibits a high energy density of 231.5 Wh kg⁻¹ and excellent cycle stability. This study provides a novel strategy for preparing HC rich in ultramicropores at low temperature, offering guidance for research on high-performance HC materials.