Oxygen-bridging and air-etching: Advanced pore-regulation engineering in hard carbons for optimized low-voltage plateau capacity

Abstract

The intrinsic sodium storage performance of hard carbons is fundamentally governed by its structure attributes, which are primarily shaped by the precursor material. Therefore, a direct manipulation of precursors at the molecular level offers considerable flexibility in engineering hard carbon architectures. This study introduces a straightforward and effective pre-carbonization approach to modulate the molecular configuration and functional groups within celluloses, employing both oxygen-bridging and air-etching to stimulate the development of closed pores during carbonization. These closed pores not only facilitate the transport of sodium ions but also serve as active sites for sodium storage, resulting in a hard carbon with an impressive specific capacity of 421.1 mA h g⁻¹ and a substantial low-voltage plateau capacity of 312.8 mA h g⁻¹. Extensive research has elucidated the formation mechanism of closed pores as well as its correlation with low-voltage plateau capacity, which will greatly forward the rational design of high-performance hard carbon anodes for next-generation sodium ion batteries.