Microstructure reconstruction via confined carbonization achieves highly available sodium ion diffusion channels in hard carbon

Abstract

Hard carbon is considered as the main candidate negative electrode material for sodium-ion batteries (SIBs) due to its high stability and electrochemical performance. However, the complex carbon structure and composition of hard carbon are difficult to achieve precise control during the preparation process, which leads to difficulties in accurately determining the attribution of electrochemical behavior. Here, we propose a confined carbonization strategy to achieve microstructure reconstruction of hard carbon, characterized by the anchoring of polymers in the mesopores of porous carbon to generate ordered carbon structures at high temperatures. The stacking of ordered carbon on micropores in porous carbon achieves the transition from exposed pores to closed pores (nano cleithral pores). Through mechanism detection, it is found that the ordered carbon structure provides sub nanochannels for sodium ion migration, which contributes to high slope capacity. In addition, the nano cleithral pores are sites filled with sodium ions and provide high plateau capacity. Benefiting from theses available sodium ion transport channels, carbon materials have achieved a transition from surface-controlled process to diffusion-controlled process in the sodium storage process via confined carbonization. The as-prepared carbon delivers a superior capacity of 356.2 mAh g^–1 (215.6 mAh g^–1 for plateau capacity) at 20 mA g^–1 with excellent rate and cycling performance. This work reveals the correlation between structure and electrochemical performance for carbon electrode, providing profound guidance for the precise preparation of high-performance carbon materials.