Regulating the pseudo graphitic layers to generate closed pores in biomass derived hard carbon anode for ultrafast-charging sodium ion batteries

Abstract

Biomass-derived hard carbon has emerged as a promising anode material for sodium-ion batteries (SIBs) due to its superior electrochemical performance and low cost. However, the poor initial coulombic efficiency and high-rate performance of hard carbon in SIBs still needs to be improved, especially for the fast-charging demand in the future. Here, we systematically investigate the structural evolution of closed pores and develop a simple two-step method to fabricate high-performance hard carbon from wood pulp. Microstructural analysis reveals that closed pores in hard carbon can be generated from longer and ordered graphitic layers and provide high plateau capacity and superior high-rate property. The optimized hard carbon anode delivers outstanding electrochemical properties: a high reversible capacity of 315.1 mAh g⁻¹ at 0.1C, superior ICE of 90.3 %, and remarkable rate capability (250.8 mAh g⁻¹ at 20C). Experimental analysis and density functional theory (DFT) calculations demonstrated that these closed pores enhance rate performance by improving electronic conductivity and reducing sodium diffusion barriers. Additionally, the excellent electrochemical performance of assembled pouch cells displays the great potential for practical application. This work provides a facile, scalable and cost-effective strategy for producing high performance hard carbon anode materials for fast-charging SIBs.