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Construction of closed pores by optimizing the length of the carbon layer is considered the most effective way to improve the electrochemical performance of hard carbon in sodium-ion batteries. However, the lack of understanding of the carbon layer growth mechanism limits the development of hard carbon. Here, Mn2+ is introduced during the pyrolysis process to control the length of the carbon layer of hard carbon. It is demonstrated that the introduction of the transition metal facilitates electron transfer to C─O bonds and thereby promotes homolytic cleavage of chemical bonds to generate free radicals. The simple aromatic radicals generated from oxygen-centered radicals, coupled with those directly derived from biomass, synergistically accelerate the formation of well-developed carbon layers, which improve the initial coulombic efficiency and plateau capacity. The optimal sample has a reversible capacity of 325 mAh g-1 and a competitive ICE of 92.7%. Pouch cell batteries exhibit a capacity retention of 280 mAh g-1 after 200 cycles and a capacity retention rate of 93.3% at 100 mA g-1. This work enables rational design of carbon structure at molecular level.
Wang et al. (Thu,) studied this question.