Regulating pore structure and pseudo-graphitic phase of hard carbon anode towards enhanced sodium storage performance

The pore structure and pseudo-graphitic phase (domain size and content) of a hard carbon anode play key roles in improving the plateau capacity of sodium-ion batteries (SIBs), while it is hard to regulate them effectively and simultaneously. This study delves into the synthesis of hard carbons with tailored microstructures from esterified sodium carboxymethyl cellulose (CMC-Na). The hard carbon (EHC-500) with maximized pseudo-graphitic content (73%) and abundant uniformly dispersed closed pores was fabricated, which provides sufficient active sites for sodium ion intercalation and pore filling. Furthermore, minimized lateral width (La) of pseudo-graphitic domains in EHC-500 is simultaneously realized to improve the accessibility of sodium ions to the intercalation sites and filling sites. Therefore, the optimized microstructure of EHC-500 contributes to a remarkable reversible capacity of 340 mAh/g with a high plateau capacity of 236.7 mAh/g (below 0.08 V). These findings underscore the pivotal role of microcrystalline structure and pore structure in the electrochemical performance of hard carbons and provide a novel route to guide the design of hard carbons with optimal microstructures towards enhanced sodium storage performance.