Microcrystalline cellulose-derived hard carbon for robust and low-potential sodium storage

Developing hard carbon with unique and regulable microstructure is the key for the development of sodium ion batteries (SIBs), while the poor low-potential sodium storage property as well as ambiguous sodium storage mechanism arising from the intricate pseudo-graphitic and graphite-like structures present a great challenge to the commercialization of SIBs. Herein, microcrystalline cellulose was proposed as carbon precursor to synthesis hard carbons by controlling carbonization temperature. As expected, the resulting hard carbons simultaneously contained pseudo-graphitic and graphite-like structures, and in situ XRD analysis suggested that a larger interlayer spacing of pseudo-graphitic structure facilitated Na⁺ insertion, whereas smaller spacing of graphite-like structure could enhance the electrical conductivity. As a result of the optimized carbonization temperature of 1400 °C, the obtained hard carbon with larger interlayer spacing, reduced defect sites, and more closed pores, displayed an initial discharge capacity of 376.7 mA h g⁻¹ with low-potential plateau capacity ratio of 57.58 % and a high initial Coulomb efficiency of 84.32 %, while an increased plateau capacity ratio of 63.91 % in the second discharge process using an ester-based electrolyte.