Unraveling the effect of the microstructure of agricultural waste plants-derived hard carbons on the sodium storage performance

To further understand the structure-activity relationship of hard carbon as the anode material of sodium-ion batteries (SIBs), four representative biomass materials with increased crystalline cellulose contents of 20.4%, 30.0%, 46.9%, and 65.3%, from the common agricultural byproducts found in the South China region are selected as precursors: rice husk (RH), straw (ST), sugar cane bagasse (SCB), and bamboo wood powders (BWP). Furthermore, the amorphous contents are separated and extracted to investigate their synergistic effect on sodium storage. It is demonstrated that, crystalline cellulose can improve the graphitization degree and form enormous narrow closed pores, thus contributing a high reversible capacity. During the pyrolysis and carbonization, hemicellulose may decompose to form a longer graphite-like layer and larger but fewer closed pores. Besides, lignin decomposes to form a porous structure, which is beneficial for ion diffusion and cycle stability. The hard carbon SCB-1300 with blocky and tubular structures is synthesized by sugarcane bagasse, which has an appropriate crystalline cellulose concentration of 46.89%, exhibiting the highest reversible capacity of 206.27 mAh g(-1) at 0.5 C, as well as high capacity retention of 95.73% after 700 cycles. Reasonable selection of biomass precursor compositions, such as high content of crystalline cellulose and lignin, may enhance the synergistic effects and thus guide developing low-cost and sustainable anode materials of SIBs with excellent electrochemical performance.