Effect of concentration of dextrose-derived hard carbon anode on the electrochemical performance for sodium-ion batteries

Hard carbons (HCs) are widely used as anode materials for sodium-ion batteries due to their availability, ease of synthesis, and low cost. HCs can store Na ions between stacked sp²-layers of carbon and micropores. In this work, hard carbons are synthesized from 1 M, 2 M, 3 M, 4 M, and 5 M dextrose solutions by hydrothermal synthesis followed by high-temperature calcination at 1100 °C in an argon atmosphere. Among all hard carbons derived from different concentrations of dextrose solutions, hard carbon derived from 3 M dextrose solution delivers superior electrochemical performance compared to other hard carbons. Hard carbon derived from 3 M dextrose solution (DHC-3 M) provides an initial reversible capacity of 273 mAh g⁻¹ with a capacity retention of 82% at the end of 100 charge–discharge cycles at 30 mA g⁻¹. Further, high-rate charge–discharge cycling at 200 mA g⁻¹ shows an initial capacity of 200 mAh g⁻¹ and retains over 61% capacity at the end of 500 cycles. The improved capacity of DHC-3 M is due to the higher d-spacing value and more disorderness, which improve the plateau region capacity due to the intercalation of Na⁺ in the carbon matrix. Besides, 3 M dextrose-derived hard carbons are less agglomerated than other concentrations and show less charge transfer resistance before and after cycling, resulting in improved electrochemical performance.