A Silicon Oxide–Carbon Anode with High Reversibility for Na-Ion Batteries

Amorphous carbon (AC) represents nowadays the most widespread anode for sodium-ion batteries (SIBs). Herein, we blended silicon oxide and few-layer graphene (FLG) within an AC matrix achieved by hydrothermal treatment and annealing of sucrose to get a highly reversible anode for SIBs. The composite has partially amorphous character with graphitic reflections, various functional groups, and micrometric morphology including submicron-to-nano particles. The anode reveals reversible electrochemical activity within various potential regions vs Na+/Na, accounting for Na-insertion/deposition with partial alloying with Si between 0.01 and 0.1 V, the Na-intercalation between 0.1 and 0.50 V, and Na-solvent complex cointercalation at a potential higher than 0.60 V. Galvanostatic cycling in sodium half-cells shows for the material a maximum capacity of ∼180 mAh g–1, with retention between 93 and 94% over 400 cycles, and average Coulombic efficiency exceeding 99%. The Na-ion full-cell exploiting the anode in a diglyme-based electrolyte and a sodium-deficient layered cathode operates at ∼3 V, with an initial capacity of 100 mAh g–1 retained over 300 cycles for 63%, and a mean Coulombic efficiency value of 99.97%. These findings suggest the composite anode and the Na-ion battery setups exploited in this work are promising for sustainable energy storage applications, tracking the way of Li-ion batteries.