Here, we report the synthesis of hard carbon materials (RH) made from natural rice husk through a single pyrolysis process and their application as an anode in sodium-ion batteries. The studies show that the electrochemical properties of RHs are affected by the treatment temperatures, which determine the materials morphology, in particular, their degree of graphitization and extent of continuous channels (nanovoids). The latter are accessible to sodium ions and significantly contribute to charge storage capacity of the produced anodes. The RHs obtained at 1600 °C deliver the highest reversible capacity of 276 mAh g−1 mainly due to insertion of sodium ions into the nanovoids. This work deepens the basic understanding of the influence of the carbonization temperature on the sodium storage mechanism.