Hard carbons are the most promising negative active materials for sodium ion storage. In this work, a simple synthesis approach is proposed to produce hard carbon microspheres (CMSs) (with a mean diameter of similar to 1.3 mm) from resorcinol-formaldehyde precursors produced via acid-catalyzed polycondensation reaction. Samples prepared at 1200, 1400, and 1500 degrees C showed different electrochemical behavior in terms of reversible capacity, initial coulombic efficiency (iCE), and the mechanism of sodium ion storage. The specific capacity contributions from the flat voltage profile (<0.1 V) and the sloping voltage region (0.1-1 V) showed strong correlation to the local structure (and carbonization temperature) determined by the interlayer spacing (d(002)) and the Raman ID/IG ratio of the hard carbons (HCs) and the rate of cycling. Electrochemical tests indicated that the HC synthesized at 1500 degrees C performed best with an iCE of 85-89% and a reversible capacity of 300-340 mAh g(-1) at 10 mA g(-1), with the majority of charge stored below 0.1 V. The d002 and the ID/IG ratio for the sample were similar to 3.7 A and similar to 1.27, respectively, parameters indicative of the ideal local structure in HCs required for optimum performance in sodiumion cells. In addition, galvanostatic tests on three-electrode half-cells cells revealed that sodium metal plating occurred as cycling rates were increased beyond 80 mA g(-1) leading to considerably high capacity and poor coulombic efficiency, a point that must be considered in full-cell batteries. Pairing the hard CMS electrodes with Prussian white positive electrode, a proof-of-concept cell could provide a specific capacity of almost 100 mAh g(-1) maintained for more than 50 cycles with a nominal voltage of 3 V.