The increasing demand of energy storage materials has attracted considerable attention of scientific community towards the development of rechargeable ion batteries (RIBs). Herein, B40 nanoclusters are theoretically analyzed for their potential application as anode material for sodium-ion batteries. DFT calculations are performed for geometrical and electrochemical properties study of Na or Na+ adsorbed A–@B40 (A– = F–, Cl– and Br–) complexes. Na+ and Na adsorbed preferably on R7 and R6 positions of boron nanocage (B40), respectively, where the interaction of Na+ is stronger in comparison to Na atom. The change in Gibbs free energy (cell potential) values of R7-B40 and R6-B40 complexes (of bare case) are -11.21 kcal mol-1 (0.49 V) and -8.92 kcal mol-1 (0.39 V), respectively. For further improvement of change in ΔG and Vcell values, halides are encapsulated (A = F–, Cl– and Br–) into boron nanocage. The Vcell of Na-ion batteries for R7– [email protected]40 and R6– [email protected] B40 (A = F–, Cl– and Br–) increases up to 3.594 V and 3.492 V, respectively. These results illustrate that the electrochemical properties of [email protected]40 nanocage explicitly depend on the nature of alkali metals and their respective halide ions.