[en] Na-ion batteries are promising candidates to replace Li-ion batteries in large scale applications because of the advantages in natural abundance and cost of Na. Silicene has potential as the anode in Li-ion batteries but so far has not received attention with respect to Na-ion batteries. In this context, freestanding silicene, a graphene-silicene-graphene heterostructure, and a graphene-silicene superlattice are investigated for possible application in Na-ion batteries, using first-principles calculations. The calculated Na capacities of 954 mAh/g for freestanding silicene and 730 mAh/g for the graphene-silicene superlattice (10% biaxial tensile strain) are highly competitive and potentials of $><!--\; >\; -->0.3\mathrm{V}$ against the Na${}^{+}$/Na potential exceed the corresponding value of graphite. In addition, the diffusion barriers are predicted to be $<<!--\; <\; -->0.3\mathrm{e}\mathrm{V}$. (paper)