The calcium-looping process for post-combustion carbon dioxide capture, an economically and technically feasible method suitable for large-scale use, has recently gained much attention. However, the capture capacity of calcium-based sorbents rapidly decreases after only a few cycles. Herein, calcium-based sorbents with enhanced cyclic CO2-capture capacity have been derived from cheap, natural raw materials by using a simple impregnation method. Limestone and shells were used as the calcium-based raw materials, with sea salt as dopant. Modified limestone had the highest CO2-capture capacity after multiple carbonation-calcination cycles. Sea-salt-doped sorbent showed a relatively stable porous surface during cycles, which resulted in a higher CO2-capture capacity.