A passive thermal diode (10), comprising: a heat source (12); a heat sink (14); a thermal coupling element (16) removably coupled to the heat source (12) and the heat sink (14); a lever (18), the lever (18) connected to the thermal coupling element (16) via a pivot point (19); and at least one spring (20) connected to the lever (18), the spring (20) comprised of a shape memory alloy, wherein the lever (18) transmits a force to displace the thermal coupling element (16) when the force is produced by the spring (20) on the lever (18).