Nuclear batteries have been developed that utilize radioactive elements to generate electrical energy. The first such battery was demonstrated in 1913 by Henry Moseley. There has been ongoing research since then in perfecting the technology. There are two basic designs for such batteries.
Thermal converters utilize the heat generated by radioactive decay to generate electricity. Thermionic converter has a hot electrode that emits electrons to a cooler electrode. Radioisotope thermoelectric generators use thermocouples. Thermocouples generated electricity by joining two dissimilar materials, heating one material and cooling the other material causes electrons flow. Thermophotovoltaic cells convert infrared light (heat) into electricity. Alkai-metal thermal to electric converter has a ceramic aluminum barrier between a high pressure zone of sodium vapor and a low pressure zone where the sodium condenses into a liquid.
Non-thermal converters do not depend on the direct conversion of heat into electricity. Direct charging generators consist of a capacitor with a layer of radioactive material on side of the insulator layer or vacuum. Electrons, positrons, alpha particles or fission products can be the charged particles that created the electrical charge which is tapped for power. Betavoltaics utilize electrons to generate electricity through semiconductor junctions. Alphavoltaics produce power through the use of alpha particles. Optoelectric generators have been designed that would generate electricity from luminescent materials excited by radioisotopes. Reciprocating electromechanical atomic batteries build up a static electric charge that bends a flexible plate until it touches another plate and discharges the charge, producing electrical power.
Most nuclear batteries make use of radioisotopes that generate either low energy beta particles or low energy alpha particles. High energy particles would generate dangerous radiation that would require heavy shielding and increase the weight and size of the battery. Plutonium-238, curium 242, curium 2-44 and strontium-90 have been used in nuclear batteries. Tritium nickel-63, promethium-147 and technetium-99 have all been tested for potential use in nuclear batteries.
Nuclear batteries are expensive and potential dangerous because they contain radioactive materials. They are also very long-lived and have a high energy density when compared to other types of batteries. There is a tradeoff between using radioisotopes which have a short half-life and generates greater power and radioisotopes which have a longer half-life and therefore a longer life as a battery. Efficiency in nuclear batteries varies from .1% to 8%. Nuclear batteries can last up to 20 years depending on the radioisotope used. They are very useful in applications which require reliable long term operation without needing any maintenance or replacement. They are especially important in space probes, underwater instruments, remote sensor stations and implantable devices such as pacemakers.
Nanotechnology research is yielding new materials and structures that could lead to advanced designs for nuclear batteries that would have a twenty five year lifespan and would be small enough to be useful in powering tiny electronic devices.
Nuclear battery from the University of Missouri:
