Abetavoltaic device (betavoltaic cell orbetavoltaic battery) is a type ofnuclear battery that generateselectric current frombeta particles (electrons orpositrons) emitted from aradioactive source, usingsemiconductor junctions. A common source used is thehydrogenisotopetritium. Unlikemost nuclear power sources which use nuclear radiation to generate heat which then is used to generate electricity, betavoltaic devices use a non-thermal conversion process, converting theelectron–hole pairs produced by the ionization trail of beta particles traversing a semiconductor.[1]
Betavoltaic power sources (and the related technology ofalphavoltaic power sources[2]) are particularly well-suited tolow-power electrical applications wherelong life of the energy source is needed, such asimplantable medical devices ormilitary andspace applications.[1]
Betavoltaics were invented in the 1970s.[3] Somepacemakers in the 1970s used betavoltaics based onpromethium,[4] but were phased out as cheaper lithium batteries were developed.[1]
Earlysemiconducting materials were inefficient at convertingelectrons frombeta decay into current, requiring higher energy, more expensive—and potentially hazardous—isotopes. The more efficient semiconducting materials used as of 2019[update][5] can be paired with relatively benign isotopes such as tritium, which produce less radiation.[1]
TheBetacel, developed byLarry C. Olsen, was one of the earliest and most successful commercialized betavoltaic batteries, and would inform the design of modern betavoltaic devices such asNanoTritium batteries.
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The primary use for betavoltaics is for remote and long-term use, such asspacecraft requiring electrical power for a decade or two. Recent progress has prompted some to suggest using betavoltaics totrickle-charge conventional batteries in consumer devices, such ascell phones andlaptop computers.[6][unreliable source?] As early as 1973, betavoltaics were suggested for use in long-term medical devices such aspacemakers.[4]
In 2018 a Russian design based on 2-micron thicknickel-63 slabs sandwiched between 10 micron diamond layers was introduced. It produced a power output of about 1 μW at apower density of 10 μW/cm3. Its energy density was 3.3 kW⋅h/kg. The half-life of nickel-63 is 100 years.[7][8][9]
In 2019 a paper indicated the viability of betavoltaic devices in high-temperature environments in excess of 733 K (460 °C; 860 °F) like the surface ofVenus.[10]
A prototype betavoltaic battery announced in early 2024 by theBetavolt company of China contains a thin wafer providing a source ofbeta particle electrons (eitherCarbon-14 ornickel-63) sandwiched between two thincrystallographic diamond semiconductor layers.[11][12] The Chinese startup claims to have the miniature device in the pilot testing stage.[13] Unveiled in January 2024, it is allegedly generating 100 microwatts of power and a voltage of 3V and has a lifetime of 50 years without any need for charging or maintenance.[13] Betavolt claims it to be the first such miniaturised device ever developed.[13] It gains its energy from a sheet of nickel-63 located in a module the size of a very small coin.[11][13] The isotope decays intostable, non-radioactiveCu-63, which pose no additional environmental threat.
In March 2025, researchers atDaegu Gyeongbuk Institute of Science and Technology (DGIST) developed a high-efficiency betavoltaic battery using carbon-14. Unlike traditional designs, it featured radiocarbon in both theanode andcathode, boosting energy conversion efficiency to 2.86%. Atitanium dioxide semiconductor with aruthenium-based dye enhanced electron transfer, creating anelectron avalanche effect.[14]
As radioactive material emits radiation, it slowly decreases in activity (refer tohalf-life). Thus, over time a betavoltaic device will provide less power. For practical devices, this decrease occurs over a period of many years. Fortritium devices, the half-life is 12.32 years. In device design, one must account for what battery characteristics are required at end-of-life, and ensure that the beginning-of-life properties take into account the desired usable lifetime.
Liability connected with environmental laws and human exposure to tritium and itsbeta decay must also be taken into consideration inrisk assessment andproduct development. Naturally, this increases bothtime-to-market and the already high cost associated with tritium. A 2007 report by the UK government'sHealth Protection Agency Advisory Group on Ionizing Radiation declared the health risks of tritium exposure to be double those previously set by theInternational Commission on Radiological Protection located in Sweden.[15]
As radioactive decay cannot be stopped, sped up or slowed down, there is no way to "switch off" the battery or regulate its power output. For some applications this is irrelevant, but others will need a backup chemical battery to store energy when it isn't needed for when it is. This reduces the advantage of high energy density.
Although betavoltaics use a radioactive material as a power source, the beta particles are low energy and easily stopped by a few millimetres ofshielding. With proper device construction (that is, proper shielding and containment), a betavoltaic device would not emit dangerous radiation. Leakage of the enclosed material would engender health risks, just as leakage of the materials in other types of batteries (such aslithium,cadmium andlead) leads to significant health and environmental concerns.[16] Safety can be further increased by transforming the radioisotope used into a chemically inert and mechanically stable form, which reduces the risk of dispersal orbioaccumulation in case of leakage.
Betavoltaic nuclear batteries can be purchased commercially. Devices available as per 2012 included a 100 μW tritium-powered device weighing 20 grams.[17]
Due to the highenergy density of radioisotopes (radioisotopes have orders of magnitude higher energy density than chemical energy sources, but much lower power density; thepower density of a radioisotope is inversely proportional to its half-life (i.e., shorter half-life translates into higher power density), and the need for reliability above all else in many applications of betavoltaics, comparatively low efficiencies are acceptable. Current technology allows for single digit percentages ofenergy conversion efficiency from beta particle input to electricity output, but research into higher efficiency is ongoing.[18][19] By comparisonthermal efficiency in the range of 30% is considered relatively low for new large scale thermal power plants and advancedcombined cycle power plants achieve 60% and more efficiency if measured by electricity output per heat input.[20] If the betavoltaic device doubles as aradioisotope heater unit it is in effect acogeneration plant and achieves much higher total efficiencies as much of thewaste heat is useful. Similar tophotovoltaics, theShockley–Queisser limit also imposes an absolute limit for a singlebandgap betavoltaic device.[21]
Since the highest energy that can possibly be extracted from a single EHP is the bandgap energy, the ultimate efficiency of a beta-battery can be estimated as
where and are semiconductor band gap and electron–hole pair creation energy respectively. The energy to generate a single EHP by a beta-particle is known to scale linearly with the bandgap as withA andB depending on the semiconductor characteristics.[22]