Betavoltaics were invented in the 1970s. Some pacemakers in the 1970s used betavoltaics based on promethium, but were phased out as cheaper lithium batteries were developed. Early semiconducting materials weren't efficient at converting electrons from beta decay into usable current, so higher energy, more expensive—and potentially hazardous—isotopes were used. The more efficient semiconducting materials used today can be paired with relatively benign isotopes such as tritium, which produce less radiation. The Betacel was considered the first successfully commercialized betavoltaic battery. The use of diamond-encapsulated carbon-14 to be extracted from nuclear waste was proposed in 2016 as a very long lived betavoltaic source. In 2018 a Russian design based on 2-micron thick nickel-63 slabs sandwiched between 10 micron diamond layers was introduced. It produced power output of about 1 microWatt at a power density of 10 μW/cm3. Its energy density was 3.3 kilowatt-hours/kg. The half-life of nickel-63 is 100 years.
Applications
The primary use for betavoltaics is for remote and long-term use, such as spacecraft requiring electrical power for a decade or two. Recent progress has prompted some to suggest using betavoltaics to trickle-charge conventional batteries in consumer devices, such as cell phones and laptop computers. As early as 1973, betavoltaics were suggested for use in long-term medical devices such as pacemakers. Although betavoltaics use a radioactive material as a power source, the beta particles used are low energy and easily stopped by a few millimetres of shielding. With proper device construction, 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 leads to significant health and environmental concerns.
Drawbacks
As radioactive material emits, it slowly decreases in activity. Thus, over time a betavoltaic device will provide less power. For practical devices, this decrease occurs over a period of many years. For tritium 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 its beta decay must also be taken into consideration in risk assessment and product development. Naturally, this increases both time-to-market and the already high cost associated with tritium. A 2007 report by the UK government's Health Protection AgencyAdvisory Group on Ionizing Radiation declared the health risks of tritium exposure to be double those previously set by the International Commission on Radiological Protection located in Sweden.
