AZoM reports that Russian scientists from the Moscow Institute of Physics and Technology (MIPT), the Technological Institute for Superhard and Novel Carbon Materials (TISNCM), and the National University of Science and Technology MISIS have upgraded the design of a nuclear battery that produces power from the beta decay of nickel-63, a radioactive isotope.
The innovative battery prototype developed by the researchers has the ability to pack nearly 3300 mW-hours of energy per gram, which is greater when compared to any other nuclear battery based on nickel-63, and 10 times higher when compared to the specific energy of commercial chemical cells. The study has been reported in the Diamond and Related Materials journal.
In 1953, Paul Rappaport hypothesized the application of semiconducting materials for transforming the energy of beta decay into electric power. Beta particles, positrons and electrons, emitted from a radioactive source have the ability to ionize atoms of a semiconductor, producing uncompensated charge carriers.
When a static field exists in a p-n structure, the charges flow in a single direction, leading to electric current generation. Batteries powered by beta decay were termed betavoltaics. The main benefit of betavoltaic cells, when compared to galvanic cells, is their longer life: Since the half-lives of the radioactive isotopes used in nuclear batteries range from tens to hundreds of years, their power output stays almost constant for a very long time.
Sadly, betavoltaic cells have a considerably lower power density when compared to galvanic cells. Without regard to this, betavoltaics were indeed used in the 1970s to power cardiac pacemakers, before being withdrawn to make way for the low-cost lithium-ion batteries, although the lithium-ion batteries have shorter lifetimes.
Betavoltaic power sources are not the same as radioisotope thermoelectric generators (RTGs), which are also known as nuclear batteries yet operate on a distinctive principle. In thermoelectric cells, thermocouples are used for converting the heat released by radioactive decay into electric power. RTGs have limited efficiency, which is dependent on temperature. However, due to their longer lifetimes and comparatively simple design, thermoelectric power sources are largely used for powering spacecraft such as the New Horizons probe and Mars rover Curiosity. Earlier, RTGs were used on unmanned remote facilities such as automatic weather stations and lighthouses. Over time, this practice was given up since it was hard to recycle used radioactive fuel, which eventually leaked into the environment.
A team of researchers headed by Vladimir Blank, the director of TISNCM and chair of nanostructure physics and chemistry at MIPT, proposed a method for increasing the power density of a nuclear battery by nearly 10 times. The physicists designed and constructed a betavoltaic battery with nickel-63 as the radiation source and Schottky barrier-based diamond diodes for energy conversion. With the prototype battery, they were able to realize an output power of nearly 1 μW, where the power density per cubic centimeter was 10 1 μW, which is adequate for a modern artificial pacemaker. Since the half-life of Nickel-63 is 100 years, the battery packs nearly 3300 mW-hours of power per gram, which is 10 times more when compared to electrochemical cells.
In the nuclear battery prototype, 200 diamond converters were interlaid with nickel-63 and stable nickel foil layers. The amount of power produced by the converter is based on the thickness of the nickel foil and the converter itself. This is because both have an impact on the number of beta particles absorbed. At present, the available prototypes of nuclear batteries are poorly upgraded due to their excessive volumes. In case the thickness of the beta radiation source is very high, the electrons emitted by it cannot escape from it. This effect is termed self-absorption. Yet, when the thickness of the source is reduced, the number of atoms that undergo beta decay in a given unit of time is proportionally minimized. Similar reasoning is applicable to the thickness of the converter.
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