Diamond battery

Currently no known prototype uses ¹⁴C as its source, there are however some prototypes that use nickel-63 (⁶³Ni) as their source with diamond semiconductors for energy conversion which are seen as a stepping stone to a possible ¹⁴C diamond battery prototype.

Moscow Institute of Physics and Technology prototype

External image
Prototype nuclear battery, Technological Institute for Superhard and Novel Carbon Materials.[5]

In 2018 researchers 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) announced a prototype using 2-micron thick layers of ⁶³Ni foil sandwiched between 200 10-micron diamond converters. It produced a power output of about 1 μW at for power density of 10 μW/cm³, at those values its energy density would be approximately 3.3 Wh/g over its 100 year half-life, about 10 times that of conventional electrochemical batteries.[5] This research was published in April of 2018 in the Diamond and Related Materials journal.[6]

Researchers are trying to improve the efficiency and are focusing on use of radioactive ¹⁴C, which is a minor contributor to the radioactivity of nuclear waste.[3]

¹⁴C undergoes beta decay, in which it emits a low-energy beta particle to become Nitrogen-14, which is stable (not radioactive).[7]

¹⁴
₆C
→ ¹⁴
₇N
+ ⁰
₋₁β

These beta particles, having an average energy of 50 keV, undergo inelastic collisions with other carbon atoms, thus creating electron-hole pairs which then contribute to an electric current. This can be restated in terms of band theory by saying that due to the high energy of the beta particles, electrons in the carbon valence band jump to its conduction band, leaving behind holes in the valence band where electrons were earlier present.[8][4]

In graphite-moderated reactors, fissile uranium rods are placed inside graphite blocks. These blocks act as a neutron moderator whose purpose is to slow down fast-moving neutrons so that nuclear chain reactions can occur with thermal neutrons.[9] During their use, some of the non-radioactive carbon-12 and carbon-13 isotopes in graphite get converted into radioactive ¹⁴C by capturing neutrons.[10] Once the graphite blocks are removed during station decommissioning their induced radioactivity qualifies them as low-level waste requiring safe disposal.

Researchers at the University of Bristol demonstrated that a large amount of the radioactive ¹⁴C was concentrated on the inner walls of the graphite blocks. Due to this, they propose that much of it can be effectively removed from the blocks. This can be done by heating them to the sublimation point of 3915 K (3642 °C, 6588 °F) which will release the carbon in gaseous form. After this blocks will be less radioactive and possibly easier to dispose of with most of the radioactive ¹⁴C having being extracted.[11]

Those researchers propose that this ¹⁴C gas could be collected and used to produce man-made diamonds by a process known as chemical vapor deposition using low pressure and elevated temperature, noting that this diamond would be a thin sheet and not of the stereotypical diamond cut. The resulting diamond made of radioactive ¹⁴C would still produce beta radiation which researchers claim would allow it to be used as a betavoltaic source. Researchers also claim this diamond would be sandwiched between non-radioactive man-made diamonds made from ¹²C which would block radiation from the source and would also be used for energy conversion as a diamond semiconductor instead of convention silicon semiconductors.[11]

Due to its very low power density, conversion efficiency and high cost it is very similar to other existing betavoltaic devices which are suited to niche applications needing very little power (microwatts) for several years in situations where conventional batteries cannot be replaced or recharged using conventional energy harvesting techniques.[12][13] Due to its longer half-life ¹⁴C betavoltaics may have an advantage in service life when compared to other betavoltaics using tritium or nickel however this will likely come at the cost of further reduced power density.

• The speech that proposed the battery
• Are Radioactive ‘Diamond Batteries’ a Real Thing?