Prototype Nuclear Battery Packs 10 Times More Power

Estimated reading time: 9 minutes

The goal of the researchers was to maximize the power density of their nickel-63 battery. To do this, they numerically simulated the passage of electrons through the beta source and the converters. It turned out that the nickel-63 source is at its most effective when it is 2 micrometers thick, and the optimal thickness of the converter based on Schottky barrier diamond diodes is around 10 micrometers.

Figure. 2. (a) Dependence of power flux from the radioactive nickel foil on its thickness. (b) Efficiency of electron absorption in the diamond converter as a function of its thickness. The two graphs indicate that the optimal thicknesses of the nickel-63 foil and the diamond converter are close to 2 and 10 micrometers, respectively. Credit: V. Bormashov et al./Diamond and Related Materials

Manufacturing technology

The main technological challenge was the fabrication of a large number of diamond conversion cells with complex internal structure. Each converter was merely tens of micrometers thick, like a plastic bag in a supermarket. Conventional mechanical and ionic techniques of diamond thinning were not suitable for this task. The researchers from TISNCM and MIPT developed a unique technology for synthesizing thin diamond plates on a diamond substrate and splitting them off to mass-produce ultrathin converters.

The team used 20 thick boron-doped diamond crystal plates as the substrate. They were grown using the temperature gradient technique under high pressure. Ion implantation was used to create a 100-nanometer-thick defective, “damaged” layer in the substrate at the depth of about 700 nanometers. A boron-doped diamond film 15 micrometers thick was grown on top of this layer using chemical vapor deposition. The substrate then underwent high-temperature annealing to induce graphitization of the buried defective layer and recover the top diamond layer. Electrochemical etching was used to remove the damaged layer. Following the separation of the defective layer by etching, the semi-finished converter was fitted with ohmic and Schottky contacts.

As the above-mentioned operations were repeated, the loss of substrate thickness amounted to no more than 1 micrometer per cycle. A total of 200 converters were grown on 20 substrates. This new technology is important from an economic standpoint, because high-quality diamond substrates are very expensive and therefore mass-production of converters by substrate thinning is not feasible.

All converters were connected in parallel in a stack as shown in figure 1. The technology for rolling 2-micrometer-thick nickel foil was developed at the Research Institute and Scientific Industrial Association LUCH. The battery was sealed with epoxy.

The prototype battery is characterized by the current-voltage curve shown in figure 3a. The open-circuit voltage and the short-circuit current are 1.02 volts and 1.27 microamperes, respectively. The maximum output power of 0.93 microwatts is obtained at 0.92 volts. This power output corresponds to a specific power of about 3,300 milliwatt-hours per gramm, which is 10 times more than in commercial chemical cells or the previous nickel-63 nuclear battery designed at TISNCM.

Figure. 3. (a) Dependence of current (black line) and battery output power (blue) on voltage. (b) Power density as a function of the resistance of the electrical load. Credit: V. Bormashov et al./Diamond and Related Materials

In 2016, Russian researchers from MISIS had already presented a prototype betavoltaic battery based on nickel-63. Another working prototype, created at TISNCM and LUCH, was demonstrated at Atomexpo 2017. It had a useful volume of 1.5 cubic centimeters.

The main setback in commercializing nuclear batteries in Russia is the lack of nickel-63 production and enrichment facilities. However, there are plans to launch nickel-63 production on an industrial scale by mid-2020s.

There is an alternative radioisotope for use in nuclear batteries: Dimond converters could be made using radioactive carbon-14, which has an extremely long half-life of 5,700 years. Work on such generators was earlier reported by physicists from the University of Bristol.

Page 2 of 3

• < Previous Page
• Next Page >