New approach to radioisotope power sources for improved efficiency and long life

The Science

Beta-voltaic radioisotope power sources (RPSs) are devices that directly convert beta particles (electrons) from a beta-emitting radioisotope source (such as nickel-63) into electrical energy. These devices have high power density, meaning they can release a large amount of power quickly when needed. They also have high energy density, meaning they store large amounts of power. They are ideal for applications like spacecraft that need power sources that can operate for many years under harsh conditions without human intervention. Researchers recently explored a new approach for making beta-voltaic RPSs more efficient at converting heat into electricity. These NextGen RPSs apply isotopes in new ways to improved converters. This gives NextGen RPSs excellent potential for providing long-term, compact power in remote and extreme environments.

The Impact

Small sensors often used in remote and/or extreme environments on land and in space require power sources that supply high energy and power density to operate continuously for 3 to 25 years. Chemical batteries can only provide short-term solutions. A beta-voltaic RPS is an alternative to a chemical battery. These RPSs can store 1,000 times as much as a chemical battery, allowing them to supply small sensors with power for many years. This research shows how beta-voltaic RPS performance can be enhanced by improving the efficiency with which they convert radioactive decay into electricity. This advance will help make RPSs even more effective for small devices that require small amounts of power and represents a promising first step to increase nuclear battery power density from microwatts to milliwatts per 1000 cm³ with the implementation of higher energy beta sources.

Summary

Beta-voltaic batteries are a type of RPS. Radioisotopes utilized in beta-voltaic batteries (e.g., Ni-63, Pm-147) are produced by the DOE Isotope Program. In traditional beta-voltaic batteries, the radioisotope is deposited onto a metal foil that is placed on top of a semiconductor converter. The interaction between the radioisotope and the converter can limit RPS performance. This research demonstrated an approach where long-lived beta-emitting radioisotopes can be used to match the power density (the ability to release power) of chemical batteries while surpassing them in energy density (the ability to store power). Researchers investigated how the converter geometry and beta-conversion can influence performance by improving on the source efficiency and surface power density. Researchers focused on a beta-voltaic battery configuration consisting of nickel-63 directly applied onto a 4-H silicon carbide polytype (4H-SiC) beta-voltaic cell. Changing from a planar converter geometry to a textured 4H-SiC beta-voltaic cell improved power density by seven times. Converter efficiency increased by two times compared to a silicon cell when researchers directly applied nickel-63 to the textured 4H-SiC beta-voltaic cell. The beta-conversion can be captured on both sides of the radioisotope source. This permits two cells to collect the beta-conversion instead of one cell and increases surface power density. This research demonstrated that the interaction between the radioisotope and converter is critical to efficient energy conversion. These NextGen beta-voltaic RPSs have excellent potential in fulfilling long-duration, compact power needs for applications in remote and/or extreme environments.



Funding

This work was supported by U.S. Army Research Laboratory and the National Aeronautics and Space Administration using nickel-63 radioisotopes supplied by the Department of Energy Isotope Program, managed by the Office of Isotope R&D and Production. The 4H-SiC cells were provided by Widetronix Inc.