Russian Scientists Upgrade Nuclear Battery Design to Increase Power Output
Metal News - Published on Mon, 04 Jun 2018
Amoz.com reported that 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 normal batteries that power toys, flashlights, clocks, and other compact autonomous electrical devices, the energy of the well-known redox chemical reactions is used. Here, transfer of electrons from one electrode to the other occurs through an electrolyte. This results in a potential difference between both the electrodes.
Upon connecting the two battery terminals by a conductor, the potential difference is eliminated when the flow of electrons starts, thus producing an electric current. Chemical batteries, also called galvanic cells, possess high power density, or the ratio of the volume of the battery to the power of the produced current.
Yet, chemical cells tend to discharge within a comparatively short period of time, restricting their usage in autonomous devices. Although some of these batteries, known as accumulators, are rechargeable, they have to be replaced for charging. This could be risky, such as in a cardiac pacemaker, or even impossible, if the battery is used for powering a spacecraft.
Nuclear Batteries: History
Luckily, chemical reactions are just one among many probable sources of electric current. In 1913, Henry Moseley was the first to invent a power generator based on radioactive decay. In his nuclear battery, a glass sphere silvered on the inside was equipped with a radium emitter positioned at the center on an isolated electrode.
Electrons emitted as a result of the beta decay of radium led to a potential difference between the central electrode and the silver film. Yet, the device’s idle voltage was very high, of the order of tens of kilovolts, and the current was very low for practical applications.
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.
Ten Times More Power
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 ?W, where the power density per cubic centimeter was 10 1 ?W, 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.
Calculations First
The aim of the team was to increase the power density of their nickel-63 battery. To achieve this, the passage of electrons through the beta source and the converters was numerically simulated. It was observed that the nickel-63 source is highly effective when its thickness is 2 ?m, and the optimal thickness of the converter depending on Schottky barrier diamond diodes is about 10 ?m.
Manufacturing Technology
The major technological problem was the fabrication of more number of diamond conversion cells that have a complex internal structure. The thickness of each converter was of the order of only tens of micrometers, such as a plastic bag in a supermarket.
Traditional mechanical and ionic methods of diamond thinning were not appropriate for this task. The scientists from TISNCM and MIPT devised a distinctive technology for fabricating thin diamond plates on a diamond substrate and splitting them off to enable mass-production of ultrathin converters.
The researchers used 20 thick boron-doped diamond crystal plates as the substrate. These plates were grown with the help of the temperature gradient method under high pressure. Ion implantation was employed to produce a 100-nm-thick defective, “damaged” layer in the substrate at the depth of around 700 nm.