Nuclear battery which could last a lifetime

 A Tiny and safe nuclear battery, could power devices for decades 

Researchers have created a nuclear battery which could turn radiation directly into electricity for decades, but without all the scary stuff associated with nuclear radiation. The research was funded by the National Research Foundation of Korea, as well as the Daegu Gyeongbuk Institute of Science & Technology Research & Development Program of the Ministry of Science and Information and Communication Technology of Korea. A small dye-sensitized beta voltaic cell has radiocarbon on both the cathode and anode to increase its energy-conversion efficiency. Called a dye-sensitized beta voltaic cell, this battery uses beta particles, which are just high-energy electrons. The magic in this battery is the material carbon-14, a radioactive isotope which emits beta particles. These particles strike a titanium dioxide semiconductor coated with a ruthenium-based dye, which knocks electrons loose in the dye, generating an electrical current.

Lithium-ion batteries, used in consumer devices and electric vehicles, typically last hours or days between charges. However, with repeated use, they degrade and need to be charged more frequently. Now, researchers are considering radiocarbon as a source for safe, small and affordable nuclear batteries which could last decades or longer without charging. The half-life for carbon-14 decay is about 5,730 years, meaning the battery could theoretically still be producing 50% of its original output after nearly six millennia. However, in the real world, the practical power output would likely degrade much sooner due to materials breaking down over such a timeframe. The frequent charging required for Li-ion batteries isn't just an inconvenience. It limits the utility of technologies that use the batteries for power, such as drones and remote-sensing equipment. The batteries are also bad for the environment: Mining lithium is energy-intensive and improper disposal of Li-ion batteries can contaminate ecosystems. But with the increasing ubiquity of connected devices, data centres and other computing technologies, the demand for long-lasting batteries is increasing.

The prototype battery has a power density of 20.75 nanowatts per square centimeter per millicurie at 2.86% efficiency. In layman's terms, that's not a lot. Roughly the size of an aspirin or so, it pumps out about 0.4% of the power needed to run a basic pocket calculator. You'd need around 240 more of these little nuclear batteries to start your times tables refresher course. It generates enough power to run medical devices like a pacemaker pulse circuit or remote environmental sensors for data logging. It could also power RFID tags or microchips, or trickle charge capacitors for things which need a bigger burst of quick energy. There are a whole host of ultra-low-power consuming tech that this type of battery would suit, and it's still in early development. Su-Il In, a professor at Daegu Gyeongbuk Institute of Science & Technology, will present his results at the spring meeting of the American Chemical Society (ACS). Better Li-ion batteries are likely not the answer to this challenge. "The performance of Li-ion batteries is almost saturated," says In, who researches future energy technologies. So, In and his team members are developing nuclear batteries as an alternative to lithium.

Despite what one might normally think of nuclear radiation, the researchers say this design is actually quite safe. The beta particles emitted from carbon-14 are already present in nearly everything, including naturally in the human body. Shielding for such a battery is as easy as a thin piece of aluminium foil. Solid state and made without flammable materials, the little nuclear batteries might be safer than lithium-ion batteries, which are prone to thermal runaway, venting and explosion. Nuclear batteries generate power by harnessing high-energy particles emitted by radioactive materials. Not all radioactive elements emit radiation that's damaging to living organisms, and some radiation can be blocked by certain materials. For example, beta particles (also known as beta rays) can be shielded with a thin sheet of aluminium, making betavoltaics a potentially safe choice for nuclear batteries. This isn't the first time atomic batteries have made the news. The first radioisotope battery was developed in 1954 by the Atomic Energy Commission in the US. It used strontium-90 as the radioactive source and converted energy from beta particles into electricity, similar to today's beta voltaic cells. Shortly thereafter, in the 1960s, Radioisotope Thermoelectric Generators (RTG) were being used in space missions, converting energy from alpha-emitting isotopes like plutonium-238, which is more potent but still relatively safe when properly shielded. The very first space mission being a US Navy satellite called Transit 4A, part of the world's first satellite navigation system and precursor to modern GPS.

To significantly improve the energy conversion efficiency of their new design, In and the team used a titanium dioxide-based semiconductor, a material commonly used in solar cells, sensitized with a ruthenium-based dye. They strengthened the bond between the titanium dioxide and the dye with a citric acid treatment. When beta rays from radiocarbon collide with the treated ruthenium-based dye, a cascade of electron transfer reactions, called an electron avalanche, occurs. Then the avalanche travels through the dye and the titanium dioxide effectively collects the generated electrons. The researchers produced a prototype beta voltaic battery with carbon-14, an unstable and radioactive form of carbon, called radiocarbon. "I decided to use a radioactive isotope of carbon because it generates only beta rays," says In. Moreover, a by-product from nuclear power plants, radiocarbon is inexpensive, readily available and easy to recycle. And because radiocarbon degrades very slowly, a radiocarbon-powered battery could theoretically last for millennia. The new battery also has radiocarbon in the dye-sensitized anode and a cathode. By treating both electrodes with the radioactive isotope, the researchers increased the amount of beta rays generated and reduced distance-related beta-radiation energy loss between the two structures. In a typical beta voltaic battery, electrons strike a semiconductor, which results in the production of electricity. Semiconductors are a critical component in beta voltaic batteries, as they are primarily responsible for energy conversion. Consequently, scientists are exploring advanced semiconductor materials to achieve a higher energy conversion efficiency, a measure of how effectively a battery can convert electrons into usable electricity.

During demonstrations of the prototype battery, the researchers found that beta rays released from radiocarbon on both electrodes triggered the ruthenium-based dye on the anode to generate an electron avalanche which was collected by the titanium dioxide layer and passed through an external circuit resulting in usable electricity. Compared to a previous design with radiocarbon on only the cathode, the researchers' battery with radiocarbon in the cathode and anode had a much higher energy conversion efficiency, going from 0.48% to 2.86%. These long-lasting nuclear batteries could enable many applications, says In. For example, a pacemaker would last a person's lifetime, eliminating the need for surgical replacements. More recently, Betavolt announced its 3-volt diamond nuclear battery that uses nickel-63 and a diamond semiconductor using the same beta particle principle that can power a device for 50 years. Arkenlight is another company that's been developing carbon-14 diamonds to produce atomic battery power for several years. While this tech isn't entirely new, recent breakthroughs in materials, efficiency, and safety are finally starting to light the path to everyday practical applications.

However, this beta voltaic design converted only a tiny fraction of radioactive decay into electric energy, leading to lower performance compared to conventional Li-ion batteries. In suggests that further efforts to optimize the shape of the beta-ray emitter and develop more efficient beta-ray absorbers could enhance the battery's performance and increase power generation. As climate concerns grow, public perception of nuclear energy is changing. But it's still thought of as energy only produced at a large power plant in a remote location. With these dual-site-source dye-sensitized beta voltaic cell batteries, In says, "We can put safe nuclear energy into devices the size of a finger."