Are you also suffering from frequent charging of your phone? Are you also troubled by the pacemaker’s regular surgery to replace the battery? Do you know how the deep sea exploration unmanned submersible can work longer? Did you know that the rover uses a special battery to extend its battery life?
In 2021, the Curiosity rover that landed on Mars uses a multi-purpose radioisotope thermoisotope battery (MMRTG), which can solve the above problems very well. Today, I will show you this magical battery-isotope Battery.
1. What are isotopes and what can isotopes do?
Isotopes refer to the same element with the same number of protons (atomic numbers) in the nucleus but different numbers of neutrons. For example, there are three isotopes of hydrogen in our daily life, namely protium (H), deuterium (D, heavy hydrogen), and tritium (T, super-heavy hydrogen). They are isotopes of each other and are different nuclei of the same element. white.
Schematic diagram of the atomic structure of protium, deuterium and tritium (image source: hand-painted by the author)
Some of these elements are very unstable and can spontaneously emit particles or rays, releasing a certain amount of energy to become stable atoms of another element. This element is a radioisotope. The process of radioactive isotopes emitting rays is the process of isotope decay, and the time required for the number of radionuclides to decay to half of the original is the half-life of radioisotopes.
For example, the half-life of 238Pu is 87.7 years, that is to say, only half of the plutonium-238 decays after a 238Pu radioactive source is placed for 87.7 years.
In addition to their role in national defense technology, many isotopes also play an important role in our daily production and life. For example, in food production, the isotope 60Co can be used to generate gamma rays to sterilize food by irradiation;
In medical and clinical aspects, more than 100 isotope treatment methods have been established, which can achieve targeted radiation on some cancer cells and prevent their continued spread in the patient’s body; in the field of energy, nuclear reactors are used to provide electricity.
In addition to the above applications, it is also possible to use the thermal energy of isotopes such as 238Pu to decay to make isotope thermoelectric cells, and to use the radiation particles released during the decay of 63Ni to make radiovolt effect isotope cells.
2. What does an isotope battery look like?
Here we focus on two kinds of batteries with more mature applications: isotope thermoelectric batteries and radiation volt effect isotope batteries.
An isotope thermoelectric cell (RTG) is a power generation device that utilizes the Seebeck effect of thermoelectric materials to directly convert the decay heat of isotopes into electrical energy. RTG consists of three parts, from the inside to the outside are the isotope heat source, the thermoelectric conversion device, and the heat dissipation shell.
The heat emitted by the isotope heat source can generate a temperature difference between the two ends of the thermoelectric material, thereby using the Seebeck effect of the thermoelectric material to generate an electric current, and the shell made of the special material can not only isolate the radiation, but also release the unused heat energy.
Typical structure of isotope thermoelectric battery (Image source: Fenglin Nuclear Team)
The radiation volt effect isotope cell is composed of a radioactive source, a semiconductor transducer device, an electrode, a shell and other structures. Its working principle is that when the radioactive source interacts with the semiconductor material, electron-hole pairs are generated through ionization excitation, and then built into the semiconductor. Under the action of the electric field, these generated electron-hole pairs are separated and collected by the electrodes, thereby realizing the conversion of the decay energy of the radioactive source into electrical energy.
3. What can isotope batteries do?
Isotope batteries have the common advantages of compact structure, high reliability, long life (can supply energy continuously for decades), no environmental impact, and no maintenance. Therefore, they can be used in some scenarios that require long-term maintenance-free or complex environments that are difficult to charge To once and for all, until retirement.
The ability of isotope batteries to resist external interference can crush common chemical batteries; at the same time, the service life of isotope batteries is mainly related to the half-life of isotopes, and the longest can even be used for a hundred years.
It is precisely because of the above advantages that the radioisotope battery has the unique skill of “can not only go up to nine days to catch the moon, but also go to five oceans to catch turtles” in the practical application field.
In 2018, my country successfully launched the lunar exploration project Chang’e “4” probe. The isotope thermoelectric battery it carried can meet the requirements of various technical indicators at a temperature of minus 190 ℃ during the dormancy of the moon night. In contrast, ordinary chemical batteries cannot work at such extreme low temperatures.
In the actual working process, the data sent back by the lunar rover showed that the isotope thermoelectric battery provided normal heating and power supply, realizing the first space application of isotope thermoelectric battery in my country.
In the depths of the ocean, where solar cells are of little use, and fuel cells and other chemical batteries have too short lifespans, isotope batteries can shine.
For example, it can be used as an energy source for submarine navigation beacons, which can ensure that the beacon flashes every few seconds for decades. work safely and reliably.
Isotope batteries also have biomedical applications. For example, in cardiac pacemakers, the commonly used lithium-iodine battery is easily interfered by electromagnetic waves, which brings inconvenience to users, and has a lifespan of about 5 years. The medical isotope battery is not susceptible to electromagnetic interference and has a long service life of about 15 years.
Some heart disease patients around the world have been implanted with pacemakers powered by isotope batteries, giving them a new lease of life.
Not only that, with the rapid development of Internet of Things technology, in order to ensure that integrated circuits (ICs), sensors, low-power devices and other micro-electro-mechanical systems (MEMS) can dissipate heat normally without affecting wireless communication signals, these electronic devices and system modules are required. Compared with ordinary chemical batteries, isotope batteries can better meet this requirement.
4. To what extent has the isotope battery developed?
From 1961, when the first U.S. artificial satellite “Explorer 1” carried isotope batteries into outer space for the first time, to the Apollo moon landing spacecraft carrying two isotope batteries to the moon, and then to 2010, a company obtained isotope batteries Product sales qualification, after decades of development, isotope batteries have been industrialized in the United States.
A similar development process from scientific research to industrialization also appeared in the Soviet Union and Russia. However, my country’s isotope batteries started late, especially in the industrialization of isotope batteries, there is still a lot of room for improvement.
According to the deep space exploration plan announced by the National Space Administration in 2018, my country will carry out exploration of the moon, Mars and Jupiter in the next three decades, which means that the localization of isotope batteries is an urgent need. At present, relevant domestic teams have increased investment in the research and development of isotope batteries, and a hundred flowers are blooming.
Isotope batteries are developing rapidly at a speed visible to the naked eye. I believe that in the future, they can also bring great convenience to all aspects of human daily life. After knowing such isotope batteries, are you excited?