Atomic Battery, or Nuclear Battery, Tritium Battery, Radioisotope Generator are used to describe a device which uses the emissions from a radioactive isotope to generate electricity. Like nuclear reactors, nuclear batteries generate electricity from atomic energy, but differ in that they do not use a chain reaction. Compared to other batteries nuclear batteries are very costly, but have extremely long life and high energy density, and so they are mainly used as power sources for equipment that must operate unattended for long periods of time, such as spacecraft and automated scientific stations in remote parts of the world. Radioisotopes provide a high energy density power source suitable for many applications. They are outstanding for small scale power. Nuclear battery technology received considerable in depth research attention for applications requiring long-life power sources for space system needs.

Types of Nuclear Batteries

Batteries using the energy of radioisotope decay to provide long-lived power (10–20 years) are being developed internationally. Conversion techniques can be grouped into two types: thermal and non-thermal. The thermal converters (whose output power is a function of a temperature differential) include thermoelectric and thermionic generators. The non-thermal converters (whose output power is not a function of a temperature difference) extract a fraction of the incident energy as it is being degraded into heat rather than using thermal energy to run electrons in a cycle. Atomic batteries usually have an efficiency of 0.1–5%. High efficiency betavoltaics have 6–8%.

  • Nuclear Atomic Battery Thermal Converters
    • Thermionic Converter Atomic Battery – Thermionic converter consists of a hot electrode which thermionically emits electrons over a space charge barrier to a cooler electrode, producing a useful power output. Caesium vapor is used to optimize the electrode work functions and provide an ion supply (by surface contact ionization) to neutralize the electron space charge.
    • Radioisotope Thermoelectric Generator – Thermoelectric converter connects pairs of thermocouples in series. Each thermocouple is formed by the junction of two dissimilar materials. One of each pair is heated and the other cooled. Metal thermocouples have low thermal-to-electrical efficiency. However, the carrier density and charge can be adjusted in semiconductor materials such as bismuth telluride and silicon germanium to achieve much higher conversion efficiencies.
    • Thermophotovoltaic Cells – Thermophotovoltaic cells work by the same principles as a photovoltaic cell, except that they convert infrared light (rather than visible light) emitted by a hot surface, into electricity. Thermophotovoltaic cells have an efficiency slightly higher than thermoelectric couples and can be overlaid on thermoelectric couples, potentially doubling efficiency.
    • Alkali-Metal Thermal to Electric Converter (AMTEC) – The alkali-metal thermal to electric converter (AMTEC) is an electrochemical system which is based on the electrolyte used in the sodium-sulfur battery, sodium beta-alumina. The device is a sodium concentration cell which uses a ceramic, polycrystalline β-alumina solid electrolyte (BASE), as a separator between a high pressure region containing sodium vapor at 900 – 1300 K and a low pressure region containing a condenser for liquid sodium at 400 – 700 K. Efficiency of AMTEC cells has been 16% to 20%.
  • Nuclear Atomic Battery Non-Thermal Converters
    • Nuclear Battery Direct Charging Generators – Direct charging generator consists of a capacitor which is charged by the current of charged particles from a radioactive layer deposited on one of the electrodes. Spacing can be either vacuum or dielectric. Negatively charged beta particles or positively charged alpha particles, positrons or fission fragments may be utilized.
    • Nuclear Battery Betavoltaics – Betavoltaics are generators of electrical current, in effect a form of battery, which use energy from a radioactive source emitting beta particles (electrons). A common source used is the hydrogen isotope, tritium. Betavoltaics use a non-thermal conversion process. Betavoltaics are particularly well-suited to low-power electrical applications where long life of the energy source is needed, such as implantable medical devices or military and space applications.
    • Optoelectric Nuclear Battery – In optolectric nuclear battery, beta-emitter (such as technetium-99) would stimulate an excimer mixture, and the light would power a photocell.
    • Reciprocating Electromechanical Atomic Batteries – Electromechanical atomic batteries use the build up of charge between two plates to pull one bendable plate towards the other, until the two plates touch, discharge, equalizing the electrostatic buildup, and spring back. The mechanical motion produced can be used to produce electricity through flexing of a piezoelectric material or through a linear generator.