A chemical power source is a device that converts chemical energy directly into electrical energy, including primary battery (also known as primary battery), storage battery (also known as secondary battery), reserve battery (also known as activated battery) and fuel cell. Batteries that can only convert chemical energy into electrical energy are primary batteries, such as zinc-manganese dry batteries, zinc-mercury batteries, and zinc-silver batteries. Batteries that can not only convert chemical energy into electrical energy, but also convert electrical energy into chemical energy are batteries. Commonly used are lead batteries, cadmium-nickel batteries and lithium batteries. The assembled battery is stored in a dry state. When in use, the electrolyte is evenly delivered to the battery cells through the distribution system by gas pressure to activate the battery. Such batteries are called reserve batteries, such as magnesium-silver batteries, zinc-silver reserve batteries, lithium-iron disulfide thermal batteries, etc. A fuel cell is a battery that uses hydrogen as the fuel and oxygen as the oxidant. The regenerative hydrogen-oxygen fuel cell can convert the battery reaction product (H2O) into reactants (H2 and O2) through electrolysis, and then reuse it to generate electricity.
Special power sources for spacecraft refer to solar cells and nuclear batteries. Solar cells are semiconductor cells that directly convert sunlight energy into electrical energy, including single crystal silicon cells and single crystal gallium arsenide cells. The nuclear batteries used in aerospace include radioisotope thermoelectric generators, nuclear reactor thermoelectric generators and nuclear reactor thermionic generators.
The main requirements for chemical power sources are:
(1) Reliable work;
(2) Easy to use and maintain;
(3) The specific power is large. The specific power refers to the output power per unit volume or weight. The volume is measured in liters (L), the weight is measured in kilograms (kg), and the power is measured in watts (W).
(4) The specific energy is large, and the amount of electric energy released by the unit mass of the electrode material participating in the electrode reaction is called the specific energy of the battery, and the energy is measured in watt-hours (W.h);
(5) The working voltage is stable and the internal resistance is small;
(6) The dry charging storage period of the primary battery and the reserve battery is long, and the wet charging storage period is long. The self-discharge of the battery is small, the number of charge-discharge cycles is allowed to be large, and the activation time of the reserve battery is short;
(7) It can withstand harsh weather conditions and working environment, and the pollution to the environment during work or failure is small.
The main requirements for special power supplies are:
(1) Sufficient mechanical strength;
(2) Good sealing;
(3) Good electrical insulation performance;
(4) Long working life.
Batteries are mostly used in the aviation field, such as battery vehicles for airport power supplies, and batteries for on-board backup power or emergency power. Fuel cells are commonly used in space shuttles. Solar cells and batteries are commonly used in Earth-orbiting spacecraft. Some space probes use nuclear batteries, and some military satellites also use nuclear batteries.