Electric vehicle
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| 3.5 Sodium-Based Batteries 3.5.1 Introduction From the s a range of batteries which use a liquid sodium negative electrode have been developed. These batteries differ from other batteries inasmuch as they run at high Batteries, Flywheels and Supercapacitors 47 temperatures. They also have the interesting feature of using one or more liquid electrodes in the form of molten sodium and using a solid ceramic electrolyte. Because of the need to operate at high temperatures they are only practical for large systems, such as electric cars – they are not suitable for scooters and cycles. They are rather more exotic than other types, as they will never be used in mobile phones or laptop computers, unlike the other types of battery we will consider in this chapter. This limitation on their market has rather impeded their commercial development. 3.5.2 Sodium Sulfur Batteries The development of these batteries started in the sand they run at temperatures between 300 and C. In order to keep the heat in the battery, the cells are enclosed in an evacuated case. The basic sodium sulfur cells have a high specific energy, six times that of lead acid cells, but in experimental batteries the mass of the enclosure typically halves this potential improvement. The negative electrode in the cells consists of molten sodium, and the positive electrode consists of molten sulfur polysulfides. The electrolyte is a solid beta alumina ceramic, which conducts the sodium ions and also separates the two electrodes. The actual cells are kept fairly small, and they are joined together and placed in an evacuated chamber to cut down heat losses. The design of the container needs careful thought as it can double the mass of the battery. Before the batteries can be used they have to be heated slowly to their working temperature. When in use the cells are essentially self-heating due to the electric current passing through the battery internal resistance. When not in use for more than a day the battery’s interior has to be kept hot by the use of electrical heaters. The electrical energy is obtained from combining sodium with sulfur to form sodium sulfide. The basic chemical formula for the reaction is Na+ xS ↔ Na 2 S x The overall characteristics of the battery are given in Table 3.4. Download 3.49 Mb. Share with your friends:
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