High temperature sodium batteries

Sodium melts at 98°C and therefore many of the materials problems experienced with the handling of liquid lithium might be expected to occur in the development of high temperature sodium batteries. However, the 

Sodium-sulphur batteries with /3-alumina electrolyte ( beta batteries ) 

As shown in Fig. 8.14 the cell is formed in principle by two liquid electrodes, the sodium negative and the sulphur positive, separated by a tube of sintered polycrystalline /3-alumina. Since sulphur is an insulator, the compartment containing the sulphur electrode is fitted with a carbon felt current collector. The cell, which may be written as 

790 Wh/kg. As indicated in the sodium-sulphur phase diagram given in Fig. 8.15, sodium pentasulphide and sulphur are not mutually soluble at the temperature of cell operation, so that two liquid phases are present in the cathode compartment and the cell voltage is invariant. As the discharge progresses and the available elemental sulphur is consumed, a series of reactions commences as the sodium pentasulphide is converted to lower polysulphides, all of which are mutually soluble  

Almost all practical sodium-sulphur cells are based on electrolytes formed as closed tubes. These are usually manufactured by isostatic pressing, or electrophoretic deposition of powdered /3-aluminas (or their precursors) 

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K.B. Hueso, M. Armand, T. Rojo, High temperature sodium batteries status, challenges and future trends . Energy Environ. Sci., 6, 734-749, 2013. 

It is claimed that the cured materials may be used continuously in air up to 300°C and in oxygen-free environments to 400°C. The materials are of interest as heat- and corrosion-resistant coatings, for example in geothermal wells, high-temperature sodium and lithium batteries and high-temperature polymer- and metal-processing equipment. 

The Ecostar used high-temperature, sodium-sulfur batteries because of their range, but they also allowed the van to go from 0-60 in 12 seconds. The Ecostar had no trouble keeping up with gas vehicles, but Ford only built about 80 Ecostars. The sodium-sulfur batteries proved to be too sensitive to cold weather. They operated at 500° Fahrenheit and caused fires in several of the demonstrator cars. 

High-Temperature Sodium-Sulfur Battery This battery employs the ionic conductivity of P-alumina, that acts as a diaphragm containing liquid sodium which serves as the negative pole of the battery (Figure 7.12). The steel casing, which usually is... 

Figure 7.12 Schematic representation of a high-temperature, sodium-sulfur battery.

J. Prakash, L. Redy, P. Nelson, and D. Vissers, High Temperature Sodium Nickel Chloride Battery for Electric Vehicles, Electrochemical Society Proceedings, 96 14, (1996). 

Sodium—Sulfur. The best known of the high temperature batteries is the sodium [7440-23-5]—s Aiu.i. [7704-34-9] Na—S, battery (66). The cell reaction is best represented by the equation ... 

The poor efficiencies of coal-fired power plants in 1896 (2.6 percent on average compared with over forty percent one hundred years later) prompted W. W. Jacques to invent the high temperature (500°C to 600°C [900°F to 1100°F]) fuel cell, and then build a lOO-cell battery to produce electricity from coal combustion. The battery operated intermittently for six months, but with diminishing performance, the carbon dioxide generated and present in the air reacted with and consumed its molten potassium hydroxide electrolyte. In 1910, E. Bauer substituted molten salts (e.g., carbonates, silicates, and borates) and used molten silver as the oxygen electrode. Numerous molten salt batteiy systems have since evolved to handle peak loads in electric power plants, and for electric vehicle propulsion. Of particular note is the sodium and nickel chloride couple in a molten chloroalumi-nate salt electrolyte for electric vehicle propulsion. One special feature is the use of a semi-permeable aluminum oxide ceramic separator to prevent lithium ions from diffusing to the sodium electrode, but still allow the opposing flow of sodium ions. 

A prerequisite of long-life sodium/sulfur batteries is that the cells contain suitable corrosion-resistant materials which withstand the aggressively corrosive environment of this high—temperature system. Stackpool and Maclachlan have reported on investigations in this field [17], The components in an Na/S cell are required to be corrosion-resistant towards sodium, sulfur and especially sodium polysulphides. Four cell components suffer particularly in the Na/S environment the glass seal, the anode seal, the cathode seal, and the current collector (in central sodium arrangements, the cell case). 

Sodium cells20-23 operate at fairly high temperatures (300-400 °C) and require an inert atmosphere (argon) in a sealed, corrosion-resistant vessel (e.g., Cr-coated steel). Furthermore, leakage of liquid Na could obviously have dire consequences. Nevertheless, sodium-sulfur cells have received serious consideration as rechargeable batteries ... 

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