Sodium sulphur batteries

During the past two decades, the sodium-sulphur battery which... 

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

For EV applications (e.g. urban delivery vans) the target figures for a commercially viable sodium-sulphur battery would be for a cycle life of... 

A fleet of Ford Ecostar vans is now operating in the US and Europe, powered by 34 kWh sodium-sulphur batteries. There have been a number of incidents in which sodium-sulphur batteries have been destroyed by the exothermic reaction which occurs when sodium and sulphur react chemically. Despite this, field trials are continuing indicating that these problems may not be insurmountable. 

Strong contenders for automotive power are the sodium/sulphur and sodium/ nickel chloride batteries, the latter known as the ZEBRA cell. ZEBRA was originally (c. 1979) an acronym devised for commercial security reasons but now it stands for the very apt Zero Emissions Batteries Research Activity . Several European car manufacturers including BMW and Mercedes have incorporated the ZEBRA cell into prototype cars, vans and buses. The performance of the battery far outstrips that of the lead/acid counterpart, as is evident from Fig. 

It follows from this brief outline that if maximum useful power is to be extracted from the cell then the electrolyte resistance must be kept to a minimum. This is dependent not only on the material but also on the geometry of the membrane which must be as thin as is practicable. As in the case of the fuel cell, the e.m.f can be calculated from thermodynamic principles. In fact the chemical reactions occurring when the sodium ions react with the sulphur are rather complex and the sodium sulphur ratios change as the battery discharges. The first product as the cell discharges is the compound Na2S5. 

Amongst other new systems under study are the sodium/sulphur battery with sodium / -alumina solid electrolyte operating at 300-375°C and Li-FeS batteries operating at about 450°C. Long-term battery research is directed towards batteries that can operate at room temperature with aqueous electrolyte, such as zinc-halogen, aluminium-air, and iron-air. 

Exposure to a chemical can cause damage at the point or site of exposure if the substance is reactive, irritant, corrosive, or caustic. Thus substances such as kettle descaler (formic acid), battery acid (sulphuric acid), caustic soda (sodium hydroxide), and bleach (sodium hypochlorite/hypochlorous acid) can cause serious, and maybe permanent, damage to the skin, the eyes or the oesophagus, and stomach if they come into contact with these parts of the body. Unfortunately, people sometimes attempt suicide by swallowing such substances for example, drinking kettle descaler or bleach causes serious damage to the lining of the gut (see case notes, p- 193). 

Review of the British Rail Sodium Sulphur Battery Programme, October 1980 R. M. Dell, J. L. Sudworth, and I. Wynn Jones, Proceedings of the 11th lECEC, State Line, 1976, p. 503. 

If the lifetime of Li-based batteries (the term lithium ion batteries for batteries with polar Li-compounds as negative electrodes is very unfortunate) can be further enhanced, they will be also of importance for electrotraction. The classical battery type used in automobiles, viz, the lead-acid accumulator, is distinctly superior in terms of long-time stability but possesses too low an energy content per unit weight as to drive automobiles. Driving car of sensible size and performance with this alone requires a battery weight on the order of 11, (This problem is not removed by using Ni-Cd accumulators,) Much effort has been undertaken to develop a sodium-sulphur cell. In the Na-S cells ... 

Sodium batteries and cells are designed such that the electrolyte is solid and the electrodes are liquid. In hermetically sealed sodium-sulphur batteries, the sodium and sulphur electrodes are heated to a molten state (300 to 350 C)... 

The sodium/sulphur system is being discussed for load levelling and car traction and is believed to be close to commercial production in the UK as a traction battery for commercial vehicles. The overall cell reaction is usually written... 

It is well known that the 3- and 3"-aluminas are sodium ion conductors with promising applications as an electrolyte for the sodium-sulphur secondary battery. They have been widely studied because of their technological and scientific interest . ... 

The Sodium/sulphur battery concept dates from 1966, en Ford s initial patents were filed. Since then, it is estimated that over 500 million has been spent on the development of this battery, of which 250 million has been spent by one group alone (DOE, personal communication). 

Variations of the sodium/sulphur battery include systems with sodium/beta-alumina/sodium tetrachloroaluminate/nickel chloride or iron chloride. The early results are encouraging and the system suffers less from the problems of the sulphur electrode, such as rechargeability, high vapour pressure, various polysulphide formations etc. 

Ionic Conductor. A material in which the charge carriers are ions rather than electrons or holes. Ionic conductors usually have crystal structures containing channels, or planes through which cations can move. B-AI2O3 (NaAl, jOj,) is an ionic conductor, used as the electrolyte in sodium-sulphur storage batteries. See... 

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