Sodium/sulfur batteries technology

TABLE 40.1 Advantages and Limitations of Sodium/Sulfur Battery Technology... 

Sodium-Sulfur Batteries. The sodium-sulfur battery consists of molten sodium at the anode, molten sulfur at the cathode, and a solid electrolyte of a material that allows for the passage of sodium only. For the solid electrolyte to be sufficiently conductive and to keep the sodium and sulfur in a liquid state, sodium-sulfur cells must operate at 300°C to 350°C (570°F to 660°F). There has been great interest in this technology because sodium and sulfur are widely available and inexpensive, and each cell can deliver up to 2.3 volts. 

Current developments in battery technology, electrochromic devices (see Box 22.4) and research into electrically powered vehicles make use of solid electrolytes (see Box 10.3). The sodium/sulfur battery contains a solid 3-alumina electrolyte. The name (3-alumina is misleading since it is prepared by the reaction of Na2C03, NaN03, NaOH and AI2O3 at 1770K and is a non-stoichiometric compound of approximate... 

T. Oshima, M. Kajita and A. Okuno (2004) International Journal of Applied Ceramic Technology, vol. 1, p. 269 - Development of sodium-sulfur batteries . 

The principle of operation is illustrated on Figure 4. The fast ion conductor 3-aluminium has been developed as the basic component of the sodium sulfur battery cell. Whether it will give birth to a new technological process is too early to predict. 

The sodium/beta battery system includes designs based on either the sodium/sulfur or the sodium/metal chloride chemistries (see Chapter 40). The sodium/sulfur technology has been in development for over 30 years and multi-kW batteries are now being produced on a pilot plant scale for stationary energy storage applications. At least two 8 MW/40 MWh sodium/sulfur batteries have been put into service for utility load leveling by TEPCO in Japan. 

Sodium/nickel chloride is a relatively new variation of the sodium/beta technology and was being developed mainly for electric-vehicle applications. There has not been nearly the effort on this chemistry as on the sodium/sulfur battery. 

Relative to other motive applications, the U.S. Air Force designed and conducted a flight experiment aboard a space shuttle to determine the effect of a micro-G environment on the performance of a small, 4-cell sodium/sulfur battery. This successful test used cells manufactured by Eagle-Picher Technologies (Table 40.5). ... 

A battery system closely related to Na—S is the Na—metal chloride cell (70). The cell design is similar to Na—S however, ia additioa to the P-alumiaa electrolyte, the cell also employs a sodium chloroalumiaate [7784-16-9J, NaAlCl, molten salt electrolyte. The positive electrode active material coasists of a transitioa metal chloride such as iroa(Il) chloride [7758-94-3] EeQ.25 or nickel chloride [7791-20-0J, NiQ.25 (71,72) in Heu of molten sulfur. This technology is in a younger state of development than the Na—S. 

Other battery technologies include sodium-sulfur which was used in early Ford EVs, and zinc-air. Zinc appeared in GM s failed Electrovette EV in the late 1970s. Zinc-air batteries have been promoted by a number of companies, including Israel s Electric Fuel, Ltd. Zinc is inexpensive and these batteries have six times the energy density of lead-acid. A car with zinc-air batteries could deliver a 400 mile range, but the German postal service found that these batteries cannot be conventionally recharged. 

This paper restricts itself to sodium-sulfur cells and batteries which use solid electrolyte cell dividers and provides a current picture of the state of scientific knowledge and technological achievement with respect to sodium-solid electrolyte-sulfur batteries. The references cited should not be construed as a complete review but should instead be viewed as an introduction to the relevant literature. 

Although the cited examples are far from being prototypes of production devices, they do validate the feasibility of fully packaged sodium-sulfur cells and provide a measure of projected performance. It seems that sufficient information is now available to permit researchers to speculate on the design of large cells and battery systems and to project the performance of such devices on the basis of anticipated technology. 

In Europe, the drive system of the Impact propelled the Opel Impuls2, a conversion vehicle based on the Opel Astra Caravan in 1991. A new, specifically developed AC induction drive unit with IGBT inverter technology was used to build a small fleet of Impuls vehicles see Figure 8.4). The fleet served as an automotive test bed for the integration of various advanced battery systems such as nickel-cadmium, nickel-metal hydride, sodium-nickel chloride, sodium-sulfur, and sealed lead-acid. 

Africa)io is a variant of sodium-sulfur technology where sulfur is replaced with a metal chloride such as NiCl2 (nickel chloride) or FeCU. It was specifically developed for applications in electric vehicles, freight transport and public transport the ZEBRA battery is more particularly intended to serve buses and utility vehicles. As with the Na-S battery, the vibrations felt in a vehicle may cause premature aging of the ceramic/metal interface. Today, such batteries are also being considered for stationary applications. 

We conclude with the point that the main competitive technologies for hydrogen batteries are redox flow batteries (VRB Power Systems) and sodium-sulfur (NaS) batteries (NGK Insulators). 

Sodium/sulfur and sodium/metal chloride technologies are similar in that sodium is the negative electrode material and beta-alumina ceramic is the electrolyte. The solid electrolyte serves as the separator and produces 100% coulombic efficiency. Applications are needed in which the battery is operated regularly. Sodium/nickel chloride cells have a higher open-circuit voltage, can operate at lower temperatures, and contain a less corrosive positive electrode than sodium/sulfur cells. Nevertheless, sodium/nickel chloride cells are projected to be more expensive and have lower power density than sodium/sulfur cells. 

This section on battery-ievel information is organized the same as Sec. 40.3. That is, battery-ievei design considerations specific to the sodium/sulfur technology are presented first. Then, brief descriptions of modern battery configurations and performance for both sodium-beta technologies are provided. For reference, a schematic diagram of an integrated sodium/ nickel-chloride battery system was shown previously in Fig. 40.5b. 

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