Sodium—sulfur system

Among high-temperature batteries, the lithium-iron sulfide systems are reasonably safe, although there are some hazards connected with the 450-500°C operating temperature. The sodium-sulfur-system impact failure hazards are primarily connected with the possibility of SO2 emissions, sodium oxide dust, and fires resulting from sodium exposure to moisture. 

Figure 2. Phase diagram of the sodium-sulfur system...

In 1967 Kummer and Weber of the Ford Motor Company described the sodium/sulfur system as a new secondary battery [11]. At almost the same time Levine and Brown published a paper on a similar system, differing only in using... 

In determining the chemical resistance, color changes of pigmented binder surfaces are measured after their exposure to various chemicals, such as water—sulfur dioxide or water—sodium chloride systems. These systems imitate the environment to which the colored articles could become exposed. 

The Na—S battery couple is a strong candidate for appHcations ia both EVs and aerospace. Projected performance for a sodium—sulfur-powered EV van is shown ia Table 4 for batteries having three different energies (68). The advantages gained from usiag a Na—S system rather than the conventional sealed lead—acid batteries are evident. 

Sodium Hypochlorite—Acid—Sodium Chlorite System. In this method, hydrochloric or sulfuric acid is added into a sodium hypochlorite [7681 -52-9] NaOCl, solution before reaction with the sodium chlorite (118). 

Though sodium-sulfur batteries have been under development for many years, major problems still exists with material stability. It is likely that the first commercial uses of this batteiy will not be for electric vehicles. Sodium-sulfur storage batteries may be more well-suited for hybrid electric vehicles or as part of a distributed energy resources system to provide power ill remote areas or to help meet municipal peak power requirements. 

The molten salt electrolyte also contributes to the safety behavior of ZEBRA cells. The large amount of energy stored in a 700 g cell, which means about 30 kWh in a 300 kg battery, is not released suddenly as heat as be expected in a system with liquid electrodes such as the sodium sulfur cell. In the case of accidental destruction of ZEBRA cells, the sodium will react mainly with the molten salt, forming A1 sponge and NaCl. -The diffusion of the NaAICI ... 

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). 

In the potassium-sulfur system the compounds K2S, K2S2, K2S3, K2S4, K2S5, and K2S6 exist and there are six eutectics [15]. All sodium and potassium sulfides and polysulfides are hygroscopic and some of them form well defined hydrates. 

Stationary battery (cell) — Rechargeable -> batteries designed to be located at a fixed place. Stationary batteries are used mainly for uninterruptible power supplies (UPS) and standby applications. These cells are usually designed for high reliability and very long -> cycle life under shallow depth of discharge (DOD) conditions. The common chemical systems utilized for the production of stationary batteries are the -> lead-acid and -> nickel-cadmium batteries. Less common, and more futuristic is the - sodium-sulfur battery designed for KW and... 

High-density power sources can be obtained from lithium- and sodium-sulfur batteries. The sulfides present in these systems are M2S, M2S2, M2S4, and M2S5. 

R. S. Gordon, W. Fischer, A, V, Virkar, in Ceramic Transactions Vol. 65, Role of Ceramics in Advanced Electrochemical Systems, P. N. Kumpta, G. S. Roher, U. Balachadran, eds., American Ceramic Society, Westerville, OH, 1996, pp. 203-237. Current review on the application of ceramics in the sodium sulfur battery and the solid oxide fuel cell. 

With magnesium-, sodium-, or ammonium-based sytems, the bisulfite and sulfite salts are all soluble at all proportions in the presence of sulfurous acid. Even magnesium sulfite, with a solubility of about 1.25 g/100 mL, cold, is about 160 times as soluble as calcium sulfite at the same temperature and its solubility increases with temperature. So liquor preparation with these sulfite salts is easier, whether for acid sulfite, bisulfite, or NSSC pulping conditions, and even for experimental tests under alkaline conditions. For ammonium-based systems, ammonium hydroxide is contacted with a sulfur dioxide gas stream for liquor preparation. Magnesium-based systems use a magnesium hydroxide slurry to contact the sulfur dioxide gas stream. Sodium-based systems normally employ sodium carbonate lumps in a sulfiting tower, in a method similar to that used for NSSC liquor preparation. Sodium hydroxide may also be used if available at low cost. 

Another type of electrical conductivity observed in ceramics is ionic conductivity, which often occurs appreciably at elevated temperature a widely used material exhibiting this behavior is zirconia doped with other oxides such as calcia (CaO) or yttria (Y2O3). For this material, atomic oxygen is the mobile ionic species. Doped zirconia finds widespread use as oxygen sensors, especially as part of automobile emission control systems, where the oxygen content of the exhaust gas is monitored to control the air-to-fuel ratio. Other applications of ionic conducting ceramics are as the electrolyte phases in solid-oxide fuel cells and in sodium-sulfur batteries. 

Metallic sodium, or sodium hydroxide and sulfur, may also be extracted from flue gas by electrolysis of molten sodium sulfide (produced in the gas desulfurization process) by application of the charging reaction of the sodium-sulfur battery. This could conceivably be converted to a power-producing system if oxygen can be reduced at the cathode without severe polarization. Again, a beta-alumina diaphragm must be used to separate the sodium sulfide from the sodium hydroxide. 

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