nas battery
Post on 07-Jul-2018
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NaS
Battery
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Cathode: molten sulfur
Anode: molten sodium
Electrolyte: solid beta-alumina.
Beta-alumina solid electrolyte
(BASE) is a fast ion conductor
material used as a membrane in
several types of molten salt
electrochemical cell. Currently
there is no known substitute
available.
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During the discharge phase,• Molten elemental sodium at the core serves as the anode,
meaning that the Na donates electrons to the external circuit.
• The sodium is separated by a beta-alumina solid electrolyte (BASE)cylinder from the container of molten sulfur, which is fabricated
from an inert metal serving as the cathode. The sulfur is absorbed
in a carbon sponge.
•
BASE is a good conductor of sodium ions, but a poor conductor ofelectrons, and thus avoids self-discharge.
• When sodium gives off an electron, the Na+ ion migrates to the
sulfur container. The electron drives an electric current through
the molten sodium to the contact, through the electrical load and
back to the sulfur container. Here, another electron reacts with
sulfur to form Sn2−, sodium polysulfide.
• The discharge process can be represented as follows:
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As the cell discharges, the sodium level drops. During the
charging phase the reverse process takes place. Once
running, the heat produced by charging and discharging
cycles is sufficient to maintain operating temperatures and
usually no external source is required.
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Safety in NaS
Pure sodium presents a hazard, because it spontaneously
burns in contact with air and moisture, thus the systemmust be protected from water and oxidizing
atmospheres.
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2011 Tsukuba Plant fire incident
On September 21, 2011, NGK-manufactured NaS
batteries for storing electricity installed at the Tsukuba,Japan, plant caught fire. Following the incident, NGK
temporarily suspended production of NaS batteries.
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Challenges
1. Corrosion of the insulators was found to be a problemin the harsh chemical environment as they gradually
became conductive and the self-discharge rate
increased.
2. Dendritic-sodium growth can also be a problem.3. High operating temperature (250-300 oC
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What we Know about NaS
Refer to technical data of EES
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Case Study:
See Project file on Classroom.
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