SODIUM SULFUR BATTERIES
Elisa Zaleski
MAT 286G Final
May 26, 2010
BATTERY BASICS
• A chemical reaction produces electrons
– Electrons travel from the (-) to the (+) electrode
– Ions travel through the electrolyte
• “Anode” = from the Greek for “way up”
– Current flows through the anode into the device
• Discharging? Negative electrode
• Charging? Positive electrode
• “Cathode” = from the Greek for “way down”
– Current flows through the cathode out of the
device
• Discharging? Positive electrode
• Charging? Negative electrode
CURRENT: NAMING THE ANODE AND CATHODE
N
Cathode
(Negative
W
Electrode)
“Way Down”
Current
Electrolyte
Anode
(Positive
E Electrode)
“Way Up”
S
Electrolytic Cell (Recharging)
NAS: THE BASICS
• Liquid sodium and liquid sulfur as the negative
and positive electrodes
• Solid ceramic as the Na+ conducting electrolyte
– β-alumina
– NaSICON (Na Super Ionic CONductor)
• Operating temperature ≅ 300oC (to maintain
the electrodes in the liquid state)
• Potential Applications:
– Electric vehicles
• Ford Ecostar 1991
– Energy storage
www.greencar.com/articles/ford-ecostar-ev.php
NAS: THE BASICS
• Key Features:
– High-energy density (~367Wh/l) with a reduction
in space required for the battery
– EMF ~ 2V
– No self-discharge
– High cycle life
• 40,000+ cycles at 20% depth of discharge (DOD)
• 4,500 cycles to 90% DOD
• 2,500 cycles to 100% DOD
– Sodium and sulfur are relatively abundant
NAS: THE CONSTRUCTION
• Solid electrolyte
separates the sodium
inner core from the
sulfur annulus
• Protective Fe-75Cr
coating is plasma
sprayed on the inner
wall to avoid
corrosion
• Configured in series
and parallel
Image courtesy of NASA Glenn Research Center
NAS: THE CHEMISTRY
2Na + xS  Na2Sx
Discharge
Charge
• Na (negative electrode)
sends electrons through
the circuit
• Na+ pass through the
electrolyte
• Na+ reacts with S to form
sodium polysulfides at
the positive electrode
• Sodium polysulfides
decompose
• Na+ passes back through
the electrolyte
DISCHARGE CYCLE
Oshima, Kajita, and Okuno, Int. J. Appl. Ceram. Technol., 1 [3] 269-76 (2004)
CHARGE CYCLE
Oshima, Kajita, and Okuno, Int. J. Appl. Ceram. Technol., 1 [3] 269-76 (2004)
POLYSULFIDE VERSUS VOLTAGE
• The polysulfide
formed changes with
state-of-charge
– At ~Na2S2 it is at full
discharge
Oshima, Kajita, and Okuno, Int. J. Appl. Ceram. Technol., 1 [3] 269-76 (2004)
TRANSPORTING NA+: β-ALUMINA
• Na2O(5-11)Al2O3
– NaAl11O17
– Non-stoichiometric
compound of Na2O
and Al2O3 that includes
β and β”
• β” = Na2O(5-7)Al2O3
– MgO added to
increase the stability at
the high sintering
temperatures
• ‘Spinel’ layers separated
by conduction planes
Oshima, Kajita, and Okuno, Int. J. Appl. Ceram. Technol., 1 [3] 269-76 (2004)
TRANSPORTING NA+: NASICON
• Superior Na+
conductivity compared
to β-alumina
• Na1+xSixZr2P3-xO12 (0<x<3)
• 3D network of ZrO6
octahedra sharing
corners with PO4 and
SiO4 tetrahedra
• Na+ located in
interstitial sites
• Mainly monoclinic
NASICON
Housecroft and Sharpe, Inorganic Chemistry, 3rd Edition 2008
NASICON VS β-ALUMINA
Housecroft and Sharpe, Inorganic Chemistry, 3rd Edition 2008
NAS BATTERIES: TAKING US OFF THE GRID?
BATTERIES: STORING ENERGY
http://www.npr.org/templates/story/story.php?storyId=110997398
NAS BATTERIES: TAKING US OFF THE GRID?
• Ceramatec is developing a low temperature
(<100oC) solid NaS battery using a NaSICON
electrolyte designed for home energy storage
– Prototype due out 2011
• Potential Specs
– 20kWh
– Daily charge/discharge cycles over 10 years
– $2000 per refrigerator sized unit
• $100/kWh or <$0.03/kWh over the battery’s lifetime
• Grid storage market expected to increase from
$365 million today to ~$2.5 billion by 2015