S ODIUM S ULFUR B ATTERIES Elisa Zaleski M AT 286G Final May 26, 2010

B ATTERY B ASICS 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

C URRENT : N AMING THE A NODE AND C ATHODE N E S W Current Electrolytic Cell (Recharging) Anode (Positive Electrode) “Way Up” Cathode (Negative Electrode) “Way Down” Electrolyte

N A S: T HE B ASICS 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 ≅ 300 o C (to maintain the electrodes in the liquid state) Potential Applications: – Electric vehicles Ford Ecostar 1991 – Energy storage

N A S: T HE B ASICS 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

N A S: T HE C ONSTRUCTION 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

N A S: T HE C HEMISTRY Discharge 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 2Na + xS  Na 2 S x Charge Sodium polysulfides decompose Na + passes back through the electrolyte

D ISCHARGE C YCLE Oshima, Kajita, and Okuno, Int. J. Appl. Ceram. Technol., 1 [3] (2004)

C HARGE C YCLE Oshima, Kajita, and Okuno, Int. J. Appl. Ceram. Technol., 1 [3] (2004)

P OLYSULFIDE VERSUS V OLTAGE The polysulfide formed changes with state-of-charge – At ~Na 2 S 2 it is at full discharge Oshima, Kajita, and Okuno, Int. J. Appl. Ceram. Technol., 1 [3] (2004)

T RANSPORTING N A + : β - ALUMINA Na 2 O(5-11)Al 2 O 3 – NaAl 11 O 17 – Non-stoichiometric compound of Na 2 O and Al 2 O 3 that includes β and β ” β ” = Na 2 O(5-7)Al 2 O 3 – 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] (2004)

T RANSPORTING N A + : N A SICON Superior Na + conductivity compared to β -alumina Na 1+x Si x Zr 2 P 3-x O 12 (0<x<3) 3D network of ZrO 6 octahedra sharing corners with PO 4 and SiO 4 tetrahedra Na + located in interstitial sites Mainly monoclinic NASICON Housecroft and Sharpe, Inorganic Chemistry, 3 rd Edition 2008

N A SICON VS β- ALUMINA Housecroft and Sharpe, Inorganic Chemistry, 3 rd Edition 2008

N A S B ATTERIES : T AKING US OFF THE GRID ?

B ATTERIES : S TORING ENERGY

N A S B ATTERIES : T AKING US OFF THE GRID ? Ceramatec is developing a low temperature (<100 o C) 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