Li-S S and Li-Air Systems: The Characterization Challenge

Transcription

1 Li-S S and Li-Air Systems: The Characterization Challenge Petr Novák Anna Evans Arnd Garsuch (BASF SE) Hermann Kaiser Pascal Maire Tiphaine Poux Holger Schneider

2 2 Go beyond Li-ion! But what is there???

3 3 Go beyond Li-ion! But what is there??? Faraday Law Q=zF m M Specific Energy W =UQ

4 4 Battery Materials 2 nd /3 rd Generation C LiMO 2 LiC Li 0.5 MO 2 4 th Generation 2 Li + y (S,O) Li 2 (S,O) y 5 th Generation? 2 LiF 2 Li + F 2 U [V] U [V] LiMO 2 / Li 0.5 MO 2 S n / S 2- n Li / Li O 2 / O mah/g 1170 mah/g 1170 mah/g Li / Li + X F 2 / 2 F mah/g U [V] Li / Li + 0

5 5 The Characterization Challenge (I) The simple ELECTROCHEMISTRY

6 6 POWER vs. Energy Density Source: J. Tester, Sustainable Energy, p. 657

7 7 What do WE normally characterize? - Specific charge of the material (mah/g) - Voltage of a half-cell (V vs. Li) - And sometimes the cycling behavior 2Li + O Li 2 O ca V 7200 Wh/kg

8 8 What is a REAL Battery? Chemistry

9 9 Specific Energy Practical Specific Energy (System) log(wh/kg) Li-SOCl 2 Mg-AgCl Zn-MnO 2 Zn-Luft Ni-H 2 Ni-Zn Pb-PbO 2 Li-CF x Li-H O 2 2 Li-Cl 2 Na-S Li-Luft Al-Luft Divide the theoretical value by 4! log(wh/kg) Theoretical Specific Energy (Chemistry)

10 10 Specific Energy 2Li + O Li 2 O ca V X 7200 Wh/kg 2000 Wh/kg This is the maximum for an ideal chemistry!

11 11 And the ENERGY EFFICIENCY? 30% of the stored energy is LOST!!! T. Ogasawara, A. Débart, M. Holzapfel, P. Novák, and P. G. Bruce, J. Am. Chem. Soc (128), p. 1390

12 12 Air, Sulfur, Lithium, Great, they are cheap! Safe? SAFETY MEASURES DISABLED!

13 13 We HAVE TO Understand All Processes Inside! Electrode e - Electrolyte Mass transport Interface (charge transfer) Mass transport Migration Diffusion : D ~ cm 2 /s Diffusion : D ~ 10-6 cm 2 /s Migration

14 14 Scientific Look into Batteries

15 15 In Situ Characterization of Battery Electrodes Neutron diffraction Atomic force DEMS diffraction microscopy X-ray Dilatometry Raman microscopy Infrared spectroscopy The in situ tree Colorimetry

16 16 The Characterization Challenge (II) The Lithium Oxygen Cell

17 17 Differential Electrochemical Mass Spectrometry Reference Electrode

18 18 DEMS How Does It Work? TIMREX KS44 Graphite 1M LiPF 6, EC:DMC (1:1) 3-electrode system (Li metal = Ref. electrode) V vs. Li/Li mv/s

19 19 The Lithium Oxygen Cell 4.2 U [V vs. Li/Li + ] Cathode composition: 25 % Carbon 33 % Binder (fluorinated polymer) 42 % MnO 2 catalyst Electrolyte: Propylene carbonate 1 M LiPF 6 Counter electrode: Lithium Current density: 250 µa/cm 2 Specific charge [mah/g] (per m cathode )

20 20 DEMS: Li 2 O 2 O 2 + Li 2 Ion Ionenstrom current [ma] U [mv] U [mv] 1E-11 1E-12 m/z = 16 m/z = 32 m/z = 41 m/z = Zeit [h] I [ma] I [ma] I [ma] U [mv] Time Zeit [h] [h] 1 0

21 21 (1995) DEMS: Li 2 O 2 O 2 + Li 2 electrode with Li 2 O 2 electrode without Li 2 O Ion current [10-11 A] m/z = 32 Voltage Time [min] Cell voltage [V] Ion current [10-11 A] m/z = 32 Voltage Time [min] Cell voltage [V] T. Ogasawara, A. Débart, M. Holzapfel, P. Novák, and P. G. Bruce, J. Am. Chem. Soc (128), p. 1390

22 22 (2000) DEMS: Reactions in the Lithium-O 2 Battery oxidation of a composite electrode containing Li 2 CO 3 in response to a stepwise increased current under Ar S. A. Freunberger, Y. Chen, Z. Peng, J. M. Griffin, L. J. Hardwick, F. Bardé, P. Novák, and P. G. Bruce, J. Am. Chem. Soc., available on web (2011). - doi: /ja

23 23 The Characterization Challenge (III) The Lithium Sulfur Cell

24 24 The Lithium Sulfur Cell Sulfur is cheap, abundant, and environmentally benign Li-S battery: Specific Charge: 1170 Ah/kg (Li 2 S) Specific Energy: ~ 2500 Wh/kg 2500 / 4 = 625 Wh/kg for the real battery

25 25 The Lithium Sulfur Cell 2.8 OK; it works. Where are the problems? U [V] C m [mah/g]

26 26 The Lithium Sulfur Cell Sulfur: Insulator (Conductivity: S/cm) Aging of electrodes (e.g., by formation of inactive precipitates such as Li 2 S and Li 2 S 2 ) Problems Dendrite formation (if Li metal is used as anode material) Polysulfide shuttle

27 27 The Lithium Sulfur Cell: Standard Separator Li 2 S y Li 2 S x S 8 Li 2 S x (x = 4-8) Li 2 S x Li 2 S y (y = 1-2)

28 28 The Lithium Sulfur Cell: No Separator

29 29 The Lithium Sulfur Cell Add a membrane! Akridge et al., Solid State Ionics, 175, 243, 2004

30 30 Li + -Conducting Membrane: Proof of Concept

31 31 The Lithium Sulfur Cell: Standard Separator st Discharge, Long-chain Polysulfides 1st Discharge, Short-chain Polysulfides 1st Charge, Short-chain Polysulfides 1st Charge, Long-chain Polysulfides (1) Formation and reduction of polysulfides: U [V] S 8 + Li Li 2 S x 2.0 (2) Reduction to the final products: Li 2 S x Li 2 S 2 + Li 2 S C m [mah/g]

32 32 The Lithium Sulfur Cell Sulfur-carbon electrode in an LiPF 6 / triglyme electrolyte after shortcutting with a lithium anode. Use colorimetry and Raman microscopy!

33 33 Confocal Raman Microscopy Laser TV CCD Notch filter Beam splitter Lenses Grating Z Y X Objective Sample XYZ-Table Hole Autofocus Slit CCD Computer

34 34 Raman Spectroscopy of Polysulfide Solutions Li 2 S 3 Intensity [arb. units] Li 2 S 3 Li 2 S 5 Li 2 S Li 2 S 5 Li 2 S 7 Intensity [arb. units] Wavenumber [cm -1 ] No significant shift in peak positions observable Wavenumber [cm -1 ] Solutions prepared by Robert Bosch GmbH

35 35 Raman Spectroscopy: The Markers Sulfur Polysulfides ν (A 2 ) g Intensity [arb. units] ν (B 8 ) 2g ν (A 1 ) g Intensity [arb. units] Raman Shift [cm -1 ] Inactive sulfur detectable Li 2 S 8 Li 2 S 7 Li 2 S 5 Li 2 S 3 Li 2 S 2 Raman Shift [cm -1 ] Decrease in signal intensity with decreasing chain length of S x 2- anions

36 36 The Lithium Sulfur Cell: Where Are We? Specific Charge [mah/g] Cycle No.

37 37 Conclusion Development of in situ methods is pure fundamental research but it helps to avoid future problems in the battery industry.

38 38 Acknowledgments BASF SE, Ludwigshafen, Germany TIMCAL SA, Bodio, Switzerland Swiss National Science Foundation European Community my group THANK YOU FOR YOUR ATTENTION! Contributors: Anna Evans Arnd Garsuch Hermann Kaiser Pascal Maire Tiphaine Poux Holger Schneider and numerous former group members, other colleagues, and friends!