Novel Carbon Materials for Electrochemical Applications

1. Novel Carbon Materials for Electrochemical Applications Giselle Sandí Chemistry Division

2. In 1785 Luigi Galvani observed, while dissecting a frog, that the frog’s legs would twitch whenever touched by a steel rod

3. Topics of Discussion • The Rocking Chair Model: Lithium Ion Batteries • Types of Electrodes • Anodes of Choice • Synthesis and Characterization of Novel Carbon Materials • Electrochemical Performance • New Directions • Acknowledgments

4. Examples of Batteries Commercially Available

5. Comparison of the energy density of the most common rechargeable batteries Lithium-Ion (High Energy) Lithium-Ion (Long Life) Silver-Cadmium Nickel-Hydrogen Lead -Acid (Automotive) Nickel Cadmium (High Energy) Lead -Acid (High Energy) Nickel-Cadmium (Sealed) Alkaline Manganese

6. Problems with metallic Li Cathode Li = Anode e- e-

7. The Rocking Chair Model Charge Li+ Li+ Cathode Electrolyte Anode Li+ Li+ Discharge

8. Types of Electrodes Anode materials Cathode materials • Pitches • Cokes • Natural graphite • Fullerenes • Synthetic carbons • Transition metal oxides • and chalcogenides • Uni-dimensional structures: TiS3, NbSe3 • Bi-dimensional structures • Metal sulfides of Ti, Nb, Ta, Mo, and W • Metal oxides of V, Cr, Fe, Co, Ni and Mn • Three-dimensional structure • Manganese oxides: -MnO2 (Mn2O4) • Organic molecules • Polymers

9. Practical Considerations • Selection of a suitable electrolyte • To minimize the decomposition that occurs during the lithiation of the carbon  formation of a passivating layer • Liquid electrolytes: LiPF6/EC/DEC • Polymer electrolytes • Low surface area carbons • Amount of lithium consumed in the formation of the passivating layer is proportional to the surface area of the carbon

10. The Novel Approach At the beginning…. Intercalation + + Silicate layer Pore + +  -nH2O + + + + Hydroxyl cation Pillared clay (PILC)

11. Carbon Precursors Linear polymer Condensation polymer similar to phenoplasts O O O Mechanism similar to Schll reaction: 2 ArH Ar-Ar + H2 Incorporation of liquid monomer followed by low temperature polymerization reaction AlCl3 H+ H H H C C C H H H Gaseous hydrocarbon is deposited in the PILC layers and pyrolized

12. Pyrene Loading Methods pyrolize at 700 °C under N2, dissolve in HF, and reflux in HCl overnight dry Styrene N2 Wash out excess and dry To vacuum C2H4 or C3H6 PILC Styrene C2H4 or C3H6 N2

13. Characterization Techniques • X-ray powder diffraction • Thermal gravimetric analysis • Scanning electron microscopy • Transmission electron microscopy • Scanning tunneling microscopy • Near-edge X-ray absorption fine structure • Small angle neutron scattering • Small angle X-ray scattering • NMR techniques • Electrochemical techniques

14. XRD of carbon samples derived from the “templating” method

15. High resolution TEM of a carbon sample synthesized using PILC/pyrene

16. C K-edge of different carbon samples

17. O K-edge of different carbon samples

18. C K-edge of different carbon electrodes

19. SANS Analysis Theory of Freltoft, Kjems, and Sinha (Phys. Rev. B. 1986) q-df  Log S (Q) 1/ 1/r Log Q () Where: df = fractal dimension r = hole radius  = cutoff length

20. Experimental parameters calculated from SANS data

21. Schematic representation of the mechanism of formation of porous carbon using PILC/pyrene Al2O3 15 Å r0 N2, 700 °C r0 3.7 Å 11.4 Å HF, HCl Al2O3

22. Coin cell used to test the electrochemical performance Electrodes were prepared using: 90% m/m carbon 5% m/m carbon black 5% m/m binder (PVDF in NMP)

23. Electrochemical parameters Where: charge is the charge capacity t0 is the starting time t is the current time I is the current value measured for this data point Applied current for 20 hrs (C/20): I20h = 18.6 (mA) x Wact (g)

24. Voltage profiles of the second cycle of various C/Li cells

25. Coulombic efficiencies obtained for C/Li coin cells cycled between 0 and 2.5 V

26. Effect of different carbon precursors on the performance of Li/C coin cells

27. Role of curved vs. planar carbon lattices in the lithium uptake Influence of a curved lattice (C60) on the nature of lithium bonding and spacing in endohedral lithium complexes The curved ring structure of the C60 facilitated the close approach of the lithiums (2.96 Å), even in the trilithiated species Interior of the C60 is large enough to easily accommodate two or three lithium atoms

28. Role of curved vs. planar carbon lattices in the lithium uptake….. • Implications: • 2.96 Å is closer than the interlithium distance in the stage-one LiC6 complex • Lithium anode capacities may be improved over graphitic carbon by synthesizing carbons with curved lattices such as corannulene • Concept was experimentally tested using corannulene as a model electrode material

29. Voltage profile of an electrode made of corannulene vs. Li

30. Electrochemical NMR • Uses: • Near electrode chemistry • Electrode-electrolyte interface • Electrolyte depletion zone • Transport properties of battery materials • Electrolyte penetration • Redox chemistry at the SEI • Li “location” and chemical nature Potentiostat Working Electrode Counter Electrode NMR Spectrometer

31. Electrochemical NMR…New approach The “old” cell The “new” toroid cavity coin cell Working electrode (current collector) and NMR detector (central conductor) Carbon sample Celgard separator Lithium Copper mesh  Standard 2032 size  In situ NMR detector  Imaging capability

32. Electrochemical NMR…Spectra obtained using the new cell A) Li intercalated into graphite, Li:C 0.8:6 B) Li-corannulene complex, Li:C  1.8:6

33. An advanced synthetic route to produce high performance carbons…..sepiolite clay A= Two tetrahedral sheets and a central magnesium octahedral sheet N= neutral sites B= cross section of an ideal fiber P= charged adsorption sites

34. XRD of sepiolite, sepiolite/propylene composite, and carbon obtained after removal of the template

35. TEM of sepiolite, sepiolite/propylene composite, and carbon obtained after removal of the template

36. Voltage profile and efficiency of carbon electrodes derived from sepiolite/propylene

37. Electrochemical NMR…Spectra obtained using the new cell

38. Cu mesh Cu mesh Polypropylene bag Electrolyte Separator Carbon Li Pouch electrochemical cell for in situ SAXS experiments

39. In situ SAXS results of a carbon electrodes a) derived from sepiolite and b) commercial graphite a Lattice expansion upon Li incorporation b There are no changes in the structure upon Li incorporation

40. Changes in the power law slope with discharge from 2.6 to 0 V

41. Summary • The novel approach for synthesizing carbon produced good • candidates for electrochemical applications • Understanding the performance of these carbons as a function of structure has been a main goal of this research • More efforts will be dedicated to conducting in situ SAXS and NMR experiments to elucidate the Li “location” upon charging and discharging electrochemical cells

42. ACKNOWLEDGMENTS This work was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, under contract number W-31-109-ENG-38. Randy Winans (CHM) Kathleen Carrado (CHM) Christopher Johnson (CMT) Rex Gerald and Robert Klingler (CMT) P. Thiyagarajan (IPNS) Sönke Seifert (CHM, APS) Roseann Csencsits (MSD) Lawrence Scanlon (Wright Patterson AFB) Lawrence Scott (Boston College)