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Graphite Intercalation with Large Fluoroanions. Dept. of Chemistry and Center for Advanced Materials, Oregon State University. Intercalation. http://www.cem.msu.edu/~pinnweb/research-na.htm. Intercalation Hosts. Ion exchange: (fixed charge density)

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Graphite Intercalation with Large Fluoroanions


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    1. Graphite Intercalation with Large Fluoroanions Dept. of Chemistry and Center for Advanced Materials, Oregon State University

    2. Intercalation http://www.cem.msu.edu/~pinnweb/research-na.htm Oregon State University

    3. Intercalation Hosts Ion exchange: (fixed charge density) smectite clay Nax+y[Al2-yMgySi4-xAlxO10(OH)2] layered double hydroxide [Mg3Al(OH)8]Cl metal phosphorous sulfide K0.4[Mn0.80.2PS3] Redox reaction: (variable charge density) metal dichalocogenide Lix[MoS2] layered oxides Lix[CoO2], Nax[MoO3] graphite K[C8], [C24]HF2 Oregon State University

    4. Energetics For clays – reaction is ion-exchange: Na+ Mont- + N(R)4+ Cl- (aqu) -> N(R)4+ Mont- + NaCl (aqu) For graphite – reaction is redox: Cx + A -> Cx+ A- ΔHrxn = I (Cx) - Ea (A) - ΔHL Oregon State University

    5. Graphite structure • C-C in-plane = 1.42 Å • Usually (AB)n hexgonal stacking • Interlayer distance = 3.354 Å Graphite is a semi-metal, chemically stable, light, strong A B Source: http://www.ccs.uky.edu/~ernst/ A Oregon State University

    6. + + + - - - Graphite Intercalation oxidant This is an acceptor-type GIC Donor-type reduces layers and intercalates cations Oregon State University

    7. GIC types ReductionM+Cx- Group 1 except Na Oxidation Cx+An- F, Br3-, O (OH) BF4-, P  BiF6- , GeF62- to PbF62-, MoF6-, NiF62-, TaF6-, Re  PtF6- SO4-, NO3-, ClO4-, IO3-, VO43-, CrO42- AlCl4-, GaCl4-,FeCl4-, ZrCl6-,TaCl6- Oregon State University

    8. Staging and dimensions Ic = di + (n - 1) (3.354 Å) For fluoro, oxometallates di≈ 8 A, for chlorometallates di≈ 9-10 A Oregon State University

    9. Graphite oxidation potentials H2O oxidation potential vs Hammett acidity Colored regions show the electrochemical potential for GIC stages. 49% hydrofluoric acid All GICs are unstable in ambient atmosphere , they oxidize H2O Oregon State University

    10. GIC special issues • Anions must be oxidatively stable • Larger anions could give larger galleries, wider range of chemistry • GICs that rapidly decompose in air or aqueous acid are hard to process further Oregon State University

    11. CxPFOS - preparation Cx+ K2Mn(IV)F6 + KSO3C8F17  CxSO3C8F17 + K3Mn(III)F6 (CxPFOS) Solvent = aqueous HF 3.35 A Oregon State University

    12. CxPFOS intercalate structure Anions self-assemble as bilayers within graphite galleries Oregon State University

    13. PFOS twist angle Chain twist defined by FC-CF tortion angle Oregon State University

    14. CxPFOS thermal stability CxPFOS KPFOS Oregon State University

    15. 1,2 Cx + K2MnF6 + LiN(SO2CF3)2 CxN(SO2CF3)2 + K2LiMnF6 oxidant anion source GIC O CF3 S N O O F3C S .. O New syntheses: chemical method 1. 48% hydrofluoric acid, ambient conditions 2. hexane, air dry Oxidant and anion source are separate and changeable. Surprising stability in 50% aqueous acid.

    16. CxN(SO2CF3)2 chem prepn Oregon State University

    17. F F F F New syntheses: N(SO2CF3)2 orientation

    18. CxN(SO2CF3)2 echem prepn 2  1 3  2 Oregon State University

    19. CxN(SO2CF3)2 - echem prepn CxPFOS CxN(SO2CF3)2 Oregon State University

    20. CxN(SO2CF3)2 anion orientation Oregon State University

    21. CxN(SO2CF3)2 thermal stability LiN(SO2CF3)2 Oregon State University

    22. Imide (NR2-) intercalates Anion MW di / Å N(SO2CF3)2 280 8.1 N(SO2C2F5)2380 8.2 N(SO2CF3) 430 8.3 (SO2C4F9) Oregon State University

    23. Other intercalated anions Anion MW di / Å C(SO2CF3)3 411 12.3 SO3C8F17 499 29.5 SO3C10F21 599 33.7 SO3C6F10(C2F5) 461 24.4 Oregon State University

    24. CxB(O2C2(CF3)4)2 Stage 1 1.13 0.85 nm 1.12 0.78 nm T Unexpected anion orientation - long axis to sheets Borate chelate GIC’s Blue: obs Pink: calc CxB(O2C2O(CF3)2)2 Stage 2

    25. Intercalation rates  Intercalate Temp / °C Reaction Anion  half-life / h SO3C8F17 20 10 N(SO2CF3)2 20 0.01 N(SO2CF3)(SO2C4F9) 70 100 N(SO2CF2CF3)2 70 500 C(SO2CF3)3 70 > 1000 SO3C6F5 20, 70 no reaction Oregon State University

    26. GIC ambient stabilities Oregon State University

    27. Application - IRP strategy 1. Intercalation 2. Removal 3. Optional cycle Targets • increase internal volume and disorder not surface area • low residual content Parameters: intercalate anion, reduction method (thermolysis, hydrolysis, hydrogenation) Oregon State University

    28. irrev reversible IRP charge-discharge • GIC is CxPFOS stage 2 • removal is by heating under N2 for 3 h • rate = C / 20 Oregon State University

    29. IRP for Li ion battery anodes e- + Cx + Li+ = CxLi Oregon State University