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2.5V open circuit - no current drawn - energy density 4 x Pb/H 2 SO 4 battery of same weight

e-. Li+. ELECTROCHEMICAL SYNTHESIS OF Li x TiS 2 TiS 2 + xLi + + xe -  Li x TiS 2 AN ATTRACTIVE ENERGY STORAGE SYSTEM???. 2.5V open circuit - no current drawn - energy density 4 x Pb/H 2 SO 4 battery of same weight.

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2.5V open circuit - no current drawn - energy density 4 x Pb/H 2 SO 4 battery of same weight

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  1. e- Li+ ELECTROCHEMICAL SYNTHESIS OF LixTiS2TiS2 + xLi+ + xe- LixTiS2AN ATTRACTIVE ENERGY STORAGE SYSTEM??? 2.5V open circuit - no current drawn - energy density 4 x Pb/H2SO4 battery of same weight Controlled potential coulometry, voltage controlled intercalation rate and x value, number of equivalents of charge passed Li metal anode: Li  Li+ +e- PEO/Li(CF3SO3) polymer-salt electrolyte or propylene carbonate/LiClO4 non aqueous electrolyte PVDF(filler)/C(conductor)/TiS2/Pt(contact) composite cathode: TiS2 + xLi+ +xe- LixTiS2

  2. E E t2g Ti(IV) delocalized t2g Ti(III) localized S(-II) 3pp VB N(E) CHEMICAL SYNTHESIS OF LixTiS2 • xC4H9Li + TiS2 (hexane, N2/RT)  LixTiS2 + x/2C8H18 • Filter, hexane wash • 0  x  1 • Electronic description LixTix(III)Ti(1-x) (IV)S2 mixed valence localized t2g states or LixTi (IV-x)S2 delocalized partially filled t2g band

  3. Li/TiS2 AN ATTRACTIVE ENERGY SOURCE BUT MANY TECHNICAL OBSTACLES TO OVERCOME • Technical problems need to be overcome with both the Li anode and intercalation cathode • Battery cycling causes Li dendritic growth at anode - need other Li-based anode materials, Li-C composites, Li-Sn alloys, also rocking chair LixMO2 configuration • Mechanical deterioration of multiple intercalation-deintercalation lattice expansion-contraction cycles at the cathode • Cause lifetime, corrosion, reactivity, and safety hazards

  4. LiCoO2 LixC6 ROCKING CHAIR LSSB Li LiCoO2

  5. Co Co OTHER INTERCALATION SYNTHESES WITH TiS2 • Cu+, Ag+, H+, NH3, RNH2, Cp2Co, chemical, electrochemical • Cobaltacene especially interesting, (Cp2Co)x+Tix3+Ti1-x4+S2 chemical-electronic description consistent with structure spectroscopy • Solid state wide line NMR shows two forms of ring wizzing and molecule tumbling dynamics, Cp2Co+ molecular axis orthogonal and parallel to layers, dynamics yields activation energies for the different rotational processes Synthesis, Cp2Co-CH3CN(solution)/TiS2(s)

  6. EXPLAINING THE MAXIMUM 3Ti: 1Co STOICHIOMETRY IN TiS2(Cp2Co)0.31 Interleaved Cp2Co(+) cations Matching trigonal symmetry of chalcogenide sheet Geometrical and steric requirements of packing transverse oriented metallocene in VDV gap

  7. INTERCALATION ZOO • Channel, layer and framework materials • 1-D chains: TiO2 channels, (TiS3 [Ti(IV)S(2-)S2(2-)], NbSe3 [Nb(IV)Se(2-)Se2(2-)]), contain disulfide and diselenide units in Oh building blocks to form chain • 2-D layers: MS2, MSe2, NiPS3 [Ni2(P2S6), ABAB CdI2 packing, octahedral alternating layers of NiS6 and P2S6 groupings with Van der Waals gap], FeOCl, V2O5.nH2O, MoO3, TiO2 (layered polymorph) • 3D framework: zeolites, WO3, Mo6S8, Mo6Se8 (Chevrel phases)

  8. TiS3 = Ti(IV)S(2-)S2(2-) intercalated cations like Li(+) in channels between chains to form LixTiS3 Ti(IV) = S2(2-) = S(2-) = Li(+) = FACE BRIDGING OCTAHEDRAL TITANIUM TRISULFIDE AND NIOBIUM TRISELENIDE BUILDING BLOCKS FORM 1-D CHAINS

  9. W O M 3-D OPEN FRAMEWORK TUNGSTEN OXIDE AND TUNGSTEN OXIDE BRONZES MxWO3 c-WO3 = c-ReO3 structure type with injected cation M(q+) center of cube and charge balancing qe- in CB, MxWO3 perovskite structure type M(q+) O CN = 12, O(2-) W CN = 2, W(VI) O CN = 6

  10. Unique 2-D layered structure of MoO3 Chains of corner sharing octahedral building blocks sharing edges with two similar chains, Creates corrugated MoO3 layers, stacked to create interlayer VDW space, Three crystallographically distinct oxygen sites, sheet stoichiometry 3x1/3 ( ) +2x1/2 ( )+1 ( )

  11. ELECTROCHEMICAL OR CHEMICAL SYNTHESIS OF MxWO3 • xNa+ + xe- + WO3 NaxWx5+W1-x6+O3 • xH+ + xe- + WO3 HxWx5+W1-x6+O3 • Injection of alkali metal cations generates perovskite structure types • M+ oxygen coordination number 12, resides at center of cube • H+ protonates oxygen framework exists as OH groups

  12. COLOR OF TUNGSTEN BRONZES, MxWO3 INTERVALENCE W(V) TO W(VI) CHARGE TRANSFER IVCT

  13. SYNTHESIS DETAILS FOR Mx’MO3 WHERE M = Mo, W AND M’ = INJECTED PROTON OR ALKALI OR ALKALINE EARTH CATION • n BuLi/hexane CHEMICAL • LiI/CH3CN • Zn/HCl/aqueous • Na2S2O4 aqueous • Pt/H2 • Topotactic ion-exchange of Mx’MO3 • Li/LiClO4/MO3ELECTROCHEMICAL • Galvanostatic cathodic reduction • MO3 + H2SO4 (0.1M) Û HxMO3

  14. VPT GROWTH OF LARGE SINGLE CRYSTALS OF MOLYBDENUM AND TUNGSTEN TRIOXIDE AND CVD GROWTH OF LARGE AREA THIN FILMS • VPT CRYSTAL GROWTH • MO3 + 2Cl2 (700°C) Û(800°C) MO2Cl2 + Cl2O • CVD THIN FILM GROWTH • M(CO)6 + 9/2O2 (500°C)  MO3 + 6CO2

  15. MANY APPLICATIONS OF THIS M’xMO3 CHEMISTRY AND MATERIALS • Electrochemical devices, chemical sensors, pH responsive microelectrochemical displays, smart windows, advanced batteries • Behave as low dopant semiconductors • Behave as high dopant metals • Electronic and color changes best understood by reference to simple band picture of M’xMx5+M1-x6+O3

  16. COLORING MOLYBDENUM TRIOXIDE WITHPROTONS, MAKING IT ELECTRICALLY CONDUCTIVE AND A SOLID BRNSTED ACIDElectronic band structure in HxMoO3 molybdenum oxide bronze, tuning color, conductivity, acidity with x

  17. ELECTRONIC AND COLOR CHANGES BEST UNDERSTOOD BY REFERENCE TO SIMPLE BAND PICTURE OF NaxMox5+Mo1-x6+O3 • SEMICONDUCTOR TO METAL TRANSITION WITH DOPING IN MxMoO3 • MoO3: Band gap excitation from O2-(2pp) to Mo6+ (5d), essentially LMCT in UV region, wide band gap insulator • NaxMox5+Mo1-x6+O3: Low doping level, narrow band gap semiconductor, narrow localized Mo5+ (d1) VB, visible absorption, essentially IVCT Mo5+ to Mo6+ absorption • NaxMox5+Mo1-x6+O3: High doping level, partially filled metallic valence band, narrow delocalized Mo5+ (d1) VB, visible absorption, IVCT Mo5+ to Mo6+ metallic reflectivity

  18. HxMoO3 TOPOTACTIC PROTON INSERTION • Range of compositions: 0 < x < 2, MoO3 structure largely unaltered by reaction, four phases • 0.23 < x < 0.4 orthorhombic • 0.85 < x < 1.04 monoclinic • 1.55 < x < 1.72 monoclinic • 2.00 = x monoclinic • Similar lattice parameters by XRD, ND of HxMoO3 to MoO3 • MoO3 high resistivity semiconductor • HxMoO3 metallic insertion material • HxMoO3 strong Brnsted acid • HxMoO3 fast proton conductor • See what happens when single crystal immersed in Zn/HCl/H2O

  19. INTRALAYER PROTON DIFFUSION 1-D proton conduction along chains Yellow transparent Protons begin in basal plane Moves from two edges along c-axis INTERLAYER PROTON DIFFUSION b-axis adjoining layers react Orange transparent PROTON FILLING Eventually entire crystal transformed Blue bronze Consistent with structural data HxMoO3 TOPOTACTIC PROTON INSERTION

  20. PROTON CONDUCTION PATHWAY IN HxMoO3

  21. PROTON CONDUCTION PATHWAY IN HxMoO3 • Part of a HxMoO3 layer • Showing initial 1-D proton conduction pathway • Apical to triply bridging oxygen proton migration first • 1H wide line NMR, PGSE NMR probes of structure and diffusion • Doubly to triply bridging oxygen proton migration pathway • Initial proton mobility along c-axis intralayer direction for x = 0.3 • Subsequently along b-axis interlayer direction • Single protonation at x = 0.36, double protonation x = 1.7 • More mobile protons higher loading D(300K) ~ 10-11vs 10-9 cm2s-1 • Proton-proton repulsion

  22. ION EXCHANGE SOLID STATE SYNTHESIS • Requirements: anionic open channel, layer or framework structure • Replacement of some or all of charge balancing cations by protons or other simple or complex cations • Classic cation exchangers are zeolites, clays, beta-alumina, molybdenum and tungsten oxide bronzes

  23. BETA ALUMINA • Recall the high T synthesis of beta-alumina: • (1+x)/2Na2O + 5.5Al2O3 Na1+xAl11O17+x/2 • Structural reminders: • Na2O: Antifluorite ccp Na+, O2- in Td sites • Al2O3: Corundum ccp O2-, Al3+ in 2/3 Oh sites • Na1+xAl11O17+x/2: defect Spinel, O2- vacancies in conduction plane, controlled by x ~ 0.2, Spinel blocks 9Å, bridging oxygen columns, mobile Na+ cations, 2-D fast-ion conductor

  24. Rigid Al-O-Al column spacers Na(+) conduction plane 0.9 nm Na1+xAl11O17+x/2 defect spinel blocks 3/4 O(2-) missing in conduction plane Spinel blocks, ccp layers of O(2-) Every 5th. layer has 3/4 O(2-) vacant, defect spinel 4 ccp layers have 1/2Oh, 1/8Td Al( 3+) cation sites Blocks cemented by rigid Al-O-Al spacers Na(+) mobile in 5th open conduction plane Centrosymmetric layer sequence in Na1+xAl11O17+x/2(ABCA)B(ACBA)C(ABCA)B(ACBA)

  25. 0.9 nm Spinel block Al-O-Al column spacers in conduction plane Oxide wall of conduction plane Mobile sodium cations GETTING BETWEEN THE SHEETS OF THE BETA ALUMINA FAST SODIUM CATION FAST ION CONDUCTOR: LIVING IN THE FAST LANE

  26. ION EXCHANGE IN Na1+xAl11O17+x/2 Thermodynamic and kinetic considerations Mass, size and charge considerations Lattice energy controls stability of ion-exchanged materials Cation diffusion, polarizability effects control rate of ion-exchange

  27. MELT ION-EXCHANGE OF CRYSTALS • Equilibria between beta-alumina and MNO3 and MCl melts, 300-350oC • Extent of exchange depends on time and melt composition • Monovalents: Li+, K+, Rb+, Ag+, Cu+, Tl+, NH4+, In+, Ga+, NO+, H3O+ • Higher valent cations: Ca2+, Eu3+, Pb2+ • Higher T melts required for higher valent cations, strong cation binding, slower cation diffusion, 600-800oC typical

  28. MELT ION-EXCHANGE OF CRYSTALS • Charge-balance requirements: • 2Na+ for 1Ca2+, 3Na+ for 1La3+ • Controlled partial exchange by control of melt composition: • qNaNO3 : (1-q)AgNO3 • Na1+x-yAgyAl11O17+x/2

  29. KINETICS AND THERMODYNAMICS OF SOLID STATE ION EXCHANGE • Kinetics of Ion-Exchange • Controlled by ionic mobility of the cation • Mass, charge, radius, temperature, solvent, solid state structural properties • Thermodynamics, Extent of Ion-Exchange • Ion -exchange equilibrium for cations • Binding activities between melt and crystal phases • Site preferences • Binding energetics, lattice energies • Charge : radius ratios

  30. CHIMIE DOUCE: SOFT CHEMISTRY • Synthesis of new metastable phases • Materials not usually accessible by other methods • Synthesis strategy often involves precursor method • Often a close relation structurally between precursor phase and product • Topotactic transformations

  31. CHIMIE DOUCE: SOFT CHEMISTRY • Tournaux synthesis of new TiO2 • KNO3 (ToC)  K2O (source) • K2O + 4TiO2 (rutile, 1000oC)  K2Ti4O9 • K2Ti4O9 + HNO3 (RT)  H2Ti4O9.H2O • H2Ti4O9.H2O (500oC) 4TiO2 (new slab structure) + 2H2O

  32. KIRKENDALL EFFECT IN TOURNAUX SYNTHESIS OF SLAB FORM OF TiO2 • 16K + - 4Ti4+ + 36TiO2 8K2Ti4O9 • 4Ti4+ - 16K+ + 9K2O  K2Ti4O9 • Overall reaction stoichiometry • 9K2O + 36TiO2  9K2Ti4O9 • RHS/LHS = 8/1 Kirkendall Ratio

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