ELECTROCHEMICAL SYNTHESIS OF LixTiS2

TiS2 + xLi+ + xe- LixTiS2 AN ATTRACTIVE ENERGY STORAGE SYSTEM???

2.5V open circuit - no current drawn - energy density 4 x Pb/H2SO4 battery of same weight

Li+

e-Controlled potential coulometry, voltage controlled intercalation rate and x value, number of equivalents of charge passed

PVDF(filler)/C(conductor)/TiS2/Pt(contact) composite cathode: TiS2 + xLi+ +xe- LixTiS2

PEO/Li(CF3SO3) polymer-salt electrolyte or propylene carbonate/LiClO4 non aqueous electrolyte

Li metal anode: Li Li+ +e-

• 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

CHEMICAL SYNTHESIS OF LixTiS2

S(-II) 3p VB

t2g Ti(III) localized

t2g Ti(IV) delocalized

N(E)

E E

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

LiCoO2

LiCoO2

LixC6

Li

ROCKING CHAIR LSSB

OTHER INTERCALATION SYNTHESES WITH TiS2

• Cu+, Ag+, H+, NH3, RNH2, Cp2Co, chemical, electrochemical

• Cobaltacene especially interesting, (Cp2Co)x+Tix

3+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

Co Co

Synthesis, Cp2Co-CH3CN(solution)/TiS2(s)

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

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)

FACE BRIDGING OCTAHEDRAL TITANIUM TRISULFIDE AND NIOBIUM TRISELENIDE BUILDING

BLOCKS FORM 1-D CHAINS

Ti(IV) = S2(2-) = S(2-) = Li(+) =

TiS3 = Ti(IV)S(2-)S2(2-) intercalated cations like Li(+) in channels between chains to formLixTiS3

3-D OPEN FRAMEWORK TUNGSTEN OXIDE AND TUNGSTEN OXIDE BRONZES MxWO3

OO

M

WW

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

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 ( )

ELECTROCHEMICAL OR CHEMICAL SYNTHESIS OF MxWO3

• xNa+ + xe- + WO3 NaxWx5+W1-x

6+O3

• xH+ + xe- + WO3 HxWx5+W1-x

6+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

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

IVCT

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/MO3 ELECTROCHEMICAL

• Galvanostatic cathodic reduction

• MO3 + H2SO4 (0.1M) HxMO3

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) (800°C) MO2Cl2 + Cl2O

• CVD THIN FILM GROWTH

• M(CO)6 + 9/2O2 (500°C) MO3 + 6CO2

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’xMx

5+M1-x6+O3

COLORING MOLYBDENUM TRIOXIDE WITHPROTONS, MAKING IT ELECTRICALLY CONDUCTIVE

AND A SOLID BRNSTED ACID

Electronic band structure in HxMoO3 molybdenum oxide bronze, tuning color, conductivity, acidity with x

ELECTRONIC AND COLOR CHANGES BEST UNDERSTOOD BY REFERENCE TO SIMPLE BAND

PICTURE OF NaxMox5+Mo1-x

6+O3

• SEMICONDUCTOR TO METAL TRANSITION WITH DOPING IN MxMoO3

• MoO3: Band gap excitation from O2-(2p) to Mo6+ (5d), essentially LMCT in UV region, wide band gap insulator

• NaxMox5+Mo1-x

6+O3: Low doping level, narrow band gap semiconductor, narrow localized Mo5+ (d1) VB, visible absorption, essentially IVCT Mo5+ to Mo6+ absorption

• NaxMox5+Mo1-x

6+O3: High doping level, partially filled metallic valence band, narrow delocalized Mo5+ (d1) VB, visible absorption, IVCT Mo5+ to Mo6+ metallic reflectivity

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 Brnsted acid

• HxMoO3 fast proton conductor

• See what happens when single crystal immersed in Zn/HCl/H2O

INTRALAYER PROTON DIFFUSION1-D proton conduction along chainsYellow transparentProtons begin in basal planeMoves from two edges along c-axis

INTERLAYER PROTON DIFFUSIONb-axis adjoining layers reactOrange transparent

PROTON FILLINGEventually entire crystal transformedBlue bronzeConsistent with structural data

HxMoO3 TOPOTACTIC PROTON INSERTION

PROTON CONDUCTION PATHWAY IN HxMoO3

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) ~ 10-11 vs 10-9 cm2s-1

• Proton-proton repulsion

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

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

Rigid Al-O-Al column spacers

3/4 O(2-) missing in conduction plane

0.9 nm Na1+xAl11O17+x/2

defect spinel blocks

Na(+) conduction plane

Spinel blocks, ccp layers of O(2-)Every 5th. layer has 3/4 O(2-) vacant, defect spinel4 ccp layers have 1/2Oh, 1/8Td Al( 3+) cation sitesBlocks cemented by rigid Al-O-Al spacersNa(+) mobile in 5th open conduction plane

Centrosymmetric layer sequence in Na1+xAl11O17+x/2

(ABCA)B(ACBA)C(ABCA)B(ACBA)

GETTING BETWEEN THE SHEETS OF THE BETA ALUMINA FAST SODIUM CATION FAST ION CONDUCTOR: LIVING IN THE FAST LANE

Al-O-Al column spacers in conduction plane

Mobile sodium cations

Oxide wall of conduction plane

0.9 nm Spinel block

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

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

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

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

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

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

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