Transcript CHM 434F/1206F SOLID STATE MATERIALS CHEMISTRY

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
Controlled potential coulometry, voltage
controlled intercalation rate and x value,
number of equivalents of charge passed
e-
Li metal anode: Li  Li+ +ePEO/Li(CF3SO3) polymer-salt electrolyte or
propylene carbonate/LiClO4 non aqueous
electrolyte
Li+
PVDF(filler)/C(conductor)/TiS2/Pt(contact)
composite cathode:
TiS2 + xLi+ +xe-  LixTiS2
CHEMICAL SYNTHESIS OF LixTiS2
• xC4H9Li + TiS2 (hexane, N2/RT)  LixTiS2 +
x/2C8H18
E
E
t2g Ti(IV) delocalized
•
Filter, hexane wash
t2g Ti(III) localized
•
0x1
S(-II) 3pp VB
N(E)
• Electronic description LixTix(III)Ti(1-x) (IV)S2 mixed
valence localized t2g states or LixTi (IV-x)S2
delocalized partially filled t2g band
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 intercalationdeintercalation lattice expansion-contraction cycles
at the cathode
• Cause lifetime, corrosion, reactivity, and safety
hazards
LiCoO2
LixC6
ROCKING CHAIR LSSB
LiCoO2
Li
OTHER INTERCALATION SYNTHESES WITH TiS2
• Cu+, Ag+, H+, NH3, RNH2, Cp2Co, chemical,
electrochemical
• Cobaltacene especially interesting, (Cp2Co)x+Tix3+Ti14+S chemical-electronic description consistent with
x
2
structure spectroscopy
Synthesis, Cp2CoCH3CN(solution)/
TiS2(s)
Co
Co
• 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
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
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(+) =
3-D OPEN FRAMEWORK TUNGSTEN OXIDE AND
TUNGSTEN OXIDE BRONZES MxWO3
W
O
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
M
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-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
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’xMx5+M16+
x O3
COLORING MOLYBDENUM TRIOXIDE WITH
PROTONS, MAKING IT ELECTRICALLY CONDUCTIVE
AND A SOLID BRNSTED 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-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
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
HxMoO3 TOPOTACTIC PROTON INSERTION
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
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
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, betaalumina, 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
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)
GETTING BETWEEN THE SHEETS OF THE BETA
ALUMINA FAST SODIUM CATION FAST ION
CONDUCTOR: LIVING IN THE FAST LANE
0.9 nm Spinel block
Al-O-Al column
spacers in conduction
plane
Oxide wall of
conduction plane
Mobile sodium cations
ION EXCHANGE IN Na1+xAl11O17+x/2
Thermodynamic and
kinetic considerations
Mass, size and charge
considerations
Lattice energy controls
stability of ionexchanged materials
Cation diffusion,
polarizability effects
control rate of ionexchange
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, 600800oC 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