RUTILE CRYSTAL STRUCTURE
z
x
y
SEEING THE 1-D CHANELS IN RUTILE
NEW METASTABLE POLYMORPH OF TiO2 BASED ON K2Ti4O9 SLAB STRUCTURE - (010) PROJECTION SHOWN
K+ at y = 3/4
K+ at y = 1/4
Different to rutile, anatase or brookite forms of TiO2
Finding the number of crystallographically inequivalent oxygen sites in the K2Ti4O9 slab and the number of each
Oxygen count 1/3 + 3/4
Oxygen count 4 + 1/2 +2 +1/3
Oxygen count 1/3 + 3/4 1/3
1/3
1/3 1/41/41/4
1/41/41/4
1/2 1/21/21/2
1 1 1 1
Topotactic loss of H2O from H2Ti4O9 to give “Ti4O8” (TiO2 slabs) plus H2O, where two bridging oxygens in slab are protonated (TiOHTiOTiOH)
[Ti(IV)4O9]2-
CHIMIE DOUCE: SOFT CHEMISTRY
• Figlarz synthesis of new WO3
• WO3 (cubic form) + 2NaOH Na2WO4 + H2O
• Na2WO4 + HCl (aq) gel
• Gel (hydrothermal) 3WO3.H2O
• 3WO3.H2O (air, 420oC) WO3 (hexagonal tunnel structural form of tungsten trioxide)
• More open tunnel form than cubic ReO3 form of WO3
Slightly tilted cubic polymorph of WO3 with corner sharing Oh WO6 building blocks, only protons and smaller alkali cations can be injected into cubic shaped voids in structure to form bronzes like NaxWO3 and HxWO3
1-D hexagonal tunnel polymorph of WO3 with corner sharing Oh WO6 building blocks, can inject larger alkali and alkaline earth cations into structure to form bronzes like RbxWO3 and BaxWO3
Hexagonal tunnels
Injection of larger M+ cations like K+ and Ba2+ than maximum of Li+ and H+ in c-WO3
Apex sharing WO6 Oh building blocks
Structure of h-WO3 showing large 1-D tunnels
MOLTEN SALT ELECTROCHEMICAL REDUCTIONS OF OXYANIONS: GROWTH OF CRYSTALS
• Molten mixtures of precursors - product crystallizes from melt - inert crucibles and electrodes like Pt, graphite CATHODE
• Reduction of TM oxides to lower oxidation state materials
• CaTi(IV)O3 (perovskite)/CaCl2 (850oC) CaTi(III)2O4 (spinel)
• Na2Mo(VI)O4/Mo(VI)O3 (675oC) Mo(IV)O2 (large crystals)
• Li2B4O7/LiF/Ta(V)2O5 (950oC) Ta(II)B2
• Na2B4O7/NaF/V(V)2O5/Fe(III)2O3 (850oC) Fe(II)V(III)2O4 (spinel)
SYNTHETIC FORM: SHAPE IS EVERYTHING IN THE MATERIALS WORLD
• When thinking about a solid state synthesis of a particular composition it is also important to plan the form of the material that will ultimately be required for a specific application
• Shape is everything when it comes to designing structure-property-function-utility relations
• Form counts - polycrystalline, nanocrystalline, film, superlattice, wire, single crystal and so forth
BASICS LSSB: INJECTION-INTERCALATION CATHODES TiO2, NbSe3, WO3, MoS2, V6O13, LixCoO2
• Li+/e- charge equivalents of anode
• Voc, EF(anode-cathode)
• Electrode-electrolyte interfacial kinetics• Polymer segment dynamics
• Polymer Tg controls crystalline vs glassy
• Li+/PEO cooperative motion effects• Goal Li+ RT conductivity• Needs liquid (low MW PEO) plastisizers• Electrode-electrolyte mechanical stability• Electrode-electrolyte chemical stability• Rocking chair architecture• Secondary battery can be cycled• Operational lifetime• Safety, environmentally correct
LiLi3NLixCLixCFLiAlLiSnLixMnO2
PEO
Li+
Li+
Li+ Li+
Li+
Li+
anode electrolyte cathode
SPE
LiCoO2
LiCoO2
LixC6
Li
ROCKING CHAIR LSSB
HOW TO SYNTHESIZE A BETTER LSSB?
Improved Performance Cathode, Anode and Electrolyte
TEMPLATE SYNTHESIS OF NANOSCALE BATTERY CATHODE MATERIALS
A BETTER BATTERY CATHODE USING NANOSCALE MATERIALS - NANODIFFUSION LENGTHS FOR Li+
DIFFUSIVE INTERCALATION
• Template synthesis is a versatile nanomaterial fabrication method used to make monodisperse nanoparticles of a variety of materials including metals, semiconductors, carbons, and polymers.
• The template method has been used to prepare nanostructured lithium-ion battery electrodes in which nanofibers or nanotubes of the electrode material protrude from an underlying current-collector surface like the bristles of a brush.
• Nano-structured electrodes of this type composed of carbon, LiMn2O4, V2O5, Sn, TiO2 and TiS2 have been prepared.
A BETTER BATTERY CATHODE USING NANOSCALE MATERIALS - NANODIFFUSION LENGTHS FOR Li+
DIFFUSIVE INTERCALATION
• In all cases, the nanostructured electrode showed dramatically improved rate capabilities relative to thin-film control electrodes composed of the same material.
• The rate capabilities are improved because the distance that Li must diffuse in the solid state (the current- and power-limiting step in Li-ion battery electrodes) is significantly smaller in the nanostructured electrode.
• For example, in a nanofiber-based electrode, the distance that Li must diffuse is restricted to the radius of the fiber, which may be as small as 50 nm.
A BETTER BATTERY CATHODE USING NANOSCALE MATERIALS - NANODIFFUSION LENGTHS FOR Li+
DIFFUSIVE INTERCALATION
• Beating mechanical stability problem of repeated intercalation-deintercalation expansion-contraction cycles
• In addition to improved rate capabilities, the nanostructured electrodes do not suffer from poor cyclability observed for conventional electrodes.
• This is because the absolute volume changes in the nanofibers are small, and because of the brush-like configuration, there is room to accommodate the volume expansion around each nanofiber.
• Improved cycle life results show nanostructured electrode can be driven through 1400 charge/discharge cycles without loss of capacity.
nc-TiO2
Nanocrystal-PEO electrolytes solid plasticisers for LSSB
Ti(IV)-X- surface coordinated anion
Li+ cation
Ti(IV)-O surface coordinated oxygen of PEO polymer chain
PEO polymer chain coordinated to Li+ cation and surface Ti(IV)
LiClO4-PEO-nc-TiO2
• LiClO4-PEO-nc-TiO2 -high surface area nanocrystalline ceramic
• Brnsted and Lewis acid-base sites - surface Ti(IV) coordination to O(CH2CH2)-
• Surface Ti(IV) binding to counteranion X-
• Polymer-particle crosslinking - no 60oC glass transition
• nc-TiO2 stabilizes glassy polymer state at RT
• Domains of local polymer disorder at PEO-nc-TiO2 interface
• Optimal anchoring promotes local structural and dynamical modifications• High RT Li+ conductivity• Excellent mechanical stability, improved stress-strain curves• Reduced reactivity with solid compared to liquid plasticizer• Less cooperative PEO segmental motion with enhanced interfacial mobility of
Li+
• Transport number t(Li+), 0.3 pristine LiClO4-PEO, 0.6 in LiClO4-PEO-nc-TiO2
nc-TiO2
nc-CERAMIC OXIDES: SOLID PLASTICISERS IN POLYMER-ELECTROLYTE LITHIUM BATERIES
• LiClO4 : PEO = 1 : 8, 10 wt% nc-TiO2 or Al2O3,
• anchoring PEO oxygens and counteranions to Brnsted/Lewis acid surface sites,
• enhanced corrosion resistance of electrodes,
• better mechanical stability PEO,
• higher Li+ conductivity & transport number,
• local disorder of polymer, loss of Tg, stabilizes RT glassy state,
• discards need for PEO-Li+ cooperative segmental motion
METHODS FOR SYNTHESIZING NANOCLUSTERS AND NANOCRYSTALS
• Vaporization of metals (thermal, laser ablation) in inert gas - condensation of mixture - Pt, Au
• Supersonic molecular beams - Knudsen cell vaporization with inert gas expansion - condensation into vacuum and mass selection and mass spectroscopy detection - Si, GaAs
• Plasma-arc vaporization - condensation - WC, SiC
• Aerosol spray pyrolysis of salt, sol-gel precursor solution - Y3Fe5O12, Mn0.8Zn0.2FeO4, PbZr0.52Ti0.48O3, YBa2Cu3O7, ZrO2, TiO2
• Microemulsions, micelles, zeolites - precursors - confined nucleation and arrested nanocluster growth - capped CdSe, FePt, TiO2, YBa2Cu3O7
LENGTH SCALES IN CHEMISTRY, PHYSICS
AND BIOLOGY
Peter Day, Chemistry in Britain
Spatial and quantum confinement and dimensionality
WHEN IS SMALL GOOD?
Sub-dividing or perforating mattermono- or polydispersed particles, crystalline or amorphous, micro (<10 Å),
meso (10-1000 Å) or macro (>1000 Å) length scale, organized or random arrangements, channels or pores, structure-composition-defects, surface
area, sites, charge, hydrophobicity, functionality
Property-function
QSEs, of e, h, or hrelative to materials size, dimensionality, interaction strength of components, interconnection and integration of parts, hierarchy
and system architecture, function
WHEN IS SMALL GOOD?
Properties that are size and shape tunablemechanical, thermal, acoustical, dielectric, surface vs bulk,
electrical, optical, electro-optical, magnetic, photonic, catalytic, photochemical, photophysical, electrochemical, separation, recognition,
composite
CAPPED MONODISPERSED SEMICONDUCTOR NANOCLUSTERS
nMe2Cd + nnBu3PSe + mnOct3PO (nOct3PO)m(CdSe)n + n/2C2H6 + nnBu3P
EgC = Eg
B + (h2/8R2)(1/me* + 1/mh*) - 1.8e2/R
Coulomb interaction between e-h
Quantum localization term
ARRESTED GROWTH OF MONODISPERSED
NANOCLUSTERS
CRYSTALS, FILMS ANDLITHOGRAPHIC
PATTERNS
nMe2Cd + nnBu3PSe + mnOct3PO (nOct3PO)m(CdSe)n + n/2C2H6 + nnBu3P
MONODISPERSED CAPPED CLUSTER SINGLE CRYSTALS
methanol
2-propanol
toluene
Rogach AFM 2002
THINK SMALL DO BIG THINGS!!!
EgC = Eg
B + (h2/8R2)(1/me* + 1/mh*) - 1.8e2/R
SELF-ASSEMBLING AUROTHIOL CLUSTERS
HAuCl4(aq) + Oct4NBr (Et2O) Oct4NAuCl4 (Et2O)
nOct4NAuCl4(Et2O) + mRSH + 3nNaBH4 Aun(SR)m
CAPPED METAL CLUSTER CRYSTAL
CLUSTER SELF-ASSEMBLY DRIVEN BY HYDROPHOBIC INTERACTIONS BETWEEN ALKANE TAILS OF
ALKANETHIOLATE CAPPING GROUPS ON GOLD NANOCRYSTALLITES
CAPPED FePt NANOCLUSTER SUPERLATTICE HIGH-DENSITY DATA STORAGE MATERIALS
ZEOLATE CAPPED SEMICONDUCTOR CLUSTERS
ZEOLATE LIGAND
Crown ether - zeolate ligand analogy - metal coordination
chemistry of zeolites
TOPOTACTIC MOCVD
Intrazeolite reaction of acid zeolite Y (HY) with known amounts of Me2Cd or Me4Sn vapors
Gives anchored MeCdY and Me3SnY, which react with H2S or H2Se to create encapsulated and zeolate capped nanoclusters Cd4S4Y and Sn4S6Y
Defined by Reitveld PXRD structure refinement
MOCVD TOPOTAXY OF INTRAZEOLITE TIN SULFIDE, CADMIUM SELENIDE AND SILICON AND GERMANIUM NANOCLUSTERS
INTRAZEOLITE CVD OF SILICON
NANOCLUSTERS
• Si2H6 + H56Y (Si2H5)8-Y
• (Si2H5)8-Y (Si8)8-Y
• Superlattice of Si8 clusters in ZY
QUANTUM CONFINED SILICON - < 5 nm -MAKING SILICON GLOW THROUGH NANOCHEMISTRY
INTRAZEOLITE TUNGTEN OXIDE NANOCLUSTERS
NANOWIRES - FABRICATION OR SYNTHESIS
• Top down advanced nanolithography fabrication methods - expensive and time consuming
• Bottom up chemical synthesis methods - economical and fast
• Creation of 1D nanowires - used as functional components and interconnects in building nanodevices and nanocircuitry through self assembly strategies
• Most successful purely synthesis methods involve vapor-solid VS, vapor-liquid-solid VLS, solution-liquid solid SLS and solution-solid SS processes
• These chemical approaches have led to carbon nanotubes, metal and semiconductor nanowires and a range of inorganic materials
• Other approaches involve structure directing templates like channels in porous alumina, hexagonal lyotropic liquid crystals and block copolymers