Download Inorganic Materials Chemistry and Functional Materials

Material Synthesis
Inorganic Materials Chemistry
and Functional Materials
Helmer Fjellvåg and Anja Olafsen Sjåstad
Lectures at CUTN spring 2016
Materials
Natural materials (wood, bone, leather, cellulose, minerals, etc..)
Metals
Semiconductors
Non-metallic inorganic materials (oxides, ceramics, glass)
Organic Polymers
Composite materials (polymer-, ceramic-, metal matrix)
2
Bulk powders
Metals-alloys
Nanoparticles
Inorganic Materials Synthesis
Surfaces
Thin films - coatings
Single crystals
Inorganic Materials Synthesis
Solid State Reactions
Nanoparticle synthesis
Solids from the gas phase
Inorganic Materials Synthesis
Solid State Reactions
Solid State Reactions
Solid state reaction: a reaction between two or more solids.
Our text book has extended the definition
to any reaction involving a solid:
•Solid/solid
•Solid/gas (Reaction, decomposition)
•Intercalation
•(Solid/liquid)
Ceramic Method – ‘Shake and Bake’
-
Direct reaction between two or more solids to form the final product. In
principle no decomposition is involved.
-
Solids do not react with solids at room temperature even if
thermodynamics is favorable; i.e. high temperatures needed.
-
Solid-solid reactions are simple to perform, starting materials
are often readily available at low cost and reactions are ‘clean’;
i.e. do not involve other elements (beneficial for the industry.)
-
Disadvantages include the need for high temperatures, the
possibility of inhomogeneity, contamination from containers etc.
7
Ceramic Method – Synthesis of YBCO
YBCO = YBa2Cu3O7x
ABO3
8
Ceramic Method – Synthesis of YBCO
YBCO = YBa2Cu3O7x
- Direct reaction between Y2O3, BaO2, CuO
(Reaction between three solid components)
- Grind to obtain large surface area (see next slide)
- Press into pellets (contact)
- Heat in alumina boat, temperature profile:
Oxidation step
9
Solid State Reactions – General Aspects
Surface area:
Surface area is increased by crushing/milling
1 cm cube: surface area 6 cm2
1 mm cubes: surface area 60 cm2
10 m cubes: surface area 6000 cm2
10 nm cubes: surface area 6000000 cm2 (600m2)
10
Ceramic Method – Synthesis of YBCO
-
Other precursors may be used; e.g. BaCO3, which may be decomposed to
fine grained BaO during the reaction.
(oxalates, nitrates, cyanides etc. also work fine). Why such precursors?
Keywords:
- Create more surface area of component by “chemical grinding”
-
Decomposition of the precursor must be performed in a controlled manner in
order to avoid violent decomposition (i.e. choosing an appropriate
temperature). Why?
Keywords:
- Splashing in furnace  alternate composition, contamination of furnace
-
Other reasons why e.g. BaCO3 or Ba-oxalate is a better precursor than BaO
in synthesis of YBCO by the ceramic method?
Keywords:
- BaO very basic oxide, i.e. react with CO2 and H2O air – alter composition
11
Ceramic Method – Synthesis of YBCO
-
Will chloride salts be suited precursors? E.g. BaCl2?
Keywords:
- Chlorides not form volatile products – i.e. reminds in the powder
-
Regrinding – Why?
Keywords:
- Reduce diffusion distances – see next slide
Note:
Many other ways of synthesizing YBCO:
Precursor methods
Sol/gel
Flux
Many melt-texturing methods
including partially melting/fluxing
12
Solid State Reactions – General Aspects
A(s) + B(s)  C(s)
• Nucleation at the interface (depends on the
degree of structural rearrangement involved)
• Formation of product layer, two reaction
interfaces
• Diffusion/counter diffusion through the
product layer - growth
Longer diffusion paths, slower reaction rate.
Simple case: lattice diffusion through a planar
layer (rate law 1/x):
dx
 k x 1
dt
x(t )  k ln(t )  C
x = thickness of layer
t = time
13
Solid State Reactions – General Aspects
How to increase rate of reaction, dx/dt?
1. Increase area of contact between reactants
2. Increase rate of nucleation
3. Increase rate of diffusion – ions through various phases
14
-
Solid State Reactions – General Aspects
How to increase rate of reaction, dx/dt?
1. Increase area of contact between reactants
(cross-reference to earlier slide)
Small particles by grinding, ball milling, freeze drying etc.
15
Solid State Reactions – General Aspects
How to increase rate of reaction, dx/dt?
2.
Increase rate of nucleation
Nucleation may be facilitated by structural similarity between the reacting
solids, or products.
For compounds produced by solid state reaction, often a structural
orientational relationship between the reactant, nuclei and product is seen.
(In the reaction between MgO and Al2O3 to form MgAl2O4 (spinel), MgO
and spinel have similar oxide ion arrangements. Spinel nuclei may then
easily form at the MgO surfaces (see below)).
16
Solid State Reactions – General Aspects
Structural similarity through - Epitactic and Topotactic
Reactions
Epitactic: structural similarity restricted to the surface / interface
between two crystals (common arrangement of ions at the interface)
Topotactic: Structural similarity through the crystal. Reaction is
controlled by the crystal structure of a reactant.
17
Solid State Reactions – General Aspects
Example: Production of the MgAl2O4 spinel from MgO and Al2O3
MgO and MgAl2O4 have O atoms in cubic close packing
Al2O3 crystallizes in a completely different structure (Rhombohedral)
Al2O3
MgO
MgAl2O4
Spinel nuclei form on the MgO surface - structural orientational relationship
as well as similar interatomic distances (topotactic reaction)
18
Solid State Reactions – General Aspects
Topotactic Reduction
Oxygen getter
Zr, NbO,..
LaNiO3-x  LaNiO3-x’ + O2(g)
Zr + O2(g)  ZrO2
LaNiO3.00
LaNiO2.75
O2
Sample
LaNiO2.50
LaNiO2.00
19
Solid State Reactions – General Aspects
How to increase rate of reaction, dx/dt?
3. Increase rate of diffusion – ions through various phases
-
Diffusion is a thermally activated process, following an Arrhenius
behavior
- High temperatures, as a rule of thumb, at 2/3 of the melting
temperature (of one component) the diffusion is sufficient to achieve solid
state reactions.
-
Reduction of diffusion distances by incorporating the cations in the
same solid precursor or perform a co-precipitation reaction – calls for
more advanced methods
20
Solid State Reactions – General Aspects
Nucleation limited reactions may be described by the Avrami-Erofeyev
equation:
x(t) = 1-exp(-ktn) {or x(t) = 1-exp(-(kt)n)}
n is a real number, usually between 1 and 3 (n>4 is often interpreted as autocatalytic
nucleation)
For n > 1 the curve is sigmoidal
Note: This is more empirical for most solid state reactions. It is difficult to talk about
reaction order and activation energy for these reactions.
x = thickness of layer
t = time
21
Will not be discussed at lecture
Solid State Reactions – General Aspects
Synthesis of BaTiO3 – nucleation of an intermediate phase
BaTiO3 - electroceramic (thermistors, capacitors, optoelectronic devices, DRAMs)
Formation of BaTiO3 by reacting BaCO3 and TiO2 is an example of a seemingly simple reaction is
more complex than expected.
Recipie – ‘Shake and bake’
BaCO3 is decomposed to reactive BaO: (Rock salt type structure, ccp of the oxide anions, Ba2+ in
octahedral sites),
TiO2 (Rutile type structure, hcp of oxide ions, Ti4+ in half of the octahedral sites)
At least three stages are involved in formation of BaTiO3 from BaO and TiO2.
• BaO react with the surface of TiO2, forming nuclei and a surface layer of BaTiO3.
• Reaction between BaO and BaTiO3 to form Ba2TiO4. NB! This is a necessary phase for
increasing migration of Ba2+ ions.
• Ba2+ ions from the Ba-rich phase migrate into the TiO2 phase and form BaTiO3.
22
Will not be discussed at lecture
Solid State Reactions – General Aspects
Reactions between two solids:
Reaction rates depends on:
• Area of contact between the reacting solids, i.e. surface area and “density”
• The rate of nucleation
• Rates of diffusion of ions (and other species)
Disadvantages, e.g.:
•Nucleation and diffusion related problems (high temperature)
•Formation of undesired phases (reaction paths) (e.g. Ba2TiO4)
•Homogeneous distribution, especially for dopants, is difficult
•Difficult to monitor the reaction directly, in-situ…??
•Separation of phases after synthesis is difficult
•Reaction with containers/crucibles
•Volatility of one or more of the components
23
Chemical Mixing in Solution
Decrease diffusion lengths by using intimately mixing of cations.
Solid precursors containing the desired cations.
Precursors for Ceramic Synthesis
1. Precursors via co-precipitation
2. Precursors via solid solutions and compounds
24
Precursors for Ceramic Synthesis
Precursor via co-precipitation:
Salts of different metals are precipitated together (as low solubility solids).
Either a solid solution or an intimate mixture of two salts.
Precursor via solid solutions and compounds:
Cations in targeted composition are incorporated in a stoichiometric solid.
Precursor converted to targeted compound via thermal decomposition at
relatively low temperature – frequently in more steps.
25
Precursor Formation – Co-precipitation
- Soluble salts of the desired cations are dissolved in solvent (usually in water)
- Trigging co-precipitation by heating (evaporation of solvent) or by addition of a
precipitating agent (forming insoluble salts)
- Hydroxides, carbonates, oxalates, formates, citrates… (What about nitrates?)
Keywords: nitrate may act oxidizing during decomposition; high solubility
Example from text book: Preparation of the spinel ZnFe2O4
1) Zinc and iron oxalate are dissolved in water in correct ratio
2) Heated to evaporate water  precipitate as fine powder, solid solution?
3) Heat to decompose:
Fe2(C2O4)3(s) + Zn(C2O4) (s)  ZnFe2O4 (s) + 4CO(g) + 4CO2(g)
Bigger grains of Fe2(C2O4)3 and Zn(C2O4) converted to finer grains or a
solid solution of Fe-Zn-Ox  better mixing of atoms
26
Carbonate Precursors
Forming a Stoichiometric Solid Solution
Target:
Formation of mixed oxides: M1xM’xO, (M, M’ = Ca, Mg, Mn, Fe, Co, Zn, Cd)
M1xM’xCO3  M1xM’xO + CO2(g)
Calcite, CaCO3
27
Carbonate Precursors – Preparation Method
Prepare a slightly acidic solution of
the targeted cations (e.g. nitrates) in
desired ratio
Add ammonium carbonate,
(NH4)2CO3 to precipitate
Filter and wash the precipitate
Calcine in appropiate atmosphere
for 0.5 – 150 hours at 800-1000 °C
Co-precipitation depends on:
•Similar solubility of the metal salts
•Similar precipitation rate
•Formation of solid solution
Successful preparation by calcination
may depend on similar
decomposition temperatures for the
metal precursors
•Structural similarity and compatibility
of the oxides
M1xM’xCO3  M1xM’xO + CO2(g)
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Carbonate Precursor Method - Example
Ca0.5Mn0.5CO3 + O2(g)  Ca0.5Mn0.5O3 + CO2(g)
CaMnO3
Low decomposition temperature
may allow formation of oxides
preserving a high oxidation state.
Formation of CaMnO3 by
standard methods requires
1300°C, days of heating and
repeated crushing/heating.
Using a carbonate precursor
CaMnO3 may be prepared at
900°C for 30 minutes.
May also be used for preparation
of low temperature phases.
Note change in oxidation state for
29
Mn in this example
Other Oxides by the
Carbonate Precursor Method
Note:
Startig with cations with oxidation state +II; Final product may have cations
with other oxidation states – choice of atmosphere during calcination.
30
Co-precipitation
Stoichiometric Solid Solutions
Hydroxides
Ln1xMx(OH)3 (Ln = La, Nd, M = Al, Cr, Fe, Co, Ni)  Ln1xMxO3
La1xyM’xM’’y(OH)3
(M’ = Ni, M’’ = Co, Cu)  La1xyM’xM’’yO3
Nitrates
Ba0.5Pb0.5(NO3)2  BaPbO3
Note:
Change in oxidation state of
Pb from +II to +IV
Cyanides
LaFe0.5Co0.5(CN)65H2O  LaFe0.5Co0.5O3
31
Stoichiometric Solid Solutions
NiFe2O4 may be prepared from: Ni3Fe6O3(OH)(OAc)1712py
200-300 ºC to burn off the organic part
Heating in air at 1000 ºC for 2-3 days
32
Will not be discussed at lecture
Formation of Metastable Solids
Some time the thermodynamically stable material is not the material with the
targeted properties
Metastable compound may be difficult to prepare using classical high
temperature routes; then soft chemistry (Chimie douce = soft chemistry)
methods is a good alternative.
Preparation of metastable phases:
1. Synthesis under conditions where the material is thermodynamically
stable followed by quenching to ambient conditions (Diamond, glasses).
2. Preparation of thermodynamically stable compounds, and transformation
of these to a metastable compound by a low temperature, soft chemistry,
method (Reduced nickelates).
3. Synthesis under non-equilibrium conditions; kinetic control of product
formation (Zeolities).
33
Formation of Metastable Solids – Example
Graphite and Diamond
Thermodynamically only small differences in stability between the two
modifications at ambient conditions. Difficult to activate phase transformation
from diamond to grafite at ambient conditions due to nucleation issues; 34
structurally very different.
Will not be discussed at lecture
Formation of Metastable Solids – Example
Metastable/stable?
II
III II
III
2LaNiO2.5  La2O3 + 2NiO
LaNiO3.00
LaNiO2.75
O2
LaNiO2.50
LaNiO2.00
35
Combustion Synthesis
1)
Applicable only for highly exothermic reactions – fuels may be added
2)
Activation from external energy source, sufficient heat is released
to maintain reaction self sustaining (electrical arc, spark, chemical reaction, etc.)
3)
Heating rates (103 to 106 K/s) – pseudo adiabatic; all produced
energy used to heat sample
4) Applicable process for many technological important solid materials
(carbides, silicides, nitrides, hydrides, alloys, etc.)
5) Good reasons for performing a combustion synthesis are:
- Less energy demanding (use energy produced)
- Short reaction times
- Small investments in processing equipment
- One pot synthesis
- Possible formation of non-equilibrium phases (fast cooling)
6) Control reaction rates by
- Addition of diluents; Increase particle size of reactants
36
Combustion Synthesis
Classification  Combustion Synthesis
Self propagating mode
Synthesis from the elements
Simultaneous combustion mode
Thermite-type reactions
Solid state metathesis
37
Classification  Combustion Synthesis
Self propagating mode(A):
Self propagating high-temperature synthesis (SHS). Combustion is initiated in a point,
and propagate rapidly through the reaction mixture. (combustion wave).
Simultaneous combustion mode(B): When the entire mixture has been heated to the
ignition temperature (Tig), reaction takes place simultaneously throughout the reactant
38
mixture (thermal explosion).
Combustion Synthesis – SHS
SHS reactions may be characterized by an adiabatic combustion
temperature (Tad)*.
Rule-of-thumb:
If Tad < 1200˚C combustion do not occur
If Tad > 2200˚C self-propagating reactions occur
If Tad is between 1200 and 2200˚C, self propagation may occur e.g. by
preheating.
Example:
Ti + Al  TiAl (Tad = 1245˚C, Tig = 640˚C)
Self-propagating if heated above 100˚C
*Tad: Temperature system is heated to if assumed all energy released is 39
consumed to heat the system without loosing energy to its surroundings
SHS
40
Classification  Combustion Synthesis
Synthesis from the elements: Carbides, silicides, borides, nitrides, oxides,
hydrides.
E.g. Ti + C  TiC (20 kg in 60-90 s, + cooling 1.5 – 2 h)
See later slides – Si3N4
Thermite-type reactions: Extension of Goldschmith process (reduction of an ore
using a metal). Mg and Al often used. MgO may be leached by hydrochloric acid.
Either reduction of an oxide to the element or reduction followed by reaction with
another element.
3Fe3O4 + 8 Al  9Fe + 4 Al2O3 (Thermite reaction) (see next few slides)
SiO2 + C + 2Mg  SiC + 2 MgO
TiO2 + B2O3 + 5Mg  TiB2 + 5MgO
Solid state metathesis (SSM): Rapid, low-temperature-initiated solid-state
exchange reactions. E.g.:
MnCl2 + Li2Fe2O4  MnFe2O4 + 2LiCl
41
Thermite reactions
3 Fe3O4 + 8 Al  9 Fe + 4 Al2O3
H reac = 849 kJ/mol
42
Thermite reactions
3 Fe3O4 + 8 Al  9 Fe + 4 Al2O3
H reac = 849 kJ/mol
43
Ceramic lining of steel pipes
Thermite reaction inside spinning pipes
(centrifugal thermite reaction)
44
Will not be discussed at lecture
Solid-State Metathesis (SSM)
- Rapid, low-temperature inisiated solid state exchange reaction
- Produces very fine scale crystallites; 10-100 nm
ZrCl4 + 4/3Li3N  ZrN + 4LiCl + 1/6N2
45
Will not be discussed at lecture
Solid-State Metathesis (SSM)
46
Will not be discussed at lecture
Solid-Gas Reactions – Use Si3N4 as example
- By combining solid and gas reactants some of the problems
by poor contact between reactants are overcome.
- Equilibrums shifted to product formation, le Chatelier’s principle*
A + B(g) = AB(s)
*Note: Le Châtelier's principle states that if a dynamic equilibrium is disturbed by
changing the conditions, the position of equilibrium shifts to counteract the change to
re-establish an equilibrium.
47
Solid-Gas Reactions – Use Si3N4 as example
Technical important routes to produce Si3N4
-
Carbothermal nitration of SiO2
Ammonolysis (NH3) of SiCl4 (g/l) or SiH4 (PV industry; Si solar cells)
Nitridation of silicon powder
Combustion
α-Si3N4
1650 oC
=
-Si3N4
-
Both modifications are hexagonal build up by corner sharing SiN4-tetrahedra
with covalent bonding
-
48
α-Si3N4 low temperature modification (< 1650˚C) has the best sintering
behavior
Solid-Gas Reactions – Si3N4
The nitridation reaction:
3Si + 2N2(g)  Si3N4
H = 760 kJ/mol
Very exothermic, but kinetics is slow below 1100 ˚C.
1) The reaction rate depends on the particle
size and purity of the starting material.
Semiconductor grade Si may be used. The
process is catalyzed by iron.
2) Due to the exothermic nature of the
reaction, the reaction rate must be carefully
controlled to keep the temperature low enough
(1250-1350 ˚C) to avoid sintering, melting and
formation of the b-phase.
3) Limit N2 access (e.g. diluting with 2040%H2) or dilute Si with Si3N4).
49
Combustion Mode, and Self Sustaining
Solid-Gas Reactions – Si3N4
Si3N4 may be prepared in a combustion mode, but high gas pressures must be
used to obtain self-sustaining reactions (avoid depletion of gas at the reaction
front). At high pressures the reaction is self propagating, and temperatures
above 1700 ˚C are reached resulting in > 95% -Si3N4.
Co-current
Counter-current
Gas flow in self-sustaining gas/solid reactions
Oxides, hydrides, nitrides, oxynitrides may be formed by heating in air
(oxygen), hydrogen, nitrogen or ammonia.
50
Will not be discussed at lecture
Decomposition and Dehydration Reactions
-
Reactions involving transport of gases away from the reaction.
-
Carbonates, oxalates, nitrates, hydroxides etc. Used for formation of
metal oxides.
- 2AlOOH  -Al2O3 + H2O
- CaCO3  CaO + CO2
- Thermal decomposition is also controlled by nucleation and growth, e.g.
surfaces, grain boundaries, dislocations.
Topochemically controlled reactions: The reactivity is controlled by
crystal structure rather than by chemistry.
Reactions my occur within the material without separation of a new phase.
51
Decomposition and Dehydration Reactions
Formation of Metastable WO3
Termodynamically stable phase WO3 with a ReO3 type structure. (monoclinic)
(corner sharing octahedra, perovskite type arrangement without the large A-cations)
Metastable hexagonal WO3 may be obtained from WO3⅓H2O by heating at 300 °C.
Structural elements in the hydrate: planes built from 6-rings of WO6 octahedra stacked
with a shift of ½ ring diameter.
In the metastable WO3 the rings are stacked on top of each other.
52
Will not be discussed at lecture
Decomposition and Dehydration Reactions
LaNiO3-x  LaNiO3-x’ + O2(g)
LaNiO3.00
LaNiO2.75
O2
LaNiO2.50
LaNiO2.00
53
Intercalation and Deintercalation
Intercalation:
Insertion of species (atoms, molecules, ions) into a crystalline host material.
The host material (and guest) may undergo perturbations in their geometrical,
chemical or electronic environment.
Two general systems:
Three dimensional lattices: with parallel channels or interconnected
channels (e.g. zeolites). Uptake is restricted by channel size.
Low dimensional host lattices:
Layered materials (2D) or materials built from chain structures (1D). Spacing
between layers or chains may change to accommodate guest species.
In this course we restrict ourselves to layered materials.
54
Chemical bonding - Layered Materials
Layered double hydroxides
Graphite (and h-BN)
MoS2
Layered silicates
Oxyhalides – FeOCl
Layered Materials
Perovskite related materials
Metal halides
MoCl2 – CrCl3
III-VI layered
Semiconductors – GaSe
Layered Materials
Neutral layers: van der Waals interactions, e.g. graphite, oxychlorides
(FeOCl) and metal disulfides
(Also compounds with neutral layers held together by covalent bonding)
Negatively charged layers separated by mobile (exchangeable) cations,
e.g. clays, transition metal phosphates
Positively charged layers separated by anions, e.g. layered double
hydroxides, MII1-xMIIIx(OH)2(An-)x/nmH2O
56
What are layered double hydroxides?
MII1-x MIIIx(OH)2(An-)x/n˙mH2O
Positively
charged layers
Hydrotalcite
group
Cations:
MII: Mg, Mn, Ni, Fe, Co, Cu, Zn, Ca
MIII: Al, Mn, Fe, Co, Cr, Ga
Anions (charge balancing):
CO32–, NO3–, Cl–, organic anions
Brucite - Mg(OH)2
Charge neutral layers
Ca(OH)2, Mn(OH)2,Ni(OH)2,
(Fe,Ni)(OH)2
P3m1
Huge flexibility in tuning chemical
composition of the
LDHs and nanoflakes
through synthesis
Synthesis of LDHs
“Crystal growth”-promoted
“Nucleation”-promoted
(e.g. Urea-method)
(Co-precipitation)
5
10
15

2( )
20
25
5
10
15
20
o
2( )
“Crystal growth”-promoted:
Good crystallinety and big crystals
Poor cation control
“Nucleation”-promoted:
Poor crystallinety and small crystals
Good cation control
H
e
InPro
25
How to intercalate target species in interlayer
gallery?
- Direct reaction with host
- Ion-exchange
- Exfoliation/Delamination
followed by
reconstruction (or flocculation)
Incorporated directly
during synthesis
59
See more details p. 51-57
Delamination of layered double hydroxides
Delamination - Exfoliation:
Weaken interlayer forces:
- External force (shear; ultrasonication)
- Soft chemistry
MII1-x MIIIx(OH)2(NO3)x˙mH2O
- Stabilizing nanoflakes in suspension
Present work:
- Solvent: Formamide
- Interlayer anion: NO3
- Ultrasonication
Nanocomposite
Delamination of layered double hydroxides
MII1-x MIIIx(OH)2(NO3)x˙mH2O – delamination - mechanism
B
nitrate
A
Formamide
Electronic Properties - Intercalation
•
Insulator host lattices: (e.g. zeolites, layered aluminosilicates,
metal phosphates, layered double hydroxides): The basic physical
properties (of the host lattice) are not changes by intercalation.
Catalysts, catalyst supports, adsorbants, ion exchangers.
•
Host lattices with redox properties: May reversibly uptake
electrons from or donate electrons (less often) to the guest. E.g.
graphite, metal dichalcogenides, metal oxyhalides… Strong changes
in the physical properties, e.g. electric conductivity. Interesting as
electrode materials for lithium batteries, electrochromic systems,
sensor materials…
62
Rechargeable (secondary) lithium batteries
64
Will not be discussed at lecture
Intercalation in Graphite
Important for Li-ion batteries
Single-atom thick graphite layers.
Interlayer distance 3.35Å (0.335nm)
Intercalation of:
Lithium (Li): 3.71Å
Potassium (K): 5.35Å
AsF5: 8.15Å
KHg: 10.22 Å (three layers of K and Hg)
Direct Synthesis
Will not be discussed at lecture
65
Classic example. TiS2:
Li + TiS2 ↔ Li+[TiS2]Important for Li-ion batteries
LixCoO2 analogue
Ti4+ reduced to Ti3+ and Li oxidized to Li+
The layers become charged (negative) and the Van der Waals
forces are replaced by Coulomb interactions. The interlayer spacing
is expanded in LiTiS2 compared to TiS2.
LixCoO2 have a similar mechanism.
Will not be discussed at lecture
66
Rechargeable (secondary) lithium batteries
Reversible lithium intercalation/deintercalation is the heart of lithium battery
electrode technology. In order to operate at ambient temperatures, a highly mobile
ion is needed which is able to penetrate into solids. Apart from protons, lithium is
the obvious choice. Lithium also have suitable redox properties.
Both electrodes in lithium batteries use reversible lithium insertion. Both are usually
layered intercalation materials. (e.g. graphite and LiCoO2)
Discharge: The difference in chemical potential for Li at the two electrodes results
in a flow of Li+ cations through the electrolyte from the cathode to the anode.
Discharge delivers energy
Charge: Reverse process, cost energy.
Max LiC6
Will not be discussed at lecture
67
Mechanistic Aspects – Staging
Staging in intercalation
During intercalation, interactions between layers are broken, and are replaced by
interactions between layers and guests.
Staging has the effect of decreasing the difficulty of breaking interlayer interactions.
Some layers are partly or completely filled, while others are empty. This is often
obtained in an ordered fashion.
The order of the staging is given as the number of layers between successive filled or
partially filled layers.
Illustrated by the easy of intercalation in MX2: Disulfides easily intercalated at milder
conditions than the diselenides, while the ditellurides have not been reported to 68
intercalate.
Staging in graphite anode
69
V.A. Sethuraman et al. / Journal of Power Sources 195 (2010) 3655–3660
TEM: Mixed staging in C- FeCl2
70
Carbothermal Reduction
• Commercially used for producing non-oxide ceramic powders
71
Carbothermal Reduction,The Acheson Process
SiC (carborundum)
• Abrasive: Cutting, grinding, lapping. In resin or ceramic matrix: Grinding
wheels, whetstones…
• Deoxidizer: in cast iron and steel to remove oxygen, for carburization
and siliconization
• Refractory material: linings in furnaces and kilns
• Electric heating elements: operation in oxidizing atmospheres up to
1500˚C.
Acheson furnace - 1896 Niagara
• Still same design in use today; Current furnaces 12-18 m long
• Extremely energy demanding – 1kg SiC requires 12 kWh
• Pure SiC is transparent
• N2 contaminations  green
• Carbon contaminations  black
72
Carbothermal Reduction,The Acheson Process
Overall reaction: SiO2 + 3C  SiC + 2CO(g)
SiO2:
Sand
Quartzite
Quartz
C:
Petrolium coke
Carbon blac
Coke
Graphite..
Assumed to be a solid
state reaction.
Particle sizes 5-10 mm
makes this less likely
73
Carbothermal Reduction,The Acheson Process
Overall reaction: SiO2 + 3C  SiC + 2CO(g)
- Extremely fast kinetics  indicative not a solid-solid reaction
- Via non stable gas specie – SiO*
C(s) + SiO2(s)  SiO(g) + CO(g)
SiO2(s) + CO  SiO(g) + CO2(g)
C(s) + CO2(g)  2CO(g)
2C(s) + SiO(g)  SiC(s) + CO(g)
74
*B2O3 reduced via B2O2; Al2O3 via Al2O
A small taste on silicon chemistry for
solar cells
Raw Materials for Metallurgical Grade Si
From sand to electricity
SiO2
and
Carbon
Metallurgical Grade Si (purity 98.5 – 99.9%)
Super Pure Si for PV (purity 99.9999 – 99.999999%)
 Chemical processing - I
 Chemical processing - II
Wafers
Cells
Modules
Systems
 Casting and cutting
 Surface treatment
 Assembly
 Power plants
How is metallurgical grade silicon produced?
Carbothermic reduction (1900-2100 oC)
SiO2(l) + 2C(s)  Si(l) + 2CO(g)
Raw Materials for Metallurgical Grade Si
SiO2
and
Carbon
Metallurgical Grade Si (purity 98 – 99%)
 Chemical processing - I
Metallurgical grade silicon = MG-Si
Purity > 98% (Fe, Al, Ca, C, Mg, Ti, Mn, Ni, Cu, V, B, P)
(Impurities are controlled by raw materials and type of electrode system
used used in the carbothermic reduction)
How is metallurgical grade silicon produced?
1900-2100 oC
SiO2(l) + 2C(s)  Si(l) + 2CO(g)
Core of furnace (hot zone):
2SiO2(l) + SiC(s)  3SiO(g) + CO(g)
SiO(g) + SiC(s)  2Si(l) + CO(g)
Outer part of the furnace (T < 1900 oC):
SiO(g) + 2C(s)  SiC(s) + CO(g)
2SiO(g)  Si(l) + SiO2(s)
Important actors
Norway
France
China
South-Africa
America
Brazil
Applications for MG-Si
1) Additive alloys (500.000 ton/year)
- Alloys of Al
2) Production of silicones
(400.000 ton/year)
3) Synthetic SiO2 (optic fibers; 100.000 ton/year)
SiCl4(g) + 2H2(g) + O2(g)  SiO2 + 4HCl(g)
4) Si for electronic and solar cell industry (50.000 + 200.000 ton/year)
- Including silane and chlorosilane production
79
From MG-Si  SiH4 (g)  Super Pure Si
REC Silicon Silane Process
REC SILICON - Moses Lake, USA
Silane production unit – approx. 9000 ton SiH4 gas per year
REC Silicon Silane Prosess
H2
MG-Si
SiCl4
Fluidised bed
Separator
HSiCl3
H2SiCl2
SiCl4
Si + 3SiCl4(g)+ 2 H2(g)  4HSiCl3(g)
SiCl4
2HSiCl3  H2SiCl2+ SiCl4
SiH4
HSiCl3
2H2SiCl2  HSiCl3+ SiH4
Destillations
*SiH4
REC silane pyrolysis units; SiH4  Si + 2H2
Super Pure Si for PV (purity 99.9999 – 99.999999%)
 Chemical processing - II
REC silane pyrolysis units SiH4  Si + 2H2
Super Pure Si for PV (purity 99.9999 – 99.999999%)
 Chemical processing - II
Working in the laboratory…..
..and out in the field…..
Wafer Production
Super Pure Si for PV (purity 99.9999 – 99.999999%)
 Chemical processing - II
From Si to wafers
1:
2:
3:
4:
Poly-Si in
crucibles
Melting in
furnace
Solidification
Bottom up
Polycrystalline
Si formation
5:
6:
7:
8:
Ingot cut in
blocks
Handling
Sawing
Wafere
Wafer produced
Areal: 154×154 (mm2)
Solar Cell Production
Process steps from wafer to module
1:
2:
3:
4:
Wafer
Etching
Doping
Anti reflecting
coating
5:
6:
7:
8:
Screen printing
Soldering
Module
production
Distribution
92
Tedlar