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CH10134 > Ion conduction > Flashcards

Ion conduction Flashcards

1
Q

Is ionic or atom diffusion faster or slower in solids than other phases

A
  1. Much slower than other phases- liquids and gas
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2
Q

Give examples of when diffusion in solids is still important in solid state technology

A
  1. Synthesis of solids (usually at high temp)

2. Ionic conductors or solid electrolytes in batteries, gas sensors and fuel cells

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3
Q

What are diffusing ions linked to

A
  1. Mobile point defects

2. Generally the lowest-energy pathway involves defect sites

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4
Q

Give 3 examples of a mobile point defect

A
  1. Vacancy mechanism
  2. Direct interstitial mechanism
  3. Interstitialy or knock-on mechanism
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5
Q

Describe a vacancy mechanism

A
  1. Ion migrates into adjacent vacant sites (continues through the lattice)
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6
Q

Describe a direct interstitial mechanism

A
  1. Migration of interstitial ion directly into an adjacent unoccupied site
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7
Q

Describe a knock-on mechanism

A
  1. Interstitial ion moved into adjacent lattice site, displacing the ion into a new interstitial site
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8
Q

Give an example of a knock-on mechanism and uses

A
  1. AgCl or AgBr

2. For Ag+ conduction (from NMR, radio-tracer experiment and computer modelling)

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9
Q

What is ionic conductivity dependent on and give an equation to show this

A
  1. Ionic conductivity (sigma) is temperature dependent and shows ‘Arrhenius behaviour’
  2. Sigma = Aexp(-Ea/RT)
  3. A= pre-exponential factor
  4. R= gas constant
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10
Q

How can the equation linking ionic conductivity to temperature be manipulated to be used on a graph

A
  1. ln(sigma)= -Ea/RT + ln(A)
  2. y= mx + c
  3. Draw graph of ln(sigma) over 1/T
  4. Slope= -Ea/RT
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11
Q

What does the gradient of the slope tell us

A
  1. The lower the gradient of the slope the lower the activation energy
  2. This leads to high ionic conductivity
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12
Q

What compound has a high ionic conductivity

A
  1. Na(Beta2prime)-Al2O3
  2. Electrolyte use in sodium batteries
  3. Has low activation energy- smallest gradient
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13
Q

Name the structure and migrating defect for Na(Beta2prime)-Al2O3

A
  1. ?

2. Na(i).

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14
Q

Name the structure and migrating defect for Y3+ doped ZrO2

A
  1. Fluorite

2. V(O)..

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15
Q

Name the structure and migrating defect for NaCl

A
  1. Rock-salt

2. V(Na)I

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16
Q

Name the structure and migrating defect for AgCl

A
  1. Rock-salt

2. Ag(i).

17
Q

Name the structure and migrating defect for Sr2+ doped LaGaO3

A
  1. Perovskite

2. ?

18
Q

What are the three types of conductors

A
  1. Ionic conductor (solid electrolyte)- medium- 0.1-10^2 sm-1
  2. Electronic conductor ( metals) - fastest 10^3-10^7sm-1
  3. Electronic insulator (diamond)- slowest 10^-7sm-1
19
Q

What is intercalation

A
  1. The incorporation (insertion) of atoms, ions or molecules into a structure with minimal structural change
  2. It involves a redox process (oxidation or reduction) and often they are reversible reaction
20
Q

Give an example of intercalation

A
  1. Lithium intercalation in rechargeable Li-ion batteries

2. Led to the portable revolution and now important for electric vehicles

21
Q

Describe what a Li-ion battery cell is composed of

A
  1. Battery cell consists of +ve electrode LiCoO2 and -ve electrode (graphite) separated by a Li+ conductivity electrolyte
  2. Both electrodes are intercalation host structures for small and light lithium
  3. Charging/discharging involves lithium intercalation (and extraction) and Li-ion conduction
22
Q

Describe what occurs at the LiCoO2 electrode

A
  1. Li(x)CoO2 x= 1.0 - Co3+ or x=0.0 Co4+
  2. Cobalt gets oxidised/reduced with x ranging from 1.0–>0.2
  3. Structure of LiCoO2 is layered with edge-sharing [CoO6] octahedra and [LiO6] octahedra
  4. Co, Li coordination number= 6
23
Q

Describe what occurs at the graphite electrode

A
  1. Has layered structure of hexagonal carbon rings, strongly bonded within the 2D layers (separated by 3.5 A)
  2. Weak interlayer interactions (Van der Waals) which allow for atom/ion intercalation between the layers.
24
Q

How does lithium intercalation occur

A
  1. In both LiCoO2 and graphite there is fast Li+ ion diffusion within the 2D layers
25
Q

What is the overall Li-ion battery cell reaction

A
  1. LiCoO2 + 6 graphite LiC6 + CoO2
  2. Forward is charge
  3. Backward discharge
26
Q

Describe the current research involving Li-ion

A
  1. LiCoO2 - replace Co which is toxic and expensive with Fe, Ni, Mn
  2. NMC electrodes Li(Ni,Mn,Co)O2
  3. NMC-622 Li(Ni(0.6),Mn(0.2), Co(0.2))O2- used in Nissan-leaf, BMW-I3
27
Q

What is another example of a compound that can be used to produce intercalation compounds

A
  1. Buckminster fullerene
28
Q

What is buckminster fullerene

A
  1. C60
  2. Football shaped with 6-membered rings and 5-membered rings of carbon
  3. Reacts with alkaline metal ions (M+) to produce intercalation compounds
29
Q

How is buckminster fullerene used

A
  1. K3C(primer)60
  2. The ion insertion leads to a superconductor at Tc around 18K
  3. 0 resistance to electronic conduction at Tc
  4. The other important property of super conductor is powerful magnetism (Meissner effect) used in NMR, MRI, and Maglev trains
30
Q

What does a graph of electrical resistance over Tc look like for a superconductor

A
  1. At specific Tc goes straight up and then diagonal line which could be semi-conductor

CH10134 (15 decks)

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