15. energy applications i: batteries. what are batteries, fuel cells, and supercapacitors, chem rev,...
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15. Energy Applications I: Batteries
What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. Brodd
Battery types: Primary Battery: Non reversible chemical reactions (no recharge)Secondary Battery: Rechargeable
Common characteristicsElectrode
complex coposite of powders of active material and conductivediluent, polymer matrix to bind the mix
typically 30% porosity, with complex surface throughout the materialallows current production to be uniform in the structure
Current distributionprimary – cell geometrysecondary – production sites within the porous electrode
parameters affecting the secondarycurrent distribution areconductivity of diluent (matrix)electrolyte conductivity,exchange currentdiffusion characteristics of reactants and productstotal current flowporosity, pore size, and tortuosisity
What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. Brodd
We will briefly look at: Lead and Lithium insertion
What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. Brodd
What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. Brodd
Require very good conductivityThroughout the systemWhich tends to lower the energyContent of the systemIn the lead acid system a significant amountOf the weight Is in the grids requiredTo hold the paste
Equivalent Circuit for a Battery
Terminals, ResistanceTo current flow of, RM
External Resistance, Rext
Internal DischargeRate (e.t.)
Capacitance of electrode
Resistance ofelectrolyte
Lead Acid Battery
Basic requirements for a battery1. chemical energy stored near the electrode ( if too far away current will
be controlled by time to get to electrode)2. The chemical form coating the electrode must allow ion transport, or
better yet, electronic conduction3. The chemical form of the energy must be mechanically robust4. The chemical form of the energy should generate a large voltage
Fitch lead book Support grids
The capacity of the battery depends onThe type of material present.
PbO e H SO PbSO Hs aq s2 2 42 2, ,
One possible mechanism:. simultaneous dissolution of PbO2 and introduction of 2eRequires electronic conductivity of PbO2 and pore space for motion of water
1. Add e, H+ and OH- to PbO2 2. Add 2nd e to reduce valence of Pb3. Add 3rd e to reduce valence while removing OH- for charge nuetrality4. PbO is more soluble than PbO2 so it dissolves and reacts with sulfate to5. Initiate formation of PbSO4, nucleation rate rises with lg conc. Sulfate, which reduces growth of large sized crystals6. PbSO4 structure is rhombic which matches the PbO2 so it can easily attach7. Therefore need to control the alletropes of PbO2 and PbO
Beta PbO2 is formed under acid and can be compressed to shorten bonds overlap induces semiconductor behavior which increases the performanceOf the battery
Alpha forms when Pb metalCorrodes – reduces lifetime ofBattery, is more compressible.
Add antiomonyTo drive reactionTo beta phase
Lead Acid battery
a.What is the potential associated with a lead acid battery with the overall reaction:
at the following concentration:[H2SO4] = 4.5 M
Pb PbO H HSO PbSO H Os s aq aq s 2 4 22 2 2 2, ,
-0.35
Vo
1.69
-(-0.35)
2.04
1.69PbO H e SO PbSO H Os aq aq s22
4 24 2 2, ,
PbSO e Pb SOs s aq422,
PbO H e SO PbSO H Os aq aq s22
4 24 2 2, ,
Pb SO PbSO es aq s
24 2,
Pb PbO H HSO PbSO H Os s aq aq s 2 4 22 2 2 2, ,
V Vn
Q Qo 0 0 5 9 2
2 0 40 0 5 9 2
2
.lo g .
.lo g
Lead Acid battery energy
Pb PbO H HSO PbSO H Os s aq aq s 2 4 22 2 2 2, ,
V QPbSO H O
Pb PbO HSO H O
s
s s aq
2 0 40 0 5 9 2
22 0 4
0 0 5 9 2
24
2
2
2
3
2.
.lo g .
.lo g
,
V Q
HSO H Oaq
2 0 40 0 5 9 2
22 0 4
0 0 5 9 2
2
12
3
2.
.lo g .
.lo g
V
2 0 4
0 0 5 9 2
2
1
4 5 4 52 2..
lo g. .
V 2 0 4 0 0 2 9 6 2 6 2 11. . . .
c. What is the free energy associated with the lead acid battery?
nFV G RT Ko ln
G 2 9 6 4 8 5 2 0 4, .
G kJ 3 9 3 6.
PbO H SO e PbSO H Oso lid aqueous aqueous so lid2 42
4 24 2 2, , ,
Dendrites are
Good: porous (makes moreOf possible energy available)
Bad: fragile, break and fall from underlying
electrode = NO CURRENT
e
No e
The type of structure that forms depends upon the rate of crystallization whichDepends upon rate of reaction which depends upon:
Loss/production of products (current)Which depends also upon the rate constant (potential dependent)
One way to “image” the various processes described above is by an Equivalent Circuit
In a simplified system
I D isch eargR ext
R apparen t erna l resis cein t tan I D isch earg
V I R Rt d ex t app 0
V I RD isch e D extarg
V I Rrem ain ing D app
As the battery is discharged the discharge voltage is the Difference between what we started with and the remainingVoltage in the battery
V V I RD isch e t D Apparg 0
Lead acid batteries can be valve regulated to control the pressure associated With
1.29 V
1.38 V
No pressure
pressurizedLower CT resistanceUnder pressure
Suggests higher Degree of interparticleContact under pressure
Insulating layer which can conduct only protons and lead
Solubility
Diffusion
Et at conducting PbO2
Solubility
Diffusion
Et at conducting PbO2
Modeled effect of diffusion
Solubility
Diffusion
Et at conducting PbO2
Modeled effect of proton conc
Solubility
Diffusion
Et at conducting PbO2
Different magnitude of dischargeChanges the solubility and proton concAs well as the conductivity of the film
I D isch eargR ext
R apparen t erna l resis cein t tan I D isch earg
V I R Rt d ex t app 0
V I RD isch e D extarg
V I Rrem ain ing D app
P V ID D
P I R I I RD ext D D ext 2
PV R
R R
ext
app ext
0
2
2
V
R RIt
ex t app
d
0
Based on V. S. Bagotsky text, Fundamentals of Electrochemistry
V V I RD isch e t D Apparg 0
P
V R
R R
ext
app ext
0
2
2
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5
Current Density
V
0
0.2
0.4
0.6
0.8
1
1.2
P
For the simplified model
Monitor structural changes at electrode as a function of the discharge power
High charge transferResistance due to insulatingPbSO4 layer
Charge transfer resistanceDecreases due formation of more porous PbO2
Small diameterOf impedanceCircle here indicatesThe fast et kinetics ofO2 reaction.
Increasing Charge transferResistance dueTo layer of PbSO4
Reaction Vo
Li++e Li -3.0K+ + e K -2.95Na+ + e Na -2.71NCl3_4H+ + 6e 3Cl- + NH4
+ -1.372H2O + 2e H2 + 2OH- -0.828Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0N2(g) + 8H+ + 6e 2NH4
+ 0.275Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Ag+ + e Ag 0.799NO3
- + 4H+ + 3e NO(g) +2H2O 0.957Br2 + 2e 2Br- 1.092NO3
- + 12H+ + 10e N2(g) +6H2O 1.246Cl2
+ 2e 2Cl- 1.36Au+ + e Au 1.83F2 + 2e 2F- 2.87
7g/mol
207g/mol
Lithium oxidation proceeds a little too uncontrollably
Lithium reduction does not not result in good attachment back to the lithium metal
Forms dendrites which can grow to Short circuit
C e L i L iC6 61
Lithium intercalated in graphite is close to metallic, formal potential differs by only 0.1 to .3 V = -2.7 to -2.9V
Anode – Solid electroactive metal salt(Can change overall charge so that it can electrostatically stabilize & localize Li+ )Potential should be very positive (far from -2.5 V for Li/C reactionSolid should conduct charge throughoutSolid should allow ion motionShould have fast kinetics (open and porous)Should be stable (does not convert to alleotropes)Low costEnvironmentally benign
M X M X exm
zx
xm
zx
1
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
M X Li M X L ixm
zx
xm
zxfa st
M X L i M X L i exm
zx
xm
zxfa st
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
L iT iS 2 L iVSe 2 L iC oO 2
L iN iO 2
Group I
Group IIV O2 5 MoO 3
Group IIISpinels
Mn O2 4
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
L iT iS 2
Smooth galvanostatic curve indicatesThat there are no sites nucleating Alleotropes of the compound.
Allotropes would alter the structure,Porosity, and the ease of intercalation,Potential, and conductivity
Went to marketIn the late 1970s
Single phaseLight weightConducting, but notReactive (oxidised or reduced)Li ion intercalates in response to double layer charging
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
L iVSe 2
Indicates various crystal forms
V Se xL i xe L i V SeIVx
IV x2 2
L i V Se x L i x e L iV SexIV x III 2 21 1
L iV Se L i e L i V SeIII II2 2 2
Lithium ion inserts in responseTo reduction of vanadium
Different phases of VSe2 have similar structuresSo the distortion is not great
octahedral
2nd is tetrahedral
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
Group II
V O2 5 MoO 3
Major phase changes in LixV2O5 (x<0.01) is well orderedЄ ( 0.35<x<0.7)is more puckered (x=1) shifting of layers (x>1) results in permanent structural changeω (x>>1) is a rock salt form
Sol gel processes of the V2O5 materials
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
Group IIISpinels
Mn O2 4
These materials have a major change in Unit cell dimensions when Mn changes Oxidation state (see B). Need to keep the Lattice parameter less than 8.23 A for goodCycling, which
1. Keeps Mn in higher oxidation state, therefore
less soluble 2. Prevents distortion in the coordination of
oxygen (Jahn-Teller) around the manganese. These distortions
will alter the oxidation and reduction potential as seen in the next slide
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301