15. Energy Applications I: Batteries
Battery types:
Primary Battery: Non reversible chemical reactions (no recharge)
Secondary Battery: Rechargeable
Common characteristics
Electrode
complex coposite of powders of active material and conductive
diluent, polymer matrix to bind the mix
typically 30% porosity, with complex surface throughout the material
allows current production to be uniform in the structure
Current distribution
primary – cell geometry
secondary – production sites within the porous electrode
parameters affecting the secondarycurrent distribution are
conductivity of diluent (matrix)
electrolyte conductivity,
exchange current
diffusion characteristics of reactants and products
total current flow
porosity, 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 conductivity
Throughout the system
Which tends to lower the energy
Content of the system
In the lead acid system a significant amount
Of the weight Is in the grids required
To hold the paste
What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and
Ralph J. Brodd
Equivalent Circuit for a Battery
External Resistance, Rext
Terminals, Resistance
To current flow of, RM
Capacitance of
electrode
Internal Discharge
Rate (e.t.)
Resistance of
electrolyte
Basic requirements for a battery
1.
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 conduction
3.
The chemical form of the energy must be mechanically robust
4.
The chemical form of the energy should generate a large voltage
ad Acid Battery
The capacity of the battery depends on
The type of material present.
Fitch lead book
Support grids

PbO2,s  2e  H2 SOaq 
PbSO

2
H

4 ,s
One possible mechanism:. simultaneous dissolution of PbO2 and introduction of 2e
Requires electronic conductivity of PbO2 and pore space for motion of wat
1.
2.
3.
4.
5.
6.
7.
Add e, H+ and OH- to PbO2
Add 2nd e to reduce valence of Pb
Add 3rd e to reduce valence while r
PbO is more soluble than PbO2 so
Initiate formation of PbSO4, nuclea
PbSO4 structure is rhombic which
Therefore need to control the alletr
Beta PbO2 is formed under acid and can be compressed to shorten bonds
overlap induces semiconductor behavior which increases the performance
Of the battery
Add antiomony
To drive reaction
To beta phase
Alpha forms when Pb metal
Corrodes – reduces lifetime of
Battery, is more compressible.
Lead Acid battery
a.What is the potential associated with a lead
acid battery with the overall reaction:
Pbs  PbO2 ,s  2 Haq  2 HSOaq 
 2 PbSO4 , s  2 H2 O
at the following concentration:
[H2SO4] = 4.5 M
Vo
1.69
PbO2 ,s  4 Haq  2e  SOaq2 
 PbSO4 , s  2 H2 O
2
PbSO4 ,s  2e 
Pb

SO

s
aq
-0.35
PbO2 ,s  4 Haq  2e  SOaq2 
 PbSO4 , s  2 H2 O 1.69
Pbs  SOaq2 
 PbSO4 , s  2e
-(-0.35)
2.04
Pbs  PbO2 ,s  2 Haq  2 HSOaq 
 2 PbSO4 , s  2 H2 O
0.0592
0.0592
V V 
log Q  2.04 
log Q
n
2
o
Lead Acid battery energy
Pbs  PbO2 ,s  2 Haq  2 HSOaq 
 2 PbSO4 , s  2 H2 O



2

PbSO4 ,s H2 O
0.0592
0.0592 
V  2.04 
log Q  2.04 
log
2
2
2
 Pb PbO HSO  H O 

s
s
aq
3
 


0.0592
0.0592 
1
V  2.04 
log Q  2.04 
log
2
2
2
 HSO  H O 

aq
3

0.0592 
1
V  2.04 
log
2
2
2
  4.5  4.5 

V  2.04  0.0296  2.6   211
.





2



2
c.
What is the free energy associated with the
lead acid battery?
 nFV   G   RT ln K
o
G  296,485 2.04
 G   393.6kJ
Dendrites are
Good: porous (makes more
Of possible energy available)
Bad: fragile, break and fall
from underlying
electrode
= NO CURRENT
e
No e

PbO2, solid  4 Haqueous
 SO42,aqueous  2e 
 PbSO4, solid  2 H2O
The type of structure that forms depends upon the rate of crystallization which
Depends 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
VDisch arg e   I D  Rext 
Rext
I Disch arg e

Vt  0  I d Rext  Rapp
Rapparent int ernal resis tan ce
I Disch arg e
 
Vremaining   I D  Rapp
As the battery is discharged the discharge voltage is the
Difference between what we started with and the remaining
Voltage in the battery
VDisch arg e  Vt 0  I D RApp

Lead acid batteries can be valve regulated to control the pressure associated
With
No pressure
1.29 V
1.38 V
Suggests higher
Degree of interparticle
Contact under pressure
Lower CT resistance
Under pressure
pressurized
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 discharge
Changes the solubility and proton conc
As well as the conductivity of the film
P  VD I D
P   I D Rext  I D   I D  Rext
R
Vt  0
ext
 Rapp

 Id
2
P
V 
R
0
app
Rext
2
Rext
 Rext

2
VDisch arg e   I D  Rext 
I Disch arg e

Vt  0  I d Rext  Rapp
Rapparent int ernal resis tan ce
I Disch arg e
Based on V. S. Bagotsky text, Fundamentals of Electrochemistry
 
Vremaining   I D  Rapp

VDisch arg e  Vt 0  I D RApp
P
V 
R
0
app
2.5
1
0.8
V
1
0.4
0.5
0.2
0
0
0
0.5
1
1.5
Current Density
For the simplified model
2
2.5
P
1.5
0.6
Rext
 Rext
1.2
2
2

2
Monitor structural changes at electrode as a function of the discharge power
Charge transfer resistance
Decreases due formation of more porous PbO2
High charge transfer
Resistance due to insulating
PbSO4 layer
Increasing
Charge transfer
Resistance due
To layer of PbSO4
Small diameter
Of impedance
Circle here indic
The fast et kine
O2 reaction.
Reaction
Li++e
K+ + e
Na+ + e
NCl3_4H+ + 6e
2H2O + 2e
Fe2+ + 2e
Pb2+ + 2e
2H+ + 2e
N2(g) + 8H+ + 6e
Cu2+ + 2e
O2 + 2H2O + 4e
O2 + 2H+ + 2e
Ag+ + e
NO3- + 4H+ + 3e
Br2 + 2e
2NO3- + 12H+ + 10e
Cl2 + 2e
Au+ + e
F2 + 2e
Li
K
Na
3Cl- + NH4+
H2 + 2OHFe
Pb
H2(gas)
2NH4+
Cu
4OHH2O2
Ag
NO(g) +2H2O
2BrN2(g) +6H2O
2ClAu
2F-
Vo
-3.0
-2.95
-2.71
-1.37
-0.828
-0.44
-0.13
0
0.275
0.34
0.40
0.68
0.799
0.957
1.09
1.246
1.36
1.83
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
C6  1e  Li   LiC6
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 reaction
Solid should conduct charge throughout
Solid should allow ion motion
Should have fast kinetics (open and porous)
Should be stable (does not convert to alleotropes)
Low cost
Environmentally benign
M
M
 M
m
x
m
x
m
x
 M
  Li
X
x  

z
X
x 
z
X
x 
z

m 1
x
fast
 


Li


fast

 M
X zx   e



M
m
x
m
x
X

x 
z
Li 


X zx   Li   e
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
Group II
V2 O5
Group I
LiTiS 2 LiVSe2
LiNiO2
LiCoO2
MoO3
Group III
Spinels
Mn2 O4
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
LiTiS 2
Smooth galvanostatic curve indicates
That there are no sites nucleating
Alleotropes of the compound.
Single phase
Went to market
Allotropes would alter the structure,
Light weight
In the late 1970s
Porosity, and the ease of intercalation,
Conducting, but not
Potential, and conductivity
Reactive (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
Indicates various crystal forms
V IV Se2  xLi   xe  Li xV IV  x Se2
LiVSe2
Li xV IV  x Se2  1  x Li   1  xe  LiV III Se2
octahedral
Lithium ion inserts in response
To reduction of vanadium
LiV III Se2  Li   e  Li2V II Se2
2nd is tetrahedral
Different phases of VSe2 have similar structures
So the distortion is not great
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
Group II
V2 O5
MoO3
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301
Major phase changes in LixV2O5
 (x<0.01) is well ordered
Є ( 0.35<x<0.7)is more puckered
 (x=1) shifting of layers
 (x>1) results in permanent structural change
ω (x>>1) is a rock salt form
Sol gel processes of the V2O5 materials
Group III
Spinels
Mn2 O4
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 good
Cycling, 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
M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301