15. energy applications i: batteries. what are batteries, fuel cells, and supercapacitors, chem rev,...

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