15. Energy Applications I: Batteries

What are Batteries, Fuel Cells, and Supercapacitors, Chem Rev, 2004, 104, 4245, Martin Winter and Ralph J. BroddBattery types: Primary Battery: Non reversible chemical reactions (no recharge)Secondary Battery: Rechargeable

Common characteristicsElectrodecomplex coposite of powders of active material and conductivediluent, polymer matrix to bind the mixtypically 30% porosity, with complex surface throughout the materialallows current production to be uniform in the structureCurrent 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. BroddWe 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. BroddRequire 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 BatteryTerminals, ResistanceTo current flow of, RMExternal Resistance, RextInternal DischargeRate (e.t.)Capacitance of electrodeResistance ofelectrolyte

Lead Acid BatteryBasic 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 bookSupport gridsThe capacity of the battery depends onThe type of material present.

One possible mechanism:.simultaneous dissolution of PbO2 and introduction of 2eRequires electronic conductivity of PbO2 and pore space for motion of waterAdd e, H+ and OH- to PbO2 Add 2nd e to reduce valence of PbAdd 3rd e to reduce valence while removing OH- for charge nuetralityPbO is more soluble than PbO2 so it dissolves and reacts with sulfate toInitiate formation of PbSO4, nucleation rate rises with lg conc. Sulfate, which reduces growth of large sized crystalsPbSO4 structure is rhombic which matches the PbO2 so it can easily attachTherefore 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 batterya.What is the potential associated with a lead acid battery with the overall reaction:

at the following concentration:[H2SO4] = 4.5 M

-0.35Vo1.69-(-0.35)2.04 1.69

Lead Acid battery energy

c.What is the free energy associated with the lead acid battery?

Dendrites are

Good: porous (makes moreOf possible energy available)

Bad: fragile, break and fall from underlying electrode = NO CURRENTeNo 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 As the battery is discharged the discharge voltage is the Difference between what we started with and the remainingVoltage in the battery

Lead acid batteries can be valve regulated to control the pressure associated With 1.29 V1.38 VNo pressurepressurizedLower CT resistanceUnder pressureSuggests higher Degree of interparticleContact under pressure

Insulating layer which can conduct only protons and leadSolubility DiffusionEt at conducting PbO2

Solubility DiffusionEt at conducting PbO2Modeled effect of diffusion

Solubility DiffusionEt at conducting PbO2Modeled effect of proton conc

Solubility DiffusionEt at conducting PbO2Different magnitude of dischargeChanges the solubility and proton concAs well as the conductivity of the film

Based on V. S. Bagotsky text, Fundamentals of Electrochemistry

For the simplified model

Monitor structural changes at electrode as a function of the discharge power

High charge transferResistance due to insulatingPbSO4 layerCharge 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

ReactionVoLi++eLi-3.0K+ + e K-2.95Na+ + eNa-2.71NCl3_4H+ + 6e 3Cl- + NH4+-1.372H2O + 2e H2 + 2OH--0.828Fe2+ + 2eFe-0.44Pb2+ + 2ePb-0.132H+ + 2e H2(gas) 0N2(g) + 8H+ + 6e2NH4+0.275Cu2+ + 2e Cu0.34O2 + 2H2O + 4e4OH-0.40O2 + 2H+ + 2eH2O20.68Ag+ + e Ag0.799NO3- + 4H+ + 3e NO(g) +2H2O0.957Br2 + 2e2Br-1.092NO3- + 12H+ + 10eN2(g) +6H2O1.246Cl2 + 2e2Cl-1.36Au+ + eAu1.83F2 + 2e2F-2.877g/mol207g/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 circuitLithium 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 benignM. 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, 4271-4301Group IGroup IIGroup IIISpinels

M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301Smooth 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 conductivityWent to marketIn the late 1970sSingle 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, 4271-4301Indicates various crystal formsLithium ion inserts in responseTo reduction of vanadiumDifferent phases of VSe2 have similar structuresSo the distortion is not greatoctahedral2nd is tetrahedral

M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301Group II

Major phase changes in LixV2O5 (x1) is a rock salt form

Sol gel processes of the V2O5 materials

M. Stanley Whittingham, Lithium Batteries and Cathode Materials, Chem. Rev. 2004, 104, 4271-4301Group IIISpinelsThese 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

Keeps Mn in higher oxidation state, therefore less soluble 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