1. Galvanic Cells - INTRODUCTION
Galvanic Cells II
Galvanic Cells - INTRODUCTION
Energy sources
How did the battery business start?
History of batteries makes history of electric energy
Galvanic Cell
As ELECTROCHEMICAL DEVICE :
Electrode reactions
Thermodynamics and kinetics
Properties of Materials
As ENERGY SOURCE :
Position on energy market
Power supply
Technology & Economy
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2. Electrical power generation
Galvanic Cells II
Electrical power generation
Fuel – combustion – heat effect – mechanical energy – generating electricity
CHEMICAL ENERGY indirectly into ELECTRICAL
Renewable energy source ( wind, water, geothermal) – transformation of work to electric energy
Galvanic, fuel, fotovoltaic cells
CHEMICAL ENERGY directly into ELECTRICAL
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3. DIFFERENT CELLS galvanic cells – primary and secondary
Galvanic Cells II
DIFFERENT CELLS
galvanic cells – primary and secondary
Chemical substances
in electrodes
Expressed as Q
Electrode
Reactions
Expressed as U
Energy = U . Q
Fuel cells
Stream of reagents
Energy = U . Q
Electrode
Reactions
Expressed as U
ISOLATED PORTABLE/TRANSPORTABLE
INDEPENDENT FORM ELECTROENERGETICAL NETWORK
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4. Some milestones in history
Galvanic Cells II
Some milestones in history
1780 L. Galvani – „animal electricity”
1800 A. Volta – pile (battery of zinc and silver discs, separated by cloth wet with salty solution)
1866 G. Leclanche – zinc – MnO2 cathode battery
1859 G. Plante’ – lead acid accu made of Pb plates,
1881 – Faury et al – pasted plates instead of solid Pb
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5. Transformation from isolated current sources to electrical network
Galvanic Cells II
Transformation from isolated current sources to electrical network
Electromagnetic induction – discovered by Faraday about 1840
Electromechanical generator – Siemens about 1857
T. A . Edison : electric bulb 1879, lighting system in NY, Ni-Fe accumulator
DC contra AC – Edison contra Westinghouse, first big power plant in America – Niagara Falls – advantages of supplying energy with AC
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6. Electrical circuits with batteries
Galvanic Cells II
Electrical circuits with batteries
Management of voltage and current – connecting the batteries
Ohm’s law in simple DC circuit : external resistance (load),internal resistance( ohmic drop on battery components), polarisation resistance (ohmic drop on reaction)
E = I ( Rinter + Rpol + Rload)
Energy and power
Energy = Q ∙U = I ∙ t ∙ U = (m / k) ∙U
Power = energy produced/consumed in time unit
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7. Observed effects of electrode reaction :
Galvanic Cells II
Electrode potential
φ= φo + RT/nF ln ( aMe / aMe(n+) )
Standard potential at unit activity of particles - φo
+ deviation from standard due to non-unit activity (concentration)
Can not be measured directly
Electrode reaction
Transport of charge or charge and mass over phase boundary electrode – electrolyte
Phases : electrode = fragment of condensed phase electronically conductive
electrolyte = ionically conducting „space”
Observed effects of electrode reaction :
Change of oxidation grade of an atom in a molecule / ion in solution
Accompanying changes : creation / decomposition of a phase
changes in phase structures
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8. Overall cell reaction A + B = C + D With E = Δ φ Anodic reaction
Galvanic Cells II
Anodic reaction
Ared →Box + n e-
Potential φox
Potential φred
Cathodic reaction
Cox + n e- →Dred
Overall cell reaction
A + B = C + D
With E = Δ φ
Electromotoric force E comes from change in free enthaply of the overall reaction,
Also combining the ΔG with electrical equivalent of energy E = -ΔG /nF
And defining Eo = ΔG o/nF for standard conditions we get Nernst equation :
E = Eo – RT / nF ln K
where K – equilibrium constant of reaction ABCD
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9. WUT - MESC - Galvanic Cells II
Signs + / - in cells convention
More negative potential on left side : Zn = Zn2+ + 2e φ = V
Less negative to the right : Cu = Cu2+ + 2e φ = 0.34 V
formal scheme for the cell
External connection / Zn / Zn SO4 aq // CuSO4 aq / Cu / external connection
Sign // sign
But .....
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10. Structure and functions of electrodes
Galvanic Cells II
Structure and functions of electrodes
A/ metallic reactive electrodes (deposition-dissolution,
formation of compounds on the surface)
Reagent and current collector(two-in-one)
Charge and mass transport – on the surface
B/ inert electrodes
metalls, graphite, semiconductors
Current collector, not a redox reagent
C/ multi-function, multi-component electrodes
electroactive component (often insulator)
electronically conducting matrix
other additives with special functions
Charge and mass transport – on triple-contact sites
Cond. matrix
Redox active
electrolyte
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11. Various types of batteries
Galvanic Cells II
Various types of batteries
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12. Specyfic energy - Energy density
Galvanic Cells II
Specyfic energy - Energy density
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13. Typical battery application
Galvanic Cells II
Typical battery application
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14. WUT - MESC - Galvanic Cells II

15. WUT - MESC - Galvanic Cells II
Zn/MnO2 Cells
Leclanche type – electrolytes lightly acidic or neutral:
anodic reaction – product: Zn salts soluble in the electrolyte
( NH4Cl, NH4OH, ZnCl2 → complexes of Zn with OH- and Cl-
Alkaline – electrolyte: concentrated KOH:
anodic reaction – product: solid ZnO – the composition ot the electrolyte does not change
Different anodic mechanism → different yields of the cells :
in alkaline cells the maximum current density is higher
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16. Zn electrode and redox cycling
Galvanic Cells II
Zn electrode and redox cycling
Solid Zn anode : Zn – 2e-→ Zn2+ in solution + 2e- → Zn as powder, needles
(→ due to specyiic features of electrocrystallization of metals)
Volumen of anode ↑ electrical contact within the anode ↓
Powder Zn anode : Zn – 2e- → ZnO ( in OH-solution) + 2e- → Zn as powder
discharge (work) charge
Zn metallurgical foil % material as energy
complex structure (Zn + conducting matrix + glue) - part of electrode „useless” as energy source
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17. WUT - MESC - Galvanic Cells II
MnO2 cathode
MnIVO2 + H2O ↔ MnIIIO(OH) + OH-
(other compounds of MnIII possible)
OH- ion takes part in the anodic reaction – formation of Zn complexes
At higher load (high current density) possible limitation of anode kinetics due to low concentration of comlexing ions
Valid for Leclanche type ( Zn complex salts soluble in the electrolyte)
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18. WUT - MESC - Galvanic Cells II
Cells with Zn anode
Cell name
Cathode
Electrolyte
OCV or EMF (V)
Daniell
Cu → Cu2+
ZnSO4/CuSO4
1.2
Anode product – soluble Zn salts
Leclanche
MnO2→MnO(OH)
(→Mn3O4 possible)
NH4Cl, ZnCl2
1.6
Alkali
KOH
1.55
Anode product - ZnO
Zinc-air
O2 → O2- (on carbon matrix)
1.45
Zinc-silver
Ag2O → Ag
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19. WUT - MESC - Galvanic Cells II
Zn - air
A : Zn → Zn2+ (as ZnO) + 4e-
C : O2 + 2 H2O + 4e- → 4 OH EMF = 1.65 V
Cathode reaction on inert catalytic electrode ( graphite + catalyst + binder)
Oxygen supply forced by underpressure in cathode space
Slow kinetics of oxygen electrode – main limitation for current value
Parasitic processes : Zn + O2
OH- + CO2
loss of water
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20. WUT - MESC - Galvanic Cells II
Electric vehicles
„zero-emission” buses and vans on tests in USA and Germany
Repleceable anodic casette of Zn with KOH (gelled)
Ca. 200 Wh/kg and 90 W/kg at 80% d.o.c.
Supercapacitor in hybrid system to boost accelaration
External regeneration of anodes
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21. WUT - MESC - Galvanic Cells II
Zn/MnO2 cells
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22. WUT - MESC - Galvanic Cells II
Zn/MnO2 cells
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23. How to get „more” from a single cell?
Galvanic Cells II
How to get „more” from a single cell?
Redox potential for Me – Men+ couples
Apply special conditions of discharge
Eliminate water from cells
Zn-Zn2+
-0.76 V
O2-OH-
0.4 V
Mg-Mg2+
-2.36 V
Ag+-Ag
0.8 V
Na-Na2+
-2.92 V
MnO2-MnO(OH)
app V
Li-Li+
-3.05 V
F2 – 2F-
2.87 V
Reserve cells
one-time discharge
non-aqueous solutions
synthesis in inert atmosphere
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24. Reserve (activated) cells
Galvanic Cells II
Reserve (activated) cells
Separated elements –
Signal to make contact electrolyte – electrodes : closing the circuit inside the cell
Activation on signal (decision) or by event (water flow, emergency)
No or poor activity if energy demand intermittent
Very long storage time (no parasitic reactions and self-discharge)
Energy supply – short time, but high current densities
inactive electrolyte :
-closed in a vessel
-solid salt to be molten
dry electrodes
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25. Reserve cells - examples
Galvanic Cells II
Reserve cells - examples
Mg anode reactions Mg + 2 H2O
Mg(OH)2 + 2H+ + 2e Mg(OH)2 + H2
(Mg covered with MgO Mg open to water,
layer, proton recombinates no contribution to current
with OH from cathode space) drawned from the cell
Both reactions take place, H2 evolution wastes part of electrode, but
Gas bubbling → intensive stirring → quick transport → high current
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26. Reserve cells – examples cont.
Galvanic Cells II
Reserve cells – examples cont.
Cathodes in Mg cells :
2 AgCl + 2e → Ag + 2 Cl-
2 CuCl + 2e → Cu + 2 Cl-
other simple salts : PbCl2 , CuSCN, Cu2I2
Overall reaction : Mg + PbCl2 = MgCl2 + Pb
Electrolytes : sea-water, simple salts specific for best cathode rate
construction: composite cathodes, mechanical separation of electrodes, soakable separators for electrolyte
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27. Water and gas activated batteries - applications
Galvanic Cells II
Water and gas activated batteries - applications
Air-sea rescue systems
Sono and other buoys
Lifeboat equipment
Diverse signals and alarms
Oceanographic and meteo eq.
And many others, including military
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28. Molten salts and thermal batteries
Galvanic Cells II
Molten salts and thermal batteries
Main parts of a thermal battery
Anodes : Li alloys : Li(20)Al, Li(40)Si (melt higher than Li – 181 and 600/7090C resp.)
Cathodes : Ca, K, Pb chromates, Cu, Fe, Co sulfides, V2O5, WO3
Electrolyte: molten LiCl-KCl eutectic 3520C
Combination with bromides
Thermal dissociation KCl = K+ + Cl-, high conductivities, simple reaction mechanism
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29. Thermal batteries – applications
Galvanic Cells II
Thermal batteries – applications
Pyrotechnic heat source – squib, burned serves as inter-cell conductor
Insulation – ceramic, glass, polymers – depends on time of discharge
(salt must be kept molten !)
Voltages – single OCV : 1.6 V (Li/FeS2) , to ca. 3 V (Ca/K2Cr2O7)
Activated life-time : minutes, in special constructions hours
Energy density : 2 – 35 Wh/kg
High currents possible
Applications – mainly military
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30. Solid electrolyte cell Na-S
Galvanic Cells II
Solid electrolyte cell Na-S
Anode Na → Na+
Cathode xS → Sx2- , x 3~5
Overall Na + xS → Na2Sx
OCV = V
Temperature 310 – 350oC
sulphur Tmelt = 118, boil= 444oC
β-alumina Na2O∙11Al2O3 , conducts Na ions σ300 C ca S/cm
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31. Solid electrolyte cell Na-S
Galvanic Cells II
Solid electrolyte cell Na-S
Can be used as rechargeable cell
Applications : stationary energy storage, motive power
Working with high-temperature cells:
warm-up on start
keep warm at intervals in operation
manage excessive heat during operation (ohmic and reaction)
Construction of stacks : electrical and heat management
Insulated enclosure
Cooling system
Heat distribution
heaters
Electrical
networking
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32. Stationary energy storage Na-S system
Galvanic Cells II
Stationary energy storage Na-S system
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33. Lithium – iodine solid electrolyte cell
Galvanic Cells II
Lithium – iodine solid electrolyte cell
Anode : Li → Li+ + 2e
Cathode : nI2∙P2VP + 2e → (n-1)I2P2VP + 2 I- (poly-2-vinylpyridine)
Overall : Li + I2 → 2 LiI
LiI thin layer on contact between Li and cathode, ionically conducting
OCV ca 2.8 V
Discharge rates 1 – 2 μA/cm2 (very low)
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34. Primary and secondary cells - basic
Galvanic Cells II
Primary and secondary cells - basic
PRIMARY
SECUNDARY
Irreversible use of electrodes
Recovery of electrodes – by supplying electrical energy we restore electrode oxidation state and structure
Anodic and cathodic process (redox) related to specified electrodes, run only once
Anodic and cathodic reactions repeat on both electrodes in charge-discharge cycles
Solid metal electrodes (one-way)
Products may be soluble
Substrates and products stay in electrode phase
Redox reaction „all-solid state”
Minimalizing changes in electrode structure and shape
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35. Secondary cells - basic
Galvanic Cells II
Secondary cells - basic
Energy density from < 20 (Pb) , 35 (NiCd), 75 (NiMeH) to 150 Wh/kg (Li-ion)
Cycling life (Pb) – (Ni-Cd)
Voltage V (Pb) V (Ni-Cd)
Flat discharge profiles
Poor charge retention (shelf life of Ni-Cd – fully discharged, Pb must be kept charged because of sulfation of plates)
Vented constructions – evolution of H2 / O2
Tight closure of cells – oxygen recombination ( at end of charge oxygen developing in anodic process diffuses to cathode and oxidates surplus of cathode material – no overpressure :
Valve-Regulated-Lead-Acid sealed Ni-Cd
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36. Lead-acid accumulator
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37. WUT - MESC - Galvanic Cells II
cycle
„negative mass”
„positive mass”
discharge
Pb → PbSO4 (oxidation)
Concentration of H2SO4 ↓
PbO2 → PbSO4 (reduction)
Concentration of H2SO4 ↓
charge
PbSO4 → Pb (reduction)
Concentration of H2SO4 ↑
PbSO4 → PbO2 (oxidation)
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38. Phenomena in discharge cycle
CH2SO4
PbSO4 – insulator ( ca Ώcm)
Vmol PbSO4 > Vmol Pb, PbO2
worse porosity
diffusion of the electrolyte into the structure impaired
R int
What happens with:
current density at U = const ?
Voltage at I = const. ?
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39. WUT - MESC - Galvanic Cells II

40. WUT - MESC - Galvanic Cells II

41. Alkaline accumulators
Ni –Cd , Ni – Fe, Ni – MeH ( 1.2V)
Ag – Zn ( 1.5V)
Ni – Zn (1.6V)
Cathode Ni
NiIII OOH + H20 + e Ni(OH)2 + OH-
Anode Cd
Cd + 2(OH-) Cd(OH)2 + 2e-
Ag-Zn : Ag2O + H2O + 2e Ag + 2 OH-
Zn + 2(OH-) Zn(OH)2 + 2e
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42. WUT - MESC - Galvanic Cells II
Ni-Cd accumulator
cycle
„masa ujemna”
„masa dodatnia”
discharge
Cd → Cd(OH)2 (oxidation)
NiOOH → Ni(OH)2 (reduction)
charge
Cd(OH)2 → (reduction)
Ni II(OH)2 → Ni IIIOOH (oxidation)
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43. WUT - MESC - Galvanic Cells II
(further electrolysis after charging effects in evolution of O2)
((further electrolysis after charging effects in evolution of H2)
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44. Oxygen and hydrogen formation in cells
Galvanic Cells II
Oxygen and hydrogen formation in cells
Reactions possible in water solution
Equilibrium potentials : E (H+/H2) = 0V , E (OH-/O2) = V
BUT – overpotentials due to phenomena at gas-solid electrode phase boundary make true potentials higher
For different metals the hydrogen evolution potential grows from:
Pt Ni Ag Zn Cd Pb (and compounds)
Still, at the end of charge/discharge cycle co-evolution of gases in cells occurs
In effect: overpressure inside the cell, - H2 i O2
„oxygen recombination” – electrodes not equivalent in charge, ex. QCd > QNi
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45. WUT - MESC - Galvanic Cells II
Basic secondary cells
Ni-Cd
Pocket electrode construction of electrodes
Sintered plates
Pb acid
Pasted plates
Tubular positive plates
Plante’ design
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46. Technology of electrode masses in Ni-Cd
Galvanic Cells II
Technology of electrode masses in Ni-Cd
Electrodes prepared in discharged state : Ni(OH)2 and Cd(OH)2 as
Additives: graphite ,”-” mass – Fe+ Ni (→ Cd crystallization)
Formation of plates : several charge-discharge cycles
Assembly and hermetic closure
Separators – ionic conductivity and oxygen diffusion (thickness ca0.2 mm)
For O2 recombination higher capacity of „-” mass (Cd) – fully charged Ni mass – O2evolution – diffusion – Cd oxidised to CdO, no possiblity of H2 formation
Compresed powder
NiSO4→Ni(OH)2
CdSO4 →Cd(OH)2
Encapsulated in steel/Ni pocket
Sintered plate
Porous Ni plate
Impregnated with Ni , Cd salts
Transformed to hydroxides „in situ”
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47. WUT - MESC - Galvanic Cells II
Nickel/Metal Hydride
Anode : NiO(OH) + 2 H2O + 2e → Ni(OH) OH-
Cathode : H2 + 2 (OH-) → 2 H2O + 2e
Hydrogen stored as hydride in metallic phase,
Capacity of metal hydride electrode c. 0.4 Ah/g -- comparable with Cd and Ni sintered plates Ah/g
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48. Scheme for reaction mechanism at Me electrode
Galvanic Cells II
Scheme for reaction mechanism at Me electrode
overcharge
charge
discharge
H2O O2
H2O
OH-
OH-
H2O
Hads
Hads
Hads H2
Me-H
Reversibility of electrode reaction, catalytic for H adsorption
and H-O2 recombination
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49. Hydrogen absorbing alloys
Galvanic Cells II
Hydrogen absorbing alloys
A – metal forming stable hydrides
B – weak hydrides, catalyst, resistance to corrosion, control Hads pressure
Class (basis)
Components
Storage Ah/kg
Remarks
AB5
(LaNi5)
A: Mischmetall, La, Ce, Ti
B: Ni, Co, Mn, Al
≈ 300
Mostly used
AB2
(TiNi2)
A: Zr, Ti
B: Ni, Fe, Cr, V
≈ 400
„Ovonic” alloys
Nickel - catalyst for H2 dissociation,, regulator for Zr, Ti, V hydride formation,
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50. Some details on production of alloys
Galvanic Cells II
Some details on production of alloys
Ni mass – traditional, new technologies for MeH electrode powder
Ovonic alloy – example : main components : Zr-Ti-V-Ni + Cr, Mn, Co, Fe...
Preparative technics: electric arc or inductive oven, Ar atmosphere
Production of powder : hydrogenation of cast alloy (volume expansion = crushing of a piece), followed by mechanical pulverisation
Sintered plates : MeH powder + Ni, Ni(CO)5 + resin →
pressing and sintering under vacuum
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51. Anodic reaction : Li = Li+ + 1e
Galvanic Cells II
Lithium cells
Atomic mass
LITHIUM
ZINC
Standard potential (V)
-3.05
-0.76
Melting point (oC)
181
419
Density (kg/m3)
534
7100
Elchem. equivalent (Ah/g)
3.86
0.82
Anodic reaction : Li = Li+ + 1e
Reactivity of metallic lithium: reduces most substances (even Teflon®)
Stable passivation – key to electrode stability
What shall we do with excess lithium?
Transport and consume in cathode reaction
Why not leave lithium cations in the electrolyte?
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52. Intercalation : Li – Li+ in matrix
Galvanic Cells II
Anode
Metallic Li (foil)
Intercalation : Li – Li+ in matrix
Stable passivation layer on discharge
Charge : mossy, dendritic deposit – corrosion of fresh Li
internal shortcutting
Main application – primary cells
Rechargeable –
attempts with polymer electrolytes
Capacity: 3.86Ah/g, in accu < 1 Ah/g
Carbon materials : coke, graphite etc.
6 – 12 C atoms take 1 lithium atom into the structure
First cycle – formation of SEI
(Solis Electrolyte Interface)
portion of Li used for reaction with electrolyte
Some transition metal compounds
Capacity: Ah/g
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53. WUT - MESC - Galvanic Cells II
Irreversible loss of capacity on first cycle, electrode : artificial graphite
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54. WUT - MESC - Galvanic Cells II

55. WUT - MESC - Galvanic Cells II
Cathodes
Redox potentials in 0 – 1 V range OCV of Li cells from 3 to 4 V
Solid: MexOy
Reduction of Me ion to lower oxidation state, like MnIVO2 – MnIIIO2
Topotactic reaction
Insertion of Li+ into host structure
Some other: V2O5, (CF)n, TiS2
Capacities: 0.31(MnO2), 0.86(CF) Ah/g
Soluble
SO2 + 2e → S2O42-
( in solution, + Lisalt ex. LiAlCl4)
Thionyl chloride:
SOCl2 + 4e → S + SO2
Sulfuryl chloride:
SO2Cl2 + 2e → SO2
(solvents for Li salt)
Capacities : ≈ 0.4 Ah/g
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56. WUT - MESC - Galvanic Cells II

57. WUT - MESC - Galvanic Cells II
Carbon layers in regular graphite
Layered structure of LiCoO2
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58. Electrolytes Conductivity, Li+ transference number
Galvanic Cells II
Electrolytes
Conductivity, Li+ transference number
Electrochemical and thermal stability
Liquid organic
Aprotic
Protective passivation layer on Li
Li salts solute and dissociate
Appropiate physical features:
stable non-toxic, nonflammable
Conductivities ≈ 1e-3 S/cm
Polymer
Li conduction via
coordination sites on polymer chains
(ex. Poly(ethylenoxide)
Solid foils, processable
More stable against Li
Conductivities : 1e-7 –1e-4 S/cm
Gel
2 in 1 : polymer matrix immobilizing liquid electrolyte
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59. WUT - MESC - Galvanic Cells II
Solution
Ionic conductivity (20oC) S/cm
1M H2SO4
10-1
Nafion® foil (H+)
10-2
1M LiBF4 in acetonitrile
10-3
PEO-LiClO4 complex
10-6
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60. WUT - MESC - Galvanic Cells II

61. WUT - MESC - Galvanic Cells II

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63. WUT - MESC - Galvanic Cells II
Step-wise intercalation of Li into graphite, observed as voltage plateaux
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64. Parameters and definitions
Galvanic Cells II
Parameters and definitions
EMF or OCV
nominal voltage (accepted as typical for a certain battery)
End (cut-off) voltage
Theoretical capacity : comes from amount of active materials
Rated capacity
Energy density (Watthour/l) and specyfic energy (Watthour/kg) : theoretical E = Q × EMF, practical E = Q×ΔU
Power density
Shelf life
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65. General discharge profile - elements
Galvanic Cells II
General discharge profile - elements
Discharge of a galvanic cell
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66. C - rate Charge / discharge current of a battery, given as
Galvanic Cells II
C - rate
Charge / discharge current of a battery, given as
I (amper) = Cn (amperhours) . M (multiply or fraction of C)
!!! Traditional convention, but units are uncorrect!!!
However, most producers and studies use this measure !!!
Ex. For a 250 mAh rated battery (declaration of producer) :
1C – rate = mA
0.1C –rate = mA and so on
We can compare batteries at equal C-rates or study discharge for a given battery at different C-rates
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67. WUT - MESC - Galvanic Cells II
Discharge profiles
Flat – minimal change in reactants and products
Step-wise – change in reaction mechanism and potential
Sloping - composition, internal R ... Change continouosly
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68. WUT - MESC - Galvanic Cells II

69. Continuous and intermittent discharge
Galvanic Cells II
Continuous and intermittent discharge
Possibilty for partial recovery of voltage during pause
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70. WUT - MESC - Galvanic Cells II
Discharge
Discharge mode – constant current / resistance / power
(time to reach cut-off U may differ)
Electrode design = f (type of service)
Max. quantity of active material = max. energy supply
Max. electrode surface = high discharge rate (current, power)
Possibility of partial restoration of voltage – stand-by intervals
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71. WUT - MESC - Galvanic Cells II