ENERGY AND POWER STORAGES - cours, examenscours-examens.org/.../10BATTERIES_ · Oxford Science...
Transcript of ENERGY AND POWER STORAGES - cours, examenscours-examens.org/.../10BATTERIES_ · Oxford Science...
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ENERGY AND POWER STORAGES
Pierre DuysinxUniversity of Liège
Academic Year 2010-2011
ReferencesR. Bosch. « Automotive Handbook ». 5th edition. 2002. Society ofAutomotive Engineers (SAE)C.C. Chan and K.T. Chau. « Modern Electric Vehicle Technology »Oxford Science Technology. 2001.C.M. Jefferson & R.H. Barnard. Hybrid Vehicle Propulsion. WIT Press, 2002.J. Miller. Propulsion Systems for Hybrid Vehicles. IEE Power & Energyseries. IEE 2004.M. Ehsani, Y. Gao, S. Gay & A. Emadi. Modern Electric, Hybrid Electric, and Fuel Cell Vehicles. Fundamentals, Theory, and Design. CRC Press, 2005.L. Guzella & A. Sciarretta. Vehicle Propulsion Systems. Introduction to modelling and optimization. 2nd ed. Springer Verlag. 2007.
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OutlineIntroduction
Energy sources characteristics
Electrochemical batteries
Ultra capacitors
Flywheels
Comparison
Characteristics of Energy Sources
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Energy source characteristicsEnergy and coulometric capacityCut-off voltage and usable capacityDischarging/charging currentState-of-chargeEnergy densityPower densityCycle lifeEnergy efficiency and coulometric efficiencyCost
Energy and coulometric capacities
Mission of EV energy sources: supply electrical energy for propulsionEnergy capacity EC [J] or [Wh]
v(t) and i(t) instantaneous voltage and currentCoulometric capacity [Ah]
For EV, energy capacity is more important and useful than coulometric capacityThe coulometric capacity (or capacity) is widely employed to describe the capacity of batteries
0
( ) ( )t
EC v i dτ τ τ= ∫
0
( ) ( )t
CC Q t i dτ τ= = ∫
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Cut-off voltage and usable capacity
Energy capacity does not represent well the energy content of electrochemical sourcesBatteries can not be discharged down to zero voltage unless being permanently damagedCut-off voltage: knee of discharging curve at which battery is considered as fully discharged, so called 100% depth of discharge (DoD)Usable energy capacity and usable coulometric capacity before cut-off
Cut-off voltage and usable capacity
Discharge curves for Powersonic VRLA batteries
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Discharging/charging current
For batteries, energy capacity and coulometric capacity vary with their discharging current, operating temperature, and ageing
The battery capacity is determined with constant current discharge-charge testsIn a typical constant current test, the battery is initially fully charged and the voltage equals the open-circuit voltage V0c.A constant discharge current is applied. After a certain time tf, called the discharge time, the voltage drops to the cut-off voltage and the battery is empty.
Discharging/charging current
Discharge curves for LiPo Ultimate PX-01 batteries
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Discharging/charging current
The discharge time is function of the discharge current. The phenomenon is often described using the Peukert equation :
‘n’ is the Peukert exponent which varies between 1 and 1.5 (e.g. in VRLA n~1.35)
This equation also express the dependency of the battery capacity on the discharge current. If the capacity is Q2* for a current I2*, the capacity for a discharge current I2 is
2n
ft Cste I −=
1
0 2* *0 2
nQ IQ I
−⎛ ⎞
= ⎜ ⎟⎝ ⎠
Discharging/charging current
Other more sophisticated models of current dependency can be found in literature:
Neural Network-based modelsModified Peukert equation for low currents (Kc a constant)
( )( )0* 1*0 2 21 1 /
cn
c
Q KQ K I I
−=+ −
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Discharging/charging current
Instead of discharge current, a non dimensionsional value called C-rate is used
The C-rate current is defined as the current I0 that discharges the battery in one hour and which has the same value as the battery capacity Q0=CC.The C rate is often written as C/k where k is the number of hours need to discharge the battery with a C-rated current, i.e. c=1/k current, a current k times lower than the rated current I0.
Example: C/5 rate for a 5 Ah battery means that kCn = 1/5*5=1A
CC (and also the EC) decreases with the increasing C rate
nI k C=
State-of-charge
The residual coulometric capacity is termed as the State-of-Charge (SOC)SOC defined as the percentage ratio of residual coulometriccapacity to usable coulometric capacity
SOC is affected by discharging current, operating temperature, and ageing
0
( )( )( )
Q tq t SOCQ t
= =
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State-of-charge and energy capacity
Variation of the state of charge in a time interval dt with discharging current i approximated using the discharge current by charge balance
where Q(i) is the amp-hour capacity of the battery at current rate iThus state of charge SOC
0 ( )dSOC i dt
dt Q i=
00 ( )
i dtSOC SOCQ i
= − ∫
State-of-charge and energy capacityIn case of charge, the state of charge must take into account the fact that a fraction of current I2 is not transformed into charge due to irreversible parasitic reactions.It is often modeled using the charging or coulometric efficiency
The coulometric counting method is simple but requires frequent recalibration points.
The energy capacity can also be related to the current
2 ( )cQ I tη= −
( , ) ( )EC V i SOC i t dt= ∫
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State of charge and energy capacity
Energy density
Energy densities = usable energy density per unit mass or volume
Gravimetric energy density or specific energy: [Wh/kg]Volumetric energy density [Wh/l]
Gravimetric energy densityThe more important because of weight penalty on consumption and driving rangeKey parameter to assess suitability to EV
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Power density
Power density = deliverable rate of energy per unit of mass or volume
Specific power [W/kg]
Power density [W/l]Specific power is important for EV applications because of acceleration and hill climbing capabilityFor batteries, specific power vary with the level of DoDSpecific power is quoted with the percentage of DoD
Cycle life
Cycle life: number of deep-discharge cycles before failure Key parameter to describe the life of EV sources based on the principle of EV storageCycle life is greatly affected by the DoD and its is quoted with the percentage of DoD.
Example: 400 cycles at 100% DoD or 1000 cycles at 50% DoD
For energy generation rather energy storage, the life is definedby the service life in hours or kilohours
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Energy efficiency
Energy efficiency is defined as the output energy over the input energyFor energy storage source, the energy efficiency is simply the ratio of the output electrical energy during discharging over the input electrical energy during charging.
Typically for batteries in the range of 60-90%
Charge efficiency defined as the ratio of discharged coulometriccharge Ah to the charged coulometric capacity Ah.
Typically for batteries in the range of 65-90%
For EV, energy efficiency is more important than charge efficiency
Energy efficiency
The energy or power losses of batteries during charging discharging appear in the form of voltage losses. Thus the efficiency of the battery during charging / discharging can be defined any operating point as the ratio of the cell voltage V to the thermodynamic voltage V0.
During discharging:
During charging
0
VV
η =
0VV
η =
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Energy efficiency
The terminal voltage is a function of the current, the energy stored or the SOC. The terminal voltage is lower in discharging and higher in charging than the electrical potential produced by chemical reactions.The battery has a high discharging efficiency with a high SOC and a high charging with a low SOC. Thus net cycle efficiency is maximum around the middle range of SOC
Cost
Cost includes: initial (manufacturing) cost + operational (maintenance) cost
Manufacturing cost is the most important one
Cost is a sensitive parameter for EV sources because it is a penalty with respect to other energy sourcesCost in €/kWh or $/kWhPresently cost in the range of 120 to 1200 €/kWh
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Ideal batteries for EV
High specific energy great range and low energy consumptionHigh specific power high performanceLong life to enable comparable vehicle lifeHigh efficiency and cost effectiveness to achieve economical operation and maintenance free
Electrochemical batteries
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Batteries: principles
Basic element of each battery is the electrochemical cellCells are connected in series or in parallel to form a batteryBasic principle of batteries
Positive and negative electrodes are immersed in an electrolyte
Batteries: principles
During discharge, negative electrodes performs oxidation reaction and drives electrons to the positive electrode via external circuit. Positive electrode performs reduction reaction that absorbs electronsDuring charge, the process is reversed and electrons are injected in negative electrode to perform reduction on negative electrode and oxidation in positive electrodes
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Lead-acid batteries
Invented in 1860, lead acid batteries are successful product formore than one centuryLow price and mature technology even if new designs are still continued to be developed to meet higher performance criteria.
Battery principle:Negative electrode: metallic leadPositive electrode: lead dioxideElectrolyte: Sulfuric acidElectrochemical reaction:
2 2 4 4 22 2 2Pb PbO H SO PbSO H O+ + ↔ +
Lead-Acid batteries: electrochemical reactions
Discharging:Anode (negative electrode): porous lead
Cathode (positive electrode): porous lead oxide
24 4 2Pb SO PbSO e− −+ → +
22 4 4 24 2 2PbO H SO e PbSO H O+ − −+ + + → +
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Lead-Acid batteries: electrochemical reactions
ChargingAnode (negative electrode)
Cathode (positive electrode)
Overall
24 42PbSO e Pb SO− −+ → +
24 2 2 42 4 2PbSO H O PbO H SO e+ − −+ → + + +
2 2 4 4 22 2 2Pb PbO H SO PbSO H O+ + +
Lead-Acid batteries: Thermodynamic voltage
Thermodynamic voltage of the battery cell is related to energy released and the number of electrons transferred in the reactionThe energy released is given by the change of Gibbs free energy ∆G usually expressed per mole quantity
In which Gi and Gj are the free energy of products i and reactant species j.
Products Reactantsi jG G G∆ = −∑ ∑
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Lead-Acid batteries: Thermodynamic voltage
In reversible conditions, all the ∆G is converted in electric energy
F=96495 F, the Faraday constant, the number of coulombs per mole and Vrev the reversible voltage
At standard conditions T=25°C, p=1 atm
revG n F V∆ = −
00
rev
GVn F∆
= −
Lead-Acid batteries: Thermodynamic voltage
The change of free energy and thus cell voltage are function of the activities of the solution species
The Nernst relationship gives the dependence of ∆G on reactants activities
R universal constant R=8,314 J/molK and T absolute temperature
0 (activities of products)ln
(activities of reactants)rev rev
RTV Vn F
⎡ ⎤= − ⎢ ⎥
⎢ ⎥⎣ ⎦
∏∏
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Lead-Acid batteries: Specific energy
Specific energy is defined as the energy capacity per unity battery weight (Wh/kg)The theoretical specific energy is the maximum energy that can be generated by unit total mass of reactants
For lead-acid batteries: Vr=2,03 and ΣMi=642g
Actual specific energy (with container, etc.):
(Wh/kg)3,6 3,6
th rspec
i i
nFVGEM M
∆= − =
∑ ∑
170 Wh/kgthspecE =
45 Wh/kgthrealE =
Lead-Acid batteries: Specific energy
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Lead-Acid batteries: Specific energy
Best specific energy is obtained with the lightest elements: H, Li, Na… for negative electrode reactantsHalogens, oxygen, S… for positive reactants
Best electrode design for effective utilization of the containedactive materialsElectrolytes of high conductivity compatible with the materials & compatible with materials in both electrolytes
Aqueous electrolytes at room temperature
Choice of metallic reactant:Aqueous electrolytes prohibits alkali which react with water
other metals with a reasonable electro negativity: Zn, Al, Fe and which are rather abundant not to be too expensive
Lead-Acid batteries: Specific power
Specific power is defined as the maximum power per unit battery weight that can be deliveredSpecific power is important for battery weight especially in high-power demand applications such as HEVThe specific power depends mostly depends on the battery internal resistance
Rint represent the voltage drop which is associated with the battery current
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int4( )peakc
VPR R
=+
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Lead-Acid batteries: Specific power
The Rint represents the voltage drop which is associated with the battery currentRint depends on two components:
Reaction activity
Electrolyte concentration
IL = limit current
logAV a n I∆ = +
ln 1CL
RT IVnF I
⎛ ⎞∆ = − −⎜ ⎟
⎝ ⎠
Lead-Acid batteries: Specific power
The voltage drop Increases with increasing in discharge currentDecreases with the stored energy
Specific energy is high in advanced batteries, but still need to be improvedSpecific energy of 300 W/kg is still an optimistic targetSome new developments with SAFT
HEV batteries with 85 Wh/kg and 1350 W/kgEV batteries with 150 Wh/kg and 420 W/Kg
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Energy sources categoriesRechargeable electrochemical batteries
Lead Acid (Valve Regulated Lead Acid=VRLA)Nickel based: Ni-Iron, Ni-Cd, Ni-Zn, Ni-MHMetal/air: Zn/air, Al/air, Fe/airMolten salt: Sodium-β: Na/S, Na/NiCl2, FeS2
Ambient temperature lithium: Li-polymer, Li-ions
SupercapacitorsUltrahigh speed flywheelsFuel cells
Lead-acid batteries
Voltages:Nominal cell voltage: 2,03 V (highest one of all aqueous electrolytes batteries)Cut-off voltage: 1,75 VVoltage depends on sulfuric acid concentration, so that voltage varies with SOCGassing voltage (decomposition electrolysis of water at 2.4 V)
Energy/ power densitySpecific energy density: 35 Wh/kgEnergy density 70 Wh/lSpecific power density: 200 W/kg
Energy efficiency: >80%Self discharge rate: <1% per 48 hoursCycle life: 500-1000 cyclesCost: 120-150 $/kWh
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Lead-acid batteriesVoltage depends on sulfuric acid concentration, so that voltage varies with SOC
Nickel-based batteries
Family of different kinds of electrochemical batteries using nickel oxyhydroxide (-OOH)
Ni-Fe invented by EdisonNi-Cd is known from 1930iesNi-MH is used in modern HEV vehicles (1990ies)Ni-Zn is still under development
Use Nickel oxy hydroxide as the active material for the positiveelectrode
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Ni-Cd batteries
Developed in the 1930ies, it is used in heavy industry for 80 yearsBattery principle:
Negative electrode: metallic cadmium CdPositive electrode: nickel oxyhydroxideNiOOHElectrolyte: KOHElectrochemical reaction:
2 2 22 2 2 ( ) 2 ( )Cd NiOOH H O Cd OH Ni OH+ + +
Ni-Cd batteries
Voltages:Nominal cell voltage: 1,2 V Cut-off voltage: 1,00 V
Energy/ power densitySpecific energy density: 56 Wh/kgEnergy density 110 Wh/lSpecific power density: 80-150 W/kg
Energy efficiency: 75%Self discharge rate: 1% per 48 hoursCycle life: ~800 cyclesCost: 250-350 $/kWh
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Ni-Cd batteries
Discharge curves of Ni-Cd
Ni-Cd batteries
Advantages:Medium specific energyMedium cycle lifeFlat curveGood performances in low temperaturesEasiness of charge
DisadvantagesCd environmentally not friendly and carcinogenicityMemory effect sensitivitySelf discharge
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Ni-MH batteries
Developed and marketed in the 1990ies, it is a rising star used in many modern HEVSimilar principle to Ni-Cd but it uses hydrogen absorbed in a metal hydride for the active material in negative electrode
Battery principle:Negative electrode: hydrogen absorbed in metal hydride: MHPositive electrode: nickel oxyhydroxide Ni(OH)2
Electrolyte: KOHElectrochemical reaction:
2( )MH NiOOH M Ni OH+ +
Ni-MH batteries
Key compound is MH, the metal alloy that is able to absorb / deabsorb hydrogen with a high efficiency with a high number of cycles.
AB5 rare-earth such us Lanthanum with NiAB2: Ti or Zr alloys with Ni
Voltages:Nominal cell voltage: 1,2 V
Energy/ power densitySpecific energy density: 70 - 95 Wh/kgEnergy density 150 Wh/lSpecific power density: 200 – 300 W/kg
Energy efficiency: 75% (70 90) Cycle life: 750-1200 cyclesSelf discharge: 6% per 48 hours Cost: 200-350$/kWh
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Ni-MH batteries
Discharge curves of Ni-MH
Ni-MH batteries
Advantages:High specific energyHigh specific powerFlat discharge curveFast chargeLow sensitivity to memory effect
DisadvantagesDo not withstand overchargingDetection of end of chargeLittle better life cycle than Ni-Cd
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Lithium-based batteries
Lithium is the lightest metallic element which allows for interesting electrochemical properties:
High thermodynamic voltageHigh energy and power density
Two major technologies of electrochemical batteries using lithium
Lithium-polymerLithium-ions
Li-ions batteries
First developed in the 1990ies, it has experienced an unprecedented raise and it is now considered as one of the most promising rechargeable battery of the futureAlthough still at development stage, it is already gained acceptance in HEV and EV.
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Li-ions battery principle
Negative electrode: lithiated carbon intercallated LixCPositive electrode: lithiated transition metal intercalation oxide Li1-xMyOz (ex LiCoO2)Electrolyte: liquid organic solution or a solid polymer
Electrochemical reaction:
for example
1x x y z y zLi C Li M O C LiM O−+ ↔ +
( ) 6 [1 ( )] 2 6 (1 ) 2y x y x y yLi C Li CoO Li C Li CoO+ − − −+ +
Li-ions batteries
Discharge: Li ions are released from negative electrodes, migrate via the electrolyte and are taken up by the positive electrode.
Possible positive electrode materials are Li1-xCoO2, Li1-xNiO2, and Li1-xMn2O4 that are stable in air, high voltage, reversibility for lithium intercalation reaction.
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Li-ions batteries
For LixC / Li1-xNiO2 battery (C/LiNiO2 or nickel based li-ion battery)Voltages:
Nominal cell voltage: 4 V
Energy/ power densitySpecific energy density: 80-130 Wh/kgEnergy density 200 Wh/lSpecific power density: 200-300 W/kg
Energy efficiency: 95% Cycle life: > 1000 cyclesSelf discharge rate: 0,7% per 48 hoursCost: 200 $/kWhHigher performance for LixC / Li1-xCoO2 but also higher cost due to Cobalt
Li-ions batteries
Advantages:High specific energy and high specific powerNo memory effectLow self dischargeNo major pollutants
DisadvantagesDo not withstand overcharging, May present dangerous behavior when misusageShort circuit due to metallic Lithium dendritic growth
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Li-polymer batteries
Li-ions battery principle:Negative electrode: lithium metalPositive electrode: transition metal intercalation oxide MyOz
Electrolyte: thin solid polymer electrolyte SPEElectrochemical reaction:
The layered structure of transition metal oxide MyOz allows lithium ions to be inserted and removed for charge and dischargeDischarge: Li ions that are formed at the negative electrodes migrate through the SPE and are inserted into the crystal structure at the positive electrode.
y z x y zx Li M O Li M O+ ↔
Li-polymer batteries
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Li-ions batteries
Thin solid polymer electrolyte: improved safety and flexibilityCapability of fabrication in various shapes and sizes and safe designsPossible positive electrode material are Vanadium oxides: V6O13
Battery Li/SPE/V6O13
Voltages:Nominal cell voltage: 3 V
Specific energy density: 155 Wh/kg Specific power density: 315 W/kg Energy efficiency: 85% Self discharge: 0,5% per month
Li-polymer batteries
Advantages:High specific energy and high specific powerNo memory effectLow self dischargeNo major pollutantsVarious shapes and sizes
DisadvantagesLower power and energy density than Li-ionsMore expensive than Li-ionsSpecific energy density: 155 Wh/kgCharging must be carefully conducted to avoid inflammation
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Supercapacitors
Capacitors and SupercapacitorsCapacitors = simple devices capable of storing electrical energy
Capacitors = electrostatic capacitorsEssential component in electronicsCapacitance ~ pF to µF
Electrolytic Double Layer Capacitors (EDLC) or ultra / supercapacitors
Capacitance ~ F – kFWorking principle: double electrolytic layer by Helmotz
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Capacitors and SupercapacitorsOne must distinguish the electrostatic capacitors from supercapacitors that use the Helmotz double layer principle
Supercapacitors: principle
Supercapacitors are based on the double layer technologyWhen carbon electrodes are immersed in aqueous electrolyte, the ions will accumulate at the porous interface of the electrode. The ions and the current carriers make a capacitors with a gap of a few nanometers
Separator
Electrolyte Electrode in porous carbon
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Supercapacitors: principle
EQUILIBRIUM CONDITION OF MATERIALS
WITH DIFFERENT ELECTRICCONDUCTIVITY
EQUILIBRIUM CONDITION OF A SYSTEMCOMPRISING OF TWO DIFFERENT MATERIALS
DOUBLEELECTRIC
LAYER
Supercapacitors: principle
Uncharged state Charging
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Supercapacitors: principle
Charged stateDischarging
SupercapacitorsAn electric double layer occurs at the boundary of the electrodeand the electrolyte.The electric double layer works as an insulator when voltage stays below the decomposition voltage of water.Charge carriers are accumulated at the electrodes and one measures a capacitance
Because of the double layer, one has two capacitances in series
1 ²2
E CV=
1 2
1 1 1C C C= +
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Electric double layer capacitor principles
Capacitance
Distance d of the layer ~1 nmC ~ 0,1 F/m²
Increase S: surface area of the electrode / electrolyte specific surface
For activated carbon, S depends on the micropores amount (<2nm)S~1000 m²/g 1000 F/g
SupercapacitorsCapacitors with double layers are limited to 0,9 volts per cell for aqueous electrolyte and about 2.3 to 2.3 V with non aqueous electrolyte Because the double layer is very thin (couple of nanometers), capacity per area is high: 2,5 to 5 µF/cm²With material with a high active area (1000 m²/g) like activated carbon one gets a capacity about 50 F/g
1000 m²/g x 5µ F/cm² x 10000 cm²/m² = 50 F/g
Assuming the same amount of electrolyte as carbon, one gets a capacity of 25 F/gHowever, the energy density is rather low: <10 Wh/kg (remind VRLA ~ 40 Wh/kg)
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Supercapacitors: equivalent electrical scheme
ССDELDEL ССDELDEL
RRleckleck RRleckleck
RRIsolIsol
RRelel
ССDEL DEL –– CapacityCapacity of Double of Double ElectricalElectrical LayerLayer
RRleckleck –– Leakage ResistanceLeakage Resistance
RRelel –– Electrolyte ResistanceElectrolyte Resistance
RRisolisol –– Isolation ResistanceIsolation Resistance
Supercapacitor Technologies
separator layer
electrode layermantle
electrode layer
mantle
separator layer
wound supercapacitor single cell (schematic)
stacked cells
Traditional - wounded cells
up to 300 -
1000 V
BALANCING SYSTEM
No balancing systemrequired
D. Sojref, European Meeting on Supercapacitors, Berlin, D. Sojref, European Meeting on Supercapacitors, Berlin, DecemberDecember 20052005
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Comparison of SuperCaps technologies
SuperCaps: manufacturing technology
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SuperCaps: manufacturing technology
Working environment:- Modular assembly and connection- Thermal exchange,- Electrical insulation- Failure mode
Supercapacitors: stacked constructions
Structure of Newcond GmbH supercaps
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SuperCaps Manufacturers
SuperCaps Manufacturers
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Super capacitors and batteries
Supercapacitors are distinguished from other class of devices for storing electrical energy such batteries
Absord / release energy much faster: 100-1000 times: (Power density ~ 10 kW/kg)Lower energy density ( Energy density < 10 kWh/kg)Higher charge / discharge current : 1000 ALonger life time: > 100.000 charge dischargeBetter recycling performances
Super capacitors and batteries
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C.J. Farahmandi, C.J. Farahmandi, AdvancedAdvanced CapacitorCapacitor World World SummitSummit, San , San Diego,CADiego,CA, July 2008, July 2008
* * 10-3 to 30 s
> 500.000> 500.0001.000Life (cycles)
10-3 to 10-6 s0,3 to 30 s*1 to 5 hrsCharge Time
< 100.000< 7000< 1000Specific Power (W/kg)
0,11 to 1010 to 100Energy Density (Wh/kg)
CapacitorSupercapacitorBattery
Supercapacitor
Envisioned applicationsWhenever a high power is requested for a short time (electric and hybrid vehicles, tramways, diesel engine starting, cranes, wind turbines, computers, lasers,…)Capacitors are generally combined with another energy source to increase power, to improve economic efficiency and to preserve ecological demandCapacitors can be used as buffer for later charging of a battery
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Envisioned applications
Major component to low carbon economy:Enhancing energy efficiency
Mobile applications: Hybrid propulsion systemsAutomobile, railway
Stationary applications:Clean Electrical Power Smart grids including renewable energy sources
New applicationsMechatronic applications: All electric systemsMedical applicationsDefense applicationsSafety applications:
Emergency systems
Transport applicationsStop & Start of engines 2020
Fast start devices of large Diesel enginesStart & stop of automobile engines
Braking Energy recovery 2020-2030KERS systems
Peak power source for acceleration 2020-2030Mild hybrid
Sub-station stabilization 2020-2030Reduction of peak power stress
Short range autonomy of railway vehicles 2020-2030Tramway and trolley in historical cities
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Mechatronic applications
Criteria for power application in transport
Intrinsic performances :high cell voltage, energy density, max temperature 60°C (…80°C…)new generation aqueous and stacked supercapacitors have to be push for high voltage and mecatronicApplications
lowest ration Rs / C (reduced losses)today: 200-300µΩ for 2600F-2,7V - 25°C (DC method) 100-200µΩfor 5000F-2,7Vtomorrow: < 100µΩ for 9000F-2,7V
power cycling reliability on vehicle mission profiles
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Criteria for power application in transport
Assembly performances :lower total serial resistance (reduce contact resistance), stacked technology
simplification of cells balancing
Safety : identified failure modes (gas leakage, …sealing box, neutralisation gas) : opening case due to over pressure, or internal electrical disconnection
Systems interface : high voltage DC bus level … high voltage assembly …chopper link
Maintenance strategy : predictive solution, replacing cell strategy
Super capacitors and batteries
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Supercapacitors: ECON
4,861,020,28175,0036,75364202300,70000,151000700,036/700
2,001,280,36100,0064,00506602300,40000,801000400,064/400
3,131,250,35100,0040,00323802300,40000,501000400,040/400
2,640,630,1876,5618,38293102300,40000,301000350,018/350
1,972,370,6675,0090,00385702300,30002,001000300,090/300
1,501,010,2860,0040,50404902300,37500,901000300,040/300
3,130,830,2375,0019,80242002300,30000,441000300,020/300
1,131,180,3356,3359,15506302300,30001,751000260,060/260
1,392,500,7050,0090,00365502300,20004,501100200,090/200
1,511,700,4756,0062,72373802300,0035160,00400028,060/28
1,371,570,4435,6440,77263002300,0055104,00400028,040/28
0,750,880,2410,8912,74151302300,0045130,00135014,012/14
0,820,930,268,179,3110952300,006095,0067014,09/14
(KW/Kg)(Kj/Kg)(Wh/Kg)(KW)(Kj)(Kg)(mm)(mm)(Ohm)(F)(A)(V)
Specific Power
Specific Energy
Specific Energy
PowerEnergyWeightHighDiameterInt. resist
CapacityCurrentVoltageType
Automotive applicationsComparison of Supercaps with respect to batteries will be demonstrated using the eco efficiency approach
Ecoefficiency: global index which accounts for both:Environmental impacts: CO2 + emissions + noiseUser satisfaction criteria (US): composite index that assesses the ability of the vehicle to meet customer’s expectations about his transport needs: Performance + Daily Cost…
Fair comparison between antagonist constraints is provided by using an optimization approach
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Automotive applicationsFind best designs by solving optimization problem
Min Environment Impact; Performance Indexdesign variables: size of energy storage, ICE engine, electric machines
Subject to:Design constraint on mass, acceleration, cost, etc.
Choice: mild hybrid busHybrid Electric with NiMH batteriesHybrid Electric with Supercap (Maxwell)Hybrid hydraulic bus
Application: bus optimizationModelling & Simulation: ADVISORVanHool A300 Bus
Typical 12 meters bus used by public operators in Belgium
Reference propulsion systemICE Man diesel engine 205 kW (here Detroit Diesel engine from ADVISOR)Number of passengers: 33-110
here 66 passengers
Driving CyclesSORT 2 Bus Drive Cycle by IUTPCommercial speed: 17 kph (urban driving situation)
Figure 5: SORT 2 drive cycle, for easy urban cycle
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Hybrid Electric Vehicles
Hybrid Hydraulic Vehicle
New reversible hydraulicmotor /pump: Low drag, high efficiency, fluid=water
Parker P2 or P3 series
Hydraulic accumulators (HP) / Reservoir (LP): high efficiency (95%)En.: 0,63 Wh/kg Power ~ 90 kW/kg
Hydac
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ECOEFFICIENCY: AN OPTIMIZATION APPROACH
A parametric study is made in BOSS QUATTRO to construct some response surface approximations of US and Ecoscore
The ecoefficiency design optimization problem is solved using a multi objective genetic algorithm (MOGA) available in BOSS-QUATTRO based on response surface method
Parametric models (scaling factors) inADVISORSimulation of performances and fuel consumption & emissions against driving cycles
Optimization: Problem Statement
Mathematical multi objective design problem statement:Minimize:
With respect to
Subject to:
max
max
201005%
20000
500000€150 200
50 100400 800
acc
engine
motor
MB
t sv kphpm kg
CP
PN
≤
≥
≥
≤
≤≤ ≤
≤ ≤
≤ ≤
coscore1 2( ) ( ( ) ; ( ) 1/ )F X f x E f x US= = =
/( , , )engine motor bat scX P P N=
50
0,7
0,72
0,74
0,76
0,78
0,8
0,82
0,84
0,86
1 1,05 1,1 1,15 1,2 1,25 1,3 1,35 1,4
Minimiser l'impact environnemental (SE)
Min
imis
er (1
/SU
)
Bus_NiMH Bus_SPCAPS Bus_Hydr
Numerical Application
Figure 5: SORT 2 drive cycle, for easy urban cycle
1
1,5
2
2,5
3
3,5
4
4,5
5
5,5
6
1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6Min (impact environnemental)
Min
(1/U
S)
Bus_NiMH Bus_SC Bus_HYDR
Numerical Application
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Hybridization of Energy Sources
Hybrid energy storage systems
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Hybrid energy storage systems
Hybrid energy storage systems
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Hybrid energy storage systems
Hybrid energy storage systems
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Flywheels
FlywheelsPrinciple: Storing energy as kinetic energy in high speed rotating disk
Idea developed 25 years ago in Oerlikon Engineering company, Switzerland for a hybrid electric bus
Weight = 1500 kg and rotation speed 3000 rpm
Traditional design is a heavy steel rotor of hundreds of kg spinning at ~1.000 rpm.
Advanced modern flywheels: composite lightweight flywheels (tens of kg) rotating at ~10.000 rpm
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Flywheels
A rotating flywheel stores the energy in the kinematic form
Jf= moment of inertia and ωf= rotation speed
The formula indicates that enhancing the rotation velocity is the key to increasing the energy storage. One can achieve nowadays rotation speed of 60,000 rpmFirst generation flywheel energy storage systems use a large steel flywheel rotating on mechanical bearings.
Newer systems use carbon-fiber composite rotors that have a higher tensile strength than steel and are an order of magnitude lighter.
212f f fE J ω=
Flywheels
Pentadyne flywheel
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FlywheelsA typical system consists of a rotor suspended by bearings inside a vacuum chamber to reduce friction, connected to a combination electric motor/electric generator.
FlywheelsWith this current technology it is difficult to couple directly the flywheel to the propelling system of the car.One would need a continuous variable transmission with a wide gear ratio variation range.The common approach consists in coupling an electric machine to the flywheel directly or via a transmission: One makes a ‘mechanical battery’The electric machine functions as the energy input / output portconverting the mechanical energy into electrical energy and vice-versa
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Flywheels
Principle of flywheels
Comparison of energy storage systems for electric and hybrid vehicles
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Energy and peak power storages
Different types of batteries:Lead-Acid: developed since 1900 with a high industrial maturityNi-Cd : developed from 1930ies, with an industrial maturityNa Ni Cl (Zebra): since 1980ies small seriesNiMH: since 1990ies, industrial productionLi-Ions: still under industrial development
Peak power sources:Double layer super capacitorsHigh speed flywheels
Energy and peak power storages
Performance criteria for selection (decreasing importance):Specific energy (W.h/kg)Specific power (W/kg)Number of charge cyclesLife timeSpecific costCharge discharge efficiencyVoltageVolumeRecycling
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Traction batteries
200200-350250-350120-150Cost [$/kW.h]
1000+1200750-1200800500-1000Life time [cycles]
90-95857075>80%Charge discharge efficiency [%]
200-300148200-30080-150150-400Specific power [W/kg]
80-1307470-9550-6035-50Specific energy [W.h/kg]
Li-IonsZebraNi-MHNi-CdLead acidBatteries
Problem of batteries w.r.t. fuels
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Problem of batteries w.r.t. fuels
8421001420Specific energy at wheel [W.h/kg]
801812Mean conversion efficiency in vehicle [%]
10511.66711.833Specific energy / PCI [W.h/kg]
Li-IonsDieselGasolineFuel
Facteur 200!
Energy density vs power density
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Energy density vs power density
Energy per volume / per weight
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Discharge characteristic time
EP
τ =
Discharge characteristic time
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Efficiency vs life cycles
Investment cost