Chris_Mi_handout

Cell Charging

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Cell Charging

zPositive Electrode Equation

-PbSO4+2H2OÆ PbO2+4H++SO42-+2e

zNegative Electrode Equation

-PbSO4+2eÆPb+ SO42-

zOverall Equation

-2PbSO4+2H2O Æ

Pb+PbO2+2H2SO4

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Battery Parameters

zBattery Capacity

-The amount of free charge generated by the active material at the negative electrode and consumed by the positive electrode

-Capacity is measured in Ah (1Ah=3,600 C or Coulomb, where 1 C is the charge transferred in 1 sec by 1A current in the MKS unit of charge).

-Theoretical capacity of a battery

•QT = xnF

•x = number of moles of limiting reactant associated with complete discharge of battery

•n = number of electrons produced by the negative electrode discharge reaction

•L is the number of molecules or atoms in a mole (known as Avogadro constant) and e0 is the electron charge, F is the Faraday constant and F=Le0

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Battery Parameters

zDischarge Rate

-is the current at which a battery is discharged. The rate is expressed as Q/h rate, where Q is rated battery capacity and h is discharge time in hours

zState Of Charge

-is the present capacity of the battery. It is the amount of capacity that remains after discharge from a top-of-charge condition

t

SoCT (t) = QT − ∫to i(τ)dτ

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Battery Parameters

zState of Discharge

-A measure of the charge that has been drawn from a battery

SoDT (t) = ∆q = ∫ttO i(τ)dτ

zDepth of Discharge

-the percentage of battery capacity (rated capacity) to which a battery is discharged

DoD(t) = QT −SoCT (t) ×100%

QT

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Technical Characteristics

zBattery can be represented with

-Internal voltage Ev

-Series Resistance Ri

Ri

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Technical Characteristics

zPractical Capacity

-Practical capacity QP of battery is always much lower compared to the theoretical capacity QT due to practical limitations. The practical capacity of a battery is given as

tcut

QP = ∫tO i(t)dt

zCapacity Redefined

-The practical capacity of a battery is defined in the industry by a convenient and approximate approach of Ah instead of Coulomb under constant discharge current characteristics

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Technical Characteristics

z Practical Capacity

-Capacity depends on magnitude of discharge current

Vt

zBattery Energy

-The energy of a battery is measured in terms of the capacity and the discharge voltage

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Battery Energy

zBattery Energy

-To calculate the energy, the capacity of the battery must be expressed in coulombs

-In general, the theoretical stored energy is

Battery Power

z Specific Energy

- The theoretical specific energy of a battery is

SET = 9.65 ×107 × nVbat mR

M M M B

zBattery Power

-The instantaneous battery terminal power is

p(t) =Vt i

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Battery Power

A Comparison of Batteries

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* No self-discharge, nut some energy loss by cooling

US Advanced Battery

Consortium (USABC)

zOversees the development of power sources for EVs

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Battery Model

zCan be represented by a capacitor in series with an

internal resistor

zBattery model in Simplorer: a capacitor is series with an internal resistor

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Fuel Cells

zGenerates electricity through electrochemical reaction that combines hydrogen with ambient air

zFunction is similar to a battery, but consumes hydrogen and air instead of producing electricity from stored chemical energy

zDifference from battery: Fuel Cell produces electricity as long as fuel is supplied, while battery requires frequent recharging

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Fuel Cells

zBeing used in space application, but has characteristics desirable to EV applications

zTremendous interest in vehicle and stationary applications

zResearch focus:

-Higher power cells

-Develop FC that can internally reform hydrocarbons

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Fuel Cells

zFuel: hydrogen and oxygen

zConcept: Opposite of electrolysis

zA catalyst speeds the reactions

zAn electrolyte allows the hydrogen to move to cathode

zFlow of electrons from anode to cathode in the external circuit produces electricity

zOxygen or air is passed over cathode

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Fuel Cell Reaction

H+

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Fuel Cell Demo

zhttp://www.plugpower.com/technology/works.cf m?vid=535864&liak=68721538

zhttp://www.plugpower.com/technology/works.cf m

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Demo Fuel Cells

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