Introduction to Batteries

Introduction to Batteries

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Description: An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy (= current). Primary batteries: cannot be recharged. Secondary batteries: rechargeable batteries that involve reversible reactions (backward and forward).

Various materials are used for the positive and negative electrodes and the electrolyte.

 
Author: N. Murer  | Visits: 371 | Page Views: 594
Domain:  Green Tech Category: Battery & Fuel Cell 
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Contents:
An introduction to Batteries
N. Murer

Outline

1. Definition and principles
2. Technology
1. Characteristics

Outline

1. Definition and principles
2. Technology
1. Characteristics

Definition
An electrical battery is one or more electrochemical
cells that convert stored chemical energy into electrical
energy (= current).
Primary batteries : cannot be recharged.

Secondary batteries : rechargeable batteries that involve
reversible reactions (backward and forward)

Example of a Li-ion battery

How it works

1. Initial state (charged) : Ecell = EOC

+

M
M
M
M

Electrolyte
Ecell = Cell voltage = potential difference between the
positive electrode and the negative electrode.

Example of a Li-ion battery

How it works

2. Discharge : Ecell < EOC (charged) (Spontaneous reactions)
e-

+

M

M+

M
M

Electrolyte
Cathode/Reduction
(Insertion)

Anode/Oxidation
(Desinsertion)

Example of a Li-ion battery

How it works

3. Charge : Ecell > EOC (discharged) (Forced reactions)

e-

+

M
M

M

M+

Electrolyte
Anode/Oxidation
(Desinsertion)

Cathode/Reduction
(Re-Insertion)

Outline

1. Definition and principles
2. Technology
3. Characteristics

Technology
Various materials are used for the positive and negative
electrodes and the electrolyte
• Lead acid batteries (PbO2-Pb)
• Alkaline batteries (Ni-MH and Ni-Cd)

• Lithium-ion batteries (LiCoO2-, LiMn2O4-,LiFePO4-C6)
• Lithium Metal Polymer, Lithium-Air, …

Technology
Name
Lead Acid

Initial Charged State

+

-

+

-

Electrolyte

PbO2

Pb

PbSO4

PbSO4

H2SO4

Nickel Cadmium NiO(OH)
Nickel-Metal
NiO(OH)
Hydride
Li1-xCoO2
Li-ion
Li1-xFePO4
Li-Metal

After discharge

Li

Cd

Main
application
Automobile
starter, PV

Ni(OH)2 Cd(OH)2

MH

Ni(OH)2

M

LixC6

LiCoO2

C6

LixC6

LiFePO4

C6

LixV3O8

Li

V2O5

KOH
LiPF6 in
organic
solvent
Polymer

Electronics

Electronics,
transportation

Technology
Lithium batteries represent now the largest share of the market

Source : www.umicore.com

Outline

1. Definition and principles
2. Technology
3. Characteristics

Characteristics
Nominal Potential
constant potential value of the battery during the discharge in V
One cell voltage : Pb = 2 V, Ni-MH = 1.2 V, Li-ion = 3.6 V

at constant current

Deep discharge or deep
charge can lead to
potentially dangerous
unwanted nonreversible reactions.
Ex : H2 production for
Ni-Cd battery.

Characteristics
Capacity
electrical charge that can be stored in a reversible way in A.h
1 mol of electrons (6.1023 e-) = 1 Faraday = 96 500 C = 26.81 A.h
Energy = Voltage x Capacity in W.h or V.A.h
Power = Voltage x Current in W
Discharge rate (or charge): current discharge value (galvanostatic
mode) expressed as a function of the theoretical capacity.
C/n cycling rate: C (theoretical capacity)/n (number of hours).
Capacity, Energy and Power are usually expressed by unit of mass or
volume for comparison purpose.

Characteristics
Stack : several batteries in series or parallel
Series
1
I

+

E1

2

-

+

E2

3

-

+

4
-

E3

+

E4

-

-

-

-

-

2

3

4

Parallel

1

Estack = E1 + E2 + E3 + E4
Istack = I1 = I2 = I3 = I4 (same current in all four elements)

+

+

Estack = E1 = E2 = E3 = E4
Istack = I1+ I2 + I3 + I4

+

+

Estack

Load

Istack

Comparison
Battery type

Leadacid

Ni-MH

Ni-Cd

Li-ion

Rechargeable
alkaline

Nominal
Potential per
cell (V)

2

1.2

1.2

3.6

1.5

Cheap

Higher capacity than
NiCd
Less sensitive than
NiCd to overcharging,
memory effect and
deep unloading

Rather cheap
High currents
allowed

Highest capacity

High capacity (ca.
2 times higher
than Ni-MH)

Heavy

More expensive than
NiCd

Toxic
Memory effect
Degrades when
overcharged
Unusable after
too deep
unloading

Expensive
Capacity
decreases, even
when not used
Explosion risk at
overheating,
over-voltage or
polarity reversal

Capacity reduced
after each cycle
(e.g. 50% after 15
cycles)

Advantages

Drawbacks

Thank you for your
attention