Download Presentation on Primary and Secondary Cells

Batteries – Primary and
Secondary Cells
Duracell Bunny Commercial
•
https://www.youtube.com/watch?v=kaF6FxmixJk
• Is the commercial telling the truth?
Symbol
A voltaic cell for demonstration purposes. In
this example the two half-cells are linked
by a salt bridge separator that permits the
transfer of ions.
Leyden Jars
• 17th century technology
• A leyden jar could hold an electric charge for some time
Using chemicals to generate a
voltage and constant current
• Alessandro Volta
• Voltaic Pile using chemicals instead of a charge
• Copper and zinc plates seperated by paper
disks soaked in a brine
Voltaic Cells
•
•
•
•
•
Two poles + and –
Need two dissimilar types of metal
Require a chemical reaction to function
Can supply a sustained current
The chemical reaction is irreversible for
Primary Cells and reversible for
Secondary Cells
• Issues with corrosion
Primary Cells
Alkaline Primary Cell
Corrosion and Leakage
Exercise:
Discuss the following and list:
• Applications where Primary Cells are used!
• Why are Primary Cells preferred to Secondary
Cells for some applications
• Applications where Secondary Cells are used!
• What are the advantages and disadvantages of
Secondary Cells?
Secondary Cells
Secondary Cells
Secondary Cells in a Car Battery
Video Lead Acid Battery (5min)
•
https://www.youtube.com/watch?v=rhIRD5YVNbs
Why are not all batteries
rechargeable?
(5min)
•
https://www.youtube.com/watch?v=Eo0q59NPNUQ
Chemistry
Zinc–carbon
An
od
e
(−)
Cat
ho
de
(+)
Max.
voltage,
theoretical
(V)
Nominal
voltage,
practical (V)
Specific
energy(
MJ/kg)
Zn
Mn
O2
1.6
1.2
0.13
Zinc–chloride
Alkaline
(zinc–manganese
dioxide)
Mn
O2
1.5
Elaboration
Inexpensive.
1.15
0.4–0.59
Moderate energy density.
Good for high- and low-drain uses.
Nickel
oxyhydroxide
(zinc–manganese
dioxide/nickel
oxyhydroxide)
1.7
Moderate energy density.
Good for high drain uses.
Lithium
(lithium–copper
oxide)
Li–CuO
1.7
No longer manufactured.
Replaced by silver oxide (IEC-type
"SR") batteries.
Lithium
(lithium–iron
disulfide)
LiFeS2
Li
Fe
S2
Lithium
(lithium–
manganese
dioxide)
LiMnO2
Lithium
(lithium–carbon
fluoride)
Li–(CF)n
1.8
1.5
3.0
Li
(CF
)n
3.6
18
Also known as "heavy-duty",
inexpensive.
1.5
Zn
Shelf life at
25 °C, 80%
capacity
(months)
3.0
1.07
Expensive.
Used in 'plus' or 'extra' batteries.
0.83–
1.01
Expensive.
Used only in high-drain devices or for
long shelf-life due to very low rate of
self-discharge.
'Lithium' alone usually refers to this
type of chemistry.
30
337[59]
120
Lithium
(lithium–chromium
oxide)
Li–CrO2
Li
Cr
O2
3.8
3.0
Mercury oxide
Zn
Hg
O
1.34
1.2
Zinc–air
Zn
O2
1.6
1.1
Zamboni pile
Zn
Ag
or
Au
Silver-oxide (silver–
zinc)
Zn
Ag2
O
1.85
1.5
Magnesium
Mg
Mn
O2
2.0
1.5
108
High-drain and constant voltage.
Banned in most countries because of
health concerns.
1.59[60]
0.8
0.47
36
Used mostly in hearing aids.
Very long life
Very low (nanoamp, nA) current
>2,000
Very expensive.
Used only commercially in 'button' cells.
30
40
Secondary Cells
(Rechargable)
Cell
v
ol
ta
g
e
Chemistry
Specific energy
(MJ/kg)
0.46
Smaller volume than equivalent Li-ion.
Extremely expensive due to silver.
Very high energy density.
Very high drain capable.
For many years considered obsolete due to high silver prices.
Cell suffers from oxidation if unused.
Reactions are not fully understood.
Terminal voltage very stable but suddenly drops to 1.5 volts at 70–80% charge (believed to
be
due to presence of both argentous and argentic oxide in positive plate – one is consumed
first).
Has been used in lieu of primary battery (moon buggy).
Is being developed once again as a replacement for Li-ion.
0.14
Moderately expensive.
Moderate energy density.
Moderate rate of self-discharge.
Higher discharge rates result in considerable loss of capacity.
Environmental hazard due to Lead.
Common use – Automobile batteries
1.86
AgZn
Lead–acid
1.
5
2.1
Comments
ithium
3.
ion
NiCd
NiMH
NiZn
1.
1.
1.
0.4
6
Very expensive.
Very high energy density.
Not usually available in "common" battery sizes.
Very common in laptop computers, moderate to high-end digital cameras, camcorders, and cellphones.
Very low rate of self-discharge.
6
Tends to require either user awareness or a dedicated management system to slow down the gradual loss of
capacity.
Terminal voltage unstable (varies from 4.2 to 3.0 volts during discharge).
Volatile: Chance of explosion if short-circuited, allowed to overheat, or not manufactured with rigorous quality
standards.
0.1
2
Inexpensive.
High-/low-drain, moderate energy density.
Can withstand very high discharge rates with virtually no loss of capacity.
4
Moderate rate of self-discharge.
Environmental hazard due to Cadmium – use now virtually prohibited in Europe.
0.3
2
Inexpensive.
Performs better than alkaline batteries in higher drain devices.
Traditional chemistry has high energy density, but also a high rate of self-discharge.
6
Newer chemistry has low self-discharge rate, but also a ~25% lower energy density.
Used in some cars.
0.3
6
Moderately inexpensive.
High drain device suitable.
Low self-discharge rate.
Voltage closer to alkaline primary cells than other secondary cells.
6
No toxic components.
Newly introduced to the market (2009). Has not yet established a track record.
Limited size availability.
Measuring the Internal resistance
of a battery
• Measure the battery cell voltage without a load
(switch is open cct.)
• Close the switch and measure V and I
• There will be a small voltage drop with the load
applied
• Multiply the value of the V-drop with I and you
will get a value for the Internal Resistance of
the battery cell
NiCad Problem
• NiCad’s suffer from so “Memory Effect”
• If they are not fully discharged and recharged
but only topped up in regular intervals the
performance of the cells degrade and they do
not seem to last very long
• It seems like the cells have memorised the
discharge level when they get recharged
Tips for reviving secondary cells
suffering from the memory effect
• Drain batteries for a long period using 120
ohms resistor
• After it is discharged recharge the battery
to it’s full potential
• Drain it again with the 120 ohms resistor
• Recharge again and repeat the process
several times
• Measure the internal resistance of the cell
and ensure that it has gone down
Reviving dead secondary cells
•
https://www.youtube.com/watch?v=1e8hHLyXAyQ
Ampere Hour
• An ampere-hour or amp-hour
• SI symbol A·h or A h; also denoted Ah
• It is a unit of electric charge, equal to the
charge transferred by a steady current of
one ampere flowing for one hour, or
3600 coulombs.
Summary
• A constant current supply can be generated
using a chemical reaction
• Batteries are made up of cells
• Cells are either primary of secondary cells
• Primary Cells – can only be used once
• Secondary Cells – can be recharged many times
• Different chemicals will make batteries more or
less effective e.g. Zinc Carbon verses Lithium
based cells