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Innovation in Li-ion
Battery
LiFePO4
Power Battery: Faster charging
and safer
performance
It
is clear that the small
capacity Li-ion (polymer)
Battery containing lithium
cobalt oxide (LiCoO2) offers a
genuinely viable option for
electronics and digital
applications. However, lithium
cobalt oxide (LiCoO2) is very
expensive and un-safe for large
capacity Li-ion Battery.
Recently lithium iron phosphate
(LiFePO4) has been becoming
"best-choice" materials in
commercial Li-ion (polymer)
Batteries for large capacity
and high power applications,
such as lap-top, power tools,
e-wheel chair, e-bike, e-car
and e-bus. A LiFePO4
battery has hybrid characters:
as safe as lead-acid battery
and as powerful as lithium ion
cells.The advantages of
large format Li-ion (polymer)
batteries containing lithium
iron phosphate (LiFePO4) are
listed as below:
1.
Fast
charging:
During
charging process, a
conventional Li-ion Battery
containing lithium cobalt oxide
(LiCoO2) needs two steps to be
fully charged: step 1 is using
constant current (CC) to get
*0% State of Charge (SOC); step
2 takes place when charge
voltage reaches 4.2V, upper
limit of charging voltage,
turning from CC to constant
voltage (CV) while the charging
current is taping down. The
step 1 (*0%SOC) needs two hours
and the step 2 (*0%SOC) needs
another two hours. LiFePO4
battery can be charged by only
one step of CC to reach *5%SOC
or be charged by CC+CV to get
**0%SOC. The total charging
time will be two
hours.
2.
Large overcharge tolerance and
safer
performance
A
LiCoO2 battery has a very
narrow overcharge tolerance,
about 0.1V over 4.2V of
charging voltage plateau and
upper limit of charge voltage.
Continuous charging over 4.3V
would either damage the battery
performance, such as cycle
life, or result in firing and
explosion. A LiFePO4 battery
has a much wider overcharge
tolerance of about 0.7V from
its charging voltage plateau
3.4V. Exothermic heat of
chemical reaction with
electrolyte measured by DSC
after overcharge is only *0J/g
for LiFePO4 verse ***0J/g for
LiCoO2 . The more is the
exothermic heat, the larger
energy heating up the battery
in its abusive condition, the
more chance toward firing and
explosion. A LiFePO4 battery
would be overcharged upto *0V
without portection circuit
board. It is suitable for large
capacity and high power
applications. From viewpoint of
large overcharge tolerance and
safety performance, a LiFePO4
battery is similar to lead-acid
battery.
3.
Self balance
Alike
lead-acid battery, a number of
LiFePO4 cells in a battery pack
in series connection would
balance each other during
charging process, due to large
overcharge tolerance. This self
balance character can allow *0%
difference between cells for
both voltage and capacity
inconsistency.
4.
Simplifying battery management
system (BMS) and battery
charger
Large
overcharge tolerance and
self-balance character of
LiFePO4 battery would simplify
battery protection and balance
circuit boards, lowering their
cost. One step charging process
would allow to use simpler
conventional power supplier to
charge LiFePO4 battery instead
to use a expensive professional
Li-ion battery charger.
5.
Longer cycle
life
In
comparison with LiCoO2 battery
which has a cycle life of **0
cycles, LiFePO4 battery extends
its cycle life up to ***0
cycles.
6.
High temperature
performance
It
is detrimental to have a LiCoO2
battery working at elevated
temperature, such as *0C..
However, a LiFePO4 battery runs
better at elevated temperature,
offering *0% more capacity, due
to higher lithium ionic
conductivity.
LiFePO4
Battery Pack
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