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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