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 digitalapplications. However, lithium cobalt oxide (LiCoO2) isvery expensive and un-safe for large capacity Li-ion Battery.Recently lithium iron phosphate (LiFePO4) hasbeen 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 ande-bus. A LiFePO4 battery has hybrid characters: as safe as lead-acid battery and aspowerful as lithium ion cells. The advantages of large format Li-ion (polymer) batteries containing lithium iron phosphate (LiFePO4) arelisted as below:
1. Fast charging:
During charging process, aconventional Li-ion Battery containing lithium cobalt oxide(LiCoO2) needstwo steps to be fully charged: step 1 is using constant current(CC) to get 60% State of Charge (SOC); step 2 takes place whencharge voltage reaches 4.2V, upper limit of charging voltage,turning from CC to constant voltage (CV) while the charging currentis taping down. The step 1 (60%SOC) needs two hours and the step 2(40%SOC) needs another two hours. LiFePO4 batterycan be charged by only one step of CC to reach 95%SOC or be chargedby CC+CV to get 100%SOC. The total charging time will be twohours.
2. Large overcharge tolerance and saferperformance
A LiCoO2 batteryhas a very narrow overcharge tolerance, about 0.1V over 4.2V ofcharging voltage plateau and upper limit of charge voltage.Continuous charging over 4.3V would either damage the batteryperformance, such as cycle life, or result in firing and explosion.A LiFePO4 batteryhas a much wider overcharge tolerance of about 0.7V from itscharging voltage plateau 3.4V. Exothermic heat of chemical reactionwith electrolyte measured by DSC after overcharge is only 90J/g forLiFePO4 verse1600J/g for LiCoO2 . Themore is the exothermic heat, the larger energy heating up thebattery in its abusive condition, the more chance toward firing andexplosion. A LiFePO4 batterywould be overcharged upto 30V without portection circuit board. Itis suitable for large capacity and high power applications. Fromviewpoint of large overcharge tolerance and safety performance, aLiFePO4 batteryis similar to lead-acid battery.
3. Self balance
Alike lead-acid battery, anumber of LiFePO4 cellsin a battery pack in series connection would balance each otherduring charging process, due to large overcharge tolerance. Thisself balance character can allow 10% difference between cells forboth voltage and capacity inconsistency.
4. Simplifying battery management system (BMS) and batterycharger
Large overcharge tolerance andself-balance character of LiFePO4 battery would simplify battery protection and balance circuitboards, lowering their cost. One step charging process would allowto use simpler conventional power supplier to chargeLiFePO4 battery instead to use a expensive professional Li-ion batterycharger.
5. Longer cycle life
In comparison withLiCoO2 battery which has a cycle life of 400 cycles,LiFePO4 battery extends its cycle life up to 2000 cycles.
6. High temperature performance
It is detrimental to have aLiCoO2 battery working at elevated temperature, such as 60C.. However, a LiFePO4 battery runs better at elevated temperature, offering 10% morecapacity, due to higher lithium ionic conductivity.