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LiFePO4 battery and LiCoO2 battery

LiFePO4 battery and LiCoO2 battery

This is the most safe, longest cycle life, and more powerful thennormal Li-Polymer battery, but generally more expensive than normalLi-Polymer battery.a-

Cylindrical LiFePO4This type is high rate, has 5C, 10C, 20C and soon. always used in power tools, model planes, electrical toys,electrical vehicles, and so

on.b- power LiFePO4This type is always used in electricalvehicales, such as ebike, escooters. golf-cart, and storage batteryin solar-wind projects. the
discharge rate is from 2C to 10C.Advantages of LiFePO4Battery:Faster charging and safer performanceIt is clear that thesmall capacity Li-ion (polymer)

Battery containing lithium cobalt oxide (LiCoO2) offers agenuinely viable option for electronics and digital applications.However, lithium cobalt oxide

(LiCoO2) is very expensive and un-safe for large capacity Li-ionBattery. Recently lithium iron phosphate (LiFePO4) has beenbecoming "best-choice"
materials in commercial Li-ion (polymer) Batteries for largecapacity and high power applications, such as lap-top, power tools,e-wheel chair, e-bike, e-car and e-bus. A LiFePO4 battery hashybrid characters: as safe as lead-acid battery and as powerful aslithium ion cells. The advantages of large format Li-ion (polymer)batteries containing lithium iron phosphate (LiFePO4) are listed asbelow:1. Fast charging:During charging process, a conventionalLi-ion Battery containing lithium cobalt oxide (LiCoO2) needs twosteps to be fully charged: step 1 is using constant current (CC) toget 60% State of Charge (SOC); step 2 takes place when chargevoltage reaches 4.2V, upper limit of charging voltage, turning fromCC to constant voltage (CV) while the charging current is tapingdown. The step 1 (60%SOC) needs two hours and the step 2 (40%SOC)needs another two hours. LiFePO4 battery can be charged by only onestep of CC to reach 95%SOC or be charged by CC+CV to get 100%SOC.The total charging time will be two hours.2. Large overchargetolerance and safer performanceA

LiCoO2 battery has a very narrow overcharge tolerance, about 0.1Vover 4.2V of charging voltage plateau and upper limit of chargevoltage. Continuous charging over 4.3V would either damage thebattery performance, such as cycle life, or result in firing andexplosion. A LiFePO4 battery has a much wider overcharge toleranceof about 0.7V from its charging voltage plateau 3.4V. Exothermicheat of chemical reaction with electrolyte measured by DSC afterovercharge is only 90J/g for LiFePO4 verse 1600J/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 battery would be overcharged up to 30V withoutprotection circuit board. It is suitable for large capacity andhigh power applications. From viewpoint of large overchargetolerance and safety performance, a LiFePO4 battery is similar tolead-acid battery.3. Self balanceAlike lead-acid battery, a numberof LiFePO4 cells in a battery pack in series connection wouldbalance each other during charging process, due to large overchargetolerance. This self balance character can allow 10% differencebetween cells for both voltage and capacity inconsistency.4.Simplifying battery management system (BMS) and batterychargerLarge overcharge tolerance and self-balance character ofLiFePO4 battery would simplify battery protection and balancecircuit boards, lowering their cost. One step charging processwould allow to use simpler conventional power supplier to chargeLiFePO4 battery instead to use a expensive professional Li-ionbattery charger.5. Longer cycle lifeIn comparison with LiCoO2battery which has a cycle life of 400 cycles, LiFePO4 batteryextends its cycle life up to 2000 cycles.6. High temperatureperformanceIt is detrimental to have a LiCoO2 battery working atelevated temperature, such as 60 ?. However, a LiFePO4 battery runsbetter at elevated temperature, offering 10% more capacity, due tohigher lithium ionic conductivity.

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