Innovation in Lithium Batteries LiFePO4 Power Battery: Faster charging and safer performance It is well established that small capacity Li-ion (polymer) batteries containing lithium cobalt oxide (LiCoO2) offer 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 Batteries. 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 power tools, e-wheel chairs, e-bikes, e-cars and ebuses. A LiFePO4 battery has hybrid characters: as safe as lead-acid batteries with lower environmental impact, 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 the 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 60% 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 (60%SOC) needs two hours and the step 2 (40%SOC) needs another two hours. LiFePO4 battery can be charged by only one step 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 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 90J/g for LiFePO4 verse 1600J/g for LiCoO2 . The more is the exothermic heat, the larger energy heating up the battery in its abusive condition, the more chance of fire or explosion. A LiFePO4 battery would be overcharged up to 30V without protection 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 Like lead-acid batteries, 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 10% difference between cells for both voltage and capacity inconsistency. 4. Longer cycle life In comparison with LiCoO2 battery which has a cycle life of approximately 400 cycles, LiFePO4 battery extends its cycle life up to 2000 cycles. 5. Simplifying battery management system (BMS) and battery charger Large overcharge tolerance and self-balance characters of LiFePO4 batteries simplify battery protection and balance circuit boards, lowering their cost. One step charging processes allows simpler conventional power supply to charge LiFePO4 batteries, instead of expensive the more expensive Li-ion battery chargers. 6. High temperature performance It is detrimental to have a LiCoO2 battery working at elevated temperatures, such as 60degrees Celsius. In fact, anything above 25 degrees can be harmful to your battery. However, a LiFePO4 battery runs better at elevated temperatures, offering 10% more capacity, due to higher lithium ionic conductivity. Comparison data among various Lithium base batteries: C-LiFePO4 LiCoO2 LiMn2O4 Li(NiCo)O2 Acceptable Not stable, dangerous CYCLE LIFE Best among all the listed Acceptable groups Unacceptable Acceptable POWER WEIGHT DENSITY Acceptable Good Acceptable Best LONG TERM COST Excellent, most High economic Acceptable High WORKING TEMP. Excellent 45C-70C Excellent, SAFETY AND ENVIRONMENTAL CONCERNS Not stable, Best among all dangerous existing batteries 1. COMMENTS - Decayed Decayed beyond extremely fast -20C ¨C 55C over 50C Decayed extremely fast below -20C and above 55C Lead Acid batteries are lower in cost and safely acceptable; however, they are extremely toxic, worse for the environment, have short cycle life, are heavy in weight, and therefore, we don't consider it as a viable group for comparison. 2. Nickel Hydride batteries have low Power Weight Density, they decay faster under high temperatures, suffer worse memory effect, and are not considered suitable for high output usage. 3. The C-coated Lithium Iron Phosphate Battery has been proven as the most environmental friendly battery. It is the safest and most suitable for high output usage on electric bikes, and also the best value for its cycle life. Source: www.goldenmotor.com