How to charge Lithium Iron Phosphate Rechargeable Lithium Ion Batteries?
Lithium iron phosphate is a type of lithium-ion battery, since the energy is stored in the same way, moving and storing lithium ions instead of lithium metal. These cells and batteries not only have high capacity, but can deliver high power. High-power lithium iron phosphate batteries are now a reality. They can be used as storage cells or power sources.
In addition, Lithium Iron Phosphate batteries are among the longest lived batteries ever developed. Test data in the laboratory show up to 2000 charge/discharge cycles. This is due to the extremely robust crystal structure of the iron phosphate, which does not break down under repeated packing and unpacking of the lithium ions during charging and discharging.
During the conventional lithium ion charging process, a conventional Li-ion Battery containing lithium iron phosphate (LiFePO4) needs two steps to be fully charged: step 1 uses constant current (CC) to reach about 60% State of Charge (SOC); step 2 takes place when charge voltage reaches 3.65V per cell, which is the upper limit of effective charging voltage. Turning from constant current (CC) to constant voltage (CV) means that the charge current is limited by what the battery will accept at that voltage, so the charging current tapers down asymptotically, just as a capacitor charged through a resistor will reach the final voltage asymptotically.
Unlike the lead-acid battery, a number of LiFePO4 cells in a battery pack in series connection cannot balance each other during charging process. This is because the charge current stops flowing when the cell is full. This is why the LiFEPO4 packs need management boards.
Large overcharge tolerance and self-balance characteristic of LiFePO4 battery can simplify the battery protection and balance circuit boards, lowering their cost. The one step charging process allows the use of a simpler conventional power supplier to charge LiFePO4 battery instead of using an expensive professional Li-ion battery charger.