Lithium iron phosphate battery is one of the safest batteries we using, and its durability and safety are definitely superior to other lithium ion batteries. So, can we overcharge lithium iron phosphate batteries? What range of voltage can be allowed it be overcharged? Under normal circumstances, the answer is NO!
What are lithium iron phosphate batteries?
The lithium iron phosphate battery is a lithium-ion battery that uses lithium iron phosphate as its positive electrode material. It is also called a LiFePO4 battery for short.
What is overcharging?
Overcharging a battery means that the battery charger is charging the battery too far past its fully-charged voltage. For example, the full-charge voltage of a monolithic lithium iron phosphate cell is 3.65V. When the charge exceeds 3.65V, it is overcharged.
What will happen when a lithium-ion polymer (LiPo) battery is overcharged?
Overcharging a battery cell will cause permanent damage to the cell. In terms of testing for safety, we internally test the different overcharge levels of the battery cells. The following are our test standards:
LiPo battery cell: No fire when the charging voltage reaches 4.8V (one of the necessary conditions)
LiFePO4 battery cell: Charging voltage reaches 10V and does not catch fire (one of the necessary conditions)
Charging with a damaged or non-corresponding charger may also cause overcharging. When the voltage is too high, a large amount of lithium ions overflow from the positive electrode, and lithium ions that cannot be absorbed by the negative electrodes can form dendrites on the surface of the battery, which can cause a short circuit inside the battery. The short-circuit current will generate a lot of heat, and the rapid temperature increase may cause the electrolyte as an organic solvent to burn (organic solvents are extremely flammable). In severe cases, it will cause a decomposition reaction of the positive electrode or the reaction of the negative electrode and the electrolyte. This can generate a large amount of gas; this can result in an explosion especially since the cells are enclosed.
If a battery doesn’t have the Battery Management System (BMS), continuously charging the battery will raise the voltage. In this situation, the lithium ions remaining in the cathode are removed and more lithium ions are inserted into the anode than under standard charging conditions.
It has been observed through ARC studies that the thermal stability of a cell is highly dependent on its state of charge. An overcharged Li-ion cell was found to have much lower thermal stability with an onset runaway temperature as low as 40ºC
Source: Science Direct
Since LiFePo4 is safer, can we over-charge it?
Our suggestion is to never over-charge/discharge a cell!
The most common causes for premature failure of LiFePO4 cells are overcharging and over-discharging. Even a single occurrence can cause permanent damage to the cell, and such misuse voids warranties. A Battery Management System (BMS) is required to ensure it is not possible for any cell in your pack to go outside its nominal operating voltage range.
What is a BMS?
The Battery Management System is a piece of hardware with an electronic system on board that manages a rechargeable battery (cell or pack) and is the link between the battery and it’s user. It can more intelligently manage and maintain each cell, improve battery utilization, prevent battery overcharge and discharge, prolong battery life, and monitor battery status.
If you need a customizable BMS to prevent overcharging or other potential issues, please contact us to get more information.