Like any other battery, Lithium Iron Phosphate (LiFePO4) battery is made of power-generating electrochemical cells to power electrical devices. As shown in Figure 1, the LiFePO4 battery consists of an anode, cathode, separator, electrolyte, and positive and negative current collectors.
The positive electrode material of lithium iron phosphate batteries is generally called lithium iron phosphate, and the negative electrode material is usually carbon. On the left is LiFePO4 with an olivine structure as the battery’s positive electrode, which is connected to the battery’s positive electrode by aluminum foil.
The charging method of both batteries is a constant current and then a constant voltage (CCCV), but the constant voltage points are different. The nominal voltage of a lithium iron phosphate battery is 3.2V, and the charging cut-off voltage is 3.6V. The nominal voltage of ordinary lithium batteries is 3.6V, and the charging cut-off voltage is 4.2V.
B. Mao, C. Liub, K. Yang, “Thermal runaway and fire behaviors of a 300 Ah lithium ion battery with LiFePO4 as cathode”, Renewable and Sustainable Energy Reviews, vol. 139, Apr 2021, 110717. Like any other battery, Lithium Iron Phosphate (LiFePO4) battery is made of power-generating electrochemical cells to power electrical devices.
As lithium ions are removed during the charging process, it forms a lithium-depleted iron phosphate (FP) zone, but in between there is a solid solution zone (SSZ, shown in dark blue-green) containing some randomly distributed lithium atoms, unlike the orderly array of lithium atoms in the original crystalline material (light blue).
In LiFePO4 batteries, the iron and phosphate ions form grids that loosely trap the lithium ions as shown in Figure 2. During the charging of the cell, these loosely trapped lithium ions easily get pulled to the negative electrode through the membrane in the middle.