LiFePO4 Safety

One important advantage over other lithium-ion chemistries is thermal and chemical stability, which improves battery safety. LiFePO4 is an intrinsically safer cathode material than LiCoO2 and manganese spinel, through omission of the cobalt, with its negative temperature coefficient of resistance that can encourage thermal runaway. The P–O bond in the (PO4)3−ion is stronger than the Co–O bond in the (CoO2))−ion, so that when abused (short-circuited, overheated, etc.), the oxygen atoms are released more slowly. This stabilization of the redox energies also promotes faster ion migration.

As lithium migrates out of the cathode in a LiCoO2 cell, the CoO2 undergoes non-linear expansion that affects the structural integrity of the cell. The fully lithiated and unlithiated states of LiFePO4 are structurally similar which means that LiFePO4 cells are more structurally stable than LiCoO2 cells.

No lithium remains in the cathode of a fully charged LiFePO4 cell. (In a LiCoO2 cell, approximately 50% remains.) LiFePO4 is highly resilient during oxygen loss, which typically results in an exothermic reaction in other lithium cells. As a result, LiFePO4 cells are harder to ignite in the event of mishandling (especially during charge). The LiFePO4 battery does not decompose at high temperatures.
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