There’s plenty of proof in academic literature. FePO4 is quite stable because of the quirks in iron’s valance up to about 500C. But the combination of of lithium skews the valance effects at high temperatures to start losing oxygen at 250C.
Please review the following literature for more information:
- C. Delacourt, P. Poizot, J-.M. Tarascon, and C. Masquelier, Nat Mater., 4, 254 (2005).
- J.L Dodd, R. Yazami, and B. Fultz, Electrochem. Solid-State Let., 9, A151 (2006).
- G. Chen, .XSong, and T. J. Richardson, J. Electrochem. Soc,. 154, 4627 (2007).
The stoichometry comes out with 2:1 moles of lfp to diatomic oxygen which is significant
The combustibility you’re referring to is a legal definition not a scientific one