# Do Lithium Iron Phosphate cathodes change color during charging and discharging while losing Li ions?

In an LFP battery, $$\ce{LiFePO4 -> FePO4 + Li+ + e-}$$. $$\ce{LiFePO4}$$ is described as a grey, reddish grey, brown, or black solid on wikipedia and $$\ce{FePO4}$$ a yellow-brown solid. If you had a window into the battery could you see this color change occurring during use?

• I am not sure, if there are (colored) salts of transition metals, that have the same color at different metal oxidation states. – Poutnik Jul 22 at 6:16
• Is LiFePO4 darker than FePO4 as described by Wikipedia solo because of the addition of carbon for conductivity in batteries? – bryan dunn Jul 31 at 23:46