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    What Happens to LiMnPO<sub>4</sub> upon Chemical Delithiation?

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    Olivine MnPO<sub>4</sub> is the delithiated phase of the lithium-ion-battery cathode (positive electrode) material LiMnPO<sub>4</sub>, which is formed at the end of charge. This phase is metastable under ambient conditions and can only be produced by delithiation of LiMnPO<sub>4</sub>. We have revealed the manganese dissolution phenomenon during chemical delithiation of LiMnPO<sub>4</sub>, which causes amorphization of olivine MnPO<sub>4</sub>. The properties of crystalline MnPO<sub>4</sub> obtained from carbon-coated LiMnPO<sub>4</sub> and of the amorphous product resulting from delithiation of pure LiMnPO<sub>4</sub> were studied and compared. The phosphorus-rich amorphous phases in the latter are considered to be MnHP<sub>2</sub>O<sub>7</sub> and MnH<sub>2</sub>P<sub>2</sub>O<sub>7</sub> from NMR, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy analysis. The thermal stability of MnPO<sub>4</sub> is significantly higher under high vacuum than at ambient condition, which is shown to be related to surface water removal
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