EPR studies of Li deintercalation from LiCoMnO4 spinel-type electrode active material

Abstract The electrochemical extraction/insertion of Li from/into LiCoMnO 4 in the potential range of 3.7–5.25 V is studied by electron paramagnetic resonance (EPR) of Mn 4+ . Structural characterization of initial LiCoMnO 4 has been performed by neutron diffraction. The EPR spectra are consistent with a single-phase mechanism of electrochemical extraction/insertion of Li from/into LiCoMnO 4 . During Li extraction, the intensity of the main EPR signal due to Mn 4+ ions in Mn 4+ /Co 3+ environment decreases drastically concomitantly with the appearance of resonance absorption from magnetically correlated Mn 4+ –Co 4+ spins. From EPR, the complex [Co n + –Mn 3+ –Mn 4+ ] clusters indicative of the oxygen non-stoichiometry of LiCoMnO 4 also take part in the electrochemical reaction, especially up to 4.7 V. During the Li reinsertion, the EPR signal from Mn 4+ ions in Mn 4+ /Co 3+ environment is recovered, but its intensity remains lower (30%) as compared to that of the initial composition, which is consistent with an unrecovered composition of LiCoMnO 4 electrode after first charge/discharge. Contrary to the narrow main signal, there is a reverse reduction of the paramagnetic ions present in the clusters, but their oxidation state as compared to the initial composition is not recovered.

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