Chemical vs. electrochemical extraction of lithium from the Li-excess Li1.10Mn1.90O4 spinel followed by NMR and DRX techniques

Abstract

Lithium extraction from the Li-excess Li_1.10Mn_1.90O₄ spinel has been performed by chemical and electrochemical methods in aqueous and in organic media, respectively. De-lithiated samples have been investigated by XRD, SEM, TG, ⁷Li and ¹H MAS-NMR techniques. The comparative study has allowed demonstrating that the intermediate de-intercalated samples prepared during the chemical extraction by acid titration are similar to those prepared by the electrochemical way in a non-aqueous electrolyte. LiMn₂O₄ based spinel with a tailored de-lithiation degree can be prepared as a single phase by controlling the pH used in chemical extraction. ⁷Li MAS-NMR spectroscopy has been used to follow the influence of the manganese oxidation state on tetra and octahedral Li-signals detected in Li-extracted samples. The oxidation of Mn(III) ions goes parallel to the partial dissolution of the spinel, following Hunter's mechanism. Based on this mechanism, a generalized chemical reaction has been proposed to explain the formation of intermediate Li⁺ de-intercalated samples during acid treatment in aqueous media. By the ¹H MAS NMR study, no evidence of Li–H topotactic exchange in the bulk of the acid treated material was found.