Delithiation Mechanisms in Acid of Spinel LiMn2-xMxO4 (M = Cr, Fe, Co, and Ni) Cathodes

by James C. Knight, Soosairaj Therese, and Arumugam Manthiram

Journal of the Electrochemical Society 2015 162 (3), A426-A431

The products formed by the chemical extraction of lithium from LiMn2-xMxO4(M = Cr, Fe, Co, and Ni) with aqueous sulfuric acid have been structurally and chemically characterized. The amount of lithium extracted is found to be proportional to the initial Mn3+ content, confirming the reaction mechanism, LiMn3+Mn4+O4 → 0.75 Mn2O4 + 0.5 Li2O + 0.5 MnO. Thus, no lithium is extracted from LiMn1.54+Ni0.52+O4 as there is no Mn3+, while complete delithiation occurs in LiMn3+Mn4+O4 to give Mn2O4. The amount of lithium extracted from the other samples is in good agreement with that calculated from the Mn3+ content. The XRD data confirm the maintenance of the spinel structure for the delithiated samples, while the redox titration confirmed the maintenance of oxygen content at 4.0, indicating that no protons were inserted into the lattice during delithiation. The findings could provide more insight on the problem of metal dissolution from cathode materials in lithium-ion batteries.

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