Physico-chemical characterization of manganese-based spinels (Co and Fe) and its application as cathodes for Li-ion batteries

D. ALBURQUENQUE; P. MÁRQUEZ; L. TRONCOSO; G. L. LUQUE; F. J. GARCIA SORIANO; J.F. MARCOF; J. ESCRIG

Congreso; 19° Congreso Internacional de Metalurgia y Materiales CONAMET-SAM; 2019

Mn-based spinel compounds have been the most studied due to the interest in their electrochemical properties [1]. Among these, LiMn2O4 spinel has been extensively investigated as positive electrode material for lithium-ion batteries because of its high theoretical energy density, high potential (approximately 4V vs. lithium metal) in addition to being environmental friendly and low cost [2]. However, it is well known that LiMn2O4 is structurally unstable leading to problem to its direct use as active material in cathodes. There are two main reasons that cause this effect: 1- the dissolution of Mn2+ into the electrolyte generated by the Jahn-Teller effect (J-T) that causes the loss of capacity during cycling; [3] and 2- the generation of new phases during charge/discharge cycles [4], which is unacceptable for commercial applications. One of the strategies to improve the structural stability of LiMn2O4 is to perform a partial substitution of manganese ions by other divalent or trivalent metal element in the 16d octahedral sites in the spinel structure in order to block the propagation of the J-T distortion.In this work, we present results obtained for LiCo0.5Mn1.5O4-δ [5] and LiFe0.5Mn1.5O4-δ [6] spinels. These ones were characterized by XRD, SEM-EDS, TEM, oxygen stoichiometry, cation distribution and XPS; their electrochemical properties were also evaluated. Oxides were synthesized using for the first time an ultrasound assisted thermal decomposition nitrates (UA-TDN). XRD and Rietveld refinement of X-ray data indicate that all samples crystallize in the Fd3m space group characteristic of the cubic spinel structure. The a-cell parameter obtained from a = 0.8117 nm (LiCo0.5Mn1.5O4-δ) and a = 0.8254 nm (LiFe0.5Mn1.5O4-δ). The elemental composition analysis (EDS) confirms the ratio Mn/Co and Mn/Fe. SEM and TEM images of LiCo0.5Mn1.5O4-δ and LiFe0.5Mn1.5O4-δ) showed the morphology of irregular polyhedral particles with average sizes of 600 and 750 nm, respectively.For each spinel, the oxides cation distributions were proposed, and , founding a good agreement between the experimental parameters a and z with the calculated ones, The ratio Mn4+/Mn3+ is higher in LiFe0.5Mn1.5O4 than LiCo0.5Mn1.5O4. XPS studies of these oxides revealed the presence of Co3+, Fe3+, Mn3+ and Mn4+. Finally, the main electrochemical measurements are presented.