High Temperature Co-doped LiMn₂O₄-Based Spinels. Structural, Electrical, and Electrochemical Characterization

Abstract

High-temperature cubic spinels were obtained by thermal treatment at 1100 °C of the corresponding LiCo y Mn 2-y O 4 (0 e y e 1) spinels. The samples were characterized by X-ray powder diffraction, thermogravimetric analysis, electron paramagnetic resonance (EPR) spectroscopy, and electrical and electrochemical measurements. The lattice parameter of the new phases in the 0.3 < y e 1 range is larger compared to the starting ones. The EPR spectra of the new compounds are also different from the starting ones. The electrical conductivity of the new phases depends on the Co content. For y > 0.65 the sharp increase in conductivity observed is associated with a change in electron hopping from Mn 3+ /Mn 4+ ions to Co 2+ /Co 3+ ones. At high temperatures, the conductivity is explained in terms of phonon-assisted polaron hopping among either Mn 3+ /Mn 4+ or Co 2+ /Co 3+ nearest neighbors. At low temperatures electron hopping beyond the nearest neighbors accounts for the conductivity. The electrochemical behavior of the new compounds as positive electrodes was analyzed. The discharge curves show both the 4 and 5 V plateau due to the Mn 4+ /Mn 3+ and Co 4+ /Co 3+ reduction, respectively. Differences in electrochemical characteristics compared to the starting samples are found. From electrochemical and thermogravimetric measurements, the oxidation states of the transition metal ions and the chemical composition of the high-temperature samples are estimated.

Synthesis of compounds, Li(MMn11/6)O4 (M=Mn1/6, Co1/6, (Co1/12Cr1/12), (Co1/12Al1/12), (Cr1/12Al1/12)) by polymer precursor method and its electrochemical performance for lithium-ion batteries

“…Table 1. The lattice parameter of the bare compound matches with the value reported by Song et al [39], and are found to be decreased for the doped spinels due to ionic size effect [40]. This also validate the fact that, the doped transition metal ions replace the Mn 3+ ions, which is bigger in ionic size compared to the Mn 4+ ions [31,39,41].…”

Capacity Fade Study of LiCo0.4Al0.1Mn1.5O4 Cathode Material for Li-Ion Batteries Cycled at Low Discharge Rates

“…The paramagnetic resonance detected here could be attributed to the presence of octahedral Mn 4+ ions that carry a half-integer spin (S=3/2) and are then EPR-active. EPR spectra recorded for as prepared sample shows ( Figure 5) the sharp signal centered at gyromagnetic factor, g ≈ 2 with Lorentzian curve with a peak to peak width (∆H pp ) of 348 mT [31]. This is in accordance with the previous studies of Stoyanova et al [32] and Nayaka et al [21].…”

Characterizations on the structural and electronic properties of thermal lithiated Li0.33MnO2

“…Manganese based oxides are among the most attractive candidates because of their economical and environmental advantages. Scientists have developed many kinds of Mn oxides, which could be sorted by 3 V (such as LiMnO 2 ) [1,2], 4 V (such as LiMn 2 O 4 ) [3,4] and 5 V (such as LiMn 1.5 Ni 0.5 O 4 ) [5,6] cathode materials in the light of discharge potentials.…”