The High Temperature Phase Diagram of Li1 + x Mn2 − x  O 4 and Its Implications

Abstract

Using thermal gravimetric analysis, we recently showed that there is a temperature dependent phase transition in Li1,,Mn2O4 which involves oxygen loss. The temperature of the phase transition, T11, depends linearly on x over the range from x = 0 to x = 0.20. Here we discuss the origin of the phase transition and show that it is caused by the disproportionation of Li1+Mn2O4 into Li2MnO3, oxygen, and Li1Mn2O4 where x' <x. X-ray diffraction measurements of samples quenched from above T1 show that this produces Li2MnO3. Furthermore, the weight loss of the samples above T1 can be accounted for by a simple model which describes the disproportionation reaction. Calculations of the rate of change of sample mass with temperature, dM/dT, agree well with the measured data. A phase diagram for the maximum attainable x in Li1Mn2O4 is presented as a function of temperature for samples heated in air. These results show that the optimum method for preparing materials with low specific surface area and large values of x is a two-step method. The first step involves heating materials with x about equal to zero to about 850 to 900°C to lower the surface area, and the second involves reacting this intermediate with additional lithium salt near 600°C, which avoids Li2MnO3 formation. Such materials with x near 0.15 show excellent capacity retention vs. cycle number in secondary lithium coin cells even at 55°C.

Surface phase diagram and stability of (001) and (111)LiMn2O4spinel oxides

“…The energies of (001) and (111) [44][45][46] which will lead to poor electrochemical performance. 44,45 We should note that above conclusions are for synthesis of LMO under equilibrium conditions …”

Studies of cycleability of LiMn2O4 and LiLa0.01Mn1.99O4 as cathode materials for Li-ion battery

“…Gao and Dahn [9,10] suggested another failure mode, oxygen loss from the spinel lattice, and 3.3 V discharge plateau, related to 4.5 V redox one, was characteristic of oxygen-deficiency spinels. Tarascon et al [11,12] proposed a mechanism for spinel to double hexagonal transformation on reversible migration of Mn ions from 16d to 16c sites during cycling to explain the existence of the two 4.5 V additional redox plateaus.…”

Synthesis and electrochemical performance of amorphous hydrated iron phosphate nanoparticles

“…Since the commercialization of lithium cobalt oxide by SONY in the early nineties, alternative cathode materials have been pursued to improve the electrochemical performances [4][5][6][7]. Among the several cathode materials, Fe-based materials have attracted extensive interest due to the low cost and environmental benignity [8][9][10][11][12][13][14][15].…”