Synthesis of layered Li 1.2+ x[Ni 0.25Mn 0.75] 0.8− xO 2 materials (0 ≤ x ≤ 4/55) via a new simple microwave heating method and their electrochemical properties

Abstract

Li 1.2+ x [Ni 0.25Mn 0.75] 0.8− x O 2 (0 ≤ x ≤ 4/55) was prepared by a new simple microwave heating method and the effect of extra Li + content on electrochemistry of Li 1.2Ni 0.2Mn 0.6O 2 ( x = 0) was firstly revealed. X-ray diffraction identified that they had layered α-NaFeO 2 structure (space group R-3 m). Linear variation of lattice constant as a function of x value supported the formation of solid solution, that is, extra Li + is possibly incorporated in structure of layered Li 1.2Ni 0.2Mn 0.6O 2 ( x = 0), accompanying oxidization of Ni 2+ to Ni 3+ to form Li 1.2+ x [Ni 0.25Mn 0.75] 0.8− x O 2 (0 ≤ x ≤ 4/55). This was confirmed by X-ray photoelectron spectroscopy that Ni 3+ appeared and increased in content with increasing x value. Charge–discharge tests showed that Li 1.2+ x [Ni 0.25Mn 0.75] 0.8− x O 2 (0 ≤ x ≤ 4/55) truly displayed different electrochemical properties (different initial charge–discharge plots, capacities and cycleability). Li 1.2Ni 0.2Mn 0.6O 2 ( x = 0) in this work delivered the highest discharge capacity of 219 mAh g −1 between 4.8 and 2.0 V. Increasing Li content ( x value in Li 1.2+ x [Ni 0.25Mn 0.75] 0.8− x O 2) reduced charge–discharge capacities, but significantly enhancing cycleability.