Nonstoichiometric Layered Li_xMn_yO₂ with a High Capacity for Lithium Intercalation/Deintercalation

Abstract

Nonstoichiometric layered Li x Mn y O2 compounds with the O3 structure (α-NaFeO2 type), space group R3̄m, were synthesized by ion exchange from the sodium precursors Na x Mn y O2. Such lithium intercalation compounds are important in the context of rechargeable lithium batteries since they offer the key advantages of lower cost, lower toxicity, and higher safety when compared with LiCoO2, which is used presently as the positive electrode in these devices. By the varying of the synthesis conditions of the precursor and the ion-exchange process, significant variations of the vacancy content on the transition metal sites could be induced. The variations in composition and defect structure were reflected in differences in the lattice parameters and hkl dependent peak broadening, observed in the X-ray diffraction data. Structural details were confirmed by Rietveld refinement using neutron powder diffraction. Lithium intercalation/deintercalation proved very sensitive to the composition and defect structure. High discharge capacities of 190−200 mAhg-1 at a rate of C/7 (corresponding to complete discharge in 7 h) could be obtained with a capacity fade of only 0.12% per cycle, at room temperature. This is significantly better than results reported previously for stoichiometric LiMnO2. All of the materials described in this work convert to a spinel-like phase on repeated intercalation/deintercalation of lithium. Such conversion involves the generation of a nanostructured spinel-like phase within each particle. The nanostructure plays a key role in accommodating, at the domain wall boundaries, stresses which normally accompany the first-order Jahn−Teller driven phase transition occurring on cycling in the 3 V region.

Investigation of layered intergrowth LixMyMn1?yO2+z (M=Ni, Co, Al) compounds as positive electrodes for Li-ion batteries

“…XRD patterns obtained for three different Na/TM ratios used in the glycine-nitrate combustion are shown in Figure 1. We also show the calculated pattern of the P2 phase Na 0.66 Ni 0.3 Mn 0.7 O 2 from Dahn's data [9] and the P3 calculated pattern reported recently by Bruce et al [10]. These results clearly demonstrate that a small change in the Na/TM ratio can drastically modify the intergrowth structure.…”

Influence of Substitution on the Structure and Electrochemistry of Layered Manganese Oxides

“…All compounds have predominantly the P2 layered structure, but several additional peaks were observed at medium angles in some of the patterns ( Figure 4). These could be indexed to a P3 structure (space group R3M) similar to that reported recently by Bruce et al, 19 in which there are three MO 2 per unit cell, and trigonal prismatic sites for Na ( Figure 1d). No superstructure peaks were detected in these patterns suggesting that there is an absence of ordering on the transition-metal sites.…”

Hydrothermal synthesis of orthorhombic LiMnO2 nano-particles and LiMnO2 nanorods and comparison of their electrochemical performances

“…In terms of their practical application as cathode electrodes in rechargeable lithium batteries, the rate capability of materials is particularly important [35]. Since the LiMnO 2 nanorods displayed high discharge capacities and good cycle stability, their rate capability was also investigated.…”