Mm Thackeray

Improved capacity retention in rechargeable 4 V lithium/lithium-manganese oxide (spinel) cells

The rechargeable capacity of 4 V LixMn2O4 spinel cathodes (0<x⩽1) has been improved by modifying the composition of the spinel electrode. Stable rechargeable capacities in excess of 100 mAh/g in flooded-electrolyte lithium cells can be achieved if LiMn2O4 is doped with mono- or multivalent cations (e.g. Li+, Mg2+, Zn2+) or, alternatively, with additional oxygen to increase the average manganese-ion oxidation state marginally above 3.5.

Spinel Anodes for Lithium‐Ion Batteries

Anodes of Li4MnsO12, Li4Ti5012, and Li2Mn409 with a spinel-type structure have been evaluated in room-temperature lithium cells. The cathodes that were selected for this study were the stabilized spinels, Li1.03Mnl.g704 and LiZnoo25Mn1.9504, and layered LiCoO2. The electrochemical data demonstrated that Li + ions will shuttle between two transition-metal host structures (anode and cathode) at a reasonably high voltage with a concomitant change in the oxidation state of the transition metal cations so that the Li § ions do not reduce to the metallic state at the anode during charge. These cells reduce the safety hazards associated with cells containing metallic-lithium, lithium-alloy, and lithium-carbon anodes.

Spinel versus layered structures for lithium cobalt oxide synthesised at 400°C

Rietveld refinements of X-ray data of LiCoO2 prepared at 400°C and a chemically-delithiated product Li0.5CoO2 using space group symmetries R3m and Fd3m are reported. Refinements in both R3m (layered-type structure) and Fd3m (spinel-type structure) give comparable fits to the data. This structural anomaly is discussed in terms of the refinements and electrochemical data obtained when lithium is extracted from LiCoO2 in non-aqueous cells at room temperature. A spinel-related model for LixCoO2 (0.5⩽x⩽1) is preferred.

An Investigation of Spinel‐Related and Orthorhombic LiMnO2 Cathodes for Rechargeable Lithium Batteries

Cathode materials that have been synthesized by reduction of lithium-manganese-oxide and manganese-oxide precursors with hydrogen at 300 to 350 C, and with carbon at 600 C have been evaluated in rechargeable lithium cells. The cathodes which initially have a composition close to LiMnO[sub 2] contain structures related to the lithiated-spinel phase Li[sub 2][Mn[sub 2]]O[sub 4] and/or orthorhombic LiMnO[sub 2]. The orthorhombic LiMnO[sub 2] component transforms gradually to a spinel structure on cycling. These cathodes are significantly more tolerant to repeated lithium insertion and extraction, when cycled over both the 4 and 3 V regions, than a standard Li[sub x][Mn[sub 2]]O[sub 4] spinel electrode (0 < x < 2).

Synthesis and structural characterization of defect spinels in the lithium-manganese-oxide system

Lithium-manganese-oxides prepared at moderate temperatures are under investigation as insertion electrodes for rechargeable lithium batteries. The structures of two defect-spinel compounds synthesised by the reaction of MnCO3 and Li2CO3 at 400°C are reported. The cation distributions in the structures were determined by neutron-diffraction to be {Li.85□.15}8a[Mn1.74Li.26]16dO4 and {Li.87□.13}8a[Mn1.71Li.29]16dO4, where 8a and 16d refer to the tetrahedral and octahedral sites of the prototypic spinel space group Fd3m, respectively. The structures are discussed in relation to the spinel system Li2O·MnO2 (y≥2.5).

A reinvestigation of the structures of lithium-cobalt-oxides with neutron-diffraction data

The structures of LT-LiCoO2 (synthesised by reaction of Li2CO3 and CoCO3 at 400°C) and its delithiated product LT-Li0.4CoO2 have been reinvestigated by neutron powder diffraction. Despite an unusually close similarity between diffraction profiles that makes it difficult to determine whether the structures are layered or spinel-like, the data confirm that the preferred structure of the LT-LiCoO2 sample made for this study is one that has a cobalt distribution which is intermediate between an ideal layered and an ideal lithiated spinel structure. On the other hand, refinement of the data of LT-Li0.4CoO2 prepared by reacting LT-LiCoO2 with acid shows, unequivocally, that a spineltype structure is formed. These structures are discussed in relation to previously reported electrochemical data obtained from Li/LT-LiCoO2 cells.

The synthesis of beta alumina from aluminium hydroxide and oxyhydroxide precursors

Abstract Two aluminium oxyhydroxides, boehmite and pseudoboehmite, and two aluminium hydroxides, bayerite and gibbsite, have been investigated as precursors for the synthesis of the solid electrolyte, beta alumina. Reaction pathways and products have been characterized by thermal analysis and powder X-ray diffraction. A solid state reaction model for the formation of β″-Al 2 O 3 is proposed.