Rosalind J. Gummow

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).

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.

Ramsdellite-MnO2 for lithium batteries: the ramsdellite to spinel transformation

A pure and highly crystalline form of ramsdellite-MnO2 has been synthesized by acid treatment of the spinels LiMn2O4 and Li2Mn4O9 at 95°C. Although the ramsdellite—MnO2 framework remains intact on lithiation at 70°C, the hexagonally-close-packed oxygen array buckles towards a cubic-close-packed structure to accommodate the inserted lithium ions. The reaction is reversible but the instability of the structure on cycling limits the utility of ramsdellite-MnO2 as a rechargeable electrode in lithium cells. The ramsdellite structure can be stabilized by reaction with LiOH or LiNO3 at 300–400°C; this reaction, which displaces manganese ions from the MnO2 framework into interstitial octahedral sites generates spinel-related domains that coexist with the lithiated ramsdellite phase. At 300°C, under vacuum, the lithiated ramsdellite phase Li0.5MnO2 transforms to the spinel LiMn2O4; at 300–400°C, in air, it oxidizes slowly and transforms to a defect spinel LiMn2O4+δ (0 < δ ⩽ 0.5) via an intermediate compound. A mechanism for the ramsdellite—spinel transition is proposed.

Characterization of LT ‐ Li x Co1 − y Ni y O 2 Electrodes for Rechargeable Lithium Cells

LT-LiCo{sub 0.9}Ni{sub 0.1}O{sub 2} prepared at 400 C with a structure that is intermediate between an ideal lithiated spinel and a layered structure has been investigated as an electrode in rechargeable lithium cells; it delivers a voltage vs. pure lithium that is significantly lower than the voltage provided by its high-temperature analogue, HT-LiCo{sub 0.9}Ni{sub 0.1}O{sub 2}, (synthesized at 900 C). The rechargeability of Li/LT-LiCo{sub 0.9}Ni{sub 0.1}O{sub 2} cells can be improved by leaching some lithium and a small amount of cobalt performance is attributed to the formation of a defect spinel phase Li{sub 0.8}[Co{sub 1.6}Ni{sub 0.2}]O{sub 4} in which the lithium ions adopt the tetrahedral A sites and the cobalt and nickel ions the B sites of an A[B{sub 2}]O{sub 4} spinel.

The versatility of MnO2 for lithium battery applications

Manganese dioxide has for many years found widespread use as a cathode material in aqueous Leclanche, zinc chloride and alkaline cells and, more recently, in nonaqueous lithium cells. However, despite the large number of polymorphic structures that exist in the manganese dioxide family, the battery industry has used y-MnOz exclusively as the positive electrode in these cells. With the advent of rechargeable lithium battery technology, research efforts have demonstrated that other MnO, structures, when processed in the correct way, provide attractive electrochemical properties for lithium cells. In this paper, some recent advances that have been made in MnOz materials technology are discussed, for example, in the development of cr-MnOz, layered-MnO,, spine]-related L&O -yMnO* 01.2.5) and ramsdellite-MnO, materials. An attempt has been made to clarify issues relating to the structural features of ‘CDMO’-type materials that are prepared by the reaction of r_MnO, with LiNOB (or LiOH) at 300400 “C.

Lithium-cobalt-nickel-oxide cathode materials prepared at 400°C for rechargeable lithium batteries

A series of compounds LiCo1−xNixO2 (0⩽x⩽1) has been synthesised at 400°C. For x⩽0.2, the products are es sentially single phase and have a cubic-close-packed oxygen-ion lattice. When used as cathodes in lithium cells these compounds discharge most of their capacity at a significantly lower voltage (3.8–3.3 V) than a standard LiCoO2 electrode synthesised at 900°C (4.4–3.8 V). The capacities obtained from nickel-doped electrodes are significantly higher than those obtained from LiCoO2 electrodes prepared at 400°C.

The effect of multivalent cation dopants on lithium manganese spinel cathodes

The cycling stability of 4 V Li ,Mn,O, electrodes in lithium. flooded electrolyte glass cells has been improved by the addition of multivalent cation dopants (Mg’+. Zn’+ and Al’+ ). Optimal dopant levelx to achieve maximum capacity and the greatest stability with repeated cycling have been determined. The effect of doping the oxygen-rich spine1 Li,Mn,O, was also determined and shown to make