Roderick S. McMillan

Lithium-ion cell based on orthorhombic LiMnO2

Abstract This paper will demonstrate that cathodes based on the high temperature form of orthorhombic LiMnO 2 , with the structure described by Hoppe, Brachtel and Jansen, have good capacity and cycle life. X-ray diffraction studies have revealed that cathodes prepared from orthorhombic LiMnO 2 undergo a structural change on being charged beyond a certain potential in which the original structure is converted to spinel Li 1− x Mn 2 O 4 . Orthorhombic LiMnO 2 has been found to have long-term stability in ambient conditions and is easily prepared in a one-step reaction.

Rechargeable cathodes based on Li2CrxMn2−xO4

Abstract Phases in the solid-state solution series Li 2 Cr x Mn 2− x O 4 were prepared as single-phase compounds over the range 0 x 3+ , with a smaller ionic radius, is substituted for Mn 3+ . The X-ray powder diffraction patterns of phases in the range 1.5≤ x 2 , while the diffraction patterns of Li 2 Cr x Mn 2− x O 4 phases over the range 0 x ≤1.25 resemble that of λ-Li 2 Mn 2 O 4 . Selected phases of Li 2 Cr x Mn 2− x O 4 were formed into cathodes and evaluated in lithium-ion cells with petroleum coke-based anodes.

Electrochemistry and structure of Li2-xCryMn2-yO4 phases

The synthesis of phases in the solid state solution series Li 2 Cr y Mn 2-y O 4 where 0 < y < 2 and their use as cathodes in lithium ion cells was reported previously [I.J. Davidson, R.S. McMillan, J.J. Murray, J. Power Sources, 54 (1995) 205-208]. This paper reports the results of electrochemical evaluations with metallic lithium anodes and on Rietveld refinements of X-ray and neutron powder diffraction data for these phases. Although these materials are prepared at moderately high temperatures, the refinements show that they have a structure similar to the monoclinic layered form of LiMnO 2 prepared by soft chemistry at low temperatures by Armstrong and Bruce [A.R. Armstrong, P.G. Bruce, Nature, 381 (1996) 499-500] and by Delmas and Capitaine [C. Delmas, F. Capitaine, Extended Abstracts of the Eighth International Meeting on Lithium Batteries (1996) 470-471]. The degree of monoclinic distortion in the initial materials has an effect on the structural changes that occur on charging. The phases with a small monoclinic distortion change to an undistorted hexagonal structure on their first charge while those with a large monoclinic distortion change to a spinel-like structure on cycling.

Electrochemistry of LiMnO2 over an extended potential range

Abstract A kinetic study of potential versus composition was conducted on orthorhombic LiMnO2 over the voltage range of 1.0 to 4.6 V with a variety of electrolyte formulations. The broad potential range enabled studying the electrochemical behaviour of the material over compositions from LiMnO2 to Li0.1MnO2. Substantial differences in the kinetics of the electrochemical processes associated with certain potential ranges were observed.

Stable form of LiMnO2 as cathode in lithium cell

The invention disclosed relates to a new method of forming spinel-related λ-Li2-x Mn2 O4, wherein 0≦x≦2, solely by electrochemical means with air-stable orthorhombic LiMnO2 as the starting material. This spinel-related material is hydroscopic, metastable and is typically made by chemical means, followed by electrochemical conversion of spinel-type LiMn2 O4. Also disclosed are new secondary lithium ion electrochemical cells employing as initial active cathode material a compound of formula LiMnO2, having a specific orthorhombic crystal structure.