Structure and Electrochemistry of Lithium-Cobalt-Oxide Spinels and Their Role in 'layered-Spinel' Composite Cathodes
Authors: Lee Eungje , Blauwkamp Joel D. , Park Joong Sun , Wu Jinsong , Dogan Fulya , Benedek Roy , Croy Jason R. , Dravid Vinayak , Thackeray Michael M. 
Published: February 2020

Introducing a spinel component into layered (LiMO2) or ‘layered-layered’ (Li2MnO3•LiMO2, typically M = Ni, Mn, Co) materials to form structurally integrated ‘layered-spinel’(LS) or ‘layered-layeredspinel’(LLS) materials has been demonstrated as a promising strategy to develop new cathode systems with enhanced electrochemical capacity and stability.[1-3] The rationale behind this approach is that 25% of the transition metal cations in the spinel component are located in the lithium-rich layers, thereby providing significant binding energy between the close-packed oxygen layers to maintain good stability at low lithium levels during the charging process. It is anticipated that these stabilizing M cations in the lithium layers, even in low concentrations, may contribute significantly to the performance of LS and LLS composite materials. However, relative to the extensive understanding of manganese-based spinel materials, little is known about the structural and electrochemical properties of lithium-cobalt-oxide (and nickel-substituted) spinel electrodes that can be synthesized in their discharged state, i.e., LiCo1-yNiyO2 (0≤y≤0.2), typically at about 400 °C;[4,5] These cobalt-based spinel electrodes, referred to as ‘lowtemperature’ LiCo1-yNiyO2 materials in the literature, have two notable advantages over lithiummanganese- oxide spinels: (1) lithium extraction from the lithiated spinel composition, LiCo1-yNiyO2, to the spinel composition, Li0.5Co1-yNiyO2 (or LiCo2-2yNi2yO4), occurs at a higher potential against lithium (~3.6V vs. 2.9V), and (2) a lower propensity for cobalt migration during the electrochemical reactions, particularly at high potentials, i.e., >4V, may be expected. This presentation will report on the structural and electrochemical properties of a series of Li2[Co1-x-yNixMny]2O4spinel materials, prepared by a ‘low-temperature’ solid-state synthesis route. The transition metal composition and synthesis conditions strongly affect the structure of these materials, and thereby their electrochemical properties. Efforts to integrate these spinel compositions into layered or ‘layered-layered’ electrode materials will be discussed.

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Acknowledgment

Support from the Vehicle Technologies Program, Hybrid and Electric Systems, in particular, David Howell, Peter Faguy, and Tien Duong at the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, is gratefully acknowledged.
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