Recent reports have indicated that a manganese oxide spinel component, when embedded in a relatively small concentration in layered xLiMnO●(1-x)LiMO (M=Ni, Mn, Co) electrode systems, can act as a stabilizer that increases their capacity, rate capability, cycle life, and first-cycle efficiency. These findings prompted us to explore the possibility of exploiting lithiated cobalt oxide spinel stabilizers by taking advantage of (1) the low mobility of cobalt ions relative to manganese and nickel ions in close-packed oxides and (2) their higher potential (~3.6 V vs. Li) relative to manganese oxide spinels (~2.9 V vs. Li) for the spinel-to-lithiated spinel electrochemical reaction. In particular, we have revisited the structural and electrochemical properties of lithiated spinels in the LiCoNiO (0≤x≤0.2) system, first reported almost 25 years ago, by means of high-resolution (synchrotron) X-ray diffraction, transmission electron microscopy, nuclear magnetic resonance spectroscopy, electrochemical cell tests, and theoretical calculations. The results provide a deeper understanding of the complexity of intergrown layered/lithiated spinel LiCoNiO structures, when prepared in air between 400 and 800 °C, and the impact of structural variations on their electrochemical behavior. These structures, when used in low concentration, offer the possibility of improving the cycling stability, energy, and power of high energy (≥3.5 V) lithium-ion cells.

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. References C. S. Johnson, N. Li, J. T. Vaughey, S. A. Hackney, M. M. Thackeray, Electrochem. Commun., 7, 528 (2005). D. Kim, G. Sandi, J. R. Croy, K. G. Gallagher, S.-H. Kang, E. Lee, M. D. Slater, C. S. Johnson, M. Thackeray, J. Electrochem. Soc., 160, A31 (2013). B. R. Long, J. R. Croy, J. S. Park, J. Wen, D. J. Miller, M. M. Thackeray, J. Electrochem. Soc, 161, A2160 (2014) R. J. Gummow, M. M. Thackeray, W. I. F. David and S. Hull, Materials Research Bulletin, 27, 327 (1992). R. J. Gummow and M. M. Thackeray, Solid State Ionics, 53, 681 (1992). 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. The submitted document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Of the three categories of cathode materials that dominate today’s lithium-ion battery industry, i.e., those with layered, spinel and olivine-type structures, layered lithium-metal-oxide systems remain the most attractive category for providing high energy densities.  Although LiCoO2 (LCO) and LiNi0.8Co0.15Al0.05O2 (NCA) remain attractive electrodes for portable consumer electronics devices and heavier duty applications (e.g., transportation), they suffer from structural and chemical instabilities at high charging potentials that limit the practical energy output of the cells.  While spinel lithium-manganese-oxide (LMO) and olivine lithium-iron-phosphate (LFP) electrodes provide superior thermal stability over layered LCO and NCA electrodes, they are disadvantaged by their low theoretical specific capacity and low packing densities, respectively, relative to the best layered systems.  The discovery that layered lithium- and manganese-rich metal oxide electrode structures, derived from the incorporation of a Li2MnO3 component, can deliver their theoretical capacity (250-260 mAh/g) [1, 2], albeit at relatively low current rates when charged continuously above 4.5 V, has resulted in worldwide efforts to bring these electrodes to the market.  Despite this advance, these lithium- and manganese-rich electrodes lack structural instability when cycled, which is not surprising given that layered-LiMnO2transforms to a spinel-type structure during repeated charge and discharge [3]. This presentation will report on recent approaches and efforts at Argonne National Laboratory to design stabilized high capacity electrode materials by exploring the phase space of structurally-integrated lithium-metal-oxide materials through a combination of processing, compositional, structural, electrochemical and theoretical studies.  The concept of designing structurally-integrated electrodes for lithium-ion cells was sparked by the existence of composite structures such as gamma-MnO2, which has been used prolifically over the years in LeClanché dry cells and alkaline cells [4].  Gamma-MnO2 occurs in nature [5] and can also be made synthetically by chemical or electrochemical methods [6]; its structure is comprised of a predominant electroactive-active component, ramsdellite-MnO2, integrated with a beta-MnO2 (rutile-type) component that is significantly less reactive to lithium uptake and provides stability to the overall electrode structure. References Z.H. Lu, J.R. Dahn, J. Electrochem. Soc. 149, A815 (2002). M.M. Thackeray, C.S. Johnson, J.T. Vaughey, N. Li, S.A. Hackney, J. Mater. Chem. 15, 2257 (2005). P. G. Bruce, A. R. Armstrong, R. L. Gitzendanner, J. Mater. Chem. 9, 193 (1999). M.M. Thackeray, S.-H. Kang, C.S. Johnson, J.T. Vaughey, R. Benedek, S.A. Hackney, J. Mater. Chem. 17, 3112 (2007). J. E. Post, Proc. Natl. Acad. Sci. USA, 96, 3447 (1999). Y. Chabre and J. Pannetier, Prog. Solid St. Chem.  23, l (1995). Acknowledgments Funding for this work from the Office of Vehicle Technologies of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, is gratefully acknowledged. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.