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 LiNi_0.8Co_0.15Al_0.05O₂ (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

1. Z.H. Lu, J.R. Dahn, J. Electrochem. Soc. 149, A815 (2002).
2. M.M. Thackeray, C.S. Johnson, J.T. Vaughey, N. Li, S.A. Hackney, J. Mater. Chem. 15, 2257 (2005).
3. P. G. Bruce, A. R. Armstrong, R. L. Gitzendanner, J. Mater. Chem. 9, 193 (1999).
4. M.M. Thackeray, S.-H. Kang, C.S. Johnson, J.T. Vaughey, R. Benedek, S.A. Hackney, J. Mater. Chem. 17, 3112 (2007).
5. J. E. Post, Proc. Natl. Acad. Sci. USA, 96, 3447 (1999).
6. 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.