Hollandite α-MnO₂, with an open tunnel structure, is of interest as a cathode material for 3 V lithium batteries [1,2] and as an electrocatalyst for Li-O₂ cells [3]. We recently proposed [4] that α-MnO₂ belong to a class of materials that can be used as the cathode in hybrid Li-ion/Li-oxygen battery systems, which can incorporate/release both lithium and oxygen during cycling with redox reactions occurring on both the transition metal ions and oxygen ions of the electrode. In this talk, we will present in-situ and operando characterization and first principles modeling results of α-MnO₂ during electrochemical cycling in conventional lithium cells and in Li-O₂ cells [5,6]. Operando synchrotron x-ray diffraction (XRD) results, combined with first principles density functional theory (DFT) modeling, indicate insertion of lithium and oxygen into, as well as partial removal of these species from, the tunnel structure during cycling. On heating hydrated α-MnO₂, in-situ XRD and Raman studies provide information about structural changes and diffusional properties of the oxygen species in the tunnel structure. DFT studies find low diffusion barriers for H₂O and H₃O⁺species in the tunnel. The implications of the results on other high-capacity, hybrid Li-ion/Li-oxygen materials will be discussed.

Acknowledgements

This work was supported as a part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences under award number DE-AC02–06CH11. Use of the Advanced Photon Source, a US DOE Office of Science User Facility operated by Argonne National Laboratory, was supported by DOE under Contract No. DE-AC02-06CH11357. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

References

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[2]  C. S. Johnson, D. W. Dees, M. F. Mansuetto, M. M. Thackeray, D. R. Vissers, D. Argyriou, C.-K Loong and L. Christensen, “Structural and Electrochemical Studies of a-MnO₂”, J. Power Sources, 68/2, 570 (1997).

[3] A. Debart, A. J. Paterson, J. Bao and P. G. Bruce, “a-MnO₂ Nanowires: A Catalyst for the O₂ Electrode in Rechargeable Lithium Batteries,” Angew. Chem. Int. Ed., 47, 4521 (2008).

[4]  M. M. Thackeray, M. K. Y. Chan, L. Trahey, S. Kirklin, and C. Wolverton, “Vision for Designing High-Energy, Hybrid Li Ion/Li-O₂ Cells,” Journal of Physical Chemistry Letters 4, 3607 (2013).

[5] L. Trahey, N. Karan, M. K. Y. Chan, J. Lu, Y. Ren, J. P. Greeley, M. Balasubramanian, A. K. Burrell, and M. M. Thackeray, “Synthesis, Characterization and Structural Modeling of High Capacity, Dual-Functioning MnO₂ Electrode/Electrocatalysts for Li-O₂ Batteries,” Advanced Energy Materials 3, 75 (2013).

[6] Yang, L. Trahey, Y. Ren, M. K. Y. Chan, C. Lin, J. Okasinski, and M. M. Thackeray, “In-Situ High-Energy Synchrotron X-ray Diffraction Studies and First Principles Modeling of α-MnO₂ Electrodes in Li-O₂ and Li-ion Coin Cells,” Journal of Materials Chemistry A 3, 7389 (2015).

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