Abstract
The large-voltage hysteresis remains one of the biggest barriers to optimizing Li/Na-ion cathodes using lattice anionic redox reaction, despite their very high energy density and relative low cost. Very recently, a layered sodium cathode Na2Mn3O7 (or Na4/7Mn6/7□1/7O2, □ is vacancy) was reported to have reversible lattice oxygen redox with much suppressed voltage hysteresis. However, the structural and electronic structural origin of this small-voltage hysteresis has not been well understood. In this article, through systematic studies using ex situ/in situ electron paramagnetic resonance and X-ray diffraction, we demonstrate that the exceptional small-voltage hysteresis (<50 mV) between charge and discharge curves is rooted in the well-maintained oxygen stacking sequence in the absence of irreversible gliding of oxygen layers and cation migration from the transition-metal layers. In addition, we further identify that the 4.2 V charge/discharge plateau is associated with a zero-strain (de)intercalation process of Na+ ions from distorted octahedral sites, while the 4.5 V plateau is linked to a reversible shrink/expansion process of the manganese-site vacancy during (de)intercalation of Na+ ions at distorted prismatic sites. It is expected that these findings will inspire further exploration of new cathode materials that can achieve both high energy density and efficiency by using lattice anionic redox.
| Original language | English |
|---|---|
| Pages (from-to) | 3756-3765 |
| Number of pages | 10 |
| Journal | Chemistry of Materials |
| Volume | 31 |
| Issue number | 10 |
| DOIs | |
| State | Published - May 28 2019 |
| Externally published | Yes |
Funding
This research is primarily supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Early Career Research Program award KC040602, under contract number DE-AC05-00OR22725. Research conducted at the NOMAD beamline at ORNL’s Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Sciences, U.S. Department of Energy. All EPR measurements were performed at the NHMFL, which is supported by National Science Foundation Cooperative agreement nos. DMR-1157490 and DMR-1644779. E.H., Z.S., and X.-Q.Y. were supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office of the U.S. DOE through the Advanced Battery Materials Research (BMR) Program, including Battery500 consortium under contract DE-SC0012704. J.N. was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office (VTO). This research used beamline ISS 8-ID of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. Electron microscopy work was performed at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, which is a U.S. DOE Office of Science User Facility (M.C. & X.L.). N.D.P., G.M.V., M.C., and X.L. were supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. This research used 11-BM, 11-ID-B beamline and electrochemistry laboratory resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357.