Abstract
The recent discovery of Li-excess cation-disordered rock salt cathodes has greatly enlarged the design space of Li-ion cathode materials. Evidence of facile lattice fluorine substitution for oxygen has further provided an important strategy to enhance the cycling performance of this class of materials. Here, a group of Mn3+–Nb5+-based cation-disordered oxyfluorides, Li1.2Mn3+ 0.6+0.5 xNb5+ 0.2−0.5 xO2− xFx (x = 0, 0.05, 0.1, 0.15, 0.2) is investigated and it is found that fluorination improves capacity retention in a very significant way. Combining spectroscopic methods and ab initio calculations, it is demonstrated that the increased transition-metal redox (Mn3+/Mn4+) capacity that can be accommodated upon fluorination reduces reliance on oxygen redox and leads to less oxygen loss, as evidenced by differential electrochemical mass spectroscopy measurements. Furthermore, it is found that fluorine substitution also decreases the Mn3+-induced Jahn–Teller distortion, leading to an orbital rearrangement that further increases the contribution of Mn-redox capacity to the overall capacity.
| Original language | English |
|---|---|
| Article number | 1802959 |
| Journal | Advanced Energy Materials |
| Volume | 9 |
| Issue number | 2 |
| DOIs | |
| State | Published - Jan 10 2019 |
Funding
This work was supported by the Umicore Specialty Oxides and Chemicals, and the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office, of the U.S. Department of Energy under Contract No. DEAC02-05CH11231, under the Advanced Battery Materials Research (BMR) Program. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors would like to acknowledge Dr. Jerry Hu and the California NanoSystems Institute (CNSI) at the University of California Santa Barbara (UCSB) for experimental time on the 500 MHz NMR spectrometer. The NMR experimental work reported here made use of the shared facilities of the UCSB MRSEC (Grant No. NSF DMR 1720256), a member of the Material Research Facilities Network. This research used resources of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, and was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. The authors thank Jingyang Wang for help of the XAS measurement. The computational analysis was performed using computational resources sponsored by the Department of Energy’s Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory, computational resources provided by Extreme Science and Engineering Discovery Environment (XSEDE), which was supported by the National Science Foundation Grant Number ACI1053575, as well as the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by the Office of Science and the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.The authors thank Dr. Huiwen Ji, Dr. Deok-Hwang Kwon, and Dr. Hyunchul Kim for helpful discussion. This work was supported by the Umicore Specialty Oxides and Chemicals, and the Assistant Secretary for Energy Efficiency and Renewable Energy, Vehicle Technologies Office, of the U.S. Department of Energy under Contract No. DEAC02-05CH11231, under the Advanced Battery Materials Research (BMR) Program. Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The authors would like to acknowledge Dr. Jerry Hu and the California NanoSystems Institute (CNSI) at the University of California Santa Barbara (UCSB) for experimental time on the 500 MHz NMR spectrometer. The NMR experimental work reported here made use of the shared facilities of the UCSB MRSEC (Grant No. NSF DMR 1720256), a member of the Material Research Facilities Network. This research used resources of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, and was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. The authors thank Jingyang Wang for help of the XAS measurement. The computational analysis was performed using computational resources sponsored by the Department of Energy's Office of Energy Efficiency and Renewable Energy and located at the National Renewable Energy Laboratory, computational resources provided by Extreme Science and Engineering Discovery Environment (XSEDE), which was supported by the National Science Foundation Grant Number ACI1053575, as well as the National Energy Research Scientific Computing Center (NERSC), a DOE Office of Science User Facility supported by the Office of Science and the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.The authors thank Dr. Huiwen Ji, Dr. Deok-Hwang Kwon, and Dr. Hyunchul Kim for helpful discussion. Z.L. planned the project with J.L. and G.C.; Z.L. designed, synthesized, characterized (XRD), and electrochemically tested the proposed compounds with the help from J.L.; B.O. and D.A.K. performed DFT calculations and analyzed the data; R.J.C. acquired and analyzed the NMR data; J.K.P. acquired and analyzed DEMS data with input from B.D.M.; Z.L. acquired and analyzed the XAS data with the help from M.B.; Y.T. acquired and analyzed the XPS data; T.L. acquired and analyzed the TEM data; T.S. performed SEM. The paper was written by Z.L. and was revised by B.O., R.J.C., and G.C. with the help of other authors. All authors contributed to discussions.
Keywords
- DFT
- Jahn–Teller distortion
- Li-excess cation-disordered cathodes
- cyclability
- fluorination