Abstract
This work presents findings on the mechanisms of hysteresis in lithium-rich cathode oxides. It is generally reported that the energy inefficiency, observed during electrochemical cycling of Li-rich electrodes, is a direct result of anion redox processes. Similarly, the coupled phenomenon of cation migration has been cited as being a mere consequence of that process with no essential ramification to hysteresis. Such works, however, have only shown correlations and not causation. Specifically, studies that clearly preclude the complete absence of either anion redox or cation migration (down to defect-level concentrations) are not reported yet. Herein, we present first principles calculations and experimental data on a bespoke Li-rich system that is indubitably immune to oxygen activity but yet exhibits significant energy inefficiency. Additionally, the results directly implicate transition metal migration as the fundamental, sole process responsible for hysteresis in this material. This study is of particular importance to the design and development of new Li-rich materials aimed at eliminating the role of oxygen and enhancing the effective cationic redox contribution to the capacity and points out the essential need to develop materials devoid of transition metal migration to interstitial sites in both layered and disordered oxides alike.
| Original language | English |
|---|---|
| Article number | 228335 |
| Journal | Journal of Power Sources |
| Volume | 471 |
| DOIs | |
| State | Published - Sep 30 2020 |
Funding
Cathode powders of nominal composition 0.5Li2TiO3•0.5LiCrO2 (Li1.2Ti0.4Cr0.4O2) were synthesized from appropriate mixtures of TiO2, Cr2O3, and Li2CO3. TiO2 and Cr2O3 were thoroughly mixed and annealed at 550 °C in air for 12 h. Subsequently, the annealed product was mixed with Li2CO3 and annealed at 850 °C in air for 36 h followed by a final washing/filtering and drying (~100 °C). For electrode preparation, the finished, lithiated oxide was ground and sieved (<150 μm) and cast as a slurry on an aluminum current collector with oxide:carbon:binder (PVDF) percentages of 78:15:7. Electrodes were punched from the laminate with a diameter of 9/16″ and assembled against lithium-metal anodes. Operando pouch cells were assembled at Argonne's Cell Analysis, Modeling, and Prototyping facility (CAMP) as shown in the supporting information, Figs. S1(a) and (b). Cycling was done at room temperature using 1.2 M LiPF6 (EC:EMC, 3:7 b y wt.) electrolyte at a rate of 9 mA⋅g-1 for beamline pouch cells and 10 mA⋅g-1 for coin-cells.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 Canadian Light Source and its funding partners. The pouch cells were produced at the U.S. Department of Energy's (DOE) CAMP (Cell Analysis, Modeling and Prototyping) Facility, Argonne National Laboratory. This research also used the computer facilities of LCRC at Argonne National Laboratory. Support from the U.S. Department of Energy's Vehicle Technologies Program (DOE-VTP), specifically from Peter Faguy and Dave Howell, 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. 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 Canadian Light Source and its funding partners. The pouch cells were produced at the U.S. Department of Energy's (DOE) CAMP (Cell Analysis, Modeling and Prototyping) Facility, Argonne National Laboratory. This research also used the computer facilities of LCRC at Argonne National Laboratory. Support from the U.S. Department of Energy's Vehicle Technologies Program ( DOE -VTP), specifically from Peter Faguy and Dave Howell, 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.
Keywords
- Anion redox
- DFT
- Disordered rock salt
- Hysteresis
- Lithium rich
- Oxygen redox
- XAFS
- XANES
- XAS