Modeling the Dissolution of Compositionally-Tuned Complex Metal Oxides from First Principles
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1
University of Iowa, United States
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2
University of Wisconsin-Madison, United States
Compositional tuning of nanoscale complex metal oxides (CMOs) can lead to enhanced performance for a variety of energy storage and production applications such as catalysts, electrochemical capacitors and fuel cells. However, what has been less studied is how these materials are transformed by the environment, and what the subsequent biological impact is. Investigations of the nanoscale CMOs in Li-ion batteries demonstrate that dissolution of these materials releases toxic metal cations that go on to adversely affect various organisms. Our study aims to address the current knowledge gap between nanomaterial design and environmental impact. We use density functional theory (DFT) methods to investigate the interplay of redox properties, oxidation state, and coordination environment of a compositionally-tuned family of CMOs of formula Lix(NiyMnzCo1-y-z)O2 (NMC). We then use electronic structure calculations, coupled with thermodynamics modeling, to predict the free energy of surface cation release for a range of Delafossite structure type CMOs with variable amounts of Ni, Co, and Mn, focused on Mn enriched compositions of NMC. We calibrate our model approach against experimental trends for incongruent dissolution as reported in the literature, and go on to delineate trends in the predicted dissolution energetics in terms of the physiochemical properties of NMC, as well as the chemical environment of the exposed solution phase. We find that the oxidation states of transition metals Ni and Co are nearly constant as a function of CMO composition, while Mn can exist in either 2+ or 4+ oxidation states. The ratio of 2+/4+ Mn cations is influenced by the identity of the nearest neighbor metals in the Delafossite structure type. The dissolution predictions show that Mn-rich compositions are inherently more prone to Mn release, and the driving force for this behavior is attributed to the varying oxidation states present in these stoichiometries. We go on to culminate our theoretical results to cast new design principles to guide the discovery of functional CMOs that are more "benign by design."
Acknowledgements
This work was supported by National Science Foundation Center under the Center for Sustainable Nanotechnology, CHE-1503408. The CSN is part of the Centers for Chemical Innovation Program. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562 through allocation ID TG-GEO160006.
Keywords:
DFT+ thermodynamics,
Sustainable nanotechnology,
Compositional tuning,
Electronic band structure,
Complex metal oxide
Conference:
National Organization for the Professional Advancement of Black Chemists and Chemical Engineers (NOBCChE) 45th Annual Conference , Orlando, Florida, United States, 17 Sep - 20 Sep, 2018.
Presentation Type:
Oral Presentation
Topic:
Computational Chemistry
Citation:
Jones
DT,
Bennett
JW,
Hamers
RJ and
Mason
SE
(2019). Modeling the Dissolution of Compositionally-Tuned Complex Metal Oxides from First Principles.
Front. Chem.
Conference Abstract:
National Organization for the Professional Advancement of Black Chemists and Chemical Engineers (NOBCChE) 45th Annual Conference .
doi: 10.3389/conf.fchem.2018.01.00022
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Received:
08 Oct 2018;
Published Online:
17 Jan 2019.
*
Correspondence:
Prof. Sara E Mason, University of Iowa, Iowa City, United States, sara-mason@uiowa.edu