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Complex metal oxides (CMOs) are used broadly in applications including electroreactive forms found in lithium-ion battery technology. Computational chemistry can provide unique information about how the properties of CMO cathode materials change in response to changes in stoichiometry, for example, changes of the lithium (Li) content during the charge–discharge cycle of the battery. However, this is difficult to measure experimentally due to the small cross-sectional area of the cations. Outside of operational conditions, the Li content can influence the transformations of the CMO when exposed to the environment. For example, metal release from CMOs in aqueous settings has been identified as a cross-cutting mechanism important to CMO degradation. Computational studies investigating metal release from CMOs show that the thermodynamics depend on the oxidation states of lattice cations, which is expected to vary with the lithium content. In this work, computational studies track changes in metal release trends as a function of Li content in Lix(Ni1/3Mn1/3Co1/3)O2 (NMC). The resulting dataset is used to construct a random forest tree (RFT) machine learning (ML) model. A modeling challenge in delithiation studies is the large configurational space to sample. Through investigating multiple configurations at each lithium fraction, we find structural features associated with favorable energies to chemically guide the identification of relevant structures and adequately predict voltage values.
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Emerging investigator series: first-principles and thermodynamics comparison of compositionally-tuned delafossites: cation release from the (001) surface of complex metal oxides
Nanoscale complex metal oxides have transformed how technology is used around the world. A ubiquitous example is the class of electroreactive cathodes used in Li-ion batteries, found in portable electronics and electric cars. Lack of recycling infrastructure and financial drivers contribute to improper disposal, and ultimately, introduction of these materials into the environment. Outside of sealed operational conditions, it has been demonstrated that complex metal oxides can transform in the environment, and cause negative biological impact through leaching of cations into aqueous phases. Using a combined DFT and thermodynamics methodology, insights into the mechanism and driving forces of cation release can be studied at the molecular-level. Here, we describe design principles that can be drawn from previous collaborative research on complex metal oxide dissolution of the Li(Ni y Mn z Co 1−y−z )O 2 family of materials, and go on to posit ternary complex metal oxides in the delafossite structure type with controlled release behavior. Using equistoichiometric formulations in the delfossite structure, we use DFT and thermodynamics to model cation release. The release trends are discussed in terms of lattice stability, solution chemistry/solubility limits, and electronic/magnetic properties. Intercalation voltages are calculated and discussed as a predictive metric for potential functionality of the model materials.
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- Award ID(s):
- 1503408
- PAR ID:
- 10198606
- Date Published:
- Journal Name:
- Environmental Science: Nano
- Volume:
- 7
- Issue:
- 6
- ISSN:
- 2051-8153
- Page Range / eLocation ID:
- 1642 to 1651
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Developing a materials perspective of how to control the degradation and negative impact of complex metal oxides requires an integrated understanding of how these nanomaterials transform in the environment and interact with biological systems. Doping with aluminum is known to stabilize oxide materials, but has not been assessed cohesively from synthesis to environmental fate and biological impact. In the present study, the influence of aluminum doping on metal ion release from transition metal oxides was investigated by comparing aqueous transformations of lithium nickel cobalt aluminum oxide (LiNi0.82Co0.15Al0.03O2; NCA) and lithium nickel cobalt oxide (LiNi0.80Co0.20O2; NC) nanoparticles and by calculating the energetics of metal release using a density functional theory (DFT) and thermodynamics method. Two model environmental organisms were used to assess biological impact, and metal ion release was compared for NCA and NC nanoparticles incubated in their respective growth media: moderately hard reconstituted water (MHRW) for the freshwater invertebrate Daphnia magna (D. magna) and minimal growth medium for the Gram-negative bacterium Shewanella oneidensis MR-1 (S. oneidensis). The amount of metal ions released was reduced for NCA compared to NC in MHRW, which correlated to changes in the modeled energetics of release upon Al substitution in the lattice. In minimal medium, metal ion release was approximately an order of magnitude higher compared to MHRW and was similar to the stoichiometry of the bulk nanoparticles for both NCA and NC. Interpretation of the release profiles and modeling indicated that the increase in total metal ion release and the reduced influence of Al doping arises from lactate complexation of metal ions in solution. The relative biological impacts of NC and NCA exposure for both S. oneidensis and D. magna were consistent with the metal release trends observed for minimal medium and MHRW, respectively. Together, these results demonstrate how a combined experimental and computational approach provides valuable insight into the aqueous transformations and biological impacts of complex metal oxide nanoparticles.more » « less
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Abstract Phase formation in multicomponent rare‐earth oxides is determined by a combination of composition, sintering atmosphere, and cooling rate. Polycrystalline ceramics comprising various combinations of Ce, Gd, La, Nd, Pr, Sm, and Y oxides in equiatomic proportions were synthesized using solid‐state sintering. The effects of composition, sintering atmosphere, and cooling rate on phase formation were investigated. Single cubic or monoclinic structures were obtained with a slow cooling of 3.3°C/min, confirming that rare‐earth oxides follow a different structure stabilization process than transition metal high‐entropy oxides. In an oxidizing atmosphere, both Ce and Pr induce a cubic structure, while only Ce plays that role in an inert or reducing atmosphere. Samples without Ce or Pr develop a single monoclinic structure. The structures formed at initial synthesis may be converted to a different one, when the ceramics are annealed in an additional atmosphere. Phase evolution of a five‐cation composition was also studied as a function of sintering temperature. The binary oxides used as raw materials completely dissolve into a single cubic structure at 1450°C in air.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9EN01304K
