Department of Chemistry , University of Iowa , Iowa City , Iowa 52242 , United States.
Department of Chemistry , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States.
Inorg Chem. 2018 Nov 5;57(21):13300-13311. doi: 10.1021/acs.inorgchem.8b01855. Epub 2018 Oct 16.
Compositional tuning of nanoscale complex metal oxides (CMOs) can lead to enhanced performance and favorable properties for a variety of energy-related applications. However, investigations of the nanoscale CMOs used in energy storage technologies demonstrate that these nanomaterials may have an adverse biological impact, highlighting a fundamental knowledge gap between nanomaterial design and the structure and properties at the end of life. CMO nanomaterials can enter the environment due to improper disposal, where they undergo subsequent (as of yet poorly understood) nanoscale transformations that may affect biological response and, ultimately, environmental fate. This points to the need for studies at the nano-bio interface that can be used to shape rules for the redesign of CMOs: materials that are are potentially more benign by design and serve as examples of sustainable nanotechnology. The example given here is to enrich lithium nickel manganese cobalt oxide, Li (Ni Mn Co)O (NMC), with Mn to create a family of materials that are less expensive and potentially less toxic to a wide range of organisms. In this paper, we investigate the structure and electronic states of Mn-rich NMC at the density functional theory (DFT) level to elucidate the interplay of redox properties, oxidation state, and coordination environment of a compositionally tuned CMO. We find that the oxidation states of Ni and Co remain mostly unaffected while Mn exists as both Mn and Mn. Our models show that the ratio of Mn and Mn varies with changes in the coordination environment, such as the identity of neighboring atoms and surface OH group coverage. The surface metal release properties of Mn-rich NMC compositions are predicted using a DFT + solvent ion model and show that Mn-rich NMC compositions are inherently more prone to dissolution than NMC and that this is attributed to the changes in oxidation state of the transition metals in Mn-rich NMC.
纳米级复合金属氧化物（CMO）的组成调谐可以提高各种与能源相关应用的性能和有利特性。然而，用于能量存储技术的纳米级 CMO 的研究表明，这些纳米材料可能具有不良的生物影响，突出了纳米材料设计与生命末期的结构和特性之间的基本知识差距。由于处理不当，CMO 纳米材料可能会进入环境，在那里它们会经历随后（目前还不太了解）的纳米级转变，这可能会影响生物反应，并最终影响环境命运。这表明需要在纳米-生物界面进行研究，以便为 CMO 的重新设计制定规则：这些材料在设计上更具良性，可以作为可持续纳米技术的范例。这里给出的示例是用 Mn 来富化锂镍锰钴氧化物 Li（Ni Mn Co）O（NMC），以形成一系列材料，这些材料更便宜，对广泛的生物体潜在毒性更小。在本文中，我们在密度泛函理论（DFT）水平上研究了富 Mn 的 NMC 的结构和电子态，以阐明组成调谐的 CMO 的氧化还原性质、氧化态和配位环境的相互作用。我们发现 Ni 和 Co 的氧化态基本保持不变，而 Mn 既存在于 Mn 中，也存在于 Mn 中。我们的模型表明，Mn 和 Mn 的比例随配位环境的变化而变化，例如相邻原子的身份和表面 OH 基团的覆盖。使用 DFT +溶剂离子模型预测了富 Mn 的 NMC 组成的表面金属释放特性，结果表明富 Mn 的 NMC 组成比 NMC 更容易溶解，这归因于富 Mn 的 NMC 中过渡金属氧化态的变化。
