Collaborative Research: Understanding Relationships Between Synthesis, Structure, Solid-State Electrochemistry, and Phase Stability in Clathrates and Related Materials

非技术描述：笼状物是一类具有笼状结构的材料，可以自然地容纳客体离子，这一特征可用于可充电电池的能量存储。然而，还需要更多的研究来了解笼合物的结构如何影响离子迁移和材料在反复电化学循环下的耐久性。通过这项由美国国家科学基金会材料研究部固体和材料化学项目支持的合作项目，亚利桑那州立大学和特拉华大学的研究人员共同确定了促进快速离子扩散的笼状化合物的结构特征，并开发了合成这些材料的新方法。因此，他们收集了将笼状化合物和相关化合物的结构效应与其物理、电化学和材料化学性质联系起来的新知识。从这些研究中获得的基础科学可能会在这些材料具有潜在应用的其他领域产生深远的影响，如超导体、热电学、光电子学、磁体和光伏。此外，两所大学和三个不同的系(材料科学、化学和物理)之间的这种合作使学生接触到多学科的研究。外联和教育活动还使学生参与，并提供跨学科培训，使他们沉浸在其直接专长领域以外的领域。技术描述：该合作项目由NSF材料研究部的固态和材料化学计划支持，确定了导致快速离子扩散的结构特征，并更好地了解了Li-Tetrel(TT)系统中的电化学驱动相变，特别是对于笼状和其他开放框架结构。这项研究的具体目标是：(1)了解TT(TT=Si，Ge，Sn)笼状和具有高离子迁移率的笼状材料的结构参数空间；(2)重新绘制Li-TT系统的相空间图，包括非平衡相，并研究这些相中的离子传输；以及(3)使用电化学来为固相合成提供信息，反之亦然，以实现笼状化合物和相关材料的新的合成方法，这些材料要么是锂离子途径的中间体，要么可以作为合成步骤的前体。通过一种结合了PI的合成、结构和电化学表征以及理论专业知识的协调方法，这项工作进一步加深了对笼状材料的电化学理解，导致对导致快速扩散路径、低离子迁移势垒和相稳定性的结构特征的新见解。采用高温库仑滴定和低温助熔剂相结合的新的合成方法来捕获动力学/亚稳态相并可控地合成高质量的单晶材料。以含有关键Li局域环境的等结构化合物为模型化合物，研究Li-TT二元(和三元/四元)化合物的离子(脱)插入过程，重点是TT=Ge。通过连接电化学和合成的独特的反馈回路，利用电化学锂化成的物相信息来设计用于合成包合物的新型前驱体，并采用化学氧化的固相反应来开发对组成进行更精细控制的电化学合成方法。同步辐射X射线研究用于表征电化学反应和/或合成过程中的局域结构和晶体结构以及相演变。在所有情况下，密度泛函理论计算都支持实验结果和指导材料设计，特别是通过确定形成能和离子传输机制。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL DESCRIPTION:Clathrates are a class of materials with cage-like structures that can naturally hold guest ions, a feature that may be exploited for energy storage in rechargeable batteries. However, more research is needed to understand how the structure of the clathrate affects ion migration and the durability of the material under repeated electrochemical cycling. Through this collaborative project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, researchers at Arizona State and University of Delaware jointly identify structural features of the clathrates that promote fast ion diffusion and develop new approaches to synthesize these materials. Thereby they gather new knowledge connecting the structural effects of clathrates and related compounds to their physical, electrochemical, and materials chemistry properties. The fundamental science gained from these studies could have far reaching impacts in other fields where these materials have potential applications, such as superconductors, thermoelectrics, optoelectronics, magnets, and photovoltaics. Additionally, this collaboration between two universities and three different departments (materials science, chemistry, and physics) exposes students to multidisciplinary research. Outreach and educational activities also engage students and provide interdisciplinary training and immerse them into areas outside their immediate field of expertise. TECHNICAL DESCRIPTION:This collaborative project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, identifies structural features that lead to fast ion diffusion and obtain better understanding of electrochemically driven phase transformations in Li-Tetrel (Tt) systems, particularly for clathrates and other open framework structures. The specific objectives of the research are to: (1) Understand the structural parameter space for Tt (Tt = Si, Ge, Sn) clathrate and clathrate-like materials with high ionic mobility; (2) Re-map the phase space of Li-Tt systems, including non-equilibrium phases, coupled with studies on understanding the ionic transport within these phases, and (3) Use electrochemistry to inform solid-state synthesis and vice versa, to enable new synthetic approaches for clathrates and related materials that are either intermediates in the lithiation pathways or can be used as precursors for the synthesis steps. Through a concerted approach combining the synthetic, structural and electrochemical characterization, and theoretical expertise of the PIs, this work furthers the electrochemical understanding of clathrate materials, leading to new insights on structural features that result in fast diffusion pathways, low ion migration barriers, and phase stability. Novel synthetic approaches combining high temperature coulometric titration and low temperature flux methods are used to trap kinetic/metastable phases and controllably synthesize high quality single-crystalline materials. Isostructural compounds containing key Li local environments are employed as model compounds to understand the ion (de)insertion processes in Li-Tt binary (and ternary/quaternary) compounds, with an emphasis on Tt = Ge. By means of a unique feedback loop connecting electrochemistry and synthesis, information about phases formed during electrochemical lithiation is used to design novel precursors for synthesis of clathrates, and solid-state reactions using chemical oxidation are adapted to develop electrochemical synthesis methods with finer control over composition. Synchrotron X-ray studies are used to characterize the local and crystalline structures and phase evolution during electrochemical reaction and/or synthesis. In all cases, density functional theory calculations support experimental findings and guide materials design, particularly by identifying formation energies and ionic transport mechanisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.