Collaborative research: Understanding relationships between synthesis, structure, solid-state electrochemistry, and phase stability in clathrates and related materials

非技术描述：包合物是一类具有笼状结构的材料，可以自然地容纳客体离子，这一特性可能被用于可充电电池的能量存储。然而，在重复电化学循环下，笼形物的结构如何影响离子迁移和材料的耐久性还需要更多的研究。通过这个由美国国家科学基金会材料研究部固态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形物的结构特征，并开发了合成这些材料的新方法。因此，他们收集了将包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对这些材料具有潜在应用的其他领域产生深远的影响，例如超导体，热电学，光电子学，磁体和光伏。此外，两所大学和三个不同部门（材料科学、化学和物理）之间的合作使学生接触到多学科研究。外展和教育活动也吸引学生，并提供跨学科的培训，使他们沉浸在他们的直接专业领域之外的领域。技术描述：该合作项目由美国国家科学基金会材料研究部固态和材料化学项目支持，确定导致快速离子扩散的结构特征，并更好地理解Li-Tetrel （Tt）系统中电化学驱动的相变，特别是包合物和其他开放框架结构。本研究的具体目标是：(1)了解高离子迁移率的Tt （Tt = Si, Ge, Sn）包合物和类包合物材料的结构参数空间；(2)重新绘制Li-Tt体系的相空间，包括非平衡相，再加上对这些相内离子传输的研究；(3)利用电化学来指导固态合成，反之亦然，为包合物和相关材料提供新的合成方法，这些材料要么是锂化途径的中间体，要么可以用作合成步骤的前体。通过将合成、结构和电化学表征以及pi的理论专业知识相结合的协同方法，这项工作进一步加深了对笼形物材料的电化学理解，从而对快速扩散途径、低离子迁移障碍和相稳定性的结构特征产生了新的见解。采用高温库仑滴定法和低温通量法相结合的新型合成方法，捕获动力学/亚稳相，可控地合成高质量的单晶材料。采用含有关键Li局部环境的同位结构化合物作为模型化合物来理解Li-Tt二元（和三元/四元）化合物中的离子（de）插入过程，重点是Tt = Ge。通过连接电化学和合成的独特反馈回路，电化学锂化过程中形成的相信息可用于设计合成笼形物的新型前驱体，而使用化学氧化的固态反应可用于开发对组成进行更精细控制的电化学合成方法。同步加速器x射线研究用于表征电化学反应和/或合成过程中的局部和晶体结构和相演变。在所有情况下，密度泛函理论计算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。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.