SUSCHEM: Exploring Specific Heating in Microwave-assisted Synthesis of Hierarchical Hybrid Nanomaterials for Future Sustainable Batteries

第1部分：非技术性电池是我们生活中无处不在的电能存储设备，可以支持从便携式电子产品到电网的任何东西。决定电池成本和性能的关键部件是电极材料。该项目由美国国家科学基金会材料研究部的固态材料和化学计划资助，旨在开发新的方法来制备可用于两种新兴电池的新型电极材料，即钠离子电池和镁离子电池。这些新型电池在电化学反应中使用地球上丰富的钠和镁离子，因此与当前最先进的锂离子电池相比，有可能显著降低储能成本，使其对大规模电能储存具有吸引力。然而，目前在这些电池中使用的单相电极材料稳定性差，寿命短，这是因为含有更大的钠离子和更高电荷的镁离子。因此，本项目的目标是由沉积在稳定的三维纳米结构碳支架上的活性电极材料组成的混合材料。这种研究方法利用纳米碳材料对微波的相对较强的吸收来加速合成过程，并创造出原本可能在分离相中不稳定的强杂化材料。除了更好地了解混合固态材料的基本性质并潜在地提高电能存储设备的性能外，该项目还为来自不同背景的学生提供跨学科培训，包括代表性不足的群体。这三个方面对于保持我国在具有重要战略意义的能源转换和存储领域的领先地位至关重要。第2部分：技术总结该项目由美国国家科学基金会材料研究部固态材料和化学计划资助，旨在开发可控的三维(3D)分层混合电极材料，用于两种新兴电池，即钠离子电池和镁离子电池，方法是使用一种创新的微波辅助合成方法在纳米结构碳模板上沉积所需的活性电极材料(金属氧化物和硫化物)。基于纳米碳模板对微波的特定吸收，快速加热会导致亚稳相的快速形核和生长，这些亚稳相结合成稳定的杂化电极材料，这是传统方法不容易合成的。不同类型的纳米碳，包括分散的还原石墨烯氧化物(RGO)纳米薄片、层叠的碳纳米管(CNTs)或电纺碳纳米纤维(CNF)以及垂直排列的碳纳米纤维(VACNf)，被研究为高导电和机械坚固的模板，以控制沉积的活性电极材料的形貌、组成和物相。这为合成含有亚稳材料的精细3D分级核壳杂化材料提供了技术，例如水合金属氧化物(V2O5·nH2O双层膜)和金属硫化物(VS4链)，它们具有更开放的结构，有利于大容量Na+离子和二价Mg2+离子的可逆存储。这种杂化层次化材料可以突破单相电极材料的固有限制，提高固体材料的导电性，缩短离子在固体材料中的扩散路径，同时显著提高电极的稳定性。微波辐射的快速加热能力缩短了材料合成过程，极大地加速了材料的发现和优化。该项目还为研究生和本科生提供纳米材料合成/表征、电化学和电能储存技术方面的跨学科培训。推广活动的目标是让堪萨斯州的K-12学生(特别是女孩)参加STEM教育，并每年让泽维尔大学的一名本科生(代表人数较少的少数族裔)参与暑期研究和进一步的职业发展。

PART 1:   NON-TECHNICAL SUMMARYBatteries are ubiquitous electrical energy storage devices in our life to support anything from portable electronics to electrical grids. A key component that determines the cost and performance of batteries is the electrode materials. This project, funded by the Solid State Materials and Chemistry Program in the Division of Materials Research at NSF, seeks to develop new methods to prepare novel electrode materials that can be used for two types of emerging batteries, i.e. sodium ion batteries and magnesium ion batteries. These new battery-types use earth-abundant sodium and magnesium ions in electrochemical reactions and hence have the potential to significantly lower the cost of energy storage compared to current state-of-the-art Li-ion batteries, making them attractive for large-scale electrical energy storage. However, currently used single-phase electrode materials in these batteries exhibit poor stability and a short lifetime due to hosting the much larger sodium ions and higher-charged magnesium ions. Therefore this project targets hybrid materials which consist of active electrode materials deposited on stable three-dimensional nanostructured carbon scaffolds. The research approach makes use of the relatively strong microwave absorption by the nanocarbon materials to accelerate the synthesis process and create strong hybrid materials that otherwise may be unstable in separated phases. In addition to creating a better understanding of the fundamental properties of hybrid solid state materials and potentially improving the performance of electrical energy storage devices, this project provides cross-disciplinary training to students from diverse backgrounds including underrepresented groups. All three aspects are critical for maintaining our nation's leading role in the strategically important fields of energy conversion and storage.PART 2:   TECHNICAL SUMMARYThis project, funded by the Solid State Materials and Chemistry Program in the Division of Materials Research at NSF, targets the development of well-controlled three-dimensional (3D) hierarchical hybrid electrode materials for two types of emerging batteries, i.e. sodium ion batteries and magnesium ion batteries, by depositing desired active electrode materials (metal oxides and chalcogenides) on nanostructured carbon templates using an innovative microwave-assisted synthesis method. Rapid heating, based on the specific microwave absorption of the nanocarbon templates, induces rapid nucleation and growth of metastable phases which combine into stable hybrid electrode materials that cannot be readily synthesized with conventional methods. Different types of nanocarbons, including dispersed nanoflakes of reduced graphene oxides (rGOs), stacked 3D films of carbon nanotubes (CNTs) or electrospun carbon nanofibers (CNFs), and arrays of vertically aligned carbon nanofibers (VACNFs), are investigated as highly conductive and mechanically robust templates to control the morphology, composition and phases of the deposited active electrode materials. This provides techniques for synthesizing delicate 3D hierarchical core-shell hybrid materials containing metastable materials such as hydrated metal oxides (V2O5·nH2O bilayers) and metal chalcogenides (VS4 chains) which have more opened structures to facilitate reversible storage of large Na+ ions and divalent Mg2+ ions. Such hybrid hierarchical materials may break the intrinsic limits of single-phase electrode materials by enhancing the electrical conductivity and reducing the ion diffusion path length in the solid materials while significantly improving the electrode's stability. The capability of fast heating by microwave irradiation shortens the materials synthesis processes and greatly accelerates materials discovery and optimization. This project also provides cross-disciplinary training to both graduate and undergraduate students in nanomaterials synthesis/characterization, electrochemistry and electrical energy storage technologies. Outreach activities are aimed at interesting K-12 students (particularly girls) in Kansas in STEM education, and engaging an undergraduate student from Xavier University (underrepresented minority) in summer research and further career development each year.