CAREER: Scalable Liquid Exfoliation Processing of Ultrathin Two-Dimensional Metal Dichalcogenides Nanosheets for Energy Storage Devices

该学院早期职业发展（CAREER）计划拨款将建立一种新的工艺，用于大规模生产原子级薄片的过渡金属二硫属化物（或TMD），其具有适合于基于能源的应用的优化特性，特别是可充电金属离子电池。TMD片材具有几种不同的功能特性，这些特性在它们的块状晶体形式或其他广泛研究的层状材料如原始石墨烯和六方氮化硼中没有实现。目前阻碍TMD商业成功的一个主要障碍是缺乏在保持所需化学和物理属性的同时进行更大规模的生产。该奖项支持基础研究，为开发涉及自发剥离的基于溶液的处理路线提供所需的知识（即，分离成单分子层）。新工艺将能够生产出千克数量的NHTMD纳米片，这将克服主要障碍，并为这些材料在能源领域的大量应用提供解锁，从廉价的制氢催化剂到高性能可充电电池和超级电容器。因此，这项研究的结果将促进美国经济，环境和公民的生活质量。这项研究跨越多个学科，包括制造，工程力学，电化学和材料科学。跨学科的方法将增加实验室研究中代表性不足的群体的参与，并对工程教育产生积极影响。该项目基于解决方案的方法可以克服现有方法所面临的挑战，例如单层片材的生产率低，片材切割成亚微米尺寸的颗粒，以及超声处理时间长（数小时至数天）。然而，还需要克服更多的科学障碍，以释放剥离式TMD在能源领域的全部潜力（例如，钠离子可充电电池）。这些问题包括：缺乏与剥离机制相关的基础科学;无法制造具有所需断裂性能的大面积纳米结构TMD电极;以及TMD/金属离子嵌入和转化化学的未探索机制。本项目旨在通过以下方式填补这些知识空白：（1）进行实验并开发理论公式，以解释本体TMD自发剥离成石墨烯片的主要机制，（2）评估剥离片与石墨烯界面的加工优势（最薄和最强的电导体）以形成复合电极，从而测试纳米结构对断裂强度和电化学存储容量的限制，以及（3）将新颖的原位和非原位实验技术与伴随的计算模型相结合，以建立TMD/金属离子嵌入化学和相变机制。

This Faculty Early Career Development (CAREER) Program grant will establish a novel process for large-scale production of atomically thin sheets of transition metal dichalcogenides (or TMDs) with optimized properties suitable for energy-based applications, specifically, rechargeable metal-ion batteries. TMD sheets possess several distinct functional properties that are not realized in their bulk crystalline form or in other widely studied layered materials such as pristine graphene and hexagonal boron nitride. One major hurdle currently impeding the commercial success of TMDs is lack of production at larger scales while maintaining desired chemical and physical attributes. This award supports fundamental research to provide needed knowledge for the development of a solution-based processing route that involves spontaneous exfoliation (i.e., separation into single molecular layers) of bulk crystals in strong acids. The new process will enable production of kilogram quantities of ultrathin TMD nanosheets, which would overcome major roadblocks and unlock a vast array of applications for these materials in the energy sector, ranging from inexpensive catalysts for hydrogen production to high performance rechargeable batteries and supercapacitors. Therefore, results from this research will promote the U.S. economy, environment, and quality of life of its citizens. This research spans across several disciplines including manufacturing, engineering mechanics, electrochemistry, and materials science. The inter-disciplinary approach will increase participation by underrepresented groups in laboratory research and positively impact engineering education.This project's solution-based approach can overcome challenges that current methods have such as low production rates of single layer sheets, scission of sheets into sub-micron sized particles, and long sonication times (hours to days). However, additional scientific barriers need to be overcome in order to unlock the full potential of exfoliated TMDs in the energy sector (for example, sodium-ion rechargeable batteries). These include, lack of basic science related to exfoliation mechanism(s); inability to manufacture large-area nanostructured TMD electrodes with desired fracture properties; and unexplored mechanism(s) of TMD/metal-ion intercalation and conversion chemistry. This project aims to fill-in these knowledge gaps by (1) performing experiments and developing theoretical formulations to explain the dominant mechanisms for spontaneous exfoliation of bulk TMDs into ultrathin sheets, (2) assessing the processing advantages of exfoliated sheets by interfacing with graphene (thinnest and strongest electrical conductor) to form composite electrodes, thereby testing the limits of nanostructuring on fracture strength and electrochemical storage capacity, and (3) combining novel in-situ and ex-situ experimental techniques with companion computational models to establish TMD/metal-ion intercalation chemistry and phase transition mechanisms.