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

这项教师早期职业发展（Career）计划的拨款将建立一种新的工艺，用于大规模生产具有优化性能的过渡金属二硫族化合物（或TMDs）的原子薄片，该薄片适用于基于能源的应用，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，这些特性在其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大规模生产，同时保持所需的化学和物理特性。该奖项支持基础研究，为开发基于溶液的处理路线提供所需的知识，该路线涉及强酸中大块晶体的自发剥离（即分离成单分子层）。新工艺将使超薄TMD纳米片的产量达到公斤级，这将克服主要障碍，并开启这些材料在能源领域的广泛应用，从廉价的氢气生产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的经济、环境和公民的生活质量。这项研究跨越了几个学科，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存在的挑战，例如单层片材的生产率低，片材切割成亚微米大小的颗粒，以及超声时间长（数小时至数天）。然而，为了在能源部门（例如，钠离子可充电电池）中充分发挥剥离tmd的潜力，还需要克服额外的科学障碍。这些问题包括：缺乏与剥离机制相关的基础科学；无法制造具有理想断裂性能的大面积纳米结构TMD电极；以及TMD/金属离子插入和转化化学的未知机制。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来解释大块tmd自发剥离成超薄片的主要机制；(2)通过与石墨烯（最薄、最强的电导体）界面形成复合电极来评估剥离片的加工优势，从而测试纳米结构在断裂强度和电化学存储容量方面的极限。(3)将新的原位和非原位实验技术与配套的计算模型相结合，建立TMD/金属离子插层化学和相变机理。

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.