EAGER: Exploiting Electrochemically-induced Phase Transformations in Mg-Li Thin Film Electrodes for Ultra-high Capacity Energy Storage

技术综述：旨在了解镁锂相变阳极在充放电过程中电化学插入/脱锂过程中的可逆相变机理。本研究的核心概念是，从纯镁阳极开始，在锂充电过程中，可以在阳极中诱导从六方镁向体心立方锂镁的相变(放电时则相反)。关键问题是薄膜微结构变量如何影响电化学诱导相变的可逆性。影响相变的主要因素是柱状晶的大小和柱间间距，以及晶向。假设可能存在一个最优的晶粒度和柱间间距，以适应相变的体积变化，充分允许在不破坏电极的情况下最大限度地存储和去除锂。这是一项高风险的研究，因为不能确定相变和体积变化调节的可逆性在电池所需的足够循环次数下是否可重复。具体地说，这项研究涉及通过溅射或PVD制备具有超细和柱状晶结构的不同厚度的镁薄膜，使用MEMS制造技术进行微机械加工以扩大柱间距，测试电化学电池以了解充放电过程中从HCP镁到体心立方锂镁可逆相变的本质，以及在充放电循环期间性能的容量、循环性和稳定性的实验确定。非技术摘要：下一代电动汽车，以及来自太阳能电池和风车的可再生能源的有效利用，将需要在电能存储和回收方面取得重大技术突破。一个高风险和高回报的研究项目被提出，旨在利用锂镁合金阳极的相变来帮助开发容量远远大于目前考虑用于电动汽车的超大容量储能电池。这项研究可能会为新一代可靠的大容量电池带来新的电极材料和结构，这反过来可能会加速低成本插电式电动汽车的发展。该项目将雇用一名研究生和一名或多名本科生，提供电池材料科学研究领域的教育和培训，并开发针对高中生的外联/招聘演示。这项研究将被整合到电池材料科学的课堂讲座中，用于能源科学与工程的研究生课程。在大学科学日招募活动期间，还将向高中生和家长介绍以“能源材料科学”为主题的公众宣传报告。

TECHNICAL SUMMARY: Research is proposed to understand the mechanism of reversible phase transformations in Mg-Li phase-changing anodes during electrochemical insertion/removal of Li in Mg thin films during the charging/discharging processes. The key concept of this research is that starting with a pure Mg anode, a phase change from HCP Mg to BCC Li-Mg can be induced in the anode during Li charging (and the reverse during discharging). The key question is how the thin film microstructural variables affect the reversibility of the electrochemically-induced phase transformations. The size and intercolumnar spacing of the columnar grains, as well as the grain orientation, are the primary variables affecting the phase transformation. The hypothesis is that there could be an optimum grain size and intercolumnar spacing that accommodates the volume change of the phase transition, fully allowing maximization of Li storage and removal without the destruction of the electrode. This is a high-risk research, because it is not certain that the reversibility of phase transformation and volume change accommodation is repeatable over the sufficient number of cycles required in batteries. Specifically, the research involves making Mg films of various thicknesses with ultrafine and columnar grain structures, either by sputtering or PVD, micromachining using MEMS fabrication techniques to extend the intercolumnar spacing, testing electrochemical cells to understand the nature of the reversible phase change from HCP Mg to BCC Li-Mg and vice-versa during charging/discharging and experimental determination of the capacity, cyclability and stability of the performance during the charge/discharge cycles.NON-TECHNICAL SUMMARY: Next-generation electric vehicles, as well as effective utilization of renewable energy from solar cells and windmills, will require major technological breakthroughs in electrical energy storage and retrieval. A high-risk and high-payoff research poject is proposed to exploit phase transformations in lithium-magnesium alloy anodes to help develop ultra-high-capacity energy storage batteries with capacities much larger than those currently under consideration for electric vehicles. The research could potentially lead to new electrode materials and structures for a new generation of reliable and high-capacity batteries, which could in turn accelerate the development of low-cost plug-in electric vehicles. The project will employ a graduate student and one or more undergraduate students, provide education and training in the area of battery materials science research, and develop outreach/recruitment presentations aimed at senior high school students. The research will be integrated into class lectures on battery materials science for a graduate course on Energy Science and Engineering. Public outreach presentations, under the theme of "energy materials science", to high school students and parents during University Science Day recruitment events, will also be made.