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

技术概述：研究了在充放电过程中，在Mg薄膜中电化学插入/去除Li时，Mg-Li相变阳极可逆相变的机理。本研究的关键概念是，从纯Mg阳极开始，在锂充电期间，阳极可以诱导从HCP Mg到BCC Li-Mg的相变（在放电期间则相反）。关键问题是薄膜微观结构变量如何影响电化学诱导相变的可逆性。柱状晶粒的尺寸、柱间间距以及晶粒取向是影响相变的主要因素。假设存在一个最佳晶粒尺寸和柱间间距，以适应相变的体积变化，从而在不破坏电极的情况下完全允许最大限度地储存和去除锂。这是一项高风险的研究，因为不确定在电池所需的足够数量的循环中，相变和体积变化调节的可逆性是否可重复。具体而言，该研究包括通过溅射或PVD制作具有超细和柱状颗粒结构的不同厚度的Mg薄膜，使用MEMS制造技术进行微加工以延长柱间间距，测试电化学电池以了解充电/放电过程中从HCP Mg到BCC Li-Mg以及反之亦然的可逆相变的性质，以及容量的实验测定。充放电循环过程中性能的可循环性和稳定性。非技术总结：下一代电动汽车，以及太阳能电池和风车等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。提出了一项高风险高回报的研究项目，利用锂镁合金阳极的相变来帮助开发超大容量储能电池，其容量远远大于目前正在考虑的电动汽车电池。这项研究可能会为新一代可靠的高容量电池带来新的电极材料和结构，从而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，并针对高中学生开展宣传/招聘演讲。这项研究将被整合到能源科学与工程研究生课程的电池材料科学课程中。在“大学科学日”招聘活动期间，还将向高中生和家长进行以“能源材料科学”为主题的公众宣传演讲。

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.