CAREER: Cationic Chemical Vapor Deposition of Lithium Battery Gel Electrolytes

将先进的锂离子电池用于车辆运输和可再生电网存储应用，可以提高国内能源安全，但其使用受到成本高和电池寿命有限的限制。电池失效的主要原因是设备内部难以量化和难以理解的不良化学副反应。由于缺乏基本的了解，工程师们更难设计出能够承受更长时间副反应的材料和设备。在混合锂电池等先进电池设计中，凝胶电解液受到青睐，因为它们允许传统电解液的类似液体的高电导率，但具有良好的机械性能，并像固体聚合物电解液一样提高了安全性。这个职业项目将对聚合物加工方法进行基础研究，以有效地将凝胶电解液沉积到电池的多孔电极中，形成薄的保护性涂层，提高对不希望发生的副反应的抵抗力，并提供结构稳定性。除了电化学储能应用之外，这些研究还将实现可扩展、快速的聚合物沉积，这些沉积在许多其他应用中具有普遍意义，例如防腐涂层、阻挡层和介电层以及光学涂层。作为教育收益，该项目将培训学生研究人员的批判性思维技能，以及反应工程、聚合物科学、先进半导体工艺和电化学能量储存等学科。PI还与罗切斯特市公共区域合作，通过互动的服务学习启发项目向高中生介绍化学工程原理。该项目中的聚合物化学气相沉积(CVD)过程是基于多相阳离子聚合的。中心假设是，作为气相前体引入沉淀室的强酸分子与表面吸附的乙烯基单体反应，生成卡宾离子，然后进行聚合。主要的研究目标是了解构成阳离子聚合物CVD的基本传输和反应过程，以便建立对沉积在多孔性锂离子电池电极内的聚合物凝胶电解质的合成和形态控制。该项目分为两个推力，第一个推力旨在建立反应机理并了解沉积薄膜的材料特性。第二个推力将研究有效平衡表面反应速度和质量传输的工艺条件，以实现多孔结构内的共形涂层。利用阳离子化学气相沉积技术可在电极孔隙率范围内合成新型凝胶电解质材料。这两个推进是高度集成的，并将协同进行，以辨别结构-性能关系和工艺条件对这些新型凝胶材料的影响。为了建立对凝胶在相关锂离子电池中的电化学行为的基础理解，重点介绍了凝胶的电化学表征，包括锂离子的传输和氧化稳定性。最初，凝胶电解质组合物将基于在传统的烷基碳酸酯液体电解质中膨胀的交联型聚乙烯吡咯烷酮。从长远来看，随着项目和储能领域的进展，将开发更多的新型凝胶组合物，以应对未来锂电池技术的实质性挑战。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The use of advanced lithium-ion batteries for vehicle transport and renewable electricity grid storage applications could improve domestic energy security, but their use is limited by high cost and limited battery lifetime. The main cause of battery failure is undesirable chemical side reactions within the device that are difficult to quantify and to understand. Because of this lack of fundamental understanding, engineers are less able to design materials and devices that can withstand side reactions for longer times. In advanced battery designs such as hybrid lithium batteries, gel electrolytes have been favored because they allow high liquid-like conductivities of conventional electrolytes yet favorable mechanical properties and enhanced safety like solid polymer electrolytes. This CAREER project will conduct fundamental research on polymer processing methods to efficiently deposit gel electrolytes inside a battery's porous electrode to form thin protective coatings that improve resistance to unwanted side reactions and provide structural stability. Beyond electrochemical energy storage applications, these studies will enable scalable, rapid polymer depositions that have general relevance in many other applications such as corrosion protection coatings, barrier and dielectric layers, and optical coatings. As educational benefits, this project will train student researchers in critical thinking skills, and in the disciplines of reaction engineering, polymer science, advanced semiconductor processing, and electrochemical energy storage. The PI has also partnered with the Rochester City Public District to introduce chemical engineering principles to high school students using interactive service-learning inspired projects.The polymer chemical vapor deposition (CVD) process in this project is based on heterogeneous cationic polymerizations. The central hypothesis is that strong acid molecules, which are introduced into the deposition chamber as vapor-phase precursors, react with surface-adsorbed vinyl monomers, generating carbenium ions that then undergo polymerization. The overarching research objective is to understand the fundamental transport and reaction processes that constitute cationic polymer CVD in order to establish synthetic and morphological control of polymer gel electrolytes deposited within porous lithium ion battery electrodes. This project is divided into two thrusts, where the first thrust seeks to establish the reaction mechanism and understand the material properties of the deposited films. The second thrust will research the processing conditions that effectively balance the rate of surface reaction with mass transport to achieve conformal coatings inside porous structures. Novel gel electrolyte materials will be synthesized within electrode porosity using cationic CVD. These two thrusts are highly integrated and will be conducted in concert to discern structure-property relationships and the effects of processing conditions in these novel gel materials. To establish foundational understanding of the gels' electrochemical behavior in relevant lithium ion battery cells, electrochemical characterization of the gels is emphasized including Li ion transport and oxidative stability. Initially, the gel electrolyte composition will be based on crosslinked poly(vinyl pyrrolidone) swollen in conventional alkyl carbonate liquid electrolytes. Over a longer term as both the project and energy storage field advance, additional novel gel compositions will be developed to address material challenges in future lithium battery technologies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.