UNS: Developing Rechargeable Li-Metal Electrodes by Controlling the Direction of Dendrite Growth

可充电锂离子电池通过存储风能和太阳能等可再生能源产生的电力，或为使用可再生能源充电的零排放电动汽车提供动力，支持可持续能源系统的发展。对于使用高能量密度锂金属电极的实验性锂离子电池来说，一个基本的可靠性问题是在充电过程中电池内部会形成锂金属晶须，最终导致电池短路，产生潜在的火灾危险并缩短电池寿命。该项目的目标是开发一种新的电极设计，以控制这种降解过程并延长电池寿命。电极设计将以对失效机制的基础科学研究为指导，以提高该实验电池设计的可靠性和安全性，从而在未来实现商业化。作为与该项目相关的教育活动的一部分，来自工程领域代表性不足群体的本科生将获得多学科背景下的暑期研究经历，学生招募工作将通过印第安纳大学-普渡大学印第安纳波利斯分校多学科本科生研究所进行协调。以锂金属为阳极的可充电锂离子电池具有比目前使用的碳基阳极高得多的电化学储能能力。然而，金属表面的缺陷为金属锂枝晶的沉积提供了成核的场所。这些微小的突起在重复循环中生长，最终刺穿分离器，接触阴极，使装置短路。该研究的总体目标是开发一种新的阳极设计，以限制枝晶生长并延长使用锂金属作为阳极的锂离子电池的寿命。在所提出的电极设计中，在隔膜上面向锂金属阳极的薄锂离子功能化碳涂层产生与锂金属阳极枝晶生长方向相反的锂枝晶。因此，当从相反方向生长的枝晶相互接触并短路时，沿通平面方向的枝晶生长最终停止。这促进了枝晶在平面方向上的生长，最终将枝晶固结成锂金属层。利用分离器上的碳集流器对电位差进行归零，实现对生长方向的控制。为了了解这些过程并利用它们来开发持久的锂金属阳极，研究计划有四个目标。第一个目标是利用透射电子显微镜和原位微x射线衍射研究金属电极内锂枝晶形成的机制。第二个目标是通过循环效率和微聚焦同步x射线衍射测量技术来阐明金属电极的容量衰减机制。第三个目标是通过比较不同的涂层技术和碳类型，以及通过墨水配方优化纳米碳形态，优化锂金属电极的功能化纳米碳层，以获得尽可能高的存储容量和循环耐久性。第四个目标是考虑使压实的锂金属枝晶层成为锂金属阳极的活性成分的策略，并表征不同电解质体系下最终阳极的电化学性能。研究成果还将用于印第安纳大学-普渡大学印第安纳波利斯分校的EV/HEV能源存储设备和系统课程的教学材料。

PI: Jian Xie Proposal Number: 1511645Rechargeable lithium ion batteries support the development of sustainable energy systems by storing electricity generated by renewable resources such as wind and solar energy, or by powering zero-emission electric vehicles charged by electricity from renewable resources. A fundamental reliability issue with experimental lithium ion batteries that use high-energy density lithium metal electrodes is the formation of lithium metal whiskers within the battery during recharging, which ultimately short out the battery, creating a potential fire hazard and reducing battery life. The goal of this project is to develop a new electrode design that controls this degradation process and prolongs battery lifetime. The electrode design will be guided by fundamental scientific investigation into the mechanisms of failure to improve the reliability and safety of this experimental battery design, so that commercial realization may be possible in the future. As part of the educational activities associated with this project, undergraduate students from under-represented groups in engineering will be given summer research experiences in a multi-disciplinary context, with student recruiting coordinated through the Multidisciplinary Undergraduate Research Institute at Indiana University-Purdue University Indianapolis.Rechargeable lithium ion batteries that use lithium metal as the anode have much higher electrochemical energy storage capacity than carbon-based anodes currently in use. However, imperfections on the metal surface serve as nucleation sites for the deposition of lithium metal dendrites. These microscopic projections grow upon repeated cycling and ultimately pierce the separator, touch the cathode, and short out the device. The overall goal of the proposed research is to develop a new anode design that confines dendrite growth and prolongs the lifetime of lithium ion batteries that use lithium metal as the anode. In the proposed electrode design, a thin lithium ion functionalized carbon coating on the separator facing the lithium metal anode generates lithium dendrites in the direction opposite to dendrite growth from the lithium metal anode. Therefore, dendrite growth along the through-plane direction is ultimately stopped when dendrites growing from opposing directions touch one another and short out. This promotes dendrite growth in the in-plane direction, ultimately consolidating the dendrites into a Li-metal layer. Controlling the growth direction is realized by zeroing the potential difference using the carbon current collector on the separator. To understand these processes and harness them to develop a long-lasting lithium metal anode, the research plan has four objectives. The first objective is to study the mechanism of lithium dendrite formation within the metal electrode using both transmission electron microscopy and and in situ micro X-ray diffraction. The second objective is to elucidate the capacity decay mechanism of the metal electrode through cycle efficiency and micro-focused synchrotron X-ray diffraction measurement techniques. The third objective is to optimize the functionalized nanocarbon layer of the lithium metal electrode for highest possible storage capacity and cycling durability, by comparing different coating techniques and carbon types, and by optimizing nanocarbon morphology through ink formulation. The fourth objective is to consider strategies to make the compacted lithium metal dendrite layer an active component of the lithium metal anode, and to characterize the electrochemical performance of the final anode with different electrolyte systems. Research outcomes will also be used to develop instructional materials for a course on Energy Storage Devices and Systems for EV/HEV at the Indiana University-Purdue University Indianapolis.