Understanding the Structural Transformations of Aluminum Foil Anodes during Electrochemical De(alloying) for Sustainable Lithium-ion Batteries

锂离子电池将通过采用电动汽车和可再生能源，在向可持续经济的过渡中发挥关键作用。然而，随着锂离子电池产量的快速增长，关键矿物(如镍、钴、石墨)的使用存在严重的供应链风险，这可能会限制国内生产。同时，需要不断提高锂离子电池的性能，特别是能量密度，以满足商业和军事应用的需求。为此，开发比传统的石墨阳极具有更高的锂存储容量和更低的成本的电池阳极势在必行。一种前景看好，但在很大程度上尚未开发的石墨替代品是铝箔，它可以将电池能量密度提高高达40%，同时提高安全性、快速充电能力和成本。然而，铝箔阳极的研究还处于起步阶段，必须揭示铝箔阳极在电化学(脱合金化)过程中结构转变的基本机理，以改善其较差的循环寿命。基础研究项目将通过整合材料科学和电化学工程的跨学科研究方法来填补这一知识空白。项目小组将与当地一所公立学校和Ysleta Del Sur Pueblo保留地的学生合作，并就清洁能源技术的重要性和STEM职业生涯中的机会等主题进行外联。在电池形成过程中(即第一次循环)，铝箔阳极的微观结构发生了根本性的变化，这在很大程度上控制了后续循环的电化学性能。假设相同的机械力化学过程在地层中引起戏剧性的结构变化，当连续重复时，导致在循环过程中的快速能力损失。本研究项目的目的是了解：(I)原始铝箔阳极的结构和成分以及形核、相变和固态扩散动力学如何控制形成过程中的结构转变，以及(Ii)形成过程中铝箔的微观结构及其在循环过程中的演变，如何控制扩散陷阱和机械退化的失效模式。这些过程的动态电化学动力学将通过在磷酸铁锂充满电池中进行操纵道阻抗谱来与循环寿命同时进行评估。在形成和延长循环的不同阶段，将使用一套广泛的材料表征技术，以了解结构转变的机制并确定相关的失效模式。这些技术将被用来研究不同成分和微观结构的铝箔阳极，范围从纯铝到纳米复合箔。形成过程中的结构变化将与操纵面动力学测量相关联，以建立初始箔结构/成分、电化学处理条件和所得箔微结构之间的定量关系。最后，通过将形成后的微观组织与测量的循环寿命进行关联，并利用先进的事后材料表征技术确定失效的根本原因，将建立全面的工艺-组织-性能关系，以指导合理设计提高循环寿命的铝箔阳极。这一新颖的策略将电池形成过程作为电极制造的最后一步，能够通过电化学工程控制微结构，这将导致开发铝箔阳极的研究工作的范式转变。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。

Lithium-ion batteries will play an essential role in the transition to a sustainable economy by enabling the adoption of electric vehicles and renewable energy sources. However, as Lithium-ion batteries production grows rapidly, there are serious supply chain risks associated with the use of critical minerals (e.g., nickel, cobalt, graphite), which may restrict domestic production. Meanwhile, continuous improvements to lithium-ion battery performance – particularly energy density – are needed to meet the demands of commercial and military applications. To that end, it is imperative to develop battery anodes with higher lithium-storage capacity and lower cost than traditional graphite anodes. One promising, yet largely unexplored, alternative to graphite is aluminum (Al) foil, which can increase battery energy density by up to 40%, while improving safety, fast charging capability, and cost. However, research on Al foil anodes is in its infancy, and the fundamental mechanisms underlying the structural transformations of Al foil anodes during electrochemical (de)alloying must be uncovered to improve their poor cycle life. The fundamental research project will fill this knowledge gap through an interdisciplinary research approach that integrates materials science and electrochemical engineering. The project team will work with a local public school and the Ysleta Del Sur Pueblo reservation students and provide outreach on topics of the importance of clean energy technologies and opportunities in STEM careers. Aluminum foil anodes undergo fundamental changes in microstructure during battery formation (i.e., the first cycle), which largely control the electrochemical performance in subsequent cycles. It is hypothesized that the same mechanochemical processes, which cause dramatic structural changes during formation, when repeated continuously, are responsible for the rapid capacity loss during cycling. The goal of this research project is to understand: (i) how the structure and composition of the pristine Al foil anode, along with the kinetics of nucleation, phase transition, and solid-state diffusion, control the structural transformations during formation, and (ii) how the foil microstructure resulting from formation, and its evolution during cycling, control the failure modes of diffusional trapping and mechanical degradation. The dynamic electrochemical kinetics of these processes will be evaluated simultaneously with cycle life by conducting operando impedance spectroscopy in lithium iron phosphate full cells. An extensive suite of materials characterization techniques will be employed at various stages during formation and extended cycling to understand the mechanisms of structural transformation and identify the associated failure modes. These techniques will be used to interrogate Al foil anodes with diverse composition and microstructure, ranging from pure Al to nanocomposite foils. The structural transformations during formation will be correlated to operando kinetic measurements to establish quantitative relationships between initial foil structure/composition, electrochemical processing conditions, and the resulting foil microstructure. Finally, by correlating the microstructure after formation to the measured cycle life, and identifying the root causes of failure with advanced post-mortem materials characterization techniques, comprehensive processing-structure-performance relationships will be established to guide rational design of Al foil anodes with improved cycle life. This novel strategy of using the battery formation process as the final step of electrode manufacturing enables control of the microstructure through electrochemical engineering, which will lead to a paradigm shift in the research efforts to develop Al foil anodes.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.