Thin-Film Formation of Insoluble Discharging Products at the Reaction Interface of Li-Air Batteries

皮：王，云提议编号：1336873机构：加州大学欧文分校题目：锂空气电池反应界面不溶放电产物的薄膜形成锂空气电池在高储能方面显示出巨大的潜力。它们的独特之处在于，正极活性物质氧气并不储存在电池中，而是从周围环境中获得。此外，在锂离子电池中使用的是锂金属，而不是锂插层石墨(LiC6)。锂空气电池的理论比能量达到11680Wh/kg，与汽油(13000Wh/kg)相当。尽管前景看好，但它们面临着科学和技术方面的挑战：一是它们的放电能力受到阴极中形成的不溶性产物的限制。已经观察到，不溶性放电产物的沉淀在反应表面形成纳米薄膜，阻碍了电化学活性，最终导致显著的电压/容量损失。然而，目前人们对其背后的物理原理知之甚少。该项目研究了反应表面的薄膜形成及其对锂空气电池性能的影响，最终目的是消除其不利影响。该项目假设，不溶性放电产品的薄膜形成根据操作条件呈现出异质结构，因此描绘异质对于理解放电电压和容量损失的潜在物理意义至关重要。第一个目标是探索典型表面形貌下的薄膜生长模式，了解薄膜结构，即薄膜性能的空间变化；第二个目标是探索薄膜形成对电池S电压损失的影响，这是在质子交换膜燃料电池中新开发的一种用于亚冷冻操作的方法：燃料电池中的产品水在反应表面结冰并阻碍电化学活性，这类似于锂空气电池中不溶性放电产物的成膜。首先，我们将分析三种表面形态：平面、圆柱形和球形。PI还将直接测量S薄膜的空间变化特性，包括化学成分、孔隙率和电阻。在后者中，PI将跟踪PEM燃料电池中结冰的情况，分析由于成膜而引起的容量和放电电压损失。诊断方法，如循环伏安计(CV)和阻抗将被用来测量反应表面损失，以及反应和氧气传输阻力。该项目预计将发展关于薄膜形成、其物理性质、化学成分以及对电化学反应活动的影响的基础知识，这对锂空气电池的开发具有重要意义。这些成果还有利于其他研究领域，如生物反应堆、其他电池系统、PEM燃料电池、高温燃料电池(阳极形成焦油)、纳米薄膜生长和电子隧道。锂空气电池技术有可能克服电动汽车的主要技术障碍，即存储能力不足。外展工作包括：1)为研究生和本科生提供多学科学习体验；2)可再生能源外展计划，强调为高中生和教师提供实践工程经验，与本科生一起参与。

PI: Wang, YunProposal Number: 1336873Institution: University of California-IrvineTitle: Thin-Film Formation of Insoluble Discharging Products at the Reaction Interface of Li-Air BatteriesLithium-air (Li-air) batteries show great potential for high capacity of energy storage. Their unique feature is that the cathode active material, oxygen, is not stored in the batteries, but obtained from the ambient environment. In addition, Lithium metal is used rather than the Li intercalated graphite (LiC6) as that in Li-ion batteries. The theoretical specific energy of Li-air batteries reaches 11,680 Wh/kg, comparable to that of gasoline (13,000 Wh/kg). Despite the great promise, they face scientific and technical challenges: one is their discharge capability limited by insoluble products formation in cathode electrodes. It has been observed that precipitation of insoluble discharging products forms a nano-scale film on the reaction surface, hampering electrochemical activity and eventually leading to significant voltage/capability loss. The underlying physics are, however, poorly understood at present. This project examines the thin-film formation at the reaction surface and its effects on Li-air battery performance, with the ultimate goal to eliminate its adverse effects.This project hypothesizes that the thin-film formation of insoluble discharging products exhibits heterogeneous structures depending on operating conditions, and thus delineating the heterogeneity is crucial to understand the underlying physics of discharging voltage and capacity losses. The first objective is to explore the film growth modes at typical surface morphologies, and understand the thin-film structure, i.e. the spatial variation of film properties; the second objective is to explore the effects of film formation on battery?s voltage loss following an approach newly developed in PEM fuel cells for subfreezing operation: product water in fuel cells freezes with ice forming at the reaction surface and hampering electrochemical activities, which is similar to the film formation of insoluble discharging products in Li-air batteries. In the first, three surface morphologies will be analyzed: planar, cylindrical, and spherical shapes. The PI will also directly measure the thin-film?s spatially varying properties, including chemical composition, porosity, and electric resistance. In the latter, the PI will analyze the capacity and discharging voltage loss due to film formation, following that of ice formation in PEM fuel cells. Diagnostics methods such as cyclic voltammeter (CV) and impedance will be applied to measure reaction surface loss, and the reaction and oxygen transport resistances. The project is anticipated to develop fundamental knowledge regarding thin-film formation, its physical properties, chemical composition, and effects on electrochemical reaction activities, significant to Li-air battery development. The outcomes also benefit other research areas, such as the biological reactors, other battery systems, PEM fuel cells, high-temperature fuel cells (tar formation in the anode), nano film growth, and electron tunneling.Li-air battery technology has the potential to overcome the major technical hurdle for electrical vehicles, i.e. the insufficient storage capability. Outreach efforts include: 1) Multidisciplinary learning experiences for graduate and undergraduate students; 2) a renewable energy outreach program which emphasizes hands-on engineering experience for high school students and teachers, participating alongside undergraduate students.