Molecular Mechanisms in Nano-filled Lithium Solid Polymer Electrolytes

技术概述：固体聚合物电解质是取代锂离子电池中液体电解质的理想选择，因为无毒的固体聚合物消除了对刚性外壳的需求，从而增加了设计灵活性，减少了处理问题。阻碍其有效应用的特点是室温电导率低，因此人们尝试了许多改性方法，并研究了它们对电导率的影响。其中一种改性是在掺杂锂的聚环氧乙烷[PEO]中加入纳米颗粒填料，这可以提高电导率，特别是在低温下。虽然这一效应已得到证实，但其作用机制尚不清楚。聚合物宿主的迁移率增加是一个常见的解释：然而最近的实验证明，即使在完全结晶的PEO中也可以获得高导电性，模拟研究表明氧化物纳米颗粒减缓了PEO的动力学。解释测量迁移率或电导率的实验需要纳米颗粒聚集、结晶和湿度的知识，然而这些变量经常没有报道。聚集是重要的，因为一个分散的系统将受到限制的聚合物宿主的影响。聚合物主体结晶动力学受锂盐和纳米颗粒的影响。由于所需的工作温度（室温）低于熔点，因此结晶时间是需要监测的重要变量。同样重要的是，要消除不同的湿度水平，因为添加纳米颗粒会增加导电性，因为实际设备不能在有水的情况下工作。该项目结合了多种技术：准弹性中子散射、宽带介电光谱和小角度中子散射，在相同的样品上，在相同的条件下进行。聚合物（PEO）、锂盐（LiClO4）和纳米颗粒（Al2O3）的特性将是固定的，而纳米颗粒的大小和浓度将围绕提供最佳导电性而变化。纳米颗粒对电导率和PEO迁移率的影响将在干燥和环境条件下以及PEO结晶所需时间前后进行测试。本研究的实际贡献将是分离纳米颗粒填料对电导率和PEO迁移率的影响，作为结晶，颗粒聚集和含水量的函数。非技术概述：新型环保高效能源包括燃料电池、太阳能电池和长寿命可充电电池。锂离子电池，这个项目的重点，是商业上可用的，与材料分离的电池的两侧[电解质]以液体或凝胶的形式。这需要一个套管，并且添加溶剂来改善锂在电解质中的运动是一个生命周期结束时的处理问题。使用固体聚合物作为电解质减轻了这些困难，但是没有溶剂，锂的运动不足以为设备供电。使用最先进的方法来表征各种组件的迁移性，该项目将确定添加纳米级填料提高设备性能的原因。这将使轻便、灵活和安全的电池能够为电脑、手机和其他设备供电。该项目使用中子散射，这是一种在用户设施中进行的实验技术，例如国家标准与技术研究所的中子研究中心。美国已经在中子散射设施上投入了大量资金，包括橡树岭国家实验室的散裂中子源，该实验室目前已开始运行，并将使全国可能容纳的中子用户数量增加两倍。这个项目的一部分是教育美国科学家使用这项技术，并开始形成这个新的用户群。

TECHNICAL SUMMARY:Solid polymer electrolytes are ideal candidates to replace liquid electrolytes in lithium-ion batteries, because the non-toxic solid polymer eliminates the need for a rigid casing resulting in increased design flexibility and decreased disposal problems. The characteristic that precludes effective application is low room-temperature conductivity, and thus many modifications have been attempted and their effects on conductivity investigated. One such modification is addition of nanoparticle fillers to lithium-doped poly(ethylene-oxide) [PEO], which increases conductivity in particular at low temperatures. Although this effect is well established, the mechanism through which it acts is not. Increased mobility of the polymer host is a frequently offered explanation: yet recent experiments prove that high conductivity may be obtained even in completely crystalline PEO, and simulation studies suggest that oxide nanoparticles slow dynamics of PEO. Interpretation of experiments measuring mobility or conductivity requires knowledge of nanoparticle aggregation, crystallization and humidity, yet these variables are frequently not reported. Aggregation is important because a dispersed system will be influenced by confinement of the polymer host. The kinetics of polymer host crystallization are influenced both by the lithium salt, and the nanoparticles. Since the desired operating temperature [room temperature] is below the melting point, time to crystallization is an important variable to monitor. It is equally important to eliminate differing humidity levels as the cause of increased conductivity with nanoparticle addition, because practical devices cannot operate in the presence of water. This project combines a variety of techniques: quasielastic neutron scattering, broadband dielectric spectroscopy, and small-angle neutron scattering, performed on the same samples, under the same conditions. The identities of the polymer (PEO), lithium salt (LiClO4), and nanoparticle (Al2O3) will be fixed, while the nanoparticle size and concentration will be varied around that established to provide optimum conductivity. The influence of nanoparticles on conductivity and PEO mobility will be tested in dry and ambient conditions, and before and after the time required to crystallize the PEO. The practical contribution of this study will be to isolate the effects of nanoparticle fillers on conductivity and PEO mobility, as a function of crystallization, particle aggregation, and water content. NON-TECHNICAL SUMMARY:New environmentally friendly and efficient energy sources include fuel cells, solar cells and long life rechargeable batteries. Lithium ion batteries, the focus of this project, are available commercially, with the material separating the two sides of the battery [the electrolyte] in the form of a liquid or gel. This requires a casing, and the solvents added to improve movement of lithium across the electrolyte are an end of life disposal problem. Using a solid polymer as the electrolyte alleviates these difficulties, but without solvents lithium movement is not sufficient to power a device. Using state of the art methods to characterize mobility of the various components, this project will determine the reasons that the addition of nano-sized fillers improves device performance. This will allow for lightweight, flexible and safe batteries to power computers, cell phones, and other devices. This project uses neutron scattering, an experimental technique performed at user facilities, such as the Center for Neutron Research at the National Institute of Standards and Technology. The US has invested considerably in neutron scattering facilities, including the Spallation Neutron Source at Oakridge National Laboratory, which is currently starting operation and will triple the number of neutron users that may be accommodated nationally. Part of this project is to educate US scientists in this technique, and begin to form this new user pool.