Molecular Mechanisms in Nano-filled Lithium Solid Polymer Electrolytes

技术摘要：固体聚合物电解质是替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，从而提高了设计灵活性并减少了处置问题。 妨碍有效应用的特征是室温电导率低，因此已经尝试了许多修改并研究了它们对电导率的影响。 其中一种改进是将纳米颗粒填料添加到锂掺杂聚环氧乙烷[PEO]中，这可以提高电导率，特别是在低温下。 尽管这种效应已得到充分证实，但其作用机制却尚未明确。 聚合物主体的流动性增加是一种经常提出的解释：但最近的实验证明，即使在完全结晶的 PEO 中也可以获得高电导率，并且模拟研究表明氧化物纳米颗粒会减慢 PEO 的动力学。测量迁移率或电导率的实验的解释需要了解纳米粒子聚集、结晶和湿度，但这些变量经常没有报告。 聚集很重要，因为分散体系会受到聚合物主体限制的影响。 聚合物主体结晶动力学同时受到锂盐和纳米颗粒的影响。 由于所需的操作温度[室温]低于熔点，因此结晶时间是需要监控的重要变量。 消除不同的湿度水平作为添加纳米粒子增加电导率的原因同样重要，因为实际设备无法在有水的情况下运行。 该项目结合了多种技术：准弹性中子散射、宽带介电谱和小角度中子散射，在相同条件下对相同样品进行。 聚合物 (PEO)、锂盐 (LiClO4) 和纳米颗粒 (Al2O3) 的特性将是固定的，而纳米颗粒的尺寸和浓度将在为提供最佳电导率而建立的范围内变化。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 结晶所需时间之前和之后进行测试。 这项研究的实际贡献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、颗粒聚集和水含量的函数。非技术概要：新型环保高效能源包括燃料电池、太阳能电池和长寿命充电电池。 该项目的重点是锂离子电池，该电池已可商用，其分隔电池两侧的材料（电解质）以液体或凝胶的形式存在。 这需要一个外壳，并且为改善锂在电解质中的移动而添加的溶剂是一个报废处理问题。 使用固体聚合物作为电解质可以缓解这些困难，但如果没有溶剂，锂的移动不足以为设备提供动力。 该项目将使用最先进的方法来表征各种组件的流动性，从而确定添加纳米填料提高器件性能的原因。 这将使轻质、灵活且安全的电池能够为计算机、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（例如美国国家标准与技术研究院中子研究中心）进行的实验技术。 美国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，该设施目前已开始运行，将使全国可容纳的中子用户数量增加两倍。 该项目的一部分是对美国科学家进行这项技术的教育，并开始形成这个新的用户库。

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.