Characterizing the Behaviors of Li-O2 Battery in a Stable Electrolyte System

电化学储能对于主要由可再生能源提供动力的未来能源基础设施至关重要。目前，尖端技术锂(Li)离子电池在能量密度方面无法充分满足日益增长的需求。在正在追求的新技术中，锂氧(Li-O2)电池是突出的，因为理论研究预测，Li-O2电池可能比锂离子电池好2到10倍。到目前为止，电池电解液的糟糕稳定性是限制这项新技术进一步发展的关键因素。这一基础研究项目将直接应对这一关键挑战。这个项目将研究一种水基电解液，这种电解液含有高水平的盐，因此在电池电极存在的情况下，它不会腐蚀或反应。通过这种方式，该项目将直接测试电极上发生的关键反应，这些反应与预测相比，限制了其整体性能。然后，该研究项目将探索如何改进Li-O2电池。该项目完成后，将推进对这项有前景的新技术的研究。与研究工作相辅相成的是开展外联活动，旨在将可再生能源研究的影响扩大到不同的受众，包括本科生研究人员、高中生研究人员和大学预科儿童及其家人。该项目将对迈向可再生能源社会的目标做出重大贡献。该项目致力于一种新策略的基础研究，该策略通过使用基于H2O的电解液来解决锂O2电池的电解液降解问题，在这种电解液中，所有已知的电解液分解途径都被阻断。将使用一种高盐浓度的电解液(称为盐中水，Wis)，以最大限度地减少H2O分解和H2O诱导的氧化物分解的潜在负面影响。该项目的研究目标是定量研究电解液分解如何导致现有Li-O2电池的低性能。这些信息对于评估作为电化学储能技术的Li-O2电池的理论最大性能属性是必不可少的；然而，对于这些信息存在知识缺口。这一差距的存在是因为之前对锂-O2电池的研究都使用了对氧物种具有反应性的电解液。因此，由于电解液分解引起的寄生化学反应已经无处不在，极大地破坏了旨在了解Li-O2电池操作的努力。Wis电解液是一种超浓缩的水溶液。当盐浓度足够高时(例如，21摩尔/1千克H2O，或21米)，所有H2O分子通过溶解盐离子而被锁定，整个溶液在相当宽的电势窗口(例如，在1.9V和4.9V之间，而不是Li/Li)内表现为非质子溶液。这种体系为锂-O2电池化学研究提供了一个独特的、有机的、无溶剂的环境。事实证明，WIS电解液在实现锂离子电池、锂硫电池以及最近的锂氧电池运营的卓越性能方面是有效的。该系统提供了一个独特的机会来检查Li-O2电池的化学，而没有与电解液的寄生化学反应有关的混杂因素。该项目的成果将是一个没有电解液分解等混杂因素的Li-O2化学知识库。该奖项反映了NSF的法定使命，并已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。

Electrochemical energy storage is of paramount importance to a future energy infrastructure that is primarily powered by renewable sources. Currently, the state-of-the-art technology, lithium (Li)-ion batteries, will not sufficiently meet increasing needs in terms of energy densities. Of the new technologies that are being pursued, lithium-oxygen (Li-O2) batteries are prominent as theoretical studies predict that Li-O2 batteries could be 2 to 10 times better than Li-ion batteries. To date, the poor stability of the battery electrolyte is a key factor that limits further advancement of this new technology. This fundamental research project will directly address this critical challenge. This project will research a water-based electrolyte that has a high level of salt so that it is not corrosive or reactive in the presence of the battery electrodes. In this way the project will directly test what key reactions occur at the electrode that limit its overall performance compared to predictions. The research project will then explore how to improve Li-O2 batteries. Upon its completion, the project will advance research on this new promising technology. The research efforts will be complemented by outreach activities designed to broaden the impacts of renewable energy research to diverse audiences including undergraduate researchers, high school student researchers, and pre-college children and their families. The project will contribute significantly to the goals of moving toward a renewable energy-powered society.This project addresses fundamental research on a novel strategy to solve the problem of electrolyte degradation of lithium-O2 batteries by using a H2O-based electrolyte, in which all known electrolyte decomposition pathways are blocked. An electrolyte with high salt concentration (referred to as water in salt, WiS) will be used to minimize potential negative influences by H2O decomposition and H2O-induced oxide decomposition. The project's research goal is to quantitatively study how electrolyte decomposition contributes to the low performance of existing Li-O2 batteries. This information is imperative to the evaluation of the theoretical maximum performance attribute of Li-O2 battery as an electrochemical energy storage technology; however, a knowledge gap exists for this information. The gap exists because previous research on Li-O2 batteries all employed electrolytes that exhibit reactivity toward oxygen species. As a result, parasitic chemical reactions due to electrolyte decomposition have been ubiquitous, greatly undermining efforts designed to understand Li-O2 battery operations. The WiS electrolyte represents a super-concentrated aqueous solution. When the salt concentration is sufficiently high (e.g., 21 mole/1 kg of H2O, or 21 m), all H2O molecules are locked down by solvating the salt ions, and the overall solution acts as an aprotic one within a reasonably wide potential window (e.g., between 1.9 V and 4.9 V vs. Li/Li+). Such a system provides a unique, organic-solvent-free environment for the studies of Li-O2 battery chemistries. WiS electrolytes have proven effective in enabling superior performance for Li-ion, Li-sulfur and, most recently, Li-O2 battery operations. The system provides a unique opportunity to examine Li-O2 battery chemistry without the confounding factors connected to parasitic chemical reactions of the electrolytes. The outcome of the project will be a knowledge base of Li-O2 chemistry without the confounding factors such as electrolyte decomposition.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.