CAREER: Engineering electrochemical reversibility in disordered materials for high energy density batteries

可再生能源的广泛采用需要可在电网规模上实施的可充电电池。这些电池必须是不易燃和廉价的，因为安全性和成本是大规模电池安装的首要问题。该CAREER项目将对先进的电池材料进行基础研究，这些材料具有更高的能量密度和循环寿命，同时在不易燃的水基电解质中运行。在可能的电网规模电池选择中，可充电锌-二氧化锰电池具有吸引力，因为其基础材料便宜、安全且广泛可用。然而，MnO2反应的可逆性需要添加Bi，有时还需要与其他过渡金属（如Cu）配对。然而，这些额外金属在分子水平上的作用尚不清楚，而这一知识对于合理设计材料以获得最佳用途非常重要。本项目利用先进的表征技术，在电池循环过程中实时观察二氧化锰与添加金属之间的电化学相互作用，解决了这一问题。观察到的结构-功能关系将被用来设计改进电池的材料。一项综合教育计划将开发材料和工具，训练研究生通过互联网和博客进行有效的科学交流。这是因为，如果每个研究人员都有能力向公众传达他们工作的重要性，那将是一场变革。将制作有关电化学和储能重要性的在线材料，以及波士顿地区K-12学生的在线科学教育材料。该项目将研究掺杂一种或多种金属阳离子的二氧化锰电极的电化学机制。先前的工作已经证明，在循环过程中，铋促进了层状硼钼矿形式的形成，这种形式是无序的或缺乏长期结构周期性的。确定这种材料中的原子位置需要基于短程顺序的技术，如x射线和拉曼光谱。在MnO2双掺杂Bi和Cu的情况下，三种金属原子（Mn， Bi和Cu）在电池运行过程中都具有电化学活性，这意味着金属之间的电子介质效应等相互作用可能很重要，这将被评估。工作将从合成具有良好特征的掺杂二氧化锰晶体模型化合物开始，从中可以建立结构基序并细化原子位置。然后，这些模型化合物的信息将用于表征循环过程中电极中的动态原子位置和相互作用，正如在现实世界的无序材料中通过operando技术观察到的那样。为了从整体上理解电极系统，将探索掺杂剂的溶解度，以解释物质通过电解质的传输，并研究Zn阳离子对MnO2机制的影响。所获得的见解将有助于可充电Zn-MnO2电池的发展，也有助于理解层状材料中多个氧化还原活性位点的电化学。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Rechargeable batteries that can be implemented at the scale of the power grid are needed for widespread adoption of renewable energy. These batteries must be non-flammable and inexpensive because safety and cost are paramount concerns for large-scale battery installations. This CAREER project will conduct fundamental research on advanced battery materials that have the potential for greater energy density and cycle life, while operating in non-flammable water-based electrolytes. Among the possible grid-scale battery options, rechargeable Zn-MnO2 batteries are attractive because the basis materials are inexpensive, safe, and widely available. However, the reversibility of the MnO2 reaction requires the addition of Bi, sometimes paired with other transition metals such as Cu. However, the action of these additional metals at the molecular level is not known, and this knowledge is important to rationally engineer the material for optimal use. This project addresses this problem by using advanced characterization techniques to observe electrochemical interactions between MnO2 and the added metals in real time during battery cycling. The observed structure-function relationships will then be exploited to engineer the materials for improved batteries. An integrated education plan will develop materials and tools to train research students in effective scientific communication through the internet and blogging. This is because it would be transformational if every researcher had skills to communicate the importance of their work to the general public. Online materials will be produced about the importance of electrochemistry and energy storage, as well as online scientific educational materials for Boston area K-12 students.This project will examine electrochemical mechanisms in electrodes with MnO2 that has been doped with one or more metal cations. Previous work has demonstrated that during cycling Bi promotes formation of a layered birnessite form of MnO2 that is disordered or lacking in long-range structural periodicity. Determination of atomic positions in such a material requires techniques based on short-range order such as X-ray and Raman spectroscopy. In the case where MnO2 is dual doped with Bi and Cu, the three metal atoms (Mn, Bi, and Cu) are all electrochemically active during battery operation, meaning interactions such as electron mediator effects between the metals may be important, and this will be assessed. Work will begin with the synthesis of well-characterized, crystalline model compounds of doped MnO2, from which structural motifs can be established and atomic positions can be refined. Information from these model compounds will then be used to characterize dynamic atomic positions and interactions in electrodes during cycling, as observed by operando techniques in real-world disordered materials. To understand the electrode system as a whole, solubility of the dopants will be probed to account for transport of species via the electrolyte, and the impact of Zn cations on the MnO2 mechanism will be studied. The insights gained will aid development of rechargeable Zn-MnO2 batteries, and also contribute to understanding the electrochemistry of multiple redox-active sites in layered materials.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.