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

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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.