476167 Highly Energy-Dense Rechargeable Alkaline MnO2-Zn Batteries for Grid-Scale Applications
Manganese dioxide (MnO2) and zinc (Zn) are key constituents of primary or single-use alkaline batteries such as Duracell and Energizer. Single-use batteries are referred to as such because they deliver their entire energy capacity just once, after which they must be discarded. Despite this limitation, primary alkaline batteries are ubiquitous in society on account of abundance, low cost and relative safety of MnO2 and Zn, and their low cost of manufacturing. Nevertheless, as environmental regulations tighten, the manufacture of these convenient energy cells necessitates a rethink. Producing a primary MnO2-Zn battery consumes more energy than what it can deliver, and the use of MnO2-Zn batteries is now a point of contention owing to their large impact on the environment. To this end, electrochemical engineering of MnO2-Zn batteries towards making these cells rechargeable would represent a quantum advance. Rechargeability greatly improves the overall energy efficiency of these cells, and preserves its cost advantages. However, this objective has proved to be a herculean challenge for a generation of battery researchers owing to fundamental limitations in the material and electrochemical properties of MnO2 and Zn. Briefly, MnO2 can theoretically deliver a capacity of approximately 617 mAh/g. It delivers this capacity through a 2-electron electrochemical reaction; wherein each electron provides roughly 308 mAh/g. MnO2 has been found to be rechargeable when the capacity has been limited to around 5-10% of the 617mAh/g. Its crystal structure breaks as more of the capacity is accessed, and it inherently forms electrochemically irreversible phases. Similar problems are associated with the zinc electrode, where higher utilization of its capacity causes dendrite formation, morphology changes and formation of inactive zinc oxides that ultimately lead to electrode failure. If the entire 2-electron capacity of MnO2 can be accessed and problems associated with the zinc electrode can be averted, MnO2-Zn batteries could, in theory, reach energy densities that are comparable to lithium-ion batteries. My current research at the City College of New York has successfully addressed these requirements. Allied with its low cost of manufacturing and safety, a rechargeable MnO2-Zn battery could be a disruptive technology for energy storage.
Our breakthrough that permits accessing the 2-electron capacity reversibly was achieved by precisely altering the crystal structure of MnO2 with dopants using a wholly novel and vastly cheaper synthetic route, and we have cycled the MnO2 electrode to well over 6000 cycles at rates that are of interest to the battery community. Besides innovative technology development, I also unearthed fundamental insights about the material and its complicated electrochemical mechanism, wherein the dopants participate in those reactions involving MnO2to prevent the formation of the electrochemically irreversible phases. Significant performance improvements were also achieved for the Zn electrode through use of complexing agents that inhibit morphological changes in Zn and localize the active material near the current collector. Novel crystal structures doped with elements that play a dual role in reducing charge transfer characteristics and encapsulating Zn were also discovered. The application of these strategies have resulted in cycling the Zn anode at 15-20% of its theoretical capacity for >900 cycles, where Zn has been known to fail at 5-8% of its of theoretical capacity in less than 300 cycles.
The cumulative improvements in the material and electrochemical properties of MnO2 and Zn have resulted in fabrication of the very first rechargeable alkaline cell that can deliver a record high energy density of ~160 Wh/L, where 100% of the 2-electron capacity of MnO2 and 15% of theoretical capacity of Zn is utilized. Theoretical calculations have shown that at ~30% utilization of the Zn theoretical capacity, a highly energy dense cell of ~250Wh/L is possible. My current work seeks to achieve these figures, and my work has laid strong foundations for the market entry of rechargeable MnO2-Zn batteries that are cheaper but equally efficient as lithium-ion batteries. Overall, my postdoctoral work has resulted in the filing of 8 patents and I have recently submitted two manuscripts to high impact factor journals. It is currently under peer-review.
Doctoral Thesis: Design and assembly of nanostructured complex metal oxide materials for the construction of batteries and thermoelectric devices My graduate research at Purdue University served as an excellent primer for my current work. My doctoral work focused on synthesis of one-dimensional, complex metal oxide nanowires for thermoelectric and lithium-ion battery applications. I bridged two distinct technical domains – energy conversion and energy storage – with nanotechnology. Some highlights of my graduate work include the conception of novel synthetic routes for production of ultrathin perovskite nanowires and formalization of template-based approached for fabrication of complex metal oxides such as calcium cobalt oxide (Ca9Co12O28). Saliently, for the latter, my work was the first demonstration of its kind wherein nanowires were synthesized specifically use in thermoelectric devices. Moreover, the thermoelectric characteristics of the nanowires were a significant improvement over competing alternatives reported elsewhere in literature. In addition, I also extended my approach to the synthesis of nanowires and nanostructures of lithium cobalt oxide (LiCoO2) and investigated the impact of nanostructuring on the electrochemical properties of the material. The theme of combining application-driven research with fundamental investigations that seek to expand our understanding about nanomaterials has been a staple of my work since my graduate tenure. My graduate work resulted in publications and 1 patent.
I am a chemical engineer specializing in materials science and electrochemistry. I have a proven track record of advancing current understanding and develop commercializable technologies for energy generation and energy storage. Moreover, I have unique experience in scaling up my research from the nano- to macro scales, as well as from the bench to market. My doctoral work focused on developing new approaches for synthesis of one-dimensional, complex metal oxide nanowires and investigating their suitability for thermoelectric and battery applications. My postdoctoral research, on the other hand, has targeted the enhancement of the electrochemical properties of battery systems through ingenious use of materials science and scaling up these batteries for use in grid-scale applications. My training, research interests and innovation record will be key building blocks of my research program on multiscale engineering for energy conversion and storage. My program will comprise three pillars: (1) materials nanoscience, (2) materials synthesis, (3) device integration and scale-up. Among other projects, I intend to develop new thermoelectric materials for high-temperature applications, and conduct fundamental investigations towards improvement of aqueous battery chemistries. Beyond energy research, I am also interested in the development of catalysts for water oxidation, mesoporous materials for CO2capture, and water purification. These pursuits will draw upon similar experimental approaches as my research program on energy.
I have considerable teaching experience and previously served as the lead teaching assistant for undergraduate and graduate courses on chemical reaction engineering and transport phenomena in the School of Chemical Engineering at Purdue University. Some of these courses were subscribed by as many as 200 students. I delivered several lectures and led all tutorial and review sessions for these courses. I was praised by the students for the clarity of my presentation and conveyance of learning objectives, and my empathy for student advancement. I was awarded the Magoon Award for Excellence in Teaching, which is the highest accolade for teaching by a student at Purdue University. I can teach any course in the core chemical engineering curricula and technical electives such as electrochemistry and materials science. I value the old virtue of using the blackboard for instruction but also appreciate the power of multimedia and internet-based teaching in broadening the scope and reach of a course.
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