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Electrolyte Engineering Toward Increasing Nonaqueous Lithium-Oxygen Battery Capacity

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Electrolyte Engineering Toward Increasing Nonaqueous Lithium-Oxygen Battery Capacity
With lithium-ion battery technology reaching its theoretical specific energy limit, electric vehicles, unmanned aerial vehicles, spacecraft and spacesuits alike require a breakthrough battery electrochemistry to unlock new range and capabilities. Among the beyond Li-ion battery chemistries studied to date, the nonaqueous lithium-oxygen battery has the highest theoretical specific energy. Critical scientific challenges prevent the realization of this high specific energy, however, including the insulating nature of the electrochemical discharge product, lithium peroxide. As lithium peroxide forms in the battery, it passivates the battery cathode, leading to low ultimate cell capacities. As a graduate student researcher at the University of California, Berkeley, I recently published work on the ability of an appropriately selected anion to increase solubility of the electrochemical intermediate to lithium peroxide formation, lithium superoxide (LiO2), by lowering the free energy of the lithium cation (Li+) in solution. I showed this increase in lithium superoxide solubility enhanced a different lithium peroxide growth mechanism, circumventing the passivation issue and increasing battery capacity. The effect of anion-induced solubility is limited, however, by the already low free energy of Li+ in solution. As a next step, I hypothesize that the addition of appropriately selected non-Li alkali metal cations to the electrolyte in nonaqueous lithium-oxygen batteries will enhance LiO2 solubility more so than the anions I previously studied by lowering the free energy of O2- in solution, resulting in a larger increase in battery capacity. To test this hypothesis, I plan to build laboratory-scale lithium-oxygen batteries containing electrolytes with and without non-Li alkali metal cations, and characterize battery capacity via galvanostatic cycling, lithium peroxide growth via scanning electron microscopy, and lithium superoxide solubility via nuclear magnetic resonance spectroscopy. More »

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