Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 30, Pages 9293-9298Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1505728112
Keywords
donor number; solubility; lithium nitrate; NMR; Li-air battery
Categories
Funding
- Laboratory Directed Research and Development Program of LBNL under US Department of Energy [DE-AC02-05CH11231]
- US DOE Vehicle Technologies Office [DE-0006869]
- Deutsche Forschungsgemeinschaft
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Among the beyond Li-ion battery chemistries, nonaqueous Li-O-2 batteries have the highest theoretical specific energy and, as a result, have attracted significant research attention over the past decade. A critical scientific challenge facing nonaqueous Li-O-2 batteries is the electronically insulating nature of the primary discharge product, lithium peroxide, which passivates the battery cathode as it is formed, leading to low ultimate cell capacities. Recently, strategies to enhance solubility to circumvent this issue have been reported, but rely upon electrolyte formulations that further decrease the overall electrochemical stability of the system, thereby deleteriously affecting battery rechargeability. In this study, we report that a significant enhancement (greater than fourfold) in Li-O-2 cell capacity is possible by appropriately selecting the salt anion in the electrolyte solution. Using Li-7 NMR and modeling, we confirm that this improvement is a result of enhanced Li+ stability in solution, which, in turn, induces solubility of the intermediate to Li2O2 formation. Using this strategy, the challenging task of identifying an electrolyte solvent that possesses the anticorrelated properties of high intermediate solubility and solvent stability is alleviated, potentially providing a pathway to develop an electrolyte that affords both high capacity and rechargeability. We believe the model and strategy presented here will be generally useful to enhance Coulombic efficiency in many electrochemical systems (e. g., Li-S batteries) where improving intermediate stability in solution could induce desired mechanisms of product formation.
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