title: Enhancing electrochemical intermediate solvation through electrolyte anion selection to increase nonaqueous Li-O2 battery capacity.
abstract: Among the "beyond Li-ion" battery chemistries, nonaqueous Li-O2 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-O2 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-O2 cell capacity is possible by appropriately selecting the salt anion in the electrolyte solution. Using (7)Li 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.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA 94720; Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720;
authors.forename: Colin M
authors.identifier: http://orcid.org/0000-0002-8826-0944
authors.initials: CM
authors.lastname: Burke
authors.affiliation: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213;
authors.forename: Vikram
authors.initials: V
authors.lastname: Pande
authors.affiliation: Institute for Combustion Technology, Rheinisch-Westfälische Technische Hochschule Aachen, 52056 Aachen, Germany.
authors.forename: Abhishek
authors.initials: A
authors.lastname: Khetan
authors.affiliation: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213; venkvis@cmu.edu bmcclosk@berkeley.edu.
authors.forename: Venkatasubramanian
authors.identifier: http://orcid.org/0000-0003-1060-5495
authors.initials: V
authors.lastname: Viswanathan
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of California, Berkeley, CA 94720; Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; venkvis@cmu.edu bmcclosk@berkeley.edu.
authors.forename: Bryan D
authors.initials: BD
authors.lastname: McCloskey
keywords: Li–air battery; NMR; donor number; lithium nitrate; solubility