Tuning Li2O2 Formation Routes by Facet Engineering of MnO2 Cathode Catalysts

In lithium-oxygen batteries, the solubility of LiO 2 intermediates in the electrolyte regulates the formation routes of the Li 2 O 2 discharge product. High-donor-number electrolytes with a high solubility of LiO 2 end to promote the formation of Li 2 O 2 large particles following the solution route, which eventually benefits the cell capacity and cycle life. Here, we propose that facet engineering of cathode catalysts could be another direction in tuning the formation routes of Li 2 O 2 . In this work, β-MnO 2 crystals with high occupancies of {111} or {100} facets were adopted as cathode catalysts in Li-O 2 batteries with a tetra(ethylene)glycol dimethyl ether electrolyte. The {111}-dominated β-MnO 2 catalyzed the formation of the Li 2 O 2 discharge product into large toroids following the solution routes, while {100}-dominated β-MnO 2 facilitated the formation of Li 2 O 2 hin films through the surface routes. Further computational studies indicate that the different formation routes of Li 2 O 2 could be related to different adsorption energies of LiO 2 on the two facets of β-MnO 2 . Our results demonstrate that facet engineering of cathode catalysts could be a new way to tune the formation route of Li 2 O 2 in a low-donor-number electrolyte. We anticipate that this new finding would offer more choices for the design of lithium-oxygen batteries with high capacities and ultimately a long cycle life.