Tuning LiO Formation Routes by Facet Engineering of MnO Cathode Catalysts.

In lithium-oxygen batteries, the solubility of LiO intermediates in the electrolyte regulates the formation routes of the LiO discharge product. High-donor-number electrolytes with a high solubility of LiO tend to promote the formation of LiO 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 LiO. In this work, β-MnO crystals with high occupancies of {111} or {100} facets were adopted as cathode catalysts in Li-O batteries with a tetra(ethylene)glycol dimethyl ether electrolyte. The {111}-dominated β-MnO catalyzed the formation of the LiO discharge product into large toroids following the solution routes, while {100}-dominated β-MnO facilitated the formation of LiO thin films through the surface routes. Further computational studies indicate that the different formation routes of LiO could be related to different adsorption energies of LiO on the two facets of β-MnO. Our results demonstrate that facet engineering of cathode catalysts could be a new way to tune the formation route of LiO 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.