Graphene Oxide Membranes for Highly Efficient Rechargeable Li-O2 Batteries: Suppressing the Crossover of Redox Mediator

Abstract

Lithium-oxygen (Li-O2) battery is a promising energy storage system with high energy density, but several challenges such as its high overpotential and poor cyclability have limited the commercialization of Li-O2 batteries. One of strategies to address such issues is introduction of redox mediators (RMs) as soluble catalysts, which have mobility for decomposition of tethered discharge products on air cathode. Although RMs are expected to efficiently perform the catalytic effects at the initial cycles, undesired crossover of RMs from cathode to Li metal anode could deteriorate the cell performance by accompanying parasitic side reactions. For instance, 5,10-dihydro-5,10-dimethylphenazine (DMPZ) was reported as an oxygen evolution reaction (OER) RM, which showed an exceptionally low charge overpotential at the first cycle, but rapidly lost its high performance due mainly to the transport of DMPZ to the Li metal during repeated operations. Here, we report an excellent suppression of RM crossover for highly efficient Li-O2 batteries using a graphene oxide (GO) membrane prepared by a facile vacuum filtration on a porous support. The size of GO nanochannels is narrow enough to selectively allow the transport of small Li+ ions while rejecting the larger DMPZ molecules. The negative surface charges of GO further repel negative ions via Donnan exclusion, greatly improving the lithium ion transference number. Ultimately, the Li-O2 cells with GO membranes maximize the redox-mediation activity of DMPZ with improved performance, achieving energy efficiency of above 80% for more than 25 cycles, and 90% for 78 cycles when the capacity limits were 0.75 and 0.5 mAh cm-2, respectively. Considering the facile method for GO membrane fabrication, combination of GO membrane and RMs can be cost-effective solution for pragmatic Li-O2 batteries.