Folding Graphene Film Yields High Areal Energy Storage in Lithium-Ion Batteries

Abstract

We show that a high energy density can be achieved in a practical manner with freestanding electrodes without using conductive carbon, binders, and current collectors. We made and used a folded graphene composite electrode designed for a high areal capacity anode. The traditional thick graphene composite electrode, such as made by filtering graphene oxide to create a thin film and reducing it such as through chemical or thermal methods, has sluggish reaction kinetics. Instead, we have made and tested a thin composite film electrode that was folded several times using a water-assisted method; it provides a continuous electron transport path in the fold regions and introduces more channels between the folded layers, which significantly enhances the electron/ion transport kinetics. A fold electrode consisting of SnO2/graphene with high areal loading of 5 mg cm(-2) has a high areal capacity of 4.15 mAh cm(-2), well above commercial graphite anodes (2.50-3.50 mAh cm(-2)), while the thickness is maintained as low as 20 pm. The fold electrode shows stable cycling over 500 cycles at 1.70 mA cm(-2) and improved rate capability compared to thick electrodes with the same mass loading but without folds. A electrode coupled with LiCoO2 cathode was assembled and delivered an areal capacity of 2.84 mAh cm(-2) after 300 cycles. This folding strategy can be extended to other electrode materials and rechargeable batteries.