Experimental and Modeling Analysis of Holey Graphene Electrodes for High-Power-Density Li-Ion Batteries

Abstract

The performances of lithium-ion batteries (LIBs) using holey graphene (HGNS) as the anode material are compared with those using non-holey graphene (GNS). The effects of graphene holes on ion transport are analyzed with a combined experiment/modeling approach involving molecular dynamics (MD) simulations. The large aspect ratio of GNS leads to long transport paths for Li ions, and hence a poor rate capability. We demonstrate by both experiments and simulations that the holey structure can effectively improve the rate capability of LIBs by providing shortcuts for Li ion diffusion through the holes in fast charge/discharge processes. The HGNS anode exhibits a high specific capacity of 745 mAh/g at 0.1 A/g (after 80 cycles) and 141 mAh/g at a large current density of 10 A/g, which are higher than the capacity values of the GNS counterpart by 75% and 130%, respectively. MD simulations also reveal the difference in lithium ion transport between GNS and HGNS anodes. The calculations indicate that the HGNS system has a higher diffusion coefficient for lithium ions than the GNS system. In addition, it shows that the holey structure can improve the uniformity and quality of the solid electrolyte interphase (SEI) layer, which is important for Li ion conduction across this layer to access the electrode surface. Moreover, quantum chemistry (QC) computations show that ethylene carbonate (EC), a cyclic carbonate electrolyte with five-membered-ring molecules, has the lowest electron binding energy of 1.32 eV and is the most favorable for lithium-ion transport through the SEI layer. A holey structure facilitates uniform dispersion of EC on graphene sheets and thus enhances the Li ion transport kinetics.

Keywords

• holey graphene
• lithium ion battery
• molecular dynamics
• diffusion
• rate capability
• solid electrolyte interphase