(Invited) Investigation of Phosphorene in Electrochemical Energy Storage Devices

Abstract

Among the family of atomically thin two-dimensional (2D) materials, phosphorene (a monolayer of black phosphorus) has special significance since it offers a direct band gap that lies in-between the zero gap graphene and various large band gap 2D transitional metal dichalcogenides. Phosphorene is an atomically thin sheet in which each phosphorus atom bonds with three neighboring atoms forming a puckered honeycomb structure. So far the research community has mainly focused on the electronic and opto-electronic applications of phosphorene such as logic transistors and photo-detectors. The exploration of this unique material in electrochemical energy storage is still very much in its infancy. In my talk, I will show that incorporation of few-layer nanosheets of phosphorene into a porous carbon nanofiber network (cathode matrix) can significantly improve the cycle life of Lithium-Sulfur (Li-S) batteries. After 500 continuous cycles of charge-discharge, the specific capacity of the Li-S battery with phosphorene is retained above 660 mAh g−1 with only ~0.053% capacity decay per cycle, much better than the baseline battery (without phosphorene) which shows ~0.25% capacity fade per cycle in only 200 cycles under the same test condition. First-principles density functional theory calculations indicate that this improvement is related to phosphorene’s ability to immobilize lithium polysulfides. The binding energy of various lithium polysulfides to phosphorene ranges from 1-2.5 eV, which is significantly greater than a carbon hexatom network (~0.5 eV). Our results also indicate that the presence of phosphorene lowers the polarization, accelerates the redox reaction and improves sulfur utilization in the battery. Such work indicates the promise of phosphorene and will give further impetus to the research community to explore the fundamental science and applications of phosphorene in the context of electrochemical energy storage.