Constructing high K+ concentration layer to expedite K+ intercalation in graphite: towards superior rate capability without trading off power density of potassium-ion batteries

Abstract

Graphite anode for potassium-ion batteries suffers poor rate capability because of the sluggish diffusion kinetics of K+. According to the rate law of chemical reactions, enrichment of K+ on the outer layer of graphite anode is expected to improve the rate capability. However, the surface of graphite is too smooth to adsorb adequate K+ to enhance rate capability. Herein, MoS2 is coated on exfoliated graphite to enrich the concentration of K+ on the surface of EG by forming K2S in high-voltage region, leading to an extremely high diffusion coefficient of up to 1000 times than that of bare graphite at the bottleneck stage, which accelerates the reaction rate of electrochemical intercalation process. Consequently, the EG/MoS2 electrode exhibits superior rate performances (125 mAh/g at 3.2 A/g), which is 11 times higher than that of EG. Moreover, the specific capacity of EG/MoS2 is 169 mAh/g at 1.6 A/g below 0.36 V, which is almost 25 times higher than that of bare EG (7 mAh/g). Our study provides new fundamental insights to boost power density of the anodes for PIBs without trading off energy density.