Polymorphic Cobalt Sulfide-Embedded Graphene Foam with Ultralong Cycling and Ultrafast Rate Capability for Potassium-Ion Batteries

Abstract

Potassium-ion batteries (KIBs) attract growing attention due to their low price and abundant resources. However, the main drawback is the large-sized potassium ions, which results in a lack of superior capacity and desirable stable materials. We herein propose the Co9S8/GF nanocomposite synthesized by a solvothermal route followed by heat treatment under the reduction atmosphere with the CoS/GF nanocomposite as the control group. The as-synthesized Co9S8 has a typical morphology of vertically arranged uniform nanosheet arrays. The Co9S8/GF nanocomposite electrode delivers a capacity of 345.65 mAh·g–1 after 600 cycles at 500 mA·g–1 and even 343.06 mAh·g–1 after 1360 cycles at 5000 mA·g–1 in KIBs. Besides, the discharge capacity can reach 461.05 mAh·g–1 after the current increases to 5000 mA·g–1 and a reversible capacity of 578.40 mAh·g–1 when the current density recovers to 250 mA·g–1 again. At last, the charge storage behaviors are mainly discussed, and the unique structure can suffer the volumetric change, especially at high current density, which opens up a novel and effective way to build the embedded porous structure for the next-generation KIB technology.