GeV 4 S 8 : a Novel Bimetallic Sulfide for Robust and Fast Potassium Storage.

Potassium-ion batteries (PIBs) have attracted much attention due to their low production cost and abundant resources. Germanium is a promising alloying-type anode with a high theoretical capacity for PIBs, yet suffering significant volume expansion and sluggish potassium-ion transport kinetics. Herein, a rational strategy is formulated to disperse Ge atoms into transition metal V-S sulfide frameworks to form a loosely packed and metallic GeV 4 S 8 medium. The theoretical prediction shows that GeV 4 S 8 is conducive to the adsorption and diffusion of K + . The V-S frameworks provide fast ion/electron diffusion channels and also help to buffer the volume expansion during K + insertion. In situ and ex situ characterizations manifest that KGe alloy clusters are constrained and dispersed by potassiated VS 2 topological structure during discharging, and revert to the original GeV 4 S 8 after charging. Consequently, as a novel anode for PIBs, GeV 4 S 8 provides a high specific capacity of ≈400 mAh g -1 at 0.5 C, maintaining 160 mAh g -1 even at 12.5 C and ≈80% capacity after 1000 cycles at 5 C, superior to most of the state-of-the-art anode materials. The proposed strategy of combining alloy and intercalation dual-functional units is expected to open up a new way for high-capacity and high-rate anode for PIBs.