Unexpected intercalation-dominated potassium storage in WS2 as a potassium-ion battery anode

Yuhan Wu,Pengbo Lyu,Jin Wen,Chenglin Zhang,Yang Xu,Min Zhou,Yaoguo Fang,Huaping Zhao,Yong Lei,Ute Kaiser,Yueliang Li

doi:10.1007/s12274-019-2543-0

Abstract

Unexpected intercalation-dominated process is observed during K+ insertion in WS2 in a voltage range of 0.01–3.0 V. This is different from the previously reported two-dimensional (2D) transition metal dichalcogenides that undergo a conversion reaction in a low voltage range when used as anodes in potassium-ion batteries. Charge/discharge processes in the K and Na cells are studied in parallel to demonstrate the different ion storage mechanisms. The Na+ storage proceeds through intercalation and conversion reactions while the K+ storage is governed by an intercalation reaction. Owing to the reversible K+ intercalation in the van der Waals gaps, the WS2 anode exhibits a low decay rate of 0.07% per cycle, delivering a capacity of 103 mAh·g-1 after 100 cycles at 100 mA·g-1. It maintains 57% capacity at 800 mA·g-1 and shows stable cyclability up to 400 cycles at 500 mA·g-1. Kinetics study proves the facilitation of K+ transport is derived from the intercalation-dominated mechanism. Furthermore, the mechanism is verified by the density functional theory (DFT) calculations, showing that the progressive expansion of the interlayer space can account for the observed results.

Highlights

Research on sodium-ion and potassium-ion batteries (SIBs and PIBs) has been rapidly increasing since the late 2000s to examine their feasibility to serve as the alternatives of lithium-ion batteries (LIBs) [1,2,3,4,5,6,7,8]
By comparing the charge/discharge processes of WS2 in SIBs and PIBs, we showed that the Na+ storage in WS2 follows the well-recognized path, i.e., a conversion reaction at the high voltage range followed by an intercalation reaction at the low voltage range, while the K+ storage in WS2 is governed by the intercalation reaction rather than the conversion reaction
Commercial WS2 powders were used as received, and the experimental details can be found in the Electronic Supplementary Material (ESM)

Summary

Introduction

Research on sodium-ion and potassium-ion batteries (SIBs and PIBs) has been rapidly increasing since the late 2000s to examine their feasibility to serve as the alternatives of lithium-ion batteries (LIBs) [1,2,3,4,5,6,7,8]. In the Na cell (Fig. 1(b)), Cycle1 discharge displays two well-defined plateaus at 0.6 and 0.25 V that correspond to the intercalation and conversion processes during the Na insertion, respectively [24, 25], delivering an initial capacity of 649 mAh·g−1.

Results

Conclusion