Rapid deposition of WS2 platelet thin films as additive-free anode for sodium ion batteries with superior volumetric capacity

One of the key issues hampering the practical application of powerful and thin sodium-ion batteries (SIBs) is low volumetric capacity. The purpose of this study is to report an innovative sputtering strategy to directly construct the vertically-aligned WS2 columnar platelet films with low-tortuosity pores (VA/LT-WS2) on an Al foil as an additive-free anode. Profiting from a 6 nm carbon overlayer on the top of the thickness-controllable film electrode (VA/LT-WS2/C), the vertical feature of WS2 and carbon layer enable high efficiency of ion and electron transportation pathways, respectively. The 2.8 mu m VA/LT-WS2/C film anode exhibits a high volumetric capacity of 1,339 mAh.cm(-3) at 100 mA.g(-1), of which 30.2% is recorded when the current density gets a 50-fold increase from 100 to 5,000 mA.g(-1). Its gravimetric capacity of 366.8 mA.g(-1) is comparable to the reported WS2 based anode materials for SIBs. Moreover, it is interesting to note that the discontinuous carbon layer (6 nm thickness) protects the presence of solid electrolyte interphase (SEI) layer from cracking caused by the volume expansion of WS2 anode, and less than 16.7% volumetric capacity fading is presented after 300 cycles. It outperforms most of the recently reported outstanding SIBs anode materials. The SIB full cell exhibited a reversible volumetric capacity of 554 mAh.cm(-3) at 50 mA.g(-1) when the additive-free anode was applied in the VA/LT-WS2/C//Na2V3(PO4)(3)/C full cell, demonstrating the potential of the physical sputtering VA/LT-WS2/C for further battery development.