Weyl semimetal orthorhombic Td-WTe2as an electrode material for sodium- and potassium-ion batteries.

Alkali metals such as sodium and potassium have become promising candidates for the next generation of monovalent-ion batteries. However, a challenge for these battery technologies lies in the development of electrode materials that deliver high capacity and stable performance even at high cycling currents. Here we study orthorhombic tungsten ditelluride or Td-WTe2as an electrode material for sodium- (SIB) and potassium-ion batteries (KIB) in propylene carbonate (PC) based electrolyte. Results show that despite larger Shannon's radius of potassium-ions and their sluggish diffusion in Td-WTe2due to higher overpotential, at 100 mA.g-1KIB-half cells showed higher cycling stability and low capacity decay of 4% versus 16% compared to SIB-half cells. Likewise, in a rate capability test at 61stcycle (at 50 mA.g-1), the KIB-half cells yielded charge capacity of 172 mAh.g-1versus 137 mAh.g-1of SIB-half cells. The superior electrochemical performance of Td-WTe2electrode material in KIB-half cells is explained based on the concept of Stokes' radius-smaller desolvation activation energy resulted in higher mobility of potassium-ions in PC-based electrolyte. In addition, the likely mechanisms of electrochemical insertion and extraction of Na- and K-ions in Td-WTe2are also discussed.

TMDs beyond MoS2 for Electrochemical Energy Storage.

Atomically thin sheets of two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted interest as high capacity electrode materials for electrochemical energy storage devices owing to their unique properties (high surface area, high strength and modulus, faster ion diffusion, and so on), which arise from their layered morphology and diversified chemistry. Nevertheless, low electronic conductivity, poor cycling stability, large structural changes during metal-ion insertion/extraction along with high cost of manufacture are challenges that require further research in order for TMDs to find use in commercial batteries and supercapacitors. Here, a systematic review of cutting-edge research focused on TMD materials beyond the widely studied molybdenum disulfide or MoS2 electrode is reported. Accordingly, a critical overview of the recent progress concerning synthesis methods, physicochemical and electrochemical properties is given. Trends and opportunities that may contribute to state-of-the-art research are also discussed.

Superior electrochemical performance of layered WTe2 as potassium-ion battery electrode.

Potassium-ion batteries or KIBs are prominent candidates among research involving post lithium-ion batteries due to abundant availability, low-cost, and low standard reduction potential of potassium metal. Although some chemistry correlation with other monovalent alkali metal-ion batteries may exist, research on KIB chemistry is still in its infancy. A relevant research aspect of KIB is the development of a stable anode material that can efficiently cycle the large K+ ions in its crystal structure within the 0 to 3 V potential window range; providing reasonable charge capacity and high reversibility. To this end, transition metal dichalcogenides or TMDs are promising electrode materials because of their favorable electrochemical properties. In this work, we study electrochemical performance of tungsten ditelluride (WTe2) TMD as working electrode in a KIB half-cell. Results show that WTe2, a telluride-based TMD, has high first cycle specific charge capacity-with up to 3.3 K+ stored per WTe2 molecule (at least 4 times that of WS2 electrode)-stable capacity of 143 mAh g-1 at 10th cycle number-outperforming WS2 (66 mAh g-1) and graphite (95 mAh g-1)-good reversibility, reasonable cycling stability, and low charge transfer resistance.

SiOC functionalization of MoS2 as a means to improve stability as sodium-ion battery anode.

The development of feasible, scalable, and environmentally-safe electrode materials that provide stable cycling performance are critical for success of beyond lithium rechargeable batteries and supercapacitors. With respect to the sodium-ion battery (SIB) anodes constituting of transition metal dichalcogenides such as molybdenum disulfide (MoS2), poor cycle stability and fast capacity degradation, due to low electronic conductivity and dissolution of chemical species in the electrolyte, hinders use of these promising layered materials as SIB anodes. Herein we report chemical functionalization in MoS2 nanosheets with polymer-derived silicon oxycarbide or SiOC with the aim to preserve MoS2 from dissolution in the SIB organic electrolyte, without compromising its role in sodiation and desodiation processes. Our results suggest that a MoS2-SiOC composite electrode is effective in bringing improved cycle stability to sodium-ion cycling over neat MoS2 even after 100 cycles.