Understanding the electrochemical reaction mechanism of VS₂ nanosheets in lithium-ion cells by multiple in situ and ex situ x-ray spectroscopy

Abstract

Recently two-dimensional layered transition metal dichalcogenides (TMDs) have attracted great scientific interest in electrochemical energy storage research. Vanadium disulfide (VS2) as an important family member of TMDs, is a promising electrode material for lithium-ion cells because of its remarkable electrical conductivity and fast Li + diffusion rate, but its electrochemical reaction mechanism is still poorly understood. Herein, we have prepared VS2 nanosheets as the electrode and systematically investigated its structural and chemical evolution during the electrochemical processes by employing both in situ and ex situ X-ray spectroscopy. The VS2 undergoes intercalation and conversion reactions in sequence during discharge and also this process is found to be partially reversible during the subsequent charge. The decreased reversibility of the conversion reaction over extended cycles could be mainly responsible for the capacity fading of the VS2 electrode. In addition, the hybridization strength between S and V shows a strong dependence on the states of charge, as directly illustrated by the intensity change of the V-S hybridized states and pure V states. We have also found that the solid electrolyte interphase on the electrode surface is dynamically evolved during cycling, which may be a universal phenomenon for the conversion-based electrodes. This study is expected to be beneficial for the further development of high-performance VS2-based electrodes.

Porous bowl-shaped VS2 nanosheets/graphene composite for high-rate lithium-ion storage

“…Those two cathodic peaks are ascribed to the phase transition during the Li + intercalation process from VS 2 to Li x VS 2 [24] . For the anodic scan, the oxidation peak in the initial cycle can be assigned to the Li + deintercalation process and the phase was transformed from Li x VS 2 to VS 2 [9,52] . It is noted that there was a weak reduction peak at 2.1 V in the second cathodic scan, which may be connected with the phase change of VS 2 during the lithium intercalation [52] .…”

Emerging Layered Metallic Vanadium Disulfide for Rechargeable Metal‐Ion Batteries: Progress and Opportunities

“…[115] For thinner VS 2 flakes, the Li + intercalation process was reversible, whereas the conversion reaction was not fully reversible in the charging process, during which part of Li 2 Sw as oxidized to S 8 with excess V. Zhang et al also found as imilarL i + storagep rocess based on the analysiso f in situ and ex situ XASr esults;t he hybridization strengthb etween Sa nd Vs trongly depended on the states of charge, and the solid-electrolyte interface (SEI) film dynamically evolved during cycling ( Figure 14 a-f 2 ). [136] Meanwhile, the VS 2 electrode also demonstrated the Li + storage mechanism of the intercalation reaction between 0.5 and 3.0 Vw ith the occurrence of a complexp hase transition for ASSLIBs (Figure 14 g). [47] Similar to other electrode materials in SCs, VS 2 materiale xhibits the electrochemical reactionm echanism of surfacee lectroadsorption with capacitance as the predominant Li + storagep rocess; pseudocapacitive behavior with weak intercalation has also been probed.…”

“…Reproducedw ith permission. [136] Copyright 2018, IOP Science.g )Schematic illustration of the ASSLIB. Reproduced with permission.…”

“…In previous reports on the VS 2 electrode, LiPF 6 in EC-DMC, [38,92,100,102,115,136] LiPF 6 in EC-DMC-DEC, [91] LiClO 4 in PC, [80] APC + LiCl in THF, [96] and LiTFSI-LiNO 3 in DOL-DME [36] were usually used as the electrolyte for LIBs. NaSO 3 CF 3 in DGM, [78,86,103,109,110,137] NaSO 3 CF 3 in TGD, [37] NaPF 6 in TEGDME, [121] and NaClO 4 in EC-PC-FEC [38,101] wereu sually used as the elec-trolyte of SIBs.…”

“…d) Charge voltage profile at 0.2 A g −1 and corresponding XAS spectra of e) S and f) V K‐edge during the first charge process. Reproduced with permission . Copyright 2018, IOP Science.…”