Theoretical Analysis of a 2D Metallic/Semiconducting Transition‐Metal Dichalcogenide NbS 2 //WSe 2 Hybrid Interface

Phase engineering of layered anode materials during ion-intercalation in Van der Waal heterostructures

Transition metal dichalcogenides (TMDs) are a class of 2D materials demonstrating promising properties, such as high capacities and cycling stabilities, making them strong candidates to replace graphitic anodes in lithium-ion batteries. However, certain TMDs, for instance, MoS₂, undergo a phase transformation from 2H to 1T during intercalation that can affect the mobility of the intercalating ions, the anode voltage, and the reversible capacity. In contrast, select TMDs, for instance, NbS₂ and VS₂, resist this type of phase transformation during Li-ion intercalation. This manuscript uses density functional theory simulations to investigate the phase transformation of TMD heterostructures during Li-, Na-, and K-ion intercalation. The simulations suggest that while stacking MoS₂ layers with NbS₂ layers is unable to limit this 2H → 1T transformation in MoS₂ during Li-ion intercalation, the interfaces effectively stabilize the 2H phase of MoS₂ during Na- and K-ion intercalation. However, stacking MoS₂ layers with VS₂ is able to suppress the 2H → 1T transformation of MoS₂ during the intercalation of Li, Na, and K-ions. The creation of TMD heterostructures by stacking MoS₂ with layers of non-transforming TMDs also renders theoretical capacities and electrical conductivities that are higher than that of bulk MoS₂.

Rational Design of Tungsten Selenide @ N-Doped Carbon Nanotube for High-Stable Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are deemed as one of the most promising energy storage systems due to their high energy density and low cost. However, their commercial application is far away from satisfactory because of limited suitable electrode materials. Herein, core-shell structured WSe₂ @N-doped C nanotubes are rationally designed and synthesized via selenizing WO₃ @ polypyrrole for the first time. The large interlayer spacing of WSe₂ can facilitate the intercalation/deintercalation of K⁺ . Meanwhile, the core-shell structured nanotube provides favorable interior void space to accommodate the volume expansion of WSe₂ during cycling. Thus, the obtained electrode exhibits superb electrochemical performance with a high capacity of 301.7 mAh g^-1 at 100 mA g^-1 over 120 cycles, and 122.1 mAh g^-1 can remain at 500 mA g^-1 even after 1300 cycles. Ex-situ X-ray diffraction analysis reveals the K-ion storage mechanism of WSe₂ @N-doped C includes intercalation and conversion reaction. Density function theory (DFT) calculation demonstrates the reasonable diffusion pathway of K⁺ . In addition, the obtained WSe₂ @N-doped C nanotubes have been used as anode material for lithium-ion batteries, which also show good rate performance and high cycle stability. Therefore, this work offers a new methodology for the ration design of new structure electrode materials with long cycle stability.