Phase Transformation of 1T′-MoS₂ Induced by Electrochemical Prelithiation for Lithium-Ion Storage

Abstract

Two-dimensional (2D) MoS 2 is one of the most representative materials of the transition metal dichalcogenide (TMD) family, which is mostly studied in the semiconductor 2H and metal 1T phases. However, the properties of the metalloid 1T′ phase remain unclear because of its immature preparation process and thermodynamic instability (metastable state). Herein, this study used theoretical calculations to discover the relationship and conditions for MoS 2 to transition between the 2H, 1T, and 1T′ phases. Meanwhile, charge and discharge voltages and current density were controlled by ion insertion technology, and then 1T′-MoS 2 with large size and definite morphology (the whole process was called "phase transition engineering") was prepared. The prepared 1T′-MoS 2 was used as the anode material for lithium-ion batteries. Compared with 2H-MoS 2 , the cyclic stability and specific capacity of 1T′-MoS 2 were greatly improved. In addition, phase transformation of natural molybdenite (2H-MoS 2 ) by phase transition engineering also yielded promising electrochemical properties. Consequently, phase transition engineering not only provided an opportunity for the phase transformation of TMDs of natural sulfide metals such as molybdenite but also offered an effective method to investigate the properties of 2D metastable polymorphic materials.

Synergistic Effect of Nitrogen–Sulfur Codoping on Honeycomb-like Carbon-Based High-Energy-Density Zinc-Ion Hybrid Supercapacitors

“…No similar redox peaks were found in the CV curves of the N-OPC (Figure b) and OPC samples (Figure c). In general, the charge storage mechanism can be studied using the relationship between the peak current ( i ) and scan rate ( v ): i = a v b where a and b are constants whose values depend on the logarithm of the scan rate – the intercept of the logarithm of the peak current and the slope of the curve . When b = 1, the capacitive behavior contributes to charge storage; when b = 0.5, the ion diffusion control contributes to charge storage; when 1 > b > 0.5, a hybrid mechanism exists in the charge storage process, i.e., capacitive behavior and ionic diffusion contribute to charge storage.…”

“…where a and b are constants whose values depend on the logarithm of the scan rate − the intercept of the logarithm of the peak current and the slope of the curve. 57 When b = 1, the capacitive behavior contributes to charge storage; when b = 0.5, the ion diffusion control contributes to charge storage; when 1 > b > 0.5, a hybrid mechanism exists in the charge storage process, i.e., capacitive behavior and ionic diffusion contribute to charge storage. As shown in Figure S4a, the b values of the oxidation and reduction peaks of NS-OPC are 0.935 and 0.859, respectively, indicating the presence of a mixed mechanism during the storage of Zn ions.…”

Progress of transition metal sulfides used as lithium-ion battery anodes

“…Compared with the 2H semiconductor phase, it has higher conductivity (approximately 107 times that of the 2H phase), larger interlayer spacing (approximately 1.0 nm), and more lithium-ion intercalation active sites. [86][87][88] The 1T phase is a metastable structure, which has not been observed in nature so far, but it can be successfully prepared under certain experimental conditions. Common preparation methods include ion intercalation (Li + , Na + , k + ), hot electrons doping method (mainly used for the preparation of single layer 1T-MoS 2 ), and mild hydrothermal/solvothermal method (changing molybdenum source, sulfur source, temperature).…”

Modulating Trinary‐Heterostructure of MoS2 via Controllably Carbon Doping for Enhanced Electrocatalytic Hydrogen Evolution Reaction

“…First, sustainable efforts in increasing the metallic phase conversion content or direct synthesis in step‐economical manners lack the features necessary for industrial applications due to unfavorable thermodynamic metastability. [ 24,25 ] Second, understanding the actual mechanism of phase transition by combining the computational and intuitively experimental methods is also urgent, which can pave the way to access the stable metallic phase in a high yield. [ 26,27 ] Finally, the identification of the heterogeneous interfaces between 2H/1T, 2H/1T′, and 1T/1T′ as active sites during HER process has never been experimentally proven nor discussed by density functional theory calculation.…”