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.
Zn-ion hybrid supercapacitors (ZHSCs) are emerging charge storage devices that inherit many of the advantages of supercapacitors and batteries. However, problems such as unsatisfactory cycling stability and low energy density need to be solved urgently, which can be accomplished by developing cathode materials with excellent properties. Herein, we report the development of performance-enhanced ZHSCs obtained by incorporating N and S heteroatoms into orange peel-based hierarchical porous carbon (NS-OPC) to facilitate Zn 2+ adsorption. The results of ex situ photoelectron spectroscopy and X-ray diffraction demonstrated the presence of −OH and Zn 2+ chemisorbed and Zn 4 SO 4 (OH) 6 •5H 2 O during charging and discharging, respectively. Density functional theory calculations show that double doping can promote the chemisorption/desorption kinetics of Zn 2+ and thus promote the electrochemical charge storage of C materials. Impressively, when used to assemble ZHSCs, the device still has an energy density of 53.9 Wh kg −1 , a high power density of 6063.75 W kg −1 , and an 86.2% capacity retention after 10,000 cycles. This study not only provides a reasonable technique for developing superior C-based electrode materials but also contributes to the understanding of the charge storage process in heteroatom-doped C materials.
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