Targeted Construction of Amorphous MoS_x with an Inherent Chain Molecular Structure for Improved Pseudocapacitive Lithium‐Ion Response

Abstract

Owing to low ion/electron conductivity and large volume change, transitional metal dichalcogenides (TMDs) suffer from inferior cycle stability and rate capability when used as the anode of lithium‐ion batteries (LIBs). To overcome these disadvantages, amorphous molybdenum sulfide (MoSx) nanospheres were prepared and coated with an ultrathin carbon layer through a simple one‐pot reaction. Combining X‐ray photoelectron spectroscopy (XPS) with theoretical calculations, MoSx was confirmed as having a special chain molecular structure with two forms of S bonding (S2− and S22−), the optimal adsorption sites of Li+ were located at S22−. As a result, the MoSx electrode exhibits superior cycle and rate capacities compared with crystalline 2H‐MoS2 (e.g., delivering a high capacity of 612.4 mAh g−1 after 500 cycles at 1 A g−1). This is mainly attributed to more exposed active S22− sites for Li storage, more Li+ transfer pathways for improved ion conductivity, and suppressed electrode structure pulverization of MoSx derived from the inherent chain‐like molecular structure. Quantitative charge storage analysis further demonstrates the improved pseudocapacitive contribution of amorphous MoSx induced by fast reaction kinetics. Moreover, the morphology contrast after cycling demonstrates the dispersion of active materials is more uniform for MoSx than 2H‐MoS2, suggesting the MoSx can well accommodate the volume stress of the electrode during discharging. Through regulating the molecular structure, this work provides an effective targeted strategy to overcome the intrinsic issues of TMDs for high‐performance LIBs.

MoS2/CN/Fe0.95S1.05 with a Hierarchical Architecture as a Long-Durable Anode for Sodium Ion Batteries

“…The storage mechanism of sodium ions can be judged by the following formula The formula expresses the function of current i and scan rate v , and a and b are constants. If b = 0.5, sodium ions can be stored by the diffusion process, whereas if the value of b is 1, the process of storing charge is controlled by the pseudocapacitance on the surface. , As shown in Figure b, the value of b calculated from oxidation (peak 1) and reduction (peak 2) is 0.92 and 0.97, respectively. This value is between 0.5 and 1, indicating that the diffusion process and the pseudocapacitance coexist in the electrochemical reaction.…”

Ab Initio Molecular Dynamics Simulations of Amorphous Metal Sulfides as Cathode Materials for Lithium–Sulfur Batteries

“…Alternative cathode materials have also been sought to explore new chemistry for sulfur conversion including lithium sulfide (Li 2 S), , organosulfides, , and binary or ternary transition metal sulfides. − A particularly interesting class of materials is amorphous transition metal sulfides (a-MS x ), where the variable valence states of the transition metal allow for possible control of the reaction mechanism through varying the metal-to-sulfur (M/S) ratio. Although these materials are promising candidates for Li–S, − sodium–sulfur (Na–S), , and all-solid-state batteries, − a detailed understanding of their electrochemical behavior is lacking. Indeed, both a conversion-type reaction and a mixture of intercalation/conversion have been reported.…”