Dual Regulation of Metal Doping and Adjusting Cut‐Off Voltage for MoSe₂ to Achieve Reversible Sodium Storage

Abstract

MoSe2, as a typical 2D material, possesses tremendous potential in Na‐ion batteries (SIBs) owing to larger interlayer distance, more favorable band gap structure, and higher theoretical specific capacity than other analogs. Nevertheless, the low intrinsic electronic conductivity and irreversible conversion of discharged products of Mo/Na2Se to MoSe2 seriously hamper its electrochemical performance. Herein, through a facile hydrothermal method combined with calcination process, Sn‐doped MoSe2 nanosheets grown on graphene substrate in the vertical direction are fabricated. Benefiting from the improved electronic conductivity contributed by the abundant defects and expanded interlamellar spacing of MoSe2 originated from Sn doping, combined with a smart strategy of raising discharge cut‐off voltage to 0.2 V during the actual performance testing for SIBs, the as‐fabricated anode material delivers superior Na‐ions storage performance in terms of electrons/ions transfer, reversible sodium storage as well as cycle stability. An ultra‐stable reversible specific capacity of 268.5 mAh g–1 at 1 A g–1 can be maintained after 1600 cycles. Moreover, the great sodium storage property in the SIB full‐cell system of the as‐obtained nanocomposite illustrates practical potential. Density functional theory calculation and in situ/ex situ measurements are employed to further reveal the storage mechanism and process of Na‐ions.

Dual modification of Ti3C2Tx MXene hybridization and cut-off voltage adjustment for MoS2 to achieve stable sodium storage performance

“…3i, the exact values of σ for the DCV-0.05, DCV-0.1, DCV-0.2, and DCV-0.3 V are 154.4, 53.2, 48.7, and 37.3 Ω s −1/2 , respectively, demonstrating that the higher discharge cut-off voltage facilitates the ionic diffusion. 50 Of note, the regular variations show high consistency with the voltage-dominated electrochemical mechanism that the higher discharge cut-off voltage will restrict the deep conversion reaction, thus modifying the kinetics of electrochemical redox. 51…”

“…However, the initial charge capacity is only 379.8 mA h g −1 , corresponding to an initial Coulombic efficiency of 57.1%, which further reveals the irreversible initial electrochemical process. 50 Besides, the gradual degradation of the discharge/charge profiles and decreased specific capacity indicate the collapse of the layered structure of the obtained MoS 2 /Ti 3 C 2 T x . 5 Increasing the discharge cut-off voltage leads to the decrease of specific capacity due to the restricted conversion reaction.…”

“…In principle, the Na + storage capacity in the target MoS 2 /Ti 3 C 2 T x is determined by both the intercalation and subsequent phase transition mechanism, where the high specific capacity can be obtained with low discharge cut-off voltage. 50 However, the deep conversion reaction accompanied by large volume change in the low voltage region degrades the layered structure of the target electrode, thus resulting in unstable cycling. 31 Theoretically, optimization of the discharge cut-off voltage inevitably sacrifices some initial specific capacity, but dramatically modifies the cycling stability and electrochemical reversibility.…”

“…20 Comparatively, the layered Ti 3 C 2 T x and (002) plane of MoS 2 can be still detected for the MoS 2 /Ti 3 C 2 T x within 0.2–3.0 V, showing clear contrast with that within 0.05–3.0 V. In general, the well-maintained morphology, combining the robust layered structure, manifests that the increased discharge cut-off voltage contributes to improving the reversibility of the electrochemical redox and retaining the inner structure of the active material. 50 To get clear understanding of the effect of discharge cut-off voltage on the working mechanism and structure stability of the target MoS 2 /Ti 3 C 2 T x , the typical illustration is depicted in Fig. 6g.…”

Thermodynamic Transformation of Crystalline Organic Hybrid Iron Selenide to FexSey@CN Microrods for Sodium Ion Storage

“…Sodium-ion batteries (SIBs) have been regarded as a promising energy storage technology, because of their exceptional advantages of abundant resource and high economic efficiency. − Because of the large theoretical capacity and good electrochemical reversibility, − inorganic metal chalcogenides (such as MoS 2 , FeSe 2 , Sb 2 Se 3 ) have attracted growing attention as anode materials of SIBs. − However, most of inorganic metal chalcogenides face some challenges in the electrochemical reactions, including poor electric conductivity, huge volume changes, and sluggish ionic transport kinetics. Thus, rational design of micronanostructures of metal chalcogenides and decoration with carbon materials are necessary to improve their capability for sodium-ion storage. − Until now, several approaches have been developed to prepare carbon-coated metal chalcogenide composites as anode materials for SIBs.…”