Few‐Layer MoSe₂ Nanosheets with Expanded (002) Planes Confined in Hollow Carbon Nanospheres for Ultrahigh‐Performance Na‐Ion Batteries

Abstract

Sodium-ion batteries (SIBs) are considered as a promising alternative to lithium-ion batteries, due to the abundant reserves and low price of Na sources. To date, the development of anode materials for SIBs is still confronted with many serious problems. In this work, encapsulation-type structured MoSe 2 @hollow carbon nanosphere (HCNS) materials assembled with expanded (002) planes few-layer MoSe 2 nanosheets confined in HCNS are successfully synthesized through a facile strategy. Notably, the interlayer spacing of the (002) planes is expanded to 1.02 nm, which is larger than the intrinsic value of pristine MoSe 2 (0.64 nm). Furthermore, the few-layer nanosheets are space-confined in the inner cavity of the HCNS, forming hybrid MoSe 2 @HCNS structures. When evaluated as anode materials for SIBs, it shows excellent rate capabilities, ultralong cycling life with exceptional Coulombic efficiency even at high current density, maintaining 501 and 471 mA h g −1 over 1000 cycles at 1 and 3 A g −1 , respectively. Even when cycled at current densities as high as 10 A g −1 , a capacity retention of 382 mA h g −1 can be achieved. The expanded (002) planes, 2D few-layer nanosheets, and unique carbon shell structure are responsible for the ultralong cycling and high rate performance.

TiO2‐Coated Interlayer‐Expanded MoSe2/Phosphorus‐Doped Carbon Nanospheres for Ultrafast and Ultralong Cycling Sodium Storage

“…According to previous research, [16][17][18][19] construction of rational nanostructures and formation of carbon-based composites are effective approaches. [23] These results confirm that sodium storage performance can be enhanced through rational nanostructure engineering. On the other hand, the interlayer-expanded structures are very critical, which can provide efficient ion migration channels, facilitating to enhance charge/discharge kinetics.…”

“…Compared with CV curves of the MoSe 2 /P-C and TiO 2 ( Figure S5, Supporting Information), the peak at 1.53 V corresponds to the Na + intercalation into anatase TiO 2 phase. [23,49] Accordingly, the oxidation peaks at 1.67 and 2.10 V are associated with the oxidation of Mo to MoSe 2 and Na x TiO 2 to TiO 2 , respectively. [23,49] Accordingly, the oxidation peaks at 1.67 and 2.10 V are associated with the oxidation of Mo to MoSe 2 and Na x TiO 2 to TiO 2 , respectively.…”

“…Briefly, the uniform PPy-PMo 12 nanospheres are first synthesized through a polymerization reaction of phosphomolybdic acid and pyrrole forming polypyrrole-phosphomolybdic acid (PPy-PMo 12 ). According to the Bragg equation, the interlayer spacing is calculated to be 1.26 nm, indicating formation of an expanded interlayer, which may be attributed to the intercalation of in situ carbon between the interlayers [23,36] during the PPy-PMo 12 precursor calcination with Se powder at 700 °C. Finally, MoSe 2 /P-C@TiO 2 nanospheres are successfully obtained after calcination with Se powder in a tube furnace.…”

“…The Mo 3d core level spectrum is shown in Figure 3A, which can be fitted into four peaks at 227.8, 230.9, 232.6, and 235.5 eV. [23] In addition, the peaks at 232.6 and 235.5 eV represent the appearance of Mo 6+ due to the partial oxidization of MoSe 2 . [23] In addition, the peaks at 232.6 and 235.5 eV represent the appearance of Mo 6+ due to the partial oxidization of MoSe 2 .…”

A 3D Trilayered CNT/MoSe2/C Heterostructure with an Expanded MoSe2 Interlayer Spacing for an Efficient Sodium Storage

“…Considering the high ramping rate (5 °C min −1 ) during the first annealing process, the expansion in our work may be due to the annealing in a confined undulated surface of the core-shell structure. [30][31][32][33] In fact, the MoSe 2 layers possess a weak van der Waals interaction between the adjacent layers that were controlled by the annealing ramping rate and structure configuration, [25,26] thereby resulting in the expansion. This expansion will not only improve the ionic storage but also increase the intrinsic conductivity.…”