Rational design and regulation of tremella-like selenium-doped MoS₂ for highly reversible sodium storage

Abstract

Molybdenum disulfide (MoS2), due to its high theoretical specific capacity (670 mAh g-1), has evoked considerable investigation interest regarding Na+ storage. Nonetheless, the irreversible conversion of original material MoS2 into...

S-doped C@MoSe2(1-x)S2x@MWCNT heterostructure as high-rate and long-cycle stability anodes for Na+ batteries

“…11c display the out-of-plane (A1g) (238 cm -1 ) and in-plane (E 2g 1 ) (283 cm -1 ) vibrational modes of Mo-Se. There is no obvious detection of signals of Mo-S out-of-plane (A1g) and in-plane (E 2g 1 ) at ~400 cm -1 , reflecting that the amount of doped S in the system is low [7]. It was observed that the strength ratio of (A1g) to (E 2g 1 ) in C@MoSe2(12.26)、 C@MoSe2(1-x)S2x@MWCNT (14.31) and PEG-200-2-C@MoSe2(1-x)S2x@MWCNT (13.82) are rather close, which confirms that the coating of carbon on MoSe2(1-x)S2x@MWCNT does not adversely affect the layered structure of the three samples [7,33].…”

“…After the second cycle, the peak at 1.4 V (discharging) is related to the conversion of MoSe2(1-x)S2x to Mo and Na2Se (Na2S). Peaks at 1.69 V (charging) is related to the conversion of Na2Se (Na2S) to Se (S), and oxidation of Mo (MoSe2(1-x)S2x) [7,27].…”

“…Sodium (Na) has chemical properties like that of lithium (Li) [1,2], and being abundant it is much cheaper than lithium [3][4][5][6]. However, due to the bigger radius of Na + (1.06 Å > 0.76 Å (Li + )), and the low mobility of Na + in anodes of sodium-ion batteries (SIB) leads to poor performance [2,[7][8][9][10][11][12][13]. Therefore, finding suitable anode materials is one of the key factors to improve the performance of SIB.…”

“…Theoretically, MoSe2 has electrochemical properties like that of MoS2, and can be used as anode material for SIB [30][31][32][33][34][35][36][37][38]. Because the relatively high conductivity (10 −4 S m −1 ) and large radius (1.6 Å) of selenium (Se), doping Se into MoS2 lattice to form S2−xSex interlayer will increase conductivity and expand interlayer spacing, thereby enhancing Na + storage capacity [7,21,[30][31][32]. For example, Liu et al constructed MoSSeNSs@NC/hC-NC for SIB, and due to the partial replacement of sulfur (S) by Se, the MoSSe delivered higher SIB storage capacity [30].…”

“…Fig.S7adisplays the survey spectrum that displays Se, C, S and Mo signals. For the Mo 3d, the Mo 3d5/2 and 3d3/2 signals are at 229.0 eV and 232.2 eV binding energy, respectively, assignable to Mo +4 state (Fig.11d)[7,[32][33][34]. For the Se 3d, the Se 3d peaks at 54.6 eV (Se 3d5/2) and 55.7 eV (Se 3d3/2) are corresponding to those of Se +2 state (Fig.11e), and the profile in Fig.11fcan be deconvoluted into three components of 161.2 (Se 3p3/2), 162.5 (S 2p3/2) and 163.5 (S 2p1/2) eV.…”