Abstract
Based on multielectron conversion reactions, layered transition metal dichalcogenides are considered promising electrode materials for sodium‐ion batteries, but suffer from poor cycling performance and rate capability due to their low intrinsic conductivity and severe volume variations. Here, interlayer‐expanded MoSe2/phosphorus‐doped carbon hybrid nanospheres coated by anatase TiO2 (denoted as MoSe2/P‐C@TiO2) are prepared by a facile hydrolysis reaction, in which TiO2 coating polypyrrole‐phosphomolybdic acid is utilized as a novel precursor followed by a selenization process. Benefiting from synergistic effects of MoSe2, phosphorus‐doped carbon, and TiO2, the hybrid nanospheres manifest unprecedented cycling stability and ultrafast pseudocapacitive sodium storage capability. The MoSe2/P‐C@TiO2 delivers decent reversible capacities of 214 mAh g−1 at 5.0 A g−1 for 8000 cycles, 154 mAh g−1 at 10.0 A g−1 for 10000 cycles, and an exceptional rate capability up to 20.0 A g−1 with a capacity of ≈175 mAh g−1 in a voltage range of 0.5–3.0 V. Coupled with a Na3V2(PO4)3@C cathode, a full cell successfully confirms a reversible capacity of 242.2 mAh g−1 at 0.5 A g−1 for 100 cycles with a coulombic efficiency over 99%.
Highlights
Sun’s group successfully synthesized interlayer-expanded MoSe2@hollow carbon nanosphere (HCNS) materials, which exhibited a specific capacity of 471 mAh g−1 after 1000 cycles at 3.0 A g−1.[23]. These results confirm that sodium storage performance can be enhanced
Its theoretical specific capacity is fairly low, it can serve as an effective protective layer for other electrode materials with severe volume expansion, such as metal oxides or metal sulfides through smart hybridization.[30,31,32,33,34,35]
The reversible capacity of MoSe2/P-C@TiO2 electrode decreases slightly in the initial 243 cycles because of the polarization when cycled at high current and delivers a little increase capacity attributed to progressive kinetic activation in the electrode.[12,31,40,48]
Summary
The reversible capacity of MoSe2/P-C@TiO2 electrode decreases slightly in the initial 243 cycles because of the polarization when cycled at high current and delivers a little increase capacity attributed to progressive kinetic activation in the electrode.[12,31,40,48] After those, a stable capacity of 214 mAh g−1 can be delivered after 8000 cycles, giving a capacity retention of 82.9% This result indicates that MoSe2/P-C@TiO2 electrode, as expected, exhibits a synthetic effect combining the advantages for the individual components. When used as cathode material for a half cell, it exhibits a capacity of 80.8 mAh g−1 at 200 mA g−1 after 100 cycles and shows a flat voltage plateau around 3.4 V (Figure S9B,C, Supporting Information), which is consistent with previous reports.[9,26,52] For a sodium-ion full battery, a discharge voltage plateau around 1.85 V can be seen from the galvanostatic discharge–charge curves at 0.5 A g−1 in the voltage range of. A reversible capacity of 242.2 mAh g−1 can be maintained after 100 cycles with the CE over 99%, suggesting a robust cyclability of MoSe2/P-C@TiO2 when applied into full cells
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