Sulfur-doped molybdenum phosphide as fast dis/charging anode for Li-ion and Na-ion batteries

Abstract

The electrode materials with high rate capability are required to meet the ever-demanding performance of rechargeable batteries. Herein, sulfur-doped molybdenum phosphide (S:MoP) is prepared using (thio)urea-phosphate-assisted strategy and investigated as anode material for Li- and Na-ion batteries. This approach provides the self-doping of sulfur in MoP lattice that stabilizes the least stable oxidation state of phosphorus (P-3) of MoP through Mo/P-S bonds, enhances the electronic conductivity, and maximizes the Li-/Na ions adsorption sites. The phase pure hexagonal S:MoP is obtained at 700 degrees C (S:MoP-7) and the complete reduction of phosphate is confirmed through X-ray diffraction as well as X-ray absorption spectroscopy. The presence of chemical bonding of Mo-P/S and P-S is detected by X-ray photoelectron spectroscopy. S:MoP-7 anode shows excellent rate capability where it delivers 112 mAh g(-1) capacity at 12.8 C rate and high stability with 436 mAh g(-1) capacity at 100th cycle at 0.1 C rate when tested in lithium-ion batteries. The S:MoP-7 as an anode exhibits high rate capability in sodium-ion batteries and delivers 133 mAh g(-1) capacity at 6.4 C rate and 307 mAh g(-1) at 0.1 C rate at the 100th cycle. The high performance of the S:MoP-7 electrode is attributed to the interconnected porous network, increased active sites for Li- and Na-ions via S-doping, and reduced charge transfer resistance as observed using electrochemical impedance spectroscopy.