Polyoxometalate derived hierarchically structured N,P-Codoped reduced graphene oxide/MoO2 composites for high performance lithium-sulfur batteries

Lithium-sulfur batteries (LSB) have a higher energy density than a practical lithium-ion battery, but they have a number of issues, including a lithium polysulfide (LiPS) shuttle and sluggish reaction kinetics, that must be addressed before they can be used in large-scale applications. Hierarchically structured MoO2 nanoparticles with N,P-codoped reduced graphene oxide (N,P-rGO/h-MoO2) are prepared by the combined procedures of the Ostwald ripening process and hydrothermal treatment, followed by homogeneously distributed hollow MoO2 nanospheres on N,P-codoped rGO sheets. The hollow structure of MoO2 can act as a physical barrier to LiPS through its interior void and volume buffering of sulfur during cycling. In addition, N and P atoms introduced with MoO2 nanoparticles not only contribute to enhanced sulfur immobilization but also promote LiPS redox kinetics. The N,P-rGO/h-MoO2@S cathode materials demonstrated a high discharge capacity of 1274.9 mAh g-1 at 0.1C with superior high-rate capacity of 374.4 mAh g-1 at 10C. Furthermore, the N,P-rGO/h-MoO2@S showed excellent long-term stability at 5 and 10C with low-capacity decay rates of 0.043 and 0.029% per cycle, respectively, even after 900 cycles. At a sulfur loading concentration of 4.2 mg cm-2, the N,P-rGO/h-MoO2@S obtained a high capacity of 5.0 mAh cm-2 with high-capacity retention of 79.7% over 250 cycles, and a relatively low fading rate of 0.08% per cycle.