Enhanced sulfide chemisorption by conductive Al-doped ZnO decorated carbon nanoflakes for advanced Li-S batteries

Lithium-sulfur batteries have attracted significant attention recently due to their high theoretical capacity, energy density and cost effectiveness. However, sulfur cathodes suffer from issues such as shuttle effects, uncontrollable deposition of lithium sulfides species, and volume expansion of sulfur, which result in rapid capacity fading and low Coulombic efficiency. In recent years, metal-oxide nanostructures have been widely used in Li-S batteries, owing to their effective inhibition of the shuttle effect and controlled deposition of lithium sulfide. However, the nonconductive metal-oxides used in Li-S batteries suffer from extra diffusion process, which slows down the electrochemical reaction kinetics. Herein, we report the synthesis of carbon nanoflakes decorated with conductive aluminium-doped zinc oxide (AZO@C) nanoparticles, through a facile biotemplating method using kapok fibers as both the template and carbon source. A sulfur cathode based on the AZO@C nanocomposites shows better electrochemical performance than those of cathodes based on ZnO and Al₂O₃ with poor conductivity, with a stable capacity of 927 mAh·g^-1 at 0.1C (1C = 1, 675 mA·g^-1) after 100 cycles. A reversible capacity of 544 mAh·g^-1 after 300 cycles was obtained even after increasing the current density to 0.5C, with a 0.039% capacity decay per cycle under a sulfur loading of 3.3 mg·cm^-2. Moreover, a capacity of 466 mAh·g^-1 after 100 cycles at 0.5C could still be obtained when the sulfur loading was increased to 6.96 mg·cm^-2. The excellent electrochemical performance of the AZO@C/S composite can be attributed to its high conductivity of the polar AZO host, which suppresses the shuttle effect while simultaneously improving the redox kinetics in the reciprocal transformation of lithium sulfide species.