“Pea-pod-like” nitrogen-doped hollow porous carbon cathode hosts decorated with polar titanium dioxide nanocrystals as efficient polysulfide reservoirs for advanced lithium–sulfur batteries

Abstract

Lithium–sulfur (Li–S) batteries have been deemed as the best alternative for the new generation energy storage devices because of their high energy densities and low cost. Enhancing the sulfur utilization, decreasing the dissolution of lithium polysulfides (LiPSs) and improving the electrical conductivity of the cathodes have become the main challenges for the successful commercialization of Li–S batteries. In this paper, use of novel “pea-pod-like” nitrogen-doped hollow porous carbon cathode hosts decorated with polar titanium dioxide nanocrystals (rod-TiO₂@C) as high-efficiency polysulfide immobilizers for advanced Li–S batteries are reported. In this ingenious nanostructure, the hollow porous carbon can not only enhance the conductivity of the cathodes, but also effectively reserve sulfur species in its internal void space and the volume expansion upon lithiation can also be alleviated. More importantly, the well-dispersed polar TiO₂ nanocrystals can significantly suppress the dissolution of LiPSs and accelerate the redox reaction by strong chemical interactions. With a sulfur content of 65.4 wt%, the rod-TiO₂@C/S cathodes can deliver an extraordinary electrochemical performance in terms of high reversibility (1017 mA h g⁻¹ after 200 cycles at 0.2C, 853 mA h g⁻¹ after 500 cycles at 0.5C), superior rate capability (605 and 509 mA h g⁻¹ at 8C and 10C, respectively) and excellent long-term cycle performance (728 mA h g⁻¹ after 1500 cycles at 1C with an extremely low capacity loss of only 0.0196% each cycle, 604 mA h g⁻¹ after 1500 cycles at 2C with a capacity loss of merely 0.0240% in each cycle). Furthermore, even under the high sulfur mass loading of 4.04 mg cm⁻² and 3.89 mg cm⁻², the stable capacity (683 mA h g⁻¹ after 300 cycles at 0.5C) and advanced rate performance (627 mA h g⁻¹ at 2C) can be acquired, respectively.