CNT threaded porous carbon nitride nanoflakes as bifunctional hosts for lithium sulfide cathode

Highlights: • A bifunctional host of porous C₃N₄/CNT is designed and prepared for Li₂S cathodes. • 3D Li₂S/p–C₃N₄/CNT cathode exhibits excellent electrochemical performance. • Porous–C₃N₄ is designed to store Li₂S and trap soluble lithium polysulfides. • CNT network is acted as a high conduction channel and stable skeleton. -- Abstract: Lithium sulfide (Li₂S) is regarded as a promising cathode material for lithium ion batteries since it can be well paired with lithium–free anodes. However, the low electronic conductivity of Li₂S and the shuttle effect of lithium polysulfides are the two biggest obstacles for commercial applications of Li₂S cathode. Herein, a bifunctional host with high electronic conductivity and high adsorption of lithium polysulfides, CNT threaded porous carbon nitride nanoflakes, is designed and prepared for Li₂S cathode. Ultrafine Li₂S particles are infiltrated into the bifunctional host to form a three-dimensional Li₂S/porous carbon nitride/carbon nanotube composite (3D Li₂S/p–C₃N₄/CNT) by facile liquid infiltration and evaporation. The as–prepared 3D Li₂S/p–C₃N₄/CNT exhibits a high initial discharge capacity of 997.5 mAh g⁻¹ at 0.2 A g^–1, superior rate capability of 432.3 mAh g⁻¹ at 2.0 A g^–1 over 600 cycles and good cycling stability. The excellent electrochemical performance of 3D Li₂S/p–C₃N₄/CNT can be attributed to the high conductivity network of CNT and ultrafine Li₂S, and the strong polar adsorption of porous carbon nitride nanoflakes.