High-performance lithium-sulfur batteries with a self-supported, 3D Li₂S-doped graphene aerogel cathodes

Lithium-sulfur (Li-S) batteries are being considered as the next-generation high-energy-storage system due to their high theoretical energy density. However, the use of a lithium-metal anode poses serious safety concerns due to lithium dendrite formation, which causes short-circuiting, and possible explosions of the cell. One feasible way to address this issue is to pair a fully lithiated lithium sulfide (Li₂S) cathode with lithium metal-free anodes. However, bulk Li₂S particles face the challenges of having a large activation barrier during the initial charge, low active-material utilization, poor electrical conductivity, and fast capacity fade, preventing their practical utility. Here, the development of a self-supported, high capacity, long-life cathode material is presented for Li-S batteries by coating Li₂S onto doped graphene aerogels via a simple liquid infiltration-evaporation coating method. The resultant cathodes are able to lower the initial charge voltage barrier and attain a high specific capacity, good rate capability, and excellent cycling stability. The improved performance can be attributed to the (i) cross-linked, porous graphene network enabling fast electron/ion transfer, (ii) coated Li₂S on graphene with high utilization and a reduced energy barrier, and (iii) doped heteroatoms with a strong binding affinity toward Li₂S/lithium polysulfides with reduced polysulfide dissolution based on first-principles calculations. 3D N- or B-doped graphene aerogel cathodes provide a highly conductive network and large surface area for Li₂S coating, facilitate fast charge transfer, and immobilize effectively the polysulfide ions. This enables a low initial charge voltage barrier, high specific capacity, high rate capability, and excellent cycling stability.