Sphere-in-fiber hybrid of N-doped carbon/cerium dioxide as an interlayer material with superior electrocatalytic performance for lithium sulfide precipitation and conversion.

The inferior conductivity and infamous "shuttle effect" of lithium-sulfur (Li-S) batteries lead to low sulfur utilization and undesired cycle stability, which both seriously affect their practical application. Here, a multifunctional nanofiber material based on cerium dioxide spheres embedded inside nitrogen-doped carbon fibers (denoted as NCF@CeO) fabricated by electrospinning technology is used as an interlayer for high-performance Li-S batteries. The nitrogen-doped carbon fiber skeleton matrix provides a through-conducting grid to accelerate electron transfer at the interface of the nitrogen-doped carbon and the CeO, and the large specific surface area guarantees a sufficient interfacial fast-redox reaction for sulfur species. CeO with a hollow structure provides strong physicochemical adsorption of lithium polysulfides (LiPSs) to weaken the migration behavior, and abundant oxygen defects as catalytic active sites are conducive to lithium sulfide conversion. The "sphere in fiber" construction minimizes the direct contact between the catalyst and electrolyte, effectively avoiding side reactions. Based on the multiple functions of nitrogen-doped carbon fibers and CeO, Li-S batteries with NCF@CeO interlayers exhibit superior electrochemical performances, including a high discharge specific capacity of 1072.9 mAh g at 0.2 C and a low capacity decay rate of only 0.063% per cycle after 1000 cycles. Moreover, the mechanisms of LiPSs adsorption-conversion and the quantification of the catalytic ability are elaborately clarified.