Ion-Conductive PCBM-Functionalized Carbon Nanotubes Based Interlayer as an Efficient Polysulfide Adsorbent: Toward the Development of Li–S Batteries with High Sulfur Mass Loading

Lithium-sulfur (Li-S) batteries are promising candidates for next-generation energy storage due to their high theoretical energy density, but their practical application is limited by the dissolution and diffusion of lithium polysulfides (LiPSs), leading to rapid capacity degradation. We report a rationally designed ion-conductive interlayer (IL) composed of phenyl-C₆₁-butyric acid methyl ester-functionalized carbon nanotubes (PCBM@CNT) to address the shuttle effect in Li-S batteries. The IL effectively immobilizes LiPSs via physical adsorption and chemical interaction with the polar ester groups (-O-C=O-CH₃) of PCBM. This functionalization enhances Li-ion diffusion, lowers the redox overpotential, and accelerates LiPS conversion, thereby improving redox kinetics and sulfur utilization. Characterizations (Raman, XPS, FTIR) confirm strong LiPS interactions with the PCBM-functionalized matrix. The developed IL-based Li-S batteries exhibit excellent performance, including ∼97% capacity recovery, an initial discharge capacity of ∼1195.7 mAh g^-1 over the first 10 cycles at 0.2 C, and long-term stability with ∼820.2 mAh g^-1 over 500 cycles at 1.0 C (decay rate ≈ 0.048% per cycle). At a high sulfur loading (∼3.4 mg cm^-2), they deliver an average specific capacity of ∼713.4 mAh g^-1 over 500 cycles at 2.0 C. The PCBM@CNT-IL strategy effectively suppresses the shuttle effect and forms an ion-conductive network without compromising the performance.