As a lithium-ion secondary battery with high energy density, lithium-sulfur batteries have very bright development prospects. But the shuttle effect is still a thorny issue in the development process. The N, O co-doped chlorella-based biomass carbon (CBBC) synthesized by chemical activation method possesses a microporous and mesoporous composite structure, large specific surface area, and good electrical conductivity. The CBBC interlayer can improve the wettability between the separator and the electrolyte, and accelerate the transmission of Li+. N, O heteroatoms have a strong chemical adsorption operation for LiPs. The modified separator restrains lithium polysulfide through physical barriers and chemical adsorption, and improves the capacity and cycle performance of lithium-sulfur batteries. The batteries with CBBC exhibit excellent cycling stability (0.067% per cycle at 0.5C) and better rate performance (918 mAh g(-1) at 2C). The first discharge capacity at 0.05C was 1540 mAh g(-1). Even after 600 cycles the discharge capacity retains 656 mAh g(-1) at 0.5C. The low price and simple preparation of CBBC interlayer is an attractive choice for improving lithium-sulfur batteries. (C) 2020 Elsevier Inc. All rights reserved.