In Situ Growth of Carbon Nanotubes on Iron Phosphate and Doped with Nitrogen and Selenium for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have been considered as one of the effective alternative energy systems to commercial lithium-ion batteries (LIBs) due to their high theoretical energy density (2600 Wh kg–1), high theoretical specific capacity (1675 mAh g–1), low cost, and abundant reserves of sulfur. However, intrinsic challenges, such as severe shuttle effect, low conductivity, and significant volume expansion, hinder their large-scale application. In this study, a novel composite (CNT/FP-N, Se), which in situ grown with carbon nanotubes (CNTs) and doped with N, Se elements, has been synthesized by utilizing commercial ferric phosphate (FP) as a precursor. Benefitting from the synergistic effects of abundant adsorption active sites of CNTs and the catalytic effects of N and Se, the shuttle effect of lithium polysulfides (LPS) can be effectively inhibited, leading to an enhancement of Li–S batteries when the CNT/FP-N, Se is utilized as separator modifier. The charge/discharge platforms can be well maintained from 0.1 to 5 C, and a capacity of 617 mAh g–1 at 5 C can be acquired. Notably, an initial capacity of 990.7 mAh g–1 at 1 C can be obtained, with a retention of 711.3 mAh g–1 after 500 cycles, corresponding to a capacity loss rate of only 0.056% per cycle. This work provides a feasible scheme for FP application in next-generation low-cost energy systems.