Partial nitriding bimetallic catalyst for high-efficiency polysulfide conversion in lithium‑sulfur batteries

Various catalysts have been employed to increase the redox kinetics of polysulfides in lithium‑sulfur batteries (LSBs), especially bimetallic particle catalysts. However, these bimetallic particles often suffer from low cycling stability due to their excessively strong adsorption properties towards polysulfide species. In this work, an N-doped FeNi₃ (N-FeNi₃) bimetallic catalyst was designed on a three-dimensional (3D) N-doped carbon composite scaffold of reduced graphene oxide and carbon nanotubes (rGO/CNT). In this design, N doping in bimetallic particles effectively balances the adsorption and desorption of Li₂S during the charge/discharge processes via metal-N coordination bonds, while retaining its high catalytic performance. Electrochemical tests indicate that the LSB assembled with an N-FeNi₃@rGO/CNT/S cathode achieves a high specific capacity of 1210 mAh g⁻¹ at 0.1C, with a high capacity retention of 64.2 % when the current density increases from 0.1 to 3.0C. More impressively, the N-FeNi₃@rGO/CNT/S cathode exhibits an ultralow decay rate of 0.033 % per cycle, which is much lower than the decay rates of the FeNi₃@rGO/CNT/S (0.039 %) and FeNi₃@rGO/S (0.055 %) after 1000 cycles at 1.0 C. In addition, a series of electrochemical tests and failure analysis indicate the N doping in the rGO/CNT scaffold not only increase the electron and ion transport during the charge/discharge processes but also enhances the anchoring of the particle catalyst to the carbon skeleton. Both effects lead to a significant improvement in long-term cycling stability.