Dual-Atom Nickel Moieties of Ni(II)₂N₄(µ₂-N)₂ Anchored on Alfalfa-Derived Developed Porous N-Doped Carbon for High-Performance Li–S Battery

A universal strategy is established for preparing the carbonaceous matrix-based atomically distributed metal catalysts M-BPC (M=Ni, Co, Fe, Cu, and Mn, and biomass-derived porous carbon (BPC)) by one-step pyrolysis of mixed metal salts and biomass alfalfa. The optimized Ni-BPC has dual-atom Ni(II)₂N₄(µ₂-N)₂ moieties, which are chemically anchored on the alfalfa-derived developed porous N-doped carbon BPC matrix. An ultrahigh specific surface area of 3133 m² g⁻¹ with huge total pore volume of 3.02 cm³ g⁻¹ is obtained for Ni-BPC. The Ni-BPC could greatly promote the redox kinetics and effectively prevent the shuttle effect of lithium polysulfides in a Li–S battery. The Li–S battery assembled with the Ni-BPC modified separator exhibits prominent rate performance with the reversible specific capacities of 1279, 1119, 1037, 948 and 787 mAh g⁻¹ at the current densities of 0.1, 0.2, 0.5, 1 and 2 C, respectively. The battery presents an ultra-long life with low capacity decay of 0.028% per cycle up to 2100 cycles at 1 C. Even under high areal S loadings of 3.9 mg cm⁻², the high discharge capacity of 976.6 mAh g⁻¹ is obtained at 0.2 C and excellent cycling stability with 61.1% capacity retention is achieved after 490 cycles.