In Situ Trapping Strategy Enables a High-Loading Ni Single-Atom Catalyst as a Separator Modifier for a High-Performance Li–S Battery

The poor electrochemical reaction kinetics of Li polysulfides is a key barrier that prevents the Li–S batteries from widespread applications. Ni single atoms dispersed on carbon matrixes derived from ZIF-8 are a promising type of catalyst for accelerating the conversion of active sulfur species. However, Ni favors a square-planar coordination that can only be doped on the external surface of ZIF-8, leading to a low loading amount of Ni single atoms after pyrolysis. Herein, we demonstrate an in situ trapping strategy to synthesize Ni and melamine-codoped ZIF-8 precursor (Ni-ZIF-8-MA) by simultaneously introducing melamine and Ni during the synthesis of ZIF-8, which can remarkably decrease the particle size of ZIF-8 and further anchor Ni via Ni–N6 coordination. Consequently, a novel high-loading Ni single-atom (3.3 wt %) catalyst implanted in an N-doped nanocarbon matrix (Ni@NNC) is obtained after high-temperature pyrolysis. This catalyst as a separator modifier shows a superior catalytic effect on the electrochemical transitions of Li polysulfides, which endows the corresponding Li–S batteries with a high specific capacity of 1232.4 mA h g–1 at 0.3 C and an excellent rate capability of 814.9 mA h g–1 at 3 C. Furthermore, a superior areal capacity of 4.6 mA h cm–2 with stable cycling over 160 cycles can be achieved under a critical condition with a low electrolyte/sulfur ratio (8.4 μL mg–1) and high sulfur loading (4.85 mg cm–2). The outstanding electrochemical performances can be attributed to the strong adsorption and fast conversion of Li polysulfides on the highly dense active sites of Ni@NNC. This intriguing work provides new inspirations for designing high-loading single-atom catalysts applied in Li–S batteries.