NiO-Ni2P/C3N4 heterostructures with synergistic adsorption-electrocatalysis functions for suppressing polysulfide shuttle effect in lithium sulfur batteries

Lithium-sulfur (Li-S) batteries, renowned for their exceptional theoretical energy density, are positioned as a leading candidate for future energy storage systems, offering a potential pathway to overcome the energy density limitations of conventional lithium-ion batteries. Nevertheless, the notorious lithium polysulfides (LiPSs) shuttle effect and sluggish redox kinetics hinder their practical application. To resolve these challenges, we report a novel NiO-Ni₂P/C₃N₄ heterostructure synthesized via an in-situ phosphation process. Herein, we present an in situ phosphorylation strategy for the construction of NiO-Ni₂P heterojunctions anchored on a conductive C₃N₄ substrate (NiO-Ni₂P/C₃N₄) for further integration into commercial polypropylene (PP) separator (denoted as NiO-Ni₂P/C₃N₄@PP). Mechanistic studies demonstrated that the NiO phase facilitated strong chemisorption of LiPSs, while the Ni₂P component reduced the energy barrier for Li₂S dissolution through optimised d-band electron transfer. Concurrently, the C₃N₄ framework enhanced the interfacial charge transfer and significantly reduced the charge transfer resistance. Benefiting from the synergistic "adsorption-transformation-conduction" triple-function, the cells with the NiO-Ni₂P/C₃N₄@PP separator exhibit remarkable cycling stability (over 300 cycles at 3C) and outstanding rate capability (82.5 % capacity retention after 200 cycles at 5C). This work provides atomic-level insights into the engineering of multi-step sulfur electrochemical heterostructures, providing a generic design paradigm for high-energy metal-sulfur batteries.