A metal-free phosphorus–oxygen/nitrogen–carbon configuration as an effective metal–nitrogen–carbon analog for accelerated lithium-sulfur redox kinetics

The practical deployment of lithium-sulfur batteries is limited by the polysulfide shuttle effect arising from sluggish sulfur redox kinetics. While metal–nitrogen–carbon (M–N–C) catalysts are effective in promoting sulfur conversion, their synthesis suffers from metal aggregation and the mass penalty of transition metals reduces the practical energy density. Here, we design a metal-free phosphorus–oxygen/nitrogen–carbon (P–O/N–C) electrocatalyst that functionally mimics M–N–C configurations, offering simplified synthesis without metal-related issues. Spectroscopic analysis confirms the formation of P–O/N–C coordination sites. Electrochemical evaluation reveals that PONCNT exhibits superior catalytic activity in accelerating polysulfide conversion, particularly for the rate-limiting Li2S nucleation process, with a low Tafel slope and high Li2S deposition capacity. Crucially, this catalytic behavior faithfully reproduces the hallmark of M–N–C catalysts: moderate polysulfide adsorption but dramatically accelerated conversion kinetics, demonstrating that enhanced kinetics, not strong trapping, is the primary origin of its performance. This work establishes a metal-free strategy for constructing M–N–C analogs, opening a pathway toward lightweight, low-cost electrocatalysts for high-energy lithium-sulfur batteries.