Enhancing built-in electric field in bimetallic selenides on few-layered MXene to accelerate polysulfide conversion in lithium-sulfur batteries

Built-in electric field (BIEF) has recently received great attention, because its significantly enhanced reaction kinetics of lithium polysulfides (LiPSs) attributed to the unique interfacial charge asymmetric redistribution and generation of suitable reaction microenvironments, could effectively relieve the major problems in lithium‑sulfur batteries (LSBs). Herein, we developed a strategy of enhancing BIEF via integrating NiCo-bimetal-selenides with MXene (Ti₃C₂T_x) to improve the reaction kinetics of LiPSs. The enhanced BIEF for such the heterostructured NiCoSe₂/MXene was verified by the calculated results of surface potentials and Zeta potentials. Density functional theory analysis confirmed the enhanced conductivity and LiPSs adsorption in the heterostructured NiCoSe₂/MXene due to the enhanced BIEF. When the NiCoSe₂/MXene with abundant void spaces was used as sulfur host material for catalysis, such the significantly enhanced BIEF not only accelerated Li⁺ transport and electrons delivery, but also reduced the energy barrier for LiPSs' conversion during charge/discharge processes, thus achieving excellent catalysis performance for sulfur electrochemistry. The developed S@NiCoSe₂/MXene cathode produced an initial capacity of 1260 mAh g⁻¹ at 0.2 C with a Coulomb efficiency of 98 % and the capacity fading rate was only 0.029 % per cycle over 600 cycles at 1 C, proving its significantly accelerated LiPSs adsorption and catalysis for the LSBs.