Coupling interfacial effect in heterogeneous RuP₂-RuP for accelerating sulfur reduction reaction of lithium sulfur batteries

The cathodic host for practical lithium sulfur (Li–S) batteries needs to meet numerous requirements, such as outstanding electron conductivity, desirable lithium polysulfide (LiPSs) adsorption ability, and efficient catalytic effect towards the redox of sulfur. Given the above considerations, an N, P, S tri-doped 3D interconnected porous carbon embedded with heterogeneous ruthenium phosphides (RuP₂-RuP@NPSC) was constructed to serve as a sulfur host for high-performance and practical Li–S battery. Strong interfacial coupling effect in the RuP₂-RuP heterojunctions endowed the active sites with favorable LiPSs adsorption ability and boosted sulfur reduction reaction. The density functional theory calculation suggested that the electronic tuning of the constructed heterojunction interface could enhance the electron transport and LiPSs adsorption ability. The higher current response of symmetric cells, larger Li₂S deposition and dissolution capacity of RuP₂-RuP@NPSC in comparison to other counterparts of RuP@NPSC, RuP₂@NPSC, and NPSC further verified the great catalytic capability of RuP₂-RuP heterojunctions. As a result, corresponding cells with RuP₂-RuP@NPSC/S electrodes delivered an impressive reversible capacity of 565 mAh g⁻¹ at 6 C, and an ultralow capacity decay rate of 0.019 % per cycle after 1000 cycles was achieved at the current of 2 C.