Defect-triggered phase transition energizes the defects in non-stoichiometric molybdenum sulfide for catalyzing polysulfide conversion in lithium sulfur batteries

Accelerating lithium polysulfide conversion by catalytic effect of host materials in sulfur cathodes is an effective strategy for improving lithium sulfur batteries. In this work, amount of sulfur vacancies is quantitatively regulated to obtain MoS_2-x with abundant defects mainly including atom vacancies and edge dislocations. It is found the defects can trigger phase transition from 2H-MoS₂ to 1T-MoS₂; more interestingly, the defects in 1T-MoS₂ provide stronger catalytic ability for polysulfide conversion than those in 2H-MoS₂. Furthermore, doping of cobalt in non-stoichiometric MoS_2-x can stabilize 1T-MoS₂ even with sulfur vacancies as high as 32 %. Acting as catalytically active sites, the abundant and stable defects significantly enhance electrochemical kinetic of the sulfur cathodes. The nitrogen-doped graphene-supported S/Co_0.22-MoS_1.36 electrode demonstrates an excellent long-cycle stability at 1C, remaining 591.8 mAh g⁻¹ after 1200 cycles with a coulombic efficiency of 98.8 % and a decay rate of 0.032 %. Even under extreme conditions such as a high areal sulfur-loading of 14.3 mg cm⁻² and lean electrolyte of 4 µL mg⁻¹, the S/Co_0.22-MoS_1.36 electrode achieves an initial areal capacity of 12.37 mAh cm⁻² with satisfactory cycling stability. These results provide novel insight and an alternative approach to developing host materials for high-performance lithium sulfur batteries.