Exploring efficient electrocatalysts for lithium−sulfur (Li−S) batteries is of great significance for the sulfur/polysulfide/sulfide multiphase conversion. Herein, we report nickel−iron intermetallic (Ni 3 Fe) as a novel electrocatalyst to trigger the highly efficient polysulfide-involving surface reactions. The incorporation of iron into the cubic nickel phase can induce strong electronic interaction and lattice distortion, thereby activating the inferior Ni phase to catalytically active Ni 3 Fe phase. Kinetics investigations reveal that the Ni 3 Fe phase promotes the redox kinetics of the multiphase conversion of Li−S electrochemistry. As a result, the Li−S cells assembled with a 70 wt % sulfur cathode and a Ni 3 Fe-modified separator deliver initial capacities of 1310.3 mA h g −1 at 0.1 C and 598 mA h g −1 at 4 C with excellent rate capability and a long cycle life of 1000 cycles at 1 C with a low capacity fading rate of ∼0.034 per cycle. More impressively, the Ni 3 Fe-catalyzed cells exhibit outstanding performance even at harsh working conditions, such as high sulfur loading (7.7 mg cm −2 ) or lean electrolyte/sulfur ratio (∼6 μL mg −1 ). This work provides a new concept on exploring advanced intermetallic catalysts for high-rate and long-life Li−S batteries.

The exploration of efficient host materials of sulfur is significant for the practical lithium-sulfur (Li-S) batteries, and the hosts are expected to be highly conductive for high sulfur utilization and exhibit strong interaction toward polysulfides to suppress the shuttle effect for long-lasting cycle stability. Herein, we propose a simple synthesis of metallic cobalt-embedded N-doping carbon nanotubes (Co@NCNT) as a “two-in-one” host of sulfur for efficient Li-S batteries. In the binary host, the N-doped CNTs, cooperating with metallic Co nanoparticles, can serve as 3D conductive networks for fast electron transportation, while the synergetic effect of metallic Co and doping N heteroatoms helps to chemically confine polysulfides, acting as active sites to accelerate electrochemical kinetics. With these advantages, the S/Co@NCNT composite delivers an excellent cycling stability with a capacity decay of 0.08% per cycle averaged within 500 cycles at a current density of 1 A g–1 and a high rate performance of 530 mA h g–1 at 5 A g–1. Further, the superior electrochemical performance of the S/Co@NCNT electrode can be maintained under a high sulfur loading up to 4 mg cm–2. Our work demonstrates a feasible strategy to design promising host materials simultaneously featuring high conductivity and strong confinement toward polysulfides for high-performance Li-S batteries.

The polysulfide shuttling and sluggish redox kinetics, due to the notorious adsorption-catalysis underperformance, are the ultimate obstacles of the practical application of lithium-sulfur (Li-S) batteries. Conventional carbon-based and transition metal compound-based material solutions generally suffer from poor catalysis and adsorption, respectively, despite the performance gain in terms of the other. Herein, we have enhanced polysulfide adsorptioncatalytic capability and protected the Li anode using a complementary bimetallic carbide electrocatalyst, Co 3 Mo 3 C, modified commercial separator. With this demonstration, the potentials of bimetal compounds, which have been well recognized in other environmental catalysis, are also extended to Li-S batteries. Coupled with this modified separator, a simple cathode (S/Super P composite) can deliver high sulfur utilization, high rate performance, and excellent cycle stability with a low capacity decay rate of~0.034% per cycle at 1 C up to 1000 cycles. Even at a high S-loading of 8.0 mg cm −2 with electrolyte/sulfur ratio=6 mL g −1 , the cathode still exhibits high areal capacity of~6.8 mA h cm −2. The experimental analysis and the first-principles calculations proved that the bimetallic carbide Co 3 Mo 3 C provides more binding sites for adsorbing polysulfides and catalyzing the multiphase conversion of sulfur/polysulfide/sulfide than monometallic carbide Mo 2 C. Moreover, the modified separator can be reutilized with comparable electrochemical performance. We also showed other bimetallic carbides with similar catalytic effects on Li-S batteries and this material family has great promise in different energy electrocatalytic systems.

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