is still hindered by some main fundamental obstacles, including the insulating nature of sulfur and lithium sulfides (Li 2 S), and the notorious shuttle effect of lithium polysulfides (LiPSs) intermediates during cycling process. The shuttle effect brings about not only the loss of the active materials but also the anode corrosion, leading to rapid capacity degradation and low Coulombic efficiency. [4,5] Carbon nanomaterials with high electrical conductivity, desirable porous structure, and controlled dimensions have been devoted to the design of sulfur hosts [6][7][8][9][10][11][12][13] or interlayers [14][15][16] to physically restrain LiPSs in the cathode area, however, the weak interactions between nonpolar carbon and polar LiPSs discount the effectiveness during the long-term cycling. Chemical trapping of LiPSs with polar transition metal compounds such as TiO 2 , MnO 2 , etc., via polar-polar interactions is an available approach to mitigate the LiPSs shuttling. [17][18][19][20][21] Nonetheless, when the sulfur content and electrode mass loading are high, the massive generated LiPSs are difficult to be immobilized due to the adsorption saturation by these compounds. The detrimental shuttle effect in lithium-sulfur batteries mainly results from the mobility of soluble polysulfide intermediates and their sluggish conversion kinetics. Herein, presented is a multifunctional catalyst with the merits of strong polysulfides adsorption ability, superior polysulfides conversion activity, high specific surface area, and electron conductivity by in situ crafting of the TiO 2 -MXene (Ti 3 C 2 T x ) heterostructures. The uniformly distributed TiO 2 on MXene sheets act as capturing centers to immobilize polysulfides, the hetero-interface ensures rapid diffusion of anchored polysulfides from TiO 2 to MXene, and the oxygen-terminated MXene surfaceis endowed with high catalytic activity toward polysulfide conversion. The improved lithium-sulfur batteries deliver 800 mAh g −1 at 2 C and an ultralow capacity decay of 0.028% per cycle over 1000 cycles at 2 C. Even with a high sulfur loading of 5.1 mg cm −2 , the capacity retention of 93% after 200 cycles is still maintained. This work sheds new insights into the design of highperformance catalysts with manipulated chemical components and tailored surface chemistry to regulate polysulfides in Li-S batteries.
The notorious shuttle effect caused by the soluble polysulfide intermediates and the sluggish conversion kinetics in sulfur cathodes greatly hinder the practical application of lithium–sulfur (Li–S) batteries. Here we systematically investigate the electrochemical performance of a series of transition metal nitrides (TMNs) for Li–S batteries. All TMNs we investigated were found to have much stronger binding strength with polysulfide intermediates than graphene and transition metal sulfides (TMSs), indicating good performance of sulfur immobilization. These TMNs can also facilitate the lithium diffusion and activate the decomposition of Li2S, suggesting the good rate performance, high reversible capacity, and long cycling life of Li–S batteries. We also demonstrated that, among the TMNs, VN exhibits great potential as the anchoring materials in Li–S batteries with enhanced electrochemical performance. Our results provide a rational strategy to design and screen the materials to achieve high performance of Li–S batteries.
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