Sandwich structural Ti_xO_y-Ti₃C₂/C₃N₄ material for long life and fast kinetics Lithium-Sulfur Battery: Bidirectional adsorption promoting lithium polysulfide conversion

Compared with traditional lithium-ion battery, lithium-sulfur (Li-S) battery shows significant advantages of high specific capacity, high energy density and low price. However, due to the shuttling and low reduction kinetics of the lithium polysulfides (LiPS), the advantages of Li-S batteries are hidden by their rapidly decreased cycle capacity, especially for the batteries with high sulfur content. Here, sulfur was sandwiched into two kinds of layered materials, namely the Ti_xO_y-Ti₃C₂ene heterojunction layer and the C₃N₄ layer, which can exert polar adsorption and Lewis acid-base interaction to LiPS, respectively. The sandwich structure not only increase the anchoring force to LiPS by the two adsorption layers, also enhance the reduction kinetics of LiPS to Li₂S by the synergistic effect of the bidirectional adsorption from the two functional layers. Experimental results consistent with theoretical calculations confirmed the accelerating effect of the sandwich structural material on LiPS reduction. According to this “anchoring and catalyzing” mechanism, the shuttle effect is effectively reduced and the reaction kinetics is greatly increased. High capacity of 749.5 mAh g⁻¹ after 2000 cycle at 0.5C is achieved. Even when the sulfur load reached 4.2 mg cm⁻², the cathode also remained 70.5% of its initial capacity after 200 cycles. Also, excellent rate capability from 0.5 to 5C was delivered. This work, as a result, demonstrates an efficient design pathway for two-component materials work together to propel the reaction kinetics and improve the electrochemical performances of Li-S batteries.