Artificial Bifunctional Protective layer Composed of Carbon Nitride Nanosheets for High Performance Lithium–Sulfur Batteries

Abstract Featuring high energy density and low cost, lithium sulfur batteries are regarded as one of the most promising next-generation energy storage technologies. However, their widespread adoption is plagued by lithium dendrite growth and parasitic reactions induced by the polysulfide shuttle effect. To address these two issues simultaneously, we propose a bifunctional artificial protective layer, which is composed of graphitic carbon nitride nanosheets joined together by a polyvinylidene fluoride binder. First-principles study results reveal that the coexistence of pyridinic and quaternary nitrogen in the g-C3N4 bulk phase is capable of facilitating a homogeneous Li ionic flux, thus leading to a more uniform lithium deposition. Meanwhile, side reactions are dramatically suppressed due to the elimination of the direct exposure of lithium metal in the liquid electrolyte environment. As a result, a high coulombic efficiency of 98% for over 250 h under the current density of 1 mA cm−2 and a cycle capacity of 1 mAh cm−2 is achieved for a Li/Cu half-cell. More remarkably, it is demonstrated that the lithium-sulfur battery with the protective layer exhibits a much prolonged cycling life (180 cycles) with a reasonable sulfur mass loading of up to 1.5 mg cm−2.