Ti3C2Tx nanosheet@Cu/Fe-MOF separators for high-performance lithium–sulfur batteries: an experimental and density functional theory study

Abstract

Lithium–sulfur (Li–S) batteries have attracted much attention due to their superior theoretical specific capacity and high theoretical energy density. However, rapid capacity fading originating from the shuttle effect, insulating the S cathode and the dendrite formation on the Li anode restrict the practical applications of Li–S batteries. Herein, we suggest novel coatings on glass fiber separators to satisfy all high-performance Li–S battery requirements. A conductive Ti₃C₂T_x (MXene) nanosheet/Fe-MOF or Ti₃C₂T_x (MXene) nanosheet/Cu-MOF layer was coated on a glass fiber separator to act as a polysulfide trapping layer. The MXene layer with high conductivity and polar surface functional groups could confine polysulfides and accelerate the redox conversions. The porous MOF layer acts as a Li ion sieve, thereby leading to the interception of polysulfides and mitigation of Li dendrite growth. The cells with the Cu-MOF/MXenes and Fe-MOF/MXene separators display superior capacities of 1100 and 1131 mA h g⁻¹ after 300 cycles, respectively, whereas the cell with a pure glass fiber separator delivers a very low capacity of 309 mA h g⁻¹ after 300 cycles. With Fe-MOF/MXene and Cu-MOF/MXene configurations, the discharge capacity, coulombic efficiency, cycling stability, and electrochemical conversion reactions are significantly improved. Our ab initio calculations demonstrate that the MXene layer dissociates lithium polysulfides into adsorbed S and mobile Li ions, which explains the experimental findings.