Bimetallic Ni–Co MOF@PAN modified electrospun separator enhances high-performance lithium-sulfur batteries

Lithium–sulfur (Li–S) batteries with high energy density are considered promising energy storage devices for the next generation. Nevertheless, the shuttle effect and the passive layer between the separator and the electrodes still seriously affect the cycle stability and life. Herein, a bimetallic Ni–Co metal–organic framework (MOF) with adsorption and catalytic synergism for polysulfides was successfully synthesized as an electrospinning separator sandwich for Li–S batteries. Introducing porous Ni–Co MOF coatings into the separator provides more adsorption catalytic sites for polysulfides, prevents their diffusion to the anode, and enhances sulfur utilization. Consequently, the improved Li–S batteries with a Ni–Co MOF@PAN (NCMP) electrospun separator delivered excellent rate performance and outstanding cycle stability, yielding an ultra-high initial capacity of 1560 mA h g−1 at 0.1 C. Notably, remarkable Li–S battery performance with a discharge capacity of 794 mA h g−1 (84.1% capacity retention) was obtained after 500 cycles, while delivering a low capacity decay rate of 0.032% during long-term cycling (up to 500 cycles) at 1 C. Surprisingly, even at the current density of 2 C, the capacity attenuation rate of 2000 cycles is only 0.034% per cycle. In addition, compared with the Celgard separator, the NCMP separator also had high thermal stability (keeping the separator outline at 200 °C) that ensured battery safety and excellent electrolyte wettability (73% porosity and 535% electrolyte absorption) and significantly enhanced the ionic conductivity and Li+ transfer number, and protected the surface integrity of the anode.