Comparative and interface tailoring investigation of solution-processed sulfur/carbon cathode for high-performance liquid and solid-state Li-S batteries

Abstract

Solid-state Li-S batteries (SS LSBs) have garnered significant attention for next-generation sustainable energy storage solutions due to their high energy density and potential safety. To address some critical challenges in SS LSB, such as the insulating of elemental sulfur, high interfacial impedance, and insufficient sulfur utilization, we prepared and tuned 60-70 wt% sulfur encapsulated into mesoporous carbon (MPC) via a solution impregnation method. The electrochemical performances of S@MPC/MWCNT composites were studied in both liquid and SS LSBs. In the liquid electrolyte (LE) Li-S system, the S@MPC-65/MWCNT composite exhibited very-high initial discharge capacities of 1438 and 1061 mAh g(-1) at 0.1C and 0.5C, respectively, with excellent capacity retention of 88.3 % at 0.5C after 300 cycles. In the SS Li-S system, the composite prepared by conventional dry mixing (DM) showed unsatisfactory electrochemical performances due to poor ionic contact between sulfur and Li6PS5Cl (LPSCl). To overcome this issue, we employed a wet mixing (WM) process using a weak polar solvent. Compared to the DM process, WM resulted in the formation of polysulfido-intermediate (3Li(+)-PS4+n3- (n > 0)) compounds between S/MPC and LPSCl, creating intimate contact between electrode material and electrolyte disk, and densely packed electrode without voids. The SS Li-S cell prepared by WM demonstrated an unprecedentedly high initial discharge capacity of 1621 mAh g(-1) at 0.1C with a remarkable improvement in capacity retention to 67.9 % at 0.5C after 300 cycles. We strongly suggest that the S@MPC-65/MWCNT composites prepared through solution-based interface-tailoring techniques are promising high-performance sulfur cathodes for LE and SS LSBs.