Optimization of Lithium–Sulfur Battery Performance via Nickel-Doped α-MnO2 Modified Separator

Lithium–sulfur batteries (LSBs) offer a theoretical energy density of 2600 Wh kg−1 but suffer from the polysulfide shuttle effect, which causes rapid capacity decay and limits practical application. To address this, we developed a bifunctional separator coating using Ni-doped α-MnO2 combined with carbon nanotubes (Ni-MnO2/CNTs). Ni doping induces lattice expansion due to the larger Ni2+ ionic radius, modulating the electronic structure to create more active sites, enhance electrical conductivity, and improve polysulfide adsorption and redox kinetics. The needle-like morphology further strengthens physical/chemical confinement of polysulfides and accelerates conversion reactions. Batteries with the Ni-MnO2/CNTs-modified separator deliver a high-rate capacity of 813 mAh g−1 at 5 C and exhibit a low capacity decay rate of 0.0399% per cycle over 1500 cycles at 2 C. Even under high sulfur loading (∼10 mg cm−2) and lean electrolyte conditions (10 μL mg−1), the cell maintains stable cycling with a decay rate of 0.0929% per cycle over 300 cycles at 0.2 C. This lattice-modulation strategy on commercial separators provides a simple, effective pathway toward high-energy-density, long-life LSBs.