Accelerating redox kinetics of sulfurized polyacrylonitrile nanosheets by trace doping of element

"Solid-solid" conversion mechanism of sulfurized polyacrylonitrile (SPAN) could eliminate the "shuttle effect" of polysulfides intermediate in LiS batteries, but it leads to poor redox reaction kinetics. Herein, traces of high conductivity elements Se and Te are doped in two-dimensional SPAN nanosheets (NS) by co-heating method. This synergistic effect enhances the conductivity of SPAN while affording a larger contact area with the electrolyte and shortening the electron/ion transport path. As a result, both the energy barrier for redox reaction and polarization for battery are decreased. At a high current density of 3 A g−1, Te0.052S0.948PAN NS and Se0.071S0.929PAN NS exhibit significantly enhanced discharge capacities of 485 mA h g−1composite and 457 mA h g−1composite, respectively, while SPAN NP only delivers a capacity of 417 mA h g−1composite. At 0.2 A g−1 current density, the capacity retention rates of Te0.052S0.948PAN NS and Se0.071S0.929PAN NS are 92.20 % and 56.10 % after 200 cycles, respectively, both higher than the 40.10 % of SPAN nanoparticles (NP). When the loading amount is further increased, Te0.052S0.948PAN NS and Se0.071S0.929PAN NS still maintain excellent electrochemical performance. In-situ Raman and XPS analysis confirms the reversible breaking and formation of CS/SS bonds during the first cycle. Additionally, XPS and SEM analysis after 100 cycles demonstrate the stable nanostructure and molecular structure of Se0.071S0.929PAN NS and Te0.052S0.948PAN NS throughout the cycling process. These results herald a new approach to high redox kinetics of SPAN by the synergistic effect of elements doping and nanoscale modulation.