Ultra-Small Ferromagnetic Fe3O4 Nanoparticles Modified Separator for High-Rate and Long Cycling Lithium-Sulfur Batteries

As a promising energy storage system with high specific capacity, lithium-sulfur (Li-S) battery is striving for a high-rate and longer lifetime. Whereas the slow redox kinetics and the shuttle effect of polysulfides (PSs) still severely restrict the performance of Li-S batteries. Here, a rational designed ferromagnetic Fe3O4 nanoparticles (FM-Fe3O4 NPs) modified separator is engineered for Li-S batteries. Moreover, the particle size of FM-Fe3O4 NPs was tuned to enhance the energy storage performance. Consequently, the cells with FM-Fe3O4 NPs modified separator achieved a high-rate and long cycling performance, the specific capacity could reach 672.8 mAh g(-1) and a low fading rate (0.028 % per cycle over 700 cycles) at a high rate of 5 C. Experimental results reveals that FM-Fe3O4 NPs could mitigate shuttle effect, enable efficient redox reactions, and protect the Li anode from severe corrosion. The performance-enhanced mechanism is further discovered by DFT calculations, the results show that FM-Fe3O4 NPs act as mediators of redox reaction to block PSs shuttle and dynamically facilitate conversion via changing the molecular structure of PSs and reducing reaction barrier. This work provides a new pathway to improving Li-S batteries based on ferromagnetic materials, which may be generalized to other advanced batteries.