The free-standing cathode fabricated with nano-CoSe₂ embedded in mesoporous carbon nanosheets towards high performance Li/SeS₂ batteries

SeS₂, a substitute to S with slightly lower theoretical capacity (1124 mAh g⁻¹) but much improved electric conductivity, requires host with special design to alleviate shuttle effect, accommodate volume variation and ensure fast redox kinetics. Herein, a facile synthesis method via hydrothermal reaction was introduced to fabricate a 3D hierarchical structure composite with CoSe₂ nano-particles uniformly distributed in mesoporous carbon nanosheets standing on carbon fiber cloth (marked as CFC-C@CoSe₂). As a whole substrate, the mesopores of CFC-C@CoSe₂ can physically restrain the intermediates migration and accommodate the volume variation, while the CoSe₂ can chemically adsorb the intermediates and catalyze their conversion to Li₂S/Li₂Se efficiently. The CFC-C@CoSe₂ exhibits stronger affinity to polysulfides/polyselenides than the contrast sample CFC-C@Co in the soaking experiment. In addition, the chemical absorption to the polysulfides/polyselenides generated by CoSe₂ was further proved via the XPS analysis. Furthermore, the CFC-C@CoSe₂-SeS₂ cathode presents 3 times higher exchange current density than the CFC-C@Co-SeS₂ cathode, suggesting the previous one holds much faster charge-transfer kinetics. Therefore, when tested at 1.0 A g⁻¹, the free-standing CFC-C@CoSe₂-SeS₂ cathode presents high initial capacity up to 943.4 mAh g⁻¹ with an outstanding coulombic efficiency. In addition, this cathode exhibits excellent rate performance, delivering 735.9, 677.8, 640.3 and 610.5 mAh g⁻¹ when cycled at 1.0, 2.0, 3.0 and 4.0 A g⁻¹, respectively. This easy fabrication method to obtain a composite with rational design may provide a novel approach for the development of next generation rechargeable batteries.