Self-Supported PPy-Encapsulated CoS2 Nanosheets Anchored on TiO2–x Nanorod Arrays Support by Ti–S Bonds for Ultra-long Life Hybrid Mg2+/Li+ Battery
Hybrid Mg2+/Li+ battery (MLIB) is an attractive energy storage device that combines the advantages of Mg- and Li- rechargeable batteries. Recently, conversion-type transitional metal sulfides (CTMS) have received growing attention as MLIB cathodes due to large theoretical capacity, but these cathodes experience huge volumetric change and dissolution of polysulfide intermediates during cycling, which cause the exfoliation of active materials and the deterioration of lifespan. Herein, self-supported PPy-encapsulated CoS2 nanosheets anchored on TiO2–x nanorod arrays support by Ti–S bonds (TiO2–x@CoS2@PPy) was prepared for MLIBs cathode. The Ti–S bonds and TiO2–x support effectively suppress the exfoliation of active material CoS2 and dissolution of polysulfide intermediates, leading to remarkable stability of the electrode during long cycles. Theoretical calculation demonstrates TiO2–x possesses stronger chemical interaction with polysulfide intermediates, CoS2 and corresponding discharge products than pristine TiO2. Additionally, the nanorod arrays structure and the outer PPy coating layer can provide superior conductive network, buffer volumetric change, and further prevent the APC electrolyte from reacting with polysulfide intermediates upon cycling. Therefore, the prepared electrodes exhibit impressive cycle stability (81.1% capacity retention at 5 A g–1 after 5000 cycles), high specific capacity (720.4 mAh g–1), superior energy density (416.5 Wh kg–1), and good rate capability.