高導電率・高容量なナトリウムイオン電池用アノード材料としての化学結合型Bi@C/多孔質炭素複合材料

Metallic bismuth is one of the promising sodium ion anodes due to its exceptional conductivity, high theoretical capacity and suitable redox potential. However, severe volume changes (∼240%) during alloying reactions hinder its further development. In this study, carbon coated Bi nanoparticles embedded in micro-sized porous carbon bundles (Bi@C) are successfully fabricated. The dual-carbon confinement superstructure with inner covalent anchoring of C-O-Bi bonds significantly relieves the volume expansion of the Bi alloy anode and improves the electron transfer rate for the Bi@C anode. This unique structure promotes a pseudocapacitive sodium storage mechanism. As a result, Bi@C exhibits an excellent rate capability of 342.2 mAh g^-1 at 15 A g^-1 and long cyclability with 320.2 mAh g^-1 after 1000 cycles at 2 A g^-1 and 82.5% capacity retention. This strategy could be applied to other alloy-type anode materials for optimizing the rate performance and cycling stability.