Facile preparation of [Bi6O4](OH)4(NO3)6·4H2O, [Bi6O4](OH)4(NO3)6·H2O and [Bi6O4](OH)4(NO3)6·H2O/C as novel high capacity anode materials for rechargeable lithium-ion batteries

Abstract

[Bi6O4](OH)4(NO3)6·4H2O, [Bi6O4](OH)4(NO3)6·H2O and [Bi6O4](OH)4(NO3)6·H2O/C, derivated from Bi(NO3)3·5H2O, are firstly investigated for the electrochemical activity as anode materials for lithium-ion batteries. Electrochemical results show that [Bi6O4](OH)4(NO3)6·4H2O can deliver a higher initial discharge specific capacity (2792.9 mAh g−1) than that of [Bi6O4](OH)4(NO3)6·H2O (832.2 mAh g−1) and [Bi6O4](OH)4(NO3)6·H2O/C (1169.3 mAh g−1). However, the capacity retention (60.3%) and reversible specific capacity (365.5 mAh g−1) of [Bi6O4](OH)4(NO3)6·H2O/C are much higher than those of [Bi6O4](OH)4(NO3)6·H2O (4.75% and 39.6 mAh g−1) and [Bi6O4](OH)4(NO3)6·4H2O (15.9% and 289.4 mAh g−1) in the first 30 cycles. The improved electrochemical properties are attributed to the decrease of crystal water in the structure and the introduction of carbon black as conductive additive and volume change buffer. The reaction mechanism of [Bi6O4](OH)4(NO3)6·H2O/C with Li is also studied in detail by using various ex-situ and in-situ techniques during the initial charge-discharge cycle. It can be found that the electrochemical reaction of [Bi6O4](OH)4(NO3)6·H2O with Li leads to the preliminary formation of metal Bi, LiNO3, LiOH, Li2O and H2O and then the alloying reaction to form Li–Bi alloys.