Two-Dimensional Bi₂O₂CO₃ Nanosheets as a Li-Ion Battery Anode with Kinetic and Theoretical Studies

A two-dimensional (2D) anode material, Bi 2 O 2 CO 3 nanosheets with a sandwich-like structure, was successfully prepared by using a facile two-step method: (i) an initial femtosecond laser ablation of a Bi target in water; and (ii) an aging treatment at room temperature. The Bi 2 O 2 CO 3 -based anode delivers a discharge capacity of 494.5 mAh g –1 at 160 mA g –1 with an efficiency >99.4% after 200 cycles, storing around 9.4 Li-ions per mol of Bi 2 O 2 CO 3 . The ex-situ analyses demonstrate that the lithiation of Bi 2 O 2 CO 3 nanosheets leads to its structural transformation, forming Li 2 CO 3, LiBi, and Li 3 Bi. Also, this exhibits a dual Li-ion storage mechanism with intercalation and capacitance contributions, which could significantly boost the capacity retention and rate capability. Moreover, density functional theory (DFT) calculations suggest that the Bi 2 O 2 CO 3 nanosheets give a theoretical gravimetric capacity of 630.5 mAh g –1, accompanied by a volumetric expansion of ∼140% upon lithiation. The analysis of the radial distribution function corroborates the structural changes of Bi 2 O 2 CO 3 nanosheets upon lithiation. Additionally, it was found that Li diffuses preferably along the [010] direction and between adjacent Bi 2 O 2 layers in an out-of-plane displacement.