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

A two-dimensional (2D) anode material, Bi2O2CO3 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 Bi2O2CO3-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 Bi2O2CO3. The ex-situ analyses demonstrate that the lithiation of Bi2O2CO3 nanosheets leads to its structural transformation, forming Li2CO3, LiBi, and Li3Bi. 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 Bi2O2CO3 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 Bi2O2CO3 nanosheets upon lithiation. Additionally, it was found that Li diffuses preferably along the [010] direction and between adjacent Bi2O2 layers in an out-of-plane displacement.