Field-effect and defect engineering tunable 2D-PDBG+ monolayer: An anode for calcium-ion batteries with ultra-high capacity and fast kinetics

The development of high-performance anodes is crucial for advancing calcium-ion batteries (CIBs). Through first-principles calculations, we propose a boron–carbon monolayer named 2D-PDBG+ as an exceptionally promising anode material. The 2D-PDBG+ monolayer exhibits remarkable structural stability and an ultra-narrow bandgap of 14 meV. Furthermore, the combination of an ultra-high theoretical capacity (2509.46 mA h g−1), a low diffusion barrier (0.45 eV), and a suitable average open-circuit voltage (0.207 V) underscores the strong potential of 2D-PDBG+ for CIBs' anode. Beyond these intrinsic advantages, a groundbreaking approach of applying an external electric field is introduced to dynamically regulate its electrochemical performance. The electric field strength and direction (−0.05 V/Å) can serve as a precise “tuning knob,” enabling reversible control over the Ca2+ adsorption strength (e.g., from −1.77 to −3.9 eV) and a marked decrease in the diffusion barrier (e.g., from 0.45 to 0.39 eV). Such a dual modulation of storage and kinetics by an external stimulus presents a paradigm shift from static material design toward dynamic performance control.