The search for new anode materials with high lithium-ion battery (LIB) capacity has attracted considerable attention due to the increasing need for electrical power. Here, we utilized first-principles calculations to develop a honeycomb-structured B2C3N monolayer, which exhibits an ultra-high Li-ion storage capacity of 2244 mA h g-1 as an anode material for LIBs. Furthermore, the calculations show that the B2C3N monolayer has a comparatively small diffusion barrier of 0.352 eV and a low open-circuit voltage of 0.134 V. The stability of B2C3N has been verified by analyzing phonon dispersion curves, conducting molecular dynamics simulations, and examining elastic constants. We have found an ultra-high capacity and efficient anode material through theoretical design, which provides a theoretical reference for responding to the global energy crisis and promoting clean energy transformation.