The development of advanced two-dimensional (2D) materials is critical for enhancing lithium-ion battery (LIB) performance. Pentagonal structures like penta-graphene and penta-BCN have shown significant potential as anode materials due to their unique configurations. In this study, we explore penta-BSiN, a related 2D material, using first-principles calculations. Our research confirms the emergence of a nonsymmetric, nonpatterned lithium packing configuration in penta-BSiN, which arises due to the anisotropic lattice parameters of the material. This packing arrangement is crucial as it significantly impacts the calculation of lithium storage capacity, highlighting the importance of careful optimization in theoretical predictions. Specifically, we find that Penta-BSiN can accommodate up to 24 lithium atoms, forming Li3BSiN with a theoretical capacity of 1520 mAh g–1, surpassing the 1455 mAh g–1 of penta-BCN, and our results demonstrate that the nonpatterned lithium packing leads to more favorable adsorption energies compared to a symmetric configuration. Additionally, penta-BSiN exhibits a low open-circuit voltage of 0.36 V and a lithium diffusion barrier of 0.34 eV, indicating good ion mobility. Our findings underscore the necessity of considering nonpatterned lithium packing when evaluating the performance of 2D materials, particularly in anisotropic structures, to ensure accurate and realistic predictions for next-generation LIB anodes.