Metal-ion batteries are key for energy storage in both portable electronics and large-scale applications. As the ion capacity of the widely used graphite electrodes is limited, 2D materials, in particular silicene, are considered for possible replacement. Here, the effects of B/Al doping on the ion capacity of silicene are studied and it is demonstrated that complex charge transfer leads to ultra-high Na capacity. Low Na/K diffusion barriers open potential for fast charge and discharge. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim