Swelling effect of 2D BC7 anode material in Li-, Na- and Mg-ion energy storage systems

The development of high-performance metal-ion batteries mainly focuses on searching for high-capacity anodes but neglects the volume expansion effect of the materials during the charge/discharge process. Using the first -principles calculation method, we examine the efficacy of bilayer BC7 as an anode material for Li/Na/Mg-ion batteries. Our results illustrate a strong swelling effect caused by the penetration of Na and Mg atoms into the interlayer space of BC7, which is responsible for a large volume expansion and renders the BC7 anodes unsuitable for Na-and Mg-ion batteries. On the other hand, intercalation of Li into the BC7 structure could deliver an acceptable volume expansion of the 2D anode and a theoretical capacity of 423.69 mAh/g, which is higher than that of commonly used anodes for Li-ion batteries.