Hexagonal BC₃: A robust electrode material for Li, Na, and K ion batteries

We have investigated the stability, maximum intercalation capacity, and voltage profile of alkali metal intercalated hexagonal BC₃ (M_xBC₃), for 0 < x ≥ 2 and M = Li, Na, and K. Our calculations, based on dispersion-corrected density functional theory, show that these intercalation compounds are stable with respect to BC₃ and their bulk metal counterparts. Moreover, we found that among all M_xBC₃ considered, the maximum stable capacity corresponds to an x value of 1.5, 1, and 1.5 for Li, Na, and K, respectively. These values are associated with large gravimetric capacities of 572 mA h/g for Na and 858 mA h/g for Li and K. Importantly, we show that metal intercalated hexagonal BC₃ has the advantage of a small open-circuit voltage variation of approximately 0.49, 0.12, and 0.16 V for Li, Na, and K, respectively. Our results suggest that BC₃ can become a robust alternative to graphitic electrodes in metal ion batteries, thus encouraging further experimental work.