Phys. Chem. Chem. Phys. 19, 24230-23239 (2017) [pdf]

Monolayer BC₂: An Ultrahigh Capacity Anode Materials for Li Ion Batteris

Deya Das, Rahul P. Hardikar, Sang Soo Han, Kwang-Ryeol Lee, and Abhishek K. Singh

There is a great interest in developing promising candidate materials for high-capacity, low cost, environmentally friendly, longer cycle life anode for lithium ion batteries. Due to better Li ad- sorption properties than graphene, boron doped graphene has been considered attractive anode material for Li-ion batteries. Using first principles density functional theory calculations, we in- vestigate the effect of increasing boron concentration on the gravimetric capacity of monolayered boron doped carbon sheets. The calculations are performed for uniformly boron doped carbon sheets, BC_x (x = 7, 5, 3, 2 and 1) as well as their non-uniformly doped counterparts, which are found to be energetically preferable for x = 5, 2 and 1. Our results indicate pronounced enhance- ment in gravimetric capacity with increasing concentration of B, till x = 2. The storage capacity of the uniformly doped BC₂ turns out to be the highest ever reported for B doped graphene sheets, which is 1.9 times (1667 mAh/g) that of previously reported value for BC₃ (J. Phys. Chem. Lett. 2013, 4, 1737-1742). This dramatic increase in the capacity of uniformly doped BC₂ occurs be- cause of availability of significantly more number of empty states above the Fermi level compared to the other BC_x sheets. Moreover, the diffusion energy barriers and open circuit voltage are found to be lower in uniformly doped BC₂, leading to better Li kinetics. For x=1, Li binds very strongly to the uniformly doped BC and higher diffusion energy barriers are found for non-uniformly doped BC, rendering them ineffective as anode materials. Our study reveals that BC₂ can be the most promising candidate for anode material for Li ion batteries owing to high Li storage capacity com- bined with low diffusion barrier and low open circuit voltage.