Hexagonal boron cluster as an anode material for divalent-ion (Ca2+) storage: A theoretical study

There has been always a persistent search for creating cheaper and efficient energy storage devices. After its discovery Li+ ion storage device has become the most preferred choice due to its high energy density. However, an ion storage device that can use Ca
²
+ ions instead of Li+ ions, will be much cheaper owing to the higher abundance of calcium. Realizing the need for developing novel ion storage devices, present study aims to investigate hexagonal boron (B
6
) cluster's ability to store divalent Ca
²⁺
ions. The calculated values of adsorption energies show that Ca
²
+ ions are well adsorbed in B
6
cluster and it reaches the maximum storage capacity when two ions are adsorbed into it with bi-pyramidal shape. We have used density functional theory (DFT) for our investigations. Both CaB
6
and Ca
2
B
6
have high specific capacities, with theoretical values 826 mAh/g and 1653 mAh/g respectively. Open circuit voltages (OCV) of the CaB
6
and Ca
2
B
6
are found to be 3.755 V and 2.993 V respectively.