Electrochemical Properties of Boron-Doped Fullerene Derivatives for Lithium-Ion Battery Applications.

The high electron affinity of fullerene C60 coupled with the rich chemistry of carbon makes it a promising material for cathode applications in lithium-ion batteries. Since boron has one electron less than carbon, the presence of boron on C60 cages is expected to generate electron deficiency in C60 , and thereby to enhance its electron affinity. By using density functional theory (DFT), we studied the redox potentials and electronic properties of C60 and C59 B. We have found that doping C60 with one boron atom results in a substantial increase in redox potential from 2.462 V to 3.709 V, which was attributed to the formation of an open shell system. We also investigated the redox and electronic properties of C59 B functionalized with various redox-active oxygen containing functional groups (OCFGs). For the combination of functionalization with OCFGs and boron doping, it is found that the enhancement of redox potential is reduced, which is mainly attributed to the open shell structure being changed to a closed-shell one. Nevertheless, the redox potentials are still higher than that of pristine C60 . From the observation that the lowest unoccupied molecular orbital of closed-shell OCFG- functionalized C59 B is correlated well with the redox potential, it was confirmed that the spin state is crucial to be considered to understand the relationship between electronic structure and redox properties.