  The structural stability and electrochemical performance of boron substituted
fluorinated graphite as a Li ion batteries cathode material are studied by
first principles calculations. The results show that boron substituted
fluorinated graphite BC3F4 possesses excellent structural stability, good
electrical and ionic conductivities. Unexpectedly, the average Li intercalation
voltage of LiBC3F4 is up to 4.44 V, which is much larger than that of LiBCF2.
The average voltage of LiBC3F4 is even larger than that of common commercial
transition metal oxides cathodes, indicating that LiBC3F4 is a breakthrough of
transition metal-free high voltage cathode materials. By comparing the Fermi
level, we found the Fermi level of LiBC3F4 is 1.38 eV lower than that of
LiBCF2, leading to the decrease of the electron filling energy for the Li
intercalation and forming much higher voltage. Moreover, LiBC3F4 shows small
volume expansion and high energy density. LiBC3F4 is a promising high voltage
cathode material for Li ion batteries. Finally, by calculating the evolution of
Li intercalation voltage and Fermi level during the discharging process, a
linear correlation between the Fermi level and Li intercalation voltage has
been found.
