DFT study on gas-phase decomposition of ethylene carbonate in the presence of LiPF6, LiBF4, PF6-, and BF4-

Abstract

The decomposition of Li-ion battery (LIB) electrolyte has been a well-known challenge that needs to be overcome. The most common electrolyte on lithium-ion batteries is LiPF6 which has all-balanced properties, while LiBF4 has been proven for its superior stability. These lithium salts are often dissolved in Ethylene Carbonate (EC) to form liquid electrolyte systems. In this work, we investigate the decomposition mechanism of EC in the presence of LiPF6, LiBF4, and their delithiated counterpart by means of first-principles density functional theory (DFT) calculations. We found that the energy barrier of decomposition on LiBF4 presence is 0.42 eV lower than on LiPF6 presence, also on BF4- presence is 0.22 eV lower than PF6- presence. This suggests that LiBF4 and BF4- presence reduces EC stability more than LiPF6 and PF6- anion. Moreover, the presence of Li+ ion increases the energy barrier of decomposition (about 0.79 eV on PF6- case, 0.59 eV on BF4- case) but decreases enthalpy change significantly (about 1.58 eV on PF6- case, 1.43 eV on BF4- case). This suggests that while the Li+ ion causes the decomposition to be slower, its presence destabilizes the EC more.