ABSTRACT
Recently, high-voltage lithium-ion batteries (LIBs) have gained a lot of attraction due to the potential application in electric vehicles. However, cathode materials and electrolytes that are readily available suffer from instability when the operating voltage is ramped up above the conventional operating voltage, due to the undesired interaction between cathode and electrolyte and the intrinsic structural instability of cathode materials. Currently, the development of high-voltage application is focused on the already-commercialized layered LiNixCoyMn1- x - yO2 (NMC) and an alternative, spinel LiNix Mn2- x O4 (LNMO), which is potentially a better option to withstand a high-voltage working condition. In this chapter, first-principles study of cathode/electrolyte interfaces of the NMC and LNMO cathode materials is discussed in detail. Density functional theory (DFT) approaches are proposed to investigate the reactivity between cathode surface and the surrounding electrolyte molecules by first calculating the Fermi level of cathode models with different crystal orientations and the electrochemical window of electrolyte molecules. After the alignment of both the Fermi level and the electrochemical window to the same reference level, it becomes possible to predict the propensity of electron transfer between the interfaces by comparing the relation of these parameters. First-principles molecular dynamics simulations of the atomic cathode/electrolyte interface models are also established, which can provide some insight to unveil the mechanism related to the degrading cycling performance of LIBs under high-voltage operation process. With the help of the first-principles calculation, macroscopic behavior of LIBs could be linked with the atomic-scale variation.
