A density functional theory based study of the electron transfer reaction at the cathode–electrolyte interface in lithium–air batteries

Abstract

The unique properties of ionic liquids such as a relatively wide electrochemical stability window and very low vapor pressure have made them promising candidates as electrolytes for improving the cyclic performance of lithium-air batteries. The local current density, which is an important parameter in determining the performance of lithium-air batteries, is a function of the rate constant of the electron transfer reactions at the surface of the cathode. In this study, a novel method based on Marcus theory is presented to investigate the effect of varying the length of the alkyl side chain of model imidazolium based cations and the operating temperature on the rates of electron transfer reactions at the cathode. The necessary free energies of all the species involved in the multi-step reduction of oxygen into the peroxide ion were calculated using density functional theory (DFT). Our results indicate that the magnitude of the Gibbs free energy for the reduction of oxygen into the superoxide ion and also for the reduction of superoxide into the peroxide ion increases with an increase in the static dielectric constant of the ionic liquid. This trend in turn corresponds to the decrease in the length of the alkyl side chain of the ionic liquid cation. Furthermore, the change in Gibbs free energy decreases with increase in the operating temperature. The inner-sphere reorganization energies were evaluated using Nelsen's four point method. The total reorganization energies of all reduction reactions increase with decrease in the length of the alkyl side chain and increase in the operating temperature. Finally, the rate constants of the electron transfer reaction involved in the reduction of oxygen were calculated. The logarithm of the reaction rate constants decreases with increase in the static dielectric constant and increases with increase in the operating temperature. Our results provide fundamental insight into the kinetics and thermodynamics of the electron transfer reactions at the cathode that will help in the identification of appropriate electrolytes for enhanced performance of lithium-air batteries.

Tuning Photoinduced Electron Transfer Efficiency of Fluorogenic BODIPY‐α‐Tocopherol Analogues

“…Here, Nelsen's four‐point method was used to calculate λ i by treating the tocopherol donor (D) and BODIPY acceptor (A) separately, as is expressed in Eq. , where, E ( a | b ) represents the energy of state “ a ” calculated at the equilibrium structure of state “ b ” and the “*” denotes the BODIPY acceptor in the excited state. The enthalpic portion of λ i is thus the sum of the relaxation energy between the cation obtained from a vertical transition from the neutral donor species and the relaxed cation, and that for the anion obtained from a vertical transition from the neutral acceptor species (in the excited state) and the relaxed anion (Table ).…”

Understanding Rechargeable Li−O2 Batteries via First‐Principles Computations

“…Based on first-principles computations, Laino et al [79] studied the reactivity of Li 2 O 2 versus propylene carbonate (PC) and reported that Li 2 O 2 can irreversibly decompose the carbonate solvent, then leading to alky carbonates. Therefore, it is extremely important to select a stable solvent which can be resistant to the decomposition in the electrochemical environment of Li 2 O 2 .…”

“…Therefore, it is extremely important to select a stable solvent which can be resistant to the decomposition in the electrochemical environment of Li 2 O 2 . Based on first-principles computations, Laino et al [79] studied the reactivity of Li 2 O 2 versus propylene carbonate (PC) and reported that Li 2 O 2 can irreversibly decompose the carbonate solvent, then leading to alky carbonates. Khetan et al [80] proposed that the highest occupied molecular orbital (HOMO) level of the aprotic solvents in LiÀO 2 batteries can be used as a descriptor to evaluate the solvent stability as shown in Figure 6.…”

Pyrrolidinium‐based ionic liquids as electrolytes for lithium batteries: A Computational Study

“…The fundamental requirement of an IL to be an electrolyte for electrochemical application is that it should possess a wide electrochemical window (ECW) providing resistance to any electrochemical oxidation and reduction. In electrochemical devices such as capacitors, lithium ion batteries, fuel cells, and dye‐sensitized solar cells, the ILs act as electrolytes . Non‐volatility and prevention of electrolyte from drying during the operations are the main advantages of ILs for use in electrochemical devices.…”

“…In electrochemical devices such as capacitors, lithium ion batteries, fuel cells, and dye-sensitized solar cells, the ILs act as electrolytes. [7][8][9][10][11][12][13][14][15] Non-volatility and prevention of electrolyte from drying during the operations are the main advantages of ILs for use in electrochemical devices.…”