COMPUTER SIMULATION OF ELECTRON TRANSFER IN LIQUID-PHASE REDOX REACTIONS OF MOLECULAR OXYGEN IN LITHIUM BATTERIES
The paper presents the results of computer simulation of electron transfer from a superoxide radical to lithium ion complexes in the near-electrode space of lithium batteries for typical liquid-phase organic solvents. Two solvents with a significant difference in the values of the static dielectric constant ε - ethylene carbonate (ε = 95,3) and dimethyl carbonate (ε = 3,1) are considered. To describe the dissolution processes, an implicit modeling approach was used within the framework of the Conductor-like Polarizable Continuum Model. Using the theory of Marcus, the activation energy of electron transfer was calculated taking into account the energy of reorganization of continuous dielectric media obtained from quantum-statistical calculations. Quantum-mechanical calculation of the complexes was carried out within the framework of the density functional theory using the hybrid functional B3LYP with the basis set 6-31+G(d,p). The calculation of the Gibbs functions was carried out by using the Hessian at 298,15 K and 1 atm. The calculation showed that in the case of a high polarizability of ethylene carbonate, the electron transfer from the superoxide radical to the complexes of lithium ions is characterized by a large positive value of the change in the Gibbs function. This indicates the thermodynamic difficulty of such a reaction under standard conditions. In the case of a weakly polar solvent, dimethyl carbonate, the potential is negative, which indicates the thermodynamic lability of electron transfer in this medium. Numerically obtained activation energies of electron transfer from the superoxide ion to the lithium ion complex are: 2,14 eV and 0,57 eV in ethylene carbonate and dimethyl carbonate media, respectively. This indicates a significantly higher probability of the removal of an electron from O2- by the lithium cation in the dimethyl carbonate than in the more polar ethylene carbonate medium.