Analysis of Lithium Insertion/Desorption Reaction at Interfaces between Graphite Electrodes and Electrolyte Solution Using Density Functional + Implicit Solvation Theory

The charge transfer reaction at the electrode/solution interface is regarded as a major component that limits the current densities of Li-ion batteries. A combination of density functional theory for the electronic structure calculations of an electrode and a reacting component with implicit solvation theory for an electrolyte solution is used for the lithium insertion/desorption reaction (<i>R</i>). At the interfaces between tilted-graphite electrodes and a 1 M LiPF₆ ethylene carbonate solution, the energy landscapes of reaction <i>R</i> are revealed under constant electron chemical potential conditions. Across the transition state where the Li forms a half solvation shell, the reacting Li inside the electrode changes to a full solvation structure in the solution accompanied by electron transfer. On graphite with two tilt angles, the activation energies at the equilibrium potentials of reaction <i>R</i> are approximately 0.6 eV, which is consistent with the electrochemical impedance spectroscopy measurements. However, opposite-sign charges are obtained on the two angle surfaces, which can be well explained by the work functions on the tilted graphite. This study paves the way for the quantitative analysis of the charge-transfer reactions in electrochemical devices under electrochemically defined environments