Molecular Dynamics Study of Graphite/Electrolyte Interfaces
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abstract
Molecular dynamics simulations of graphite-electrolyte interfaces arc performed on 3D unit cells with periodic boundary conditions at lithium concentrations between 0 and 17% in the carbon phase. The liquid electrolyte consists of a mixture of cyclic carbonates and LiPF6. Staging phenomena, structural changes in the modeled graphite systems, charge distribution on the atoms, and lithium-ion diffusion coefficients are evaluated as a function of lithium concentration in the solid phase. Transitions between ordered carbon structures arc detected in the model systems. Repulsive lithium-lithium interlayer interactions are predominant during the intercalation process. Calculated solid phase diffusion coefficients of lithium ions for a state of charge between 0 and 17% are in the range 10 8 to 10 9 cm2/s. The maximum increase of graphite interlayer spacing found when the lithium ions are intercalated varies from 6 to 10% depending on the degree of intercalation. An electrostatic double layer is formed between the solid and the electrolyte phase: the average charge at each side of the solid/liquid interface is strongly dependent on the composition and electronic properties of the electrolyte. 2001 The Electrochemical Society. [DOI: 10.1149/1.1.1372216] All rights reserved.
