The performance of lithium-ion secondary batteries is strongly dependent on the ease of ion transport through electrode-electrolyte interfaces [1]. Ion solvation structures near the interface as well as the chemistry of the electrode surface, in particular the edge termination of graphite electrodes, can impact Li ion transport into and out of the electrode. Understanding these effects is critical to optimizing battery performance. We have performed molecular dynamics simulations of organic liquid electrolytes in contact with graphite electrodes, with and without electric field, to understand the relationship between ion solvation structure and transport near the interface. A prototypical electrolyte consisting of ethylene carbonate (EC) organic solvent containing dissolved LiPF6 salt was studied, in contact with armchair-edge oriented graphite anode electrodes. Various surface terminations of the graphite, including H and OH, were compared. We have used molecular dynamics to study the structure and transport of solvated Li ions in ethylene carbonate (EC) electrolyte in contact with armchair-edge terminated graphite. We find that Li+ maintains a well-structured first solvation shell in EC even when an electric field is present. The bulkier PF6– does not present a strong solvation structure and exhibits higher mobility in an electric field. We found an energy barrier for Li+ insertion into graphite, particularly when the surface was hydroxyl terminated. Lithium extraction, however, was facile even against an applied electric field.

Molecular structure and ion transport near electrode-electrolyte interfaces in lithium-ion batteries

249th National Meeting (2015)

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Molecular structure and ion transport near electrode-electrolyte interfaces in lithium-ion batteries<br />