Li-ion storage systems have made great impact on the development of personal electronics and have the potential to revolutionize energy distribution in the transportation sector.  While significant effort has been invested to optimize the materials present within lithium ion batteries, the behavior at the interfaces of these materials remains poorly understood.  An important challenge remains the formation of surface films at the electrode-electrolyte interface due to side reactions with the organic electrolyte. These films reduce the charging capacity of the battery and hence inhibit battery performance during repeated charge cycling.  On the other hand, these surface layers permit lithium ion transport and have been referred to as a solid electrolyte interphase (SEI) separating the electrode and electrolyte.  Given the lack of experimental resolution of the structure of the SEI, there remains a substantial need to understand the effects of this layer and its composition on the overall transport properties of the electrochemical system.  Insertion of Li-ion into the SEI is coupled to desolvation of the organic electrolyte surrounding the ion.  A simple yet accurate force field for the electrolyte has been developed using force-matching from ab initio MD simulations and an image charge method to describe electrode polarization.  Simulations utilizing this force field have revealed the structure of the electrolyte at the electrode surfaces as a function of applied voltages and the presence of the SEI.  Using these force fields with a combination of two enhanced sampling methods, namely metadynamics and umbrella sampling, the energy landscapes for ion transport through the electrolyte and the SEI have been studied for a combination of graphitic electrodes and experimentally relevant carbonate electrolytes.

Molecular insight into charge transport in Li-ion batteries

245th National Meeting (2013)

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