Lithium and sodium ion binding in nanostructured carbon composites
Dayton G. Kizzire, Alexander M. Richter, David P. Harper, David J. Keffer
Abstract
High charge capacity in lithium and sodium-ion batteries can be achieved using anodes composed of nanostructured carbon composites. The tailoring of the nanostructure to achieve both high loading and low irreversible binding depends upon the binding mechanisms of the ion. In this work, reactive molecular dynamics simulations are performed on model carbon composite anodes to investigate and to compare the binding mechanisms of lithium and sodium ions. In composites composed of both crystalline and amorphous domains, lithium ions bind preferentially at the interface between the amorphous and crystalline domains, rather than via the standard intercalation mechanism observed in graphitic anodes. In these same composites, sodium ions bind preferentially in the crystalline domain, even though the intercalation of sodium in graphitic anodes is not a viable mechanism for charge storage. The difference in mechanisms is explained through a comparison of the binding energies in the carbon composite to the energies of the respective metals and metal hydrides.