Electric double layer studies of Li electrode-PEO-LiTFSI electrolyte by constant potential simulations

Electrochemical interfaces are highly complex, but important to understand to enable new and better battery technologies. Here, the structure and transport properties of the interface between Li metal and PEO-LiTFSI polymer electrolyte, including the electric double layer, are investigated by density functional theory computations and molecular dynamics simulations. Significant charge transfer is observed for a neutral short PEO chain when approaching the Li surface. The interfaces next to the negative and positive electrodes are different; the negative interface is being dominated by the polymer and Li+, while the anions make up more of the positive interface. Adsorption of Li+ ions on the Li slab is observed at high salt concentrations (0.98-3.56 mol L-1) and potential differences (0-4 V). The adsorption energy of the Li+ ions at the interface does not correlate with the Li+ transport kinetics, which is very slow, particularly next to the negative electrode. Slow interface kinetics might contribute to slow charge transfer and non-uniform Li plating. The adsorption of Li+ is only slightly affected by the electric potential difference between the electrodes.