Effect of Vinylethylene Carbonate and Fluoroethylene Carbonate Electrolyte Additives on the Performance of Lithia-Based Cathodes.

Nanolithia-based materials are promising lithium-ion battery cathodes owing to their high capacity, low overpotential, and stable cyclic performance. Their properties are highly dependent on the structure and composition of the catalysts, which play a role in activating the lithia to participate in the electrochemical redox reaction. However, the use of electrolyte additives can be an efficient approach to improve properties of the lithia-based cathodes. In this work, vinylethylene carbonate (VEC) and fluoroethylene carbonate (FEC) were introduced as electrolyte additives in cells containing lithia-based cathode (lithia/(Ir, Li2IrO3) nanocomposite). The use of additives enhanced the electrochemical performance of the lithia-based cathodes, including the rate capability and cyclic performance. Especially, their available capacity increased without modifying the cathodes. Results of X-ray photoelectron spectroscopy (XPS) analysis confirmed that the additives form interface layers at the cathode surface, which contain Li2CO3, more carbon reactants, and more LiF than the interface layer formed with the pristine electrolyte. The Li2CO3 and carbon reactants may improve rate capability by facilitating Li+ transport, and LiF may stabilize the Li2O2 (and/or LiO2) produced by the oxygen redox reaction with lithia. Therefore, the additive-enhanced electrochemical performance of the cell is attributed to the effects of the interface layer derived from additive decomposition during cycling.