Solvent control of the nucleation-induced voltage hysteresis in Li-rich LiFePO4 materials

Abstract

Phase transformations during the reversible ion insertion into metal-ion battery materials have been extensively studied due to the importance of understanding the mechanisms of (de)lithiation and controlling the battery performance. In this work, we demonstrate that the electrolyte, which is typically neglected in the studies of phase transformation mechanisms, plays an essential role in governing the kinetics of nucleation. We compare nucleation rates for Li-rich LiFePO4 materials in carbonate and aqueous electrolytes and show that the nucleation rate is an order of magnitude higher in aqueous electrolyte. Consequently, this leads to a decrease in the hysteresis of the charge and discharge curves in an aqueous medium by 30%, i.e., a significant increase in the energy efficiency of cells with an aqueous electrolyte. We provide a detailed characterization of the lithium-ion intercalation kinetics and formulate assumptions about the possible reasons for the solvent dependence of the nucleation kinetics.