The role of electrolyte upon the SEI formation characteristics and low temperature performance of lithium-ion cells with graphite anodes

摘要

Quarternary lithium-ion battery electrolyte solutions containing ester co-solvents in mixtures of carbonates have been demonstrated to have high conductivity at low temperatures (<-20°C). However, in some cases the presence of such co-solventsdoes not directly translate into improved low temperature cell performance, presumably due to the formation of ionically resistance surface films on lithiated carbonaceous anodes. In order to understand this behavior, a number of lithium-graphite cellshave been studied which possess different electrolytes that contain various ester co-solvents, including methyl acetate (MA), ethyl acetate (EA), ethyl propionate (EP), and ethyl butyrate. The charge/discharge characterization of these cells indicatesthat the higher molecular weight esters result in electrolytes which possess superior low temperature performance in contrast to the lower molecular weight ester-containing solutions, even though these solutions display lower conductivity values. Thistrend is understood as being related to the resistive nature of the SEI films formed on carbon electrodes in the presence of these electrolytes.