The effect of high temperature exposure upon the performance of lithium ion cells

The effect of electrolyte type upon the resilience of lithium-ion cells to high temperature storage has been investigated in experimental MCMB carbon-Li_xNi_yCo_1-yO₂ three-electrode cells. A number of electrolytes have been studied where the solvent mixtures have been varied, with the intention of determining the impact of ethylene carbonate (EC)-content upon performance, as well as, the presence of nonconventional linear carbonates (ie., di-2,2,2-trifluoroethyl carbonate and dipropyl carbonate). In addition to determining the reversible and irreversible capacity losses sustained as a result of high temperature storage (55° to 70°C), a number of electrochemical measurements (AC impedance, Tafel polarization and linear polarization) have been performed to determine the impact of the high temperature exposure upon the electrode kinetics and the nature of the electrode surface films. It was observed that cells containing electrolytes with high EC-content (>50% EC by volume) displayed superior resilience to high temperature storage, in contrast to cells containing low EC-content electrolytes (<25% EC by volume) which displayed much larger irreversible capacity losses and poorer lithium intercalation/deintercalation kinetics after exposure to high temperatures