Measurement of Parasitic Reactions in Li Ion Cells by Electrochemical Calorimetry

A method for measuring the energy produced from parasitic cell reactions in lithium ion cells by electrochemical calorimetry is described. Negative electrode symmetric cells were charged and discharged by high precision current sources in an isothermal heat flow calorimeter while the cell voltage was accurately measured. Two sources of graphite of different BET surface areas were investigated. Symmetric cells of Li4Ti5O12 and lithium/graphite half cells were also measured by this method. The measured parasitic energy was well correlated to the loss of active Li, or coulombic efficiency, confirming the source of the parasitic energy as the heat of reaction occurring between the lithiated electrodes and the electrolyte. The effect of electrode formulation was also explored. Electrochemical calorimetry of symmetric cells is an excellent method to study new material sets to determine which will lead to extended cell lifetime.