Be it an energy generating cell or an energy consuming cell, efficiency of an electrochemical cell has traditionally been looked at as a product of voltage efficiency and current efficiency. Voltage efficiency takes care of the impact of ohmic losses in electrode and electrolyte, polarization losses at the electrode due to charge transfer reaction and polarization losses due to mass transfer limitations. Current efficiency takes care of the impact of parasitic reactions and the effective utilization of reactants. Can there be additional energy loss leading to efficiency loss that is not captured in either via voltage or via current efficiency? Turns out there are such losses indeed happening in electrochemical cells, albeit at a small magnitude. With the miniaturization of devices, especially that of batteries, powering our miniaturized electronic devices, improving energy efficiency leads one to understand ALL of the losses occurring. Understanding of these minor losses during the design phase also leads one to evaluate/screen new cell or battery chemistry’s impact on the life and reliability of these devices.
So how does one go about making a sensitive enough measurement to understand the parasitic losses that are not captured by voltage and current efficiencies? Using Lithium batteries as an example and taking the study of electrolytes and their additives as case study, Downie et al of Dalhousie University in Canada (Journal of the Electrochemical Society, 163(2), A35-A42, (2016)) and Krause et al of Corporate Materials Research Laboratory at 3M (Journal of The Electrochemical Society, 164 (4) A889-A896 (2017) have demonstrated that performing calorimetric measurements along with electrochemical measurements during cycling of batteries can shed light on the parasitic losses. Using this combined study, they showed the impact of oxidation of electrolyte at high voltages as well as the impact of additives in the electrolyte.
Increased phenomenological understanding of ALL the processes occurring in an electrochemical cell will be the key to design and develop cells meeting performance and life expectations. These studies teach us an efficient way to do the same. For more details, please go through the full articles, which are available via Open Access.
Downie et al, The Impact of Electrolyte Composition on Parasitic Reactions in Lithium Ion Cells Charged to 4.7 V Determined Using Isothermal Microcalorimetry, 10.1149/2.0081602jes
Kruase et al, Measurement of Li-Ion Battery Electrolyte Stability by Electrochemical Calorimetry, 10.1149/2.1651704jes