Importance of Coulombic Efficiency Measurements in R&D Efforts to Obtain Long-Lived Li-Ion Batteries

Researchers and companies around the world are now recognizing the importance of high-precision coulometry to obtain long lived lithium ion batteries. Many researchers and users of Li-ion cells try to demonstrate lifetime by doing rapid charge-discharge cycles around C-rate or even faster, where every full cycle can take 2 h or less. In 2010, Smith and colleagues proposed that high accuracy measurements of the coulombic efficiency of Li-ion cells could be used to help determine their lifetime. Basically, if there are no unwanted parasitic reactions occurring in a Li-ion cell and if the electrodes show no mechanical degradation, then the coulombic efficiency of that cell will be exactly unity. The greater the departure of the CE from unity, under fixed testing conditions, the shorter the lifetime of the Li-ion cell. It is also worth noting that beyond lithium ion technologies such as non-aqueous Na-ion and Mg-ion will also need to attain extremely high coulombic efficiencies to attain decades-long lifetimes. High-precision coulometry will be essential in the development of those technologies as well.