The impact of a trace amount of water in an electrolyte on the performance of Li‐ion batteries—An empirical kinetic model approach

Abstract

A spiral wound-type lithium-ion battery (LIB) was assembled with an NCM532 cathode, a graphite anode and an electrolyte containing 1 M LiPF6 in EC/DEC (1:1 by wt). Different amounts of trace water, from 100 to 900 ppm, were intentionally added into the electrolyte. After stabilizing, the water and the hydrofluoric acid contents in the electrolyte were determined with Karl Fischer titration and coulometric titration, respectively. The performance of the LIBs made with the electrolytes of different amounts of trace water was investigated and the effects of the trace water in the electrolyte were revealed. An empirical model was used in this study to calculate the LIBs capacity attenuation constant. By varying the temperature, the activation energy of capacity decay can also be obtained based on the Arrhenius equation. The results indicated that added trace water up to 900 ppm may not significantly harm the cyclic stability of LIBs at least around room temperature. The capacity fade for the cells with the addition of 300 ppm water was slower than those without water addition. The activation energy of capacity decay was also found to be higher as the contents of added trace water are in the range of 100-400 ppm. This suggests a cost-reducing process of LIBs manufacture in the moisture control respect. Novelty statement Different amounts of trace water were intentionally added into the electrolyte and variation of water as well as formed HF contents were determined by Karl Fischer titration and coulometric titration, respectively. The kinetic information of water reacted with LiPF6 was then obtained. After introducing those electrolytes into the LIB cells, the performances of those LIBs were investigated and the capacity attenuation constants and capacity decay activation energies upon those LIBs were calculated through a newly suggested empirical kinetic model.