Improving the Lifetime and Cycle Life of NMC/Graphite Li-Ion Cells Charged to 4.4 or 4.5V

Abstract

Significant extra capacity and energy density can be obtained from NMC/graphite cells by increasing the upper voltage cutoff from 4.2V to 4.5V. However, when this is done, parasitic reactions between the charged NMC electrodes and the electrolytes accelerate and cell lifetime is compromised. In this lecture, I will review recent work in our laboratory that has focussed on increasing the lifetime of NMC/graphite Li-ion cells charged to 4.4 or 4.4V. This work has centered around: 1) Quantifying parasitic reactions using Ultra High Precision Coulometry, Isothermal Battery Microcalorimetry and Automated Cycling/Impedance Spectroscopy measurements; 2) Reducing the rate of parasitic reactions through the use of electrolyte additives; and 3) Using surface science techniques, e.g. XPS, to understand how these electrolyte additives function. The results of this work are NMC622/graphite, NMC532/graphite, NMC422/graphite and NMC111/graphite cells which have improved properties for high voltage use. This work has been carried out by a large number of graduate students and post doctoral fellows including Dr. Mengyun Nie, Dr. Jian Xia, Dr. Lenaic Madec, Dr. David Hall, Dr. David Yaohui Wang, Lin Ma, Kathlyne Nelson, Laura Downie, Remi Petibon, Julian Self, Leah Ellis, Deijun Xiong and Chris Burns. Collaborations with researchers at 3M Company, including Dr. Ang Xiao, Dr. Bill Lamanna and Dr. Kiah Smith have been vital for this work. The authors acknowledge Dr. Jing Li of BASF for supply of many of the electrolyte solvents and additives used in these studies. Dr. Yong-Shou Lin and Dr. David Wang of ATL Battery Co. are acknowledged for the supply of some of the dry pouch cells used in these studies. The authors thank the Natural Sciences and Engineering Research Council of Canada and 3M Canada Company for funding of this work.