Achieving Lithium-Ion Cells with Improved Performance and Lifetime

Abstract

For commercial use, among many other requirements, lithium-ion batteries must deliver sufficient calendar- and cycle-life. Increased lifetime can enable the adoption of advanced battery materials with higher energy density or lower material cost, compounded with the possibility of reducing levelized energy cost and waste. For cells with optimized electrode materials, electrode-electrolyte reactions are the predominant source of failure. Improvements to electrolyte formulations can help mitigate these reactions and significantly extend the life of a given cell. These improvements can include the quantity and type of salt, solvent and electrolyte additive. In this report, initial work on understanding the role of the electrolyte salt, LiPF6, and also additives and solvent, in high voltage operation of Li[Ni0.5Mn0.3Co0.2]O2 (NMC532)/artificial graphite cells and high state of charge operation of LiFePO4 (LFP)/artificial graphite cells will be discussed in the context of making improvements to cell lifetime. It is shown that when LiPF6 is selected as an electrolyte salt, NMC cells and LFP cells achieve longer lifetime with higher and lower concentrations of LiPF6, respectively. Additionally, the role of two salts, LiPF6 and LiFSI in unique, low voltage Li[Ni0.5Mn0.3Co0.2]O2/artificial graphite cells is discussed, and unprecedented lifetime potential is demonstrated with the use of LiFSI.