Can One Project Cell Lifetime Using Wide Temperature Range Ultra-High Precision Coulometry?

Abstract

Using low charge voltage with Li-ion cells significantly extends their lifetime. This makes them advantageous in enabling the implementation of Li-ion batteries for widespread renewable energy storage1. Li[Ni0.83Mn0.06Co0.11]O2/graphite (Ni83/graphite) cells combined with dimethyl-2,5-dioxahexane carboxylate (DMOHC) as electrolyte solvent and lithium bis(fluorosulfonyl)imide (LiFSI) as salt, operating to upper cutoff voltages of 3.8 or 3.9 V, can achieve incredible capacity retention and reduce gassing while cycling at 85°C2. Since these cells have exceptional lifetime projected to be decades when cycling at room temperature, there is keen interest in using high temperatures to screen cell performance in an accelerated manner3. However, how to project a high-temperature lifetime to room temperature remains to be determined.Ultra-high precision coulometry (UHPC) can give valuable insight into cell degradation within weeks of cycling4. This has been applied to Ni83/graphite cells using a blend of DMOHC and diethyl carbonate (DEC) as electrolyte solvent, LiFSI as salt, and vinylene carbonate (VC) and ethylene sulfate (DTD) as additives. Figure 1 shows the results of UHPC measurements on a series of cells over a wide temperature range between 20-100°C to help determine pathways to project cell lifetime under normal use conditions. The results present exceptional performance at high temperatures and indicate a clear relation between degradation mechanisms and temperature. Remarkably, they also demonstrate similar capacity fade rates when the cycling temperature is increased from 55°C to 100°C. The potential causes of this are further elucidated by post-mortem electrolyte analysis of the measured cells. REFERENCES C. P. Aiken, T. Taskovic, and J. R. Dahn, J. Electrochem. Soc., 169, 090523 (2022).T. Taskovic, A. Eldesoky, C. P. Aiken, and J. R. Dahn, J. Electrochem. Soc., 169, 100547 (2022).T. Taskovic, A. Eldesoky, W. Song, M. Bauer, and J. R. Dahn, J. Electrochem. Soc., 169, 040538 (2022).A. J. Smith, J. C. Burns, D. Xiong, and J. R. Dahn, J. Electrochem. Soc., 158, A1136–A1142 (2011). Figure 1 . Fractional capacity fade per hour (a), fractional charge endpoint slippage per hour (b), and coulombic inefficiency (CIE) per hour (c) of Ni83/graphite cells with 1 M LiFSI in DMOHC:DEC (20:80 w/w) with 2 wt% VC and 1 wt% DTD calculated at cycle 19 of UHPC cycling at different temperatures. Notice that the y-axis is logarithmic. Figure 1