Fundamentals

Depletion Of LiPF6 During Calendar Aging Hinders Fast Charging Capability Electrolyte oxidation at the positive electrode causes a decrease of LiPF6 concentration in the electrolyte. This reduction of LiPF6 concentration is not observable from slow-rate capacity checks or DC pulses, but severely impacts fast charging performance. Hartmann et al. use single-layer pouch cells to clearly demonstrate the effect of LiPF6 concentration on low- and high-rate performance. This work highlights the critical need for oxidatively stable electrolytes to enable consistent fast-charging performance for EVs throughout their lifetime.

Artificial LiPF6 variation in single-layer pouch cells (left) validates LiPF6 depletion as the dominant cause of rate capability loss of calendar aged cells (right). LiPF6 depletion in calendar aged cells was verified by ion chromatography and NMR, and reaction pathways for LiPF6 detailed in the work. Left Discharge rate capability at 25 °C in single-layer pouch cells with different electrolyte LiPF6 concentrations. Electrodes were extracted from a beginning-of-life commercial high-nickel 85% NMC and Graphite cell. Right Discharge rate capability at 25 °C for single-layer pouch cells calendar aged at 45 °C under a constant voltage hold for 1 month.

Source: Hartmann et al, Journal of the Electrochemical Society 171 060506

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