Authors: Alexander Smith and Rakel Wreland Lindström
Title: Rapid cycling of Li-ion cells for cold climates
Affiliation: Royal Institute of Technology, KTH
Abstract
To ensure electric vehicles as a convenient and viable transportation solution, battery lifetime must be improved by better understanding the conditions and signs of aging. Power-optimized cylindrical NMC-LMO/graphite Li-ion cells were cycled in sub-ambient and room temperatures at 1C and 3C rates over the full SOC range (0-100%). Conditions were selected to investigate aging in cold climates with increased risk for Li plating. Differential voltage analysis, differential thermal voltammetry, and electrochemical impedance spectroscopy were conducted in situ to study degradation.
Ambient cycling at 1C rate caused the earliest end-of-life (80% remaining capacity) after 2500 equivalent cycles. At 3C rate and 10°C, cells lasted longer; slower late-life degradation contributed to a lifespan of >3500 equivalent cycles. In all cases, loss of cyclable lithium was the dominant mode of capacity fade, confirmed by dV/dQ. Ongoing post mortem analysis will elucidate specific aging mechanisms.