Electrochemical Investigations on Capacity Fading of Advanced Lithium-Ion Batteries after Storing at Elevated Temperature

Capacity fading of advanced lithium-ion batteries after elevated temperature storage was investigated by three-electrode measurements. Capacity fading of a battery increases by increasing the state-of-charge (SOC) during storage, especially at elevated temperatures. The reversible capacity of a battery at decreases from (79.3% capacity retention) after . At room temperature, a battery SOC influences the capacity fading only slightly; after of storage, the reversible capacity decreases from (98.2% capacity retention). Individual effects by the anode, cathode, and electrolyte on capacity fading are analyzed with three-electrode electrochemical ac impedance. The major contribution, from X-ray photoelectron spectroscopy (XPS) and energy-dispersive spectroscopy results, comes from cathode degradation as a result of cobalt dissolution at the surface layer. A minor contribution comes from the continuous reactions between lithiated mesocarbon microbead (MCMB) electrode and electrolyte components, which in turn thicken the SEI film and consume available lithium ions. From X-ray diffraction and XPS results, high-temperature storage influences only the surface properties of MCMB and electrodes; bulk properties remain unchanged.