Journal of Power Sources, Vol.327, 714-725, 2016
The influence of cycling temperature and cycling rate on the phase specific degradation of a positive electrode in lithium ion batteries: A post mortem analysis
The influence of cycling temperatures and cycling rates on the cycling stability of the positive electrode (cathode) of commercial batteries are investigated. The cathode is a mixture of LiMn2O4 (LMO), LiNi0.5Co0.2Mn0.3O2 (NCM) and LiNi0.8Co0.15Al0.05O2 (NCA). It is found that increasing the cycling temperature from 25 degrees C to 40 degrees C is detrimental to the long term cycling stability of the cathode. Contrastingly, the improved cycling stability is observed for the cathodes cycled at higher charge/discharge rate (2C/3C instead of 1C/2C). The microstructure analysis by X-ray powder diffraction reveals that a significant capacity fading and an increased overvoltage is observed for NCM and NCA in all the fatigued cathodes. After high number of cycling (above 1500 cycles), NCM becomes partially inactive. In contrast to NCM and NCA, LMO shows a good cycling stability at 25 degrees C. A pronounced degradation of LMO is only observed for the fatigued cathodes cycled at 40 degrees C. The huge capacity losses of NCM and NCA are most likely because the blended cathodes were cycled up to 4.12 V vs. the graphite anode during the cycle-life test (corresponds to 4.16 V vs. Li+/Li); which is beyond the stability limit of the layered oxides below 4.05 V vs. Li+/Li. (C) 2016 Elsevier B.V. All rights reserved.