Investigation of various layered lithium ion battery cathode materials by plasma- and X-ray-based element analytical...

In this work, the transition metal dissolution (TMD) from the respective ternary layered LiMO₂ (M = Mn, Co, Ni, Al) cathode active material was investigated as well as the lithiation degrees of the cathodes after charge/discharge cyclic aging. Furthermore, increased nickel contents in LiNi_xCo_yMn_zO₂-based (NCM) cathode materials were studied, to elucidate their influence on capacity fading and TMD. It was found, that the TMD from nickel-rich cathode materials, e.g., LiNi_0.6Co_0.2Mn_0.2O₂ or LiNi_0.8Co_0.1Mn_0.1O₂, did not differ significantly from the TMD from the stoichiometric LiNi_1/3Co_1/3Mn_1/3O₂. In detail, the TMD from the cathode did not exceed a maximum of 0.2 wt% and was uniformly distributed on all analyzed cell parts (separator, anode, and electrolyte) using total reflection X-ray fluorescence. Moreover, the investigated electrolyte solutions showed that increased Ni contents come with more nickel dissolution of the respective material. Additionally, inductively coupled plasma optical emission spectroscopy analysis on the respective charge/discharge cyclic-aged cathode active materials revealed lithium losses of 20% after 50 cycles. However, only a minimum amount of capacity loss (= 1.5 mAh g^-1) can be attributed to active material loss.