Unraveling transition metal dissolution of Li1.04Ni1/3Co1/3Mn1/3O2 (NCM 111) in lithium ion full cells by using the total reflection X-ray fluorescence technique

• Investigation of the transition metal dissolution of Li1.04Ni1/3Co1/3Mn1/3O2.
• Application of the total reflection X-ray fluorescence (TXRF) technique.
• Experiments on the cycle number and cut-off cell voltage during charge.

In this work we investigated the transition metal dissolution of the layered cathode material Li1.04Ni1/3Co1/3Mn1/3O2 in dependence on the cycle number and cut-off cell voltage during charge by using the total reflection X-ray fluorescence technique for the elemental analysis of the specific lithium ion battery degradation products.We could show that with ongoing cycling transition metal dissolution from the cathode increased over time. However, it was less pronounced at 4.3 V compared to elevated charge cut-off voltages of 4.6 V. After a maximum of 100 cycles, we detected an overall transition metal loss of 0.2 wt‰ in relation to the whole cathode active material for cells cycled to 4.3 V. At an increased charge cut-off voltage of 4.6 V, 4.5 wt‰ transition metal loss in relation to the whole cathode active material could be detected. The corresponding transition metal dissolution induced capacity loss at the cathode could thus be attributed to 1.2 mAh g−1. Compared to the overall capacity loss of 80 mAh g−1 of the complete cell after 100 galvanostatic charge/discharge cycles the value is quite low. Hence, the overall full cell capacity fade cannot be assigned exclusively to the transition metal dissolution induced cathode fading.

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