Understanding the lithium loss in 5 Ah multilayer pouch cells with silicon-dominant anodes and NCA cathodes during cyclic aging

In this work, we demonstrated that cyclic aging leads to loss of lithium (Li) from the LiNi 0.8 Co 0.15 Al 0.05 O 1.985 (NCA) electrode of multilayer pouch cells, with the lost Li found in the silicon (Si)-dominant anode. Electrochemical data showed that less Li is retrieved from the Si electrode during discharge at a 70 % state of health (end of life) than at the beginning of life. To investigate this process, in operando neutron diffraction of full cells was employed during cycling and revealed smaller changes to the a and c unit cell parameters of the NCA electrode at the end of life than at the beginning of life. Prompt gamma neutron activation analysis conducted on electrodes extracted from these cells confirmed that some of the Li lost from the NCA is found in the Si counter electrode. • Neutron diffraction shows reduced NCA unit cell change in aged cells. • NCA lithiation decreases with aging, indicating lithium inventory loss. • Silicon anode traps lithium, confirmed by elemental analysis. • Lithium consumption related to SEI formation on the silicon anode.