Fig. 5. - Li Ion Cell Structure. A) Four functional components: a positive cathode consisting of a lithium metal oxide, a negative anode, typically a lithium graphite, a separator segregating the oppositely charged electrodes but permitting Li ionic flow, and an electrolyte, which insulates the passage of electrons within the battery. The solid electrolyte interphase (SEI) is a protective layer coated at the anode during the cell formation process; B) In discharge, the de-intercalated Li ion flow travels toward the anode. The anode is oxidized as electron flow travels toward the cathode, which is reduced. In charging, the process is the opposite; C). A Li ion polymer pack typically used to power personal mobility devices; D) An X-ray image shows the multilaminated structure of a single battery cell where each layer represents an anode and cathode layer as a functional unit of a Li ion battery. Image reproduced with permission from Wang et al.