Fig. 5: Comparison of Li distribution with the increasing number of cycles.
From: Evolution and expansion of Li concentration gradient during charge–discharge cycling
a Schematic illustration of Li accommodation sites during the charge–discharge process. TMs occupy 3b Li sites in the Li layer during the charging process. This irreversible TM migration depletes the number of Li accommodation sites in the Li layer. In contrast, Li ions simply refill a few vacant 3b Li sites, avoiding the 3a TM sites during the discharge process. Thus, a local Li deficiency originates from the lack of Li accommodation sites, depleted by the irreversible TM migration. b Schematic illustrations of the Li distribution evolution with the increasing number of cycles. The Li concentration gradient along the radial direction, which is lower at the surface and higher in the central area, evolves during cycling. The depth of the gradient and the extent of Li depletion both increase with the increasing number of cycles owing to the lack of Li accommodation sites.
