However, the large voltage hysteresis which is thought to be a signature of the transition metal migration that accommodates oxygen dimer formation in lithium-rich systems is notably absent in LiNiO 2 . It has been argued that the spectroscopic signs previously attributed to bulk oxygen dimerization in nickel-based cathode materials might instead reflect metal-ligand rehybridization , or that they can be explained via a distinction between bulk and surface redox activities, with dimerization primarily occurring near the surface .