La-Doped Ultrahigh-Nickel Layered Oxide Cathode with Enhanced Cycle Stability for Li-Ion Batteries

Currently, ultrahigh-nickel layered oxide is one of themost promisingcathodes for lithium-ion batteries, with the advantages of high theoreticalcapacity and low cost. However, some problems in ultrahigh-nickellayered oxides are more serious, such as irreversible structural transformation,particle cracking, and side reactions at the electrode/electrolyteinterface, resulting in the fast decay of the discharge capacity andmidpoint potential. In this work, La doping is introduced into ultrahigh-nickellayered LiNi0.9Co0.1O2 oxide to improvethe cycle stability on both discharge capacity and midpoint potential.As demonstrated, La can be doped successfully into the subsurfaceof LiNi0.9Co0.1O2 oxide, and themorphology of the oxide microspheres is not changed obviously by Ladoping. Compared with the pristine sample, the La-doped sample presentsimproved electrochemical performance, especially good cycle stabilizationon both discharge capacity and midpoint potential. In addition, aftera long-term cycle, the La-doped sample still maintains a relativelycomplete spherical morphology. It means that the pillaring effectof La with a large radius is helpful in accommodating the volume changecaused by the insertion/extraction of Li ions, thus easing the anisotropicstress accumulation and microcrack growth inside the microspheresof the La-doped sample.