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

Currently, ultrahigh-nickel layered oxide is one of the most promising cathodes for lithium-ion batteries, with the advantages of high theoretical capacity and low cost. However, some problems in ultrahigh-nickel layered oxides are more serious, such as irreversible structural transformation, particle cracking, and side reactions at the electrode/electrolyte interface, resulting in the fast decay of the discharge capacity and midpoint potential. In this work, La doping is introduced into ultrahigh-nickel layered LiNi _0.9 Co _0.1 O ₂ oxide to improve the cycle stability on both discharge capacity and midpoint potential. As demonstrated, La can be doped successfully into the subsurface of LiNi _0.9 Co _0.1 O ₂ oxide, and the morphology of the oxide microspheres is not changed obviously by La doping. Compared with the pristine sample, the La-doped sample presents improved electrochemical performance, especially good cycle stabilization on both discharge capacity and midpoint potential. In addition, after a long-term cycle, the La-doped sample still maintains a relatively complete spherical morphology. It means that the pillaring effect of La with a large radius is helpful in accommodating the volume change caused by the insertion/extraction of Li ions, thus easing the anisotropic stress accumulation and microcrack growth inside the microspheres of the La-doped sample.