Regulating the cationic rearrangement of Ni-rich layered oxide cathode for high-performance Li-ion batteries

Abstract

Enormous effort has been paid to improve Ni-rich cathode's performance by suppressing surface residues and enhancing microscopic surface ordering (high Ni3+/Ni2+). Herein, strong alkali-mediated chemical oxidation of commercial precursor is employed to directly synthesize Ni-rich NCA cathode sintering under an oxygen atmosphere. Because of the limited lithium source, the lithium residue over the polycrystalline material is controlled; of course, a certain fraction of lithium has been lost and substituted by Ni2+, even pre-oxidized the precursor. XPS studies suggest that the percentage of oxidized nickel (Ni3+) is comparably higher at the surface than core (∼100 nm in depth) and retained during the lithiation. The synthesized material initially shows a high reversible lithiation efficiency of 90.6% at 0.05 C. The capacity degradation in the life-cycle study at 0.2 C could be endorsed to the combination of lithium inventory and active metal loss along with typical kinetic limitations, as diagnosed from the derivative dQ/dV plot. The high initial coulombic efficiency and discharge capacity with low polarization further confirm superior surface ordering and low surface residue. This study demonstrates that the pretreatment of the precursor is one of the effective strategies to regulate the cationic arrangement to achieve improved electrochemical performance.