Chemically Bonded Biphase Coating of Ni-Rich Layered Oxides with Enhanced High-Voltage Tolerance and Long-Cycle Stability

Stabilizing the crystalline structure and surface chemistry of Ni-rich layered oxides is critical for enhancing their capacity output and cycle life at a high cutoff voltage. Herein, we adopted a simple one-step solid-state method by directly sintering the Ni0.9Co0.1(OH)2 precursor with LiOH and Ta2O5, to simultaneously achieve the bulk material synthesis of LiNi0.9Co0.1O2 and in situ construction of a rock-salt Ta-doped interphase and an amorphous LiTaO3 outer layer, forming a chemically bonded surface biphase coating on LiNi0.9Co0.1O2. Such a cathode architectural design has been demonstrated with superior advantages: (1) eliminating surface residual alkali, (2) strengthening the layered oxygen lattice, (3) suppressing bulk-phase transformation, and (4) facilitating Li-ion transport. The obtained cathode exhibits excellent electrochemical performance, including a high initial reversible capacity of 180.3 mAh g–1 at 1.0 C with 85.5% retention after 300 cycles (2.8–4.35 V) and a high initial reversible capacity of 182.5 mAh g–1 at 0.2 C with 87.6% retention after 100 cycles (2.8–4.5 V). Notably, this facile and scalable electrode engineering makes Ni-rich layered oxides promising for practical applications.