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 NiCo(OH) precursor with LiOH and TaO, to simultaneously achieve the bulk material synthesis of LiNiCoO and construction of a rock-salt Ta-doped interphase and an amorphous LiTaO outer layer, forming a chemically bonded surface biphase coating on LiNiCoO. 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 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 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.