O3‐Type Layered Ni‐Rich Oxide: A High‐Capacity and Superior‐Rate Cathode for Sodium‐Ion Batteries

Inspired by its high-active and open layered framework for fast Li⁺ extraction/insertion reactions, layered Ni-rich oxide is proposed as an outstanding Na-intercalated cathode for high-performance sodium-ion batteries. An O3-type Na_0.75 Ni_0.82 Co_0.12 Mn_0.06 O₂ is achieved through a facile electrochemical ion-exchange strategy in which Li⁺ ions are first extracted from the LiNi_0.82 Co_0.12 Mn_0.06 O₂ cathode and Na⁺ ions are then inserted into a layered oxide framework. Furthermore, the reaction mechanism of layered Ni-rich oxide during Na⁺ extraction/insertion is investigated in detail by combining ex situ X-ray diffraction, X-ray photoelectron spectroscopy, and electron energy loss spectroscopy. As an excellent cathode for Na-ion batteries, O3-type Na_0.75 Ni_0.82 Co_0.12 Mn_0.06 O₂ delivers a high reversible capacity of 171 mAh g^-1 and a remarkably stable discharge voltage of 2.8 V during long-term cycling. In addition, the fast Na⁺ transport in the cathode enables high rate capability with 89 mAh g^-1 at 9 C. The as-prepared Ni-rich oxide cathode is expected to significantly break through the limited performance of current sodium-ion batteries.