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 Na0.75Ni0.82Co0.12Mn0.06O2 is achieved through a facile electrochemical ion‐exchange strategy in which Li+ ions are first extracted from the LiNi0.82Co0.12Mn0.06O2 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 Na0.75Ni0.82Co0.12Mn0.06O2 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.