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

Abstract 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 O 2 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 O 2 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 O 2 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.