P2-type layered Na x MnO 2 cathode shows great potential in practical sodium ion batteries, especially for grid-level applications due to its ecofriendly and cost-effective sodium and manganese resources, and high theoretical specific capacity. However, several obstacles including severe phase transitions of P2-O2 and P2-P2′, low redox potential of Mn 3+ /Mn 4+ , disproportionation reaction and Jahn-Teller distortion of Mn 3+ , and deficient behavior have already hindered its practical applications. Herein, a Li, Cu co-doping strategy to tackle the mentioned obstacles by activating the oxygen redox is presented. The Li, Cu co-doped material exhibits solid solution reaction without any phase transitions as proved by in situ X-ray diffraction measurement and reduces the dissolution of active manganese element. With this modification treatment, it can dramatically raise the cycling stability from 30.4% to 80.1% after 150 cycles and simultaneously improves the deficient behavior due to the capacity contribution of oxygen redox at high voltage. More importantly, the coin-cell type sodium ion full cell assembled with this cathode and commercial hard carbon anode delivers a promising energy density of 225.1 Wh kg -1 .
Low‐cost sodium‐ion batteries (SIBs) have been extensively considered as a supplement or even a replacement for successful lithium‐ion batteries. However, the practical application of SIBs is limited by their energy density and cyclic performance, which are mainly constrained by the cathode side. Therefore, the development of advanced cathode materials is essential for the practical application of SIBs. Among the various cathode materials, layered transition metal oxides (LTMOs) are highly promising candidates due to their compact crystal structure, low‐cost, ease of preparation, and similarities to successful Li‐based LTMOs. Unfortunately, the bottleneck issues faced by Na‐based LTMOs, such as severe phase transitions, sluggish diffusion kinetics, and interface deterioration, pose significant challenges in achieving high‐performance cathodes. In this review, a comprehensive overview and summary of recently reported modification strategies for layered oxides are provided and the structure–function–performance relationship is refined. A perspective on the outlook and development direction for Na‐based LTMOs cathodes is also provided. This review comprehensively explores the modification strategies of Na‐based LTMOs, providing a new horizon for future research on Na‐based LTMOs.
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