Yong-Ning Zhou

MgO-coated NCLMFMC exhibits enhanced Na ⁺ diffusion with reversible phase transition behaviour and a stable interfacial structure during Na-ion battery cycling.

Exploring alternative battery systems to lithium‐ion batteries becomes essential and urgent with the explosive growth of the electric vehicle and energy storage markets. Benefiting from resource abundance, low redox potential of Ca metal, and prospective high volumetric capacity, rechargeable calcium‐ion batteries (CIBs) have recently attracted considerable attention in the field of energy storage. There is a breakthrough in the study of reversible precipitation/stripping of Ca metal at room temperature for anodes, but the cathodes for CIBs still suffer from low reversible capacity and poor cycle stability. This paper provides a comprehensive overview and recent progress of the cathode materials for CIBs, including metal oxides, Prussian blue analogs, polyanion materials, and organic cathodes. The features and modification strategies of each type of cathode material are discussed thoroughly. Finally, current issues of CIB cathodes and prospective solutions are presented.

Promoting oxygen redox is an effective strategy to boost capacity in layered cathode materials for sodium‐ion batteries. P‐type Li‐ and Mn‐based layered oxide cathodes are among the most promising candidates for triggering oxygen redox, but they face significant challenges, including low initial coulombic efficiency (due to sodium deficiency) and severe Jahn–Teller distortion when Mn ⁴⁺ is reduced to Mn ³⁺ . In this work, Jahn–Teller distortion is effectively alleviated and initial coulombic efficiency is remarkably improved in a P2‐type layered oxide cathode Na _0.75 Li _0.2 Mn _0.7 Fe _0.1 O ₂ (LMF‐75), through the synergy of Fe substitution and increased Na content. Fe substitution effectively suppresses MnO ₆ octahedra distortion and promotes coupled redox between oxygen and transition metals, thereby improving oxygen redox reversibility. The increased Na content significantly improves the initial coulombic efficiency and regulates Mn redox, thus reducing Mn ³⁺ formation and alleviating the associated Jahn–Teller distortion. As a result, the synergy of Fe substitution and increased Na content efficiently enhances structural stability and electrochemical performance. The LMF‐75 cathode delivers a high reversible capacity of 196.7 mAh g ⁻¹ , an initial coulombic efficiency of 92.6%, and outstanding cycling stability of 96.2% capacity retention after 100 cycles. This synergistic strategy provides a promising approach for designing high‐performance Li‐ and Mn‐based cathode materials.

Lattice oxygen redox (LOR) in P2-type layered oxides is an effective strategy to break through the limit of energy density of conventional cathodes due to its high redox potential (>4 V vs Na⁺/Na) as well as extra capacity. Nevertheless, LOR-induced local structure distortion and irreversible phase transitions cause serious electrochemical performance degradation, hindering practical applications. Herein, we propose that the generation of the OP4 phase can be replaced with the Z phase by introducing the Sb element with a higher ionic potential and strong covalent bonds within the TMO₆ octahedron. Z phase transition is realized by constraining interlayer slipping between adjacent transition metal (TM) layers compared to OP4, which reduces the strain in the layered structure, lowers the Na⁺ diffusion energy barrier, and creates more efficient Na⁺ diffusion channels. Consequently, Sb-substituted oxides demonstrate excellent kinetics, rate capability (79 mAh g^-1 at 1 A g^-1) in half cells, and a high energy density of 487 Wh kg^-1 (on cathode) in full cells.

P3‐type manganese‐iron‐based cathodes with high specific capacity and abundant resource have attracted considerable attention for sodium‐ion batteries. However, the long‐term cycle stability of P3‐type cathodes is still not satisfactory. In this work, we design a new quaternary manganese‐iron‐based cathode material (P3‐Na _0.54 Mn _0.64 Fe _0.16 Mg _0.1 Cu _0.1 O ₂ ) by Cu substitution. The strong covalent Cu–O bonds improve the structural stability and the reversibility of O redox during charge and discharge processes. Cu substitution also mitigates the structure change with less unit cell volume variation, and improves the Na‐ion transport kinetics effectively. As a result, NMFMC delivers much improved cycling stability and rate capability compared with NMFM. It reveals that the charge compensation of NMFMC is mainly contributed by Mn ^3+/4+ , Fe ^3+/3.5+ and O ^2−/− during the charge and discharge processes, and Cu substitution can also enhance the activity and reversibility of Fe redox. This strategy provides a new pathway toward improving the stability and O redox reversibility of P3‐type cathode materials for sodium‐ion batteries.

MgO coating reduces Li/Ni mixing for Ni-rich Co-free layered cathode materials and stabilizes the interfaces, thus enhancing their cycling stability.