University of Chinese Academy of Sciences

Since the birth of lithium-ion batteries (LIBs) in the 1990s, LIBs have been extensively used in various fields owing to their high specific capacity, excellent rate performance and cycle performance. However, with the increasing shortage of lithium resources, it is extremely urgent to develop a candidate to replace lithium-ion battery. Sodium ion batteries (SIBs) have aroused considerable attention due to the similar working principle to LIBs and the abundant Na resources. Among all the key components the cathode plays a critical role on the electrochemical performance and the cost of the entire battery. It is, therefore, highly desirable to explore the high-performance cathode materials for SIBs. In recent years, the oxygen redox chemistry in the charge compensation has attracted more and more attention in Li-rich oxide cathodes for LIBs or Na-rich and Na-deficient oxide cathodes for SIBs. However, as for O3-type (Na-full) oxides-based cathode materials of SIBs, the oxygen redox chemistry has been rarely reported.

Recently, Prof. LIU Xiangfeng’s team at University of Chinese Academy of Sciences (UCAS) worked with their cooperators to reveal the anion redox chemistry in O3-type NaMn_1/3Fe_1/3Ni_1/3O₂ (MFN) cathode material, and proposed an integrated strategy combining ZrO₂ coating and Zr⁴⁺ doping to tune the anionic redox chemistry and crystal structures which improves the activity, reversibility, and stability of O²⁻. Oxygen redox reactions with high reversibility and cyclic stability mainly occur between 4.0 V and 4.3 V. The structure of Na-O-TM is regulated by Zr⁴⁺ doping, and the electronic state of O-2p occupies a higher energy level by the regulation of Na-O-TM structure. The electrons can migrate from O^2- more easily and O²⁻/O⁻ contribute more capacity. Zr⁴⁺ doping optimizes the lattice structure, enlarges the Na layer, and decreases TMO₂ layer, which reduces the diffusion resistance of Na and increases the structural stability. ZrO⁺₂ layer effectively mitigates the corrosion of the electrolyte and ensures the integrity of the structure, which inhibits the formation of Na₂CO₃ on the surface and decreases CO₂ release. This study not only reveals the anion redox chemistry in O3-type layered oxide cathode material but also is available for insights into regulating the redox activity, reversibility, and stability of oxygen.

This work was published in Energy Storage Materials entitled “Revealing the Anionic Redox Chemistry in O3-Type Layered Oxide Cathode for Sodium-Ion Batteries”(2021, 38, 130-140. DOI：10.1016/j.ensm.2021.03.004). YU Yang, a doctoral student of UCAS is the first author, Prof. LIU Xiangfeng is the corresponding author. This work was supported by National Natural Science Foundation of China, the Chinese Academy of Sciences and Natural Science Foundation of Beijing Municipality. This work was also supported by the Fundamental Research Funds for the Central Universities.

△The oxygen redox chemistry in O3-type NaMn1/3Fe1/3Ni1/3O2 cathode for Na-ion batteries has been reported and an integrated strategy combining ZrO2 coating and Zr4+ doping has been proposed to tune anionic redox chemistry and crystal structures. The modulation mechanism of oxygen redox chemistry has also been unraveled.

Editor: GAO Yuan