Superstructure Variation and Improved Cycling of Anion Redox Active Sodium Manganese Oxides Due to Doping by Iron

Abstract

Anionic redox provides an effective way to overcome the capacity bottleneck of sodium‐ion batteries. A dominant role is played by the arrangement of alkali A and transition metal M in the NaxAyM1‐yO2 superstructure. Here, in situ X‐ray diffraction and ex situ 7Li nuclear magnetic resonance of P2 type Na0.6Li0.2Mn0.8O2 with ribbon‐ordered superstructure illustrate structural changes and explain the evolution of the electrochemical behavior of electrodes comprising this active mass, during cycling. Upon substitution of a small amount of manganese by iron, Na0.67Li0.2Mn0.73Fe0.07O2 is formed with a honeycomb‐ordered superstructure. Experimental characterizations and theoretical calculations elucidate the effect of iron on oxygen redox activity. The iron‐doped material considerably outperforms the undoped Na0.6Li0.2Mn0.8O2 as a cathode material for rechargeable Na‐ion batteries. This research reveals the effect of superstructure transformation on the electrochemical properties and offers a new perspective on element substitution in anionic redox active cathode materials.

Pulse-Assisted Low-Temperature Sintering to Enhance the Fast-Charging Capability for P2-Layered Na-Based Cathodes

“…The last one is assigned to the symmetric stretching vibration (A1g) of TM-O . 49 The Raman peaks with slight shifts suggest no significant phase transformation, which coincides well with the in situ XRD analysis.…”

Realizing High-Performance Cathodes with Cationic and Anionic Redox Reactions in High-Sodium-Content P2-Type Oxides for Sodium-Ion Batteries

“…The typical charge/discharge GITT profile for the first cycle and the corresponding Na diffusion coefficients are shown in Figure f. The D Na + values of NLMC range from 10 –12 cm 2 s –1 to 10 –15 cm 2 s –1 , which is a moderate value for Na-deficient oxides. − Also, during charging, an obvious decrease of the Na diffusion coefficient was observed at high potential. In the anionic oxidation process, the preceding anionic activation plateau unavoidably causes some irreversible oxygen loss and permanently modifies the electrochemical profile due to the oxygen network distortion and rearrangement of TM ions.…”

Comprehensively Strengthened Metal‐Oxygen Bonds for Reversible Anionic Redox Reaction

“…Excessive lattice oxygen oxidation in Li-doped Na x TMO 2 is a common phenomenon, which causes O 2 release easily. [33,[44][45][46] To confirm the effective suppression of excessive O 2− oxidation in NLAM, in situ DEMS is conducted to monitor the gas production during charge/discharge. Upon charging, the evolution of CO 2 can be clearly detected and its amount reaches the maximum at the end of charge (Figure 4e), which is associated with the decomposition of Na 2 CO 3 in cathode electrolyte interface and oxidation of electrolyte at high voltage.…”