Na-Rich Disordered Rock Salt Oxyfluoride Cathode Materials for Sodium Ion Batteries

Abstract

The existing classes of Na-based cathode materials and their chemistries are still limited, mainly with respect to the increasing demand for alternative post-Li technologies. In this letter, a newly synthesized Na-rich disordered rock salt (DRS) oxyfluoride with the nominal composition Na2MnO2F is reported as a cathode candidate for Na-ion batteries (SIBs). Rietveld refinement analysis confirmed that the synthesized compound has a DRS structure with larger lattice compared to Li-rich homologues. During the first cycle, up to 1.7 Na+/f.u. can be extracted at a slow rate, while a better capacity retention and cycling stability are obtained at high rate, reminiscent of electrode–electrolyte interaction. Further, X-ray absorption fine structure (operando and ex situ) confirmed the Mn oxidation state evolution upon cycling in agreement with the cyclic voltammetry redox profile, emphasizing the reversible Na+ (de)insertion and change of the Mn local ordering. This work is an additional input to the limited series of cathode candidates for SIBs.

Crystallography of Active Particles Defining Battery Electrochemistry

“…This structural type has been thoroughly reviewed. [88,89] More recent literature has looked at the impact of cation variation, both transition metals [90] and the active ion [91] and focused on overcoming the inherently low charging rates of the percolation channels. [92] Perovskite structured min-erals have traditionally been used for photo voltaic cells due to their ability to release electrons when irradiated by solar light, however, they are now being more closely researched for their potential as electrode active materials in rechargeable batteries.…”

New insights into tunnel-type NaxMnO2−yFy with high performance and excellent cycling stability: the impact of F-doping

“…For example, anionic doping can strongly modify the crystallographic structure and the electrochemical behaviour of the sodium manganese oxides. 12 Shi et al prepared Na 0.44 MnO 1.93 F 0.07 with a layer–tunnel hybrid structure, where the layer type was a major phase, and the observed maximum discharge capacity was 149 mA h g −1 . 13 Zan et al reported that after F-doping the tunnel-type Na 0.4 MnO 2 , the resulting samples with general formula Na x MnO 2− y F y were intergrowth materials of tunnel-type and layer-type (P2) structures that exhibited improved cycling stability.…”

High‐Entropy Co‐Free O3‐Type Layered Oxyfluoride: A Promising Air‐Stable Cathode for Sodium‐Ion Batteries

“…In addition, we selected oxyfluorides over oxides for their ability to suppress oxygen loss during long-term cycling; because the M─F bond has a more ionic nature than the M─O bond, the working potential is also expected to be increased. [26,32] The general issue of poor air stability of layered materials is also addressed in this work; a large interlayer space and low Na content allow the insertion of water and carbonate ions into the TMO 2 slabs, which is the main reason for poor air stability. [33,34] Therefore, we chose an O3 structure, to which we added Mg to decrease the interlayer distance.…”

“…In addition, we selected oxyfluorides over oxides for their ability to suppress oxygen loss during long‐term cycling; because the M─F bond has a more ionic nature than the M─O bond, the working potential is also expected to be increased. [ 26,32 ]…”