Effects of Mn‐Doping on the Structural and Electrochemical Properties of Na₃Ni₂SbO₆ for Sodium‐Ion Battery.

Abstract

Recently, layered O'3-Na 3 Ni 2 SbO 6 has been investigated as a unique cathode material for Na-ion batteries due to the good electrochemical performance via O'3-P'3 phase transitions in the voltage range between 2.0 and 4.0 V vs Na + /Na. However, at present it is not well understood whether transition metal doping of the pristine structure could improve the phase transition kinetics during charge/discharge. In this study, we synthesized Mn-doped Na 3 Ni 2-x Mn x SbO 6 (x = 0, 0.25, 0.5) layered oxides and investigated their feasibility as cathode materials for Na-ion batteries using ex-situ X-ray diffraction (XRD) coupled with DFT calculations. The results show that light Mn doping (x = 0.25) energetically enhances the O'3-P'3 phase transition kinetics with smaller unit-cell-volume changes. However, the heavily doped (x = 0.5) sample suffers from large polarization, which could be attributable to the reduced two-phase reaction range and a large unit-cell-volume change upon sodium extraction.[a] Dr.

Elevating Operation Voltage and Suppressing Phase Transition for Honeycomb‐Layered Cathodes by a Dual‐Honeycomb Structure Strategy

“…It should be noted that the rate performance of Te−0.8 is the best compared to other honeycomb‐layered cathode materials reported so far. [ 6,10,11,22,33 ] The outstanding rate capability can be attributed to the improved conductivity of both electrons and Na + ions due to the unique dual‐honeycomb structure and proper widening of the interlayer spacing. The evolution of discharge medium voltages of Te−0, Te−0.8, and Te−1.0 for 1000 cycles at 1C is shown in Figure 3d.…”

“…It should be noted that the rate performance of TeÀ0.8 is the best compared to other honeycomb-layered cathode materials reported so far. [6,10,11,22,33] The outstanding rate capability can be attributed Electrochemical impedance spectroscopy (EIS) measurements were performed to investigate the effect of Te substitution on sodium-ion diffusion. Figure 3e Galvanostatic intermittent titration technique (GITT) tests of TeÀ0, TeÀ0.2, TeÀ0.5, TeÀ0.8, and TeÀ1.0 under the thermodynamic equilibrium conditions were employed to further compare the diffusion kinetics in both materials during the first charging process.…”

“…[26,32] However, the phase transition still exists and the substitution of electrochemically active Ni 2þ element by inert elements inevitably results in a sacrifice of capacity. [33] In addition, the lower electronegativity of these elements might lead to a decreased operation voltage according to the inductive effect, [7,8] which results in low energy density. This inspires us to introduce high valence Te 6þ with high electronegativity to substitute the Sb 5þ site rather than the Ni 2þ site in Na 3 Ni 2 SbO 6 .…”

Structural degradation mechanisms and modulation technologies of layered oxide cathodes for sodium‐ion batteries

“…[ 19,20 ] Among them, layered transition‐metal (TM) oxides Na x TMO 2 (TM, TM ═ Fe, Mn, Ni, Co, Cr, Ti, V, Cu, and their combinations, 0 < x ≤ 1, the most common structures of Na x TMO 2 are P2, P3, and O3) have been extensively exploited due to their high capacities, good stability, and simple synthesis procedures, and are thus extensively being exploited. [ 21 ] However, some significant issues still restrict their commercialization: (i) Charge ordering, Na + /vacancy ordering, and complicated phase transitions (P2–O2, [ 22 ] P2–OP4, [ 23,24 ] P2–P′2, [ 25 ] O′3–P′3, [ 26 ] O3–OP2, [ 27 ] and O3–O3″ [ 28 ] ) occur during electrochemical cycling, which causes large expansion, shrinkage of the lattice volume, and deterioration in electrochemical performance. Limiting the voltage range is an effective method to avoid the complex phase transitions.…”