Excellent air storage stability of Na-based transition metal oxide cathodes benefiting from enhanced Na−O binding energy

O3-Type Na0.95Ni0.40Fe0.15Mn0.3Ti0.15O2 Cathode Materials with Enhanced Storage Stability for High-Energy Na-Ion Batteries

“…In contrast, the sodium layer spacing of the substituted samples gradually decreased, which is considered beneficial for improving the air stability (Figure 1c). 17,24 The corresponding Rietveld refined data indicate that Ni, Fe, Mn, and Ti ions occupy the 3b Wyckoff sites, which is well consistent with the design for substitution of Fe 3+ and Ti 4+ in the TM layers (Tables S1−S5). Figure 1d clearly shows the structural change after the Fe/Ti cosubstitution, i.e., the thickness of the slab increases, the interlayer spacing of Na + decreases.…”

“…Among various sodium cathode candidates, layered transition metal oxides Na x TMO 2 (where TM refer to transition metal ion) have attracted much attention due to its advantages such as high specific capacity, simple preparation, and environmental friendliness. − Compared with P2- and P3-type layered oxides, the sufficient sodium content enables O3-type layered oxides to be advantageous over counterparts in full-cell applications. − However, their cycle life is still subject to undesired structural degradation caused by transition metal slab sliding upon charging to high voltages (>4 V), leading to fast capacity decay and poor cycling stability in NIBs. − In addition, most O3-type materials suffer from notable performance deterioration when storing in a humid environment, which undoubtedly increases their cost of transportation and preservation. ,,− For O3-NaNi 0.5 Mn 0.5 O 2 , when the charging cutoff voltage is greater than 4.1 V, its specific capacity is up to 180 mAh g –1 . , However, a series of complex phase transitions (O3–O′3–P3–P′3–P3′–O1) cause significant internal stress, leading to the collapse of layered structure, resulting in capacity decay and poor rate performance. ,, In addition, when O3-NaNi 0.5 Mn 0.5 O 2 was exposed to air for 2 h, the structure changed from O3 phase to O′3- and P3-Na 1– y Ni 0.5 Mn 0.5 O 2 , which also leads to the degradation in electrochemical performance. , Undoubtedly, further practical application of O3-type layered oxides for NIBs requires addressing both phase transition reversibility during deep desodiation and humid sensitivity when exposed to ambient air.…”

Boosting the Ultrastable High-Na-Content P2-type Layered Cathode Materials with Zero-Strain Cation Storage via a Lithium Dual-Site Substitution Approach

“…Sodium ion batteries (SIBs) have been regarded as a prospective alternative to lithium-ion batteries (LIBs) owing to the merits of sodium abundance in the Earth’s crust and the low price of sodium resources. − Exploiting long-life cathode materials with superior reliability plays an utmost role in the commercial application of SIBs. Among most candidates, layered oxides Na x TMO 2 (TM represents transition metals) have gained considerable attention due to high theoretical specific capacity, feasible synthesis, and environmental benignity. − Considering the coordination of the Na-ions [i.e., octahedral (O) or prismatic (P)] and the number of the O-ion layer or TMO 6 layer in a one-unit cell (typically, 1–3), Na x TMO 2 cathode materials are categorized into P2, P3, O2, and O3 phases. ,,, P2-type and O3-type layered oxides are better suited to functioning as cathode materials for SIBs.…”

“…Such a low initial Na-content of P2-type phase could induce a low specific capacity and notable structural alterations during Na-extraction/insertion, thereby leading to structural instability and capacity fade throughout extended cycles . In an attempt to improve the cyclic stability of P2-type Na x TMO 2 , various dopants, such as Li + , Mg 2+ , Ti 4+ , Zn 2+ , Fe 3+ , and Co 3+ , have been utilized for mitigating the Na + /vacancy arrangement and the P2 → O2 phase transformation. However, this trade-off in performance is accompanied by a decline in specific capacity, as the introduction of dopants diminishes the amount of redox-active TM-ions .…”

Design of Cu‐Substituted O3‐Type NaFe0.5Mn0.5O2 Cathode Materials for Sodium‐Ion Batteries

“…[13] Huang et al obtained cathode materials with excellent air stability from the perspective that the weakened orbital hybridization between TMÀ O can effectively regulate the charge transfer between sodium and oxygen, so as to build stronger NaÀ O binding energy, which provides a new perspective for obtaining cathode materials with improved air stability. [14] Yao et al reported that the six-TM ring structure with high symmetry can still maintain its pristine structure after air exposure, demonstrating that the highly symmetric structure can effectively improve the stability of the crystal structure for SIBs, thereby effectively suppressing its side reactions with humid air. [15] Numerous studies have also investigated doping high percentages of nickel into O3-type Fe/Mn-based oxide cathode materials.…”