Deep sodium extraction/insertion of sodium cathodes usually causes undesired Jahn–Teller distortion and phase transition, both of which will reduce structural stability and lead to poor long‐cycle reliability. Here we report a zero‐strain P2‐ Na2/3Li1/6Co1/6Mn2/3O2cathode, in which the lithium/cobalt substitution contributes to reinforcing the host structure by reducing the Mn3+/Mn4+redox, mitigating the Jahn–Teller distortion, and minimizing the lattice change. 94.5 % of Na+in the unit structure can be reversibly cycled with a charge cut‐off voltage of 4.5 V (vs. Na+/Na). Impressively, a solid‐solution reaction without phase transitions is realized upon deep sodium (de)intercalation, which poses a minimal volume deviation of 0.53 %. It attains a high discharge capacity of 178 mAh g−1, a high energy density of 534 Wh kg−1, and excellent capacity retention of 95.8 % at 1 C after 250 cycles.
Deep sodium extraction/insertion of sodium cathodes usually causes undesired Jahn–Teller distortion and phase transition, both of which will reduce structural stability and lead to poor long‐cycle reliability. Here we report a zero‐strain P2‐ Na2/3Li1/6Co1/6Mn2/3O2cathode, in which the lithium/cobalt substitution contributes to reinforcing the host structure by reducing the Mn3+/Mn4+redox, mitigating the Jahn–Teller distortion, and minimizing the lattice change. 94.5 % of Na+in the unit structure can be reversibly cycled with a charge cut‐off voltage of 4.5 V (vs. Na+/Na). Impressively, a solid‐solution reaction without phase transitions is realized upon deep sodium (de)intercalation, which poses a minimal volume deviation of 0.53 %. It attains a high discharge capacity of 178 mAh g−1, a high energy density of 534 Wh kg−1, and excellent capacity retention of 95.8 % at 1 C after 250 cycles.
more » « less- NSF-PAR ID:
- 10429021
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie
- Volume:
- 135
- Issue:
- 28
- ISSN:
- 0044-8249
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Vanadium multiredox‐based NASICON‐Na
z V2−y My (PO4)3(3 ≤z ≤ 4; M = Al3+, Cr3+, and Mn2+) cathodes are particularly attractive for Na‐ion battery applications due to their high Na insertion voltage (>3.5 V vs Na+/Na0), reversible storage capacity (≈150 mA h g−1), and rate performance. However, their practical application is hindered by rapid capacity fade due to bulk structural rearrangements at high potentials involving complex redox and local structural changes. To decouple these factors, a series of Mg2+‐substituted Na3+y V2−y Mgy (PO4)3(0 ≤y ≤ 1) cathodes is studied for which the only redox‐active species is vanadium. While X‐ray diffraction (XRD) confirms the formation of solid solutions between they = 0 and 1 end members, X‐ray absorption spectroscopy and solid‐state nuclear magnetic resonance reveal a complex evolution of the local structure upon progressive Mg2+substitution for V3+. Concurrently, the intercalation voltage rises from 3.35 to 3.45 V, due to increasingly more ionic VO bonds, and the sodium (de)intercalation mechanism transitions from a two‐phase fory ≤ 0.5 to a solid solution process fory ≥ 0.5, as confirmed by in operando XRD, while Na‐ion diffusion kinetics follow a nonlinear trend across the compositional series. -
more » « less
Abstract The oxygen stacking of O3‐type layered sodium transition metal oxides (O3‐NaTMO2) changes dynamically upon topotactic Na extraction and reinsertion. While the phase transition from octahedral to prismatic Na coordination that occurs at intermediate desodiation by transition metal slab gliding is well understood, the structural evolution at high desodiation, crucial to achieve high reversible capacity, remains mostly uncharted. In this work, the phase transitions of O3‐type layered NaTMO2at high voltage are investigated by combining experimental and computational approaches. An OP2‐type phase that consists of alternating octahedral and prismatic Na layers is directly observed by in situ X‐ray diffraction and high‐resolution scanning transmission electron microscopy. The origin of this peculiar phase is explained by atomic interactions involving Jahn–Teller active Fe4+and distortion tolerant Ti4+that stabilize the local Na environment. The path‐dependent desodiation and resodiation pathways are also rationalized in this material through the different kinetics of the prismatic and octahedral layers, presenting a comprehensive picture about the structural stability of the layered materials upon Na intercalation.
-
null (Ed.)Exotic perovskites significantly enrich materials for multiferroic and magnetoelectric applications. However, their design and synthesis is a challenge due to the mostly required recipe conditions at extremely high pressure. Herein, we presented the Ca 2−x Mn x MnTaO 6 (0 ≤ x ≤ 1.0) solid solutions stabilized by chemical pressure assisted with intermediate physical pressure up to 7 GPa. The incorporation of Mn 2+ into the A-site neither drives any cationic ordering nor modifies the orthorhombic Pbnm structure, namely written as (Ca 1−x/2 Mn x/2 )(Mn 1/2 Ta 1/2 )O 3 with disordered A and B site cationic arrangements. The increment of x is accompanied by a ferromagnetic to antiferromagnetic transition around x = 0.2, which is attributed to the double-exchange interactions between A-site Mn 2+ and B-site Mn 3+ . Partial charge disproportionation of the B-site Mn 3+ into Mn 2+ and Mn 4+ occurs for x above 0.8 samples as manifested by X-ray spectrum and magnetic behaviors. The coexistence of B-site Mn 3+ (Jahn–Teller distortion ion) and B′-site Ta 5+ (second-order Jahn–Teller distortion ion) could be energetically responsible for the absence of A-site columnar ordering as observed in other quadruple perovskites with half of the A-sites occupied by small transition-metal cations. These exceptional findings indicate that exotic perovskites can be successfully stabilized at chemical and intermediate physical pressure, and the presence of Jahn–Teller distortion cations at the same lattice should be avoided to enable cationic ordering.more » « less
-
Combining experimental and theoretical studies, we investigate the role of R-site (R = Y, Sm, Bi) element on the phase formation and thermal stability of R 2 (Mn 1−x Fe x ) 4 O 10−δ ( x = 0, 0.5, 1) mullite-type oxides. Our results show a distinct R-site dependent phase behavior for mullite-type oxides as Fe is substituted for Mn: 100% mullite-type phase was formed in (Y, Sm, Bi) 2 Mn 4 O 10 ; 55% and 18% of (Y, Sm) 2 Mn 2 Fe 2 O 10−δ was found when R = Y and Sm, respectively, for equal Fe and Mn molar concentrations in the reactants, whereas Bi formed 54% O10- and 42% O9-mixed mullite-type phases. Furthermore, when the reactants contain 100% Fe, no mullite-type phase was formed for R = Y and Sm, but a sub-group transition to Bi 2 Fe 4 O 9 O9-phase was found for R = Bi. Thermogravimetric analysis and density functional theory (DFT) calculation results show a decreasing thermal stability in O10-type structure with increasing Fe incorporation; for example, the decomposition temperature is 1142 K for Bi 2 Mn 2 Fe 2 O 10−δ vs. 1217 K for Bi 2 Mn 4 O 10 . On the other hand, Bi 2 Fe 4 O 9 O9-type structure is found to be thermally stable up to 1227 K. These findings are explained by electronic structure calculations: (1) as Fe concentration increases, Jahn–Teller distortion results in mid band-gap empty states from unstable Fe 4+ occupied octahedra, which is responsible for the decrease in O10 structure stability; (2) the directional sp orbital hybridization unique to Bi effectively stabilizes the mullite-type structure as Fe replaces Mn.more » « less
