Impact of Ti and Zn Dual‐Substitution in P2 Type Na_2/3Ni_1/3Mn_2/3O₂ on Ni–Mn and Na‐Vacancy Ordering and Electrochemical Properties

Abstract

High‐entropy layered oxide materials containing various metals that exhibit smooth voltage curves and excellent electrochemical performances have attracted attention in the development of positive electrode materials for sodium‐ion batteries. However, a smooth voltage curve can be obtained by suppression of the Na+‐vacancy ordering, and therefore, transition metal slabs do not need to be more multi‐element than necessary. Here, the Na+‐vacancy ordering is found to be disturbed by dual substitution of TiIV for MnIV and ZnII for NiII in P2‐Na2/3[Ni1/3Mn2/3]O2. Dual‐substituted Na2/3[Ni1/4Mn1/2Ti1/6Zn1/12]O2 demonstrates almost non‐step voltage curves with a reversible capacity of 114 mAh g−1 and less structural changes with a high crystalline structure maintained during charging and discharging. Synchrotron X‐ray, neutron, and electron diffraction measurements reveal that dual‐substitution with TiIV and ZnII uniquely promotes in‐plane NiII–MnIV ordering, which is quite different from the disordered mixing in conventional multiple metal substitution.

Boosting the Reversibility and Kinetics of Anionic Redox Chemistry in Sodium-Ion Oxide Cathodes via Reductive Coupling Mechanism

“…The continuous lattice constant variation extracted from the operando XRD patterns is presented in Figure S15. Intriguingly, the maximum unit cell volume change of P2-NCLMO is merely 1.26%, which is much smaller than those of the previously reported P2-type sodium-ion oxide cathodes (Figure c), ,,− accounting for the excellent cycling stability of P2-NCLMO.…”

New Strategy to Build a High-Performance P′2-Type Cathode Material through Oxygen Vacancies and Mg Substitution for Sodium-Ion Batteries

“…Generally, the smoother charge−discharge curve has better cycle performance. 28 Ovs & Mg-sub has the advantages of high capacity and high-capacity retention rate, and the curve is smoother than Ovs while retaining 2.9 and 3.5 V plateaus. In addition, Ovs & Mgsub demonstrated excellent cycle performance during long cycle testing, with a capacity of 110.3 mAh g −1 and a capacity retention rate of 83.4% after 300 cycles at a current of 400 mA g −1 , as shown in Figure 3i.…”

“…The charge–discharge curves of Mg-sub materials are smoother than those of Ovs. Generally, the smoother charge–discharge curve has better cycle performance . Ovs & Mg-sub has the advantages of high capacity and high-capacity retention rate, and the curve is smoother than Ovs while retaining 2.9 and 3.5 V plateaus.…”

Ceria Heterostructure Suppresses Oxygen Release of Na-Ion Battery Cathode Materials

“…Recently, manganese-based layered oxides have been reported as a potential cathode candidate for sodium ion batteries because of their high capacity, low cost, and environmental friendliness . Meanwhile, the exploitation of oxygen anionic redox in Na 2/3 TM 1– x Mn x O 2 (TM = Cu, Mg, Zn, Ni, or Li) cathode provided an effective strategy to break through the energy density limitation of the Na-ion batteries. − As an archetypal compound, the Na 2/3 Ni 1/3 Mn 2/3 O 2 (NNM) cathode can achieve an energy density as high as 600 Wh kg –1 through the combination of Ni 2+ /Ni 3+ cationic redox and O 2– /O 2 n– anionic redox. − However, the O 2– /O 2 n– redox is usually accompanied by irreversible oxygen evolution (O 2 n– → O 2 ) from the surface lattice, resulting in undesirable voltage fading and metal dissolution. ,,,− Therefore, stabilizing the surface lattice to suppress oxygen release and metal dissolution is of significant value for the achievement of high energy density SIBs with long cycling stability.…”