Improving Structural and Moisture Stability of P2-Layered Cathode Materials for Sodium-Ion Batteries

Abstract

P2-type Ni/Mn-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs). However, ground challenges, e.g., irreversible phase transition during cycling, moisture instability, and inferior electrochemical performance, greatly impede their practical applications. Herein, a series of Cu-substituted P2− Na 0.6 Ni 0.3−x Mn 0.7 Cu x O 2 (0 ≤ x ≤ 0.2) cathode materials for SIBs are fabricated and the mechanisms responsible for their improved electrochemical performances are comprehensively investigated. It is discovered that Cu dopants with strong electronegativity could stabilize the crystal structure by inhibiting the common P2−O2 phase transition, leading to improved cycling stability. The expanded interlayer spacing after Cu doping is facilitated for the charge transfer kinetics, which ensures excellent rate performance. In addition, all Ni, Mn, Cu, and O participate in the charge compensation upon sodiation and desodiation through reversible redox reactions. More importantly, Cu substitution improves the moisture stability of the cathode materials because the Cu 2+ /Cu 3+ redox couple increases the initial charging potential. This work provides a promising guidance for the design of low-cost, high-performance, and air-stable cathode materials with both cationic and anionic redox activities for SIBs.

Local Construction of Mn-Based Layered Cathodes through Covalency Modulation for Sodium-Ion Batteries

“…Note that the diffraction peaks located at ∼26.5, 65.3, and 78.2°originate from Al foil. 10,41 During the charge process, no new peaks can be found in NMMO until 4.2 V (Figure 4a), suggesting a single-phase reaction during this region. With the 43,44 Notably, the characteristic peak of the Mg 2+ /Mn 4+ honeycomb ordering arrangement in NMMO disappears at the end of charge and reappears during the following discharge with a reduced magnitude.…”

Layered oxide cathodes for sodium‐ion batteries: From air stability, interface chemistry to phase transition

“… 67 The suppression of inoxidizability enhancement and spontaneous Na extraction rendered O3‐NaNi 0.45 Cu 0.05 Mn 0.4 Ti 0.1 O 2 exhibiting superior air stability without any structural changes even after water immersion. The reported Na x TMO 2 compounds with Cu incorporation such as O3‐NaFe 0.4 Mn 0.49 Cu 0.1 Zr 0.01 O 2 , 68 O3‐Na[Li 0.05 Mn 0.50 Ni 0.30 Cu 0.10 Mg 0.05 ]O 2 , 69 P2‐Na 2/3 Ni 1/6 Mn 2/3 Cu 1/9 Mg 1/18 O 2 , 70 P2‐Na 0.7 Mn 0.9 Cu 0.1 O 2 , 71 P2‐Na 0.8 Mn 0.6 Ni 0.2 Cu 0.1 Mg 0.1 O 2 , 72 and P2‐Na 0.6 Ni 0.2 Mn 0.7 Cu 0.1 O 2 , 73 all have been proven to be air‐stable. The incorporation of Cu into layered oxides seems to be crucial for improving the air stability of these compounds.…”

“…67 The suppression of inoxidizability enhancement and spontaneous Na extraction rendered O3-NaNi 0.45 Cu 0.05 Mn 0.4 Ti 0.1 O 2 exhibiting superior air stability without any structural changes even after water immersion. 73 all have been proven to be air-stable. The incorporation of Cu into layered oxides seems to be crucial for improving the air stability of these compounds.…”

P2-Type Moisture-Stable and High-Voltage-Tolerable Cathodes for High-Energy and Long-Life Sodium-Ion Batteries

“…Two main peaks at the L3 and L2 edges are due to the electronic transitions from the metal 2p 3/2 and 2p 1/2 core levels to an unoccupied 3d level. The two L3 split peaks L3 high and L3 low correspond to Ni 3+/4+ and Ni 2+ , , respectively. With an increase of charge voltage, the Ni 3+ /Ni 4+ ratio gradually increased both in the bulk and at the surface, demonstrating that the Ni 2+ /Ni 3+ /Ni 4+ couples are active for the charge compensation in the voltage range of 2.5–4.35 V. However, there is still a considerable amount of Ni 2+ remaining in the bulk.…”