Exposed {010} Crystal Surfaces Drive High Rate Performance and Cyclability in Air Stable P2-Type Cathode for Na-Ion...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Particle morphology and synthesis conditions significantly influence the electrochemical behavior of layered oxide cathodes.
• Developing high-performance cathode materials is crucial for advancing sodium-ion battery technology.

Purpose of the Study:

• To synthesize and characterize various crystal structures (P2, O3, P2/O3) of dual pillar-ion doped NaₓMn₀.₄₇Ni₀.₃₃Ti₀.₁Al₀.₁O₂.
• To investigate the impact of synthesis conditions on the electrochemical properties of these layered oxides.
• To identify the optimal composition and structure for high-performance sodium-ion battery cathodes.

Main Methods:

• Varying sodium content and calcination temperature to achieve different layered oxide structures.
• Electrochemical testing including galvanostatic cycling, rate capability measurements, and cyclic voltammetry.
• In situ and ex situ characterization techniques such as electrochemical impedance spectroscopy (EIS), distribution of relaxation times (DRT) analysis, and X-ray diffraction (XRD).

Main Results:

• The P2-type sample (Na₀.₇₇Mn₀.₄₇Ni₀.₃₃Ti₀.₁Al₀.₁O₂) exhibited excellent electrochemical properties, delivering a reversible specific capacity of 141.5 mAh g⁻¹ at 0.1C and 93% capacity retention after 100 cycles.
• This P2 cathode demonstrated superior rate performance due to larger Na⁺ conducting lateral {010} surfaces, retaining 84% capacity at 2C compared to 0.1C.
• Temperature-dependent EIS and DRT analysis revealed a significantly lower charge-transfer activation energy (≈0.54 eV) for the P2-Na₀.₇₇ sample compared to its O3 counterpart (≈0.97 eV).
• Ex situ XRD confirmed that the P2-dominant framework of the Na₀.₇₇-850 cathode remained stable during cycling (2.0-4.0 V) with low lattice strain, unlike the O3-Na₁.₀₀ sample which underwent an unfavorable O3↔P3 phase transformation.
• A full cell (Na₀.₇₇-850||hard-carbon) achieved 85% capacity retention after 100 cycles.

Conclusions:

• The P2-type layered oxide Na₀.₇₇Mn₀.₄₇Ni₀.₃₃Ti₀.₁Al₀.₁O₂ is a highly promising cathode material for sodium-ion batteries.
• Optimized synthesis conditions leading to a P2 dominant structure enhance Na⁺ diffusion kinetics and structural stability during cycling.
• The material's excellent rate capability, high capacity, and long-term cycling stability highlight its potential for practical energy storage applications.