Li-based layered nickel-tin oxide obtained through electrochemically-driven cation exchange.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Layered transition metal oxides are crucial for rechargeable batteries.
• Tuning the composition and structure of these oxides is key to improving electrochemical performance.
• Understanding ion exchange mechanisms is vital for designing new electrode materials.

Purpose of the Study:

• To synthesize and characterize a novel Li-based layered nickel-tin oxide, Li_0.35Na_0.07Ni_0.5Sn_0.5O₂.
• To investigate the structural and electrochemical properties of the synthesized material.
• To elucidate the factors limiting its electrochemical activity.

Main Methods:

• Electrochemical Li⁺ for Na⁺ exchange in O3-NaNi_0.5Sn_0.5O₂.
• Rietveld refinement of powder X-ray diffraction data for crystal structure analysis.
• Electron diffraction and scanning transmission electron microscopy for microstructural investigation.
• Bond-valence sum and density functional theory calculations for theoretical support.

Main Results:

• Successful synthesis of Li_0.35Na_0.07Ni_0.5Sn_0.5O₂ with an O3 stacking sequence and reduced unit cell volume.
• Observation of short-range Ni/Sn ordering, similar to honeycomb structures in Li₂MO₃ oxides, driven by charge differences.
• Demonstrated reversible Li⁺ (de)intercalation of ~0.21 Li⁺ within the 2.8-4.3 V vs. Li/Li⁺ range.
• Limited electrochemical activity attributed to the formation of a surface Li/Ni disordered rock-salt barrier layer.

Conclusions:

• The synthesized Li_0.35Na_0.07Ni_0.5Sn_0.5O₂ retains the parent O3 structure but exhibits unique Ni/Sn ordering.
• The material shows limited reversible lithium storage capacity due to the formation of an insulating surface layer.
• Further research is needed to mitigate the formation of the barrier layer for potential applications in energy storage.