Revisiting the ion dynamics in Li _x CoO₂ and Na _x CoO₂

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Layered oxides (AMO2) are critical cathode materials for lithium-ion and sodium-ion batteries.
• Understanding ion diffusion is key to optimizing battery performance.
• Differentiating intrinsic ion mobility from material properties is a significant challenge.

Purpose of the Study:

• To investigate and compare the self-diffusion coefficients of lithium ions (Li+) and sodium ions (Na+) in various layered oxide structures.
• To elucidate the fundamental mechanisms governing Li+ and Na+ transport in battery electrode materials.
• To provide insights for designing advanced battery materials with enhanced ion mobility.

Main Methods:

• Utilized *operando* muon spin spectroscopy to probe ion dynamics in real-time.
• Employed molecular dynamics simulations to model and quantify ion diffusion.
• Investigated O3-LiₓCoO₂, O3-NaₓCoO₂, and P2-NaₓCoO₂ materials.

Main Results:

• Sodium ion (Na+) diffusion is superior in P2-type structures compared to O3-type, attributed to reduced electrostatic interactions.
• In O3-type structures, lithium ion (Li+) exhibits faster diffusion than sodium ion (Na+).
• The larger ionic radius of Na+ impedes its mobility within the O3-type lattice.

Conclusions:

• Intrinsic ion diffusion rates are dependent on both the ion type and the layered oxide crystal structure.
• Electrostatic interactions and ionic size are critical factors influencing ion transport in battery materials.
• This study offers fundamental insights into ion transport mechanisms, guiding the development of high-performance lithium- and sodium-ion batteries.