Lithium tracer diffusion in LiNi_0.33Mn_0.33Co_0.33O₂ cathode material for lithium-ion batteries

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Lithium nickel manganese cobalt oxide (LiNi0.33Mn0.33Co0.33O2) is a key cathode material for lithium-ion batteries.
• Lithium diffusion kinetics critically impact battery performance, including charge/discharge rates, capacity, and material stability.

Purpose of the Study:

• To investigate lithium (Li) tracer self-diffusion in LiNi0.33Mn0.33Co0.33O2.
• To determine the diffusion mechanism and activation energy in the temperature range of 110–350 °C.

Main Methods:

• Utilized stable lithium-6 (6Li) tracers for diffusion studies.
• Employed Secondary Ion Mass Spectrometry (SIMS) for precise depth profiling analysis.
• Investigated polycrystalline sintered bulk samples with an average grain size of 50 nm.

Main Results:

• Lithium diffusion coefficients follow the Arrhenius law, yielding an activation enthalpy of (0.85 ± 0.03) eV.
• Diffusion is attributed to migration through structural vacancies, with a fixed concentration due to a ~10% lithium deficiency.
• Extrapolated room temperature diffusivities are considerably lower than those reported from electrochemical measurements.

Conclusions:

• The study elucidates the fundamental mechanism of lithium diffusion in LiNi0.33Mn0.33Co0.33O2 via vacancies.
• The determined activation energy provides insights into the rate-limiting steps for lithium transport.
• Discrepancies with electrochemical data highlight the need for further investigation into measurement techniques and material states.