Lithium Tracer Diffusion in Sub-Stoichiometric Layered Lithium-Metal-Oxide Compounds

Abstract

Cathode materials based on lithium-metal-oxide compounds are an essential technical component for lithium-ion batteries, which are still being researched and continuously improved. For a fundamental understanding of kinetic processes at and in electrodes the Li diffusion is of high relevance. Most cathode materials are based on the layered LiCoO2 (LCO) and LiNi0.33Mn0.33Co0.33O2 (NMC333). In the present study Li tracer self-diffusion is investigated in polycrystalline sintered bulk samples of sub-stoichiometric Li0.9CoO2 at 145 °C ≤ T ≤ 350 °C and compared to Li0.9Ni0.33Mn0.33Co0.33O2 in the temperature range between 110 and 350 °C. For analysis, stable 6Li tracers are used in combination with secondary ion mass spectrometry (SIMS). The Li tracer diffusivities D* of both compounds with a sub-stoichiometric Li concentration are identical within error limits and can be described by the Arrhenius law with an activation enthalpy of (0.76 ± 0.13) eV for LCO and (0.85 ± 0.03) eV for NMC333, which is interpreted as the migration energy of a single Li vacancy. This means that a modification of the transition metal (M) layer composition within the LiMO2 structure does not significantly influence lithium diffusion in the temperature range investigated.