Bulk and grain boundary Li-diffusion in dense LiMn₂O₄ pellets by means of isotope exchange and ToF-SIMS analysis

Lithium diffusion in LiMn₂O₄ pellets is studied by means of isotope exchange and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). A ⁶Li-enriched film deposited by Pulsed Laser Deposition (PLD) on a dense LiMn₂O₄ pellet with natural abundance of lithium isotopes is used to study the tracer diffusion of lithium. The measured profiles are analyzed by numerical models describing the ⁶Li tracer diffusion from the film into the pellet. Experiments in the Harrison type B regime of diffusion kinetics allow for the distinction and simultaneous determination of bulk and grain boundary diffusion coefficients. Changing the experimental conditions to reach Harrison type A behavior yields effective diffusion coefficients for lithium tracer diffusion in LiMn₂O₄. Activation energies for bulk and grain boundary diffusion were obtained from experiments at different temperatures. Our values are critically compared to previous studies.