Lithium diffusion in ion-beam sputtered amorphous LiNi0.33Mn0.33Co0.33O2 films after electrochemical cycling

LiNi0.33Mn0.33Co0.33O2 is an actual active cathode material for Li-ion batteries. One of the key factors influencing the rate capability and long-term performance of such cathodes is the diffusion of lithium ions within the material. Diffusion governs the insertion and extraction of lithium during cycling, directly impacting the battery efficiency and lifespan. In this study, we investigate the lithium diffusion properties of ion-beam sputtered amorphous LiNi0.33Mn0.33Co0.33O2 films as cathodes after continuous electrochemical cycling and compare the results to uncycled films. Tracer diffusion experiments as a function of temperature were done with 6Li tracers and Secondary Ion Mass Spectrometry in depth profile mode. Chemical diffusivities at room temperature were determined by Electrochemical Impedance Spectroscopy. The results reveal that after galvanostatic cycling the diffusivities significantly increase, while the activation enthalpy of diffusion is reduced. This trend is qualitatively supported by chemical diffusivities. We attribute this enhancement in diffusivity to the persistent lithium-deficient state of the electrode after cycling.