A group I’ve worked with before at Brookhaven National Lab have just published a paper looking at LiFePO₄ de-lithiation visualized by XANES tomography. The cut-away view above shows that the Li initially transports preferentially from the left side, along the y-axis. This is followed by the z-direction, and then finally isotropic de-lithiation in the shrinking core at the end. (The red arrows in the bottom row illustrate this.) The paper can be found here.