We now investigate the role of anisotropic and concentration-dependent Li diffusivity, elastic stiffness, and lattice dimension changes in Li-ion dynamics, dislocation formation, mechanical failure, and capacity loss in composite cathode materials. A Ni-rich NMC811 particle with a diameter of 12 µm is embedded in the Li 6.6 La 3 Ta 0.4 Zr 1.6 O 12 solid electrolyte. Three types of simulations are performed: (i) a cathode particle with isotropic and constant material properties, (ii) a single crystal cathode particle and (iii) a polycrystal cathode particle with anisotropic and concentration-dependent material properties. As demonstrated by solid-state nuclear magnetic resonance characterisation, the Li diffusion coefficient drops sharply, over two orders of magnitude, as the Li content exceeds 80%. (Fig. ). The atomic lattice dimension change during (dis)charge is measured by operando synchrotron X-ray diffraction (XRD) experiments , as shown in Fig. . The a and b lattice parameters increase upon lithiation by maximum 2%. The c lattice parameter exhibits a nonmonotonic behaviour, rapidly increasing at the initial stage of discharge by up to 4%, and then gradually collapsing to 1.95% as the Li site fraction exceeds 0.37. These dimensional changes are attributed to the change of Ni oxidation states, and the modification of the interlayer spacing between the O 2-planes . Nanoindentation mechanical experiments and first-principles calculations indicate that delithiation results in a reduction of the elastic modulus of NMC cathodes (Fig. ) . To the authors' knowledge, the five independent stiffness parameters for NMC811 were only measured or predicted at fully lithiated and delithiated states . The elastic stiffness at fully lithiated state was used here. Fig. show that anisotropic diffusion and state-of-charge dependent diffusivity result in secondary particles with Li-rich peripheries and Li-poor cores upon lithiation. This heterogeneous Li distribution is insufficient to enable a high Li-ion flux uniformly throughout the particle, thereby leading to a significant increase in over-potential and a consequent sharp reduction in cell voltage during galvanostatic discharge. Therefore, as shown in Fig. , the half cell rapidly approaches the cut-off voltage of 3V, with the inner core of the particle remaining in a Li-deficient state, resulting in a substantial capacity loss. Fig. shows that anisotropic and concentration-dependent diffusion results in a normalised capacity loss of 0.12 for single crystal cathodes and 0.18 for polycrystal cathodes at a discharge rate of 1 C, comparing to the isotropic case (nC Fig. Effect of anisotropic and concentration-dependent electrochemical and mechanical properties of NMC cathodes in Li-ion dynamics, dislocation formation, interface mechanics, and electrochemical performance. a Li concentration-dependent diffusivity on the basal plane . b Anisotropic and Li concentration-dependent lattice dimension changes . c Elastic stiffness parameters at fully lithiated and delithiated states . d-g Distribution of Li concentration, dislocation-induced shear, and maximum principle stress at 1 C, within a cathode particle with isotropic and constant material properties (d), within a single crystal particle (e), a polycrystal particle (f ) under discharge, and a polycrystal particle under charge (g), all with anisotropic and concentration-dependent material properties. h Voltage-capacity profiles under discharge and charge. i The average dislocation-induced shear deformation as a function of distance from the particle edge. j Statistical variability in the maximum principle stress distribution at the cathode/solid-electrolyte interface.