Columnar order in jammed LiFePO ₄ cathodes: Ion transport catastrophe and its mitigation

The high-rate, high-capacity potential of LiFePO ₄-based lithium-ion battery cathodes has motivated numerous experimental and theoretical studies aiming to realize such performance through nano-sizing, tailoring of particle shape through synthesis conditions, and doping. Here, a granular mechanics study of microstructures formed by dense jammed packings of experimentally and theoretically inspired LiFePO ₄ particle shapes is presented. A strong dependence of the resultant packing structures on particle shapes is observed, in which columnar structures aligned with the [010] direction inhibit diffusion along [010] in anisotropic LiFePO ₄. Transport limitations are induced by [010] columnar order and lead to catastrophic performance degradation in anisotropic LiFePO ₄ electrodes. Further, judicious mixing of nanoplatelets with additive nanoparticles can frustrate columnar ordering and thereby enhance the rate capability of LiFePO ₄ electrodes by nearly an order of magnitude.