Columnar order in jammed LiFePO4 cathodes: ion transport catastrophe and its mitigation

The high-rate, high-capacity potential of LiFePO4-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 LiFePO4 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 LiFePO4. Transport limitations are induced by [010] columnar order and lead to catastrophic performance degradation in anisotropic LiFePO4 electrodes. Further, judicious mixing of nanoplatelets with additive nanoparticles can frustrate columnar ordering and thereby enhance the rate capability of LiFePO4 electrodes by nearly an order of magnitude.