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

Abstract

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.