Optimization of LiFePO4 wet media milling and regressive population balance modeling

Abstract

LiFePO4 (LFP) is a low cost cathode material for Li-based batteries, but its low intrinsic ionic and electronic conductivity require sub micron particles to achieve acceptable energy capacity and charge and discharge rates for automotive applications. Consequently, for top-down syntheses, grinding energy and throughput are critical to maintain its cost advantage versus alternative processes and materials. Here, we demonstrate that an aqueous media mill reduces LFP powder from 27μm (d50) to 0.2μm. We applied a Taguchi experimental design to assess the effect of LFP loading (0.20–0.30), yttria-stabilized zirconia media (YSZ) size (0.3–0.5mm), surfactant-to-LFP mass ratio (0–0.008), and mill rotation rate (40–80Hz) on specific throughput and effective grinding energy. The 0.3mm YSZ media reduced the LFP powder at a specific throughput of 0.40kgLFP/kgmedia/h at an LFP loading of 0.30 (mass fraction of LFP to suspension), a surfactant-to-LFP mass ratio of 0.008 and a mill rotation rate of 60Hz. Under these conditions, the effective grinding energy was 0.32kWh/kgLFP.The Austin II Population Balance Model characterizes the change in particle size distribution with time: the deviation between the model and the experimental data was 0.026μm for each of the particle fractions d10, d50 and d90. This empirical model describes throughput at any given target particle size at the optimum operating condition.