Effect of a macropore structure on cycling rates of LiCoO₂

Macroporous LiCoO₂ powders were synthesized in order to investigate the effect of a macropore structure upon high rate cycling capabilities of this cathode material for lithium-ion batteries. Monodisperse poly(methyl methacrylate) spheres, centrifuged to produce a cubic close-packed template, were infiltrated with a mixture of lithium acetate and cobalt acetate, then dried and heated to produce the desired R3̄m phase of LiCoO ₂. Poly(ethylene glycol) or platinum modifiers were added to improve the macroporosity. Products were characterized by powder X-ray diffraction and scanning electron microscopy. Macropores were not as well ordered as in other inverse opal materials due to crystallite growth, though the electrode particles still contained open, interconnected pores. Cyclic voltammetry and galvanostatic cycling experiments were performed on coin cells prepared with the macroporous LiCoO₂ powders. The expansion and contraction of the small particles in the walls with cycling led to swelling and particle disconnections, and consequently poor cyclability. However, the macroporous electrodes exhibited marked improvement in specific discharge capacities at higher cycling rates relative to bulk materials. The open electrode architecture facilitated an increase in the charge/discharge rate of Li batteries by reducing the solid-state diffusion distances through the electrode particles.