Fabrication of cellular and lamellar LiFePO₄/C Cathodes for Li-ion batteries by unidirectional freeze-casting method

Abstract

Highly porous lamellar and cellular cathodes for Li-ion batteries were fabricated from additive-stabilized aqueous suspensions of lithium iron phosphate and carbon black by the unidirectional freeze-casting method and characterized by optical microscopy, scanning electron microscopy, mercury porosimetry, helium pycnometry and X-ray microtomography. The size and orientation of the pores in the specimens were controlled through the variation of the freezing parameters. The diameters of the pores, which are in the range from 0.7 to 30 µm, as well as the wall thickness, decrease as the cooling rate increases. Pore volume and total porosity increase while the solid content of the suspension decreases. The specimen’s structure was changed from lamellar to cellular by increasing the gelatin concentration and solid content in the suspensions. The lamellar specimens demonstrate higher porosity (82–84%) than the cellular samples. Cathodes with lamellar structure possess higher specific capacity and less loss of energy density in comparison to those having cellular structure.