Spray pyrolysis synthesis of nanostructured LiFe_xMn _2-xO₄ cathode materials for lithium-ion batteries

A series of partially Fe-substituted lithium manganese oxides LiFe _xMn_2-xO₄ (0 ≦ x ≦ 0.3) was successfully synthesized by an ultrasonic spray pyrolysis technique. The resulting powders were spherical nanostructured particles which comprised the primary particles with a few tens of nanometer in size, while the morphology changed from spherical and porous to spherical and dense with increasing Fe substitution. The densification of particles progressed with the amount of Fe substitution. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The as-prepared powders were then sintered at 750°C for 4 h in air. However, the particles morphology and pure spinel phase of LiFe _xMn_2-xO₄ powders did not change after sintering. The as-sintered powders were used as cathode active materials for lithium-ion batteries, and cycle performance of the materials was investigated using half-cells Li/LiFe_xMn_2-xO₄. The first discharge capacity of Li/LiFe_xMn_2-xO₄ cell in a voltage 3.5-4.4 V decreased as the value x increased, however these cells exhibited stable cycling performance at wide ranges of charge-discharge rates.