Three-volt lithium-ion battery consisting of Li[Ni1/2Mn3/2]O4 and Li[Li1/3Ti5/3]O4:: Improvement of positive-electrode material for long-life medium-power applications

A long-life medium-power three-volt lithium-ion battery consisting of Li[Ni1/2Mn3/2]O-4 (P4(3)32) and the zero-strain lithium insertion material of lithium titanium oxide (LTO; Li[Li1/3Ti5/3]O-4) was described with emphasis on the processing method to prepare Li[Ni1/2Mn3/2]O-4 for long-life applications. The preparation conditions were re-examined by thermogravimetric analysis, scanning electron microscopy, FT-IR, powder X-ray diffraction, and electrochemical methods. Well-defined crystals having the (111) facets of octahedra are essential for long-life application, which can be made by heating a reaction mixture at a temperature higher than 900 degrees C in air for 12 h, and characteristic absorption bands of the superlattice structure in IR spectra were also needed for both a high rechargeable capacity more than 135 mAh g(-1) with a flat operating voltage and long cycle life, which can be made by heating the well-defined crystals at 700 degrees C in air for at least 12 h, i.e., two-step solid-state reaction. To demonstrate the long-life medium-power three-volt lithium-ion battery, the 2000-cycle test of the cell under a positive-electrode-limited capacity was performed at 3.33 mA cm(-2) or 259 mA g(-1) based on the Li[Ni1/2Mn3/2]O-4 weight from 1.0 to 3.5 V at room temperature. Based on the results, no noticeable increase in polarization was observed even after 2000 cycles although the capacity faded ca. 15%. The unexpected capacity fading is described in terms of an imbalance in the coulombic efficiencies associated with the complex chemistry at positive and negative electrodes by the electrolyte.