Nanosize LiNiyMn2 ? yO4 (0 < y ? 0.5) spinels synthesized by a sucrose-aided combustion method. Characterization and electrochemical performance

Abstract

Nanosize crystalline cathode materials of LiNi_yMn_{2 − y}O₄ (0 < y ≤ 0.5) composition and spinel-type structure have been obtained by a single-step sucrose-aided self-combustion method. The as-prepared samples contained some amorphous organic impurities that were removed after a short period of heating at 500 °C. The pure single-phase spinels have been characterized by X-ray diffraction, transmission electron microscopy, chemical analysis, and nitrogen sorption isotherms. The samples consist of particles (ca. 24 nm size) that are aggregated in clusters (ca. 1 µm size) in which mesopores (10–80 nm size) appear among the particles. Additional heating at 800° and 1000 °C produces a slight increase in the cubic lattice parameter and a pronounced increase in particle size (>100 nm). Electrical conductivity decreases as the Ni content increases in accordance with an electron hopping mechanism between Mn³⁺ and Mn⁴⁺ ions. The 500 °C- and 800 °C-heated LiNi_0.5Mn_1.5O₄ samples show good electrochemical behaviour at 4.7 V as cathode materials. The capacity (132.7 mA h g⁻¹) found is close to the nominal capacity (146.7 mA h g⁻¹) and remains constant for current densities in the range C/24–2C (where C = 2.6 mA cm⁻²). At higher current densities (2C–10C) the capacity decreases progressively. The cyclability at the C current density is ca. 99.7% for both samples.