Low-temperature synthesis of LiNi_0.5Mn_1.5O₄ grains using a water vapor-assisted solid-state reaction

Highlights: • Particle growth of LiNi_.5Mn_1.5O₄ at a low temperature is achieved in water vapor. • Water vapor affects the change of shape of LiNi_.5Mn_1.5O₄ at high temperatures. • The truncated particles are formed in water vapor. • The cathode properties of LiNi_.5Mn_1.5O₄ obtained in water vapor are evaluated. - Abstract: LiNi_0.5Mn_1.5O₄ (LNMO) spinel is one of the candidates for the cathodes of high-energy lithium-ion batteries because of its high operating voltage of 4.7 V. However, its use at high voltages leads to the decomposition of common organic electrolytes, resulting in a cycle degradation of the batteries. Although morphological control of LNMO particles involving their size and shape is an effective approach to suppressing electrolyte decomposition, the particle growth relying on diffusion in the solids has limitations of temperature and time. Here, we report the particle growth of LNMO at a low temperature using water vapor. By heating porous Mn₂O₃ spheres with Li and Ni sources as a precursor, we obtain spherical LNMO particles at 500 °C in both air and water vapor. The growth of primary particles is promoted by water vapor, and consequently, the obtained LNMO cathode exhibits better properties than those observed in air. Water vapor also affects the change of shape of LNMO at higher temperatures, leading to the formation of truncated particles from the spheres. Compared to conventional heating processes, this water vapor-assisted particle growth offers a low-temperature control of particle morphologies, particularly for materials that decompose easily at high temperatures.