Single crystal synthesis, crystal structure and electrochemical property of spinel-type LiCoMnO₄ as 5 V positive electrode materials

Abstract

Micrometer-sized single crystals of spinel-type LiCoMnO₄ were synthesized by heating a mixture of LiOH·H₂O, CoCl₂, and MnCl₂ with a molar ratio of Li:Co:Mn = 1.5:1:1 at 750°C. X-ray diffraction (XRD) pattern and scanning electron microscopic (SEM) image showed that LiCoMnO₄ has cubic spinel structure with well-formed octahedral crystal shapes. The size of the obtained LiCoMnO₄ single crystal particles was about 1–3 µm. Rietveld analysis using power XRD data confirmed the cubic spinel-type structure with space group Fd-3m, and the lattice parameter of a = 8.05812(14) Å. The tetrahedral 8a site was occupied by both Li and Co atoms with the occupancy values of Li/Co = 0.958/0.042. Electrochemical measurement exhibited the reversible Li-ion extraction and insertion reactions at high potentials. The discharge profile with the discharge capacity of 107 mAh g⁻¹ showed three voltage plateaus at 5.1, 4.9, and 3.9 V; the former two corresponded to the redox reaction of Co³⁺/Co⁴⁺ and the latter was to the redox reaction of Mn³⁺/Mn⁴⁺, respectively.