Synthesis of LiNi0.5Mn1.5O4 by solid-state reaction with improved electrochemical performance

Research highlights: → 5 V cathode materials LiNi0.5Mn1.5O4 are synthesized from the metal acetates precursors. → Two-step solid-state reaction method leads to the electrode material with better electrochemical properties. → Two-step method results in Fd3m symmetry while one-step method leads to P4332 symmetry. → Raman spectra can help to determine the space group. - Abstract: LiNi0.5Mn1.5O4 spinel samples were synthesized by a two-step solid-state reaction method. Manganese acetate and nickel acetate were mixed together in a molar ratio of 3:1 and reacted at 500 deg. C to form a mixed Ni-Mn oxide, which reacted subsequently with lithium acetate at 900 deg. C to form a LiNi0.5Mn1.5O4 powder. For comparison, manganese acetate, nickel acetate and lithium acetate were mixed together in a molar ratio of 3:1:2 and directly reacted in one-step at 900 deg. C. The LiNi0.5Mn1.5O4 powder synthesized from the two-step process shows enhanced conductivity and improved rate performance. X-ray diffraction and Raman spectroscopy analyses indicate that the two-step sample has a space group of Fd3-bar m while the one-step sample has a space group of P4332. The cyclic voltammetry test has confirmed that lithium-ion cells with the two-step sample in the positive electrode exhibit lower impedance than those with the one-step sample.