Peculiarities of structure, morphology, and electrochemistry of the doped 5-V spinel cathode materials LiNi0.5-x Mn1.5-y M (x+y) O-4 (M = Co, Cr, Ti; x plus y=0.05) prepared by mechanochemical way

摘要

The pure LiNi0.5Mn1.5O4 and doped spinels LiNi0.5-x Mn1.5-y M (x+y) O-4 (M = Co, Cr, Ti; x + y = 0.05) were prepared by mechanochemically assisted solid state synthesis using a high-energy AGO-2 planetary mill. The activated samples were annealed at 700 and 800 A degrees C in oxygen and then characterized by x-ray powder diffraction (XRD) and neutron powder diffraction (NPD) with Rietveld refinement, high-resolution transmission electron microscopy (HRTEM) and electron microdiffraction, Fourier transform infrared spectroscopy (FTIR), galvanostatic cycling and galvanostatic intermittent titration technique (GITT). The structure of the high-temperature (HT) samples (800 A degrees C) is well refined with the single Fd-3m spinel. On the contrary, the low-temperature (LT) samples (700 A degrees C) are two-phase spinels with the 5-10 % fraction of the P4(3)32 phase depending on the substitution ion. The dopants preferably substitute for Ni ions that correlates with the appearance of the Li (y) Ni1-y O by-product (3-7 %). The rock salt-structured phase was observed on the surface of the particles coherently conjugated with the LT spinel crystal bulk. For all doped samples, two pairs of redox peaks are observed on the dQ/dV plots revealing the prevalence of the disordered spinel phase. However, the separation between the peaks increases for the HT samples resulting in better charge-discharge performance as compared with the undoped spinel. Lithium diffusion coefficient (D (Li+)) of the doped HT spinels estimated by GITT is two orders of magnitude higher than that of the undoped spinel. The highest rate capability is observed for the Ti-doped HT spinel due to larger lattice parameter.