Ni/Mn ratio and morphology-dependent crystallographic facet structure and electrochemical properties of the high-voltage spinel LiNi_0.5Mn_1.5O₄ cathode material

Abstract

The LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel is an attractive cathode material for next generation lithium-ion batteries as it offers a high power capability with a discharge voltage of 4.7 V and a theoretical capacity of 147 mA h g À1 . In this paper, porous LNMO microspheres/cubes, which are constructed with nanometer-sized primary particles with different Ni/Mn ratios, have been synthesized by a facile method that involves the use of MnCO 3 microspheres/cubes as the self-supporting template. The effects of the morphology of the MnCO 3 and the Ni/Mn ratio on the physicochemical and electrochemical properties of the as-synthesized LNMO materials were investigated in detail. Scanning electron microscopy (SEM) observation shows that the morphology of the porous MnCO 3 has an important effect on the morphology and degree of dispersion of the obtained LNMO spinels, so as to the electrochemical performance. XPS and XRD results show that the Ni/Mn ratio has a significant impact on the Mn 3+ content, phase purity (rock-salt phase) and crystallographic facet orientations of the LNMO-based cathode materials. In particular, the Mn 3+ content, rock-salt phase and high-active (111) facet in the LNMO spinels were found to be adjusted by the Ni/Mn ratio. With the presence of a reasonable Mn 3+ content, high-active facet, the absence of the impurity phase (rock-salt phase) as well as the large cationic disorder in the Cr-doping LNMO spinels, the rate performance and capacity retention of the product could be significantly improved. All these findings show the important roles of the synergic effects of the morphology and the composition on the improvement of the electrochemical performance of LNMO-based cathode materials.

Constructing tri-functional modification for spinel LiNi0.5Mn1.5O4 via fast ion conductor

“…It has been reported that the radius of Mn 3+ (0.645 Å) is larger than that of Mn 4+ (0.530 Å), so the lattice parameter increase of LNMO after LLAZO modifying is mainly caused by foreign ions migrating into the lattice of LNMO from coating layer, which could lead the transform of Mn 4+ to Mn 3+ . 67 In Figure S2, the Raman spectra of all materials were compared to investigate the local structure change of LNMO. According to previous studies, the peak located at 630 cm -1 could be attributed to the symmetric Mn-O stretching mode (A1g) in the MnO6 octahedron of LNMO.…”

Preparation and Electrochemical Properties of High‐Voltage Spinel LiNi0.5Mn1.5O4 Synthesized by using Different Manganese Sources

“…Wan et al. had been reported that the enlarged lattice parameter a which was attributed to the highest Mn 3+ content and the ratio of Mn 3+ to Mn 4+ (Mn 3+ /Mn 4+ ) increases with the decrease of the Ni/Mn ratio in the samples. It further confirms that various Mn oxidation states influence the amount of Mn 3+ content and the configuration of Ni/Mn in the octahedral sites.…”

“…In order to figure out the content of Mn with different valence states in the as‐synthesized LNMO, the high‐resolution XPS measurements for the binding energy of the four samples and the fitted spectra of Mn 2p 3/2 peaks are plotted in Figure . The Mn 2p 3/2 peak in each sample can be well fitted to two components of Mn 3+ and Mn 4+ which also was reported in earlier research . The relative percent of manganese in different valence states calculated by peak area ratios are summarized in Table .…”

“…The percentage of Mn 3+ in LNMO‐4 collected by XPS shows the largest value, up to 27.85 %, much more than in LNMO‐1 (14.60 %), LNMO‐2 (13.72 %) and LNMO‐3 (13.72 %). Besides figuring out the surface manganese content via XPS analysis, Mn 3+ in LNMO also can be estimated by the initial discharge curves . The capacity percentages in Table are calculated from the capacity between 3.80 and 4.25 V which are divided by the total discharge capacity and can be qualitatively used to evaluate the relative concentration of Mn 3+ ions in the spinel LNMO .…”

Understanding the Role of Solution Equilibrium and Precipitation Rate on Precursor Composition for Lithium-ion Battery Active Materials

“…This means that there may exist a phase transition in this range from spinel to layered structure, or a mixture of both two phases exist within this whole range. Whatever the case is, the layered phase structure has a severe risk of phase segregation for Mn content, since Li-Mn-O cannot stay stable in a layered structure 5,59,[122][123][124] . Such phase segregation may cause the electrode degradation and render the cycle life much shorter.…”