Octahedral and Porous Spherical Ordered LiNi0.5Mn1.5O4 Spinel: the Role of Morphology on Phase Transition Behavior and Electrode/Electrolyte Interfacial Properties

LiNi_0.5Mn_1.5O₄ compound as positive electrode of the lithium ion battery with high specific energy or high specific power, has a good application prospect in the field of electric vehicles such as PHEV/EVs. The influence of the morphology of ordered LiNi_0.5Mn_1.5O₄ on phase transition behavior and electrode/electrolyte interfacial properties is investigated, including octahedral and porous spherical morphologies. Three phases named LiNi_0.5Mn_1.5O₄ (Li1), Li_0.5Ni_0.5Mn_1.5O₄ (Li0.5) and Ni_0.5Mn_1.5O₄ (Li0) are detected by in situ X-ray diffraction (XRD) measurement with high time resolution in the octahedral and porous spherical ordered LiNi_0.5Mn_1.5O₄ materials during charge and discharge, and the phase transition kinetics of the two samples at high discharge rate and after charge-discharge cycles are elucidated. It is a clear demonstration that the high-rate capability and cycle life of LiNi_0.5Mn_1.5O₄ material are influenced by crystal morphology. The porous spherical LiNi_0.5Mn_1.5O₄ material exhibits better rate performance, associated with the fast reaction kinetic of Li0.5 phase formation. It is noticed that the coexistence of three cubic phases in the initial discharge stage is observed in the cycled octahedral sample, resulting in a higher capacity fading after 200 cycles at room temperature and 1 C. However, the porous spherical sample exhibits a poor cyclic performance at 55 °C and 1 C. This may be attributed to the fact that the porous spherical sample with high specific surface area leads to an accelerated decomposition of the electrolyte at 55 °C, and the thick interfacial film and high content of LiF on the electrode surface are formed.

Urea-assisted hydrothermal synthesis of a hollow hierarchical LiNi0.5Mn1.5O4 cathode material with tunable morphology characteristics

The particle morphology and size of LiNi_0.5Mn_1.5O₄ material can be controlled by changing the precursors' morphology and size, which can be controlled by reactant concentration.

A porous hierarchical micro/nano LiNi0.5Mn1.5O4 cathode material for Li-ion batteries synthesized by a urea-assisted hydrothermal method

The U/TM ratio has a significant influence on the phase composition, particle morphology and size of the carbonate precursor, thus leading to different electrochemical properties of the LiNi_0.5Mn_1.5O₄ material.

Enhanced electrochemical property of FePO4-coated LiNi0.5Mn1.5O4 as cathode materials for Li-ion battery

Pristine LiNi_0.5Mn_1.5O₄ and FePO₄-coated one with Fd-3m space groups were prepared by a sol-gel method. The structure and performance were studied by X-ray diffraction (XRD) rietveld refinement, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS) mapping, electrochemical impedance spectroscopy (EIS) and charge-discharge tests, respectively. The lattice parameters of all samples almost remain the same from the Rietveld refinement, revealing that the crystallographic structure has no obvious difference between pristine LiNi_0.5Mn_1.5O₄ and FePO₄-coated one. All materials show similar morphologies with uniform particle distribution with small particle size, and FePO₄ coating does not affect the morphology of LiNi_0.5Mn_1.5O₄ material. EDS mapping and HRTEM show that FePO₄ may be successfully wrapped around the surfaces of LiNi_0.5Mn_1.5O₄ particles, and provides an effective coating layer between the electrolyte and the surface of LiNi_0.5Mn_1.5O₄ particles. FePO₄ (1wt%)-coated LiNi_0.5Mn_1.5O₄ cathode shows the highest discharge capacity at high rate (2C) among all samples. After 80 cycles, the reversible discharge capacity of FePO₄ (1wt%) coated LiNi_0.5Mn_1.5O₄ is 117mAhg^-1, but the pristine one only has 50mAhg^-1. FePO₄ coating is an effective and controllable way to stabilize the LiNi_0.5Mn_1.5O₄/electrolyte interface, and avoids the direct contact between LiNi_0.5Mn_1.5O₄ powders and electrolyte, then suppresses the side reactions and enhances the electrochemical performance of the LiNi_0.5Mn_1.5O₄.