Effects of Si doping on structural and electrochemical performance of LiNi0.5Mn1.5O4 cathode materials for lithium-ion batteries

Recent Progress of High Voltage Spinel LiMn1.5Ni0.5O4 Cathode Material for Lithium-Ion Battery: Surface Modification, Doping, Electrolyte, and Oxygen Deficiency

High voltage spinel LiMn1.5Ni0.5O4 (LMNO) is a promising energy storage material for the next generation lithium batteries with high energy densities. However, due to the major controversies in synthesis, structure, and interfacial properties of LMNO, its unsatisfactory performance is still a challenge hindering the technology's practical applications. Herein, this paper provides general characteristics of LiMn1.5Ni0.5O4 such as spinel structure, electrochemical properties, and phase transition. In addition, factors such as electrolyte decomposition and morphology of LMNO that influence the electrochemical performances of LMNO are introduced. The strategies that enhance the electrochemical performances including coating, doping, electrolytes, and oxygen deficiency are comprehensively discussed. Through the discussion of the present research status and presentation of our perspectives on future development, we provide the rational design of LMNO in realizing lithium-ion batteries with improved electrochemical performances.

Enhanced Electrochemical Performance of the LiNi0.5Mn1.5O4 Cathode Material by the Construction of Uniform Lithium Silicate Nanoshells

In order to alleviate the rapid capacity decay caused by the instability of the crystal structure and electrode/electrolyte interface, a series of Li₂SiO₃-coated LiNi_0.5Mn_1.5O₄ materials have been prepared via the lithium acetate-assisted sol-gel method followed by a short-term calcination process. During the sol-gel process, TEOS is hydrolyzed, condensed, and polymerized with the assistance of lithium acetate to form a Li⁺-embedded [Si-O-Si]_n network structure to ensure the uniformity of the coating. By changing the amount of TEOS and lithium acetate, the coating thickness can be precisely controlled, whose effects on the structural and electrochemical properties of LiNi_0.5Mn_1.5O₄ materials are intensively investigated. The results show that the material with an appropriate thickness of Li₂SiO₃ coating exhibits a larger primary particle size and reduced secondary particle agglomeration. The uniform Li₂SiO₃ coating with appropriate thickness can not only improve Li⁺ ion diffusion kinetics but also suppress side reactions and CEI growth at the electrode/electrolyte interface. Besides, the interaction of Li₂SiO₃ with HF can alleviate electrode corrosion and the dissolution of transition metal ions. All the abovementioned factors together promote the significant improvement of the electrochemical performance of Li₂SiO₃-coated LiNi_0.5Mn_1.5O₄ materials.

Excitonic effects in the optical spectra of Li2SiO3 compound

Li2SiO3 compound exhibits unique electronic and optical properties. The state-of-the-art analyses, which based on first-principle calculations, have successfully confirmed the concise physical/chemical picture and the orbital bonding in Li-O and Si-O bonds. Especially, the unusual optical response behavior includes a large red shift of the onset frequency due to the extremely strong excitonic effect, the polarization of optical properties along three-directions, various optical excitations structures and the most prominent plasmon mode in terms of the dielectric functions, energy loss functions, absorption coefficients and reflectance spectra. The close connections of electronic and optical properties can identify a specific orbital hybridization for each distinct excitation channel. The presented theoretical framework will be fully comprehending the diverse phenomena and widen the potential application of other emerging materials.

A hydrothermal synthesis of Ru-doped LiMn1.5Ni0.5O4 cathode materials for enhanced electrochemical performance

An Ru-doped spinel-structured LiNi_0.5Mn_1.5O₄ (LNMO) cathode has been prepared via a simple hydrothermal synthesis method. The as-prepared cathode is characterized via Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size distribution analysis, X-ray photoelectron spectroscopy (XPS) and electrochemistry performance tests. The FTIR spectroscopy and XRD analyses show that the Ru-doped LNMO has a good crystallinity with a disordered Fd3̄m space group structure. The disordered structure in the cathode increased and the Li_xNi_1−xO impurity phase decreased when Ru addition increased. SEM shows that all samples are octahedral particles with homogeneous sizes distribution, and the particle size analysis shows that the Ru-doped samples have smaller particle size. XPS confirms the existence of Ru ions in the sample, and reveals that the Ru induce to part of Mn⁴⁺ transfers to Mn³⁺ in the LNMO. The electrochemical property indicated that the Ru-doped cathode exhibits better electrochemical properties in terms of discharge capacity, cycle stability and rate performance. At a current density of 50 mA g⁻¹, the discharge specific capacity of the Ru-4 sample is 140 mA h g⁻¹, which is much higher than that of the other samples. It can be seen from the rate capacity curves that the Ru-doped samples exhibit high discharge specific capacity, particularly at high current density.

An Ru-doped spinel-structured LiNi_0.5Mn_1.5O₄ (LNMO) cathode has been prepared via a simple hydrothermal synthesis method.