Crystallinity Control of a Nanostructured LiNi_0.5Mn_1.5O₄ Spinel via Polymer‐Assisted Synthesis: A Method for Improving Its Rate Capability and Performance in 5 V Lithium Batteries

Abstract

Li–Ni–Mn spinels of nominal composition LiNi0.5Mn1.5O4, which are functional materials for electrodes in high‐voltage lithium batteries, are prepared by thermal decomposition of mixed nanocrystalline oxalates obtained by grinding hydrated salts and oxalic acid in the presence of polyethyleneglycol 400. Their structure, microstructure, and texture are established from combined X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction, transmission electron microscopy (TEM), IR spectroscopy, and N2 absorption measurements. The polymer tailors the shape of particles, which adopt a nanorodlike morphology at low temperatures (400 °C). In fact, the nanorods consist of highly distorted oriented nanocrystals connected by a polymer‐based film as inferred from IR and XPS spectra. The electrochemical properties of spinels in this peculiar form are quite poor, mainly as a result of the high microstrain content of their nanocrystals. Raising the temperature up to 800 °C partially destroys the nanorods, which become highly crystalline nanoparticles approximately 80 nm in size. At this temperature, the polymer facilitates crystal growth; this leads to highly crystalline polyhedral nanoparticles as revealed from TEM images and microstrain data. Following functionalization as a cathode in lithium cells, this material exhibits a very good rate capability, coulombic efficiency, and capacity retention even upon cycling at voltages as high as 5 V. Moreover, it withstands fast‐charge–slow‐discharge processes, which is an important cycle‐life‐related property for commercial batteries.

Influence of Synthesis, Dopants and Cycling Conditions on the Cycling Stability of Doped LiNi0.5Mn1.5O4Spinels

“…This suggests a higher occupation of the 8a tetrahedral site with transition metal ions. 13,35,36 In the case of LNMFTO it is most likely that either Mn 3+ or Fe 3+ change position from the 16d to the 8a site, since Ni 2+ ions tend to occupy the octahedral 16d site. 36 Furthermore a clear asymmetry of the diffraction peaks, especially the 400 peak, is visible.…”

Suppressing Irreversible Capacity in Low Cost Disordered Carbons for Li-Ion Batteries

“…Despite their acceptable electrochemical properties, these disordered carbons have two drawbacks for practical use in LIBs, namely, ͑i͒ a wide potential window for insertion-desinsertion ͑0-3 V͒, which can be easily solved by using high voltage cathodes such as LiMn 2 O 4 or, better, LiNi 0.5 Mn 1.5 O 4 , 17 and ͑ii͒ a high IC compared to RC. The latter problem is more serious because the LIB requires an excess of cathodic material not usable to operate on further cycling, which reduces the mean specific energy provided by the battery.…”

Electrochemical performances discharged to lower potential for LiNi0.5Mn1.5O4 cathode material synthesized by PAA-assisted co-precipitation method

“…Besides, the method is relatively low cost. However, particle aggregations and the lack of size uniformity are observed in the resulting powder due to the un-dispersed mixture and the high temperature sintering process [7].…”