Synthesis And Modification Of High Voltage Spinel Lini_0.5Mn_1.5O₄Cathode Material

Seeking new electrode materials with a high energy density is critical for the development of large power lithium ion batteries. Spinel LiNi0.5Mn1.5O4is of great interest due to its high working potential around4.7V, low cost, and environmental benign. In general, spinel LiNi0.5Mn1.5O4has two types of space groups:P4332and Fd3m. As to LiNi0.5Mn1.5O4with the space groups of P4332, there are two-phase transition processes during the lithium ion extraction/insertion, which gives rise to a relatively poor kinetic properties, while for LiNi0.5Mn1.504-s with the space groups of Fd3m, the phase transition is single phase behavior and its rate capabilities is good. However, it is difficult to prepare of pure spinel LiNi0.5Mn1.504-s due to the formation of LixNi1-xO as a second phase. Moreover, the small amount of Mn3+ions in LiNi0.5Mn1.504-s will produce Mn2+ions, which dissolve into the electrolytes, leading to the capacity loss, especially cycled at elevated temperatures. Therefore, how to improve rate performances of LiNi0.5Mn1.5O4and cyclic performances of LiNi0.5Mn1.5O4at a high operated temperature is a key point to research. In this work, the effects of re-treated in air, Fe doping and coating on the electrochemical properties of LiNi0.5Mn1.5O4are investigated respectively. The main contents are summarized as follows:1、LiNi0.5Mn1.5O4and LiNi0.45Fe0.1Mn1.45O4were synthesized via one-step spray drying method. LiNi0.5Mn1.5O4was re-treated in air at650℃. Their structures and electrochemical properties were studied by XRD, Raman spectroscopy, SEM and charge-discharge test. The results indicated that the space group of the LiNi0.5Mn1.5O4transformed from Fd3m to P4332when the sample was re-treated in air at650℃. The cyclic performances of LiNi0.5Mn1.5O4at50℃was effectively improved by re-treating in air at650℃, but the improvement of rate performances were not quite satisfactory. Fe doping eliminated impurity phase and stabilized the structure of LiNi0.5Mn1.5O4. LiNio.45Fe0.1Mn1.45O4presented the improved electrochemical performance over pristine LiNi0.5Mn1.5O4. The electrode delivered a capacity of128.4mAh g-1with a capacity retention of71%in100cycles at5C rate at50℃.2、Al-doped ZnO (AZO)-coated LiNi0.5Mn1.5O4material was prepared by sol-gel method. The structural and electrochemical properties of the bare and coated LiNi0.5Mn1.5O4were studied. The analysis of electrochemical impedance spectra (EIS) indicated that AZO-coated LNMO possesses the lowest charge transfer resistance compared to the bare LNMO and ZnO-coated LNMO, which may be responsible for improved rate capability. Moreover, AZO-coated LNMO electrode showed a remarkable improvement in the cyclic performance at a high rate at elevated temperature due to the protective effect of AZO coating layer. The electrode delivered a capacity of120.3mAh g-1with a capacity retention of95%in50cycles at5C rate at50℃.3、It is difficult to prepare of pure spinel LiNi0.5Mn1.5O4due to the formation of NiO as a second phase. The formation of NiO has important influence in the electrochemical performances of the spinel LiNi0.5Mn1.5O4material. Based on this point, NiO-coated LiNi0.5Mn1.5O4material was prepared by sol-gel method. The results demonstated that there was no structural change of the LiNi0.5Mn1.5O4after NiO coating. NiO-coated LiNi0.5Mn1.5O4showed that improved electrochemical performances over LiNi0.5Mn1.5O4. Even at5C rate at50℃, the NiO-coated LiNi0.5Mn1.5O4delivered a capacity of126.7mAh g-1with the capacity retention of94%after50cycles.