Synthesis And Modification Of LiNi_0.5Mn_1.5O₄ As High Voltage Cathode Material

As the emergence of oil crisis and the increase of environmental pollution, Lithium-ion batteries as efficient and clean enery conversion equipment got much attention from the countries all over the world. Lithium-ion batteries were widely used in portable electronics, electric vehicles, large power supply, the secondary charge and storage areas, which required high energy density. Therefore, the research of high energy density cathode materials become the key to the development of lithium ion batteries.Spinel LiNi0.5Mn1.5O4 with three-dimensional (3D) Li+diffusion channels is considered to be one of the most prospective cathode materials owing to extremely cyclic stability and relatively high specific energy with a plateau at around 4.7 V. However, the electrochemical properties of LiNi0.5Mn1.5O4 are strongly affected by Mn3+ concentration, Mn dissolution and impurities, which make the synthesis of LiNi0.5O4 with superior performances a challenge.The materials of LiNi0.5Mn1.5O4 were prepared by solid-state reaction under different calcination temperature and holding time. The inorganic salt MnO2, Ni(OH)2 and LiOH-H2O were chosen for raw materials. The analysis of the structure and electrochemical properties were used to explore the best conditions of synthesizing high-performance LiNi0.5Mn1.5O4. Cationic and anionic doping in LiNi0.5Mn1.5O4 has been prepared via the same method as well. The effect of substitution on the structure, morphology, and electrochemical properties were investigated. The results indicate that all synthesized materials have a phase-pure spinel structure with a space group of Fd3m and no obvious impurity phase peaks. Excellent cycle life is measured for these 5 V Cr and (or) F-doped electrodes. When the charge/discharge rate returns to 1C after the test of rate capability (0.1～5C), the capacity can be completely recovered and the capacity retention is about 98.6%,98.8% and 96.2% after 100 cycles for LiNio.45Cro.o5Mni.504,LiNio.45Cro.o5Mni.503.9Fo.i and LiNi0.5Mn1.5O3.9F0.1 respectively. Rate capability is greatly influenced by the relative content of Mn3+. Furthermore, the experiment found that the amount of Mn3+ is according to the following sequence LiNio.45Cr0.05Mn1.5O4> LiNi0.45Cr0.05Mn1.5O3.9F0.1>LiNi0.5Mn1.5O4> LiNi0.5Mn1.5O3.9F0.1. In conclusion, Mn3+ concentration in the lattice can be increased with a small amount of Cr substitution while decreased with low temperature F substitution, which provide us an effective approach to tune the Mn3+ concentration and evaluate its influences on the electrochemical performances of the high-voltage spinels.