Structure And Performance Optimization Of LiNi_0.5Mn_1.5O₄ Spinel Cathode Material For Lithium-ion Batteries

The Li Ni0.5Mn1.5O4(LNMO) spinel is an attractive cathode candidate for next generation lithium-ion batteries because it offers high power capability with an operating voltage of 4.7 V and a theoretical capacity of 147 m Ah/g. However, its commercialization is plagued by severe capacity fade. In this paper, porous LNMO materials were synthesized by self-templated method. Specially, the morphology and size of LNMO particles can be controlled by the morphology and particle size of Mn CO3 precursor. The main work in the research was following: 1) Mn CO3 precusors with various sizes and morphologies were prepared to obtain the LNMO material with the best electrochemical performance; 2) Investigation the effect of calcination temperature on the electrochemical properties of LNMO materials; 3) Optimization the electrochemical performance of the LNMO materials by adjusting the mol ratio of Ni and Mn elements; and 4) The Cr-doped LNMO material with excellecnt rate and cycle performance was obtained and the mechanism of the improvement of the electrochemical performance was discussed.Based on the above-mentioned results, it was concleded that:(1) The cubic LNMO material with ~3 μm particle size exhibits the best electrochemical performance;(2) calcination temperature of 800 ℃ is the best choice for the preparation LNMO-based material;(3) the mol ratio of Ni/Mn has a great influence on the Mn3+ concentration, phase purity and the intensity of the active [111] facet in LNMO materials by the XRD and XPS analysis, and the Mn-rich LNMO(Li Ni0.45Mn1.55O4) shows the best cycling and rate performance because of the absence of impurity rocket phase and the highest intesty of active [111] facet;(4) the Cr-doped LNMO sample(Li Ni0.45Mn1.5Cr0.05O4) shows excellent rate and cycle performance, with specific discharge capacities of 131.3 and 117.3 m Ah/g at 0.5 and 10 C rates, respectively and 91.2% capacity retention ratios after 1000 cycles at 5 C rate, which is attributed to the proper Mn3+ content, the absence of rock-salt phase and the high intensity of the active [111] facet in the Cr-doped LNMO sample.