| Spinel LiMnO4 has been considered as the candidate cathode material of power sourse for electrical vehicles (EVs) owing to its advantages such as abundance of Mn resources, inexpensiveness, easy preparation, high working voltage and environmental friendliness. However, it is critical that the serious disadvantage of the products prepared by solid-state method, capacity fading hinders its wide application, espacially at elevated temperatures or large current densities. In this study, the phase inversion method was used to synthesize the pristine and Al-doped LiMn2O4 materials. The morphologies and crystal structures of the products were characterized by the scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively. The electrochemical performances of them were investigated at various voltage states, temperatures and electrolytes by the cyclic voltammograms (CV) and galvanostatic measurements.The submicrometer LiMn2O4 grains with three-dimemsionally interconnected pores were synthesized by phase invesion method using PMMA as polymer template. The products, which prepared at the optimizing condition, showed the best electrochemical performance. In organic electrolyte, they deliver the initial capacites of 124,114,87 and 60 mAh·g-1 at 0.2,1,2 and 4C, respectively. The Li+ ions diffusion coefficiency of the LiMn2O4 electrode reached the order of magnitude of 10-9 cm2·s-1. In addition, the electrochemical properties of the as-prepared LiMn2O4 in aqueous electrolytes were also studied. The results revealed that the first discharge capacities were 108 and 87 mAh-g-1 at 0.2C and 1C rate, respectively. The corresponding capacity retentions are 88% and 50% after certain cycles.The three-dimensional macroporous Al-doped LiMn2O4 samples were suscessfully prepared by the same method above-mentioned. Through comparation of the electrochemical performances of the samples doped with different amounts of Al element, which calcinated at various temperatures and time, the LiAl0.1Mn1.9O4 shows the best results. It can deliver the initial capacites of 135.6,131.2,116.8,106.1,91.6, and 70.2 mAh-g-1 at the 0.2,1,2,4,8, and 10C, respectively, when operated in the potential range of 3.0-4.3 V in organic electrolyte. More importantly, they can still deliver the capacity of 120 mAh-g-1 at 0.2C after cycling in the potential range of 2.5-4.3 V, in which the products suffer from the lattice distortion from the Jahn-Teller effect. After 50 cycles, the LiAl01Mn1.9O4 shows 87.5% of the capactiy retention when charged and discharged at 1C and 55℃, which is much better than that of the undoped LiMn2O4. In aqueous electrolyte, it delivered a capacity of 127.5 mAh·g-1 at 1C, and 62.4 mAh·g-1 even at 40 C. When it was charged at 60C and discharged at 1C, the LiAl0.1Mn1.9O4 still gave a capacity of 60 mAh·g-1 significantly, showing 97% of the coulomb efficiency.The three-dimensional macroporous LiMn2O4 was prepared by using the colloidal crystal template of PMMA micro-spheres. When charged and discharged at the rates of 0.2,1,2,4 and 5C, it delivers the initial capacities of 113.1,106.1,91.6, 80.8 and 59.8 mAh·g-1, respectively. The Li(Ni1/3Co1/3Mn1/3)O2 was prepared by the phase invesion method, and its electrochemical performances in organic and aqueous electrolytes were investigated preliminarily. Unfortunately, the results are not satisfied. Further studies should be done to promote the electrochemical performances of this sample. |
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