| Recently, spinel type LiMn2O4 has been considered as one of the most promising high-power cathode materials for lithium ion batteries due to its excellent intrinsic properties, such as high operation potential, safety, environmental friendliness, low cost and easy preparation and so on. However, LiMn2O4 cathode suffers from constant capacity fading in the charge-discharge processes, which is even worse at elevated temperature. In this work, spinel LiMn2O4, which was prepared via melt-impregnation method, was modified with Cu3(PO4)2 nano-particles and doped with Cu2+, respectively, to improve its cycle performance.LiMn2O4 materials were synthesized by melt-impregnation method and solid state method, respectively. The results show that the electrochemical performance of LiMn2O4 material prepared by melt-impregnation method is superior to that prepared by solid state method. The effect of Li/Mn ratios on the physical properties and electrochemical performance is also studied for Li1+xMn2O4 materials and the results indicate that cycle performance of Li1+xMn2O4 materials enhances with the increase of Li/Mn ratio. The initial discharge capacities of Li1+xMn2O4 materials with Li/Mn=1:2,1.02:2,1.03:2 and 1.05:2 at 1 C rate are 125.9,123,119.2 and 116.9 mAh g"1, respectively. And they are 106.6,113.4,112.1 and 115.6 mAh g"1 after 100 cycles, the capacity retention is 84.6%,91.9%,93.9% and 98.3%, respectively. The cycle capability of Lii+Mn2O4 materials is improved with the increase of the Li/Mn ratio, and it is found that the Li1+xMnO4 material with Li/Mn= 1.05:2 has the best electrochemical performance.The Cu3(PO4)2-modified Li1.02Mn2O4 cathode materials with different coating contents were synthesized via chemical deposition method for the first time. It shows that Li1.02Mn2O4 cathode coated with 2 wt.% Cu3(PO4)2 has the best electrochemical performance. The initial discharge capacities of bare material and 2 wt.% Qu3(PO4)2-coated Li1.02Mn2O4 material at 1 C rate are 123 and 126.8 mAh g-1, respectively. The capacity retention after 100 cycles is 91.9% and 92.8%, respectively. The electrochemical performance of surface-modified material at elevated temperature (55℃) is also improved. The capacity retention of bare and Cu3(PO4)2-coated Li1.02Mn2O4 samples is 67.4% and 74.7% after 100 cycles at 1 C rate, respectively. The better electrochemical performance of Cu3(PO4)2-coated materials at room and high temperatures demonstrates that Cu3(PO4)2 modification is an effective way to improve the cyclic capability of spinel LiMn2O4.Cu2+ -doped LiMn2-xCux04 materials with various doping amounts were similarly prepared by melt-impregnation method. The cycle performance of Cu2+-doped LiMn2-xCuxO4 materials is improved with increase of Cu2+-doped content, but the discharge capacity decreases gradually. The initial discharge capacities of LiMn2-xCuxO4(x=0,0.02,0.04 and 0.06) materials at 1 C rate are 125.9,119.9,117.5 and 112.2 mAh g-1, respectively. And they are 106.6,102.2,108.8 and 105.2 mAh g-1 after 100 cycles, the capacity retention is 84.6%,85.2%,92.6% and 93.9%, respectively. It is also found that the cyclic capability of doped materials is enhanced with the increase of doping content, which is attributed to reduction of Mn3+/Mn4+ ratio in spinel structure and suppression of Jahn-Teller effect. |
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