Improvement of elevated-temperature performance of Li1.02Cr0.1Mn1.9O4 cathode material by silicious surface modification was studied. The Li1.02Cr0.1Mn1.9O4 cathode material was treated by silanes coupling agent and t...Improvement of elevated-temperature performance of Li1.02Cr0.1Mn1.9O4 cathode material by silicious surface modification was studied. The Li1.02Cr0.1Mn1.9O4 cathode material was treated by silanes coupling agent and then heated at 580 ℃ to remove organic material. The structures of the modified and unmodified Li1.02Cr0.1Mn1.9O4 were characterized by SpectraPlus, SEM and XRD. The results show that the surface layer of Li1.02Cr0.1Mn1.9O4 material is found to be rich in silicious compound. X-ray diffraction show that all the samples have perfect spinel structure. The electrochemical characterization of modified Li1.02Cr0.1Mn1.9O4 cathode material was tested. The cycle stability of charge/discharge at 55℃ is improved. The results of the charge/discharge curves show that the modified Li1.02Cr0.1Mn1.9O4 has better performance than those unmodified according to the inhibition of decline of reversible capacity of spinel Li1.02Cr0.1Mn1.9O4. Therefore, cycle performance is improved so obviously that 86.03% of the initial capacity is preserved after 100 cycles.展开更多
The phase transition of Li2Mn2O4 spinel at high temperature was investigated by XRD, TG/DTA, average oxidation state of Mn and cyclic voltammeric techniques. The results reveal that the Li2Mn2O4 spinel is unstable. At...The phase transition of Li2Mn2O4 spinel at high temperature was investigated by XRD, TG/DTA, average oxidation state of Mn and cyclic voltammeric techniques. The results reveal that the Li2Mn2O4 spinel is unstable. At high temperature, it is easy to transform into [Li2-2x]tet[Mn2-xLix]octO4, which accompanies the formation of Li2MnO3 impurities. The phase transition is associated with the transfer of Li+ from tetrahedral 8a sites to octahedral 16d sites. With the increasing sintering temperature from 450 ℃ to 850 ℃, the phase structure varies from lithiated-spinel Li2Mn2O4 to Li4Mn5O12-like to LiMn2O4-like and finally to rock-salt LiMnO2-like. In addition, a way of determining x with average oxidation state of Mn and the content of Li2MnO3 was also demonstrated.展开更多
We study the electronic structures of LiMn2O4 by x-ray and ultraviolet photoelectron spectroscopy （XPS, UPS） and resonant photoelectron spectroscopy （RPES）. XPS data suggest that the average oxidation state of Mn ...We study the electronic structures of LiMn2O4 by x-ray and ultraviolet photoelectron spectroscopy （XPS, UPS） and resonant photoelectron spectroscopy （RPES）. XPS data suggest that the average oxidation state of Mn ions is 3.55, probably due to the small amount of lithium oxides on the surface. UPS and RPES data imply that Mn ions are in a high spin state, and RPES results show strong Mn3d-O2p hybridization in the LiMn2O4 valence band.展开更多
文摘Improvement of elevated-temperature performance of Li1.02Cr0.1Mn1.9O4 cathode material by silicious surface modification was studied. The Li1.02Cr0.1Mn1.9O4 cathode material was treated by silanes coupling agent and then heated at 580 ℃ to remove organic material. The structures of the modified and unmodified Li1.02Cr0.1Mn1.9O4 were characterized by SpectraPlus, SEM and XRD. The results show that the surface layer of Li1.02Cr0.1Mn1.9O4 material is found to be rich in silicious compound. X-ray diffraction show that all the samples have perfect spinel structure. The electrochemical characterization of modified Li1.02Cr0.1Mn1.9O4 cathode material was tested. The cycle stability of charge/discharge at 55℃ is improved. The results of the charge/discharge curves show that the modified Li1.02Cr0.1Mn1.9O4 has better performance than those unmodified according to the inhibition of decline of reversible capacity of spinel Li1.02Cr0.1Mn1.9O4. Therefore, cycle performance is improved so obviously that 86.03% of the initial capacity is preserved after 100 cycles.
基金Project(20406024) supported by the National Natural Science Foundation of China Project(76600) supported by the Postdoctoral Science Foundation of Central South University, China
文摘The phase transition of Li2Mn2O4 spinel at high temperature was investigated by XRD, TG/DTA, average oxidation state of Mn and cyclic voltammeric techniques. The results reveal that the Li2Mn2O4 spinel is unstable. At high temperature, it is easy to transform into [Li2-2x]tet[Mn2-xLix]octO4, which accompanies the formation of Li2MnO3 impurities. The phase transition is associated with the transfer of Li+ from tetrahedral 8a sites to octahedral 16d sites. With the increasing sintering temperature from 450 ℃ to 850 ℃, the phase structure varies from lithiated-spinel Li2Mn2O4 to Li4Mn5O12-like to LiMn2O4-like and finally to rock-salt LiMnO2-like. In addition, a way of determining x with average oxidation state of Mn and the content of Li2MnO3 was also demonstrated.
文摘We study the electronic structures of LiMn2O4 by x-ray and ultraviolet photoelectron spectroscopy （XPS, UPS） and resonant photoelectron spectroscopy （RPES）. XPS data suggest that the average oxidation state of Mn ions is 3.55, probably due to the small amount of lithium oxides on the surface. UPS and RPES data imply that Mn ions are in a high spin state, and RPES results show strong Mn3d-O2p hybridization in the LiMn2O4 valence band.
