Spinel LiMn2O4 microspheres and hollow microspheres with adjustable wall thickness have been prepared using controllable oxidation of MnCO3 microspheres precursors and following solid reactions with lithium salts. Sca...Spinel LiMn2O4 microspheres and hollow microspheres with adjustable wall thickness have been prepared using controllable oxidation of MnCO3 microspheres precursors and following solid reactions with lithium salts. Scanning electron microscopy （SEM） investigations demonstrate that the microsphere morphology and hollow structure of precursors are inherited. The effect of hollow structure properties of as-prepared LiMn2O4 on their performance as cathode materials for lithium-ion batteries has been studied. Electrochemical performance tests show that LiMn2O4 hollow microspheres with small wall thickness exhibit both superior rate capability and better cycle performance than LiMn2O4 solid microspheres and LiMn2O4 hollow microspheres with thick wall. The LiMn2O4 hollow microspheres with thin wall have discharge capacity of 132.7 mA.h-g^-1 at C/10 （14.8 mA.g^-1） in the first cycle, 94.1% capacity retention at C/10 after 40 cycles and discharge capacity of 116.5 mAh-gq at a high rate of 5C. The apparent lithium-ion diffusion coefficient （Dapp） of as-prepared LiMn2O4 determined by capacity intermittent titration technique （CITT） varies from 10-11 to 10-8.5 cm2.s^-1 showing a regular ＂W＂ shape curve plotted with test voltages. The D app of LiMn2O4 hollow microspheres with thin wall has the largest value among all the prepared samples. Both the superior rate capability and cycle stability of LiMn2O4 hollow microspheres with thin wall can be ascribed to the facile ion diffusion in the hollow structures and the robust of hollow structures during repeated cycling.展开更多
Spherical Li-rich lithium manganese oxide（LMO） spinel material was synthesized by an ion implanted method assisted by polyalcohol doped with Niobium and Phosphate simultaneously.The material was characterized by sca...Spherical Li-rich lithium manganese oxide（LMO） spinel material was synthesized by an ion implanted method assisted by polyalcohol doped with Niobium and Phosphate simultaneously.The material was characterized by scanning electron microscopy,X-ray diffraction and BET specific surface area analysis.The electrochemical performances were investigated with galvanostatic techniques and cyclic voltammetry.The synthesis process was investigated with TG/DSC.The results show that the lithium ion can be immersed into the pore of manganese dioxide at a low temperature with the ion implanted method.The prepared materials have a higher discharge capacity and better crystallization than those prepared by solid phase method.The doped Nb can improve the capacity of the Li-rich LMO spinel and reinforce the crystal growth along（111） and（400） planes.The crystal grains show circular and smooth morphology,which makes the specific surface area greatly decreased.Phosphate-doped LMO spinel exhibits good high-rate capacity and structure stability.The prepared Li（1.09）Mn（1.87）Nb（0.031）O（3.99）（PO4）（0.021）delivers a discharge capacity of 119mAhg^-1 at 0.2C（1C=148mAg^-1） and 112.8 mAhg^-1 at 10 C,the discharge capacity retention reaches 98% at 1 ℃ after 50 cycles at 25 ℃ and 94% at 55 ℃.展开更多
The hydrothermal synthesis of single-crystallineβ-MnO2 nanorods and their chemical conversion into single-crystalline LiMn2O4 nanorods by a simple solid-state reaction were reported.This method has the advantages of ...The hydrothermal synthesis of single-crystallineβ-MnO2 nanorods and their chemical conversion into single-crystalline LiMn2O4 nanorods by a simple solid-state reaction were reported.This method has the advantages of producing pure,single-phase and crystalline nanorods.The LiMn2O4 nanorods have an diameter of about 300 nm.The discharge capacity and cyclic performance of the batteries were investigated.The LiMn2O4 nanorods show better cyclic performance with a capacity retention ratio of 86.2% after 100 cycles.Battery cyclic studies reveal that the prepared LiMn2O4 nanorods have high capacity with a first discharge capacity of 128.7 mA·h/g.展开更多
Regular spherical chromium doped spinel lithium manganese oxides （LiCr0.04Mn1.96O4） with an average particle size of about 20μm were prepared by the slurry spray drying process. The materials were compared with non...Regular spherical chromium doped spinel lithium manganese oxides （LiCr0.04Mn1.96O4） with an average particle size of about 20μm were prepared by the slurry spray drying process. The materials were compared with non-spherical LiCr0.04Mnl.96O4 materials prepared by the common drying process, and all materials were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, laser particle analyzer and Brunaner-Emmett-Teller （BET） specific surface area test. Electrochemical performances of these cathode materials were studied by cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS） and Li/LiCr0.04Mn1.9604 battery test. The results show that the spherical active material is single spinel structure, compact, and with narrow particle size distribution and low BET specific surface area. Compared with the non-spherical material, the spherical material prepared by the spray drying process shows a lower electrochemical impedance, a fewer electrochemical polarization and a better charge/discharge rate capability and capacity retention at elevated temperatures.展开更多
Spinel LiCo0.09Mn1.91O3.92F0.08 as cathode material was modified with LiCoO2 by the sol-gel method, and the crystal structure, morphology and electrochemical performance were characterized with XRD, SEM, EDS, AAS and ...Spinel LiCo0.09Mn1.91O3.92F0.08 as cathode material was modified with LiCoO2 by the sol-gel method, and the crystal structure, morphology and electrochemical performance were characterized with XRD, SEM, EDS, AAS and charge-discharge test in this paper. The results show that a good clad coated on parent material can be synthesized by the sol-gel method, and the materials with modification have perfect spinel structure. LiCo0.09Mn1.91O3.92F0.08 materials coated by LiCoO2 improve the stability of crystal structure and decrease the dissolution of Mn into electrolyte. With the LiCoO2 content increasing, the specific capacity and cycle performance of samples are improved. The capacity loss is also suppressed distinctly even at 55 ℃.展开更多
The formation process of solid electrolyte interphase（SEI） film on spinel LiMn2O4 electrode surface was studied by electrochemical impedance spectroscopy（EIS） during the initial storage in 1 mol/L LiPF6-EC：DMC：D...The formation process of solid electrolyte interphase（SEI） film on spinel LiMn2O4 electrode surface was studied by electrochemical impedance spectroscopy（EIS） during the initial storage in 1 mol/L LiPF6-EC：DMC：DEC electrolyte and in the subsequent first charge-discharge cycle. It has been demonstrated that the SEI film thickness increased with the increase of storage time and spontaneous reactions occurring between spinel LiMn2O4 electrode and electrolyte can be prevented by the SEI film. In the first charge-discharge cycle succeeding the storage, the electrolyte oxidation coupled with Li-ion insertion is evidenced as the main origin to increase the resistance of SEI film. The results also confirm that the variations of the charge transfer resistance（Rot） with the electrode potential（E） can be well described using a classical equation.展开更多
Li1+xMn2?yO4 spinels with various Li/Mn ratios were synthesized by a solid-state reaction. By X-ray diffraction analysis, Li2MnO3 was detected as a second phase with increasing the Li/Mn ratio; and the role of Li2MnO3...Li1+xMn2?yO4 spinels with various Li/Mn ratios were synthesized by a solid-state reaction. By X-ray diffraction analysis, Li2MnO3 was detected as a second phase with increasing the Li/Mn ratio; and the role of Li2MnO3 in Li1+xMn2-yO4 spinel was discussed. A slow scanning cyclic voltammetry(CV) at the rate of 0.1 mV/s was adopted to characterize the evolutions of 4 V and 5 V plateaus of Li1+xMn2-yO4 spinels. An additional Li+ insertion in 4 V region was observed in both Li-lack and Li-rich spinels at 3.95 V, which is different from the general Li+ insertion with weak Li-Li interaction and strong Li-Li interaction; and this plateau disappeared in the subsequent cycles. The 4.4 V/3.8 V plateaus correspondent to Li+ insertion and extraction of Li2MnO3 were discussed, and these plateaus have a high reversibility with cycling. The 5 V plateau was found only in the Li-rich samples, and this plateau has a tendency to emerge at higher voltage region with increasing Li/Mn ratio.展开更多
Multidoped spinel LiCo0.02La0.01Mn1.97O3.98Cl0.02 was synthesized by solid-state method. The structure and electrochemical performance were characterized by XRD, ESEM, particle size distribution analysis, specific sur...Multidoped spinel LiCo0.02La0.01Mn1.97O3.98Cl0.02 was synthesized by solid-state method. The structure and electrochemical performance were characterized by XRD, ESEM, particle size distribution analysis, specific surface area testing, galvanostatic cycling and electrochemical impedance spectroscopy. The XRD analysis shows that the sample exhibits pure spinel phase. The substitution of Co, La for Mn and Cl for O in the LiMn2O4 stabilizes the structural integrity of the spinel host, which in turn increases the electrochemical cycleability. The electrochemical experiments confirm that the capacity of the LiCo0.02La0.01Mn1.97O3.98Cl0.02 electrode maintains 90.6% of the initial capacity at 180th cycle.展开更多
LiF-coated LiMn2O4 samples were prepared via a chemical method. X-ray diffraction(XRD) patterns show that the bare LiMn2O4 and the LiF-coated LiMn2O4 samples are all spinel structure in Fd 3mspace group. The apparent ...LiF-coated LiMn2O4 samples were prepared via a chemical method. X-ray diffraction(XRD) patterns show that the bare LiMn2O4 and the LiF-coated LiMn2O4 samples are all spinel structure in Fd 3mspace group. The apparent morphologies,the spectroscopic properties and the LiF distributions of the as-prepared samples were studied by scanning electronic microscopy(SEM),Fourier infrared spectroscopy(FTIR),transmission electronic microscopy(TEM),selected area electron diffractometry(SAED) respectively. The LiF-coated LiMn2O4 gets a more stable surface than bare LiMn2O4,and changes the interaction between the cathode material and the electrolyte. Therefore,it can endure overcharge in the secondary lithium batteries,and achieve better electrochemical performances even when charged to 4.7 V and 4.9 V.展开更多
基金Funded by the National Natural Science Foundation of China(Nos.20803056,11474226)the Fundamental Research Funds for the Central Universities(WUT:2015-IB-001,WUT:2016-IB-005)
文摘Spinel LiMn2O4 microspheres and hollow microspheres with adjustable wall thickness have been prepared using controllable oxidation of MnCO3 microspheres precursors and following solid reactions with lithium salts. Scanning electron microscopy （SEM） investigations demonstrate that the microsphere morphology and hollow structure of precursors are inherited. The effect of hollow structure properties of as-prepared LiMn2O4 on their performance as cathode materials for lithium-ion batteries has been studied. Electrochemical performance tests show that LiMn2O4 hollow microspheres with small wall thickness exhibit both superior rate capability and better cycle performance than LiMn2O4 solid microspheres and LiMn2O4 hollow microspheres with thick wall. The LiMn2O4 hollow microspheres with thin wall have discharge capacity of 132.7 mA.h-g^-1 at C/10 （14.8 mA.g^-1） in the first cycle, 94.1% capacity retention at C/10 after 40 cycles and discharge capacity of 116.5 mAh-gq at a high rate of 5C. The apparent lithium-ion diffusion coefficient （Dapp） of as-prepared LiMn2O4 determined by capacity intermittent titration technique （CITT） varies from 10-11 to 10-8.5 cm2.s^-1 showing a regular ＂W＂ shape curve plotted with test voltages. The D app of LiMn2O4 hollow microspheres with thin wall has the largest value among all the prepared samples. Both the superior rate capability and cycle stability of LiMn2O4 hollow microspheres with thin wall can be ascribed to the facile ion diffusion in the hollow structures and the robust of hollow structures during repeated cycling.
基金supported by a grant from the National High Technology Research and Development Program of China(863 Program)(No.2008AA11A102)
文摘Spherical Li-rich lithium manganese oxide（LMO） spinel material was synthesized by an ion implanted method assisted by polyalcohol doped with Niobium and Phosphate simultaneously.The material was characterized by scanning electron microscopy,X-ray diffraction and BET specific surface area analysis.The electrochemical performances were investigated with galvanostatic techniques and cyclic voltammetry.The synthesis process was investigated with TG/DSC.The results show that the lithium ion can be immersed into the pore of manganese dioxide at a low temperature with the ion implanted method.The prepared materials have a higher discharge capacity and better crystallization than those prepared by solid phase method.The doped Nb can improve the capacity of the Li-rich LMO spinel and reinforce the crystal growth along（111） and（400） planes.The crystal grains show circular and smooth morphology,which makes the specific surface area greatly decreased.Phosphate-doped LMO spinel exhibits good high-rate capacity and structure stability.The prepared Li（1.09）Mn（1.87）Nb（0.031）O（3.99）（PO4）（0.021）delivers a discharge capacity of 119mAhg^-1 at 0.2C（1C=148mAg^-1） and 112.8 mAhg^-1 at 10 C,the discharge capacity retention reaches 98% at 1 ℃ after 50 cycles at 25 ℃ and 94% at 55 ℃.
基金Project(2008AA031205)supported by the National High-tech Research and Development Program of China
文摘The hydrothermal synthesis of single-crystallineβ-MnO2 nanorods and their chemical conversion into single-crystalline LiMn2O4 nanorods by a simple solid-state reaction were reported.This method has the advantages of producing pure,single-phase and crystalline nanorods.The LiMn2O4 nanorods have an diameter of about 300 nm.The discharge capacity and cyclic performance of the batteries were investigated.The LiMn2O4 nanorods show better cyclic performance with a capacity retention ratio of 86.2% after 100 cycles.Battery cyclic studies reveal that the prepared LiMn2O4 nanorods have high capacity with a first discharge capacity of 128.7 mA·h/g.
基金supported by the National High-Tech Research and Development Program of China(No.2006AA11A160)
文摘Regular spherical chromium doped spinel lithium manganese oxides （LiCr0.04Mn1.96O4） with an average particle size of about 20μm were prepared by the slurry spray drying process. The materials were compared with non-spherical LiCr0.04Mnl.96O4 materials prepared by the common drying process, and all materials were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, laser particle analyzer and Brunaner-Emmett-Teller （BET） specific surface area test. Electrochemical performances of these cathode materials were studied by cyclic voltammetry （CV）, electrochemical impedance spectroscopy （EIS） and Li/LiCr0.04Mn1.9604 battery test. The results show that the spherical active material is single spinel structure, compact, and with narrow particle size distribution and low BET specific surface area. Compared with the non-spherical material, the spherical material prepared by the spray drying process shows a lower electrochemical impedance, a fewer electrochemical polarization and a better charge/discharge rate capability and capacity retention at elevated temperatures.
文摘Spinel LiCo0.09Mn1.91O3.92F0.08 as cathode material was modified with LiCoO2 by the sol-gel method, and the crystal structure, morphology and electrochemical performance were characterized with XRD, SEM, EDS, AAS and charge-discharge test in this paper. The results show that a good clad coated on parent material can be synthesized by the sol-gel method, and the materials with modification have perfect spinel structure. LiCo0.09Mn1.91O3.92F0.08 materials coated by LiCoO2 improve the stability of crystal structure and decrease the dissolution of Mn into electrolyte. With the LiCoO2 content increasing, the specific capacity and cycle performance of samples are improved. The capacity loss is also suppressed distinctly even at 55 ℃.
基金the National Key Basic Research Program of China(No.2002BC211804)
文摘The formation process of solid electrolyte interphase（SEI） film on spinel LiMn2O4 electrode surface was studied by electrochemical impedance spectroscopy（EIS） during the initial storage in 1 mol/L LiPF6-EC：DMC：DEC electrolyte and in the subsequent first charge-discharge cycle. It has been demonstrated that the SEI film thickness increased with the increase of storage time and spontaneous reactions occurring between spinel LiMn2O4 electrode and electrolyte can be prevented by the SEI film. In the first charge-discharge cycle succeeding the storage, the electrolyte oxidation coupled with Li-ion insertion is evidenced as the main origin to increase the resistance of SEI film. The results also confirm that the variations of the charge transfer resistance（Rot） with the electrode potential（E） can be well described using a classical equation.
基金Project(2002CB211800) supported by the National Basic Research Program of China
文摘Li1+xMn2?yO4 spinels with various Li/Mn ratios were synthesized by a solid-state reaction. By X-ray diffraction analysis, Li2MnO3 was detected as a second phase with increasing the Li/Mn ratio; and the role of Li2MnO3 in Li1+xMn2-yO4 spinel was discussed. A slow scanning cyclic voltammetry(CV) at the rate of 0.1 mV/s was adopted to characterize the evolutions of 4 V and 5 V plateaus of Li1+xMn2-yO4 spinels. An additional Li+ insertion in 4 V region was observed in both Li-lack and Li-rich spinels at 3.95 V, which is different from the general Li+ insertion with weak Li-Li interaction and strong Li-Li interaction; and this plateau disappeared in the subsequent cycles. The 4.4 V/3.8 V plateaus correspondent to Li+ insertion and extraction of Li2MnO3 were discussed, and these plateaus have a high reversibility with cycling. The 5 V plateau was found only in the Li-rich samples, and this plateau has a tendency to emerge at higher voltage region with increasing Li/Mn ratio.
基金Project(20273047) supported by the National Natural Science Foundation of China
文摘Multidoped spinel LiCo0.02La0.01Mn1.97O3.98Cl0.02 was synthesized by solid-state method. The structure and electrochemical performance were characterized by XRD, ESEM, particle size distribution analysis, specific surface area testing, galvanostatic cycling and electrochemical impedance spectroscopy. The XRD analysis shows that the sample exhibits pure spinel phase. The substitution of Co, La for Mn and Cl for O in the LiMn2O4 stabilizes the structural integrity of the spinel host, which in turn increases the electrochemical cycleability. The electrochemical experiments confirm that the capacity of the LiCo0.02La0.01Mn1.97O3.98Cl0.02 electrode maintains 90.6% of the initial capacity at 180th cycle.
基金Project (2002CB211800) supported by the National Basic Research Program of Chinaproject (000Y05-21) supported by the Excellent Young Scholar Research Fund of Beijing Institute of Technologyproject (20060542012) supported by the Teaching and Research Fund of Beijing Institute of Technology
文摘LiF-coated LiMn2O4 samples were prepared via a chemical method. X-ray diffraction(XRD) patterns show that the bare LiMn2O4 and the LiF-coated LiMn2O4 samples are all spinel structure in Fd 3mspace group. The apparent morphologies,the spectroscopic properties and the LiF distributions of the as-prepared samples were studied by scanning electronic microscopy(SEM),Fourier infrared spectroscopy(FTIR),transmission electronic microscopy(TEM),selected area electron diffractometry(SAED) respectively. The LiF-coated LiMn2O4 gets a more stable surface than bare LiMn2O4,and changes the interaction between the cathode material and the electrolyte. Therefore,it can endure overcharge in the secondary lithium batteries,and achieve better electrochemical performances even when charged to 4.7 V and 4.9 V.
