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1.
Exchange current density of spinel LiMn2 O4 was studied by linear polarization. The relationship of the kinetic property with the structure of spinel LiMn2 O4 was investigated by studying the effect of the doping and surface coating on the kinetic properties of electrode material. The results show that the exchange current density of spinel LiMn2 O4 electrode increases with the increase of the amount for lithium intercalation at first, and then decreases. The maximal exchange current density appeares at the 80%-90% lithium intercalation. The similar phenomenon was observed on the doped spinel LiMn2 O4 electrode. Doping can enhance the exchange current density of spinel LiMn2 O4 material. However, the degree of the doping effect varies with the doped element varying. Surface coating can also enhance the exchange current density of spinel material, and the increment of value is higher than that of doped ones. 相似文献
2.
Guo Hua-jun Li Xin-hai Zhang Xin-ming Zeng Su-ming Wang Zhi-xing Peng Wen-jie 《中南工业大学学报(英文版)》2005,12(1):44-49
LiNi0.45Co0.10Mn0.45O2 was synthesized from Li2CO3 and a triple oxide of nickel, cobalt and manganese at 950 °C in air. The structures and characteristics of LiNi0.45Co0.10Mn0.45O2, LiCoO2 and LiMn2O4 were investigated by XRD, SEM and electrochemical measurements. The results show that LiNi0.45Co0.10Mn0.45O2 has a layered structure with hexagonal lattice. The commercial LiCoO2 has sphere-like appearance and smooth surfaces, while the LiMn2O4 and LiNi0.45Co0.10Mn0.45O2 consist of cornered and uneven particles. LiNi0.45Co0.10Mn0.45O2 has a large discharge capacity of 140.9 mA · h/g in practical lithium ion battery, which is 33.4% and 2.8% above that of
LiMn2O4 and LiCoO2, respectively. LiCoO2 and LiMn2O4 have higher discharge voltage and better rate-capability than LiNi0.45Co0.10Mn0.45O2. All the three cathodes have excellent cycling performance with capacity retention of above 89.3% at the 250th cycle. Batteries
with LiMn2O4 or LiNi0.45Co0.10Mn0.45O2 cathodes show better safety performance under abusive conditions than those with LiCoO2 cathodes.
Foundation item: Project(50302016) supported by the National Natural Science Foundation of China; Project(2005037698) supported by the Postdoctoral
Science Foundation of China 相似文献
3.
The spinel LiMn2O4 used as cathode materials for lithium-ion batteries was synthesized by mechano-chemistry fluid activation process, and modified
by doping rare-earth Sm. Thesting of X-ray diffraction, cyclic voltammograms, charge-discharge and SEM was carried out for
LiMn2O4 cathode materials and the modified materials. The results show that the cathode materials doped rare earth Li
x
Mn2−y
Sm
z
O4 (0.95⩽x⩽1.2, 0⩽y⩽0.3, 0⩽z⩽0.2) exhibit standard spinel structure, high reversibility of electrochemistry and excellent properties of charge-discharge.
In EC: DMC(1 : 1)+1 mol/L LiPF6 electrolyte with discharge capacity more than 130 mA · h/g, and its capacity is deteriorated less than 15% after 300 cycles
at room temperature and less than 20% after 200 cycles at 55°C. At the same time, Crystal Field Theory was applied to explain
the function and mechanism of doped rare earth element.
Foundation item: Project (02JJY2081) supported by the Natural Science Foundation of Hunan Province 相似文献
4.
为明晰Li Mn1.5Ni0.5O4正极材料的动力学性能,采用水热辅助共沉淀法合成了尖晶石Li Mn1.5Ni0.5O4正极材料,并采用扫描电镜(SEM)、X射线粉末衍射(XRD)和电化学阻抗(EIS)研究了材料的结构和锂离子嵌脱动力学.实验结果表明:共沉淀法制备的Li Ni0.5Mn1.5O4材料颗粒呈均匀球形,且平均粒径较小,粒度分布较窄.在循环过程中,Li Ni0.5Mn1.5O4的电荷转移电阻增大,锂离子扩散系数减小,进而电子电导率和离子电导率下降.温度升高后,Li Ni0.5Mn1.5O4材料的溶液电阻变化不大,但是电荷转移电阻逐渐增大,锂离子扩散系数逐渐减小;此外,随着温度的升高,Li Ni0.5Mn1.5O4材料的溶解速度加快,从而导致SEI膜的厚度增大.Li Ni0.5Mn1.5O4材料的嵌脱锂动力学与温度和循环次数有密切关系. 相似文献
5.
In order to obtain a new precursor for LiFePO4, Fe2P2O7 with high purity was prepared through solid phase reaction at 650 ℃ using starting materials of FeC2O4 and NH4H2PO4 in an argon atmosphere. Using the as-prepared Fe2P2O7, Li2CO3 and glucose as raw materials, pure LiFePO4 and LiFePO4/C composite materials were respectively synthesized by solid state reaction at 700 ℃ in an argon atmosphere. X-ray diffractometry and scanning electron microscopy(SEM) were employed to characterize the as-prepared Fe2P2O7, LiFePO4 and LiFePO4/C. The as-prepared Fe2P2O7 crystallizes in the Cl space group and belongs to β-Fe2P2O7 for crystal phase. The particle size distribution of Fe2P2O7 observed by SEM is 0.4-3.0 μm. During the Li^+ ion chemical intercalation, radical P2O7^4- is disrupted into two PO4^3- ions in the presence of O^2-, thus providing a feasible technique to dispose this poor dissolvable pyrophosphate. LiFePO4/C composite exhibits initial charge and discharge capacities of 154 and 132 mA·h/g, respectively. 相似文献
6.
以硝酸铟(In(NO3)3·xH2O)、对苯二甲酸(H2BDC)、六水合硝酸钴(Co(NO3)· 6H2O) 为原料, 首先采用一锅油浴法合成了含有Co2+ 的铟基金属有机框架材料(MOFs) Co2+/CPP-3(In) 材料, 然后在450 ℃ 下焙烧制备Co3O4/In2O3 复合物气敏材料, 将Co3O4/In2O3 复合物的粉体制作成传感器, 并对其气敏性能进行研究。利用扫描电子显微镜和X 射线衍射仪(XRD) 对双金属MOFs Co2+/CPP-3(In) 材料和Co3O4/In2O3 复合物进行表征, 采用静态配气法测试其气敏性能。结果表明, Co3O4/In2O3(nCo : nIn = 0.4 : 1) 样品的形貌保留了其MOFs 前驱体的棒状结构, 棱柱形框架更为突出, 表面呈凹陷状, 棒体中间粗两边细, 六角截面和棒体均布满了孔洞。结合EDX 和XRD
表征结果, Co2+/CPP-3(In) MOFs 前驱体完全转化成Co3O4/In2O3 复合物; Co3O4/In2O3(nCo : nIn = 0.4 : 1) 复合物在
70 ℃ 下对5×10-6 H2S 的气敏性能最优, 响应值达到153, 是同条件下纯备In2O3对H2S 响应值的5 倍, 并且有较好的重复性、选择性和稳定性。 相似文献
7.
Baijun Yan Jianhua Liu Yunduo Dai Qifeng Shu Zhihua Ren 《北京科技大学学报(英文版)》2007,14(5):395-398
The molar heat capacities of La2Mo209 and La1.9Sr0.1MO209-δ were obtained using the differential scanning calorimetry (DSC) technique in a temperature range from 298 to 1473 K. The DSC curve of La2Mo209 showed an endothermal peak around 834 K corresponding to a first-order monoclinic-cubic phase transition, and the enthalpy change accompanying this phase transition is 5.99 kJ/mol. No evident endothermal peak existed in the DSC curve of La1.9Sr0.1MO209-δ, but a broad thermal anomaly existed in its heat capacity curve at around 832 K. In addition, the heat capacity values of La2Mo209 and La1.9Sr0.1MO209-δ began to decrease at 1196 and 1330 K, respectively. The non-transitional heat capacity values of La2Mo209 and La1.9Sr0.1MO209-δ were formulated using multiple regression analysis in two temperature ranges. 相似文献
8.
Luminescent properties of BaO-La2O3-B2O3 glasses with dopant 总被引:4,自引:0,他引:4
The luminescent properties of glasses synthesized in air atmosphere by conventional high temperature process were stud{ed. The emissions spectra of Eu^2 and Eu^3 were observed in BaO-La2O3-B2O3-Eu2O3 glasses.The results show that the broad emission peaks at 430 nm correspond to 5d→4f emission transition of Eu^2 , the sharp emission peaks at 592, 616, 650 and 250 nm correspond to 5^D0→1Fj(j=1--4) emission transition of Eu^3 ,respectively, which indicates that the BaO-La2O3a-B2O3-Eu2O3 glass can convert ultraviolet and green omponents of sunlight into blue and red light so as to increase the intensity of blue and red light, respectively. The luminescent in--tensity of Eu^2 increases with increasing the molar ratio of Tb^3 in BaO-La2O3-B2O3-Eu2O3a-Tb4O3 glasses, whereas the luminescent intensity of Eua^3 decreases. So the luminescent intensity of Eu(Ⅲ,Ⅱ) is influenced by Tb^3 .These phenomena can be explained by electron transfer mechanism; Eu^3 (4f6) Tb^3 (4f^8)→Eu^2 (4f′) Tb^4 (4f′). Taking advantage of the luminescent properties of BaO-La2O3-B2O3-Eu2O3 glasses, light-conversion glass for agriculture can be produced. 相似文献
9.
4.25Cu-0.75Ni/NiFe2O4 cermets were prepared by doping NiFe2O4 ceramic matrix with the mixed powders of Cu and Ni or Cu-Ni alloy powder as the electrical conducting metallic elements.
The effects of technological parameters, such as the adding modes of metallic elements, the ball milling time, the sintering
time and the sintering temperature, on the relative density and resistivity of the cermets were studied. The results show
that the resistivity of 4.25Cu-0.75Ni/NiFe2O4 cermets decreases with increasing temperature, and has a turning point at 590 °C, which is similar to that of NiFe2O4 ceramic. The sintering temperature and adding modes of metallic elements have a great influence on the properties of 4.25Cu-0.75Ni/NiFe2O4 cermets. When the sintering temperature increases from 1200 °C to 1300 °C, the relative density increases from 89.86% to
95.33%, and the resistivity at 960 °C decreases from 0.11 Ω · cm to 0.03 Ω · cm, respectively. When the metallic elements
are added with the mixed powders of Cu and Ni, the cermets of finely and uniformly dispersed metallic phase, high density
and electric conductivity are obtained. The relative density and resistivity at 960 °C are 90.23% and 0.04 Ω · cm respectively
for the cermet samples sintered at 1200 °C for 2 h, which are both better than those of the cermets prepared under the same
technique conditions but with the metallic elements added as 85Cu-15Ni alloy powders.
Foundation item: Project (G1999064903) supported by the National Key Fundamental Research and Development Program of China; project(2001AA335013)
supported by the National High Technology Research and Development Program of China; project (50204014) supported by the National
Natural Science Foundation of China 相似文献
10.
为研究使用过一硫酸盐(PMS)的高级氧化技术去除水体中微量有机污染物的高效可行方法,通过柠檬酸辅助溶胶-凝胶法制备纳米CuFe_2O_4材料,以其为非均相催化剂,探究CuFe_2O_4/PMS体系对诺氟沙星(NFX)的降解性能.采用X射线衍射仪、电子透射显微镜、BET手段对材料进行表征,考察煅烧温度对纳米CuFe_2O_4结构及催化性能的影响,并试验纳米CuFe_2O_4的重复使用性和稳定性.探讨纳米CuFe_2O_4投加量、PMS浓度、溶液初始pH对CuFe_2O_4/PMS体系降解NFX性能的影响,并探究该体系的氧化活性物种及降解机理.结果表明:制备纳米CuFe_2O_4的最佳煅烧温度为400℃,该温度下纳米CuFe_2O_4晶型较好,比表面积较大,且表现出较高的催化活性;在纳米CuFe_2O_4/PMS体系中,控制NFX初始质量浓度为5 mg/L,最适宜的反应条件为:纳米CuFe_2O_4投加量为0.1 g/L、PMS浓度为0.5 mmol/L、初始溶液pH为9.5,该条件下反应30 min后NFX的去除率高达99%;纳米CuFe_2O_4能有效活化PMS生成·OH和SO_4~-·,SO_4~-·是实现NFX快速降解的主要活性物种. 相似文献
11.
The cathode materials LiMn2O4 and rare earth elements La-doped or La and F dual-doped spinel lithium manganese oxides were synthesized by the citric acid-assisted sol-gel method. The synthesized samples were investigated by differential thermal analysis (DTA) and thermogravimetry (TG) measurements, X-ray diffraction (XRD), scanning electronic microscope (SEM), cyclic voltammetry (CV), and charge-discharge test. XRD data shows that all the samples exhibit the same pure spinel phase, and the LiLa0.01Mn1.99O3.99F0.01 and LiLa0.01Mn1.99O4 samples have smaller lattice parameters and unit cell volume than LiMn2O4. SEM indicates that LiLa0.01Mn1.99O3.99F0.01 has a slightly smaller particle size and a more regular morphology structure with narrow size distribution. The charge-discharge test reveals that the initial capacities of LiMn2O4, LiLa0.01Mn1.99O4, and LiLa0.01Mn1.99O3.99F0.01 are 129.9, 122.8, and 126.4 mAh·g−1, and the capacity losses of the initial values after 50 cycles are 14.5%, 7.6%, and 8.0%, respectively. The CVs show that the La and F dual-doped spinel displays a better reversibility than LiMn2O4. 相似文献
12.
The kinetics of Fe3O4 formation by air oxidation of slightly acidic suspension of Fe(OH)2 was studied. The effects of initial concentration of Fe(II), temperature, partial pressure of oxygen, air flow rate and stirring
rate on the oxidation rate were investigated. The results show that Fe3O4 formation is composed of two-step reaction, the first step is the formation of Fe(OH)
2
+
by oxidation of Fe(OH)+ complex ions, the second step is the formation of magnetite by dehydration and deprotonation of Fe(OH)+ and Fe(OH)
2
+
. The oxidation reaction is zero-order with respect to the concentration of Fe(II) and around 0.5-order with respect to partial
pressure of oxygen, and oxygen transfer process is rate-limiting step of oxidation reaction with apparent activation energy
of 2.74 kJ · mol−1. 相似文献
13.
采用水热法合成富锂三元正极材料,探究了最佳包覆比例下Al_2O_3包覆对材料的电化学性能影响.采用扫描电镜(SEM)和X射线衍射仪(XRD)表征了富锂三元正极材料的表面形貌和结构,通过循环伏安(CV)、交流阻抗(EIS)技术分析了材料电化学性的影响因素.结果表明,通过异丙醇铝水解制得了氧化铝包覆层,提高了材料的比容量,稳定了材料的结构. 相似文献
14.
为高效地去除水中环境激素类污染物,采用共沉淀法合成了氧化石墨烯负载钴尖晶石铁氧体(GO/CoFe_2O_4)催化剂,催化过硫酸盐(PMS)去除水中邻苯二甲酸二丁酯(DBP).采用SEM、TEM、XPS、XRD对催化剂进行表征,研究不同条件下催化PMS去除水中DBP的效果,提出催化PMS反应机理.结果表明,GO/CoFe_2O_4为颗粒状尖晶石结构,室温下,DBP初始浓度为2μmol/L、催化剂投量为0.1 g/L、PMS浓度为20μmol/L、pH为7时,GO/CoFe_2O_4催化PMS体系对DBP的去除率可达89%,使用5次后催化效果仅降低5%.该新型复合催化剂高效、具有磁性、方便回收,具有良好的工程应用前景. 相似文献
15.
尖晶石 LiMn2O4 正极材料是在原有锂电池正极材料 LiCoO2 、LiNiO2 、LiMnO2 的基础上研发出来的优选
正极材料, 它相较于 LiCoO2 材料价格更加低廉热稳定性加强且安全性能有所提高。采用 Mg2+ 掺杂 LiMn2O4正极
材料, 利用基于密度泛函理论的第一性原理对 LiMg0.5Mn1.5O4 晶格常数与能带结构、态密度进行计算与分析。结
果表明: 新材料 LiMg0.5Mn1.5O4 的空间群为 F4332, 掺杂后晶胞参数 a 明显减小, 晶胞体积收缩; 掺杂量为 0.5 时明
显比掺杂量 0.125 时 Fermi 能量和能量密度高。Mg 2+ 掺杂能影响 LiMn2O4 的晶体结构, 形成更加稳定的共价键。
掺杂量会改变 LiMn2O4 的空间群影响到结构稳定性, 所以掺杂量不宜过大。 相似文献
16.
采用水热法合成SrBi2Ta2O9(SBT)纳米粉体,成型后采用常规烧结法制备SBT陶瓷.利用XRD和SEM研究陶瓷的物相和微观形貌;利用介电温谱研究陶瓷的介电性能.结果表明:采用水热法能够制备出颗粒细小均匀、结构致密且物相纯净的SBT陶瓷;其居里温度为375℃,对应的介电常数为114.54. 相似文献
17.
The corrosion resistance of NiCrAl+(ZrO2+Y2O3) thermal barrier coating, formed with the plasma spraying technique, on the 18 - 8 steel surface was investigated. The phase
structure and morphology of the coating were analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy
(SEM). The electrochemical corrosion behavior of the coating in 1.0 mol/L H2SO4 solution was studied by using electrochemical measurement methods. The results show that the gradient plasma spraying coating
is composed of the NiCrAlY coating and the (ZrO2+Y2O3) top coating, and the coating thickness is 360 μm. The microhardness of coating reaches 1 100 HV. The corrosion resistance of the plasma sprayed coating of the 18 - 8 steel
surface is about 5 times as great as that of the original pattern. The corrosion resistance of the coating is enhanced notably.
Foundation item: Project (5040202140) supported by Scientific Research Common Program of Beijing Municipal Commission of Education 相似文献
18.
Chai Li-yuan Su Wei-feng Peng Bing Wang Yun-yan Wei Shun-wen Yuan Chun Yu Yan-fen Hao Yun 《中南工业大学学报(英文版)》2006,13(1):17-22
A novel technology of in-situ coating Al2O3 on the surface of H4TiO4 was developed to prevent the aggregation of nano-TiO2 powders and improve the dispersibility and thermal stability in the way of forming a uniform coating layer. The heterogeneous
nucleation was conducted to prepare the precursor of nano-TiO2 and then Al2O3 was coated on the surface of precursor. The effects of Al2O3 in-situ coating on the properties of nano-TiO2 were investigated. The results show that H4TiO4 can be dispersed well under alkaline condition (pH 8.5) and the heterogeneous nucleation can be controlled easily. The optimized
uniform coating layer is obtained by adding 5% (mass fraction) and 10% of Al2O3 and the aggregation of nano-TiO2 powders is effectively inhibited and the dispersibility is obviously improved. The crystal sizes of TiO2 powders are 12.3, 11.4 and 8.7 nm after coating 0,5% and 10% of Al2O3 respectively. Al2O3 on the surface of particulates in amorphous phase could increase the thermal stability of nano-particles after calcined at
550 °C.
Foundation item: Project(04GK2007) supported by Hunan Industrial Key Project of Science and Technology 相似文献
19.
LiMn2O4 powder as a cathode materials for rechargeable lithium-ion batteries was prepared by solid-state reaction from LitCO3 and electrolytic MnOz at different sintering periods (2, 6, 18, and 32 h). X-ray diffraction (XRD) patterns of the prepared samples are identified as the spinel structure with a space group of Fd3 m. The lattice parameters almost remain the same as the sintering periods increase. The sample with a sintering period of 32 h shows good cycling performance at both low and nigh current densities, and also elevated temperature. It is believed that the excellent electrochemical behavior of this sample results from its good crystallinity and large grain size compared with other samples. Different electrochemical measurements were conducted to investigate the electrochemical properties of spinel LiMn204. 2008 University of Science and Technology Beijing. All rights reserved. 相似文献
20.
LiCo1/3Ni1/3Mn1/3O2 was coated by a layer of 1.0 wt% CeO2 via sol-gel method. The bared and coated LiMn1/3Co1/3Ni1/3O2 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammogram (CV) and galvanotactic
charge-discharge test. The results show that the coating layer has no effect on the crystal structure, only coating on the
surface; the 1.0 wt% CeO2-coated LiCo1/3Ni1/3Mn1/3O2 exhibits better discharge capacity and cycling performance than the bared LiCo1/3Ni1/3Mn1/3O2. The discharge capacity of 1.0 wt% CeO2-coated cathode is 182.5 mAh·g−1 at a current density of 20 mA·g−1, in contrast to 165.8 mAh·g−1of the bared sample. The discharge capacity retention of 1.0 wt% CeO2-coated sample after 12 cycles reaches 93.2%, in comparison with 86.6% of the bared sample. CV results show that the CeO2 coating could suppress phase transitions and prevent the surface of cathode material from direct contact with the electrolyte,
thus enhance the electrochemical performance of the coated material. 相似文献