Structure characteristics and electrochemical properties of LiMn2O4 modified by LiCoO2

In order to improve the cycle performance of LiMn2O4, the modified LiMn2O4 was prepared by solid-state reactions using LiMn2O4 and LiCoO2 as precursors. XRD and EDS were used to study the structure properties of the modified LiMn2O4. The electrochemical properties of the modified LiMn2O4 were also investigated, The results show that Li and Co atoms could insert into the LiMn2O4 crystal lattice and a newly formed spinel phase, modified LiMn2O4 was obtained. The modified LiMn2O4 exhibits excellent cycle ability at room and elevated temperatures compared to pure LiMn2O4. The improved electrochemical stability of the modified LiMn2O4 attributes to the entrance of Li and Co ions inserted into the spinel crystal structure.     

Electrochemical Characterization of Surface-modified LiMn2O4 Cathode Materials for Li-ion Batteries

To improve the performance, the surface of 12Mn2O4 was coated with very fine MgO , Al2O3 and ZnO by solgel method, respectively. The structure and morphology of the coated materials were investigated by X-ray diffraction （ XRD ）, X-ray photoelectron spectroscopy （ XPS ） and scanning electron microscopy （SEM）. The charge and discharge performance of uncoated and surfnce modified 12Mn2O4 spinel at 25℃ and 55 ℃ were tested, using a voltage window of 3.0-4.35 V and a current deasity of 0. 1 C rate. There is a slight decrease in the initial discharge capacity relative to that of uncoated UMn2 O4, bat the cycle ability of 12 12Mn2O4 coated by metal-oxide has remarkably been improved. The EIS measuremeuts of uncoated and Al2O3 -coated 12Mn2O4 were carried out by a model 273 A potentiostatl galvanistat controUed by a computer using M270 software, and using a freqnency response analyzer （ Zsimpwin ） combined with a potentiostate （ PAR 273）. Coaseqnently, the reason for the improved cycle properties is that the surface modification reduces the dissolution of Mn , which results from the suppression of the electrolyte decomposition, and suppresses the formation of passivation film that acts as an electronic insulating layer. In conclusion, the use of surface modification is an effective way to improve the electrochemical performance of 12Mn2O4 cathode material for lithium batteries.     

The Mechanism of Sol-Gel Synthesis of Normal Spinel LiMn2O4 with Chelation of Citric Acid

The sol-gel process of citric acid chelating with metal cations for the synthesis of normol spinel LiMn2O4 and the reaction mechanion mechavism were investigated by means of XRD,TG-DTA,and SEM ,the results show that at the beginning lithium citrate and chelate compound of citic acid with manganese ions formed ,and then with heating the esterification and condensation reacions occured between them and glyol ,The products obtained are polymers in which metal cations are distibuted homogeneously on atomic scale that ensur hight reacivity to cations of Li^ and Mn^2 ,Firing the gel grepared by this process ,the lattice diffusions of solid reactant ions caused by non-homogeneity of reactants are elinimated and avoided .At 400℃ phase-pure LiMn2O4 with nanometer scale crystallization having precise stoichiometry and perfect crystallization can be obtained ,The model of chelate coordinated of double -molecule between citric acid and Mn^2 in the gel network is proosed ,It is important for explaining the dispersion state of Mn^2 and the formaiton process of gel by this model.     

薄膜LiMn2O4阴极制备研究进展

尖晶石状LiMn2O4是制备高能量密度的锂离子电池的一种很有发展前景的阴极材料。评论了近年来制备薄膜阴极的方法,包括化学酸基溶解法、溶胶-凝胶法、激光焙烧法、增强型等离子体化学气相淀积法、脉冲激光法、电子束喷射沉积法和射频磁控溅射法。着重分析了能够和IC、MEMS工艺良好集成的射频磁控溅射的方法,提出了工艺路线,并规划了下一步工作。     

微波合成LiMn2O4正极材料及其电化学性能的研究

本文以Li2CO3 、MnO2为原料,采用微波热处理合成锂离子电池正极材料LiMn2O4,研究了热处理温度,Li/Mn摩尔比对产物结构和电化学性能的影响,同时研究了微波热处理和传统热处理两种加热方式的差别.通过X射线衍射（XRD）、扫描电镜（SEM）、恒电流充放电测试分别对产物的结构、形貌及电化学性能进行表征,结果表明：采用微波法在750℃保温15 min,快速地制备出尖晶石型LiMn2O4,纯度高,尺寸分布均匀,约100-300 nm;于0.1C倍率下,以微波法制备的正极材料首次放电比容量可达112.38 mA·h/g,1C倍率充放电50次循环后,容量保持率为91.6％;以传统方法制备的正极材料0.1C倍率下首次放电比容量为94.07 mA·h/g,1C倍率充放电50次循环后,容量保持率为71.4％     

凝胶燃烧法合成尖晶石LiMn2O4粉体及其表征

以丙氨酸和水杨酸为络合剂和燃料,采用凝胶燃烧法制备了锂离子电池正极材料尖晶石LiMn2O4粉体.对凝胶前驱体及烧结产品进行了TG-DTA、XRD分析;通过循环伏安、交流阻抗及充放电测试对该产品的电极过程动力学性质及充放电性能进行了表征.结果表明,该方法烧结温度低、时间短,制备的产品为纯相尖晶石结构;不同电位下溶液电阻、膜电容均保持稳定,Li 扩散系数为10-12～10-10 cm2/s.该材料具有较好的充放电性能.     

Sol-Gel Synthesis of Normal Spinel LiMn_2O_4 and Its Characteristics

1　ＩｎｔｒｏｄｕｃｔｉｏｎＮｏｒｍａｌｓｐｉｎｅｌＬｉＭｎ2 Ｏ4 ｐｏｓｓｅｓｓｅｓｓｐｅｃｉｆｉｃｍｅｍｏｒｙｅｆｆｅｃｔｆｏｒｌｉｔｈｉｕｍｉｏｎ .Ｍａｎｇａｎｅｓｅｉｓｒｉｃｈｉｎｎａｔｕｒａｌｒｅ ｓｏｕｒｃｅｓａｎｄｈａｓｎｏｐｏｌｌｕｔｉｏｎｔｏｔｈｅｅｎｖｉｒｏｎｍｅｎｔ .Ｅｘｔｒａｃ ｔｉｏｎｏｆｍｉｃｒｏ ｌｉｔｈｉｕｍｆｒｏｍｓｅａｗａｔｅｒａｎｄｓａｌｔ ｌａｋｅｂｒｉｎｅｂｙｌｉｔｈｉｕｍｍａｎｇａｎｅｓｅｏｘｉｄｅｉｓｒｅｇａｒｄｅｄａｓｔｈｅｍｏｓｔｐｒｏｓｐｅｃ ｔｉｖｅ…     

制备工艺对LiMn2O4纯度及性能的影响

研究了制备工艺对LiMn2O4纯度的影响机理,同时对LiMn2O4正极在充放电过程中的容量衰减机理进行了探讨.试验结果表明,以硝酸锂和硝酸锰为原料,采用柠檬酸络合法制备纳米LiMn2O4粉体时,前驱体的分解温度区间小,分解速度快,在焙烧过程中容易产生缺氧,使有机物发生炭化,不利于Li、Mn原子的直接结合,因而随着焙烧温度的升高,LiMn2O4的纯度呈下降趋势,300℃预处理可提高纯度;在放电过程中,LiMn2O4颗粒表面发生立方相向四方相(a=0.576 0nm,c=0.945 9nm,轴比c/a=1.642)的相变,导致容量衰减.     

Sol—Gel Synthesis of Normal Spinel LiMn2O4 and Its Characteristics

Normal spinel LiMn2O4 was synthesized by sol-gel method using lithium nitrate,manganese nitrate,citric acid and ethylene glycol as raw materials.LiMn2O4 was characterized by XRD,TG-DTA,IR,SEMand AAS,The optimum conditions for the synthesis were explored.Citric and ethylene glycol were mixed with molar ratio of 0.25,and the mixtrue was esterified at 140℃ for 4 hours.Then lithium nitrate and manganese nitrate were added with molar ratio of 0.6,In the system,the total molar of cations was equal to that of citric acid.At last,reflux the system at 105℃ for 2 hours,Dried gel was fired at 600℃ for 8 hours.Particle diameters of raw product were about 100nm mainly.Further research shows that lithium ion of LiMn2O4 is easy to be extracted,and normal spinel λ-MnO2 can be obtained after lithium ion extraction.     

二次锂离子电池的正极材料LiMn2O4的制备和性能研究

叙述尖晶石型LiMn2 O4正极材料的高温固相制备方法 ,分析合成条件对其性能的影响 ,通过XRD、SEM、ICP等方法 ,研究合成材料的结构、组分及电化学性能。     

Preparation and properties of 4.25Cu-0.75Ni／NiFe2O4 cermet

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     

二次氧化-沉淀法分离LiMn2O4中的锂和锰

以（NH4）2S2O8为氧化剂，采用二次氧化－沉淀法分离LiMn2O4中的锂和锰，分别得到了纯度为98.02%的Li2CO3和99.88%的MnO2，其元素的回收率分别达到88.95%和96.08%。反应的最佳条件为pH值为9-12，体系煮佛10min，沉淀汾离后，母液中的Li^ 用饱和（NH4）2CO3进行沉淀回收。     

尖晶石型LiMn2O4亚微米粉体的制备与结构性能表征

采用无机盐溶胶一凝胶法制备了LiMn2O4尖晶石亚微米粉体,探讨了工艺参数对LiMn2O4化合物形成的影响.采用XRD、SEM、TEM研究了样品的晶体结构及其表面形貌.以其作为光催化剂对水溶性染料(活性艳红K-2G)进行了光催化性能研究,通过吸光度法表征了样品的光催化活性,采用重铬酸钾法研究了降解后染料溶液的化学需氧量,并根据配位场理论探讨了光催化反应的机理.结果表明,800℃热处理的LiMn2O4样品已完全形成尖晶石型晶体结构,晶粒呈长约300～400 nm,宽约100～200 nm,厚约100 nm的短柱状.在可见光辐射下对染料溶液的降解脱色率和总有机碳去除率分别为76.5%和53.3%,是一种新型具有可见光活性的催化材料.     

尖晶石LiMn2O4的容量衰减与性能改进

尖晶石LiMn2O4是制作锂离子电池正极的很有希望的材料。但研究中发现,LiMn2O4在高温下和循环过程中,存在着容量衰减现象。它是目前制约尖晶石LiMn2O4走向商品化生产的关键性因素。综述了LiMn2O4容量衰减的原因和抑制措施,分析出容量衰减的原因,主要包括活性物质的化学稳定性和LiMn2O4结构稳定性两个方面。其中HF造成的锰的溶解是主要原因。采取掺杂富锂核与富锂相结合的措施,可以有效地抑制LiMn2O4的容量衰减,改善其循环性能。     

Thermodynamic study of K2CrO4-KAlO2-KOH-H2O and NaeCrO4-NaALO2-NaOH-H2O systems

Phase diagrams of complex multi-component aqueous chromium salt system are the important theoretical bases for increasing the recovery ratio of chromium and reducing the poisonous waste in the chromate production process. Phase equilibrium of multi-component system has been calculated from the limited known data with thermodynamic models. The phase equilibriums of KOH-K2CrO4-H2O, KOH-KAlO2-H2O, NaOH-Na2CrO4-H2O and NaOH-NaAlO2-H2O systems were calculated with thermodynamic models. The solubilities of Cr and Al was measured in the systems at different temperatures. The results were compared with experimental data and they are consistent with each other. It shows that the lower concentration of KOH (or NaOH) is favorable for thecrystallization of KAlO2 (or NaAlO2) and higher concentration of KOH (or NaOH) is favorable for the crystallization of K2CrO4(Na2CrO4). Therefore, K2CrO4 (or Na2CrO4) can be separated from KAlO2 (or NaAlO2) with controlling the KOH concentration in solutions of KOH-K2CrO4-KAlO2-H2O or NaOH-Na2CrO4-NaAlO2-H2O systems.     

Electrical conductivity of Cu/（10NiO-NiFe2O4） cermet inert anode for aluminum electrolysis

Cu/(10NiO-NiFe2O4) cermets containing mass fractions of Cu of 5%, 10%, 15% and 20% were prepared, and their electrical conductivities were measured at different temperatures. The effects of temperature and content of metal Cu on the electrical conductivity were investigated especially. The results indicate that the metallic phase Cu distributes evenly in 10NiO-NiFe2O4 ceramic matrix. The mechanism of electrical conductivity of Cu/(10NiO-NiFe2O4) cermets obeys the rule of electrical mechanism of semiconductor, the electrical conductivity for cermet containing 5% Cu increases from 2.70 to 20.41 S/cm with temperature increasing from 200 to 900 ℃. The change trend of electrical conductivity with temperature is similar with each other and it increases with increasing temperature and content of metal Cu. At 960 ℃, the electrical conductivity of cermet increases from 2.88 to 82.65 S/cm with the content of metal Cu increasing from 0 to 20%.     

Densification and sintering dynamics of 10NiO-NiFe2O4 composites doped with CaO

The effects of CaO content in the range from 0 to 4.0%, and sintering temperature on the phase composition, relative density and electrical conductivity of 10NiO-NiFe2O4 composites doped with CaO were studied. The results show that there is no change of structure for NiO or NiFe2O4; there is apparent oxygen absorbing and releasing behavior during the heating process in air for 10NiO-NiFe2O4 composites. Introduction of CaO can accelerate the densification of 10NiO-NiFe2O4 composites. The maximum value of relative density is 98.75% for composite doped with 2.0% CaO and sintered at 1 200 ℃, which is beyond about 20% for the undoped composites. The sintering activated energy of sample containing 2% CaO decreases by 15.87 kJ/mol, compared with that of the undoped sample.     

锂离子电池正极材料LiCexNdxMn2-2xO4（x=0～0.018）的Pechini合成及表征

采用X射线衍射仪、电池测试系统等,研究了采用Pechini法合成的锂离子电池正极材料LiCexNdxMn2-2xO4（x=0、0.012、0.014、0.016、0.018）的组织结构、首次充放电性能、循环稳定性能等。结果表明：当稀土元素掺入量较少（x≤0.014）时,样品由尖晶石型LiMn2O4相组成,否则,样品中将出现微量的杂质相（CeO2、Nd2O3）;适量的稀土元素掺杂将使LiMn2O4样品的初始容量减小、循环稳定性能增加。LiCe0.014Nd0.014Mn1.972O4样品具有较好的循环稳定性能,其初始放电容量为124.8 mAh/g,经30次循环充放电后的容量保持在116.3 mAh/g,容量保持率为93.2%。     

Synthesis of MnxZn（1-x）Fe2O4 Nanopartieles by Ball-milling Hydrothermal Method

SMnxZn1-xFe2O4 （x=1,0.9,0.8,0.7,0.6,0.5,0.25,0） nanoparticles were prepared by ball-milling hydrothermal and investigated by X-ray diffraction, DTG and TEM. Nanocrystallite grain size was determined by X-ray linewidth to be from 63 A to 274 A. The thermal properties indicate absorbed water still remain at low temperature, crystalline wate will be decomposed from 230 ℃ to 260 ℃, partial Mn^2＋ will be oxidized near 730 ℃. TEM shows the ferrite particles pocess a spherical morphology and uniform nanosize.     

Synthesis and X—ray Powder Diffraction Characterization of A New Niobate Crystal Ba4Na2VNb9O30

A new niobate crystal Ba4Na2VNb9O30 was synthesized in BaO-Na2O-V2O5-Nb2O5 system for the first time.Its shape, optical properties ,melting point and chemical stability were studied.X-ray powder diffraction study determined that this compound assumes a tetragonal tungsten bronze structure with space group P4bm(100) and lattice parameters a=b=12.4275(2), c=3.970(3). The new compound may be one kin of photorefractive srystals.