层状正极材料LiNi0.5Co0.25Mn0.25O2的结构及电化学行为

采用溶胶-凝胶方法制备了正极材料LiNi_0.5Co_0.25Mn_0.25O₂。XRD、XPS测试结果表明：LiNi_0.5Co_0.25Mn_0.25O₂中阳离子排列有序度较高，层状结构明显；Co、Mn分别以+3、+4价形式存在，Ni以+2、+3价形式存在，且Ni²⁺与Ni³⁺的含量之比约为1∶1。SEM测试结果表明：正极材料LiNi_0.5Co_0.25Mn_0.25O₂结晶粒径较均匀。充放电测试结果表明：与LiCoO₂相比，尽管LiNi_0.5Co_0.25Mn_0.25O₂的放电电压平台较低，但放电容量较高；在恒流充电模式下，当充电截止电压由4.35 V升高至4.75 V时，首次放电容量由179 mAh·g^-1增至201 mAh·g^-1，50次循环后，容量保持率由74.95%增至78.48%；在先恒流再恒压的充电模式下，电池首次放电容量为212 mAh·g^-1，50次循环后，容量保持率提高到87.71%。循环伏安测试表明：在2.80～4.80 V扫描范围内，该正极材料发生Ni²⁺/Ni³⁺，Co³⁺/Co⁴⁺两对电化学反应。EIS测试表明：随着充电截止电压的增大，该正极材料的传荷电阻变小。     

LixNi0.5Co0.5O2的态密度计算及电化学性能研究

>为获得综合性能更好的锂离子二次电池正极材料, 分析了Co掺杂对Li_xNiO₂电化学性能的影响. 采用密度泛函DFT理论对Li_xNiO₂和Li_xNi_0.5Co_0.5O₂的平均放电电压和态密度进行了计算. 同时, 用共沉淀法制备了Li_xNiO₂和Li_xNi_0.5Co_0.5O₂锂离子二次电池正极材料, 并对其进行了XRD结构分析和恒流充放电测试. 实验和计算结果表明: 随锂离子嵌入正极(电池放电), 电池的电压逐渐降低, 材料的态密度峰向低能量方向移动; 与Li_xNiO₂相比, Li_xNi_0.5Co_0.5O₂的电压平台相对较高(当0.25≤x≤0.5), 而且在Li^＋嵌/脱时, Li_xNi_0.5Co_0.5O₂的结构变化相对较小; Co离子的掺入, 减小了NiO₆八面体的畸变度, 使材料的电化学稳定性得以提高. 在钴掺杂镍酸锂体系中, NiO₆和CoO₆具有相互的稳定作用.     

LixNi0.5Co0.5O2的态密度计算及电化学性能研究

>为获得综合性能更好的锂离子二次电池正极材料, 分析了Co掺杂对Li_xNiO₂电化学性能的影响. 采用密度泛函DFT理论对Li_xNiO₂和Li_xNi_0.5Co_0.5O₂的平均放电电压和态密度进行了计算. 同时, 用共沉淀法制备了Li_xNiO₂和Li_xNi_0.5Co_0.5O₂锂离子二次电池正极材料, 并对其进行了XRD结构分析和恒流充放电测试. 实验和计算结果表明: 随锂离子嵌入正极(电池放电), 电池的电压逐渐降低, 材料的态密度峰向低能量方向移动; 与Li_xNiO₂相比, Li_xNi_0.5Co_0.5O₂的电压平台相对较高(当0.25≤x≤0.5), 而且在Li^＋嵌/脱时, Li_xNi_0.5Co_0.5O₂的结构变化相对较小; Co离子的掺入, 减小了NiO₆八面体的畸变度, 使材料的电化学稳定性得以提高. 在钴掺杂镍酸锂体系中, NiO₆和CoO₆具有相互的稳定作用.     

钴掺杂镍酸锂的密度泛函计算及电化学性能

LiNiO₂ and LiNi_0.5Co_0.5O₂ cathodes for lithium-ion batteries were synthesized with co-precipitation method and their electrochemical property was characterized by Galvanostatic cycling. Meanwhile, plane-wave pseudopotential method base on density functional theory was used to calculate average cell voltage and the electronic structure of LiNiO₂ and LiNi_0.5Co_0.5O₂. The experimental and computational results showed that the average voltage of the cell decreased as Li-ion intercalated to the host cathode (discharge); The potential of Li_xNi_0.5Co_0.5O₂ was higher than that of Li_xNiO₂ (when 0.25≤x≤0.5). The calculations also indicated that the distortion of the NiO₆ octahedron in Li_xNiO₂ was decreased by Co-doped. During the Li-ion intercalates to the host cathode, the micro-structures of NiO₆ and CoO₆ in the Li_xNi_0.5Co_0.5O₂ were mutually stabilized, the Jahn-Teller effect was weakened and the electrochemical properties of the materials were enhanced.     

以α型氢氧化物前驱体制备LiNi0.8Co0.15Al0.05O2及其电化学性能

本文采用球形Al/Co部分取代α型Ni(OH)₂为前驱体成功制备了锂离子电池正极材料LiNi_0.8Co_0.15Al_0.05O₂。首先采用氢氧化钠与碳酸钠为沉淀剂合成出Al/Co部分取代α型Ni(OH)₂,然后将之与LiOH·H₂O混合,最后在氧气气氛中不同温度下热处理8 h,即可得到球形LiNi_0.8Co_0.15Al_0.05O₂材料。X射线衍射结果表明,LiNi_0.8Co_0.15Al_0.05O₂材料为α-NaFeO₂相。扫描电镜结果表明,材料颗粒形貌为球形。热重分析结果表明合成LiNi_0.8Co_0.15Al_0.05O₂的主反应温度在700～750 ℃之间。振实密度测试结果表明, 750 ℃下制备的LiNi_0.8Co_0.15Al_0.05O₂材料可达2.2 g·cm^-3。恒流充放电结果表明,该材料在0.5 mA·cm^-2电流密度下,在3.0～4.3 V间的首次充电容量可达210.3 mAh·g^-1,首次放电容量为179.7 mAh·g^-1,充放电效率为85.4%。与采用以β-Ni_0.85Co_0.15(OH)₂为前驱体合成的LiNi_0.85Co_0.15O₂和Al掺杂的LiNi_0.8Co_0.15Al_0.05O₂相比,尽管其首次放电容量与放电效率都有所降低,但循环性能有所提高,50周期后容量仍为初始容量的89.5％。研究表明,以球形Al/Co部分取代α型Ni(OH)₂作为前驱体为球形氧化镍钴铝锂材料的制备提供了一条新的途径。     

新型中温固体氧化物燃料电池阴极材料Fe掺杂Sm0.5Sr0.5CoO3性能研究

本文系统研究了新型中温固体氧化物燃料电池(IT-SOFC)阴极材料Sm_0.5Sr_0.5Co_1-xFe_xO_3－δ(SSCF)的晶体结构、热膨胀系数、导电率及电化学性能。固相合成的Sm_0.5Sr_0.5Co_1-xFe_xO_3－δ化合物均为单相材料，随着掺Fe量的不同，SSCF的晶体结构发生变化，在0≤x≤0.4时，SSCF为正交晶系钙钛矿结构，在0.5≤x≤0.9时，SSCF为立方晶系钙钛矿结构。Fe掺杂可以显著的改善Sm_0.5Sr_0.5CoO₃的热膨胀系数，随着Fe含量的增加，热膨胀系数减小。在800℃下，SSCF导电率均大于100 S·cm^-1。随着Fe含量的增加，极化电阻增大；含量x=0.4时，极化电阻达到最大值；之后，随Fe含量的增加，极化电阻减小，在700～800 ℃时，Sm_0.5Sr_0.5Co_0.2Fe_0.8O_3－δ表现出了良好的氧催化活性。     

锂离子电池正极材料LiNi0.75-xCoxMn0.25O2的合成及电化学性能研究

以LiOH·H₂O、Ni(OAc)₂·4H₂O、Co(OAc)₂·4H₂O和MnO₂为原料，在水热反应釜中预处理，然后进行高温固相反应，合成了一系列锂镍钴锰氧化物LiNi_0.75-xCo_xMn_0.25O₂(x=0.05,0.10,0.15,0.20,0.25)。通过X射线衍射(XRD)、扫描电子显微镜（SEM）和电化学性能测试对所得样品的结构、形貌、粒径及电化学性能进行了表征。结果表明，当x=0.20时，所合成的正极材料具有很好的α-NaFeO₂型层状晶体结构，晶胞参数a=0.286 1 nm，c=1.416 4 nm， V=0.100 4 nm³，以50 mA·g^-1的电流密度在3～4.3 V(vs Li/Li⁺)充放电时，首次放电比容量达172.5 mAh·g^-1，首次放电效率高达90.9%，30个循环后其放电比容量依然保持在161.1 mAh·g^-1。     

xLi2MnO3-(1-x)LiNi0.7Co0.3O2的低温燃烧合成及电化学性能研究

采用低温燃烧法合成了锂离子电池正极材料xLi₂MnO₃-(1-x)LiNi_0.7Co_0.3O₂,对合成产物的结构、形貌和电化学性能进行了系统的研究, 通过单因素试验对合成条件和材料的组成进行了优化。结果表明:采用低温燃烧法合成的富锂层状正极材料具有α-NaFeO₂型层状结构、球状形貌和良好的电化学性能;其最佳合成条件为:回火温度850℃, 回火时间20 h;Li₂MnO₃的最佳配比为x=0.7.在此条件下合成的0.7Li₂MnO₃-0.3LiNi_0.7Co_0.3O₂,最高放电比容量达到263.1 mAh·g^-1,并具有良好的循环性能和倍率性能。     

Li2CO3、NiO和电解MnO2合成高容量LiNi0.5Mn1.5O4及其表征

Well-developed crystalline LiNi_0.5Mn_1.5O₄ was prepared by solid-state reaction using Li₂CO₃, NiO and electrolytic MnO₂ at high heating and cooling rate. X-ray diffraction (XRD) patterns and scanning electron microscopic (SEM) images showed that LiNi_0.5Mn_1.5O₄ synthesized at 900 ℃ and 950 ℃ had cubic spinel structure with clearly defined shape. LiNi_0.5Mn_1.5O₄ spinel phase decomposed at 1 000 ℃ accompanying with structural and morphological degradation. TG measurement revealed that the weight loss during heating process could be mostly gained in cooling process, and the upward tendency of weight loss during heating process decreased, while that of irreversible weight loss rapidly increased with the increase of temperature. LiNi_0.5Mn_1.5O₄ powders prepared at 900 ℃ for 12 h delivered the maximum discharge capacity of 134 mAh·g^-1 with good cyclic performance at 2/7 C. In addition, by adjusting the calcination time at 900 ℃, the capacity and cycling performance of LiNi_0.5Mn_1.5O₄ were further enhanced.     

纳米结晶体Ni0.5Zn0.5Fe2O4对高氯酸铵热行为及分解反应动力学的影响

采用差示扫描量热法(DSC)、热重和微分热重(TG-DTG)及固相原位反应池/快速扫描傅立叶变换红外联用技术(hyphenated in situ thermolysis/RSFTIR)研究了纳米结晶体Ni_0.5Zn_0.5Fe₂O₄与高氯酸铵(AP)组成的混合物的热行为和分解反应动力学。结果表明：Ni_0.5Zn_0.5Fe₂O₄使得AP的低、高温分解放热峰温分别提前17.44 K和27.74 K,并使得对应的分解热分别增加3.7 J·g^-1和193.7 J·g^-1。Ni_0.5Zn_0.5Fe₂O₄并不影响AP的晶转温度和晶转热。Ni_0.5Zn_0.5Fe₂O₄使得AP的TG曲线出现3个阶段,并使得后2个失重阶段的初始和终止温度都有所提前。凝聚相分解产物分析表明Ni_0.5Zn_0.5Fe₂O₄加速了凝聚相AP的分解及氨气的释放。含Ni_0.5Zn_0.5Fe₂O₄的AP的高温分解反应的动力学参数E_a=238.88 kJ·mol^-1,A=1018.59 s^-1,动力学方程可表示为dα/dt=10^18.99(1-α)[-ln(1-α)]^3/5e^-2.87×104T。始点温度(T_e)和峰顶温度(T_p)计算得出AP的热爆炸临界温度值分别为:574.83 K和595.41 K。分解反应的活化熵(ΔS^≠)、活化焓(ΔH^≠)和活化能(ΔG^≠)分别为:109.61 J·mol^-1·K^-1、236.49 kJ·mol^-1及172.58 kJ·mol^-1。     

Eu0.5RE0.5Fe0.5Mn0.5O3的57Fe Msosbauer谱研究

利用固相反应合成了Eu0.5RE0.5Fe0.5Mn0.5O3(RE=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Y)等化合物。测量了其XRD谱及57FeMssbauer谱。实验发现,随着RE原子序数的增加,样品的晶胞体积减小,Fe在化合物中处于Fe3+的高自旋状态,57Fe的四极裂矩与样品的畸变参数D成线性关系。     

水热法合成K0.5Bi0.5TiO3纳米陶瓷粉体

K_0.5Bi_0.5TiO₃(KBT)nanocrystalline particles were hydrothermally synthesized from Bi(NO₃)₃·5H₂O, TiO₂ and KOH. The crystal phase, chemical composition and microstructure were characterized by XRD, XRF, Raman scattering spectroscopy and TEM. The results indicated that the products were pure perovskite structured K_0.5Bi_0.5TiO₃ with chemical stoichiometry and perovskite structure. The TEM observation revealed that the particles possessed a feature of cubic shape and a nano-scale of about 40 nm. The KBT ceramics sintered at 1 040 ℃ from hydrothermal powders show higher density and better electric properties than that prepared by a solid-state reaction method.     

针状纳米Ni_(0.5)Zn_(0.5)Fe_2O_4的沉淀/凝胶-溶胶法制备及性能

以FeCl2、Zn(NO3)2、Ni(NO3)2和NaOH为原料,借助针状α-FeOOH做为中间体,用共沉淀法和柠檬酸法相结合的方法制得掺有镍和锌的针状纳米α-FeOOH,在其表面包裹镍和锌的柠檬酸配合物后,经热处理制得了针状的纳米Ni0.5Zn0.5Fe2O4,并通过控制共沉淀法过程中镍和锌的掺入量,有效地控制了针状纳米Ni0.5Zn0.5Fe2O4的粒径和长径比。利用XRD、TEM对样品的物相﹑形状和粒径进行表征。结果表明:共沉淀过程中Ni和Zn的掺入量对制备的Ni0.5Zn0.5Fe2O4的形状有重要的影响,随着镍和锌的掺入量的增加,制得的针状纳米Ni0.5Zn0.5Fe2O4的直径逐渐减小,长径比先增加后减小,当nNi∶nZn∶nFe=0.3∶0.3∶2时,样品的长径比达到最大为20左右。利用振荡样品磁强计(VSM)对样品进行磁性能研究,结果表明针状Ni0.5Zn0.5Fe2O4矫顽力主要取决于样品的各向异性,随着样品的长径比增加,各向异性增加,矫顽力增加。随温度的提高,晶体结构趋于完善,样品的矫顽力下降。     

Ultrasonic-assisted synthesis of PMMA/Ni0.5Zn0.5Fe2O4 nanocomposite in mixed surfactant system

PMMA/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite with superparamagnetic behavior was synthesized by in situ emulsion polymerization of methylmethacrylate (MMA) monomer in the presence of Ni_0.5Zn_0.5Fe₂O₄ colloidal suspension assisted by ultrasonic irradiation. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). XRD and FT-IR spectra confirmed the formation of PMMA/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite. TEM images showed that Ni_0.5Zn_0.5Fe₂O₄ nanoparticles with the particle sizes of about 12 nm were well dispersed in the polymer matrix. The nanocomposite at room temperature exhibited superparamagnetic behavior under applied magnetic field. The formation mechanism of PMMA/Ni_0.5Zn_0.5Fe₂O₄ nanocomposite was proposed as well.     

Unusual oxidation states give reversible room temperature magnetocaloric effect on perovskite-related oxides SrFe0.5Co0.5O3

The magnetic properties and the magnetocaloric effect are presented for the perovskite-related oxide SrFe_0.5Co_0.5O₃ prepared using electrochemical oxidation. SrFe_0.5Co_0.5O₃ exhibits a second order paramagnetic-ferromagnetic transition close to room temperature (T_C=330 K). The maximal magnetic entropy change ΔS_M^Max , the maximal adiabatic temperature change ΔT_ad and the refrigerant capacity are found to be equal to respectively 4.0 J/kgK, 1.8 K and 258 J/kg while raising the B-field change from 0 to 5 T.     

Structural evolution of Na0.5K0.5NbO3 at high temperatures

Changes in structure and dielectric properties at elevated temperatures have been investigated on single-crystals of sodium potassium niobate, Na_0.5K_0.5NbO₃, grown by the flux method. Single-crystal X-ray diffraction studies revealed that the crystals underwent orthorhombic-tetragonal and tetragonal-cubic phase transitions at 465 and 671 K during heating and 446 and 666 K during cooling, respectively. Both transitions were accompanied by volumetric discontinuities of collapse upon heating and expansion upon cooling, suggesting that the transitions were of the first order. The coordination numbers of an Nb showed a decreasing tendency with decreasing temperature, i.e., 6 in cubic, 5+1 in tetragonal and 4+2 in orthorhombic. An Na atom occupied a slightly different position from the K atom in 12-fold coordination, resulting in fewer coordination numbers of 8+4 in cubic and tetragonal and 7+5 in orthorhombic. The spontaneous polarisation (P_s) estimated from the atom positions and formal charges were approximately 0.29 C m⁻² in orthorhombic and 0.18 C m⁻² in tetragonal. The contribution of the alkaline oxide components to P_s was estimated to be approximately 15% in both ferroelectric forms. The temperature-induced transitions were also confirmed through the dielectric constant and dielectric loss at various frequencies and the differential scanning calorimetry.     

CuO/Ti0.5Zr0.5O2催化剂对NO+CO反应的催化作用

环境治理是当今社会面临的一大主要问题。目前,城市空气污染日趋严重,特别是工厂和汽车排放的大量未燃烧的烃类、CO、NOx是主要的空气污染物。其中,氮氧化物(NOx)排放状况尤其严重,它的排放会给环境和人们生活带来严重危害,因此,如何有效地消除NOx已成为目前环境保护中一个非常     

Sol-Gel Template Synthesis of Highly Ordered LiCo0.5Mn0.5O2 Nanowire Arrays and Their Structural Properties

Highly ordered LiCo_0.5Mn_0.5O₂ nanowire arrays were prepared using porous anodic aluminum oxide (AAO) template from sol-gel solution containing Li(CH₃COO), Co(CH₃COO)₂, and Mn(CH₃COO)₂. Electron microscope results showed that uniform length and diameter of LiCo_0.5Mn_0.5O₂ nanowires were obtained, and the length and diameter of LiCo_0.5Mn_0.5O₂ nanowires are dependent on the pore diameter and the thickness of the applied AAO template. X-ray diffraction and electron diffraction pattern investigations demonstrate that LiCo_0.5Mn_0.5O₂ nanowires are a layered structure of LiCo_0.5Mn_0.5O₂ crystal. X-ray photoelectron spectroscopy analysis indicates that the most closely resembling stoichiometric layered LiCo_0.5Mn_0.5O₂ material has been obtained.     

Ce0.5Zr0.5O2修饰的Ni/SiC、Fe/SiC和Co/SiC催化燃烧甲烷性能

以铈锆固溶体（Ce_0.5Zr_0.5O₂）修饰的高比表面积SiC为载体,采用两步浸渍法制备了Ni、Fe和Co基催化剂,研究了其在煤层气催化燃烧脱氧中的催化活性和稳定性. 利用X射线衍射（XRD）、X射线光电子能谱（XPS）、电感耦合等离子体质谱（ICP-MS）、高分辨透射电子显微镜（HRTEM）、比表面积（BET）、热重分析（TGA）和H₂程序升温还原（H₂-TPR）对催化剂进行了表征. 分析结果表明,Ni、Fe和Co部分进入Ce_0.5Zr_0.5O₂固溶体晶格内部,导致催化剂体相形成更多的缺陷;同时Ce_0.5Zr_0.5O₂固溶体有助于加速金属氧化物和金属之间氧化还原过程的进行,促进了氧吸附、传输和对甲烷的活化. 另外,SiC和Ce_0.5Zr_0.5O₂固熔体良好的抗积碳性能,有效避免了催化剂在富甲烷反应气氛中因积碳而失活,从而使三种催化剂均具有优良的催化燃烧脱氧活性和稳定性. 其中,Co/Ce_0.5Zr_0.5O₂/SiC活性最高,可在320 ℃活化催化甲烷,并在410 ℃实现完全脱氧.     

碳包覆LiFe0.5Co0.5PO4固溶体正极材料的制备及其电化学性能

分别以四水磷酸铁（FePO₄·4H₂O）和二水草酸亚铁（FeC₂O₄·2H₂O）为铁源,采用简单便捷的流变相法制备了碳包覆LiFe_0.5Co_0.5PO₄固溶体材料（LiFe_0.5Co_0.5PO₄/C,简称为LFCP/C）。采用X射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）、恒流充放电等测试手段对复合材料的物相、形貌结构和电化学性能进行了表征和测试。结果表明,2种铁源得到的材料均为橄榄石晶型结构且结晶度良好,二者在颗粒尺寸分布、碳包覆效果和电化学性能方面具有显著的差别。用作锂离子电池正极材料时,以FeC₂O₄·2H₂O为原料得到的LFCP/C具有更优异的电性能：在2.5~5.0 V电压范围内,0.1C倍率下（1C=150 mA·g^-1）,放电比容量为137.5 mAh·g^-1,在10C仍具有57.6 mAh·g^-1的放电比容量;0.5C循环100次后容量仍保持78.1%。该样品更佳的电化学性能主要得益于其更小的平均颗粒尺寸,更高的比表面积和理想的碳包覆效果。