无锂助熔剂B_2O_3对Li_(1.3)Al_(0.3)Ti_(1.7)(PO_4)_3固体电解质离子电导率的影响

采用固相法制备锂离子电池用固体电解质磷酸钛锂铝Li_(1.3)Al_(0.3)Ti_(1.7)(PO_4)_3(LATP),研究了不同烧结温度以及助熔剂对LATP固体电解质离子电导率的影响.采用X射线衍射、能谱分析、扫描电镜和交流阻抗等方法,研究样品的结构特征、元素含量、形貌特征以及离子导电性能.结果表明,在900?C烧结可以获得结构致密、离子电导率较高的纯相LATP陶瓷固体电解质.与添加助熔剂Li BO2的样品进行对比实验发现,采用B_2O_3代替LiBO_2作为助熔剂也可以提高烧结样品的离子电导率,并且电解质的离子电导率随助熔剂添加量的增大,先增大后减小,其中添加质量百分比为2%的B_2O_3的样品具有最高的室温离子电导率,为1.61×10~(-3)S/cm.     

An electrochemical investigation of Li intercalation in the sol-gel LiMn2O4 spinel oxide

An alternative approach for obtaining the LiMn₂O₄ spinel phase is provided by the use of the sol-gel method in aqueous solution. The main electrochemical properties of the sol-gel LiMn₂O₄ phase are reported. In addition to chronopotentiometric and voltammetric experiments, the kinetics of the electrochemical insertion–extraction of lithium in Li_xMn₂O₄ (0.25<x<1) has been investigated using ac impedance spectroscopy. The strong variation of the chemical diffusion coefficient D_Li vs x, in the range 10⁻⁸–10⁻¹¹ cm² s⁻¹ (D_Li is found to be maximum for x=0.55) is critically discussed.     

Pressure dependence of the thermal stability in LiMn2O4

Structural stability in terms of the decomposition temperature in LiMn₂O₄ was systematically investigated by a series of high-temperature and high-pressure experiments.LiMn₂O₄ was found to have structural stability up to 5 GPa at room temperature.Under ambient pressure,the compound decomposed at 1300℃.The decomposition temperature decreased with increasing pressure,yielding more complex decomposed products.Below the decomposition temperature,the crystal structure of LiMn₂O₄ varied with pressure.The presented results in this study offer new insights into the thermal and pressure stability of LiMn₂O₄ materials as a cathode for lithium-ion batteries that can operate under extreme conditions.Therefore,these findings may serve as a useful guide for future work for improving lithium-ion batteries.     

Enhanced ionic conductivity in LAGP/LATP composite electrolyte

Nasicon materials(sodium superionic conductors) such as Li_(1.5)Al_(0.5)Ge_(1.5)(PO_4)_3(LAGP) and Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3(LATP) have been considered as important solid electrolytes due to their high ionic conductivity and chemical stability.Compared to LAGP, LATP has higher bulk conductivity around 10~(-3) S/cm at room temperature; however, the apparent grain boundary conductivity is almost two orders of magnitude lower than the bulk, while LAGP has similar bulk and grain boundary conductivity around the order of 10~(-4) S/cm. To make full use of the advantages of the two electrolytes, pure phase Li_(1.5)Al_(0.5)Ge_(1.5)(PO_4)_3 and Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3 were synthesized through solid state reaction, a series of composite electrolytes consisting of LAGP and LATP with different weight ratios were designed. XRD and variable temperature AC impedance spectra were carried out to clarify the crystal structure and the ion transport properties of the composite electrolytes. The results indicate that the composite electrolyte with the LATP/LAGP weight ratio of 80:20 achieved the highest bulk conductivity which shall be due to the formation of solid solution phase Li1.42 Al0.42 Ge0.3 Ti1.28(PO4)3, while the highest grain boundary conductivity appeared at the LATP/LAGP weight ratio of 20:80 which may be due to the excellent interfacial phase between Li_(1+x)Al_xGe_yTi_(2-x-y)(PO_4)_3/LATP. All the composite electrolytes demonstrated higher total conductivity than the pure LAGP and LATP, which highlights the importance of heterogeneous interface on regulating the ion transport properties.     

流延法制备高锂离子电导Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3固态电解质及其环氧树脂改性

以溶胶凝胶法合成的高纯Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3(LATP)纳米晶体粉末为原料,通过流延法成膜,在950℃下煅烧5 h合成LATP固态电解质片;对其进行环氧树脂改性后,能量色散X射线光谱元素图像表明环氧树脂完全浸入LATP内部,可以有效防止水渗透.研究发现流延法合成的LATP固态电解质在25℃?C时电导率高达8.70×10~(-4)S·cm~(-1)、活化能为0.36 eV、相对密度为89.5%.经过环氧树脂改性后电导率仍高达3.35×10-4S·cm-1、活化能为0.34 e V、相对密度为93.0%.高电导隔水的环氧树脂改性LATP固态电解质可作为锂金属保护薄膜用于新型高比容量电池.     

溶剂热制备锂电池负极材料CNT-ZnFe2O4及其电化学性能

为了改善锂离子电池负极材料ZnFe₂O₄导电性差和循环寿命低的缺点,利用溶剂热反应方法制备了ZnFe₂O₄,并通过复合碳纳米管对ZnFe₂O₄进行改性。充放电测试结果表明：经过50次充放电后,碳纳米管复合改性后的ZnFe₂O₄容量保持在860 mA·h·g^-1,具有较好的循环稳定性。碳纳米管具有良好的导电性与导热性,改善了ZnFe₂O₄导电性差的缺点。     

Electron density distribution of LiMn_2O_4 cathode investigated by synchrotron powder x-ray diffraction

Electron density plays an important role in determining the properties of functional materials. Revealing the electron density distribution experimentally in real space can help to tune the properties of materials. Spinel Li Mn2 O4 is one of the most promising cathode candidates because of its high voltage, low cost, and non-toxicity, but suffers severe capacity fading during electrochemical cycling due to the Mn dissolution. Real-space measurement of electron distribution of Li Mn2 O4 experimentally can provide direct evaluation on the strength of Mn–O bond and give an explanation of the structure stability.Here, through high energy synchrotron powder x-ray diffraction(SPXRD), accurate electron density distribution in spinel Li Mn2 O4 has been investigated based on the multipole model. The electron accumulation between Mn and O atoms in deformation density map indicates the shared interaction of Mn–O bond. The quantitative topological analysis at bond critical points shows that the Mn–O bond is relatively weak covalent interaction due to the oxygen loss. These findings suggest that oxygen stoichiometry is the key factor for preventing the Mn dissolution and capacity fading.     

电池正极材料中Li+运动特性的7Li NMR研究

利用变温⁷LiNMR实验对Li-电池正极材料LiMn₂O₄和LiCoO₂中Li⁺的运动特性进行了研究,结果表明,随实验温度的提高,LiMn₂O₄的⁷LiNMR谱线窄化,表明其中Li⁺迁移能力增加,而LiCoO₂的谱线无变化.此外随温度提高,LiMn₂O₄的⁷Li的T₁变短,而LiCoO₂的T₁变长,产生这种不同变化趋势的原因在于LiMn₂O₄和LiCoO₂晶相结构的差异造成其中Li⁺迁移能力的差别,它们各自的相关时间τ_c使⁷Li核的T₁分别位于T₁-τ_c曲线极小点两侧.     

助熔剂BaF2在制备BaSi2O5:Pb2+过程中的机理

采用高温固相合成法制备出BaSi₂O₅:Pb²⁺荧光体。考察了BaF₂的加入量对产物紫外发射强度的影响。用差示扫描量热分析,X射线衍射,光致发光光谱研究了掺入助熔剂BaF₂后BaSi₂O₅:Pb²⁺紫外发射强度显著增强的机理,并从热力学角度对实验结果作了分析。研究表明少量BaF₂的掺入加快了反应速度;降低了BaSi₂O₅:Pb²⁺形成温度,在高温下与SiO₂反应生成SiF₄气体,生成的SiF₄再与BaCO₃反应形成结晶良好的BaSi₂O₅:Pb²⁺荧光体。     

In situ formed FeS2@CoS cathode for long cycling life lithium-ion battery

Pyrite FeS₂ exhibits an ultrahigh energy density (1671 W·h·kg^-1, for the reaction of FeS₂+4Li=Fe+2Li₂S) in secondary lithium-ion batteries, but its poor cycling stability, huge volume expansion, the shuttle effect of polysulfides, and slow kinetic properties limit its practical application. In this work, we synthesize a composite structure material CoS on FeS₂ surface (FeS_x@CoS, 1 < x ≤ 2) by using a cobalt-containing MOF to improve its cycle stability. It is found that CoS inhibits the side reactions and adsorbs polysulfides. As a result, the modified FeS₂ shows a higher discharge capacity of 577 mA·h·g^-1 (919 W·h·kg^-1) after 60 cycles than 484 mA·h·g^-1 (778 W·h·kg^-1) of bare pyrite FeS₂. This efficient strategy provides a valuable step toward the realization of high cycling stability FeS₂ cathode materials for secondary lithium-ion batteries and enriches the basic understanding of the influence of FeS₂ interfacial stability on its electrochemical performances.     

LiGd(W_yMo_(1-y))_2O_(8-x/2)F_x∶Eu~(3+)红色荧光粉的制备和发光特性

采用高温固相法制备了LiGd(W_yMo_(1-y))_2O_(8-x/2)F_x∶0.4Eu~(3+)(x=0~1,y=0~1)系列白光LED用红色荧光粉。通过扫描电子显微镜、X射线衍射仪、红外光谱仪、荧光光谱仪对荧光粉的形貌、结构、光学性能进行了表征。结果表明,Eu~(3+)、F-和WO_4~(2-)的掺杂没有改变LiGd(MoO_4)_2的四方晶系白钨矿结构;F~-和WO_4~(2-)最佳掺杂量分别为x=0.6,y=0.4。在396 nm激发下,LiGd(W_(0.4)Mo_(0.6))_2O_(7.7)F_(0.6)∶0.4Eu~(3+)的发光强度比未掺杂样品提高了60%,量子效率可达66.23%。当温度升高至100℃时,样品的发射强度降为25℃时的76.6%。在460 nm激发下,样品的最强窄带发射峰位于617 nm处,归属于~5D_0→~7F_2跃迁,色坐标为(0.649 9,0.346 3)。5D0能级的荧光寿命曲线遵循单指数规律衰减,随着F-掺杂浓度的增加,5D0能级的荧光寿命不断增加,归因于低声子能量的F-掺入有效减小了能量的无辐射跃迁概率。所制备的LiGd(W_(0.4)Mo_(0.6))_2O_(7.7)F_(0.6)∶0.4Eu~(3+)荧光粉有望应用于白光LED。     

SrAl2O4∶Eu2+,Dy3+长余辉发光材料的喷雾热解制备及其表征

采用喷雾热解两段法制备了SrAl₂O₄∶Eu²⁺ ,Dy³⁺长余辉发光材料,并利用XRD、SEM、荧光长余辉亮度测试等方法分析了不同制备工艺条件下SrAl₂O₄∶Eu²⁺ ,Dy³⁺发光材料的结构、形貌以及发光性能的变化。结果表明:采用喷雾热解两段法可制备出球形SrAl₂O₄∶Eu²⁺ ,Dy³⁺长余辉发光材料,SrAl₂O₄∶Eu²⁺ ,Dy³⁺的晶体结构与α-SrAl₂O₄磷石英晶体结构相同。热解温度、还原温度、添加剂对产物的形貌、粒度分布、发光性能有较大影响。较之高温固相法,喷雾热解法制备的SrAl₂O₄∶Eu²⁺ ,Dy³⁺具有发光性能好、形貌好、粒度分布窄等优点。     

模拟核素固化体Gd2Zr2-xCexO7(0≤ x≤ 2.0)的物相及化学稳定性研究

为研究钆锆烧绿石固化Pu(Ⅳ)的相变化情况及化学稳定性, 以Gd₂O₃, ZrO₂为原料, Ce(Ⅳ)作为Pu(Ⅳ)的模拟替代物质, 采用冷压热烧结的方法制备出Gd₂Zr_2-xCe_xO₇(0≤ x≤ 2.0)系列样品. 分别在40 °C和70 °C的合成海水中, 对固化体的长期浸出性能进行研究. 借助粉末X射线衍射仪对所制备样品的物相信息进行收集, 利用等离子体质谱仪对固化体的浸出浓度数据进行分析. 研究结果表明: 当x ≤0.08时, 固化体保持为烧绿石相; 当x>0.08时, 固化体转变为具有缺陷的萤石型结构相. 固化体中Gd³⁺, Zr⁴⁺和Ce⁴⁺在合成海水中, 随着浸泡时间的延长浸出浓度逐渐上升, 70 °C下的浸出浓度高于40 °C下的浸出浓度. 在42 d时, 固化体中Gd³⁺的最大浸出浓度在0.032 μg·ml^-1以下, Zr⁴⁺的最大浸出浓度在0.003 μg·ml^-1以下; Ce⁴⁺的最大浸出浓度在0.032 μg·ml^-1以下.     

Ho,Yb: Tb3Ga5O12纳米粉体制备及发光性能研究

以Tb₄O₇和Ga₂O₃(化学计量比为3: 5)、Ho₂O₃、Yb₂O₃为原料,其中Yb³⁺的掺杂浓度为8at.%,Ho³⁺的掺杂浓度分别为0.5at.%、1at.%、1.5at.%、2.0at.%,以碳酸氢铵为沉淀剂,在1 200 ℃下烧结10 h得到了Ho,Yb: Tb₃Ga₅O₁₂(Ho,Yb: TGG)纳米粉体。对样品进行了XRD物相分析、热重-差热分析、红外光谱分析以及扫描电镜分析、上转换发射光谱分析。实验结果表明,温度为1 200 ℃下样品平均晶粒尺寸为38.10 nm。在泵浦源为980 nm激发下,Ho³⁺掺杂浓度为1.5at.%,Yb³⁺掺杂浓度为8at.%时,在红、绿、蓝波段范围内出现了明显的上转换发光现象,并对其形成机理进行了讨论。分析认为,Ho³⁺由激发态⁵S₂,⁵F₄向基态⁵I₈跃迁,实现了绿光输出,而Ho³⁺由激发态⁵F₅和⁵F₃向基态⁵I₈跃迁,分别实现了红光和蓝光输出。     

Improvement of electrochemical properties of the spinel LiMn2O4 using a Cr dopant effect

A series of LiCr_xMn_2−xO₄ spinels were synthesised by the Pechini method which enables dopant Cr ions to distribute at Mn sites homogeneously. Neutron diffraction and EDS analysis confirmed that Cr ions do occupy 16d sites (octahedral intestial) evenly in the spinel structure. The Cr dopant effect improves the cyclability of spinel LiMn₂O₄ electrodes and decreases the self-discharge rate substantially. Cyclic voltammetry and AC impedance spectroscopy were employed to characterise the reactions of lithium insertion into and extraction from LiCr_xMn_2−xO₄ electrodes. It was found that a thicker surface layer was formed on the surface of the pure LiMn₂O₄ electrode than on the LiMn₂O₄ electrode.     

Coulometric titrations of electrolytes in water by a solid state ionic device using Nafion and Tosflex membranes

A solid state ionic device to titrate electrolytes in water was produced, and the performance of the device was examined. The device named the coulometric titration apparatus is a three-component electrochemical cell like an electrodialyzer. The central component, the analyzing room, is a container of the sample solution. The sample solution, 10⁻¹ M H₂SO₄, NaOH, Na₂SO₄, or 10⁻⁷–10⁻² M Na₂SO₄, is separated from the cathode and the anode room solutions, 10⁻² M H₂SO₄, NaOH, or Na₂SO₄, by Nafion-117 and Tosflex IE-SF34 membranes working as the anion and the cation blocking electrodes, respectively. The quantity of electricity to extract whole electrolytes in the sample solution is evaluated from the peak area of the titration curve. The sample concentration is successfully determined by the calibration curve method, with the quantity of electricity and the sample volume (6 ml) in the range from 10⁻¹ to 10⁻⁵ M.     

白光LED用蓝绿色荧光粉Sr1-xBax Al2O4:Eu2+的发光性质

采用高温固相法在还原气氛中合成Sr1-xBaxAl2 O4:Eu2+荧光材料.XRD显示,当钡掺杂量x＜0.4时,对应样品主要为单斜SrAl2 O4晶体结构;当x≥0.4时,对应样品主要为简单六方BaAl2 O4晶体结构.在360nn激发下,样品的发射光谱随x的增加由单一的绿光发射(λmax=516nm)逐渐转变为蓝绿...     

Polymer electrolyte plasticized with PEG-borate ester having high ionic conductivity and thermal stability

We have focused on the PEG-borate ester as a new type of plasticizer for solid polymer electrolyte composed of poly(ethyleneglycol) methacrylate (PEGMA) and lithium bis-trifluoromethanesulfonimide (LiTFSI). The PEG-borate ester shows good thermal stability and high flash point. Ionic conductivity of the polymer electrolyte increases with increasing amount of the PEG-borate ester and exhibits values greater than 10⁻⁴ S cm⁻¹ at 30 °C and 10⁻³ S cm⁻¹ at 60 °C. Furthermore, PEG-borate ester has three EO chains whose lengths are variable, and various ionic conductivities are expected to depend on EO chain length. As a result, polymer electrolyte containing the PEG-borate ester whose EO chain length is n=3 shows highest ionic conductivity. Furthermore, polymer electrolytes containing PEG-borate esters show excellent thermal and electrochemical stability. The electrolytes are thermally stable up to 300 °C and electrochemically up to 4.5 V vs. Li⁺/Li.     

Zn2SiO4(ZnB2O4):Mn2+,Sm3+发光材料的制备与荧光性能

使用高温固相法首次合成了Zn2SiO4(ZnB2O4):Mn2+,Sm3+发光材料,探讨了烧结温度、Sm2+含量对样品荧光性能的影响.利用X射线衍射(XRD)、荧光光谱等分析手段对Zn2SiO4(ZnB2O4):Mn2+,Sm3+粉末的结构、发光性能进行了表征.确定了该荧光材料的最佳合成条件,离子掺杂浓度等.实验结果表...     

氧化铟/聚(3,4-乙烯二氧噻吩)复合材料的微结构及其热电性能研究

通过化学氧化合成的方法将纳米In_2O_3复合到聚(3,4-乙烯二氧噻吩)(PEDOT)中得到In_2O_3/PEDOT复合材料.利用X射线衍射、红外光谱、电子显微镜及正电子湮没等方法对复合材料的微观结构进行了系统研究,同时对材料的热学和电学性能进行了表征.结果表明,当In_2O_3的含量在22 wt%以下时,In_2O_3能很好地分散到PEDOT基体中.热电性能测试则显示In_2O_3/PEDOT复合材料的导电率随In_2O_3含量增加明显增大.纯PEDOT的电导率仅为7.5 S/m,而含12.3 wt%In_2O_3的复合材料的电导率达到25.75 S/m.该复合材料相应的功率因子(68.8×10~(-4)μW/m·K~2)相对于纯的PEDOT(14.5×10~(-4)μW/m·K~2)提高了近4倍.另外,复合材料的热导率相对于纯PEDOT也有所降低.最终复合材料的热电优值由0.015×10~(-4)提高到了0.073×10~(-4).结果表明,In_2O_3/PEDOT复合材料的热电性能相对于纯PEDOT的热电性能得到了比较明显的提高.