Effect of VO43- Substitution on the Electrochemical Properties of a LiSn2(PO4)3 Anode Material

VO₄^3- anion was used to partially substitute for PO₄^3- in the Nasicon compound of LiSn₂(PO₄)₃ via a sol-gel method. XRD analysis revealed that the VO₄^3--substituted samples did not have a single LiSn₂(PO₄)₃ phase, and some secondary phases like SnO₂ and SnP₂O₇ appeared. Introduction of the VO₄^3- anion did not prevent the LiSn₂(PO₄)₃ compound from decomposing during the initial lithiation; however the VO₄^3- anion substitution remar-kably enhanced the rate capability and cycling performance of the products because they reduced the charge transfer impedance, increased the lithium ion diffusion, and strengthened the role of the Li₃PO₄ matrix due to the precipitation of the Li₃VO₄phase. Of the substituted samples, the sample with a nominal composition of LiSn₂(PO₄)_2.5(VO₄)_0.5 delivered a capacity of 449.2 mA·h/g at a rate of 0.25 C after 25 cycles and 373.8 mA·h/g at 2 C rate. Those values surpassed some previous reports on LiSn₂(PO₄)₃ and the LiSn₂(PO₄)₃/C composites. Accordingly, the partial substitution of phosphorus by vanadium in LiSn₂(PO₄)₃ is a feasible technique to remarkably improve its electrochemical properties.     

Li3Fe2(PO4)3/C正极材料的电化学性能及其反应机理研究

采用溶胶凝胶及高能球磨制得Li₃Fe₂(PO₄)₃/C材料,利用多种物理及其电化学技术观察材料形貌,表征材料结构及电化学性能,用电化学原位XAFS等初步研究Li₃Fe₂(PO₄)₃/C超理论容量电化学反应机理. 结果显示,Li₃Fe₂(PO₄)₃/C的结构为单斜晶系,空间群P21/n. 2.0 ~ 4.0 V电位区间,10 mAh·g^-1电流密度,Li₃Fe₂(PO₄)₃/C电极的首周期放电比容量为129 mAh·g^-1,达到其理论容量. 若电位区间拓宽至2.0 ~ 4.95 V,其首周期放电比容量高达165 mAh·g^-1,超出理论的“额外”容量30%. 电化学原位XAFS测试未观察到明显的Fe³⁺/Fe⁴⁺氧化还原对参与电化学反应,初步推测“额外”容量可能来自于该复合材料的高浓度表面缺陷.     

Nd3+-doped Li3V2(PO4)3 cathode material with high rate capability for Li-ion batteries

A series of Nd3+-doped Li3NdxV2àx(PO4)3(x = 0.00, 0.02, 0.05, 0.08 or 0.1) composites are synthesized by the rheological phase reaction method. The XRD results indicate that Nd3+ions have been successfully merged into a lattice structure. Doped samples show good electrochemical performance in high discharge rate and long cycle. In the potential range of 3.0–4.3 V, Li3Nd0.08V1.92(PO4)3exhibits an initial discharge capacity of 115.8 m Ah/g at 0.2 C and retain 80.86% of capacity retention at 2 C in the 51 st cycle.In addition, Li3Nd0.05V1.95(PO4)3holds at 100.4 m Ah/g after 80 cycles at 0.2 C with a capacity retention of92.4%. Finally, the CV test proves that the potential polarization of Li3Nd0.08V1.92(PO4)3decreased compared with the un-doped one.     

SO_4~(2-)功能化处理对Fe_2O_3催化剂上氨选择性催化还原NO_x性能的促进机理研究

采用沉淀法制备了Fe(OH)_3和Fe_2O_3。通过硫酸化处理得到SO_4~(2-)/Fe(OH)_3和SO_4~(2-)/Fe_2O_3两种催化剂,并将其应用于氨选择性催化还原NO_x(NH_3-SCR)反应,研究了SO_4~(2-)功能化处理对Fe_2O_3催化剂上NH_3-SCR脱硝性能的促进机理。结果表明,与纯的Fe_2O_3相比,硫酸化处理得到的催化剂上SCR活性得到显著提升;其中,SO_4~(2-)/Fe(OH)_3表现出更加优异的催化性能,在250-450℃时NO_x转化率高于80%,且具有优异的稳定性和抗H_2O+SO_2性能。XRD、Raman、TG、FT-IR、H_2-TPR、NH_3-TPD和in situ DRIFTS等表征结果显示,硫酸功能化处理能抑制Fe_2O_3的晶粒生长,同时SO_4~(2-)与Fe~(3+)结合形成硫酸盐复合物,提高了催化剂表面酸性位点的数量和酸强度,抑制了Fe_2O_3上的氨氧化反应,从而提高了其脱硝催化性能。     

Multi-functional Photoelectric Sensor Based on a Three-fold Interpenetrated Cd(II) Coordination Polymer for Sensitively Detecting Different Ions

Athree-fold interpenetrated cadmium coordination polymer[Cd₃(BTC)₂(H₂O)₉]·2H₂O(CP 1)(H₃BTC=1,3,5-benzenetricar-boxylic acid) was selected and synthesized to investigate its photoelectric properties. CP 1 showed excellent sensitivity for Cr₂O₇^2- and Fe³⁺, low limit of detection(LOD:0.39 µmol/L for Cr₂O₇^2- and 1.72 µmol/L for Fe³⁺) and stability as electrochemical sensor. More importantly, fluorescence sensing studies indicated that CP 1 exhibits sensing activity for Fe³⁺, Fe²⁺, and MnO₄^- with good cyclic stability and selectivity. Low LOD and high-sensitivity capability of CP 1 make it a potential multifunctional photoelectric sensor.     

三元掺杂改性锂离子电池正极材料Li3V2(PO4)3

以柠檬酸为螯合剂和还原剂, NH₄VO₃为钒源,通过溶胶-凝胶法制备了锂离子电池正极材料Li₃V₂(PO₄)₃及其三元掺杂体系Li_2.85Na_0.15V_1.9Al_0.1(PO₄)_2.9F_0.1.分别采用X射线衍射(XRD)、高分辨透射电子显微镜(HRTEM)、能量损失谱(EELS)、拉曼(Raman)光谱、扫描电子显微镜(SEM)、X射线能谱(EDS)、恒流充放电、循环伏安(CV)和交流阻抗谱(EIS)等技术对材料的微观结构、颗粒形貌和电化学性能进行分析.结果表明:在残余碳包覆的基础上, Na、Al、F三元掺杂有利于稳定Li₃V₂(PO₄)₃的晶体结构,进一步减少颗粒团聚和提升材料导电特性,促进第三个锂离子的脱出和嵌入,从而显著改善Li₃V₂(PO₄)₃的实用电化学性能.未经掺杂的Li₃V₂(PO₄)₃原粉在1/9C、1C和6C倍率下的可逆比容量分别为141、119和98 mAh·g^-1,而三元掺杂改性材料在1/9C、1C、8C和14C倍率下的比容量分别为172、139、119和115 mAh·g^-1.在1C倍率下循环300圈后,掺杂体系的比容量依然高达118 mAh·g^-1,比原粉高出32.6%.值得注意的是,这种三元掺杂还使Li₃V₂(PO₄)₃的多平台放电曲线近似转变为一条斜线,显示出可能不同的储锂机制.     

流变相法制备海藻酸基碳包覆Li3V2(PO4)3材料的电化学性能

Li₃V₂(PO₄)₃/C (LVP/C) cathode materials were successfully prepared by a rheological phase method using alginic acid as the carbon source. The X-ray diffraction (XRD) patterns demonstrate that all the samples contain pure LVP with the same monoclinic structure. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that LVP/C materials have a uniform particle size. The LVP/C sample with 10% (w) alginic acid shows the best cycling stability. It delivers a discharge capacity of 117.5 mAh·g^-1 (3.0-4.3 V), which can be maintained at 116.5 mAh·g^-1 after 50 cycles at a rate of 0.1C. Its capacity retentions of 99.1% (3.0-4.3 V) and 76.8% (3.0-4.8 V) after 50 cycles are prominently higher than those of pristine Li₃V₂(PO₄)₃, which are 89.7% (3.0-4.3 V) and 62.39% (3.0-4.8 V). These outstanding electrochemical performances are mainly attributed to the alginic acid-based carbon coating, which can increase the electronic conductivity of materials and buffer the mechanical damage of the active materials during the Li ion insertion/extraction process, thus improving the electrochemical performance of the LVP/C samples.     

新型Lewis固体酸Ce~(3+)-Ti~(4+)-SO_4~(2-)/MWCNTs制备及催化酯化反应合成生物柴油性能研究

采用高温浸渍法,通过Ce~(3+)、Ti~(4+)和浓硫酸磺化反应对多壁纳米碳管进行了改性处理,制备了Lewis酸型固体酸催化剂Ce~(3+)-Ti~(4+)-SO_4~(2-)/MWCNTs,并采用透射电镜、拉曼光谱、X射线光电子能谱、吡啶吸附红外光谱、X射线荧光光谱、X射线衍射光谱和NH_3程序升温脱附等多种测试技术对催化剂的物理化学特性和结构特征进行了表征。以Ce~(3+)-Ti~(4+)-SO_4~(2-)/MWCNTs为油酸与甲醇经酯化反应合成生物柴油的催化剂,对其催化性能进行了研究。结果表明,当醇油物质的量比为12∶1,催化剂与反应物质量比为1%,反应温度为65℃,反应5 h,油酸转化率为93.4%。催化剂Ce~(3+)-Ti~(4+)-SO_4~(2-)/MWCNTs在重复使用八次后,油酸的转化率仍为80.8%,由此表明其具有较高的催化活性和稳定性。高催化活性和稳定性是因为,纳米碳管的C 1s结合能较一般炭材料低,使得电子在其管状结构中的流动和逃逸非常容易,从而有助于负载于纳米碳管之上的活性组分之间发生强烈的相互作用,最终促使Ce~(3+)和Ti~(4+)分别与SO_4~(2-)形成稳定的配位键,增大催化剂的晶化程度,并使SO_4~(2-)与纳米碳管结合的更加牢固,增强了催化剂的稳定性,减少了催化剂中活性组分的流失。最后,由于SO_4~(2-)与Ce~(3+)的强相互作用,在不增加纳米碳管表面缺陷的情况下,改变了Ti~(4+)-SO_4~(2-)中表面原子的化学状态,使得S~(6+)离子和Ti~(4+)离子的吸电子能力增加,使催化剂以Lewis酸性活性位为主,避免了SO_4~(2-)/MWCNTs因为以Brnsted酸位为主,而在富含水的反应介质中,由于水合反应而降低其催化活性的现象发生。     

磷酸钒锂/石墨烯复合正极材料的制备及表征

通过三聚氰胺甲醛树脂(MR)中的羟基与石墨烯氧化物(GO)中的羧基发生的沉淀反应来制备功能化的氧化石墨烯前驱体,然后利用溶胶-凝胶及高温热处理方法制备磷酸钒锂/石墨烯复合材料,利用此材料制备了电池电极,并对电极材料进行了结构和电化学表征。结果表明,所得磷酸钒锂为单斜晶系结构,石墨烯堆叠程度显著降低,也有效避免了磷酸钒锂颗粒的团聚,提高了材料的电化学性能。电池的充放电曲线极化较小,在3.0~4.3 V的区间内20 C倍率仍有86 mA·h/g的可逆容量。0.1 C循环100次后容量为119.7 mA·h/g,容量保持率94%。在3.0~4.8 V的高电压区间,10 C倍率下可逆容量80 mA·h/g,0.1 C循环100次后仍有145.6 mA·h/g的可逆容量。优异的循环和倍率性能以及较低的碳含量符合锂离子正极材料实用的要求。     

Measurement of Solid-liquid Equilibria in Quaternary System Li+, K+//SO42-, B4O72--H2O at 288 K

In order to utilize the brine resources in China, the solid-liquid equilibria in quaternary system Li⁺, K⁺//SO₄^2-, B₄O₇^2--H₂O at 288 K was studied by the isothermal solution equilibrium method. Solubilities and densities of solutions were determined experimentally. According to the experimental data, the equilibrium phase diagrams, density-composition diagram and corresponding water content diagram of the quaternary system were plotted. Double salt KLiSO₄ was found in the reciprocal quaternary system Li⁺, K⁺//SO₄^2-, B₄O₇^2--H₂O at 288 K. The quaternary system has three invariant points, seven univariant curves and five fields of crystallization. The five crystallization regions correspond to Li₂B₄O₇·3H₂O, Li₂SO₄·H₂O, K₂B₄O₇·4H₂O, K₂SO₄ and KLiSO₄, respectively. The crystallization field of salt Li₂B₄O₇·3H₂O is the largest, whereas that of Li₂SO₄·H₂O is the smallest. The experimental results show that Li₂SO₄·H₂O has a strong salting-out effect on other salts.     

Ba_3Y(PO_4)_3∶Dy~(3+),Eu~(3+)单基质白光荧光粉的制备与发光性能

为了探究在Dy~(3+)掺杂Ba_3Y(PO_4)_3荧光粉中共掺Eu~(3+)离子对其发光性能的影响,我们采用传统高温固相法制备了一系列Dy~(3+)、Eu~(3+)单掺杂和共掺杂Ba_3Y(PO_4)_3荧光粉。通过X射线衍射(XRD)、荧光发射光谱和荧光衰减曲线对样品进行了表征。结果表明,所制备的荧光粉呈闪铋矿立方相。在近紫外光激发下,Ba_3Y(PO_4)_3∶Dy~(3+)发射光谱在487和578 nm处有两个窄带发射峰,呈冷白光发射;Ba_3Y(PO_4)_3∶Eu~(3+)发射光谱的窄带发射位于594和616 nm处,呈发橙红光。在Ba_3Y(PO_4)_3∶Dy~(3+),Eu~(3+)中,由于Eu~(3+)离子补偿Dy~(3+)冷白光发射所缺的红色组分,从而实现了色纯度高、色温适中的暖白光发射。进一步探索了Ba_3Y(PO_4)_3∶Dy~(3+),Eu~(3+)荧光粉发光机理。所制备的Ba_3Y(PO_4)_3∶Dy~(3+),Eu~(3+)单基质白光荧光粉在白光近紫外激发白光二极管(UVWLED)领域具有潜在应用价值。     

纳米MgO掺杂改善LiNi1/3Co1/3Mn1/3O2正极材料

将氢氧化物共沉淀法制备的(Ni_1/3Co_1/3Mn_1/3)（OH）₂在500℃热处理5 h得到具有尖晶石结构、纳米尺寸的氧化物M₃O₄(M=Ni_1/3Co_1/3Mn_1/3).将其与LiOH及不同量的纳米MgO混合均匀,并在850℃热处理24 h制备了Li(Ni_1/3Co_1/3Mn_1/3)_1/xMg_xO₂（x=0,0.01,0.02,0.03,0.04,0.05）正极村料.随着Mg掺杂量的增大,正极材料的晶胞参数增大;少量的Mg掺杂增大了锂离子的扩散系数,而过度掺杂却使锂离子扩散系数有所降低,其中Li(Ni_1/3Co_1/3Mn_1/3)_0.98Mg_0.02O₂的锂离子扩散系数最大,其脱出和嵌入扩散系数分别为D_Li-dein=29.20×10^-11cm²·S^-1和D_Li-in=4.760×10^-11cm²·s^-1;其以3C倍率充放电的平均放电比容量为139.3 mAh·g^-1,比未掺杂的原粉约高9.5 mAh·g^-1;另外其循环性能也得到了大幅度改善.     

酸性溶液中Fe2+ /Fe3+相互转换对电极还原行为的影响

采用线性扫描伏安法和循环伏安法研究了含有Cl^-、SO₄^2-的酸性溶液中Fe²⁺/Fe³⁺相互转换对电极反应和Fe³⁺还原过程的影响. 结果表明: [Fe]_T=1 mol·L-1条件下,溶液中Fe³⁺/Fe²⁺的还原析出过程经过两个阶段：(1) E=0.35 V左右Fe³⁺还原成Fe²⁺过程; (2) E=-0.3 V之后H+的还原同时Fe²⁺离子与OH^-相结合生产Fe(OH)₂; Fe³⁺/Fe²⁺的相互转化主要影响Fe³⁺的第一还原阶段的还原峰电流和峰电位. |ipa/ipc|值随c(Fe³⁺ )/c(Fe²⁺ )增大而增大,且扫描速度慢时影响大,扫描速度快时影响小; 0.50 mol·L^-1 Fe²⁺+0.50 mol·L^-1 Fe³⁺时,随扫描速率的变化|ipa/ipc|值变化最小(|i_pa/i_pc|≈1.20). 同时,c(Fe³⁺ )/c(Fe²⁺ )也影响平衡电位,平衡电位随c(Fe³⁺ )/c(Fe²⁺ )增大而正移,电位从E₁=0.501 V升至E₅=0.565 V.     

新型磷-钒-氧层状化合物[H2en]2[H3O]6[Co(H2O)2(VO)8(OH)4(PO4)8]的水热合成与晶体结构

金属磷酸盐材料在吸附、离子交换、离子传导和催化剂方面有潜在的应用前景[1～5]. 近年来, 通过水热反应合成了一些A-V-P-O化合物. 在这些化合物中, A一般为碱金属或有机阳离子, 如层状结构的[H2N(C4H8)2NH2][(VO)4(OH)4(PO4)2][6] 和[H2N(C2H4)3NH2][(VO)8(HPO4)3(PO4)4*(OH)2]*2H2O[6], 一维链状结构的 [H2NCH2CH2NH3(VO)(PO4)][7], 手性双螺旋结构的 [(CH3)2NH2]K4[(VO)10(H2O)2(OH)4(PO4)7]*H2O[8]以及具有三维骨架结构的化合物 [H3N(CH2)3NH3K(VO)3(PO4)3][9], [H3N(CH2)3NH3]2[V(H2O)2(VO)6(OH)2(HPO4)3(PO4)5]*3H2O[10]和[H3N(CH2)2NH3][(VO)3(H2O)2(PO4)2(HPO4)4][11].     

VO1-4+阳离子与n-CmH2m+2 (m = 3, 5, 7)烷烃的反应性研究：氧含量和碳链长度的影响

Vanadium oxides are one of the most important heterogeneous catalysts that are widely used to oxidize hydrocarbon molecules into value-added chemicals. In order to reveal the mechanisms and the nature of active sites, numerous experimental and theoretical studies have been reported on the reactivities of gas-phase vanadium oxide clusters toward small molecules. However, there has been very limited research on the chemical reactivity changes associated with the oxygen contents of vanadium oxides and the carbon chain lengths of alkanes. In this work, the reactions of vanadium oxide ions VO₁₋₄⁺ with alkanes (n-C_mH_2m+2, m = 3, 5, 7) were systematically investigated by time-of-flight mass spectrometry and the reactions of VO₁₋₃⁺ with pentane were further studied by density functional theory calculations. Experimental results show that in the reactions of VO⁺, VO₃⁺, and VO₄⁺ with n-C₅H₁₂, in addition to the major adsorption processes, the activation of the C―H and C―C bonds of n-C₅H₁₂ was observed. The activation of both the bonds was observed experimentally during the reaction of VO₂⁺ with n-C₅H₁₂ with large branching ratios. Among the vanadium oxide cations studied, VO₂⁺ shows the strongest oxidizability and the generation of lighter alkanes and alkenes dominates the reactions; VO⁺ is more reactive than VO₃⁺. VO₄⁺ pocesses only one η²-O₂ unit. Due to the weak bond between VO₂⁺ and η²-O₂, the η²-O₂ unit is released in VO₄⁺/n-C₅H₁₂ system leading to the formation of VO₂⁺; thus VO₄⁺ cations reflect some reactivity of VO₂⁺. Although the oxidation states in the vanadium oxide clusters increase from +Ⅲ in VO⁺ to +Ⅴ in VO₂⁺ and +Ⅳ in VO₃⁺, the reactivity does not gradually increase. Moreover, the reactivity of the mononuclear vanadium oxide cations also does not exhibit a gradually increasing trend with the increase in oxygen content. Based on the observed reactivity trend, the adsorption channels gradually become weak as the carbon chain lengths increase; meanwhile, the dehydrogenation and C―C bond activation channels gradually become obvious and some oxygen transfer products appear. Therefore, much lighter fragments of alkanes/alkenes will be obtained if linear alkanes with more carbon atoms were reacted with VO₁₋₄⁺. The theoretical results are generally consistent with those obtained from the experiments. The various reaction channels and versatile reactivity of the mononuclear vanadium oxide cations investigated in this study not only offer new insights into gas-phase reactions but also shed light on the processes occurring on the surfaces of the corresponding condensed-phase catalysts.     

Effects of doping Fe cations on crystal structure and thermal expansion property of Yb2Mo3O12

Crystal structures and thermal expansion properties of Yb_(2-x)Fe_xMo_3O_(12)(x=0.0,0.6,1.0,1.1,1.4) solid solutions have been studied by X-ray powder diffraction(XRPD) at different temperatures.Rietveld analysis of the XRPD data shows that Yb_(2-x)Fe_xMo_3O_(12) solid solutions adopt orthorhombic structure and have variable thermal expansion coefficients controlled by the ratio of Yb~(3+) to Fe~(3+).Yb_2Mo_3O_(12) shows anisotropic negative thermal expansion property,induced by the reductions in average Yb-O-Mo angle and average apparent Mo2-O bond length with increasing temperatures.As more Yb~(3+) substituted by Fe~(3+),the linear thermal expansion coefficients of Yb_(2-x)Fe_xMo_3O_(12) increase from negative to positive.A near-zero thermal expansion coefficient of 0.55×10~(-6)K~(-1) for Yb_(0.6)Fe_(1.4)Mo_3O_(12) is observed in the temperature range of 573-873 K     

Li3V2(PO4)3/C正极材料在不同电压区间的电化学行为及容量衰减原因

采用溶胶-凝胶法制备锂离子电池正极材料Li₃V₂(PO₄)₃/C. 通过恒电流充放电测试、循环伏安(CV)、电化学阻抗谱(EIS)等方法, 研究了Li₃V₂(PO₄)₃/C 在不同电压区间的电化学行为(3.0-4.5 V和3.0-4.8 V). 结果表明, 3.0-4.8 V电压区间的循环性能和倍率性能均不及3.0-4.5 V电压区间的. 3.0-4.5 V区间0.1C (1C=150mA·g^-1)倍率首次放电比容量为127.0 mAh·g^-1, 循环50次后容量保持率为99.5%, 而3.0-4.8 V区间的分别为168.2 mAh·g^-1和78.5%. 经过高倍率测试后再回到0.1C倍率充放电, 3.0-4.5 V和3.0-4.8 V的放电比容量分别为初始0.1C倍率的99.0%和80.7%. 经过3.0-4.8 V电压区间测试后, 少部分第三个锂离子能够在低于4.5V的电压脱出, 使3.0-4.5 V电压区间的放电比容量提升了7.4%. CV结果表明3.0-4.8 V区间的容量损失主要表现为第一个锂离子的不可逆损失. 极片的X射线衍射(XRD)和X射线光电子能谱(XPS)分析测试结果表明经过3.0-4.8 V测试后, Li₃V₂(PO₄)₃的结构发生了轻微的改变. 电感耦合等离子体(ICP)测试结果表明循环后的电解液中含有少量的V. 结构变形和V溶解可能是Li₃V₂(PO₄)₃在3.0-4.8 V区间容量衰减的主要原因.     

溴代酞菁铁配合物的光谱电化学性质研究

本文对μ-氧-四溴酞菁铁配合物([TBPcFe]₂O)的电化学性质及光谱电化学性质进行了研究。结果表明,μ-氧-四溴酞菁铁在所研究的电压区问内经历了三个单电子氧化还原反应,其半波电势为0.06V,—0.75V及—1.33V(相对于甘汞电极),分别对应于Fe³⁺/Fe³⁼、Fe²⁺/Fe⁺及TBPc^2-/TBPc^3-电对的氧化还原反应。光谱电化学性质研究亦观察到相应酞菁配合物的特征光谱。     

新型层状氟化磷酸铝[C4H12N2][Al2(PO4)2(H2O)2F2]的水热合成与表征

自从1982年Wilson等发现一类新型微孔材料磷酸铝分子筛(AlPO4-n)以来,大量具有新颖结构的磷酸铝化合物被合成出来,它们在催化、离子交换、吸附和主-客体组装等方面均具有潜在的应用前景,这类化合物大多是在水热或溶剂热体系中和有机模板剂存在条件下合成的,1978年,Flanigen等首先在反应体系中加入氟离子作矿化剂合成了硅晶体,后来,氟离子方法在硅铝体系和金属磷酸盐体系中也得到了广泛的应用,氟离子在反应过程中起到矿化剂或结构导向剂的作用,     

碳热还原辅助溶胶-凝胶法制备氟代聚阴离子型嵌/脱锂材料LiVPO4F/C

采用碳热还原辅助溶胶-凝胶法合成了锂二次电池正极材料LiVPO₄F/C, 探讨煅烧温度和煅烧时间对所制备材料纯度、结构和电化学性能的影响. 采用X射线衍射(XRD), 扫描电子显微镜(SEM), 恒流充放电, 电化学阻抗谱(EIS)和循环伏安(CV)等手段对不同煅烧温度和时间所得的材料进行结构表征和电化学性能测试. 当煅烧时间为4 h 时, 温度为450 ℃时, 能够得到纯相LiVPO₄F/C, 在0.1C、0.5C和1.0C倍率下, 电池放电比容量分别为193.2、175.6 和173.7 mAh·g^-1. 随着煅烧温度升高, Li₃V₂(PO₄)₃杂相逐渐增多, 650 ℃煅烧后的材料Li₃V₂(PO₄)₃ 成为主相. 优化煅烧时间也能够有效控制Li₃V₂(PO₄)₃ 杂相的生成, 能得到电化学性能良好的LiVPO₄F/C. 当煅烧温度为550 ℃时, 反应3 h后得到的产物综合电化学性能最优.