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。     

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.     

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.     

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.     

Nitrogen-doped Carbon Coated Na3V2(PO4)3 with Superior Sodium Storage Capability

Cathodes with high cycling stability and rate capability are required for ambient temperature sodium ion batteries in renewable energy storage application. Na₃V₂(PO₄)₃ is an attractive cathode material with excellent electrochemical stability and fast ion diffusion coefficient within the 3D NASICON structure. Nevertheless, the practical application of Na₃V₂(PO₄)₃ is seriously hindered by its intrinsically poor electronic conductivity. Herein, solvent evaporation method is presented to obtain the nitrogen-doped carbon coated Na₃V₂(PO₄)₃ cathode material, delivering enhanced electrochemical performances. N-Doped carbon layer coating serves as a highly conducting pathway, and creates numerous extrinsic defects and active sites, which can facilitate the storage and diffusion of Na⁺. Moreover, the N-doped carbon layer can provide a stable framework to accommodate the agglomeration of the electrode upon electrode cycling. N-Doped carbon coated Na₃V₂(PO₄)₃(NC-NVP) exhibits excellent long cycling life and superior rate performances than bare Na₃V₂(PO₄)₃ without carbon coating. NC-NVP delivers a stable capacity of 95.9 mA·h/g after 500 cycles at 1 C rate, which corresponds to high capacity retention(94.6%) with respect to the initial capacity(101.4 mA·h/g). Over 91.3% of the initial capacity is retained after 500 cycles at 5 C, and the capacity can reach 85 mA·h/g at 30 C rate.     

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.     

Improved electrochemical properties in the Li3Fe2(PO4)3 by titanium and vanadium doping

Ti⁴⁺ ions were introduced to the VO₄^3- substituted Li₃Fe₂(PO₄)₃ by sol-gel method. Simultaneous substitution of Ti⁴⁺ for Fe³⁺ and VO₄^3- for PO₄^3- in the Li₃Fe₂(PO₄)₃ resulted in a net improvement in the rate capability and cycling performance, as compared with the single Ti⁴⁺ or VO₄^3- substituted compound.     

Electrochemical properties of niobium and phosphate doped spherical Li-rich spinel LiMn2O4 synthesized by ion implantation method

Spherical Li-rich lithium manganese oxide(LMO) spinel material was synthesized by an ion implanted method assisted by polyalcohol doped with Niobium and Phosphate simultaneously.The material was characterized by scanning electron microscopy,X-ray diffraction and BET specific surface area analysis.The electrochemical performances were investigated with galvanostatic techniques and cyclic voltammetry.The synthesis process was investigated with TG/DSC.The results show that the lithium ion can be immersed into the pore of manganese dioxide at a low temperature with the ion implanted method.The prepared materials have a higher discharge capacity and better crystallization than those prepared by solid phase method.The doped Nb can improve the capacity of the Li-rich LMO spinel and reinforce the crystal growth along(111) and(400) planes.The crystal grains show circular and smooth morphology,which makes the specific surface area greatly decreased.Phosphate-doped LMO spinel exhibits good high-rate capacity and structure stability.The prepared Li_(1.09)Mn_(1.87)Nb_(0.031)O_(3.99)(PO_4)_(0.021)delivers a discharge capacity of 119mAhg~(-1) at 0.2C(1C=148mAg~(-1)) and 112.8 mAhg~(-1) at 10 C,the discharge capacity retention reaches 98% at 1 ℃ after 50 cycles at 25 ℃ and 94% at 55 ℃.     

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.     

磷酸钒钠Na_3V_2(PO_4)_3电化学储能研究进展

锂离子电池在全球范围内的广泛应用加剧了对锂资源的消耗,其成本和原料将限制其未来发展。钠与锂具有相似物理化学性质,并且储量丰富。根据锂离子"摇椅式"电池原理,富钠离子化合物可类似富锂离子正极材料,提供可脱嵌的钠离子及结构。钠离子较锂离子大,其可逆脱嵌反应要求材料结构具有较大的容钠位与离子迁移通道。聚阴离子体磷酸钒钠Na_3V_2(PO_4)_3属于钠离子超导体(NASICON)材料,其NASICON结构骨架形成了稳定的容钠位,并且开放的三维离子迁移通道利于提高钠离子的扩散。Na_3V_2(PO_4)_3作为电池正极材料,具有理想的比容量、电压平台与循环稳定性,从而受到了广泛关注。本文首先介绍了Na_3V_2(PO_4)_3结构特点,其次结合团队已有的工作基础对Na_3V_2(PO_4)_3在钠离子电池、混合离子电池、水系电池,混合超级电容器等体系中的应用与反应机理进行了阐述;总结了基于Na_3V_2(PO_4)_3设计的复合材料与结构并探讨了Na_3V_2(PO_4)_3可能存在的问题与未来发展趋势。     

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。     

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.     

Synthesis of carbon-coated Li4Ti5O12 and its electrochemical performance as anode material for lithium-ion battery

Carbon-coated Li_4Ti_5O_(12) sample was synthesized by a sol-gel method. The Li_4Ti_5O_(12) powders were obtained by calcinations of the gels at 750, 800, 850,900 ℃ at N_2 atmosphere. The structure, morphology and electrochemical properties of the materials were characterized by SEM, XRD and charge and discharge. The final product sintered at 850 ℃ demonstrates excellent performance with a specific capacity of 163.5 mAh/g after 100 cycles at 1C. Furthermore, the discharge specific capacity of the sample can retain 80 mAh/g at 10C.     

Equilibrium diagram of KPO3–Y(PO3)3 system, chemical preparation and characterization of KY(PO3)4

Microdifferential thermal analysis (μ-DTA), X-ray diffraction (XRD) and infrared (IR) spectroscopy were used for the first time to investigate the liquidus and solidus relations in the KPO₃–Y(PO₃)₃ system. The only compound observed within the system was KY(PO₃)₄ melting incongruently at 1033 K. An eutectic appears at 13.5 mol% Y(PO₃)₃ at 935 K, the peritectic occurs at 1033 K and the phase transition for potassium polyphosphate KPO₃ was observed at 725 K. Three monoclinic allotropic phases of the single crystals were obtained. KY(PO₃)₄ polyphosphate has the P2₁ space group with lattice parameters: a=7.183(4) Å, b=8.351(6) Å, c=7.983(3) Å, β=91.75(3)° and Z=2 is isostructural with KNd(PO₃)₄. The second allotropic form of KY(PO₃)₄ belongs to the P2₁/n space group with lattice parameters: a=10.835(3) Å, b=9.003(2) Å, c=10.314(1) Å, β=106.09(7)° and Z=4 and is isostructural with TlNd(PO₃)₄. The IR absorption spectra of the two forms show a chain polyphosphates structure. The last modification of KYP₄O₁₂ crystallizes in the C2/c space group with lattice parameters: a=7.825(3) Å, b=12.537(4) Å, c=10.584(2) Å, β=110.22(7)° and Z=4 is isostructural with RbNdP₄O₁₂ and contains cyclic anions. The methods of chemical preparations, the determination of crystallographic data and IR spectra for these compounds are reported.     

锂离子电池负极材料Li3V2(BO3)3/C 复合材料的合成及电化学性能研究

本文以草酸锂、五氧化二钒、硼酸为原料,二水合草酸为碳原和还原剂,无水乙醇为分散剂,采用球磨法合成了Li₃V₂(BO₃)₃/C（LVB/C）复合材料前驱体,后经高温热处理得到LVB/C复合材料. 采用TG-DTA技术对前驱体进行了热分析,通过XRD、SEM、EDS等技术研究了烧结条件对 LVB/C 材料的晶体结构、微观形貌、含碳量的影响. 通过恒流充放电测试、循环性能测试、循环伏安测试和电化学阻抗测试等技术研究了烧结条件对 LVB/C 材料电化学性能的影响. 电化学测试结果表明,800 ℃下烧结10 h得到的样品电化学性能最佳,在50mA•g^-1电流密度下,首次充放电比容量分别为427.6mAh•g^-1和669.1 mAh•g^-1,循环10次后,容量保持率分别为55.4 %和35.2 %.     

The system CePO4–K3PO4

The phase diagram of the system CePO₄–K₃PO₄ has been determined based on investigations by differential thermal analysis, X-ray powder diffraction, IR spectroscopy and optical microscopy. The system contains only one intermediate compound K₃Ce(PO₄)₂, which melts incongruently at (1500±20)°C. This compound is stable down to room temperature and exhibits a polymorphic transition at 1180°C. It was confirmed that the low-temperature form β-K₃Ce(PO₄)₂ crystallizes in a monoclinic system, space group P2₁/m with unit cell parameters a=9.579 (5), b=5.634 (6), c=7.468 (5) Å; =γ=90°, β=90.81 (3)°; V=403.083 Å³.     

Dy3+离子掺杂的全色荧光粉Ca9La(PO4)7的制备及发光特性

采用高温固相法合成了Ca₉La(PO₄)₇:Dy³⁺发光材料. 荧光粉的晶体结构和微观尺寸由X射线粉末衍射(XRD)仪和扫描电子显微镜(SEM)测定. 光致激发和发射光谱发光揭示了材料的光学特性. 实验结果显示: Ca₉La(PO₄)₇:Dy³⁺能够有效吸收紫外-可见光(300-460 nm)而被激发, 呈现一系列的吸收峰. 样品在350 nm近紫外光激发下, 有较强的蓝光(481 nm)和黄光(573 nm)两个窄带发射, 混合成优质的白光发射, 该白光色坐标在国际照明委员会(CIE)色品图中分布在无色点D65 (0.313, 0329)周围. 随着掺杂Dy³⁺离子的摩尔分数的增加, 两种发射均发生浓度猝灭现象, Dy³⁺离子的最佳掺杂为0.05(摩尔分数), 电偶极-电偶极相互作用是主要的猝灭机理.     

Excess capacity on compound phases of Li2FeTiO4 composite cathode materials synthesized by hydrothermal reaction using optional titanium sources to boost battery performance

Li₂FeTiO₄ composites have been produced using commercial LiAC, FeCl₂ and different titanium sources by hydrothermal synthesis (HS) at 175 ℃ and subsequent annealing at 700 ℃. Impure phase TiO₂, Fe₂O₃ and FeTiO₄ were detected out among the Li₂FeTiO₄ composites with different titanium sources. Micron and nano-sized particles of Li₂FeTiO₄ were prepared from various titanium raw materials, with nano-sized particles predominating when titanium raw materials were layered hydrogen titanate nanowire (H₂Ti₃O₇NW, HTO-NW) and titanium oxide nanotubes (TiO₂NB). The Li₂FeTiO₄ composites synthesized by HTO-NW shows a primary particle size of 50-200 nm of high crystallinity staggered with undissolved nanowire with a diameter size of about 100 nm. The samples using one-dimensional nanometer titanium oxide (TiO₂ NB) as the raw material can get a super high initial discharge capacity of 367.8 mAh/g at the rate of C/10 and excellent cycling stability. The selection of raw materials and adopting multi-phase modification can be considered as an effective strategy to improve the electro-chemical properties of Li₂FeTiO₄ composite cathode materials for the lithium secondary battery.     

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.     

单斜Li3V2(PO4)3/C复合材料的制备及其电化学性能

以LiOH·H2O、V2O5、H3PO4和蔗糖为原料,采用软化学法制备了锂离子电池正极材料Li3V2(PO4)3/C.通过X射线衍射(XRD)、扫描电镜(SEM)对产物的结构和形貌进行表征,采用恒电流充放电、电化学阻抗考察了产物的电化学性能.结果表明.当煅烧温度达到700℃时,杂质相衍射峰消失,所得的样品为纯相的单斜Li3V2(PO4)3.颗粒粒度为1～2 μm;在3.0～4.5 V电压范围内以0.2C倍率充放电,首次放电比容量达到148.2 mAh·g-1,第50次循环比容量仍为144 mAh·g-1,容量保持率为97%,具有良好的循环性能;另外,样品还具有很好的倍率性能和高温性能.