Mo掺杂LiFePO4正极材料的第一性原理研究

基于第一性原理密度泛函理论计算了LiFePO₄和LiFe_1-xMo_xPO₄(x=0.005,0.01,0.015,0.02,和0.025)的电子结构和锂离子扩散能垒。结果显示掺杂后的LiFe_0.99Mo_0.01PO₄样品具有最大的(101)晶面间距,由此可知LiFe_0.99Mo_0.01PO₄沿[101]晶向具有最宽的锂离子扩散通道。未掺杂的LiFePO₄的锂离子扩散能垒为4.289eV,而掺杂后LiFe_0.99Mo_0.01PO₄降为4.274eV,经过计算得出掺杂样品LiFe_0.99Mo_0.01PO₄的锂离子扩散系数增为未掺杂LiFePO₄的1.79倍,表明Mo掺杂有利于改善LiFePO₄的锂离子扩散能力。态密度图显示,掺杂Mo后导带底附近的峰强度增强,对LiFePO₄电子导电性能的提高是有利的。因此,掺杂Mo有益于提高LiFePO₄的锂离子扩散能力和电子导电能力。结合我们的实验结果比较得知,在磷酸铁锂性能的改善上,相比电子导电能力,锂离子扩散能力的提高起到了更重要的作用。     

钇掺杂对磷酸亚铁锂薄膜光波导传感元件气敏特性的影响

利用水热法合成出LiFePO4和钇(Y)掺杂的LiFePO4粉体,并作为敏感试剂,用浸渍-提拉法固定在锡掺杂玻璃光波导表面,分别研制了LiFePO4和LiFe0.99 Y0.01 PO4薄膜/锡掺杂玻璃光波导传感元件.用这些薄膜传感元件对挥发性有机气体进行检测,并比较了它们的气敏特性.结果表明,掺杂Y后LiFePO4薄...     

锂离子电池正极材料LiFePO4在Fe位掺杂的研究进展

橄榄石型LiFePO4是近年发展起来的一种锂离子电池正极材料,但是LiFePO4的电子导电率低和锂离子扩散速度慢限制了其实用化,需要改进.其中一种很有效的方法就是在LiFePO4的晶格中掺杂金属离子,使其产生晶格缺陷,促进Li+扩散,改善晶体内部的导电性能.LiFePO4有Li(M1)和Fe(M2)2个金属位,可使用金属离子对其改性.本文综述了对锂离子电池正极材料LiFePO4在Fe(M2)位掺杂的研究进展.LiFePO4在Fe(M2)位的掺杂主要采用Mn2+,Ni2+,Co2+,Mg2+等几种金属离子.     

稀土Sm掺杂LiFePO4/C正极材料的结构和电化学性能

采用高温固相法制备LiFe1-xSmxPO4/C(x=0,0.06,0.08,0.10)锂离子电池正极材料,并用XRD,SEM,CV及EIS等方法进行结构和电化学性能的测试。结果表明,通过该法制得的样品均具有橄榄石型晶体结构。Sm的掺杂可明显细化颗粒,并导致LiFePO4晶格中c轴方向的P-O键长增加,其中x=0.08样品P-O键长最大(0.152 8 nm),明显大于未掺杂样品的键长(0.142 2nm)。电化学性能测试表明,掺杂后LiFePO4的放电容量增加,循环稳定性能提高。在-20～40℃的温度区间内,放电容量随温度的升高而增加,其中x=0.08的样品40℃时放电容量为159 mAh.g-1,但测试温度达到60℃时,放电容量急剧下降。EIS测试表明Sm的掺杂可以明显改善电极表面电化学反应的动力学性能,降低电荷转移电阻,提高交换电流密度。     

镱掺杂LiFePO4/C正极材料结构和电化学性能

采用高温固相法制备LiFe1-xYbxPO4/C(x=0,0.06,0.08,0.10)锂离子电池正极材料,并用X射线衍射(XRD),扫描电镜(SEM),循环伏安测试(CV)及交流阻抗测试(EIS)等方法进行结构和电化学性能的测试。XRD分析结果表明LiFe1-xYbxPO4/C(x=0,0.06,0.08,0.10)样品具有橄榄石型晶体结构。Yb的掺杂导致LiFePO4晶格中c轴方向的P-O键长增加,其中x=0.08样品具有最长的P-O键长。SEM图表明Yb的掺杂可明显细化颗粒,其中x=0.08时样品粒径为200 nm,比未掺杂样品降低了约2.5倍。电化学性能测试表明,Yb的掺杂使样品的放电容量增加,循环稳定性能提高。在-20～40℃温度区间内,放电容量随温度的升高而增加,其中x=0.08的样品40℃时放电容量为150 mAh.g-1,但测试温度达到60℃时,放电容量急剧下降。EIS测试表明Yb的掺杂可以明显改善电极表面电化学反应的动力学性能,降低电荷转移电阻,提高交换电流密度。     

铝掺杂LiFePO4的表面成分结构及电化学性能研究

锂离子电池正极材料掺杂LiFePO4的报道已很多,而涉及掺杂LiFePO4的表面成分及结构的研究仍很少见.本文采用溶剂热法一步制得了表面富Al的LiFePO4正极材料.TEM测试证实LiFePO4的表面形成均匀的无定型包覆层;俄歇电子能谱和软X射线吸收谱均表明其表面的包覆层为部分Al替代Fe的LiFe1-x Alx PO4.表面富Al(x=0.02)的LiFePO4显示了较好的电化学倍率性能和低温性能,-10oC下充放电,电压范围2.2~4.2 V、0.1C倍率,电极的放电比容量为98 mAh·g-1,0.5C倍率放电比容量可达70 mAh·g-1.这归因于Al的加入改变了材料体相及表面的电子结构,增加了体相电子的传导及表面离子的传导.     

高倍率性能正极材料LiFe_(0.9)Mg_(0.1)PO_4的结构

应用高温固相反应合成锂离子电池正极材料LiFePO4和LiFe0.9Mg0.1PO4.不同浓度的K2S2O8水溶液氧化LiFe0.9Mg0.1PO4制备部分脱锂两相混合物Li0.4Fe0.9Mg0.1PO4及完全脱锂单相化合物Li0.1Fe0.9Mg0.1PO4.X射线衍射物相分析(XRD),选区电子衍射(SAED)和高分辨原子图像(HRTEM)测试表明,脱锂相Li0.1Fe0.9Mg0.1PO4是单相化合物,没有发生相分离.点阵参数计算表明,LiFe0.9Mg0.1PO4体系嵌锂相和脱锂相的晶格错配度与LiFePO4体系相比有所降低,这正是锂离子电池正极材料LiFe0.9Mg0.1PO4具有高倍率循环充放电比容量的结构基础.     

锂离子电池正极材料LiFePO4的结构和电化学反应机理

十年来的研究并没有对LiFePO4的电化学反应机理形成准确一致的认识.复合阴离子(PO4)3-的应用使铁基化合物成为一种非常理想的锂离子电池正极备选材料.然而,LiFePO4的晶体结构却限制了其电导性与锂离子扩散性能,从而使材料的电化学性能下降.本文主要考虑充放电机理、相态转变、离子掺杂、锂离子扩散、电导、电解液、充放电动力学等因素的影响,从理论与实验角度综述了关于LiFePO4的电化学反应机理的研究进展.     

快离子导体Li3V2(PO4)3包覆LiFePO4的结构和性能

通过机械活化将快离子导体Li3 V2(PO4)3包覆在LiFePO4 表面, 制备了性能优异的复合正极材料9LiFePO4@Li3 V2(PO4)3. 用XRD, SEM, HRTEM, EDS和电化学测试等手段研究了材料的物理化学性能. 结果表明, 包覆后的材料含有橄榄石结构的LiFePO4、单斜晶系的Li3 V2(PO4)3 和正交晶系的Li3 PO4; LiFePO4颗粒表面包覆了一层Li3 V2(PO4)3, 且部分V3+进入LiFePO4晶格内部, 使其晶格参数减小, 包覆后的LiFePO4的交换电流密度和锂离子扩散系数均提高了1个数量级. 电化学测试结果表明, 包覆后的LiFePO4的倍率性能及循环性能都得到显著改善, 在1C和2C倍率下, 包覆后的LiFePO4的首次放电比容量较包覆前分别提高了34.09%和78.97%, 经150次循环后容量保持率分别提高了27.77%和65.54%; 并且5C时容量为121.379 mA·h/g(包覆前LiFePO4在5C下几乎没有容量), 循环350次后的容量保持率高达94.03%.     

聚阴离子掺杂LiMnO_(2-y)X_y(X=BF_4~-,SiO_3~(2-),MoO_4~(2-),PO_4~(3-),BO_3~(3-))材料的合成及其电化学性能

采用水热法合成了聚阴离子掺杂LiMnO2-yXy(X=BF4-,SiO32-,MoO42-,PO43-,BO33-,y=0.01、0.03、0.05)锂离子电池正极材料。通过X射线粉末衍射(XRD)、X光电子能谱(XPS)、扫描电镜(SEM)和恒电流充放实验,研究了不同掺杂离子和掺杂量对产物结构和电化学性能的影响。结果表明,少量聚阴离子的掺杂未改变正交LiMnO2的晶体类型,但增大了材料晶胞体积,改善了材料的电化学循环性能。电化学交流阻抗(EIS)测试结果表明,聚阴离子掺杂增大了材料电荷转移阻抗,但明显提高了材料中Li+的扩散能力。     

Physical and electrochemical properties of La-doped LiFePO4/C composites as cathode materials for lithium-ion batteries

Olivine-type LiFePO₄ is one of the most promising cathode materials for lithium-ion batteries, but its poor conductivity and low lithium-ion diffusion limit its practical application. The electronic conductivity of LiFePO₄ can be improved by carbon coating and metal doping. A small amount of La-ion was added via ball milling by a solid-state reaction method. The samples were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM)/mapping, differential scanning calorimetry (DSC), transmission electron microscopy (TEM)/energy dispersive X-ray spectroscopy (EDS), and total organic carbon (TOC). Their electrochemical properties were investigated by cyclic voltammetry, four-point probe conductivity measurements, and galvanostatic charge and discharge tests. The results indicate that these La-ion dopants do not affect the structure of the material but considerably improve its rate capacity performance and cyclic stability. Among the materials, the LiFe_0.99La_0.01PO₄/C composite presents the best electrochemical behavior, with a discharge capacity of 156 mAh g^?1 between 2.8 and 4.0 V at a 0.2 C-rate compared to 104 mAh g^?1 for undoped LiFePO₄. Its capacity retention is 80% after 497 cycles for LiFe_0.99La_0.01PO₄/C samples. Such a significant improvement in electrochemical performance should be partly related to the enhanced electronic conductivities (from 5.88?×?10^?6 to 2.82?×?10^?3 S cm^?1) and probably the mobility of Li⁺ ion in the doped samples. The LiFe_0.99La_0.01PO₄/C composite developed here could be used as a cathode material for lithium-ion batteries.     

Effects of heteroatoms on doped LiFePO4/C composites

A series of supervalent cation doped Li_1–x M_0.01Fe_0.99PO₄/C composites (M?=?Ti, Zr, V, Nb, and W) were synthesized by solid-state reaction. The effects of the heteroatoms were studied by X-ray diffraction, cyclic voltammetry, and electrochemical impedance measurement. After doping, the lattice structure of LiFePO₄ is not destroyed and the reversibility of lithium ion intercalation and deintercalation is improved. The diffusion coefficient of lithium ions depends on the radius of the heteroatoms. As the radius of the heteroatom is larger, the diffusion coefficient increases.     

Enhancement of electrochemical properties of niobium‐doped LiFePO4/C synthesized by sol–gel method

LiFePO₄/C and LiFe_1–xNb _xPO₄/C composites were synthesized using a sol–gel method. The influence of niobium doping on the constitution, morphology, and electrochemical properties of the samples was studied in detail. X‐Ray diffraction patterns indicate that appropriate Nb doping does not alter seriously the structure of LiFePO₄. Electrochemical characterization of the electrodes showed that the Li‐ion batteries based on LiFe_1–xNb _xPO₄/C electrode exhibited better charge/discharge performance than those based on LiFePO₄/C. The LiFe_0.95Nb_0.05PO₄/C‐based cell had the specific capacity of 157, 121, and 85 mAh/g at 0.2, 2, and 5 C, respectively, in comparison with 126, 94, and 52 mAh/g for the LiFePO₄/C cell. The results show that the addition of niobium promotes the electrochemical performance of the materials especially at high charge/discharge rates of the battery.     

两步固相法合成LiFe1-xNbxPO4/C复合正极材料及其电化学性能

以LiH₂PO₄和FeC₂O₄·2H₂O为原料, 采用分步添加聚乙烯醇和葡萄糖两种碳源的方式, 通过两步固相法合成了碳包覆的LiFePO₄材料. 700℃下处理的产物结晶良好, 颗粒分布均匀, 具有良好的电化学性能, 0.1C和1C倍率下放电比容量分别为157.3 和138.3 mAh·g^-1. 在碳包覆的基础上, 选择高价Nb⁵⁺进行铁位取代获得了复合改性的LiFe_1-xNb_xPO₄/C (x=0.005, 0.01, 0.015, 0.02)材料. 优化的LiFe_0.99Nb_0.01PO₄/C 材料显示了良好的倍率充放电能力和循环稳定性, 0.1C和5C倍率下放电比容量分别为160.5 和136.0 mAh·g^-1, 5C倍率下循环50 次后比容量保持在134.8 mAh·g^-1, 容量保持率为99.1%. 循环伏安测试结果表明, Nb⁵⁺离子掺杂减少了锂离子扩散阻力, 降低了充放电过程中的动力学限制, 提高了电极的可逆性.     

Enhanced high rate and low temperature electrochemical properties of LiFePO4/C composites by doping samarium ion

The olivine-type samarium-doped LiFe_{1 ? x} Sm _x PO₄/C (x?=?0, 0.01, 0.02, 0.03, 0.04, and 0.05) composites were synthesized via liquid-phase precipitation reaction combined with the high-temperature solid-state method. The structure, morphology, and electrochemical performance of the samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, energy dispersive spectroscopy, galvanostatic charge–discharge, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy. The results showed that the small amount of Sm³⁺ ion-doped can keep the olivine microstructure of LiFePO₄, modify the particle morphology, decrease polarization overpotential and charge transfer resistance, and enhance exchange current density, thus improve the electrochemical performance of the LiFePO₄/C. However, the large doped content of Sm³⁺ ion can form more SmPO₄, which can weaken the electrochemical performance of LiFePO₄/C. Among all the doped samples, LiFe_0.99Sm_0.01PO₄/C showed the best rate capacity, cycling stability, and low temperature performance. The LiFe_0.99Sm_0.01PO₄/C sample exhibited the initial discharge capacity of 148.1, 133.4, 117.5, and 106.6 mAh g^?1 at 1C, 2C, 5C, and 10C, respectively. In addition, the discharge capacity of the material was 94.8 mAh g^?1 after 800 cycles at 10C. Moreover, the initial discharge capacity of 0.1C, 0.2C, 0.5C, and 1C were 104.4, 96.2, 53.9, and 50.8 mAh g^?1 at ?20 °C.     

Site-dependent electrochemical performance of Mg doped LiFePO4

Exotic metal (EM) doping in LiFePO4 materials could mitigate their poor electronic conductivity and electrochemical performance. This effect is believed to be dependent on the EM dwelling site, which has yet been well clarified due to experimental difficulty. Herein, we report on Mg-doped LiFePO₄ samples with dopant in two distinct sites, namely the Li_1 − 2xMg_xFePO₄ and LiFe_1 − xMg_xPO₄, using a specially designed two-step reaction. The conductivity and electrochemical test results are a clear indication that the performance of the doped LiFePO₄ samples is highly Mg site dependent, consistent with theoretical analysis.     

The improvement of the high-rate charge/discharge performances of LiFePO4 cathode material by Sn doping

Nanocrystalline LiFePO₄ and LiFe_0.97Sn_0.03PO₄ cathode materials were synthesized by an inorganic-based sol–gel route. The physicochemical properties of samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and elemental mapping. The doping effect of Sn on the electrochemical performance of LiFePO₄ cathode material was extensively investigated. The results showed that the doping of tin was beneficial to refine the particle size, increase the electrical conductivity, and facilitate the lithium-ion diffusion, which contributed to the improvement of the electrochemical properties of LiFePO₄, especially the high-rate charge/discharge performance. At the low discharge rate of 0.5 C, the LiFe_0.97Sn_0.03PO₄ sample delivered a specific capacity of 158 mAh g⁻¹, as compared with 147 mAh g⁻¹ of the pristine LiFePO₄. At higher C-rate, the doping sample exhibited more excellent discharge performance. LiFe_0.97Sn_0.03PO₄ delivered specific capacity of 146 and 128 mAh g⁻¹ at 5 C and 10 C, respectively, in comparison with 119 and 107 mAh g⁻¹ for LiFePO₄. Moreover, the doping of Sn did not influence the cycle capability, even at 10 C.     

Low-temperature synthesis of a green material for lithium-ion batteries cathode

Abstract

Battery technology is an important anthropogenic source of the heavy metals which are highly threatening to human health. A category of rechargeable lithium batteries that is of great interest is the set of batteries where the cathode material is a lithium iron phosphate (LiFePO₄). LiFePO₄ is an environmentally friendly and safe lithium-ion battery cathode material, but it has a key limitation, and that is its extremely low-electronic conductivity, a problem that can be greatly overcome by zinc-doping LiFePO₄. For the first time to our knowledge, a low-temperature method, that is advantageous both economically and technologically, for the synthesis of a zinc-doped LiFePO₄ is presented. Since the method appears to be applicable for synthesizing various zinc-doped LiFePO₄ compounds with the general formula LiFe_1?x Zn _x PO₄ (0<x<1), it is very promising for the production of a green cathode material for lithium-ion batteries.     

Characterization of the Optical and Gas Sensitivities of a Nickel-Doped Lithium Iron Phosphate Thin Film

The influence of heat-treatment temperature on the optical properties (refractive index, transmittance, and attenuation) and gas sensitivities of nickel-doped lithium iron phosphate (LiFe_0.99Ni_0.01PO₄) thin films were discussed. LiFe_0.99Ni_0.01PO₄ was synthesized in one step using hydrothermal methods and fixed to tin-diffused glass as a sensing film by spin-coating before calcination at different temperatures. The obtained thin films were characterized by refractive index, thickness, attenuation, and porosity, as well as gas sensing performances for benzene, toluene, and xylene. The experimental results indicated that the LiFe_0.99Ni_0.01PO₄ thin films dried at 450°C displayed higher refractive indices, good transparency, and less attenuation; thus, the resulting sensor of a LiFe_0.99Ni_0.01PO₄ thin film/tin-diffused optical wave-guide exhibited a greater response to xylene in the concentration range of 0.1–1000?ppm.