Electrochemical properties of Nano-LiFePO<Subscript>4</Subscript> prepared by hydrothermal reaction

LiFePO4 nanorods were facilely synthesized under hydrothermal condition. The crystalline structure and particle morphology of LiFePO4 powders were characterized by X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). The electrochemical properties of LiFePO4/Li cells were investigated by galvanostatic test and cyclic voltammetry (CV). The XRD result demonstrated LiFePO4 powder had an orthorhombic structure with a space group of Pnma. The synthesized LiFePO4 nanorods exhibited a...     

Technical optimization of LiFePO_4 preparation by water quenching treatment

A technique of combination of vacuum firing and water quenching was applied to the synthesis of LiFePO4 powder. The sample was prepared by heating the pre-decomposed precursor mixtures sealed in vacuum quartz-tube, followed by water quenching at the sintering temperature. The synthetic conditions were optimized by orthogonal experiment. The results indicate that the fast quenching treatment can avoid the overgrowth of single crystal and improve its availability ratio of active material. The sintering temperature has the greatest effect on the electrochemical performance of sample. Next is the molar ratio of Li to Fe and the sintering time, respectively. The samples prepared in the optimized technical condition has the highest reversible discharge specific capacity of 149.8 mA·h/g.     

LiFePO4高温固相合成工艺优化研究

采用正交试验法优化LiFePO4固相反应合成工艺,研究预烧温度、合成温度、保温时间等对锂离子电池正极材料LiFePO4电化学性能的影响。结果表明,预烧温度350℃、合成温度650℃、保温时间12h为最佳合成工艺条件。按最佳合成工艺所制样品的首次放电比容量达151．7mA·h／g,循环充放电30周后,其放电比容量仍为140．9mA·h／g。     

低成本动力锂离子电池磷酸铁锂正极材料的合成及性能

磷酸铁锂作为动力锂离子电池的正极材料的首选,正逐渐走向市场.以廉价的Li₃PO₄,FePO₄,Fe粉为原料,一步合成了LiFePO₄/C正极材料,系统研究了葡萄糖、蔗糖和柠檬酸三种不同的碳源对磷酸铁锂性能的影响.采用TG-DTA,XRD,SEM,TEM等手段对产物进行了表征,并研究了其电化学性能.实验结果表明,以葡萄糖为碳源的LiFePO₄/C性能最好,样品颗粒呈球形,表面光滑,分散性好,颗粒表面包覆有2 nm厚的石墨碳层,颗粒之间有碳纤维连接.该样品在0.1 C充放电时首周放电容量达到162.1 mAh/g,20周之后仍然保持在155 mAh/g,显示出良好的循环性能.     

Effect of cooling modes on microstructure and electrochemical performance of LiFePO4

LiFePO4 was prepared by heating the pre-decomposed precursor mixtures sealed in vacuum quartz-tube. Three kinds of cooling modes including nature cooling, air quenching, and water quenching were applied to comparing the effects of cooling modes on the microstructure and electrochemical characteristics of the material. The results indicate that the water quenching mode can control overgrowth of the grain size of final product and improve its electrochemical performance compared with nature cooling mode and air quenching mode. The sample synthesized by using water quenching mode is of the highest reversible discharge specific capacity and the best cyclic electrochemical performance, demonstrating the first discharge capacity of 138.1 mA·h/g at 0.1C rate and the total loss of capacity of 3.11% after 20 cycles.     

Cu微粒包覆Cu/LiFePO4正极材料的制备及性能研究

用高温固相反应法制备Cu微粒包覆的锂离子电池正极材料Cu/LiFePO4。采用X射线衍射、场发射扫描电镜对材料的物相结构和颗粒形貌进行分析和观察,采用恒流充放电、慢扫描循环伏安法和电化学阻抗谱法测试材料的电化学性能。结果表明,Cu微粒包覆使复合材料颗粒分散更均匀,结晶更明显;Cu/LiFePO4（n（Cu）∶n（Li）=1∶15）正极材料首次放电比容量最高为142.8 mA.h/g,与纯LiFePO4正极材料的对应值151.7 mA.h/g相比有所下降;虽然Cu微粒的加入在一定程度上能够提高材料的电子导电率,但在第一周充电时Cu即发生不可逆氧化,导致该复合材料具有较低的放电比容量和较大的首次不可逆容量损失。     

Synthesis and characterization of CePO4 nanorods via solvothermal process

One-dimensional cerium phosphate(CePO4) nanorods were successfully synthesized by a facile and simple solvothermal method at 150 ℃ for 12 h, using Ce(NO3)3·6H2O and NaH2PO4·2H2O as the starting materials. Phase and morphologie of the as-synthesized CePO4 products, characterized by XRD, FESEM, and TEM, were proved to be perfect and uniform hexagonal CePO4 nanorods with aspect ratio of more than 100. The photoluminescence(PL) spectrometer was used to investigate the optical properties of the assynthesized hexagonal CePO4 nanorods.     

Synthesis and performance of carbon-modified LiFePO_4 using an in situ PVA pyrolysis procedure

LiFePO4/carbon composite cathode material was prepared by granulating and subsequent pyrolysis processing in N2 at- mosphere with polyvinyl alcohol (PVA) as the carbon source. The influences of carbon content on the microstructure and battery performance were investigated. Single LiFePO4 phase and amorphous carbon can be found in the products. A special mi- cro-morphology of the optimum sample was observed. The discharge capacity of the cell with the optimum cathode was 135 mAh·g?1, close to the charge capacity of 153 mAh·g?1 at 17 mA·g?1. The influence of ambient temperature on the cell capacity was investigated. The temperature dependence of its electrochemical characteristic was evaluated by using AC impedance spectroscopy. A new equivalent circuit based on the charge and mass transfer control process in an electrode was proposed to fit the obtained AC im- pedance spectra. The tendency of every element in the equivalent circuit was used to interpret the temperature dependence of the ca- pacity of the optimum cathode.     

双碳源在LiFePO4/C微波固相合成中的协同效应

以Li2CO3,FeC2O4·2H2O和NH4 H2 PO4为前驱体,分别以葡萄糖和葡萄糖/乙炔黑为碳源,利用微波加热合成了LiFePO4/C正极材料.用X射线粉末衍射（XRD）和扫描电镜（SEM）对材料进行了表征,用四探针法测定了材料的电导率.研究了碳源与微波温度对材料微结构和电化学性能的影响,发现由于乙炔黑的协同效应,用双碳源在600℃反应即可得到最佳电化学性能的LiFePO4/C,而仅用葡萄糖作碳源反应需要在较高温度（如700℃）下进行.     

La2O3对LiFePO4正极材料的修饰改性研究

采用碳热还原法合成橄榄石型LiFePO4正极材料,并用溶胶-凝胶法在其表面修饰La2O3颗粒。通过X射线衍射（XRD）、场发射扫描电镜（FE-SEM）等方法对表面修饰前后的LiFePO4进行表征,分析了表面修饰前后LiFePO4物理性质的变化,并进行了恒流充放电测试和循环伏安测试,研究了表面修饰对LiFePO4电化学性能的影响。结果表明,La2O3表面修饰没有改变LiFePO4材料的晶体结构,LiFePO4材料经La2O3修饰后,其电化学性能显著改善。     

化学研磨法制备磷酸铁锂正极材料的结构性能研究

磷酸铁锂被认为是最有可能应用于锂离子动力电池的正极材料.采用化学研磨法制备了磷酸铁锂,并对其结构和电化学性能进行了研究.结果表明：相对于传统高温固相法,化学研磨法可以有效细化磷酸铁锂的颗粒和晶粒,所得材料0.1 C放电容量为132 mAh/g,明显高于传统固相法112 mAh/g的容量.     

Synthesis and performance of carbon-modified LiFePO4 using an in situ PVA pyrolysis procedure

LiFePO4/carbon composite cathode material was prepared by granulating and subsequent pyrolysis processing in N2 atmosphere with polyvinyl alcohol (PVA) as the carbon source. The influences of carbon content on the microstructure and battery performance were investigated. Single LiFePO4 phase and amorphous carbon can be found in the products. A special micro-morphology perature dependence of its electrochemical characteristic was evaluated by using AC impedance spectroscopy. A new equivalent circuit based on the charge and mass transfer control process in an electrode was proposed to fit the obtained AC impedance spectra.The tendency of every element in the equivalent circuit was used to interpret the temperature dependence of the capacity of the optimum cathode.     

Technical optimization of LiFeP04 preparation by water quenching treatment

A technique of combination of vacuum firing and water quenching was applied to the synthesis of LiFePO4 powder. The sample was prepared by heating the pre-decomposed precursor mixtures sealed in vacuum quartz-tube, followed by water quenching at the sintering temperature. The synthetic conditions were optimized by orthogonal experiment. The results indicate that the fast quenching treatment can avoid the overgrowth of single crystal and improve its availability ratio of active material. The sintering temperature has the greatest effect on the electrochemical performance of sample. Next is the molar ratio of Li to Fe and the sintering time, respectively. The samples prepared in the optimized technical condition has the highest reversible discharge specific capacity of 149.8 mA·h/g.     

锂离子电池正极材料LiNixFe1-xPO4的制备及其性能

为提高锂离子电池正极材料LiFePO4的充放电性能，用Ni对LiFePO4进行掺杂，研究了Ni掺杂量对LiFePO4性能的影响，在LiNixFe1-xPO4（x=0，0．01，0．03，0．05，0．10）材料中，LiNi0.03Fe0.97PO4具有比LiFePO4更好的电化学性能，用80mA／g的电流进行充放电时，第2次放电比容量为133．278mAh／g，循环20次后为127．655mAh／g．     

Preparation of LiFePO4 for lithium ion battery using Fe2P2O7 as precursor

In order to obtain a new precursor for LiFePO4, Fe2P2O7 with high purity was prepared through solid phase reaction at 650 ℃ using starting materials of FeC2O4 and NH4H2PO4 in an argon atmosphere. Using the as-prepared Fe2P2O7, Li2CO3 and glucose as raw materials, pure LiFePO4 and LiFePO4/C composite materials were respectively synthesized by solid state reaction at 700 ℃ in an argon atmosphere. X-ray diffractometry and scanning electron microscopy(SEM) were employed to characterize the as-prepared Fe2P2O7, LiFePO4 and LiFePO4/C. The as-prepared Fe2P2O7 crystallizes in the c1 space group and belongs to β-Fe2P2O7 for crystal phase. The particle size distribution of Fe2P2O7 observed by SEM is 0.4-3.0μm. During the Li ion chemical intercalation, radical P2O4-O7 is disrupted into two PO3-4 ions in the presence of O2-, thus providing a feasible technique to dispose this poor dissolvable pyrophosphate. LiFePO4/C composite exhibits initial charge and discharge capacities of 154 and 132 mA·h/g, respectively.     

尖晶石型锰酸锂制备及其电化学性能

锰酸锂被认为是取代商品锂离子电池正极材料的LiCoO2候选材料.以二氧化锰、醋酸锰及氢氧化锂为原料,蒸馏水为分散剂,在空气气氛下进行分段烧结,控制烧结温度和时间,制备了锂离子电池正极材料锰酸锂.用X射线衍射仪,电子扫描电镜对产物的结构特征、微观表面形貌和恒流充放电性能进行了表征.结果表明:所制得正极材料为尖晶石型锰酸锂,结晶度高,无杂质相,材料颗粒的粒径均匀,首次放电比容量为117.3 mAh/g(0.5 mA/cm2,2.8~4.4 V,vs.Li+/Li);50次循环后,放电比容量为107.9 mAh/g,不可逆容量损失为9.4 mAh/g,比容量保持率为92.0%.得到了很好的综合电化学性能.     

基于18650型磷酸铁锂动力电芯的产热和电化学行为分析

测试某知名进口和国产的A款和B款18650磷酸铁锂动力电芯在室温（25℃）、低温（–20℃）和高温（55℃）下不同放电倍率的温度性能、产热行为和电化学性能,分析两款电芯放电容量、放电电压平台、交流阻抗、电芯过充循环后直流内阻随着荷电状态的变化规律.结果表明环境温度和放电电流越高,电芯最高温度和温升斜率急剧增加;室温10 C放电时,B款最高温度比A款增加13.2%; B款电芯低温工况大电流放电时,电芯仅放出2.65%的电量,几乎失去正常放电电压平台;电芯的直流内阻随着荷电量的增加呈下降的趋势,过充导致电芯的直流内阻最大增加24.19%.     

Mn2+掺杂对LiFePO4正极材料结构、性能及嵌锂动力学的影响

为了改善橄榄石型LiFePO4正极材料的性能,采用高温固相法合成了Mn掺杂的LiMnxFe1-xPO4(x=0,0.10,0.25,0.40,0.50)材料.采用X射线粉末衍射、扫描电子显微镜、充放电测试、循环伏安和电化学阻抗谱研究了材料的结构、电化学性能和锂离子嵌脱动力学.结果表明,锰掺杂的LiFePO4样品颗粒分布比较均匀,具有较小的平均粒径和窄的粒度分布,LiMnxFe1-xPO4是纯相的橄榄石结构.在不同倍率下,LiMn0.4Fe0.6PO4具有最高的放电容量和最好的动力学性能.Mn的掺杂提高了LiFePO4材料的可逆性、锂离子扩散系数和放电容量,减小了电荷转移电阻,进而提高了其动力学性能.     

Effect of Fe(III) impurity on the electrochemical performance of LiFePO_4 prepared by hydrothermal process

Lithium iron phosphate (LiFePO4) was synthesized from LiOH, FeSO4 and H3PO4 by a hydrothermal process at 180℃. The samples were characterized by X-ray diffraction, scanning electron microscopy and chemical analysis. Electrochemical performance of the samples was tested in terms of charge-discharge capacity and cycling behavior. The results indicated that Fe(III) impurity had obvi- ously effect on the electrochemical properties of LiFePO4, and the formation of Fe3 was caused by the oxidation of Fe2 in the dissolving and feeding processes accompanying the increase of pH value. It was found that the precipitation separation was effective in decreasing the content of Fe3 in the solu- tion of FeSO4 and the sealed feeding was useful in preventing the conversion of Fe2 to Fe3 . When the content of Fe3 < 0.5 wt%, the hydrothermally synthesized LiFePO4 calcined at 750℃ with sucrose as carbon source exhibited an initial discharge capacity of 154.9 mAh·g-1 at the rate of 0.1 C (1 C = 150 mA·g-1) and the cycling retention rate could reach 98% after 50 cycles at room temperature.     

锂离子电池正极材料Li0.97Re0.01FePO4的合成及性能

采用固相反应法合成了锂离子电池正极材料Li0.97Re0.01FePO4（Re=Er,Y,Gd,Nd,La）,采用X射线衍射、恒电流充放试验对掺杂试样的微观结构和电化学性能进行测试。试验结果表明：掺杂稀土金属离子对LiFePO4的晶体结构没有影响,与LiFePO4相比,掺杂Er^3＋,Y^3＋,Gd^3＋的试样具有优良的循环性能和倍率性能,而掺杂Nd^3＋,La^3＋的试样的循环性能和倍率性能较差。掺杂试样中,Li0.97Re0.01FePO4的电化学性能最佳,在C/10和1C（1C=120mA·g^-1）倍率下放电容量均最大。