碳含量对LiFePO4/C复合正极材料性能的影响

Olivine-type LiFePO4/C composite cathode materials were synthesized by a solid-state reaction method in an inert atmosphere. The glucose was added as conductive precursors before the formation of the crystalline phase. The effects of glucose content on the properties of as-synthesized cathode materials were investigated. The crystal structure and the electrochemical performance were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, laser particle-size distribution measurement and electrochemical performance testing. The material has a single crystal olivine structure with grain-sizes ca. 100-200 nm. SEM micrographs and the corresponding energy dispersive spectrometer （EDS） data confirm that the carbon particulates produced by glucose pyrogenation are uniformly dispersed among the LiFePO4 grains, ensuring a good electronic contact. Impedance spectroscopy was used to investigate the ohmic and kinetic contributions to the cell performance. It is found that increasing the carbon content leads to a reduction of the cell impedance due to the reduction of the charge transfer resistance. The galvanostatically charge and discharge tests show that the material obtained by adding 10% C （by mass） gives a maximum discharge capacity of 140.8mA·h·g^-1 at the same rate （C/10）. The material also displays a more stable cycle-life than the others.     

改进的共沉淀-微波法合成正极材料LiFePO_4/C

采用改进的共沉淀-微波法,利用自制加料装甓合成了橄榄石型LiFePO_4/C复合正极材料.应用X射线衍射(XRD)、循环伏安(CV)以及恒电流充放电测试等方法对目标材料进行了结构表征和电化学性能测试.实验结果表明微波烧结8 min的样品具有单一的橄榄石型晶体结构和较好的电化学性能,0.2 C倍率下充放电测试表明,其首次放电比容量158.09 mAh/g,20次循环后,容量没有明显衰减.0.5、1、2C倍率下的平均放电容量分别为135.42、98.40、83.79 mAh/g,循环过程中样品表现出较好的循环稳定性.     

Factor affecting rate performance of undoped LiFePO4

Undoped lithium iron phosphate (LiFePO₄) was prepared and characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. The material has a single crystal globular structure with grain-sizes ca. 100-150 nm. It was used to prepare composite electrodes containing different amounts of carbon (10, 15 and 20 wt.%, respectively) used as cathodes in non-aqueous lithium cells. By increasing the carbon content, an increase in the overall electrochemical performance was observed. Impedance spectroscopy was used to investigate the ohmic and kinetic contributions to the cell overvoltage. It was found that increasing the carbon content leads to a reduction of the cell impedance as a consequence of the reduction of the charge transfer resistance. The poor performance exhibited at very high discharge rates is a direct consequence of the high value of the charge transfer resistance. A further decrease of the charge transfer resistance in high carbon content cathodes (20 wt.% carbon) was obtained by improving the powder mixing procedure. The cell performance of well mixed, high carbon content electrodes was better than our previously obtained results in terms of higher capacity retention both for different discharge rates and repeated cycling. For currents larger than a 3 C rate, a severe capacity fade affected the electrodes. It was concluded that the electronic contact at the LiFePO₄/carbon interface plays a decisive role in material utilization at different discharge rates which affects the capacity fade upon cycling.     

LiFePO_4/C复合材料的制备和性能

采用高温固相合成法二次灼烧工艺制备锂离子电池正极复合材料LiFePO4/C。经300℃和650℃二次灼烧,得到了从纳米到亚微米尺寸的LiFePO4和LiFePO4/C复合材料。X射线衍射(XRD)结果表明,所得到的LiFePO4和LiFePO4/C样品具有单一的橄榄石型晶体结构,且具高纯度。在多种碳源(如乙炔黑、Vulcan XC-72碳黑、鳞状石墨、各向异性石墨和葡萄糖)制备的LiFePO4/C复合材料中,以葡萄糖为碳源合成的样品具有最好的电化学性能。在电池工作温度由室温提高到40℃时,由于复合材料的电子电导率增大和锂离子在材料中的扩散速度加快,电池的充放电循环性能明显提高。     

高密度LiFePO4正极材料的合成与性能

以高温固相法制备了高密度的LiFePO4正极材料,利用XRD、SEM、粒度分析、交流阻抗以及充放电测试等方法研究了前驱体Li3PO4和FePO4的比例与LiFePO4的物理性能和电化学性能的关系。其中,在Li3PO4与FePO4物质的量比为3：2时,制备的LiFePO4正极材料振实密度高达1.4g／cm^3,以0.1C放充电时,其首次放电比容量为159.0mA·h／g,体积比容量为222.6A·h／L,循环25次后,容量保持率达94.0％。     

电池正极材料Li3V2-2x/3Mnx（PO4）3/C的制备及性能研究

以V2O5、NH4H2PO4、Li2CO3、(CH3COO)2Mn.4H2O原料,以葡萄糖和抗坏血酸为复合还原剂及碳源,通过常温还原-低温烧结法制备锂离子电池正极材料Li3V(2-2x/3)Mnx(PO4)3/C(x=0,0.03,0.06,0.09,0.12)。通过X射线衍射(XRD),扫描电镜(SEM),恒电流充放电测试对该正极材料的物相、结构、微观形貌以及电化学性能进行了表征。结果表明,Mn2+的掺杂对磷酸钒锂电化学性能的发挥影响很大,其中当锰掺杂量x=0.09时材料表现出最佳的电化学性能,0.2 C倍率条件下首次放电比容量131 mAh/g,循环50次后容量衰减仅为4.02%。     

掺杂改性LiFePO_4正极材料制备及表征

采用微波热合法制备了掺杂LiFePO4锂电池用正极材料。通过XRD、SEM表征了材料的晶体结构和形貌,采用恒电流充放电法研究了材料的电化学性能。XRD结果表明,掺杂后的材料晶相为橄榄石型磷酸铁锂;SEM测试结果表明,加热时间延长促使材料颗粒团聚长大,且结晶完整,颗粒分布均匀。对电池的电化学测试表明,制备的掺杂LiFePO4材料表现出优良倍率性能和循环稳定性,充放电比容量分别为131.7 mAh/g和123.8 mAh/g,10次循环后比容量没有明显衰减。     

硫掺杂纳米Li2FeSiO4/C制备与电化学性能

采用固相反应法制备了 Li2FeSiO4-xSx/C (x=0,0.01,0.02,0.03)纳米正极材料。通过 X 射线 衍射（XRD）、扫描电子显微镜（SEM）、能量色散光谱仪（EDS）、X 射线光电子能谱（XPS）、拉 曼光谱（Raman）、红外吸收光谱（FTIR）及恒流充放电测试研究了材料的微观形貌、晶体结构和 电化学性能。结果表明，Li2FeSiO3.98S0.02/C 形貌呈纳米球状，平均粒径为45.38nm，纳米尺寸的粒径有利于缩短Li+的扩散途径；碳包覆抑制纳米晶粒的生长，可以增强材料的导电性；硫掺杂能扩大材料的隧道间距，加快了Li+的迁移速率。Li2FeSiO3.98S0.02/C 表现出较高的充放电比容量、优异的倍率性能以及循环稳定性，在 0.1C 下首次放电比容量高达 180.1mAhg -1，在 10C 下放电比容量为 85mAhg-1,1C 下循环 100 次后的容量保持率为 91.3%。     

锂离子正极材料Li（Ni_（1/3）Co_（1/3）Mn_（1/3））O_（2-x）F_x的合成与电化学性能

采用沉淀法合成一系列Li（Ni1/3Co1/3Mn1/3）O2-xFx正极材料（0≤x≤0.5）;用X射线衍射仪和扫描电镜仪分析了合成产物的晶体结构及表面形貌;利用充放电仪测定产物的电化学性能,结果表明Li（Ni1/3Co1/3Mn1/3）O1.7F0.3的电化学性能最佳,首次充放电比容量分别达181.9、174.0 mA.h/g,材料的结构在循环过程中保持稳定,倍率性能变好,电化学阻抗明显降低。     

Synthesis and characterization of high-density LiFePO4/C composites as cathode materials for lithium-ion batteries

To achieve a high-energy-density lithium electrode, high-density LiFePO₄/C composite cathode material for a lithium-ion battery was synthesized using self-produced high-density FePO₄ as a precursor, glucose as a C source, and Li₂CO₃ as a Li source, in a pipe furnace under an atmosphere of 5% H₂-95% N₂. The structure of the synthesized material was analyzed and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical properties of the synthesized LiFePO₄/carbon composite were investigated by cyclic voltammetry (CV) and the charge/discharge process. The tap-density of the synthesized LiFePO₄/carbon composite powder with a carbon content of 7% reached 1.80 g m⁻³. The charge/discharge tests show that the cathode material has initial charge/discharge capacities of 190.5 and 167.0 mAh g⁻¹, respectively, with a volume capacity of 300.6 mAh cm⁻³, at a 0.1C rate. At a rate of 5C, the LiFePO₄/carbon composite shows a high discharge capacity of 98.3 mAh g⁻¹ and a volume capacity of 176.94 mAh cm⁻³.     

Effect of CeO2-coating on the electrochemical performances of LiFePO4/C cathode material

The effect of CeO₂ coating on LiFePO₄/C cathode material has been investigated. The crystalline structure and morphology of the synthesized powders have been characterized by XRD, SEM, TEM and their electrochemical performances both at room temperature and low temperature are evaluated by CV, EIS and galvanostatic charge/discharge tests. It is found that, nano-CeO₂ particles distribute on the surface of LiFePO₄ without destroying the crystal structure of the bulk material. The CeO₂-coated LiFePO₄/C cathode material shows improved lithium insertion/extraction capacity and electrode kinetics, especially at high rates and low temperature. At −20 °C, the CeO₂-coated material delivers discharge capacity of 99.7 mAh/g at 0.1C rate and the capacity retention of 98.6% is obtained after 30 cycles at various charge/discharge rates. The results indicate that the surface treatment should be an effective way to improve the comprehensive properties of the cathode materials for lithium ion batteries.     

5VLiNi0．5Mn1．5O4正极材料掺杂Rh离子改性研究

采用固相烧结法成功合成了Rh掺杂的LiNi0．5Mnl．504正极材料。通过XRD测试和充放电测试表征了材料的晶体结构和电化学性能。结果表明Rh掺杂可以有效提高LiNi05Mnl504在大电流密度（5c和10c）条件下的放电电量,并可以显著改善IOC充放电条件下的循环性能。     

铜掺杂碳包覆磷酸铁锂的微波合成及性能研究

研究了铜掺杂碳包覆磷酸铁锂（LiFePO₄）的微波合成。通过X射线衍射（XRD）表征了样品的化学组成和晶体结构,通过扫描电镜（SEM）考察了样品的微观形貌。分别用铜掺杂磷酸铁锂、碳包覆磷酸铁锂、铜掺杂碳包覆磷酸铁锂作为锂离子电池正极材料,进行了电化学性能测试比较。充放电测试表明,微波合成的铜掺杂碳包覆磷酸铁锂具有良好的充放电性能和循环寿命,首次放电比容量达到145 mA•h/g,循环30次后比容量仍然有143.5 mA•h/g,为初始容量的98.96%,容量几乎无衰减。     

以溶液法制备的钠掺杂锂离子电池正极材料Li3-xNaxV2(PO4)3/C

以溶液法为制备方法、以葡萄糖为碳源合成了一种钠离子掺杂的锂离子电池正极材料Li_3-xNa_xV₂（PO₄）₃/C（x=0、0.01、0.03、0.05、0.07）。XRD结果显示组成相为单斜晶型,与标准Li₃V₂（PO₄）₃衍射峰完全一致。微量钠掺杂并未改变产物的相组成与晶体结构,但使得晶胞参数有所变化,这种变化有利于提高锂离子的扩散系数。SEM与TEM谱图显示材料颗粒基本为近似椭圆形,粒径分布均匀,碳包覆层完整。充放电测试显示Li_2.97Na_0.03V₂（PO₄）₃/C试样的倍率性能最好,在12C倍率下放电比容量约为100mAh/g,循环伏安测试也证明该试样的锂离子扩散系数较高,比纯相Li₃V₂（PO₄）₃提高了约2个数量级。     

金属离子浓度对LiNi_(0.5)Co_(0.2)Mn_(0.3)O_2材料结构及电化学性能影响研究

采用液相共沉淀+高温煅烧法制备正极材料LiNi0.5Co0.2Mn0.3O2,利用XRD、SEM及恒电流充放电等等分析手段,研究不同金属离子浓度合成镍钴锰酸锂前驱体对最终产品晶体结构、形貌及其电化学性能的影响。结果表明:金属离子浓度为2.0 mol/L时,所制备材料晶型层状结构发育完整,粒径分布均匀,球形度高且表面光滑,材料首次放电比容量达172.5 mAh/g,首次库伦效率为90.84%。     

磷酸亚铁锂-磷酸钒锂复合材料制备方法研究

以固相法制备出了磷酸亚铁锂-磷酸钒锂复合正极材料.采用X-射线衍射仪(XRD)、电子扫面电镜(SEM)、激光粒度分析仪、碳硫分析仪以及X-光电子能谱仪等对制备出的复合材料进行表征,发现该材料以磷酸亚铁锂和磷酸钒锂的晶形结构为主,其中有少量的杂质成分;该材料颗粒粒度较细、粒度分布窄且均匀,颗粒表面光滑、碳包裹状况良好,同其它方法制备的复合材料比较在碳含量差不多的情况下具有较优的导电率.对材料进行了电化学性能表征认为该材料的电化学性能比较优异,0.1C放电容量达到190 mA·h·g-1以上,10C可以达到120 mA·h·g-1,20C放电容量仍有85 mA·h·g-1且循环稳定性均较好;1C进行1000次循环之后仍然保持120 mA·h·g-1的容量,具有较高的实用价值.     

Synthesis of bimetallic sulfide CuCo2S4 and its application in lithium-sulfur batteries

Lithium-sulfur batteries have received extensive attention in recent years due to the high specific energy. However, their development needs to overcome many problems such as the shuttle effect of intermediate products, the insulation of sulfur, and the volume expansion of the cathode. To effectively suppress the shuttle effect, this paper uses a method derived from Prussian blue analogs to synthesize a spinel bimetallic sulfide CuCo₂S₄ and use it for the cathode of lithium-sulfur batteries. XRD, SEM, TEM, BET, XPS and other characterizations were used to analyze the crystal structure and morphology of the synthesized materials, and the electrochemical performance of the CuCo₂S₄-S composite cathode was tested by cyclic voltammetry and galvanostatic charge and discharge process. Studies show that the CuCo₂S₄-S cathode exhibits excellent electrochemical performance. The first initial capacity is 959 mA·h·g^-1 at the rate of 0.2C, and 591 mA·h·g^-1 remains after 100 cycles. The high discharge specific capacity and good cycling stability are attributed to the hollow structure inside the CuCo₂S₄ material that can accommodate the active material sulfur and play a role in physical confinement; at the same time, the polar CuCo₂S₄ can effectively chemically adsorb polysulfides and suppress capacity loss caused by the shuttle effect of polysulfides.     

Effects of nitrogen-doped carbon nanotubes on the discharge performance of Li-air batteries

Carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (N-CNTs) were synthesized using a floating catalyst chemical vapor deposition method and characterized by scanning electron microscopy (SEM), transmission electron microscopy, Raman and X-ray photoelectron spectroscopy. The study found that the as-prepared CNTs and N-CNTs showed different discharge capacity as cathode materials in Li-air battery. To further study the reason why N-doping improves the electrochemical performance exceptionally, the discharge products on the two kinds of nanotubes were detected by SEM, XRD and Raman. SEM study showed, for the first time, that more uniform distribution of discharge products on the surface of CNTs arising from N-doping affected the boost of discharge capacity, a result which was discussed in detail. In comparison to non-doped CNTs, nitrogen doping was considered to be a promising way to improve the performance of carbon based cathode material for Li-air batteries.     

双金属硫化物CuCo2S4的合成及其在锂硫电池中的应用

锂硫电池因较高的比能量近年来得到了广泛的关注，然而其发展需要克服中间产物的穿梭效应、硫的绝缘性和正极体积膨胀等诸多问题。为了有效抑制穿梭效应，采用普鲁士蓝类似物衍生的方法合成了一种尖晶石结构的双金属硫化物CuCo₂S₄，并将其用于锂硫电池正极。利用XRD、SEM、TEM、BET、XPS等手段对合成的材料的晶体结构、形貌等性质进行分析，采用循环伏安法及恒流充放电对CuCo₂S₄-S复合正极的电化学性能进行测试。研究表明，CuCo₂S₄-S正极展现出优异的电化学性能，在0.2C倍率下首次放电容量为959 mA·h·g^-1，经过100个循环后容量保持在591 mA·h·g^-1。较高的放电比容量和良好的循环稳定性归因于CuCo₂S₄材料内部的中空结构可容纳活性物质硫，并起到物理限域作用；同时，极性CuCo₂S₄可有效地化学吸附多硫化物，抑制多硫化物的穿梭效应造成的容量损失。     

Effective enhancement of the electrochemical properties for Na2FeP2O7/C cathode materials by boron doping

In recent years, the composite materials based on polyanionic frameworks as secondary sodium ion battery electrode material have been developed in large-scale energy storage applications due to its safety and stability. The Na₂FeP₂O₇/C (theoretical capacity 97 mA·h·g^-1) is recognized as optimum Na-storage cathode materials with a trade-off between electrode performance and cost. In the present work, The Na₂FeP₂O₇/C and boron-doped Na₂FeP_2-BO₇/C composites were synthesized via a novel method of liquid phase combined with high temperature solid phase. The non-metallic element B doping not only had positive influence on the crystal structure stability, Na⁺ diffusion and electrical conductivity of Na₂FeP₂O₇/C, but also contributed to the high-value recycling of B element in waste borax. The structure and electrochemical properties of the cathode material were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), The X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and charge/discharge cycling. The results showed that different amounts of boron doping had positive effects on the structure and electrochemical properties of the material. The initial charge/discharge performances of born doped materials were improved in comparison to the bare Na₂FeP₂O₇/C. The cycle performance of the Na₂FeP_1.95B_0.05O₇/C showed an initial reversible capacity of 74.8 mA·h·g^-1 and the high capacity retention of 91.8% after 100 cycles at 1.0 C, while the initial reversible capacity of the bare Na₂FeP₂O₇/C was only 66.2 mA·h·g^-1. The improvement of apparent Na⁺ diffusion and electrical conductivity due to B doping were verified by the EIS test and CVs at various scan rate. The experimental results from present work is useful for opening new insight into the contrivance and creation of applicable sodium polyanionic cathode materials for high-performance.