锂离子电池正极材料LiFePO_4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.     

锂离子电池复合正极材料xLiFePO4·yLi3V2(PO4)3的复合机制

以FePO4·xH2O、V2O5、NH4H2PO4和Li2CO3为原料, 以乙二酸为还原剂, 通过湿化学还原-低温热处理方法制备出锂离子复合正极材料xLiFePO4·yLi3V2(PO4)3. X射线衍射(XRD)结果表明, 合成的材料中橄榄石结构的LiFePO4和单斜晶系的Li3V2(PO4)3两相共存; 从复合材料中LiFePO4、Li3V2(PO4)3相对于相同条件下制备的纯相LiFePO4和Li3V2(PO4)3的晶格常数变化以及结合高分辨透射电子显微镜(HRTEM)、能量散射X射线(EDAX)的结果可以看出, 在复合材料xLiFePO4·yLi3V2(PO4)3中存在部分V和Fe, 分别掺杂在LiFePO4和Li3V2(PO4)3中, 并形成固溶体; X射线光电子能谱(XPS)结果表明, Fe/V在复合材料中的价态与各自在LiFePO4和Li3V2(PO4)3中的价态保持一致, 分别为+2 和+3价. 充放电测试表明, 制备出的复合正极材料电化学性能明显优于单一的LiFePO4和Li3V2(PO4)3; 循环伏安测试表明, 复合正极材料具有优良的脱/嵌锂性能.     

钒改性锂离子电池正极材料LiFe0.5Mn0.5PO4/C电化学性能

采用高温固相反应,以NH4VO3为钒源合成了化学计量式为(1-x)LiFe0.5Mn0.5PO4-xLi3V2(PO4)3/C (x=0,0.1,0.2,0.25,1)的钒改性磷酸锰铁锂正极材料.电化学测试表明钒改性能明显提高磷酸锰铁锂材料的充放电性能,其中x=0.2时得到的0.8LiFe0.5Mn0.5PO4-0.2Li3V2(PO4)3/C(标记为LFMP-LVP/C)材料电化学性能最好,其0.1C倍率时的放电比容量为141 mAh·g-1.X射线衍射(XRD)分析指出LFMP-LVP/C材料的微观结构为橄榄石型LiFe0.5Mn0.5PO4/C和NASICON型Li3V2(PO4)3组成的双相结构.能量色射X射线谱(EDS)分析结果指出,Fe、Mn、V、P元素在所合成材料中的分布非常均匀,表明所制备材料成分的均一性.Li3V2(PO4)3改性使材料的电导率明显提高.LiFe0.5Mn0.5PO4的电导率为1.9×10-8 S· cm-1,而LFMP-LVP材料电导率提高到2.7×10-7 S·cm-1.与纯Li3V2(PO4)3的电导率(2.3×10-7 S·cm-1)相近.电化学测试表明钒改性使LFMP-LVP/C材料充放电过程电极极化明显减小,从而电化学性能得到显著提高.本文工作表明Li3V2(PO4)3改性可成为提高橄榄石型磷酸盐锂离子电池正极材料电化学性能的一种有效方法.     

钒改性锂离子电池正极材料LiFe0.5Mn0.5PO4/C 电化学性能

采用高温固相反应,以NH4VO3为钒源合成了化学计量式为(1-x)LiFe0.5Mn0.5PO4-xLi3V2(PO4)3/C(x=0,0.1,0.2,0.25,1)的钒改性磷酸锰铁锂正极材料.电化学测试表明钒改性能明显提高磷酸锰铁锂材料的充放电性能,其中x=0.2时得到的0.8LiFe0.5Mn0.5PO4-0.2Li3V2(PO4)3/C(标记为LFMP-LVP/C)材料电化学性能最好,其0.1C倍率时的放电比容量为141mAh·g-1.X射线衍射(XRD)分析指出LFMP-LVP/C材料的微观结构为橄榄石型LiFe0.5Mn0.5PO4/C和NASICON型Li3V2(PO4)3组成的双相结构.能量色射X射线谱(EDS)分析结果指出,Fe、Mn、V、P元素在所合成材料中的分布非常均匀,表明所制备材料成分的均一性.Li3V2(PO4)3改性使材料的电导率明显提高.LiFe0.5Mn0.5PO4的电导率为1.9×10-8S·cm-1,而LFMP-LVP材料电导率提高到2.7×10-7S·cm-1.与纯Li3V2(PO4)3的电导率(2.3×10-7S·cm-1)相近.电化学测试表明钒改性使LFMP-LVP/C材料充放电过程电极极化明显减小,从而电化学性能得到显著提高.本文工作表明Li3V2(PO4)3改性可成为提高橄榄石型磷酸盐锂离子电池正极材料电化学性能的一种有效方法.     

《化学通报》网络版(Chemistry Online)2004年第4期论文摘要

[w0 2 5 ]磷酸铁锂锂离子电池正极材料的研究进展Research Progress on Li Fe PO4Cathode Materials for L ithium- ion Batteries吕正中　周震涛 (华南理工大学材料科学与工程学院　广州　 5 10 6 41)从材料的制备、改性、粒径控制、结构与性能等几方面综述了近年来对橄榄石型磷酸铁锂 (Li Fe PO4)锂离子电池正极材料的研究进展。材料的粒度大小及其分布、离子和电子的传导能力以及其中 Fe( )的含量对产品的电化学性能影响很大。在制备时 ,采用惰性气氛、掺杂导电材料和控制晶粒生长制备纳米粉体是获得性能优良的Li Fe PO4的有效方…     

Ti4+离子掺杂对Li3V2(PO4)3晶体结构与性能的影响

采用溶胶凝胶/碳热还原法合成了锂离子电池正极材料Li3V2(PO4)3及其掺Ti化合物Li3-2x(V1-xTix)2-(PO4)3. 电化学测试结果表明, 经Ti4+离子掺杂后材料的充放电性能及循环性能明显提高. 与纯相Li3V2(PO4)3在3.58、3.67和4.08 V出现三个平台相比, 掺杂后材料的前两个平台发生简并且平台趋于模糊的倾斜状态. 这种趋势随掺杂量的增大而增强. 差热分析(DTA)表明掺杂生成了稳定的酌相产物. 采用X射线衍射和Rietveld方法表征了化合物的晶体结构, 结果表明, 三个不同位置Li的不完全占据导致晶体中产生阳离子空穴, 使材料在常温下的离子电导率提高了3个数量级. 锂离子混排提高了样品的电导率和充放电比容量.     

新型聚阴离子型正极材料的合成、结构表征及电化学性能

寻求廉价、安全、环境友好并具有高比能量的可充锂电池正极材料成为目前锂离子电池材料研究的热点之一.聚阴离子型正极材料(如:橄榄石型LiFePO4材料)作为新一代锂离子电池正极材料引起了人们的广泛关注[1-3],给锂离子电池正极材料带来了安全、廉价、环境友好的q希望,为动力及储能电池的发展提供一个很好的材料体系选择.硅酸盐材料(Li2MSiO4,M为金属元素)理论上可以允许可逆的嵌脱两个锂,因而具有较高的理论容量,例如Li2MnSiO4理论比容量可达到333mAhg-1,Li2CoSiO4为325 mAhg-1.     

锂离子电池正极材料Li_3V_2(PO_4)_3/C的制备及电化学性能

以球磨结合焙烧的方法制备锂离子电池正极材料Li3V2(PO4)3/C.XRD、EIS表征及以该材料作正极的恒电流循环测试表明,所得产物为晶体结构发育良好的单斜晶系Li3V2(PO4)3.在0.1C、0.25C和0.5C倍率下,首次放电比容量分别为150.6、134.1和107.1mAh·g-1.0.25C循环130周后容量保持率为87.3%,而0.5C循环105周后容量保持率仍达到87.2%.锂离子在材料中的嵌入、脱出伴随明显的两相转变过程.电荷传递阻抗和SEI膜阻抗是影响材料倍率性能的主要因素.     

FTIR研究LiFePO4的充放电过程

随着便携式电子设备的日益普及,人们对支撑这些设备运行的后备电源提出了越来越高的要求.锂离子电池与传统的铅酸和镍镉电池相比具有更大的电动势、更大的比能量(120～150 Wh/kg,是常用的Ni-Cd电池的2～3倍)以及较好的充放循环性能,因此成为目前使用较多的高性能便携能源设备.作为锂离子电池的重要组成部分,正极材料一直是人们重点研究的一个内容,目前应用较广的是LiCoO2,它具有放电电压高、放电平稳、高倍率放电性能好、比能量高、循环性好和生产工艺简单等优点,但由于Co的毒性大、储量低导致这种材料不环保、价格高,并且由于Co4+的高氧化性使LiCoO2只能获得理论值一半的容量,并存在一定的过充电安全隐患,因此人们一直在寻找更好的正极材料.1997年Padhi等人[1]首次报道了具有橄榄石结构的LiFePO4可以作为锂离子电池正极材料,这种材料具有较平坦的3.4 V电压平台、较高的比容量(大于160 mAh/g)、所含元素储量丰富、绿色环保、易于制备和安全性好等优点,被认为是有望替代LiCoO2的正极材料,成为近年来这一研究领域的热点.为了了解LiFePO4的电化学反应机理,Padhi[1]和Takahashi[2]等人用XRD研究了LiFePO4化学脱锂和电化学脱锂后的结构变化,表明Li+的脱嵌过程中LiFePO4和PO4两相共存.Burba等人[3]也使用FTIR和Raman光谱研究了LiFePO4化学脱锂后的结构变化,表明分子光谱是研究LiFePO4结构变化的很好手段,为了更深入理解LiFePO4电化学反应过程中的变化, 本文使用FTIR对LiFePO4在充放电过程中不同充放电阶段的结构变化进行了研究.     

Mo掺杂LiFePO_4正极材料的第一性原理研究(英文)

基于第一性原理密度泛函理论计算了LiFePO4和LiFe1-xMoxPO4(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LiFe0.99Mo0.01PO4样品具有最大的(101)晶面间距,由此可知LiFe0.99Mo0.01PO4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4.289 eV,而掺杂后LiFe0.99Mo0.01PO4降为4.274 eV,经过计算得出掺杂样品LiFe0.99Mo0.01PO4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。     

Synthesis and Electrochemical properties of Phospho-olivine Type LiFexM(1-x)PO4(1 ≥x≥0) Compounds

Olivine-type LiFePO4 appears to be the best candidate for large size Lithium ion batteries compared with conventional cathode materials such as LiCoO2, LiNiO2 and LiMnO4 based on cost,environmental benign and safety. In addition, LiFePO4 has a large theoretical capacity of 170 mAhg-1, good cycle stability, and a flat discharge potential of 3.4V versus Li/Li+. However, its low ionic/electronic conductivity limits the electrochemical prosperities of this material, especially its rate capability. Many efforts have been devoted to increase and optimize the conductivity of LiFePO4 besides minimizing the particle size and making an intimate carbon coating around the particles, though it is not the way to change intrinsically the electrical conductivity of LiFePO4.In this research, LiFePO4 was synthesized by solid-state reaction. A discharge capacity of around 110mAhg-1 was achieved under a low current density of 17mAg-1 at room temperature. In order to compounds were prepared, respectively. As an example, LiFe0.9Ti0.1PO4 had the same XRD pattern as LiFePO4 but more developed crystalline intensity. The charge-discharge capacities of LiFe0.9Ti 0.1PO4 at the first cycle were 134mAhg-1 and 129 mAhg-1, respectively. The efficiency of charge-discharge was larger than 96%. A reversible capacity of 110 mAhg-1 was obtained after 20cycles and the capacity retention was over 85%. Moreover, the discharge voltage flat was maintained at 3.4V verse Li/Li+ after the first cycle. At even higher rates, it also exhibited good electrochemical performances.     

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%.     

Structural study of the Li(0.5)Na(0.5)MnFe2(PO4)3 and Li(0.75)Na(0.25)MnFe2(PO4)3 alluaudite phases and their electrochemical properties as positive electrodes in lithium batteries

The alluaudite lithiated phases Li(0.5)Na(0.5)MnFe(2)(PO(4))(3) and Li(0.75)Na(0.25)MnFe(2)(PO(4))(3) were prepared via a sol-gel synthesis, leading to powders with spongy characteristics. The Rietveld refinement of the X-ray and neutron diffraction data coupled with ab initio calculations allowed us for the first time to accurately localize the lithium ions in the alluaudite structure. Actually, the lithium ions are localized in the A(1) and A(1)' sites of the tunnel. M?ssbauer measurements showed the presence of some Fe(2+) that decreased with increasing Li content. Neutron diffraction revealed the presence of a partial Mn/Fe exchange between the two transition metal sites that shows clearly that the oxidation state of the element is fixed by the type of occupied site. The electrochemical properties of the two phases were studied as positive electrodes in lithium batteries in the 4.5-1.5 V potential window, but they exhibit smaller electrochemical reversible capacity compared with the non-lithiated NaMnFe(2)(PO(4))(3). The possibility of Na(+)/Li(+) ion deintercalation from (Na,Li)MnFe(2)(PO(4))(3) was also investigated by DFT+U calculations.     

Aluminium-doped LiFePO4 single crystals. Part I. Growth, characterization and total conductivity

Single crystals of Al-doped LiFePO4 (1% Al) were grown by an optical floating zone technique. After cleaving from the as-grown ingot they exhibited a blackish-green color. The grown crystals have been characterized by the Laue X-ray technique, single-crystal and powder X-ray diffraction. Phase composition has been determined by chemical analysis to be Li0.985+/-0.009Fe0.984+/-0.12Al0.0126PO3.993+/-0.06. Secondary ion beam spectroscopy (SIMS) indicates a homogeneous distribution of doped Al in the single crystal block. The total conductivities are shown to be electronic conductivities and have been measured along different directions with the help of the cell Ti/LiFe(Al)PO4/Ti. The samples exhibit effectively two-dimensional electronic conductivities along b- and c-directions similar as in pure LiFePO4. This decrease of conductivity on Al-doping compared with undoped crystals is in agreement with our previous conclusion of p-type conductivity of LiFePO4. Unlike nominally pure material not only the association of holes with lithium vacancies plays an important role but also purely ionic association.     

Electrochemical property: Structure relationships in monoclinic Li(3-y)V2(PO4)3

Monoclinic lithium vanadium phosphate, alpha-Li(3)V(2)(PO(4))(3), is a highly promising material proposed as a cathode for lithium-ion batteries. It possesses both good ion mobility and high lithium capacity because of its ability to reversibly extract all three lithium ions from the lattice. Here, using a combination of neutron diffraction and (7)Li MAS NMR studies, we are able to correlate the structural features in the series of single-phase materials Li(3-y)V(2)(PO(4))(3) with the electrochemical voltage-composition profile. A combination of charge ordering on the vanadium sites and lithium ordering/disordering among lattice sites is responsible for the features in the electrochemical curve, including the observed hysteresis. Importantly, this work highlights the importance of ion-ion interactions in determining phase transitions in these materials.     

Microwave-assisted solvothermal synthesis and characterization of metastable LiFe(1-x)(VO)(x)PO4 cathodes

Vanadyl ion substituted LiFePO(4) cathodes of the form LiFe(1-x)(VO)(x)PO(4) for 0 ≤ x ≤ 0.25 have been synthesized by a rapid microwave-solvothermal process at <300 °C within 10 min. Clear evidence of vanadyl ion substitution is demonstrated, despite a large size difference between Fe(2+) and (VO)(2+), by characterizing the products structurally, spectroscopically, and electrochemically. The vanadyl ion substitution is accompanied by the formation of iron vacancies in the lattice and Fe(3)O(4) impurity phase, which increases with increasing (VO)(2+) substitution for Fe(2+) and could be removed with a magnetic stir bar. The formation of iron vacancies, along with the oxidation of some Fe(2+) to Fe(3+) to maintain charge neutrality, results in a decrease in the unit cell volume with increasing x despite the substitution of larger (VO)(2+) for Fe(2+). Charge-discharge data of the vanadyl ion substituted samples suggest suppression of the two-phase plateau behavior that is characteristic of LiFePO(4). Electrochemical data collected without any carbon coating reveal that the capacity and rate capability decreases, but the capacity retention improves with (VO)(2+) substitution.     

Effects of Co~（2＋）Doping on the Crystal Structure and Electrochemical Performance of LiFePO_4

Co2+-doped LiFePO4/C composite material was prepared by solid-state synthesis method using Fe2O3,Li2CO3 and NH4H2PO4 as the starting materials.The structures and elec-trochemical performance of samples were studied by XRD,SEM and constant current charge-discharge method.The results showed that the Co2+ doping did not change the crystal structure of LiFePO4.The unit cell volume changed with the increase of Co2+,and reached the maximum at x = 0.04.The LiFe0.96Co0.04PO4/C sample proved the best electrochemical properties.Its initial discharge capacity was 138.5 mA·h /g at 1 C rate.After 30 cycles,the capacity remained 127.7 mA·h /g,and the capacity retention rate was 92.2%.     

Spectroscopic understanding of ultra-high rate performance for LiMn(0.75)Fe(0.25)PO4 nanorods-graphene hybrid in lithium ion battery

Comprehensive X-ray absorption near-edge structure spectroscopy at the C, O and Li K-edges and the Mn, Fe, and P L-edges of LiMn(0.75)Fe(0.25)PO(4) nanorods-graphene has been reported in great detail. Compared to that of free standing graphene and LiMn(0.75)Fe(0.25)PO(4), the intimate interaction between the nanorods and graphene via charge redistribution has been unambiguously confirmed. This interaction not only anchors the nanorods onto the graphene but also modifies its surface chemistry, both of which afford the nanorods-graphene hybrid an ultra-high rate performance in lithium ion batteries. Such knowledge is important for the understanding of hybrid nanomaterials for lithium ion batteries and allows rational design for further improvements in performance.     

钛离子掺杂对LiFe0.6Mn0.4PO4/C 电化学性能的影响

采用固相法合成了钛离子掺杂LiFe0.6Mn0.4PO4/C正极材料.通过X射线衍射(XRD)、扫描电镜(SEM)以及电化学测试,对合成材料的结构、形貌和电化学性能进行了表征.结果表明:钛离子掺杂未影响材料的晶型结构,但显著改善了材料的电化学性能;Li(Fe0.6Mn0.4)0.96Ti0.02PO4/C材料表现出优异的倍率性能,0.1C倍率下其比容量为160.3mAh.g-1;在10C倍率下,比容量为134.7mAh.g-1;特别是在20C高倍率下仍然具有124.4mAh.g-1的放电比容量.电化学交流阻抗谱(EIS)和循环伏安(CV)测试结果说明,通过钛离子掺杂导致材料阻抗和极化的减少是材料倍率性能改善的主要原因.