Electrochemical properties of LiFePO4 prepared via hydrothermal route

第26卷第3期无机材料学报Vol. 26No. 3 2011年3月Journal of Inorganic Materials Mar. , 2011文章编号: 1000-324X(2011)03-0265-06 DOI: 10.3724/SP.J.1077.2011.00265碳包覆LiFePO4的结构与性能研究张冬云1,2, 张培新1,3, 林木崇3, 刘琨2, 袁秋华3,许启明1, 罗仲宽3, 任祥忠3(1. 西安建筑科技大学材料科学与工程学院, 西安 710055; 2. 广西大学化学化工学院, 南宁 530004; 3. 深圳大学化学与化工学院, 深圳 518060)摘要: 为了研究碳包覆对LiFePO4结构的影响, 以柠檬酸为碳源, 采用机械活化−高温固相法, 合成了不同碳包覆量的LiFePO4/C复合正极材料. 通过XRD、SEM、BET、HRTEM、选区电子衍射(SAED)、交流阻抗谱(ACI)和恒电流充放电等现代分析方法, 全面研究了碳包覆量不同时, LiFePO4/C复合正极材料的结构、形貌和电化学性能, 并对C包覆对结构影响的成因进行了分析. 结果表明, 柠檬酸高温分解后生成无定形碳非晶物质, 在LiFePO4颗粒表面包覆形成一种网络结构, 抑制了颗粒的生长; C包覆影响了晶体的生长方向和微观结构, LiFePO4/C的优势生长为方向; 交流阻抗分析表明包覆后锂离子扩散系数比未改性的LiFePO4提高了两个数量级, 且各项阻抗值均降低, 从而提高了材料的离子及电子电导性、放电性能和循环性能.关键词: 锂离子电池; 正极材料; LiFePO4; 结构; 碳包覆中图分类号: TM912文献标识码: AProperty and Structure of Carbon-coated LiFePO4ZHANG Dong-Yun1,2, ZHANG Pei-Xin1, 3, LIN Mu-Chong3, LIU Kun2, YUAN Qiu-Hua3,XU Qi-Ming1, LUO Zhong-Kuan3, REN Xiang-Zhong3(1. School of Materials Science and Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China;2. School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China;3. School of Chemistry andChemical Engineering, Shenzhen University, Shenzhen 518060, China)Abstract: LiFePO4/C composite cathode materials containing different amounts of carbon were fabricated by me-chanical activation–high temperature solid state reaction using citric acid as a carbon source, with the aim to study the effect of carbon-coating on LiFePO4 internal structure. The crystal structure, surface morphology and electro-chemical properties of the obtained composites coated with various carbon contents were investigated by the tech-niques of XRD, SEM, BET, HRTEM, SAED, AC Impedance spectra, and constant current charge-discharge testing.And the structural changes originating from the carbon-coating were also analyzed. Under high temperature, citric acid was decomposed into network-like structure amorphous carbon, and coated on the surface of LiFePO4 particles, which could inhibit the grain growth and cause the smaller sizes. The crystal growth direction and micro-structure of LiFePO4/C were significantly influenced by carbon-coating that resulted in growing along [121] direction pref-erentially. According to AC Impedance spectra measurements, all the impedances of carbon coated LiFePO4 de-creased evidently, and the diffusion coefficient of Li ions increased by up to two orders of magnitude compared with uncoated LiFePO4, indicating the ion and electric conductivity, discharge capacity and cycling performance were收稿日期: 2010-05-20; 收到修改稿日期:2010-07-01基金项目:国家自然科学基金(50874074, 50474092); 广东省自然科学基金(8151806001000028); 深圳市科技计划资助项目(ZYC200903250150A); 深圳市功能高分子重点实验室开放基金(FP20090104)National Natural Science Foundation of China(50874074, 50474092); Natural Science Foundation of GuangdongProvince(8151806001000028); Shenzhen Government’s Plan of Science and Technology(ZYC200903250150A);Open Research Fund of Shenzhen Key Laboratory of Functional Polymer(FP20090104)作者简介: 张冬云(1971−), 女, 博士研究生, 副教授. E-mail: zdy_89@通讯联系人: 张培新, 教授. E-mail: pxzhang2000@266 无机材料学报第25卷greatly improved.Key words: lithium-ion batteries; cathode materials; LiFePO4; structure; carbon-coating近年来, 锂离子电池正极材料的研究与开发受到世界许多先进国家的高度重视[1-2], 然而电子电导率较低及锂离子扩散系数小限制了其应用. 目前国内外对LiFePO4的研究工作主要集中在材料的制备方法、工艺[3-4]、相关机理及性能改善的实验[5]研究上. 研究表明通过表面碳包覆[6-7]和金属离子掺杂[8-9]等技术手段可减小材料的颗粒尺寸, 增大材料的电导率, 从而提高LiFePO4的电子、离子传导率及其电化学性能.根据锂电池的工作原理, 晶格颗粒之间的导电性对电性能也非常重要, 提高颗粒间的导电性有利于Li+在颗粒间的穿梭能力, 从而改善材料的高倍率性能. 通过对LiFePO4进行碳包覆改性, 可以提高颗粒间的表观电导, 减少极化, 同时可以为LiFePO4提供电子隧道, 补偿Li+脱嵌过程中的电荷平衡, 提高其充放电的可逆性. Huang等[10]在原料中加入碳粉或其它添加剂后, 可以改善该材料的充放电性能,并且认为材料和碳是否紧密接触以及小的磷酸亚铁锂颗粒是提高容量的关键. 因此, 有必要对LiFePO4碳包覆后的结构进行研究, 以加深认识.基于上述考虑, 本工作对碳包覆前后的LiFePO4进行结构分析和充放电性能、交流阻抗谱研究, 以研究碳包覆改性的LiFePO4的结构和锂离子扩散的关系, 从而探讨使复合材料电化学性能提高的微观结构成因.1实验采用机械活化−高温固相法合成LiFePO4/C复合材料. 以Li2CO3(AR), FeC2O4·H2O(AR), NH4H2PO4(AR)为原料, 柠檬酸(AR)为碳源, 丙酮为介质, 球磨后的前驱体烘干, 转移至管式炉中, 在氩气(99.99%)保护下于350℃预分解6h, 冷却后取出, 充分研磨, 于氩气气氛中650℃下恒温20h, 得到LiFePO4/C.物相分析采用X射线粉末衍射仪(Bruker D8, 德国), 扫描范围为15°~60°. 表面形貌采用扫描电镜SEM(S-3400N, 日本). 比表面积测试在Nova1200e型比表面仪(美国康塔公司)上进行, 以N2为吸附质, 在液氮温度77K下进行吸/脱附, 样品于110℃真空下预处理3h. TEM测试在JEM2100型透射电镜(日本JEOL公司)上进行.25℃下采用恒电流充放电法测定材料的比容量和循环性能. 实验电池以金属锂片为负极, 隔膜采用Celgard2400, 电解液为l mol/L LiPF6/EC+DMC (1:2 vol%), 在无水厌氧手套箱中(Unilab2000, 德国)内组装成扣式电池后, 用Land电池测试系统(CT2001A, 中国)测试材料的充放电比容量. 充放电方式为先恒流充电, 静置, 再恒流放电. 充电电流均为0.1C, 充放电电压范围为2.6~4.2V.2结果与讨论2.1 LiFePO4/C复合材料的结构与形貌图1为不同碳包覆量的LiFePO4/C复合正极材料的XRD图谱. 各样品均有尖锐的衍射峰, 说明结晶很好. 与LiFePO4的标准XRD图谱(JCPDS 83-2092)完全一致, 没有观察到明显的杂质峰, 说明所合成的LiFePO4/C为单一的橄榄石结构. 图中也没有观察到晶态碳的衍射峰, 说明柠檬酸经过高温烧结后生成的碳最终以无定形的形式存在材料中. 由LiFePO4/C复合材料的晶胞参数(表1)可以看出, 包覆碳后, 晶胞体积随着碳包覆量的增加逐渐下降; 相对于未包覆的LiFePO4, LiFePO4/C复合材料各主要衍射峰的半峰宽基本上呈增加趋势, 且各衍射峰的强度逐渐减弱. 根据谢乐公式, 峰的宽化说明晶粒尺寸的减小, 因此碳包覆可以减小晶粒尺寸, 达到细化颗粒的目的.由SEM照片(图2)可见, 所有样品的表面形貌无规则: 未包覆碳的LiFePO4颗粒较大, 平均粒径图1 不同碳包覆量的LiFePO4/C复合材料的XRD图谱Fig. 1 XRD patterns of LiFePO4/C coated with different car-bon contents第3期张冬云, 等: 碳包覆LiFePO 4的结构与性能研究 267表1 不同碳包覆量的LiFePO 4/C 复合材料的晶胞参数及XRD 半峰宽Table 1 Crystal parameters of LiFePO 4/C coated with different carbon contentsLattice parametersHalf-width of main diffraction peaks (FWHM/rad)carbon content/wt%a /nmb /nmc /nmV /nm 3 (101)(111) (211) (311) 0 1.03375 0.60079 0.469050.29131 0.148 0.156 0.1360.1454 1.03237 0.60007 0.469180.29065 0.128 0.179 0.1800.2066 1.03189 0.60028 0.468870.29043 0.150 0.270 0.2100.1738 1.02947 0.59970 0.469500.28985 0.168 0.207 0.2520.20510 1.02819 0.59787 0.469490.28861 0.225 0.312 0.2060.244图2 碳包覆LiFePO 4的SEM 照片Fig. 2 SEM images for LiFePO 4 coated with different carbon contents ((a)-(e) corresponding to carbon content: 0, 4wt%, 6wt%, 8wt% and 10wt%)为1μm 左右, 存在一定的团聚; 包覆碳后, 粒径变小, 颗粒大小分布趋向均匀, 二次粒子的大小在200~500nm 之间. 由图中还可以看出, 包覆碳后样品的表面形貌变得更加蓬松和粗糙, 这是由于柠檬酸高温分解生成的无定形碳均匀地包覆在颗粒表面, 而这种无定形碳颗粒本身就具有多孔粗糙的表面.对LiFePO 4/C 复合正极材料进行BET 研究, 测得比表面积分别为: 5.56、12.43、20.26、32.81、41.68 m 2/g. 样品的比表面积随着碳包覆量的增加而增大, 表明晶体尺寸的减小. BET 和XRD 、SEM 的研究结果相一致: 碳包覆可以有效地抑制晶粒团聚, 使粒径分布趋向均匀.2.2 LiFePO 4/C 复合材料的电化学性能研究图3为LiFePO 4/C 复合材料在0.1C 倍率下的第二次充放电曲线. 与LiFePO 4相比, LiFePO 4/C 的放电比容量均提高, 充放电平台延长, 且充放电平台间的电压差减小, 说明碳包覆样品在充放电过程中极化小, 电化学性能优良. 含碳量为8wt%样品的放电比容量最大为150.5mAh/g, 达到理论容量的89%, 比未包覆的LiFePO 4提高了将近40%的比容量, 且具有最低的充电平台电位(3.45V)和最高放电平台电位(3.41V), 两平台间的电位差最小, 说明极化最小, 具有优良的电化学性能. 但含碳量为10%的样品放电比容量有所下降, 仅为135.6 mAh/g, 说明碳含量并不是越大越好.图4为LiFePO 4/C 复合材料0.1C 放电时的循环性能. 可以看出, 包覆碳后材料的循环性能得到有效的改善. 随着碳包覆量的增加, LiFePO 4/C 的循环性能逐步提高, 当碳含量为8wt%时, LiFePO 4/C 放电比容量最高, 容量最稳定, 具有最好的循环性能,268无 机 材 料 学 报 第26卷图3 0.1C 倍率下, LiFePO 4/C 的第二次充放电曲线Fig. 3 Second charge and discharge curves of LiFePO 4/C at rate of 0.1C图4 0.1C 倍率下, LiFePO 4/C 的循环性能Fig. 4 Cycling performance of LiFePO 4/C at rate of 0.1C基本无衰减.由于碳含量为8wt%的LiFePO 4/C 复合材料在0.1C 下表现出优良的电化学性能, 对其进一步进行高倍率的电性能研究, 充电倍率仍为0.1C , 放电倍率依次为0.1C 、0.5C 、1.0C 、2.0C , 第二次充放电曲线及前50次循环性能图如图5、图6所示.由图5可以看出, 样品在0.1C 、0.5C 、1.0C 、2.0C 的放电平台电位分别为3.41、3.38、3.35、3.28V , 逐图5 LiFePO 4/C 在不同的放电倍率下的第二次充放电曲线 Fig. 5 Second charge and discharge curves of LiFePO 4/C at different discharge rates图6 LiFePO 4/C 在不同的放电倍率下的循环性能Fig. 6 Cycling performance of LiFePO 4/C at different dis-charge rates (8wt%C)渐降低, 说明随着放电倍率的提高, 电池极化增大,造成可逆容量的损失; 第二次放电比容量分别为150.5、136.3、129.9和111.2 mAh/g, 容量依次下降. 循环性能图表明, 充放电循环50次后, 容量保持率分别为100%、95.4%、94.4%和89.3%, 特别是在2.0C 的放电倍率下循环50次后容量仍有101.0 mAh/g, 表现出优良的循环性能.2.3 碳包覆膜的形态研究碳包覆能提高LiFePO 4的电化学性能, 理论上说, 进行C 包覆改性时, 应该使C 均匀分布在正极材料表面, 以便整个表面能同时进行Li 的嵌入和脱出, 从而提高电流密度. 为了进一步了解无定形碳在颗粒表面的存在状态, 对LiFePO 4/C 复合材料进行HR-TEM 和SAED 研究.图7为包覆前后的TEM 照片. 由图7(a)可以看出纯相的LiFePO 4的一次颗粒近似球形, 存在团聚现象, 一次颗粒的大小分布范围较宽, 粒径在130~ 400nm 之间. 由图7(b)可以看出, 碳在颗粒的表面和颗粒间形成网络结构, 因此可以认为是包覆在颗粒表面的具有良好导电性的碳膜使材料性能提高. 包覆在颗粒表面的碳使得LiFePO 4/C 的二次颗粒晶形不是很明显, 大小在50nm 左右, 说明在合成LiFePO 4/C 复合材料的过程中, 原位形成的碳包覆有效抑制了颗粒的长大, 同前面的XRD 、SEM 、BET 的研究结果一致.图8为LiFePO 4/C 的高分辨透射电镜(HRTEM)及选区电子衍射(SAED)测试结果. 图8(a)显示出晶格中的原子以点阵的方式有序的排列, 没有观察到位错、孪晶等一维和二维缺陷, 最外层包覆一层厚度在2nm 左右的非晶物质, 此非晶层与LiFePO 4晶体结合完好, 故其可能是包覆在LiFePO 4晶体表面的无定形碳膜层. HR-TEM 和SAED 数据表明晶格第3期张冬云, 等: 碳包覆LiFePO 4的结构与性能研究 269图7 LiFePO 4包覆C 前后的TEM 照片Fig. 7 TEM images of LiFePO 4 before and after C-coating(a) LiFePO 4; (b) LiFePO 4/C图8 LiFePO 4/C 的HRTEM 照片(a)及选区电子衍射图(b) Fig. 8 HRTEM images of LiFePO 4/C (a) and the correspond-ing SAED pattern (b)中晶体生长方向为晶面间距0.3918nm 和0.4245nm 的两个晶面, 分别对应于LiFePO 4的(210)和(101)面. 由(210)和(101)面求得的晶带轴指数为[121], 因此LiFePO 4/C 的优势生长为[121]方向. 张淑萍等[11]也采用TEM 和SAED 研究了溶剂热法合成的LiFePO 4与导电添加剂的关系, 合成了沿[201]方向生长的棒状的LiFePO 4晶体, 并认为取向机理可能在于添加剂对晶体生长的吸附阻止作用. 而本课题组前期研究表明掺Nb 磷酸铁锂晶体生长方向为[112][12], 说明合成工艺、C 包覆和掺杂后由于缺陷的不同而使晶体生长方向不同, 从而影响了微观结构和其电化学性能.2.4 交流阻抗谱分析Li 离子的扩散性能是涉及正极材料性能优劣的关键因素, 锂离子在LiFePO 4电池正极材料中的扩散过程包括正极材料内部的扩散迁移、正极材料和膜界面的传递以及表面膜中扩散. 可通过交流阻抗(ACI)分析研究碳包覆如何降低材料的极性, 从而提高Li 离子的扩散性能.图9中点为样品的交流阻抗图谱实验值, 曲线是根据充放电时电极中锂离子运动过程由图中所示等效电路用Zview 软件拟合的结果. 可以看到, 拟图9 交流阻抗谱拟合等效电路及图谱Fig. 9 AC Impedance spectra and equivalent circuit of ACI modeling合曲线能较好地与实验值吻合, 说明本文所选用的等效电路能较好地描述锂离子在LiFePO 4电极中的扩散过程, 拟合的误差较小. 该图反映了锂离子在LiFePO 4电池正极材料中的三个扩散过程: 高频区(略为压缩的半圆)为锂离子在表面膜中扩散, 中高频区反映活性物质和膜界面电荷传递, 低频区(线性部分)反映锂离子在正极材料内部的扩散. 可以看到包覆后的样品较纯LiFePO 4的明显变小, 表明扩散阻力的减小.表2是阻抗的拟合结果, 包括溶液电阻(R s )、电极表面膜的阻抗(C 1和R 1)、LiFePO 4颗粒与表面膜之间以及LiFePO 4颗粒与颗粒间的阻抗(用电极双层电容C dl 与电化学反应电阻R ct 描述)、锂离子在LiFePO 4颗粒内部扩散引起的电阻(用Warburg 电阻Z w 描述). R ct 在整个阻抗中所占比例最大, 纯LiFePO 4的提高一个数量级; 从钝化膜阻抗R 1来看, 改性不利于钝化膜的形成, 从而减少锂离子在电极表面迁移阻抗. 对包覆改性后的材料而言, 各种阻抗值均降低, 从而提高了材料的电子电导性、放电性能和循环性能.此外, 由于Warburg 阻抗代表的是电极反应过程中的锂离子的扩散过程, 此阻抗表现为低频区的一条与坐标成45°的直线, 因此可计算出包覆前后锂离子的扩散系数D [13]分别为 1.19×10−14和1.54×10−12, 包覆后的样品比纯LiFePO 4的提高了两个数量级, 这是因为碳包覆使正极材料粒径减小, 从而促进锂离子的内部扩散.表2 阻抗拟合结果Table 2 Fitting results of impedance parameters Sample R s / ΩC 1/μFR 1/ ΩC dl /μFR ct / ΩLiFePO 4/C 8.17 2.6015 10.57 5.262 49.70LiFePO 417.991.0915 93.162.857 669.9270 无机材料学报第26卷以上研究表明碳包覆提高了LiFePO4的电化学性能, 主要有两方面原因: 首先碳包覆可以在LiFePO4颗粒表面形成一种具有良好导电性的碳网络结构, 不仅加强颗粒间的接触, 而且提高了颗粒间的电导率, 为充放电过程中电子的传输提高良好的通道, 减少了极化, 从而提高充放电的可逆性. 其次, 均匀包覆在颗粒表面的碳膜层可以在晶体生长过程中抑制晶粒的长大, 减小晶粒尺寸, 细化颗粒, 增加材料的比表面积, 晶粒的减小可以缩短Li+的脱嵌路径, 提高Li+的扩散系数, 而且比表面的增大使材料与电解液接触面积增加, 从而扩大了Li+的相间扩散面积. 但碳含量过多时, 反而会引起材料性能的下降, 这是因为碳含量过大, 造成单位面积的正极片中活性物质LiFePO4的含量减少, 容量下降; 如果包覆在颗粒表面的碳膜过厚, 可能造成Li+在表面的扩散困难; 碳含量过大, 材料的比表面积过大会导致极片涂膜过程和充放电循环过程出现掉粉的现象, 导致循环性能变差; 同时碳含量的增加将使材料的振实密度降低, 也影响其实际应用. 因此碳的包覆量应控制在一定的程度.3结论以柠檬酸为碳源, 通过机械活化−高温固相法制备了不同碳包覆量的LiFePO4/C复合正极材料, 通过对不同碳包覆量的LiFePO4的结构、形貌和电性能的研究, 得到如下结论:1) 柠檬酸高温分解后生成无定形碳非晶物质, 在LiFePO4颗粒表面包覆形成一种网络结构, 抑制了晶体颗粒的长大, 比表面积随着碳含量的增加而增大. 碳的加入没有改变LiFePO4的橄榄石结构.2) 电化学性能研究表明, 碳包覆提高了材料的充放电性能和循环性能. 以碳理论含量8wt%为最佳, 太大反而降低电化学性能.3) 碳包覆影响了晶体的生长方向和微观结构, 从而影响其电化学性能, LiFePO4/C的优势生长为[121]方向.4) 交流阻抗分析表明包覆后锂离子扩散系数比纯的LiFePO4提高了两个数量级, 且各项阻抗值均降低, 从而提高了材料的离子及电子电导性、放电性能和循环性能. 参考文献:[1] Padhi A K, Nanjundaswamy K S, Goodenough J B. Phospho-olivines as positive-electrode materials for rechargeable lithium batteries. Journal of the Electrochemical Society, 1997, 144(4):1188−1194.[2] Chen G Y, Song X Y, Richardson T J. Electron microscopy studyof the LiFePO4 to FePO4 phase Transition. Electrochemical and Solid-State Letters, 2006, 9(6): A295−A298.[3] Kim D H, Kim T R, Im J S, et al. A new method to synthesize oli-vine phosphate nanoparticles. Physica Scripta, 2007, T129: 31−34.[4] 张培新, 文衍宣, 刘剑洪, 等(ZHANG Pei-Xin, et al). 化学沉淀法制备掺杂磷酸铁锂的结构和性能研究. 稀有金属材料与工程(Rare Metal Mat. Eng.), 2007, 36(6): 954−958.[5] 卢俊彪, 唐子龙, 张中太, 等(LU Jun-Biao, et al). LiFePO4材料的制备与电池性能的研究. 无机材料学报(Journal of Inorganic Materials), 2005, 20(3): 666−670.[6] Kim J K, Choi J W, Cheruvally G, et al. A modified mechanicalactivation synthesis for carbon-coated LiFePO4 cathode in lithiumbatteries. Materials Letters, 2007, 61(18): 3822−3825.[7] Dominko R, Bele M, Gaberscek M, et al. Impact of the carboncoating thickness on the electrochemical performance of LiFePO4/C compostites. Journal of the Electrochemical Society, 2005, 152(3): A607−A610.[8] Chung S Y, Blocking J T, Chiang Y M. Electronically conductivephospho-olivines as lithium storage electrodes. Nature Materials,2002, 1: 123−128.[9] 陈宇, 王忠丽, 于春洋, 等(CHEN Yu, et al). 掺杂Mo的LiFePO4正极材料的电化学性能. 物理化学学报(ActaPhys-Chem. Sin.), 2008, 24(8): 1498−1502.[10] Huang H, Yin S C, Nazar L F. Approaching theoretical capacity ofLiFePO4 at room temperature at high rates. Electrochem. Solid State Lett., 2001, 4(10): A170−A172.[11] 张淑萍, 倪江锋, 周恒辉, 等(ZHANG Shu-Ping, et al). 溶剂热法控制合成规则的LiFePO4颗粒. 物理化学学报(ActaPhys-Chem. Sin.), 2007, 23(6): 830−834.[12] 林木崇. 锂离子电池正极材料LiFePO4的掺杂缺陷及电化学性能的研究. 深圳: 深圳大学硕士论文, 2010.[13] Liu H, Cao Q, Fu L J, et al. Doping effects of zinc on LiFePO4cathode material for lithium ion batteries. Electrochemistry Com-munications, 2006, 8(10): 1553−1557.。

磷酸铁锂工作电压简介磷酸铁锂是一种广泛应用于锂离子电池中的正极材料，其工作电压是指在电池放电过程中，正极材料磷酸铁锂的电位变化范围。

磷酸铁锂工作电压的确定对于电池的性能和安全性具有重要意义。

本文将对磷酸铁锂工作电压的相关内容进行全面、详细、完整且深入地探讨。

什么是工作电压工作电压是指电池在正常使用过程中所能达到的最高电压和最低电压。

对于磷酸铁锂电池而言，工作电压一般指的是在放电过程中，正极材料磷酸铁锂的最高电位和最低电位。

磷酸铁锂的化学性质磷酸铁锂的化学式为LiFePO4，其结构由锂离子（Li+）、铁离子（Fe2+）和磷酸根离子（PO43-）组成。

磷酸铁锂具有较高的比容量、较低的自放电率、较好的循环寿命和较高的安全性能，因此被广泛应用于电动汽车、储能系统等领域。

磷酸铁锂电池的工作电压范围磷酸铁锂电池的工作电压范围一般为2V-4.2V。

具体来说，磷酸铁锂电池的充电电压一般为4.2V，放电截止电压一般为2V。

这个工作电压范围是为了保证电池的性能和安全性而确定的。

影响磷酸铁锂工作电压的因素温度温度是影响磷酸铁锂电池工作电压的重要因素之一。

一般来说，温度越高，电池的放电电压会有所增加，而温度越低，电池的放电电压会有所降低。

充放电速率充放电速率也会对磷酸铁锂电池的工作电压产生影响。

较高的充放电速率会导致电池电压的下降，而较低的充放电速率则会导致电池电压的上升。

循环次数随着循环次数的增加，磷酸铁锂电池的工作电压可能会发生变化。

一般来说，随着循环次数的增加，电池的放电电压会有所下降。

锂离子扩散速率锂离子的扩散速率也会对磷酸铁锂电池的工作电压产生影响。

较慢的锂离子扩散速率会导致电池电压的下降，而较快的锂离子扩散速率则会导致电池电压的上升。

总结磷酸铁锂电池的工作电压范围一般为2V-4.2V，其中充电电压为4.2V，放电截止电压为2V。

影响磷酸铁锂电池工作电压的因素包括温度、充放电速率、循环次数和锂离子扩散速率。

了解和控制这些因素对于提高磷酸铁锂电池性能和保证其安全性具有重要意义。

综述专论化工科技,2005,13(6):38～42SCIENCE &T ECHNO LOG Y IN CHEM ICA L I ND UST RY收稿日期:2005-07-05作者简介:孙　悦(1981-),女,辽宁盘锦人,辽宁石油化工大学硕士研究生,现从事应用电化学研究。

＊＊通讯联系人。

＊基金项目:辽宁省教育厅基金项目(2004D068)。

锂离子电池正极材料LiFePO 4的研究进展＊孙　悦,乔庆东＊＊(辽宁石油化工大学石油化工学院,辽宁抚顺113001)摘　要:LiFePO 4作为新一代首选的正极材料,具有材料来源广泛、价格便宜、热稳定性好、比能量高、无吸湿性、对环境友好等优点。

笔者综述了LiFePO 4的结构特征、充放电机理、合成方法及改性研究。

关键词:锂离子二次电池;正极材料;磷酸亚铁锂中图分类号:T M 912.9 文献标识码:A 文章编号:1008-0511(2005)06-0038-05 目前,锂离子电池作为一种高性能的二次绿色电池,已在各种便携式电子产品和通讯工具中得到广泛的应用。

截至2002年,锂离子二次电池的总产量为8.62亿只。

根据市场调查表明,2005年锂离子二次电池需求约为12亿只,而2010年则可达到13.5亿只左右[1]。

因此,新型电池材料特别是正极材料的研究至为关键。

1990年,日本SONY 公司首次成功地推出商品化的锂离子二次电池,其正极材料采用钴酸锂(LiCoO 2)。

由于钴酸锂制作工艺简单、材料热稳定性能好、循环寿命长,虽然价格昂贵、有毒、安全性能不好,但至今为止钴酸锂仍是最主要的锂离子二次电池正极材料。

随着对电池的成本低、高比能量、循环性能好、高安全性和对环境友好等的要求,锂离子二次电池正极材料进入迅速发展阶段[2,3]。

除层状结构的钴酸锂外,过渡金属氧化物如层状结构的LiNiO 2和尖晶石结构的LiMn 2O 4也是主要的正极材料[4]。

其中LiNiO 2理论容量较高(约275mAh /g ),但热稳定性差、制备困难、易发生副反应、生成的产物影响电池的容量和循环性能;LiM n 2O 4循环性能差、比容量较低(理论比容量仅约为148mAh /g ),这主要是由于M n 3+易发生歧化[5]反应和Jahn -Teller 畸变效应。

湖南农业大学全日制普通本科生毕业论文FePO4制备工艺对流变相法合成LiFePO4/C性能的影响EFFECTS OF FEPO4 REACTION CONDITIONS ONELECTROCHEMICAL PROPERTIES OF LIFEPO4/C BYRHEOLOGICAL PHASE METHOD学生姓名：李季年级专业及班级：2010级材料化学(2)班指导老师及职称：钟美娥讲师学院：理学院湖南·长沙提交日期：20年月湖南农业大学全日制普通本科生毕业论文（设计）诚信声明本人郑重声明：所呈交的本科毕业论文（设计）是本人在指导老师的指导下，进行研究工作所取得的成果，成果不存在知识产权争议。

除文中已经注明引用的内容外，本论文不含任何其他个人或集体已经发表或撰写过的作品成果。

对本文的研究做出重要贡献的个人和集体在文中均作了明确的说明并表示了谢意。

本人完全意识到本声明的法律结果由本人承担。

毕业论文（设计）作者签名：20 年月日目录摘要 (1)关键词 (1)1 前言 (2)1.1 LiFePO4的研究现状 (2)1.2 LiFePO4与FePO4.2H2O的结构及特点 (3)1.3 锂离子电池的工作原理 (4)1.4 课题设计思路 (5)2实验部分 (6)2.2 试验方法 (7)2.2.1 样品的的制备与实验方案设计 (7)2.2.2 LiFePO4材料的结构表征 (8)2.2.3 电极的制备及模拟电池的装配 (8)2.2.4 模拟电池的电性能测试 (8)3 结果与讨论 (8)3.1 不同碳锂比 (8)3.2 不同反应温度 (9)3.3 不同反应pH (10)3.4 不同搅拌速度 (11)3.5 不同碳源 (11)3.6 掺杂 (12)4 实验结果的总结............................................................................ 错误!未定义书签。

磷酸锰铁锂的分解温度磷酸锰铁锂是一种锂离子电池正极材料，具有高能量密度、长循环寿命和较高的工作电压等优点。

但是，磷酸锰铁锂也存在着分解和失效的问题，尤其是在高温下。

本文将就磷酸锰铁锂的分解温度及相关参考内容进行探讨。

磷酸锰铁锂的分解温度是指其在加热过程中开始失去活性或结构改变的温度。

一般来说，磷酸锰铁锂的分解温度取决于多种因素，如化学成分、晶体结构、添加剂等，因此不同材料的分解温度会有所差异。

磷酸锰铁锂通常是由磷酸锰锂（LiMnPO4）和磷酸铁锂（LiFePO4）两种相互掺杂的化合物组成。

在正常使用条件下，磷酸锰铁锂的分解温度往往在200°C至250°C之间。

然而，在高温条件下，尤其是超过350°C时，磷酸锰铁锂的结构会发生严重变化，导致材料的电化学性能下降，丧失长循环寿命的特点。

为了提高磷酸锰铁锂的热稳定性和循环寿命，研究人员通过不断改进材料制备工艺、优化添加剂配方等方式进行了大量的研究工作。

以下是一些相关研究的参考内容：1. Chen Z, et al.（2012）. "Improving electrochemical performance of LiFePO4–Li3 V2(PO4)3 composite cathode material by Li3V2(PO4)3-coating.” Journal of Power Sources, 218, 208-215.该研究通过在磷酸锰铁锂颗粒表面涂覆Li3V2(PO4)3，提高了材料的热稳定性和电化学性能。

2. Zuo X, et al.（2014）. "Structure and electrochemical performance of LiMnPO4 coated with Li3PO4 by sol–gel method.” Journal of Thermal Analysis and Calorimetry, 115(1), 585-590.该研究采用溶胶-凝胶方法，在磷酸锰铁锂颗粒表面涂覆Li3PO4薄层，提高了材料的热稳定性和电化学性能。

收稿日期：2009-02-23作者简介：王蕊（1968-），女，工程师，1990年毕业于黑龙江大学，现从事于环境保护工作。

文章编号：1002-1124（2009）06-0024-03Sum 165No.06化学工程师ChemicalEngineer2009年第6期锂离子电池作为一种高性能的可充绿色电源，近年来已在各种便携式电子产品和通讯工具中得到广泛应用，并被逐步开发为电动汽车的动力电源，从而推动其向安全、环保、低成本及高比能量的方向发展[1,2]。

其中，新型电极材料特别是正极材料的研制极为关键。

橄榄石型的LiFePO 4自1997年被应用于锂离子电池正极材料以来，以其热稳定性好、循环性能优良、原材料丰富、价廉无污染等优点，深受研究者的重视[3-5]。

但是由于该材料的电子电导率低、Li +扩散系数小等因素导致其电性能较差。

通过添加导电剂等方式来提高电导率，合成粒径分布均匀、具有高比表面积的材料以提高活性材料的利用率是改善其电化学性能的有效途径[6-8]。

本文以溶胶凝胶法制备了LiFePO 4，并研究了络合剂的种类和比例对LiFePO 4电化学性能的影响。

1实验部分1.1试剂与仪器实验所需药品LiOH ·H 2O 、Fe(NO 3)3·9H 2O 、NH 4H 2PO 4、草酸、EDTA （乙二胺四乙酸）、柠檬酸、无水乙醇、NH 3·2H 2O 、N,N-二甲基吡咯烷酮(NM P)、乙炔黑等实验所用试剂均为市售分析纯，所有的溶液都用三次蒸馏水配置。

利用D/max-rB 型旋转阳极X-射线粉末衍射仪(日本理学电机株式会社)检测产品的物相，其中Cu-K α射线的波长为0.15418nm ，采用石墨单色器，扫描速度5°·min -1，阶宽0.02°(2θ)。

行星球磨机(南京大学仪器厂)；SK-2-2-12型管式电阻炉（哈尔滨龙江电炉厂）；电热恒温鼓风干燥箱（上海精宏实验设备有限公司）；数显式电热恒温水浴锅（北京医疗设备有限公司）；CHI660C 型电化学工作站(上海晨华)；BK-6016AR/2二次电池性能测试仪(深圳蓝奇科技有限公司)。

Electrochimica Acta 92 (2013) 248–256Contents lists available at SciVerse ScienceDirectElectrochimicaActaj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e l e c t a c taGel-combustion synthesis of LiFePO 4/C composite with improved capacity retention in aerated aqueous electrolyte solutionMilica Vujkovi´c a ,Ivana Stojkovi´c a ,Nikola Cvjeti´canin a ,Slavko Mentus a ,b ,∗,1a University of Belgrade,Faculty of Physical Chemistry,P.O.Box 137,Studentski trg 12-16,11158Belgrade,Serbia bThe Serbian Academy of Sciences and Arts,Kenz Mihajlova 35,11158Belgrade,Serbiaa r t i c l ei n f oArticle history:Received 2October 2012Received in revised form 3January 2013Accepted 5January 2013Available online 11 January 2013Keywords:Aqueous rechargeable Li-ion battery Galvanostatic cycling Gel-combustion Olivine LiFePO 4LiFePeO 4/C compositea b s t r a c tThe LiFePO 4/C composite containing 13.4wt.%of carbon was synthesized by combustion of a metal salt–(glycine +malonic acid)gel,followed by an isothermal heat-treatment of combustion product at 750◦C in reducing atmosphere.By a brief test in 1M LiClO 4–propylene carbonate solution at a rate of C/10,the discharge capacity was proven to be equal to the theoretical one.In aqueous LiNO 3solu-tion equilibrated with air,at a rate C/3,initial discharge capacity of 106mAh g −1was measured,being among the highest ones observed for various Li-ion intercalation materials in aqueous solutions.In addition,significant prolongation of cycle life was achieved,illustrated by the fact that upon 120charg-ing/discharging cycles at various rates,the capacity remained as high as 80%of initial value.The chemical diffusion coefficient of lithium in this composite was measured by cyclic voltammetry.The obtained val-ues were compared to the existing literature data,and the reasons of high scatter of reported values were considered.© 2013 Elsevier Ltd. All rights reserved.1.IntroductionThanks to its high theoretical Coulombic capacity (170mAh g −1)and environmental friendliness,LiFePO 4olivine became a desir-able cathodic material of Li-ion batteries [1,2],competitive to other commercially used cathodic materials (LiMnO 4,LiCoO 2).As evidenced in non-aqueous electrolyte solutions,a small vol-ume change (6.81%)that accompanies the phase transition LiFePO 4 FePO 4enables Li +ion insertion/deinsertion reactions to be quite reversible [1–3].The problem of low rate capability,caused by low electronic conductivity [4,5],was shown to be solv-able to some extent by reduction of mean particle size [6].Further improvements in both conductivity and electrochemical perform-ances were achieved by forming composite LiFePO 4/C,where in situ produced carbon served as an electronically conducting con-stituent [5,7–27].Ordinarily,both in situ formed carbon and carbon black additive,became unavoidable constituent of the LiFePO 4-based electrode materials [28–37].Zhao et al.[27]reported that Fe 2P may arise as an undesirable product during the synthesis of LiFePO 4/C composite under reducing conditions,however,other authors found later that this compound may contribute positively∗Corresponding author at:University of Belgrade,Faculty of Physical Chemistry,P.O.Box 137,Studentski trg 12-16,11158Belgrade,Serbia.Tel.:+381112187133;fax:+381112187133.E-mail address:slavko@ffh.bg.ac.rs (S.Mentus).1ISE member.to the electronic conductivity and improve the electrochemical per-formance of the composite [28–30].Severe improvement in rate capability and capacity retention was achieved by partial replace-ment of iron by metals supervalent relative to lithium [31–37].Thus one may conclude that the main aspects of practical applica-bility of LiFePO 4in Li-ion batteries with organic electrolytes were successively resolved.After the pioneering studies by Li and Dahn [38,39],recharge-able Li-ion batteries with aqueous electrolytes (ARLB)attracted considerable attention [40–50].The first versions of ARLB’s,suf-fered of very low Coulombic utilization and significantly more pronounced capacity fade relative to the batteries with organic electrolyte,regardless on the type of electrode materials [43].For the first time,LiFePO 4was considered as a cathode material in ARLB’s by Manickam et al.in 2006[44].He et al.[46],in an aqueous 0.5M Li 2SO 4solution,found that LiFePO 4displayed both a surprisingly high initial capacity of 140mAh g −1at a rate 1C and recognizable voltage plateau at a rate as high as 20C,which was superior relative to the other electrode materials in ARLB’s.Recently,the same authors reported a high capacity decay in aer-ated electrolyte solution,amounting to 37%after only 10cycles [48].In the same study,they demonstrated qualitatively by a brief cyclovoltammetric test,that a carbon layer deposited from a vapor phase over LiFePO 4particles,suppressed the capacity fade [48].Inspired by the recent discoveries about excellent rate capa-bility [46]but short cycle life [48]of LiFePO 4in aerated aqueous solution,we attempted to prolong the cycle life by means of protecting carbon layer over the LiFePO 4particles.Therefore we0013-4686/$–see front matter © 2013 Elsevier Ltd. All rights reserved./10.1016/j.electacta.2013.01.030M.Vujkovi´c et al./Electrochimica Acta92 (2013) 248–256249synthesized LiFePO4/C composite by a fast and simple glycine-nitrate gel-combustion technique.This method,although simpler than a classic solid state reaction method combined with ball milling[44,48],was rarely used for LiFePO4synthesis[19,27].It yielded a porous,foamy LiFePO4/C composite,easily accessible to the electrolyte.Upon the fair charging/discharging performance was confirmed by a brief test in organic electrolyte,we examined in detail the electrochemical behavior of this material in aqueous electrolyte,by cyclic voltammetry,complex impedance and cyclic galvanostatic charging/discharging methods.In comparison to pure LiFePO4studied in Ref.[48],this composite displayed markedly longer cycle life in aerated aqueous solutions.The chemical dif-fusion coefficient of lithium was also determined,and the reasons of its remarkable scatter in the existing literature were considered.2.ExperimentalThe LiFePO4/C composite was synthesized using lithium nitrate, ammonium dihydrogen phosphate(Merck)and iron(II)oxalate dihydrate(synthesized according to the procedure described else-where[51])as raw materials.Our group acquired the experience in this synthesis technique on the examples of spinels LiMn2O4 [52]and LiCr0.15Mn1.85O4[53],where glycine served as both fuel and complexing/gelling agent to the metal ions.A stoichiometric amount of each material was dissolved in deionized water and mixed at80◦C using a magnetic stirrer.Then,first glycine was added into the reaction mixture to provide the mole ratio of glycine: nitrate of2:1,and additionally,malonic acid(Merck)was added in an amount of60wt.%of the expected mass of LiFePO4.The role of malonic acid was to decelerate combustion and provide con-trollable excess of carbon[14].After removing majority of water by evaporation,the gelled precursor was heated to initiate the auto-combustion,resulting in aflocculent product.The combustion product was heated in a quartz tube furnacefirst at400◦C for3h in Ar stream,and then at750◦C for6h,under a stream of5vol.%H2in Ar.This treatment consolidated the olivine structure and enabled to complete the carbonization of residual organic matter.The VO2powder prepared by hydrothermal method was used as an active component of the counter electrode in the galvanostatic experiments in aqueous electrolyte solution.The details of the syn-thesis and electrochemical behavior of VO2are described elsewhere [54,55].The considerable stoichiometric excess of VO2was used,to provide that the LiFePO4/C composite only presents the main resis-tive element,i.e.,determines the behavior of the assembled cell on the whole.The XRD experiment was performed using Philips1050diffrac-tometer.The Cu K␣1,2radiation in15–70◦2Ârange,with0.05◦C step and2s exposition time was used.The carbon content in the composite was determined by its com-bustion in theflowing air atmosphere,by means of thermobalance TA SDT Model2090,at a heating rate of10◦C min−1.The morphology of the synthesized compounds was observed using the scanning electron microscope JSM-6610LV.For electrochemical investigations,the working electrode was made from LiFePO4/C composite(75%),carbon black-Vulcan XC72 (Cabot Corp.)(20%),poly(vinylidenefluoride)(PVDF)binder(5%) and a N-methyl-2-pyrrolidone solvent.The resulting suspension was homogenized in an ultrasonic bath and deposited on electron-ically conducting support.The electrode was dried at120◦C for 4h.Somewhat modified weight ratio,85:10:5,and the same drying procedure,were used to prepare VO2electrode.The non-aqueous electrolyte was1M LiClO4(Lithium Corpo-ration of America)dissolved in propylene carbonate(PC)(Fluka). Before than dissolved,LiClO4was dried over night at140◦C under vacuum.The aqueous electrolyte solution was saturated LiNO3solution.The cyclic voltammetry and complex impedance experiments were carried out only for aqueous electrolyte solutions,by means of the device Gamry PCI4/300Potentiostat/Galvanostat.The three electrode cell consisted of a working electrode,a wide platinum foil as a counter electrode,and a saturated calomel electrode(SCE) as a reference one.The experiments were carried out in air atmo-sphere.The impedance was measured in open-circuit conditions, at various stages of charging and discharging,within the frequency range10−2−105Hz,with7points per decade.Galvanostatic charging/discharging experiments were carried out in a two-electrode arrangement,by means of the battery testing device Arbin BT-2042,with two-terminal connectors only.In the galvanostatic tests in non-aqueous solution,working electrode was a2×2cm2platinum foil carrying2.3mg of compos-ite electrode material(1.5mg of olivine),while counter electrode was a2×2cm2lithium foil.The cell was assembled in an argon-filled glove box and cycled galvanostatically within a voltage range 2.1–4.2V.The galvanostatic tests in the aqueous electrolyte solution were carried out in a two-electrode arrangement,involving3mg of cathodic material,as a working electrode,and VO2in a multi-ple stoichiometric excess,as a counter electrode.According to its reversible potential of lithiation/delithiation reaction[55],VO2per-formed as an anode in this cell.The4cm2stainless steel plates were used as the current collectors for both positive and negative electrode.The cell was assembled in room atmosphere,and cycled within the voltage window between0.01and1.4V.3.Result and discussion3.1.The XRD,SEM and TG analysis of the LiFePO4/C compositeFig.1shows the XRD patterns of the composite LiFePO4/C pre-pared according to the procedure described in the Experimental Section.As visible,the diffractogram agrees completely with the one of pure LiFePO4olivine,found in the JCPDS card No.725-19. The narrow diffraction lines indicate complete crystallization and relatively large particle dimensions.On the basis of absence of diffraction lines of carbon,we may conclude that the carbonized product was amorphous one.Fig.2shows the SEM images of the LiFePO4/C composite at two different magnifications.Theflaky agglomerates,Fig.2left,with apparently smooth surface and low tap density,are due to a partial liquefaction and evolution of gas bubbles during gel-combustion procedure.These agglomerates consist of small LiFePO4/CFig.1.XRD patterns of LiFePO4/C composite in comparison to standard crystallo-graphic data.250M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256Fig.2.SEM images of LiFePO 4/C composite at two different magnification,20000×and 100000×.composite particles visible better at higher magnification,Fig.2,ly at the magnification of 100,000×,one may see that the size of majority of composite particles was in the range 50–100nm.The mean particle diameter,2r,as per SEM microphotograph amounted to 75nm.This analysis evidences that the gel-combustion method may provide nanodisprsed particles,desirable from the point of view of rate capability.For instance,Fey et al.[16]demonstrated that particle size reduction from 476to 205nm improved the rate capa-bility of LiFePO 4/C composite in organic electrolyte,illustrated by the increase of discharge capacity from 80mAh g −1to 140mAh g −1at discharging rate 1C.Also,carbon matrix prevented particles from agglomeration providing narrow size distribution,contrary to often used solid state reaction method of synthesis,when sintering of ini-tially nanometer sized particles caused the appearance of micron sized agglomerates [22].The SEM microphotograph (Fig.2)alone did not permit to rec-ognize carbon constituent of the LiFePO 4/C composite.However,carbonized product was evidenced,and its content measured,by means of thermogravimetry,as described elsewhere [9].The dia-gram of simultaneous thermogravimetry and differential thermal analysis (TG/DTA)of the LiFePO 4/C composite performed in air is presented in Fig.3.The process of moisture release,causing a slight mass loss of 1%,terminated at 150◦C.In the temperature range 350–500◦C carbon combustion took place,visible as a drop of the TG curve and an accompanying exothermic peak of the DTA curve.However,the early stage of olivine oxidation merged to some extent with the late stage of carbon combustion,and therefore,the minimum of the TG curve,appearing at nearly 500◦C,was not so low as to enable to read directly the carbon content.Fortunately,as proven by XRD analysis,the oxidation of LiFePO 4at tempera-ture exceeding 600◦C,yielded only Li 3Fe 2(PO 4)3and Fe 2O 3,whatFig.3.TGA/DTA curve of LiFePO 4/C under air flow at heating rate of 10C min−1.corresponded to the relative gain in mass of exactly 5.07%[9].Therefore,the weight percentage of carbonaceous fraction in the LiFePO 4/C composite was determined as equal to the difference between the TG plateaus at temperatures 300and 650◦C,aug-mented for 5.07%.According to this calculation the carbon fraction amounted to 13.4wt.%,and by means of this value,the electro-chemical parameters discussed in the next sections were correlated to pure LiFePO 4.Specific surface area of LiFePO 4,required for the measurement of diffusion constant,was determined from SEM image (Fig.2).Assuming a spherical particle shape and accepting mean particle radius r =37.5nm,the specific surface area was estimated on the basis of equation [17,22,45,46]:S =3rd(1)where the bulk density d =3.6g cm −3was used .This calculation resulted in the value S =22.2m 2g −1.In this calculation the contri-bution of carbon to the mean particle radius was ignored,however the error introduced in such way is more acceptable than the error which may arise if standard BET method were applied to the com-posite with significant carbon ly,due to a usually very developed surface area of carbon,the measured specific sur-face may exceed many times the actual surface area of LiFePO 4.3.2.Electrochemical measurements3.2.1.Non-aqueous electrolyte solutionIn order to compare the behavior of the synthesized LiFePO 4/C composite to the existing literature data,available predominantly for non-aqueous solutions,a brief test was performed in non-aqueous 1M LiClO 4+propylene carbonate solution by galvano-static experiments only.The results for the rates C/10,C/3and C,within the voltage limits 2.1–4.2V,were presented in Fig.4.The polarizability of the lithium electrode was estimated on the basis of the study by Churikov [56–67],who measured the current–voltage curves of pure lithium electrode in LiClO 4/propylene carbon-ate solutions at various temperatures.To the highest rate of 1C =170mA g −1in nonaqueous electrolyte,the corresponding cur-rent amounted to 0.25mA,which was equal to the current density of 0.064mA cm −2through the Li counter electrode.According to Fig.2in Ref.[67],for room temperature,the corresponding over-voltage amounted to only 6mV.Since lithium electrode is thus practically non-polarizable in this system,the voltages presented on the ordinate of the left diagram are the potentials of the olivine electrode expressed versus Li/Li +reference electrode.The clear charge and discharge plateaus at about 3.49V and 3.40V,respec-tively,correspond to the LiFePO 4 FePO 4phase equilibria [5].At discharging rate of C/10,the initial discharge capacity,within the limits of experimental error,was close to a full theoreticalM.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256251Fig.4.The initial charge/discharge curves (a)and cyclic performance (b)of LiFePO 4/C composite in 1M LiClO 4+PC at different rates within a common cut-off voltage of2.1–4.2V.Fig.5.Charge/discharge profile and corresponding cyclic behavior of LiFePO 4/C in 1M LiClO 4+PC at the rate of 1C.capacity of LiFePO 4(170mAh g −1).This value is higher than that for LiFePO 4/C composite obtained by glycine [19],malonic acid [14]and adipic acid/ball milling [15]assisted methods.As usual,the discharge capacity decreased with increasing discharging rate (Fig.4b),and amounted to 127mAh g −1at C/3,and 109mAh g −1at 1C.For practical application of Li-ion batteries,a satisfactory rate capability and long cycle life are of primary importance.The charge/discharge profiles and dependence of capacity on the cycle number at the rate 1C are presented in Fig.5.The capacity was almost independent on the number of cycles,similarly to theearlier reports by Fey et al.[37–39].For comparison,Kalaiselvi et al.[19],by a glycine assisted gel-combustion procedure,with an additional amount (2wt.%)of carbon black,produced a similar nanoporous LiFePO 4/C composite displaying somewhat poorer per-formance,i.e.,smaller discharge capacity of 160mAh g −1at smaller discharging rate of C/20.On the other hand,better rate capability of LiFePO 4/C com-posite,containing only 1.1–1.8wt.%of carbon,in a non-aqueous solution,was reported by Liu et al.[21].For instance they mea-sured 160mAh g −1at the rate 1C,and 110at even 30C [21].This may be due to a thinner carbon layer around the LiFePO 4olivine particles.However the advantage of here applied thicker carbon layer exposed itself in aqueous electrolyte solutions,as described in the next section.3.2.2.Aqueous electrolyte solution3.2.2.1.Cyclic voltammetry.By the cyclic voltammetry method (CV)the electrochemical behavior of LiFePO 4/C composite in satu-rated aqueous LiNO 3solution was preliminary tested in the voltage range 0.4–1V versus SCE.The cyclic voltammograms are pre-sented in Fig.6.The highest scan rate of 100mV s −1,tolerated by this material,was much higher than the ones (0.01–5mV s −1)used in previous studies in both organic [13,24,25]and aqueous electrolyte solutions [47,48].Since one deals here with the thin layer solid redox electrode,limited in both charge consumption and diffusion length,the voltammogram is more complicated for interpretation comparing with the classic case of electroactive species in a liquid solution.A sharp,almost linear rise of current upon achieving reversible potential,with overlapped rising parts at various scan rates,similar to ones reported elsewhere [21,25],resembles closely the voltammogram of anodic dissolution ofaFig.6.Cyclic voltammograms of LiFePO 4/C in saturated LiNO 3aqueous electrolyte with a scan rate of 1mV s −1(left)and at various scan rates in the range 1–100mV s −1.252M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256Fig.7.Anodic and cathodic peak current versus square root of scan rate forLiFePO 4/C composite in aqueous LiNO 3electrolyte solution.thin metal layer [56],which proceeds under constant reactant activity.Since the solid/solid phase transitions LiFePO 4 FePO 4accompanies the redox processes in this system [5,8,57,58],the positive scan of the voltammograms depict the phase transition of LiFePO 4to FePO 4,while the negative scan depicts the phase transi-tion FePO 4to LiFePO 4.As shown by Srinivasan et al.[5],LiFePO 4may be exhausted by Li not more than 5mol.%before to trans-form into FePO 4,while FePO 4may consume no more than 5%Li before to transform into LiFePO 4,i.e.cyclic voltammetry exper-iments proceeds under condition of almost constant activity of the electroactive species.Although these aspects of the Li inser-tion/deinsertion process do not fit the processes at metal/liquid electrolyte boundary implied by Randles–Sevcik equation:i p =0.4463F RT1/2C v 1/2AD 1/2(2)this equation was frequently used to estimate apparent diffusion coefficient in Li insertion processes [5,17,21,46,59].To obtain peak current,i p ,in amperes,the concentration of lithium,C =C Li ,should be in mol cm −3,the real surface area exposed to the electrolyte in cm 2,chemical diffusion coefficient of lithium through the solid phase,D =D Li ,in cm 2s −1,and sweep rate,v ,in V s −1.The Eq.(2)pre-dicts the dependence of the peak height on the square root of sweep rate to be linear,as found often in Li-ion intercalation processes [17,21,25,59,60].This condition is fulfilled in this case too,as shown in Fig.7.The average value of C Li may be estimated as a reciprocal value of molar volume of LiFePO 4(V M =44.11cm 3mol −1),hence C Li =2.27×10−2mol cm −3.The determination of the actual surface area of olivine is a more difficult task,due to the presence of carbon in the LiFePO 4/C ly,classical BET method of sur-face area measurement may lead to a significantly overestimated value,since carbon surface may be very developed and participate predominantly in the measured value [15].Thus the authors in this field usually calculated specific surface area by means of Eq.(1),using mean particle radius determined by means of electron microscopy [17,22,45,46].Using S =22.2m 2g −1determined by means of Eq.(1),and an actual mass of the electroactive substance applied to the elec-trode surface (0.001305g),the actual electrode surface area was calculated to amount to A =290cm 2.This value introduced in Randles–Sevcik equation yielded D Li ∼0.8×10−14cm 2s −1.From the aspect of capacity retention,the insolubility of olivine in aqueous solutions is advantageous compared to the vanadia-based Li-ion intercalation materials,such as Li 1.2V 3O 8[61],LiV 3O 8[62]and V 2O 5[63],the solubility of which in LiNO 3solution was perceivable through the yellowish solutioncoloration.Fig.8.The Nyquist plots of LiFePO 4/C composite in aqueous LiNO 3solution at var-ious stages of delithiation;inset:enlarged high-frequency region.3.2.2.2.Impedance measurements.Figs.8and 9present the Nyquist plots of the LiFePO 4/C composite in aqueous LiNO 3solution at various open circuit potentials (OCV),during delithiation (anodic sweep,Fig.8)and during lithiation (cathodic sweep,Fig.9).The delithiated phase,observed at OCV =1V,as well as the lithi-ated phase,observed at OCV =0V,in the low-frequency region (f <100Hz)tend to behave like a capacitor,characteristic of a surface thin-layered redox material with reflective phase bound-ary conditions [64].At the OCV not too far from the reversible one (0.42V during delithiation,0.308V during lithiation),where both LiFePO 4and FePO 4phase may be present,within the whole 10−2–105Hz frequency range,the reaction behaves as a reversible one (i.e.shows the impedance of almost purely Warburg type).The insets in Figs.8and 9present the enlarged parts of the impedance diagram in the region of high frequencies,where one may observe a semicircle,the diameter of which corresponds theoretically to the charge transfer resistance.As visible,the change of open circuit potential between 0and 1V,in spite of the phase transition,does not cause significant change in charge transfer resistance.The small charge transfer resistance obtained with the carbon participation of 13.4%,being less than 1 ,is the smallest one reported thus far for olivine based materials.This finding agrees with the trend found by Zhao et al.[27],that the charge transfer resistance scaleddownFig.9.The Nyquist plots of LiFePO 4/C composite in aqueous LiNO 3solution at var-ious stages of lithiation;inset:enlarged high-frequency region.M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256253Fig.10.The dependence Z Re vs.ω−1/2during lithiation at 0.308V (top)and delithi-ation at 0.42V (down)in the frequency range 72–2.68Hz.to 1000,400and 150 when the amount of in situ formed carbon in the LiFePO 4/C composite increased in the range 1,2.8and 4.8%.For OCV corresponding to the cathodic (0.42V)and anodic (0.308V)peak maxima,the Warburg constant W was calculated from the dependence [21]:Z Re =R e +R ct + W ω−1/2(3)In the frequency range 2.7–72Hz,almost purely Warburg impedance was found to hold (i.e.the slope of the Nyquist plot very close to 45degrees was found).At the potential of cathodic current maximum (0.42V),from Fig.10, W was determined to amount to 7.96 s −1/2.At the potential of anodic maxima,0.308V, W was determined to amount to 9.07 s −1/2.In the published literature,for the determination of diffusion coefficient on the basis of impedance measurements,the following equation was often used [66,68,69]:D =0.5V M AF W ıE ıx2(4)where V M is molar volume of olivine,44.1cm 3, W is Warburg con-stant and ıE /ıx is the slope of the dependence of electrode potential on the molar fraction of Li (x )for given value of x .However,the potentials of CV maxima in the here studied case correspond to the x range of two-phase equilibrium,where for an accurate deter-mination of ıE /ıx a strong control of perturbed region of sample particles is required [69],and thus the determination of diffusion coefficients was omitted.3.2.2.3.Galvanostatic measurements.The galvanostatic measure-ments of LiFePO 4/C in saturated LiNO 3aqueous solution were performed in a two-electrode arrangement using hydrother-mally synthesized VO 2[55]as the active material of thecounterFig.11.Capacity versus cycle number and charge/discharge profiles (inset)for thecell consisting of LiFePO 4/C composite as cathode,and VO 2in large excess as anode,in saturated LiNO 3aqueous electrolyte observed at rate C/3.electrode.Preliminary cyclovoltammetric tests of VO 2in saturated LiNO 3solution at the sweep rate 10mV s −1,evidenced excellent cyclability and stable capacity of about 160mAh g −1during at least 50cycles.The voltage applied to the two-electrode cell was cycled within the limits 0and 1.4V.Due to a significant stoichiometric excess of VO 2over LiFePO 4/C composite (5:1)the actual voltage may be considered to be the potential versus reference VO 2/Li x VO 2electrode.Fig.11shows the dependence of the discharging Coulombic capacity of the LiFePO 4/C composite on the number of galvano-static cycles at discharging rate C/3,as well as (in the inset)the voltage vs.charging/discharging degree for 1st,2nd and 50th cycle.The charge/discharge curves do not change substantially in shape upon cycling,indicating stable capacity.For an aqueous solution,a surprisingly high initial discharge capacity of 106mAh g −1and low capacity fade of only 6%after 50charge/discharge cycles were evidenced.This behavior is admirable in comparison to other elec-trode materials in aqueous media reported in literature (LiTi 2(PO 4)3[42],LiV 3O 8[57]),and probably enabled by a higher thermody-namic stability of olivine structure [1].Fig.12presents the results of cyclic galvanostatic investigations of LiFePO 4/C composite in aqueous LiNO 3solution at various dis-charging rates.The charging/discharging rate was initially C/3for 80cycles and then was increased stepwise up to 3C.ThecapacityFig.12.Cyclic performance of LiFePO 4/C in saturated LiNO 3aqueous electrolyte at different charging/discharging rates.。

LiFePO4正极材料倍率性能改善的研究进展王旭峰;冯志军;张华森;丛欣泉;曾佑鹏【摘要】Olivine-type lithium iron phosphate (LFP) was used as cathode material of lithium ion battery due to its good electrochemical performance,such as stable charging and discharging platform and steady structure during cycling of Li ions.What's more,it had high safety,non-toxic and polluting-free,as well as long cycle life and rich rawmaterial.However,there was a instinct drawback of olive structure that baffles the marketization of LEP in the field of electrical vehicle,and that was the poor rate performance.The main approaches to improve rate performance of LEP include ion doping,surfacecoating,nanocrystallization,ect.On the base of improved approaches mentioned above,the methods in enhancing rate performance of LFP were reviewed in recent years.%橄榄石型磷酸铁锂(LFP)作为锂离子电池正极材料,具有良好的电化学性能、平稳的充放电平台、稳定的充放电结构,而且无毒、无污染、安全性能好、循环寿命长、原材料来源广泛.然而由于其本身结构的缺陷,导致其倍率性能低下,这将直接影响该材料在动力汽车市场的应用.改善其倍率性能的方法主要有离子掺杂、表面包覆、合成纳米材料.以这几类改性方法为主线,综述了近年来LFP倍率性能改善的研究进展.【期刊名称】《电源技术》【年(卷),期】2017(041)008【总页数】4页(P1202-1205)【关键词】锂离子电池;正极材料;磷酸铁锂;倍率性能【作者】王旭峰;冯志军;张华森;丛欣泉;曾佑鹏【作者单位】南昌航空大学材料科学与工程学院,江西南昌330063;南昌航空大学材料科学与工程学院,江西南昌330063;南昌航空大学材料科学与工程学院,江西南昌330063;南昌航空大学材料科学与工程学院,江西南昌330063;南昌航空大学材料科学与工程学院,江西南昌330063【正文语种】中文【中图分类】TM912锂离子电池以其能量密度高、使用寿命长、无记忆效应、可再次充放电、轻巧、工作电压高、无污染等优点，成为便携式产品和动力车载电池发展的主要方向。

一维纳米功能材料的静电纺丝制备及其性能研究的开题报告论文题目：一维纳米功能材料的静电纺丝制备及其性能研究摘要：一维纳米功能材料因其独特的物理化学性质，已成为研究热点。

静电纺丝是一种制备一维纳米材料的常用方法。

在本研究中，我们将以聚丙烯酸(PAA)为模板，通过静电纺丝制备出一维纳米锂离子电池正极材料LiFePO4@C。

通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外光谱仪(FTIR)等工具对材料的结构和性质进行了表征。

同时，利用循环伏安(CV)和恒流充放电测试等方法，对LiFePO4@C的电化学性能进行了评估。

通过SEM和TEM的结果，我们得知制备出的材料呈现典型的一维纳米结构，并具有良好的分散性和均匀性。

FTIR的结果表明，材料表面覆盖了一层碳包裹层，这是锂离子电池正极材料的重要特征之一。

CV和恒流充放电测试的结果表明，制备出的LiFePO4@C材料具有优异的电化学性能，包括高比容量、优异的循环性能和较好的倍率性能。

本研究的结果表明，静电纺丝是一种制备一维纳米功能材料的有效方法。

制备出的LiFePO4@C材料具有良好的电化学性能，有望应用于锂离子电池等领域。

关键词：一维纳米功能材料；静电纺丝；锂离子电池正极材料；电化学性能Abstract:One-dimensional nanofunctional materials have become a research hotspot due to their unique physical and chemical properties. Electrospinning is a common method for preparing one-dimensional nanomaterials. In this study, we used polyacrylic acid (PAA) as a template to prepare one-dimensional nanomaterials LiFePO4@C, whichis a positive electrode material for lithium-ion batteries, through electrospinning. The structure and properties of the material were characterized by scanning electron microscopy (SEM), transmissionelectron microscopy (TEM), Fourier transform infrared spectrometer(FTIR), and other tools. At the same time, the electrochemicalproperties of LiFePO4@C were evaluated by cyclic voltammetry (CV)and constant current charge-discharge tests.The results of SEM and TEM showed that the prepared materialhad a typical one-dimensional nanoscale structure, good dispersion, anduniformity. The FTIR results showed that the material was covered with a layer of carbon encapsulation, which is an important feature of positive electrode materials for lithium-ion batteries. The results of CV and constant current charge-discharge tests showed that the prepared LiFePO4@C material had excellent electrochemical properties, including high specific capacity, excellent cycling performance, and good rate performance.The results of this study indicate that electrospinning is aneffective method for preparing one-dimensional nanofunctional materials. The prepared LiFePO4@C material has good electrochemical properties and is expected to be applied in the field of lithium-ion batteries.Keywords: one-dimensional nanofunctional materials; electrospinning; positive electrode material for lithium-ion batteries; electrochemical properties。

第9卷第1期2003年2月电化学ELECTROCHEM I STRYV O .9N O.1feb.2003文章编号：1006-3471（2003）01-0009-06L i fePO4新型正极材料电化学性能的研究施志聪，李晨，杨勇!（厦门大学化学系，固体表面物理化学国家重点实验室，福建厦门361005）摘要：采用固相反应结合高速球磨法，合成了锂离子电池新型正极材料L i fePO4，并对该材料进行碳包覆处理；采用XRD、SEM、元素分析以及价态化学分析等方法对样品进行表征.实验表明，L i fePO4具有3.4V的放电电压平台，而且包覆碳后的磷酸铁锂具有更好的电化学性能，首次放电容量达147mA／g，充放电循环100次后容量只衰减9.5%.关键词：锂离子电池；正极材料；磷酸铁锂；电化学性能中图分类号：O646.54；TM911.1文献标识码：A绿色环保锂离子二次电池近年来已在各种便携式电子产品和通讯工具中得到广泛应用，并被逐步开发为电动汽车的动力电源.此中，新型电极材料特别是正极材料的研制至为关键.众所周知，已经商品化的L i C OO2和正受广泛研究的L i N i O2，L i M nO4正极材料各具特色，而作为新型锂离子电池正极材料的正交晶系橄榄石型L i fePO4则兼具上述各种材料的优点，特别是其价格低廉，热稳定性好，对环境无污染等更使它成为最有潜力的正极材料之一.最近，国际上不同的研究小组对该电极材料体系进行了广泛的研究［1!11］，其中H uan g等通过包覆碳改善材料的电子电导率［11］，改性后的L i fePO4复合材料在0.5C倍率下首次放电容量可达153 mA／g，已具备实际应用的可能性.本文采用高速球磨和固相反应相结合的方法，在优化实验条件后合成出不包覆碳的和包覆碳的L i fePO4两种材料；包覆碳后的磷酸铁锂具有更好的电化学性能，首次放电容量达147mA／g，充放电循环100次后容量只衰减9.5%；此外，还讨论了包覆碳后L i fePO4材料的电化学性能之所以改善的原因.!实验!.!材料合成（1）L i OH·H2O（AR），feC2O4·2H2O（自制）和NH4H2PO4（AR）以摩尔比1i1i1混合，在无水乙醇（AR）介质中高速球磨6（转速500／r p m），球磨后前驱体转移至管式炉（上海实验电炉厂），通高纯氮气（流速800c m3／m i n）保护，于600C恒温36，产物为不包覆碳的L i fePO4（以L i fePO4表示）.收稿日期：2002-11-19!通讯联系人，E-m ai ：yy an g"x m 国家杰出青年基金（29925310），国家“973”项目资助（2）反应物及其配比同（1），在含有甲醛-间苯二酚树脂（自制）的无水乙醇（AR ）介质中高速球磨，其他实验过程与上述（1）相同，合成出包覆碳的L i feP04（以L i feP04／C 表示）.!."材料表征采用日本R i g LkL RotafleX D ／M AX -RC 多晶转靶X -射线衍射仪（C L K !辐射，!=0.15406n m ，石墨单色器）对合成产物进行物相分析，扫描范围15"45 ，扫描速度8 ／m i n.合成材料中fe 2+的含量（占全铁量）采用化学分析法（重铬酸钾容量法）测定，步骤如下：样品用4m o l ／L 的HC l （预先通高纯氮除去溶解氧）溶解，迅速密封后置阴暗处3h 以上，然后抽滤除杂质，加硫磷混合酸掩蔽fe 3+，以二苯胺磺酸钠（0.2%）为指示剂，K 2C r 207标准溶液滴定.合成产物的含碳量由CE E lantech inc .的EA lll 0型元素分析仪（采用动态闪燃和气相色谱分析技术）测定.通过SEM （LE01530fiel d Em ission SEM ，0Xf ord instrL m ent ）观察合成产物的形貌和微结构.!.#充放电测试采用涂膜法制备电极，以NM P 为溶剂，将原料按比例（L i feP04I 乙炔黑I PVDf =75I 20I 5）混合，转速500／r p m ，机械球磨3h 成正极浆液，再将浆液涂在预处理过的铝箔上，经充分干燥，压片后得到正极片.在惰性气体保护的M BRAUN 手套箱中，以金属锂片为对电极，1m o l ／L L i Pf 6／EC -DM C （1I 1）为电解液，C el g erd 2300为隔膜，组装成2025型扣式电池，在ARbi n 公司的BT 2043型充放电仪上进行0.1C 充放电性能测试，充放电条件：电压范围2.7"4.1V ，电流密度0.019mA ／g ."结果与讨论图1a ，b 分别为未包覆碳和包覆碳的L i feP04两种合成产物的XRD 谱图.图中除了杂质峰（!-L i 3P04，#-fe 203）外，表征物相L i feP04和L i feP04／C 的谱峰均与Y a m ada 等报道的一致［7］，对比图1a ，b ，包覆碳的L i feP04材料（a ）吸收峰峰高较之未包覆碳的相对稍低，这是因为包覆碳后，L i feP04／C 材料的非晶态物质含量增加了，而晶态物质含量的减少则导致XRD 吸收峰峰高降低.但不论是包覆碳或未包覆碳，两者的吸收峰位均同，说明L i feP04材料表面包覆碳后并没有影响到其内部晶格结构，L i feP04仍然保持正交晶系橄榄石型结构.表1列出由上述XRD 谱图分别计算得到的L i feP04和L i feP04／C 晶胞参数，结果与J CPD S 卡标准值（PDf #40-1499）甚为接近.由于fe 2+很容易被氧化为fe 3+，在高温固相合成时，难免会生成含fe 3+的杂相，造成晶格发生变化，晶体的嵌锂能力变弱，最终导致材料的性能变差，为此鉴定材料中的fe 2+含量（占全铁量）有其必要.经化学分析（重铬酸钾容量法）测试，得L i feP04和L i feP04／C 两材料的fe 2+含量（占全铁量）分别为93%和87%.·01·电化学2003年图1L i fePO 4（a ）和L i fePO 4／C （b ）的XRD 图谱fi g .1XRD p ro file o f t he L i fePO 4（a ）and L i fePO 4／C （b ）sa m p le表1L i fePO 4和L i fePO 4／C 的晶胞参数T ab.1P ara m eters f or cr y stal ce lls o f t he obtai ned sa m p lesS a m p les na m ea ／n mb ／n mc ／n m PDf !40-1499L i fePO 4L i fePO 4／C 0.60190.59770.60081.03471.03181.03010.47040.46650.4664表2列出对L i fePO 4／C 材料元素分析的两次平行测试，从结果看，可证明碳在L i fePO 4／C 材料上的包覆很均匀，含碳量平均值为6.37%.材料中所含的微量氢（0.45%）可能来自吸附的水分或者是实验时加入但并未完全裂解的有机物中的氢.表2材料L i fePO 4／C 的含碳量T ab.2C arbon content o f t he obtai ned L i fePO 4／C sa m p le L i fePO 4／CC （%）~（%）N （%）N o.1N o.26.3776.3550.4580.43500对比L i fePO 4和L i fePO 4／C 两种材料的SEM 图（图2）可以发现，L i fePO 4表面较光滑均匀，而L i fePO 4／C 则表面粗糙，具有丰富的微结构，比表面积增大很多，实验表明：含碳量6.0%的L i fePO 4／C 样品，其比表面积可达41.7m 2／g ，而不包覆碳的L i fePO 4比表面积只有4.5m 2／g［12］.·11·第1期L i fePO 4新型正极材料电化学性能的研究a b图2l i fePO 4（a ）和l i fePO 4／C （b ）的SEM 图像（1110000）fi g .2SEMi m a g e o f t he l i fePO 4（a ）and l i fePO 4／C （b ）sa m p le a b 图3l i fePO 4和l i fePO 4／C 两种材料于室温下的首次充放电曲线（a ）比较和循环性能曲线（b ）比较fi g .3C om p arison o f char g e ／d ischar g e p ro files （a ）and c y cli n g p erf or m ance （b ）f or t he l i fePO 4and l i fePO 4／C sa m p les at 22C图3分别示出l i fePO 4和l i fePO 4／C 两种材料的0.1C 充放电及其循环性能变化，如图所示两种材料均具有很平稳的3.4V 充放电平台.在充放电实验末期，由于纯材料电子电导较低的原因导致电极极化更大，所以l i fePO 4的充放电平台比l i fePO 4／C 的平台上升（充电时）或下降（放电时）得更快.l i fePO 4的首次充放电容量依次为150mA h ／g 和138mA h ／g ，充放电效率为92.0%；而l i fePO 4／C 的首次充放电容量依次为154mA h ／g 和147mA h ／g ，充放电效率为95.5%，可见l i fePO 4／C 比l i fePO 4具有更高的初始容量和更低的不可逆容量.由图3b 可以看出，l i fePO 4充放电循环100次后放电容量为111mA h ／g ，容量衰减19.6%；而·21·电化学2003年L i feP04／C 充放电循环100次后放电容量仍保持134mA h ／g ，容量只衰减9.5%，明显具有更优异的循环性能.综上可得：L i feP04包覆碳后性能得以改善的原因是由于锂离子L i feP04中的扩散速率较小，其自身的电子电导率也较低，造成该材料锂离子嵌入脱出的可逆性能较差；而经过碳包覆后，不仅材料的电子电导率得到了提高，而且比表面积也相应增大，有利于材料与电解质充分接触，从而改善了微粒内层锂离子的嵌入脱出性能，进而提高材料的充放电容量和循环性能.考虑到在合成的L i feP04／C 材料中fe 2+含量（占全铁量）只有87%.若再进一步改善惰性气氛保护条件和优化原料配比，则有望合成出性能更好的L i feP04／C 材料.!结论在优化实验条件后合成出L i feP04及L i feP04／C 材料，其中包覆碳后的L i feP04比未包覆碳的L i feP04具有更高的容量，更好的循环性能.这和L i feP04经包覆碳后，其电子电导率的提高以及材料表面丰富微结构的存在有很大关系.The E lectroche m ical Perf or m ance S t udies on Novel L i feP04C at hode M ateri als f or L i-i on batteriesS~I zhi-con g ，L I Chen ，YANG Y on g !（S t ate k e y Lab f Or Ph y sical C he m istr y O f S Olid Sur f ace ，D e P art m ent O f C he m istr y ，X ia m en unioersit y ，X ian m en 361005，C hina ）Abs tr act ：T he cat hode m aterials o f L i feP04and L i feP04coated w it h carbon w ere s y nt hesizedb y m eans o f so li d state reaction and ball m illi n g .T he sa m p les w ere characterized b y X -ra y diffrac-tion ，scanni n g electron m icrosco py ，g as-p hase ele m ent anal y sis and titration anal y sis m et hods.E lectroche m ical tests o f t w o ki nds o f m aterials show ed t hat bot h o f t he mexhi bit a 3.4V dischar g e vo lta g e p lateau ，how ever ，t he coated sa m p les de m onstrated t he i m p roved p erf or m ance i n ter m s o f dischar g e ca p acit y and c y clic stabilit y .Ke y Wor ds ：L it hi u m ionbatteries ，C at hode m aterials ，L it hi u m f erric p hos p hate ，E lectro-che m ical p erf or m ance Re f er ences ：［1］P adh i A K ，N an j undasw a m y K S ，G oodenou g h J b.Phos p ho -o livi nes as p os itive-e lectrode m aterials f orrechar g eab le lit h i u m batteries ［J ］.J .E lectroche m.S oc .，1997，144（4）：1188!1194.［2］P ros i n i P P ，zane D ，P as C uali M.I m p roved e lectroche m ical p erf or m ance o f a L i feP04-based com p os ite cat h-ode ［J ］.E lectroch i m ica A cta ，2001，46：3517!3523.·31·第1期L i feP04新型正极材料电化学性能的研究［3］A ndersson A S ，T hom as J O.T he source o f first-c y cle ca p acit y loss i n L i fePO 4［J ］.J .PoW er S ource ，2001，97!98：498!502.［4］T akahash i M ，T ob ish i m a S ，T ake i K ，et al .Characterization o f L i fePO 4as t he cat hode m aterial f or rechar g e-ab le lit h i u m batteries ［J ］.J .PoW er S ource ，2001，97-98：508!511.［5］P ros i n i P P ，L is i M ，S caccia S ，et al .S y nt hes is and characterization o f a m or p hous h y drated fePO 4and itse lectrode p erf or m ance i n lit h i u m batteries ［J ］.J .e lectroche m.S oc .，2002，149（3）：A 297-A 301.［6］Y an g S ，Zavali j P Y ，W h itti n g ha m M S.~y dro t her m al s y nt hes is o f lit h i u m iron p hos p hate cat hodes ［J ］.e lectroche m istr y C omm un ications ，2001，3：505!508.［7］Y a m ada A ，Chun g S C ，~i noku m a K.O p ti m ized L i fePO 4f or lit h i u m batter y cat hodes ，［J ］.J .e lectroche m.S oc .，2001，148（3）：A 224!A 229.［8］Y a m ada A ，K udo Y ，L i u K Y.reaction m echan is m o f t he o livi ne-t yp e L i !（M n 0.6fe 0.4）PO 4［J ］.J .e lec-troche m.S oc .，2001，148（7）：A 747!A 754.［9］Y a m ada A ，Chun g S C.C r y stal che m istr y o f t he o livi ne-t yp e L i （M n "fe 1-"）PO 4and （M n "fe 1-"）PO 4asp oss i b le 4v cat hode m aterials f or lit h i u m batteries ［J ］.J .e lectroche m.S oc .，2001，148（8）：A 960!A 967.［10］Y a m ada A ，K udo Y ，L i u K Y.Phase d ia g ra m o f L i !（M n "fe 1-"）PO 4（0!!，"!1）［J ］.J .e lectroche m.S oc .，2001，148（10）：A 1153!A 1158.［11］~uan g ~，Y i n S C ，N azar L f .A pp roach i n g t heoretical ca p acit y o f L i fePO 4at room te m p erature at h i g hrates ［J ］.J .e lectroche m ical and so li d-state letters ，2001，4（10）：A 170!A 172.［12］L I Chen （李晨），Characterization and e lectroche m ical p erf or m ance stud ies on nove l L i fePO 4cat hode m ateri-als ［D ］.x ia m en ：B S c t hes is o f x ia m en U n ivers it y ，2002.·41·电化学2003年LiFePO4新型正极材料电化学性能的研究作者：施志聪， 李晨， 杨勇作者单位：厦门大学化学系,固体表面物理化学国家重点实验室,福建,厦门,361005刊名：电化学英文刊名：ELECTROCHEMISTRY年，卷(期)：2003,9(1)被引用次数：57次1.Yang S;Zavalij P Y;Whittingham M S Hydrothermal synthesis of lithium iron phosphate cathodes[外文期刊] 20012.Prosini P P;Lisi M;Scaccia S Synthesis and characterization of amorphous hydrated FePO4 and its electrode performance in lithium batteries[外文期刊] 2002(03)3.Takahashi M;Tobishima S;Takei K Characterization of LiFePO4 as the cathode materialfor rechargeable lithium batteries[外文期刊] 2001(0)4.Andersson A S;Thomas J O The source of first-cycle capacity loss in LiFePO4 20015.Prosini P P;Zane D;Pasquali M Improved electrochemical performance of a LiFePO4-based composite cathode[外文期刊] 2001(23)6.李晨Characterization and electrochemical performance studies on novel LiFePO4 cathode materials 20027.Huang H;Yin S C;Nazar L F Approaching theoretical capacity of LiFePO4 at room temperature at high rates 2001(10)8.Yamada A;Chung S C Crystal chemistry of the olivine-type Li(MnyFe1-y)PO4 and (MnyFe1-y)PO4 as 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锂电池正极材料LiFePO4机理分析研究（结构和缺陷、锂离子扩散通道、嵌锂脱锂相转变机制等）1引言LiFePO4因其优异的综合性能被认为是最具潜力的动力电池正极材料之一,引起了广泛的关注和深入的研究。

大量的研究工作主要集中在LiFePO4的合成制备和性能优化方面,LiFeP04的可逆容量和倍率性能都得到了很大的改善。

进一步提高LiFePO4的电化学性能，需要对LiFePO4的充放电微观机制有深入的认识，包括两相界面的迁移，Li+的扩散机制，结构形貌对性能的影响等。

2 LiFePO4结构与缺陷、掺杂改性2.1 LiFePO4的结构[1]LiFePO4晶体结构属Pmnb空间群，晶胞参数a=0.6011nm、b=1.0338nm、c=0.4695nm 每个晶胞含有4个LiFePO4单元。

在晶体结构中氧原子以稍微扭曲的六方紧密堆积方式排列Fe与Li分别位于氧原子的八面体中心,形成变形的八面体。

P原子位于氧原子的四面体中心位置。

LiO6八面体共边形成平行于[100]Pmnb的LiO6链。

锂离子在[100]Pmnb与[010]Pmnb方向上的性质相异，这使得(001)面上产生显著的内应力,[010](锂离子通道之间)方向的内应力远大于[100](锂离子通道)方向的内应力。

所以[100]Pmnb方向是最易于Li+离子扩散的通道。

图1 LiFePO4的橄榄石型结构[1]通过LiFePO4晶体结构可以看出,因为FeO6八面体被PO34-分离,降低了LiFePO4材料的导电性;氧原子三维方向的六方最紧密堆积限制了Li+的自由扩散。

2.2 LiFePO 4的本征缺陷更好的了解电极正极材料中可能存在的点缺陷类型及与之相关的类型，对研究者们更加全面的理解正极材料的电化学行为意义深远。

化学热力学中的缺陷形成能对缺陷的形成有着重要的意义。

其中肖特基缺陷，弗伦克尔缺陷以及阳离子反位缺陷等本征原子缺陷成为了研究者们研究各种电极材料缺陷化学的主要途径。

锂离子电池正极材料LiFePO 4的结构和电化学反应机理连王亮1, 2 马华培1 李法强1 诸葛芹1(1 中国科学院青海盐湖研究所 西宁 810008；2中国科学院研究生院 北京 100039) 摘 要 十年来的研究并没有对LiFePO 4的电化学反应机理形成准确一致的认识。

复合阴离子(PO 4)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， LiFePO 4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LiFePO 4的电化学反应机理的研究进展。

关键词 LiFePO 4 机理 影响因素 正极材料 锂离子电池The Structure and Electrochemical Mechanism of LiFePO 4 as Cathode of Lithium IonBatteryWang Lianliang 1, 2, Ma Peihua 1, Li Faqiang 1, Zhu Geqin 1(1 Qinghai Institute of Salt Lakes, Chinese Academy of Science, Xining 810008;2 Graduate School of Chinese Academy of Science, Beijing 100039)Abstract The electrochemical mechanism of LiFePO 4 as cathode material for lithium ion batteries during charging and discharging is still under debate after ten years of research. The use of polyanion, (PO 4)3-, makes it possible for iron-based compound to be one of the potential promising cathode material for lithium ion batteries. However, the interior structure of LiFePO 4 determines the diffusion of electrons and lithium ions, and therefore deteriorate its electrochemical performance. From theoretical part and the aspect of practices of experiment, inner reactions during the processes of charging/discharging, phases transition, ion-doping, diffusion of lithium ions, conductivity, interactions between cathode material and electrolytes and the electrochemical kinetic of LiFePO 4 based lithium ion batteries are described in this paper.Key words LiFePO 4, Mechanism, Factors, Cathode material, Lithium ion battery自从1997年Padhi 等开创性的提出锂离子电池正极材料LiFePO 4以来, LiFePO 4 已经成为可充电锂离子电池正极材料的研究热点之一。

作者简介:李海英（1983-），女，工程师。

主要从事新能源材料方面的研究。

橄榄石型磷酸铁锂（LiFePO 4）因比容量较高、安全性能好、环境友好、使用寿命长等优点被认为是动力型锂离子电池理想的正极材料之一[1-2]。

由于LiFePO 4为半导体，其电子电导率（~10-9S ·cm -1）和锂离子扩散系数（10-10S ·cm -1~10-15cm 2·S -1）极低，严重影响了其电化学性能的发挥，从而限制其在电动汽车上的大规模应用[3]。

目前，主要利用碳包覆[4]、离子掺杂[5]和颗粒纳米化[6]等方法可有效提高LiFePO 4的电子电导率和锂离子扩散系数，进而提高其电化学性能。

但仅通过单一的金属离子掺杂[7]或碳包覆的方法以提高锂离子扩散系数的成效是有限的，这样由材料离子扩散性差所带来的电池高倍率放电性能和低温性能差的问题仍然制约着LiFePO 4在动力型锂离子电池中的大规模应用。

研究表明，采用碳包覆高性能正极材料LiFePO 4的制备及表征李海英1，岳波2，黄小丽2，王俊安2，李延俊2(1.四川省能源投资集团有限责任公司,四川成都610063;2.四川科能锂电有限公司,四川成都610063)摘要：采用颗粒纳米化技术与雾化干燥相结合的方法合成了高性能的LiFe 0.98Ti 0.02PO 4-x F x /C （x=0.00，0.02）正极材料。

利用X-ray 粉末衍射仪、场发射扫描电子显微镜和蓝电测试系统对合成材料的晶体结构、颗粒形貌和电化学性能进行了表征。

结果表明，采用该方法可明显降低一次颗粒粒径，同时引入Ti-F 掺杂可进一步提高产品的电化学性能。

LiFe 0.98Ti 0.02PO 3.98F 0.02/C 表现出最好的电化学性能，其0.1C 首次放电比容量和库伦效率分别为163.9mAh/g 和97.3%；1C 放电比容量为144.3mAh/g ，循环50次后容量保持率为98.8%，表现出了较高放电比容量和良好的循环性能。

锰掺杂对纯化磷酸铁制备磷酸铁锂电池正极材料的影响李光明;刘小瑜;张家玮;吴敏昌;乔永民;王利军【摘要】以废弃磷化渣为原料,利用酸液水热过滤法对磷化渣提纯.将所得纯度较高的磷酸铁为铁源,通过加入锰盐来制备含有掺杂锰元素的前驱体,经过高温还原后可得到掺杂锰元素的磷酸亚铁锂/碳电池正极材料.利用X射线衍射仪、X射线荧光光谱仪、扫描电子显微镜和LAND测试仪对不同组成的磷酸铁锂/碳电池正极材料的颗粒形貌、物相及扣式电池的电化学性能进行表征.结果表明:掺杂锰元素的磷酸亚铁锂/碳材料在大倍率下仍能保持较高的容量保持率,这对于制作大倍率电池具有重要的意义.【期刊名称】《上海第二工业大学学报》【年(卷),期】2018(035)004【总页数】5页(P263-267)【关键词】磷化渣;磷酸铁锂;正极材料;离子掺杂【作者】李光明;刘小瑜;张家玮;吴敏昌;乔永民;王利军【作者单位】上海第二工业大学环境与材料工程学院,上海201209;上海第二工业大学环境与材料工程学院,上海201209;上海第二工业大学环境与材料工程学院,上海201209;上海杉杉科技有限公司,上海201209;上海杉杉科技有限公司,上海201209;上海第二工业大学环境与材料工程学院,上海201209【正文语种】中文【中图分类】TB3320 引言磷化渣是金属表面预处理时,磷化过程的必然产物,它是一种淡黄色固体废渣。

根据磷化渣中主要组分的不同,可分为锰系和铁系磷化渣。

磷化渣的主要成分为磷酸铁(FePO4)、磷酸锰[Mn3(PO4)2)]和磷酸锌[Zn3(PO4)2],可能还含有少量Ca、Ni等金属离子[1-2]。

磷化渣属于HW17类型危险固体废物,被记录在《国家危险废物名录》之中,对其处置需要经过严格的管控和处理[3]。

目前的主要处理方式以填埋为主,但会对周围的土壤、水体和大气造成严重污染。

如果能将FePO4或Mn3(PO4)2从磷化渣中提取出来,用作制备磷酸亚铁锂和磷酸锰锂正极材料的主要原料,既可以实现磷化渣的资源化综合利用,又可以降低磷酸亚铁锂正极材料的原料成本[4]。