水热法制备LiFePO4正极材料

本文以制备LiFePO4正极材料存在的问题为主线,从提高产物纯度、控制样品形貌和提高材料性能三方面综述了目前水热合成LiFePO4的研究进展,同时也从节省原料、降低成本及产业化方面对水热合成LiFePO4进行了展望.本文虽以水热制备LiFePO4为主线,但在相关章节也涵盖了对溶剂热、超临界、多元醇和离子热等相关低温合成...     

优化碳包覆对正极材料LiFePO4/C高倍率性能的影响

碳包覆层的结构和形态对LiFePO4正极材料的电子电导率影响很大. 本文以聚丙烯和葡萄糖为碳源, 二茂铁为催化剂前驱体, 采用原位固相法合成LiFePO4/C复合材料, 并对其微观结构和形貌, 碳的结构与含量, 电化学性能进行分析. 结果表明, 聚丙烯热解形成的碳包覆层石墨化程度高, 可提高材料的高倍率放电性能. 二茂铁的加入有助于优化包覆层的碳结构. 制备的LiFePO4/C复合材料具有优异的高倍率电化学性能, 10C (1C=170 mA·g-1)放电比容量达到145 mAh·g-1.     

锂离子蓄电池正极材料LiFePO4研究进展

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展，而具有橄榄石结构的LiFePO4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源，但自身也存在缺点。综述了锂离子电池正极材料LiFePO4的研究进展。系统地阐述了LiFePO4的晶体结构特征及性能、多种合成方法以及掺杂多种导电材料和控制晶体生长制备纳米粉体对材料性能的影响。对该材料的应用前景进行了展望，并提出了下一步可能的研究趋势。     

包覆碳掺CoLiFePO4正极的电化学性能研究

应用水热法在200 oC下合成了橄榄石结构LiFePO4正极材料,合成过程中添加蔗糖作为包覆用碳源,并同时掺Co. 实验表明,包覆碳掺Co能更有效地改善LiFePO4电极的电化学性能. 样品可后退火处理,400 oC 退火LiFePO4样品结晶度和颗粒尺寸均影响了其电化学性能,包覆碳掺CoLiFePO4样品可使颗粒细化,改善电极倍率性能.     

LiFePO_4表面碳包覆方法中碳源的碳化及碳源选择

LiFePO4材料表面碳包覆可以有效地提高材料的电导率,从而进一步提高材料的容量和放电性能.但碳包覆所用的碳源不同,其效果也不尽相同.结合笔者实验室工作,分析了不同碳源的碳化过程,并结合碳包覆的工艺,对LiFePO4碳包覆方法中碳源的选择及碳包覆方法作了讨论.     

机械活化辅助多元醇法合成锂离子正极材料LiFePO4

以LiH2PO4和还原铁粉为原料,通过机械液相活化法获得了棒状形貌的[Fe3(PO4)2·8H2O+Li3PO4]前驱体,然后在三甘醇(TEG)介质中采用多元醇工艺制备了LiFePO4材料.为提高其电导率,以聚乙烯醇(PVA)为碳源,对纯相LiFePO4进行碳包覆改性.通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、恒电流充放电和电化学阻抗谱(EIS)等测试方法对制备的材料进行了表征.结果表明:采用机械活化辅助多元醇法可在低温下合成结晶良好的LiFePO4,碳包覆改性的LiFePO4/C材料导电性能得到改善,电荷转移阻抗减小,1C、2C倍率下放电容比量分别为139.8、129.5mAh·g-1,具有良好的倍率性能和循环稳定性.     

一氧化碳还原法制备磷酸铁锂—反应机理和动力学

由CO还原FePO4和LiOH前驱体合成LiFePO4正极材料,应用XRD、SEM表征材料结构和形貌、充放电曲线测试电化学性能.结果表明,LiOH过量5%合成的LiFePO4样品颗粒度约200 nm,包覆碳后LiFePO4电极0.1C放电容量可达158 mAh/g.高温现场XRD对该合成反应作实时监控,借助时间分辨图谱分析,检测出Li3Fe2(PO4)3中间物.动力学研究表明成核与生长是该合成过程的速控步骤,反应活化能为89.44 kJ/mol.     

拉曼光谱在锂离子电池研究中的应用

综述拉曼光谱(Raman spectroscopy)在锂离子电池碳负极材料、尖晶石LiMn2O4和LiFePO4正极材料、聚合物和室温熔盐电解质以及电极/电解质界面膜研究中的应用,分析了非原位拉曼测试手段与原位拉曼测试手段的优缺点,展望了这一领域目前有待解决的问题和可能应用的新技术.     

LiFePO4的合成及其热分析动力学

在惰性气氛下, 以Li2CO3、FeC2O4·2H2O和NH4H2PO4为原料, 用高温固相方法合成了橄榄石型LiFePO4材料. 利用不同升温速率的热重及差热分析研究了固相合成LiFePO4的反应动力学. 研究表明, LiFePO4的高温固相合成过程可分为三个步骤, 利用Doyle-Ozawa法和Kissinger法分别计算了各个反应阶段的表观活化能. 用Kissinger法确定每个反应阶段的反应级数和频率因子, 并给出了各个阶段的动力学方程. 根据动力学研究的结果, 采用优化的固相 分段法合成了碳包覆改性的LiFePO4正极材料. 利用X射线衍射、扫描电镜及恒流充放电对材料进行了物性表征及性能测试. 结果表明, 该材料具有单一的橄榄石结构, 颗粒尺寸细小均匀, 0.1C倍率放电时表现出良好的电化学性能.     

掺碳制备锂离子电池正极材料LiFePO4

采用固相法合成LiFePO4和掺碳的LiFePO4,并对不同掺碳量的LiFePO4进行电化学性能测试,室温条件下,在0.1 C倍率下充放电,样品d(ωC=8.5%)的初始放电容量为151.7 mA·h/g.10次循环后,其放电比容量仍有149.5 mA·h/g,容量损失较小.这表明,在合适的制备工艺条件下,掺碳能获得结构稳定、电化学性能良好的锂离子电池正极材料LiFePO4.     

pH对溶胶-凝胶法制备的锂离子电池正极材料磷酸铁锂的形貌及电化学性能的影响

采用溶胶-凝胶法制备了锂离子电池正极材料LiFePO_4;探讨了pH对磷酸铁锂的形貌及电化学性能的影响.结果表明,随着pH的升高,LiFePO_4的粒径减小,粒径分布变窄,电化学性能提高.在不同pH下制备的LiFePO_4材料以0.2C的倍率放电,首次放电比容量分别为126.8mAh/g、132.4mAh/g、145.6mAh/g.     

Review on Li-insertion/extraction Mechanisms of LiFePO_4 Cathode Materials

The work distills the main mechanisms during the lithium insertion/extraction of LiFePO_4 cathode materials. The "diffusion-controlled" and "phase-boundary controlled" mechanism are especially illustrated. Meanwhile, some recent observation and analyses by in-situ or in operando on the Li-insertion/extraction of LiFePO_4 are summarized and prospected.     

Cathode materials for lithium ion batteries prepared by sol-gel methods

Improving the preparation technology and electrochemical performance of cathode materials for lithium ion batteries is a current major focus of research and development in the areas of materials, power sources and chemistry. Sol-gel methods are promising candidates to prepare cathode materials owing to their evident advantages over traditional methods. In this paper, the latest progress on the preparation of cathode materials such as lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, vanadium oxides and other compounds by sol-gel methods is reviewed, and further directions are pointed out. The prepared products provide better electrochemical performance, including reversible capacity, cycling behavior and rate capability in comparison with those from traditional solid-state reactions. The main reasons are due to the following several factors: homogeneous mixing at the atomic or molecular level, lower synthesis temperature, shorter heating time, better crystallinity, uniform particle distribution and smaller particle size at the nanometer level. As a result, the structural stability of the cathode materials and lithium intercalation and deintercalation behavior are much improved. These methods can also be used to prepare novel types of cathode materials such as nanowires of LiCoO₂ and nanotubes of V₂O₅, which cannot be easily obtained by traditional methods. With further development and application of sol-gel methods, better and new cathode materials will become available and the advance of lithium ion batteries will be greatly promoted.     

New sol-gel synthetic route to phospho-olivines as environmentally friendly cathodes for Li-ion cells

A new sol-gel synthetic route was developed to prepare single-phase phospho-olivines LiMPO4 (M = Fe or Mn), potential cathode materials for the next generation of Li-ion secondary batteries. Triethyl phosphite was used as phosphate organic precursor, with absolute ethanol as solvent. The sol-gel synthesis ensures homogeneity of the precursors at the nanometric scale and improved reactivity, allowing to obtain very small agglomerates and crystal grain size. Several carbon sources were used in order to improve the electrochemical performances of the samples. Galvanostatic cycling tests of the cathodic materials were made on coin cells with Li metal as anode in order to study the influence of the synthesis and the structural-morphological characteristics on the electrochemical performance of the phosphate/C composite.     

Recent progress on lithium-ion batteries with high electrochemical performance

Lithium-ion batteries(LIBs) have been widely used in many fields such as portable electronics and electric vehicles since their successful commercialization in the 1990 s. However, the electrochemical performance of current commercial LIBs still needs to be further improved to meet the continuously increasing demands for energy storage applications. Recently, tremendous research efforts have been made in developing next-generation LIBs with enhanced electrochemical performance. In this review, we mainly focus on the recent progress of LIBs with high electrochemical performance from four aspects, including cathode materials, anode materials, electrolyte, and separators. We discuss not only the commercial electrode materials(LiCoO_2,LiFePO_4, LiMn_2O_4, LiNi_xMn_yCo_zO_2, LiNi_xCo_yAl_zO_2, and graphite) but also other promising next-generation materials such as Li-, Mn-rich layered oxides, organic cathode materials, Si, and Li metal. For each type of materials, we highlight their problems and corresponding strategies to enhance their electrochemical performance. Nowadays, one of the key challenges to construct high-performance LIBs is how to develop cathode materials with high capacity and working voltage. This review provides an overview and future perspectives to develop next-generation LIBs with high electrochemical performance.     

Zr4+离子掺杂对LiFePO4结构及电化学性能的影响

应用固相反应法于惰性气氛下合成掺Zr的L iFePO4正极材料.考察Zr4+掺杂浓度对于目标化合物结构及其电化学性能的影响.XRD,交流阻抗和恒流充放电测试等实验表明,少量的Zr4+掺杂并未影响目标材料产物的结构,反而有利于降低L iFePO4电荷转移反应的阻抗,从而有利于克服该电极过程中的动力学限制.该正极材料表现出优良的倍率放电性能,在0.1C倍率下,L i0.99Zr0.01FePO4的首次放电比容量达135.6mAh.g-1.30次循环后,容量衰减仅3.8%.     

锂离子蓄电池正极材料LiFePO4研究进展

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展,而具有橄榄石结构的LiFePO_4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源,但自身也存在缺点。综述了锂离子电池正极材料LiFePO_4的研究进展。系统地阐述了LiFePO_4的晶体结构特征及性能、多种合成方法以及掺杂多种导电材料和控制晶体生长制备纳米粉体对材料性能的影响。对该材料的应用前景进行了展望,并提出了下一步可能的研究趋势。     

聚合物热解法还原制备LiFePO4锂离子电池正极材料

应用聚丙烯酸盐热解还原法制备L iFePO4/C材料.经XRD和SEM分析,该材料具有橄榄石结构,结晶程度高,粒度分布均匀,粒径约100 nm.恒流充放电实验表明,该材料放电容量为138 mAh/g,循环性能良好.证实聚丙烯酸盐热解还原法是一种制备L iFePO4材料的新型实用方法.     

Pure LiFePO4 with high energy density prepared by water quenching treatment

A compound"vacuum firing and water quenching"technique was presented in the synthesis of LiFePO_4 cathode 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 results indicate that using the"fast quenching"treatment can succeed in controlling overgrowth of the grain size of final product and improving its utilization ratio of active material.The sample synthesized by this technique has the high reversible discharge specific capacity and good cyclic electrochemical performance.