橄榄石型结构LiFePO4锂电池正极材料实用化的障碍和途径

橄榄石型结构LiFePO4因其结构特征和潜在的低成本而有望成为下一代锂离子电池正极材料。但是要使LiFePO4商业化必须开发出适于规模化生产高性能LiFePO4正极材料的工艺。本文在综合分析LiFePO4制备方法、导电性改善及填充密度提高途径的基础上，认为可借鉴Ni-MH电池正极材料球形Ni（OH）2制备技术发展经验，从理论上深入研究LiFePO4的形成过程，通过控制橄榄石型结构LiFePO4材料的结晶度、晶粒大小及形貌、元素分布、界面结构来满足高容量、大比功率及长循环寿命的要求。     

新型锂离子电池正极材料的研究进展

分析了橄榄石型磷酸锂铁(LiFePO4)的晶体结构,评述了近年来各种制备LiFePO4的方法,包括固相反应法、水热合成法、液相共沉淀法以及其他多种方法。介绍了国外对于提高LiFePO4的性能所进行的改性研究,并对其发展方向作出了展望。     

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.     

Effect of Carbon Content on Electrochemical Properties of LiFePO_4/C Composite Cathode

Olivine-type LiFePO_4/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 LiFePO_4 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.     

橄榄石型正极材料LiMPO4研究进展

从合成与性能、结构分析与电化学反应机理、发展趋势等几个方面总结了近年来有关橄榄石型正极材料LiMPO4(M代表Mn、Fe、Co等金属离子)的研究进展。Li(MnyFe1―y)PO4是一单相固溶体,而当y>0.8时MnyFe1-yPO4 不稳定。Lix(Mn0.6Fe0.4)PO4有一个4.1 V的两相平台(0≤x ≤0.6, Mn3 /Mn2 )和3.5 V的单相平台(0.6≤x≤1.0, Fe3 /Fe2 ),而LixFePO4只有一个3.4 V的两相平台。材料的粒径及其分布、导电能力和Fe3 的含量是影响产品性能的关键因素。利用惰性气氛、掺杂导电材料和制备粒度分布均匀的纳米粉体是获得性能优良的LiMPO4的有效方法。     

共沉淀-焙烧法制备LiFePO4

采用共沉淀法合成了无定形磷酸亚铁与磷酸锂的混合前驱体,这种前驱体在700℃下于还原性气氛中保温5.5h制得橄榄石型磷酸铁锂.采用XRD、FTIR、SEM和TG/DSC等手段对前驱体和焙烧产物的成分、结构、形貌及其热分解过程进行了研究.由不同热处理温度及反应时间下的LiFePO4转化率算得磷酸锂与磷酸亚铁在400～700℃下生成磷酸铁锂的反应速率常数和表观反应活化能(26.9kJ/mol).结果表明,Fe3(PO4)2与Li3PO4反应生成LiFePO4的过程主要由Li 、Fe2 在固相介质中的扩散速率所控制.因此,Fe3(PO4)2和Li3PO4的均匀混合有利于降低LiFePO4的焙烧温度和缩短反应时间.     

锂离子蓄电池新型正极材料LiFePO4的研究进展

锂离子蓄电池正极材料的研究正在向低成本、有利于环保、高比能量、高循环特性的方向发展,橄榄石型磷酸铁锂LiFePO4颇受关注。重点介绍了近年来LiFePO4的各种制备方法和充放电机理,以及为提高该材料的电化学性能进行的掺杂改性研究,并对其发展前景做出了展望。LiFePO4理论比能量为170mAh·g-1,电压3.5V(vs.Li/Li ),环境友好,成本低廉,热稳定性较好,适合作为锂离子蓄电池的新型正极材料。