Synthesis of Na_2MnPO_4 F/C with Different Carbon Sources and Their Performances as Cathode for Lithium Ion Battery

采用湿法球磨和原位热解碳包覆相结合的方法,分别以硬脂酸、柠檬酸、聚乙二醇-6000(PEg-6000)、β-环糊精为碳源,制备了不同结构的nA_2MnPO_4f/C复合材料,并研究了它们作为锂离子电池正极材料的电化学行为.通过X射线衍射(Xrd)、扫描电镜(SEM)、bET比表面积测试、恒流充放电等表征手段,比较和分析了产物的结构、形貌及电化学性能.研究结果表明,由不同碳源制备的材料在形貌和颗粒尺寸上有明显差异,进而对它们的电化学性能造成很大影响.影响电化学性能的关键因素在于材料一次颗粒的大小.其中,以柠檬酸为碳源制备的样品呈现出典型的微纳结构和最小的一次颗粒(10-40 nM).并给出最佳的电化学性能:在1.5-4.8 V电压范围内,以5MA·g~(-1)充放电电流获得的首次放电比容量约为80MAH·g~(-1),且循环稳定性良好.Na_2MnPO_4 F/C composites were synthesized by wet ball milling and in situ pyrolytic carbon coating.Stearic acid,citric acid,poly(ethylene glycol) 6000,and β-cyclodextrin were used as carbon sources in the synthesis process.The structures,morphologies,and electrochemical performances of the as-synthesized Na_2MnPO_4 F/C composites were further investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),Brunauer-Emmett-Teller surface area analysis,and galvanostatic chargedischarge tests.Distinct differences were observed in the morphologies and sizes of the Na_2MnPO_4 F/C particles obtained from different carbon sources,and this significantly affected their electrochemical performances.It was found that the primary particle size of the Na_2MnPO_4 F/C material is a key factor in the electrochemical performance.The sample synthesized using citric acid as the carbon source had a micro-nano structure,with the smallest primary particle size of 10-40 nm,and displayed the best electrochemical properties.It delivered an initial discharge capacity of 80 mAh·g~(-1) under a current density of 5mA·~(-1) in the voltage range of 1.5-4.8V,and displayed good cycling performance.国家自然科学基金(50574063;21021002;21003102); 四川大学青年科学家基金(2011SCU11081); 高等教育博士点科研基金(20120181120103)资助~

Synthesis of Nanostructured LiNi_(1/3)Co_(1/3)Mn-(1/3)O-2 by AmmoniaEvaporation-Induced Synthesis and Its Electrochemical Properties as a Cathode Material for a High-Power Li-Ion Battery

采用氨蒸发诱导法成功制备出纳米结构lInI1/3CO1/3Mn1/3O2正极材料,借助X射线衍射(Xrd)分析、扫描电镜(SEM)、透射电镜(TEM)、高分辨率透射电镜(HrTEM)、能量分散谱(EdS)和比表面测试等表征手段及恒电流充放电测试研究了其晶体结构、微观形貌和电化学性能.研究表明该方法制备出的材料具有良好的α-nAfEO2层状结构,阳离子混排程度低.纳米片交错堆积而成核桃仁状形貌,片与片之间形成许多纳米孔,而且纳米片的侧面属于{010}活性面,能够提供较多的锂离子的脱嵌通道.在室温下及3.0-4.6 V充放电范围内,该材料在电流密度为0.5C、1C、3C、5C和10C时放电比容量分别为172.90、153.95、147.09、142.16和131.23MAH？g-1.说明其具有优异的电化学性能,非常有潜力用于动力汽车等高功率密度锂离子电池中.We report on an ammonia-evaporation-induced synthetic method for nanostructured LiNi1/3Co1/3Mn1/3O2 cathode material.Powder X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), high- resolution transmission electron microscopy(HRTEM), energy- dispersive X- ray spectroscopy(EDS), Brunauer-Emmett-Teller nitrogen sorption, and galvanostatic charge-discharge tests were applied to analyze the crystal structure, micromorphology, and electrochemical properties of nanostructured LiNi1/3Co1/3Mn1/3O2.The results show that it has a well-ordered layered α-NaFeO2 with little cation mixing.A walnutkernel- like morphology is formed by nanosheets, leading to a nanoporous material.The lateral plane of nanosheets are {010}-faceted, which could provide multiple channels for Li+-ion migration.The electrochemical properties of the lithium cells used this material as cathode are excellent: the specific discharge capacity at 0.5C,1C, 3C, 5C and 10 C is, respectively, up to 172.90, 153.95, 147.09, 142.16, and 131.23 mAh?g-1between 3.0and 4.6 V at room temperature.These excellent features will make the nanostructured LiNi1/3Co1/3Mn1/3O2 become a positive electrode material of potential interest for useful applications, such as in electric vehicles and hybrid electric vehicles.四川大学青年基金(2011SCU11081); 教育部高校博士学科点科研基金(20120181120103)资助项目~

Preparation and Electrochemical Lithium Intercalation Performance of Segmented Carbon Nanofibers

以泡沫镍为催化剂 ,在 6 0 0和 70 0℃下 ,以CVD法热解乙炔气体制备大量的纳米碳纤维 .随着制备温度增加 ,纳米碳纤维直径变小 ,竹节状含量减少 ,d0 0 2 值减小 ,微晶片层平面Lc 和La 值增大 ,碳材料的可逆容量则下降 .分别用透射电镜、X射线衍射和拉曼光谱观察和测定了纳米碳纤维的形貌、微结构 ,发现在不同条件下生长的纳米碳纤维有不同的形貌和结构 .对纳米碳纤维的电化学嵌锂性能的研究表明 ,纳米碳纤维的结构对其电化学嵌锂容量和充放电循环寿命起重要影响 ,制备温度越低 ,纳米碳纤维的石墨化程度越差 ,可逆嵌锂容量相应要高一些Segmented carbon nanofibers were prepared by pyrolysis of acetylene on foam Ni at 600 and 700℃ in a fixed bed flowed-reactor. The morphology, microstructure and lithium insertion properties of these carbon nanofibers were investigated by TEM, XRD, Raman and electrochemical methods. Through TEM observations, it was found that this kind of carbon nanofibers was composed of lens-like segments with nearly equal separation stacking along the nanofiber axis. When the reaction temperature was 600℃, segmented carbon nanofibers were the major production. However, when the reaction temperature increased to 700 ℃, the content of segmented carbon filaments decreased and their diameter became smaller. The crystallite size d 002 and L c were determined by the 002 carbon Bragg peak of XRD patterns using the Bragg and Scherrer formulas. The intensity ratios of the 1350 cm -1 line and the 1580 cm -1 line (R=I D/I G) was used to evaluate the L a value, which was inversely proportional to the effective crystallite size in the direction of the graphite plane (L a). With the reaction temperature increased, the d 002 value decreased, L a and L c values increased, which indicated the degree of crystallinity increased. Segmented carbon nanofibers were used as positive electrodes of C/Li cells. The first charge capacities of C/Li cells were 480 and 300 mAh/g for samples produced at 600 and 700℃, respectively. The samples at 600℃ showed capacities higher than the theoretical value of graphite, which was attributed to accommodation of more lithium at the edge of graphene layers and on the surface of graphene layers according to the mechanisms of lithium insertion in carbons prepared by low-temperature pyrolysis of hydrocarbons. As confirmed by the XRD and Raman spectra, the samples at 700℃ had larger L a and L c, which led to the capacity decreasing.国家自然科学基金 (6 0 2 710 0 9);; 浙江省自然科学基金 (5 0 110 9,2 0 0 0 5 3)资助项

Preparation and electrochemical lithium intercalation performance of segmented carbon nanofibers

Segmented carbon nanofibers were prepared by pyrolysis of acetylene on foam Ni at 600 and 700degreesC in a fixed bed flowed-reactor. The morphology, microstructure and lithium insertion properties of these carbon nanofibers were investigated by TEM, XRD, Raman and electrochemical methods. Through TEM observations, it was found that this kind of carbon nanofibers was composed of lens-like segments with nearly equal separation stacking along the nanofiber axis. When the reaction temperature was 600degreesC, segmented carbon nanofibers were the major production. However, when the reaction temperature increased to 700degreesC, the content of segmented carbon filaments decreased and their diameter became smaller. The crystallite size d(002) and L-c were determined by the 002 carbon Bragg peak of XRD patterns using the Bragg and Scherrer formulas. The intensity ratios of the 1350 cm(-1) line and the 1580 cm(-1) line (R =I-D/I-G) was used to evaluate the L-a value, which was inversely proportional to the effective crystallite size in the direction of the graphite plane (L-a). With the reaction temperature increased, the d(002) value decreased, L-a and L-c values increased, which indicated the degree of crystallinity increased. Segmented carbon nanofibers were used as positive electrodes of C/Li cells. The first charge capacities of C/Li cells were 480 and 300 mAh/g for samples produced at 600 and 700degreesC, respectively. The samples at 600degreesC showed capacities higher than the theoretical value of graphite, which was attributed to accommodation of more. lithium at the edge of graphene layers and on the surface of graphene layers according to the mechanisms of lithium insertion in carbons prepared by low-temperature pyrolysis of hydrocarbons. As confirmed by the XRD and Raman spectra, the samples at 700degreesC had larger L-a and L-c, which led to the capacity decreasing

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