LiMn_2O_4的高温比容量衰减研究

采用高温固相法合成了LiMn2 O4电极材料 ,运用电化学和阴极膜X射线衍射等方法研究了LiMn2 O4在高温 (≥ 50℃ )下 ,循环时比容量衰减的现象及其衰减机理。结果表明 ,温度越高 ,LiMn2 O4的自放电越严重 ;贮存时间越长 ,LiMn2 O4的可逆容量损失越大 ,平均放电电压越低 ;高温下LiMn2 O4中Mn的溶解是造成比容量衰减的重要原因。通过掺杂微量元素的方法能有效地改善尖晶石LiMn2 O4的高温循环性能     

导电氧化物AZO对尖晶石型LiMn_2O_4高温性能的改善及研究

采用溶胶凝胶法对尖晶石型LiMn2O4正极材料进行铝掺杂氧化锌(AZO)包覆改性,并通过XRD、SEM、EDS、TEM、EIS、ICP-AES和充放电测试等手段对其结构,形貌及电化学性能进行表征。研究结果表明,AZO包覆层有效的阻止了LiMn2O4颗粒和电解液的直接接触,抑制了高温下锰溶解,明显改善了LiMn2O4的高温循环性能。1.5wt%AZO包覆的LiMn2O4正极材料在高温(55℃)1C时,首次放电比容量为114 mAh·g-1,经过100次循环后,容量保持率仍高达95.4%,远高于未包覆LiMn2O4的70.6%。此外,1.5wt%AZO包覆的LiMn2O4表现出了优越的大倍率放电性能,在10C下放电比容量能达到99 mAh·g-1。     

Fe3O4／TiO2磁性催化剂的制备及在污水治理中的应用

以纳米Fe3O4为载体,以钛酸四丁酯为前躯体,用溶胶-凝胶法在Fe3O4表面包覆TiO2层,制备Fe3O4／TiO2光催化材料．透射电镜（TEM）、X射线衍射（XRD）、X射线光电子能谱（XPS）和红外光谱（IR）分析表明,TiO2在纳米Fe3O4颗粒表面形成很好的包覆层．用Fe3O4／TiO2光催化材料对工业上难处理...     

尖晶石LiMn_2O_4的表面改性研究

采用溶胶_凝胶法合成尖晶石LiMn2 O4 ,并以LiCoO2 对其进行包覆 ,用XRD、SEM、EPMA等方法对修饰的尖晶石结构和性能进行研究 .结果表明 ,经包覆的LiMn2 O4 在 70 0℃焙烧 10h所得的晶粒是表层富含Co的立方尖晶石 ,而且晶粒中Co3+的含量呈现出从表到里递减的梯度分布 .以该材料作锂离子电池正极 ,虽初始容量稍有降低 ,但能有效地降低Mn2 +在电解质中的溶解 ,而且对Jahn_Teller效应有一定的抑制作用 ,包覆的LiMn2 O4 尖晶石正极材料比未包覆的有更好的循环性能     

Al3+对尖晶石型LiMn2O4正极材料的表面掺杂包覆改性

采用表面掺杂包覆改性的方法对LiMn2O4尖晶石型锂离子电池正极材料进行改性.以Al为表面掺杂元素,Al(NO3)3为原料,研究了Al3+掺杂量为7.1%(原子分数)时不同温度(300、400、500、600、700、750、800℃)下的改性效果.研究发现,随着热处理温度的升高,改性样品的最大比容量先升高后降低,在700℃达到最大值;循环衰减先增大后降低再增大;这是由于随着热处理温度的升高,包覆层逐渐分解并与LiMn2O4颗粒反应固溶,在750℃完全固溶,衰减达到极小值,而后固溶层向颗粒内部扩散,导致包覆层对颗粒免受电解液溶解的保护能力变弱,因而容量衰减增大.其中700℃热处理5h的样品最大比容量为133.6mAh·g-1,循环50周衰减3.4%.研究表明Al3+表面掺杂包覆改性有利于促进LiMn2O4尖晶石型锂离子电池正极材料的商业化生产,具有大规模应用的前景.     

LaF_3表面修饰LiMn_2O_4的合成方法及电化学性能的研究(英文)

通过高温固相法制得尖晶石LiMn2O4,然后在通过简单易行的无水乙醇蒸干法包覆LaF3来修饰LiMn2O4。利用XRD,SEM来表征LaF3修饰的LiMn2O4的结构和形貌特征,并通过电化学测试研究LaF3修饰LiMn2O4的高温和常温下的电化学性能,另外结合电化学阻抗谱(EIS)和循环伏安(CV)考察表面修饰的锰酸锂的循环阻抗和循环可逆性。结果显示:经LaF3修饰过的LiMn2O4仍具有尖晶石结构,并且具有良好的电学性能。其中,以3wt%的修饰效果最好,常温循环100次和高温循环50次的循环保持率分别是91%和90%;而且,EIS和CV分别表明经LaF3修饰的LiMn2O4的电荷传递阻抗明显减小,其循环可逆性也明显提高。     

锂离子电池LiMn2O4正极材料的高温改性

锂离子电池LiMn2O4正极材料的高温改性;锂离子电池;正极材料;尖晶石;LiMn2O4;包覆     

锂离子电池正极材料研究的新动向和挑战

调研了全球锂离子电池正极材料LiCoO2、LiNiO2、LiMn2O4、LiFePO4 LiNi0.8 Co0.2 O2和Li(CoMnNi)1/3O2的学术研究论文和技术专利申请与授权数按年和语言分布情况。综述了前4种材料作锂离子电池正极材料尚存在的问题和解决对策进展。例如,通过掺杂其他元素、表面包覆、细化材料颗粒及改善正极结构设计来提高正极材料的充放电容量、寿命、功率密度和电池高功率密度使用时的安全性。     

Li改性MnO_2及LiMn_2O_4催化NH_3-SCR反应性能研究

采用高温固相反应法、Pechini合成方法和柠檬酸配位法,制备了系列锂锰复合氧化物LiMn2O4催化剂,应用于NH3-SCR反应,并与固相反应法合成的MnO2进行了比较。采用N2吸附-脱附、扫描电镜、X射线衍射、H2程序升温还原、NH3程序升温脱附、NO程序升温脱附和X射线光电子能谱对LiMn2O4催化剂进行表征。结果表明,引入Li有利于提高锰基催化剂的SCR活性和抗硫性。Pechini法制备LiMn2O4的NO转化率可在130~260℃达到90%以上;固相反应法制备LiMn2O4的NO转化率大于90%的温度为90~310℃;MnO2的温度窗口则仅为140~280℃。与MnO2相比,引入Li可形成LiMn2O4结构,因此,催化剂中更多的锰离子保持在相对较低的价态Mn3+,并调整表面活性氧含量;同时,Li的存在调变了LiMn2O4表面的酸位,从而减少高温下MnO2表面容易发生的NH3非选择性氧化,改善其催化NH3-SCR反应的温度窗口,也增强了抗硫性。     

碳包覆球形LiMn2O4的固相合成及电化学性能

以MnSO4为原料,采用溶液结晶法先制备球形MnO2。以所制得的MnO2和LiOH·H2O为原料,采用高温固相法制备了球形LiMn2O4粉体材料。将间苯二酚和甲醛按1:2的摩尔比均匀混合继续搅拌1h,在85℃下干燥后,球磨2h,得到橘红色碳凝胶粉末。以80:20的质量比将所制得的球形LiMn2O4和碳凝胶混合后,在550℃下烧结6h,得到碳包覆的球形LiMn2O4颗粒。从XRD结果可以看出,包覆碳前后的LiMn2O4结晶程度较好,没有杂质峰出现。在2?=18.76,36.28,44.17,58.36,64.14°分别出现对应于(111),(311),(400),(511),(440)晶面的衍射峰,可归属为单一的尖晶石结构。由于裂解碳属于无定型态并且含量较少,因此在XRD图谱中观察不出其衍射峰。但从图中可以看出,碳的存在并不影响尖晶石LiMn2O4的晶体结构。从SEM图像中可以看,球形颗粒的表面有一层致密的碳包覆层。EDX检测得出,锰、氧和碳含量分别为66.68%、26.9%、6.42%。组装的电池采用锂片作为负极,电解液为1mol·L-1 LiFP6/EC DEC(1:1体积比)。恒流充放电测试在3.2～4.4V范围内进行:以0.5C的电流密度,碳包覆球形LiMn2O4电极在25℃和55℃温度下首次放电容量分别为122 mAh·g-1和115 mAh·g-1,而未包覆的电极其对应的首次放电容量分别为119 mAh·g-1和112 mAh·g-1。同时测评两种电池的循环性能,25℃下碳包覆和未包覆电极循环100次后容量分别为111 mAh·g-1,102 mAh·g-1,容量保持率为91%和86%;55℃下,循环50次后容量衰减率分别为0.3%和0.5%。由此可见,碳包覆LiMn2O4材料的放电及循环性能都优于未包覆材料,可归结于以下原因:裂解的无定形碳提高了电极材料的电子电导率,增强了离子在电极表面的传递速度,两种协同作用使得含有少量碳的电极材料可以充放电完全,库仑效率较高,循环过程中减小电极表面的极化;在高温环境下,LiMn2O4电极容量衰减主要是由于电解液中含氟电解质电离出F-所形成的HF对电极具有强的腐蚀性。采用包覆的方法,在球形颗粒表面形成的碳层可以减少活性物质在电解液中的裸露面积从而减少其对电极的侵蚀,提高电池的循环寿命;另外,碳保护层可以使活性物质颗粒保持良好的接触,循环多次后仍能保持较高容量。利用交流阻抗技术及renew软件对所得阻抗谱进行拟合,可以得出包覆与未包覆的两种电极的电荷转移电阻为16.28O和45.02O。由此表明,碳包覆层增强了Li 在电极表面的脱嵌能力,抑制了Jahn-Teller效应以及电化学极化。     

Synthesis and characterization of phosphate-modified LiMn2O4 cathode materials for Li-ion battery

<正>LiMn_2O_4 spinel cathode materials were modified with 2 wt.%Li-M-PO_4(M=Co,Ni,Mn) by polyol synthesis method.The phosphate surface-modified LiMn_2O_4 cathode materials were physically characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDS).The charge-discharge test showed that the cycling and rate capacities of LiMn_2O_4 cathode materials were significantly enhanced by stabilizing the electrode surface with phosphate.     

Synthesis and electrochemical properties of chemically substituted LiMn2O4 prepared by a solution-based gel method

Lithium manganese oxide, LiMn(2)O(4), and its substituted samples LiM(0.05)Mn(1.95)O(4) (M=Al, Co, and Zn) were first prepared by a cost-saving and effective new solution-based gel method using a mixture of acetate and ethanol as the chelating agent. The physical properties of the synthesized samples were investigated by thermogravimetry/differential thermal analysis, X-ray diffraction, and scanning electronic microscopy. The as-prepared powders were used as positive materials for a lithium-ion battery, whose charge/discharge properties and cycle performance were examined. The results revealed that all the substituted samples had better cycle performance than pure LiMn(2)O(4). Among these synthesized materials, the LiCo(0.05)Mn(1.95)O(4) sample had the best cycle performance. After 30 cycles, its capacity loss was only 3%. Therefore, cyclic voltammetry and electrochemical impedance spectroscopy were employed to characterize the reactions of Li ion insertion into and extraction from LiCo(0.05)Mn(1.95)O(4) electrodes.     

A Raman Study of Spinel LiMn2O4

A Raman study was carried out for LiMnzO4, which was synthesized via the mixture of Mn3O4 and LiNO3 sintered at different temperatures. It is shown that there are two kinds of Raman spectra for LiMn2O4 at different sintering temperatures, while the X-ray diffraction patterns of LiMnzO4 sintered at different temperatures are the same. Five Raman bands observed for the materials sintered below 500 ℃ are consistent with the theoretical prediction for spinel structure based on the group theory. Only two Raman bands were observed for the materials sintered at temperatures higher than 500 ℃. The best preparation condition for obtaining a good spinel LiMn2O4 is suggested based on the Raman study.     

Enhancement of the electrochemical properties of LiMn2O4 through Al3+ and F- co-substitution

The cathode-active materials LiMn2O4, LiAl0.1Mn1.9O4, and LiAl0.1Mn1.9O3.9F0.1 were synthesized by a microwave-assisted sol-gel method. The influence of different doping elements on the structural and electrochemical properties of the as-prepared samples was investigated by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical experiments. The results indicated that fluorine plays an important role in controlling the morphology, and the doped aluminum could enhance significantly the stability of spinel-type LiMn2O4. The initial discharge capacity of the Al3+ and F- co-substituted specimen reached 129.8 mA h/g and has a high capacity retention after 40 cycles. The outstanding electrochemical properties of LiAl0.1Mn1.9O3.9F0.1 make it a possible promising cathode material for lithium-ion batteries.     

单斜层状LiMn0.97Al0.03O2-x(PO4)x材料的合成及其电化学性能

以Na₂CO₃, (CH₃CO₂)₂Mn·4H₂O, Al₂O₃, Na₃PO₄·12H₂O和CH₃COOLi·2H₂O为原料, 通过2次高温固相法和一步水热离子交换法得到一系列铝和磷掺杂的LiMn_0.97Al_0.03O₂, LiMnO_1.99(PO₄)_0.01和LiMn_0.97Al_0.03O_2-x(PO₄)_x(x=0.01, 0.03, 0.05)化合物. 用X射线衍射(XRD)表征了前驱体及交换产物的晶体结构, 用扫描电镜(SEM) 测定了晶体的形貌. 通过X射线光电子能谱(XPS)、傅里叶红外光谱及恒电流充放电测试, 研究了掺杂离子对合成材料结构及电化学性能的影响. 研究结果表明, Al-PO₄复合掺杂综合了Al³⁺掺杂提高材料的电化学反应活性和减低材料的电化学反应阻抗以及PO₄^3-掺杂增大材料的晶胞体积的特点, 提高材料中Li⁺的扩散能力, 有效地抑制了材料由于Jahn-Teller效应引起的结构畸变, 改性后的LiMnO₂正极材料既保持了较高的容量又获得了良好的电化学循环性能.     

锂离子电池正极材料LiMn2O4的合成与晶体结构（英）

Spinel LiMn₂O₄ powders were prepared using two-step synthesis method consisting of solid-state reaction method and citrate modified sol-gel method. The effects of the calcination temperature and the Li/Mn ratio of raw materials were studied on the physicochemical and electrochemical properties of the spinel LiMn₂O₄ powders, such as crystallinity, lattice constant and density. The title compound was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polycrystalline LiMn₂O₄ powers calcined at 750 ℃ were found to be composed of very uniformly-sized microcrystal with an average particle size of 300 nm. The improvement in electrochemical properties was mainly attributed to the process of re-grinding by absolute alcohol.     

锂离子电池正极材料LiMn_(2-2x)Sm_xSr_xO_4的合成及电化学性能

采用高温固相反应合成了一系列的LiMn2-2xSmxSrxO4正极材料(0≤x≤0.1);采用X射线衍射仪分析了合成产物的晶体结构;利用充放电试验测定了产物的电化学性能,利用电化学阻抗谱分析了产物的电化学循环机理.结果表明,所合成的LiMn2-2xSmxSrxO4(x=0,0.01,0.02,0.03,0.04,0.05)样品均保持尖晶石相,属于Fd3m空间群.LiMn1.9Sm0.05Sr0.05O4的电化学性能最佳,首次放电容量为96.8 mAh/g,在3.0~4.4 V区间内50次循环后容量保持率超过96%.与此同时,LiMn2O4和LiMn1.90Sm0.05Sr0.05O4的电极阻抗变化不同,进而影响其电化学性能.     

非均匀成核法表面包覆氧化铝的尖晶石LiMn2O4研究

采用高温固相法合成尖晶石LiMn2O4,以非均匀成核方式对其进行包覆氧化铝的表面处理.通过XRD、SEM、粒度分析等技术对表面处理前后的LiMn2O4进行表征,分析了表面处理前后LiMn2O4物理特性的变化,并结合电化学性能测试,研究了表面处理工艺对LiMn2O4电化学容量与循环性能的影响.未经表面处理的LiMn2O4在1 C倍率下初期放电容量为86.5 mA•h•g－1,50次循环充放电后容量衰减26.3％.表面包覆0.5％、1％(w)氧化铝的LiMn2O4在1 C倍率下的初期放电容量分别为96.0、80.1 mA•h•g－1,经过50次循环后,容量分别降低7.0％、5.6％.实验结果表明,表面处理后的LiMn2O4循环性能显著提高,而且随着氧化物含量的增加,循环性能增强,但放电容量降低.