Synthesis and Characterization of LiCoxMn2-xO4 Cathode Materials

LiCoxMn2.04 cathode materials for lithium ion batteries were synthesized by mechanical activation-solid state reaction at 750 ℃ for 24 h in air atmosphere, and their crystal structure, morphology, element composition and electrochemical performance were characterized with XRD, SEM, ICP-AES and charge-discharge test. The experimental results show that all samples have a single spinel structure, well formed crystal shape and uniformly particle size distribution. The lattice parameters of LiCo Mn2-xO4 decrease and the average oxidation states of manganese ions increase with an increase in Co content. Compared with pure LiMn2O4, the LiCo Mn2xO4 （x=0.03-0.12） samples show a lower special capacity, but their cycling life are improved. The capacity loss of LiCo009Mn191O4 and LiCo0.1Mn1.88O4 is only 1.85% and 0.95%, respectively, after the 20th cycle. The improvement of the cycle performance is attributed to the substitution of Co at the Mn sites in the spinel structure, which suppresses the Jahn-Teller distortion and improves the structural stability.     

尖晶石型正极材料LiCrxMn2-xO4的电化学特性

采用高温熔融固相浸渍法合成了掺杂铬元素的尖晶石型锰酸锂LiCrxMn2-xO4.XRD测试结果显示所合成的产品均为尖晶石结构.以该活性物质作为锂离子电池的正极材料,通过充放电测试、微分容量以及循环伏安方法的研究表明,掺铬尖晶石型LiCrxMn2-xO4材料在充放电电压区间内所发生的电化学反应经历两个阶段,同时表明铬的掺入能够有效抑制尖晶石型锰酸锂材料的可逆容量的衰减,提高了材料的稳定性.     

尖晶石型正极材料LiCrxMn2-xO4的电化学特性

采用高温熔融固相浸渍法合成了掺杂铬元素的尖晶石型锰酸锂LiCrxMn2-xO4。XRD测试结果显示所合成的产品均为尖晶石结构。以该活性物质作为锂离子电池的正极材料，通过充放电测试、微分容量以及循环伏安方法的研究表明，掺铬尖晶石型LiCrxMn2-xO4。XRD材料在充放电电压区间内所发生的电化学反应经历两个阶段，同时表明铬的掺入能够有效抑制尖晶石型锰酸锂材料的可逆容量的衰减，提高了材料的稳定性。     

锂离子电池正极材料LiMgxMn2-xO4的合成及性能

利用相转移法合成了LiMgxMn2-xO4前驱体,在电炉中于一定温度下烧结一定时间,得到锂离子电池正极材料粉体,并利用XRD、SEM、IR等对材料粉体进行结构形态表征.考察焙烧温度、焙烧时间、Mg的掺杂含量等对产物结构和电化学性能的影响.实验结果表明:当Mg的掺杂量x=0.06,于750℃焙烧15 h时所制备的样品材料结构稳定且呈尖晶石型,样品电极的充放电性能良好,首次放电比容量达125 mAh/g,放电平稳,样品电极可逆循环性能良好.     

锂离子电池正极材料LiMn2O4掺杂及对其性能的影响

综述了近年来掺杂锂离子正极材料尖晶石LiMn2O4的元素及方法，阐述了在锂离子正极材料LiMn2O4中掺杂钴、铬、镍、铝、稀土、钒后对材料性能的影响．结果表明，掺杂均不同程度地改善材料的循环稳定性，但对容量大都产生不利影响．     

Mn含量对正极材料LiMn_xCo_(0.2)Ni_(0.8-x)O_2的结构与电化学性能的影响

通过共沉淀法合成了具有层状结构的锂离子电池正极材料LiMnxCo0.2-Ni0.8-xO2。采用XRD、XPS和恒流充放电等测试手段研究了Mn含量变化对正极材料LiMnxCo0.2Ni0.8-xO2的物理性质与电化学性能的影响。结果表明:Mn含量的增加会引起元素O和Ni的氧化态降低,使得Ni由+3价逐渐转变为+2价,而Mn的氧化态却始终保持+4价不变;尽管Mn含量的增加会使材料的充放电比容量有所降低,但是材料的结构稳定性和热稳定性会得到改善。XRD测试结果表明样品LiMnxCo0.2Ni0.8-xO2(0≤x≤0.5)都具有标准的-αNaFeO2层状结构。此外,从Mn含量的变化引起的样品晶胞参数的变化表明,当0≤x≤0.25时LiMnxCo0.2Ni0.8-xO2可能形成的是假固溶体,当Mn含量由0.3增加到0.5时形成的是真固溶体。     

掺杂元素Co、Cr、La对尖晶石型锰酸锂电化学性能的影响

采用高温固相法合成了掺杂Co、Cr、La元素的尖晶石型锰酸锂Li1.02Co0.02M1xM2yMn1.98-x-yO4电池材料;X射线衍射(XRD)表征所合成的产物呈现出良好的尖晶石型结构材料;扫描电子显微镜(SEM)显示合成材料均具有良好的粒径分布(2~3μm)及外貌。以该活性物质作为锂离子电池正极材料,经充放电测试研究表明:掺杂的尖晶石型锰酸锂正极材料Li1.02Co0.02M1xM2yMn1.98-x-yO4能够更好地抑制尖晶石型锰酸锂材料的可逆容量在充放电过程中的衰减,循环性能有了很大改善,表现出更好的电化学可逆特性,100次循环后放电容量仍能保持初始容量的95%以上。作为锂离子电池正极材料LiCoO2的替代材料,该研究为锰酸锂尖晶石型正极材料的改性提供了一种新方法。     

掺杂元素Co、Cr、La对尖晶石型锰酸锂电化学性能的影响

采用高温固相法合成了掺杂Co、Cr、La元素的尖晶石型锰酸锂Li1.02Co0.02M1xM2yMn1.98-x-yO4电池材料;X射线衍射（XRD）表征所合成的产物呈现出良好的尖晶石型结构材料;扫描电子显微镜（SEM）显示合成材料均具有良好的粒径分布（2～3μm）及外貌.以该活性物质作为锂离子电池正极材料,经充放电测试研究表明：掺杂的尖晶石型锰酸锂正极材料Li1.02Co0.02M1xM2yMn1.98-x-yO4能够更好地抑制尖晶石型锰酸锂材料的可逆容量在充放电过程中的衰减,循环性能有了很大改善,表现出更好的电化学可逆特性,100次循环后放电容量仍能保持初始容量的95%以上.作为锂离子电池正极材料LiCoO2的替代材料,该研究为锰酸锂尖晶石型正极材料的改性提供了一种新方法.     

Na3-xLixV2(PO4)3正极材料的制备与电化学性能研究

通过溶胶-凝胶法合成了锂离子掺杂的磷酸钒钠(Na_(3-x)Li_xV_2(PO_4)_3)正极材料,探究了不同锂离子掺杂量对材料组成、结构及电化学性能的影响和离子传输机理。研究结果表明,锂离子的引入并不改变Na_3V_2(PO_4)_3的主晶相,但是会造成晶胞体积的减小。锂离子通过激活Na_3V_2(PO_4)_3中的Na(1)位点来提高电化学性能。具有蜂窝状结构的Na_(2.96)Li_(0.04)V_2(PO_4)_3具有较好的电化学性能,在30 C下首次放电比容量达到104.9 mAh·g~(-1),经过350次循环后其放电比容量为77.52 mAh·g~(-1);库伦效率接近100%;其钠离子的扩散系数为2.02×10~(-13) cm~2·s~(-1)。     

Effect of sintering time on the electrochemical properties of spinel LiMn_2O_4 synthesized by solid-state reaction

LiMn_2O_4 powder as a cathode materials for rechargeable lithium-ion batteries was prepared by solid-state reaction from Li_2CO_3 and electrolytic MnO_2 at different sintering periods(2,6,18,and 32 h).X-ray diffraction(XRD)patterns of the prepared samples are identified as the spinel structure with a space group of Fd(?)m.The lattice parameters almost remain the same as the sin- tering periods increase.The sample with a sintering period of 32 h shows good cycling performance at both low and high current densities,and also elevated temperature.It is believed that the excellent electrochemical behavior of this sample results from its good crystallinity and large grain size compared with other samples.Different electrochemical measurements were conducted to investi- gate the electrochemical properties of spinel LiMn_2O_4.     

Structure and electrochemical properties of LiLaxMn2-xO4 cathode material by the ultrasonic-assisted sol-gel method

Powders of spinel LiLaxMn2_xO4 were successfully synthesized by the ultrasonic-assisted sol-gel (UASG) method.The structure and properties of LiLaxMn2_xO4 were examined by X-ray diffraction (XRD),Fourier transform infrared (FT-IR) spectros-copy,scanning electronic microscopy (SEM),galvanostatic charge-discharge test,and cyclic voltammetry (CV).XRD results showthat the La3+ can partially replace Mn3+ in the spinel and the doped materials with La3+ have a larger lattice constant compared with pristine LiMn2O4.FT-IR indicates that the absorption peak of Mn3+-O and Mn4+-O bonds has a red and blue shift with the increase of doping lanthanum in LiLaxMn2_xO4,respectively.The charge-discharge test exhibits that the initial discharge capacity of LiLaxMn2_xO4 drops off,and the capacity retention increases gradually at C/5 discharge rate with the increase of doping lanthanum,and LiLa0.01Mn1.99O4 has a higher discharge capacity and a better cycling performance at 1C discharge rate.CV reveals that the dop-ing La3+ is beneficial to the reversible extraction and intercalation of Li+ ions.     

Structure and electrochemical properties of La, F dual-doped LiLa0.01Mn1.99O3.99F0.01 cathode materials

The cathode materials LiMn2O4 and rare earth elements La-doped or La and F dual-doped spinel lithium manganese oxides were synthesized by the citric acid-assisted sol-gel method. The synthesized samples were investigated by differential thermal analysis (DTA) and thermogravimetry (TG) measurements, X-ray diffraction (XRD), scanning electronic microscope (SEM), cyclic voltammetry (CV), and charge-discharge test. XRD data shows that all the samples exhibit the same pure spinel phase, and the LiLa0.01Mn1.99O3.99F0.01 and LiLa0.01Mn1.99O4 samples have smaller lattice parameters and unit cell volume than LiMn2O4. SEM indicates that LiLa0.01Mn1.99O3.99F0.01 has a slightly smaller particle size and a more regular morphology structure with narrow size distribution. The charge-discharge test reveals that the initial capacities of LiMn2O4, LiLa0.01Mn1.99O4, and LiLa0.01Mn1.99O3.99F0.01 are 129.9, 122.8, and 126.4 mAh·g-1, and the capacity losses of the initial values after 50 cycles are 14.5%, 7.6%, and 8.0%, respectively. The CVs show that the La and F dual-doped spinel displays a better reversibility than LiMn2O4.     

Effect of sintering time on the electrochemical properties of spinel LiMn2O4 synthesized by solid-state reaction

LiMn2O4 powder as a cathode materials for rechargeable lithium-ion batteries was prepared by solid-state reaction from LitCO3 and electrolytic MnOz at different sintering periods （2, 6, 18, and 32 h）. X-ray diffraction （XRD） patterns of the prepared samples are identified as the spinel structure with a space group of Fd3 m. The lattice parameters almost remain the same as the sintering periods increase. The sample with a sintering period of 32 h shows good cycling performance at both low and nigh current densities, and also elevated temperature. It is believed that the excellent electrochemical behavior of this sample results from its good crystallinity and large grain size compared with other samples. Different electrochemical measurements were conducted to investigate the electrochemical properties of spinel LiMn204. 2008 University of Science and Technology Beijing. All rights reserved.     

Structure characteristics and electrochemical properties of LiMn2O4 modified by LiCoO2

In order to improve the cycle performance of LiMn2O4, the modified LiMn2O4 was prepared by solid-state reactions using LiMn2O4 and LiCoO2 as precursors. XRD and EDS were used to study the structure properties of the modified LiMn2O4. The electrochemical properties of the modified LiMn2O4 were also investigated, The results show that Li and Co atoms could insert into the LiMn2O4 crystal lattice and a newly formed spinel phase, modified LiMn2O4 was obtained. The modified LiMn2O4 exhibits excellent cycle ability at room and elevated temperatures compared to pure LiMn2O4. The improved electrochemical stability of the modified LiMn2O4 attributes to the entrance of Li and Co ions inserted into the spinel crystal structure.     

MgO和ZrO2包覆对正极材料结构和电性能的影响

通过共沉淀法制备了前驱体Ni1/3Co1/3-xMn1/3（OH）2,然后与LiOH·H2O、不同金属氧化物（MgO、ZrO2）分别混合制备锂离子电池正极材料LiNi1/3Co1/3-xMn1/3MxO2（M=Mg,Zr）.通过X射线衍射（XRD）、扫描电镜（SEM）、高精度电池测试系统、交流阻抗对材料结构和电化学性能进行了表征。实验结果表明,包覆MgO后,材料的结构发生变化,而包覆ZrO2没有改变正极材料的结构。与无包覆的正极材料相比较,包覆ZrO2材料的首次放电量为119.07 mAhg-1,20次循环后容量保持率为92.64%,放电量仍达到110.31 mAhg-1。     

Effects of Al, F dual substitutions on the structure and electrochemical properties of lithium manganese oxide

Spinel LiMn2O4 and F, Al-doped spinel LiAl0.05Mn1.95O3.98F0.02 have been synthesized by a soft chemistry method using adipic acid as the chelating agent. The synthesized spinel materials were characterized by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and charge-discharge testing. The results indicate that all the samples have high phase purity, and fluorine is important in controlling the morphology; the doped aluminum enhances the stability of spinel LiMn2O4. The charge-discharge tests indicate that LiAl0.05Mn1.95O4 has high capacity retention, which is 92.60% of the initial after 50 cycles. It is found that the novel compound LiAl0.05Mn1.95O3.98F0.02 with smaller particles can offer much higher capacity, whose initial discharge capacity is 126.5 mAh?g-1. The cyclic voltammetric experiments disclose the enhanced reversibility of the F, Al3 -modified spinel as compared with the undoped spinel.     

空气中合成锂离子电池正极材料LiNi1-xTixO2

以N i(OH)2、TiO2和LiOH.H2O为原料,采用固相反应法在空气中合成了LiN i1-xTixO2(x=0.025、0.050、0.100),用XRD研究了合成材料的物相和结构,用SEM研究了合成材料的形貌,用电池性能测试仪研究了合成材料的电化学性能.结果表明,原料中的n(Ti)/n(N i Ti)值对合成材料的结构和电化学性能影响很大.少量的钛可以进入LiN iO2的晶格形成LiN i1-xTixO2固溶体,而钛含量过大则会出现杂相.n(Ti)/n(N i Ti)值为0.050的样品结构有序度最高,充放电容量最大.