2009年8月吉林师范大学学报(自然科学版)№.3第3期Journal of Jilin N ormal University (Natural Science Edition )Aug.2009收稿日期:2008205228 基金项目:吉林省科技厅项目(20060423)第一作者简介:王　昕(19642),女,吉林省四平市人,现为吉林农业工程职业技术学院副教授.研究方向:无机化学.尖晶石型锰酸锂前驱体的制备与表征王　昕1,张伟娜2(1.吉林农业工程职业技术学院,吉林四平136000;2.吉林师范大学化学学院,吉林四平136000)摘　要:二次锂电池由于比能量高和使用寿命长,已经成为便携式电子产品的主要电源.本实验以LiNO 3和Mn (NO 3)2为原料,应用溶胶-凝胶法制备出了LiMn 2O 4粉体,通过XRD 方法测试了不同温度下灼烧的晶型,随着温度的升高,样品颗粒经历了由疏松到团聚,再到均匀分布的过程,其中700℃时制备的材料具有最佳晶型.还研究了产品的充放电循环性能,经过50次循环后容量降只有4.21%,说明制备的LiMn 2O 4粉体具有优良的充放电循环可逆性能,这对材料更好地发挥其电化学性能起到很好的促进作用.关键词:锂离子电池;尖晶石型LiMn 2O 4;溶胶-凝胶法中图分类号:T M911 文献标识码:A 文章编号:1674238732(2009)0320113202 锂离子电池是继镍镉电池、镍氢电池之后的第三代可充电绿色电池.锂离子电池因其比能量大、电压高、放电性能稳定等优点被广泛应用于手提电话、笔记本电脑、摄录一体机等电子设备.目前,用于锂离子电池的正极材料主要是LiC O 3,LiNiO 2和LiMn 2O 4[126].但锰具有资源丰富、价格低廉、安全、无污染等诸多优点,是极有发展前景的锂离子电池正极材料.而且尖晶石型LiMn 2O 4具有独特的三维隧道结构,有利于Li +的嵌入或脱出,因此受到普遍关注LiMn 2O 4.赵铭姝等[7]采用高温固相分段法在氧气气氛下制备的锰酸锂材料具有较高的初始比容量(>140mAh/g ),但循4次后降为100mAh/g ;李智敏等[8]在空气气氛下,用固相分段焙烧法合成的LiMn 2O 4初始放电量达122mAh/g ,20次循环后容量损失4.4%;唐新村等[9]采用低温固相分段烧结方法制备的锰酸锂循环50次后容量衰减了14.5%.K ang H K 等[10]用共晶自混合方法制备的尖晶石型LiMn 2O 4正极材料20次循环后容量保持率为98.2%得到了比较满意的结果.但固相反应所需温度较高,反应条件苛刻.本文采用温和的溶胶2凝胶法制备LiMn 2O 4前躯体,并对其结构和充放电循环性能进行测试.1　实验部分(1)试剂和仪器:实验所用试剂柠檬酸、硝酸锂、硝酸锰、氨水(0.1m ol/L )均为分析纯;水(H 2O )为超纯二次蒸馏水.T B 23型电子控温磁力搅拌器(上海富华仪器有限公司),DT 2200型电子天平(北京天平仪器厂),D82ADDS 型X 射线衍射仪(美国)等仪器.(2)实验步骤:将0.5m ol/L 的LiNO 3和Mn (NO 3)2溶液按1.1∶1摩尔比混匀,水浴加热反应,用NaH 2C O 3溶液调节混合液的pH 值为一定值,65℃陈化6.0h 后的胶体经过滤、水洗、恒温干燥后得到锰酸锂前驱体粉末,然后研磨预烧后得到尖晶石型锰酸锂前驱体粉末.2　结果与讨论2.1　结构特征分析在空气中,制备的反应前驱体(pH =7.5条件),分别于300、400、500、600、700、800℃恒温氧化灼烧24h 制备产物.从前驱体和不同温度下制备的产物的XRD 图谱可以看出,前驱体己经具备尖晶石LiMn 2O 4晶格,但是峰强度较弱,峰型不完整,见图1.500℃以下灼烧制备的试样衍射峰弱,半峰宽较大,这可能是反・311・应不完善或形成的微量杂相而致[11].500℃以上灼烧制备的试样出现一些杂峰,该峰系Mn2O3引起的.这是因为当pH值较低时,会形成低价的锰氧化物.制备过程中,pH值的局部不均匀,易导致这种低价的锰氧化物出现.同时,温度过高,反应时间过长,尖晶石结构的LiMn2O4会分解成为LiMnO2和Mn2O3.图谱还显示出随着灼烧温度的升高,LiMn2O4的衍射峰形变尖锐,半峰宽下降.这表明随着灼烧温度的升高,内应力消除,晶粒结构亦趋向完善,晶粒变大.因此,选择最佳煅烧温度为700℃.2.2　产物的充放电循环可逆性能分析用在700℃下恒温24h合成的尖晶石型LiMn2O4作为正极材料,与金属锂片对电极组装成实验电池,以0.2mA/cm的电流密度在室温下充放电循环50次考察材料的循环可逆性能,实验结果如图2所示.由图2可以看出,50次循环后产物的放电比容量由初始的135.5mAh/g下降到129.8mAh/g,比容量只下降了4.21%,表明该电极材料具有良好的循环可逆性能.这可能是由于本实验所合成的材料具有完美的尖晶石结构,在充放电过程中晶格结构能保持稳定、不易发生晶格畸变所致.图1　样品不同灼烧温度的XR D图谱 图2　最佳合成条件下样品的充放电循环性能图3　结论(1)本文用溶胶2凝胶法制备出了二次锂电池正极材料前躯体LiMn2O4超细粉末;通过XRD研究了不同温度下灼烧的晶型,分析说明该超细粉末为尖晶石结构,其最佳煅烧温度为700℃.(2)在上述最佳条件下合成的前躯体LiMn2O4超细粉末具有优良的充放电循环可逆性能.其首次循环放电比容量可达到135.5mAh/g50次循环后的比容量还有129.8mAh/g;容量降只有4.21%,且随着后续反应时间的延长,材料的放电比容量下降.参　考　文　献[1]T arascon J M,et al.Synthesis conditions and Oxygen stoichiometry effects on Li insertion intothe spinel LiMn2O4[J].J.E lectrochem.S oc,1994,141(6):1421～1431.[2]Lee Y S,Sun Y K,Nahm K 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photoinduced refractive indexchange in photorefractive lithium niobatecrystal[J].Jpn.J.Appl.Phys.,1998,37:225～227.[7]K MS S,LEE J W,PARKJ K.Enhancement of the recording stability of a photorefractive polymer com posite by the introduction of a trapping layer[J].Appl.Phys.Lett.,2003,83(15):3045～3047.[8]K ip D.Photorefractive waveguides in oxide crystals:fabrication,properties,and applications[J].Appl Phys(B).,1998.67:131～150.E ffect of Slit Width on the Writing W aveguide in LiNbO3∶Fe CrystalCHEN Xiao2xiao(C ollege of Physics,Jilin N ormal University,S iping136000,China)Abstract:Planar optical waveguide were written in Fe2doped lithium niobate crystals(LiNbO3∶Fe)using single slit diffraction method.The effect of single slit width on the writing waveguide in LiNbO3∶Fe crystal was discussed through the control of the width of the single slit.The results indicated that the slit width had certain in fluence on the writing planar optical waveguide in crystal.K ey w ords:Fe2doped lithium niobate crystals;planar optical waveguide;single slit width(上接第114页)The Preparation and Characterization of Spinel Phase LiMn2O4PrecursorWANG Xin1,ZH ANG Wei2na2(1.Jilin V ocational T echnology C ollege in Agriculture Engineering,S iping136000,China;2.C ollege of Chem istry,Jilin N ormal University,S iping136000,China)Abstract:Secondary Lithium battery has been primary power for the convenient electron products owing to its high spe2 cific capacities and long using life.In this paper,LiMn2O4P owers was prepared using s ol2gel methods with LiNO3and Mn(NO3)2as the materials.The XRD analysis were used to observe the crystal m orphology at different tem perature. The results shows that the particle of the sam ple changed from looseness to reuniter,then to the even dispersion as the tem perature increased.The best crystal structure of the prepared materials was in the700℃.And the charge2discharge circular property of the product had been studied,the capacity only reduced4.21%after fifty times circle which showed better charge2discharge circular reversibility of the prepared LiMn2O4.This offers advanced function to the elec2 trochemical property of the materials.K ey w ords:lithium2ion battery;spinel LiMn2O4;s ol2gel method・・117。