【作者】 周文佳；

【导师】 力虎林；

【作者基本信息】 兰州大学 ， 分析化学， 2008， 博士

【摘要】 锂离子电池和超级电容器是目前两种重要的电化学能量储存装置。锂离子电池因工作电压高、能量密度大、循环寿命长、自放电率低、“绿色”环保等众多优点而倍受人们关注,目前已广泛地应用于小型用电器中,并正积极地向国防工业、空间技术、电动汽车、静置式备用电源（UPS）等领域发展。电化学电容器是一种新型的储能装置,结合了物理电容器高功率及传统电池高能量密度的优点,其应用领域广泛,已成为新型化学电源研究中的热点之一。本论文综述了当前该两类器件电极材料的最新研究进展,并就相关电极材料的制备,改性以及在这两类能量储存装置中的应用进行了深入的研究,主要内容如下:1.对LiMn₂O₄正极材料进行了不同阳离子掺杂的改性研究。采用溶胶-凝胶法制备了多种阳离子掺杂型LiM_0.05Mn_1.95O₄（M=Al,Cr,Fe）正极材料并对其电化学性能进行了深入研究。实验结果表明,金属阳离子的掺杂有效地抑制了LiMn₂O₄材料的Jahn-Teller畸变效应,增强了尖晶石结构中宿主内部原子间结合力,提高了材料结构的稳定性,进而显著改善了LiMn₂O₄尖晶石的循环稳定性。对比测试结果发现,不同的掺杂金属离子对LiMn₂O₄正极材料电池性能的改善效果也不相同,其中Cr掺杂型LiCr_0.05Mn_1.95O₄正极材料具有最好的循环稳定性,循环30周后,其容量衰减仅为5%,相对于纯的LiMn₂O₄循环性能有了明显提高。针对掺Cr型LiCr_xMn_2-xO₄正极材料,考察了不同Cr掺杂量对样品晶体结构和电化学性能的影响。随着Cr掺杂量增加,晶胞参数变小,晶胞体积缩小,有利于稳定尖晶石结构,提高循环稳定性,但初始容量也因电活性Mn³⁺的损失而有所降低。综合比较,当Cr掺杂量即X=0.05时,具有最好的电池特性。2.通过硝酸银热分解反应合成了金属Ag表面修饰的Ag/LiMn₂O₄复合材料。由于金属银是优良的导体,它的引入可以加速电子的传递,有效地提高了锂离子在LiMn₂O₄正极材料中的迁移速率,从而降低了电池的内阻,减少了不可逆容量损失,大大改善了纯LiMn₂O₄电极材料的循环稳定性和高倍率充放电性能。电化学测试结果显示,所得Ag/LiMn₂O₄复合材料具有良好的电池行为和高的容量保持率。在C/3下,Ag（0.1）/LMO化合物的首次放电容量为114.6 mAh/g,循环30周后容量保持率高达97.6%;在1C下的初始放电容量保持了C/3初始放电容量的92%。此外,我们还就Ag包覆量对该复合材料电化学性能的影响进行了深入研究。3.首次采用超声辅助流变相法制备了尖晶石型LiAl_0.05Mn_1.95O₄锂离子电池正极材料。实验结果证明采用该方法对样品的前驱体进行处理,有利于反应物的充分分散和混合,与传统固相法相比,在一定程度上可以缩短样品的焙烧时间,且制得的LiAl_0.05Mn_1.95O₄具有理想的尖晶石结构和规则的形貌,其粒径分布均匀并具有优良的电化学性能。首次放电容量达111.6 mAh/g,循环70次后容量保持率仍高达90.6%。因此,经济有效的超声辅助流变相法可以作为一种简便易行、非常有应用前途的制备锂离子电池正极材料的方法。此外,我们利用交流电化学阻抗技术,研究了锂离子在LiAl_0.05Mn_1.95O₄电极材料中,在整个充放电过程里的嵌入和脱出行为。4.以Brij 56/Co（NO₃）₂水溶液体系的六角相溶致液晶为模板,利用恒电位电沉积技术在钛基底上成功制备出了新型有序介孔H_I-e Co（OH）₂薄膜电极材料。小角X射线衍射（XRD）,透射电镜（TEM）等测试证明该介孔薄膜材料具有规则的纳米孔阵列结构,柱状孔呈六角排列,其孔中心对孔中心距约为7 nm。这种独特的有序纳米孔结构不仅提供了电解液和OH^-离子快速进出电极表面的通道,而且可以使活性离子扩散到Co（OH）₂的本体相,充分利用电极材料的电活性位发生氧化还原反应,为该材料高比电容的实现提供了重要的形貌基础。初步的研究表明该材料具有成本低、比容量高、循环稳定性好等优点,所制备的H_I-e Co（OH）₂薄膜在4 A/g的放电电流下具有高达1084 F/g的比电容值,是一种优秀的超级电容器电极材料。5.系统研究了电沉积条件（沉积电位,沉积温度,沉积基底）对介孔Co（OH）₂薄膜结构和性能的影响。采用X射线衍射（XRD）,扫描电镜（SEM）和透射电镜（TEM）进行物理表征来考察沉积电位、沉积温度和沉积基底对薄膜表面形貌的影响;使用循环伏安法（CV）和计时电位法等电化学方法系统研究了沉积电位、沉积温度以及沉积基底对薄膜电化学容量的影响。实验结果表明,沉积电位以及沉积温度对H_I-e Co（OH）₂薄膜的电化学电容有着十分显著的影响。在固定电位-0.75 V vs.SCE,沉积温度50℃下于Ti基底上得到的H_I-e Co（OH）₂薄膜在8 A/g的放电电流下可获得1018 F/g的单电极比电容。同时,不同沉积基底,对电化学容量也有显著的影响,当采用具有三维空间立体网孔结构的泡沫Ni网作为基底时,电化学容量可提高至2646 F/g,这主要归功于泡沫Ni网比Ti片具有更大的比表面积,有利于活性物质的高度分散和充分反应。更多还原

【Abstract】 At present,lithium ion battery and electrochemical capacitor are two kinds of important energy storage equipments.On account of high working voltage,large energy density,long cycle life,low self discharge rate and green environmental conservation,lithium ion battery has attracted much attention and has been widely applied in mini-type electric instruments presently.Meanwhile,the lithium ion batteries are developing toward the fields of space technology,national defense industry,electromotive vehicle and UPS actively.Electrochemical capacitor is a new type of energy storage equipment,which combines the advantages of both dielectric capacitors that can deliver high power within a very small period and conventional rechargeable batteries that have high energy densities.Therefore,electrochemical capacitors also have a wide range of applications and have already become one of the research interests related to new chemical energy sources studies.In this thesis,we have reviewed the newest development in the research of electrode materials of both lithium ion battery and electrochemical capacitor devices, prepared relevant electrode materials and explored their applications in these two kinds of devices in detail.The main content is as follows:1.The improvement of the performance of LiMn₂O₄ cathode materials by doping the spinel with different cations have been studied in detail.A series of LiM_0.05Mn_1.95O₄（M=Al,Cr,Fe） materials are prepared by the sol-gel method.The experimental results indicated that metal-doping could improve the cycle performance of LiMn₂O₄ due to the inhibition of Jahn-Teller distortion and could enhance the atomic cohesive force in the cathode hosts to strengthen their stability.Compare these doped LiMn₂O₄,it is clear to see that different metal ions have different improving effect to the LiMn₂O₄.Among these Al,Cr and Fe doped materials,the substituted chromium manganese oxide spinel(LiCr_0.05Mn_1.95O₄) had the best cycle performance, and the capacity loss was only 5%of its initial capacity after 30 cycles.Besides,we have also investigated the influence of Cr doping content on the structure and electrochemical properties of the LiCr_xMn_2-xO₄ cathode materials.It is evident that, the lattice parameter and crystal volume decrease with increasing the Cr content, which is beneficial to the stability of the spinel structure and could improve the cyclability of the material.However,the initial capacitance decreases to some extent with increasing the Cr doping content due to the loss of Mn³⁺.According to the results, it is found that when X（Cr doping content）=0.05,the doping material has the best battery performance.2.A series of Ag/LiMn₂O₄ composites with different Ag additive contents were prepared by thermal decomposition of AgNO₃ added to the pure LiMn₂O₄ powders. Because of the high electronic conductivity of metal Ag,Ag additive could significantly increase the electronic conductivity of Ag/LiMn₂O₄ composites,make the transfer rate of Li-ion in Ag/LiMn₂O₄ composites higher,lower the resistance of the cell,reduce the irreversible capacity loss and f’mally improve the cycling stability and rate capability.The electrochemical tests results indicate that Ag/LiMn₂O₄ composites have very good battery properties and capacity retention rate.At the discharge rate of C/3,the initial discharge capacitance of Ag（0.1）/LMO composite is 114.6 mAh/g,after 30 cycles,its capacitance retention rate is still as high as 97.6%. The initial discharge capacity ratio of（1C）/（C/3） is 92%.Besides,the influence of the Ag additive contents on the electrochemical properties of the Ag/LiMn₂O₄ composites is also investigated in detail.3.Spinel-type LiAl_0.05Mn_1.95O₄ cathode materials have been firstly synthesized by a simple ultrasonic assisted rheological phase（UARP） method.The experiments results reveal that using this novel method to deal with the precursor is beneficial to the complete dispersion of the reactant.Compared with the solid-state reaction（SSR） method,the UARP method could shorten the calcination time to some extent.The LiAl_0.05Mn_1.95O₄ product prepared via this new method has a good crystallinity with fine cubic spinel structure and exhibits a regular morphology with homogeneous particle size distribution.The electrochemical properties focused on the LiAl_0.05Mn_1.95O₄ by this new method have also been investigated in detail.According to these tests results,it is obviously to see that the newly prepared sample delivers a relatively high initial discharge capacity of 111.6 mAh/g,presents excellent rate capability and reversibility,and shows good cycling stability with capacity retention of 90.6%after 70 cycles.Meanwhile,the electrochemical impedance spectroscopy （EIS） investigations were employed to study the electrochemical process of Li⁺ ions with the synthesized LiAl_0.05Mn_1.95O₄ electrode detailedly.4.A novel ordered mesoporous cobalt hydroxide film（designated H_I-e Co（OH）₂） has been successfully electrodeposited on titanium substrate from the hexagonal lyotropic liquid crystalline phase using surfactant Brij 56 as the structure-directing agent.Low-angle X-ray diffraction（XRD） and transmission electron microscopy （TEM） studies indicate that the film electrodeposited from liquid crystal template has a regular nanostructure consisting of a hexagonal array of cylindrical pores with a repeat center-to-center spacing of about 7 nm.This special ordered nanoporous structure creates the fast electrochemical accessibility of the electrolyte and OH^- ions not only to the surface of the electrode materials but also to the bulk of the Co（OH）₂ phase,which is very helpful for making full use of the electroactive sites to take place the faradic reaction,providing an important morphological foundation for a high specific capacitance.Cyclic voltammeter（CV） and galvanostatic charge/discharge measurements show that the ordered mesoporous H_I-e Co（OH）₂ film electrode has excellent electrochemical capacitance between potential range of -0.1-0.45 V,and a maximum specific capacitance as high as 1084 F/g could be achieved in 2 M KOH solution at a charge-discharge current density of 4 A/g.Meanwhile,the properties of Co（OH）₂ film electrodeposited from aqueous solution without templates（designated Aq-e Co（OH）2） are also discussed for comparison.Preliminary studies show that the film has many merits such as low-cost,high special capacitance and good cycle properties,suggesting its potential application in electrochemical capacitors.5.Experimental electrodeposition parameters such as deposition potentials, deposition temperatures and deposition substrates are varied to analyze their influences on the electrochemical capacitor behavior systematically.The films are physically characterized by X-ray diffraction（XRD）,scanning electron microscopy （SEM） and transmission electron microscopy（TEM） to determine the effects of deposition potentials,temperatures and substrates on the surface morphology. Electrochemical techniques such as cyclic voltammetry（CV） and chronopotentiometry are used to systematically study the effects of deposition potentials,temperatures and substrates on the capacitance of the films.The investigation show that the deposition potentials and temperatures have obvious influence on the H_I-e Co（OH）₂ film.The capacitive performance of the H_I-e Co（OH）₂ film achieved the highest value of 1084 F/g at a discharge current density of 4 A/g when it is electrodeposited at -0.75 V under the deposition temperature of 50℃. Meanwhile,different deposition substrates also have great influence on the films,the ordered mesoporous Co（OH）₂ film on foamed Ni mesh has much higher specific capacitance（maximum:2646 F/g） than that of the film on Ti plate（maximum:1018 F/g） at the same discharge current density of 8 A/g.,which is mainly because that the foamed Ni mesh substrate with much larger surface area than Ti plate could enhance the utilization and the capacitance of Co（OH）₂ film greatly.更多还原