【作者】 于福新；

【导师】 张海朗；

【作者基本信息】 江南大学 ， 应用化学， 2008， 硕士

【摘要】 近年来,人们对锂离子二次电池正极材料进行了大量的研究。LiCOO2材料由于高电压、高容量和循环性能优异,目前是商业应用的主要材料。LiNiO2也被作为一种有潜力的正极材料被广泛研究。锂离子蓄电池具有比能量高、自放电率低、工作电压高、对环境友好及无记忆效应等优点,具有十分广阔的应用前景。正极材料的研究是锂离子二次电池的核心技术之一。尖晶石型LiMn2O4正极材料由于其资源丰富,价格便宜,对环境友好,合成工艺简单,安全性好,被公认为是新一代锂离子电池最有希望的正极材料之一,但是该材料目前还存在初始容量较低、容量衰减快等问题。本文概述了锂离子电池正极材料的研究和发展现状,对尖晶石型LiMn2O4正极材料的衰减机理做了详细说明,总结了现有的几种改进方法,还对该材料的各种制备方法做了简单介绍。本文首先研究了焙烧温度对溶胶—凝胶法合成尖晶石锰酸锂正极材料结构和性能的影响,得到如下结论:在我们的实验条件下,焙烧时分三段(150℃焙烧8小时→300℃焙烧12小时→750℃焙烧12小时)进行即得到纯相的、性能较好的尖晶石锰酸锂。通过XRD、SEM对材料的性能进行了表征,并用所制备的材料制作成电池,通过充放电测试,进一步研究了材料的电化学性能。在750℃下,LiMn2O4的首次放电比容量为127.9 mAh/g,循环35次后其放电比容量仍保持在114.8 mAh/g,容量保持率为89.8%。对尖晶石锰酸锂进行体相阴阳离子掺杂是本文的研究重点。通过Ni2+、F-阴阳离子复合掺杂制备了掺杂改性尖晶石LiNixMn2-xO4-yFy(x=0.03、0.05、0.1;y=0、0.05、0.1),考察了温度和掺杂量的影响,通过XRD、SEM对材料的性能进行了表征,并用所制备的材料制作成电池,进一步研究了材料的电化学性能。研究认为Ni2+掺杂都能改善尖晶石锰酸锂正极材料的循环性能,F-能够提高初始放电比容量,综合考虑稳定放电比容量与循环性能,750℃时烧结12 h得到的LiNi0.1Mn1.9O3.95F0.05粉体具有较好的电化学性能,首次放电比容量达106.1 mAh/g,循环35次后,其放电比容量保持在102.4 mAh/g,容量保持率为96.5%。通过Cr3+、F-进行掺杂改性合成了LiCrxMn2-xO4-yFy(x=0.03、0.05、0.1;y=0、0.05、0.1),考察了不同的温度和掺杂量的影响,通过XRD、SEM对材料的性能进行了表征,并用所制备的材料制作成电池,进一步研究了材料的电化学性能,通过本实验测试,获得了最佳合成条件:温度为750℃,x=0.1,y=0.05,此物质为LiCr0.1Mn1.9O3.95F0.05,初次放电比容量为110.9 mAh/g,循环35次后,其放电比容量保持在108.5 mAh/g,容量保持率为97.9%。总体上来讲,阳离子掺杂虽然在一定程度上降低了材料的比容量,但都能够明显提高材料的循环性能,而阴离子掺杂会提高材料的比容量,但是会使材料的循环性能变差,选择理想的阴阳离子掺杂和最佳配比是今后提高尖晶石锰酸锂电化学性能的研究方向。更多还原

【Abstract】 During these years, many investigations have been made on the cathode materials of lithium-ion rechargeable bateries. LiCoO2 has been commercialized for its high potential, high capacity and excellent recharge ability. LiNiO2 has also been developed as the substitutive cathode. However, cobalt and nickel compounds have economic and environmental problems, and the preparation of stoichiometric LiNiO2 is extremely difficult.Lithium-ion batteries have a good prospect in application for its favorable advantages of high voltage, high specific capacity, long cycling life and non-pollution.Cathode is the key of the development of lithium-ion batteries. LiMn2O4 spinel is believed to be the most promising cathode material for lithium-ion batteries.because.of its abundant resources, low cost, simple synthesis processing environmental friendly nature. However, the low initial capacity and poor cyclability prevent LiMn2O4 spinel from wide application. Several mechanism about the attenuation of LiMn2O4 spinel and some ways to improve the performance of this cathode material has been illuminated in the paper.In the present work, LiMn2O4 spinel compound was synthesized by means of the so called sol-gel process. The effects of the calcination process on the structure and properties of the LiMn2O4 spinel materials were discussed.The experimental results show that pure spinel phase of LiMn2O4 cathode was obtained under the experimental conditions of 750℃. Heating process was divided into 3 stages, i.e.150℃8 h—650℃12 h—750℃12 h. Their structure and electrochemical properties were characterized by means of XRD, SEM techniques. The initial discharge specific capacity of LiMn2O4 is 127.9 mAh/g, The LiMn2O4 spinel compound has a high capacity retention of 89.8% after 35 cycles.The important investigation points in the present thesis was modification of LiMn2O4 by ions-doping. Ni2+andF--doping spinels (LiNixMn2-xO4-yFy (x=0.03,0.05,0.1;y=0,0.05,0.1)) were prepared.The effects of sintering temperature and dopant content were studied. Their structure and electrochemical properties were characterized by means of XRD,SEM techniques. The LiNi0.1Mn1.9O3.95F0.05 powder with high discharge capacity and cycling performance is prepared at sintering temperature of 750℃. The initial discharge specific capacity of LiNi0.1Mn1.9O3.95F0.05 is 106.1 mAh/g,The powder has a high capacity retention of 96.5% after 35 cycles.Cr2+and F-doping spinels (LiCrixMn1.97O4-yFy (x=0.03,0.05,0.1 ; y=0,0.05,0.1)) were prepared. The effects of sintering temperature and dopant content were discussed. Their structure and electrochemical properties were characterized by means of XRD,SEM techniques. The LiCr0.1Mn1.9O3.95F0.05 powder with high discharge capacity and cycling performance is prepared at sintering temperature of 750℃. The initial discharge specific capacity of LiCr0.1Mn1.9O3.95F0.05 is 110.9 mAh/g, The powder has a high capacity retention of 97.9% after 35 cycles.Generally speaking, the cycling performance of spinel LiMn2O4 was evidently improved through cation doping even though the specific capacity of materials were reduced to some extent. Howere, the specific capacity of spinel LiMn2O4 was evidently improved through anion doping even though the cycling performance of materials were reduced to some extent. In order to improve electrochemical properties of spinel LiMn2O4, we will look for the ideal doping ions and gain the best ratio in the future.更多还原