【作者】 周华；

【导师】 张海朗；

【作者基本信息】 江南大学 ， 化学工艺， 2008， 硕士

【摘要】 尖晶石LiMn2O4具有高电压、高安全性、低污染、低成本、资源丰富等优点使其成为新一代锂离子电极正极材料研究热点之一,但是该材料目前还存在初始容量较低、容量衰减较快等问题,这严重阻碍了其商业化进程。目前解决该问题采用最多的是阳离子掺杂、阴离子掺杂、阴阳离子共掺杂等改性方法。本文的主要工作内容是研究尖晶石型锰酸锂正极材料的离子体相掺杂改性,以改善材料的电化学性能。研究了以不同的锂源采用熔融浸渍法制备尖晶石型锰酸锂,及阴阳离子复合掺杂,对尖晶石锰酸锂晶体结构和电化学性能的影响。本文首先采用熔融浸渍法,分别以硝酸锂、氢氧化锂为锂源,合成尖晶石LiMn2O4,随着煅烧温度的升高,硝酸锂为锂源合成的尖晶石样品晶胞参数逐渐增大,其初始容量也逐渐增大;氢氧化锂为锂源源合成的尖晶石样品晶胞参数随着煅烧温度的升高而减小,其初始容量也逐渐减小。相比而言,氢氧化锂为锂源合成尖晶石LiMn2O4电化学性能也较好。分别以硝酸锂、氢氧化锂为锂源,采用氟镁掺杂改性制备的样品LiMn1.9Mg0.1O4-y,通过XRD测试可以看出样品为纯的尖晶石相,说明了氟镁掺杂进尖晶石结构中。而合成的样品在材料的结晶程度和形貌都有很大的改善,其循环性能也得到了较大的提高。当镁的量不变,掺杂氟对样品的性能影响最为明显,随着掺氟量的增加,样品LiMn1.9Mg0.1O4-yFy(y=0.03,0.05,0.1)容量逐渐增加。相比而言,氢氧化锂为锂源合成尖晶石LiMn1.9Mg0.1O4-yFy(y=0.03,0.05,0.1)电化学性能也较好,这与合成尖晶石LiMn2O4规律一致。而采用氟铝掺杂改性制备的样品LiMn1.9Mg0.1O3.97F0.03,其初始容量低,电化学性能较差。对尖晶石锰酸锂进行了阴阳离子的多元复合掺杂改性,通过筛选掺杂元素的组合方案、控制掺杂的量、选择不同的锂源,制备出了既具有高的初始容量又有良好的充放电循环性能的尖晶石型锰酸锂正极材料,并从理论上探讨了尖晶石锰酸锂容量衰减的原因,从材料的晶体结构和电化学特性等方面分析了掺杂改性改善尖晶石锰酸锂循环性能的作用机理。更多还原

【Abstract】 Spinel LiMn2O4 is one of the most promising cathode for lithium ion battery for its high working voltage,high safty,low pollution,low cost,abundant resources.The low initial capacity and its rapid decrease of the spinel haven’t been improved up to now,However the commercial applications of LiMn2O4 are badly blocked by its poor cycling performance.Through the most widely adopted method to overcome the problems was cation doping,anion doping or co-doping.This dissertation is intending to investigate the modification of spinel lithium manganese cathode material for lithium-ion batteries by ion doping, so as to improve its electrochemical performance. Spinel LiMn2O4 were synthesized by a melting-impregnation method with different source of lithium .Cation(Mg,Al )and anion (F) co-doping methods were adopted to modify the spinel LiMn2O4 cathode. Their effects on the crystal structure and electrochemical properties of the result spinel lithium manganese were studied respectively. Firstly, Spinel LiMn2O4 were prepared by a melting-impregnation method with lithium nitrate and lithium hydroxide respectively. with the calcination temperature increased , when used lithium nitrate as the source of the lithium , the cell parameters of spinel samples increased gradually. Its initial capacity is gradually increased,also.when used lithium hydroxide as the source of the lithium, the lattice constants of spinel samples decreased Its initial capacity is gradually reduced. In contrast, the electrochemical properties of LiMn2O4 spinel with lithium hydroxide as the source of the lithium is better. F-Mg co-doped spinel LiMn1.9Mg0.1O4-yFy were synthesized by melting-impregnation methods as above-mentioned. Their microstructure were examined by powder XRD analysis , All samples were identified as a pure spinel phase with a space group Fd3m where lithiumions occupy the tetrahedral (8a) sites, Mn3+, Mn4+ andAl3+ ions reside at the octahedral (16d) sites, and O2? and F? ions are located at the 32e sites. the crystal degree, morphology and cycling performance are greatly improved , When the same amount of magnesium in spinel,the effect of fluorine-doping on samples is the most obvious ,with the increase of fluorine, the initial discharge capacity of LiMn1.9Mg0.1O4-yFy(y=0.03,0.05,0.1)gradually increase. In contrast, when used lithium hydroxide as the source of the lithium, the electrochemical performance of LiMn1.9Mg0.1O4-yFy (y = 0.03,0.05,0.1) is better, It is the same as LiMn2O4 spinel. when used lithium hydroxide as the source of the lithium, the electrochemical performance of LiMn1.9Mg0.1O4-yFy (y = 0.03,0.05,0.1) is better,also.However,electrochemical property of LiMn1.9Al0.1O3.97F0.03 were prepared by melting-impregnation methods as above-mentioned. Al and F dual-doped LiMn2O4 could gain worse electrochemical properties and have lower initial capacity than only the Mg and F co-doped LiMn2O4.The modified spinel cathode material with some cations and anions multiplex doped were synthesized for the first time. By choosing a different lithium source and controlling the doping quantum, perfect spinel lithium manganese cathode were produced which have high initial capacity as well as good cycle performances at room temperature. The causes of the capacity fading of spinel lithium manganese were discussed. The action mechanism of ion doping was analyzed in terms of the crystal structure and electrochemical properties.更多还原