高倍率锂镍钴锰复合氧化物材料的制备技术

【作者】 王海燕；

【导师】 唐爱东； 黄可龙；

【作者基本信息】 中南大学 ， 应用化学， 2008， 硕士

【摘要】 为获得高倍率锂镍钴锰复合氧化物（简称锂镍钴锰氧）锂离子电池正极材料,本文从改进制备方法,对材料分别进行掺杂和包覆改性三方面进行了研究,结果发现材料倍率性能都得到了提高,其中包覆改性的效果最好。具体结论如下:在碳酸盐共沉淀法中引入超声波技术合成锂镍钴锰氧正极材料,采用X射线衍射法（XRD）、扫描电镜法（SEM）、循环伏安法（CV）和充放电测试等手段,对材料进行表征与电化学性能研究。SEM显示材料颗粒分散均匀,平均粒径约200 nm。电化学研究表明,引入超声波技术,在900℃下煅烧制备的材料在0.1C下首次放电比容量为156 mAh/g,在1C下前40次循环后容量保持率为96%。在2C、5C、10C下的放电比容量分别为129.3 mAh/g、114mAh/g、95.5mAh/g。前5次循环容量基本没有衰减,显示了较好的倍率性能。以乙二醇为分散剂,采用固相掺杂方式制备掺杂Al、Mg的锂镍钴锰氧材料。对比研究发现,在0.1 C下未掺杂材料循环10次后容量衰减11%,掺杂Mg、Al后首次容量有所下降,但循环性能得到改善,衰减分别为2.5%、3.3%。在1C下,未掺杂,Mg和Al掺杂的材料前10次容量衰减分别为24.8%、14.6%和15.9%,掺杂材料的倍率性能要比未掺杂的材料要好。采用化学沉淀法先后对原始材料进行Al₂O₃和AlF₃的包覆,考察了不同AlF₃包覆量对电化学性能的影响。透射电镜图（TEM）表明Al₂O₃和AlF₃包覆层厚度分别为10nm、3nm,后者包覆层薄且均匀。研究发现最佳AlF₃包覆量为1.5wt%。在2C下,包覆后的材料100次循环后,放电容量保持率为90.9%,而原始材料仅为47.4%。在5C下,前者前20次容量保持率为87.6%,后者为64.5%。对于AlF₃包覆的材料,在2C下,前100次的保持率达90.2%。在5C下前50次循环容量保持率为91.4%,而原始材料的为52.6%。AlF₃包覆后的材料体现了比Al₂O₃更高的倍率性能。交流阻抗（EIS）研究表明电荷传递阻抗的微小变化是Al₂O₃和AlF₃包覆材料倍率性能都要好于原始材料的主要原因。另外,两者都能有效改善材料在高电位和高温下的循环稳定性,后者效果更好。更多还原

【Abstract】 Improved preparation method,doping and modification technology were carried out as follow in this paper,in order to obtain LiNi_1/3Co_1/3Mn_1/3O₂ with high rate capability.The results showed that all the measures could improve its rate capability,and modification technology indicated best inproved rate capability.LiNi_1/3Co_1/3Mn_1/3O₂ was prepared by a carbonate co-precipitation methode combined with a ultrasonic technique,followed by a high temperature solid state reaction,and the effect of calcined temperature and ultrasonic technique to material were also taken.Scanning electron macroscopy（SEM）,X-ray diffraction（XRD）,cyclic voltammetry（CV） and charge-discharge cycling were used to investigate the material’s characters and electrochemical performance.The particle size was about 200nm and its distribution was uniform,as observed by SEM.Initial discharge capacity of LiNi_1/3Co_1/3Mn_1/3O₂ prepared with above method combined with a ultrasonic technique and then calcined at 900℃was 156.3 mAh/g at 0.1 C-rate.That of 137.8 mAh/g,129.3 mAh/g,114.4 mAh/g,95.5 mAh/g were also gotten at 1 C,2 C,5 C,10 C,respectively. The electrode showed good rate capability since little capacity fade appeared after 5 cycles at such different rates,even at 10C and 96%of initial discharge capacity was maintained after 40 cycles at 1 C.The layered LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials doped by A1 and Mg were prepared,taking glycol as dispersant.The effects of different doped element（Al,Mg）on electrochemical properties of the synthesized materials were also studied.The bare material showed 11%capacity fade of its first discharge capacity after 10 cycles at 0.1 C-rate.Cycling properties of the doped element（Al,Mg）materials were improved.Their capacity fade rates were only 2.5%and 3.3%,respectively,after 10 cycles. At 1 C-rate,the capacity fade of bare material,Mg and Al dopant ones after 10cycles were 24.8%,14.6%and 15.9%,which indicated that the dopant material had better rate capability than that bare one.Al₂O₃ and AlF₃ were coated on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ particle,respectively,by chemical precipitation method and the effects of different coated contents on their electrochemical performance were studied.The thicknesses of Al₂O₃ and AlF₃ coated layer were about 10 nm and 3 nm,respectively,displaying by TEM.It’s found that the material with 1.5 wt%coated content has best electrochemical performance.The 1.5 wt%Al₂O₃ coated LiNi_1/3Co_1/3Mn_1/3O₂ at 2 C-rate showed 90.9% capacity retention of its initial discharge capacity,while the bare one showed only 47.4%.At 5 C-rate,the capacity retention of coated one after 20 cycles was 87.6%,while the bare one’s was 64.5%.As for the AlF₃ coated one,the capacity retention at 2 C-rate was 90.2%。At 5 C-rate, the capacity retention after 50 cycles of the bare and AlF₃ coated ones were 52.6%and 91.4%,respectively.It’s obviously that the AlF₃ coated one showed better rate capability than Al₂O₃ coated one.The results of EIS showed that the little change of charge transfer resistance of both Al₂O₃ and AlF₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ at higher charge-discharge rate was the main reason why the electrochemical performance improved obviously.Besides,Al₂O₃ and AlF₃ coated layer could improve the cyclic stability at high cut-off voltage or high operating temperature.更多还原