Electrochemical and solid-state NMR studies on LiCoO2 coated with Al2O3 derived from carboxylate-alumoxane
Electrochemical and solid-state NMR studies on LiCoO2 coated with Al2O3 derived from carboxylate-alumoxane
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DOI：
10.1016/j.jpowsour.2006.01.076
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发表时间：
2006-12
影响因子：
9.2
通讯作者：
G. Fey;H. Kao;P. Muralidharan;T. P. Kumar;Yung-Da Cho
中科院分区：
文献类型：
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作者：
G. Fey;H. Kao;P. Muralidharan;T. P. Kumar;Yung-Da Cho
在LiCoO_2阴极表面涂覆不同质量分数的由甲氧基乙氧基乙酸铝氧烷(MEA-Al_2O_4)制得的Al_2O_3，然后在723K空气中焙烧10h。用X射线衍射仪、扫描电子显微镜、能谱仪、透射电子显微镜、BET、XPS/ESCA和固态27Al魔角旋转核磁共振技术对表面修饰后的LiCoO2样品的结构和形貌进行了表征。Al_2O_3涂层在芯材表面形成一层平均厚度为20 nm的薄层。相应的~(27)Al-MAS核磁共振谱与由MEA-Al_2O_3生成的原始Al_2O_3的核磁共振谱基本相同，表明当涂层质量分数低于1wt.%时，铝原子的局域环境没有明显变化。这为Al_2O_3存在于堆芯材料表面提供了直接证据。包覆1wt.%Al_2O_3的LiCoO_2的连续循环稳定性是纯LiCoO_2的13倍。对原始材料和涂层材料的电化学阻抗行为的比较表明，原始阴极性能的失效与连续循环时颗粒-颗粒电阻的增加有关。涂层通过抑制原始LiCoO2在充放电过程中发生的特征结构相变(从六方到单斜再到六方)来改善阴极性能。
The surface of LiCoO2cathodes was coated with various wt.% of Al2O3derived from methoxyethoxy acetate-alumoxane (MEA-alumoxane) by a mechano-thermal coating procedure, followed by calcination at 723K in air for 10h. The structure and morphology of the surface modified LiCoO2samples have been characterized with XRD, SEM, EDS, TEM, BET, XPS/ESCA and solid-state27Al magic angle spinning (MAS) NMR techniques. The Al2O3coating forms a thin layer on the surface of the core material with an average thickness of 20nm. The corresponding27Al MAS NMR spectrum basically exhibited the same characteristics as the spectrum for pristine Al2O3derived from MEA-alumoxane, indicating that the local environment of aluminum atoms was not significantly changed at coating levels below 1wt.%. This provides direct evidence that Al2O3was on the surface of the core materials. The LiCoO2coated with 1wt.% Al2O3sustained continuous cycle stability 13 times longer than pristine LiCoO2. A comparison of the electrochemical impedance behavior of the pristine and coated materials revealed that the failure of pristine cathode performance is associated with an increase in the particle–particle resistance upon continuous cycling. Coating improved the cathode performance by suppressing the characteristic structural phase transitions (hexagonal to monoclinic to hexagonal) that occur in pristine LiCoO2during the charge–discharge processes.