一种碳纳米管改性富锂锰基正极材料的策略

A Strategy for Carbon Nanotubes Modified Lithium-Manganese-Rich Cathode Material

采用一种新策略对Li1.184[Ni0.15Mn0.516Co0.15]O2进行改性,即通过气流破碎、高压均质混合分散和喷雾干燥的方法得到与碳纳米管复合的富锂锰基正极材料(CNT@LMR)。使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)和拉曼光谱(Raman)的方法对改性的材料进行了表征,发现碳纳米管导电网络均匀地分布在富锂锰基正极材料的表面,而且在材料内部的一次颗粒之间也有大量的碳纳米管存在。电化学性能测试表明,碳纳米管改性后的富锂锰基正极拥有更好的倍率性能和循环寿命。在5C倍率下经过改性的富锂锰基正极的放电比容量为141.4 mAh·g^-1,远高于未改性的富锂锰基正极的放电比容量(76.6 mAh·g^-1)和碳纳米管仅作为富锂锰基正极导电剂时的放电比容量(110.7 mAh·g^-1)。在1C倍率下循环100次后,碳纳米管改性的富锂锰基正极的容量保持率在87.2%,高于富锂锰基正极(77.8%)。不同循环次数下的电化学阻抗谱表明,均匀分布在富锂锰基正极材料表面的碳纳米管网状结构有效地改善了电极/电极液的界面反应,抑制了电极固体电解质界面(SEI)膜的增厚和减缓了电极的极化。同时,材料内部的碳纳米管导电网络降低了一次颗粒间的内阻并加快了电极的电荷转移过程。

Li1.184[Ni0.15Mn0.516Co0.15]O2-modified carbon nanotubes network composite (CNT@LMR) cathode materials were synthesized by a novel strategy that adopted these technologies of compressed air crush, high pressure micro-fluidization dispersion and spray dehydration. The microstructures and morphologies were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD) and Raman spectroscopy, which indicated that CNTs conductive network were uniformly distributed on the surface of lithium-manganese-rich (LMR) and existed between primary particles from LMR inside. The novel network structure built on Li-rich cathode material not only took advantage of CNTs as conductive additives, but also combined the characteristic of CNTs network acts as a surface modification layer. The electrochemical tests demonstrated that CNTs modified LMR electrode had higher rate capability and cycle stability. For example, CNT@LMR had discharge specific capacity of 141.4 mAh·g^-1 at 5C-rate, compared to the capacity of pristine LMR (76.6 mAh·g^-1) and composite LMR electrode with CNT conductive additives (110.7 mAh·g^-1). After 100 cycle tests at 1C-rate, the capacity retention of CNTs modified LMR was 87.2% compared to pristine LMR of 77.8%. According to electrochemical impedance spectroscopy (EIS) with different cycle tests, CNTs network structure on the surface of LMR improved electrode/electrolyte interface reaction, restrained solid electrolyte interphase (SEI) film growth and polarization of LMR electrode, and CNTs conductive network inside LMR reduced resistance and accelerated charge transfer process for primary particle.