通过对两种天然鳞片石墨进行微膨胀处理得到微膨石墨, 然后以微膨石墨为基体采用化学气相沉积(CVD)法于微膨石墨的孔洞结构中原位生长碳纳米管, 制备了碳纳米管/微膨石墨复合负极材料. 电化学测试结果表明两种复合材料分别具有443和477 mAh/g的首次可逆容量. 两种复合材料在0.2C倍率下循环充放电30次后容量均能保持95%以上; 在1C下循环充放电50次后, 可逆容量分别稳定在259和195 mAh/g. 微膨胀处理形成的微纳米级孔洞以及原位碳纳米管的网络结构, 提供了更多的储锂空间, 并能够有效地缓冲电极材料在充放电时的体积变化; 电解质溶液浸润在纳米孔洞中, 有利于缩短锂离子的扩散路径, 提高倍率循环性能; 同时原位生长的类似常春藤形的碳纳米管可以起到桥梁的作用, 避免“孤岛”的形成, 增强了复合材料的导电性能.
Micro-expanded?flake?graphite (MEFG) and micro-expanded?spherical?graphite (MESG) were prepared from two kinds of natural graphite by intercalation reaction and rapid heating processes. Then carbon nanotubes/ micro-expanded?graphite (CNTs/MEG) composites were prepared by chemical vapor deposition (CVD) process, for which CNTs were grown in the pores of micro-expanded?graphite. Electrochemical test results?show that first discharge/ charge capacities of CNTs/MEFG and CNTs/MESG could respectively accommodate up to 443 and 477 mAh/g. Both of the prepared CNTs/MEG composites keep more than 95% capacities after 30 cycles at the rate of 0.2C and their capacities are stable at?259 and 195 mAh/g after 50 cycles at 1C rate, respectively. The nanoporous structure and the CNTs network can improve the discharge capacities and effectively?buffer the volumetric change of the composite electrode materials in the charge/discharge process. The diffusion path of Li+ can be reduced because of the electrolyte solution that filled in the nanopores, which significantly improves the rate capability of the electrodes. In addition, the growing ivy-like CNTs could improve the electric conductive property of the composites in the charge/discharge process.
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