Sol-gel synthesis and electrochemical performance of porous LiMnPO4/MWCNT composites

Abstract

Porous LiMnPO4 and LiMnPO4/MWCNT (multi-walled carbon nanotube) composites were prepared using a citric acid assisted sol-gel method. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), nitrogen adsorption-desorption isotherms (BET), and transmission electron microscopy (TEM) were performed to characterize their morphologies and structures. The results indicated that fine-sized, well-crystallized olivine LiMnPO4 was synthesized. The interlaced carbon nanotube networks were intimately embedded and incorporated into the porous LiMnPO4 particle to form highlyconductive three-dimensional (3D) networks. The LiMnPO4 particle and LiMnPO4/MWCNT composite had rich hierarchical pores. A detailed analysis showed that the average pore size was in the mesoporous range and specific surface areas of 73.7 and 69.9 m2·g-1 were obtained, respectively. Compared with the LiMnPO4 particle the LiMnPO4/MWCNT composite exhibited much higher specific capacity. When discharged at a rate of 0.05C and 2C the capacities were 108.8 and 33.2 mAh·g-1, respectively. The MWCNT effectively improved the electronic conductivity of the hybrid materials as shown by electrochemical impedance spectroscopy (EIS). The improved electrochemical performance of the LiMnPO4/MWCNT electrode is attributed to the enhanced electrical conductivity caused by the tighterbinding of the carbon nanotubes with the LiMnPO4 primary particles as well as by the interconnected open pores with a high surface area. © Editorial office of Acta Physico-Chimica Sinica.