Modification Of Carbon Nanotubes On LiFePO₄for Lithium Ion Batteries

Olivine-structured LiFePO4is considered as a promising cathode material for lithium ion batteries,due to its advantages such as environmentally friendliness, high specific capacity, excellent cycle performance, abundant raw materials, inexpensive price and high safety. However, it suffers from low conductivity and poor rate performance, which prevents it from commercial use. Several methods have been reported to improve its electrochemical performance, including surface coating, minimizing the particle size, and lattice doping. Carbon coating is considered as the most efficient way to improve the electronic conductivity. The traditional additive material with carbon lamellas in carbon black, are circumferentially oriented and block much of the particle interior, rendering the majority of matrix useless. As a kind of potential carbon material, carbon nanotubes(CNTS) have been regarded as an ideal conductive additive for LiFePO4due to its unique ID tubular structure, high electrical and thermal conductivities and extremely large surface area. In our work, LiFePO4was coated by CNTs from two aspect:in suit an ex suit. We are aimed at building CNTs conductive network on LiFePO4to improve its electric performence.On the one hand, CNTs as conductive agent for ex suit coating on LiFePO4. Mechanical stirring and ultrasonic were used to build CNTs conductive network structure. The CNTs network was formed at the condition of3wt%purified CNTs and5wt%PVDF. In this case, the dischrage capacity of LiFePO4are obtained as120,80mAh/g for discharge rates of2and5C,20%and47%capacity attenuation compared with the capacity at0.2C rate, and145.5mAh/g at0.25C rate,retaining96.25%after50cycles.On the other hand, CNTs as a kind of carbon suorce for in suit coating on nano-LiFePO4, which was prepared by ball milling. In this work, with the help of PVDF and percusor carbonized, the CNTs network was formed by means of stirring and ultrasonic. As a result, the dischrage capacity of LiFePO4are obtained as140,116,92mAh/g for discharge rates of2,5,10C,9.68%,25.16%,40.64%capacity attenuation compared with the capacity at0.2C rate, and151mAh/g at0.25C rate retaining100%after50cycles.