Investigation of graphitic carbon foams/LiNiPO4 composites

Abstract

The characterization of composites consisting of graphitic carbon foams coated with a structured lithium nickel phosphate is reported. The LiNiPO4 as cathode material for lithium-ion batteries is prepared by a Pechini-assisted sol-gel process. The coating is performed by soaking the graphitic carbon foams in aqueous solutions containing lithium, nickel salts, and phosphates at 70 °C for 2–4 h and then by treating in flowing air and nitrogen. The formation of the olivine-like structured LiNiPO4 is confirmed by X-ray diffraction analysis performed on powders prepared under very similar conditions. However, crystalline reflections attributed to Li4P2O7 and to Ni3P as secondary phases have been observed. The morphological investigation revealed the presence of a layer on the graphitic foams that consists of interconnected blend of grains with different size. The voltammetric curves show values of the mean peak maxima in the anodic region between 5.1–5.3 V and in the cathodic region at ~4.9 V. The electrochemical measurements deliver a discharge specific capacity of 86 mAhg−1 (at discharge rate of C/10 and RT). The electrochemical impedance spectroscopy data confirm an increase of the electrical resistance after cycling and the decrease of the ionic contribution which indicate the formation/growth of phases behaving like resistors.