Nanomaghemite synthesis and investigation of its performance as an anode in Li-ion battery

By: Mohammad Golmohammad

Supervisor: Prof. Farhad Golestanifard , Dr. Alireza Mirhabibi

Advisor: Dr. Erik Kelder

Iran University of Science and Technology

March 2016

Abstract: In this research, nano-maghemite with an average particle size of 11nm was synthesized employing design of experiment and optimization of co-precipitation method to be studied as an Li-ion battery anode. Investigation of co-precipitation parameters showed that pH and Fe3+/Fe2+ are more effective than time and temperature on particle size. For studying particle size effect on performance, nano maghemite with average particle size of 22 & 41 nm were synthesized by increasing stirring time. For investigation of morphological effect, in addition to semi-spherical particles, pseudo-needle and flaky particles with nearly same surface area (112±7 m2.g-1) were synthesized. Moreover, for understanding the effect of porosity, porous powder with specific surface area of 285 m2.g-1 was synthesized. The anode body was doctor bladed using primary powder with a binder and a conductive agent. Galvanostatic charge–discharge cycling of 11nm sample at 500 mA.g-1 current density exhibited reversible capacity of 430 mAh.g-1 which was higher than 22nm (380 mAh.g-1) and 41nm (290 mAh.g-1) samples. The reason for this increment is attributed to the higher surface area and smaller Li ion diffusion length of smaller particles. Galvanostatic charge–discharge for pseudo-needle sample showed reversible capacity of 510 mAh.g-1 which was higher than those of platelet and semi-spherical samples (470 and 430 mAh.g-1). This higher reversible capacity is due to the morphological effect and easier stress relief of volume changes during charge and discharge. Galvanostatic charge–discharge cycling of porous sample showed approximately 720 mAh.g-1 reversible capacity which is remarkably higher than other samples. The reason for this extinguished performance of the latter anode was thought to be dependent upon the role of pores in increasing the surface area and resistance against volume changes during lithium insertion/extraction. Finally, iron state in discharge cycling were investigated by X-ray diffraction pattern and X-ray photoelectron spectroscopy and the reaction of maghemite with lithium were proposed. The result of this research disclosed that increasing surface area and governing shape and size of pristine maghemite particles result in the increment of reversible capacity and cyclability which make maghemite a good candidate as an anode for Li-ion battery.

Keywords: Li-ion battery; nanomaghemite; co-precipitation method; particle morphology; reversible capacity 

                     

Images from left to right: semi-spherical particles, pseudo-needle and flaky particles