A comparison among FeF3·3H2O, FeF3·0.33H2O and FeF3 cathode materials for lithium ion batteries: Structural, electrochemical, and mechanism studies

• Published in: Journal of power sources 2013-09, Vol.238, p.501-515
• Main Authors: Liu, Li, Guo, Haipeng, Zhou, Meng, Wei, Qiliang, Yang, Zhenhua, Shu, Hongbo, Yang, Xiukang, Tan, Jinli, Yan, Zichao, Wang, Xianyou
• Format: Article
• Language: English
• Subjects: Applied sciences; Cathode materials; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrochemical properties; Exact sciences and technology; Iron fluorides; Lithium ion batteries; Materials
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2013.04.077

FeF3·3H2O, FeF3·0.33H2O, and FeF3 have been synthesized via a liquid-phase method followed by heat treatment at different temperatures. The structure and performance of these iron fluorides have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), charge–discharge test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). Though FeF3·3H2O, FeF3·0.33H2O, and FeF3 have different crystalline structures, they can achieve the identical reversible electrochemical conversion reaction from Fe3+ to Fe0 in the wide voltage range (1.0–4.5 V vs. Li+/Li). Among these three iron fluorides, FeF3·0.33H2O shows the best electrochemical performance. Moreover, ball milling with acetylene black combined with limiting cut-off voltage can further improve its electrochemical performance. FeF3·0.33H2O/C composite delivers excellent electrochemical performance in the voltage range of 2.0–4.5 V. Its capacity retentions remain as high as 83.8% and 83.3% after 100 cycles at 0.1 and 5 C, respectively. This study suggests a potential feasibility to prepare the optimal crystal structure of iron fluorides as high-performance cathode material for lithium-ion batteries. •The properties comparison of FeF3·3H2O, FeF3·0.33H2O, and FeF3 has been firstly investigated.•The electrochemical reaction mechanism of FeF3·3H2O has been firstly studied.•The electrochemical reaction mechanism of FeF3·0.33H2O also include conversion reaction has been firstly proved.•FeF3·0.33H2O has the best electrochemical performance among these three iron fluorides has been demonstrated.