Understanding Phase Nucleation and Distribution in Conversion Materials: FeF2 and FeOF
EMSL Project ID
48387
Abstract
Lithium ion batteries are the top candidates for portable electronics and important for on-board energy storage in plug-in hybrid electric vehicles as well as fully electric vehicles due to their high energy and power density. One group of materials that shows promising characteristics is FeF2 and FeOF conversion materials. They have several advantages including high theoretical capacity, low cost, low toxicity, and better safety. Their conversion reactions have been experimentally evidenced by several techniques. However, several critical issues remain unexplained such as poor cycling, high voltage hysteresis, and the correlation between state of charge and both phase nucleation and distribution.During conversion reactions of FeF2 and FeOF, phase nucleation and distribution are directly correlated with the state of charge. The main challenge has been identification of light elements distribution, such as Li, O and F, with high spatial resolution. Atom probe tomography (APT) is an ideal technique to precisely identify phase distribution since it can map the type and 3-D location of each atom to within less than a nanometer. A detailed knowledge of the phase distribution and reaction mechanism can help researchers design more effective materials for energy storage applications. APT is a powerful technique for studying phase boundaries and distribution of light elements, especially when combined with high-resolution transmission electron microscopy (HR-TEM) and electron energy loss spectroscopy. Despite the advances in recent years on the APT analysis of a wide variety of materials, very little work has been done on the family of materials used in Li-ion batteries. We intend to establish standards in this technique for the identification of phase distribution, an integral factor in electrode performance. The use of XPS and nano-SIMS would also be complimentary in confirming the oxidation state of elements and phase-distribution respectively observed by APT and STEM/EELS studies.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2014-10-01
End Date
2015-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members