Study of Diffusion Kinetics and Microstructure for FeF3-CF (Carbon-Fiber) 3D Composite Electrodes

Wednesday, May 14, 2014
Grand Foyer, Lobby Level (Hilton Orlando Bonnet Creek)
H. Zhou (Oak Ridge National Laboratory), S. K. Martha (Indian Institute of Technology Hyderabad, Oak Ridge National Laboratory), J. Li, S. Pannala, N. J. Dudney, J. Nanda (Oak Ridge National Laboratory), J. Wang, and P. V. Braun (University of Illinois at Urbana-Champaign)
Recently, we investigated the role of electrode architecture on the capacity retention and hysteresis of iron (II and III) fluoride conversion compound.1 The unique electrode architecture consists of nanometer sized iron fluoride particles (~ 25-50nm) coated with multilayer graphitic platelets and bound to an electronic backbone comprising of an interconnected network of carbon fibers (5-9 µm diameter).  The carbon coated fluoride particles are bound to the carbon fiber through a carbonaceous binder derived from petroleum pitch.2 This unique combination of reduced particle size and electrode architecture significantly improves the local electronic conductivity enhancing the electrochemical performance such as better capacity retention and C-rate performance. Further, we observe a significant reduction of voltage hysteresis to ~ 0.9V compared to 1.5 V for normal FeF3 slurry electrodes3. Electrochemical cycling at elevated temperature (60oC), improves the reaction transport kinetics yielding almost theoretical specific capacity (700 mAhg-1) with reasonably good cycle life with a small concomitant reduction in the hysteresis (Figure 1). The estimated overall energy density based on the active mass of FeF3 in the electrode is about 1650 Wh kg-1covering both the intercalation and conversion window (1.5–4.5 V). The overall performance of this 3D-structured cathode is impressive, and may provide a new cathode/electrode concept for next generation high energy density batteries.

Figure 1. (a). Voltage vs. capacity profiles of a Li/FeF3 cell (on carbon fiber) cycled between 1.5 V and 4.5 V (C/50 rate) at 60oC. (b) Capacity plotted as a function of cycle number for the Li/FeF3 cell. Capacity is evaluated based only on FeF3 active material. 

Although initial cycle life looks promising, we notice capacity fade after 50 cycles clearly suggesting that further investigation are needed to understand the diffusion kinetics and/or structural stability of various intermediate conversion phases.  We will present detailed investigation  of various reaction phases and the kinetics of FeF3 and FeF2 electrodes at room temperature, 45 and 60 °C based on potentiostatic intermittent titration (PITT), electrochemical impedance spectroscopy (EIS), electron microscopy (S/TEM) and X-ray diffraction (XRD).


This research is sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.


  1. S. K. Martha, J. Nanda, H. Zhou, J. C. Idrobo, N. J. Dudney, S. Pannala, S. Dai, J. Wang, and P. V. Braun, RSC Advances. (Accepted 2013).
  2. S. K. Martha, N. J. Dudney, J. O. Kiggans and J. Nanda, J. Electrochem. Soc., 159, A1652-A1658 (2012).
  3. P. G. Bruce, B. Scrosati, and J-M. Tarascon, Angew. Chem. Int. Ed., 47, 2930-2946 (2008).