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Soft Chemical Approach to Surface Modification of Olivine-Type LiFePO4 nanoplatelets and Their Electrochemical Properties

Wednesday, May 14, 2014
Grand Foyer, Lobby Level (Hilton Orlando Bonnet Creek)
C. George and A. Paolella (Italian Institute of Technology, Italy)
Abstract: Olivine phosphate (LiFePO4) is a remarkable cathode material1-4 for lithium ion (Li-ion) batteries due to its high theoretical capacity (Q= 170 mA h g-1), exceptional cycling stability, low cost, environmental compatibility and safety.  Conventionally, on this material a carbon coating5 has widely been attempted for better Li ions kinetics and cycling (charge/discharge). Here, we report a colloidal synthesis route to prepare platelet-shaped (~10 nm thick) LiFePO4  nanocrystals (NCs). We then explore soft chemical strategies for the surface preparation of phospho-olivine platelet NCs by a treatment with either lithium fluoride (LiF) or lithium hexafluorophosphate (LiPF6).  The NCs were given, for instance, a coating of LiF to yield core-shell type structures (LiFePO4 core and LiF shell) as shown in Figure.1a-b. The core-shell NCs were extensively characterized with the aid of several structural and compositional techniques (via X-ray diffraction, high-resolution electron microscopy, and electron energy loss spectroscopy), highlighting their morphological/structural features relevant for high-rate capable electrodes. We then illustrate the electrochemical properties (via cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy) of core-shell NCs in Li metal half-cells by comparing their carbon coated NC counter parts.


Reference:

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(2) Kang, B.; Ceder, G. Nature 2009, 458, 190-193.

(3) Gibot, P.; Casas-Cabanas, M.; Laffont, L.; Levasseur, S.; Carlach, P.; Hamelet, S.; Tarascon, J.-M.; Masquelier, C. Nat.Mat 2008, 7, 741-747.

(4) Nishimura, S.-i.; Kobayashi, G.; Ohoyama, K.; Kanno, R.; Yashima, M.; Yamada, A. Nat.Mat 2008, 7, 707-711.

(5) Wang, J.; Sun, X. Energy & Environmental Science 2012, 5, 5163-5185.

Figure.1 a) Transmission electron microscopy (TEM) image of   LiFePO4NC samples a) pristine; b) after a treatment with lithium fluoride (LiF)