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In-Operando Electron Paramagnetic Resonance Spectroscopy - Formation of Mossy Lithium on Lithium Anodes and Lithium Plating on Graphite Anodes during Charge/Discharge Cycling
In this work we propose to use in-operandoelectron paramagnetic resonance (EPR) spectroscopy as a new analytical technique for the time resolved and quantitative determination of lithium microstructures both on lithium metal and graphite anodes. We present a novel cell design which can be cycled directly in the cavity of the EPR spectrometer and which has been successfully benchmarked against a standard cell design.
Firstly, we investigate the morphological changes of a lithium metal anode during cycling of a Li/LiFePO4 (LFP) cell as case study to demonstrate the capabilities of electrochemical in-operando EPR spectroscopy.[4] Figure 1 shows the voltage profiles and the evolution of the EPR resonance of the lithium anodes using a standard electrolyte with or without fluoroethylene carbonate (FEC) additive, which is known to reduce lithium dendrite formation.[5]In comparison to the standard electrolyte, the FEC additive significantly increases the reversibility of the lithium stripping/plating process. These results are also confirmed by ex-situ SEM images of cycled electrodes.
Secondly, we investigate lithium plating on graphite electrodes during the cycling of graphite/LiFePO4 (LFP) cells. Since plated lithium (due to low temperatures or high C-rates) can chemically intercalate into the underlying graphite at open circuit conditions, a dedicated in-operando technique like EPR has to be used for a thorough study of lithium plating on graphite.[6]
Figure 1: Overview of cycling of in-operando EPR cells containing electrolyte without additive (black) and with 10 wt-% FEC (red). Top and bottom panel: Voltage profiles according to cycling procedure shown above top panel; blue 'SEM1’ and ‘SEM2’ markers indicate positions where ex-situ SEM images of lithium anodes were recorded. Central panel:Normalized intensity of EPR signal obtained by double integration of recorded first derivate Li spectrum.
References:
[1] J. T. Vaughey, G. Liu, J.-G. Zhang, MRS Bull. 2014, 39, 429–435.
[2] Z. Li, J. Huang, B. Yann Liaw, V. Metzler, J. Zhang, J. Power Sources 2014, 254, 168–182.
[3] R. Bhattacharyya, B. Key, H. Chen, A. S. Best, A. F. Hollenkamp, C. P. Grey, Nat. Mater. 2010, 9, 504–10.
[4] J. Wandt, C. Marino, H-A. Gasteiger, P. Jakes, R-A. Eichel, J. Granwehr, submitted 27th August 2014.
[5] R. Mogi, M. Inaba, S.-K. Jeong, Y. Iriyama, T. Abe, Z. Ogumi, J. Electrochem. Soc. 2002, 149, A1578–A1583.
[6] V. Zinth, C. von Lüders, M. Hofmann, J. Hattendorff, I. Buchberger, S. Erhard, J. Rebelo-Kornmeier, A. Jossen, R. Gilles, J. Power Sources 2014, 271, 152–159.
Acknowledgements:
Experimental support by Hans Kungl, Magnus Graf, Johannes Landesfeind and Yi-Chun Lu as well as financial support by BMW AG, by the Bavarian Ministry of Economic Affairs and Media, Energy and Technology (EEBatt project; TUM) and by the German Federal Ministry of Education and Research (BMBF-project DESIREE, grant number 03SF0477A; IEK-9) are gratefully acknowledged.