Topic Advanced Cell Testing: In-Operando observation of Formation of Mossy Lithium and Lithium-Dendrite Growth on Lithium Anodes during Charge–Discharge Cycling by Electron Paramagnetic Resonance Spectroscopy

The formation of mossy lithium and lithium dendrites so far prevents the use of lithium metal anodes in lithium ion batteries. To develop solutions for this problem (e.g., electrolyte additives), in-operando measurement techniques are required to monitor mossy lithium and dendrite formation during electrochemical cycling. Here we present a novel battery cell design that enables in-operando electron paramag-netic resonance (EPR) spectroscopy. It is shown that time-resolved in-operando EPR spectroscopy during electrochemical cycling of a lithi-um-metal/LiFePO4 (LFP) cell provides unique insights into the lithium plating/dissolution mechanisms, which are consistent with ex-situ scanning electron microscopy (SEM) analysis. To demonstrate the viability of the in-operando EPR method, two cells using different electrolytes were studied. When using an electrolyte containing fluoroethylene carbonate (FEC) additive, a higher reversibility of the lithium anode and reduced formation of micro-structured (mossy/dendritic) lithium were observed.

J. Wandt, C. Marino, H.A. Gasteiger, P. Jakes, R.-A. Eichel, J. Granwehr, Energy Environ. Sci. 8 (2015) 1358-1367