Although ubiquitous in consumer electronics, Li-ion batteries can be improved on many levels. Through this work, we aim to understand and control the formation of the solid electrolyte interphase (SEI) between high capacity anodes and non-aqueous battery electrolytes. Additives are routinely used to enhance the cycle life and coulombic efficiency of high capacity anodes (silicon, tin, and lithium, for example), with little understanding of the mechanism underlying the improvements. The high capacity anode chosen for this study is tin. Thin films of tin have been coated onto quartz crystal microbalance sensors and cycled in an electrochemical quartz crystal microbalance (EQCM). The effect of the additive/co-solvent fluoroethylene carbonate (FEC) has been evaluated. Coin cell studies have also been undertaken and confirm that FEC increases couloumbic efficiency, thus decreasing the irreversible capacity loss. The additive amount of 2% FEC is enough to derive the benefits in the cells at a slow cycling rate, while 5% FEC is required for the cells cycled at a higher rate. Using EQCM, the processes of the decomposition of the electrolyte on the electrode surface and Li alloying/dealloying with Sn were characterized quantitatively by surface mass change at the molecular level. EQCM studies demonstrated that the mass accumulated per mole of electrons (mpe) was varied in different electrochemical processes, which reveals that the reduction products of the electrolyte with/without FEC are different. The results of tin studies may have similarities to the effect of FEC on other anode surfaces.

Investigations of solid electrolyte interphase formation on high-capacity Li-ion battery anodes

248th National Meeting (2014)

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