Potentiostatic Li Electrodeposition in LiTFSI-PC Electrolyte

Li metal was potentiostatically electrodeposited on Niwire in1 M LiTFSI (lithium bis(trifluoromethanesulfonyl)imide)/PC (propylenecarbonate) up to 8000 mC cm(-2). The morphologicalvariations of Li electrodeposited at 0 to -1000 mV were observedwith an optical microscope. Extremely localized precipitates developedat cathodic potentials more positive than -100 mV, whereasa transition to uniform and smoother morphology appeared at more negativepotentials than -100 mV. These observations, combined withex situ SEM observations, suggested the importance of comprehendingthe electrodeposition behavior at the very early stage. Then, a uniquetechnique of double-pulse potential scheduling composed of nucleation(& eta;(nucl.) and t (nucl.)) andgrowth (& eta;(growth) and t (growth)) periods to separate the growth stage from nucleation was introduced.Newly designed scheduling illustrated that no growing nucleus greaterthan 1 & mu;m in diameter was recognized on the Ni substrate atthe first cathodic potentials (& eta;(nucl.)) more positivethan -100 mV over t (growth) of 1800s under the presence of SEI (solid electrolyte interphase). At largeroverpotentials, such as -400 mV, Li nucleation and growth clearlyappeared to be taking place under a uniform SEI as in the case ofgalvanostatic electrolysis at higher current densities. The analysisof the current-time variation at -400 mV showed relativelygood agreement with the instantaneous 3-D nucleation and growth modelproposed by Scharifker and Hills. Based on the model, the diffusioncoefficient of Li+ in the SEI was estimated to be 3.3 x10(-10) cm(2) s(-1).

Automated summary

By observing the morphological variations of Li electrodeposited at different potentials, it was found that cathodic potentials more positive than -100 mV resulted in localized precipitates, while more negative potentials led to uniform morphology. A unique double-pulse potential scheduling technique was introduced to separate the growth stage from nucleation. At -400 mV, Li nucleation and growth occurred under a uniform solid electrolyte interphase.