Lithium Dendrite Formation in Li/Poly(ethylene oxide)–Lithium Bis(trifluoromethanesulfonyl)imide and N-Methyl-N-propylpiperidinium Bis(trifluoromethanesulfonyl)imide/Li Cells

Lithium metal dendrite growth in Li/poly(ethylene oxide)–lithium bis(trifluoromethanesulfonyl)imide and in an ionic liquid, -methyl- -propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI) composite solid polymer electrolyte/Li was examined by direct in situ observation. Lithium dendrite formation was observed after 15 h of polarization at and at on . The onset time was increased to 35 h at by the addition of PP13TFSI into up to 1.44 mol. The dendrite onset time decreased with increasing current density and deviated from Sand's law in the current density range of at . The electrical conductivity of was enhanced, and the interface resistance between Li and was suppressed by the addition of PP13TFSI. The lithium ion transport number of the composite electrolyte decreased with increasing in . The suppression of the lithium dendrite formation could be explained by the low resistance of the interface layer between lithium and the composite polymer electrolyte.