Effect of nano-silica filler in polymer electrolyte on Li dendrite formation in Li/poly(ethylene oxide)–Li(CF 3SO 2) 2N/Li

Abstract

Lithium dendrite growth in Li/poly(ethylene oxide) (PEO)–Li(CF 3SO 2) 2N (LiTFSI)–nano-SiO 2/Li was examined using direct in situ observation under galvanostatic conditions at 60 °C. Both the onset time of dendrite formation and the short-circuit time of the cells were extended by the addition of nano-SiO 2 filler into the polymer electrolyte, of which an acid-modified nano-SiO 2 filler was the most effective. The onset time was dependent on the current density in the range from 0.1 to 1.0 mA cm −2. Li dendrite growth in Li/PEO 18LiTFSI/Li at 60 °C for current densities of 0.1 and 0.5 mA cm −2 started at 125 and 15 h, respectively. PEO 18 LiTFSI with addition of 10 wt% acid-modified 50 nm SiO 2 showed extended dendrite formation onset times of 250 h at 0.1 mA cm −2 and 32 h at 0.5 mA cm −2. The suppression of dendrite formation at the Li/PEO 18 LiTFSI interface could be explained by enhancement of the conductivity and suppression of the interface resistance between lithium and the polymer electrolyte by addition of the nano-SiO 2 filler. The electrical conductivity of 4.1 × 10 −4 S cm −1 and interface resistance of 405 Ω cm 2 for PEO 18 LiTFSI at 60 °C were respectively increased to 7.2 × 10 −4 S cm −1 and decreased to 77 Ω cm 2 by the addition of 10 wt% acid-modified nano-SiO 2.