Effect of co-doping nano-silica filler and N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide into polymer electrolyte on Li dendrite formation in Li/poly(ethylene oxide)-Li(CF3SO2)2N/Li

Lithium metal dendrite growth in Li/poly (ethylene oxide)-lithium bis (trifluoromethanesulfonyl) imide (PEO₁₈LiTFSI), nano-silica, and N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13TFSI) composite solid polymer electrolyte/Li was investigated by direct in situ observation. The dendrite onset time decreased with increasing current density and deviated from Sand's law in the current density range of 0.1-0.5 mA cm⁻² at 60 °C. Lithium dendrite formation was not observed until 46 h of polarization at 0.5 mA cm⁻² and 60 °C, which is a significant improvement compared to that observed in Li/(PEO₁₈LiTFSI)/Li, where the dendrite formation was observed after 15 h polarization at 0.5 mA cm⁻² and 60 °C. The suppression of dendrite formation could be explained by the electrical conductivity enhancement and decrease of the interface resistance between Li and the polymer electrolyte by the introduction of both nano-SiO₂ and PP13TFSI into PEO₁₈LiTFSI. The electrical conductivity of 4.96 × 10⁻⁴ S cm⁻¹ at 60 °C was enhanced to 7.6 × 10⁻⁴ S cm⁻¹, and the interface resistance of Li/PEO₁₈LiTFSI/Li of 248 Ω cm² was decreased to 74 Ω cm² by the addition of both nano-SiO₂ and PP13TFSI into PEO₁₈LiTFSI.