The highly concentrated lithium bis(fluorosulfonyl)imide/1,2–dimethoxyethane electrolyte is in the good graces of researchers due to its excellent electrochemical performance in lithium-metal batteries. However, our study reveals that the more concentrated electrolyte incurred more drastic lithium-dendrite growth. Minimum onset time (tsc) of lithium-dendrite formation of only 7.4 and 18.6 h are observed in 4 M lithium bis(fluorosulfonyl)imide/1,2-dimethoxyethane electrolyte galvanostatically polarized at current densities of 1.0 and 0.5 mA cm−2, respectively. In contrast, tsc are as long as around 56 and > 190 h in 1 M electrolyte at 1.0 and 0.5 mA cm−2, respectively. We found that 1 M electrolyte has comprehensive advantages in many respects, including Li+ transference number (0.61), salt diffusion coefficient (1.47 × 10−5 cm2 s−1), ionic conductivity (1.52 × 10−2 S cm−1), low polarization potential and solid electrolyte interphase protection, which collectively make contributions to outstanding lithium-dendrite suppression.