Liquid electrolyte plays a key role in commercial lithium batteries to allow conduction of lithium ion between cathode and anode. Traditionally, taking into account the ionic conductivity, viscosity and dissolubility of lithium salt, the salt concentration in most of liquid electrolytes is typically less than 1.2 mol/L. We propose a new class of “Solvent-in-Salt” (SIS) electrolytes with high salt concentration, in which salt holds a dominant position in the lithium ion transport system. It remarkably enhances cyclic and safety performance of the next-generation high-energy rechargeable lithium batteries via an effective suppression of lithium dendrite and shape change of metallic lithium anode. First, when used in lithium-sulfur battery, the power of this electrolyte is further demonstrated that lithium polysulphide dissolution is inhibited, thus overcoming one of the most challengeable technological hurdles: “polysulphide shuttle phenomenon”. Consequently, a Coulombic efficiency nearing 100% and long cycling stability are achieved. Second, when used in lithium-NCA pouch cell, the ca. 3Ah cell exhibits over 150 cycles.