A new class of Solvent-in-Salt electrolyte for high-energy rechargeable metallic lithium batteries.

Liquid electrolyte plays a key role in commercial lithium-ion 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 liquid electrolytes is typically less than 1.2 mol l(-1). Here we show a new class of 'Solvent-in-Salt' electrolyte with ultrahigh salt concentration and high lithium-ion transference number (0.73), in which salt holds a dominant position in the lithium-ion transport system. It remarkably enhances cyclic and safety performance of next-generation high-energy rechargeable lithium batteries via an effective suppression of lithium dendrite growth and shape change in the metallic lithium anode. Moreover, when used in lithium-sulphur battery, the advantage of this electrolyte is further demonstrated that lithium polysulphide dissolution is inhibited, thus overcoming one of today's most challenging technological hurdles, the 'polysulphide shuttle phenomenon'. Consequently, a coulombic efficiency nearing 100% and long cycling stability are achieved.